Solutions 1. Replace with a new container of material. 2. Ensure granulator is clean.
Cause : Inadequate purging
Solutions 1. Use compatible purging materials. 2. Use correct purging time & temperature. 3. Check machine nozzle, HR manifold and thermocouples are functioning correctly. 4. Inspect for pits and material traps on the machine screw & barrel. 5. Inspect screw non-return valve for material traps.
Cause : Material is overheated
Solutions 1.Check material melt and processing temps against manufacturers recommendations. 2. Check machine nozzle, HR manifold & nozzle thermocouples.
Blisters and Bubbles in Part
Cause: Trapped air
Solutions
1. Clean all parting line vents. 2. Ensure there is adequate venting on the cavity, core & runners. 3. Reduce the clamp pressure to the minimum amount necessary. 4. Resurface the part line to ensure vents have not hobbed into mould plates. 5. Increase back pressure to push air trapped between pellets out from the melt through the hopper. 6. Change the direction of polymer flow in the part to avoid air traps. 7. Change injection speed to help alter location of air entrapment.
Cause : Degraded polymer
Solutions
1. Set melt temperature to manufacturer’s recommendations. 2. Reduce heating time of polymer. 3. Reduce residence time of polymer melt in barrel and hot runner. 4. Change to 100% virgin material. 5. Purge machine on restart. 6. Reduce screw RPM. 7. Check actual barrel temperatures for over-riding. Ensure correct drying time (not over or under drying).
Brittleness
Cause: Degraded polymer
Solutions
1. Set melt temperature to manufacturer’s recommendations. 2. Reduce residence time of polymer melt in barrel and hot runner. 3. Ensure correct drying time (not over or under drying). 4. Reduce heating time of polymer. Reduce screw RPM.
Cause : Contamination
Solutions
1. Replace with new material. 2. Purge barrel and hot runner.
Burn Marks at the End of the Fill
Cause: Trapped air ‘dieseling’ (pressure in cavity igniting the air/plastic burning the part)
Solutions
1. Clean all parting line vents. 2. Ensure there is adequate venting on the cavity, core & runners. 3.Resurface the part line to ensure vents have not hobbed into mould plates. 4. Reduce the clamp pressure to the minimum amount necessary. 5. Increase back pressure to push air trapped between pellets out from the melt through the hopper. 5. Change the direction of polymer flow in the part to avoid air traps. 6. Change injection speed to help alter location of air entrapment.
Burn Marks on the Gate
Cause : Material Shear Sensitivity
Solutions
1. Use a less shear sensitive material. 2. Use a less shear sensitive additive or colorant. 3. Run 100% virgin material. 4. Reduce residence time of material in moulding machine and hot runner system.
Burrs or sharp edges at the gate well
Solutions
1. Polish the gate well area to eliminate rough surfaces and sharp edges. 2. Change gate type.
Cause : Hot Runner System
Solutions
1. Check for foreign material or material traps in gate well. 2. Check for wear on the end of the tip. Replace tip if worn. 3. Check tip height is correct when in the hot position, and not blocking or too far from gate. 4. Check material melt and processing temps against manufacturers recommendations. 5. If valve gate is used check the pin is adjusted for full opening.
Cracking and Crazing Finish on Part
Cause : Material pellets are contaminated
Solutions
1. Replace with a new container of material. 2. Ensure granulator is clean. 3. Eliminate regrind as a possibility. 4. Remove colorant if being used.
Cause : Chemical contamination on mould
Solutions
1. Clean the mould. 2. Change the mould handling procedures.
Cause : Incorrect Moulding
Solutions
1. Reduce packing time or/and pressure. 2. Check for hot spots in mould possibly causing excessive shrinkage. 3. Ensure correct draft on mould. 4. Polish mould faces. 5. Remove any undercuts in mould.
Delaminating
Material pellets are contaminated
Solutions
1. Replace with a new container of material. 2. Ensure granulator is clean. 3. Eliminate regrind as a possibility. 4. Remove colorant if being used.
