PARTS OF TYRE

Tread

The tread is the part of the tire that comes in contact with the road surface. The portion that is in contact with the road at a given instant in time is the contact patch. The tread is a thick rubber, or rubber/composite compound formulated to provide an appropriate level of traction that does not wear away too quickly. The tread pattern is characterized by the geometrical shape of the grooves, lugs, voids and sipes. Tires that are fully worn can be re-manufactured to replace the worn tread. This is known as retreading or recapping, a process of buffing away the worn tread and applying a new tread.

Bead

The bead is that part of the tire that contacts the rim on the wheel. The bead is typically reinforced with steel wire and compounded of high strength, low flexibility rubber. The bead seats tightly against the two rims on the wheel to ensure that a tubeless tire holds air without leakage. The bead fit is tight to ensure the tire does not shift circumferentially as the wheel rotates. The width of the rim in relationship to the tire is a factor in the handling characteristics of an automobile, because the rim supports the tire's profile.

Sidewall

The sidewall is that part of the tire that bridges between the tread and bead. The sidewall is largely rubber but reinforced with fabric or steel cords that provide for strength and flexibility. The sidewall transmits the torque applied by the drive axle to the tread to create traction. The sidewall, in conjunction with the air inflation, also supports the load of the vehicle.

Plies

The body ply is a calendared sheet consisting of one layer of rubber, one layer of reinforcing fabric, and a second layer of rubber. The earliest textile used was cotton; later materials include rayon, nylon, polyester, and Kevlar. Passenger tires typically have one or two body plies. Body plies give the tire structure strength. Truck tires, off-road tires, and aircraft tires have progressively more plies. The fabric cords are highly flexible but relatively inelastic

Breaker/ Belts

Belts are calendered sheets consisting of a layer of rubber, a layer of closely spaced steel cords, and a second layer of rubber. The steel cords are oriented radially in radial tire construction, and at opposing angles in bias tire construction. Belts give the tire strength and dent resistance while allowing it to remain flexible. Passenger tires are usually made with two or three belts.

Inner Liner The inner liner is an extruded halo butyl rubber sheet compounded with additives that result in low air permeability. The inner liner assures that the tire will hold high-pressure air inside, without the air gradually diffusing through the rubber structure.

Manufacturing Process

There are six basic processes in the manufacturing of tires:

1. Mixing of carbon blacks, elastomers and chemicals in the Ban bury Mixer to form the rubber compounds.2. Calendaring the fabrics and steel cord and coating them with rubber.3. Extruding the treads and sidewall components.4. Manual assembly of the green tire components on tire building machines.5. Vulcanizing or curing the tire with heat and pressure.6. Final finishing, including inspection, storage and shipping. (A certain portion of finished tires are also repaired in the final finishing process.)

Tyre Manufacturing Process:

Tire is an advanced engineering product made of a lot more than rubber. Fiber, textile, and steel cord are just some of the components that go into the tires inner liner, body plies, bead assembly, belts, sidewalls, and tread. It requires the latest technology, heavy equipment, precision instruments and most importantlyqualified people.

Major processes involved in the tyre manufacturing are the mixing of the rubber compound; preparation of the fabric cord, steel cord, and bead wire; calendaring of the inner liner, steel belt and ply cord; extrusion, of the tires sidewall and tread; and the actual building, curing, and inspection of the tires. The process can be illustrated as follows,

Rubber/Ingredient Bead Wire Mixing Storages Flippering Fillering Bead Winding Flipper Beads Insulation Tread Storage Tread & sidewall Extrusion Band StorageBand BuildingBias CuttingCalendaringFabricTyre Building Dept.Green Tyre Insp.Curing Dept. (finished product)

The production process of tire is starting with mixing. In this process, rubber and other components are mixed in a Ban bury mill for obtaining the rubber compound. The process include two steps

1. Making of Master Batch, that include rubber, activator, filler, oil and antioxidant 2. Addition of accelerator and Sulphur to master batch to prepare Final Batch

The final batch obtained is called a rubber compound and is the main intermediate product for tyre production. The preparation breakup of a rubber compound is called a recipe and it consist of the following,

