Brazing parts – bronze equivalent to solder paste

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Brazing parts – bronze equivalent to solder paste

This topic has 9 replies, 6 voices, and was last updated 23 July 2024 at 22:56 by Bill Phinn.

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23 July 2024 at 13:02 #743044
migman
Participant
@migman
Hi All,

My background is electronics but in latter years have been messing about with a mig welder.

Recently I have been trying to join more delicate components that simply won’t tolerate that level of heat and have therefore invested in a modest brazing torch and some cans of MAPP gas. It’s often a fiddly task trying to hold/clamp small parts whilst fluxing and heating and generally trying to keep one’s eyebrows in tact, my question is this, has anyone here used or experimented with bronze paste (if indeed there is such a thing)? My experience of flow soldering makes me wonder if there is an equivalent for brazing – is it possible to add some material (similar to a flow solder paste) in between parts and let the heat work it’s magic, the bronze paste flowing at the prescribed temperature.

I am aware that you can buy bronze powder (ground to a fine mesh size 240-350 Microns), but cannot find it mixed in a compound – could it be mixed with some brazing flux and wiped in between parts?

Any thoughts would be appreciated,

Thanks very much
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23 July 2024 at 13:04 #743059
JasonB
Moderator
@jasonb
Silver solder paste is available which can be used for small parts.

Myself I don’t have aproblem fluxing the work and then feeding in a rod when things are hot enough. You can get thinner section silver solder rod or just beat a larger rod flat and cut into strips with tin snips.
23 July 2024 at 14:10 #743066
Bazyle
Participant
@bazyle
I think regular bronze dust will have a lot of oxidised surface area so will carry a lot of dross into the joint. Perhaps get a new uncontaminated file, degrease it, and file some bronze as needed under a layer of flux paste so it never sees air. Try it on a test piece and let us know if it works.
23 July 2024 at 15:19 #743080
Clive Foster
Participant
@clivefoster55965
Clipping off small pieces of silver solder and placing them in the joint before fluxing and final assembly ready to heat works well. Because silver solder follows the heat it’s relatively easy to get the solder going the right way into the joint rather than coating the hottest part. The small pieces method is more economical with silver solder too. Like many folk who only silver solder occasionally I tend to over do things when simply introducing a rod leaving excess silver solder to be cleaned off.

With small parts the most troublesome thing is the way the flux / water mix can lift and shift things as it bubbles up to working temperature. Using flux powder direct is more predictable but harder to get full coverage.

Once a year (or less) just isn’t enough to keep my skills hot.

Clive
23 July 2024 at 16:13 #743085
bernard towers
Participant
@bernardtowers37738
If you mix flux with meths it does not bubble up so doesn’t spread where you dont need it so generally you need a lot less and if it doesn’t spread neither does your silver solder (less expense). And as Keith Hale (CuP Alloys) always said the silver solder you can see is not doing any work its the stuff you cant see that makes the joint. By the way how are you keeping Keith.
23 July 2024 at 22:14 #743169
migman
Participant
@migman
On 23 July 2024 at 13:04 JasonB Said:

Silver solder paste is available which can be used for small parts.

Myself I don’t have aproblem fluxing the work and then feeding in a rod when things are hot enough. You can get thinner section silver solder rod or just beat a larger rod flat and cut into strips with tin snips.

Hi Jason,

Great idea, will definitely try that – silver solder paste is really expensive,

Thank you,

Chris
23 July 2024 at 22:23 #743170
migman
Participant
@migman
On 23 July 2024 at 14:10 Bazyle Said:

I think regular bronze dust will have a lot of oxidised surface area so will carry a lot of dross into the joint. Perhaps get a new uncontaminated file, degrease it, and file some bronze as needed under a layer of flux paste so it never sees air. Try it on a test piece and let us know if it works.

Never even considered that Bazyle, I’m rethinking the procurement of the powder anyway based on the responses from you guys here. I think there is scope here from some testing though, I will add a post if I get the chance to do it.

Cheers,

Chris
23 July 2024 at 22:28 #743171
migman
Participant
@migman
On 23 July 2024 at 15:19 Clive Foster Said:

Clipping off small pieces of silver solder and placing them in the joint before fluxing and final assembly ready to heat works well. Because silver solder follows the heat it’s relatively easy to get the solder going the right way into the joint rather than coating the hottest part. The small pieces method is more economical with silver solder too. Like many folk who only silver solder occasionally I tend to over do things when simply introducing a rod leaving excess silver solder to be cleaned off.

With small parts the most troublesome thing is the way the flux / water mix can lift and shift things as it bubbles up to working temperature. Using flux powder direct is more predictable but harder to get full coverage.

Once a year (or less) just isn’t enough to keep my skills hot.

Clive

Hi Clive – you clearly have a lot of experience doing this, I only have flux paste at present although I have watched a few YT videos such as https://www.youtube.com/watch?v=0ti2VQbn_A0 and wondered if the powder mixed into paste was a good idea or a sales push by Solpro. I suspect I’ll buy some and try it,

Thanks for your input, much appreciated,

Chris
23 July 2024 at 22:40 #743174
migman
Participant
@migman
On 23 July 2024 at 16:13 bernard towers Said:

If you mix flux with meths it does not bubble up so doesn’t spread where you dont need it so generally you need a lot less and if it doesn’t spread neither does your silver solder (less expense). And as Keith Hale (CuP Alloys) always said the silver solder you can see is not doing any work its the stuff you cant see that makes the joint. By the way how are you keeping Keith.

Thank you Bernard, duly noted – really useful info regarding CuP Alloys too (I hope Keith is fit and well),

Kind regards,

Chris
23 July 2024 at 22:56 #743175
Bill Phinn
Participant
@billphinn90025
I’m not sure why you want to bronze braze as opposed to silver braze. Can you explain?

Silver brazing/soldering is adequate for delicate components. All my silver jewellery work was done with silver solder of various temperature grades: hard, medium, easy, and extra easy. For non-hallmarking silver soldering I generally use Johnson Matthey Silverflo 55 solder with Easy Flo 2 flux powder mixed into a paste. On bigger work I also feed with rods, as Jason suggests. Dipping a heated rod into dry flux powder (at the right temp. the powder will stick to the rod) means you don’t need to apply flux paste to the joint at all.

I reserve bronze brazing for repairing or joining steel components subject to heavy usage, though these are not necessarily big components. I use two different kinds of bronze rod: silicon bronze rods and manganese bronze rods. The first has better gap filling characteristics, the latter better flow characteristics.

For bronze brazing I generally use Sif Bronze flux powder, though I’ve also used Easy Flo 2 successfully.

BTW, the flux paste mix shown in the video is too watery for most purposes, even after the demonstrator has added several dollops of extra powder.
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