In Reply to: Nylons posted by Dharmesh Sachdev on 12/22/02 at 3:27 PM:
I can't say exactly what the problem is. Zinc stearate is a very common incredient in compounded plastics - many compounders use it as a 'mold release' for their materials.
Zinc stearate is capable of high temperatures, but the specific formulation of the additive may not. For example, the carrier in the additive may have some problems.
If the black spots are scattered around the profile, then it is probably remnants of a colored material that was run previously. This is also common in injection molding.
I would try running without the zinc and see what happens.
Sorry I can't be more useful - extrusion is not my strength!