Bruce;
Were your pieces that failed conventionaly brazed or fillet brazed? What
type of joint? Materials, etc?
Headers are probably a classic example of brazing (or even fillet brazing)
misapplication. Fusion welding is the only way to go for high- heat exhaust
applications.
There have been hundreds of race car tube chassis fabricated in the UK by
fillet brazing and they have been very sucessful. Torch brazing, like torch
welding, spreads the heat over a wider area of the joint; unlike fusion
welding, fillet brazing is done at a far lower temperature so there is much
lower locked-in stress in the structure and distortion is far less of a
problem. Failures at the edge of the "heat affected zone" (HAZ) do not occur
like they do with fusion welding. A large fillet will also distribute joint
stress over a wider area of the tubing--- especially helpful when joining
very thin material. Welding 0.035" tubing takes alot more skill than fillet
brazing the same stuff. Properly done, strength & toughness should be
similar.
I'm not saying fillet brazing is the answer to everything-- it isn't.
Applied correctly, though, it is a great technique with lots of advantages.
As I suggested in my last posting, fillet braze up some joints and also
fusion weld up some similar ones of equal size tubing of the same material.
Then beat the crap out of both-- you'll see just how tough both are.....or
how bad a job you've done. Give it a try.
Regards, Neil Tucson, AZ
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