troubleshooting tips to cure your sheet extrusion headaches.

Did the sheet problem disappoint you?
Here are some remedies for the extrusion experts at Dow Jones plastics technology services and development that will help you get back into operation --
Whether you\'re squeezing out a single-layer product or a coex product.
General extrusion problems and trouble-shooting information for some specific applications such as film have been widely provided, but unfortunately this is not the case for sheet extrusion.
At Dow Plastics\'s technical services department, we recently started filling this gap by compiling some of the knowledge we have gained from our paper line experience.
The resulting trouble shooting guidelines provide solutions to common problems that affect the manufacture of single and co-extruded sheets.
Any guide of this type must be summarized to some extent to accommodate the various extrusion devices that can be used for paper.
For example, a roll stack can have three, four, or five rolls, and the mold can be a single-
Tube or tube.
Some of the solutions we recommend may be more suitable for certain device configurations than others, but regardless of the device type, the general principles behind each proposal should be established.
The broad nature of the proposed solution also reflects the complexity of many extrusion problems --i. e.
, More than one corrective action is usually required to solve a given problem.
With this in mind, the information in this guide first introduces the most common causes and solutions, but be aware that a combination of some actions may be necessary in order to get rid of certain diseases.
If all the others fail, you may have to consider changing the design of the device.
Our experience has shown that the design of screws, molds, and roller stacks can have a significant impact on most of the issues listed in this guide.
But before you consider replacing any device, the guidelines below show that there are a lot of possible remedies to try first.
Air retention may lead to problems with single-layer and co-extruded plates, marks, pits or dimples: 1.
Reduce the temperature in the first and second barrel areas. 2.
Reduce screw speed. 3.
Remove the fine from the re-grind. 4.
If double plug is used, unplug the ventstage screw. 5.
If single-stage screw. 6.
Check if the vacuum system is operating properly. 7.
Keep the level of the Hopper unchanged.
It may be caused by water: 1.
Increase the drying temperature. 2.
Increase drying time. 3.
Check the dryer operation for proper dew point and desiccant regeneration. 4.
If double plug is used, unplug the ventstage screw. 5.
Check if the vacuum system is operating properly. 6.
Use a dry hopper. 7.
Use a nitrogen blanket on the Hopper.
It may be caused by volatile substances: 1.
Cool the melt to minimize degradation. 2.
If double plug is used, unplug the ventstage screw. 3.
Check if the vacuum system is operating properly.
It may be caused by the retention of volatile substances between flakes and coils: 1.
Increase ventilation. 2.
Adjust the dead lip in the area corresponding to trapping. 3.
Use a jet to blow out volatile substances from the nip area. 4. Adjust die-
The roll is high to minimize the coverage of the paper on the roll. 5.
Reduce the melting temperature. 6.
If double plug is used, unplug the ventstage screw. 7.
Check if the vacuum system is operating properly. 8.
Check the hot spots on the mold.
It may be caused by insufficient melting Library at the clip: 1.
Reduce the rolling speed of establishing banks. 2. Decrease roll-
The gap of Construction Bank. 3.
Adjust the die limit bar and/or die lip to optimize the flow uniformity of the die. 4.
Optimize mold temperature to improve mold flow. 5.
Increase the extrusion rate to fill the bank. 6.
Move the mold close to the roll clip. 7.
Check if there is any fluctuation in the extruder.
It may be caused by the lack of clean equipment: 1. Clean chill-
Rolling polishing-roll surfaces. 2.
Clean the rollers in the conveyor. 3.
Eliminate static electricity and minimize dust pickupup.
It may be caused by the excessive cooling speed: 1.
Increase the temperature of the roller when in contact with the problem surface.
The line in the direction of the machine may be caused by mold defects: 1. Clean die-
Lip area with soft tool-
Preferably wood or copper. 2.
Remove and clean the mold. 3. Polish or re-
Flat die surface. 4.
Polished damaged mold-lip face. 5.
Refinish mold lip to 90 [degrees]angle.
It may be caused by water: 1.
Please see the solution to the moisture problem in the section above about Pock marks, pits or dimples.
