Tire Report

MANUFACTURING OF TYRES

GAGAN DEEP MALIK (06000645) ME-4303

MECHANICAL ENGINEERING DEPARTMENT INSTITUTE OF TECHNOLOGY BANARAS HINDU UNIVERSITY VARANASI-221005

Introduction Tires are quite a complicated piece of technology to grip the road and help stop the road bumps being transferred to the vehicle. It has to do this also without excessive wear, damage or permanent deformation in all the extremes of conditions that driving on the road throws at it. Rubber Pneumatic tires can deform slightly at the point of contact with the road for instance in order to take up small irregularities in the road surface the suspension and chassis are spared the vibration that would be transferred if the tires were solid. Tires are constructed in different layers using different materials. According to working conditions like weather, road surface, load, speed etc. tires are provided with different shapes, tread pattern and material properties.

Tire construction:

Radial tire construction construction

Bias tire

Fig. 1 The tire is an assembly of numerous components that are built up on a drum and then cured in a press under heat and pressure. Heat facilitates a polymerization reaction that crosslinks rubber monomers to create long elastic molecules. These polymers create the elastic quality that permits the tire to be compressed in the area where the tire contacts the road surface and spring back to its original shape

under high-frequency cycles. Typical components used in tire assembly are listed on the next page.

Inner liner The inner liner is an extruded halobutyl rubber sheet compounded with additives that result in low air permeability. The inner liner assures that the tire will hold highpressure air inside, without the air gradually diffusing through the rubber structure. Body ply The body ply is a calendered 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. The cords in a radial tire run perpendicular to the tread. Some older tires used diagonal bias tires, tires in which the fabric ran at an angle to the tread. Cap plies Some tires have cap plies, an extra layer or two of polyester fabric to help hold everything in place. These cap plies are not found on all tires; they are mostly used on tires with higher speed ratings to help all the components stay in place at high speeds. Sidewall The sidewall provides lateral stability for the tire .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. 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 sulfur in the rubber cross-link to produce copper sulfide, which improves bonding of the bead to the rubber. Beads are inflexible and inelastic, and provide the mechanical strength to the tire it needs to stay seated on the wheel rim and to handle the forces applied by tire mounting machines when the tires are installed on rims.

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.

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 tire strength and dent resistance while allowing it to remain flexible. These belts help the tire stay flat so that it makes the best contact with the road. Passenger tires are usually made with two or three belts. Tread The tread is a thick extruded profile that surrounds the tire carcass. 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 tires include an extruded component between the belt package and the tread to isolate the tread from mechanical wear from the steel belts. Other components Tire construction methods vary somewhat in the number and type of components, as well as the compound formulations for each component, according to the tire use and price point. Tire makers continuously introduce new materials and construction methods in order to achieve higher performance at lower cost. All of these components are assembled in the tire-building machine. This machine ensures that all of the components are in the correct location and then forms the tire into a shape and size fairly close to its finished dimensions

Car tire types: There are several different types of car tire that you, the humble consumer, can buy for your car. What you choose depends on how you use your car, where you live, how you like the ride of your car and a variety of other factors. The different classifications are as follows.

Performance tires or summer tires Performance tires are designed for faster cars or for people who prefer to drive harder than the average consumer. They typically put performance & grip ahead of longevity by using a softer rubber compound. Tread block design is normally biased towards outright grip rather than the ability to pump water out of the way on a wet road. The extreme example of performance tires are "slicks" used in motor racing, so-called because they have no tread at all. All-round or all-season tires These tires are what you'll typically find on every production car that comes out of a factory. They're designed to be a compromise between grip, performance, longevity, noise and wet-weather safety. For increased tire life, they are made with a harder rubber compound, which sacrifices outright grip and cornering performance. For 90% of the world's drivers, this isn't an issue. The tread block design is normally a compromise between quiet running and water dispersion - the tire should not be too noisy in normal use but should work fairly well in downpours and on wet roads. All-season tires are neither excellent dry-weather, nor excellent wet-weather tires, but are, at best, a compromise. Wet-weather tires Rather than use an even harder rubber compound than all-season tires, wet weather tires actually use a softer compound than performance tires. The rubber needs to heat up quicker in cold or wet conditions and needs to have as much mechanical grip as possible. They'll normally also have a lot more siping to try to disperse water from the contact patch. Aquachannel tires are a subset of winter or wet-weather tires and I have a little section on them further down the page. Snow & mud or ice : special winter tires

Winter tires come at the other end of the spectrum to performance tires, obviously. They're designed to work well in wintery conditions with snow and ice on the roads. Winter tires typically have larger, and thus noiser tread block patterns. In extreme climates, true snow tires have tiny metal studs fabricated into the tread for biting into the snow and ice. The downside of this is that they are incredibly noisy on dry roads and wear out both the tire and the road surface extremely quickly if driven in the dry. Mud & snow tires typically either have 'M&S' stamped on the tire sidewall. Snow & Ice tires have a snowflake symbol.