Degraded material
Solutions
1. Replace with a new container of material. 2. Replace regrind material.
Incompatible additives
Solutions
1. Run natural material to verify then change to a compatible concentrate.
Dimensional Inconsistency of Part
Cause : Material Variations
Solutions
1. Try a new bag of material. 2. Ensure same brand and grade of material is being used. 3. Ensure same additives are being used.
Cause : Melt Pressure
Solutions
1. Increase the melt fill pressure (and velocity of melt).
Cause : Machine Variations
Solutions
1. Ensure adequate melt fill pressure. 2. Ensure consistent pack and hold pressures. 3. Reduce delay between pack and hold pressures. 4. Ensure screw non return valve ring is working properly and not worn. 5. Check for wear on machine screw & barrel. 6. Check machine hydraulics are consistent.
Dimensional Variations
Cause : Part is too small
Solutions
1. Increase the packing pressure. 2. Increase pack time. 3. Ensure uniform cooling in cavity. 4. Ensure adequate ventingResize cavities.
Cause : Part is too large
Solutions
1. Reduce the packing pressure. 2. Reduce pack time. 3. Ensure that switchover from fill to pack occurs at less than 100% full. 4. Resize cavities.
Cause : Part is too small near gate
Solutions
1. Increase the packing pressure. 2. Increase pack time. 3. Ensure uniform cooling in cavity. 4. Increase the shot weight. 5. Increase melt cushion in machine barrel. 6. Ensure material temperature is within manufacturers recommended specifications.
Cause : Part is too small at end of fill
Solutions
1. Ensure fill time is consistent. 2. Incorrect material grade. 3. Increase fill rate. 4. Ensure material temperature is within manufacturers recommended specifications. ns.
Cause : Part is too large at end of fill
Solutions
1. Ensure fill time is consistent. 2. Incorrect material grade. 3. Ensure that switchover from fill to pack occurs at less than 100% full. 4. Reduce fill rate. Ensure material temperature is within manufacturers recommended specifications.
Symptom : Flashing
Cause : Clamp Force
Solutions
1. Increase clamp pressure. 2. Ensure machine clamp is locking. 3. Use machine with adequate clamp tonnage. 4. Reduce packing pressure. Reduce hold pressure.
Cause : Mould Issues
Solutions
1. Clean mould. 2. Check mould for damage or wear. 3. Inspect all shut-off areas. 4. Insufficient venting.
Cause : Incorrect Moulding
Solutions
1. Ensure fill time is consistent. 2. Ensure pack and hold pressures are constant. 3. Increase fill time. 4. Decrease fill pressure.
Cause : Material
Solutions
1. Incorrect material grade. 2. Ensure material temperature is within manufacturers recommended specifications.
Cause : Deflection
Solutions
1. Check for deflection on platen. 2 Check for wear on tie bars and bushes. 3. Increase mould support strength. 4. Increase mould plate thickness/strength. 5. Increase support strength and clamping around hot runner cavity. 6. Change to different type of clamp system; toggle vs. hydraulic.
Gate Blush
Cause : Mould
Solutions
1. Change the gate location to a less important surface. 2. Increase the gate size. 3. Change the angle of the plastic entering the cavity. 4. Add a dimple opposite the gate.
Cause : Machine
Solutions
1. Lower the initial injection speed. 2. Lower the mould temperature at the gate.
Jetting
Cause : Mould Design
Solutions
Move the gate or change the angle of material entry so that the incoming material is directed on to a cavity wall. (e.g. a face perpendicular to the gate)
Poor Surface Finish on the part
Cause : Mould & machine settings
Solutions
1. Cavity pressure is not even. 2. Foreign build-up on the mould surface. 3. Increase the packing pressure and/or time. 4. Change the injection velocity.
