Tire Recycling Used tires have become a dilemma

Used tires have become a dilemma for many nations. Growing tire stockpiles in the United States, for example, create both fire and health hazards. Landfill space is limited. In addition, tires represent a significant resource. Both legislative and market forces are currently spurring the development of a tire recycling industry.

According to Washington's Scrap Tire Management Council, the United States has already accumulated 2 to 3 billion used tires. Moreover, about 240 million tires are added to these stockpiles every year (5:28). The discards consist of 200 million automobile tires and 40 million truck tires (3:1217). The state of California alone produces approximately 20 million used tires annually.

Such stockpiles create numerous environmental problems. Used tires do not degrade easily (17:211). Under certain conditions, tires may take as long as 80 years to disintegrate (18:70). In addition, they take up valuable landfill space. On its side, a single tire occupies about four square feet. Indeed, used tires represent about 1% of all municipal solid waste. The United States' landfills are filling up. Used tires are not only bulky, they trap air. This has a tendency to make landfills unstable. Finally, tires also don't stay covered up. Just like a glacial rock, a buried tire tends to "float:" over time, they work their way to the surface. In fact, certain states have passed laws banning tires from their landfills; moreover, man

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dition, to the tearing/milling processes, the machines may also shred tires by a shearing process. Small mobile shredding machines generally have a power range of between 50 and 200 horsepower (3:1218). Production rates for shredders may range from between 100 and 500 tires per hour. These rates depend on the type and capacity of the particular machine, as well as the shred size being produced. Eldin et al. (1993), however, notes that during actual operations production rates are determined, not so much by the shredding machines, as by various other practices specific to each particular company. The study reported observed rates of between 50 and 150 tires per hour at Wisconsin shredding sites (3:1218). The size of the tire chips which are actually produced by a shredding machine depends both on the design of the machine and the setting of its cutting blades. Under certain circumstances, very small chips may be produced by processing tires through more than one shredder. Each shredding cycle will generally produce finer tire chips. Vibrating screens, or classifiers, may be employed to sort out the chips. Such equipment separates out chips of a specified maximum size. This coarser material can then be fed back throug

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