Tyre Manufacturing Process - An Introduction

TYRE MANUFACTURING PROCESS – A DETAILED REPORT ON BIAS TYRE MANUFACTURING

INTRODUCTION

Few inventions have affected society more profoundly than the pneumatic tyre which not only changed the way people travelled, but even today influences where and how we live. Pneumatic tyres are the most versatile and probably the first Engineering product made out of polymers and has made it possible the evolution of sophisticated, personalised land transportation system. It is on pneumatic tyre the world's second largest industry viz. Road Transport Industry employing the largest manpower is founded. Without the pneumatic tyre, the development of motor vehicle transport would not have been possible. It may be noted that more than 40% of world's rubber production finds its way in to pneumatic tyres.

THE PNEUMATIC TYRE - A BRIEF HISTORY

It was John Boyd Dunlop who in 1888 developed successfully the pneumatic tyre and before that Railways offered the only means of long distance travel by land and the horse furnished most of day-to-day transportation.

For those living in that day, the practical world usually consisted of the distance they could travel in a day or two by whatever mode of transportation happened to be available. Holiday travel was a luxury enjoyed only by the Rich. It simply was not an option for most working people.

In rural areas, generation after generation lived and died. in sleepy hamlets, where the same few families intermarried, sometimes with important genetic consequences. Others, born in cities often were obliged to live in dizzy industrial sections in order to be near the factories where they worked.

Much of this was soon to change with the coming of the "transportation age" in which the air-inflated tyre played a necessary role.

The pneumatic tyre widened the horizons of average people and altered their way of life first by popularising the bicycle and then the automobile, ultimately society itself was changed.

With widespread use of the automobile, came the need for improved roads and sturdier bridges, which created employment for many. Meanwhile new service industries sprang up around the automobile and tourism.

The revolution in transportation, created by the automobile meant increased freedom of movement and better living conditions for many.

But it also brought sudden growth and unanticipated problems such as traffic death and highway litter to suburban and rural communities. Society's very fabric changed; populations of the industrialised countries in Europe and North America mingled as never before and many former cultural differences were dissolved in the process.

Warfare took on new and more terrible proportions, brought increased military mobility and spread battle lines over hundreds or even thousands of kilometers.

Around the world the building of the automobile and its component parts soon became many nations' largest industry.

Today more than 400 million pneumatic tyres are produced annually worldwide. Pneumatic tyres over the past century have grown so numerous and impervious to ageing, that their eventual disposal has become a problem of serious proportions in all the industrialised countries.

How it began?

Some say it started with the wheel - believed to have been invented around 3500 BC, possibly as an extension of materials earlier practice of rolling a log under a heavy object in order to move it. Over the time, the log was shortened into thinly cut circular sections held together by an axle. This was done to eliminate unnecessary weight, thereby reducing the effort required to get the assembly rolling. Early, wheels were often two or three segments of wood held together by wooden or metal cross members. A hole in the wheel's exact center carried a hub, which revolved on a fixed axle. Most vehicles of that time had only two wheels.

The first tyre was made from cured pieces of wood called felloes, attached to the bare wheel as a running surface.

Large headed nails were sometimes driven into the surface of the wood to resist abrasion and thereby prolong the tyre's life.

Later, as the wheel maker's art continued to develop, tyres themselves often were fashioned from metal. This extended the tyre's life, but did little to improve the rider's comfort or reduce vehicles wear caused by vibration and road shock.

Technically advanced societies including those of the Egyptians and Romans began placing softer materials such as leather, over the tyre's running surface in an effort to soften the ride.

Thus began the revolutionary process, which ultimately led first to the solid rubber tyre and later the air inflated, or pneumatic tyre. Speed was the primary motivating factor. As vehicle speed increased so also did perception of the need to reduce vibration and road shock.

This situation changed little even after mechanical power began to replace muscle in transportation. Early self-propelled vehicles, beginning in 1769 with the steam

powered military tractor Invented by French Engineer Nicholas Joseph Chagnot, rolled almost exclusively on iron wheels.

Heavy and slow, these road steamers continued to run on low flexible wheels until the introduction of solid rubber tyres for such applications nearly a century later. One reason for rubber's late arrival was that it was not a suitable material for such

demanding use until "tamed" through the process of vulcanisation discovered by Charles Goodyear and licensed in the 1840s in the US and UK.

