How Are Tires Manufactured?
Tires are just about everywhere. They are on all types of cars, trucks, SUVs, buses and industrial vehicles. They enable movement through different terrains with relative ease. Tires can even have an after-life benefit in the form of fuel or as a swing. What appears to be a simple construction of rubber is actually a complex creation with several different layers and materials.
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Inside Layer
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The rim is the inner most layer of the tire. This is a metal circle that is made of either steel or aluminum. It supports the shape of the tire and allows the tire to be attached to the wheel of the vehicle. The rim is generally attached to the wheel through metal supports and is often covered with a hubcap. The rest of the tire is then attached to the rim, allowing air to flow between the rim and the rest of the tire, keeping it inflated.
Inner Liner
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The inner liner rises up from the tire in an upside down "U" fashion. This is where the air is held, in the empty space between the rim and the inner liner. Most tires do not use air tubes anymore--as was common in the past--but rather have the air float in this area. Butyl rubber or a halogenated butyl rubber compound is most often used to create this inner liner. The inner liner is very thin, although the exact thickness varies per tire. It is produced through a system called calendering--the process of pressing a material to make it dense but thin--due to the thin structure of the inner liner.
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Bead Filler
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The bead filler holds the inner liner to the rim. This contains the bead wire, which is a long wire loop that circles the perimeter of the tire several times. This wire is surrounded by several thick layers of a hard rubber so as not to damage the other components of the tire. A chipper, a rubber material pushed around the bead filler, is also attached to the bead filler to protect the side wall and a flipper, a rubber locking device, holds everything in place.
Body Ply
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The body ply are two strips of steel and fabric that have been calendered into thin strips that provide support and protection to the tire. Rubber is then pressed between the cords and steel to provide a protective shell over the steal and fabric, making for a stable and solid tire construction. The strength and quality of the tire is determined by the gaps in cords, the rigidity of the construction and the bonding between the surfaces. This is then covered with a nylon cap. The cap does not completely cover the body ply, but rather it sits between the ply and the tire tread.
Rubber Tread and Side Walls
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The rubber of the tires is often a mixture of both rubber and a filler. This makes the rubber more suitable for dealing with the different conditions that the tire will be used in. The different tire qualities include tires created to handle snow, rain or wet weather conditions, tires for preformance and racing, or the more common all season tires. The most common types of rubber used for tires include natural rubber, styrene-butadiene rubber, polybutadiene rubber and butyl rubber, although other types of rubber is also used in tire manufacturing. Black carbon and silica are frequently added to the rubber in different amounts to provide the rubber with different qualities. The rubber is mixed and formed through a machine process that provides the rubber in the form of a slap, which is simply a continuous line of rubber.
Treading and Side Walls
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Tire tread and sidewalls are formed through a process called extrusion. This process includes forcing raw rubber components in a machine that presses them into the desired shape. This is done by heating the rubber to a desired temperature and then passing it through a shaping head. The same machine used to extrude the tread of the tire cannot be used to extrude the side walls due to the extreme difference in texture and size of the tread verses the sidewalls. More than one extrusion head and machine may be necessary for the side walls, especially if a decorative side wall is being designed, such as a white walled side wall.
Assembly
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Each component of the tire is assembled by use of machinery and robots. This is done at high temperatures and pressures to ensure that all of the components hold together properly. Once assembled the tire cures for a set period of time at a set temperature. This time and heat ratio depends on the specific rubber compounds used in the tire-making process and the usage of the tire. Inspectors then examine each tire after the curing of the tire. Tires that do not pass inspection are then recycled and used in the creation of other tires.
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- Photo Credit tire image by Orlando Florin Rosu from Fotolia.com
