ASSEMBLY: Fasteners

from DESIGN WORLD_FASTENER ENGINEERING HANDBOOK 2022

by WTWH Media LLC

WELDING: Materials

How to keep fasteners from loosening?

Article courtesy of JW Winco

Ensuring fasteners remain tightly sealed in applications prone to vibration is a question engineers frequently attempt to solve. Eventually, vibration loosens fasteners by creating relative motion between the threads. This occurs to all nuts and bolts subject to movement, no matter how well you tighten them. Loose fasteners are certainly a maintenance nuisance but also a hazard in several applications, including in power generation, transportation, manufacturing, and others. The result can lead to accelerated wear, damaged parts, reduced equipment longevity, and safety concerns. Adequate torque is an obvious fi rst step to ensuring fasteners are properly installed. Using washers to lengthen the ratio of clamped length is another option for certain applications. The washer can add extra friction to the joint and maintain the clamping force. Vibration-proof fasteners o er another alternative. These are fasteners specifi cally designed to cope with small movements and vibrations typical of some applications.

Understanding vibration-proof fasteners Quality counts. Some fasteners are better designed to cope with vibration than others. For example, vibration-proof fasteners are engineered to prevent self-loosening due to vibration. These include hex nuts with nylon inserts, jam nuts, lock nuts, slotted hex nuts, tooth lock washers, lock washers, and spring washers. Such fasteners may have a unique thread design that distributes stress more evenly or an extra clamping system that reduces rotation. There are also spring plungers with a nylon locking element that are ideal for applications with limited space. They use a spring force to apply pressure, so the ball or nose remains positioned or locked. PFB (Polyamide) patch types are a threadjamming material that also provides some anti-vibration properties that can hold ball plungers in place. Vibration-proof fasteners are a must for certain applications, such as those subject to heavy vibration and challenging conditions. These types of fasteners are better able to handle movement and prevent self-loosening for added security.

Unfortunately, there is no failsafe solution. The e cacy of vibrationproof fasteners will depend on the application, so maintenance checks are essential.

Tips for choosing vibration-proof fasteners • Consider the application. What environmental factors must it withstand? What amount of stress is typically placed on the fasteners? • Is heat a factor? High temperatures are commonly used in critical industries, such as the energy, aerospace, automotive,semi conductor sectors, and others. Specialty fasteners that can withstand harsh conditions (and vibration) are required in these industries. • Know the shear strength and the ability of the fastener to withstand lateral force without breaking. • Ensure regular maintenance and repairs. Is there a need for disassembly? If so, you’ll want to consider low to medium-strength fasteners, which require hand tools. Higher-strength fasteners typically need the application of heat for disassembly. Either way, regular maintenance checks are critical in high-vibration or harsh conditions. • Thread size makes a di erence. Smaller thread sizes make it more challenging to remove fasteners, whereas larger thread sizes typically reduce the e ectiveness of the bond. Know the needs of your application to make the wisest choice. Also, work with a quality manufacturer or supplier who can make the ideal recommendations for your project.