Until vulcanisation became widespread, rubber tendered to become sticky during hot weather only to turn bitter and inflexible in colder months - neither characteristic being desirable in a tyre.

Robert W Johnson of Middlesex, England, patented the first pneumatic carriage tyre in 1845. It is thought to be the earliest attempt to use air and vulcanised rubber in a vehicle tyre.

From all accounts, these pneumatic, tyres performed well and received positive reviews in the press. Johnson's tyres were said to be both "noiseless" and "comfortable" and to greatly reduce the tractive effort required. Nevertheless, pneumatic tyres still did not come into popular use at that time because of their high cost.

Meanwhile, solid rubber tyres gradually increased in popularity.

It was the advent of the diamond framed safety bicycle for the pneumatic tyre following its re-innovation in 1888 by John Boyd Dunlop. This, in turn launched the worldwide tyre industry, as we know it today. Virtually all that remained to assure the future of the pneumatic was to fit such tyres on the horseless carriage and Edward and Andre Michelin of France accomplished that in 1895. The Michelin brothers determined to prove the air-inflated tyre acceptable for automobiles, drove a pneumatic equipped car that year in a race from Paris to Bordeaux and back.

The pneumatic soon proved as a big boon to the automobile as, it had previously been to the bicycle. Other manufacturers including B F Goodrich and Dunlop quickly followed suit.

The motor age was dawning and with it the birth of a whole new industry based on the automobile. Soon the rubber industry was growing as fast as the world was shrinking under this new mode of transportation.

The latest in pneumatic tyre development is radial tyres. Radial tyre is the result of man's quest for high-speed mobility on land. M/s Michelin Tyres first developed radial tyres in 1948. Rapid radialisation of pneumatic tyres took place in Europe in the early seventies followed by USA. Today 95% of passenger car tyres and 80% of Truck tyres in the West are radials.

Pneumatic Tyres – chronology of Developments

1839 VULCANISATION CHARLES GOODYEAR1845 PATENT ON AIR TUBE DEVICE R.W.THOMPSON1888 PNEUMATIC TYRE REINVENTED JOHN BOYD DUNLOP1895 FIRST TYRE ON AUTOMOBILE EDWARD & ANDRE MICHELIN1898 BEAD & RIM JACK WELCH1903 FIRST TYRE ON AIR CRAFT1904 FLAT TREAD1905 NON SKID TREAD PATTERN1913 FIRST PATENT ON RADIAL CONCEPT-CHRISTIAN HAMILTON GRAY

THOMAS SLOPPER, ENGLAND 1925 COTTON CORD REPLACES SQUARE WOVEN 1931 FIRST SYNTHETIC RUBBER1931 FIRST PNEUMATIC REAR TRACTOR TYRE 1937 STEEL WIRE TYRE CORD1938 RAYON TYRE CORD1942 NYLON – FIRST SYNTHETIC TYRE CORD1943 SYNTHETIC RUBBER TYRES1947 NYLON TYRE CORD COMMERCIALISED1948 FIRST COMMERCIAL RADIAL TYRE MICHELIN,FRANCE1950 TUBELESS TYRES1953 TEXTILE(RAYON) BELTED RADIAL ‘CINTURATE’,PIRELLY,ITALY1960 STEEL RADIAL UNIROYAL1962 POLYESTER TYRE CORD1965 LOW ASPECT RATIO (70&80) TYRES1967 FIRST TYRE DESIGNED FOR VERY HIGH SPEED

‘XVR’, MICHELIN 1967 FIBRE GLASS AS BELT MATERIAL 1967 BIAS BELTED TYRES1968 H - SPEED RATED RADIAL PIRELLI, ITALY 1970 RADIAL ACCEPTED AS O.E.IN U.S. FORD 1971 MOON TYRES1971 V - SPEED RATED RADIAL PIRELLI,ITALY1974 ARAMID AS BELT MATERIAL GOODYEAR1975 ‘TRX’ CONCEPT FOR RACING TYRES MICHELIN,FRANCE1977 FIRST GRAND PRIX RACING TYRES MICHELIN, FRANCE 1983 RADIAL AIRCRAFT TYRES MICHELIN & GOODYEAR1983 RADIAL MOTOR CYCLE TYRES MICHELIN,PIRELLY & GOODYEAR 1986 ALL SEASON RADIAL TYRE GOODYEAR1991 AQUATREAD RADIAL TYRE GOODYEAR 2000 EXTENDED MOBILITY TYRES2002 GREEN TYRES

Pneumatic Tyre – The Basic Functions

Tyre is the most important component of any vehicle and it establishes the only contact between the vehicle and the road. The performance of the vehicle is largely dependent on the capability of the tyre.

