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Author | Topic: Shear or friction heat |
Xanstarr Member Posts: 4 |
posted August 15, 2005 09:50 PM
Help....I'm running ridgid pvc on a 31/2" nrm 24:1. I'm having alot of problems with shear( friction) heat. My target pounds per hour is 200 but I'm only able to produce about 120 pounds per hour. Whenever I try to increase the screw speed to get more production, the friction heat makes it impossible to do so.Please help IP: Logged |
Tom C Moderator Posts: 578 |
posted August 16, 2005 08:50 AM
Mr. X Please provide more information. I believe we have the people here who can fix your problem. What are RPMs, Output, Amp draw, and melt temperature at the conditions you have tried? What are the barrel temperatures set and measured? How is the barrel cooled, Air, Water, or none? What is the screw design? What is the formulation? ------------------
Tom Cunningham
Extrusion Technical Services www.ExtrusionTechnicalServices.com IP: Logged |
2beeps Moderator Posts: 100 |
posted August 16, 2005 03:58 PM
Also, are you running PVC as a powder blend,in a vented extruder?? Or pellets? If powder dry blend, then a "crammer", or vertical screw in the hopper is often used to enhance output rates at a given screw RPM,supplying the feed zone with sufficient material to be "worked" by the screw. As to frictional heat, as Tom states, it's important to know your heat profiles,amps,and especially lube balance in your formulation. IP: Logged |
Xanstarr Member Posts: 4 |
posted August 16, 2005 04:37 PM
I'm using a reprocessed pellet at 60% and recycled blister pac at 40%, The extruder is drawing about 50 amps. Barrel temps are 280 275 270 265. I've been trying to run the temps lower and it's been helping a bit. I believe it's a barrier screw ,air cooled barrel.Melt temp is around 380. I use a screen pack , (1) 20 mesh screen. IP: Logged |
Tom C Moderator Posts: 578 |
posted August 16, 2005 05:22 PM
I'm not the PVC guy here, but blister pack PVC is not the same a rigid PVC. From what I read it can be quite different. Try your process without the blister regrind frist to see how things work out. ------------------
Tom Cunningham
Extrusion Technical Services www.ExtrusionTechnicalServices.com IP: Logged |
Xanstarr Member Posts: 4 |
posted August 20, 2005 06:29 PM
We have to run blister pac to keep cost down. Any suggestions would be gratful IP: Logged |
Tom C Moderator Posts: 578 |
posted August 20, 2005 07:39 PM
It is likely that the bulk density of the regrind and scrap are keeping your rates low. Try working with the first zone temperature to improve rate. Look for increases in amp draw. Try something like 265F in the first zone and increase to 365F towards the die. If you can't maintain a stable extrusion with those temperatures you might have a worn extruder. ------------------
Tom Cunningham
Extrusion Technical Services www.ExtrusionTechnicalServices.com IP: Logged |
J Inman Senior Member Posts: 5 |
posted August 21, 2005 11:19 AM
I had a lot of trouble with burn-off for a while but started watching where temp spikes occurred during start up and raised low zones and dropped high zones areally large boost in output followed. Next I lowered the feed zone by small increments again better output there does seem to be a imit that will be readily obvious when going too far but Ido run straight virgin an d have a mixing instead of a barrier screw(same 20 mesh screen though. IP: Logged |
Xanstarr Member Posts: 4 |
posted August 22, 2005 08:28 PM
I tried the lower temps and what a big difference. The friction heat has been reduced a great deal. Thank you to everyone for all your help. IP: Logged |
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