Ejection System and Cooling System for Injection Molding

July 29, 2024
Posted by admin

1. Design of cooling system for injection molding
During the plastic injection process, the uneven cooling rate of the plastic parts will also cause the uneven shrinkage of the plastic parts. This difference in shrinkage leads to the generation of bending moment and warpage of the plastic part.
If the temperature difference between the mold cavity and core used in injection molding flat plastic parts is too large. Since the melt close to the surface of the cold mold cavity cools down quickly, the material layer close to the surface of the hot mold cavity will continue to shrink, and the uneven shrinkage will cause the plastic part to warp.

Injection molding of epilator housing

In addition to considering that the temperature on the inner and outer surfaces of the plastic part tends to be balanced, the temperature on each side of the plastic part should also be considered to be consistent. That is, when the mold is cooled, try to keep the temperature of the cavity and the core uniform throughout, so that the cooling speed of the plastic parts is balanced. So that the shrinkage everywhere is more uniform, effectively preventing deformation. Therefore, the arrangement of cooling water holes on the mold is very important. After the distance from the pipe wall to the surface of the cavity is determined, the distance between the cooling water holes should be as small as possible to ensure that the temperature of the cavity wall is uniform. At the same time, since the temperature of the cooling medium increases with the increase of the length of the cooling water channel, the cavity and core of the mold will have a temperature difference along the water channel. Therefore, the water channel length of each cooling circuit is required to be less than 2m. Several cooling circuits should be set up in large molds, and the inlet of one circuit is located near the outlet of the other circuit. For long plastic parts, a cooling circuit should be used to reduce the length of the cooling circuit, that is, to reduce the temperature difference of the mold, so as to ensure uniform cooling of the plastic parts.

Injection molding of electric drill shell

Design of ejection system for injection molding
The design of the ejection system also directly affects the deformation of the plastic part. If the layout of the ejection system is unbalanced, it will cause an imbalance in the ejection force and deform the plastic part. Therefore, when designing the ejection system, it should strive to balance with the demoulding resistance. In addition, the cross-sectional area of the ejector rod should not be too small to prevent the plastic part from being deformed due to excessive force per unit area (especially when the demoulding temperature is too high). The ejector pin should be arranged as close as possible to the part with the largest demoulding resistance. Under the premise of not affecting the quality of plastic parts (including use requirements, dimensional accuracy and appearance, etc.), as many ejector pins as possible should be installed to reduce the overall deformation of plastic parts.
When soft plastic is used to produce large deep cavity and thin-walled plastic parts, due to the high demoulding resistance and soft material, if a single mechanical ejection method is completely adopted, the plastic parts will be deformed or even pushed through. Or produce folding and cause plastic parts to be scrapped. It will be better to use multi-component combination or combination of gas (hydraulic) pressure and mechanical ejection.