Gap Sealant

I would use a 2-part epoxy if the stainless steel fitting were not re-usable, which it is. As for the potential for contact corrosion, this has never been an issue.

Thanks

What else did you omit that may be useful in making a decision?

I would at least consider machining a piece for purpose out of one material, whatever or whichever might be most suitable....

Considering the difference in coefficients of expansion I'd use a silicone sealant.
You imply that mechanical strength or rigidity isn't required ('cos you say gap sealant rather than fixing).
Although you do say bond, which implies there is little or no gap and you are trying for a mechanical joint.
Which is it? Or is it both?
Del

Silicone is not an option due to unwanted lateral movement of the fitting in the extrusion. As mentioned earlier, I have used the aforementioned Loctite products, but sometimes they cure anaerobically and sometimes they don't, even though the installation procedure is identical. I need to increase the incidence of leaks to zero and I am not there yet.

Shim with plastic then fill with epoxy, isolates and become rigid with no contact between parts

"I need to increase the incidence of leaks to zero and I am not there yet."

Eureka! I think I have the solution.

Mill the aluminum rod so it has a taper along the length that fits through the hole in the steel plate, from 0.1mm less than the hole to 0.1mm GREATER than the hole. Upon insertion, the aluminum will deform and produce a friction fit that should be watertight, since the aluminum is under pressure within the hole.

The plate is aluminum,and the fitting is stainless.The fitting needs to be expanded.

So get a larger fitting and mill it into the shallow taper, the plate will deform around the fitting, and you get that super-tight friction fit.

I'm not sure but I think the geometry of his connection may require a shear-strength bond and silicone will shear easily. Epoxy may be more suitable for this application.

I wonder though if silicone and a clamp might work? If the clamp cancels the shear then the silicone would seal just fine.

I have no drawings so I'm flyin' blind here.

Braze them together.

What about a flexible press tite gasket with a hose clamp?

https://www.sealingdevices.com/flexible-graphite-gaskets

Neoprene gasket with a compression fit or are you now going to tell us the liquid is actually a solvent of neoprene. I wonder about your vibration environment.

In the photo you can see the stainless steel fitting and where it goes.Beside it is another hole for the second fitting. The extrusions you see circulate water. There is no way to use anything other than a sealant, whether it be a thread locker, a retaining compound or something else.And it needs to be removed, therefore no epoxy etc.

Any suggestions?

https://www.amazon.com/J-B-Weld-31314-Temperature-Silicone/dp/B00ID8IUJY

You could restrict lateral movement with an exterior clamp on the back that encompassed the joint...You would have to work out the details as to what would work in this situation, but a simple clamp design should work...

Have you thought about freezing the part then using a press to push it into the bore ?

When it's frozen, put a piece of shrink tubing on it, shrink the tube and use silicone lube on the outside, then when it warms up, the piece should be snug in the bore.

I can't see what goes where. The longer rod doesn't look like stainless, judging by the rust. The shorter one appears to have O-rings.

How thick is the aluminium part? Does the join need to take any mechanical loads, specially longitudinal?

Yup, exactly what I thought... needs a re-design.
I'm out.
Kris

<sigh>

The pic doesn't tell the whole story. The rusted piece is a broken bolt that fixes a water manifold over the two stainless fittings (only one shown) after they have been glued in. The O-Rings keep the water within the system from the opposite side. What you see are extrusions that are all water cooled. Due to the thickness of the aluminum extrusion, no threads can be cut. So, a re-design is not possible. I am now going with Retaining Compound Loctite 620 with an accelerator 7649 and see if this works.

Your gap seems to be well above the recommended for 620....

...the 638 seems better suited...but you have to work fast....these both cure anaerobically, which means it might help the curing to purge the lines with nitrogen and seal for 24 hrs....

A re-design is always possible. A re-design may not be practical due to financial or time constraints but it is always possible.

The question comes down to how many temporary band aids can be attempted before metal fatigue or other demons of entropy force the issue.

There's never enough time/money to do it right the first time.

There seems to always be enough time/money to attach band aids again and again.

threads

Hmm, I wonder what those worn out O-rings are made of?

I'll try one more time to make a case for epoxy.

If you are familiar with glass transition temperature (T_g)of polymers, this may make sense, if not read up.

