The condensed material of sprue sticks to the sprue of molds, which poses difficulty for ejection.The causes thereof are due to the high injection pressure, insufficient cooling in sprue, oversmall draft in sprue, incorrect design of fit between bush and nozzle of sprue, insecure assembly of molds, incorrect design of device for condensed material in ejection runner (pulling rod or cold-slug well etc), as well as

insufficient dosage of mold release agent. Solutions:

1 Properly reduce injection pressure and dosage of injection;
2 Reinforce cooling for sprue;
3 Properly design dimension of the spherical concave on the outer bush of sprue according to the

spherical radius of nozzle for the injection machine;
4 Correctly design dimension of mold retainer-ring and ensure that the central line of nozzle

accords with the central line of sprue of injection mold during assembly;
5 Increase draft of sprue;
6 Correctly design the pulling rod or cold-slug well of condensed materials in the ejection runner; 7 Ensure smooth inner surface of sprue, wherein the processing trace of inner surface should

stretch along the ejection direction of condensed materials in the sprue; 8 Properly increase dosage of mold release agent.