EXTRUSION Troubleshooter - Plastics Touchpoint

March Paul WallerPlastics Touchpoint Group, to Fix Ugly Rolls Appearance counts. Ugly rolls offilm are often rejected, even when thegauge variation of the film itself is wellwithin specification. It is often impos-sible to measure the slight gauge vari-ation that can build up over thousandsof layers to produce a bump in the rolldiameter. So operators must under-stand how to diagnose the cause orcauses of deformed rolls and adjustwinding for changes in raw materials,processing conditions, and winders use some combinationof nip pressure, web tension, and drivetorque to control film winding. Nip-rollpressure controls roll hardness byremoving air entrapped between lay-ers as the film winds. Web tension con-trols roll hardness as well, but cancause other problems, especially whenwinding elastic materials like poly-ethylene. PE film relieves stress bychanging shape over time, so rolldeformity may not show until severalhours after the roll is completed. Drivetorque from the center is a better wayto control stress as film helps as well.

www.ptonline.com March 2005 41 EXTRUSION Troubleshooter causes are winding film too warm or applying too much web tension or lay-on pressure. This problem can also occur with coextruded film where the

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