Manufacturing Processes - Tyre
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  • 1. Tyre Manufacturing Processes Arvind Boudha Seminar Report (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)
  • 2. INDEXCONTENTS Page1. Introduction 32. Tyre Components & Their Significance 43. Raw Materials Used 64. 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 135. Future 146. References 15
  • 3. 1. Introduction Tyres are the only point of contact of the vehicle with the road. The intentions of thedriver are finally executed by the tyres only, hence the quality and design of the tyres isimportant. The rubber tube inflated with air supports the whole weight of the car, but therubber tube cannot directly come in contact with the road as it cannot resist wear and it lacksstrength. Tyre encases the rubber tube. Tyres must perform a certain number of functions forthe 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 vehicles path depends upon ability of tyre to hold itscourse by maintaining proper traction with the road. It should stand upto transversal forceswithout drifting from its path.Carrying load: Tyres should carry lot of weight usually more 50 times its own weight not onlywhen it is in motion but also at rest. Car usually weighs around 1.6 tonnes and the area ofcontact of a single tyre with road is size of a post card. Hence each tyre experiences acompressive stresses of the order of few MPa.Cushioning: Tyres absorb the shock due to obstacles or irregularities present on the surface ofthe 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 itsoriginal shape when stress is removed, with the tyre lasts, or in other words, keeps its optimumperformance level for millions of wheel revolutions. The tyre’s wear depends on its conditionsof use (load, speed, condition of the road surface, state of the vehicle, style of driving, etc.) butabove all the quality of its contact with the ground. Pressure therefore plays a major role. estress cycle occurring at very high frequencies.Transmitting Drive: Tyres transmit drive namely the engines usable power, braking effortwith the help of the friction. Superior quality and efficient design of the tyre helps in makingcomplete use of engines power and braking facility.Long Lasting Life: Tyres should be able to give optimum performance for millions ofrevolutions. 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. Henceability to hold air without allowing it to diffuse is important. [1][2][3]
  • 4. 2. COMPONENTSTyre 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]It is an extruded halobutyl rubber sheet compounded with additives that result in low airInner Linerpermeability. The inner liner assures that the tire will hold high-pressure air inside, without theair gradually diffusing through the rubber structure.The body ply is a calendered sheet (two or more sheets are rolled together such thatBody Plymechanically they are bonded) consisting of consecutive layers of rubber and reinforcing fabric.
  • 5. They give the structural strength to the tyre. Passenger tyres typically have one or two bodyplies. Truck tires, off-road tires, and aircraft tires have progressively more plies. The fabriccords are highly flexible but relatively inelastic. The textile materials used are cotton in earlyyears now replaced by rayon, nylon, kevlar, polyester.Sidewalls are non-reinforced extruded profiles with additives to give the sides of the tire goodSidewallsabrasion resistance and environmental resistance. Additives used in sidewall compoundsinclude antioxidants and antiozonants to protect the tyre from decomposition when exposed toultra violet light. Sidewall extrusions are nonsymmetrical and provide a thick rubber area toenable molding of raised letters and sidewall ornamentation.Beads are bands of high tensile-strength steel wire encased in a rubber compound. Bead wire isBeadscoated with special alloys of bronze or brass. Coatings protect the steel from corrosion. Copperin the alloy and sulphur in the rubber cross-link to produce copper sulphide, which improvesbonding of the bead to the rubber. Beads are inflexible and inelastic, and provide themechanical strength to fit the tyre to the wheel. Bead rubber includes additives to maximizestrength and toughness.The apex is a triangular extruded profile that mates against the bead. The apex provides aApexcushion between the rigid bead and the flexible inner liner and body ply assembly. It isalternatively called as "filler" in literature and industry.Belts are calendered sheets consisting of a layer of rubber, a layer of closely spaced steel cords,Belt Packageand 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 resistancewhile allowing it to remain flexible. Passenger tires are usually made with two or three belts.The tread is a thick extruded profile that surrounds the tire carcass and this is the layer whichTreadcomes directly in contact with the. Tread compounds include additives to impart wearresistance and traction in addition to environmental resistance. Tread compound developmentis an exercise in compromise, as hard compounds have long wear characteristics but poortraction whereas soft compounds have good traction but poor wear characteristics.Many higher-performing tyres include an extruded component between the belt package andCushion Gumthe tread to isolate the tread from mechanical wear from the steel belts.[4][5][6]