Cause : Contamination in the material
Solutions
1. Change to 100% virgin material. 2. Purge machine on restart. 3. Ensure granulator is clean. 4. Ensure material dryer and conveyer systems are clean. 5. Check for water or oil leak into the material flow or cavity. 6. Reduce moisture in surrounding air. 7. Adjust temperature to reduce condensation on cavity surfaces.
Cause : Temperature
Solutions
1. Ensure uniform cooling in cavity. 2. Set melt temperatures in barrel and runner system to manufacturers recommendations. 3. Check all heater control thermocouples are operating correctly.
Streaking
Cause : Degraded Polymer
Solutions
1. Set melt temperature to manufacturer’s recommendations. 2. Reduce heating time of polymer. 3. Reduce residence time of polymer melt in barrel and hot runner. 4. Change to 100% virgin material. 5. Change to natural colour. 6. Purge machine on restart. 7. Reduce screw RPM. 8. Check actual barrel temperatures for over-riding. Ensure correct drying time (not over or under drying).
Cause : Temperature
Solutions
1. Set melt temperatures in barrel and runner system to manufacturers recommendations. 2. Check all heater control thermocouples are operating correctly.
Cause : Mould & Machine settings
Solutions
1. Increase backpressure. 2. Change barrel rear zone temperature to encourage polymer to stick to the wall of the barrel. 4. Slow screw speed to promote shear deeper in barrel. 5. Change screw. 6. Use a low-shear mixing nozzle that has minimal pressure loss. 7. Change the style of hot runner tip to discourage colour or additive separation.
Ripples or Waves on Part Faces
Cause : Material Viscosity
Solutions
1. Increase the fill rate to reduce material viscosity. 2. Verify that switchover occurs when the mould is less than 100% full.
Cause : Machine Setting
Solutions
1. Increase the packing rate. 2. Decrease the packing pressure and/or time. 3. Poor machine response when switching from filling to packing pressure, (allowing the polymer time to solidify).
Cause : Temperature
Solutions
1. Set melt temperatures in barrel and runner system to manufacturers recommendations 2. Change the mould temperature
Short Shot
Cause : Machine Setting
Solutions
1. Increase the packing pressure. 2. Increase pack time. 3. Increase the shot weight. 4. Reduce the fill time. 5. Increase melt cushion in machine barrel. 6. Ensure that switchover from fill to pack occurs at less than 100% full. 7. Ensure machine nozzle orifice and sprue are same diameter.
Cause : Temperature
Solutions
1. Ensure uniform cooling in cavity. 2. Ensure material temperature is within manufacturers recommended specifications.
Cause : Mould
Solutions
1. Ensure gate is not blocked. 2. Ensure minimal pressure drop of runner system and cavity.
Shrinkage
Cause : Machine setting
Solutions
1. Increase the packing pressure. 2. Increase pack time. 3. Increase the shot weight. 4. Improve the fill time. 5. Increase melt cushion in machine barrel. 6. Ensure that switchover from fill to pack occurs at less than 100% full.
Cause : Mould Settings
Solutions
1. Ensure the mould has sufficient cooling. 2. Increase turbulent coolant flow. 3. Ensure coolant lines are free of blockage. 4. Ensure material temperature is within manufacturers recommended specifications.
Sink Marks and Voids
Solutions
Solutions
1. Remove thick wall sections. 2. Increase mould cooling. 3. Reduce pressure drop in mould and runner system. 4. Ensure adequate venting. 5. Ensure vents are not blocked. Ensure correct mould clamping.
Cause : Machine
Solutions
1. Check for wear on screw non return valve. 2. Check for wear on screw and barrel. 3. Increase fill pressure and time. 4. Increase pack pressure and time. 5. Increase the shot weight. 6. Increase melt cushion in machine barrel. 7. Ensure that switchover from fill to pack occurs at less than 100% full.
Cause : Material
Solutions
1. Change to easier filling material. 2. Check for contamination and replace if necessary. 3. Add a filler to the material. Use a foaming agent in the material.
