Pressure control for two-colour injection moulding processes

The two most important processes in two-colour injection moulding are filling and pressure-holding.


1. Injection pressure

In the current two-colour injection moulding process, the injection pressure of almost all injection machines is based on the pressure applied to the plastic by the top of the plunger or screw. The role of injection pressure in injection moulding is to overcome the resistance to the flow of plastic from the barrel to the cavity, to give the melt a rate of filling the mould and to compact the melt.

2. Plasticising pressure

In injection, the size of the plasticizing pressure is with the design of the screw, the quality of the product requirements and the type of plastic need to change, if these circumstances and screw speed are constant, then increase the plasticizing pressure will strengthen the shear effect, that is, will increase the temperature of the melt, but will reduce the efficiency of plasticization, increase the backflow and leakage, increase the driving power.

In addition, two-colour injection moulding process to increase the plasticising pressure can often make the temperature of the melt uniform, the mixing of the colour material uniform and the discharge of gas in the melt. In general operation, the decision of the plasticizing pressure should be in the premise of ensuring the excellent quality of the product, the lower the better, the specific value is different with the variety of plastic two-colour moulds used, but usually rarely exceed 20 kg / cm2.