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Plastic Product Material and Process Selection Handbook Part 7

Tham khảo tài liệu 'plastic product material and process selection handbook part 7', kỹ thuật - công nghệ, cơ khí - chế tạo máy phục vụ nhu cầu học tập, nghiên cứu và làm việc hiệu quả | 194 Plastic Product Material and Process Selection Handbook Injection Area Process Control Figure 4.2 Three basic parts of an injection molding machine courtesy of Plastics FALLO The part taken from the mold is in most cases a finished product ready to be packed and shipped or ready to be used as a part of an assembled unit. In contrast to metal forming there is very little if any wasted material in injection molding. For cold runner TP systems most runners and sprues are reground and reused. By using hot runner molds the sprue and runner systems remain in a melted state in the mold and become part of the next finished part Chapter 17 . The hot runners can be thought of as an extension of the plasticizing chamber. IM lends itself readily to automation in varying degrees depending upon the ingenuity of the machine and mold designers. The machine manufacturer can usually add components to the basic machine to implement any desired automatic arrangement. Molding cycles are relatively fast and with new mold design developments constantly in progress and centering on faster heat transfer within the mold the molding cycle is continually being reduced. Modern methods of material handling both of the raw plastic and the finished product are becoming more generally employed further reducing costs of the finished part Chapter 18 . The reduction of raw material inventory is seriously considered and studies of production control methods are no longer uncommon even by the small molder. Methods such as these are important in making molded parts less expensive to manufacture. 4 Injection molding 195 Plastic is usually purchased in pellet form and heated in the plasticizer and or preheated prior to entering the plasticator until it reaches a viscous state in which it can be forced to flow into the mold cavities. Each plastic differs in its ability to flow under heat and pressure. For the best result correct melting temperature injection pressure and mold filling speed must be .