All-terrain tires All-terrain tires are typically used on SUVs and light trucks. They are larger tires with stiffer sidewalls and bigger tread block patterns. The larger tread block means the tires are very noisy on normal roads but grip loose sand and dirt very well when you take the car or truck off-road. As well as the noise, the larger tread block pattern means less tire surface in contact with the road. The rubber compound used in these tires is normally middle-of-the-road - neither soft nor hard. Mud tires At the extreme end of the all-terrain tire classification are mud tires. These have massive, super-chunky tread blocks and really shouldn't ever be driven anywhere other than loose mud and dirt. The tread sometimes doesn't even come in blocks any more but looks more like paddles built in to the tire carcass.

Tire construction types: Bias tire (or cross ply) construction utilizes body ply cords that extend diagonally from bead to bead, usually at angles in the range of 30 to 40 degrees, with successive plies laid at opposing angles forming a crisscross pattern to which the tread is applied. The design allows the entire tire body to flex easily, providing the main advantage of this construction, a smooth ride on rough surfaces. This cushioning characteristic also causes the major disadvantages of a bias tire: increased rolling resistance and less control and traction at higher speeds.

Belted bias A belted bias tire starts with two or more bias-plies to which stabilizer belts are bonded directly beneath the tread. This construction provides smoother ride that is similar to the bias tire, while lessening rolling resistance because the belts increase tread stiffness. However the plies and belts are at different angles, which lessens performance compared to radial tires. Radial Radial tire construction utilizes body ply cords extending from the beads and across the tread so that the cords are laid at approximately right angles to the centerline of the tread, and parallel to each other, as well as stiff stabilizer belts directly beneath the tread. The advantages of this construction include longer tread life, better steering control, and lower rolling resistance. Disadvantages of the radial tire include a harder ride at low speeds on rough roads and lower grip ability at low speeds.

Solid Many tires used in industrial and commercial applications are non-pneumatic, and are manufactured from solid rubber and plastic compounds via molding operations. Solid tires include those used for lawn mowers, skateboards, golf carts, scooters, and many types of light industrial vehicles, carts, and trailers. One of the most common applications for solid tires is for material handling equipment (forklifts). Such tires are installed by means of a hydraulic tire press. Semi-pneumatic Semi-pneumatic tires have a hollow center, but they are not pressurized. They are light-weight, low-cost, puncture proof, and provide cushioning.These tires often come as a complete assembly with the wheel and even integral ball bearings. They are used on lawn mowers, wheelchairs, and wheelbarrows. Tires that are hollow but are not pressurized have also been designed for automotive use, such as the Tweel (a portmanteau of tire and wheel) which is an experimental tire design being developed at Michelin. The outer casing is rubber as in ordinary radial tires, but the interior has special compressible polyurethane springs to contribute to a comfortable ride. Besides the impossibility of going flat, the tires are intended to combine the comfort offered by higher-profile tires (with tall sidewalls) with the resistance to cornering forces offered by low profile tires. They have not yet been delivered for broad market use.

Tire Composition:[1] Rubber (Natural and synthetic)

38 %

Fillers (Carbon black, silica, carbon chalk)

30 %

Reinforcing materials (steel, rayon, nylon)

16 %

Plasticizers (oils and resins)

10 %

Chemicals for vulcanisation (sulphur, zinc oxide, various 4% chemicals) Chemicals as antioxidents to counter ozone effects and 1% material fatigue Miscellaneous

1%

Materials:[2] •

Natural rubber, or polyisoprene is the basic elastomer used in tire making

•

Styrene-butadiene co-polymer (SBR) is a synthetic rubber which is often substituted in part for natural rubber based on the comparative raw materials cost

•

Polybutadiene is used in combination with other rubbers because of its low heat-buildup properties

•

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. Bromobutyl is superior to chlorobutyl, but is more expensive

•

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 build up reinforcement

•

Sulphur crosslinks the rubber molecules in the vulcanization process

•

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 tire

Manufacturing process: Tire plants are traditionally divided into five departments that perform special operations. These usually act as independent factories within a factory. Large tire makers may set up independent factories on a single site, or cluster the factories locally across a region.