Tyres have been improved over the years so that today’s tyres can operate safely and efficiently at high speeds for sustained periods under large loads on wet and dry roads, in hot or cold, on dirt or gravel roads or on modern high speed "Auto bans" (express highways). Tyres have been designed for dependable service on a wide variety of vehicles.

Aircraft, for example, is equipped with tyres for taking off and landing, though there is an unwanted weight penalty as the tyres do not function for 99% of vehicle operation time. However, no substitute has been developed yet.

Tyres are the means of mobility in Earthmovers, off the road vehicles, tractors that are moving on soft soil and other various road vehicles.

For a better understanding of the pneumatic tyre, it is important to know the various performance requirements expected out of it. There are certain basic performance requirements, which are found to be essentially the same for all types of pneumatic tyres, even though their relative importance differs with each type. There are other features, which are distinctly different depending on the kind of tyre and the service conditions. It is these features that make an aircraft tyre different from an earthmover tyre or an ADV tyre from a truck tyre.

Bias tyre requirements:

1. Cushion the vehicle ride:

A Pneumatic tyre is the first line of defense against road shocks and its unique property of cushioning provides comfort. Cushioning is imparted by the air, and the ability of the tyre membrane to deform radially.

2. Carry the load:

A Pneumatic tyre must carry the load when mounted on a rim and inflated to the required pressure. In other words pneumatic tyre must form an air container of adequate strength disposed in the radial direction to hold the air pressure acting

radially.

3. Transport the load:

While doing so a pneumatic tyre is required to transmit driving torque and breaking torque efficiently to the ground, to put the vehicle in motion. Good tyre to road grip coupled with adequate strength disposed in the circumferential direction underneath the tread of the tyre is required for efficient transporting.

4. Develop adequate cornering force:

It is the unique ability of a pneumatic tyre, to develop adequate cornering force to counter the centrifugal force or any other lateral force like wind force and retain the vehicle on the road while negotiating curves etc., that enabled the development of road transport industry. Excellent grip combined with its ability to undergo lateral deformation helps the pneumatic tyre to develop cornering force.

5. Economic Performance:

Every revolution of the tyre leads to periodic strains radially, circumferentially and laterally and these necessitate adequate flex fatigue life for the materials and the structure, and wear resistance for economic service life.

In addition to these general requisites today’s tyres must meet the various standards laid down by the vehicle manufacturers and consumers. Thus a rear tractor tyre should have the capability to transmit high torque efficiency on loose soil and give adequate floatation. An aircraft tyre needs to be as small and light as possible and at the same time should have high load carrying capacity, high impact resistance and excellent directional stability. To site a few of the specific tyre requirements: directional stability, rolling resistance, impact resistance, speed capability, run flat resistance, puncture resistance, weather resistance, re-treadability, mileage, low cost, crack resistance floatation, grip in loose soil, etc.

6. Durability:

A tyre passes through cycles of compression and deflection during its revolution. Long life of a tyre can be improved by the incorporation of less flexing elements of treads, pattern depth and desired distribution of land and sea in the tread pattern.

7. Low Rolling Resistance:

This is an important function since lower rolling resistance means less fuel consumption and much saving of fuel costs. This can be achieved by adequate load, inflation pressure running temperature and road conditions besides constructional aspects.

8. Road Holding Ability:

Road holding ability of a tyre is a very important factor from the safety point of view. Basic polymers of the tread compound, road conditions tread pattern design, inflation pressure, total area of the contact patch, etc. affects the road holding ability of a tyre.

9. Transmission of driving & breaking torque:

Pneumatic tyre should provide mobility in forward, lateral and vertical directions. Besides this, tyre traction on dry and wet roads should also be controlled. Tread pattern design affects this characteristic while rib type tread pattern design offers better lateral traction, lug type offers better forward traction.

10. Minimum noise :

The rolling tyre displaces air by aerodynamic effects, carcass and tread vibrations and air pumping, etc. Noise level depends upon pattern features and operating conditions.

