FASTENER ENGINEERING HANDBOOK 2020

December 2020

Engineering www.fastenerengineering.com

2020

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Strength in flexibility My grandpa used to tell me how important it was to be flexible in life. “That which yields is not always weak,” he’d say, adding that it took him too long to learn this lesson. It’s been years since he’s passed but I think he failed to give himself enough credit.

He was born a few years after the 1918 pandemic but he grew up during the Great Depression and lived through (and fought in) World War II. He immigrated to North America, learned the local customs and language, and opened a business — an iron and welding company.

It went through ups and downs, as most companies do, but he ran it for nearly three decades. And, I have to guess that one key to its resilience was his flexibility. Word had it that my grandpa was not always easy to work with, but he was open to new ideas and enjoyed innovation and challenges.

I’ve wondered how he would have managed the last year, given the current pandemic and its hardship on families and businesses. His words of advice came back to me after interviewing several companies to learn how they’ve coped and changed to best handle the COVID restrictions. Somewhat unexpectedly, most of the manufacturers and distributors in the fastener industry we spoke with were doing well. And some were doing better than ever.

One common denominator: flexibility. The companies that excelled also embraced change.

They’ve altered schedules, allowed for remote work, created virtual offices (with “live” product demos or how-to videos), developed e-commerce platforms, or implemented software updates to digitalize the supply chain or enhance a web presence. The changes have varied per company but those with resilience seemed to have recognized the importance of offering digital accessibility and welcoming new options for success.

The hope, of course, is that 2021 will eventually allow for greater freedom and opportunities to travel and meet in-person, or attend conferences and events offscreen, away from a computer. But until then, flexibility (and technology) has allowed for new ways to connect and for many businesses to continue.

In the fastener industry — one which is essential to the critical devices and everyday products we rely on — this is no small feat. For those companies that have continued to push forward through uncertainty and serve their customers, gratitude and congratulations are warranted.

Here’s hoping 2021 offers more certainty and fewer challenges, requiring a little less flexibility for a change.

In this Handbook, we provide insight into common fastener questions and interests for a range of products, materials, and applications. There’s also an informative Q&A article on frequently asked fastener questions (under “Training”). Thanks for reading! We wish you all a positive and productive year.

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Contents 12 • 2020

28 _RETAINING RINGS

What factors should you consider before choosing an expoxy?

What are retaining rings and where are they used?

6 _ADHESIVES: Threadlocker

32 _RIVETS

When is a chemical threadlocker preferred over mechanical locking?

When are rivet nuts an ideal choice for an application?

8 _BOLTS

36 _SCREWS: Sealing Fasteners

What to consider when reusing bolted joints?

What are sealing fasteners and when should you use them?

10 _GALLING

38 _SCREWS: Self-tapping vs.

What is fastener galling and can it be prevented?

Self-drilling

How to ensure bolted joint integrity when using a compression limiter

16 _KNOBS What features should be considered when choosing knobs for a project?

18 _MANUFACTURING How is stamping used in manufacturing?

20 _MATERIALS Material choices: When are plastic parts ideal?

24 _NUTS What is a castellated nut and when is it used?

56 _AD INDEX DESIGN WORLD

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4 _ADHESIVES: Epoxies

12 _JOINTS

52 _PROFILES

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26 _PINS What purpose do press-fit pins and receptacles serve?

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What is the difference between self-tapping and self-drilling screws?

40 _SEALS How do gaskets perform as industrial seals?

42 _SPRINGS What factors should be considered before choosing springs for fastening?

44 _TOOLS What tools are used in industrial fastening?

46 _TRAINING What are some critical fastener facts every supplier and user should know?

48 _WASHERS When are washers used with fasteners and why?

50 _WELDING What is laser plastic welding and how has it advanced?

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ADHESIVES: EPOXIES

There are several factors to assess when choosing an epoxy.

Consider partnering with an epoxy supplier that can offer expert advice to ensure you get the most out of an adhesive.

What factors should you consider before choosing an epoxy?

Jeffrey Sargeant • Technical Director • Meridian Adhesives Group Electronics Division Certain assemblies lend themselves poorly to the use of mechanical fasteners. Such components may add weight and eventually rust. Fortunately, adhesives provide an answer in many cases and offer several benefits as a bonding method.

Adhesives can be used to bond complex geometries and, typically, reduce the weight and size of a finished product or assembly. These substances also distribute a bond’s stress over the entire surface of the bonding area rather than concentrating it at specific points, which can lead to a more durable hold.

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Epoxies are one of the most common classes of adhesives, but the term “epoxy” covers a range of materials. Epoxies are available in several types and configurations. Here are a few additional features.

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Color and appearance. Epoxies are available as a clear substance or in a selection of colors — including black, white, gray, tan, and others — to match the application. They can also be transparent or made opaque through the use of fillers and colorants.

Viscosity. A range of viscosities is accessible, which allows for the selection of a material with the physical consistency needed for the ideal bond gap and geometry. This includes lowviscosity adhesives that can penetrate thin spaces or high and paste-like viscosity to fill wider or irregularly shaped spaces. Low-viscosity epoxies are also used to impregnate fabrics or foams to create structural and functional composites.

Cure time and methods. Epoxies can be customized to match several different cure types, depending on the application. For example, roomtemperature adhesives let an epoxy cure without the use of supplemental heat. Others may call for an elevated temperature from thermal or infrared (IR) ovens.

Different cure times are also available and may be necessary, including adhesives that set in just a few minutes to those that take several hours.

Choosing the correct cure time depends on the application, available process time, and equipment. Additionally, some epoxies cure quickly by exposure to UV or visible light. The speed of UV curing lets manufacturers reduce overall production time.

Packaging type. Typically, epoxies are supplied in two components that are weighed and mixed for the quantity needed at the time of use. This means a user can maintain the maximum shelf life for the adhesive and avoid waste.

However, for increased simplicity, many substances are now supplied in dual-barrel cartridges with static mixing

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Certain epoxies can protect electrical components against heat, dust, and moisture, making them an ideal bonding choice for applications that must maintain electrical or thermal conductivity.

tips that dispense the two components — which are premixed in the proper mix ratio. This allows a user to apply a reproducible uniform mixed adhesive.

In some instances, epoxies may also be supplied in a frozen, premixed form, which must be thawed right before use.

This method of delivery is popular in the electronics industry.

In addition to the above characteristics, there are many epoxies available that are formulated to enhance specific functional properties.

many of these substances suitable for exposure to harsh chemicals and environments, including several acids, bases, organic solvents, fuels, fluids, as well as fresh and salt water.

Some epoxies are also formulated to meet flameresistance requirements, including those for applications that must maintain certain standards (such as for the Underwriters Laboratories, a global safety certification, or the Federal Aviation Administration for aircraft safety, and others). The specialty epoxies also provide additional device life in harsh environments.

Electrical and/or thermal conductivity.

Adhesives are frequently used in electronic and electromechanical assemblies. In these applications, epoxies can be applied to bond materials that need to maintain electrical or thermal conductivity between them.

For example, epoxies can bond heat sinks to parts of an electronic assembly Adhesion to substrates. The additives and that generate heat during their operation. chemistry of epoxies can be adjusted to A thermally conductive epoxy provides enhance adhesion to several materials for a more efficient thermal transfer to such as metals, glass, filled or unfilled the heat sink to increase heat dissipation. plastics, textured or smooth surfaces, Electrically conductive epoxies can be wood, concrete, and other construction used to bond components that require an substrates. This means designers electrical connection for passage of the are nearly unlimited by the choice electrical signals or static discharge. of materials available for building or Such bonding features give design and construction. process engineers increased flexibility to fabricate reliable and high-performing Flexibility. Generally, epoxies are quite devices. rigid, but some substances can endure Of course, the criteria for selecting an substrate bending or twisting without epoxy — such as the processing time, losing adhesion. This is where the true performance properties, and cost — will value of an adhesive is apparent. Since it’s affect a user’s final decision. It’s advisable applied over an entire bond area, it can to ask an expert epoxy supplier that can better withstand stresses, reducing the provide the ideal recommendations. chance of bond failure.

Chemical and flame-resistance. One important property of epoxies is their resistance to many chemicals. This makes www.fastenerengineering.com

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ADHESIVES: threadlocker

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When is a chemical threadlocker preferred over mechanical locking?

Simla Ay • Technical Marketing Writer • Hernon Manufacturing Mechanical fasteners — such as split washers, double or nylon nuts, or toothed-flanged bolts — are often used to lock threaded assemblies into place.

Although these components are typically effective, they can add weight to an application and are more challenging to apply on an industrial scale or at highspeed in an assembly line.

Sometimes mechanical locking mechanisms also require a special order or additional inventory spaces.

Over time, they can rust and damage the appearance or functionality of an application. However, chemical threadlockers offer an alternative that prevents fasteners from loosening.

They are anaerobic adhesives formulated to seal and lock threaded fasteners into place after tightening.

Threadlockers are recommended for use anytime a threaded fastener will be exposed to vibration, repeated impacts, or when it’s imperative to maintain a product’s structure and function.

How they work Several different types of threadlockers are available for use, depending on the bolt materials and requirements of the application.

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Threadlockers fill the gap between the threads of a nut and bolt. Typically, there’s a range of about 15% metal-tometal contact between the two (and this is where friction occurs), but the remaining 85% of the threads are not in contact. Threadlockers work by filling DESIGN WORLD

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Wicking grades are available to penetrate pre-assembled fasteners.

this gap and increasing the area of friction between the mated surfaces.

Only a small amount — typically just a drop — of threadlocker is required for most applications. The threadlocker is applied near the end of the male threads and away from the bolt head.

As a bolt is screwed into a nut or retaining piece, the adhesive will coat the female threads. Once the fastener is fully tightened, the threads will bear down on one another, leaving a small amount of liquid threadlocker as oxygen is pushed out. This anaerobic environment, or the absence of free oxygen, triggers threadlocker curing and the threaded assemblies will lock into place.

Threadlockers are available in a variety of strengths, colors, and grades, and there are several important factors to consider when choosing this type of adhesive.

For example, the strength is generally denoted by color:

• Low-strength (purple): these low-strength bonds can be disassembled using hand tools. This is important when disassembly is routine.

• Medium-strength (blue): these medium- strength assemblies require power tools for disassembly. They’re used for critical joints that may only rarely need disassembly.

Fastener size is another important consideration when choosing the ideal strength and viscosity of the adhesive required. For example, high-strength threadlockers are most often used on fasteners between three-quarters of an inch, up to one inch in diameter — and usually used with heavy equipment.

Screws that are less than one-quarter-inch in diameter, such as calibration screws or gauges, are typically locked by low-strength formulations.

Wicking The application method is also important to consider when selecting a threadlocker. If applied during the assembly of a part, any grade can be used based on the requirements. However, for parts that are already assembled, consider a wicking grade.

A wicking threadlocker is a low-viscosity liquid for penetrating and locking pre-assembled parts. This type of threadlocker lets the parts remain complete and requires no disassembly or reassembly of the fasteners to work properly. Wicking can also be used to retrofit threadlockers into already-assembled fasteners, where disassembly is next-to-impossible.

This means it’s a valuable option for overcoming certain challenges in the manufacturing process.

