Where the
world gathers for metal finishing
Q&As since 1989


-----

Dryer needed for passivated SS parts >5" long

I'm experiencing rust on SS (300, 440 & 17-4PH) parts passivated in a 50% nitric solution with a tap water rinse followed by shop air to dry. I believe the problem to be incomplete drying, i.e., some water is left behind to evaporate. I do not have this problem with my smaller parts (<5" in length) but then I dry them using a heated centrifugal dryer. I'm considering a larger centrifugal dryer (with 18" x 18" basket) for my larger parts but I'm concerned about possible damage resulting from the increased mass. How are other people drying their parts? Are ovens and/or vacuum ovens used? Does anyone know of a supplier of small (~4' cube) ovens or vacuum ovens equipped with fans or some other means of circulating the air? Thank you.

Kevin J. Perez
- Pottstown, Pennsylvania
1999

---

1999

I would encourage you to read the numerous letters in this section on passivation. There is some real good word in some of them. If the part is rusting after being blown dry, how in the world is it passing a saltspray or similar QC test? In short, your parts have not been truly passivated. By 300, I asume you mean 303Se or similar. The 400 series are mainly iron with little or no nickel, so are hard to passivate. Never had much problem with 17-4. If the quality of passivation is not an issue, use heated rinse water. You might add a few percent of isopropyl alcohol [on eBay or Amazon] to act as a surface tension reducer and faster evaporating solution. A cheap heater box is relatively easy to construct and would help.

James Watts
- Navarre, Florida