Brazing Stainless Steel... / General Science and Electronics / Forums

Forums

4hv.org :: Forums :: General Science and Electronics

« Previous topic | Next topic »

Brazing Stainless Steel...

1 2 3 next

Move Thread

LAN_403

Patrick

Mon Mar 18 2013, 07:09PM

Registered Member #2431 Joined: Tue Oct 13 2009, 09:47PM
Location: Chico, CA. USA
Posts: 5639

( this is an entirely different purpose from my "soldering of nickel" thread. )

Im having trouble getting good wetting and flow from my nickel-silver brazing rods to the Stainless.
iM wondering if the loss of true mapp gas is a contributing factor? I now only have the "Map // Pro" crap now.

Im using alot of flux, its the right knind of rod and flux (HAR-14FC-18), im getting it clean, tight fit-up and shiny, then red-yellow hot, the rod melts but they are slow to flow and cappillary into the joint.

should i use OXy-acetylene?

Is there any advise for my circumstance? Id be grateful.

Platinum

Mon Mar 18 2013, 10:02PM

Registered Member #3926 Joined: Fri Jun 03 2011, 08:32PM
Location: UK.
Posts: 525

Do you have a TIG set you could use, this would save alot of trouble, or even a MIG set with SS filler (308L is the best, as this welds most grades of SS)

You can weld SS with oxyacetylene with SS Filler rods used in TIG welding. If everyone is using the TIG sets at work, I use this method. With acceptable results. Make sure you use flux with this method. If I remember alot more acetylene is used, with a neutral flame.

Ash Small

Mon Mar 18 2013, 10:32PM

Registered Member #3414 Joined: Sun Nov 14 2010, 05:05PM
Location: UK
Posts: 4245

You could try using pure copper for brazing stainless. It's a long time since I've done it, but I seem to remember it can be much easier. I can't remember what flux I used, but google should turn something up. If not, just try using what you have, or whatever is easily available. (I know I used to use borax and/or boric acid on occasions). It's probably 20 years or more (at least) since I last tried it.

Patrick

Mon Mar 18 2013, 11:31PM

Registered Member #2431 Joined: Tue Oct 13 2009, 09:47PM
Location: Chico, CA. USA
Posts: 5639

im trying to avoid thermal distortion, but i guess TIG'ing could do less heating too.

Hazmatt_(The Underdog)

Tue Mar 19 2013, 12:09AM

Registered Member #135 Joined: Sat Feb 11 2006, 12:06AM
Location: Anywhere is fine
Posts: 1735

You will probably have to TIG it.

Oxy-Acetylene will cause the stainless to catch fire.

A big problem with torching stainless, and exposing it to an oxygen atmosphere, is that the Nickle content oxidizes, which you cannot solder to, and the Chromium diffuses, causing the metal to become brittle and crack. Get it too hot, and it will combust.

I was researching how to repair one of my stainless vacuum traps and found that oxidation is avoided by industry during welding/soldering by the use of an ammonia or intert gas atmosphere, and intense heating, but who has that capability in their backyard!

Most of us dont.

But if you TIG your workpiece, you should be okay.

doctor electrons

Tue Mar 19 2013, 12:47AM

Registered Member #2390 Joined: Sat Sept 26 2009, 02:04PM
Location: Milwaukee Wisconsin
Posts: 381

Use a low temperature silver solder and the appropriate flux and you'll be fine. When in doubt, tig it!

Carl A. Willis

Tue Mar 19 2013, 06:27AM

Registered Member #9640 Joined: Wed Jan 16 2013, 07:53AM
Location: Albuquerque, New Mexico
Posts: 26

Brazing of stainless steel with silver alloys is usually pretty straightforward. I do quite a bit of it.

Flux is important. It is sold in two varieties: "white" (suitable for small, delicate work) and "black" (suitable for heavy-duty jobs). Look for suitable flux by these names. It is inexpensive and probably available locally in a welding supply store. If not, eBay is a great source.

Temperature is important. You must be able to reach a uniform, cherry-red color or the braze alloy won't melt. MAPP gas is fine. Acetylene is fine. Propane is fine. (All are typically combined with oxygen in a premix blowpipe torch). A slightly reducing flame is recommended, but it doesn't matter too much as long as you don't overheat the metal.

Cleanup is important. First, get the hardened flux off the finished joint by dropping the still-hot part into hot water. Pickling improves the surface appearance and restores the protective "stainless" properties to the alloy. To pickle 304 stainless after brazing or welding, obtain some Whink (hydrofluoric acid) from WalMart or other business with a well-stocked cleaning aisle, and some 70% nitric acid (can usually be obtained by the gallon jug from a metal plating shop; expect to pay about $50 cash for the privilege). Mix the Whink, the nitric acid, and some warm tap water in about a 1:1:1 ratio and drop the part in it. Lift it out every few minutes to wipe off the surfaces with a sponge (black junk often comes loose). Be sure to wear gloves. Dilute HF is not a problem usually, but in the presence of dilute nitric acid it becomes much more corrosive to tissues and it causes very annoying delayed burns under the fingernails. Parts are usually suitably pickled in under a couple hours and come out looking great. The pickling solution can be stored and reused.

-Carl

Ash Small

Tue Mar 19 2013, 09:47AM

Registered Member #3414 Joined: Sun Nov 14 2010, 05:05PM
Location: UK
Posts: 4245

Here's an example of stainless steel refrigeration equipment brazed using copper:

Hazmatt_(The Underdog)

Tue Mar 19 2013, 07:23PM

Registered Member #135 Joined: Sat Feb 11 2006, 12:06AM
Location: Anywhere is fine
Posts: 1735

I'd always recommend staying away from even dilute HF. It really is nasty stuff, and can cost you your fingers, or worse.

Carl, if you have been burned by HF, you should talk to a physician. HF targets the Calcium in your bones and causes irreversible damage over time.

Something to think about.

Carl A. Willis

Tue Mar 19 2013, 09:23PM

Registered Member #9640 Joined: Wed Jan 16 2013, 07:53AM
Location: Albuquerque, New Mexico
Posts: 26

Hazmatt_(The Underdog) wrote ...

I'd always recommend staying away from even dilute HF. It really is nasty stuff, and can cost you your fingers, or worse.

Sure, abstinence is the only 100% effective protection. However: poisonous, corrosive fluorides are practically unavoidable if you get into brazing. They are in the flux (the name of the element itself attests to this use). They are in the pickle bath. They are hazardous materials and a wealth of relevant MSDSs are available online to deliver the canonical safety admonitions about handling them. It goes without saying that this information--whether for Whink, or flux, or whatever--should be the reference of first recourse for anyone unfamiliar with the products. If these kinds of warnings are one's only frame of reference, however, it is easy to conjure up scary scenarios that have little grounding in reality because the nuances are not discussed. HF at the ~2-3M concentration found in Whink, and recommended for use removing rust stains from clothing, is practically edible (used to taste like lemon juice, but they have put a bitterant in it now), whereas 40% reagent HF (which is not easy to obtain) will flay a man, eat his bones, AND ruin the glaze on his bathroom sink before he can say "calcium gluconate injection". I don't always wear gloves when I use Whink, but when I do, it's because there is nitric acid added to that Whink, giving it an appetite for live cuticle. And you know, come to think of it, goggles might not be a bad idea either! Safety first!

-Carl

1 2 3 next

Moderator(s): Chris Russell, Noelle, Alex, Tesladownunder, Dave Marshall, Dave Billington, Bjørn, Steve Conner, Wolfram, Kizmo, Mads Barnkob