As the mold for plastic injection molding is continued to be used, the slide core or ejector pin, ejector sleeve, and center pin, etc., can cause what is called "galling". "Galling" is the abnormal wear of sliding surfaces, and the causes of abnormal wear are classified as follows.

1. Abrasive wear

This is a form of abnormal wear that can occur easily if there is a difference in the hardness of the materials of the sliding mold parts. This is the phenomenon of a harder material scratching the softer material and getting fused to it.

2. Adhesion wear

In this condition, the projecting parts of mold parts hit against each other and become adhered to each other at the locations where the contact is very severe, and the adhered part falls off becoming wear dust, and the wear continues.

3. Fatigue wear

Fatigue occurs when a mold part repeatedly moves and stops, and this causes wear in this condition. This is the condition when flaking has taken place (peeling off of scales).

4. Fretting Corrosion

This is a form of wear in which wear of the pitching shape occurs in the regions where parts mate with each other with a relatively small clearance. This occurs very often in square keys and key grooves.

5. Corrosion wear

In a corrosive atmosphere of chemical constituents, moisture, or ions, etc., arising from the plastic, wear of the mold parts occurs due to the generation of a potential difference between the two.

When galling occurs, fatal damage is caused to the cavity and the core, and when there is defective movement of the ejector pin or the slide core, it is highly likely to result in breakage of the mold. In order to prevent galling, it is necessary to carry out the appropriate lubrication control, and to use mold parts that are maintenance free.