Simply put, Tg is the point at which cured rigid epoxies become rubber like. Even hi-temp epoxies have a Tg, above which you can simply pull the two pieces apart, clean and reuse. I do not believe a hi-temp epoxy is required here.

An industrial heat gun can be used for this. Remember the Al extrusion will conduct heat away much faster the SS so concentrate the heat the SS plug.

You're on your won from here.

Sounds rather time consuming ...

No, not really.

Have you ever done it? I have.

Actually, threading the ID of the Al piece and ordering or machining threads on the SS nipple and screwing it together with TFE tape as a sealant sounds cost effective overall.

I think he just needs the proper O-rings, and skeletal support clamps.....and yes I have a heat gun , but also have tried heating aluminum with water involved, remember you wouldn't be able to move the collectors apart until the epoxy was softened and the stainless fitting is buried in the aluminum extrusion....and if it's not water in those pipes it's probably some special heat exchanger fluid which would make it even more problematic....then you might have a problem accessing electric for the heat gun and end up dragging a 200' extension cord all over the place......and a threaded fitting would present the problem of having to align the collectors together at the time when the fitting tightened up, the stainless would probably split the aluminum or strip the threads at some point in time...jus sayin'

My take is that the system is down, drained and dissembled as shown in the pic.

We used TFE tape by the carton and had the manufacturing engineer come in and give a class on the subject to the assemblers. Three wraps is all that is required and the fitting only needs to be snug to seal against 40 PSI. Splitting plastic fittings by over tightening was unheard of.

I get what you are saying about over tightening but it's unlikely if done properly. (torque wrench) One of my pet peeves is over tightening of threaded fittings when they don't need it.

The OP may be gone for the weekend or forever so any more speculating won't help.

Yeah, I don't think he's into any major changes, just wants to make what he has work with minimal effort, I get that....but at some point people start shrugging their shoulders at you and saying, can you fix this or what? ...then you better have a plan that's going to work ready....Everybody has their own row to hoe as they say....

I am curious why both parts can not be made from aluminum for stability of the fitment during temperature changes? It would keep cost down compared to the ss nipple.

The fitting needs to be stainless due to the possibility of corrosion, which would cause the final assembly to fail if it were aluminum.

Consider this : https://www.muggyweld.com/video/soldering-stainless-steel-aluminum/

It is a low temperature(350F) solder for dissimilar metals,with a 20,000 psi bonding strength.

Easily removed when required due to the low melt temperature.

You are welcome.

Can't solder or braze due to the bead interfering with the placement of a manifold block over the fittings.

Good suggestion, though.

Thanks

No need to form a bead."Sweat" the solder into the gap,not leaving an external bead.

Pre-tin (apply a thin coating of the solder to both parts),then heat both parts to fuse together.No interference from a bead,and a 20,000 psi bond.

<...corrosion...> What are the wetting fluids, please?

Water that is supposed to be treated with an inhibitor, but this is not always done due to poor maintenance practices in the plant.

Yep. Given there is a metal-to-metal corrosion concern one needs to eliminate one of the metals. Replace the fittings with ones made from PTFE, like this, for example:

http://www.micromold.com/threaded_piping.html?gclid=EAIaIQobChMIiufdt5ba2AIViArTCh2laATyEAAYAyAAEgIDMvD_BwE

(not an endorsement).

Modern plastics have such potential. Why would one use metal when plastic can do a better job (rhetorical question - NNTR)?

i agree with the solder method. You would be able to salvage both parts. As a master welder i have assembled many dissimilar metals in skid systems and elsewhere. i use ss fittings with aluminum all the time along with brass if i am not worried about the bling. never had a problem with corrosion between the two. carbon steel , yeah you made a battery and the aluminum will corrode .

<...you...> Er, this particular username is not connected to the individual(s) carrying out the repair.

There is always the possibility of to swage the ss fitting to achieve a tighter fit,then use the Loctite .

For a single use,such as yours, as your application,a hand punch type would probably be the best.One could be made easily in your shop .

Expand it slowly and in steps until you have a snug fit

https://www.youtube.com/watch?v=STl8aYYcpb4

It would be very considerate and beneficial for the members of this forum to hear back from you on the final solution to the problem.

Sorry about that. I would like to close the thread on this.