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6.0 POLYMER PROCESSING

6.2.8 THE MOLD

1. The purpose of the mold is to shape the injected liquid plastic to the required
dimensions and hold the material until it cools and can be ejected as a solid part (Figure

6.4). The simplest type of mold consists of two halves, which contain a cavity or
impression. One half of the mold is stationary and generally contains the sprue through
which the polymer melt is injected.
2. The moving half mold is bolted to the moving platen, and generally contains the ejection

mechanism, either pins or plate.
3. The ejection of the molding from the mold is by ejector pins or plate.
4. Ejector pins can be operated either mechanically or hydraulically. Hydraulic ejection is
used where the machine is not attended and a number of ejection strokes are required.

5. Ejector plates are used where there is not enough area for pins or an even ejection is
required. The plate can be actuated by rods, chains or hydraulically.
6. In most cases the ejector pin or plate is operated by a set screw hitting a stop. When the
mold opens.
7. The two halves of the mold must mate together accurately so that no leakage of plastic

can occur at the split line.
8. To increase the production rate of the process, cooling channels are included in the
mold. This allows the mold temperature to be controlled.

Figure 6.4. Picture of the mold.

BPLK 150 DME 1083