Letter 22002

Stopping destructive properties upon hot copper by PVC sheeting [California] 

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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

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

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
- FL

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.

Todd Osmolski Charlotte Plating, Inc. Charlotte, NC USA

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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