Eureka! (soldering stainless)

[Knife_man]

Not sure if this is the right place.

So I've been having a mare getting anything to stick to stainless.

I'm from the UK and can't find any acid based flux in reasonable amounts. I've tried every plumbing flux I can get my hands on and unsurprisingly they didn't work.

I then ordered a liquid flux for stainless from China which also didn't work , can't tell you what it is as it all in Chinese but it was the cheapest on ebay.

I then ordered at quite a price some stay-clean which people swear by imported from the USA. Which I'm still waiting for.

I then read a post which I will probably never find again suggesting that using stainless flux AND copper flux at the same time works and IT WORKED. I think what's happening is that the stainless flux cleans the surface but boils off before it's hot enough , then the copper flux takes over and keeps the surface clean long enough for soldering but that's just a guess.

So if anyone from the UK is in the same predicament as me try using different types of flux at the same time it just might work.

[Saltpork]

What are you soldering stainless to? Stainless to stainless, stainless to copper?

[Knife_man]

What are you soldering stainless to? Stainless to stainless, stainless to copper?

Stainless ferrule to copper.

[Deplorable]

Stay clean contains a small amount of hydrochloric acid along with zinc and ammonium chloride.
One could try making up your own solution.

[OtisT]

A big challenge with soldering stainless to copper is getting the temp of both pieces right at the same time. It’s easy to get one piece too hot or not hot enough when the other piece hits the right temp.

You have to be more patient with stainless because it takes longer to heat up and more work (torch movement) to get it to heat evenly. I found success by heating the stainless first, very slowly bringing it up to temp and taking lots of pauses so the heat spreads more evenly. When the stainless is getting close to temp, expand your torch use to include heating the copper. It takes some practice to figure out how to do this, the mass of each piece being one factor to manage.

When you get the heat right, all the rest is much much easier.

Otis

[Demy]

Agree with Otis, I had to learn things like this with practice....if you heat too much non-stick oxides form on the surface, if too little it doesn't melt. A good enough flux is obtained by dissolving pure zinc in hydrochloric acid.

[squigglefunk]

i found great success in heating the copper part mainly and barely heating the stainless part, very few issues soldering stainless and copper this way using liquid flux and stay brite silver bearing solder

[ThomasBrewer]

I had the best success by individually wetting out each piece with a layer of flux/solder on the mating surfaces, then heating them both to join the solder pads.

[Knife_man]

The problem I was getting was that I couldn't get hold of suitable flux in the UK.

Tested availible fluxes by abrading a scrap price of stainless and applying flux ,placing a small price of solder in the middle of the flux and then heating slowly from underneath. That way as soon as I hit the correct temp the solder will melt and in theory wet out the surface.

The plumbing solder just sat there but held the molten solder in place until it had turned to a black goop. The stainless flux(chinese) would vigorously boil and then by the time the solder melted it would bead up and roll off the surface.

I just wanted to share my finding for any other UK residents who were having difficulty getting hold of good flux suitable for stainless.