Styrene Acrylonitrile (SAN) - Troubleshooting Common SAN Processing Problems

  • Black Specks
    • Check for contaminated material, particularly if regrind is being used.
    • Decrease injection pressure, decrease booster time
    • Decrease stock temperatures to minimize polymer and additive degradation
    • Increase stock temperatures to reduce trapped air
    • Increase stock temperatures and purge to loosen degraded resin
    • Examine nozzle seat, cylinder walls and valves for dead spots
    • Examine screw , screw tip and end cap for charred material
    • Examine screw , screw tip and end cap for rough surfaces
    • Examine heater bands and controls for malfunctions. Locate hot spots.
    • Correct mismatch nozzle
    • Be sure runner system is streamline
  • Blisters
    • Reduce screw rpm
    • Increase injection back pressure
    • Raise mold temperature
    • Relocate gate
    • Material needs additional regrinding
    • Regrind not mixed sufficiently with Virgin material
    • Material contaminated
    • Lower injection speed
    • Properly dry material
  • Blush
    • Relocate gate
    • Increase mold temperatures
    • Reduce injection fill speed
    • Analyze and adjust melt temperature accordingly
    • Analyze and adjust nozzle temperature accordingly
    • Pre-dry material
    • Increase the number and / or size of cold well slug
    • Increase injection pressure
    • Increase gate diameter
  • Brittleness
    • Increase mold temperatures
    • Check regrind levels
    • Improve cooling channels to prevent heat build up
    • Be certain material is dry
    • If gate is to thin, increase gate size
    • Part designed with abrupt wall section transitions, sharp fillets, or radii
  • Bubbles
    • Check for clogged vents
    • Increase injection pressure
    • Be certain material is dry
    • Note: Bubbles and Voids are two different problems
    • Increase the number of vents
    • Improve the location of vents
    • Increase injection forward time
    • Increase feed zone temperature
    • Minimize or eliminate suck back
    • Match nozzle and sprue
  • Burns
    • Check for clogged vents
    • Examine heater bands and controls for malfunctions. Locate hot spots.
    • Relocate gate
    • Decrease injection speeds
    • Decrease injection pressures
    • Increase mold temperature of a cold mold
    • Analyze screw rpm and adjust accordingly
    • Decrease back pressures
    • Analyze and adjust stock temperatures
    • Check residence time of polymer in the barrel
    • Vent cavity at point of air entrapment
    • Vent runner system
    • Increase gate dimensions
    • Increase nozzle diameter
    • Use a lower compression ratio screw
  • Cracks
    • Increase mold temperatures
    • Reduce fill rates
    • Lower pack pressures
    • Slow ejector speeds
    • Slow mold open speeds
    • Use lubricated material grades if possible
    • Minimize sharp corners on part
    • Put parts in an insulated container to cool
  • Delamination / Lamination
    • Examine heater bands and controls for malfunctions. Locate hot spots.
    • Be certain material is dry
    • Examine resin for contamination and foreign materials.
    • Check for dissimilar resins being mixed, particularly if regrind is being used.
    • Increase stock temperatures
    • Use higher back pressure, change screw speed, use a higher compression screw
    • Increase injection speed if inadequate
    • Remove sharp corners at gate
    • Reduce stock temperature
    • Lower nozzle temperatures
    • Decrease screw speeds
    • Reduce back pressures
    • Check for contamination
    • Decrease residence time, Shorten overall cycle
    • Check for sufficient venting
    • Discoloration
    • Set mold temperatures to recommended conditions
  • Excessive Shrinkage
    • Increase injection pressure
    • Increase injection hold time, and /or pressure
    • Increase length of cooling cycle
    • Lower melt temperatures
    • Decrease mold temperatures
    • Analyze gate location and relocate as needed
    • Decrease gate land length to improve cavity pack
    • Check for a worn check valve assembly, barrel or screw
    • Ensure there is a proper cushion
  • Flow Lines
    • Increase mold temperatures
    • Increase melt temperature
    • Increase runner size
    • Increase gate size and/or relocate as needed
    • Increase cold slug well size or number
    • Increase back pressure
    • Check for color concentrate carrier compatibility
  • Jetting
    • Increase mold temperatures
    • Decrease injection speeds
    • Analyze and adjust stock temperatures
    • Decrease gate land length
    • Increase sprue, runner or gate size
    • Check nozzle heater band
    • Change gate location so the material will impinge off the opposite wall
  • Mold Flash
    • Be certain material is dry
    • Decrease injection pressures
    • Slow fill speed
    • Transfer to hold pressure sooner
    • Adjust shot size
    • Check for parting line seal, steel may be collapsed
    • Adjust clamp pressure to maximum for that mold / press combination.