This adhesive moves between fastened threads using a capillary action, so it can flow through narrow spaces without any assistance.

Wicking is associated with the color green to differentiate it from the other threadlocker types. It is important to note that localized heating and hand tools are required for disassembly when wicking is selected.

• High-strength (red): only used for permanent bonds. Disassembly is not easy and usually requires a combination of high heat and power tools.

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BOLTS

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Figure 1

What to consider when reusing bolted joints?

Nord-Lock Group

A bolt is installed in a factory without lubrication and everything works fine… until the first time the bolt is removed and reused. Then, the problems start. Why? In the design process, an engineer sets the preload range for a joint (as shown in Figure 1) so the parts don’t open or start to slide — ensuring the yield strength will not be exceeded on any of the parts.

The friction coefficients are a part of the calculation to find the nominal torque needed to achieve the correct preload. The bolt contact area is flattened during the first tightening operation due to the surface roughness and irregularities.

What happens during reuse is that the friction increases because of the bigger contact area generated during the first tightening. This means you need a higher tightening torque to achieve the same preload you had in the first tightening.

If instead, you simply use the same initially recommended tightening torque during reuse, the result is less achieved preload.

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Tightening without lubrication The graph in Figure 2 illustrates an M12 grade 8.8 bolt, which has been tightened for the first time and then reused without any lubrication. The design engineer’s preload range is marked in blue. The first-time tightening is clearly inside that range and everything works fine.

However, because of friction effects, the first time the fastener is reused a higher tightening torque is needed to get the required preload. An example might be a machine that has been working fine since it came from the manufacturer. Then, the first maintenance overhaul is done after, for example, a year. .

When the bolt is reused, following the instructions from the manufacturer, and tightened to what is thought to be the correct torque, the achieved preload is below the range originally determined by the engineer.

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Figure 2

This is when problems occur. The preload is too low and the parts can start to slide, meaning the joint will loosen and/or the bolt breaks.

Reusing bolted joints without proper lubrication is quite a gamble. It may be tempting not to use lubrication to save time — or, it may not be possible due to hygiene reasons, for example.

But it’s important to be aware that a drop in preload between the first-time installation and the first reuse without lubrication can be very large and vary a lot.

This means the achieved preload cannot be accurately predicted. If lubrication is not used, then it would be safer to change the fasteners each time, rather than to reuse them. If the fasteners are to be reused, then it is strongly recommended to use a good, uniform lubrication.

It is extremely important that the bolts are cleaned and lubricated again with the same lubrication. This will restore the friction conditions to its original level, maintaining the clamp load within the predefined range (see Figure 3).

Figure 3

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GALLING

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What is fastener galling and can it be prevented?

UC Components

Galling is a common type of wear that can occur when fastening or disassembling threaded components. It can result in damage or seizing of these components.

Galling — also called cold-welding or cold-fusing — happens when two fastener surfaces are placed under heavy pressure and lock together. Thread galling can occur when pressure and friction cause the bolt threads to seize to the threads of a nut or a tapped hole. Essentially, it’s a rapid form of wear and tear.

This is a frustrating problem because it occurs quite regularly during installation when fasteners are tightened. Galling is rarely a gradual process and is typically more common in alloys that selfgenerate an oxide surface film for corrosion-protection, such as stainless steel, aluminum, and titanium.

What’s more is that galled nuts and bolts may pass all of the required inspections (such as for mechanical, threads, material strength, etc.) and still fail to function properly.

Why does galling happen so easily?

When two fasteners are tightened together pressure builds between the contact threads and this can break the oxide coatings on the

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components. Without this protective layer, the exposed metals rub against one another, generating heat. Eventually, they’ll fuse together.

With minor galling, it’s possible to remove the fasteners without too much difficulty. However, in severe cases, the fastener surfaces will completely fuse, making it nearly impossible to remove them without cutting the bolt or splitting the nut. Despite this tight hold that ensures the fasteners will not loosen (which is usually a good thing in fastening), the affected galled joints can still fail from fatigue.

As a result, the parts can become stripped, sheared, or twisted off

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Uniquely designed fasteners are available that reduce galling. Research your options before use. Without the hassle of galled or stuck fasteners, downtime is minimized.

completely, negatively affecting the overall quality, reliability, and durability of the fasteners and the application. Galling can also increase maintenance and repair costs because the fasteners will need to be removed and replaced, and any holes left in the application will require filling.

In high or ultra-vacuum systems, the materials can become cold-fused together due to thermal expansion and a lack of moisture created by the vacuum. Screws threaded into blindtapped holes are often affected by galling and components made of stainless steel are particularly susceptible.

Can galling be avoided?

Unfortunately, little is known on how to completely control galling, but it can be minimized. Material choices matter and those that possess low, work-hardening rates are often prone to galling, so choose wisely.

One of the best ways to avoid galling is to use a lubricant or an “anti-seize” product. Such lubricants are available in several varieties and many are specifically formulated for use on alloys.

It’s worth noting that in certain applications, such as with ultra-high vacuum systems and other clean applications, the use of anti-seize lubricants is not a viable option. This is because it presents too much risk of contamination and an unclean interior of the vacuum chamber. In such cases, another option is necessary, which may involve using different alloys.

Before choosing the ideal fasteners for an application, first consider the factors that can impact galling, including

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the design (of the fastener and the application), the applied load and degree of movement expected, and the surface finish and hardness.

A few ways to minimize galling:

• Use a finish, such as a coating or plating, that’s made to prevent galling • Design components using different alloys to lower the possibility of galling • Choose fasteners with smoother surfaces to reduce friction • Use coarse rather than fine threads, such as a 2A- 2B fit —they have a larger thread allowance and can handle greater wear and tear • Slow the assembly speed of a threaded fastener to reduce the chances of heat buildup and galling • Consider the design tolerances, ensuring a tight enough mechanical fit to prevent vibration and wear, but with sufficient clearance to prevent galling • Always use the proper installation torque and never over-tighten fasteners • Any debris in the threads of a fastener can greatly increase the chances of galling so always use clean parts Balancing a fasteners’ properties to get the best performance while preventing galling is possible, but not easy.

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JOINTS

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How do you ensure joint integrity when using a compression limiter?

Tara B. Meinck • Application Engineer • SPIROL International Corporation, U.S.A.

Flanged bolt

Washer

Headed Compression Limiter

Compression limiters are used to protect plastic components in bolted joints and maintain a threaded fastener’s clamp load by eliminating plastic creep.

To function properly, the bearing surface beneath the bolt’s head must extend over the compression limiter to contact the plastic component. If this bearing surface is too small, the host component may be unretained by the bolt, resulting in a poor joint.

There are several methods to ensure sufficient bearing surface under a bolt’s head, including the use of a flanged bolt, washer, or a headed compression limiter.

One important question to ask before assembly: exactly how much plastic should be compressed? Ideally, the length of a compression limiter is equal to or slightly less than the host thickness. The amount of material compressed under a bolt’s head will vary depending on the application’s loading and plastic properties.

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However, this area of compression must be large enough to withstand forces that might pull the assembly apart, yet small enough to allow sufficient plastic compression so that the limiter contacts both the bolt and the mating component.

Assembly considerations Several factors including the speed and assembly method must be considered when determining the ideal and most cost-effective solution for a specific application.

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In one example, various fastener combinations were manually assembled to determine the approximate differences in efficiency.

These are the results: ASSEMBLY SPEED

Fastener configuration Flanged bolt, symmetrical compression limiter Bolt, headed compression limiter Washer, bolt, symmetrical compression limiter

Average speed (in seconds) 1.24 1.44 2.48

The assembly with a flanged bolt was the quickest, followed by that with a headed compression limiter — which is important to orient properly. As expected, the addition of a third component (a washer) significantly slowed the assembly process, requiring twice the assembly time.

If an assembly is automated, it’s imperative to ensure the design is as efficient as possible. The addition of a third component, such as a washer, might be undesirable in this case because of feeding and alignment challenges.

Other possible factors affecting efficiency include the number of components used and the ease of orientation. Bolts, headed compression limiters, and some washers require orientation. Due to their relatively lowhead to outer-diameter ratio and short length, headed compression limiters and washers are more difficult to mechanically orient than bolts.

Conversely, symmetrical compression limiters require no orientation.

An assembly with a flanged bolt requires one component’s orientation and those with a headed compression limiter or washer require two components to be oriented.

The use of a headed compression limiter or flanged bolt in serviceable assemblies may be ideal because the washers for such applications could not be omitted accidentally during re-assembly. These are also preferable in applications where there are multiple assembly locations or poor qualitycontrol.

Cost considerations Typically, fasteners are the least expensive components in an assembly.

The following table shows the representative costs for each component combination discussed based on an annual usage of one-million assemblies that incorporate an M6 joint.

The relative cost differences between the bolts and compression limiters vary depending on the component supplier and the characteristics of the bolts. Of these three potential combinations, the method with a washer, bolt, and non-headed compression limiter provided the lowest component cost for controlling a bearing surface.

However, as noted, the cost of the fastening components is generally the least significant compared to the overall cost of an assembly.

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Plastic compressed by a bolt’s bearing surface area (highlighted in red).

Cost considerations ESTIMATED COST OF THE INDIVIDUAL COMPONENTS

(per 1,000 pieces)

Component Washer Bolt Flanged bolt Symmetrical compression limiter Headed compression limiter

$USD $5 $42 $83 $20 $100

ESTIMATED COST OF THE COMBINED COMPONENTS

(per 1,000 pieces)

Fastener configuration Washer, bolt, symmetrical compression limiter Flanged bolt, symmetrical compression limiter Bolt, headed compression limiter

$USD $67 $103 $142

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JOINTS

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Overall cost analysis Fastener configuration

Washer, bolt, symmetrical compression limiter Flanged bolt, symmetrical compression limiter Bolt, headed compression limiter

Component cost

Average assembly speed

Total assembly costs

(per million; USD)

(in seconds)

(USD)

$67,000

2.48

$101,444

$103,000

1.24

$120,222

$142,000

1.44

$162,000

This table shows the estimated overall cost analysis of each configuration, assuming it’s $50/hour for labor to assemble one-million components.

What’s missing in this analysis are the administrative costs for ordering, handling, and maintaining the inventory of components. The addition of a third component may also increase these expenses.

If the assembly process is automated, the technology required to feed and orient a washer will also increase the cost. Regardless, a flanged bolt or washer can replace a headed compression limiter in most applications to augment efficiency and lower the overall cost of the assembly.

Always consult an application engineer who specializes in fastening and joining to ensure a properly configured joint is used for each application.

The use of a headed compression limiter or flanged bolt in serviceable assemblies may be ideal because the washers for such applications could not be omitted accidentally during re-assembly.

These are also preferable in applications where there are multiple assembly locations or poor quality-control.

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KNOBS

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What features should be considered when choosing knobs for a project?

John Winkler • CEO, Former Office of the President • JW Winco

Knurled knob

Control knob

Few other machine components seem more elementary than a knob. Yes, those handles that allow users to firmly and comfortably grip an area of machinery to open, operate, or control it.

These devices may seem simple, but they are often essential, practical, and imperative to good design. Knobs are used to transmit a force between a person’s hand and an object. There are many possible configurations for this simple part and choosing the right type is key to the optimal function of a machine. For example, knobs may be axisymmetric, multi-lobed, spherical, or T-shaped.

