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Nitrided Acme screw galling


We are having a galling problem with our Acme screw. Materials are 4340 ion nitrided both parts. Pressures are 3000 psi. Grease is aeroshell 17. We need 2 million rev of life at 2 rpms. We get approx. 100,000 then galling starts. Does you know of any quick fixes?

Peter Mackay
- Irvine, California

My experience has been that it is a poor practice to run the same metal or coating against itself. Against a nitrided part, consider electroless nickel or chrome plating. Both have a natural lubricity and are hard. Both wear well under most conditions. Either one should work better against a nitrided surface. Plate the cheapest one to plate to start out. Or plate a few of each and see which coating lasts the best on which part. One part has to be sacrificial to a minor extent to the other.

James Watts
- Navarre, Florida

Try Cryogenically Processing both parts. It will increase the galling resistance.

F. J. Diekman
- Streamwood, Illinois

Low buck quick fix, try powdered graphite mixed with high pressure blue moly axle grease (for disk brakes) on shafting and reduce loading onset speed. Also helical scoring of load bearing thread faces helps to retain lube (similar in principle to oiled sintered bronze). Scoring can be done by hand with steel brush wheel on a drill or grinder. But go easy or the tolerances will run out. It won't look pretty but it works.

BV [last name deleted for privacy by Editor]
- San Antonio, Texas

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