4. Effect of polymer physical properties on the injection cycle

The polymers' low thermal conductivity, very high viscosity and variations in specific volume play a major role in injection molding.

The viscosity of plastics is very high at injection temperatures. It is on the order of 100,000 to 10 million times that of water under forming conditions.

This implies, on the one hand, very high injection pressures (up to 200 MPa), and on the other hand, significant temperature variations generated by the importance of the viscous dissipation phenomenon in the feed device as well as in the cavity, in the absence of specific precautions.

What's more, the low thermal conductivity of plastics - a thousand times lower than that of copper - means that cold feed channels can be used, but requires a long cooling time, depending on thickness.