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Letter 22002
Stopping destructive properties upon hot
copper by PVC sheeting
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What is the process that happens to copper when it is used as a
heating tool at approx. 450 degrees f. and it comes in constant
contact with melting PVC plastic sheeting. Is there a particular type
of copper that I could use that won't self distruct in this
situation?
Gary St. Thomas
- Folsom, CA, USA
First of three simultaneous responses +++
The problem is that at elevated temperatures, PVC resins decompose
slightly. Injection molding dies and even heat sealing equipment must
be protected from the corrosive effects of the resin decomposition
products.
The resin itself will decompose to hydrogen chloride gas (the
active ingredient in hydrochloric acid)or in some cases, free
chlorine. Granted, only parts per million of this decomposition
occur, but it is enough to corrode copper.
Injection molding dies for rigid and flexible PVC and rigid CPVC
are usually made of type 316 stainless steel. Heat sealing (a
misnomer since the sealer uses radio frequency to generate heat) bars
are usually copper, but they will often have a PTFE tape on all
contact surfaces to prevent pitting and corrosion.
Chuck Reichert
- Seattle, WA
Second of three simultaneous responses +++
Chrome plating might work, but I have doubts. EN would work better
and Teflon coplated in EN should work very well. Not too many shops
do this type of plating.
James Watts
- Navarre, Florida
Third of three simultaneous responses +++
Bare copper will be attacked by hot PVC. The part will work much
better, last longer and still conduct heat well if it is coated with
electroless nickel.
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Anything that comes in contact with melt PVC will will be in
contact with chlorides (among the most active ions and even more if
hot). Copper is somewhat more corrosion resistant than for instance
steel, but there are alloys based on nickel that are better (such as
electroless nickel) When inertness is a must and a metal is required
the choices point to the more noble metals such as gold, platinum,
etc.
Guillermo Marrufo
Monterrey, NL, Mexico
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