It may be caused by equipment damage: 1. Polish or re-
The plate damaged the cold ice roll. 2.
Check the wear. (
See the wear solution in the section below. )
It may be caused by unstable bank size: 1.
Adjust the roller temperature. 2. Adjust die-to-nip distance. 3.
Check if there is any fluctuation in the extruder.
The horizontal line may be caused by the paper sticking to the roller (s): 1.
Reduce the roller temperature. 2.
Reduce the melting temperature. 3.
Close the mold to the roll to prevent the paper from sagging before the roll. 4. Clean the roll.
Could be caused by rolling.
Driving Problem: 1. Reduce pull-
Avoid \"pulling\" the paper on the cold roller. 2.
Increase the tension to ensure that the paper does not fall off the bottom roller. 3.
Adjust the rolling drive chain.
It may be caused by the winding machine\'s excessive power supply to the pull roller: 1.
Reduce tension of winding machine. 2. Increase pull-roll-nip pressure.
It may be caused by changes in equipment: 1.
By isolating the power supply for each drive, check and eliminate the voltage change for the entire line. 2.
Check and suppress the vibration of all equipment. (
First, isolate the volume-
Stack to see if there is a fault. )
It could be caused by paper cutting. off: 1.
Install the \"hump\" section in the conveyor between the pull roller and the shear.
It may be caused by a rolling Bank at nip roll: 1.
Reduce the size of the bank by increasing the polishing
Roll speed, reduced extrusion speed and/or open rollers-nip gap.
Improper operation of the extruder may lead to a change in the thickness of the machine direction: 1.
Check if there is any fluctuation in the extruder.
It may be caused by rolling banks: 1.
Reduce the size of the bank by increasing the polishing
Roll speed, reduced extrusion speed and/or open rollers-nip gap.
It may be caused by the problem of the volume: 1.
Wash the roll clean2.
Check the rolling bearing for wear. 3.
Check the concentricity of the roller. 4. Check roll-nip pressure (\"pli\")
Make sure there is enough pressure to keep the roll seam constant.
Probably the surface reason.
Temperature change of roller surface :(Tip: Cooling-
[Fluid temperature change should not exceed 2]degrees]
F from entrance to exit. )1.
Increase the recycling rate of roller coolant. 2.
Reduce extruder output
It may be caused by excessive winding of the winding machine: 1.
Adjust the tension of the winding machine. 2.
Increase the press pressure on the pull roller.
Could be caused by rolling.
Drive Change: 1.
Adjust the roller drive.
The horizontal thickness change may be caused by the mold adjustment: 1. Adjust die-lip gap. (
Tip: the typical start-up gap is 110-
120% of the required plate thickness. )2.
Adjust the press bar to keep all bolts tight. 3.
Cold Dead thick area;
Hot in thin areas. (
The effect of this action is limited. )
It may be caused by roller adjustment: 1.
Adjust the roll seam to the appropriate settings. (
Tip: The typical first gap is about 1-
2% more than the required plate thickness.
The typical second gap is the same or slightly smaller thickness as the required plate. )2.
Balance and/or increase pressure to better distribute inconsistent mold flows. 3.
Reduce roller pressure and minimize roller bending. 4.
Check the rolling bearing for wear.
May be by nonUnified Bank: 1.
Adjust the die limit bar and/or die lip to optimize the flow uniformity of the die. 2.
Adjust the mold temperature to optimize the flow uniformity of the mold. (
The effect of this action is limited. )3.
Check if there is any fluctuation in the extruder.
The horizontal coil may be caused by improper roller temperature: 1.
Increase the temperature on the surface of the concave sheet. (
Tip: If the edges of the paper curl down and \"curl down\" occurs, increase the temperature of the intermediate roller.
Reduce the intermediate roller temperature if the edge of the paper is curled.
In both cases, change the third suggestion when the curling is \"superimposed up\"
Roller temperature opposite the middle
Change of roller temperature.
The Crystal effect may change these suggestions. )
Paper curled in the direction of the machine may be caused by excessive tension. Roll: 1. Reduce pull-roll tension. 2. Reduce pull-roll speed.
Improper processing conditions or equipment may cause low gloss: 1.