Compounding and mixing Compounding is the operation of bringing together all the ingredients required to mix a batch of rubber compound. Each component has a different mix of ingredients according to the properties required for that component. Mixing is the process of applying mechanical work to the ingredients in order to blend them into a homogeneous substance. Various grades of natural and synthetic rubber are combined with carbon black, sulphur and chemical products in an internal mixer to meet specific compound requirements. The resulting blend is called the "master batch". Internal mixers are often equipped with two counterrotating rotors in a large housing that shear the rubber charge along with the additives. The mixing is done in three or four stages to incorporate the ingredients in the desired order. The shearing action generates considerable heat, so both rotors and housing are water-cooled to maintain a temperature low enough to assure that vulcanization does not begin. After mixing the rubber charge is dropped into a chute and fed by an extruding screw into a roller die. Alternatively, the batch can be dropped onto an open rubber mill batch off system. A mill consists of twin counter-rotating rolls, one serrated, that provides additional mechanical working to the rubber and produces a thick rubber sheet. The sheet is pulled off the rollers in the form of a strip. The strip is cooled, dusted with talc, and laid down into a pallet bin. The ideal compound at this point would have a highly uniform material dispersion; however in practice there is considerable non-uniformity to the dispersion. This is due to several causes, including hot and cold spots in the mixer housing and rotors, excessive rotor clearance, rotor wear, and poorly circulating flow paths. As a result, there can be a little more carbon black here, and a little less there, along with a few clumps of carbon black elsewhere, that are not well mixed with the rubber or the additives.

Mixers are often controlled according to the power integration method, where the current flow to the mixer motor is measured, and the mixing terminated upon reaching a specified total amount of mix energy imparted to the batch.

Component preparation Components fall into three classes based on manufacturing process - calendering, extrusion, and bead building. The extruder machine consists of a screw and barrel, screw drive, heaters, and a die. The extruder applies two conditions to the compound: heat and pressure. The extruder screw also provides for additional mixing of the compound through the shearing action of the screw. The compound is pushed through a die, after which the extruded profile is vulcanized in a continuous oven, cooled to terminate the vulcanization process, and either rolled up on a spool or cut to length. Tire treads are often extruded with four components in a quadraplex extruder, one with four screws processing four different compounds, usually a base compound, core compound, tread compound, and wing compound. Extrusion is also used for sidewall profiles and inner liners. The calender is a set of multiple large-diameter rolls that squeeze rubber compound into a thin sheet, usually of the order of 2 meters wide. Fabric calenders produce an upper and lower rubber sheet with a layer of fabric in between. Steel calenders do so with steel cords. Calenders are used to produce body plies and belts. A creel room is a facility that houses hundreds of fabric or wire spools that are fed into the calender. Calenders utilize downstream equipment for shearing and splicing calendered components. The bead core is formed by aligning, and then coating plated steel wires with rubber. After, it is wound on a coil a certain number of times to form bead rings, which provide a specific diameter and strength for a particular tire.

Tire building Tire building is the process of assembling all the components onto a tire building drum. Tire-building machines (TBM) can be manually operated or fully automatic. Typical TBM operations include the first-stage operation, where inner liner, body plies, and sidewalls are wrapped around the drum, the beads are placed, and the assembly turned up over the bead. In the second stage operation the belt package and tread are applied and the green tire is inflated and shaped.

fig. 2 All components require splicing. Inner liner and body plies are spliced with a squareended overlap. Tread and sidewall are joined with a skived splice, where the joining ends are bevel-cut. Belts are spliced end to end with no overlap. Splices that are too heavy or non-symmetrical will generate defects in force variation, balance, or bulge parameters. Splices that are too light or open can lead to visual defects and in some cases tire failure. The final product of the TBM process is called a green tire, where green refers to the uncured state.

Curing Curing is the process of applying pressure to the green tire in a mold in order to give it its final shape, and applying heat energy to stimulate the chemical reaction between the rubber and other materials. The heat also bonds all of the tire's components together. This is called vulcanizing.In this process the green tire is automatically transferred onto the lower mold bead seat, a rubber bladder is inserted into the green tire, and the mold closes while the bladder inflates. As the mold closes and is locked the bladder pressure increases so as to make the green tire flow into the mold, taking on the tread pattern and sidewall lettering engraved into the mold. The bladder is filled with a recirculating heat transfer medium, such as steam or hot water. Temperatures are in the area of 350 degrees Fahrenheit with pressures around 350 PSI. Passenger tires cure in approximately 15 minutes. At the end of cure the pressure is bled down, the mold opened, and the tire stripped out of the mold. The tire may be placed on a PCI, or post-cure inflator, that will hold the tire fully inflated while it cools. There are two generic curing press types, mechanical and hydraulic. Large off-road tires are often cured in ovens with cure times approaching 24 hours.

