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A TYRE REBORN

Retreading breathes new life into your worn used tyres

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A TYRE REBORN

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contents Rubber: the natural choice

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The origins of rubber; how is it made?

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SPEED KILLS

Excessive speed, load and pressure can limit the life span of your tyres

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real QUESTIONS real ANSWERS Bridgestone Middle East & Africa FZE P.O. Box 16813, Jebel Ali Free Zone Dubai, UAE For correspondence with this publication please write to us through our postal address or by email to realanswers@bridgestone.ae. An electronic version of this publication is available at www.bridgestone-mea.com

Engineering the construction of tyres

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Just how is a truck tyre ‘built’ today?

Tread patterns: making an informed choice

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Selecting the most suitable tyre pattern for your operations

Fitting tube-type tyres right

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A guide to the safe mounting and demounting of tube-type truck tyres

Know your enemies

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The do’s and don’ts in vehicle load/speed and tyre pressure Nicholas Publishing International FZ-LLC

P.O. Box 500573, Loft Office 1, Entrance C, G06, Dubai Media City, UAE Tel: +971 4 3671867 Fax: +971 4 3908022

Breathing new life into worn tyres

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How are worn-out tyres retread?

For editorial enquiries, contact Michael Gordon, Special Projects Editor michael.gordon@npimedia.com Tel: +971 4 3671867

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january 2009 real questions real answers

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| foreword

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FOREWORD The market has changed considerably since our last issue of Real Questions Real Answers and so has our magazine.

We have refocused the publication to give our readers a comprehensive guide to the proper utilisation and optimisation of their assets in reflection of the ever increasing pressure of cost competitiveness.

This new-look magazine is designed to be an authoritative voice for the industry on the selection, utilisation and maintenance of fleet tyres throughout the Middle East and Africa. From this issue onwards, we will be addressing the issues that concern you, our readers, the most.

We have taken on board all of the invaluable comments you sent us after our successful launch issue, and we have adapted these into the magazine to ensure we continue to address your technical tyre requirements.

In this issue we will detail how a tyre progresses from the latex sap, derived from trees, through to the durable tyres your fleets rely on. We have a feature explaining how rubber is manufactured, which will flow into a piece on how tyres are 'built', followed by a guide to selecting the most appropriate tyre for your operations, a piece on mounting and demounting your tyres safely and finally an illustration on how used tyres are given new life with retreading.

As we continue to change and grow as a magazine, stage by stage, we urge you to continue sending us your feedback and questions. As I explained, this magazine is a vehicle to make your life easier as fleet owners, so do let us know whatever it is that is holding you back and we will endeavour to help you unlock your potential.

Send your questions to realanswers@bridgestone.ae and we will try to answer them in our forthcoming issues. As partners in the tyre business we can work together to find all the necessary solutions.

In the meantime I hope you enjoy our latest offering and that it provides you with the Real Answers you need.

Hiroshi Nakanishi, Director Technical Service & Commercial Tyre Marketing

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| Product Profile

Traditional methods of removing sap from the Hevea Brasiliensis tree are still used today

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| Product Profile

Rubber: the natural choice Natural rubber was first discovered over 250 years ago and by the early 20th century man learnt to synthetically reproduce this natural wonderstuff. Today, rubber is used extensively in many applications, both natural and synthetic, not least in the production of tyres.

Is rubber entirely natural or can it be man-made?

There are two common forms of rubber in use today – natural and synthetic.

Natural rubber is tapped as a sap from trees and the synthetic rubber is created as a derivative of petroleum.

Today the bulk of the rubber produced is the synthetic variety but nature still makes a better quality product than man.

Does the industry utilise more natural or synthetic rubber in its manufacturing process?

Approximately 70 percent of all rubber used globally is synthetic, according to the Rubber Manufacturers Association (RMA)*, and in the production of tyres the split is 60/40 in favour of natural rubber (of course depending on the type of tyre).

Natural rubber offers superior properties over synthetic in most truck tyre applications. For example, natural rubber lasts a long time and tends to run cool – especially under severe conditions.

It also has very high tensile strength, which means the tyre can easily withstand repeated flexing and can still spring back to its original shape.

It offers superior resistance against cut/chip and tears for tyres that operate in on-and-off roads.

Apart from tread, natural rubber is particularly good in the tyre casing, where the bonds must be maintained between the steel cords and the rubber.

However, natural rubber is not so effective for wet traction and uneven wear.

Until engineers can invent an absolutely perfect synthetic polymer that does everything well, various combinations of manmade polymers will be blended with different amounts of natural rubber to achieve the right balance for the tyre application.

So different tyres have different rubber compounds?

Exactly. For a highway tyre, the engineers would blend various compounds that create a tread that is best for long, even tyre wear, low heat build-up and high tensile strength.

For on/off-highway tyres the engineers blend different polymers – including natural rubber – so the tread compound promotes durability and cut, chip and tear resistance.

How many chemical types of rubber are there?

There is only one chemical type of natural rubber, but there are approximately twenty different types of synthetic rubber and within each type there are many distinguishable grades.

What exactly is natural rubber?

Natural rubber is an elastic hydrocarbon polymer, or elastomer. An elastomer is a material with the mechanical (or material) property that it can undergo much more elastic deformation under stress than most materials and still return to its previous shape without permanent deformation.

It is derived from a milky colloidal suspension, or latex, found in the sap of certain trees – most commonly today, the Hevea Brasiliensis (Para Rubber Tree).

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What is the chemical composition of natural rubber?

Natural rubber is made up predominantly of polyisoprene, a polymer of isoprene, which is one of the most well known natural polymers. The composition also includes a small percent of other materials, such as proteins, fatty acids, resins and inorganic materials.

Is the Hevea Brasiliensis the only rubber producing tree?

The Hevea Brasiliensis is the most widely commercially used rubber plant because it responds to wounding by producing more latex. Other plants containing latex include Figs (Ficus Elastica), Castilla (Panama Rubber Tree), Euphorbias, Lettuce, The Common Dandelion, Taraxacum Kok-Saghyz (Russian Dandelion), Guayule and Scorzonera Tau-Saghyz.

| Product Profile

natural rubber in many cases, especially when improved material properties are needed.

