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SYMPTOM TYPICAL CAUSE
Screw rotating during injection Worn or damaged non-return valve and/or cylinder allows

screw to move forward without pushing the plastic
causing the screw to rotate

Inability of screw to hold a cushion Worn or damaged non-return valve and/or cylinder
permits screw to move forward without pushing and
packing the plastic in the mould

Longer than normal recovery time Reduced plasticizing efficiency resulting from worn
cylinder and/or screw

Increase in overall cycle time Caused by all of the above. Worn cylinder, screw and
non-return valve result in slower and inefficient

plasticizing
Defective, streaked or non-uniform Poor melt quality resulting from worn cylinder and/or
appearing parts screw
Metal particles in parts Flaking or peeling of screw plating or cylinder lining
Dark or burned specks in parts Cylinder and/or screw worn or pitted, allowing plastic to

gather in wear spots and degrade

Difficulty in achieving a color change Plastic hangs up in worn areas of cylinder or screw
requiring repeated cycles to clear out
Extruder Machine may experience many of the injection moulding symptoms plus those listed below:
TYPICAL CAUSE
SYMPTOM

Increased screw speed (RPM) to Worn cylinder and/or screw reduce plasticizing
efficiency requiring higher screw speed to maintain
maintain normal output
output

Above normal melt temperature As clearance between the screw and cylinder
increases, plastic flows through the clearance causing

excessive shear
As the flights of conveying elements are worn, conveying efficiency is reduced.
Symptom: feed limitation and backup into main feed port. Increasing screw speed
will compensate efficiency reduction but it also accelerate wear rate.

When the tips of kneading elements are worn, melting and mixing efficiency are
reduced.
Symptom: Un-melted resin appears at side feeder and additives appear in
vacuum vent or on screen.

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