Letter 31020

Stainless steel screws gall going into aluminum  

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We are assembling a tool for our customer which consists of stainless steel screws going into aluminum material. In several cases, galling has been an issue. Have you ever heard of such problem and what would be causing this? Is there anything we can do to prevent it?

Vy Nguyen
contract manufacturing - Houston, Texas

Friction, and heat, cause galling. You should be able to fix the problem by using a lubricant, maybe a vanishing oil. If you can't use a lubricant due to the application then you can chill the screws before insertion or slow down the screw setting operation so that heat doesn't build up so fast. I've seen cold air used to provide cooling for one application and it worked really well...

It ain't much... but it's all I've got.

Jeff Watson - Pearland, TX

Try another metal for either part because aluminum and stainless steel are incompatable alloys that are susceptable to galvanic corrosion under the best conditions.

Jeff Swayze
- Kelowna, B.C., Canada

Vy, when we have stainless screws going into aluminum we have the stainless fasteners cadmium plated (still available in the States) and/or anodize the aluminum. Either of these should fix both the galling and the galvanic corrosion concern.

Lee Gearhart metallurgist East Aurora, NY

SOME RECOMMENDATIONS ARE:

*INSTALL COATED HELICAL INSERTS INTO THE ALUMINUM TO ENGAGE YOUR ST STL SCREWS. THIS SOLVES YOUR GALLING ISSUE AS WELL AS COMPATABILITY ISSUES

*USING A LUBRICANT SUCH AS LPS P/N 00116 GREASELESS LUBRICANT WORKS WELL

*CHECK THE TAPPED HOLES WITH A GAUGE TO SEE IF YOUR TAPPED HOLES ARE UNDERSIZED. THEY MAY NEED TO BE CHASED TO THE OPTIMAL THREAD MAX/MIN DIAMETERS.

Domenick Signorino
- Edinburg, Virginia

Try coating the screws with an Electroless Nickel/Teflon Composite coating with at least 10% Teflon by volume. A normal thickness of .0002" should do the trick.

Paul Szymanowski
- Erie, PA, USA

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