What are the causes and solutions for shrinkage of preforms in preform injection molding process?
In the preform injection molding process, preform shrinkage is a common problem, which may cause defects such as inaccurate preform size and uneven surface. The following is an analysis of the causes and solutions for preform shrinkage:
Cause analysis:
1. Improper material ratio: The raw material ratio of the injection molded bottle preform is incorrect, resulting in insufficient or excessive shrinkage of the preform, resulting in shrinkage.
2. Improper setting of injection molding process parameters: Improper setting of parameters such as temperature, pressure, speed, etc. of the injection molding machine, such as insufficient injection pressure and insufficient holding time etc, may cause excessive shrinkage of the preform.
3. Mold design problem: unreasonable design of the mold cooled system, uneven cooling, or uneven wall thickness design of the mold may cause shrinkage differences in the preform during the cooled process, resulting in shrinkage.
4. Improper post-processing: Insufficient cooling time or improper cooling method after injection molding may also cause shrinkage of the preform.
Solutions:
1. Optimize the material ratio: Ensure that the raw material ratio of the injection molded bottle preform is correct to reduce shrinkage caused by material problems.
2. Adjust the injection molding process parameters: appropriately increase the injection pressure and speed to increase the fluidity and filling of the melt; extend the holding time and pressure to ensure that the plastic is fully replenished during the cooled process.
3. Improve mold design: optimize the water cooled system of the mold to ensure uniform cooling; reasonably design the wall thickness of the mold to avoid too thick or too thin parts.
4. Strengthen post-processing: Ensure sufficient cooled time after injection molding, and adopt appropriate cooling methods, such as using a cold water bath or air cooling, to reduce the temperature of the preform and reduce shrinkage.
In summary, in order to solve the problem of preform shrinkage in the preform injection molding process, it is necessary to take comprehensive measures from multiple aspects such as material ratio, injection molding process parameter adjustment, mold design improvement, and post-processing enhancement. It can effectively improve the quality and production efficiency of the preform.