Splay
Cause : Contaminated Material Solutions
Solutions
1. Ensure material is properly dry. 2. Ensure dryer performance is adequate and dryer is operating correctly. 3. Ensure correct drying time to material manufacturers recommendations. 4. Ensure the environment is within the dryers specifications (e.g. dew point, humidity, etc.). 5. Reduce the time between material drying and entering the machine barrel. 6. Ensure dried material does not sit in hopper for too long. 7. Radius sharp corners and edges to reduce shear. 8. Change to 100% virgin material. 9. Purge machine on restart. 10. Ensure granulator is clean. 11. Ensure material dryer and conveyer systems are clean. 12. Check for water or oil leak into the material flow or cavity. 13. Reduce moisture in surrounding air. 14. Adjust temperature to reduce condensation on cavity surfaces. 15. Set melt temperature to manufacturer’s recommendations.
Cause : Machine Settings
Solutions
1. Reduce or remove screw decompression. 2. Increase screw backpressure. 3. Ensure adequate heat is added into the polymer before barrel compression zone. 4. Check for wear on screw non return valve. 5. Check for wear on screw and barrel. 6. Check screw and barrel and non return valve to reduce shear in material.
Sticking in cavities or on cores
Cause : Machine Settings
Solutions
1. Adjust fill pressure and time. 2. Adjust pack and hold pressure and time. 3. Ensure that switchover from fill to pack occurs at less than 100% full.
Cause : Material
Solutions
1. Set melt temperature to manufacturer’s recommendations.
Cause : Mould
Solutions
1. Polish cavities and cores. 2. Ensure direction of polish is in the direction of ejection. 3. Remove burrs, sharp edges, undercuts, marks and dents from mould surfaces. 4. Add extra ejectors or air blast.
Warp
Cause : Mould & part cooling
Solutions
1. Ensure uniform cooling in the cavity and core. 2. Ensure adequate cooling is applied to the mould. 3. Ensure part wall sections are uniform thickness.
Cause : Temperature
Solutions
1. Set melt temperatures in barrel and runner system to manufacturers recommendations. 2. Check all heater control thermocouples are operating correctly.
Cause : Machine setting
Solutions
1. Ensure that switchover from fill to pack occurs at less than 100% full. 2. Increase pack pressure and time. 3. Increase fill pressure and time.
Weld lines
Cause : Mould
Solutions
1. Move gate position to remove or improve where molten material flows meet during injection. 2. Radius all corners and sharp edges to improve material flow. 3. Increase part wall thickness to improve material flow.
Cause : Machine setting
Solutions
1. Increase fill pressure and or time. 2. Increase pack and hold pressure and or time.
Cause : Degraded Material
Solutions
1. Set melt temperature to manufacturer’s recommendations. 2. Reduce heating time of polymer. 3. Reduce residence time of polymer melt in barrel and hot runner. 4. Change to 100% virgin material. 5. Change to natural colour. 6. Purge machine on restart. 7. Reduce screw RPM. Check actual barrel temperatures for over-riding. 8. Ensure correct drying time (not over or under drying).
Gate Drooling
Cause : Degraded polymer
Solutions
1. Set melt temperature to manufacturer’s recommendations. 2. Reduce heating time of polymer. 3. Reduce residence time of polymer melt in barrel and hot runner. 4. Change to 100% virgin material. 5. Purge machine on restart. 6. Reduce screw RPM. 7. Check actual barrel temperatures for over-riding. 8. Ensure correct drying time (not over or under drying).
Cause : Temperature
Solutions
1. Set melt temperatures in barrel and runner system to manufacturers recommendations. 2. Check all heater control thermocouples are operating correctly. 3. Increase cooling at the gate area. 4. Increase the amount of cooling in the mould plates.
Cause : Mould & machine settings
Solutions
1. Reduce the diameter of the gate. 2. Reduce the backpressure on the machine. 3. Use screw decompression. 4. Insulate the hot runner system from the mould to reduce heat transfer to the mould plates.
