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Cooling stage of plastic injection molding

In plastic injection molding tools, the design of the cooling system is very important. This is because the molded plastic product can only be cooled and solidified to a certain rigidity, and then the plastic product can be prevented from being deformed due to external force after being demolded. Since the cooling time accounts for about 70% to 80% of the entire molding cycle, a well-designed cooling system can greatly shorten the molding time, improve injection molding productivity, and reduce costs. An improperly designed cooling system will lengthen the molding time and increase costs; uneven cooling will further cause warpage and deformation of plastic products.

According to experiments, the heat that enters the mold from the melt is generally dissipated in two parts, one of which 5% is transferred to the atmosphere by radiation and convection, and the remaining 95% is conducted from the melt to the mold. Due to the action of the cooling water pipe in the mold of the plastic product, the heat is transferred from the plastic in the mold cavity to the cooling water pipe through the mold base through heat conduction, and then is taken away by the cooling liquid through heat convection. A small amount of heat that is not taken away by the cooling water continues to be conducted in the mold, and escapes into the air when it comes into contact with the outside world.

The molding cycle of plastic injection molding consists of clamping time, filling time, holding pressure time, cooling time and demolding time. Among them, the cooling time accounts for the largest proportion, about 70% to 80%. Therefore, the cooling time will directly affect the length of the molding cycle of plastic products and the size of the output. The temperature of the plastic product in the demolding stage should be cooled to lower than the thermal deformation temperature of the plastic product to prevent the plastic product from relaxing due to residual stress or warping and deformation caused by the external force of demolding.

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