1. Material decomposition

1. Sufficient purging.

2. Lower resin temperature.

3. Shorten residence time in cylinder.

2. Insufficient purging

3. Contamination of foreign materials

1. Sufficient purging

1. Low resin temperature and/or low pressure when flow fronts meet in weld line

1. Raise the mold temperature (buried cartridge heaters in weld sections).

2. Elevate resin temperature.

3. Increase injection speed.

4. Change the resin to a higher flow grade.

5. Increase holding pressure.

6. Enlarge gate size.

2. Insufficient degassing

1. Enlarge gas vent size at weld.

3. Design problem

1. Provide weld escape.

2. Change flow pattern into welds by adjustment of thickness.

1. Volatile components like moisture, decomposed gas and air entrapped in plasticization

2. Air pocket generation by unbalanced flow in cavity

1. Sufficient drying material.

2. Don't raise resin temperature too high.

3. Lower screw revolution speed. Increase screw back pressure.

4. Enlarge gas vent size.

5. Degas from runners.

3. Contamination of foreign materials

1. Sufficient purging

1. Insufficient degassing

1. Slow injection speed. When restricted product shape, adjust V-P switching position or use multi-stage injection method.

2. Enlarge gas vent size.

3. Lower resin temperature and/or mold temperature.

1. Contamination of solid resin which solidifieds at cylinder head

1. Raise cylinder temperature. When nozzle-touched operation, raise mold temp.

2. Enlarge slag well of runner.

3. Retreat back cylinder every cycle.

1. When melt resin goes out from a narrow place to a wide place in mold, if its speed is too fast, resin sometimes runs out in a strand shape and does not touch cavity surface. As result, jetting, strand-like marks on molded piece occur.

1. Enlarge gate size. Alter gate position.

2. Slow initial running rate at the gate.

3. Lower resin viscosity; i.e., elevate resin temperature and/or mold temperature, use higher flow grades.

4. Increase holding pressure.

1. Insufficient pressure

1. Increase holding pressure.

2. Raise mold temperature and/or resin temperature.

3. Enlarge gate size.

4. Increase injection speed.

5. Use high-flow grade.

2. Insufficient degassing

1. Enlarge gas-vent size.

3. Cold slag, jetting

1. Refer to each section in this page.

1. Residual jetting pattern on surface

Primary measure: Prevent jetting.

1. Refer to section on jetting.

Secondary measure:

Make jetting mark unnoticeable if jetting occurs.

1. Elevate mold temperature.

2. Increase holding pressure.

3.Alter the gate position (Make straight length short after resin passes through the gate).

-(a) After the gate position to the section where flow comes in contact with the core.

-(b) Move the gate position to a thin wall section.

-(c) Use a tub gate.

2. Residual flow pattern on the surface due to flow rate change, generated when resin passes corner sections or sections of non-uniform wall thickness

1. Make comers rounded.

2. Make sections where wall thickness changes gently inclined and rounded.

3. Insufficient degassing

1. Enlarge gas vent size.

1. Surface sink with shrinkage of inner part due to insufficient cooling of thick wall and rib section and insufficient inner pressure in the cavity.

1. Lower mold temperature.

2. Enlarge sprue, runners and gates.

3. Increase holding pressure. Prolong holding time.

4. Keep cushion amount of material until gate seals.

5. Minimize rib thickness to approximately one-third of base thickness.

6. Decrease thickness of thick wall sections.

1. Contamination of foreign materials

1. Sufficient purging

2. Shear delamination

1. Raise the mold and/or resin temperature.

2. Enlarge gates size.

3. Decrease product thickness.

4. Lower holding pressure.

5. Lower injection speed.

3. Large gas generation

1. Don't raise resin temperature too high.

2. Sufficient material drying.

3. Don't make revolution speed too high. Don't lower screw back pressure too low.

4. Lower holding pressure.

5. Lower injection speed.

6. If regrind material was used, lower ratio of regrind.

1. Air catching

1. Lower screw revolution speed. Increase screw back pressure.

2. Lessen suck-back amount.

2. Surface delamination

1. Raise mold temperature.

2. Lower injection speed.

3. Enlarge gate size.

4. Increase wall thickness (of too thin parts only)

5. Suppress jetting.

3. Large gas generation

1. Don't raise resin temperature too high.

2. Sufficient drying.

3. Shorten resident time in cylinder.

1. Anisotropy due to glass fiber orientation

1. Increase wall thickness.

2. In case of ribbed product design, set gate on shorter side of product. In addition, set direction of rib for same direction of resin flow.