Ultimately, a knob must have a sufficient area and ergonomic shape to transfer the force required for use comfortably into the user’s hand — typically through a range of angles when the handle is moved. The ideal knob choice will provide this ergonomic interface.

When deciding on a style, consider the type and material used for the knob based on the application and environment it will be used in. Moisture, for example, may affect the user’s grip and this could

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be a safety issue. Also, consider the knob’s metal insert, which is molded into the material that’s used during manufacturing. It’s this insert that provides the knob its strength, which in turn enables maximum torque.

Here are a few different types of knobs, including certain advantages and disadvantages, so you can select the right one for your application.

Ball knobs. This type is ideal for applications that require movement in any direction. Ball knobs usually offer a comfortable grip and are easy to wipe down and keep clean. However, avoid

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using a ball knob in applications that deal with moisture or grease because it will become slippery and tough to handle.

Control knobs. These knobs are specifically used for precise control or adjustment of devices and may be referred to as instrument, electronic, or electrical knobs. Control knobs allow for the exact positioning of machines or equipment.

They come in a variety of styles and can include a revolving handle or scale markings for measurement.

Tapered knob

Knurled knobs. This group encompasses a variety of knob styles (round, push-pull, clamping, mushroom, tapered, etc.)

— and always with ridges or knurls at the rim to provide a non-slip grip. The knurled rim is the answer for greasy or wet environments where a slippery or unsecured grip is unsuitable or a safety hazard. The ridges can make cleaning a challenge, however, so this may be a poor choice in certain cases, such as for cleanrooms or food applications.

Push-pull knobs. These simple knobs vary in style but are

Pointer knobs. This is a type of control knob but in a pointer

Tapered knobs. The length of these knobs makes them

shape. The design makes it easy to operate with a thumb and finger. It works well when an application involves a few options or repeated settings (such as off/on or open/closed).

It’s also ideal when the application requires some sort of scale marking.

excellent for side-to-side or up and down movements. They’re particularly good for applications that operate by grasping and rotating from a 90-degree angle. This means they work well as the handle grip at the end of an operating lever, gear stick, or handwheel. But bear in mind that unless fluted or knurled, tapered knobs can be slippery in wet or greasy environments.

typically easy to operate and control because of a larger head.

Solid push-pull knobs are simple to clean and unlike openbacked styles, which collect dirt or other contaminants. If the application involves a lot of use or stress, opt for a type made of metal or with a metal insert. Push-pull knobs can also get quite slippery to grip, so you may want to consider a style that’s knurled at the rim.

Prong or multi-lobed knobs. The protrusions on a prong knob are longer (certain star knobs may also fall in this category), increasing the leverage of the operator’s fingers.

This means they’re ideal for higher torque requirements.

In lighter torque applications, one finger may be all that’s required to turn a prong knob. The downside of this style is an increased surface area, which makes it slightly more difficult to clean. Also, if steady, unbroken turning is required, go with a crank or handwheel instead.

T-handle knobs. The two-lobe design of these knobs provides for an easy grip, allowing for optimal leverage and control for inand-out operations or rotating ones. T-handle knobs also offer a strong clamping force, however, avoid using too much torque (as it might twist the insert out of the knob). If your application involves a limited space where only one hand can reach, these knobs work quite well. If the user is at an awkward angle, a prong knob might be preferred.

Wing nuts or screw knobs. Essentially, these knobs are a two-pronged knob designed for frequent tightening and loosening. They typically function in applications where the operator needs to apply torque using only a thumb and finger, and fit well in confined spaces. Metal or metal-insert wing nuts can achieve a good clamping force.

Wing nut or screw knob

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Pointer knob

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MANUFACTURING

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Metal stamping is a fast and costeffective solution, particularly for large-quantity manufacturing needs.

How is stamping used in manufacturing?

Blanking, piercing, and stamping are highly cost-effective ways to produce a large number of parts from sheet metal.

Stamping is the manufacturing process by which a metal sheet is pressed to form a specific shape. Fasteners — such as nuts, bolts, washers, rings, clamps, and others — are often made by stamping sheets of aluminum, steel, or copper.

Typically, stamping involves cold forming a piece of sheet metal by using a stamping press. Cold forming is a manufacturing process that deforms metal using dies.

In the press, a tool and die surface form the sheet metal into the desired shape.

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Stamping is similar to blanking and piercing, and these processes are often used in combination. Each one requires press equipment. Blanking is the manufacturing process in which a geometric shape (typically DESIGN WORLD

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called a “blank”) is formed by feeding a coil of sheet metal into a press and die.

In this method, the blank is essentially punched out from the large metal sheet.

Piercing involves a shearing process where a punch and die are used to form holes or notches in the required part. In general, piercing metal provides an extremely clean cut at high output rates. There are also specialized types of piercing, such as lancing, notching, shaving, and others.

A single-stage stamping operation fully forms the component in a single stroke of the press. Multi-stage stamping uses a series of presses, each with different tools and dies, which progressively deform the part into its final form. Stamping operations are suitable for short or long production runs. The high-volume processes are often fed from a coil of sheet steel.

Fasteners with flat profiles, such as plain washers, are typically fully formed by using the blanking and piercing processes. However, additional stamping is usually needed if the component requires a more complex or threedimensional shape. Let’s take Belleville washers, for example. The Belleville is also referred to as a conical spring washer because its shape is similar to a conical shell, which flattens out when pressure is applied to it.

During manufacturing, the Belleville washer is often first blanked from a coil of sheet steel and then its central hole is pierced. At this stage, it appears similar to an extra-large plain washer. To form the conical shape, therefore, a final stamping process is typically necessary.

Stamping may also be used to form bent teeth or tabs on several types of lock washers. Lock washers are designed to prevent a threaded fastener from loosening, thanks to these teeth or tabs that are intended to increase friction and locking.

Metal stamping is an intricate and often a multi-step process. After all, manufacturing complex parts requires precision. These processes are used

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in a vast array of industries, such as for manufacturing electronic components, utensils and cookware, or automotive and aircraft parts.

There are several types of stamping operations. Here are three examples:

• Progressive die stamping, which is ideal for long runs and uses a sequence of stamping stations with different functions.

• Four- or multi-slide stamping,

which is ideal for complex components, and uses four sliding tools (instead of one vertical slide) to shape the workpiece. It’s also called multi or four-way stamping.

• Deep-drawing stamping, which is commonly used, and involves the use of metal dies to form blank sheets of metal into the desired shape.

is placed through rollers, compressed, and then squeezed. Cold forging involves deforming metal, often via hammering, pressing, or rolling.

When cold forging is used to produce symbols or lettering on a part, this is also referred to as stamping. For instance, many fasteners, such as bolt heads and nuts, have information such as their grade stamped into them. Overall, speed, accuracy, and cost savings are the benefits of stamping processes.

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Other cold-forming processes, such as cold rolling or forging, are widely used in the high-volume production of fasteners — such as nuts, bolts, and screws. Cold rolling is when sheet metal

A selection of washers produced using a combination of blanking, piercing, and stamping processes.

From left to right: Belleville, extralarge plain, lock (with internal teeth), external tab, and spring lock washers.

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MATERIALS

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PEEK, or polyetheretherketone, is one type of highperformance plastic, which serves as an ideal material for fasteners in many critical or demanding applications.

Material choices: When are plastic parts ideal?

Barbara Gerard, • CEO • Craftech Industries, Inc.

Although most of the world’s fasteners are produced from metal, that choice is gradually changing for some engineers and designers. Depending on the application, a switch to plastic offers several material advantages.

Plastic fasteners are typically lightweight and flexible, yet also strong, reliable, and cost-effective. What’s more: they fail to rust, which is a benefit because this means less maintenance and replacements.

As one example, PEEK (or polyetheretherketone) is a type of plastic that offers high-performance engineering and versatility. This material has an extremely stable chemical structure that’s rare to find in other plastics, making it ideal

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for use in fasteners in demanding applications and industries. PEEK is often used in components for the auto, aerospace, marine, nuclear, oil and gas, and electronics sectors.

If you’re considering plastic fasteners, however, there are several questions you’ll want to ask first to ensure you make the ideal choice for your project.

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1. What exactly are you looking for?

First, you’ll need to know what type of fastener that’s required for your application…an anchor, bolt, pins, or screws? Also, what dimensions do you need or can they range? Fully understanding your application requirements is the first step. Often, a diagram or drawing can help an expert fastener manufacturer or distributor suggest the ideal options.

2. Will your application be exposed to elements and, if so, which ones?

Whether it’s extreme temperatures, vibration, or chemicals, it’s important to consider the elements fasteners will be exposed to before choosing the type and material. This means noting the environment (indoor or outdoor), potential exposure levels (such as from UV rays or electrical conductivity), and the likelihood of moisture or chemicals, which may lead to rust or degradation of the components.

Here are a few examples where the properties of plastic components may offer the best durability: For chemical resistance: There are plastics available that can hold up to almost any chemical exposure, which is one area where this material offers far greater benefits than metal. Swimming pool parts that are exposed to chlorine is one example.

For non-conductivity: Plastic materials with low conductivity are available and commonly used as thermal insulators.

3. What are your quality requirements?

Do you need parts that fit the ANSI (American National Standards Institute) or DIN (Deutsches Institut für Normung) For non-flammability: This is critical for standards, which ensure the safety parts potentially exposed to extreme and reliability of certain products? Do temperatures, gas, or flames. Flammability you require an ISO-certified supplier? tests measure a material’s combustibility, ISO (the International Organization for smoke-generation, and ignition Standardization) is a global, independent temperatures. Additives can ensure organization that develops standards and plastics are non-flammable. certifications to ensure the quality, safety, and efficiency of products.

For UV-ray exposure: Certain plastics What testing is required and will you hold up extremely well to UV rays. For require certification of the material used? others, a UV inhibitor can often be added Does the fastener require particularly tight to help lessen the detrimental effects. tolerances?

Knowing the quality requirements for For water-absorption: If the application your application from the start can save is likely to be exposed to water, unexpected material changes for the this could affect the weight of the fasteners and downtime due to ineffective components. Mechanical, electrical, choices later on. and dimensional properties can also be affected.

4. What plastic material is the ideal choice?

For wear and tear: This is a common You’ve decided that plastic is the best concern for equipment that’s subject to material for your application. However, harsh conditions, such as continuous the type selected is critical because it will vibrations — such as the bearings used affect the function, longevity, appearance, in automobiles, generators, or wind and cost of the project. turbines. Some plastics offer excellent These are important considerations. wear-resistance for such conditions.

For example, some materials can be

Several types and grades of plastic materials are available for fasteners, depending on the application.

For extreme temperatures: In general, plastics can withstand maximum service temperatures up to 300° C or 572° F. .

For low-outgassing: Outgassing is a release of gasses or impurities, which is a major concern in the semiconductor and aerospace industries, where there are high-vacuum environments. There are strict requirements for the purity of plastics for outgassing but certain types of this material are capable of measuring up.

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MATERIALS

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machined, but not molded. The opposite is also true. There are plastics as strong as stainless steel, yet the addition of glass or carbon fibers can make such materials even stronger, depending on the measure of strength required (such as tensile, compressive, or impact).

