Sciencemadness Discussion Board - Flux for soft soldering stainless steel

Flux for soft soldering stainless steel

wg48temp9 - 10-7-2021 at 07:43

From patent US3660127A a few examples of flux for soldering stainless steel, most examples use OTC materials. I have not tried any of them yet.

and just incase your google is broken the patent is at: https://patents.google.com/patent/US3660127A/en

zed - 10-7-2021 at 21:14

Ummm. Anodize the stainless in a copper sulfate solution, when the stainless turns black, reverse the polarity and plate out copper on the stainless steel. Rinse, dry, flux and solder. Should be no problem.

Strength of bond? I don't know.

draculic acid69 - 11-7-2021 at 01:04

Strength of bond is probably not going to be very strong. For structural integrity I'd guess no good, for electrical connection yeah it might hold. just get it welded.

wg48temp9 - 11-7-2021 at 01:09

Quote: Originally posted by zed

Ummm. Anodize the stainless in a copper sulfate solution, when the stainless turns black, reverse the polarity and plate out copper on the stainless steel. Rinse, dry, flux and solder. Should be no problem.

Strength of bond? I don't know.

Generally in electroplating practice they go to a lot of trouble to clean the part and in particular to remove surface oxide. So anodising the SS first seems like a terrible idea to me.

wg48temp9 - 11-7-2021 at 01:36

Quote: Originally posted by draculic acid69

Strength of bond is probably not going to be very strong. For structural integrity I'd guess no good, for electrical connection yeah it might hold. just get it welded.

Yes TIG welding is the way to go if the distortion is not significant. but my TIG welding skill is terrible. But it is getting better but slowly. After getting zinc fume fever a few times from practicing with zinc plated steel I have not had much practice. I need a fume extraction welding table. in effect an upside down fume hood LOL

johnsonnamedborris99 - 12-7-2021 at 00:35

thats what tig welding is for

Fulmen - 12-7-2021 at 02:19

Quote: Originally posted by wg48temp9

I need a fume extraction welding table.

Nah, all you need is clean steel. Zinc will f*ck up both you and your weld.

wg48temp9 - 12-7-2021 at 12:14

Quote: Originally posted by Fulmen

Quote: Originally posted by wg48temp9

I need a fume extraction welding table.

Nah, all you need is clean steel. Zinc will f*ck up both you and your weld.

Having been, as you put it f*cked up, (flue like symptoms) by inhaling an estimated few mg of zinc oxide dust a few times, I am going to take the advice of many including mine and take precautions to avoid inhaling any welding fumes.

Ideally I want a positive pressure welding helmet. I do have an auto darkening mask (best thing since sliced bread LOL) Since being given a battery powered vacuum cleaner, I have considered using its blower to supply clean air to a hood I will have to attach to my mask.

Fulmen - 12-7-2021 at 12:46

Honestly, it's not that hard. None of your suggestions are bad, far from it, but they aren't necessary as long as you stay away from plated metal. You can't weld through it, and grinding the metal clean presents another source of exposure.

I've been TIG-welding a fair bit of stainless the last few months, most of the time I don't even bother turning on the extraction fan (I do for cutting and grinding).
Now if you're also using MIG or stick some smoke control is required so why not do it right from the start. Just saying you can do TIG without it.

markx - 29-7-2021 at 05:26

Hydrochloric acid and zinc chloride in combination with a silver bearing solder work pretty good on soldering stainless. Surfaces must be cleaned abrasively beforehand to remove most of the oxide coating. I have not had much of a success with phosphoric acid based concoctions.
Electrolytically etched surfaces can sometimes be notoriously difficult to solder, so I would stay away from that path.

Of course nothing beats TIG welding....it is a wonderful method for joining basically all known alloys. Nowadays machines are very compact and have a plethora or modes to perform quite the magic on precision melting of metals.

[Edited on 29-7-2021 by markx]

Panache - 7-8-2021 at 02:31

Stick or arc welding with stainless rods is a no brainer and ensures adequate 'penno' on the weld (thats penetration for all you welding jargon ignooramiuses!).
Problem is doing any fine work, fuck no.

wg48temp9 - 8-8-2021 at 00:29

Quote: Originally posted by Panache

Stick or arc welding with stainless rods is a no brainer and ensures adequate 'penno' on the weld (thats penetration for all you welding jargon ignooramiuses!).
Problem is doing any fine work, fuck no.

Unfortunately its mostly fine work joining SS vacuum flanges to SS tubes with wall thicknesses from about 0.5mm to 2mm with diameters of 25mm to 100mm. With my skill level it will not be possible with stick welding, a bit like trying to weld a car body with a stick welder. It has to be MIG or TIG.

Panache - 8-8-2021 at 15:53

Quote: Originally posted by wg48temp9

Quote: Originally posted by Panache

Oh ive got a box of new stainless vacuum flanges and other associated high vacuum miscellleana, if you want them you csnhave them, let me know and I will post photos, theres a bunch of various parani gauges. (Sorry not gauges just the detectors) some flanged through electrical shit etc.
It was all new parts gotten from the thermo fischer waste bin...they love buying companies, closing them down and throwing all the parts!

Panache - 13-8-2021 at 03:28

And here’s a group shot omitting the 576478548(it’s probably not that many),annealled, individually packaged, copper seal rings in the various sizes.
I’m in Melbourne Australia though....there’s also all those piraña ( detectors if you want some ...the thread is in the materials section, it bugged out initially so the photo isn’t till the end of the thread.

