Soft soldering copper to stainless. What flux

[newbiboozer]

I am using soft solder its BOC brand Comweld 965 lead free says its food and surgical grade. Its fantastic copper to copper with bakers fluid type flux. I'm trying to solder 4" copper pipe to stainless 4" ferrule and can only get it to take to the cu with the bakers I have some other gp type paste flux called easyflow that will get it to stick to the stainless but not the cu. Anyone got experience with this type of stuff or know what I need to look for in a flux for cu to ss.

[Ducatiboy Stu]

From memory when I built my AG kettle and was silver soldering copper to SS I used cigweld 965 flux...it was a real PITA and you need to be patient. Try tinning both peices first then join and solder them

[newbiboozer]

Thanks mate. Is the flux usually used for this a liquid and does anyone know what is in it. Acid type ?

[Ducatiboy Stu]

Liquid

MSDS lists ingredients http://jr.chemwatch.net/backpack/msdspdf.exe?mode=SAP&passop=checkpass&user=cigwelloutback&pwd=aaaPm3&partno=321890&pdf=y

[newbiboozer]

Thanks for that mate i looked for hskf an hour for thst. Is there another product I could use in a different brand if I can't get that brand.

[Yummyrum]

Hi newbi , I just soldered up a flange onto my new Pot yesterday with this .I had absolutely no problems with it . Make sure both the copper and SS are very clean and use the flux .Heat only the copper. If it looks like the solder hasn't taken to the SS just paint on a bit more flux (I use a good bristle paint brush) and the solder will almost follow the flux

Pot still.jpg

[Ducatiboy Stu]

Make sure you use a NATURAL brissel brush.

I had issuse on the stainless side of things, but that was due to the crap quality stainless...