Troubleshooting guide for Sheet Extrusion Applications
Sheet Extrusion Troubleshooting
Problem
Probable Cause
Suggested Remedy
Temperature Setting
Temperature setting are crucial parameter for proper plastic processing ,hence one should check temperature controller, thermocouple and solid state relay(SSR)
- when you cold start the machine ,wait for 2hours.
Bubbles in sheet
- Material contains too much moisture
- Melt filter screen too coarse
- Increase drying time or increase drying temperature
- Use fine mesh screen backed up by a coarser screen on screen plate
Small dimples
Dirt adhering to calendar rolls
Clean calendar rolls with dry wipe cloths
Lines in the extrusion direction
- Die lines (if the lines are parallel to the sheet extrusion direction and are continuous)
- Moisture or volatile matter in material would give broken lines parallel to the sheet extrusion direction
- Remove one die lip and clean both die lips
- Pre-dry the material
Shiny spots all over the sheet
First roll is too hot
Reduce the temperature
Depression and pockets
- Cooling rolls too cold
- Air entrapment
- Adjust the roll temperature
- Slow down the screw, keep temperature at the hopper zone as low as possible, increase back pressure
Holes all over the surface
Pull-out rolls too hot
Reduce temperature of rolls
Distorted blisters
Die too hot
Reduce temperature of front section of die
Weld marks
Torpedo portion of the die too cold
Raise temperature of torpedo
Variation in sheet thickness
- Uneven die opening
- If sheet is thin at the edges-spreader bars not properly placed
- Adjust the die lip opening
- Adjust spreader bars
Slugs in sheet
- Die contamination
- Too much regrind material
- Damaged screen/filter pack
- Clean die
- Reduce or stop use of regrind material
- Replace the damaged screen
Low out-put
- Screw design not proper
- Screw speed too low
- Flow properties of material or M.I of material not selected properly
- Use the right type of screw
- Increase the screw speed
- Use material of higher M.I, use hopper dried material, determine the optimum temperature programmes, provide adequate screw cooling
