Five reasons for shrinkage of injection mold products

No matter what injection molding products, it is inseparable from the injection mold, but sometimes the injection mold shrinkage phenomenon, so what are the reasons for the injection mold shrinkage.

1. Thermal expansion and cold shrinkage of plastics

In the process of plastic mold molding, it is necessary to melt the plastic raw materials. At this time, the melting temperature reaches 200 ~ 300 degrees, and the plastic raw materials are heated to expand. However, in the cooling process of the injection mold, the temperature decreases, and its volume potential must shrink.

2. Changes in the chemical structure of plastics

For example, in the molding process of thermosetting plastics, the resin molecules change from linear structure to body structure, and the volume mass of the shape structure is larger than that of the linear structure, and its total volume becomes smaller, so the shrinkage phenomenon occurs.

3. Residual stress change

In the process of injection molding, due to the shear force of molding pressure, anisotropy, mixing heterogeneity of additives and mold temperature

After molding, there is residual stress in the injection mold, which will gradually decrease and redistribute. As a result, the plastic mold shrinks again, which is generally called post shrinkage.

4. Gate section size

Different injection molds have different cross-section sizes. Large gate helps to increase the cavity pressure and prolong the gate closing time, so that more melt can flow into the cavity

5. Plastic varieties

Generally speaking, crystalline plastics, such as PP and PA, exhibit larger shrinkage and wider shrinkage range than crystalline plastics such as PC, PS and ABS.

The reasons for the large shrinkage of crystalline plastics are the influence of thermal expansion coefficient of plastics and the condensation of melt during the formation of crystalline structure.

The above five points are the causes of injection mold shrinkage, so for injection molding factory, when producing injection molding products, we must often check the quality of injection mold.

About PTJMould Industrial Company Limited

PTJmould is a China mold maker of plastic molds- injection mold, die casting moulds, plastic blow molding, rotational molding, medical plastic injection molding, two shot plastic injection molding, insert molding, overmolding, metal injection molding, micro injection molding, powder injection molding, ceramic injection molding, liquid injection molding, husky injection molding, household mold, casting mold, die mold tool, custom molds, china moulds, rapid prototyping tooling, plastic prototyping tooling, punch press tooling, die and tooling for mobile/ cell phone parts, automotive parts, vacuum cleaners, rechargeable tools, telephones, copiers, computers, multimedia speakers, and many other electronic products and household appliances. And also a plastic product manufacturer, mold manufacturer China– plastic parts, plastic water tank, plastic balls, plastic containers, plastic buckle, plastic anchor, plastic hanger, plastic spoon, plastic pipe fitting, plastic tumble, plastic tableware, plastic cups, plastic bottles, plastic tray, plastic cosmetic container, plastic case, plastic food container, plastic chairs, plastic caps, plastic cap closure, plastic tubes, plastic water pipes, plastic knobs, plastic tubing, plastic utility boxes, plastic racks and so on.