Gaulding or "galling" of morse tapers 1

[tsb15]

I have a 17-4 ph stainless steel shaft utilizing a morse taper with a stub acme thread below it to join two tools used in an oilfield application. The thread is to allow the connection to be pulled in tension. The problem is the taper tends to gauld when in use due to being overtorqued. The amount of torque applied can not be regulated accurately downhole and changing the connection is not practical due to tool design. Any ideas to stop or reduce the gaulding? Possibly surface finish, surface treatments, shot peening, spray on lubricants, etc?

 

[NickE]

1) Spelt Galling....

2) you might want to try Ni-based anti-sieze compound. or possibly MoS2. Stainless steels have a tendancy to gall due to how thin the oxide layer is on the surface. Coatings can help significantly.

I dont have any experience with downhole environments, if you can change materials that may help also.

I have also heard that soem parts are silver plated to prevent galling.

 

[unclesyd]

I use these materials extensively with 17/4 PH to prevent similar problems with extruder components.

http://www.socousa.com/showprod_detail.asp?pid=8O4&type=cat&id=2&prid=102

http://www.jetlube.com/NewFiles/eng.html

As you mention overtorquing, are you seeing any thread deformaton?

 

[btrueblood]

You could also use Nitronic 60 alloy, it has anti-gall properties.

 

[tsb15]

Unclesyd,
No, haven't seen any thread deformation. Would disimilar metals make the galling worse...4140 joined to the 17-4 PH? IE would making both components of 17-4 reduce the galling of the morse taper male "shank"?

 

[unclesyd]

Don't make both components from 17/4 as the threshold galling stress of 17/4/17/4 is 2 to 3 ksi. As posted by tsb15 the use of Nitronic 60 might be way to go if it has the strength needed. If you go with Nitronic 60//17/4 Ph, 50 + ksi galling stress, keep the heat treatment at H1100. Nitronic 60 works well with many materials.

4140//17/4 PH is not a good combination.

Not knowing the full operating conditions of your application it is not appropriate to make to specific recommendations.
Does the materials have to meet any standards or conditions like API or Nace?

 

[tsb15]

I appreciate the help guys. I will try the Nitronic 60.

 

[tlee123]

Remember, a taper connection is held by friction. Lubricants that reduce the coefficient of friction are a bad idea. Keep looking into material combinations.

 

[Sparweb]

Assuming the tools are supposed to thread together, tighten the morse tapers together, and then turn backwards to do work, then could you reverse the thread direction to make the thread tightening turn in the same direction as the working direction?

 

[DesignerMike]

I have had some success using "armaloy" coating (brand name I think).

I believe it is a plasma spray of Chromium on the surface. We used it in place of chrome-plating since it did not require undersizing the components, chrome build-up and then a re-machining afterwards. Unfortunately I didn't stay at the company long enough to see the long term results.
Lubricating sounds like a bad idea on a morsetaper designed to lock-in-place and handle torque.

Different materials will be your best bet if you can change...also you may be able to heat treat one part to get dis-similar hardnesses.

Try the Materials Forum too. This really falls into a material properties field, and there are some great experts lurking there.

 

[vzeos]

The point that tlee123 made is correct. If you ever noticed the Morse taper on a commercial twist drill, the end of the drill has a tang that fits into a slot in the machine tool spindle. The purpose of the tang is to force the drill bit to turn during heavy drilling loads. It sounds like you first need to grind or lap the male and female tapers to obtain a tight fit. You then need to design a torque resisting element into your tool, such as a tang, a key, a pin or a flat.

 

[rorschach]

I'm in the downhole biz too, some things I'd try:
Definitely try nitronic 60, problem may be finding it in the size you need. It can only be strengthened by cold work so anything over say 2 to 2-1/2 inches o.d. won't be cold worked. Nitronic 60 is also not allowed per NACE 01-75 if that is a requirement. Nitronic 50 is but annealed only so strength is probably going to be an issue. NEVER use stainless on stainless if you can at all avoid it. I have a 25% chrome/718 Inconel EB weld coupon set paperweight at home that galled together. It was an expensive lesson. Trashed a coupon set that cost several thousand dollars during incoming inspection. I still cringe when I look at it.

Some other things you might try is glass bead blasting/peening and/or copper plating opposite parts. (blast the pin and plate the box would be the combinantion I'd use.) This is done by all the premium thread connection suppliers (VAM-PTS, Hunting, Hydril, Nippon Steel, etc.) for anything that is stainless/nickel based. Or just use drill pipe thread dope (very good anti-gall properties and it won't wash out) on the mating surfaces before they are mated up. The idea about the tang is a good one if rotation is an issue. I would not rely on the taper to transmit the load. a key or tang would fix that. even better, do all of the above.

 

[RRBD]

I would advise against lapping the two tapers together, especially if you want to get them apart again. Most tapers are ground with with slightly different angles (seconds) which is why they come apart when needed. A tang drive sounds good. I know it sounds funny, but, chalk will help this slightly.I have had a similar problem in my shop and an oldtimer recommended this. Anyway, I lost 20 bucks to him when it worked.
Scott