Increase the melting temperature by increasing the temperature in the last two barrel zones. 2.
Raise the mold temperature to equal to the melting temperature. 3.
Increase the roller temperature. 4.
Adjust the mold to get even flow. 5.
Adjust the roll seam to maintain good contact with the paper. 6. Increase roll-nip pressure. 7.
Add an upper light device between the mold and the roller.
It may be caused by poor melting consistency: 1.
Increase head pressure to improve mixing. 2.
Use a static mixer in the transmission line.
Inconsistent specifications may lead to inconsistent or incomplete gloss: 1.
Adjust the mold lip. 2.
Adjust the limit bar. 3.
Check if there is any fluctuation in the extruder.
It may be caused by excessive melting temperature: 1.
Reduce the temperature in the last or two barrel areas. 2.
Reduce mold temperature. 3. Change screen-Change the screen.
May be by non
Uniform roller temperature: 1. Check [Delta]
Roll Face T. (
Tip: coolant should have 【Delta]T of 2 [degrees]
F or less from roller inlet to outlet. )2.
Check the hot spots around the roller and clean the flow.
It may be caused by volatile interception between paper rolls: 1.
Increase ventilation. 2.
Adjust the dead lip in the area corresponding to trapping. 3.
Use jet to blow out volatile substances from the rollnip area. 4. Adjust die-
The roll is high to minimize the coverage of the paper on the roll. 5.
Reduce the melting temperature. 6.
If double plug is used, unplug the ventstage screw. 7.
Check if the vacuum system is operating properly. 8.
Check the hot spots on the mold.
Rolling bank may cause rough surface of plate: 1.
Reduce the size of the bank by increasing the polishing
Roll speed, reduce extrusion speed and/or turn on the roll-nip gap.
It may be caused by material problems: 1.
Remove any incompatible re-grinding. 2.
Increase mixing in extruder by valve or finer screenChange the screen. 3.
Use a static mixer. 4.
Make sure the previous material has been completely removed. (
Tip: proper cleaning of all melting channels
Screw, barrel screen packaging, conveyor line and mold-
And solid-
Handling Equipment-pneumatic-
Conveyor system, dryer and grinder. )5.
Eliminate moisture. (
Please see the solution to the moisture problem in the section above about Pock marks, pits or dimples. )
Could be caused by scrolling settings
Up conditions: 1.
Raise the roller temperature to slow setting. 2.
Reduce the roll seam to the polishing sheet. 3. Increase roll-
\"Push out\" The pressure roughness. 4.
Clean rolling surface. 5. Re-
Roll with damaged surface.
The excessive or inconsistent Roller speed may lead to plate orientation relative to the mold pass rate: 1. Reduce chill-roll speed. 2.
Increase extrusion rate. 3.
Reduce mold clearance.
It may be caused by the large size of the bank: 1. Increase chill-roll speed. 2.
Reduce extrusion rate.
It may be caused by incorrect distance of mold/clamping point: 1. Reduce die-
The minimum set nip distance. 2.
Align the mold face with the center line of the roller.
Probably due to excessive pulling. Roll: 1. Decrease pull-roll speed. 2. Increase chill-roll speed.
It may be caused by incorrect cooling rate of polymer: 1.
If the melting temperature is too low, Please increase the temperature of the last bucket or two and/or increase the mold temperature. 2.
If the difference between the melting temperature and the roller temperature is too wide, increase the roller temperature and/or reduce the melting temperature.
The brittle of the plate may be caused by excessive orientation: 1.
See the solution to the orientation problem above. 2.
Adjust the roll seam to the appropriate settings. (
Tip: The typical first gap is about 1-
More than 2% of the required plate thickness.
The typical second gap is the same or slightly smaller thickness as the required plate. )
It may be caused by cold rolls: 1.
Increase the roller temperature.
It may be caused by poor melting consistency: 1.
Increase head pressure to facilitate better mixing. 2.
Use a static mixer in the transmission line. 3.
Reduce rework levels. 4.
Reduce additive content
For example, concentrate the color.
Too high temperature or too long residence time may cause discoloration of paper: 1.