Gate Freeze Off
Cause : Degraded polymer
Solutions
1. Decrease the amount of cooling at the gate. 2. Increase the nozzle temperatures within the material manufacturers recommendations. 3. Check all heater control thermocouples are operating correctly. 4. Improper heat control of nozzle.
Cause : Temperature
Solutions
1. Increase the gate diameter slightly. 2. Insulate the hot runner nozzle from the mould to reduce heat loss from the nozzle.
Stringing or Tails on the Part
Cause : Temperature
Solutions
1. Reduce the hot runner melt temperature. 2. Check all heater control thermocouples are operating correctly. 3. Increase cooling at the gate area. 4. Increase the amount of cooling in the mould plates.
Cause : Mould & machine settings
Solutions
1. Check the condition of the hot nozzle tips, replace if necessary. 2. Reduce the diameter of the gate. 3. Reduce the backpressure on the machine. 4. Use screw decompressionInsulate hot nozzle from mould plates.
Cause : Not enough contact between nut and mould to dissipate heat
Solutions
1. Use bush nut or sprue nut with increased contact area to dissipate heat from nut.
Premature wear of Torpedo Tip (mult- hole or single-hole)
Cause : Tip is too far forward in nozzle cavity resulting in higher friction in gate area
Solutions
1. Check the nozzle cavity dimensions and correct them so they match approval drawings.
Increased nozzle operating temperature
Cause : Nozzle is too far forward cavity
Solutions
1. Correct the nozzle cavity so the dimensions match the approval drawings.
Cylinders do not work
Cause : Mould & Machine settings
Solutions
1. Check lines, fitting pipes, and pump for leaks and blockages. 2. Inspect cylinders for too many bends in feed pipes, restrictive fittings or valves. Replace if necessary.
Seized Cylinders
Cause : Mould & Machine settings
Solutions
1. Check alignment of cylinder, manifold and nozzle is correct. 2. Supply more cooling around cylinder.
Cylinders jam when hot
Cause : Mould & Machine settings
Solutions
1. Check alignment of cylinder, manifold and nozzle is correct. 2. Supply more cooling around cylinder. 3. Re-align spacers to prevent spacers rubbing on shut off pin retainer.
Melt leaks from around valve pin seal
Cause : Valve pin seal too loose in manifold
Solutions
1. Check diameters of bush and manifold hole. 2. Check height of seal and manifold hole.
Melt leaks between seal and pin
Cause : Machine & Mould
Solutions
1. Check alignments of system. 2. Replace pin and seal as a unit. 3. Check melt MFI. 4. Reduce fill pressure.
Melt sticks to front of pin
Cause : Too much heat in pin
Solutions
1. Reduce nozzle and gate temperature. 2. Increase cooling time.
Pin does not shut off or bush nut is damaged
Cause : Incorrect nozzle expansion calculation
Solutions
1. Adjust pin position with pin retainer and half nut.
Manifold will not reach temperature
Cause : Temperature
Solution
1. Check thermocouple is tight and functions correctly. 2. Check heater circuit.
Manifold is slow to reach temperature
Cause : Temperature
Solutions
1. Check both heaters to ensure one heater has not shorted or wiring is not loose 2. Increase air gap to 10 mm minimum or use insulation board. Add insulation board to back plate or reduce coolant flow to back plate. 3. Check the thermocouple.
Unstable manifold temperature
Cause : Temperature
Solutions
1. Check thermocouple is not loose.
Manifold leaks from nozzle faces
Cause : Manifold, Mould and Nozzle
Solutions
1. Recheck temperature expansion calculations and correct. 2. Check and correct the machining of manifold heights. 3. Change back plate of back plate material is too soft 3. If the manifold run at avery high temperature for a short time; check for damage and replace damaged or crushed parts. 4. Replace any O-rings.
