Extrusion die drool: What you can—and can't—do about it


"Drool" is a disturbing word, conjuring up images of rabid dogs and senile people. However, it does not upset everyone, as there is a beer named Moose Drool, which enough people drink to keep the company (Big Sky in Montana) in business. Anyway, I'm talking here about what are more politely called die deposits—the bits of molten plastic that stick to the face of the die and, occasionally, drop off onto the product.

This can cause serious problems, or no problem at all, if the product is black and surface blemishes don't matter in its application. For the rest, the result may be undesirable streaks or just bits of dark (oxidized) plastic that are visible on the product surface. If the product is subject to stresses, the bits can act as stress concentrators and lead to earlier or lower-stress failure. A classic case was a failure of a gas distribution pipe in Bowie, MD, where the installers bent the pipe over a rock in the trench, which sufficiently stressed the pipe at an "inclusion" for it to crack and leak enough gas into a home to fuel a fatal explosion.

Such inclusions at the inner surface of a pipe or tube (irreverently called "boogers") are especially nasty because they can't be seen, but just drop off the die onto the inner surface.
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