In injection molding molds, the design of cooling system is very important. This is because the molded plastic products can only be cooled and solidified to a certain rigidity, and the plastic products can be prevented from deformation due to external forces after demoulding. Since the cooling time accounts for about 70% to 80% of the entire molding cycle, a well-designed cooling system can significantly shorten the molding time, improve injection molding productivity, and reduce costs. Improper design of cooling system will elongate the molding time and increase the cost; Uneven cooling will further cause warping deformation of plastic products.
According to the experiment, the heat from the melt into the mold is roughly dissipated in two parts, one of which 5% is transferred to the atmosphere by radiation and convection, and the remaining 95% is transmitted from the melt to the mold. Due to the role of cooling water pipe in the mold, the heat is transferred from the plastic in the mold cavity to the cooling water pipe through the heat conduction through the mold frame, and then taken away by the cooling liquid through the heat convection. A small amount of heat that is not taken away by the cooling water continues to conduct in the mold and spills into the air after contact with the outside world.
The molding cycle of injection molding die is composed of clamping time, filling time, holding time, cooling time and stripping time. Among them, the cooling time accounts for a significant proportion, about 70% to 80%. Therefore, the cooling time will directly affect the length of the plastic product molding cycle and the size of the output. The temperature of plastic products at the demoulding stage should be cooled to lower than the thermal deformation temperature of plastic products to prevent the relaxation of plastic products due to residual stress or the warping and deformation caused by the external force of demoulding.
Factors that affect the cooling rate of products are: plastic product design. Mainly plastic products wall thickness. The greater the thickness of the product, the longer the cooling time. In general, the cooling time is about proportional to the square of the thickness of the plastic product, or proportional to the 1.6 square of the diameter of the large flow channel. That is, the thickness of plastic products is doubled, and the cooling time is increased by 4 times.
Injection molding die material and cooling method thereof. Mold materials, including mold core, cavity material and mold frame material, have a great influence on the cooling rate. The higher the thermal conductivity of the mold material, the better the effect of transferring heat from the plastic per unit time, and the shorter the cooling time.
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