What do I need to solder copper and SS?

[John51]

I've seen gas torches go from £20 to over £60 on the bay. Paying a bit too much imo is preferable to wasting 100% of the cost due to the torch not being fit for purpose.

What should I be looking for?

[MrCat]

I bought a propane torch - you need a gas cylinder rather than a canister - it looks like this

http://www.transtools.co.uk/store/prod_7982/construction-tools/torches/rothenberger-airprop-industrial-propane-brazing-torch-set.html

The torch is hot enough to melt copper never mind braze it...

I also checked CupAlloys FAQ out http://www.cupalloys.co.uk/ and bought flux and silver solder specifically for the job. I also got a hearth from them. Having used the hearth a few times it's really a good thing to have.

The hearth and torch have allowed me to properly anneal 4m rolls of 6mm copper - I can get the entire roll up to temp rather than having to do it in sections.

[John51]

Both links bookmarked. Thanks.

That torch looks the business, could earn a living building stills with it.

As if I didn't have enough toys tools.

[stubbydrainer]

g'day John51
your going to need a good flux as well, you guys over there wouldn't have our brand , but the stuff I use is Zinc Cloride 30% w/v, just make sure you always sit the bottle on plastic ( my bench is steel )

cheers
Stubs

[ant]

zinc chloride is for low temp soldering with lead free solder 200 something deg C Borax is for high temp brazing/hard solder/silver solder 400-600 something deg C which would burn the zinc flux up.

[stubbydrainer]

whoops, I thought it was soft solder you were talkng about

[ant]

Easy mistake to make when the original topic title mentions solder.

I just bought some smartprice zinc chloride batteries from asda. They were in the bargain sale for 10p a pack of six instead of 90p so I got them even though they were only aaa. Because they are the cheapies they don't have the protective steel case over the zinc which makes them easier to take apart than a better brand. I disassembled a pack of six tonight and got a quantity of black powder and zinc metal for my trouble. I will weigh them soon and report the quantities. I would probably use larger batteries if I were collecting used ones for free or if they were on sale too.

I will research to see if the black powder can be used directly to make flux for soft soldering stainless and I know the zinc metal can be dissolved in Hydrochloric acid to make flux.I bought 20 packs as I use that size anyway and for a couple of quid thought it a reasonable punt for some cheap flux.

If it works and you try this yourself be extremely careful about the black powder. Zinc chloride is a very toxic salt. wash your hands and tools when you have finished. Work over a piece of paper. Keep track of the powder. Don't eat drink or smoke whilst working. Wear latex or nitrile gloves while working. The zinc is a soft metal easily cut. A rare situation where the cheapies are actually better for purpose than the better quality examples.

[ant]

Well I should research before I post. The powder is a mix of carbon, manganese dioxide and ammonium chloride. Zinc chloride is produced in the reaction when the cell discharges. This eats the zinc away as it is formed from the zinc. It is the white goop that comes out of old leaky cells. So I will probably package the powder and carbon rods up in case I find a use for them and dissolve the zinc metal in hydrochloric which I already have. I will report on the weight of the zinc, the amount of acid I use and the amount of flux I end up with from one six pack of triple A's. I could do the whole atomic weight and molar quantity thing to calculate the result from the weight of the zinc but I am lazy so feel free to do that for me as I will probably just play with it and see.

Discharged cells would give a lower yield as the efficiency of recovering the formed zinc chloride from the other goop and then converting the remaining zinc with hydrochloric will be less than just converting all the zinc directly to begin with. Of course if you have enough free used cells any zinc you recover from them is going to mount up and be better than buying new unused cells in most cases. But you will then be dealing with toxic zinc chloride paste so be careful.

[ant]

OK curiosity got the better of me and if I am right it should take 12ml of 33% conc HCl to dissolve 1g of zinc with a slight acid excess; around 4% ish. Gives me a baseline to work with.

[ant]

15.5g of zinc in a six pack of cheap unused aaa batteries. 186mm of HCl should total out at around 200ml of flux. I read some flux is up to 20% HCl as well as zinc chloride. My 4% ish might not cut it. I will try and see. Could always add another 300ml ish of acid to bring the strength up. Give me an even half litre of flux off a six pack of triple A. Not too bad if it works.

Needless to say zinc chloride solution and acid are both nasty stuff so together should be viewed as hazardous to the careless. Watch you don't get a Darwin award.

[ant]

Took exactly twice as much zinc as I calculated so some early morning math error in there somewhere. Also the volume did not increase due to the removal of the displaced hydrogen as bubbles of gas. Otherwise I seem to have flux. Need to get an old soldering gun now as easier to use than the flame for this low temp flux.

[YHB]

Ant,

Nice to hear from you again, I missed your posts.

Are you still working on your still or have you been side-tracked developing this new flux?

[John51]

For the Burco lid I'm going with a 54mm brass tank connector, the 64mm hole saw arrived yesterday so will attempt the cut sometime today.

It's still relevant info for me ant, so thanks for posting as another project I'm thinking of, (a non synthetic amazing still,) involves soldering 2 x 15mm copper pipes into a 1.5mm stainless steel plate.

[ant]

Glad to be of service John.

YHB I have been in one of my stops but hope to be in one of my starts again soon. Not so much the flux for the low temp soldering; it was easy enough to do. I filtered it in the end to remove traces of manganese etc I had carelessly allowed to remain on the zinc. Just a coffee filter into an old lime juice bottle. darkish green glass I thought would be good for shelf life.

Just my day job and life taking up time and lack of motivational energy. Want to get hold of an old style Weller soldering gun to do the low temp solder with. The homebrew beer people report good success with this combined with the proprietary american brand of the flux I looked up and copied. Not so much new as new to me and home-made for a reasonable saving.

[chubby_78]

hi all

iv got some silver solder rods and flux on the way
i was just wondering if i could sodler a stainless steel bowl to a stockpot lid

or is the only way to do it is weld it ?