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| Author | Topic: carbon burst during shift |
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mark g Member Posts: 4 |
posted November 16, 2005 07:18 AM
  
i am a supervisor on a sheet extrusion line,during the shift we experience several burst of carbon can anybody tell me the cause of this.we operate a amut 130 mm twin srew we run clear pvc sheet ------------------ IP: Logged |
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ETS Test Member Posts: 4 |
posted November 16, 2005 12:27 PM
Check the paper on Gels on my site, on the downloads page. www.ExtrusionTechnicalServices.com Tom Cunningham [This message has been edited by ETS Test (edited November 16, 2005).] IP: Logged |
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mark g Member Posts: 4 |
posted November 17, 2005 10:39 AM
hello again,i not sure what i am looking for on your page,the extruder which i operate is only 1 year old.the problem with carbon burst as been there since the beginning.the material suppliers say its caused because of our vac chambers im not convinced ihave been in extrusion for 17 years now you never stop learning but i have experienced quit alot of problems.thanks for any help IP: Logged |
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Tom C Moderator Posts: 977 |
posted November 17, 2005 11:43 AM
Sorry, the link to the Gels paper is boken. I will post again when it is fixed. ------------------
Tom Cunningham
Extrusion Technical Services www.ExtrusionTechnicalServices.com IP: Logged |
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Tom C Moderator Posts: 977 |
posted November 17, 2005 11:46 AM
Is your machine a twin screw exruder? What type of twin screw, counter or co-rotating? What material are you running? Is your machine vented? Is it a vacuum vent? Is the vent located on top of the barrel, or on the side? ------------------
Tom Cunningham
Extrusion Technical Services www.ExtrusionTechnicalServices.com IP: Logged |
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mark g Member Posts: 4 |
posted November 18, 2005 06:07 AM
hello again,tha machine is amut 130 twin srew,the srews are togeather and rotate anti clockwise.the machine is vented at the top of the barrel,it has 4 holes the volatiles are sucked out by a wet vaccum sytstem.the material we use is 60/40 mix,60%virgin pvc and pulverized recycled.we make pvc clear sheet only.the problem with the vac theory for me is,why does it release the carbon all at once.if it is a built up at the vent which is being released would it not sometimes release a bit at time,it never does it comes out every few hours all at once.the carbon burst become more frequent when there are alot of water in the material i now this because when i release the lid of the vents to clean the chambers the gases are high.the pvc company says it keeps the mix the same! IP: Logged |
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Tom C Moderator Posts: 977 |
posted November 18, 2005 04:37 PM
Since the extruder is a fully intermeshed counter rotating type, the carbon is not likely coming from the screws, as they are self cleaning. The other potential sources are the feedstock, the vent, and the adaptor/die. I would; Run without regrind for a while to see if the regrind is the source. Pitch the vent piping down and away from the extruder so condenates can't run back into the extruder. Check under the vent diverter to see if there is any carbon buildup. Check the barrel after the screw, the adaptor, and the die for carbon desposits. Good luck. ------------------
Tom Cunningham
Extrusion Technical Services www.ExtrusionTechnicalServices.com IP: Logged |
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the plastic surgeon Senior Member Posts: 6 |
posted November 28, 2005 01:04 PM
i run clear pvc sheet as well, but on single screws. how wide / thick of sheet? are the black chunks coming out of the die in a particular part of the sheet more so than other parts of the sheet? what does the die and gate/adapter look like when you tear it down? how well chromed is your die? IP: Logged |
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stevet Senior Member Posts: 5 |
posted February 10, 2010 12:00 PM
Hi I have not heard it called carbon burst before and I assume you are seeing a smattering of carbon either specs or particles aprox 1-2mm in dia. normally called black spec or contamination If this is occurring regularly you either have hang up of material in the extruder/barrel/or processing too hot –high levels of regrind make the problem worse. The barrel vent is one area where hold up occurs but it shouldn't be occurring that often. Next time you clean the Die see if the burn up is in the Die head or from the barrel .Check there are no steps in the plastic flow channel from extruder to the Die where plastic can hold up. In the area you find the burn check all the thermocouples are located deep enough. They must press against the bottom of the hole not rest in the hole otherwise it cannot conduct the heat. This is the biggest reason for burn up as the thermocouple gives a reading 10 to 20 deg below the actual temperature. I use a hand held pyrometer to cross check for excessive temperature. Many of the temperature zones will have more than one heater band. A band down in a zone often causes your problem as the other one stays on continuously to compensate. Hope this helps//and gives you some ideas. Stevet IP: Logged |
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stevet Senior Member Posts: 5 |
posted February 10, 2010 12:03 PM
Hi should also mention- is you PVC grade correctly heat stabalised. Stevet IP: Logged |
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