Natural rubber, is the basic elastomer used in tyre making. Styrene-butadiene co-polymer (SBR) is a synthetic rubber which is often substituted in part for natural rubber based on the comparative Poly butadiene is used in combination with other rubbers because of its low heat-buildup properties. Halo butyl rubber is used for the tubeless inner liner compounds, because of its low air permeability. Carbon Black, forms a high percentage of the rubber compound. This gives reinforcement and abrasion resistance. Silica, used together with carbon black in high performance tires, as a low heat buildup reinforcement. Sulphur crosslinks the rubber molecules in the vulcanization process. Vulcanizing Accelerators are complex organic compounds that speed up the vulcanization. Activators assist the vulcanization. The main one is zinc oxide. Antioxidants and antiozonants prevent sidewall cracking due to the action of sunlight and ozone. Textile fabric reinforces the carcass of the tyre.

The approximate composition of rubber compound is as follows

Raw material By weight (%)

Rubber 60

Carbon black 25

Antioxidant 1

Vulcanizing agents 3

Others 10

Natural Rubber Natural Rubber is an elastomer derived from latex, a milky colloid produced by some of the plants like Hevea brasiliensis. These plants produce latex when they are wounded as a healing mechanism. The latex is collected in a vessel and it is allowed to coagulate which gives you the solid rubber which can be further processed in to sheets. The coagulation process can be controlled by chemicals like Ammonia, Formic acid. Ammonia decelerates the coagulation process whereas Formic acid accelerates it. The purified natural rubber is same as polyisoprene.

The monomer of Natural Rubber is 2-methyl-1, 3-butadiene, CH2=C (CH3)-CH=CH2. The required properties of rubber like elasticity, is mainly dependent on the cis form of C5H8 rather than its Trans counterpart. As the natural rubber is formed by coagulation of latex, the relative proportions of cis and Trans are fixed which can result in degradation of desired properties.

Synthetic Rubber Synthetic rubber can be made from the polymerization of a variety of monomers including isoprene (2-methyl-1, 3-butadiene), 1, 3-butadiene, chloroprene (2-chloro-1, 3-butadiene), and isobutylene (methyl propene) with a small percentage of isoprene for crosslinking. These and other monomers can be mixed in various desirable proportions to be copolymerized for a wide range of physical, mechanical, and chemical properties.

The monomers can be produced pure and the addition of impurities or additives can be controlled by design to give optimal properties. Polymerization of pure monomers can be stereo specifically regulated through various catalysts to achieve the desired cis or Trans double bonds.

Halo butyl rubber is used for the tubeless inner liner compounds, because of its low air permeability. The halogen atoms provide a bond with the carcass compounds which are mainly natural rubber.

Carbon Black Carbon black is a material produced by the incomplete combustion of heavy petroleum products such as coal tar, ethylene cracking tar etc., It is a form of amorphous carbon that has a high surface-area-to-volume ratio and significantly lower PAH (polycyclic aromatic hydrocarbon). It is used as a pigment and reinforcement filler in the tyre. It helps in conducting heat away from the tread and belt area of the tire, reducing thermal damage and increasing tire life. While a pure styrene-butadiene rubber has a tensile-strength of no more than 2.5MPa, and almost non-existent abrasion resistance, compounding it with 50% of its weight of carbon black improves its tensile strength to 20MPa and considerable wear resistance. The black color of the tyre is due to carbon black, if we want to have another colour with the same reinforcing properties fumed silica is used. Fumed Silica It is also known as pyrogenic silica as it is produced in a flame, consisting of microscopic droplets of amorphous silica fused into branched, chainlike, three-dimensional secondary particles which then agglomerate into tertiary particles. The resulting powder has an extremely low bulk density and high surface area. Its three-dimensional structure results in viscosity-increasing behaviour when used as a thickener or reinforcing filler.

Fumed silica also provides better trade-off for fuel efficiency and wet handling due to a lower rolling loss compared to carbon black-filled tires. Traditionally silica fillers had worse abrasion wear properties, but the technology has gradually improved to where they can match carbon black abrasion performance.

