- 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
- Moisture condition parts
- Material is over dried
- 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
- 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
- Toughened grades more susceptible
- Set mold temperatures to recommended conditions
- Discoloration
- Examine heater bands and controls for malfunctions. Locate hot spots.
- 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
- 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
- Different colors will affect shrinkage
- 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