Thread: Brazing

I was asked if I could mend a break in a chrome plated steel walking frame and thought that this would be a good candidate for brazing.

I haven't done any brazing since my days as an apprentice about 35 years ago and then I had access to all the right gear (oxy/acetylene etc).

But I thought how hard can it be? looked up a few tutorials, thought I could use my Taymar blow torch and set off to bunnings to get some brazing rod and flux.

Ha! first Bunnings I went to didn't have ANY brazing rod or flux. The second Bunnings had some dusty old unmarked brazing rod but no flux.

Went to Mitre 10 and bought some Bernzomatic Nickel/silver flux coated brazing rod (blue). Got home and the blow torch just burnt off the flux and nothing else. Went back to Mitre 10 and bought a Yellow tip brazing rod. They didn't have any flux. Went to GasWeld - no brazing rod and no flux (I still can't believe that!), went to another Mitre 10 and bought a plastic jar of CigWeld "COMWELD Copper and brass flux". The directions say: "Specially developed for braze welding copper OR steel".

Got home and tested all on a couple of 2-1/2" nails. Did all the documented things, cleaned, cleaned, ground to shiny metal, cleaned again coated with flux, brought up to red heat (I think, I am red-green colour blind) added the rod which melted and just formed into round blobs and dripped of the nails (i.e. did not "wet" the steel at all). Tried again with 1/8" and 1/16" plate/sheet. Same result - no "wetting" of the target material.

I have tried the flux in powder form and in paste form (by adding a little water). I have tried cleaning with detergent, acetate, hydrochloric acid, and grinding. All to no avail.

Am I completely off the track here? Am I using the right brazing rod/flux? if not, what do I need? and where can I get it? (I am in Sydney and there does not seem to be a large range available to hobbyists here).

Whilst I can repair the frame some other way, brazing is something I would like to be able to do a little of as long as the cost is not prohibitive.

Any advice would be much appreciated.

Hi garym

I have not brazed with anything but an oxy setup before.
Are you getting enough heat in to the work?

I have a big pack of CIG Pink rods in the shed, and haven't had any particular issues brazing steel.

If it were me, I would weld the break with oxy/acet and bit of tie wire. I have done heaps of repairs on bike frames using this method for some of the local kids, and the welds stand up the jumping abuse these bikes get.

Proberly a heat problem, as an alternative you could get the closest fitting copper tube that will slide/fit over the chrome frame cut a 4-5 cm length slide it over the break and silver solder it


Rgds

Thanks for the reply Fossil (doesn't feel right calling you that).

Originally Posted by Fossil

Hi garym

I have not brazed with anything but an oxy setup before.
Are you getting enough heat in to the work?

I have a big pack of CIG Pink rods in the shed, and haven't had any particular issues brazing steel.

If it were me, I would weld the break with oxy/acet and bit of tie wire. I have done heaps of repairs on bike frames using this method for some of the local kids, and the welds stand up the jumping abuse these bikes get.

I must admit that I don't think that I'm getting enough heat to bring the steel up to the correct temperature (although I am getting it to yellow heat in the case of the nail test).

I would love an oxy/acetylene set but it seems hard for hobbyists to obtain the gas bottles these days, and I am not sure if the small amount of brazing I am likely to do (granted that there are a lot of other uses) would justify the cost.

May I ask where you sourced your set from? and can you give me an indication of the cost?

When you say you would "weld the break with oxy/acet" are you referring to a fusion weld?

Thanks again.

i used cig blue rods and mapp gas to weld 2mm steel tube to 1mm tube. i had to heat for ages until it was red over a large area. if you put the rods under direct flame when at steel brazing temperature they will just blob and wont melt to the parent metal. i had to scratch the rods over the red part until i could see it spreading to the parent metal in a thin way (like with silver solder at a lower temp) edit: this was while the flame was only indirectly heating the rod+area. after that the rods braze to the thin brass layer easily.

Originally Posted by Ashore

Proberly a heat problem, as an alternative you could get the closest fitting copper tube that will slide/fit over the chrome frame cut a 4-5 cm length slide it over the break and silver solder it


Rgds

Ahh! but what exactly do you mean by "silver solder"? In effect I thought that "silver soldering" was more-or-less what I was trying to do (the brazing rod is yellow tip which I think means it contains 2% silver). The difference between "silver soldering" and brazing is not clear to me unless you are referring to a much higher content of silver (and therefore lower melting temp)? I haven't been able to source any higher silver content rod. The idea of the tube was one I was going to fall back on if the braze wasn't strong enough, however if I can't get the braze/silver solder to wet the steel this method won't work either.

Cheers.

Originally Posted by garym

Ahh! but what exactly do you mean by "silver solder"? .

"Hard soldering" or "silver soldering" (performed with high-temperature solder containing up to 40% silver) is also often a form of brazing, since it involves filler materials with melting points in the vicinity of, or in excess of, 450 °C.

http://en.wikipedia.org/wiki/Soldering

Originally Posted by faex

i used cig blue rods and mapp gas to weld 2mm steel tube to 1mm tube. i had to heat for ages until it was red over a large area. if you put the rods under direct flame when at steel brazing temperature they will just blob and wont melt to the parent metal. i had to scratch the rods over the red part until i could see it spreading to the parent metal in a thin way (like with silver solder at a lower temp) edit: this was while the flame was only indirectly heating the rod+area. after that the rods braze to the thin brass layer easily.

