Tyre Manufacturing Processes

Seminar Report

Arvind Boudha

(Roll No. 08011044)

Sateesh Kumar

(Roll No. 08011045)

Srimannarayana

(Roll No. 08011046)

Febin Koyan

(Roll No. 08011047)

Department of Metallurgical Engineering and Materials Science

Indian Institute of Technology, Bombay

(September 2011)

INDEX

CONTENTS Page

1. Introduction 3

2. Tyre Components & Their Significance 4

3. Raw Materials Used 6

4. Tyre Manufacturing Process

4.1 Compounding and Banbury mixing 9

4.2 Milling 10

4.3 Extruding and Calendering 11

4.4 Component Assembly and Building 11

4.5 Curing and Vulcanizing 12

4.6 Inspection and Finishing 13

5. Future 14

6. References 15

1. Introduction Tyres are the only point of contact of the vehicle with the road. The intentions of the

driver are finally executed by the tyres only, hence the quality and design of the tyres is

important. The rubber tube inflated with air supports the whole weight of the car, but the

rubber tube cannot directly come in contact with the road as it cannot resist wear and it lacks

strength. Tyre encases the rubber tube. Tyres must perform a certain number of functions for

the smooth functioning of the vehicle namely- steering, carrying a load, cushioning, rolling,

transmitting drive and long lasting life.

Steering: Tyres should steer the vehicle with precision irrespective of surface of the road,

weather conditions. The stability of a vehicle's path depends upon ability of tyre to hold its

course by maintaining proper traction with the road. It should stand upto transversal forces

without drifting from its path.

Carrying load: Tyres should carry lot of weight usually more 50 times its own weight not only

when it is in motion but also at rest. Car usually weighs around 1.6 tonnes and the area of

contact of a single tyre with road is size of a post card. Hence each tyre experiences a

compressive stresses of the order of few MPa.

Cushioning: Tyres absorb the shock due to obstacles or irregularities present on the surface of

the road, providing a comfort travel to the passenger as well as ensuring long life of the vehicle.

The main characteristic of tyre is its ability to yield when stress is applied and return to its

original shape when stress is removed, with the tyre lasts, or in other words, keeps its optimum

performance level for millions of wheel revolutions. The tyre’s wear depends on its conditions

of use (load, speed, condition of the road surface, state of the vehicle, style of driving, etc.) but

above all the quality of its contact with the ground. Pressure therefore plays a major role. e

stress cycle occurring at very high frequencies.

Transmitting Drive: Tyres transmit drive namely the engine's usable power, braking effort

with the help of the friction. Superior quality and efficient design of the tyre helps in making

complete use of engine's power and braking facility.

Long Lasting Life: Tyres should be able to give optimum performance for millions of

revolutions. Life of a tyre depends on a variety of factors like quality of contact with the road,

load, speed, driving style etc.,

Most of the functions of tyre can be achieved with proper maintenance of air pressure. Hence

ability to hold air without allowing it to diffuse is important. [1][2][3]

2. COMPONENTS Tyre is a composite structure consisting of many layers. They usually consist of

1. Inner liner

2. Body ply

3. Side wall

4. Beads, Apex

5. Belt Package

6. Tread

7. Cushion Gum.

Fig.2.1 Schematic of the components of a tyre [9]

Inner Liner

It is an extruded halobutyl 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.

Body Ply

The body ply is a calendered sheet (two or more sheets are rolled together such that

mechanically they are bonded) consisting of consecutive layers of rubber and reinforcing fabric.

They give the structural strength to the tyre. Passenger tyres typically have one or two body

plies. Truck tires, off-road tires, and aircraft tires have progressively more plies. The fabric

cords are highly flexible but relatively inelastic. The textile materials used are cotton in early

years now replaced by rayon, nylon, kevlar, polyester.

Sidewalls

Sidewalls are non-reinforced extruded profiles with additives to give the sides of the tire good

abrasion resistance and environmental resistance. Additives used in sidewall compounds

include antioxidants and antiozonants to protect the tyre from decomposition when exposed to

ultra violet light. Sidewall extrusions are nonsymmetrical and provide a thick rubber area to

enable molding of raised letters and sidewall ornamentation.

Beads

Beads are bands of high tensile-strength steel wire encased in a rubber compound. Bead wire is

coated with special alloys of bronze or brass. Coatings protect the steel from corrosion. Copper

in the alloy and sulphur in the rubber cross-link to produce copper sulphide, which improves

bonding of the bead to the rubber. Beads are inflexible and inelastic, and provide the

mechanical strength to fit the tyre to the wheel. Bead rubber includes additives to maximize

strength and toughness.