Synthetic rubber is made from petrochemical feedstocks, and crude oil is the principal raw material.

The tree is cut in a practiced method to gain the maximum sap whilst not overly harming the tree

How is synthetic rubber produced?

General purpose synthetic rubber is produced principally from two gases: butadiene, a by-product of petroleum refining; and styrene, captured either in the coking process or as a petroleum refining by-product.

When these two gases are mixed, in the presence of soapsuds in a reactor, the result is liquid latex. The dry rubber in this milky liquid is then coagulated into crumbs, washed, dried and baled ready for shipment.

Henry Wickham

What is latex?

The latex that plants produce is discharged from cuts and abrasions as a milky sap.

All latexes are emulsions (aqueous suspensions of insoluble materials), which can include alkaloids, terpenes, resins, phenolics, proteins, and sugars.

However, not all latexes are elastic. It is only those that contain long-chain hydrocarbons that are elastic.

The elastic latex is tapped from the tree, collected and left to coagulate before it is compressed to remove any water, leaving only the strong and pliable material know as rubber.

For how long will a rubber plant continue to produce latex?

The economic life period of rubber trees in plantations is around 32 years – 7 years in the immature phase and around 25 years in the productive phase.

FAC T

The Port first Eu uga rop of w l from B ean to r cloth ater-rep razil, wit eturn to e , h ll that shocked ent rub sample b h s p on t e was b eople s erised he c harg rought t o much o co e of u witc hcra rt ft.

What are the origins of natural rubber production?

Today, 90 percent of rubber production comes from plantations of rubber trees in Southeast Asia.

The Para Rubber Tree initially grew in South America and the region remained the main source of what limited amount of latex rubber was consumed during much of the 19th century.

In 1876, the eminent explorer, author, and plant collector Henry Wickham gathered thousands of seeds from Brazil, and returned to England where he germinated them at Kew Gardens, London.

The seedlings were then sent to Ceylon (now Sri Lanka), Indonesia, Singapore and British Malaya (now Malaysia) – which later became the world’s largest rubber producer.

What is synthetic rubber?

Synthetic rubber is any type of artificially made (or man-made) polymer material, which acts as an elastomer. Synthetic rubber serves as a substitute for

6

Removing the froth from the latex

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BRIDGESTONE

| Product Profile

Dandelions are a surprising source of latex

Kew Gardens, where the first rubber plants were grown in the UK

Oil refinery

Advantages of synthetic rubber?

With natural rubber you get what you get, but with synthetic you can make the rubber exactly the way you want it. You can make rubber that is good at reducing rolling resistance, demonstrates better fuel efficiency, and can be processed more easily.

What led to the accelerated development of synthetic rubber?

During World War II the United States became cut off from virtually all of its sources of natural rubber in the Pacific and so to meet the nation's needs the government built synthetic rubber plants. Synthetic rubber production jumped from 8,000 tonnes in 1941 to 820,000 tonnes in 1945, according to the RMA.

When was the synthetic rubber for tyres first discovered?

Although synthetic rubbers were first pioneered in 1909, by the Bayer laboratory in Elberfeld, Germany, led by Fritz Hofmann, it was not until 1935 that German chemists synthesised the first series of copolymer synthetic rubbers, known as “Buna rubbers”.

One such Buna rubber, known as Government Rubber Styrene (GRS), is a copolymer of butadiene and styrene.

It became the basis for US synthetic rubber production during World War II and today it remains the primary synthetic rubber for the manufacture of tyres.

This process of vulcanisation made it possible to use rubber in many applications, including raincoats, overshoes, and eventually tyres. 

What makes rubber elasticised?

*Extracts taken from the website of the Rubber Manufacturers Association

The elastic behaviour of most elastic materials, such as the metal used in springs, is caused by bond distortions.

When force is applied, bond lengths deviate from the (minimum energy) equilibrium and strain energy is stored electrostatically. Rubber is different in that strain energy is stored thermally and converted to kinetic energy.

What is the effect of temperature change on rubber?

Natural rubber is sticky and easily deforms when hot and becomes hard and brittle when cold, which is why winter tyres use a softer version of rubber than normal tyres.

How is rubber strengthened against this temperature change?

The strengthening of rubber was finally remedied by the discovery of the process of vulcanisation.

This curing process involves high heat, pressure and the addition of sulphur or other equivalent curatives and it both strengthens the rubber and makes it elastic.

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| Process Review

Engineering the construction of tyres A tyre is a very complex combination of different materials and components. There are foundations, reinforcements and layer upon layer of engineering.

What follows is a detailed breakdown of the process required to transform tree sap into road worthy tyres.

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| Process Review

tread 'cap' tread 'base' undertread belts

Is a tyre a simple moulded unit?

No, that is a common misconception. From the outside a tyre looks pretty simple, but it is in fact 'built' from many parts and materials.

Just how many parts are there in a typical truck and bus tyre?

The average truck and bus tyre has at least 16 or more components each of which may be made up of several parts, including several different kinds of steel and many different types and compounds of rubber.

mini-sidewalls

What is the function of each of the tyre components?

belt edge inserts and fillers

As explained, there are many components within a tyre that are manufactured separately and brought together in a 'build' process. Each of the components has a dedicated function, as follows: • The tread 'cap' grips the road. It is designed to wear slowly for high traction and long tread life • The tread 'base' shields the casing from tread heat for cooler running and this can provide better retreadability • The undertread gives additional protection to belts to improve retreadability • The belts hold the tread flat for superior traction and wear and are designed to resist penetration • The mini-sidewalls join the tread stock to the sidewall stock, while protecting the tread base from exposure • The belt edge inserts and fillers maintain the optimum belt shape for a long casing life • The sidewalls transmit steering, driving and braking forces to the tread • The innerliner seals the air chamber to resist inflation pressure loss and to prevent the cord from rusting • The casing ply is the 'foundation' framework for the whole tyre • The soft bead filler helps provide a softer ride and smoother handling • The hard bead filler stiffens the bead area for better durability and retreadability. Together the hard filler and soft filler provide a transition of flexibility from the very rigid bead to the very flexible sidewall area • The chafer shields the bead against wheel flange and mounting abrasion • The bead bundle stiffens the tyre edge and grips the tyre to the rim

sidewalls innerliner casing ply soft bead filler hard bead filler chafer bead bundle

How does the tyre manufacturing process begin?

