Metal finishing Q&As since 1989

-----

HCr Galvanic Corrosion Alternate?

I've got a problem with galvanic corrosion of pass roller in a coating process. The rollers are Aluminum shell, stainless shaft, but HCr face polished to a 4Ra. We place a small charge on our paper before coating, just after coating the charge is dissapated through the rollers. The first few suffer from a pitting/corrosion believed to be caused by the charge dissapating. The rolls were replaced with a non-conductive ceramic, which holds up great. The problem moved in the machine direction to the next chrome plated (conductive) rollers. I am thinking that maybe I could use a tungsten carbide coated roller since it is sprayed on and not electroplated, but am not sure if it would stand up to charge dissapation. I found some info about true galvanic corrosion of tungsten carbide in saltwater with dissimilar metals in it, etc, etc. I'm not sure that this is the same thing. Any info or experiences?
Thanks,

Brian G
Paper Coatings - South Carolina
2005

No specific experience but if you are to try with WC coating, select a grade with nickel binder. Most common is cobalt binder which is harder and more tough but has less resistance to corrosion.

Guillermo Marrufo
Monterrey, NL, Mexico
2005

---

We use a Nickel base for the chrome already. I'm not sure what "WC" is though?

Brian G
- South Carolina
2005

Ed. note: WC is tungsten carbide, Brian, tungsten is also known as Wolfram.