If weight is a concern, different plastics vary appreciably but most are less than metal. There’s also a wide cost variance between plastics and recycled materials can sometimes offer considerable savings. Plastic components can also be molded in almost any color and certain types can be made transparent. The choice is yours and it will depend on the application.

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5. How many parts are needed?

As with many components, higher quantities can translate to a lower cost per part. Quantity can also dictate the most appropriate manufacturing process. For small and moderate volumes, machining is often the right approach. For higher volumes, molding parts are typically more cost-effective — and consistent. Just keep in mind that if a mold needs to be built for your part, there are associated costs and a time commitment.

As with any important purchase, choosing a knowledgeable supplier for plastic components is key. Look for one with insight into the different materials available for fasteners that can offer strong technical support.

Structural Adhesives to Replace Traditional Fasteners

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NUTS

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A castellated nut is a type of lock nut with slots or notches that allow it to be pinned to prevent rotation.

What is a castellated nut and when is it used?

A castellated nut, also known as a castle nut, typically has three slots or notches cut into one end — appearing similar to the crenelated battlements of a medieval castle. It works as a positive-locking device, meaning it remains fixed after installation and resists vibration.

Castellated nuts are similar to slotted nuts but have a cylindrical top where the slots are formed. This rounded section permits a pin to be secured tighter to the nut than is possible with a slotted nut. With slotted nuts, the notches are cut directly into the flat face of the nut.

Typically, castellated nuts are used with a bolt, threaded rod, or a screw with a pre-drilled radial hole, where a pin can

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be used to secure the fasteners. The nut is attached and a pin is passed through the notches and the hole in the screw, which prevents the nut from turning.

Several types of pins may also be used for this purpose. These include: A cotter pin: also known as a split pin, this is a fastener with twin tines that are bent apart to prevent removal after insertion.

An R-clip: also known as a hairpin, or a cotter or hitch pin, this is a sprung metal fastener where one straight leg is inserted into the hole and one profiled leg grips the outside of the nut.

Safety or locking wire: a wire, which is passed through the notches and the hole, and then twisted and anchored to secure the nut.

Although castellated nuts are resistant to movement and vibration when properly installed, they are easy to remove if necessary. This makes these components a popular choice for certain applications, such as securing the position of a bearing onto a spindle.

You’ll often find them on the axles of vehicles, where they hold the wheels and bearings. They’re commonly used in the automotive, aircraft, and locomotive industries.

However, castellated nuts are unsuited to applications that require a specific preload or that are exposed to extremely high vibration or prolonged stress. As fine-tuning the torque is virtually impossible with these components, they’re better suited for low-torque applications.

With six of the notches spaced at 60-degree intervals, a castellated nut can only be locked if the notch

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corresponds to the hole. After correct torquing, it’s necessary to turn the nut again up to 30 degrees (in either direction) to locate the hole.

Castellated nuts are usually threaded with a defined standard thread form — either a unified inch fine (UNF) or a unified inch coarse series (UNC). The thread diameter is typically 1/4 to 1-1/2 inches in varying nut widths and heights, depending on the application.

These components are generally manufactured in steel or stainless steel, with other materials available. For example, a zinc coating can provide corrosion-resistance in wet or humid environments.

WHAT DO YOU THINK? Connect and discuss this and other engineering design issues with thousands of professionals online

Understanding locking devices A lock nut is a component that resists loosening under vibration and torque. There are several types of lock nuts, but they can be broadly divided into those that use friction to prevent loosening and those that offer a positive-locking device — such as the castellated nut.

Positive-locking devices can freely rotate to tighten and loosen. They only lock when a positive action is performed to secure them into a set position, such as when a pin is inserted. For example, the castellated nut will bear against an inserted pin through the threaded shaft and this prevents the nut from rotating.

Conventional nuts — a mechanical fastener with a threaded hole — may also be locked, but this requires the application of threadlocker or drilling and pinning. So, a lock nut can save considerable installation time for an application.

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PINS

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What purpose do press-fit pins and receptacles serve?

Mill-Max Mfg. Corp.

Often the products that we take for granted are critically important and imperative to equipment safety. For example, the quality of the fasteners that secure the skin to the airframe on an aircraft is integral because failure could be catastrophic.

The same can be said about the press-fit pins and receptacles applied to interconnect electronic modules. A press-fit connection is one where a contact terminal is pressed into a printed circuit board (PCB) and a receptacle serves as the outlet. These components fasten electronic applications that may provide power to critical equipment and technology — sometimes even to lifesaving devices.

In fact, the electronic circuitry interconnected by press-fit pins and receptacles is so broad in application that their role in system performance is significant to our everyday life. Individual pins and receptacles may be used for the transmission of signals from power-on down to a logic level. This is why the design and manufacture of these components must include incredible attention to detail.

There are two main types of press-fit pins: a solid pin that has a solid press-in zone and a compliant pin, which offers an elastic press-in zone. Press-fitting uses material displacement, where the pin deforms both the mating hole shape and its diameter. Compliant press-fit pins are the exception as they conform to the hole size when inserted.

Press-fit pins and receptacles are the most versatile types of interconnection components for electrical and electronic applications and are often categorized into two distinct categories, including:

A press-fit barb for non-plated through-holes. Many pins, receptacles, and spring-pin connectors use this design for retention purposes in insulators or plastic housings.

1 Those used for PC boards with plated through-holes (solderless press-fit) 2 Those used for non-plated through-holes, such as bare PC board holes, plastic housings, and insulators

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There are also solderless press-fit pins and receptacles that are used in applications where soldering is unreliable or economical, such as thickly printed circuit boards and backplanes.

Typically, press-fitting is just the more efficient manufacturing solution for: • Bringing power or control signals onto surface-mount technology (SMT) boards via cable, discreet wires, or a daughter card • Board stacking applications • Adapter boards for footprint translation (useful when a chip is converted from a through-hole to an SMT package) When pressed into plated holes on circuit boards, a properly sized hole and press-fit will form a gas-tight connection. This gas-tight connection provides a reliable electrical interface that’s characterized by a stable impedance and no oxidization.

However, since applications vary, the physical configurations of how the pins and receptacles mount and function also vary.

• Daughterboard to a PC motherboard • Component to a PC board • Module to a PC board • Cable to a PC board • Cable-to-cable • Fuse

Advantages of specialized precision machining include: • Seamless construction that prevents contact contamination from wave or reflow soldering • Specialized press-fit feature geometries (such as triangle, square, hexagon, or octagon, etc.) to meet the hole-size requirements of specific applications • Lead-in countersinks on pin receptacles to facilitate the pin alignment • Pin and receptacle shells are typically brass alloy, 360 1⁄2 hard, for strength, conductivity, and thermal properties • Multi-finger beryllium copper contact clip scores the mating device lead for gas-tight electrical connections, providing the ideal power and force distribution • Two-piece receptacle construction (shell and contact clip) allows for cost-efficient plating combinations for excellent solderability and conductivity

Applications include control functions, power, data, signal, and radio frequency.

Different sizes are also available to suit various form factors.

The approach to press-fit pins and

Of course, the quality and construction of these components can vary considerably depending on the manufacturer. To ensure reliability, press-fit pins and receptacles should be machined to tight

Purpose and functions Pins or receptacles, whether used individually or in pairs, can be useful to terminate a single wire to a PC board.

Used in groups, these components are ideal for applications such as:

receptacles is unique, applying specialized tolerances and plated with metals that precision-machined pin technology that provide the highest possible conductivity offers several advantages over stampedand corrosion protection. and-formed connectors. Stamped-andformed is a manufacturing process where the pins and sockets are stamped out of a sheet of flat metal and then formed to a specified shape.

Precision-machined pin technology allows large pieces of material to be WHAT DO shaped into extremely precise parts that YOU meet exact specifications — which is THINK? important for miniature press-fit pins Connect and discuss this and other engineering design issues with that must fit a specific application. This thousands of professionals online process may involve high-speed turning, drilling, milling, and cutting operations.

For example, precision machining can turn pin diameters as small as .008 inches and as large as .250 inches.

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A press-fit knurl for non-plated through-holes. Here, vertical serrations are machined around the diameter of an interconnect pin, which provides a retention feature for press-fitting in a nonplated PC board hole or insulator. It also prevents the rotation of the pin.

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RETAINING RINGS

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What are retaining rings and where are they used?

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Retaining rings — also known as snap rings or circlips — are metal fasteners installed into a groove on a shaft or in a housing or bore to retain an assembly. The devices keep parts in place using a compact, lightweight design that requires fewer machining operations than other fastening techniques.

Engineers specify retaining rings based on an application’s: • • • • •

Installation and removal requirements Rotational speed Conditions and operating environment Expected force load(s) on the ring Cost

Retaining rings can range in size from 1mm to 1m in diameter. Different combinations of size, shape, style, and material result in designs that work in a variety of industries

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Tapered section retaining rings or circlips.

and applications. A standard automobile, for example, can have more than 50 retaining rings spanning systems from steering to power train to passenger safety.

Retaining rings are also used in several other applications, such as fitness equipment, wind turbines, bearing retention, bicycles, doorknobs, gas pumps, office equipment, and many others.

Design considerations Retaining rings can be classified into three main categories based on design.

Tapered and constant section retaining rings describe a nearly complete circle with a gap between two free ends.

Tapered-section rings decrease in width from the top of the ring to the free ends. Installed, they make continuous contact within their installation groove.

Some tapered-section rings are designed for axial installation feature

lugs that make them easier to expand and place.

Constant section rings, in contrast, have the same width throughout their circumference. The resulting stiffer crosssection results in contact at three points within the installation groove. These simple, easy-to-produce rings typically do not have lugs.

Spiral rings are made from flat wire that’s coiled two or three times around the circumference. They make a 360-degree contact within their groove and have a constant width around their circumference. Spiral rings are rarely designed with installation lugs but, instead, have notched ends that aid in their removal.

When choosing the ideal component, consider the preferred installation method and the frequency with which you’ll be installing and removing the rings.

Meeting demands When choosing a retaining ring style, you’ll first want to consider the demands of the application. Some styles of tapered section rings offer a significant radial spring force that can handle high RPM applications and high loads. However, others are far less suitable for high speeds

Snap rings or constant section retaining rings.

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RETAINING RINGS

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or forces, so be sure to check each style’s ratings.

Spiral rings tend to work well with high loads, particularly in applications where resilience to dynamic loading is necessary.

Typically, spiral rings have lower RPM capabilities than tapered section rings. However, some designs like spiral rings with patented locking features, keep the product tightly in place. These devices are balanced and available in materials and styles that include light or heavy-duty, depending on the force load required.

Although constant-section rings are typically used in applications with lower load and speed requirements, several styles are available that can bear significant loads at a reasonable cost.

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Choosing well When choosing the ideal component, consider the preferred installation method and the frequency with which you’ll be installing and removing the rings. For instance, the lugs on axially installed tapered-section retaining rings make them easy to install and uninstall with commonly available tools, such as retaining ring pliers. Keep in mind, designers must ensure they leave clearance for the lugs and room for the pliers to fit within the design.

