May03
Trouble Shooting Guide for Plastic Injection

Trouble Suggested Remedies (Solutions)
DIMENSIONAL PROBLEMS  
Shot-to-shot dimensional variations
  • Increase injection pressure
  • Maintain uniform pad (cushion)
  • Repair leaking back flow value if pad cannot be maintained
  • Increase screw forward time
  • Maintain uniform cycle
  • Eliminate un-melted particles (see below)
  • Use larger machine or screw designed for DELRIN
Warping
彎曲變形
  • Balance mold temperature
  • Decrease mold temperature
  • Increase/decrease screw forward time
  • Increase/decrease injection pressure
  • Clean water channels in mold; improve mold cooling system
  • Improve part design
  • Change or add ejector pin locations

EJECTION PROBLEMS  
Parts stick in mold
黏模
  • Decrease injection pressure
  • Decrease injection rate
  • Decrease screw forward time
  • Increase cycle (possible only temporarily)
  • Use mold release temporarily
  • Correct mold defects (undercuts)
Sprue sticking
澆口堵塞
  • Remove burrs on sprue
  • Correct alignment between sprue and nozzle
  • Decrease screw forward time
  • Increase nozzle temperature
  • Increase mold cooling time
  • Use nozzle orifice smaller than sprue bushing
  • Increase taper of sprue
  • Use mold release temporarily
FILLING PROBLEMS  
Short Shots
短料
  • Maintain uniform pad
  • Repair leaking back flow value if pad cannot be maintained
  • Increase injection pressure
  • Increase injection rate
  • Increase melt temperature
  • Increase mold temperature
  • Enlarge vents
  • Change vent location
  • Increase overall cycle
  • Use screw designed for DELRIN
  • Use larger machine or injection unit
Voids in parts
  • Increase injection pressure
  • Increase screw forward time
  • Decrease injection rate
  • Decrease melt temperature; improve melt uniformity
  • Repair leaking back flow value if pad cannot be maintained
  • Enlarge vents
  • Improve gate size or location
  • Eliminate any restrictions in runner or nozzle
Weak Welds
熔接線
  • Increase injection pressure
  • Increase injection rate
  • Increase melt temperature, but avoid excessive temperature
  • Increase mold temperature
  • Avoid mold release spray
  • Enlarge vents
  • Change vent or gate location
  • Use larger machine or injection unit
MELT QUALITY PROBLEMS
Mold deposit
黏膜
  • Decrease injection rate
  • Decrease melt temperature
  • Avoid resin contamination
  • Correct hold-up spots in cylinder, screw, nozzle assembly
  • Increase gate size, flare gate
  • Enlarge vents
  • Change vent location
  • Use hopper drier to improve reground resin
Odor
氣味
  • Observe melt appearance (gassing) and measure melt temperature
  • Reduce cylinder temperatures if melt temperature is high.
  • Avoid resin contamination
  • Reduce overall cycle to decrease holdup time
  • Correct hold-up spots in cylinder, adaptor, nozzle, screw tip and check value assembly
  • Use smaller injection unit
Un-melted Particles
顆粒未融
  • Increase cylinder temperature
  • Increase back pressure
  • Reduce screw RPM
  • Use hopper drier to preheat resin
  • Increase overall cycle
  • Use screw designed for DELRIN
  • Use larger machine or injection unit
SURFACE PROBLEMS
Black sports or brown streaks
黑點/條紋
  • Decrease cycle
  • Avoid resin contamination
  • Correct hold-up spots in cylinder, screw, nozzle assembly
Blush, Frost, and Folds
變色/折疊
  • Decrease injection rate
  • Increase mold temperature
  • Change gate location
Gate Smear
  • Increase mold temperature
  • Decrease mold temperature
  • Change gate location 
Jetting
擠壓
  • Increase melt temperature
  • Increase or decrease injection rate
  • Increase gate size, flare gate
  • Change gate location
Pits, Orange peel, Wrinkles
傷痕、脫皮、皺摺
  • Increase injection pressure
  • Increase injection rate
  • Increase screw forward time
  • Increase mold temperature
  • Increase melt temperature
  • Enlarge vents
  • Increase gate size
Sinks
下陷
  • Repair leaking back flow value if pad cannot be maintained
  • Increase injection pressure
  • Increase screw forward time
  • Increase or decrease injection rate
  • Decrease mold temperature
  • Decrease melt temperature
  • Increase gate size
  • Change gate location
Splay
  • Decrease melt temperature if it is too high
  • Reduce cycle to decrease holdup time
  • Avoid resin contamination
  • Increase or decrease injection rate
  • Correct hold-up spots in cylinder screw, nozzle assembly
  • Increase size of small gate

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