Bonding copper to stainless steel

[Boomer343]

Well folks in the past I have used the diverse talents and experiences of board members and now I'll ask again.

I have a special project that is consuming, as usual, more time and resources than I had anticipated....and I'm usually on the worst case senario band wagon ....

So I have a 1/2 " copper tube, a stubout so it is a little thicker than regular copper plumbing pipe. I am inserting a 25mm x 1 mm piece of stainless steel into it with a small tab 5 mm coming through the other side of the tube. Basically a knife through a tube.

So I can use acid flux and get solder to stick but it needs to withstand vibration and I'm not confident of it lasting under stress. If I increase the heat and use silver brazing then I weaken the stainless because it is so thin and the gas torch is just not that accurate.

So....I have in my past used 2 part adhesives to put steel decks onto truck deck frames and bonded alloy trailers parts togehter with 2 part glues.

My thought is to set the pieces up as I have for soldering/brazing and fill the tube with a two part adbesive. I can put a couple of holes into the "blade" and roughen things up and it is all new clean material.

So I'm looking for direction or suggestions....I can't afford to have these come apart at 12000 (small) oscillations per minute so any help appreciated.....

Thanks in advance from a mad scientist....or just an old fool as my wife calls me....VBG

[BlkBird]

As long as it's not structural this stuff might work.  Biggest problem is that you need the "gun" to squeeze it out properly and that add substantially to the cost


3M Automix Panel Bonding Adhesive - 08115


 

[Rick Hall]

... then I weaken the stainless because it is so thin and the gas torch is just not that accurate.

Last I checked... SS doesn't really heat treat, at least the 300 series. You should be able to get it red hot with no ill effects. Use a smaller tip on the torch, seriously, perhaps find someone to TIG?

What say you use a silver bearing solder, not a silver solder used in HVAC work. Perhaps pre-heat everything at 500 degrees in you kitchen oven. Pencil iron may work then.

Commercial epoxies should work OK in a vib environment. Something like West or MAS, I know they build planes with West. Leave the JB crap for fixing tennis rackets and toilets. Scuff it up good, and pre-clean with IPA or acetone just before bonding.

Is there any way you can upset one/more of the parts? Like a rivet, or prong on the copper that gets peened in, or bent over/into the SS bit?



Rick

[Boomer343]

Blkbird I've used the products like that in the past and as you say the gun etc add to the cost. I may be able to solder the SS tab that comes through the other side or even braze it in.....that would hold the position for an adhesive fill....damn glue suppliers keep changing the tube/gun sizes....

Rick part of the problem is I don't know the stainless I am working with....yeah I know... blind leading the blind....it is a mfg piece but it is inexpensive/massed produced so I doubt it meets any astm standards.

I can get a tight fit on the wide part of the blade both edge to edge and flat to flat. I'll check into those adhesives you mentioned and can roughen and clean no problem.

[Rick Hall]

I just thought of furnace brazing. Not sure that's in your budget though. Silicone bronze filler rods will meld with almost any metal. Not sure those are in your budget either

Now it's been a few years since I 'retired' from machine shop, but I remember 300 series is not magnetic (or ever so slightly magnetic), and 400 series was. Put a magnet on it.

303 and 304 where by far the most common back in my day, 316 for special apps (that I can't remember). 400 series for it's hardenability and moderate corrosion resistance, like knife blades.

SS is corrosion resistant because it forms a surface oxide, almost the minute after you machine the surface. This oxide can be accelerated/deepened by a process call passivating, basically an acid bath. Much like aluminum, SS needs a good cleaning before bonding/welding.

Rick

[Boomer343]

Rick work with me here...simplify...simplify.....VBG

Right now this is very much a small cottage industry.....brought about because I said I could make this part and if I can be sure they will last then once I get it set up well heck I could be like Snarf or TCro !

I'm limited on my equipment...hell the business manager went off like a rocket on a new dremel rotary tool...

My neighbour dropped by with some magic flux made by Certanium called Flux 34....he figures about 35 or 40 years old from when he sold their products...probably has chemicals that have been banned in the solar system....just might work!

Thanks for the suggestions ...gets a person to refocus and consider a few more angles....

[Rick Hall]

Couple of people that frequent this forum know I can keep stuff private.... Should be able to figure my address, send a pix/sketch is you can, or if you want to.

Sounds like you want to insert a single edge razor blade into a handle made if heavy duty 1/2" copper tube.

If using an epoxy fill/bond, jam the tube into a chunk of styrofoam, creating a plug that will prevent the filler from filling the whole tube. The plug can be removed with modest heat (200F) and a pick, if removal of the plug is important. Acetone will work too, but it'll take a lot! Use West/MAS epoxy with some of my 'proprietary' fillers/stretchers. Drill/grind a couple of holes in the SS knife blade to key it into the epoxy mix.

Flux is flux, no hazardous chemicals that I've know of. Case hardening steels in a cyanide salt bath like we used to do though...

Rick

[Boomer343]

Rick I sent you an email....at least I think and hope I did...

