Today's KNOWLEDGE Share:Clamping Force

Today's KNOWLEDGE Share

So, while molding a large area part with an amorphous polymer, you are experiencing clamp excess during fill..

You cannot change the part design, so your first reaction is to enlarge the sprue to reduce total pressure.

Force=Pressure X area after all..

In fact, you should do the opposite.

A lower diameter sprue will indeed increase total pressure to fill. But the higher shear heating in the runner, combined with high temperature dependence of viscosity in amorphous polymers will result in a lower viscosity material entering the cavity. Projected area of the runner is negligible, so a thinner sprue will reduce the maximum clamp tonnage needed to fill ! Despite total pressure being higher.

And no increased risk of material degradation, since you keep the barrel at a safe temperature.

Source:Vito leo

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