The authoritative public forum
  for Metal Finishing since 1989
-----

Phosphate and oil finish degrading?

June 16, 2008

Team-
For many years we have used a standard "off the shelf hardware" that is steel, that comes with a "PHOSPHATE PLUS ONE COAT SPECIAL OIL DIP" applied.
Until now, we have no reported issues with it (until now).

The mfr gave me this information on the part and finish:
Salt Spray Exposure - Red Rust: 72 Hours
Salt Spray Exposure - White Rust: N/A
Customer Cross Reference
GM: GMW3179 CODE G

Normally this finish is dark in color, with a satin luster.
We have found some that appear to be changing appearance, and have a whitish speckled look.
We actually sent some that appeared normal, from Houston to Japan, and they changed appearance during shipment.





I am not familiar with how a phosphate and oil finish looks when it degrades.

Does anyone have an educated guess for cause of color change?

Thanks for your attention,

Jon Perdue
product designer - San Jose, Ca.

---

Jon,

Have you realized you are using gelatinized steel pretreated by zinc phosphate and prevented by oil? The info from mfg is typical for your application; also, the difficulty you are running into is typical for phosphating operation. You may need some help to maintain your phosphating bath in good shape to consistently product dark parts.

Jun Zhang
- Cincinnati, Ohio
June 26, 2008