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| Author | Topic: die builup |
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novadan Senior Member Posts: 21 |
posted November 16, 2009 08:12 AM
  
We are experiencing alot of die buildup on one of our extruders. Our supplier of our PE anylized the buildup to confirm it was a mix of PP/PE(we blend). This buildup has been going on for years and we come to live with the fact. Our extruder run time is approx 72-84hrs before it needs to be shutdown for a die change. This hasnt been the case until about 7yrs ago. When I first started here the extruder would run an easy 1 1/2 weeks to 2 weeks. Something apparently happened to the supply of material that we cannot have replaced. My trouble is with this fact- our extruder has two die heads which we usually run simultaneously, this is when we get 72hrs. But we have the capability to run one die when needed. When we run one die we get a longer run time(approx 120hrs). all the settings of the extruder are the same except the #2 die is shut off. The extruder is run with metering pumps and the screw rpm is set on auto to run a specific pressure. Any ideas why the longer run time due to the buildup on two dies as apposed to one die, Thanks IP: Logged |
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Steve H Moderator Posts: 427 |
posted November 16, 2009 08:35 PM
My guess would be that with one die blocked off, you are getting a slightly greater volume of material through the open die, at a faster rate, this is enough to ablade the buildup and slow it's rate up. Three things you could try to delay having to shut down- when you are about to shut down, dose in PPA (Polymer Processing Aid+ Anti Oxident). Before start up, clean the lips/lands of your dies (wherever the buildup occurs) with Silicon grease. And dose a smaller quantity of PPA into the material. The PPA will "coat" the internal surfaces of the die and slow down the rate of dielip buildup, the grease coats the outer edge of the die lip and does the same thing, the ongoing addition of PPA maintains the intial coat built up by shutting down/starting up with a high dose, the Anti-Ox slows down the rate at which the PP/PE mix degrades with cooldown/heat up occurs. IP: Logged |
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Tom C Moderator Posts: 978 |
posted November 27, 2009 11:16 AM
See my article on the subject at: http://www.ptonline.com/articles/200901ts1.html ------------------ Tom Cunningham www.ExtrusionTechnicalServices.com IP: Logged |
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stevet Senior Member Posts: 7 |
posted February 16, 2010 06:34 AM
Hi It could be that the grades are too far apart and the temperature is too hot for the easy flow grade. When running two dies the screw speed would be higher giving more frictional heat making the problem worse.Masterbatches often suffer from this problem as they are made from easy flow grades. Stevet IP: Logged |
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