Thanks faex. That is just what is happening (the blobbing). I haven't been able to get the metal hot enough to melt the rod without direct flame so that's probably my problem, MAPP would be much hotter than what I am getting from my Taymar. What you describe seems a lot like 'tinning' when soft soldering - it makes sense. I did try a form of this by filing the rod and mixing the file shavings with flux and then trying to get the mix to 'melt' by indirect heat, but I couldn't get it hot enough I don't think.

I assume the CIG blue rods would be the same as the Bernzomatic blue rod I tried first? i.e. Nickel Silver - self fluxing?

Anyway it looks like I will have to go MAPP or oxy/acet.

Cheers

G'day Garym,
In my experience (limited) you are wasting your time trying to braze with propane etc alone.
I have been using SBA (silver brazing alloy) 245 with great success on small jobs over the years on straight propane. I believe SBA 245 is commonly called silver solder and has a relatively low melting point.

Barry Hicks

Originally Posted by Barry Hicks

G'day Garym,
In my experience (limited) you are wasting your time trying to braze with propane etc alone.
I have been using SBA (silver brazing alloy) 245 with great success on small jobs over the years on straight propane. I believe SBA 245 is commonly called silver solder and has a relatively low melting point.

Barry Hicks

Thanks Barry - I suspect you're right.

Where did you get the SBA 245 from?

Cheers.

Originally Posted by garym

I added the rod which melted and just formed into round blobs and dripped of the nails (i.e. did not "wet" the steel at all).

Brazing and Silver brazing are almost the same technique. The difference being in the temperature at which the filler bonds with the parent metal.
The critical element in both applications is that the parent metal temperature is hot enough to melt the filler material. The heat source, heats the parent metal not the filler material.
The question is ,are you brazing with a bronze based filler material or are you silver brazing. Bronze based wire is a gold colour when polished clean and silver based is a platinum colour.

I strongly suspect you don't have the technique correct.

Grahame

Originally Posted by Grahame Collins

Brazing and Silver brazing are almost the same technique. The difference being in the temperature at which the filler bonds with the parent metal.
The critical element in both applications is that the parent metal temperature is hot enough to melt the filler material. The heat source, heats the parent metal not the filler material.
The question is ,are you brazing with a bronze based filler material or are you silver brazing. Bronze based wire is a gold colour when polished clean and silver based is a platinum colour.
Grahame

Thanks Grahame, that's pretty much how I understood it, however, can you clarify a couple of things for me? Is the colour of the "silver braze" due to the higher silver content (the gold coloured rod I am using does contain 2% silver) or is it a completely different thing? Does the platinum coloured rod have a tip colour?

Originally Posted by Grahame Collins

I strongly suspect you don't have the technique correct.
Grahame

I'm damn sure of it!

Cheers.

The silver content would have a bearing on the colour.

There is a blue tip coded silver solder Comweld SBA 245.From my memory it runs 40-50% silver content.

2% silver content does not not sound right at all

Putting the flame on the filler will cause it to go molten before the parent metal is hot enough to bond with it.

Fluxing is with brazing (bronze) is by warming the metal first,then throw a pinch of powdered flux on the hot metal which then sticks to it. Doing it the other way- putting flux on cold metal, then heating, lets most of the flux get blown away by the flame. The filler is wiped onto the metal and is melted by it, only if the metal is hot enough.

Fluxing with Silver Brazing is by a borax based liquid which goes on the cold metal. When the metal heats up under flame and turns the liquid to a dried toothpaste look. Further heating will eventually turn the flux clear like water.thats the time you wipe the SBA on the hot metal and it will run immediately.

That help ?
Grahame

G'day again Garym
Graheme C obviously knows what he is talking about!
SBA 245 seems to be widely available in places that sell welding type gear. I bought my last lot in a little place in Atherton in FNQ and I have bought it at a CIG outlet in Townsville.

Barry Hicks

Originally Posted by Grahame Collins

The silver content would have a bearing on the colour.

There is a blue tip coded silver solder Comweld SBA 245.From my memory it runs 40-50% silver content.

2% silver content does not not sound right at all

Putting the flame on the filler will cause it to go molten before the parent metal is hot enough to bond with it.

Fluxing is with brazing (bronze) is by warming th metal first,then throw a pinch of powdered flux on the hot meta which then sticks to it.Doing it the other way- puting flux on cold metal ,then heating,lets most of the flux get blown away by the flame. The fillier is wiped onto the metal and is melted by it only if the metal is hot enough.

Fluxing with Silver Brazing is by a borax based liquid which goes on the cold metal. When the metal heats up under flame and turns the liquid to a dried toothpaste look. Further heating will eventually turn the flux clear like water.thats the time you wipe the SBA on the hot metal and it will run immediately.

That help
Grahame

Thanks for the clarification Grahame.

I get the 2% from a statement I found on the web:
"Silver solder has a % of silver. Yellow tip 2%, Brown 15% and Blue 45%"

However, this is anecdotal and I have been unable to verify it from a reliable source.

So, it looks like I am using a high melting temp version of silver solder, with flux meant for brazing (i.e. Boric Acid + Sodium Metaborate) as it is definitely a powder (I have tried making it into a paste by adding water).

I nearly bought the silver solder flux but it was a third the quantity of the brazing flux and a third more expensive (penny pinching costs me again, doh!).

Can you suggest a source for Comweld SBA 245?

Thanks very much for your assistance, lot's of good tips there.

Cheers.

Gary