Constant-section rings are manufactured to ensure a controlled edge condition on the mating surface for less wear from sharp edges. The absence of lugs gives this style a low clearance but requires a tapered mandrel or cone for installation.

Spiral rings are also free of sharp edges. They are the most difficult to install, often via a tapered mandrel or cone — but they also offer the lowest clearance of the three style types. Generally, spiral rings are ideal for tamper-proofing. For easier removal, simply choose an end type that renders the spiral rings easy to uninstall with a flat-head screwdriver.

The cost and availability of each style of retaining ring are likely also important. The greater the load and speed capabilities of a tapered section retaining ring typically means a higher cost.

Constant section rings might offer a less costly choice of meeting the performance requirements of an application.

Since spiral rings are coiled from flat wire, their manufacture requires less tooling than stamped parts. This means it’s faster and more cost-effective to create spiral rings with custom sizes and shapes compared to other retaining ring styles.

The application requirements, installation practices, and budget are all factors to consider when choosing a retaining ring style.

WHAT DO YOU THINK? Connect and discuss this and other engineering design issues with thousands of professionals online

The Emerson logo is a trademark and a service mark of Emerson Electric Co. © 2020 Emerson Electric Co.

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5G TECHNOLOGY WORLD Delivers the Latest 5G Technology Trends

5G Technology World is EEWorldOnline’s newest site covering 5G technology, systems, infrastructure, and wireless design and development.

Get caught up on critical 5G information, check out the following articles on 5GTechnologyWorld.com: Massive MIMO performance testing: Emulate the channel Performing MIMO testing using real-world conditions is critical for successful 5G deployments. www.5gtechnologyworld.com/massive-mimoperformance-testing-emulate-the-channel

5G is hot, keep your components and systems cool 5G’s antennas and the devices that drive them generate more heat than their LTE predecessors. That creates new cooling problems for wireless devices and systems. www.5gtechnologyworld.com/5g-is-hot-keep-yourcomponents-and-systems-cool

5G moves into production, causes test issues 5G Technology World talks with Teradyne’s Jeorge Hurtarte, who explains components and over-the-air production test of 5G components. www.5gtechnologyworld.com/5g-moves-intoproduction-causes-test-issues

IEEE 1588 adds timing performance while reducing cost and risk GPS and GNSS have been the standards for network timing, but they have security issues. A Master clock and IEEE 1588 reduces the risk and lowers installation costs. www.5gtechnologyworld.com/ieee-1588-adds-timingperformance-while-reducing-cost-and-risk

For additional content, go to: www.5gtechnologyworld.com

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RIVETS

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When are rivet nuts an ideal choice for an application?

Industrial Rivet & Fastener Rivet nuts are internally threaded fasteners that are anchored from just one side of a workpiece or application. They’re an excellent component to use to add strength to thin materials, which is particularly important as the manufacturing trend is moving toward thinner and lighter substrates — such as soft sheet metals, thin hardened aluminum or steel skins, plastics, composites, and/or carbon fiber.

Joining thin materials is a major challenge with more conventional threaded fasteners. In such cases, the threads of a bolt have little material with which to form a strong and secure attachment. Fastener pull-out strength is a concern, which refers to the force applied to pull or tear a fastener out of an application. Rivet nuts can remedy joint pull-out issues in several ways.

Here are a few examples.

Rivet nuts…

• Stay permanently affixed. The connection of a rivet nut that’s joined to thin sheet metal is substantially stronger compared to other joining technologies.

It’s possible to use alternative fastening technologies — such as clinch nuts, u-nuts, and weld nuts — however, each one has certain disadvantages. For example, these components require access to both sides of an application, which is not always possible.

Ease of accessibility, in combination with a lower installed cost and greater installation convenience, makes rivet nuts an ideal choice. Additionally, rivet nuts allow for applied forces in multiple directions and are extremely difficult to remove once installed.

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• Provide substantial bolt/screw engagement. Pull-out forces are first determined by the ability of a fastener’s threads to withstand the load applied to it, followed by the bearing surface area and the joints’ clamp force.

In thin sheet metal, tapping, thread cutting, and thread forming screws have limited thread contact and engagement with the radial wall. A conventional bolt and nut may provide sufficient features for pull-out strength, but fail to provide the ease of assembly or strength required for most blind applications.

Alternatively, rivet nuts offer thread engagement and a reliable bearing-surface area and clamp force. These components also offer the ease of assembly necessary to significantly improve pull-out.

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A selection of different types of rivet nuts.

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RIVETS

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• Radially fill a hole. Compared to the use of a screw or bolt alone, rivet nuts radially swell to the shape of a hole. This prevents the weakening of substrates due to vibration over time. Maintaining the rigidity of the joined materials is also imperative to joint strength and a reliable hold.

• Offer a unique design. A rivet nut’s head and body design allow for the joining of dissimilar materials, which increases the pull-out and torque-out.

Similar to pull-out, torque-out refers to the amount of torque necessary to spin (rather than pull) a fastener out of an application. Oftentimes materials, such as plastics, can be weakened by a bolt’s clamp load. The clamp load is limited

An inserted (left) and installed (right) rivet nut in an area with a very tight clearance, which would be difficult to achieve with other fasteners.

by the strength of the joined materials, the fastener, and the threads’ ability to tighten — and especially when joining dissimilar materials.

However, by using rivet nuts, a user can select the ideal clamp load for one material (such as plastics), and then set a different torque or clamp for the joined assembly (say, plastics that are mounted to a steel frame). This could include using Grade 2 and Grade 5 bolts to further improve the assembly’s clamp load, pull-out, and overall joint strength.

• Make wide, blind-side bearing surfaces possible. Rivet nuts work by generating a slight upset or bulge on the blind side of the bearing surface. If combined with an ideally suited material strength and hole size, it’s unlikely a rivet nut will pull-out. But much thinner or weaker materials might still yield such a risk.

Fortunately, rivet nuts can be designed with special features that expand the blind side bulge to distribute pull-out loads over a broader surface area — thereby increasing the pull-out. Such designs include bulge-control features and four-wing versions, which work similarly to a molly fastener by providing broad distribution of the bulge formed by the riveting process. (A molly bolt is a specialty expandable fastener originally designed to help fasten objects to hollow walls.)

These features of a rivet nut dramatically improve pullout in the thinner and softer materials trending today.

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SCREWS: SEALING FASTENERS

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Sealing screws are designed to seal out contaminants and prevent leaks.

What are sealing fasteners and when should you use them?

Kim Keating • Director of Customer Success • ZAGO Manufacturing Co. Sealing fasteners are highly specialized fasteners that include sealing screws, nuts, bolts, and washers. These types of fasteners are used in several industries because of their unique ability to protect conventional machinery and complex equipment with high-tech properties. For example, these components are a staple in the military and aerospace sectors, sealing critical applications such as fuel pumps of jet and rocket engines, satellite equipment, and others.

Unlike ordinary fasteners, sealing fasteners are configured with a rubber O-ring (or a rubber element) that when squeezed, permanently seals out contaminants. This can include disinfectants, oil, gas, humidity, dust, moisture, or any debris or chemicals that can damage or destroy equipment while, at the same time, preventing equipment leakage of toxins into the environment (i.e. acid leakage from lithium batteries).

Diagram of a sealing screw.

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The design Sealing fasteners are engineered with a groove under the head of the screw or the face of the nut that — when combined with a rubber O-ring and tightened — squeezes outwardly to form a 360-degree, leak-proof hermetic seal.

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The undercut groove ensures that the O-ring will not break or crack once the screw is torqued. The metal-to-metal contact prolongs the life of the O-ring, which stays uncompromised under pressure.

Sealing fasteners are specifically designed to withstand harsh weather conditions and extreme temperatures.

Examples include when an unmanned underwater vehicle surveys the icy depths of the ocean floor or an unmanned vehicle operates in the extreme heat of the desert.

These components are also vibration and pressure-resistant, outperforming typical fasteners in highly pressurized environments. Such applications may include pneumatic pumps used in medical ventilators, pressure valves in industrial machinery, or rocket engines orbiting in space.

The benefits Since sealing fasteners can withstand harsh weather conditions and extreme atmospheres and temperatures, these components are ideal for use in autonomous robots and drones, including batteries and sensors. Such benefits make it possible for robots to venture into environments for long periods of time and perform tasks that are dangerous for humans — such as surveilling damaged power lines, windturbine blades, or even collecting and transmitting critical information about climate change from the Arctic.

Sealing fasteners are made of corrosion-resistant metals, such as stainless steel and steel alloys, titanium, or brass and Monel. This means they can easily be cleaned and are impervious to alcohol and other disinfectants.

These sanitary benefits make these fasteners a safe choice for sealing invasive and non-invasive medical instruments and equipment, ranging from laser scopes and surgical robots to kidney dialysis machines.

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Sealing fasteners are also available in different drives, head recesses and styles, and thread sizes. Rubber O-rings are offered in Silicone, Fluorosilicone, Viton, Neoprene, Buna-N, Teflon, and EPDM material.

Silicone rubber is a popular option because of its vast temperature range (62° to 204° C | 80° to 400° F) and its ability to withstand low temperatures without becoming brittle. However, it is not an optimal solution for oil resistance (Buna-N compound is resistant to petroleum-based substances).

The application If you’re unsure when to use sealing fasteners, there are three simple questions to ask. If the answer to any of the following questions is “yes,” then sealing fasteners are an ideal choice to protect and optimize the functionality of an application or equipment.

Does your high-asset machinery or sensitive equipment need an air-tight, hermetic seal to…

1 Ensure protection from possible exposure to oil, gases, liquids, chemicals, dust, dirt, moisture, salt water, or other contaminants?

2 Withstand extreme pressure, temperature, and/or weather conditions?

3 Prevent the seepage of pollutants leaking into the environment?

The standards Military-grade sealing screws and O-rings that meet the requirements of the Military Standard MS3212/MS3213/ NASM 82496 and are pressure-tested to 1500 psi are available through select manufacturers. This is also true of FDAapproved O-rings.

When purchasing sealing fasteners, it’s important to buy from a manufacturer that’s been certified or that meets the standards of DFARS, REACH, RoHS, and DEKRA and offers NEMA-ready solutions for electrical enclosures.

WHAT DO YOU THINK? Connect and discuss this and other engineering design issues with thousands of professionals online

Sealing fasteners are used to seal all sorts of equipment whether on land, in the air, or at sea, including: • Aircraft engines and motors • Circuit boards • Conveyor belts • Data centers • Drones and drone ports • Earphones • Electric charging vehicle units • HVAC systems

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• Invasive / Non-invasive medical devices • LED / Smart lighting • Night-vision goggles • Rechargeable batteries • Robots and co-bots • Sensors • 3D cameras / LiDAR technology

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SCREWS: SELF-TAPPING vs. SELF-DRILLING

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Self-drilling, flat-head screws.

What is the difference between self-tapping and self-drilling screws?

Screws that have particularly sharp threads, which can carve into a material, are often referred to as self-drilling screws. However, there’s a distinction worth noting when working with these types of screws that can make a significant difference in their use and application.

Typically, the screws are categorized into two types that are defined as “selfdrilling” or “self-tapping” — and these types are not interchangeable. Technically, both of these types of screws will tap their own threads (as most screws do to some degree), but the self-drilling screws are unique.