Three Dimensional performance requirement:

Thus a pneumatic tyre has to carry the vertical load and deform vertically to cushion the ride (X-direction). Transmit traction/breaking torque in the ‘Y’ direction to get the vehicle in motion and develop cornering/transmit steering torque in the lateral direction for vehicle control (Z direction). It has to perform in all the three directions simultaneously and efficiently without compromising each other. It may be noted that no engineering product so far developed has a three-dimensional heavy-duty performance capability.

Types of Tyre Construction:

The most important component of pneumatic tyre is its carcass. The carcass has two types of constructions, viz., Bias construction and Radial construction.

1. Bias ply tyre or cross ply tyre :

PLY

PLY

In this type the reinforcing cords extend diagonally across the tyre from bead to bead. The bias angle of the cord path to the centerline of the tyre generally ranges from 25 to 40 degrees. The cords run in opposite directions in each successive layer (or ply) of reinforcing material, resulting in a criss-cross pattern.

2. Radial tyre

PLY

BELT

In the radial tyre, the plies of reinforcing cords extend transversely from bead to bead. That is, the cords are substantially perpendicular to the direction of tyre travel. On top of the plies, there is an inextensible belt composed of several layers of cords to restrict the circumferrential growth of tyres. The belt cords are actually low angle (18 - 22°) and the carcass plies are 88°.

Pneumatic Tyre – Components and Functions

Crown

Si

d e w al l

B e a d

A r e a

ChaferPly Turn upBead

FlipperBead Cores

Bead Filler

Inner Liner

Interior ofCasing

Inner pliesOuter plies

Breakers

Under Tread

Tread

1. Carcass:

Crown

Bead Heel

Chafer

Bead CoreBead Filler

Inner Lining

Under Tread

Tread pattern

Sid

ew

all

B e a d

a r e a

Bead Toe

Tread Groove

Interior Casing

Cap Ply

Belt

Body Ply

BeltBelt

The performance requirements were built into the early pneumatic tyres through the so-called 'bias construction'. A bias tyre has a carcass, which is made of reinforcement layers of fabric cords crossed over each other to the tread centerline. The number of such crossed layers called plies is a function of the tire's load carrying capacity and related inflation pressure and can range from 2 plies for scooter tyre to as much as 40 plies or more in an earthmover tyre. The fabric cords generally used are Rayon, Nylon and Polyester. A bias construction is continuous in its carcass structure from bead to bead. It is the most important component of the pneumatic tyre and it provides the necessary strength to the tyre: radially to hold inflation pressure, circumferentially for efficient transmission of traction/braking force and laterally to counter centrifugal forces while cornering/driving. The rubber matrix holds the fabric structure in its relative position and absorbs the shear strain while undergoing radial, circumferential and lateral deformation. Carcass is thus a high strength flexible membrane.

Bias Angle:

The performance of a bias carcass depends on the bias angle. Bias angle is the angle, which the cord makes with the circumferential centerline of the tyre. It is the equilibrium angle between radial force of inflation pressure and circumferential forces of traction/braking directional control and centrifugal force. Thus if the requirement is weighed more towards load the angle will be in the range of 38° - 40° and the angle drops as the emphasis shift to speed and directional stability like in racing tyres, where the angle is as low as 26°.

Belt & Breaker:

The belts are narrow layers of rubber coated tyre cord material directly under the tread in the crown of the tyre. The belts have a lower angle than the carcass plies and act to restrict the carcass plies. Due to their high lateral stiffness, the belt permits the tyre to resist deformation in the footprint. Belts raise the modulus of the tread area. Poor tread wear, lateral stability and cornering power that is expected of a radial ply tyre is nullified by the belt, which actually improves these properties when compared to a bias ply tyre.

Breakers have nearly the same angle as the carcass plies and do not restrict the carcass plies. A low denier, low EPI fabric is used for the breakers. A lower EPI fabric, due to the additional gap between cords takes up more rubber thereby providing better bond between tread and casing as well as it provides impact resistance. This also helps in providing stability to the tread and in distributing forces uniformly throughout the structure. Breakers improve the plunger strength of a tyre.

2. Inner liner (Drum Squeegee) :

Usually for tube type tyres, the inner liner is a thin layer of compound usually calendered direct on to the under side of the first ply. Some times, instead of calendering the inner liner to the first ply, they are taken as squeegee sheet and are applied to the building drum as the first operation in tyre building. Inner liner serves to insulate fully the tyre cords from the inner tube and thereby prevent tube-chafing

damage. It also protects the cords from possible degradation due to atmospheric moisture absorption. Inner liner also prevents the diffusion of mould release agent into the carcass plies during tyre curing, thus preventing problems with ply adhesion.

