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Titanium bolts used for anodize racking are breaking

We are using commercial grade titanium bolts for holding parts for anodizing in sulfuric acid at low temp(25-30F). Lately we have seen that titanium bolts are breaking inside the parts after anodizing. Does any one knows the reason for breaking ? or is there any method by which you can rejuvenate old bolts by some heat treatment or some other process ? Please respond.

Shanti Raikar
anodizing specialized parts - San Jose, California, USA
2004

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2004

Shanti,

Judging by the tank temp that you mentioned, it appears you are doing hardcoat. Titanium bolts should not be used for racking hardcoat parts, as the current carrying capability of titanium is about 40% less than Aluminum. I'm betting you are trying to push too much current though these bolts, causing them to overheat, and fuse to the aluminum threads (I learned this lesson quite sometime ago). I've been hardcoating for 17 years, and I never use titanium for contact points for hardcoat.

Marc Green
anodizer - Boise, Idaho

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That happens all too frequently with Type II anodizing as well, even even when done at very low current density. What may also be causing this is the fit of the bolt in the threaded hole; its allowing electrolyte to seep into the threads, where it anodizes the aluminum and thus reduces the thread clearances, which causes binding. This effect also increases the connection resistance, sometimes by a lot, a very bad situation in itself.

Paul Yursis [deceased]
- Columbia, Maryland, USA

Ed. note: it is our sad duty to advise of the passing of Paul Yursis in August 2005.
Here is a brief obituary by Mike Caswell.

I would to add to the recommendations that are correct that you do need alum. contact points especially when hardcoating, and I also have found that when using titanium contacts (like on small parts) that it will make the titanium brittle. But If you are using titanium bolts to hold parts as long as you are not relying on the titanium for current they will not get brittle and will not crack

Chris Snyder
plater - Charlotte, North Carolina
2004