Injection moulding process variables and their causes
2. Faulty pump; cavitation
3. Faulty relief valve
4. Overheated or cold oil
2. Air, water, or sludge in oil
3. Faulty control valve
4. No accumulator, and pump too small for required rate o f flow
2. Thermocouple malfunction
3. Faulty temperature controller
4. Hot spot in cylinder
2. Worn cam follower on feed control
3. Worn and leaking check ring (back-flow stop valve)
4. Incorrect screw-back speed
5. Malfunction of pressure reduction switching
6. Nozzle dribble
7. Leakage at nozzle/sprue bush
2. Dirt or rust in cooling channels
3. Cooling channels wrongly connected
2. Mould distorted
3. Mould badly vented
4. Mould badly constructed
5. Mould badly designed
To sum up the discussion of the causes and cures of faults in injection moulded components, Table should be consulted. Here, the main faults are listed on the left. In the second column is a generalized cause，and possible remedies are listed on the right，together with the appropriate text references. Such a table should be used with discretion; nothing is more valuable in the diagnosis and cure of faults than a thorough knowledge of the process and the ability to apply that knowledge to the problem in hand.
Faults in injection moulding
Sinks and voids
Weld and flow marks
Poor surface finish
properly
Increase injection rate
Increase cylinder and mould
temperature
Increase feed
Improve mould venting
Increase size of gate，sprue, and
runner
venting
Flash
Warping
of cavity
Use minimum hold-on pressure
and time
Fill more quickly
splash marks
Decomposition
material
Reduce effects of mechanical heating
Eject over larger area
melt too high
Surface cracking
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