EJECTION SYSTEM in injection moulding

After the moulding has solidified and cooled down, it has to be removed from the mould. It would be ideal if gravity could separate the part from cavity or core after mould opening. The moulding is kept in place, however, by undercuts, adhesion and internal stresses and, therefore, has to be separated and removed from the mould by ejection system.

Ejection system is usually actuated mechanically by the opening stroke of the moulding machine. If this simple arrangement is not sufficient ejection can be performed pneumatically or hydraulically.

Ejection system is normally housed in the moving half of the mold. Mold opening causes the mechanically actuated ejector system to be moved towards the parting line thus ejecting the component.

Four factors should be considered in designing the ejection mechanism:

· Shape and geometry of the part.

· Type of material and wall thickness.

· Projected production volume.

· Component position relative to the parting line.

The basic ejection techniques are:

· Pin ejection.

· Blade ejection.

· Sleeve ejection.

· Valve ejection.

· Air ejection.

· Stripper plate ejection.

According to shape, material wall thickness, component position relative to parting plane and aesthetic considerations the pin ejection technique is chosen for the part ejection.