Threadlocker for stainlees steel

[bobbkr2]

I am trying to lock two mating 316 stainless steel threaded (5/16-32) parts together permanently. I need them to hold 100 in-lb breakaway torque after curing. I have tried both Loctite 262 and 2760 and the breakaway torque is only around 50 in-lb. Any suggestions? I was going to try some 3M structural adhesive (epoxy) next.

 

[moltenmetal]

If your 316 parts behave like the generic 18-8 stuff we see 'round here, then you should clean the parts well, apply a typical bolting stress for carbon steel components, and wait a bit. The parts will gall together, preventing disassembly!

 

[drawoh]

bobbkr2,

I am satisified with Loctite 242 for stainless steel screws, but I have never tried to measure the break-away torque. We do want to be able to remove our screws.

I have used Loctite RC635. According to Loctite literature, stainless steel is an "inactive" material, and it requires primer. RC635 with primer is practically impossible to take apart. I suggest you read up on this. The primer might work for the 262 as well.

JHG

 

[btrueblood]

Google is your friend.

http://tds.loctite.com/tds5/docs/2760-EN.pdf

Is a datasheet for one of your threadlockers. In there, a 3/8 steel bolt is shown to have a breakaway torque of only 70 in-lb. after full cure, and stainless fasteners are listed as obtaining only about 25-50% of the strength of plain steel fasteners. The other compound,

https://tds.us.henkel.com//NA/UT/HNAUTTDS.nsf/web/B232AF8B746FAC96882571870000D618/$File/262-EN.pdf

does a little bit better...but note the cure speed for stainless steel fasteners.

You could try higher-strength anaerobic adhesives (Loctite 277 is one), and use the primer/activators listed on the datasheets for those, and wait the prescribed cure time before testing...

 

[bobbkr2]

I am still having problems getting a strong enough bond between these parts. I tried some 3M DP-110 (gray) epoxy and increased the breakaway torque to 80 in-lb. Still not as strong as the OEM part which had a breakaway torque of 105 in-lb.

 

[vc66]

Want 'em together permanently? Weld 'em.

V

 

[CoryPad]

I assume the failure is adhesive (between the adhesive and the metal surfaces) and not cohesive (within the adhesive). If so, you may want to use a primer, like 3M Scotch-Weld EC-3901:

http://multimedia.3m.com/mws/mediawebserver?66666UuZjcFSLXTtnxf2OXz6EVuQEcuZgVs6EVs6E666666--

You may also want to try pre-applied thread adhesive rather than the hand applied stuff. Here is a link:

http://solutions.3m.com/wps/portal/...E3E02LECIE20S0S0_nid=W1817Z7NV5be197V3FT0LJgl

 

[flash3780]

Want 'em together permanently? Weld 'em.

Agreed. Bolts are not a preferred method of making permanent connections. Rivets, welds, brazes, and adhesive bonds are generally more suited to permanent attachments.

If the design drives you to a bolted connection, you could always lock-weld the head of the bolt. However, you have to be careful not to put to much heat into the bolt such that you lose your preload.

I'm surprised you were able to remove the bolts with Loctite 2760 (strong stuff). I'd talk to the Loctite rep or try Loctite 266 or 277. You'll also want to be sure that the threads and the hole are both clean before installation. If not, you won't get the bond you're looking for.

As mentioned above, 300 series stainless threaded into to itself is notorious for galling up. I'm surprised that you're able to take it apart to begin with. Maybe the Loctite is preventing galling?

 

[iainuts]

What is the initial torque applied to the bolts? If it's less than 100 in lb, that may be an issue. My experience is that breakaway torque is a function of initial torque used to tighten. I'd expect Locktite 262 to make the breakaway torque at least as high as the initial torque. Epoxy should even higher yet.