soldering to 300 stainless?

dsergison · Sep 7, 2006

I need to attach little 1/8" dia 1/4" long SS tube sections in holes in a 1/8" thick o-1 flat stock.

I tried silver bearing solder paste as bought in the little syringe, with no joy. also some silver stay brite wire and electrical paste flux. I cant get the SS tube to wet.

Evan · Sep 7, 2006

I have used silver bearing wire solder to solder SS very successfully. It's all in the flux. Electrical flux isn't nearly active enough. The flux in the wire solder I use is a highly active chlorine based flux. I haven't ever used the solder paste so don't know what it contains but if it is advertised for use with electrical components it won't work.

[edit]

SS is attacked by chlorides so the flux needs to be a chlorine compound. You could try a little wipe with muriatic acid. Don't breath the fumes.

bluchip · Sep 7, 2006

The fuel header tanks in some ragwing Pipers are 304? SS and are simple sheet rolled and soldered with some type of soft solder. I used one once and resoldered it quite easily with 60/40 and tinstyter (ruby fluid) flux/cleaner. No trick at all.

tomwalz · Sep 7, 2006

Also Fluorine based fluxes. We braze to some stainless with standard Black Flux.
We use Bag-22, Bag-24, Bag-3 and similar. If you use a paste it is a mix of flux and solder. It would help if you posted both the kind of alloy and the ratio of alloy to flux in the paste.

In brazing problem we always look at surface preparation first. Make sure it is clean and grease free. We don’t like solvents very much but they can work well. We prefer a saponifying agent with free rinsing additives. We solve a lot of brazing problems by spraying the parts with Easy Off oven cleaner first.

Get an eye dropper and put one drop of water on the parts. If it forms a bubble then clean the parts. If it flows out into a little, flat shape then it is almost certainly clean enough.

Some stainless will form Chromium compounds upon heating in air which makes it impossible to braze. To rework these you need to physically remove the affected surface. If you can I would use abrasion.

Tom

3t3d · Sep 7, 2006

I had a customer that had the SS gold plated to promote soldering.
For those small parts, it was about $70.

This might not apply here, but someone else might benifit from some latteral thinking.

Pete

jim rozen · Sep 7, 2006

Tin the stainless tube with a flux specifically
designed for soft soldering stainless. They
are muriatic acid based and quite active. I
use Dunton's which is a liquid.

Once you tin it (I would suggest a 95 tin, 5
percent silver solder for this) you can
then sweat it to your other piece with a much
less active flux.

Jim

dsergison · Sep 7, 2006

thanks. I'll order some today.

Billy Boy · Sep 7, 2006

I've used a "killed" muriatic flux with great success on 304, 308, and 316. I bought it from McMaster. They call it Stainless Steel Flux. Now that I know the score a bit better it would seem that you can make your own real easy by desolving a chunk of zinc in a jar of muriatic... but you should be careful as this stuff is powerful, dangerous and highly toxic!

Good luck.

B

Butcher · Sep 7, 2006

Make SURE your surface is clean. I usually clean with solvent to get the big stuff off, and just before I start, I wash with liquid dish washing soap and hot water. It seems to clean the surface the best.

bcstractor · Sep 7, 2006

ESAB S200 flux and Harris Safety Silv 56. You need the right combination of flux and solder.

But it looks great when done. You do have to heat till the flux goes liquid before applying the solder (after it first dries out).

Chris P

dsergison · Sep 7, 2006

I get no joy in soldering. I tried every combination of:

I tried a fresh can of black acid paste brazing flux, that says right on it as the first item, for stainless steel. crap.

and rosin, crap.

I sanded my parts, and cleaned with laquer thinner. crap

I tried again my silver bearing paste. crap.

Stay-Brite silver solder, crap.

Every time cleaning to bright new metal and trying laquer thinner or not.... still crap.

with pencil iron. crap

with mapp torch. crap.

dsergison · Sep 7, 2006

so the black paste turns to a rubbery stuff, and then goes liquid again? huh...?

dsergison · Sep 7, 2006

I used to have some harris Stay-Brite wire and flux. (little $10.00 1/2 oz kit) but the flux is gone.

I have been trying with the wire with Harris high temp 700-1800 black brazing flux, as well as electrical rosin.

