Silver Solder Problem

[myles]

Hi there. Am having a problem trying to solder a stainless bowl onto a stainless pot. Have been using a Bernzomatic MAP torch with the Bernzomatic nickle silver braising rod and it just will not flow. Googled the braising rod and it seems it may not have enough silver in it.

I have ordered some Cupalloy 49% silver solder and the appropriate flux instead ( recomended for stainless steel). Just wanted to know if anyone has previously had trouble with the Bernzomatic brand before. Don't realy want to resort to oxy acetylene as I deliberately bought a very thin stock pot as it is going in a double boiler. Had thought the oxy might be a bit to agressive on such a thin material and burn through it.

[Dnderhead]

most use lead free solder. not brazing rod

[BW Redneck]

Stainless just doesn't like to wet very well with most solders out there. I cannot say from experience, but others (maybe Gingerbreadman?) have said that it's like pushing a puddle around more than anything like pouring water into a joint.

[rad14701]

The two big issues with soldering stainless are 1) whetting, as BW Redneck mentioned, and 2) heat dissipation/retention issues, which make proper adhesion even more difficult... I've gone so far as to apply a heat sink to make thermal transfer more manageable...

[Hack]

I've just finished soldering a 2" copper pipe to a stainless mixing bowl with silver solder for my new column. It gave me fits until I figured out a couple of tricks. Maybe they'll help you. I had taken the copper pipe and hammered over the end to give about a 1/4" flange around the end of it as a mating surface to the mixing bowl. I had trouble getting solder to stick to the bowl at first. I ended up having to tin the mating surface of the bowl with solder first. I had a couple of different fluxs to choose from a paste flux and a liquid flux. Although I usually prefer a paste flux when soldering but the liquid worked better on this. I noticed that the liquid flux's label said it was good for stainless while I don't think the paste said for sure. I also picked up some pointers on the novice how to solder thread. Pintoshine has posted some good info on it. I ended up using my electric soldering iron set to its highest setting to get the stainless tinned. The trouble I was having with the torch was that it would overheat the flux and burn it on the stainless leaving a black brown gack on the surface that the solder wouldn't stick to. The stainless needs a clean shiny surface to work with. So, using the soldering iron, I'd squirt liquid flux on the area to be tinned. Then I'd heat it with the iron. Once it was hot enough I'd apply the solder to the iron, not the stainless. It would then form a small puddle and I'd work my way around. Sometimes I'd have to reapply the flux to get the tinning to stick.

I know this next part doesn't exactly apply to your situation but maybe something I say will spark an idea. Once I got the tinning done the next challenge was to get the copper pipe soldered to the bowl. Initially I had trouble with the thin stainless bowl expanding and contracting differently with the heat and messing up my solder joints, because I was tring to work my way around the pipe with the heat. What ended up working was applying the heat to the 2" pipe about an 1 1/2" up the pipe. The idea isthat since the copper transfers heat very well it would eventually heat uniformly and melt the solder tinning all the way around at once. Once that happened, while maintaining heat I added a bit of solder here and there to fill the gaps and was done. There is a big difference in the way stainless and copper conduct heat. A few seconds after taking the heat away the stainless bowl was cool enough to touch while the copper remained too hot to touch for several minutes.

Since you are trying to solder stainless to stainless, I'd try tinning both of the mating surfaces as I described. Then I'd try to get it tacked together in a few places around it. Then I'd try to go and fill in the gaps by doing a bit here and a bit there, rather that trying to work in a steady line all the way around.

[myles]

Well for those out there that want to try this in the future I got it sorted. Unlike some of the others folk that have comented on this and other threads I am not using electric. Partly because I don't have an electric soldering iron that gives out enough heat for this job but mainly because I am comfortable working with gas. I suppose I am really brazing - although that and silver soldering are interchangeable terms.

I ended up getting CupAlloy high temperature flux and silver solder rods. Both 49% silver and 56% silver solders. I used a MAP gass torch to heat the stainless to red hot and tacked it together with the 49% silver solder, them filled in the rest with the 56% which has a slightly lower melting point. Both solders flowed and wicked perfectly. No different to using normal soft solder on copper just MUCH stronger. Was thorough about cleaning and going over the stainless with wire wool and then fluxed immediately to stop re-oxidisation.

In truth I have to say I don't like working with stainless steel and would rather work in copper but I wanted to build a hybrid pot with a stainless bottom and a copper top. Fixing the stainless bowl on is just the first step to help bridge the gap between the boiler and the outer pot in the double boiler, and i will end up cutting most of it off again. Next step will be to fix the copper bowl on and build the water seal junction to connect up the short column that links to my lynn arm. Will still be using the silver solder for strength on the copper-copper joins.

[wombat_831]

i had problems silver soldering brass to stainless it took my grandads old shellite blowtorch as the mapgas was crap and 2 yrs later it peeled off the stainless but is still stuck on the brass and lastnite i tried to silver solder my 2" booka column plates with the mapgas and again not enough heat even in just 2ft of tube so i stuck it on the gas burner on the stove for some extra heat and only just got enough so i had to redo some spots with the oxy at work today

[rangaz]

One of the major problems (besides the actual soldering part) I had when I first used a stainless bowl was that the solder cracked off of the bowl fairly quickly and started to rust, then finally broke. Through Uni I have since learned that stainless becomes damaged when heated during soldering with a torch. The effect is called sensitization and it causes SS to rust quite quickly in environment where it would normally not rust.
Anyway, I just scrapped the SS bowl idea and instead beat a section of 3" copper flat and cut it into shape then soldered it to the head. It was a bit more effort to make the copper disc but the frustration it saved me with the flimsy bowl was well worth it

[myles]

Thanks for that. Don't like the idea of stainless starting to rust. The idea was to have a copper boiler but with the lower section more durable. If this does not work in a few years I may well have to build an all copper job instead.

[Dnderhead]

I thank most overheat stainless steel and burn ,and you also need a aggressive flux like , phosphoric acid or zinc chloride/ammonium chloride
you cant use soldering "paste" type flux

[myles]

I gather there is a problem when the stainless reaches a temperature over 800 degrees that later causes rusting. Most of the solders seem to have melting points of 680 - 700 ish , and they say to keep the liquid solder below 750 degrees.

Thats all well and good, but from my own experience which is VERY limited I think I will probably go through lots of stock pots before I make a pristine good still.

I wouldn't do the bowl on a stock pot the same way next time. For this build I used a bowl bigger than the pot to create the overhang for it to sit on a double boiler. That meant I was soldering the pot inside the bowl on the sloping sides which got a bit awkward. It did get a bit too hot in a few places. I imagine it would be easier joining a bowl rim that is the same size as the top of the stock pot.

It should still work - and if it is not as pretty as I would like, it will make do untill I build the next one. I hope I will eventually end up with a pristine home built copper whisky still - oh in 30 years or so!!!!

[Hack]

The trick with the stainless is to tin it first and like dnderhead said, use a good flux and don't overheat it.

[jim81147]

http://www3.towerhobbies.com/cgi-bin/wt ... XFS75&P=ML" onclick="window.open(this.href);return false;" rel="nofollow

I have had very good results using this solder and flux for soldering brass and copper to SS.