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How to avoid rusting of stainless steel parts from sanding blocks?

October 6, 2011

We use 303 Stainless Steel, which is a free-machining steel (through the addition of carbon and sulfur). We are currently investigating a passivation process that seems to be yielding rust-free results on our machined parts so far. Here are the steps to that process:

1. Rinse the parts in room temp water
2. Clean in agitated alkaline solution (pH = 12) for 1 hour at room temp
3. Rinse in room temp water
4. Clean in agitated acidic solution (7-14% CitriSurf 2050 by vol) for 30 min at room temp
5. Rinse in room temp distilled water
6. Air-gun blow dry parts individually

I'm concerned that the use of sanding blocks and sanding paper made of Aluminum Oxide may be adding a risk of rust after this process. Is this the case? Should we be sanding before this process? Would this process negate this risk of rust exposure if performed after sanding on the Aluminum Oxide paper/blocks?

Thanks all.

Chris Slavin
Product Designer - Ridgefield, Connecticut, USA

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November 15, 2011

Chris,
Aluminum oxide shouldn't be a cause for concern unless they have been used on carbon steel. The thing you need to avoid is iron contamination. However, it is normal procedure that passivation is the very last process. All mechanical work on the part should be done prior to passivation.

Ray Kremer
Stellar Solutions, Inc.

McHenry, Illinois

If you are currently having issues with rust, the passivation tank may not be within operating conditions. Mr. Kremer is correct in that passivation should be the last process for a part. If you change your procedures and still have issues with rust, check the passivation tank. It may need an add.

Aimee Longacre
- Savannah, Georgia, USA
November 22, 2011