How to Reduce Wear and Improve the Performance of Injection Molding Screws

Injection molding screws operate for extended periods under high temperature, high pressure, high mechanical torque, and high friction. The first few factors are required by the process conditions, while wear caused by friction is unavoidable.

Generally, screws undergo surface nitriding treatment to increase surface hardness, i.e., improve wear resistance. However, if the causes of wear are ignored and no measures are taken to minimize wear, the screw's service life will be significantly reduced.

The following explains the causes of screw wear and methods to reduce it:

1. Each type of plastic has an ideal plasticizing temperature range. The barrel processing temperature should be controlled to be close to this range. Granular plastic enters the barrel from the hopper and first reaches the feeding section, where dry friction inevitably occurs. When this plastic is insufficiently heated and melts unevenly, it easily leads to increased wear on the barrel's inner wall and the screw surface. Similarly, in the compression and homogenization sections, if the plastic's melting state is disordered and uneven, wear will also increase.

2. The rotational speed should be properly adjusted. Because some plastics contain reinforcing agents such as glass fibers, minerals, or other fillers, these substances often exert a much greater frictional force on metals than on molten plastic. When injection molding these plastics, using high rotation speeds increases the shear force on the plastic and also causes the reinforcing agents to produce more shredded fibers. These shredded fibers contain sharp ends, significantly increasing the abrasive force. Inorganic minerals also have a considerable scraping effect when sliding at high speeds across metal surfaces. Therefore, the rotation speed should not be set too high.