I dont think I'm not getting to that (brazing flux) heat range, but I did not know it goes liquid again. is it BAD to use it cooler than the heat range?

I cant even get the stainless rod tinned by it's self. scrubbing it with the iron, wire, etc..

thanks

jim rozen · Sep 7, 2006

The rosin will not work unless you tin with
the hot flux first.

The black flux is for brazing. Won't work
with soft solder. Don't use it.

Likewise white borax flux.

For what you want to do a small solder gun
or iron will supply plenty of heat. The
thermal conductivity of stainless is nearly
zero, so you have to chase the solder around
to get it wetted all around.

And if it isn't clean before you put the muriatic
acid flux on it, it will be afterwards.

Jim

dsergison · Sep 8, 2006

Jim,

I cant find Duntons at any retailer online.

so I'm going to get some more Harris stay-bright?

thanks for all your help. Youre spot-on.

P.S. I like my tig so much better, but these parts are way to small. If I never need to solder/braze again that would suit me fine.

Gazz · Sep 8, 2006

If you want to use silver solder, you have to have sufficient heat. I think your MAPP torch should be plenty. Clean your metal pieces with abrasive paper and don't worry to much about solvents unless the parts are very greasy or oily. Fixture them up so that everything is held together they you want it and apply the appropriate flux - I've used the black Harris stuff with good results. Heat your assembly gently at first to get the moisture to boil out and then verify that everything is still in the right place. Apply the heat to the bar stock and avoid the tubing. They will overheat rather quickly, boil the flux off and cause a layer of oxidation to form on them which is no good. Use a wire type silver solder and dip the end in the flux. When you think the piece is hot enough touch it with the wire and it should melt and flow, wetting to both pieces. If you put the end of the silver solder wire directly in front of the torch and your workpiece is not hot enough, it will just ball up so be careful of that. Coax the wetted solder along to where you need it with the torch and a soldering pick if you have to. Sounds like a relatively simple job but if you still have problems, get a bigger torch.

dsergison · Sep 8, 2006

the two parts together are the size of a quarter.
enough heat is not a prroblem.

that method does not work at all with the stainless. (for me)

I cant even wet solder to the stainless with an iron. it melts but just balls up. it's all very clean.

I think Jim R has the answer. muriatic based low temp flux.

tomwalz · Sep 8, 2006

Flux absorbs oxygen and keeps the parts form oxidizing. It has some cleaning properties but it is safest not to count on it to do much cleaning. Black Flux from Harris, Lucas Milhaupt or Wolverine (used to be Engelhard) is Potassium salts of Boron and Fluorine

The salts are in a water based slurry. The salts will settle out so mix the flux before using it. When you heat the flux the water will boil out first. This can move small parts so watch and plan for it. Once the flux has had the water boiled out of it, it does sort of look like rubber. As you keep heating the flux will turn liquid and flow out evenly over a clean surface.

When you are though brazing and the flux is room temperature you should be able to readily remove it with warm water and a steel or brass brush. You can also scrape it off with a thumbnail under warm water. Hot flux is extremely good glue. Wait for it too cool. If you have a layer of gray left after brazing you have not used up all your flux. If the Black flux has all turned clear you have used it up. You allowed oxygen to get to the braze joint.

If you have already heated the stainless steel without proper flux protection you may have created chromium compound which make it virtually unbrazeable until they are removed.

We would first flux both parts then wind a ring of the braze alloy, dip it in flux and preposition it around the joint. Then we would flux over that and heat.

The other ways described can also work very well. I am just offering another way to do it that we like better.

Tom

tomwalz · Sep 8, 2006

If this still doesn't work then send me a couple parts and I will see what I can do no charge.

tom

jim rozen · Sep 8, 2006

TomW's suggestions are spot on - for high
temperature silver brazing. The flux he
suggests won't work at all for soft soldering
(below 800F) work.

McMaster Carr carries a generic liquid acid
flux for stainless steel, it might be the
duntons. Even if not, I suspect it would work.

When using it, have plenty of ventilation, also
the overspray will blow around and get on you.
Wash afterwards with plenty of soap and water.

If you find youself itching at some spot after
using it, go back and scrub that spot real well,
you got a bit of flux on your skin.

Safety glasses a must.

Jim

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