Calendering and Extrusion: Reading the Common Defects
What surface roughness, edge tearing, die swell and blisters each point to in the upstream compound.
Extrudate and calendered sheet defects are usually symptoms of a compound or process condition, not of the die or the rolls themselves. Reading them correctly saves a lot of trial and error.
Defect to cause map
- •Rough or torn surface (melt fracture) — die temperature too low, or extrusion rate too high for the compound's viscosity.
- •Edge tearing on calendered sheet — compound too nervy, often from high polymer viscosity or insufficient filler; raising the filler level or adding a processing aid usually helps.
- •Excessive die swell — high elasticity in the compound, typically from high molecular weight polymer or low filler loading.
- •Blisters or porosity — moisture, volatile content or trapped air; check filler moisture and storage conditions first.
- •Variable gauge — temperature drift across the calender rolls or inconsistent feed temperature.
The two parameters that fix most problems
Temperature and shear rate. Before reformulating, try adjusting die or roll temperature and line speed — most calendering and extrusion defects respond to process settings once the compound itself is within its normal viscosity range.
Ask your supplier for the compound's Mooney viscosity at the temperature your process actually runs at, not just the standard test temperature. ## Need the documents or today's price? Send us the grade, quantity and destination port — we return a quotation with COA and MSDS attached. Email manager@fipolymer.com or use the inquiry form on this site.