How It's Made: Car Tires

Historically, wheels were made of metal or wood. With the invention of air-filled car tires in the early part of the 20th century, the ride was revolutionized. The inflated rubber tires could better absorb the bumps on the road, and the addition of tread gave the invention serious traction. Car tires have come a long way in the last century. The modern summer tire is made of 10 to 15 different components, which include natural and synthetic rubber, chemical additives, and carbon black, a pigment. Giant blenders mix these ingredients under heat and tremendous pressure. There are various formulations for different parts of the tire. In each case, the result is gummy rubber dough, which machinery then rolls into sheets to await further kneading and processing. Polyester fabric unrolls into a machine called a calendar. The calendar is equipped with rollers that apply warm rubber to both sides of the fabric. This produces a rubberized fabric that will be used to reinforce the tire. This fabric ply is needed because rubber alone isn't sturdy enough to make a tire. Numerous cotton cords now spin off bobbins simultaneously. Machinery pulls them onto the warm rubberized fabric. They land on a bit of an angle and adhere. This cording creates channels that provide pathways for venting air during the actual tire building. Making rubber for tread requires three different rubber formulations. Extruders shape the three streams of rubber, and then they enter a dye that forms them into one. Many paint rollers apply different colored stripes. It's a coding system for identification of the ingredients during processing. To avoid tension, the system creates slack in the feed. A blade slices the tread rubber to length. Next, many steel cables uncoil at once to make the bead, the part of the tire that gives it the strength it needs to stay on the wheel rim. Machinery arranges the cables in the desired configuration and encases them in rubber. More equipment rolls the bead material into hoops, sized to fit the wheel rim. They're now ready to build the tire. Using a special rotating drum, a worker arranges the two bead hoops on it. Next up is an airtight piece of rubber that will act as an inner tube, followed by the corded ply. Inflated bladders roll the rubber around the bead on both sides and then retract. A server applies sidewalls to the beads. Little rollers fold the sidewalls over the beads. This completes the inner part, or skeleton, of the tire. They assemble the outer layer separately, beginning with strips of rubber embedded with steel cord. The system wraps this rubber around a second tire building drum. Next up are narrow strips of rubber ply. The computerized system winds them with just the right amount of tension for a graduated effect. They're now ready for the last layer, the tread rubber. Machinery applies it to the ply. It's time for the two tire fabrications to become one. A transfer ring collects the assembly and transfers it to the inner part. Compressed air inflates the tire to shape it, and all the sticky layers adhere together. The machine rolls the edge of the tread rubber over the sidewalls. They now have what's known in the industry as a green tire, an uncured tire without tread pattern. Next, it's into a mold to bake and shape the tire. The two parts of the mold come together like a waffle iron. Inside, hot steamy bladders expand to shape the tire and transfer the tread pattern to it. This specific tread pattern is designed for summer tires. This cut out of a car tire demonstrates how all the layers have been fused together. The time in the hot pressurized mold has caused the rubber to vulcanize, a chemical reaction that transforms it from a weak and sticky substance to one that's strong and elastic. A worker trims excess rubber. After final inspections confirm the tire shape is uniform and geometrically correct, the tire is ready for shipment. It's time for the rubber to hit the road.