The tyre manufacturing process begins in the rubber tree plantations of South-East Asia [as explained in the rubber production feature on page 4], where a sloping cut is made in the bark of the tree from which the latex bleeds and is collected.

The latex is then combined with carbon, oil, sulphur and other chemicals and undergoes a number of proprietary processes. The result is black sheets of rubber that can then be heated and inter-woven with steel for added rigidity. These woven sheets form the main basis of the tyre.

Are any materials added to the rubber during this process?

From left to right: carbon powder, sulphur powder, aromatic oil, zinc stearate

There are many chemicals added to the rubber to improve its strength and rigidity. Of the key chemical components carbon black is the largest, followed by sulphur, zinc stearate, wax, accelerator and antioxidants.

Carbon black makes up about 30 percent of the tyre. This is a lot when you consider carbon black is a very light fine powder.

Rubber reinforced with carbon black is much more abrasion-resistant, stronger, slower wearing and is easier to process than rubber alone. Carbon black also helps protect rubber against ultraviolet (UV) light from the sun.

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| Process Review

What purpose does the steel have?

MIXING PROCESS

Mix materials

The steel makes up around a fifth of the tyre's weight and is an essential component, especially for the 'Three Bs,' Beads, Belts and Body. Just as the carbon black acts as a sort of 'rebar' for the 'concrete' of the rubber, the steel cord in a radial tyre acts a bit like the steel frame of a modern building.

The steel must first be treated with a special coating to help it adhere to the rubber in the tyre. The coating is tightly bonded to the wire, and in turn, bonds tightly to the rubber during processing.

Cool

Natural/synthetic rubber Form into sheet strips

Carbon black

ďƒ&#x;

Sulfur and other chemical agents

What purpose do the remaining chemicals serve?

TREAD EXTRUDING PROCESS Apply heat to make rubber elastic

Cut to tire length

Extrude rubber

The sulphur is a very important vulcanising agent, which strengthens the rubber and gives qualities of strength and elasticity that one associates with tyres.

Small amount of zinc stearate and waxes can help control the cure rate and make rubber a bit easier to process. They also help prevent oxidation.

The accelerators help control the speed of the cure, so everything ends up fully cured, without having to spend excessive time in the mould.

Steel Belt and Steel Ply Cord Manufacturing process Coat steel cord with rubber

CUTTING PROCESS

Cut at proper angle into specific length and width

First of all the rubber compound must be prepared for use on different tyre specifications and for the different tyre components. All of the materials (natural/synthetic rubber, carbon black, sulphur and other chemical agents) are mixed together and pressed to form rubber sheets. This is done in a mill, which is commonly called a 'Banbury mixer', after the name of its inventor. The rubber sheets are then cooled and loaded into pallets delivered to the manufacturing process of the different tyre components.

Coat with rubber

BEAD-MAKING PROCESS Align bead wires Bead wire

What is the first step in bringing these materials together to form a tyre?

Coil to form bead

did you know

Oxygen in the air and ozone (a special type of oxygen molecule), can break down rubber molecules, making rubber brittle, causing cracks, and rapid wear. So we add antioxidants and antiozonants to protect the tyre.

For this reason it is important not to clean your tyre's sidewall with unknown products with petroleum based chemicals that can remove the protection, causing tyres to age prematurely.

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How is this rubber sheet shaped to form different tyre components?

There are two different processes to shape the rubber into the individual components of the tyre: Calendering for the inner liner, body ply and belts, and extrusion for the tread, bead, fillers and sidewalls.

Calendering means “pressing the rubber compounds between large rollers”. The calender machine is equipped with three or more steel rollers which revolve in opposite directions, forcing the rubber compound to adhere to the cords.

Extrusion means “forcing the rubber compound through a die”. The die is a metal mould in the shape of the tyre component to be manufactured. This distributes the rubber volume into the appropriate final shape and dimensions.

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Tread, sidewall Body ply, steel belt

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Attach bead

"Green" tire

Apply sidewall, steel belt,

What is the 'Tread' extruding process?

After heating the rubber to soften it, the tread is extruded to create a cross sectional shape.The extruded tread is completely cooled and cut into lengths suited for individual tyres.

What is the steel belt / body ply manufacturing process?

 

In the case of belt and body plies, the steel cord is sandwiched between the rubber sheets and cut into length with given angles for individual tyres.

What is the bead manufacturing process?

The bead core is made of steel and is rubber coated by extrusion.The bead filler is also extruded and applied to the bead and they are placed on a rack ready for assembly.

How are these components assembled to form the tyre?

inspection process

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Apply heat and pressure to green tire

Trim and perform appearance inspection and balance/uniformity check

Thus we have to change the shape of the tyre to receive the belts and tread. A rubber bladder inflates the layer we have already put on and at the same time, the drum shortens itself - pushing the wheel edges of the various layers together to form a shape of a green tyre.

Once the belt and tread are placed, the drum TAM starts spinning and as it does, rollers come in and press all of the various parts together. This is called stitching and the pressure squeezes out any air that might be trapped between the layers.

At this point what we call the green tyre is ready.

Note that there is no pattern on the tread at this point of time.

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building process

Bead

| Process Review

The inner liner, body ply, bead with bead filler, sidewalls, belts and tread are assembled in sequence to form the 'green' tyre.

The tyre is built on a Tire Assembly Machine (TAM).

It is the “workbench”, on which the tyre builder will assemble all the parts that make up the green tyre.

Essentially this is a big, horizontal drum with a diameter the same size as the final “hole” in tyre.

