Laminating Plates Together . . . Brazing?

imwilliam · Oct 1, 2020

Hey,

I remember as a teenager taking a tour of a plant where they built fuel controls and they built them by making very thin sections, stacking those sections and then brazing them together in a furnace.

So I'd like to do something similar, stack a sheet of stainless, a sheet of copper and then another sheet of stainless, sort of laminate them together. The shape would be rectangular if it matters. But the joint can't just be around the edges because I'm then going to take that "stock" and cut something out of it so I want the "stick" to be throughout the joint so the pieces I cut out will stay together.

Any ideas on this, how I could go about it? I think it could be done in a vacuum furnace, but those are pricey for a side project and I'm not sure if even that would work joining flat plates together. Would a regular heat treat furnace do it with some extra prep and flux? What about a torch? Could I use copper itself to join the two stainless plates?

Any thoughts on this would be appreciated.

Halcohead · Oct 1, 2020

Size?

Yes this can be done with brazing, I would default to silver solder. Whether a torch is enough or you need a furnace depends on you size and flatness needs. Google this, brazing sheets together is commonly done in jewelry and metalsmithing.

For small parts diffusion bonding is also an option. Look up mokume gane.

wheels17 · Oct 1, 2020

I used to work at a plant that used -90F refrigeration to recover evaporated solvents from a recirculating air loop. We had huge air to air heat exchangers (2x12 foot inlet and outlet, 14 feet high,3 feet thick) for heat recovery made by Modine. The units were made of copper sheet, and had several hundred parallel plates with little Zs between the plates (think 60s radiators, same tech).

They had a jig where the components would be laid up with a flux/powdered braze combination painted on all contact areas. The fixture would compress the whole stack and it would be put into a big vacuum furnace for brazing. They reduced the cooling load by 90% on airflow up to 10,000 cfm going from 150-200 degrees F to -90 degrees F.
Modine doesn't seem to be in that type of business any more, but they do still make brazed heat transfer devices.

I think stainless to copper to stainless success would depend greatly on the type of stainless used. Thermal expansions would have to be carefully matched. 316 is very close to copper, but 410 is way away, and you'd probable be making potato chip shapes.

You might want to contact Welding Techniques | NobelClad to look at their products. They make laminated materials, but unless you are lucky enough to need something they already make, I'm sure the cost would be exorbitant. Explosive lamination would be the most fun.

Someone must make the nickel/copper/nickel laminate made for US coins, but I couldn't find out who made that in a quick search.

Explosion Welding Process - YouTube

richard newman · Oct 1, 2020

For a stainless/copper/stainless sandwich the stresses should be balanced and not cause distortion. Sort of like cold rolled plate. Just my WAG, no experience here.

Limy Sami · Oct 1, 2020

Quite what the OPs end game is I'm at a loss, but it sounds a lot like I was taught as a bi-metallic strip.

Bimetallic strip - Wikipedia.

Bill D · Oct 1, 2020

I think the US Mint uses explosive welding to weld clad coin sheets together before punching out the slugs.
Bill D

Joe Gwinn · Oct 1, 2020

Magnetrons (like in microwave ovens) are made by stacking punched copper sheets and brazing them in a hydrogen atmosphere. This yields full-face brazing, and the result is vacuum-tight. This was invented by Raytheon in WW2, and is what made airborne radars practical - machining that odd shape from solid copper took a skilled machinist about a month.

I read in a textbook on brazing that people do the same with steel sheets brazed with pure copper.

So I'd hazard that stainless steel will work, so long as it's clean enough. I'd find such a textbook and look it up, but that book belonged to a library.

Because the steel is thicker than the copper braze metal, and copper is soft, there won't be any differential strains due to temperature change - the steel will win, hands down, and the copper will comply.

Joe Gwinn

DDoug · Oct 1, 2020

Bill D said:
I think the US Mint uses explosive welding to weld clad coin sheets together before punching out the slugs.
Bill D

....and the "zig-zag" depressions that form the coolant channels would be gone in a millisecond.....

imwilliam · Oct 1, 2020

Halcohead said:
Size?

Yes this can be done with brazing, I would default to silver solder. Whether a torch is enough or you need a furnace depends on you size and flatness needs. Google this, brazing sheets together is commonly done in jewelry and metalsmithing.

For small parts diffusion bonding is also an option. Look up mokume gane.

So this Mokume Gane looks interesting, I watched a few videos on youtube and ordered a book on Amazon. It's not exactly what I'm looking for results wise, but as a way of simply binding plates together, it might be an option.

Oh, and regarding size, the pieces I want to pull out would be smaller than the "sheet" I'd be making, so the "stock" could be 6in wide by 12inlong, could be a little bigger or smaller; by half even, but the total thickness would be .375 or less I'd think

Thanks

imwilliam · Oct 1, 2020

wheels17 said:
I used to work at a plant that used -90F refrigeration to recover evaporated solvents from a recirculating air loop. We had huge air to air heat exchangers (2x12 foot inlet and outlet, 14 feet high,3 feet thick) for heat recovery made by Modine. The units were made of copper sheet, and had several hundred parallel plates with little Zs between the plates (think 60s radiators, same tech).

