Pressure

Typically, the following types of pressure are controlled in the process:

(i) Injection pressures

· The first stages of injection will fill the mould. Once the mould is filled, an additional amount of packing pressure is used until the gate freezes off.



(ii) Screw back pressure

· Screw back pressure is pressure put on the back of the screw. Typically this is done to increase mixing; such as when color concentrate is added. In some cases, to break up glass filler. (This is not recommended) When the pressure at the front of the screw is greater than the screw back pressure, the screw moves back.

(iii) Clamp pressure

· The clamp pressure is the pressure required to keep the mould closed during the injection phase. Maximum clamp pressure is achieved when the parts are packing.