Compression molding press|Principles of Plastic Compression Molding

Dec 07, 2021

Compression molding press

Compression molding is mainly used for thermosetting plastics, but also for thermoplastics. When molding thermosetting plastics, the molding material placed in the mold cavity changes from a solid state to a viscous state due to high temperature and high pressure, and fills the cavity in this state. At the same time, the polymer produces a cross-linking reaction. With the deepening of the reaction, the molten material gradually turns into a solid, and finally demoulded to obtain a plastic part.
When molding thermoplastics, the solid state becomes viscous and fills the cavity. The difference from molding thermosetting plastics is that there is no cross-linking reaction. Therefore, after the cavity is filled, the mold needs to be cooled to solidify , In order to demould and obtain plastic parts.
Because thermoplastics need to be heated and cooled alternately during compression molding, the production cycle is long and the efficiency is low. Therefore, with the continuous development of injection molding technology, there are not many cases of using compression to produce thermoplastic parts, but for some fluidity When poor thermoplastics (such as PTFE, etc.) cannot be injection molded, compression molding is considered.
Compared with injection molding, the advantages of compression molding are that ordinary hydraulic presses can be used, and the structure of the compression mold is simple (no pouring system). In addition, the internal orientation of the compressed plastic part is small, the molding shrinkage rate of the plastic part is small, and the performance is uniform. Its shortcomings are long molding cycle, low production efficiency, high labor intensity, difficult to control the precision of plastic parts, short mold life, and it is not easy to realize automated production.

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