Page 119 - Module DMV20173

6.0 POLYMER PROCESSING

6.2.9 GATES FOR INJECTION MOLDING

1. Gate is a constriction between the feed system and the mold cavity, and serves several
purposes. Freezes rapidly and prevents material either entering or leaving the mold.

2. Provides an easy means of separating molding from the feed system and it provides
small portion of the feed system where there is a very rapid shearing of the material.
3. Incorrect gating is one of the most frequent causes of faults in injection molding.

EXERCISE 6.2

What are the functions of gates in injection molds?

7.2.10 HOT RUNNERS

1. The hot runner system has the sprue and runner remaining molted all the time.

2. This has the advantage that only the molding requires to solidify, which for thin walled
components will be much faster that the sprue.
3. There is no degating necessary, and no sprue and runner to recycle and it is often used
in conjunction with a pin gate.

4. The sprue and gate are kept molten with electric heaters and an insulating nozzle.

7.2.11 CORES

1. Designers may require a design that is so complex that it cannot be made from a two
part mold, such as a re-entrant feature.
2. Thus to reduce the part may entail a mold with cores.
3. To enable the component to be withdrawn from the mold, the cores will have to be

operated before or during the mold opening cycle.
4. This can be done by hydraulics or actuated by the machine’s hydraulics, or by guide pins
set at an angle to move the core as the mold opens.
5. The cores slide in guides that are locked into position by angled heel plates as the mold
locks up.

BPLK 151 DME 1083