Polymer & Plastics · Solve a Problem
Apparent Die Shear Rate & Melt-Fracture Predictor
Sharkskin and melt fracture are a shear-rate problem before they are a material problem. Enter the die geometry and output and the tool returns apparent wall shear rate, with a warning band for the region where a polymer processing aid or a die-gap change is normally required.
γ̇-2A
Apparent Shear Rate
γ̇slit = 6Q / (w·h²) | γ̇circular = 4Q / (π·R³)
cm³/s
mm
Apparent shear rate γ̇
2,357.9
s⁻¹
Regime
Melt-fracture risk
Melt Fracture Risk High
γ̇ > 1000 s⁻¹ in the die land — deploy a Fluoropolymer Processing Aid (PPA) Masterbatch immediately (typ. 500–1500 ppm active fluoropolymer) to coat the die wall, suppress sharkskin and stabilise the extrudate surface.
AllZone · Engineering
Use this when
- The surface goes matt or shark-skinned when you push line speed.
- You are sizing a new die and want to stay under the critical shear rate.
- You need to decide between slowing the line and adding a processing aid.
How the number is produced
- Circular die: apparent shear rate = 4Q ÷ πR³.
- Slit die: apparent shear rate = 6Q ÷ WH².
- Volumetric flow Q is derived from mass output and melt density.
Materials for this job
Engineering aid only. Validate against your own instrumented trial, the polymer datasheet and the applicable ASTM / ISO method before locking a process window or a specification.
Related knowledge & tools
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