The tip of a self-drilling screw is shaped with a point and flute that resembles a drill bit. A notched area in the tip behaves as a reservoir to receive chips or filings as the material is carved away by the screw (when drilled). Thanks to this specialized tip, 38

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the self-drilling screw allows assemblers to skip the initial step of drilling a pilot hole. This feature makes self-drilling screws a time-saving and cost-effective choice for certain applications.

In contrast, a self-tapping screw typically requires an initial pilot hole before the fastening process can begin, and can have a sharp, flat, or blunt tip.

These types of screws are still incredibly common, with several styles and types available (and may also be referred to by their intended use — such as concrete, drywall, or wood screws).

When choosing the correct type of screw, it’s important to first consider the application, including the thickness and hardness of the material.

Here’s a rule of thumb: All self-drilling screws are self-tapping, but not all selftapping screws are self-drilling.

Essentially, a self-drilling screw is a self-tapping screw with the added feature of the drill point. With either type, the screws carve mated threads into the substrate for a tight fit. Both types of screws are typically made out of hard steel or stainless steel that has been treated to increase its hardness. A screw must be stronger and more durable than the material it will drill into to prevent failure of the joint or damage to the screw, material, or fastening tool.

These screws rarely require lock washers or other types of locking fasteners to prevent loosening.

Self-tapping and self-drilling screws are typically the fasteners of choice for construction, HVAC (heating, ventilation, and air conditioning), and other industries because of their ability to create a precise fit. They can be used to fasten several different materials, such as metal, aluminum, wood, drywall, and plastic.

Self-tapping screws are also suitable for thin sheet metal (one or two layers) and masonry applications.

Like most fasteners, these screws are also available in a wide variety of sizes.

Manufacturers often recommend an applied force and driver motor speeds when fastening a self-tapping or selfdrilling screw, based on the screw size.

Bottom line: although all self-drilling screws are self-tapping screws, these two fasteners are not interchangeable.

Mixing up the two can lead to errors and application failures.

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Zinc-coated, self-tapping screws.

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SEALS

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A gasket is a type of mechanical seal that can fasten the space between two or more mating surfaces.

These components are used in many applications, such as for creating a high-pressure seal between pipe flanges in industrial pipework.

How do gaskets perform as industrial seals?

Industrial seals are used to prevent leakage, hold pressure, and deflect contamination at interfaces between components. These components are used at static and dynamic interfaces.

Dynamic interfaces are typically linear (such as the seal between pistons and cylinders) or rotary (such as the seal between bearing housings and axles). Adhesives and gaskets are typically used as static seals. Examples of static interfaces include the entry point of bolts and screws, and the interface between an engine block and cylinder head.

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Adhesives, or sealants, include a range of substances that are capable of holding materials or two items together. A gasket is a flexible spacer that sits between two mating components. It’s made of a material that’s more malleable than these components, allowing it to fill any ridges or gaps due to surface imperfections.

The mating surfaces are often nominally planar and a gasket is cut from sheet material to fill the gaps between them.

Typically, a gasket is shaped as a ring or sheet and is available in several materials, such as rubber, polymers, metal, fiberglass, paper, felt, and others.

A gasket works by forming an air-tight seal between stationary components that can resist fluctuations in pressure and temperature. Such components are typically bolted together, exerting considerable pressure on the gasket.

As a result, it’s extremely important that gaskets are correctly specified and installed for their intended application and operating conditions. Incorrect gasket applications can damage an otherwise perfect assembly.

Along with pressure and temperature considerations, certain applications might have corrosive substances, unwanted gas, liquid emissions, or hygiene requirements (such as with medical device equipment). In other cases, electrical or electromagnetic forces might be a concern.

The primary purpose of most gaskets is as a seal, preventing ingress or escape of fluids. However, these components can do more than that. They can dampen and reduce sounds or vibrations. Some types are commonly used in appliances, HVAC systems, industrial machinery, and other equipment. Others are flexible enough to function as a safety pressure release. For example, it may be a vital

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function of a pipe gasket that if pressure builds, the gasket will fail before the pipe bursts.

When choosing a gasket, an oftenoverlooked consideration is whether it’s reusable. Several gaskets allow parts to be disassembled and then put back together, with the original gasket forming a seal once again.

Some gaskets, however, can only be tightened to form a seal once and then must be replaced if the components are taken apart.

A few different types of gasket include:

It’s extremely important that gaskets are correctly specified and installed for their intended application and operating

• Gaskets cut from sheet material – to seal engine and gearbox housings (such as the head gasket in an engine)

conditions. Incorrect

• Gaskets cut from neoprene rubber – to create a weatherproof seal, typically used in electrical enclosures

damage an otherwise

• Pipe gaskets – that resemble a large washer and sit between pipe flanges

gasket applications can perfect assembly.

• O-rings – a torus-shaped loop of elastomer that can be seated in a groove and compressed to form a seal.

Gaskets ideally serve as a type of seal against pressure or vibration. However, other product choices are available depending on the application. Adhesives can reduce the time and cost of certain assemblies. Sometimes they’re used to permanently bond a gasket.

But that also means they’re more difficult to disassemble than mechanical fasteners — and not reusable.

Additionally, a spacer (meaning a length of tube or even a washer) or a shim (a narrow wedge used for packing or leveling) might be the ideal choice to fill small assembly gaps between parts. Know your options and research the pros and cons of every component before making a choice.

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SPRINGS

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Springs are mechanical devices that store energy.

These devices are useful in many applications because they offer a controlled application of force or torque, in addition to their ability for storing and releasing energy.

What factors should be considered before choosing springs for fastening?

Small, interchangeable components may seem like a trivial consideration in the majority of applications. However, springs are an exception and care should be taken when choosing these components.

Mechanical springs are typically a helical metal coil that can extend or compress and when released, returns to its original shape. A spring can exert pressure, rotational force, or a pulling strength in several ways.

Choosing the ideal spring for an application will depend on several factors — including the application itself. It’s also important to determine the expected load or force and its environment. The spring’s size, material, and placement are dependent on such factors.

Here are a few more important considerations.

Specification It’s critical a spring fits its intended use and application. There are micro springs for electronic or medical devices and larger, heavy-duty ones used for industrial equipment and sectors such as aerospace, automotive, agriculture, and energy.

Factors to account for when specifying a spring’s size include the: • Size and weight of the intended load • Requirement of the spring, including the maximum deflection (or travel distance) • Mounting location and configuration One key consideration is to ensure the spring is not subject to excess load to ensure longevity and reduce wear or failure.

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Types of springs Typically, manufacturers will specify a spring’s design tolerances.

Take a compression spring, for instance. The outside diameter of such a coil spring will expand when compressed, which is a critical factor if the spring is placed in a tube or a bore during assembly. If the tolerance range is positive, the spring’s dimensions may be slighter larger and this could add to the assembly size.

In compression springs, the maximum deflection must also be less than the difference between the spring’s free length (uncompressed) and its solid length (fully compressed). This means pre-loading the spring, so its initial position is shorter than the free length.

On the other hand, extension springs are rated with a maximum operating length, after which the spring may be at risk of permanent deformation.

There are several types of springs. A few common types of mechanical springs include: Compression springs are open-coil helical springs that resist compressive forces. This means when a heavy object or force is applied to the spring, it condenses, storing the force until released. The more pressure or weight that’s placed on the spring, the more energy or strength the spring exerts.

Compression springs are common and used in several applications, including pens, mattresses, and automotive suspension systems.

Torsion springs are helical springs that exert a force or torque in a radial direction to create load. Unlike compression springs, which are designed to keep mechanisms apart, torsion springs hold two mechanisms together. A torsion spring’s tightness is proportional to the energy it stores. To release this energy, tension must be removed from the spring. Objects that use torsion springs include clipboards and mousetraps.

Conditions What conditions will the spring be subject to? For example, harsh conditions or temperatures eventually lead to damaged or unreliable operation. Damp or wet conditions, including condensation, can result in material corrosion and degradation of the spring. Humidity and extreme heat can also lead to the expansion of metal fasteners.

Vibration can be a factor in certain applications, which can cause unnecessary wear, imbalance, or misalignment. Unplanned downtime can result but in critical applications, such as in aerospace equipment, safety may be at risk.

First, assess the environment and potential hazards to select the ideal spring material. High-quality materials, such as high-grade stainless steel, can increase temperature resistance. A protective coating may also be necessary in certain cases to reduce corrosion.

Helical vibration isolators, which are multi-directional wire rope isolating devices, can protect against shock and vibration. Vibration isolators can be used in several applications, including for fragile electronic equipment or heavy machinery (and during operation or while in transit).

Materials Springs that rust, wear, or break quickly are of little value and can pose a safety hazard. Take the time to evaluate and choose a spring with the ideal material for the application. This will include an assessment of the operating temperature and corrosion-resistance requirements.

Every metal has a maximum operating temperature rating.

Springs are often made of stainless steel but different grades can offer different features. For example, Grade 302 stainless steel is often used to resist solvents and chemicals, making it a good option for certain medical or laboratory equipment. Grade 17-7 stainless steel is more durable, however, and offers a higher level of temperature resistance. It’s often used in the automobile or energy sectors.

There are also a variety of coatings or finishes that can protect springs from harsh conditions or elements, depending on the application. Generally, it’s best to consult with a fastener expert.

Remember, an application is only as strong as its weakest part.

Choose wisely.

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Extension (or tension) springs absorb and store energy, and create a resistance to a pulling force between two mechanisms. Typically, extension springs have hook or loopend configurations that can attach to other mechanisms. The spring will attempt to pull these items together if they separate.

Extension springs are used in tensioning devices, switches, and levers.

Wire form consists of wire that has been bent into a specific shape for a set purpose — and quite commonly as a spring.

But they may lack the helix or coil configuration as part of their design (think instead of a spring cotter pin). These components offer versatility and can feature complex and customized shapes that can range in size. As a result, wire form is used in several industries and the shape and material employed is dictated by the final application.

Extension springs are coiled springs that can be stretched to increase their length, causing tension force in the device.

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TOOLS

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A selection of tools for installing fasteners.

What tools are used in industrial fastening?

There are several types of fasteners and so, too, are there many different tools for securing and removing these components. The choice may seem simple — a screwdriver for a screw, a hammer for a nail — but generally there’s more to making a wise decision for a project. It’s important to consider the application and the fastener itself, including its type, material, shape, bit and thread size, and so on.

The use of an incorrect tool is a serious safety hazard and can lead to an insecure joint or attachment, a broken or faulty fastener, or a damaged application. Misuse or the wrong choice can also lead to injury to the user.

Certainly, there are several general-purpose tools used for fastening, such as the hammers to drive nails or align parts, and the drills to create holes or drive fasteners.

However, there are also advanced torque tools (with cordless and digital options), and specialized tools for tightening threaded fasteners, inserting rivets, and applying adhesives or welding.

Before choosing the optimal tool for your application, do the research or ask an expert to ensure the safest, most accurate fit. Always follow the manufacturer’s

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instructions, inspect and maintain tools before use, wear personal protective gear when required, and know your work environment.

Tightening threaded fasteners Tools for use on threaded fasteners include screwdrivers, drivers, spanners, sockets, keys, and ratchets. Air-powered or electrical tools can also be used. The choice will depend on the fastener (such as the head and thread size) and the application. For example, certain projects may have limited access or less versatility than others.