The tyres are built inside out, starting with the inner liner. The tyre builder wraps this on the drum, and then applies the body ply.

The body ply is then turned around the preassembled bead/filler, and wire and nylon chafers are added, depending on the specification of the tyres.The sidewall rubber is then added.

So is the tyre now ready for the tread?

Not so quickly. We have been wrapping flat components around a drum whose size is closer to that of the wheel.

However, the circumference of the belt and tread is a lot greater than that of a wheel.

How is this 'green' tyre finished and ready for the road?

The green tyre must be vulcanised, or cured, by applying heat and pressure in special machines to produce the finished tyre.

During vulcanisation, the soft green-tyre is transformed into the tough road-worthy tyre. The green tyre is placed in a curing mould and is subjected to intense pressure and adequate heat internally and externally for a specified period of time.

The long hydrocarbon chains of natural rubber are randomly intertwined with one another but have no molecular links between them. By mixing sulphur with the natural rubber and heating the mixture, sulphur cross-links are formed between the rubber molecules. This hardens the rubber and gives it the qualities of strength and elasticity that one associates with rubber tyres.

Simultaneously, the tread pattern and sidewall information is moulded on the exterior of the tread and sidewall.

So is the tyre now ready to be shipped off?

Not quite. Every Bridgestone tyre has to undergo a strict quality check on a variety of inspection machines and at the hands of a skilled human inspector. Only those tyres that pass these strict inspections can be sold to a customer. 

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| DESIGN ENGINEERING

Tread patterns: making an informed choice Tyres are made up of different components, such as tread, casing, belts and beads. The structure of these components and the materials used (such as rubber compounds, steel etc.) are mixed, matched and designed for optimum performance for the user’s operating conditions.

For a fleet, choosing the right tyre for the right operating conditions is vital in getting maximum performance from the tyre and thereby maximising the return on investment from tyres.

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Why can’t you have one tyre for all operations?

While it may be possible to use one tyre for all operations the tyres will never give maximum performance. In order to maximize the performance of tyres in varying operations they must be tailor made in terms of the pattern design, the rubber compounds and the internal construction.

| DESIGN ENGINEERING

Type of vehicle

Operation

Positive aspects

Negative aspects

Requirement from tyres

Coach

Long haul

• Drive in straight line and minimal scrubbing thus tyre wear rate is slow leading to better mileage

• Relatively high speeds over sustained period of time. Thus there is high heat generation in the tyres

• Resistance to irregular wear (on long mileage tyres, irregular wear can onsiderably lower tyre life) • Good steering and driving performance.

• Low rolling resistance • Better heat resistance

Type of vehicle

Operation

Positive aspects

Negative aspects

Requirement from tyres

City Bus

Short haul

• Relatively slow speeds and thus lower heat

• Frequent braking and acceleration leads to fast wear and low mileage • Scrub scuffing (sidewall) is common

• High wear life.

• Resistance to cutting and abrasion by curb scuffing (reinforced sidewall, protector rib)

Why is it necessary to tailor the manufacturing in this way?

The requirements from the tyre vary depending upon the operating conditions and axle position.Tyres are designed for the job they do, as you can see from the comparison between a coach and a city bus (shown right).

Is there a simple process to choose the right tyre?

Unfortunately there is no single solution for choosing the right tyre and the decision should be left to a tyre professional. The operation has to be carefully studied and an optimal pattern has to be considered.

Bridgestone has numerous pattern designs in its line-up, which are custom designed for different operating conditions

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Whe roll n a trea in a un only o d is des igne ne i-dir be fi ection directio d to a n n wea e tuned l patter , as in r, we n, it fo trac t perfo r optim can tion um rma char n acte ce and ristic s

How many pattern designs are there?

Most tyres can be generally grouped under four basic pattern designs, rib, lug, rib-lug and block, based on the operations undertaken. However, these are just broad classifications and there is no hard and fast rule.

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1. Rib: Rib tyres are suitable for driving on paved roads and highways. As the grooves run along the circumference of the tyre (longitudinal grooves), it provides: • Excellent driving stability • Less rolling resistance • Less noise generation • Superior water drainage performance 2. Lug: Lug tyres are suitable for driving on unpaved roads and building sites. The grooves run in a lateral direction, offering: • Superior driving and braking forces • Stronger traction force • Superior resistance to cut

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3. Rib-Lug: Rib-lug tyres are suitable for driving on normal paved roads and unpaved ones at a middle/low speed. The combination of rib and lug patterns offers: • Increased driving stability and skidding prevention from the rib-type pattern • Effective transfer of traction and braking forces from the lug-type pattern 4. Block: Block tyres offer good performance when driving on normal paved roads.

In this pattern the blocks are individually arranged, thus offering: • Superior traction and braking forces • Excellent driving stability on normal paved road • Superior wet traction

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a

| DESIGN ENGINEERING

What is the function of tyre pattern components?

b

Every groove, shape and sipe has a meaning and a lot of complex technologies are considered when designing a pattern. Let us take a look at some of the examples: a) Stress Relief Sipes Sipes are the small slits in the tread blocks of a tyre, which allow a better contact between a tyre and a wet road surface. They also reduce the size of the tread blocks to assist cooling. Some tyres such as the G582, R150 have stress relief sipes that relieve the contact pressure at rib edges, prevent river wear problems and give a higher removal mileage. However, it can lead to sipe tear and cut/chip resistance if used on severe off-road surfaces. b) Stone Ejectors: The stone ejectors prevent the stone from lodging in the tread grooves and damaging the casing. A reduction in stone drilling improves the casing durability.

d

Rounded shoulder

tapered shoulder

squared shoulder

c) Tie Bar The tie bar reduces the movement of blocks and helps to reduce the ‘Heel and Toe’ wear typically found on the block pattern. It also helps to reduce the block tearing that occurs due to the scrubbing and dragging of tyres especially when used on un-paved roads. d) Shoulder design: It is interesting to note that the shoulder design can affect the resistance to edge wear and handling stability.

c

resistance to edge wear

Fair

handling stability

Excellent

Good

Good

FAC T

Excellent

Bec desig ause th ep n engin s are so attern prot eered precisely they ecte d by a a pa re tent

Fair

Does the rubber compound vary too?