  • 6. 3. RAW MATERIALS USED The above mentioned tyre components use a broad variety of materials like differentrubber compounds, different types of carbon black, fillers like clay and silica, chemicals orminerals added to accelerate/decelerate vulcanisation. The tyres also have several types offabric for reinforcement, several kinds and sizes of steel. Some of the steel is twisted or braidedinto strong cables.Table 3.1 Approximate amount of various materials used in different tyres[9] Natural Rubber is an elastomer derived from latex, a milky colloid produced by some ofNatural Rubberthe plants like Hevea brasiliensis. These plants produce latex when they are wounded as ahealing mechanism. The latex is collected in a vessel and it is allowed to coagulate which givesyou the solid rubber which can be further processed in to sheets. The coagulation process canbe controlled by chemicals like Ammonia, Formic acid. Ammonia decelerates the coagulationprocess whereas Formic acid accelerates it. The purified natural rubber is same aspolyisoprene. The monomer of Natural Rubber is 2-methyl-1,3-butadiene,CH2=C(CH3)-CH=CH2. Therequired properties of rubber like elasticity, is mainly dependent on the cis form of C5H8 ratherthan its trans counterpart. As the natural rubber is formed by coagulation of latex, the relativeproportions of cis and trans are fixed which can result in degradation of desired properties. Synthetic rubber can be made from the polymerization of a variety of monomersSynthetic Rubberincluding isoprene (2-methyl-1,3-butadiene), 1,3-butadiene, chloroprene (2-chloro-1,3-butadiene), and isobutylene (methylpropene) with a small percentage of isoprene forcrosslinking. These and other monomers can be mixed in various desirable proportions to be
  • 7. 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 becontrolled by design to give optimal properties. Polymerization of pure monomers can bestereospecifically regulated through various catalysts to acheive the desired cis or trans doublebonds.Fig.3.2 Various Polymerized products obtained from polymerization of polyisopreneVarious kinds of synthetic rubbers are used in the tyre components like Styrene-butadiene,Polybutadiene because of the relatively low materials cost, low heat-buildup propertiesrespectively. Halobutyl rubber is used for the tubeless inner liner compounds, because of its low airpermeability. The halogen atoms provide a bond with the carcass compounds which are mainlynatural rubber. Carbon black is a material produced by the incomplete combustion of heavy petroleumCarbon Blackproducts such as coal tar, ethylene cracking tar etc., It is a form of amorphous carbon that has ahigh surface-area-to-volume ratio and significantly lower PAH (polycyclic aromatichydrocarbon). It is used as a pigment and reinforcement filler in the tyre. It helps in conductingheat away from the tread and belt area of the tire, reducing thermal damage and increasing tirelife. While a pure styrene-butadiene rubber has a tensile-strength of no more than 2.5MPa, andalmost nonexistent abrasion resistance, compounding it with 50% of its weight of carbon blackimproves its tensile strength to 20MPa and considerable wear resistance. The black color of thetyre is due to carbon black, if we want to have anyother color with the same reinforcingproperties fumed silica is used.
  • 8. It is also known as pyrogenic silica as it is produced in a flame, consisting of microscopicFumed Silicadroplets of amorphous silica fused into branched, chainlike, three-dimensional secondaryparticles which then agglomerate into tertiary particles. The resulting powder has an extremelylow 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 alower rolling loss compared to carbon black-filled tires. Traditionally silica fillers had worseabrasion wear properties, but the technology has gradually improved to where they can matchcarbon black abrasion performance. Natural Rubber is sticky, deforms easily when warm, and is brittle when cold.VulcanizationVulcanization is a chemical reaction which helps in betterment of some of the properties likeremoves the sticky behavior, increases the youngs modulus etc., in this chemical reactionelements/compounds like Sulphur are added which have the ability to form cross-linksbetween the long chain polymer molecules, converting the rubber from a thermoplastic to athermosetting polymer. The extent of vulcanization reaction can be controlled by acceleratorsand retarders.A derivative of aniline called thiocarbanilide, zinc oxide accelerates the action ofsulfur to rubber, leading to shorter cure times. An antioxidant is a molecule capable of preventing oxidation of other molecules. We sayAntioxidantsomething is oxidized if it loses electrons, hence moving to a higher oxidation state. Oxidationreactions can produce free radicals which can result in polymerization.As the tyre componentsare exposed to sunlight free radicals may get generated, antioxidants essentially terminatethese free radicals preventing extraneous polymerization reactions. Antioxidants basicallyundergo oxidation reaction themselves, thus preventing oxidation of other compounds.Antioxidants are reducing agents such as thiols, ascorbic acid, polyphenols. Rubber contains an unsaturated double bond, as the tyre is always exposed toAntiozonantatmosphere ozone gas present in the atmosphere may break the double bond in to aldehydesor ketones. Thus reducing the degree of polymerization results into the degradation ofproperties. Cracks start to appear on the tyre, which are called as ozone cracks. Antiozonantsare chemical compounds that prevent or slow down the degradation of material caused byozone gas in the air. Paraffin wax acts as an antiozonant by the means of formation of a surfacebarrier.
