PLASTIC INJECTION TROUBLESHOOTING
  • Short Molding
  • Reasons
    Possible Solutions
    Low melt temperature Check feed rate
    Nozzle runner inlet diameter too small Increase injection pressure and rate
    Injection pressure too low Increase melt temperature, cylinder temperature and backpressure
    Inadequate hold time Increase mold temperature and hold time
    Increase runner and runner inlet diameter
  • Sprue Sticking
  • Reasons
    Possible Solutions
    Injection pressure too high Reduce melt temperature, cylinder temperature, screw speed, backpressure
    Injection rate too high Reduce injection pressure and rate
    Melt viscosity too high Reduce injection and hold times
    Mold surfaces too polished Check mold closure
    Mold temperature too high Check if mold plates parallel
  • Splash Marking, Streaking, Gas Marking
  • Reasons
    Possible Solutions
    Material may contain moisture Dry material before use
    Gas created during degradation Check for contamination
    Increase mold temperature
    Reduce injection speed
  • Flow Marks
  • Reasons
    Possible Solutions
    Melt not homogeneous due to low mold and furnace temperature Increase temperatures gradually
    Runner inlet too small Increase runner inlet diameter
    Reduce injection speed
  • Weld Marks
  • Reasons
    Possible Solutions
    Furnace temperature too low Increase injection pressure, rate and hold time
    Injection pressure too low Increase mold and melt temperatures
    Trapped gas Open vents in joints
    Material of incorrect viscosity Use material with high viscosity to ensure proper welding of joints
    Mold surfaces greasy Change runner inlet location if problem persists after test shot
  • Voids
  • Reasons
    Possible Solutions
    Gas and moisture present Increase injection pressure and hold time
    Unbalanced mold filling Use maximum injection rate
    Reduce mould temperature
    Increase runner diameter and runner inlet diameter
    Widen runner inlets that are too slow
  • Blisters
  • Reasons
    Possible Solutions
    Gas and moisture present Increase injection pressure and hold time
    Unbalanced mold filling Increase mold temperature
    Reduce injection rate and feed rate
    Increase runner diameter and runner inlet diameter
    Widen runner inlets that are too slow
  • Warping and Distortion
  • Reasons
    Possible Solutions
    Properties altered depending on drawing direction (isotropy) Equalize mold temperature of both halves
    Uneven mold core temperatures Ensure even force when ejecting part
    Part ejected before cool Check part location after knockout from mold
    Increase injection time and mold closing speed
    Reduce melt temperature
    Try different mold temperatures
  • Brittleness
  • Reasons
    Possible Solutions
    Melt temperature too high Reduce melt temperature
    Runner, runner diameter and runner inlet diameter too small Check for contamination
    Material too tough Dry material before use
    Humidify molded part (nylon)
    Decrease amount of regrind use
  • Oversized or Undersized Part
  • Reasons
    Possible Solutions
    Inconsistent molding time and mold draw rate Use uniform cycles
    Hold time less than draw rate Ensure even feed across all cycles
    Higher draw rate at joints Fill mold as quickly as possible
    Increase runner inlet size
    Check that runner, runner inlet and runner distribution are even