On Mon, 14 Dec 2015 18:43:35 -0600, "Terry Coombs"
wrote:

wrote:
On Sun, 13 Dec 2015 20:03:38 -0600, "Terry Coombs"
wrote:

The day I picked up the stove grates I also picked up a small "fire
pot" that was cracked/broken . The break is across a 2" horizontal
then about 1" vertical - kind of like an angle iron but not at 90° .
I attempted a repair on it yesterday , beginning with a tack at the
corner and one at the horizontal edge . That part went well ... but
when I tried to fill in between the two tacks it keeps cracking . I
have a hammer handy and begin peening before my helmet clears ... I
have not preheated this piece because of the size and awkwardness,
and I think that's what's killing me . The TIG heat is so localized
that the nearby mass of iron is acting as a chill and sucking the
heat out so fast I can't peen fast enough to stop the cracking . I
can't heat the whole part , but I can heat the repair area . The
part is like an oval sleeve , with nothing to restrict expansion in
any direction so I think I can safely heat just that area . The
question is how hot and will this help keep it from cracking ? I
tried some CI strips first , then the Invar 42 , same results with
both fillers ./
Are you anywhere near a pottery supply company? If so, get some
ceramic wool and wrap the piece after heating. As to how hot in my
experience if I heat cast iron to about 700 degrees it won't crack. I
have had the best luck heating to a dull red heat when observed in low
light, wrapping in ceramic wool, and welding. It's a pain because
everything is so hot but on the other hand no peening is required and
no cracking is happening. I have used this method with brazing rod,
aluminum bronze rod, stainless steel rod, and nickel alloy rods.
Eric

I don't have a pottery supply near , but I do have a large pile of
fiberglass batts . You think they'll work at the temps you use ? The grates
aren't so awkward in shape , I plan to build an enclosure with firebricks
and preheat with my foundry burner . Heat 'em both up and let one soak while
I weld on the other , swap as they cool .
I don't know about the fiberglass batts because I think they use some
sort of glue to hold the fibers together. Tear a small chunk off and
point a torch at it to see if it burns. Not too close because the tiny
glass fibers may burn while in the torch flame. Your enclosure idea
is a good one. Lay the grate on some more fire brick while welding so
that it doesn't lose heat through conduction. You know, I bet the
fiberglass would be fine if it was just used to cover the part while
it was being welded. Try it. It just occurred to me that a fireplace
shop may also have ceramic woll.
Eric