① Extrusion inflation equipment. Extrusion inflation equipment is very simple, which is generally composed of extruder, die head, air ring and cooling device, film thickness control system, herringbone plate, traction device, corona treatment device and winding device. a. Extruder. The extruder is the main part of the extrusion system, which mainly includes the screw, barrel, hopper, thermocouple and filter screen. Figure 3-9 is the schematic diagram of the extruder. Screw diameter, screw length diameter ratio and screw thread compression ratio are several important parameters of the extruder, and their value ranges are generally 45? 150mm、24:1? 30:1 and 1.8:1? 2.5:1。 The main function of the screw is to promote plastic particles, heat, compress, melt and plasticize plastic particles. The barrel generally has 3? There are 6 heating units, and each unit has a cooling fan, which is convenient for accurate control of the barrel temperature. There is a cooling device at the feeding place of the barrel to prevent the raw materials from heating and caking at the feeding place. The filter screen is generally 80/100/800 mesh structure. The filter screen is used to increase the resistance and the density of the melt, so that the material flow can be pushed in a straight line, and impurities can be filtered out. In addition, the extruder has a very important parameter – inflation ratio/which has a great impact on the performance of the film. The blowing ratio is the ratio of the film diameter to the mandrel or annular die diameter. The greater the blowing ratio, the better the transparency and luster of the film, and the better the mechanical strength. However, if the blowing ratio is too large, the film bubble is too large, the film is too thin, and the thickness is not large, and the film is easy to wrinkle. Generally, the blowing ratio is 2? 3 is preferred.