Vulcanization Natural Rubber is sticky, deforms easily when warm, and is brittle when cold. Vulcanization is a chemical reaction which helps in betterment of some of the properties like removes the sticky behaviour, increases the young's modulus etc., in this chemical reaction elements/compounds like Sulphur are added which have the ability to form cross-links between the long chain polymer molecules, converting the rubber from a thermoplastic to a thermosetting polymer. The extent of vulcanization reaction can be controlled by accelerators and retarders. A derivative of aniline called thiocarbanilide, zinc oxide accelerates the action of sulphur to rubber, leading to shorter cure times.

Antioxidant An antioxidant is a molecule capable of preventing oxidation of other molecules. We say something is oxidized if it loses electrons, hence moving to a higher oxidation state. Oxidation reactions can produce free radicals which can result in polymerization. As the tyre components are exposed to sunlight free radicals may get generated, antioxidants essentially terminate these free radicals preventing extraneous polymerization reactions. Antioxidants basically undergo oxidation reaction themselves, thus preventing oxidation of other compounds. Antioxidants are reducing agents such as thiols, ascorbic acid, and polyphenols.

Antiozonant Rubber contains an unsaturated double bond, as the tyre is always exposed to atmosphere ozone gas present in the atmosphere may break the double bond in to aldehydes or ketones. Thus reducing the degree of polymerization results into the degradation of properties. Cracks start to appear on the tyre, which are called as ozone cracks. Antiozonants are chemical compounds that prevent or slow down the degradation of material caused by ozone gas in the air. Paraffin wax acts as an antiozonant by the means of formation of a surface barrier.

CALENDARING

Calendaring is a process in which dipped nylon fabric or steel cords are coated with thin layer of rubber compound to form rubberized sheets including plies, squeeze, chafers and flippers. There is two types of calendars called

1. 3 Roll calendar 2. 4 Roll calendar

A 3 roll calendar produces non fabric sheets that include squeezes and inner liner while 4 roll calendar produces fabric sheets that include plies, chafers and flippers. From calendaring department, flipper will be sent to bead department and chafer to building department. Plies produced are sent to Bias cutting department. There plies are cut at an angle ranging from 50 to 70 degrees and are spliced end to end to produce band.

EXTRUSION

A part of Rubber compound from the mixing department is received by Extrusion department for the production of tread and sidewall. Tread and sidewalls are produced by the technique of extrusion through an extruder. Cross section and dimensions of tread and sidewalls should be so precise because they both account for almost 50% of the weight of a green tyre. Improper extrusion results in imbalance and underperformance of a tyre. The extruded product will be water cooled and cut into pieces of specific length and angle using a skiver. The extruded products will be sent to Building department for the building of green tyres within minimum time as per spec.

BEAD

The bead is that part of the tire that contacts the rim on the wheel. The bead is typically reinforced with steel wire and compounded of high strength, low flexibility rubber. The bead seats tightly against the two rims on the wheel to ensure that a tubeless tire holds air without leakage. The bead fit is tight to ensure the tire does not shift circumferentially as the wheel rotates. The width of the rim in relationship to the tire is a factor in the handling characteristics of an automobile, because the rim supports the tire's profile

A part of rubber compound from mixing is received by bead department. A given number of metal wires are coated with this rubber compound and is extruded to get wound bead. This extruded wound bead is rounded over a core drum and cut to desired sizes. Along with this there is a filler extrusion process to extrude filler. This filler is attached to the extruded bead to obtain fillered bead. Fillered bead is covered with a flipper to form a flippered bead or simply bead of desired size and quality. This bead is then sent to Building department for the building of green tyre.

All the products from the above departments are sent to Building department for the production of green tyre

GREEN TYRE BUILDING

Green tyre building is the process of making green tyre using the products received from Band building, Extrusion and Bead department. The following products are received by the building department for building green tyre

1. Tread 2. Side wall 3. Bead 4. Band

These products are assembled on a drum under specification to form a green tyre.