They had a jig where the components would be laid up with a flux/powdered braze combination painted on all contact areas. The fixture would compress the whole stack and it would be put into a big vacuum furnace for brazing. They reduced the cooling load by 90% on airflow up to 10,000 cfm going from 150-200 degrees F to -90 degrees F.
Modine doesn't seem to be in that type of business any more, but they do still make brazed heat transfer devices.

I think stainless to copper to stainless success would depend greatly on the type of stainless used. Thermal expansions would have to be carefully matched. 316 is very close to copper, but 410 is way away, and you'd probable be making potato chip shapes.

You might want to contact Welding Techniques | NobelClad to look at their products. They make laminated materials, but unless you are lucky enough to need something they already make, I'm sure the cost would be exorbitant. Explosive lamination would be the most fun.

Someone must make the nickel/copper/nickel laminate made for US coins, but I couldn't find out who made that in a quick search.

Explosion Welding Process - YouTube

That explosion welding is amazing, had no idea such a thing is possible. Thanks for the video

imwilliam · Oct 1, 2020

Joe Gwinn said:
Magnetrons (like in microwave ovens) are made by stacking punched copper sheets and brazing them in a hydrogen atmosphere. This yields full-face brazing, and the result is vacuum-tight. This was invented by Raytheon in WW2, and is what made airborne radars practical - machining that odd shape from solid copper took a skilled machinist about a month.

I read in a textbook on brazing that people do the same with steel sheets brazed with pure copper.

So I'd hazard that stainless steel will work, so long as it's clean enough. I'd find such a textbook and look it up, but that book belonged to a library.

Because the steel is thicker than the copper braze metal, and copper is soft, there won't be any differential strains due to temperature change - the steel will win, hands down, and the copper will comply.

Joe Gwinn

So I'm fairly sure this can be done with a vacuum furnace, but all of the ones I've inquired about are over the top expensive. This is a small side project, nothing that warrants the prices I've seen for a vacuum furnace. Now a regular furnace, that might be doable if it will do the job, I'm just not sure it will.

TheBigLebowski · Oct 1, 2020

I was at one of the 3d printing shows (RAPID + TCT) last year and I saw something extremely cool. There was a company there that came up with a way to sonic weld thin strips of material together. The end product would be a solidly bonded bar made of different materials.

I think this is the exact company I saw. Fabrisonic 3D Printing | 3D Printing Without Melting

I personally don't think 3d printing is quite what people crack it up to be, but that was the one thing at that show that really blew my skirt up.

:EDIT

Per their website, it looks like they will quote making a chunk of material for you, might be worth getting a quote?

https://fabrisonic.com/3dprinting/wp-content/uploads/2018/04/creating-new-colla.png

Joe Gwinn · Oct 4, 2020

imwilliam said:
So I'm fairly sure this can be done with a vacuum furnace, but all of the ones I've inquired about are over the top expensive. This is a small side project, nothing that warrants the prices I've seen for a vacuum furnace. Now a regular furnace, that might be doable if it will do the job, I'm just not sure it will.

Yes, that's the industrial-scale approach. The classic small-run dodge is a SS foil bag filled with methane, which is largely hydrogen and cracks at furnace temperature. There are also fluxes that people use. And some braze metals don't require flux. I'd look into some handbooks on brazing.

For pure copper, some phosphorus-bearing braze metals (many with silver as well) will braze copper to copper without flux. A little googling shows that there are many flux-less braze metals for stainless steel; all require a zero-oxygen environment, which can be an argon atmosphere.

Rob F. · Oct 4, 2020

imwilliam said:
So this Mokume Gane looks interesting, I watched a few videos on youtube and ordered a book on Amazon. It's not exactly what I'm looking for results wise, but as a way of simply binding plates together, it might be an option.

Oh, and regarding size, the pieces I want to pull out would be smaller than the "sheet" I'd be making, so the "stock" could be 6in wide by 12inlong, could be a little bigger or smaller; by half even, but the total thickness would be .375 or less I'd think

Thanks

You can try making mokume with stainless, I think it should work. But with mokume it is easier to make a smaller thicker piece, then feed to through a roller to thin it. How critical is it the laminations are an even thickness? rolling should keep them pretty even, thinning on a hammer not so much.

Most nice kitchen pans are SS and aluminum, but if you look a few are copper and stainless, finding a SS-copper-SS might take some looking, as well as a fat wallet.

imwilliam · Oct 5, 2020

Joe Gwinn said:
Yes, that's the industrial-scale approach. The classic small-run dodge is a SS foil bag filled with methane, which is largely hydrogen and cracks at furnace temperature. There are also fluxes that people use. And some braze metals don't require flux. I'd look into some handbooks on brazing.

