Wall screw out the screw, can be made of the overall structure, but are usually equipped with a jacket, so as to be used as steam or thermal oil heating, or for circulating water cooling, the purpose of which is to make the extrusion accurately adjust the functional sector temperatures. Most of the screw are equipped with pressure sensors and temperature sensors, and equipped with a temperature control device. Screw typically made from grooves on the inner surface shape, some linear grooves, some spiral grooves. Spiral grooves, downstream of the booster, straight grooves, prevents downstream. Thus, linear grooves can cause low flow rates, but the shearing effect is larger. The clearance distance between the screw and screw, usually kept to a minimum, so as to reduce the leakage flow.