In tubeless tyres, the inner lining in the air-retaining member and is usually calendered as a two layer laminate having stepped edges.

3. Bead:

Bead consists of rigid steel wire rings on either side of the tyre around which the flexible torroidal carcass is tied. The bead is dimensionally rigid and hence offers a firm fit on to the steel rims. This in turn enables faithful transmission of engine, brake, and steering torques from the rim on to the flexible carcass.

4. Clinch Area:

The area just above the bead is termed clinch area. The flexible carcass detaches from the rigid rim at this area and hence is subjected to excessive stress/strain while the rim transmits load, torque and centrifugal forces to the tyre. Hence this area needs to be reinforced in proportion to the load, torque the tyre is expected to carry/transmit. Thus a rear heavy-duty drive tyre will have more fabric reinforcement at the clinch area than a front free rolling tyre. This reinforcement is Generally done by raising the turn up heights of the ply, chafer, etc. Care should be taken such that the extra reinforcement is gradually tapered such that no sharp change leading to stress concentration occurs in the structure.

Clinch Strip (Rim Strip):

The clinch strip may be considered as an extension to the lower edge o the sidewall, introduced as a further anti abrasion measure on radial tyres which are more subject to rim chafing than the cross ply tyre. Clinch strip is a very high modulus compound and this stiffens the clinch area further, thus minimising the flexing and heat build up there. Moreover, by restricting the flexing area of the sidewall, the clinch strip improves the steering response of radial tyres

Bead Apex:

The bead apex is a high modulus rubber compound, located on the top face of the bead, its primary function is to pack out the area of the structure immediately above the bead coil and so provide a steady gradation of thickness between the latter and the sidewall zone, the thickness of which is only that of the casing plies and sidewall rubber.

This component has been eliminated from many of the conventional passenger car tyres with small coils, there being sufficient compound and compound flow during moulding to fill the void adequately. It has to be retained in the radial ply tyres, in which high sidewall deflections occur, and in large tyres of multi-bead construction. The stress-carrying zone in the low wall region has to be spread to avoid rim chafing or structural break up. In the case of tyres where there is high sidewall flexing, in the absence of apex, that portion which is above the bead will act as a hinge about which the flexing takes place and result in premature failure of that region.

Bead Flipper:

Flipper is a rubber-coated fabric that encloses he bead and acts as a further reinforcement to the bead portion. Emphasis is on the avoidance of localised circumferential stress lines, which could promote looseness, or cord break up under constant flex conditions. Usually flippers are used only in large tyres like, truck tyres, rear tractor tyres, etc

5. Tread:

It is the patterned rubber mass moulded on to the crown of the toroidal carcass and is the wearing portion of the tyre. The carcass being a continuous bias structure from one bead to the other, essentially takes a near circular shape from bead to bead on inflation. This makes the crown radius small and hence lowers road conflict area and non-uniform load distribution. This deficiency of the bias carcass is off set by beefing the shoulders of the carcass with extra rubber mass in order to get a flatter contact and more uniform load distribution. However, this extra rubber on the shoulders put a high penalty on the speed and load capability of a bias tyre due to more heat generation and accumulation. In heavy-duty tyres, these extra rubber wedges in the shoulders are specially designed compounds with minimum heat generation.

The carcass transmits all the forces on to the ground through the tread at the contact patch. The tread being a rubber mass undergoes considerable deformation while transmitting these forces as well as engaging on the road deformities. These deformations of the tread cause excessive stress/strain concentration at the tread to carcass interface and consequent premature failures. In order to dilute this concentration, a graded structure is opted for the bias carcass in which the outermost layers in contact with tread are low modulus suspended plies called Breakers with high gauge of insulation rubber (generally low EPI 840/2 Nylon) followed by intermediate layer of outer plies and real pressure bearing inner plies.

Tread Pattern:

Tread pattern gives the basic styling to the tyre and is of great sales value. It is important that not only it should be functional but also it should look so. The most important considerations are grip, wear and noise.

On a clean dry road surface, the maximum grip is given by a completely smooth tread surface. However the slightest presence of moisture on the road will transform the smooth tyre into something lethally dangerous. Besides styling, tread pattern has two basic function (1) it must provide bite and, (2) provide drainage.

