On Sun, 3 Jan 2016 20:40:30 -0600, "Terry Coombs"
wrote:

wrote:
On Mon, 04 Jan 2016 08:24:56 +0700, John B.
wrote:

On Sun, 3 Jan 2016 11:56:25 -0600, "Terry Coombs"
wrote:

I have decided to give up and admit those wood stove grates have
defeated me . I have done a lot of research in addition to the
excellent advice y'all have given me and this just ain't happening .
These grates have been repeatedly overheated in a high-carbon
environment , and have apparently absorbed so much carbon as to
render them unrepairable .
First I tried preheat to 500-600° F and TIG welding the cracks
with both cast strips and with the Invar 42 . The problem is that
the surface of the CI just ablates , it will not puddle . I did get
some very small "beads" molten , but the filler would not fuse and
puddle . Next was preheat and brazing rod , it refused to wet the
surface and stick . When I did get it to stick on some places , it
cracked as the part cooled .
Today I tried some new brazing rod with preheat , same deal , it
refuses to wet the surface . Since nothing else has worked I
figured I had nothing to lose so fired up the MIG and tried a short
bead with heavy peening as the weld cooled . And it won't stick
either . I'm figuring that with nothing else working it's pretty
much futile to try with stick . So tomorrow I get to call the guy
and tell him the bad news ... but for some reason I don't think
he's going to mind too much . The stove (I got to see it the other
day when I delivered the other piece I repaired) is much older than
mine , and has been cobbled on some before . And he's got another
stove installed where he had this one ... I suspect he was kind of
expecting these to be unrepairable , I pretty sure I'm not the
first guy he's asked to fix them . The others apparently had the
good sense to say no .

I might add that most "muffler shops" say that they won't weld to
existing used exhaust pipe for the same reason.

I have successfully welded to old exhaust many times, but there IS a
limit - and aluminized steel is a bit more tricky. With AMC's old
ceramic coated exhaust it was a total exercise in futility..

When it comes to manifolds,I have welded a lot of cracked cast - but
if you get "burned cast" - forget it. It just falls apart when you hit
it with torch or rod.

Which is pretty much what's happening here , it just goes away when I hit
it with the TIG .
And it doesn't even send a shower of sparks. Almost like trying to
weld a sand core. when you do it with a torch