HOME FAQs BOOKS JOBS: Help Wanted Suggestions you are here: Hotline/Forum => Letter 20004

Removing Dichromate from tubing and replacing with Phosphate

I am working on developing a re-lifeing process for 4130 Steel Tubes that have previously been Cadmium plated with a Di-Chromate seal and then painted. I would like to lightly plastic media blast the paint off and apply phosphate rather than chromate for paint adhesion purposes (ref QQ-P-416 [link is to spec at TechStreet] ). Question is... In what condition should the tubes be in before I send them out to be Phosphate coated? I hope not to have to Strip and Replate the Cad but to simply just replace the Chromate with Phosphate.

Any input is greatly appreciated.

Chad Parkhill
- Phoenix, Arizona, USA

++++

I think you'll find it difficult -- but not impossible -- to remove the paint and the chromate without removing the cadmium plating--see letter 9406. However, these days the industry tends to not use cadmium for corrosion resistance, unless a combination of its properties is required (lubricity and freedom from gummy corrosion products, for example).

So, as long as you're getting rid of the chromate, it may be a good time to substitute zinc or zinc alloy plating for the cadmium. Some of the cadmium is going to end up in the phosphatizer's waste stream anyway from the etching that occurs during phosphatizing and they're not likely to be pleased about that anyway. Good luck.

Ted Mooney, P.E.
finishing.com
Brick, New Jersey

ANSWER or FOLLOW UP POST an unrelated QUESTION HOT Topics

Disclaimer: It is not possible to diagnose a finishing problem or the hazards of an operation via these pages. All information
presented is for general reference and does not represent a professional opinion nor the policy of an author's employer. The
internet is largely anonymous; some names may be fictitious and some recommendations may be deliberately harmful.

If you are seeking a product or service related to metal finishing, please check these Directories: