19-09-2007, 08:54 PM
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تاريخ التسجيل: Jul 2007
المشاركات: 346
معدل تقييم المستوى: 0
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Whole Tires
A typical scrapped automobile tire weighs 9.1 kg (20 lb). Roughly 5.4 kg (12 lb) to 5.9 kg (13 lb) consists of recoverable rubber, composed of 35 percent natural rubber and 65 percent synthetic rubber. Steel-belted radial tires are the predominant type of tire currently produced in the United States.(2) A typical truck tire weighs 18.2 kg (40 lb) and also contains from 60 to 70 percent recoverable rubber. Truck tires typically contain 65 percent natural rubber and 35 percent synthetic rubber.(2) Although a majority of truck tires are steel-belted radials, there are still a number of bias ply truck tires, which contain either nylon or polyester belt material.
Slit Tires
Slit tires are produced in tire cutting machines. These cutting machines can slit the tire into two halves or can separate the sidewalls from the tread of the tire.
Shredded or Chipped Tires
In most cases the production of tire shreds or tire chips involves primary and secondary shredding. A tire shredder is a machine with a series of oscillating or reciprocating cutting edges, ****** back and forth in opposite directions to create a shearing motion, that effectively cuts or shreds tires as they are fed into the machine. The size of the tire shreds produced in the primary shredding process can vary from as large as 300 to 460 mm (12 to 18 in) long by 100 to 230 mm (4 to 9 in) as wide, down to as small as 100 to 150 mm (4 to 6 in) in length, depending on the manufacturer, model, and condition of the cutting edges. The shredding process results in exposure of steel belt fragments along the edges of the tire shreds.(3) Production of tire chips, which are normally sized from 76 mm (3 in) down to 13 mm (1/2 in), requires two-stage processing of the tire shreds (i.e., primary and secondary shredding) to achieve adequate size reduction. Secondary shredding results in the production of chips that are more equidimensional than the larger size shreds that are generated by the primary shredder, but exposed steel fragments will still occur along the edges of the chips.(3)
Ground Rubber
Ground rubber may be sized from particles as large as 19 mm (3/4 in) to as fine as 0.15 mm (No. 100 sieve) depending on the type of size reduction equipment and the intended application.
The production of ground rubber is achieved by granulators, hammermills, or fine grinding machines. Granulators typically produce particles that are regularly shaped and cubical with a comparatively low-surface area. The steel belt fragments are removed by a magnetic separator. Fiberglass belts or fibers are separated from the finer rubber particles, usually by an air separator. Ground rubber particles are subjected to a dual cycle of magnetic separation, then screened and recovered in various size fractions.(4)
Crumb Rubber
Crumb rubber usually consists of particles ranging in size from 4.75 mm (No. 4 sieve) to less than 0.075 mm (No. 200 sieve). Most processes that incorporate crumb rubber as an asphalt modifier use particles ranging in size from 0.6 mm to 0.15 mm (No. 30 to No. 100 sieve).
Three methods are currently used to convert scrap tires to crumb rubber. The crackermill process is the most commonly used method. The crackermill process tears apart or reduces the size of tire rubber by passing the material between rotating corrugated steel drums. This process creates an irregularly shaped torn particle with a large surface area. These particles range in size from approximately 5 mm to 0.5 mm (No. 4 to No. 40 sieve) and are commonly referred to as ground crumb rubber. The second method is the granulator process, which shears apart the rubber with revolving steel plates that pass at close tolerance, producing granulated crumb rubber particles, ranging in size from 9.5 mm (3/8 in) to 0.5 mm (No. 40 sieve). The third process is the micro-mill process, which produces a very fine ground crumb rubber in the size range from 0.5 mm (No. 40 sieve) to as small as 0.075 mm (No. 200 sieve).(4)
In some cases, cryogenic techniques are also used for size reduction. Essentially, this involves using liquid nitrogen to reduce the temperature of the rubber particles to minus 87oC (-125oF), making the particles quite brittle and easy to shatter into small particles. This technique is sometimes used before final grinding.(5
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