Thin wall molding is a relative term that implies the flow length is long with respect to the part thickness and material viscosity…

Question:

Our thick PVC parts require a higher packing pressure than the injection pressure, yet the training states this is typically the case for thin-wall molding. In our case, the parts are often over 0.300″ thick… can you please explain this?

My Response:

In your case, the walls are thin relative to the flow length for the very high polymer viscosity of rigid PVC. I recommend running a rheology curve (or at least a speed study), take a picture of the shorts and take notes at each speed (ie gate appearance, part appearance, burning, etc.). With PVC (& CPVC), the viscosity is very high, but the polymer is also very sensitive to shear thinning which allows for some reduction.