Question: Need help soldering to a stainless steel flask

[KGDiebold]

You got a newbie here. Inspired by some Scott Hardy flasks that I have seen, I thought I would start out by purchasing a flask and then adding some embellishments. I purchased a cheap round stainless flask and wanted to added a sterling overlay to the front. I sawed out a piece that is about 3" in diameter and used Harris Stay-Clean flux with Harris Stay-Brite solder. I pre-tinned the silver and everything went as I expected. When I tried to solder it to the flask I couldn't get it to stick. I learned a few things from this failure (yes I have to order a new flask and more silver!). I had some Handy Flux nearby, so I tried it, and with too much heat, did get it to stick. This is actually a brazing flux with active temp of 1050-1700 deg. So I think I have a flux problem since it did stick. I was aiming for a low temp solder as I don't know how the flask is made and don't want to cause a leak. I also see that I need to heat the entire piece, as localize heat caused the material to expand with nowhere to go, causing it to distort the material into a convex shape. So a few questions - does anybody have a recommendation for solder and flux that will work with the stainless? This is a $6.00 Chinese made flask, no telling what the material really is, but it doesn't appear to be plated. It's also very thin material. Am I better off looking for an epoxy as a solution? I was wanting to add something to some stainless steel shot glasses as well, so I'll have the same problem there. All your advice is appreciated.

 

[Dave London]

J.B. Weld is your friend MTC

 

[monk]

i got some awhile back from micro mark. not sure, but i think it was tix. anyway, what i got will work on ss, and is low temp.\the printing on the tube is faded badly, so am not sure if it is tix. micro mark.com, or rio should have some.

 

[Doctorslava]

I just want to make it clear for myself. You want use a low temperature solder and do not want to braze? First of all you need to heat a flask ( industrial heat gun?) because it is a big heat sink. I had good results with stainless steel flux from mcmaster. Item #7695A5. Also before wetting the surface with solder you can use 800 grit sandpaper. If you use a torch and soft silver solder, use a Handy Flux for low temperature soldering. Just make sure you have a good vent because it contains fluoride. For Hard silver solder I used a Stay-Silv by Harris.

 

[Archie Woodworth]

First off, before adding heat, make sure you remove cap...if you don't you could have the start of a remodeling project...Like, you could blow up the flask and surrounding workshop. Moving beyond that, you might want to consider checking with a local jeweler and see if they will laser weld it for you...lots less heat and way more controllable. Otherwise, go with Dave's suggestion and just glue it on with JB Weld.

 

[KGDiebold]

Thanks for looking out for me Archie. The lid was off! I don't think laser weld is right. I'm just goofing around looking for projects and ways to learn that doesn't make me go broke when I make mistakes. A drawer full of engraving plates makes me want to look for something more entertaining. After engraving last night on my wrinkled flask, I realized that, with my limited experience, I will produce nicer work by having the silver glued to some wood where I have a solid work piece, and then JB weld it to the flask. The thin, hollow flask added additional challenges! The handmade flasks I see others produce probably have a little more structure to them. Monk and Doctorslava, I found flux for stainless on both McMaster and Rio websites. I'll have something on hand for next time. Thank you for your help.

 

[farmer57]

SS is typically hard to solder to using low heat process.
Tix solder might do it, just use 'tix' brand flux and since you will need to heat much of the flask - might need to use 'anti-flux' to limit flow of flux-solder. You might be able to limit the flow with fresh sharpie 'border' as well.
If you're having problems with the warping - you might want to experiment with half the bottle sitting in the water but will need good heat source such orca torch or such.
Cheers.

 

[Dave Friedman]

I solder stainless steel very frequently...... Low temp. Stay-Brite silver solder flows around 430-degrees..... You MUST first bring the entire flask "Up to temperature" (flux will start to bubble) not try and solder just a small area...... this heating takes time and patience, probably slow heating for 5-10 minutes. then your solder will flow.
Dave Friedman

 

[KGDiebold]

Dave, do you use Stay Clean flux, or one of the other fluxes suggested in this thread that lists that it is for stainless?

 

[Dave Friedman]

Yes, you can certainly use the Stay-Brite soldering flux. I use an all-purpose liquid soldering flux:
weldcote metals Liquid Soldering Flux Lot#5118-01.
Do NOT use brazing flux (borax).