Automatic Ejection


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To take full advantage of the short cure cycles obtained with injection molding, an automatic ejection system is required [2,8].
Thin sections can be stripped from the mold by a compressed air jet. Simply shaped and flat parts can be removed by a rotating brush. Delicate parts can be removed by a robot pulling device, which places each part on a turntable, rather than ejecting it into a tote box.
Many rubber moldings, however, do not lend themselves to automatic ejection, but assistance in removal can be provided by mechanical or hydraulic mechanisms, which retain the molding in the most suitable part of the mold for easy stripping. Ejection is better suited to thick moldings with good hot tear strength and those with bonded metal inserts. When ejector pins are used to push directly on the rubber, a mushroom or miter type of pin is recommended in preference to a straight pin, which may be inhibited in its action by rubber stretching.


The ideal mold design would produce either no flash or would make flash removal simple, as pointed out above. However, some parts, especially multi-cavity molds, will need deflashing. There are a number of techniques for deflashing. The most efficient involves chilling to ±150 °C and then tumbling or shot blasting. The latter will handle complex parts, even items with inaccessible internal flash.