a) Check and clean all parting line vents and make sure they are open and
clean.

b) Check for proper and adequate venting on the cavity, core and runner.

c) Check for over-clamping. Reduce the clamp pressure to the minimum amount
necessary.

d) Remove or reduce suck-back.

e) Increase back pressure to 'squeeze' air trapped between pellets out of the
melt and out through the hopper.

f) Change the direction of polymer flow to avoid air entrapment.

a) Check the melt temperature of material – set to mid-range of
manufacturer’s recommended temperature.

b) Change to 100% virgin material.

c) Purge machine, restart on cycle and check material residence time in the
barrel.

d) Reduce screw RPM.

e) Check the actual barrel temperatures for proper settings or over-riding.

f) Proper drying: both over-drying and processing at a moisture level that is
too high will degrade certain plastic materials.

Drying at temperatures and times that are acceptable for the base resin may
not be acceptable for some additives, especially impact modifiers. These may
degrade because of overheating or over-drying, etc.

a) Change the material additives.

b) Set the melt temperature at mid-point of manufacturer’s recommended
temperature.

c) Reduce residence time in the barrel.