The tread needs to have a quantity of reasonably sharp well-defined edges that will engage with the road surface to provide some mechanical rather than merely frictional transmission of torque. These biting edges need to be transverse for good traction and braking and longitudinal for steering and cornering - directional stability. Thus there are basically two types of tread patterns viz. (1) Lug type where the biting edges are in transverse direction and (2) Rib type, where it is in longitudinal direction. Most vehicle maneuvers involve both, except for the degree of each, and their needs can be met by resolving these forces into diagonal resultants and thus

by diagonal biting edges in the tread pattern. Thus if a tyre is required to transmit traction/braking torque more i.e., when it is on the drive axle, the resultant pattern will be more towards transverse lug and are still known as lug type tyres. And if the tyre is required more directional stability and control i.e., when it is on the steering axle, the resultant pattern will be more towards circumferential ribs and are still known as rib type tyres. A combination of these two basic patterns is sometimes used as a compromise for both drive wheel and steering wheel, especially in off the road application, and is termed as semi lug tyres.

Modern radial tyres come with tread pattern featuring island blocks and studs, which look very aggressive and functional and have tremendous sales appeal. In such pattern care must be taken such that the blocks are of adequate dimensions and support so that they do not distort very much resulting in a sort of heel and toe rolling and wear of the blocks.

If there is water on the road, the tyre may never come sufficiently close to the road surface for these biting edges to engage with it. The water may build up in front of the tyre as a wedge, which at high speed will be driven underneath to raise the tyre clear of the road and makes it completely water born (aquaplaning) resulting in total loss of control. In order to prevent this, water must either be swept aside or be channeled away. Sweeping aside is virtually difficult at high speeds, especially with the wider radial tyres of today. Thus a satisfactory drainage of the middle portion of the contact zone can only be achieved by the provision of longitudinal passages, which act as pipes at the contact zone. Therefore the grooves in the center of tread needs to be fairly straight a sufficiently wide and deep to allow large quantities of water to pass through them at high speeds. It may be mentioned that better results are obtained with multiple narrow grooves than with smaller number of wide ones.

When a tyre is rolling on a wet road surface, the front third of the contact patch is responsible for the channeling away bulk of the water, the middle third must do the final drying and mopping up and the last third provides the grip. The mopping up at middle third demands many small slits and grooves called Sipes rather than a few large ones, which act as reservoirs for the final drying. Large treads blocks without sipe is a potential source of aquaplaning. Sipes are small incisions like knife cuts generally closed at each end and set at an angle to each other. This also adds greatly to the styling of the tyre apart from providing large number of biting edges in all directions. In a radial tyre since the tread elements are free from distortions due to the rigid backing of the belt, it is possible to put more and more Sipes into the tread elements to obtain corresponding improvement in wet grip, without in many way impairing mileage.

6.Sidewall:

Sidewall is a thin layer of rubber on either sides of the carcass essentially to protect the carcass from external degrading agent like moisture, oxygen, ozone etc. and also from physical damages.

In addition to the above components a bias tyre has filler, flipper and chafer in the bead area. Filler is a hard rubber compound reshaped and applied over the bead in order to fill the void above flat bead bundle and to give a smooth tapered shape for the carcass. It also adds stiffness to the clinch area. Flipper is a coated fabric strip applied around the filtered bead to hold them together and assist in holding the bead during the building stage.

7. Chafer

Chafer is a square woven coated nylon fabric applied around the carcass in the bead area to protect it from chaffing against the rim. It also protects the carcass from damages during mounting/demounting operations.

Pneumatic Tyre – Importance of Safety:

Pneumatic tyre is the only contact with the ground the vehicle has and is the first line of defense against all road shocks such as Impact, damage, etc. Any failure of pneumatic tyre is catastrophic and can cause extensive damage to the vehicle and the inmates. Further the tyre undergoes millions of stress-strain cycles during its life, as a result of which, extensive fatigue occurs to the rubber matrix, both cord and to the structure. Hence it is essential to give high level of safety factor for the strength in the design of the tyre and is to the tune of 8 to 10 times the calculated tension on the carcass.

