Kimberly Hardy, age 9, of Shepherdsville, Ky., for her question:
HOW DO THEY MAKE RUBBER TIRES?
Where would our automobiles, motorcycles, bicycles, buses, motorhomes, trucks, tractors and even wheelbarrows be without pneumatic tires? Pneumatic tires are those filled with compressed air. We would certainly find life a bit
hard to live without these tires. They absorb the shock and strain created by bumps in the roads and provide us with comfortable, safe feelings as we travel.
The pneumatic tire was invented in 1845 by a Scottish engineer named Robert Thomson. All vehicles then were equipped with wooden wheels and steel tires. The solid rubber tire came along in 1870 and was stronger than Thomson's invention. Then in 1888 a Scottish veterinarian named John Dunlop improved on the earlier pneumatic tire.
Before an automobile tire can be made today, the rubber must be mixed with sulfur and other chemicals, cord fabric must be coated with rubber and rubberized fabric must be cut into strips. These three separate operations are handled by special machines.
A Banbury machine is used to mix the rubber with the chemicals. Sulfur and other chemicals strengthen the rubber and increase its resistance to wear. The rubber comes from the machine in sheets.
Cord fabric is manufactured of fiberglass, polyester, nylon or rayon. A calendering machine blends the fabric with the rubber sheeting. The triple rollers of this machine squeeze the cords and the rubber together, producing a rubberized fabric.
A cutting machine then slices the rubberized cord into strips.
A tire is then built by hand on a slowly rotating roller called a drum. The drum has the same diameter as the wheel on which the tire will be used. As the drum turns, a workman called a tire builder wraps an inner liner around the drum. Then he wraps the rubberized cord fabric around the drum, ply by ply. Most tires are either two ply or four ply.
After the plies are in place, the tire builder adds two beads. Each bead is made of two or more steel wire strands that have been twisted together into a hoop and covered with hard rubber. Then the builder adds the side walls and the tread. The various parts of the tire are then united by a set of rollers in a process called stitching.
Finally the uncured tire is vulcanized. Vulcanization makes a rubber product hard, strong and elastic. A last step puts the tire in a steel mold that puts on the tread pattern.
The equipment that puts on a tire's tread pattern operates much like a giant waffle iron. It is closed, heat is applied and an air bag is filled with steam. The steam presses the tire against the mold. The air bag and the mold squeeze and press the tire into its final shape, complete with tread.