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How Is A Tire Built?

How Is A Tire Built?

         Today I thought I'd share how a tire is built.  Knowing how a tire is built is not that important, but knowing how and why to care for your tires is.  I thought knowing how a tire is built would help you understand why tire care is so important.

         Few people realize how the tires on their vehicle are made.  They also don't realize the importance of their tires being properly inflated.  So, inflation.  There is no tire that can be safe on your vehicle if it's under-inflated.  Not a one.  That was the majority of the problems with the Ford Explorers in the late 90's and early 2000's.  An under-inflated tire will overheat at any speed.  The vehicle manufacturer specifies the tire pressure on the vehicle, not the tire manufacturer.  Ford had specified a pressure that was too low for Ford Explorers.  Why?  Because people complained about the rough ride on Ford Explorers.  Drive your vehicle over a hot road, maybe in the deep south, with under-inflated tires, and it's going to fail.  How will it fail?  The tread will become very soft and pliable, and eventually rip off the wheel.  Now you're riding on a blend of rubber that is not meant to work as a tread.  It will quickly fail, often explosively.

         I worked at the Firestone Tire Plant in Decatur Illinois for six years as a Electrical Maintenance Technician.  I learned a lot about tire building, even though I was a Maintenance Technician.  This entry is about how tires were made at this plant.

                   So how is a tire built?  First, you have to realize that there are about 12 different blends of rubber used on a tire.  So, first things first.  Rubber, from a rubber tree is naturally white. In an are of the tire plant, Natural and synthetic rubbers are combined with various chemicals like carbon black, silica, and oils to create a rubber compound with specific properties.  Depending on where that rubber will be used on the tire will determine how much of each compound is used.  This rubber is blended in an area called the Banbury's.  In the Firestone Plant I worked at, we used powdered Carbon Black to turn the rubber black.  Newer plants use pellets or granules to  accomplish this.

         Tire Building
         1.  Let's start building a tire.  One of the things needed, is the Bead, to seal the tire to the rim.  A special blend of rubber is used,.  It extrudes from the extruder on to the wire that forms the bead.  This wire is wrapped a certain number of times around a cylinder type device.  Once the necessary amount of wire is wrapped, it is cut, and moved to the side by the operator.

         2.  The all important tread.  This is a completely different blend of rubber, mixed to be used as Tread.  Another, larger extruder forces the raw, uncured rubber compound through a specialized die plate that gives the tread rubber its specific shape and dimensions.  It is cut to length by this machine for the specific tire and placed on flat metal pallets by the operator.  The pallets are hinged and hold about 2 lengths of tread per pallet, maybe 10-15 pallets per set.

         3.  Sidewall.  The sidewall is built much like the Tread using a different rubber compound.  It too is cut to length for the specific tire.

         4..  Calenders:  There are two calenders used.  One makes the Fiberglass belt, the other makes the Steel Belt  The Fiberglass calender pulls the fiberglass sheet from a large roll, then pulls it over a series of mills where it has a special blend of rubber milled around it.  This is wrapped around a large metal drum for use elsewhere.  The Steel Belt Calender pulls the steel from large cylinders and threads them through the same kind of setup used on the Fiberglass Calender.  The most important thing in setting this up, is that those steel threads cannot cross!  Once the rubber is milled around the metal threads it is wrapped around a large metal drum for use elsewhere.

         3. Tire Building:  Now with all the tire components built, the tire is assembled by an operator at a tire machine.  Each component is placed in a certain area for use.  The components are assembled layer by layer on a tire building machine, forming the "green tire".  First, that bead is placed on either side, far apart.  The sidewall is then fed to the Tire Machine.  Its ends are carefully sealed by the Tire Builder using a hot knife and a special glue.  The Fiberglass belt is next, it is cut by the tire builder and sealed.  Now the Steel Belt is next, it too is cut to length by the tire builder.  The tire builder presses a foot switch to rapidly spin the 'Green Tire.  Now the Tread is applied.  Remember, that tread is pre-cut for the specific tire being built.  The machine is stopped, and the Tire Builder carefully seals the ends with glue.  The tire is now complete, and looks a bit like a volcano with a mirror image side to side.  The tire is placed on a rack and sent to the curing area.  Not that so far, the tire is only held together by glue!

         4. Curing (where I worked in the plant):The green tire is placed in a mold, and heat and pressure are applied using high pressure hot water and steam. This process, known as vulcanization, it bonds the components together and shapes the tire, including imprinting the tread pattern.  The mold has a movable top section, and a stationary bottom section.  The sections are moved together by the machine, with very high pressure applied to seal the molds together.  Each tire is 'baked' for a specified time period, based on the tire being built.  Once baking has finished, it is sent to a cooling rack on the press and inflated.  Once the cooling period is complete, the tire is discharged to a conveyor belt where it is sent to Final Finish where it is inspected, and a lot of the pin vents are ground off.

         5. Final Finish:  Excess material is trimmed, and the tire undergoes rigorous quality control tests, including inflation and balancing, before being placed on a pallet to be stored, and eventually sent to a Firestone store.