| Problems | Possible Causes | Suggested Solutions |
| Insufficient material feeding | - Caking at hopper bottom
- Back pressure insufficient or cylinder temperature too low causing inadequate melting
- Barrel temperature is too low causing inadequate material melting. Especially when 70% of the capacity is injected.
- Screw speed in too fast
| - Have cooling water pass hopper bottom
- adjust back pressure or increase barrel temperature
- Reduce screw speed
|
| Short Shot | - Poor melting of material
- Insufficient material flow
- Nozzle diameter, gate runner too small
- Injection pressure is too low
- Dwell time too short
- Insufficient charge volume in the barrel
- Air resistance, no gas escape
- Product too thin
- Abrasion of screw
| - Increase temperature of barrel and mold
- Use material with better flow properties
- Repair faulty part
- Increase injection pressure
- Lengthen dwell time
- Increase back pressure, charge volume
- Increase air vents
- Reconsider mold design
- Replace screw
|
| Too much flash | - Injection pressure too high
- Injection speed too fast
- Material flow too soft
- Clearance of mold surface
- Mold temperature too high
| - Lower injection pressure
- Adjust with flow control bulb
- Use hard flow material
- Make smaller clearance
- Lower mold temperature
|
| Weld lines | - Barrel temperature too low
- Injection pressure too low
- Air pockets
- Insufficient material flow
- Oil on mold surface
- Distance between gate and weld point too far
| - Increase barrel temperature
- Adjust injection pressure; widen runner, gate
- Increase air vents
- Use soft-flow material
- Remove mold and clean the oil on the mold
- Study gate position
|
| Flow Mark | - Un-uniform melting of material causing by low temperature of mould and barrel
- Gate too small
| - Increase temperature by step
- Widen the size of the gate
- Decrease the injection speed
|
| Poor cavity filling | - Barrel and mold temperature are too low
- Injection pressure and/or speed are too high
- Material flow is too high, i.e. material is too soft
- Injection starts before clamping pressure has been applied
| - Increase temperature of Barrel and mold
- Adjust injection pressure and flow control to fill cavity slowly
- Use harder material
- Delay injection starting time
|
| Fragility | - Melting temperature is too high
- Size of runner, sprue, gate are too small
- Material is too hard
| - Decrease barrel temperature
- Review the runner, spure and gate design
- Use softer material
|
| Mold Shrinkage | - The shorter the curing time is, the larger the molding shrinkage
- The shorter the dwell time is, the larger the shrinkage ratio
- The smaller the gate cross section area, the larger the shrinkage ratio
| |
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