1C0DFE96-DC0A-4FF5-89A9-A719A9F45A5B.jpeg - 3.2MB

stamasd - 22-9-2021 at 11:38

Soldering stainless steel is going to be a futile endeavor. And if TIG welding is not an option, I suggest a 3rd option: brazing. One uses silver solder and specific fluxes for that. It can be done with a propane torch, and requires less skill than TIG. It should be good enough for low vacuum - wouldn't guarantee for high vacuum though.

(edit) there are instructional videos for brazing stainless steel all over youtube.

[Edited on 22-9-2021 by stamasd]

markx - 23-9-2021 at 05:42

Quote: Originally posted by stamasd

Soldering stainless steel is going to be a futile endeavor. And if TIG welding is not an option, I suggest a 3rd option: brazing. One uses silver solder and specific fluxes for that. It can be done with a propane torch, and requires less skill than TIG. It should be good enough for low vacuum - wouldn't guarantee for high vacuum though.

(edit) there are instructional videos for brazing stainless steel all over youtube.

[Edited on 22-9-2021 by stamasd]

I would not say that soldering stainless steel is a futile attempt. I've been successful on many attempts with silver bearing solder and hydrochloric acid based flux. Soldering thermometer ports into reflux column e.g. Soldering copper pipes to thin stainless mounting plate in a heat exchanger. So it can be done and has a purpose in lack of other options. The joints lack the strength of a weld or braze, but for small parts that do not have to endure a lot of stress it makes sense. Soldering is also desirable if distortion of the parts is to be avoided. Brazing and especially welding of stainless shall induce a lot of stress distortion even when done skillfully and with undue involvement of extra heat. I guess it all depends what kind of conditions the joint has to survive....if they are decently mild, then a soldered connection may do quite ok as far as practical purposes are considered.

wg48temp9 - 23-9-2021 at 06:11

Quote: Originally posted by stamasd

Soldering stainless steel is going to be a futile endeavor. And if TIG welding is not an option, I suggest a 3rd option: brazing. One uses silver solder and specific fluxes for that. It can be done with a propane torch, and requires less skill than TIG. It should be good enough for low vacuum - wouldn't guarantee for high vacuum though.
(edit) there are instructional videos for brazing stainless steel all over youtube.
[Edited on 22-9-2021 by stamasd]

Thanks for the suggestion. I did consider that but I thought the distortion and oxidation would damage the vacuum flanges.

I checked out the video (the link below) of a guy silver soldering a SS coupling to a SS pot using a small propane torch. It did easily melt the silver solder though I don't know what type of silver solder it was. The oxidation did not look significant so I will try it after I order the lowest melting temperature silver solder I can buy.

https://www.youtube.com/watch?v=OpMFQFi6Hh4

wg48temp9 - 23-9-2021 at 06:59

Quote: Originally posted by Panache

And here’s a group shot omitting the 576478548(it’s probably not that many),annealled, individually packaged, copper seal rings in the various sizes.
I’m in Melbourne Australia though....there’s also all those piraña ( detectors if you want some ...the thread is in the materials section, it bugged out initially so the photo isn’t till the end of the thread.

Thanks for the offer. I guess the cost of posting almost anything bigger than a letter from Australia to the UK will be expensive. Sorry for the delay in replying to you.

I have some noisey vacuum gauges and I eventually splashed out (~£40) on a used full range gauge believed to be good. I tested it on one of my well used and noisy vacuum pumps filled with filtered oil. It went down to about 30 microns but the reading was fluctuating +/-30 microns. Possibly caused by the pulsing from the pump. When I turned off the pump the oil was sucked up in to the gauge is less than minute while the oil level in the sight glass dropped about about 15mm. Ouch! I guess the gauge is out of calibration now.

[Edited on 9/23/2021 by wg48temp9]

stamasd - 23-9-2021 at 08:23

Quote: Originally posted by wg48temp9

For stainless steel to be used for vacuum, I recommend using a "hard" silver solder, i.e. a solder with a high % of silver. That does not mean that it will have a higher melting point though: compare the 35% silver and the 56% silver solders below
https://www.harrisproductsgroup.com/en/Products/Alloys/Brazi...
https://www.harrisproductsgroup.com/en/Products/Alloys/Brazi...

the 56% silver solder actually melts at a lower temperature than the 35% one. It's still above 600C though. I'd recommend the 56% one.

(edit) and even though the filler material is called "solder", the procedure is still brazing not soldering.

(edit2) and if you're looking for the best way to make non-permanent unions of vacuum parts, i.e. gaskets, the best material for vacuum gaskets in my experience is pure indium. It's very soft, does not leak, and it's completely recyclable. You can reuse it indefinitely to make custom gaskets as it melts at low temperature. I use custom molds made from silicone rubber for that. The major downside of indium is the cost. It's expensive. But a little goes a long way. For instance, you need less than 3g to make a gasket for a KF50 joint.

[Edited on 23-9-2021 by stamasd]

wg48temp9 - 28-9-2021 at 13:53

Apparently most silver solders contain zinc in addition to silver and copper. Zinc is not recommended for high vacuum use because of its high vapor pressure.

So I thought I should check what its vapour pressure is near room temperature. It appears to be less than 10^-10 bar at 400K so it is probably not significant for anything I want to do.

I found the following graphs plotting the vapour pressure vs temperature. of the common elements. They may be useful to others.

Sorry I directly loaded the second graph from the original paper (https://www.powerstream.com/vapor-pressure.htm. ) its full size so its huge.

[Edited on 9/29/2021 by wg48temp9]