Taper and Ejection

Normally, a generous draft taper should be provided for easy ejection of the artefact, consistent with the design of the produet. The ejeetion of PP artefacts is not very difficult and sometimes a taper of 0.5 is suffieient. If enough taper is not possible, mouldings can be produced with very low or even no taper, provided that ample load-bearing area is provided for the ejection and that the thiekness of the moulding is sufficient to avoid buckling or permanent deformation. 

PP is a resilient plastic which stretches rather than cracks if ejector pins of inadequate area are employed. It is not a very hard or rigid material so the rule is to use ejectors that are as large as possible. Ejectors inevitably leave witness marks on the mouldings. Hence, it is preferred for ejectors to operate on side walls, ribs or bosses. When ejector pins are to be positioned in flexible areas of moulding, they should be of ample diameter. 

Cylindrical ejector pins are most commonly used. However, rectangular pins or blade ejectors could be used in constricted areas. A stripper plate acts on the entire wall of the part and so distributes the ejection force. Air assisted ejection of thin walled articles could be used. 

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