According to the use of plastics are divided into general purpose plastics and engineering plastics. Among them, engineering plastics can be used as engineering structural materials and substitute for metal manufacturing machine parts and so on. For example, polyamide, polycarbonate, polyformaldehyde, ABS resin, polytetrafluoroethylene, polyester, polysulfone, polyimide, etc. Engineering plastics has small density, high chemical stability, good mechanical properties and superior electrical insulation, easy processing and forming characteristics, widely used in automotive, electrical, chemical, machinery, instruments, meters and other industries, also used in space travel, rockets, missiles, etc.