    • Go to a larger press if the machine is undersize
    • Use a higher flow material if the end use requirements permits
    • Check mold supports
    • Decrease size of vents if oversized, increase number of vent if necessary
    • Balance cavities to within 90 % of fill
  • Parts stick in mold
    • Decrease injection pressures
    • Decrease injection rate
    • Decrease screw forward time
    • Analyze and adjust mold temperature
    • Correct mold defects
    • Use alternative mold releases (Internal, external)
  • Short Shots
    • Increase mold temperatures
    • Increase injection pressure
    • Use a higher flow material if the end use requirements permits
    • Increase feed to maintain a consistent cushion
    • Increase injection speed
    • Increase boost or high pressure time
    • Increase melt temperature if to low (Check spec.)
    • Use a short sprue with an extended nozzle
    • Enlarge gates, sprue and runners
    • Provide additional mold vents
    • Relocate gates
    • Check for worn check ring, screw and barrel
    • Check for bridging at the throat, reduce rear zone temp., check cooling in throat area
    • Insure the nozzle orifice is not too small
  • Sink Marks
    • Increase injection pressure
    • Analyze and adjust mold temperature
    • Provide additional mold vents
    • Increase injection hold time, and /or pressure
    • Increase length of cooling cycle
    • Lower melt temperatures
    • Check for a worn check valve assembly, barrel or screw
    • Increase shot size
    • Enlarge runner and gates to prevent freeze-off before part can be packed properly
    • Decrease land length of gate and sprue
    • Relocate gates on or as near as possible to thick sections
    • Decrease rib thickness to approx. 75 % or less of adjoining wall
    • Differential mold temperatures; Lower mold surface temperature opposite rib side
    • Adjust feed to increase cushion
  • Splay Marks / Silver Streaking
    • Check for contamination
    • Be certain material is dry, test for moisture
    • Reduce residence time
    • Reduce decompression
    • Decrease screw rpm
    • Adjust injection back pressure
    • Decrease melt temperature
    • Reduce nozzle temperature and /or go to larger nozzle
    • Go to larger sprue
    • Increase gate dimension, and/or reduce gate land
    • Check for burrs in runner or gate
    • Provide additional mold venting
    • Check for water leaks in the tool
  • Surface Finish (Low Gloss)
    • Increase mold temperatures
    • Increase mold temperatures
    • Increase injection pressure
    • Increase injection forward time
    • Increase melt temperature
    • Increase melt temperature
    • Increase injection speed
    • Be certain material is dry, test for moisture
    • Prepare mold surface to give the gloss expected for the molded item
    • Vent cavity at the point of air entrapment
    • Relocate gate so that melt flow impinges on the a mold surface, not directly into cavity
    • Analyze and adjust injection pressure
    • Analyze and adjust injection speed
    • Check for material contamination
    • Check that sprue, runner and gate are a sufficient size
    • Clean mold surface
    • Check for sufficient feed, increase cushion accordingly
    • Increase gate size
    • Provide adequate venting
    • Remove and clean mold
  • Voids
    • Raise mold temperature
    • Increase injection pressure
    • Increase injection forward time
    • Increase feed allotment if the cushion is too small
    • Decrease the feed allotment for to much cushion
    • Reduce rib thickness
    • Relocate gate near heavy sections
    • Eliminate heavy wall sections
  • Warping
    • Analyze and adjust injection speed
    • Increase mold close time
    • Increase packing time
    • Analyze and adjust holding pressure
    • Increase melt temperature and reduce injection pressure to reduce molded in stress
    • Adjust melt temperatures to match the temperature profile suggested for specific grade
    • Adjust mold temperatures to the requirements for your specific grade
    • Equalize temperatures of both halves of the mold
    • Correct mold temperature variations
    • Reduce variation in wall thickness
    • Fixture parts during post molding cooling
    • Relocate gates to avoid thin sections, ribs or curved sections
    • Adjust gate dimension to improve flow of resin
    • Be sure gates are balanced on multiple gated parts
    • Check for parts hanging up in the tool on mold open and part ejection
  • Weld Lines
    • Increase melt temperature
    • Increase injection pressure and speed
    • Provide adequate venting in cavities and runner system
    • Vent cavity at point of weld / air entrapment
    • Analyze and adjust gate, nozzle and sprue size
    • Decrease distance from gate to weld line by using multiple gates
    • Change gate location to alter flow pattern
    • Use a smaller amount or change type of mold release, additives and colorants
    • Increase the thickness of the weld line area or add a rib