Cooling Rubber Waste

The German company Gotic is a specialist in the production of reduction machines and grinders for the chemical, food, pharmaceutical and synthetic industries. They use a specially developed screw heat exchanger with nitrogen cooling, which conveys rubber waste, simultaneously cooling it with liquid nitrogen (-196ºC). This screw heat exchanger with cryogenic application will be used for the recycling of rubber tyres. The addition of liquid nitrogen causes the rubber to go below the glass transition temperature and become hard and brittle. This makes it suitable to be grinded in a pin mill into fine powder (cryogenic grinding). This powder is suitable to be re-used in new rubber and synthetic products. Cryogenic grinding is the grinding of hard, thermoplastic material applying cryogenic temperatures. This makes the rubber so brittle it can be grinded very fine without modifying the characteristics of the rubber. The screw heat exchanger conveys the frozen rubber to the grinder over a distance of 2,500 mm with a capacity of 1.6m3/hour. During the conveyance liquid nitrogen is injected in the product at 4 points. The paddles of the screw mix the rubber well with the nitrogen. The conveyor has a jacketed tube, with a vacuum for better insulation. The screw can be removed easily with fastening clamps at the outlet side, which allows proper cleaning of the screw.