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Brazing Brass

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James Alford05/12/2017 07:11:29
263 forum posts
57 photos

I hope that someone can offer some advice.

I am repairing a brass radiator shell for an Austin 7. At some time in the past, the shell has been chopped and shortened; the joint has now failed.

I have made brass plates and riveted the parts together, having cleaned the parts with a wire brush first. I am using SifBronze flux powder (pink), number 1 rods and MAP gas to get the parts red hot.

On one side of the repair, the braze flowed well and has joined the parts, but on the other side, with the same technique, the braze simply sits on the flux, which has melted like glass. The braze is behaving like solder does on dirty steel with no flux.

I applied the flux as a dry powder; would mixing it to a paste with water or meths be likely to improve matters?

James.

Bob Rodgerson05/12/2017 07:59:45
514 forum posts
158 photos

Hi James,

It may be that the flux is deteriorating due to being held at too high a temperature for too long, though I haven't had experience with this type of flux.

If mixing flux with water use a little washing up liquid in the water, this helps the flux to spread over the metal so that no areas dry up and become bare before heating.

Russell Eberhardt05/12/2017 08:03:54
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2077 forum posts
75 photos

I'm surprised that the radiator shell didn't melt! Cherry red temperature is 800 to 900 C while the melting point of brass is 900 to 940 C! I'm not sure what number 1 rods are but I would use soft solder and an acid flux.

Is this one of the painted radiator shells or the later chrome plated one? If it was chromed you will need to remove the chrome where you are soldering.

Russell

CuP Alloys 105/12/2017 08:27:54
123 forum posts

Hello James

Like Russell, I think you have done extremely well to join brass sheet together using Sifbronze No 1 which is basically 60/40 brass doctored with a little silcon and manganese to alter the flow characteristics a little. Its melting temperature is 865 - 895 deg C!

In all cases of brazing and soldering, if the filler metal melts but does not flow - THERE IS A FLUX PROBLEM.(Remember that silver soldering is just one facet of the brazing process)

It matters not what you mix the flux powder with - the problem will remain. The flux is not removing all the oxides present. And no amount of wire brushing at the start will help.

I would suggest you re-examine your technique.

Do a prelininary test to ensure that the flux is removingall the oxides or is getting hot enough to do its job.

Consider using a lower melting point filler metal like a 55% silver solder or a soft solder. The latter was probably used in the first place!

Examine your heating technique. Is it developing the right heat pattern to promote capillary flow. This is the fundamental principle behing brazing and soldering.

For more information **LINK**

regards

Keith

James Alford05/12/2017 08:29:35
263 forum posts
57 photos
Bob.

I suspect that you have a point about overheating the flux. Thank you for the suggestion about washing up liquid.

Russell.

I have to admit that I was a little apprehensive about overheating the shell. It is a later style with the stamped badge. There is no chrome. I had considered soft solder, but was originally unsure whether it would be strong enough. I am swaying that way, though.

James
Ian S C05/12/2017 08:59:51
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6491 forum posts
216 photos

Radiators are stuck together with high melting point tin lead solder.

Ian S C

Russell Eberhardt05/12/2017 09:24:27
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2077 forum posts
75 photos
Posted by Ian S C on 05/12/2017 08:59:51:

Radiators are stuck together with high melting point tin lead solder.

Ian S C

Yes, but this is a separate decorative shell, distinct from the core. It is a one piece pressing that supports the bonnet. They did often develop cracks.

(Assuming my memory is correct. It's been many years since I worked on one)

Russell

J Hancock05/12/2017 10:02:40
149 forum posts

As previous posts , plus I think you may have a sealing problem round those rivets.

Remember, once you have used soft solder there is no going back to brazing or silver solder.

Unless you like making radiators of course.

vintagengineer05/12/2017 10:40:30
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305 forum posts
5 photos

I use high melting point silver solder for radiator shells as the quality of the brass can be suspect!

James Alford05/12/2017 18:03:37
263 forum posts
57 photos

Thank you for all of the replies. I shall give up on the SifBronze as I have no desire to melt the actual radiator surround.

I some very old sticks of solder that have quite a high melting point, albeit far lower than the SifBronze, and shall try that instead.

Luckily, it is a purely cosmetic part that will be painted, so the rivet holes can be finished off with some sort of body filler, if needs be.

James.

Neil Wyatt06/12/2017 12:38:04
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Moderator
11871 forum posts
542 photos
64 articles
Posted by James Alford on 05/12/2017 18:03:37:

Thank you for all of the replies. I shall give up on the SifBronze as I have no desire to melt the actual radiator surround.

I some very old sticks of solder that have quite a high melting point, albeit far lower than the SifBronze, and shall try that instead.

Luckily, it is a purely cosmetic part that will be painted, so the rivet holes can be finished off with some sort of body filler, if needs be.

James.

Beware, they may be plumber's solder for wiped joints and a devil to work neatly. Consider a silver-bearing soft solder such as Comsol; Cup do at least one of these. Stronger and higher MP than normal solder, but melts at a low enough temperature to reduce distortion so good for sheet brass.

Neil

Phil P06/12/2017 13:04:22
393 forum posts
111 photos

Hi James

Forget Sifbronze you will damage the shell, and forget soft solder the joint will not withstand the vibration and will fail in use very quickly.

Silver solder is definitely the way to go, that is how the shell on my own Austin 7 special was joined.

Phil

Speedy Builder506/12/2017 15:54:50
1298 forum posts
94 photos

Hi james, if you have riveted the joint, there is little need for further strengthening. Use soft solder as used on plumbing joints (not plumbers solder which is for lead wiped joints) and out of preference use the lead bearing solder sold on reels, not the lead free. Ensure all is clean, use the acid liquid flux used for plumbing which will additionally clean the joint. "Paint" the flux on and leave for a few minutes, heat the area gently with a small gas torch and apply the solder and it should be a good one. These old rad shells have fatigue cracks in them and have "de-zinkified" over the years and become brittle - well they are 80 odd years old! When all done, use hot soapy water to clean off the flux residue.
You could use silver solder, but its just a more expensive way of doing the job.
BobH (1932 A7 saloon owner)

James Alford07/12/2017 07:20:32
263 forum posts
57 photos

Thank you for the suggestions. The rivets are temporary, to hold the repair plates in place whilst being soldered.

I have ordered some of the ComSol lead/silver solder from Cup Alloys, as suggested.

Regards,

James

CuP Alloys 107/12/2017 09:27:49
123 forum posts

Hi James.

Thank you.

If you require any further information, call us. Only too pleased to help.

Keith

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