China Plastic Molding

Compression Molding

In compression molding, a measured quantity of thermosetting resin is placed in a mold. The mold is heated, pressure is applied, and the molten resin completely fills the mold cavity. The resin undergoes chemical reaction while hardening to a permanent from.
Molding materials commonly used are: phenolic, alkyd resin, diallyl phthalate, melamine, and urea. These resins are available in the form of line powders, granules, flakes and rope. These are also believed as PREFORMS ( is a perform the specified amount of resin is compressed and sticks together like an aspirin table). A perform contains just enough resin t fill the mold and to allow for a slight flash (extraplastic attached to molding along parting line which must be removed before the part is completed). Plastics pastes or rope preweighted into slugs, are used the same way.
In compression molding a charge of resin is placed in an open two-part heated mold. The mold is then closed. Pressures from 1000 to 10000 psi are applied by a hydraulic press. Mold temperature which range from 280 to 4000, cause the resin to melt and flow through the opening of the mold cavity. When polymerization is removed. Mold temperatures can be maintained and the product removed hot as the thermosetting material is in a solid state. The next charge can be placed in the mold immediately.
The mold for compression molding can be a single or multiple cavity type. Molds are usually made of tool steel and are highly polished to produce the desired product finish. The mold halves are bolted to the upper and lower platens of the hydraulic press for automatic opening and closing during the molding cycle.
If the molding process is manually operated, the operator prepares the charge, loads the molds, removes the molded product and often trims the flsh during the cure period. Compression molding done on automatic pressures requires a cycle in which the molding compound is fed directly into each mold cavity, compressed, cured, and the product ejected from the press. If inserts are required in the product they are usually placed in the open mold by the machine operator.

Posted by SINO-Marry
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