Pneumatic Tyre – Markings

Markings on tyres give valuable information regarding the specifications, capabilities and intended applications of the tyres. The common types of markings on an automobile tyre are listed in below:

Common Tyre Markings

1. Tyre Size Designation2. Manufacturer's/Agents Name3. Brand Name and Extensions4. Ply Rating/Load Range5. Single/Dual Max. Load and corresponding inflation pressure6. Maximum selling price.7. Collaborator’s name8. Mould Number9. Drawing Number10. Serial Number and date of production11. TWI (Tread Wear Indicator)12. Radial13. Carcass ply material (Other than rayon14. Tubeless15. Made in ‘---‘16. Use radial tubes only17. Regroovable

18. VAI (Visual Alignment Indicator)

19. Direction of rotation20. Standards marking (ISI, DOT, ECE)

21. Number and types of Plies/belts on S.W. and tread area22. Safety Warning

23. Quality grades (Labels)

Tyre Size Designation

Of the numerous markings on tyres, the tyre size design0ation requires further elaboration. Tyre size designation is an international tyre code identifier and accurately describes the type of tyre, tyre section width, tyre aspect ratio, type of construction etc. Several methods are in existence for marking the tyre size. The most important ones are as follows:

1. Conventional Numeric System:

a. Bias

5.90 15 C

5.90 – Nominal Section Width in Inches 15 – Rim Diameter in Inches C – Load Range

b. Radial

165 SR 15 C

165 – Nominal Section Width in Millimeter S – Speed symbol R – Radial Construction Indicator 15 – Rim Diameter in Inches C – Load Range

2. ISO system

a. Passenger Car Tyres

185/ 70 R 13 84 H

185 – Nominal Section Width (185mm)70 – Nominal aspect ratio (70%) R – Tyre construction Code (Radial)13 – Nominal rim diameter (13mm)84 – Load index (500 Kgs.) H – Speed symbol (210 KM/hr.)

Note:1. Reinforced tyres have the additional marking "REINFORCED"2. Winter tyres have the additional marking "M+S" or (MS, M&S, M.S.)

3. Spare tyres designed for temporary use have the additional marking "TEMPORARY USE ONLY".4. High pressure 'T' tyres have a 'T' prefix in the size designation.

Eg: T105/80-D 82 or T1OS/80-D 13 82

b. Light Truck Tyre

165 / 95 R 13 98 / 96 L LT

L – Speed Symbol 98 / 96 – Single/Dual Load Index

c. Truck Tyre

255/70 R 22.5 140 / 137 J

J – Speed symbol

BIAS TYRE MANUFACTURING PROCESS

INTRODUCTION

Pneumatic tyre is a high performance composite product. The raw materials used for its manufacturing can be divided into three groups :

1. Rubber and Rubber additives2. Fabric reinforcements (Tyre cords – Steel, Nylon, Polyester)3. Wire reinforcements (Bead wife)

The process of tyre manufacturing is the art of processing the above materials and assembling the various components into the final product. The process of tyre manufacturing is complicated by the numerous raw materials, equipment and processes used for the same. We shall now consider the processes involved in the manufacture of a Bias Truck Tyre (Please see flow diagram attached)

1. COMPOUND MIXING

Mixing the required additives into rubber makes a compound. This mixing is accomplished in two or more steps using a Banbury mixer. The mixing is done in the chamber of the Banbury mixer under high shear and pressure using the rotors of the machine so that the ingredients are uniformly dispersed inside the rubber matrix. Different rubber compounds (differing in the recipe) are used in the different components of the tyre.

The rubber compound is thus used for the preparation of different components in subsequent stages of manufacture. The major components of a bias truck tyre are :

1) Tread - Made from rubber compound2) Sidewall - -do-3) Tread cushion - -do-4) Plies - Made from dipped tyre cord and compound

5) Chafer - Made from dipped square woven fabric and compound

6) Flipper - Made from dipped tyre cord and compound7) Filler - Made from rubber compound8) Bead - Made from bead wire and rubber compound9) Squeegees - Made from rubber compound10) Breakers - Made from dipped tyre cord and rubber

compoundNaturally, the compounds prepared in the Banbury go to the respective equipment and process for further processing.

2. CEMENTS PREPARATION

Various Cements, Solutions, Lubricants and paints are prepared in the Cement House using rubber compound solvents and other raw materials. These are then used at various stages of tyre manufacturing.

