Cold Weld - Non Toxic?

[nomaam22]

Hello:

I am working on a drinking container where I have to adhere 304 stainless steel tubing to 301 full hard stainless steel shim metal.

I am not able to weld the two materials together so I was looking at cold welding the two items together. However, after the cold weld has set it will be submerged in drinking water for long periods of time so it can not be toxic (or let go).

So far we have been testing different Loctite and JB cold weld brands but both companies are not recommending them for our application as they are not approved for use within such products.

Any suggestions?

Thanks.

 

[btrueblood]

By cold weld you mean epoxy adhesive?

Search for the term "NSF approved epoxy". NSF-61 I believe is the standard for potable water systems/devices.

The temperature at which your device is intended (or unintentionally exposed to) will probably also be useful for a manufacturer of adhesives to know.

 

[nomaam22]

Yes I am referring to epoxy adhesives.

Do you recommend any particular NSF-61 epoxy products which would provide a strong bond between stainless steel products? The temperatures I'm working with will be average room temperatures.

Thanks.

 

[btrueblood]

No, I have no recommendations for you. Suggest you contact or peruse the websites of adhesive manufacturers. Try 3M, Master-Bond, Loctite... Google will probably be your friend here.

 

[MikeHalloran]

If you flare the tubing, how much bond area can you get?



Mike Halloran
Pembroke Pines, FL, USA

 

[unclesyd]

What are your thicknesses?

Micro-Tig will probably do the job if not laser welding.

 

[nomaam22]

I am not flaring the tube, the bond area is fairly small, half inch wide shim metal bonded to the side of the tube.

With regards to the tickness of the metal, the tube is .25 OD, and the shim metal is 3 thou

Will Micro-tig destroy such thin metal?

 

[nomaam22]

Both 3M and Master-Bond replied to my inquiry and told me they had no products that would fit my problem... seems odd.

 

[MikeHalloran]

You have essentially zero bond area.
No responsible adhesive supplier would recommend that.



Mike Halloran
Pembroke Pines, FL, USA

 

[btrueblood]

Suggest you rethink your idea. Syd and Mike have given some good advice. Brazing might work too. If you have trouble with the 301 shim and welding, changing to a more weldable alloy (304...) is not impossible.

 

[ornerynorsk]

Is there any mechanical configuration that will work? Spring clip, shrink fitting, etc. Just throwing things out there as I have no idea what the configuration of your application is.

 

[nomaam22]

I need to secure the small 0.25 OD tube within a half inch tube opening (also about half inch in length) and I was going to use the shim metal to hold it in place as it needs to have a very low profile within the larger tube and also have a nice appearance.

I was not able to locate any type of spring clip or "locking ring" type of solution that would both work well and look good. The shim metal is great but I need to adhere the two together.

Any ideas would be great.

Thanks.

 

[btrueblood]

A sketch might help.

 

[nomaam22]

I drew up a basic sketch in paint and uploaded it to the following link

http://img405.imageshack.us/img405/9883/tubeintube.png

 

[MikeHalloran]

Annotation on the sketch talks about something that would be present, but isn't shown.
Something closer to a drawing might be more clear.

The issue that's still unresolved is where the shim stock goes. Is its plane of symmetry normal to the axis of the tubes, or does it intersect either, or contain either?

Secondary issue: Do you intend for the tubes to be concentric?



Mike Halloran
Pembroke Pines, FL, USA

 

[nomaam22]

Here is another image

http://img404.imageshack.us/i/tubeintube2.png/

This image shows the shim metal in place attached to the inner tube which allows the inner tube to stay in place within the larger tube. I hope this image clears up the idea of the shim metal being used to hold the small tube in place. We've tested it and it works well, however, we don't have a good / safe adhesive to use so we're not sure what to do to hold it in place.

 

[MikeHalloran]

Ah. That's a much better image for conveying your intent.

I still don't see a lot of bond area, unless the shim stock is formed around both tubes.

Consider this: Make the shim stock longer and put two gentle bends in it, so it takes the shape of a bulged triangle, which you bulge a little more to push the smaller tube into.

That makes the assembly self-fixturing, and may provide enough friction for retention; that's not clear from what we know so far.

If friction alone is not sufficient, you can (with some tooling cost) spot weld the shim to both tubes, or just put a dab of TIG weld on the accessible ends.




Mike Halloran
Pembroke Pines, FL, USA

 

[nomaam22]

The shim is only bonded to the smaller tube so it can be removed from the larger tube when needed.

Friction seems to be enough to hold the smaller tube with shim in place within the larger tube.

I have not tried bending the shim yet but if it can be done and self-fixturing then it would be great.

We are looking at large production so we need a method where we can construct many units with minimal time and costs.

 

[nomaam22]

Just an update,

The self-fixture design regarding bending the metal failed to hold the tube in place as it would twist from its own weight.

I took the metal to a shop and had it both spot welded and TIG welded and both destroyed the metal as it was too thin.

Any other thoughts? Does anyone know of a type of locking ring currently being sold that would work or a type of spring/wire/crimp?

 

[btrueblood]

You need to use a shop that is experienced in welding thin material. As unclesyd suggested, google the term "micro tig". I have had .002 to .005" thick SS304 diaphragms welded to support rings using an automated micro-tig process.