Silver Soldering - Brass Fittings

[Gooner]

After reading a few threads on this forum I went and bought a BernzOmatic with the MAPP gas from Bunnings to do some silver soldering.

After some stuff ups, I have found that I can easily join 1/2" copper pipes using this unit.

However, I am yet to successfully join copper pipe to a brass wall fitting. I have attached a photo of the offending piece.

It takes a long time to heat up the piece of brass, so initially I concentrate the flame more on the fitting. Eventually it gets hot enough (red hot) so that the solder melts on touch, but the solder doesn't seem to run into the join as readily compared to when joining copper/copper and therefore results in a small leak. I can only assume that the join isn't hot enough or the flux I am using is incorrect. (?)

I am using "Bakers Solderine" soldering flux that I picked up from Bunnings. I have cleaned both copper and brass very well using emery and stainless steel pad. I slightly heat up the brass fitting, apply some flux using a brush, join, heat and solder. I have tried both 2% and 15% silver solder. No luck.

Any ideas/tips? Would be much appreciated.

Also, if I have a "successful" join, what are the chances it may fail in future? E.g. if not done properly can the join corrode, crack, break down., etc?

Thanks.

[DJ’s Timber]

You don't need to heat the brass and copper before applying the flux.

Not familiar with the Bakers Solderine flux, is it a smooth creamy paste type, typically white.

Normally you heat till the paste goes opaque which indicates that the brass has reached the right temperature to apply the silver solder, avoid heating directly on the join where the paste is but next to it on the brass and there should be enough heat transfer to the copper.

Also you shouldn't need to heat the brass till red hot, the brass can start oxidizing at this temperature.

[watson]

G'day Gooner,
I reckon Baker's Soldering flux is the wrong stuff for the job.I think its more for Lead/tin soldering......you need silver soldering flux or brazing flux

[Gooner]

G'day Gooner,
I reckon Baker's Soldering flux is the wrong stuff for the job.I think its more for Lead/tin soldering......you need silver soldering flux or brazing flux

Reading both replies, I think you are right. The flux seems to quickly boil, burn away and even ignite. By the time the solder melts, the flux is gone.
It is a greenish liquid paste. Looks kinda like jelly that has been put through a blender.

[jmk89]

The flux for silver soldering is borax mixed to toothpaste consistency. Bakers is great for Lead/tin soldering (which is usually all you need for water plumbing) but not for silver.

[watson]

Good One Jeremy,
I'd forgotten about borax paste, which is the main component of a lot of commercial fluxes:doh:
And I've used it in the past with the mapp gas gun that Gooner has got.

[Gooner]

The flux for silver soldering is borax mixed to toothpaste consistency. Bakers is great for Lead/tin soldering (which is usually all you need for water plumbing) but not for silver.

Thanks for that. Thats the info I need. Bakers main ingredient is Zinc Chloride.

I was playing around with the stupid thing till 5am.

[rrich]

It always helps to clean the parts being joined. Usually rubbing the parts with steel wool until bright and shiny helps a lot.

[Gooner]

I went out and bought the right silver solder flux today. Much better. The flux didn't burn away and once the solder melted it ran into the join.

Haven't tested it out yet but I am confident that this time the copper to brass join will work

Thanks guys.