Choosing the right compounds for the tread surface is extremely critical. Most of Bridgestone tyres in the Middle East and Africa regions are designed with ‘Cap’ and ‘Base’ compound. The base compound protects the internal belt package from the excessive heat generated in the tyres, and the top compound is designed to give a better wear-life and resistance to irregular wear, since it comes in contact with the road surface.

Many different compound variations are researched and developed to create a varying resistance to heat, irregular wear, tear, cut/chip and wet performance, etc.

Cap Compound

Base Compound

Why are so many different rubber compounds necessary?

It is the intention of Bridgestone to meet every operating condition requirement. Rubber compounds have certain characteristics and there is always a compromise between wear life, cut resistance, heat durability and wet grip. For example, in the case of cap compounds, if you increase the wear volume then wear life increases; however one has to compromise on the heat resistance. Similarly if you increase the cut resistance the heat resistance decreases.

This is also the case with base compounds, if you make it more heat resistant then the cut resistance decreases. The right combination in the selection of cap compounds and base compounds is critical to achieve the best performance.

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Do the same considerations apply to the internal construction?

| DESIGN ENGINEERING

Basic tyre construction

Internal construction has to be analysed and optimised for the best performance from the view point of real-life situations, wherein the tyre is inflated and is in actual operation. At the same time various factors have to be considered such as the optimal footprint, heat endurance strain on the belt ends, and strain on the ply end, etc. Thus the shape of the casing, the belt construction, bead construction, etc., is critical.

Bead area

bead Bundle

How are these complicated calculations achieved?

Bridgestone uses a computerised process, called CTDM (Comprehensive Tire Design Method), which optimises the tread design, casing shape, materials and construction for maximum tyre performance.

Using this proprietary software, engineers are able to optimise the performance characteristics of each specific tyre line.

cross-section shown

Inner liner Belts

Casing ply

Are there similar variations in belt construction?

Belt construction can differ depending on the severity of the road surfaces that vehicles operate on. When operating on off-roads, the belts need to provide enough 'enveloping power' or change shape when passing over obstacles to withstand the tread cuts, punctures and impacts on the roads.

Whereas, rigid belts are required to provide even wear and control when operating on highway surfaces.

sidewall area Tread shoulder area

How does the bead construction differ across the tyre patterns?

Bead construction is continually optimised with technological advancement, but the number of bead wire turns and the reinforcement with chafers could differ, with each pattern, depending upon the severity of the load conditions and the stress on the ply ends.

With so many variations how can operators chose the right tyre?

The selection of a suitable pattern should be left to the tyre professionals. Based on a study of the market conditions, Bridgestone develops and recommends different tyre line ups for each market.

When selecting a suitable pattern, the most important aspect is the operating condition. This requires careful study of several factors, such as load, road surface, operating route, fitment position, speed, driving habits, tyre damage past history, etc. Based on the analysis of these factors a suitable pattern is recommended.

Why do so many operators use the same tyres if they are so specific?

It is true that over a period of time in a given market, some tyre patterns become popular for some sectors, such as for dump trailers that operate on highways.

However, the operating conditions can change over time. Importantly within a given type of fleet, unique operations and problems can exist which may require the use of a different pattern.

So the key point is always consult a tyre professional?

Correct! A tyre professional with good knowledge on pattern applications can advise on the best tyres to be used for any given operation. 

did you know

The Bridgestone Group is the largest tyre and rubber company in the world, operational in 26 countries worldwide. Bridgestone has 76 tyre and tyre related plants, 20 raw material plants and 86 diversified plants.

Diversified products include chemical and industrial products, sporting goods and bicycles.

real questions real answers january 2009

PRECISION PATTERNS.indd 15

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BRIDGESTONE

| Correct Maintenance

Fitting tube-type tyres right There are always a certain amount of dangers to be cautious of when mounting and demounting tyres. The process requires specialist skills and should be left to professionals who have the proper training and equipment.

MOUNTING CONCERNS.indd 16

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BRIDGESTONE

| Correct Maintenance

w

hen changing any tyre it is very important to change the various components related to mounting new tyres. This includes the wheel weights, the valve, the valve cap, flap and the tube.

Furthermore, you must always clean and inspect the wheels and tyres carefully because bent or damaged flanges, rust build-up, dirt or damage to the wheel can make it impossible for the tyre’s bead to seat properly. If the bead does not sit properly the tyre will not be concentric, which can lead to irregular wear and ride disturbance.

What are the fundamental requirements in demounting tyres?

There are several fundamental points that need addressing before any tyre is changed.

Before you even loosen the wheel nuts you must secure the tyre and rim assembly to the vehicle, remove the valve core and deflate the tyre completely. If you are working on duals, or twin wheels, you MUST deflate both tyres completely.

You may now remove the tyre and rim assembly from the truck and place it on the floor, side ring up.

Once the wheel is removed you can insert the hooked end of bead breaker (an indispensable tool for breaking down the bead or leading edge of the side wall) tool between the side ring and the side wall of the tyre.

The arm of the bead breaker hooks on the rim, then the wide foot breaks the bead with ease when you press the handle down.

You should continue prying progressively around the tyre until the bead is completely free from the side ring and then carry out the same procedure to break the opposing side bead.

Does the method of demounting differ for each wheel type?

While the principles are the same across the makes and models of wheels and tyres, there are requirements specific to a three-piece wheel, a twopiece wheel and a cast spoke wheel (Trilex Rim).

WARNING Before working on any tyre/rim assembly, be sure that you are trained and thoroughly familiar with the safety guidelines. Any improper servicing of the tyre/rim assemblies can lead to serious, even fatal, accidents for you or others around you. It is imperative that you follow the recommended mounting and demounting procedures carefully.