Green Tyre Preparation

Though tyre curing, as such, is a process associated with tyre curing press, there are several small but equally important processes being performed for defect free product. These small processes are process-aids for main curing process. They are

1. JammingTread splicing is jammed with a jamming machine by applying a force of about 4 Kg/Cm2 To strengthen splicing.

2. Green Tyre Poking After building the tyre, it is subjected for tyre poking. This process helps to remove trapped air in carcass or between carcass and tread. Skipping of this operation will increase the chances of ply blows and tread blows.

3. Painting Tyre must be uniformly painted from inside from toe to toe. Insufficient or non uniform painting will result in bladder buckling or ply separation defect. It will cause spread cord defect and lead to low bladder life due to uneven stretch in bladder. At the same time excessive painting should be avoided as it starts flaking and drops on floor acts as foreign matter. All the green tyres must be painted from outside with C223 solution uniformly, from mid sidewall to bead heel. Insufficient or inadequate painting will certainly cause light side or snag bead defect.

4. Shaping of a tyre and shaping pressure Green truck tyre being very thick and solid mass of rubber which when tried to mould without shaping it or with less shaping, it will not get molded properly. Final product may look ok externally but it will not be ok or acceptable with respect to its cured tyre layout. In short it will not match with designed dimension in cured tyre.

CURING

Tyre curing is a process of converting a green tyre into a cured tyre by means heat energy supplied through various heat sources which are in the form of hot water, high pressure steam and cold water. The entire process causes both physical and chemical changes in a green tyre while getting transformed in to a cured tyre.

Physical change is that, the shape and size of the green tyre gets changed / molded into a desired pattern and size. Desired pattern and size can be obtained with the help of mould. Chemical change A green tyre is made up of various natural rubber compounds containing natural rubber, Sulphur and various chemicals. Natural rubber molecule is made up of long chain of isoprene units. These isoprene units get crossed linked with the Sulphur atoms on heating. Chemically, curing is nothing but bridging formed between linear polymer chains, leading to a three dimensional network structure known as cross linking. This is an irreversible process. It turns green rubber in to cured mass. This cured mass (chemically crossed linked polymer) can neither be melted on further heating nor dissolved in a solvent. Prolonged or drastic heating will, however, lead to the degradation of the polymer.

The Curing process

After shaping the mould will be closed and there starts the curing process. Different curing Medias are used inside the mould for making temperature variations and they are, Low pressure steam (LP steam) High pressure steam (HP steam) Hot water (HW) Cold water (CW)

The total set of activities that starts from the heating up of bladder to ejecting of cured tyre from mould is called the Curing Cycle. The various steps of Curing Cycle are

1. High Pressure Steam at 15.5 Kg/cm2 and 200 C is passed into the bladder. Its duration varies from cycle to cycle.

2. Dome steam is passed in dome at 5th minute of operation normally at 145C and 155C

3. Hot water entry step- Hot water is passed into bladder. It is followed by heating with hot water at 17.5/20.0/25.0 Kg/cm2 and 176C according to the sizes. Its duration varies from cycle to cycle

4. Hot water recovery step. During this step precious hot water is recovered by pushing it out with steam. The step is called as steam blow back (SBB).

5. Cold water hold step. By the end of SBB step, heating part of tyre is considered to be over and fifth step onwards tyre is subjected for cooling by filling in cold water in it. Duration of this step is 1min for PCI inside specs.

6. Cold water circulation step. To fasten cooling, cold water is circulated in bladder. Duration of this step is 3 min.

7. All off step. During this stage bladder is drained off by opening the drains like internal drain and cold water return. Duration of this step is 0.5 min.

8. Vacuum step. During this stage bladder is deflated to remove all the traces of cold water. Duration of this step is 0.5 min.

9. Press opens and tyre gets ejected from mould. Now the tyre is ready for mounting on PCI.

FINAL INSPECTION

After the PCI operation the tyres are sent to the Final inspection Department (FID) for visual inspection. There each and every tyres will be visually inspected by skilled people. Here they check for any defects in the cured tyre and if found they will be classified and stored separately for QA verification. If the defect for a particular batch is more than 20% then the curing operations will be stopped for analysis and correction. Defect free products will be transferred to Finished Product Storage (FPS) department.

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