1) Self-weight G; 2) Torque M required to overcome material resistance; 3) Axial force P generated by material pressure.
　

The screw is generally scrapped due to long-term wear and the gap between the screw and the barrel is too large and cannot be extruded normally. However, there are also examples of damage caused by improper design or operation caused by working stress exceeding the strength limit. Therefore, the screw should also meet certain strength requirements. 4) The dangerous section of the screw is generally at the smallest thread root diameter in the feeding section.