Screw and barrel material selection

During the extrusion process, the screw is often exposed to working conditions such as high torque, high temperature, high speed, and high pressure. Sometimes it is also exposed to harsh conditions such as high wear and corrosion. Therefore, the selection of screw materials should consider issues such as strength, wear resistance, and corrosion resistance. . For combined co-rotating twin screws, since the screw adopts a mandrel structure, the strength problem of the screw is transformed into a strength problem of the mandrel. Because the mandrel is limited by the structure, has a small cross-section, and bears a large torque, it is necessary to choose a high-strength mandrel material. Screw elements generally do not have strength problems, because the torque endured by the entire screw is distributed to each screw element is very small, and the spline stress-bearing surface on the screw element that bears the circumferential force will not have insufficient strength. Therefore, the determination of the wall thickness between the center hole of the combined screw element and the root diameter of the screw element is generally not based on strength considerations, but on brittle fracture after heat treatment. The minimum wall thickness of the screw element that can ensure that brittle fracture does not occur after heat treatment Sufficient to meet strength requirements.

Most of the former domestic screw manufacturers used 38CrMoAlA steel, and the screws were nitrided after being made. Some foreign manufacturers also use chlorinated steel to make screws. The thickness of the nitride layer is generally 0.3~0.5mm, which can meet general requirements.