The thermal expansion coefficients of plastics and metals differ by 5 ~ 10 times. Therefore, when the plastic products with metal inserts are cooled, the shrinkage degree of the two products is different. Because the plastic shrinkage is relatively large, it tightly hugs the metal insert, and the plastic inner layer around the insert is under compressive stress, while the outer layer is under tensile stress, resulting in stress concentration< br />
The following points should be paid attention to when setting juice inserts to help reduce or eliminate internal stress: < br / >
& nbsp; a. Whenever possible, select plastic parts as inserts< br />
& nbsp; b. As far as possible, metal materials with small difference from plastic thermal expansion coefficient shall be selected as insert materials, such as aluminum, aluminum alloy and copper< br />
& nbsp; c. Coating a rubber or polyurethane elastic buffer layer on the metal insert and ensuring that the coating does not melt during molding can reduce the shrinkage difference between them< br />
& nbsp; d. Degreasing the surface of metal inserts can prevent grease from accelerating the stress cracking of products< br />
& nbsp; e. Metal inserts shall be properly preheated< br />
& nbsp; f. The thickness of plastic around the metal insert shall be sufficient. For example, if the outer diameter of the insert is D and the plastic thickness around the insert is h, the plastic thickness h of the aluminum insert is ≥ 0.8d; For copper inserts, the plastic thickness h ≥ 0.9 D< br />
& nbsp; g. Metal inserts shall be designed in a smooth shape, preferably with exquisite rolling patterns< br />