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Consider the ergonomics Achieving an accurate torque level when fastening can be a challenge. Insufficient preload caused by an inaccurate tightening method is a frequent cause of bolted joint failure.

However, advances in digitalization with certain tools are changing the way torque is applied, providing greater accuracy, performance, and accountability. Many torque tools now offer built-in torque gauges and readings for better accuracy.

Drilling holes Several types of fasteners, including bolts and rivets, require a hole to be drilled before installation. Drill types include handheld drill-drivers, electric drills, drill presses, milling machines, and orbital drilling machines.

Drills and manual milling machines create holes the same size as the drill bit or cutting tool that’s used to create the hole.

When a CNC milling or orbital drilling machine does so, the cutting tool is a smaller diameter than the final hole. As the tool advances into the material, it moves in a spiral path. This means the diameter of the final hole will be the diameter of the cutting tool plus the diameter of the spiral path. This type of drilling produces cleaner holes, lower reaction forces, and less vibration.

Installing rivets Traditional solid rivets are a highly effective fastener that has been widely used in the construction of aircraft and large steel structures. Hammers and anvils were conventionally used to form their heads after the rivets are properly fitted. But this requires access from both sides of the hole, with the anvil placed against one end of the rivet and the hammer striking the other end.

Where once handheld hammers were used, these tools have been largely replaced by hand-held air hammers or automated drilling and riveting machines, which use hydraulic or electromagnetic presses.

When only one side of an application is accessible, blind rivets are an ideal choice. These components are installed from one side, by drawing their integral mandrel back through their body. Special riveters are used to draw the mandrel. Manual tools include plier-type riveters, which are typically compact and inexpensive, and lazy-tong rivet tools, which can install rivets that require great force.

Electric and cordless rivet guns have also advanced to include features for easier and more accurate use, such as auto-feed capabilities that let operators align workpiece holes in one hand while riveting with the other.

Applying adhesives Some tools used in the application of adhesives are dispensers, such as caulk guns or dispensing nozzles (for precise dot or bead placement). Also, in electronics assembly, jetting is a common application method because it allows for dispensing adhesives in small spaces.

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Safety is paramount for each project and at every worksite. Hydraulic torque wrenches have pinched off fingers because of improper use. Long and messy cords from power tools can easily get in the way and cause trips or falls.

Heavy tools and repeated handling can also lead to over-exertion and injury, including damage to hands and wrists, shoulders, and the lower back. Advances in ergonomic tools may help reduce worker fatigue and injuries while increasing performance.

Additionally, reducing the weight of heavy power tools or combining features of several tools into one (to avoid downtime from having to switch from one to the other), may increase worker safety and efficiency. Depending on the tool and application, there are also adaptors, attachments, and holders that can better support the user.

Do your research. Use the right tool for the job — and the right tool for the user.

Generally, adhesives are now supplied in containers designed to enable easy application — meaning it serves as the tool.

Brushes, sprays, spreaders, weighted rollers, and other application methods may be used, including equipment for the bonding process, such as those used to apply heat. For example, glue guns are a commonly used tool to apply hot glue.

Welding Welding may be performed using a gas torch, electric arc, ultrasound, or high-energy beam (either laser or an electron).

Each of these options requires different tools. Different forms of arc welding are used for fastening, including spot, stick, MIG, and TIG welding.

These require tools with different power suppliers, supplies of shielding gas, and wire feeds. Angle grinders, a handheld power tool that can be used for a variety of metal fabrication jobs that include cutting, are typically used to prepare joints for welding.

Welding also requires the proper protective gear. Ensure safety is the top priority when assembling any project.

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TRAINING

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Training and product knowledge lead to greater safety, accuracy, and confidence on the job. It’s important to know your fastener facts.

What are some critical fastener facts every supplier and user should know?

Fastener Training Institute An icon in the fastener industry, the late Joe Greenslade taught mechanical fastener technology for 45 years and published more than 300 related articles. He served eight years as the Director of Engineering & Technology at the Industrial Fasteners Institute, a trade organization that has served the interests of North American mechanical fastener manufacturers since 1931.

Greenslade answered thousands of fastener technology questions from around the world. He once wrote: “As in most things in life, a relatively small body of knowledge provides the answers to the most frequently asked questions.”

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In 2015, he compiled a list of his most frequently asked questions with answers that cover the specifying, inspecting, and installing of mechanical fasteners — and more. Here are 15 of those questions and his answers (including a few added points from the non-profit Fastener Training Institute), which are simple and direct.

They’re an ideal resource for suppliers and users when on the road to becoming a fastener expert.

fastener it will be used with, choose a nut with a proof load strength that is equal to or greater than the minimum bolt tensile strength.

FTI: The proof load capacity of nuts and the ultimate tensile strength of screws and bolts can be found in the various fastener standards, including those published by the American Society of Testing & Materials (ASTM), the Society of Automotive Engineers (SAE), and the International Standards Organization (ISO).

What are the major differences between hex bolts and hex cap screws?

Joe Greenslade (JG): The major difference is that hex cap screws have washer faces, LB dimensions, and a chamfered point. Hex bolts do not.

Fastener Training Institute (FTI): LB is the body length of the cap screw. Chamfered point refers to the end of a cap screw, beveled to protect the first thread from damage — and to facilitate entry into an internally threaded part, such as a tapped hole or nut.

What style of nut is used with structural bolts?

JG: Heavy hex nuts are used with structural bolts.

FTI: Heavy hex nuts are slightly larger and thicker than standard finished hex nuts. There are several grades and the heavy pattern is typically used with a large diameter and high-strength bolts.

What is the inherent danger of zinc-plating socket head cap screws?

JG: The inherent danger of zinc-plating socket head cap screws is hydrogen embrittlement (HE). To lessen the probability of failure from HE when zinc-plating socket head cap screws, bake after plating at 400° F for 14-24 hours and test.

FTI: HE, or hydrogen embrittlement, is a permanent loss of ductility in a metal or alloy caused by hydrogen in combination with stress — either applied externally or from internal residual stress. Generally, HE is classified under two broad categories based on the source of hydrogen: internal hydrogen embrittlement (IHE) and environmental hydrogen embrittlement (EHE), according to the “Fundamentals of Hydrogen Embrittlement in Steel Fasteners,” by Salim Brahimi.

Why should plated or coated socket products never be used in an application that’s outside or in a damp environment?

JG: Plated or coated socket products should never be used in an application outside or in a damp environment because their hardness is over HRC 39, which makes them susceptible to stress corrosion failure, also referred to as environmental hydrogen failure (EHE).

How do you select a nut grade to match with the bolt or screw it will be used with?

JG: The desired mode of failure of a bolted joint is the complete fracturing of the bolt or screw instead of the stripping of the thread of the nut or in the internally threaded component. To select the ideal nut grade to match the

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What are the most common material and strengths for inch machine screws?

JG: The most common material for this type of screw is carbon steel and the most common strength of 60,000 PSI. FTI: The American Society of Mechanical Engineers (ASME) defines machine screws as featuring a diameter of up to 0.75 inches. They can be smaller than 0.75 inches in diameter, but they cannot be larger than this size. In addition to the diameter, machine screws are characterized by uniform threading. Uniform threading means the exterior threading — the helical ridges on the outside of the screw — remain the same size from the top of the screw to the bottom.

When 0.0001-inch of plating is applied to an externally threaded fastener, how much does the pitch diameter increase?

JG: The pitch diameter of an externally threaded fastener increases by 0.0004 inches when 0.01 inch of plating is applied.

What are the types of inch tapping screws?

JG: As follows…

• Thread forming screws: Types A, AB, B, C • Thread cutting screws: Types T (23), BT (25), D (1), F, BF • Thread rolling screws: Type TRS When a customer reports a fastener failure, what information should be gathered before starting to try to remedy the problem?

JG: Identify the exact part number, lot number, precise description of the failure, and/or pictures of failed parts. Identify where the parts are used, obtain information about how the parts are driven, and how the tightening is controlled. Finally, gather a sample of broken and unused parts for analysis.

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WASHERS

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Flat washers are used to protect surfaces by evenly distributing torque when a bolt or screw is tightened.

When are washers used with fasteners and why?

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A washer is a thin plate with a concentric hole that’s typically used to evenly distribute the load of a threaded fastener. Before a threaded fastener (such as a screw) is driven into a surface, a washer may be placed through the end for greater protection.

This prevents the bolt head and nut from scratching or indenting the surfaces of the two fastened parts, which could ultimately loosen the fastener. Additionally, driving a screw into wood might cause the wood to crack around the surface and a washer helps to reduce this from happening.

Several different types of washers are available to suit different applications. For example, vibration-isolating washers are designed to absorb vibrations. These components are made of a soft material, such as plastic or urethane. Occasionally, metal washers are also used as spacers to increase the distance between the parts being fastened.

Two of the most recognized washers are flat and spring washers. Let’s review each one.

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A spring washer offers axial flexibility that’s intended to prevent loosening of the fastener with which it’s paired.

However, the effectiveness is limited to only certain applications.

Flat washers The role of flat washers is to increase the size of a screw’s bearing surface area, reducing the surface pressure applied on the fastened object.

Looseness can result when the bearing surface sinks under the surface pressure, so using a flat washer diminishes the likelihood of this effect. This is particularly important if the contact area between a screw’s bearing surface and the object being fastened is small or if it’s made of a soft material, such as aluminum or resin.

Since flat washers are generally manufactured by pressing metal, one side has rounded corners and one side has burrs.

There is no fixed rule about which side should be placed up or down but placing the burred side facing down is typically ideal, and especially if bearing surface pressure is a concern.

However, these burrs can also mark the surface of the fastened object during tightening so, for certain applications, it may be better to put the rounded side down to avoid plate peeling.

Spring washers Spring (or locking) washers are made by cutting out part of a flat washer so that it can form a twisted shape. As a result, a spring action or an elastic force operates. Unlike flat washers, which are placed on both the bolt and nut side, spring washers only go on the nut side of the fastener to establish a bond.

Originally, these washers were thought to be effective against looseness because of the increased frictional force provided by the cut part, which “bites” into the bearing surface. In theory, the sharp edges of the washer (which are also sometimes serrated) dig into the nut and mounting surface and prevent counterclockwise-rotation or loosening. This would make these components ideal in high-vibration machinery.

Unfortunately, this locking effect due to “biting” is limited to applications in which the material of the fastened object is softer than the metal washer. Essentially, the elastic force of the spring washer is negligible compared to the axial force of the screw that’s tightened. So, when the elastic force of a spring washer just starts to take effect, the screw is already in a loosened state.

What’s more is the sharp hold from spring washers typically leave the bearing surface scratched, which is not ideal for repeated installation or removal. There are certainly examples of the use of spring washers paired with flat ones in attempts to avoid damaging the bearing surface. But this is rarely effective and the result is little if any locking effect.

In general, washers are used to distribute a fastener’s load, reducing friction and loosening. Regardless of which washer is chosen, however, tightening with the proper torque is the best way to ensure a reliable hold and a safe application.