  • 9. 4. TYRE MANUFACTURING PROCESSFig. 4.1 SCHEMATIC OF TYRE MANUFACTURE [10] A Banbury mixer combines rubber stock, carbon black and other chemical ingredients to4.1 Compounding and Banbury mixingcreate a homogeneous rubber material. Time, heat and raw materials are factors utilized toengineer 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 initiatethe mixing process. Hundreds of components are combined to form rubber utilized for tyremanufacturing. 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 havebeen reduced by improvements in administrative and engineering controls. However, concernremains due to the nature and quantity of components which make up the exposure.
  • 10. 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] Shaping of rubber begins in the milling process. At the completion of the Banbury4.2 Millingmixing 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 operationof the turning rolls. Older mills usually had trip wires or bars which could be pulled by theoperator if he or she is got caught in the mills. Modern mills have body bars at about knee levelthat are automatically triggered if the operator is caught in the mills. Most facilities haveextensive emergency rescue procedures in place for workers trapped in mills. Mill operatorsare 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]
  • 11. The calender operation continues to shape rubber. The calender machine consists of one or4.3 Extruding and Calenderingmore (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 rubbercomponents. The extruder functions by forcing rubber through dies of appropriate shape. Theextruder consists of a screw, barrel or cylinder, head and die. A core or spider is used to formthe 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 inthe process. Also, the workers at the end of the extrusion operation are exposed to a highlyrepetitive task of placing the tread onto multi-tiered carts. This operation is often referred to asbooking 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 bebooked contribute to the ergonomic impact of this operation. Numerous changes have beenmade to lessen this, and some operations have been automated. The tyre assembly machine consists of a rotating drum, on which the components are4.4 Component Assembly and Buildingassembled, 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 thecomponents 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 ofrepetitive motion operations. Components, often in heavy rolls, are placed onto the feedingportions of the assembly equipment. This may entail extensive lifting and handling of heavyrolls in a limited space. The nature of assembly also requires the tyre builder to perform aseries of similar or identical motions on each assembly. Tyre builders utilize solvents, such ashexane, which allow the tread and plies of rubber to adhere. Exposure to the solvents is an areaof concern. After being assembled, the green tyre is sprayed with a solvent- or water-basedmaterial to keep it away from adhering to the curing mould. These solvents potentially exposethe spray operator, material handler and curing press operator. Nowadays, water-basedmaterials are mostly used.
  • 12. Fig. 4.4 Operator assembling a tyre on a single-stage tyre machine [10] Curing press operators place green tyres into the curing press or onto press loading4.5 Curing and Vulcanizingequipment. Curing presses in operation in North America exist in a variety of types, ages anddegrees of automation (fig 5). The press utilizes steam to heat or cure the green tyre. Rubbercuring 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]
  • 13. Following curing, finishing operations and inspection remain to be performed before the4.6 Inspection and Finishingtyre 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, excesslayers 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 isrepetitive motion. The tyre finishing or grinding operations typically expose workers to curedrubber dust or particulate. This contributes to respiratory illness in workers in the finishingarea. In addition, a potential exists for solvent exposure from the protective paint which is oftenused to protect the side-wall or tyre lettering. After finishing, the tyre is ready to be stored in awarehouse or shipped from the plant. [8]
  • 14. 5. The Future Constant improvements in rubber chemistry and tire design are creating exciting newtires 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 testedby computer, now feature unique asymmetrical bands for improved traction and safety on wetor snowy roads. Tire design engineers are also experimenting with non-pneumatic tires that can nevergo flat because they dont contain air under pressure. One such non-pneumatic tire is simplyone slab of thick plastic attached to the wheel rim. The plastic curves out from the rim to apoint where a rubber tread is secured to the plastic for contact with the road. Such a tire offerslower rolling resistance for greater fuel economy and superior handling because of a greaterarea of contact between tread and road. [11]
  • 15. REFERENCES1. http://www.michelin.re/zma/front/affich.jsp?codeRubrique=20060922131123&lang=EN2. http://www.bridgestone.co.in/tyre/tyrecare/safedriving.asp3. www.hankooktyre.com.au/Tech/Functions.aspx?pageNum=3&subNum=4&ChildNum=24. http://en.wikipedia.org/wiki/Tire_manufacturing5. http://www.jktyre.com/Customer_Service/Tyre_Components.aspx6. http://www.indiacar.com/infobank/how_tyres_work.htm7. Wikipedia articles Natural rubber, Synthetic rubber, Carbon black Fumed silica Vulcanization, anti oxidants and anti ozonants8. www.emt-india.net/process/tyre/pdf/TyreManufactureProcess001.pdf9. wrap.org.uk/downloads/2__Composition_of_a_Tyre__May_2006.4d2e4682.2856.pdf10. www.emt-india.net/process/tyre/pdf/TyreManufactureProcess001.pdf11. http://www.enotes.com/how-products-encyclopedia/tire