Re: Metal traces in PVC pipe?

["Tesla list" <tesla@xxxxxxxxxx>]

Original poster: "Scott Hanson" <huil888@xxxxxxxxxxxx>

Garry -

I think Terry may have been speaking a bit figuratively when mentioned
".....interesting impurities in the plastic.  Dirt, bug remains, floor
sweepings... ". I wouldn't expect to section a piece of PVC pipe and find a
nice juicy June bug curled up inside.

Certainly it IS possible for PVC pipe to contain impurities. For
non-critical applications like sewer & drain pipe, its probable that 
the raw PVC resin
contains a percentage of "reground" material, recycled from scrapped 
PVC from any
number of sources. The higher the percentage of regrind, the greater the
potential for introducing contamination.

However, both the resin supplier and the pipe manufacturer take precautions
to remove as much foreign material as possible because any hard stuff in
the raw resin can damage the screw, barrel or the die of the extruding
machine. Additionally, the extruding machine itself has a filter screen just
prior to the extrusion die as last chance to remove any contaminants before
they reach the die.

As far as the pipe containing whole "bugs", this is impossible. Much of the
heat to soften the resin comes from the "shearing" action of the resin
caught between the rotating extrusion screw and the barrel, so just 
about anything other than
metal chips or sand gets thoroughly ground up. The resin is carefully dried
prior to loading in the extruder, and as the temperature of the PVC as it
exits the extrusion die is around 350 degrees F, there is essentially no free
moisture in the pipe at this time.

Regards,
Scott Hanson