Aluminum Threads Galling - How to Prevent

[leeave96]

I have a about a 3.5 inch tube connection that needs to be plugged with a threaded plug. The tube and plug threads are 3.5-10UN. Tolerance is 2A and 2B respectively. The tube material is aluminum, 6061-T651. The plug material is brass C360 half hard (H02) temper.

The idea of different materials was to try to eliminate galling of the threads - but there is some galling.

Any ideas as to how to prevent galling for this application? The desired plug material would be aluminum for weight, but again I am concerned about galling.

Would anodizing help?

Would a different type thread help? If so, any recommendations?

Thanks!
Bill

 

[CoryPad]

Forget the brass and different thread type. Just use a lubricant (wax, oil, PTFE, etc.). You can use simple ones if your joint is not demanding (petrolatum, motor oil, thread masking tape, etc.).

Anodizing would help.

If you want an engineered coating, try:

OKS 1700 from OKS

http://www.oks-germany.com

One of the Delta products from D[ö]rken

http://www.doerkenusa.com

http://www.doerken-mks.de/

One of the 5XX coatings from Magni:

http://www.themagnigroup.com

Regards,

Cory

Please see FAQ731-376 for tips on how to make the best use of Eng-Tips Fora.

 

[KENAT]

Possibly dumb question but...

Have the threads been inspected to make sure they are correctly formed?

KENAT, probably the least qualified checker you'll ever meet...

 

[drawoh]

leeave96,

I have designed all sorts of aluminium parts that thread into one another. We have used much finer threads than 10tpi on diameters 3" and higher, and they work fine.

At least one of the aluminium parts must be anodized. It is better if both are. Forget about chemical film finishes such as Alodine.

Another solution is for one of the parts to be some other material such as brass. I am surprised this did not work. Perhaps you should follow Kenat's advice and check the threads. Also, watch out for thermal expansion and contraction.

JHG