ďƒ&#x; real questions real answers january 2009

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BRIDGESTONE

| Correct Maintenance



 continuous side ring split lock ring

rim base

When the bead is broken from the rim, what are the demounting procedures for each style of wheel? On a three-piece wheel: • Push the side ring and tyre bead down to remove the lock ring • Insert the tapered end of the tyre lever into the notch, near the split in the lock ring • Push the tyre lever downward and pry the lock ring outward to remove from the gutter of the rim base • Use the hooked end of a second tyre lever to completely remove the lock ring • While progressively working around the tyre, lift off the side ring • Turn the assembly over and unseat the remaining tyre bead from the rim and lift it from the tyre

Mounting/demounting tyre lever

18

january 2009 real questions real answers

MOUNTING CONCERNS.indd 18

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| Correct Maintenance



BRIDGESTONE

On a two-piece wheel: • To remove the split side ring insert the tapered end of the tyre lever in the ring split • Push the lever a little until you find the gap between the split ring and rim gutter • Use the hooked end of another tyre lever and insert it between the gutter and the ring gap (ring notch) • Lift the split ring using lever 2 and use tyre lever 1 for further removal of the side ring • Work progressively using tyre lever 1 and 2 until you completely remove the side ring • Turn the assembly over and unseat the remaining tyre bead from the rim, lifting the rim from the tyre fixed flange split side ring

gutter

rim base

bead seat

Double mounting lever – one end to open the rim and the other to close it

FAC T

Th idea e TRIL EX lw and heel sy wheel s s t ind ivid railers tem fo ystem . u r is a n dev al stu Its hig truck s, b rdy elop h-p coll ed an comp recisio uses abo o d n n , t ent est ra ma tion wit ed in c s were nuf actu h veh lose rers icle .



 

On a cast spoke wheel (Trilex Rim): • To separate the rim parts insert the rim opening end of a double mounting lever in the slot provided.

Secure the lever end properly in the slot and use a hammer if required • To remove the rim parts apply force on the other side of the lever • Separate part of the rim from the assembly • Remove the other parts of the detachable rim and check for damages

real questions real answers january 2009

MOUNTING CONCERNS.indd 19

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BRIDGESTONE

| Correct Maintenance



Why is mounting a tyre a potentially dangerous exercise?

When you are dealing with high air pressures there is a chance that the tyre can either fault and explode or pries free of the rim – either way the force of the blast would be huge.

What safeguards should be made when inflating the correctly fitted tyre?

You MUST ensure that when you inflate the tyre the assembly is securely housed in a safety cage.With the valve now harder to reach the inflation can be achieved with an extension hose fitted with an air gauge and a clip-on air chuck.

WAIT - While inflating you must stand clear of the assembly. Inflate the tyre to the recommended pressure to seat the beads and constantly monitor it to ensure the beads are properly seated.

BEFORE removing the assembly from the safety cage or restraining device - check to ensure that the rim components are properly seated.

WARNING You MUST ensure that when you inflate the tyre the assembly is securely housed in a safety cage. With the valve now harder to reach the inflation can be achieved with an extension hose fitted with an air gauge and a clip-on air chuck.

What are the fundamental requirements in mounting tyres?



First and foremost you must inspect the tyre and rim for any damage, and then make sure that the tyre size and rim size match exactly.

You can then insert the tube into the tyre and partially inflate it to no more than 3 PSI, so as to round out any wrinkles or creases in the tube.

Now you must apply tyre lubricant to the inside and outside surfaces of both beads and lubricate the portion of the tube that appears between the beads. Proper lubrication can reduce bead damage, makes mounting easier and helps the tyre’s bead fit easily into the proper place on the rim flange.

You MUST always avoid water-based lubricants, as they can make the wheel and steel tyre cord rust, and petroleum-based lubricants as they can, over time, destroy the rubber. Bridgestone recommends the use of a vegetable oil-based lubricant for truck tyre mounting.



Does the orientation of the tyre matter when mounting?

Some tyres are directional and must be mounted with a certain orientation. Their external side (outside) is sometimes marked.

Does the method of mounting differ in relation to the wheel variation?

While the principles are the same across the makes and models of wheels and tyres, there are requirements specific to a three-piece wheel, a twopiece wheel and a cast spoke wheel (Trilex Rim).

20

WARNING You MUST always avoid water-based lubricants, as they can make the wheel and steel tyre cord rust, and petroleum-based lubricants as they can, over time, destroy rubber. Bridgestone recommends a vegetable oil-based lubricant for truck tyre mounting.

january 2009 real questions real answers

MOUNTING CONCERNS.indd 20

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What are the specific mounting procedures for each variant of wheel?

| Correct Maintenance



BRIDGESTONE

For both a three-piece wheel and a two-piece wheel the intial procedures are similar: • Insert the flap and lubricate • Lay the rim flat on the floor with the gutter side up and align the tube valve with the rim valve in slot centre • Push the tyre onto the rim and insert the valve through the valve slot

or

WARNING If the assembly is not aligned properly, deflate and correct it. NEVER hammer on an inflated or partially inflated tyre/rim assembly.





Two-piece • Ensure the side ring split is opposite the valve stem • Place the leading end (end without notch) of the side ring into the groove in the rim base • Walk the side ring into place and ensure it is fully seated in the gutter • Check again for the proper engagement of the side ring

Three-piece • Place the side ring on the rim base and ensure that it is positioned properly below the gutter in the rim base • S nap the leading end (end without notch) of the lock ring into the gutter of rim base • While progressively using the tyre lever, place the lock ring into position and check to ensure it is fully seated in the gutter • Check again for the proper engagement of the lock ring

The mounting procedures differ significantly for a cast spoke wheel (Trilex Rim), over a two or three-piece wheel, predominantly because the rim is not one solid unit, but instead is made up of three identical components.

Once the basic mounting procedures have been applied you must: • Place the first part of the rim between two beads with the valve stem properly passing through the valve slot provided in the rim part • Place the second rim part close to valve side with the bead properly sitting on the rim flange • Gently slip the third piece of the rim into place, thus creating a full circle, but ensuring that the rim piece ends are properly joining • Use the rim closing end of the tyre lever and insert it in the mounting slot on the piece of rim numbered one • To fix the rim assembly turn the other end of the lever so that both ends of rim pieces fix properly • Remove the end of the mounting lever smoothly, and check the fitment of all parts properly



The procedures for mounting a cast spoke wheel differ, why is that?