Apex

The apex is a triangular extruded profile that mates against the bead. The apex provides a

cushion between the rigid bead and the flexible inner liner and body ply assembly. It is

alternatively called as "filler" in literature and industry.

Belt Package

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 tyre strength and dent resistance

while allowing it to remain flexible. Passenger tires are usually made with two or three belts.

Tread

The tread is a thick extruded profile that surrounds the tire carcass and this is the layer which

comes directly in contact with the. Tread compounds include additives to impart wear

resistance and traction in addition to environmental resistance. Tread compound development

is an exercise in compromise, as hard compounds have long wear characteristics but poor

traction whereas soft compounds have good traction but poor wear characteristics.

Cushion Gum

Many higher-performing tyres include an extruded component between the belt package and

the tread to isolate the tread from mechanical wear from the steel belts.[4][5][6]

3. RAW MATERIALS USED The above mentioned tyre components use a broad variety of materials like different

rubber compounds, different types of carbon black, fillers like clay and silica, chemicals or

minerals added to accelerate/decelerate vulcanisation. The tyres also have several types of

fabric for reinforcement, several kinds and sizes of steel. Some of the steel is twisted or braided

into strong cables.

Table 3.1 Approximate amount of various materials used in different tyres[9]

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 (methylpropene) 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

stereospecifically regulated through various catalysts to acheive the desired cis or trans double

bonds.

Fig.3.2 Various Polymerized products obtained from polymerization of polyisoprene

Various kinds of synthetic rubbers are used in the tyre components like Styrene-butadiene,

Polybutadiene because of the relatively low materials cost, low heat-buildup properties

respectively.

Halobutyl 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 nonexistent 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 anyother color 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 behavior 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 behavior, 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

sulfur 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, 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.

4. TYRE MANUFACTURING PROCESS

Fig. 4.1 SCHEMATIC OF TYRE MANUFACTURE [10]

4.1 Compounding and Banbury mixing

A Banbury mixer combines rubber stock, carbon black and other chemical ingredients to

create a homogeneous rubber material. Time, heat and raw materials are factors utilized to

engineer material composition. The ingredients are generally provided to the plant in pre-

weighed packages or are prepared and weighed by the Banbury operator from bulk quantities.

Measured ingredients are placed onto a conveyor system, and the Banbury is charged to initiate

the mixing process. Hundreds of components are combined to form rubber utilized for tyre

manufacturing. The components include compounds which act as accelerators, anti-oxidants,

anti-ozonants, extenders, vulcanizers, pigments, plasticizers, reinforcing agents and resins.

Most constituents are unregulated and may not have had extensive toxicological evaluations.

Generally speaking, the Banbury operators' occupational exposures to the raw materials have

been reduced by improvements in administrative and engineering controls. However, concern

remains due to the nature and quantity of components which make up the exposure.

Fig.4.2 Mill with a trip bar located too high to be effective. The operator, however, has large gloves which would be pulled into the mill before his fingers [10]

4.2 Milling

Shaping of rubber begins in the milling process. At the completion of the Banbury

mixing cycle, rubber is placed onto a drop mill. The milling process shapes the rubber into flat,

long strips by forcing it through two set rolls rotating in different directions at different speeds.

Mill operators are generally concerned with safety hazards associated with the open operation

of the turning rolls. Older mills usually had trip wires or bars which could be pulled by the

operator if he or she is got caught in the mills. Modern mills have body bars at about knee level

that are automatically triggered if the operator is caught in the mills. Most facilities have

extensive emergency rescue procedures in place for workers trapped in mills. Mill operators

are exposed to heat as well as noise.

Fig. 4.3.a)Mill for calender line with a body bar guard that shuts down the mill if tripped by workers[10]

Fig. 4.3.b) Drop mill and dryer with canopy hood and trip wires [10]

4.3 Extruding and Calendering

The calender operation continues to shape rubber. The calender machine consists of one or

more (often four) rolls, through which the rubber sheets are forced.

The calender machine has the following functions:

• To prepare compounded rubber as a uniform sheet of definite thickness and width

• To place a thin coat of rubber on a fabric (“coating” or “skimming”)

• To force rubber into the interstices of fabric by friction (“frictioning”)

The rubber sheets coming off the calender are wound on drums, called “shells,” with fabric

spacers, called “liners,” to prevent sticking.

The extruder is often referred to as a “tuber” because it creates tube-like rubber

components. The extruder functions by forcing rubber through dies of appropriate shape. The

extruder consists of a screw, barrel or cylinder, head and die. A core or spider is used to form

the hollow inside of tubing. The extruder makes the large, flat section of tyre treads.

