Special support may be necessary near the gate position.A classic example of this is with tunnel gates. An ejection position must be chosen so that the gate is sheared off cleanly and ejected without any tendency to hang-back.
Similar problems can occur with tab-gated components, which may shear off and tear
into the part, resulting in a reject. This is more likely to happen with brittle materials, and
accordingly adequate ejection support must be provided for such parts.
Overfeed gates, used in three-plate moulds, are also a potential source of problem. Often,
this type of gate is substantial in size and difficult to break off. In these cases the ejection must be phased in, with a sequenced opening of the tool. Sequenced opening ensures the
gate is broken away from its runner before ejection takes place.
Ejection Balance
An ejection system can contain many ejector pins and often these can be quite slender.
Such pins can easily buckle or start to score if the ejection system is not balanced or
guided.
Family tools (tools that produce parts with different geometry from each other, e.g., a lid
and a base on the same tool) invariably lead to an out of balance ejection system, as the
ejectors are not symmetrically positioned. In these cases, it is good design practice to
guide the ejection system with bushes to avoid any problems occurring.
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