Excessive Shrinking

Excessive Shrinking

Remedies: Decreasing the barrel temperature allows the molecules and voids to expand and contract normally and provide consistent shrinkage values. Shrinkage is impossible to predict accurately, but keeping the material and mold temperatures at the right settings (as recommended by the material suppliers) will minimize the effective shrinkage.Get more news about Shrinkless Expanding Machine,you can vist our website!

◇ INSUFFICIENT INJECTION PRESSURE OR TIME

Remedies: Increase the amount of pressure or the time applied. Upon initial startup, the mold should be filled incrementally starting with intentional short shots (if the mold design allows) and progressively increasing pressure shot-by-shot until the mold is filled and packed properly. Then, parts should be inspected for critical dimensions. If the mold is new, and dimensions are incorrect, the mold should be returned to the moldmaker for adjustments. If the mold has already been in production and the dimensions are wrong, process parameters can be adjusted to make the part shrink less or more, whichever is required.

◇ INADEQUATE COOLING TIME
Remedies: Adjust the cooling time portion of the cycle. It is true that longer cycles make the part more expensive but there is a minimum amount of time required for the resin to form a proper skin. It depends on what material is being molded. A general rule-of-thumb for a part with a wall thickness of 0.100'', the cooling time should be 20 seconds. The overall cycle would then be 25-30 seconds.

◇ INSUFFICIENT CUSHION AND/OR HOLD TIME
Remedies: Maintain a cushion that is somewhere between 1/8'' and 1/4'' at the end of the injection stroke. This provides something against which hold pressure can be applied. The amount of time for holding pressure should be long enough for the gate to freeze, normally 3-4 seconds.

◇ EXCESSIVE NON-RETURN VALVE CLEARANCE
Remedies: Inspect the non-return valve mechanism and replace worn or damaged components. This wear is normal but is accelerated by molding materials that have reinforcements (such as glass) in them. The valve should be inspected at least every three months.