 Are there any final checks once the tyre is fully inflated?

When mounting is completed, be sure that the valve caps are tightened so as to ensure your new tyres are as airtight as possible.

As a final step, check that the wheel bolts are tightened after about 100 kilometres/65 miles. 

real questions real answers january 2009

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BRIDGESTONE

| pure tech

UNDER-INFLATION HEAV INTERNAL FRICTION TYR FAILURE HEAT GENERA operating temperature INFLATION Know HEAVY OVER FRICTION your TYRE TEMPER HEAT GENERATION PRE enemies temperature 50째C TY 20

10

OPERATING

0

Excessive heat build up inside a tyre is the primary reason for failures, making it the number one enemy of tyres.

E

xcessive heat build up is often caused by underinflation, heavy overload and higher speeds, so controlling these factors can help in prolonging the life of your tyre.

The actual construction of a tyre and the choice of rubber compounds used can help control this heat build up and stave off tyre failures, but that is an entirely different subject altogether. In terms of utilisation, maintenance is one of the most important things to consider.

What are main causes of heat generation inside a tyre?

Heat build up inside the tyre can occur from internal friction, tyre to tube friction and the absorption of heat from the road and atmosphere.

22

Flat at the point of contact

COntact patch of a tyre

january 2009 real questions real answers

22-23 KNOW YOUR ENEMIES.indd 22

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TE

BRIDGESTONE

| pure tech

AVY OVERLOAD HIGH S YRE TEMPERATURE 70° °C RATION PRESSURE LOAD temperature 50°C TYRE WEAR ERLOAD HIGH SPEEDS I ERATURE 70°C TYRE FA RESSURE LOAD SPEED operating TYRE WEAR TYRE TEMPERATURE

Index %

100

100

Tyre wear

80

60

30°C

50°C

70°C

50

TEMPERATURE

Accumulated Breakdown (%)

Tyre temperature

99.9 99 95 90 80 60 40 10

0.1

0.01

110 120

130

140

150

160

170

180

Tyre temperature °C

What is the effect of speed on heat generation?

90

6.75

8.0

Inflation Pressure (kg/cm2)

What is the principal cause of internal friction?

Bias tyre

Heat generation index

150

100

Radial tyre

50

100

What is the effect of this internal heat?

The excessive temperature inside leads to a faster wear rate (tyre life is reduced) and it causes a reduction in the bond strength (steel to rubber, nylon to rubber, rubber to rubber).

So the reduction in bond strength leads to tyre failures?

Absolutely. Due to the weak bonds it becomes easy for the components of the tyres to separate, such as separation between casing and belts or between individual belts. This is a common cause of tread peel as you often see on the roads.

150

200

Load (% against the maximum recommended load) Note: Radial tyres have an advantage over bias tyres on heat generation

150

If we suppose the tyre is subject to a constant load, the more the tyre is underinflated the greater its deformation would be and thus the higher the heat generation.

Absolutely! The same deformation occurs if the load is increased and the pressure remains the same.

100

5.50

When a tyre rolls, it is never round. It becomes flat at the point of contact and the sidewall is flexing all the time.

In other words rubber is being constantly deformed and released. The constant deformation and release causes friction between the molecules of the compound, sulphur and rubber, which in turn generates heat.

Yes. The rubber compound used can have a varying resistance to heat build up. Also, tyre construction plays a big part in resistance to heat build up tyre failures.

However, there is a limit beyond which the tyre fails.

What determines this limit varies from tyre to tyre but excessive deformation and speed of deformation will lead to tyre failures.

Does the same principal apply to the weight of the load?

Tyre size: 10.00-20 HT-Lug

110

Heat generation index

60

But isn’t the tyre designed to resist deformations and heat build up?

How does the tyre pressure affect deformation?

1.0

0.0001

Heat generation index

G

40

Tyre size: 10.00R20 14PR Radial HWJ Rib 10.00R20 14PR Bias HT-Lug Inf. Pressure: Bias 6.75kg/cm2

Radial 7.25kg/cm2 Load: 100% under recommended load Amb. temp: 30°C Bias tyre

100 Radial tyre 50 40

60

80

Speed (km/h) Note: Radial tyres have an advantage over bias tyres on heat generation

As the speed of the vehicle increases so does the rate of deformation and the release. This directly impacts on heat generation.

So tyre failure is a combination of pressure, load and speed?

That is correct. That is why it is vital to use the right pressure, to avoid overloading and to control the speed.

How do I know what the correct levels for pressure, load and speed are?

Look at the tyre’s sidewall. The size of the tyre and its corresponding service description (eg. 146/143L) indicates the service conditions that the tyre can withstand without reaching its critical temperature, e.g. 3000kg @ 120 km/h, and, of course, at the pressure specified on the tyre sidewall [we will cover this in more detail in another issue].

How important is tyre selection?

The first step in tyre selection is to consider the load and speed capacity of the tyre, along with the operating conditions. 

real questions real answers january 2009

22-23 KNOW YOUR ENEMIES.indd 23

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BRIDGESTONE

| expert’s corner

Breathing new life into worn tyres Retreading of used tyres is an important tool for any fleet, allowing them to substantially extend the lifespan of one of their key assets – the truck/bus tyre.

RETREADING.indd 24

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BRIDGESTONE

| expert’s corner

F

or fleets, the lowest possible cost-per-kilometre is achieved with a good tyre management programme that includes the use of good quality new tyres and retreads.

Today, modern commercial truck/bus tyres are built to last more than one tyre life. In the US two out of three replaced tyres are retreaded ones.

One of the leading truck tyre retreaders in the Middle East is Bandag, which is now a part of Bridgestone group.

What follows is a detailed illustration of the precure retread process Bandag uses to turn your worn tyres into safe and reliable retreads.

First of all, what do you mean by retread tyres?

