Three standards of plastic injection moulding process

Update:19 Apr 2018

In the injection production, the plastic injection moul […]

In the injection production, the plastic injection moulding process cooling time accounts for about 80% of the entire injection production cycle. Poor cooling often results in warping of the article or surface defects that affect the dimensional stability of the article. Reasonable arrangements for injection, pressure maintenance and cooling time can improve product quality and productivity.

The cooling time of a part usually refers to the time from when the plastic melt fills the cavity of the injection mould to when the part can be opened and removed. The time standard for taking out the parts can be opened, often the parts have been fully cured, with a certain degree of strength and rigidity, and will not be deformed and cracked when the mould is ejected.

Even if the same plastic is used for moulding, the cooling time varies depending on the wall thickness, the temperature of the molten plastic, the demoulding temperature of the moulded part, and the temperature of the injection mould. The formula that can calculate the cooling time 100% correctly in all cases is not published yet, and only the calculation formula is based on appropriate assumptions. The calculation formula also differs depending on the definition of cooling time.

At present, the following three standards are usually used as reference for cooling time:

1.The temperature of the center layer of the thickest part of the plastic injection moulded part is cooled to the time required for the plastic below the heat distortion temperature;

2.The average temperature in the cross-section of the plastic injection-moulded workpiece, and the time required for cooling to the die temperature of the specified product;

3.The thickest part of the wall of the crystalline plastic moulded part The temperature of the central layer, the time required to cool to below its melting point, or the time required to reach the specified percentage of crystallization.