[Miss Silvera]

Why not use Silver solder or this   http://www.brownells.com/.aspx/pid=25526/Product/STL-1260-SILVER-BRAZE

They use this to mount front sights and ribs to guns and it is under a lot of pressure and vibrations...

[MAN OF BLUES]

The real key is the fluxing procedure, the stainless requires a hydrochloric acid type flux, and the copper needs to be clean, and pre tinned prior to the braze attempt, then the parts are assembled, and the steel part heated, and the joint fed with the braze/solder. This keeps the oxide layer down on the stainless surface until it reaches the wetting/bonding temp of the solder.
these splain it somewhat, but the last link is the kicker....
and of course, it comes from BEER BREWER's....who are next to gods in the heirarchy of life....

found this in my searches;
"You can use EUTECSIL 1020XFC, which is elastic flux-coated silver alloy for low heat joining of ferrous and non-ferrous metals ..
You have to heat broadly along the joint line with a carburizing oxy-acetylene flame, then touch 1020XFC rod to joint until the flux is melted off and then feed it into joint, keeping the flame cone roughly one inch away, and continue melting the rod until a continuous fillet is observed ..
Allow deposits to solidify, then quench in water and wash away flux residues .."

and also this;
"Yes, you can solder stainless steel and copper together. It's done all the time in breweries. It takes a special flux. Use a lead free solder. First tin the copper with solder. Apply flux to the stainless steel, and fit the two piece togethers. Then heat the joint, while feeding more solder into the joint once it is hot. Use a propane torch. It's important to tin the copper first, then flux the SS. Using this method will protect the SS from the air until it is hot enough to apply the solder. Don't over heat the SS since it will oxidize and become brittle."

here's the good stuff:
http://www.brewingtechniques.com/library/backissues/issue2.6/palmer.html


 

[Rick Hall]

Rick I sent you an email....at least I think and hope I did...

Message received.

[MAN OF BLUES]

another interestic video, not as exact as you are attempting.... but interesting.
Brazing Copper to Steel


http://youtu.be/m4ooVKKzSK0

[Boomer343]

Well it turns out that I did the old assume....looked like stainless, worked like stainless but it is magnetic....oldest trick in the book and I missed it. So it is a tool steel of some sorts which explains some things about why I could get solder to stick to it.

Going to look into the vids, thank MOB.

Rick and I have been kicking around a few solutions.

Beer, good beer..... is one of life's pleasures....

BTW my neighbour also dropped off some Eutectic silver brazing rods he has had since well a long tme....

[Nosmo]

For a non-heated alternative, Loctite Depend 330 structural adhesive.

I used to use it in aircraft repair to bond aluminum structure together.  Usually you'll break the metal before you'll break the bond.  I use it now in the things I build to bond super-slick silicone based rubber to hard-anodized aluminum parts.  I have yet to find anything this stuff won't hold together.  But heat is used to break the bond for disassembly, so if your metal thingy will get hot, then it wouldn't be the ticket.

http://www.henkelna.com/cps/rde/xchg/henkel_us/hs.xsl/full-product-list-7932.htm?countryCode=us&BU=industrial&parentredDotUID=productfinder&redDotUID=0000000I1J

[Boomer343]

Nosmo the issue seems to be that because what I would be doing is filling the space around the blade inside the copper tube then there would be a falling off on the adhesive strength. From the charts on the Loctite product sheets the largest gap they tested at is .5 of a mm....I'm at about 5 mm on either side of the blade.

[B.D.F.]

Some stainless steels are magnetic. Surgical stainless, what we know in the US as the 4XX series (420, etc.), is both heat treatable and magnetic and a true stainless steel.... that will rust moderately. If the steel you have is magnetic, and there is enough carbon in it, it will also heat treat so any type of hard soldering will risk (over 800 F) risks making the steel brittle.

Unless there is a lot of strain put on the blade, soft soldering will probably work fine. Soft solders will rival copper in hardness and actually be tougher than copper so the copper tube will probably fail before the bond between the copper and the steel. Of course I have not seen the application so that is a general tendency rather than a hard opinion.

Brian

Well it turns out that I did the old assume....looked like stainless, worked like stainless but it is magnetic....oldest trick in the book and I missed it. So it is a tool steel of some sorts which explains some things about why I could get solder to stick to it.

Going to look into the vids, thank MOB.

Rick and I have been kicking around a few solutions.

Beer, good beer..... is one of life's pleasures....

BTW my neighbour also dropped off some Eutectic silver brazing rods he has had since well a long tme....

[Boomer343]

BDF thanks for the input....I'm pretty sure the material I'm working with isn't 4xx series stainless. In my prototypes I'm finding that because of the high frequency oscillations that any imbalance causes problems. I tried wrapping the blade around the outside of the tube and using rivets to fasten but it's too imbalanced.

So after thinking about it some more and to avoid affecting the blade steel I'm going to run the blade through both sides of the copper tube and use some Braze 505 to put it together and have a flush surface. Then I'll tack the edges on the other side. I have a tight fit between the blade and the copper but next have to refine my  layout and machining of the copper tube. Getting past the point of a sharpie and a straight edge and my hairy eyeball is proving to need a haircut....