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Galling problem in type 302SS T-bolts

We are T-Bolt manufacturer's. T-Bolts are 1/4-28 Thd'd, made of 302 Stainless Steel Material (not plated). In 5 years of making these bolts we have received two complaints of Galling from the field. Threads meet the customer specification (in hardness, tensile strength, etc.), but we are having difficulty finding the cause for this Galling. The mating part (on which we have very little info), is made of same material and is Silver plated. The application is a clamp which at times is removed for servicing. It is during one of these removals that the threads were found Galled. What could be the reasons for galling? What areas should we look in for our analysis? Do you think thread laps or plating buildup would have anything to do with galling? Please advise. Thanks.

Sanjiv Chaturvedi
- Chicago, Illinois
2003

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The problem may be lack of silver plating on the particular part, rather than an excess of it; the silver is there to prevent the natural galling tendency of stainless steel.

Ted Mooney, P.E.
Striving to live Aloha
finishing.com - Pine Beach, New Jersey
2003

Threads are notoriously difficult to plate so will have a minimal amount in the valleys. Frequent use of the threads will gradually squeeze the silver to new locations. The highest pressure areas will eventually have the silver virtually removed and will gall when under appropriate pressure and movement. Once the galling starts, it gets worse rapidly, possibly approaching logarithmic. A metallurgist might be able to tell you a lot more, if he had them in his/her lab.

James Watts
- Navarre, Florida
2003

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Threads could have galled due to lack of plating adhesion. Stainless requires extra activation by way of a Woods nickel strike, cathodic sulfuric, etc. (ref. ASTM B253 ). Is the silver still on the galled threads? As Ted stated, this application generally requires thin plating, such as 0.0001 - 0.0002 inch. Too much is bad and may actually cause problems. Look on the front page of this month's Plating & Surface Finishing journal for an aircraft igniter (fancy aero term for spark plug). It employs thin silver for anti-gall; we used to do the job before it, like many manufacturers in the formerly industrial Northeast, migrated south. Now I just cruise finishing.com looking for conversation and reminiscing about days gone by. Enough editorializing, good luck with your investigation.

P.S. Are the threads roll formed? This too can lead to poor plating and possible galling potential.

Milt Stevenson, Jr.
Syracuse, New York
2003

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Sorry your work has been heading south, Milt, but having just returned from vacation in the Florida Keys I can understand the attraction :-)

Seriously, a bigger problem in my estimation is the huge move to China by the Freeload 500, which will destroy all of America's small manufacturing businesses, and finally America. Enough editorializing for me, too :-)

Ted Mooney, P.E.
Striving to live Aloha
finishing.com - Pine Beach, New Jersey
2003