Extruder and calender operators may be exposed to talc and solvents, which are used in

the process. Also, the workers at the end of the extrusion operation are exposed to a highly

repetitive task of placing the tread onto multi-tiered carts. This operation is often referred to as

booking treads, because the cart looks like a book with the trays being the pages.

The configuration of the extruder as well as the weight and quantities of tread to be

booked contribute to the ergonomic impact of this operation. Numerous changes have been

made to lessen this, and some operations have been automated.

4.4 Component Assembly and Building

The tyre assembly machine consists of a rotating drum, on which the components are

assembled, and feeding devices to supply the tyre builder with the components to assemble

(see figure 80.7). The components of a tyre include beads, plies, side walls and treads. After the

components are assembled, the tyre is often referred to as a “green tyre”.

Tyre builders and other workers in this area of the process are exposed to a number of

repetitive motion operations. Components, often in heavy rolls, are placed onto the feeding

portions of the assembly equipment. This may entail extensive lifting and handling of heavy

rolls in a limited space. The nature of assembly also requires the tyre builder to perform a

series of similar or identical motions on each assembly. Tyre builders utilize solvents, such as

hexane, which allow the tread and plies of rubber to adhere. Exposure to the solvents is an area

of concern. After being assembled, the green tyre is sprayed with a solvent- or water-based

material to keep it away from adhering to the curing mould. These solvents potentially expose

the spray operator, material handler and curing press operator. Nowadays, water-based

materials are mostly used.

Fig. 4.4 Operator assembling a tyre on a single-stage tyre machine [10]

4.5 Curing and Vulcanizing

Curing press operators place green tyres into the curing press or onto press loading

equipment. Curing presses in operation in North America exist in a variety of types, ages and

degrees of automation (fig 5). The press utilizes steam to heat or cure the green tyre. Rubber

curing or vul-canization transforms the tacky and pliable material to a non-tacky, less pliable,

long-lasting state.

Fig.4.5 Passenger and light truck Bag-o-matic McNeal curing press ventilated with a ceiling fan,

Akron, Ohio, US [10]

4.6 Inspection and Finishing Following curing, finishing operations and inspection remain to be performed before the

tyre is stored or shipped. The finishing operation trims flash or excess rubber from the tyre. This excess rubber remains on the tyre from vents in the curing mould. Additionally, excess layers of rubber may need to be ground from the side walls or raised lettering on the tyre. One of the major health hazards that workers are exposed to while handling a cured tyre is repetitive motion. The tyre finishing or grinding operations typically expose workers to cured rubber dust or particulate. This contributes to respiratory illness in workers in the finishing area. In addition, a potential exists for solvent exposure from the protective paint which is often used to protect the side-wall or tyre lettering. After finishing, the tyre is ready to be stored in a warehouse or shipped from the plant. [8]

5. The Future

Constant improvements in rubber chemistry and tire design are creating exciting new tires that offer greater mileage and improved performance in extreme weather conditions. Manufacturers now offer tires estimated to last up to 80,000 miles. Treads, designed and tested by computer, now feature unique asymmetrical bands for improved traction and safety on wet or snowy roads.

Tire design engineers are also experimenting with non-pneumatic tires that can never go flat because they don't contain air under pressure. One such non-pneumatic tire is simply one slab of thick plastic attached to the wheel rim. The plastic curves out from the rim to a point where a rubber tread is secured to the plastic for contact with the road. Such a tire offers lower rolling resistance for greater fuel economy and superior handling because of a greater area of contact between tread and road. [11]

REFERENCES

1. http://www.michelin.re/zma/front/affich.jsp?codeRubrique=20060922131123&lang=EN

2. http://www.bridgestone.co.in/tyre/tyrecare/safedriving.asp

3. www.hankooktyre.com.au/Tech/Functions.aspx?pageNum=3&subNum=4&ChildNum=2

4. http://en.wikipedia.org/wiki/Tire_manufacturing

5. http://www.jktyre.com/Customer_Service/Tyre_Components.aspx

6. http://www.indiacar.com/infobank/how_tyres_work.htm

7. Wikipedia articles Natural rubber, Synthetic rubber, Carbon black Fumed silica Vulcanization,

anti oxidants and anti ozonants

8. www.emt-india.net/process/tyre/pdf/TyreManufactureProcess001.pdf

9. wrap.org.uk/downloads/2__Composition_of_a_Tyre__May_2006.4d2e4682.2856.pdf

10. www.emt-india.net/process/tyre/pdf/TyreManufactureProcess001.pdf

11. http://www.enotes.com/how-products-encyclopedia/tire