DESIGN WORLD

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An alternative

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As an alternative to conventional spring or lock washers, eccentric lock washers can be combined with commercially available hex nuts to prevent screw loosening. These washers require no special tools for fastening. This means they are as easy to use as flat or spring washers.

In terms of design, these components consist of a bearing washer and an eccentric washer. When the eccentric washer is wedged into a bolt, the bearing washer changes the commercially available hex nut into an anti-loosening nut.

This is based on the locking principle, which works like this: • By tightening the hex nut, the eccentric washer wedges into the bolt.

• The bearing washer presses the hexagon nut into the bolt.

• As the bearing washer pushes the hexagon nut, the frictional force between the hexagon nut and the bolt increases and prevents loosening.

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WELDING

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A top-down view of a typical laser-welding process. The tube-like structures at the top are laser diodes, positioned around the perimeter of a welding tool (shown in gray). The inset at left shows how laser beams are projected through a waveguide (the yellow layer) at the base of the welding tool, through the transparent part (gray), and into the absorptive part (blue). As heat accumulates in the weld zone (the interface between the parts), they’re compressed together to make a clean, finished weld.

All images courtesy of Emerson

What is laser plastic welding and how has it advanced?

Priyank Kishor • Global Product Manager Laser Welding for Branson at Emerson For manufacturers that strive to deliver a sense of craftsmanship to their products, plastics can pose a challenge because they lack the cachet of older, more conventional materials. The same is true for the methods of assembling plastic products, which are typically optimized for speed and simplicity instead of cleanliness or aesthetics.

Nonetheless, several higher-end electronic, automotive, and medical device manufacturers are now delivering quality assemblies of plastic parts, thanks to laserwelding technology. This gentle and ultra-clean joining process is remarkably versatile.

When compared to friction-based joining processes, such as ultrasonic welding, laserbased technology can join a broader range of polymer materials. In ultrasonic welding, high-frequency ultrasonic acoustic vibrations are applied to workpieces that join under the pressure. However, laser welding can quickly provide reliable hermetic seals, precisely

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An example of a laser welder that provides high-volume welding of small, medium, and large parts — the Branson GLX Micro Laser.

aligned parts, and nearly invisible weld joints in a single cycle that lasts only seconds.

The process is simple: Laser welding uses light generated by laser diodes in the 980-nanometer wavelength. This light is concentrated through fiberoptic bundles connected to the weld tooling, and then accurately aimed through wave guides that are positioned to cover the weld area of the parts. The concentration of the bundles over a part varies according to the heating density required for welding.

This ability to specifically control and focus the beam leads to extremely clean, precise welds with little “slag” or need for rework. Plus, focusing the laser with such precision results in a greater power density with much less heat generation.

This form of welding is fit for a cleanroom production area just as much as in a busy manufacturing plant.

Traditional laser welding – requires the use of two distinct parts in each assembly. The part closest to the light source is made with material that’s “transmissive” or clear to the laser wavelength. The mating part uses material that’s “absorbent” or black to the wavelength of the laser light.

“Clear-on-clear” laser welding – A recent innovation makes it possible to weld two transmissive or “clear-onclear” parts. The key to this process is to precision-treat the weld surface of one of the clear parts with a biocompatible laser absorber before welding. The laser absorber consists of microparticles of pigment dye or carbon black that are suspended in a carrier fluid, such as isopropyl alcohol or acetone.

During the welding process, the laser energy hits the absorber and consumes it, releasing heat energy that conducts through the weld zone of both of the mating parts. Then, the two parts are bonded together under compressive force.

Low-force laser welding – Advancements in actuator technology, used on the laser welder, is now enabling precise welds of extremely small and delicate plastic parts. When combined with an advanced laser’s ability to precisely aim heat energy, the actuator can manage low-clamping forces. This simplifies the joining of parts, which can be extremely small, complex in geometry, or embedded with electronic components, wiring, or sensors.

When ultra-low compressive forces are used in the welding process, the risk of part deflection, bending, cracking, or damage to embedded electronics is virtually eliminated.

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Today’s products — whether cars, appliances, computers, or wearable devices — demand superior design, functionality, and execution in assembly to maximize usability and durability. As laser-welding technology has evolved, it’s delivering craftsmanship and aesthetics to a wide range of materials and for several applications.

Two clear mating parts (shown on the right) can be laser welded into a finished assembly (on the left) by using an innovative new laser-welding process. One of the clear parts must first be treated with a laser-absorbing solution before welding.

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NBK America NBK’s historic past since 1560 has allowed it to provide new value to customers by constantly renewing itself. The NBK brand stands for strong design, precise manufacturing and sales of products based upon the needs of its customers. NBK provides high-precision, high-performance specialty screws and machinery components such as the following: Low Profile, Small Head, Vacuum Ventilation, Seizing / Galling Resistant, Specialty Metal (Inconel, Hastelloy, etc.), Miniature, Captive, Clamping, Tamper Resistant, Plastic, Loosening Resistant, Ball Roller (Transfer), Roller Chain Bolts, Spring Plungers, Knobs, and more. Furthermore, NBK has Flexible Shaft Couplings, Wireless Positioning Units, Clampers, and additional products. We can customize these products flexibly should the need arise.

NBK products are used in advanced industries, such as manufacturing equipment for automation, robotics, semiconductors, and medical devices.

NBK America LLC 307 East Church Road, Suite 7 King of Prussia, PA 19406 Phone: 484-685-7500 Fax: 484-685-7600 Email: info.us@nbk1560.com

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Pivot Point Pivot Point is a designer and manufacturer of Non-Threaded Fasteners - i.e. Clevis Pins, Cotter Pins, Quick-Release Pins/Devices, Wire Rope Cable Assemblies, and more. A family-owned company, the Leitzke family’s manufacturing heritage dates back to the 1920’s, and continues today in Pivot Point’s line of classic, and unique, fastening solutions.

Wide stock selection and endless customization options allow us to solve application challenges on tight timelines, fixed budgets, and with creative solutions. Pivot Point is known for our inventive, original, fastening solutions like our SLIC Pin (a quick-locking pin, self-contained, pin and cotter), Bow-Tie Locking Cotter, Rue Ring Locking Cotter, U-Lock Nylon Tether and others. Our state-of-the-art Wisconsin manufacturing facility features in-house pin design as well as automation capabilities, making Pivot Point a powerhouse in fastening solutions - at prices that can compete with imports. Pivot Point is proud to offer Digital Product Training – a live interactive session that covers “Non-Threaded Fastener Basics”.

The training is tailored to industries, teams and individuals, and schedules. Full of application examples, product comparisons, and technical information, the 1 hour (or less) session is intended to round-out the knowledge of any design engineer. Reach out today and let us know how we can help.

Pivot Point, Inc. PO Box 488 761 Industrial Lane Hustisford, WI 53034 Phone: (800) 222-2231 Fax: (920) 349-3253 Email: mail@pivotpins.com DESIGN WORLD

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Würth Engineering: A Great Way to Outsource Fastener Problems Whether your business is in manufacturing, energy, transportation, heavy equipment, recreation, construction, agriculture, or military, WINA’s team has experience in your area. Spanning the United States, WINA’s team of 21 professionals bring a wide range of experience by industry, with over 380 years of working knowledge to apply to the solution of your issues.

Würth’s Part to Print Reviews will compare your current inventory with your drawing requirements to confirm that your parts and drawings are consistent, as well as meeting your standards.

Würth uses an International Part Number Database to manage SKU’s across our customers’ sites.

This enables standardization of part numbers and descriptions, both within Würth’s system and within our customers’ systems. Criteria include diameter, length, head style, property class, plating, standards, and more.

The database makes it easy to help our customers simplify and standardize their descriptions, as well as rationalize similar sizes, materials, and coatings.

Their technical team works on Value Added and Value Engineering (VAVE) projects for our customers.

Some projects are as simple as a consolidation of similar fastener sizes or materials to achieve cost savings. Other projects are as complex as taking over a large kit that the customer is building onsite and freeing up personnel and space resources that the customer can take advantage of, in addition to product cost savings. Others include the proposal of more cost-effective manufacturing processes, such as changing from screw machines to cold forming operations, or from casting to powdered metallurgy.

For more information, please contact us at: www.wurthindustry.com info@wurthindustry.com (877) 999-8784

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FASTENER FASTENER DESIGN WORLD

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Selecting the Optimal Washer Flat: Generally used for load disbursement Tab/Lock: Designed to effectively lock an assembly into place Finishing: Often found on consumer products Wave: For obtaining loads when the load is static or the working range is small Belleville: Delivers the highest load capacity of all the spring washers Fender: Distributes a load evenly across a large surface area Shim Stacks: Ideal for simple AND complex applications

Boker’s Inc. 3104 Snelling Avenue Minneapolis, MN 55406-1937 Phone: 612-729-9365 TOLL-FREE: 800-927-4377 (in the US & Canada)

bokers.com

Branson PulseStaker from Emerson Offers Unique Temperature Control With the new Branson™ PulseStaker™ technology from Emerson, you can now swage and stake plastic parts with exceptional precision and outstanding aesthetic results. Unlike conventional heated swaging tips that offer only one temperature setting, PulseStaker tips can vary their temperatures, delivering instant heating or cooling pulses that melt, form and solidify strong part-to-part bonds without the risk of sticking or burning.

The unique temperature control offered by the PulseStaker process enables you to swage and stake parts with complex curves and contours, closely positioned or delicate features, heat-sensitive PCBs or circuits, and even high-glass-fill content or chrome plating.

Learn more at Emerson.com/Branson

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Ad Index Boker’s Inc. ..........................................IFC

SALES

Ellsworth Adhesives ......................... 22

Jami Brownlee

Emerson ...............................................30

jbrownlee@wtwhmedia.com 224.760.1055

Ming Tai Industrial ........................... IBC

Mike Caruso

NBK America LLC ................................ 15

mcaruso@wtwhmedia.com 469.855.7344

Pivot Point Inc. ................................... 23

Bill Crowley

Würth Industry North America .... BC

bcrowley@wtwhmedia.com 610.420.2433

Zago .......................................................34

Jim Dempsey

jdempsey@wtwhmedia.com 216.387.1916

2020

Michael Ference

mference@wtwhmedia.com 216.386.8903 @mrference

Vendors in the fastener industry

Mike Francesconi

Courtney Nagle

cseel@wtwhmedia.com 440.523.1685 @wtwh_CSeel

LEADERSHIP TEAM

Publisher Mike Emich

memich@wtwhmedia.com 508.446.1823 @wtwh_memich

Managing Director Scott McCafferty

smccafferty@wtwhmedia.com 310.279.3844 @SMMcCafferty

EVP

mfrancesconi@wtwhmedia.com Marshall Matheson 630.488.9029 mmatheson@wtwhmedia.com 805.895.3609 Neel Gleason @mmatheson ngleason@wtwhmedia.com 312.882.9867 @wtwh_ngleason

NBK America LLC ............................... 52 Pivot Point Inc. ...................................53 Würth Industry North America .....54

Jim Powers

jpowers@wtwhmedia.com 312.925.7793 @jpowers_media

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DESIGN WORLD

12/6/20 2:20 PM

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Tel: 886-2-26228651 Fax: 886-2-26220202 E-mail: mtis@powerspring.com.tw www.powerspring.com.tw

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