Check if the heater and thermocouple are working properly. 2.
Reduce the last bucket or two
Reduce mold temperature and/or reduce mold temperature. 3.
Reduce head pressure by replacing a clean or thicker screen and/or opening the available valves, tight bars and/or die lip. 4.
Clean the rear of deckle regularly.
Remove deckles if it fails. 5.
Simplify the flow path by using a smooth transition and/or elbow with a longer bending radius. 6.
Check the loss of plating or other corrosion.
It may be caused by insufficient color concentrate or concentrate segregation in the feed hopper: 1.
Raise the concentrated color to the specified level. 2.
Add color essence to the feeding port. 3.
Redesign the hopper for mass flow, not funnel flow.
Paper pollution may be caused by equipment problems: 1.
View the solution for discolored paper. 2.
Check if the screen is broken. 3.
Check for plating loss that may result in black spots.
It may be caused by material problems: 1.
Check to see if there is dirt, packaging waste, gel, etc. 2.
Check if there is any pollution in the re-grinding flow. 3.
Check airvey system and Hopper-
Loading procedures for possible pollution sources. 4.
Remove excess powder from resin.
The pollution on the paper may be caused by static electricity: 1.
Dissipate static electricity on paper. 2.
Improve the cleanliness around the production line.
It may be caused by equipment pollution: 1.
Clean the surface of the cold roller and the polished roller. 2.
Cleaning of Conveyor idler Wheel.
It may be caused by the degraded material falling on the paper: 1. Clean die lips. 2. Clean build-
Up from the surface around the mold.
Pollution may lead to poor transparency: 1.
Reduce rework levels. 2.
For solutions to pollution, see the section above.
It may be caused by poor equipment maintenance: 1.
Surface of polishing roller. 2.
Cleaning screws and downstream equipment. 3.
For a solution to wear, see the section below.
It may be caused by improper temperature: 1.
While maintaining the appropriate level of crystal, adjust the roller temperature to obtain the appropriate cooling rate. 2.
Ensure the resin is completely melted by increasing the temperature of the last or two barrel zones and/or by increasing the mold temperature.
It may be caused by poor mixing: 1.
Increase head pressure. 2.
Use a static mixer in the transmission line.
It may be caused by rolling banks: 1.
Reduce bank size by increasing polishing
Roll speed, reduce the extrusion speed, or open the roll-nip gap.
Damaged or dirty pieces can cause wear-
Handling Equipment: 1.
Clean roller. 2.
Remove burrs or rough spots on idler rollers. 3.
Non-coated rollersstick surface. 4.
Clean roll. 5.
Replace or repair the damaged pull roller. 6.
Looking for shear damage-feed and out-
Provide area and repair as required. 7.
Insert slide when cutting-
Feed and discharge.
The only problem with the Coex sheet shape instability may be caused by excessive shear stress at the interface of the mold: 1.
Increase the relative thickness of the skin layer. 2. Increase die-lip opening. 3.
Reduce total throughput. 4.
Reduce the viscosity of the skin layer by increasing the temperature of the skin layer or using a resin with a higher MFR. 5. Raise die-
Lip temperature.
Under a given set of process conditions, wave instability may be caused by a mismatch in the flow properties of different layers: 1.
Make the structure more symmetrical. 2. Increase skin-
By switching to lower layer viscosity
MFR resin or reduce the melting temperature of the skin layer. 3. Decrease core-
By changing to a higher layer viscosity
MFR resin or by increasing the melting temperature of the core layer. 4.
Different mold designs are used.
For example, a multi-manifold mold is often helpful. 5.
The correct speed in the feed does not matchblock.
The thickness of the horizontal uneven layer may be caused by non-
Uniform melting temperature: 1.
Set up mold, feed block and transfer-
Line temperature close to melting temperature. 2.
Use a static mixer or add a mixing part to the screw. 3.
Reduce screw speed. 4.
Increase head pressure to improve mixing.
It may be caused by the interaction of flow/equipment: 1. Optimize skin-
By changing the melting temperature in the extruder, mold and feed block to layered the flow. 2. Optimize core-
By changing the melting temperature in the extruder, mold and feed block to layered the flow. 3.
