Sr. No.	Problem / Trouble	Probable Cause/s	Remedy
1.	Non-uniform thickness	- Die-gap is unevens - Die temperatures not In balance - Material changing through die	- Adjust the die gap with the die lips - Balance the die temperatures. - Restrict flow at material before it reaches die lips. Install screen pack to increase back pressure.
2.	Poor mechanical properties	- The most important factor affecting the physical properties of sheet is : Extruder output	- All the variables have to be balanced to produce sheet with good physical properties and uniform gauge at an economical speed
3.	Die lines	- Plate-out built-up - Scratches on die lips	- Remove and clean die determine nature of plate-out, review polymer recipe with resin supplier, extruder - Polish lips
4.	Surging in extruder	- Uneven melt conditions in extruder - Erratic polymer feed	- Raise heat in front zones of extruder Check feed throut for Bridging - Make certain hopper level is constant
5.	Orange peel surface	- Surface viscosity in die too high	- Raise die temp. Raise heat in last zone of extruder
6.	Dark specks and streaks	- Polymer Degrading - Contaminants in melt	- Lower melt temp. Reduce screw speed Modify screw to decrease flight clearance Modify screw to decrease compression ratio - Clean die lips Pull screw and examine for pitted chrome Check die design and streamline if necessary Clean hopper and securely cover Pull screw and examine screw shank for oily or carbonaceous buildup If using regrind, examine regrind for contamination Examine virgin polymer pellets for back speck contamination
7.	Lines in machine direction	- Damage or corruption on die lips - Surface scratches on polishing roll. - Polymer hang-up between die lip and die body	- Disassemble die and clean thoroughly; examine with 30X loupe for corrosion Take scrapings of buil-up, chemically analyse and determine if build-up is from polymer - Clean and optically examine polishing rolls. Resurface if necessary - Check mating surfaces for misalignment, damaged areas Check die design and streamline if necessary
8.	Curved lines in crossmachine direction	- Melt bank too larg - Melt folding	- Reduce melt bank to pencil-thick diameter - Check extruder output to determine if surging is occurring. If so, add melt pump
9.	Gels in sheet	- Melt has cold spots - Polymer crosslinking	- Increase heat in last zone of extruder Increase die temperature - Reduce heat infirst zone of extruder Reduce screw speed to minimize shear heating Reduce regrind level Examine regrind for contamination Increase antioxidant package in polymer
10.	Dull spots on sheet surface	- Sheet picking plate-out off chill roll - Nonuniform cooling in chill roll - Sheet intermittenly lifting from chill roll	- Increase first chill roll temperature Discuss alternate adduct packages with resin supplier - Clean flow channels is chill roll - Use air knife to hold hot sheet against first chill roll
11.	Brittle sheet	- Certain polymers are too wet	- Throughly dry polymer hroughly dry regrind
12.	Hazy sheet	- Polymer crystallizing typical of PET, PP - Adduct package wrong - Microscopic bubbles inside sheet	- Throughly dry polymer Increase melt temperature Reduce first chill roll temperature Reduce melt bank Increase extrusion rate - Review adduct package with polymer supplier Increase or decrease melt temperature to determine general effect Increase or decrease first chill roll temperature to determine general effect - Polymer wet; throughly dry polymer Polymer degrading ; lower melt temperature, reduce residence time Adduct decomposition ; review aduct package with polymer supplier
13.	Internal holes in sheet	- Moisture - Air - Degrading polymer - Decomposing adducts	- Dry polymer Dry regrind Seal hopper or use inert gas layer - Increase heat in first zones of ext. Decrease heat in last zones of extruder Increase back pressure on melt pump - Decrease screw speed Decrease temperature profile throughout extruder Decrease back pressure on melt pump Reduce regrind concentration - Review adduct package with resin supplier
14.	Melt freeze off	- Melt temperature too low - Screen too cold	- Increase die temperature Increase heat in last zone for extruder - Check for burned-out heater bands Intermittent when screens are changed ; preheat screens
15.	Surface roughness in sheet	- Contamination - Unmelted pellets - Moisture Trapper air - Unpolished low spots - Insufficient roll stack polish	- Check incoming virgin resin for contamination Check regrind for contamination - Increase heats on first zones of extruder Decrease extruder throughput rate Increase gear pump back pressure Change screw to higher compression ratio screw Switch to barrier screw - Dry polymer throughly Move extruder die closer to chill roll Use air knife to hold sheet against chill roll Lay sheet on roll at 300º to 330º angle Increase melt bank diameter slightly Check vertical alignment of chill roll and die - Increase melt bank diameter Adjust vertical alignment of chill roll and die Adjust die lips to increase flow in low spots - Increase roll stack temperature Decrease roll gap Increase bottom roll speed slightly

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