Tig brazing to minimise distortion.... school me.

[lchris21]

Morning all,
Got a small project on the horizon which includes replacing the filler neck on a steel motorcycle petrol tank. I've done a few repairs over the years, mods etc and have noticed some production tanks have the filler neck, or fuel pump flanges etc brazed in?
The Tig weld repairs I've carried out just with some patches to old tanks, the odd bung, pipe etc has not really distorted to badly.
This job will involve the complete removal and replacement of the filler neck, that's going to stare you in the chops! so I'm concerned the stresses induced during the forming of the tank will decide to make their great escape during the welding process. With a wonky cap as a result.
Will using some flavour of silicon bronze filler reduce the heat and fingers crossed the potential distortion?
I've used the tig, cool, tig, cool technique on small flatter sections some other jobs in the past, which had limited or random success in reducing distortion?
Cheers

 

[Brad93]

If you really want to limit distortion then gas braze.

You won't be able to TIG braze very well over original brazing as it will be full of zinc which will vaporise under a TIG arc.

You can do some neat joints with TIG brazing but it's very slow and you need everything to be very clean.

 

[Brad93]

You don't have to allow to cool you just need to be able to back the amps off so you're not melting parent material. More heat in the joint is better as the filler will flow and melt more readily.

 

[Brad93]

Gas lens is a good idea.

 

[voipio]

What about sweating the filler cap on using solder? It will use the least amount of heat, and there's not much stress on the parts during service.

 

[minimutly]

Silver solder?

 

[Brad93]

Soft solder is a good shout

 

[lchris21]

Cheers. It's not got a welded or brazed neck at the moment. So no danger of contamination from previous brazing. I've not got gas for traditional brazing so that's out.
Thought the lower heat input might help reduce shrinkage on cooling?
I've worked on tanks off quite modern bikes and noticed some of the fittings are brazed on?

 

[lchris21]

I'll do some research on silver soldering

 

[Ali]

Reminded me of this https://www.mig-welding.co.uk/forum...sm-tank-shrinkage-problems.67675/#post-887507

 

[lchris21]

Just had a read through..thanks @Ali

 

[RichardM]

I'd go for silver solder, less heat input. If you can roll the tank opening so it makes it more stable.

 

[brightspark]

soft solder will be fine and easy to do i used to make my own steam wallpaper strippers with stainless tanks and soft solder the brass car radiator filler caps in on them

 

[Brad93]

Bear in mind silver solder needs a very close fitting joint.

Soft solder is far more forgiving

 

[lchris21]

in process making the neck at moment so fit up will be in hands of the creator

 

[lchris21]

Impatience got the better of me .....not too bad in the end, lots of air cooling and good fit up, small 10mm sections in opposite quadrants....very little distortion. Bit on one side where it keyholed on a thin stretched part of the tank. My painter has had much much worse off me

 

[minimutly]

Impatience got the better of me .....not too bad in the end, lots of air cooling and good fit up, small 10mm sections in opposite quadrants....very little distortion. Bit on one side where it keyholed on a thin stretched part of the tank. My painter has had much much worse off me

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Nice, as usual. Does your tig do pulsed DC? I tried it for the first time the other day on some silly thin stuff - worked quite well.

 

[lchris21]

Yes it has a pulse settings. Takes a bit of fiddling with but you can get decent results with some pre run practice

 

[Paul.]

Compressed air quenching works nicely doesn't it, that's exactly how I would have approached that job, nice work well done.