Modify the slot shape or flow configuration of the feedblock. 4.
Modify mold design
Multi-manifold molds can help.
May be caused by improper equipment settings-
On or operation: 1.
Check if the temperature is operating properly-
Control System 2.
Retract the limit bar of the mold to minimize the flow interruption. 3.
Remove the remaining traffic limit-
Such as sharp corners, melting thermocouple, etc. 4. Clean build-
From equipment.
Uneven layer thickness in the direction of the machine may be caused by improper extrusion operation: 1.
Check if there is any fluctuation in the extruder. 2.
Reduce the size of the rolling bank at the cold roller. 3.
Check if the pull roller of the rolling stack is working properly. (See roll-
Promote the resolution of the above-mentioned horizontal lines. )(Note: Zig-
Zag and wave instability will give the machine
Leave in direction thickness. )
Too thick brittle layer may lead to insufficient toughness of the plate: 1.
Reduce the thickness of the brittle layer. 2.
Raise the horizontal plate
Thickness uniformity, especially at the edge of the plate. (
See the solution for horizontal uneven layer thickness. )3.
Use a tougher polymer instead.
It may be caused by excessive grinding level: 1.
Reduce rework levels. 2.
Restore toughness using additives.
Probably due to orientation: Please see the solution to the orientation problem above. Non-
Uniform paper color may be caused by a change in the skin
Layer thickness: 1.
Increase the thickness of the skin layer. (
See solution below
Thin layer problem. )2.
Eliminate fine spots on the skin layer. (
For the problem of uneven skin layer thickness, see the above solution. )
It may be caused by poor mixing of re-grinding: 1.
Use a static mixer. 2.
Increase head pressure. 3.
Re-grind by adding a capacity booster. (
See also the solution for the rough paper surface above and the discolored paper. )
The degradation of Layer 1 may be caused by thermal decomposition: 1.
Reduce the temperature of the extruder barrel end and downstream equipment. 2.
Reduce head pressure to improve screw efficiency by cleaning the screen, using a thicker mesh, opening the mold lip and/or shortening the conveyor line. 3.
Check dead corners and streamlined flow channels by using a scan elbow and/or removing the melt
Immersion thermocouple. 4.
Reduce contact with thermal equipment.
Package heat, for example-
Sensitive Polymer of another polymer. 5.
Arrange sheets for heating
On May 1, the sensitive layer cooled on the cold roller due to chemical reaction: 1.
Remove troublesome additives
Such as color or re-grinding
Feed from extruder. 2.
Stable ingredients using additives. 3.
Check the compatibility between all materials in the coex structure.
The layer is too thin.
Drawing Block: 1.
Increase the output of the feed layer extruder. 2.
If it is not possible to increase the output of the extruder, please slow down the speed of the other extruder.
The layer is too thick, probably because it is too thick.
Drawing Block: 1.
Reduce the extruder output of the feed layer. 2.
If it is not possible to reduce the output of the extruder, Please speed up the other extruder.
The paper curling edge may be caused by uneven cooling of the layer on one side of the paper: 1. Set roll-
Stack the temperature to minimize the curl. 2.
Adjust the melting temperature of a single layer. 3. Adjust layer-
Uniform thickness. (
See the above solution for uneven layer thickness and non-uniform layer thickness
Uniform paper color. )
It may be caused by adhesive problems: 1.
Use separate resin layers for adhesives or other types of adhesives. A lower-
Adhesive adhesive, for example, promotes better moisture. 2.
Add adhesiveLayer thickness. 3.
Use adhesive with higher tensile strength. 4.
Increase melting contact time. 5.
Increase the melting temperature of the adhesive.
It may be caused by improper operation of the equipment: 1. Set chill-
Rolling speed matching with polymer moldexit speed.
Joseph Bauer, from Midland Dow Plastics, Michigan.
It\'s a technology-
Professional service engineer engaged in applied manufacturing technology.
The trouble-shooting information of this article is also provided by his technical colleagues.
Service engineers including John Hegan, Joe Dolly, Bill Kirk, Todd Hogan, Phil Wagner, and Bob Wisley.