Final finish After the tire has been cured, there are several additional operations. Excess rubber from the curing process is removed, and the tire is trimmed to order. Tire uniformity measurement is a test where the tire is automatically mounted on wheel halves, inflated, run against a simulated road surface, and measured for force variation. Tire balance measurement is a test where the tire is automatically placed on wheel halves, rotated at a high speed and measured for imbalance.Large commercial truck/bus tires, as well as some passenger and light truck tires, are inspected by Xray machines that can penetrate the rubber to analyze the steel cord structure.In the final step, tires are inspected by human eyes for numerous visual defects such as incomplete mold fill, exposed cords, blisters, blemishes, and others.

Reading a tire: You can find out all the basics about a tire simply by reading the information on the side (or sidewall).

Fig. 3

Tire Type

Defines the proper use of the tire. "P" means this is a passenger car tire. "LT" means it is for a light truck and T for temporary, or spare tires. Tire Width Width of the tire measured in millimetres from sidewall to sidewall. Since this measure is affected by the width of the rim, the measurement is for the tire when it is on its intended rim size. Aspect Ratio Ratio of the height of the tire's cross-section to its width. 65 means that the height is equal to 65% of the tire's width. High performance tires usually have a lower aspect ratio than other tires. This is because tires with a lower aspect ratio provide better lateral stability. When a car goes around a turn lateral forces are generated and the tire must resist these forces. Tires with a lower profile have shorter, stiffer sidewalls so they resist cornering forces better.

Fig.4

Construction This tells you how the tire was put together. The "R" stands for radial, which means that the body ply cords. These cords are layers of fabric that make up the body of the tire, and run radially across the tire from bead to bead. A "B" indicates the tire is of bias construction, meaning that the body ply cords run diagonally across the tire from bead to bead, with the ply layers alternating in direction to reinforce one another. Wheel Diameter The width of the wheel from one end to the other in inches. Load Index Indicates the maximum load in pounds that a tire can support when properly inflated. You will also find the maximum load in pounds and in kilograms elsewhere on the tire sidewall. The rating "105," for example, corresponds to a load capacity of 2039 pounds (924.87 kg). Speed Rating Shows the maximum service speed for a tire. "H" for example means that the tire has a maximum service speed of 130 mph. S indicates that the tire can handle speeds up to 112 mph (180.246 kph). DOT Means the tire is compliant with all applicable safety standards established by the U.S. Department of Transportation (DOT). Adjacent to this is a tire identification or serial number; a combination of numbers and letters with up to 12 digits.

Uniform Tire Quality Grading System (UTQG) Except for snow tires, US federal authorities require manufacturers to grade passenger car tires based on three factors: tread wear, traction, and temperature resistance. Tread Wear This grade measures the wear rate of the tire when tested under controlled conditions. "100" is taken to represent a basic quality standard, and a tire graded "200" would wear twice as long on the test track as one graded "100". More than 100 is better, with 100 being the baseline, and less than 100 being poorer. Note: Tread wear grades are valid only for comparisons within a manufacturer's product line. They are not valid for comparisons between manufacturers. Traction

Traction grades represent the tire's ability to stop on wet pavement. The grade is based upon "straight ahead" braking tests, and does not indicate cornering ability. "A" is best, "B" is intermediate, and "C" is acceptable. Temperature The temperature grades represent the tire's resistance to the generation of heat, from "A" (Best) through "B" (Intermediate) to "C" (Acceptable). Note: Federal law requires that all tires meet at least the minimal requirements of Grade C. The rating is a measure of how well the tire dissipates heat and how well it handles the buildup of heat. The temperature grade applies to a properly inflated tire that is not overloaded. Underinflation, overloading or excessive speed can lead to more heat buildup. Excessive heat buildup can cause tires to wear out faster, or could even lead to tire failure.

References:

Websites 1. http://tyre bible1.htm

(fig.2)

2. http://en.wikipedia.org 3. http://www.howstuffworks.com/ (fig.4) 4. http://eu.goodyear.com/uk_en/advice/tiretutor/

(fig.3)

5. http://know_your_tyres.jsp.htm (fig.1)

Research papers 1. www.energymanagertraining.com/tyre/pdf/TyreManufactureProcess001.pdf 2. www.researchandmarkets.com/tire_manufacturing_except_retreading.pdf 3. www.tirefailures.com/whitepaper.pdf