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| Author | Topic: extrusion problem |
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luizamal Senior Member Posts: 5 |
posted February 21, 2005 05:35 PM
   
i have a problem with extrusion line (is a new Line) for pp rafia grade, we can not controll de thickness of the sheet, it changes continuosly when go out to the die head , we checked all the items that the factory told us but we didnt find any thing, we have 5 extrusion lines more (old lines and we dont have any problema, can some body to help us? IP: Logged |
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Tom C Moderator Posts: 630 |
posted February 21, 2005 06:25 PM
Luiz, Please provide more information on the screw design and process conditions. Specifically describe the behavior of the motor amps while the extruder is running. ------------------
Tom Cunningham
Extrusion Technical Services www.ExtrusionTechnicalServices.com IP: Logged |
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luizamal Senior Member Posts: 5 |
posted February 22, 2005 09:11 AM
quote: IP: Logged |
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Steve H Moderator Posts: 374 |
posted February 22, 2005 01:28 PM
Luiz, some info on your settings for the barrel temps, and what you are getting in the way of melt pressure and temp would also be helpful. And welcome to the single screw forum too ------------------ If at first you don't succeed, skydiving is not for you. IP: Logged |
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michman Member Posts: 3 |
posted August 16, 2005 04:46 PM
it sounds to me like a hydrolic problem; this is allowing the embossing roll to float. quote: IP: Logged |
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pyth Member Posts: 2 |
posted October 29, 2005 10:37 AM
observe the main motor if its running fast or slow, it depends on the pressure read in the gear pump that was feeding the die with plastic materials..i mean there are two possibilities here..either the temperature parameters isnt right or clogging in the main hopper entrance feeding the screw..inputted materials will affect the transducer in the gear pump.. IP: Logged |
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lotte Member Posts: 2 |
posted November 01, 2005 07:48 AM
Hi Luiz, What does rafia stand for? Is the thickness problem across the web or do you get thickness variation in extrusion direction? Kind regards, IP: Logged |
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luizamal Senior Member Posts: 5 |
posted November 01, 2005 11:48 AM
quote: IP: Logged |
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luizamal Senior Member Posts: 5 |
posted November 01, 2005 11:59 AM
thanks, I have the thickness variation in the extrusion direction. I reviewed the feed hold and did not find any problem , but the machine does not have polymer pump, however we have more equipment with out this device and dont have any trouble regards IP: Logged |
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Tom C Moderator Posts: 630 |
posted November 01, 2005 08:13 PM
On new lines take up equipment motors and extrusder motors have tuning parameters to help keep the RPMs steady. The tuning of these motors should be checked first to make sure they maintain steady RPMs. Once that is checked, see if the extruder produces a relativily steady head pressure. If the head pressure is steady, polymer flow out of the die should be steady unless it is coming out too fast. In the case of coming out too fast melt fracture can occur and the will result in very fast thickness changes over very short distance. There are cures for this problem. If the die head pressure is not steady, look for the duration of the pressure cycles and report back here, where we may be able to help you further. Good Luck, ------------------
Tom Cunningham
Extrusion Technical Services www.ExtrusionTechnicalServices.com IP: Logged |
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luizamal Senior Member Posts: 5 |
posted November 02, 2005 12:39 PM
Dear Tom Thanks in advance for your help. the machine doesnt have pressure transducer but I have a new one in the store, where do you think we must place it?, before or after exchange filter.? Thanks luis IP: Logged |
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Tom C Moderator Posts: 630 |
posted November 02, 2005 02:40 PM
Exchange filter? I would place it right after the screw and before the breker plate and any filter screens. ------------------
Tom Cunningham
Extrusion Technical Services www.ExtrusionTechnicalServices.com IP: Logged |
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ravi Senior Member Posts: 13 |
posted November 10, 2005 01:22 AM
If the variation is in across the machine direction check whether the heaters in the die are working as also the controls for these. Ensure as less process temperature variation as possible and change controls if necessary. processing at higher temperatures than necessary also creates flow problem. so, try reducing the processing temperatures with an eye on the main motor load. check for oxidation at die lip.This may take place due to the chemicals in the additives which may not be compatible or may not withstand the processing temperature.Change the additive if necessary and check. Ensure proper mixing of the additives. If it is loaded automatically by the hopper loader don't load too much of raw material in the lower hopper as the additives of higher density may settle down and create a variation the the mix. If the Die width is high the thickness of the sheet is to be set, once you reach the production speed as the flow may vary according to the throughput. (die design fault) Scrape the die lip before startup and ensure that they are cleared of any oxidized residue which may hinder the flow. Use the die lip gaurd during the shutdown to keep the exit flooded and avoid oxidation. If the thickness variation is in the linear direction (machine direction)the flow variation may be there from the extruder for any of the following reasons: variation in extruder Screw RPM, screw wear off, processing temperature variations due to control defects or frictional heat, inconsistent pulling by the godets due to improper contact of the rubber pressure rollers or variation in motor speed or jerking in the transmission, too much of turbulence in the quenching tank water which has to be reduced by providing proper baffles, water carriage in the film if high will also hinder the smooth flow on downstream due to friction and cause variation in line speed, etc... IP: Logged |
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lotte Member Posts: 2 |
posted November 10, 2005 08:31 AM
Hi Luis, Did you manage to install the pressure transducer? Regards, IP: Logged |
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