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12 and modified until the contaminated atmosphere is eliminated. When handling a thermoplastic material, the biggest danger is often one of spilled material. Because of the shape of the pellets, the spilled material makes the floor very slippery and can cause falling injuries. Therefore, any spilled material must be collected immediately and disposed of in an approved way. This usually means sweeping up the spilled material and placing it an appropriately labeled bag for reclamation. Burns Some extruders operate at temperatures of as high as 750 ̊F/400 ̊C or above. As any temperature above 140 ̊F/60 ̊C is unpleasant to touch, burns must be recognized as a common source of accidents in the extrusion processing industry. It is one of the reasons that a cover or guard usually protects the extruder barrel. Like any other guard it should not be needlessly opened, or removed, as it is there for protection of both the operators and the equipment. At the processing temperatures employed, hot thermoplastic mate- rials (resins) behave like hot melt adhesives and can be very difficult to remove from the skin. These resins are organic materials that have high spe- cific heats and low thermal conductivities. Thus, as the hot melt contains a large amount of heat, severe burns can result. The burning process can be very painful as the hot melt releases the heat it contains very slowly. An instinctive reaction, when hot melt comes into skin contact, is to pull the hot melt away with a bare hand, but this simply transfers the hot, sticky resin to another area. One should quickly scrape off the resin, plunge the covered area into cold water and obtain medical advice. Resin Decomposition and Fumes Thermoplastic materials (resins) are organic materials, which, generally, have low thermal stability. At the processing temperatures employed they can easily be degraded to give unpleasant, irritating odors and, if seriously overheated, they can produce a large quantity of noxious gas. Such gases should not be inhaled, and treated as harmful. This means that if, for example, the extruder barrel is stripped for cleaning it should be done in an extremely well ventilated area. Gloves, long sleeved overalls and a facemask should be worn when the barrel and screw are stripped and cleaned. If the gas produced by resin decomposition becomes trapped inside the machine, it can cause serious accidents. It can blow hot resin (plas- tic or melt) from the nozzle or even through the hopper. In the worst case, it could produce an explosion and cause damage to the machine, such as shear- ing the bolts holding the die/nozzle. Thus one should be careful and follow the correct operating procedures, particularly at the start up of an extrusion oper- ation. Rolls Rolls, such as the rubber covered rolls for pulling and steel rolls for cooling, are widely used in extrusion processing. The gap between them, called the ‘nip’ or ‘bite’, is very dangerous, as it is capable of trapping fingers or clothing causing serious injury. Such nips must be guarded, treated with respect, and avoided. Long hair should be kept covered; neckties and other loose clothes should not be worn as they can also become trapped. Be particularly careful if you have to wear gloves as these can become trapped; it is probably best to make the gloves as small as is convenient (for example, slit the backs and remove the cuffs). Learn a start-up technique that avoids the possibility of trapping a hand in the nips. Above all, find out what to do if something, orPDF Image | Dynisco Extrusion Processors Handbook
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