3. FABRIC DIPPING

Raw fabric (Nylon) as received is having very poor adhesion to the rubber compound and has poor dimensional stability. During the dipping process an adhesive coating (e.g. : Resorcinol, Formaldehyde, VP Latex dip) is applied to the surface of the fabric to improve adhesion. The fabric is also stretched and hot-set to increase the dimensional stability. Dipping is accomplished in a Dip Unit and the dipped fabric is then used for the preparation of different components as mentioned above.

4. EXTRUSION

Here, components of the tyre like tread and sidewall are prepared from rubber compounds using a Dual Extruder. Extrusion is the process by which the rubber compound is given definite continuous shape. A thin sheet of rubber compound prepared using a small 2-roll calender is applied to the bottom side of the tread. This component is called tread cushion. The continuous profile is then cooled, and cut to require length, which is used in the assembling of tyre at tyre building.

5. CALENDERING

Fabric calendering is the process of coating both sides of the dipped fabric using rubber compound. This is accomplished using a 4-roll ‘Z’ type calender. The coated fabric is cooled and wound in liners (in continuous length) to avoid sticking. This goes to the next stage of ply cutting.

6. PLY CUTTING (BIAS CUTTING)

For assembling a tyre several plies are used. For example a 16PR Nylon truck tyre uses 8 plies and two breakers. Each ply is cut from the coated fabric rolls prepared by calendering. This process of ply cutting is accomplished in a Bias Cutter. Each ply is cut at definite width and angle and wound in liners. The cut plies then go to 3-roll calender for squeegee application. Components like chafer and flipper are also made at the Bias Cutter. These are further slit using a slitter into smaller widths and wound into rolls. Chafer rolls from slitter go to the tyre building and flipper rolls go to the bead flipping.

7. SQUEEGEE CALENDERING / SQUEEGEE APPLICATION

Squeegee calendering is the process of making thin sheet of rubber compound usually by using a 3 roll or 4-roll calender. Squeegees are used at the inner most layer of the tyre (drum squeegee) and also in between the different plies (ply squeegees). Drum squeegee is prepared in the 4-roll ‘Z’ calender. It is would in liners and the squeegee rolls are sent to tyre building for assembling. The ply squeegee preparation and its application on to the cut plies are accomplished simultaneously at the 3-roll calender. After squeegee application the plies are sent to tyre building for assembling.

8. BEAD PREPARATION

Bead preparation consists of three stages:

a) Bead windingb) Bead filleringc) Bead flipping

9. BEAD WINDING

Here, several wires (strands) are passed through the head of a Bead Extruder and coated with rubber compound. The coated tape so formed is wound into bundles of definite turns and strands and of definite diameter. The process is accomplished using a machine called The Bead Winding Machine.

10. BEAD FILLERING

Here, a triangular shaped continuous rubber profile (called bead filler) is extruded using a cold feed extruder and applied on to the bead bundle using a fillering machine.

11. BEAD FLIPPING

The flipper fabric prepared at the Bias Cutter and slitter is applied around the fillered bead bundles. This is accomplished using a bead-flipping machine.

12. TYRE BUILDING OR TYRE ASSEMBLING

Tyre Building is the process of assembling various components into the semi finished product called a “Green Tyre”. A Tyre Building Machine accomplishes this. The components like Drum Squeegee, Plies, (with squeegee applied on to it) are assembled using a Tyre Building Drum. The flipped beads are applied from the ends and locked in using the ply ends, breaker and chafer are applied next. Finally, the tread and sidewalls are applied. The assembly (Green Tyre) is taken out after collapsing the drum.

13. TYRE CURING

The green tyre is inspected and then applied with a Lubricant on the inside and an anti-blemish paint on the outside sidewall area. The Green Tyre is also awled to facilitate easy removal of any trapped air during the final shaping and moulding operation. The Green Tyre is shaped and given the final contour using the appropriate tyre curing moulds (fitted to tyre curing presses) by the application of pressure and temperature. The rubber compound gets vulcanised during curing and becomes tough and elastic and provides all the desired properties required in the tyre.

The curing times vary depending upon the size of the tyre varying from 18’ for a Passenger car tyre to one hour for Truck tyres.

14. POST CURE INFLATION

Nylon tyres after press curing are kept under high-pressure inflation to help shape retention and to reduce growth in service. This process of cooling the tyre under high inflation pressure is called Post Cure Inflation (PCI).

15. INSPECTION

The tyres after PCI are subjected to vent trimming. The tyres are then inspected 100% for visual defects. The tyres are also statistically sampled and tested for conformance to BIS specifications and then warehoused.