1. Unstable or no supply of resin pellet into cylinder while metering

1. Adjust screw revolution speed. Lower screw back pressure.

2. Lower resin temperature.

3. Change resin grade and/or screw pattern.

4. When using regrind, use uniform pellet shape and size as much as possible. Reduce powdered resin as much as possible.

1. Grasp of a core-pin

1. Raise holding pressure.

2. Raise mold temperature.

2. Overfilling into ribs and bosses

1. Lower holding pressure.

2. Lower mold temperature.

3. Mold design problem

1. Increase drafts of circumference of the cavity, bosses and ribs. And/or add ejector pins.

1. Gas void
Entrapping gas in cylinder or through injection. Moisture, decomposition of resin and air.

1. Raise holding pressure. Enlarge size of gate, runner and sprue.

2. Locate gate as near voids position as possible

(usually thick wall part).

3. Sufficient material drying.

4. Lower resin temperature.

5. Shorten molding cycle.

6. Lower screw revolution speed. Raise screw back pressure.

7. Decrease injection speed.

8. Enlarge gas vent size.

2. Vacuum void
Inner molten resin is pulled to surface due to fast solidification of surface layer, then voids occur in inner section.

1. Locate gate at the thickest section of molding.

2. Enlarge gate, runner, sprue, and nozzle in accordance with thickness of molding. Increase gate thickness to more than 50%-60% of wall thickness of molding.

3. Increase holding pressure. Prolong holding time.

4. Keep cushion until gate seals.

5. Ensure working of non-return valve does not cause back flow during holding time.

6. Raise mold temperature.

7. Decrease injection speed.

8. Changeto a high viscosity grade.

1. Adhesion and build-up of degraded resin, additive agent, etc. on surface of mold.

1. Lower resin temperature.

2. Sufficient material drying.

3. Shorten resident time in cylinder.

4. Raise mold temperature.

5. Decrease injection speed.

6. Enlarge gas vent size.

7. If regrind material was used, lower ratio of regrind.

8. Clean mold.

1. MD (Mold deposit)

1. Measures against mold deposit
-(a) Sufficient material drying
-(b) Don't raise resin temperature too high.
-(c) Enlarge gas vent size.
-(d) Raise mold temperature.

2. Cleaning cavities
-(a) Ultrasonic cleaning of core in a solvent.

2. Insufficient resin's pressing for cavity

1. Increase holding pressure and time.

2. Enlarge runners and gates.

3. Raise mold temperature.

4. Raise resin temperature.

5. Increase injection speed.

1. Poor mold releasability

1. Refer section of "poor mold releasability" in this page.

2. Embrittlement of molded product due to degradation or hydrolysis of resin.

1. Adjust resin temperature.

2. Shorten resident time in cylinder.

3. Sufficient material drying.

4. Raise mold temperature and prolong cooling time for improving polymer crystallinity.

1. Low viscosity of material

1. Lower cylinder temperature, especially at nozzle.

2. Use a higher viscosity grade.

2. High pressure in cylinder

1. Lower screw revolution speed and back pressure. Back pressure should be set 0.2 MPa at least.

2. Sufficient drying material.

3. Lower cylinder temperature.

4. Increase suck-back amount.

1. Resin in sprue top is not solidified

1. Lower cylinder temperature. especially at nozzlet.

2. Lower mold temperature.

3. Quicken mold opening speed and widen mold opening distance.

4. Change kind, shape or type of nozzle; i.e., using shut-off type nozzle, make nozzle hole smaller.