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gbakker Member Posts: 2 |
posted March 16, 2005 06:37 PM
   
Having problems with the finish of a small window frame we are producing. Run for years but walls getting heavy margins and cost reduction demanded new tooling. Same shape, same die design just went from an 060." wall to approx. .045. Appear to be getting lots of turbulence on the surface of parts of the die. Running on a CM 55. Part weighs about 92 g/ft need to run about 13-14ft/min. Only way to eliminate the surface turbulance is to increase heats to 380-390,or keep heats at 355 and run at 6-7'/min. We have dropped the land, added adapters between venturi and die, no change. Any thoughts. IP: Logged |
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Tom C Moderator Posts: 481 |
posted March 16, 2005 07:30 PM
Sounds like shark skin caused by high shear stress at the polymer-wall interface. Higher die heat and/or lower production rates reduce the problem as you have seen. It is possible that the new die has sharper transitions to the narrower walls which will increase stress. Additionally the change in wall thickness may redistribute the flow, causing high flow areas and increased stress. Die flow analysis is available to help in resolving these problems shown here; Another solution for PVC is to include additives and lubricants to increase slip. Hopefully one of the PVC guys here can make formulation recommendations. ------------------
Tom Cunningham
Extrusion Technical Services www.ExtrusionTechnicalServices.com IP: Logged |
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gbakker Member Posts: 2 |
posted March 17, 2005 11:51 AM
Thanks Tom, we are pulling the die apart today to try and streamline any hangups that may be present so following the same line of thought. Will try again Monday. Thanks. IP: Logged |
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