Patent GB-1513695-A (GB)
Title: Process for reclaiming rubber metal and fabric from tyre scrap
IPC: B29B17/00
Filed: 1976-07-21
Abstract: 1513695 Comminuting at low temperatures AIR PRODUCTS & CHEMICALS INC 21 July 1976 [15 Aug 1975 28 April 1976] 30475/76 Heading B2A [Also in Division C3] In a process for recovering components from tyre scrap containing magnetic components and non-magnetic fibre cord and rubber components, the tyre scrap is cooled to such a temperature as to cause embrittlement of the rubber component, and, the cooled scrap is comminuted and subjected to a first magnetic separation followed by a series of screening and density classification operations, a magnetic separation, a combined freezing and grinding operation and, finally, a separation operation resulting in a product crumb having a particle size not greater than 1/20".  As shown, whole tyres are cut in a shredder 1 into relatively small pieces from which dirt and other contaminants are removed in vibratory screener 2 by an upward flow of air. The tyre pieces are then passed through a cryogenic freezer 3 which operates by injection or spraying of liquefied nitrogen and the cooled pieces after crushing in a hammer mill 4 are classified in one or more magnetic separators into a ferrous fraction and a non-ferrous rubber and fibre cord fraction containing residual magnetic components. After subjecting the ferrous fraction to a burning operation, a purified metal e.g. steel, product is obtained. The non-ferrous fraction is separated in a multi-screen deck 7 into overs fractions 32, 8 and 9 and a bottoms fraction 10. Each fraction is directed to a cyclone separator incorporated in the deck 7 so that dust and at least a portion of light fibre cord portion is removed from the heavier rubber portion. The first overs fraction 32 is ground in a mill 33 and after separation of dust in a cyclone 34 is returned to screening deck 7. The second overs fraction 8 may be classified over a gravity table 11, which has an inclined vibrating screen through which fluidising air is passed upwardly, into a top cut 11a comprising the heavier crumb rubber particles, a middle cut 12 comprising fibre cord with attached rubber and liberated rubber, and a bottom cut 13 consisting of the lighter fibre cord with a small portion of attached rubber. Bottom cut 13 is sent to a beater mill 28 for stripping the fibre cord of rubber or alternatively, to hammer mill 4 or grinding mill 33. If gravity table 11 is not employed, then overs fraction 8 is sent to beater mill 28, or to grinding mill 33 for removal of rubber from the fibre cord and then returned to screening deck 7 for reprocessing. The third overs fraction 9 is classified over a second gravity table 14 into a bottom cut 15 which is combined with bottom cut 13 and sent to beater mill 28; a middle cut 16 which is recycled with middle cut 12 to the screening deck 7; and a top cut 17, comprising the more dense crumb rubber, which is passed through a magnetic separator 18 for separating associated residual magnetic components and is combined with top cut 11a, after the latter has also passed through a magnetic separator 19, and passed through a destoner 20 where stones, glass and other contaminants are removed. The de-stoned material which comprises relatively clean rubber, is further sized-reduced in a pair of cryogenic freezergrinders 21, 22 which produce a common stream 23. The bottoms fraction 10 from screening deck 7 is passed through a magnetic separator 24 from which the non- magnetic fraction is combined with stream 23 and fed to a vibrating screener 25 for final separation into a bottoms fraction 26 consisting of clean rubber crumb, which may be packaged for re-use, and an overs fraction 27 which is combined with the destoned material for re-cycle into the freezergrinders. Liberated rubber and fibre cord effluent from beater mill 28 is conveyed to a defiberizer 29 from which crumb rubber is returned to screening deck 7 and clean fibre cord is conveyed to a baler 30 for packing.