When the tyres are in service, the part that is in contact with the ground, called the 'tread', wears out. However, the tread is only a percentage of the total tyre. Even if the tyre is worn out, the major part i.e. the casing is usually intact and can last much longer. By retreading, a new tread is applied to the useful casing to give the tyre a new life.

How cost effective are retread tyres?

With a lower production cost than a new tyre, in general, a good retread can be available at around 50 percent the price of a good quality new tyre (varying by market).The performance is also comparable to new tyres.

Where is the catch?

There is no catch. a. As in the case of new tyres, it is necessary to choose a reliable retread manufacturer who provides durable as well as good mileage retreads. b. It is important to maintain the tyres when new so that the casing will be good for retreading. The maintenance of retread tyres is also vital in case of further retreads. c. Controlling the pull point of tyres (removal point) is also important to obtain more casings for retread.

Just how safe are retread tyres?

Retreads are not only cost effective, but they are also dependable, reliable and safe. Professional retreaders adhere to stringent industry standards at every step of the retreading process. It would be interesting to note that all commercial aircrafts and even military aircrafts use retread tyres and some of them are retreaded as many as 12 times.

The ITRA (International Tire & Rubber Association Foundation, Inc., USA) mentions that tyre strength tests sponsored by the American Retread Association dramatically illustrate that a worn tyre has approximately the same body strength as a comparable new tyre. The retread tyres are used safely every day on school buses, fire engines and ambulances, etc. (note the above is as per US market).

How safe is retreading for Middle East and African conditions?

Retread tyres have not been widely used in all regions of the Middle East and Africa, but they are getting more popular and have proved very durable and safe in some of the most demanding operations.

How environmentally sound are retread tyres?

Tyres are basically petrochemical products. It takes approximately 83 litres of oil to manufacture one new truck tyre where as it only takes approximately 26.5 litres of oil to produce a retread. Most of the oil is used to build the casing, and this can be reused in the retreading process.

With every retread you can save one tyre from going to landfill or a similarly costly disposal option.

How often can a truck tyre be retread?

A truck tyre can often be safely retreaded several times but it would depend upon several factors such as the severity of the operations, the age, maintenance conditions, etc.

did you know

Peyman Younes, Director of Marketing & Corporate Communications, Roads & Transport Association in Dubai, said: “We are working on a campaign with Dubai Police to conduct spot checks on heavy vehicles across the emirate. We are checking the quality of all tyres to ensure they adhere to our long standing regulations.

“There have been no changes to these guidelines.

We do not have an issue with retreading as long as it is within the guidelines for tyres in terms of the size of tread and the traction.”

real questions real answers january 2009

24-27 RETREADING.indd 25

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BRIDGESTONE

| expert’s corner

Just how are tyres retreaded?

What is the first step?

Initial inspection

The first step is the initial inspection, which is perhaps one of the most important steps in the retreading process. This hands-on visual inspection, from bead to bead, inside and out, is done to find and mark all visible defects. Bandag strictly follows a 7-step methodology for a detailed and thorough inspection. At the end of the initial inspection, information like casing condition, casing age and fleet specifications are considered to determine if the tyre can be retreaded.

The latest introduction of Bandag is the ‘7400 Insight’ casing analyser which utilises shearographic technology to examine the casing conditions and flaws very accurately. The casing is subjected to a vacuum while lasers measure surface anomalies (such as expanding pockets of air). An animated visual of the anomalies aids in determining the casing’s condition.

In the Bandag manufacturing process, the tyres are inspected at every stage and can be rejected if not deemed suitable for retreading.



Once the tyre is passed for retreading how is it prepared?

Once the tyre has passed the inspection, it moves to the buffing stage where the old tread is removed from the casing.

During the buffing stage, the tyre is loaded on to the buffing machine. The tyre is then set on a rotational spin while the buffing rasp removes the remaining old tread rubber. It is important to buff the casing to the correct shape, size and texture to receive the new tread.

Bandag also utilises a fully ss and computerised buffing machine that ce ro p n spectio ring process The in u can complete this operation within ant nufact a rt o m p e im th ally as are equ ew tread when four minutes per tyre. re the n

FACT

Buffing

as

ing a ty retread

 Skiving

So the tyre tread has been removed, is it ready for retreading?

26



No. While in operation, the tyres receive many cut/ bruises. Many of these damages extend deep and may not be completely removed during the buffing stage. All such damages have to be cleaned and removed using proper tools (skiving). Any major repair will have to be attended to also. All the skives and repairs are then filled with uncured rubber to retain the casing integrity.

Repair

Filling

january 2009 real questions real answers

RETREADING.indd 26

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BRIDGESTONE

| expert’s corner

How is the new tread attached to the tyre casing?

First of all the retreader selects the appropriate tread design (as per fleet specification) and of proper width matching to the casing. The tread is then cut into the correct length and a bonding layer (cushion gum) is applied to the tread base.

The tread is then applied to the casing. It is very critical to apply the tread in a straight and even fashion to ensure the best uniformity for a longer tread life and lower operating cost.

 Tread application

Tread adhesion

Enveloping

Is the tyre now ready for use?

No. The tyre is covered with a rubber envelope and mounted on to a rim assembly. This is done to ensure that the adhesion process is maximised and is very consistent during the curing process.

Next is the curing process, wherein the assembly is hung inside a chamber (autoclave) where temperature and pressure are maintained for a duration specified by the system in order to complete the bonding of tread to the casing. The chamber is controlled by a microprocessor to maintain the parameters within a very narrow margin. Once a tyre is retread properly, the bond line is the strongest portion of the tyre.

thank s

Curing

Mounting for inspection

Our since rest than Al Dobo ks go to wi Lim franchise ited, Bandag e, for all support the extended to us in photog raph their facil ing ity.







So the tyre is ready for use once it is cured?

Not quite, the final step is a thorough final inspection to ensure that the correct work has been done, based on customers requirements.

The tyres are first removed from the curing chamber and then inspected for quality and integrity. 

Final inspection

real questions real answers january 2009

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OBC ADVERT.indd 28

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