For pure copper, some phosphorus-bearing braze metals (many with silver as well) will braze copper to copper without flux. A little googling shows that there are many flux-less braze metals for stainless steel; all require a zero-oxygen environment, which can be an argon atmosphere.

I'm running across the SS foil bag technique quite a bit, but I haven't read anything about filling the bag with methane, just paper that burns up the remaining oxygen in the bag. How would you fill the bag with methane, and by "cracks at furnace temperature" you mean it burns up?

I find a lot on brazing, but not much on furnace brazing on a small scale without a vacuum furnace.

You think a SS foil bag would help with diffusion welding in a furnace as well? Because right now I'm leaning towards diffusion welding rather than brazing. Questions that remain are if the SS foil bag will suffice and whether I can get the necessary pressure on the plates with some sort of screw/clamping fixture.

imwilliam · Oct 5, 2020

Rob F. said:
You can try making mokume with stainless, I think it should work. But with mokume it is easier to make a smaller thicker piece, then feed to through a roller to thin it. How critical is it the laminations are an even thickness? rolling should keep them pretty even, thinning on a hammer not so much.

Most nice kitchen pans are SS and aluminum, but if you look a few are copper and stainless, finding a SS-copper-SS might take some looking, as well as a fat wallet.

I'm looking for even laminations so to the extant that mokume is diffusion welding, I think it applies, but that's not the end product I'm shooting for.

As far as the pans go, I did go ahead and get All Clad, but not the copper stainless because it was way expensive and I'm guessing I'm just not a good enough cook to really appreciate the difference . But the normal All Clad while expensive, is nice stuff and I sort feel like since I make my living in manufacturing I ought to support other US manufacturers when I can.

Joe Gwinn · Oct 5, 2020

imwilliam said:
I'm running across the SS foil bag technique quite a bit, but I haven't read anything about filling the bag with methane, just paper that burns up the remaining oxygen in the bag. How would you fill the bag with methane, and by "cracks at furnace temperature" you mean it burns up?

The paper uses the oxygen up, leaving a lot of carbon, but not much on the scale of steel alloys, thereby preventing scaling, but isn't aggressive enough to remove the oxide from metal surfaces.

Fill the bag with methane by building a small metal tube into the bag, through which one feeds the gas. Or two tubes if flow-through is needed. At brazing temperatures, the methane will crack to hydrogen and carbon. Some will be used up scavenging any oxygen left in the bag.

Hmm. Non-catalytic thermal cracking of methane requires about 1200 C (2200 F), which may be too hot for some or most brazing alloys. Wel, the alternative is vacuum, or an argon blanket.

I find a lot on brazing, but not much on furnace brazing on a small scale without a vacuum furnace.

You think a SS foil bag would help with diffusion welding in a furnace as well? Because right now I'm leaning towards diffusion welding rather than brazing. Questions that remain are if the SS foil bag will suffice and whether I can get the necessary pressure on the plates with some sort of screw/clamping fixture.

You'll need to do some experiments, but I'd hazard that if you put the stack into a foil bag and seal the bag after purging it thoroughly with argon, you will be able to braze the stack applying clamping force through the bag foil sheets. I don't know the time-temperature-pressure curves for diffusion bonding, but it is widely done, so there must be a solution. I gather that you can use a longer time than large-scale production would tolerate. But the pressure will need to come from outside the hot zone - things turn limp at those temps.

Archer120x · Oct 5, 2020

imwilliam said:
Hey,

I remember as a teenager taking a tour of a plant where they built fuel controls and they built them by making very thin sections, stacking those sections and then brazing them together in a furnace.

That was Woodward. I used to machine those. Material was soft, I think it was 4000 series so the aluminum braze would stick. Ah the good old days...

For copper and stainless, silver braze and flux? Silver or solder bearing flux for an experiment?

Scottl · Oct 5, 2020

For what you want to do soft solder in a paste formulation would probably be best. Assuming the overall size is not too large it could be heated with a MAAP gas torch with fire bricks to contain the heat. I've many times soldered stainless, copper and brass using a tin/lead solder with 2% silver.

imwilliam · Oct 5, 2020

Archer120x said:
That was Woodward. I used to machine those. Material was soft, I think it was 4000 series so the aluminum braze would stick. Ah the good old days...

For copper and stainless, silver braze and flux? Silver or solder bearing flux for an experiment?

Hey Archer, that's exactly where I saw it. Struck me as so clever and left an impression that's lasted all these years.

Some sort of silver or solder bearing flux is probably worth a try, particularly if I can heat it with a torch as Scotti mentions below.

Laminating Plates Together . . . Brazing?

Plastic

Stainless

Stainless

Titanium

Diamond

Diamond

Stainless

Diamond

Plastic

Plastic

Plastic

Aluminum

Stainless

Diamond

Plastic

Plastic

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