Overlay bronze weld/braze question.

[Cato]

I wasn't sure where to put this question. It's a motorbike frame, but not yet happening so the automotive projects didn't seem right. It's about welding, but not actual welds and I won't be doing it, so the welding sections didn't seem right.

Anyway, an idea for one of the upcoming bike projects is to have a lacquered frame. 1970s Japanese machine welding isn't the prettiest, so I was wondering about cleaning up the existing welds with a flap wheel and dremmel to remove the spatters/snots etc then having them bronze welded over for purely cosmetic purposes.

Is this feasible/possible? The thickness wouldn't need to be much, so does that make it more difficult to achieve an attractive finish? Will adding heat at the existing weld sites cause problems?

 

[Brad93]

Never a good idea

 

[Cato]

Never a good idea

Care to expand?

 

[Brad93]

Basic metallurgy

 

[Cato]

Basic metallurgy

That clears it up nicely thanks.

 

[Brad93]

That clears it up nicely thanks.

No problem

 

[Cato]

There's a fair bit of info on bronze welding bike frames around the motorbike forums, and from the manufacturers who make/made frames that way (Harris, Rickman etc). So if I went down that route I could get a frame built up, but that seems like overkill.

Most of the info/questions seem to end up with the 'debate' around silicon vs nickel bronze with the latter being deemed more suitable for strength without cracking issues. As this would be cosmetic and essentially a filler that shouldn't be a factor. Hence my question on a welding forum.

No use

I know.

 

[Brad93]

There will be a reason no one can be bothered to reply to you cato, i just cant put my finger on it...

 

[Brad93]

You've got a frame that's been from the sounds of it, Mig welded or TIG welded. A high strength joint on likely a chrome-molybdenum based alloy steel frame.
That makes a very strong joint, but if done with the right filler metal, it will actually be a lower yield than the tube. Which is correct.
Under matching filler gives crack resistant and very durable joints in thin wall chromoly frames.

Multipass welds risk forming transition zones within the lower layers of deposited weld metal, and if multipass welds were required, then Preheat and PWHT would be called for.

Brazing is ideal for chromoly tubing as no transition zones are formed due to the lack of fusion and gentle heatwide heating zone that occurs when brazing takes place basically anneals the tube as you go.
About 47ksi is the yield braze which again is undermatching but brazing is very ductile giving good fatigue life.

Brazing over deposited weld metal in a restrained weldment is potentially going to lead to them transition zones forming beneath the braze.

You're also increasing the leg length and throat thickness of a joint, in a stressed application, where flexibility and ductility is very important. You're making a joint even stiffer. That's great if it's going to be static, but it's not, it's going to be subject to all sorts of dynamic loads.

Don't try and make a silk purse of a sows ear. If you want a brazed frame, build a brazed frame or go to one of the experts in building such frames.

But I'm sure you'll discount all this because you read so on such and such forum. Or perhaps you'll say no no no, and then follow this forums advice anyway like with the lathe thread.

 

[JEZGUZ]

Lead loading for the smooth finish??

 

[Cato]

You've got a frame that's been from the sounds of it, Mig welded or TIG welded. A high strength joint on likely a chrome-molybdenum based alloy steel frame.
That makes a very strong joint, but if done with the right filler metal, it will actually be a lower yield than the tube. Which is correct.
Under matching filler gives crack resistant and very durable joints in thin wall chromoly frames.

Multipass welds risk forming transition zones within the lower layers of deposited weld metal, and if multipass welds were required, then Preheat and PWHT would be called for.

Brazing is ideal for chromoly tubing as no transition zones are formed due to the lack of fusion and gentle heatwide heating zone that occurs when brazing takes place basically anneals the tube as you go.
About 47ksi is the yield braze which again is undermatching but brazing is very ductile giving good fatigue life.

Brazing over deposited weld metal in a restrained weldment is potentially going to lead to them transition zones forming beneath the braze.

You're also increasing the leg length and throat thickness of a joint, in a stressed application, where flexibility and ductility is very important. You're making a joint even stiffer. That's great if it's going to be static, but it's not, it's going to be subject to all sorts of dynamic loads.

Don't try and make a silk purse of a sows ear. If you want a brazed frame, build a brazed frame or go to one of the experts in building such frames.

But I'm sure you'll discount all this because you read so on such and such forum. Or perhaps you'll say no no no, and then follow this forums advice anyway like with the lathe thread.

A welding forum would seem to be the best place to ask for information on welding, so I did. As I mentioned, and you hint at above, there are a lot of posts on motorbike and car forums about welding, but taking advice from those sources seems risky at best. Your answer above is exactly the information I was after. Your first answer, whilst accurate having seen this one, didn't really help.

As for the lathe thread and what I'll do with the information you've provided here, they're completely different aren't they? I can see no opinion in your reply, just facts and information which directly answers the question. It's information which is useful to me and no doubt anyone else needing it, or just interested. The lathe thread had pages of opinions, answering a question which was never asked. That seems to happen a lot on here, the lathe thread being just one example of many.

As you mention the lathe thread, maybe an update is in order. I could have kept quiet about buying one, but I'm not precious about it so saw no reason not to say I had. I bought it when an opportunity arose completely out of the blue. However, I should have stuck to my plan. I've had it taking up space for I think 9 months now, and it hasn't been turned on since the day I got it. So when I asked if someone wanted the infrequent work because I wouldn't have enough of it to justify buying one I was right. My bad for caving, no harm done, I may use it when I retire.

It's a shame if you've been offended or upset at my response, it wasn't my intention and I thought I was quite restrained in that thread. That said I can't say I'm going to lose any sleep over it. It clearly bothered you so it begs the question, why reply to my question at all?

 

[Cato]

Lead loading for the smooth finish??

The factory machine welds aren't too bad, just the odd snot and spatter, the bronze welding idea was just for aesthetics with a clear coated frame. So as that's a bad idea I'll just dress the messy bits with a flap wheel and it should look nice when sprayed up.

 

[brightspark]

The factory machine welds aren't too bad, just the odd snot and spatter, the bronze welding idea was just for aesthetics with a clear coated frame. So as that's a bad idea I'll just dress the messy bits with a flap wheel and it should look nice when sprayed up.

surely with a clear coated frame you would see the brass colour where it has been brazed and filled

 

[indy4x]

@brightspark the way I read it was that was the idea behind brazing the frame, make it look attractive

 

[Cato]

surely with a clear coated frame you would see the brass colour where it has been brazed and filled

That was the idea. It's not a new approach, very little is with bikes, but it's about the overall look.

As it's not a goer I'll do something else so no worries at this stage.

 

[stuvy]

surely with a clear coated frame you would see the brass colour where it has been brazed and filled

thats the idea to make a dull frame look nicer