As a response to the Fill Time, Viscosity & Molding Economics blog I received this question…
With respect to a in-mold rheology test, why should we choose to process on the right-hand side of the curve?
As the shear rate, or flow rate, of the polymer increases… the viscosity decreases. This rheological behavior is unique to polymers and is called ‘shear thinning’.
When graphing this, viscosity is plotted on the vertical, ‘Y axis’ and shear rate is plotted on the horizontal, ‘X axis’. Shear thinning will appear as a steep decline in the viscosity of the polymer as the shear rate increases.
Once most of the shear thinning occurs the polymer’s viscosity starts to level out. After this point, the viscosity will remain relatively consistent – resulting in a more stable process. For this reason, you should process on the right hand side of the curve.
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