On Mon, 15 Apr 2013 14:32:36 -0400, "Steve W."
wrote:

Ed Huntress wrote:
On Mon, 15 Apr 2013 13:04:02 -0400, "Steve W."
wrote:

Ed Huntress wrote:
On Mon, 15 Apr 2013 11:32:06 -0400, "Steve W."
wrote:

Ed Huntress wrote:

It is an ART to repair a casting that won't crack again! A big part of
that is in the pre-heat and cool-down phases of the weld. I've had
mostly good luck but a bit of bad luck. A lot depends on the metal and
the phase of Venus.
Indeed it is an art. When the welding equipment companies, or other
researchers, do a metallographic analysis of cast iron welds, the
results will leave you wondering how it ever works at all. The weld
and heat-affected zone typically is like a layer cake of weirdness.

Anyone who can get good results *consistently* is worth his pay.

BTW, the guy who allegedly was the highest-paid c.i. welder in the
world, an Italian who did nothing else, was hired and shipped in many
years ago by Bill Harrah to weld a crack in the block of his priceless
Bugatti Royale. He did it with O/A and c.i. rod. It worked, even
though it doubtless had oil in the (then) 60-year-old cast iron.

I don't know how he did the pre-heat or stress relief.

Yeah the haz in a cast weld gets interesting. Areas of carbon migration,
grain structure changes and lot's more.

Gas works real good for thin wall iron. You have to watch your flame
real close and only fill enough to ensure a good bond. Then watch it
real close for contraction while it cools. Add enough filler and you get
a good bond and repair, go under and it will crack again due to the
tension stress at the site. If you go over it will probably crack in a
different area due to the stress the extra material adds as it act's
like a wedge.
That sounds like things I've read, but I've never attempted it. I have
enough to keep me busy with mild steel. g

It must require a combination of experience, knowledge, and a
highly-developed feel for the materials and the work. And I'll bet
that several senses are working at the same time -- touch, vision,
hearing, and even smell.

As they say, it's quite an art.

Takes a bit of sorcery as well. I do quite a bit for the local farmers
and construction outfits. Tell them up front that MY repair will hold
BUT no guarantee that there won't be a failure doe to unknowns in the
castings. Nothing like a slag inclusion or localized carbon content
changes to ruin the party. Older castings tend to be easier to deal with
due to less "unknown scrap" in the cast pours of the day but you still
need to pay close attention.

Ideally with something like a used block or head where it has been in
oil I like to toss it in a vat for a couple days to leach out as much
oil as possible. That way you don't burn more carbon into the iron when
you heat it up. Then you preheat above operating temps and hold it there
while you weld. That is the fun part....

Have you tried methods other than gas welding? Like, nickel rods with
a stick welder, or anything else?

The subject interests me a lot, although I think I'll probably remain
an observer. I don't play with engines like I used to.


Yep. Gas, stick, MIG. High nickel rods, cast rods, brass, even used mild
steel rod on one. All depends on the size of the casting, location of
the damage and the actual stress on the area.

Something like a freeze crack in the side of a block where the only
stress is from cooling water and no real stress then a simple clean up
and braze works. Just be sure you stop drill the cracks and clean it
well then overlay the repair well past the damage to catch that hairline
fracture you don't see with the dye..

Cylinder heads or block webs are the fun ones. Large castings are
generally not real bad with a stick machine and the correct rod IF you
can get them above operating temps so the casting and weld can
expand/contract equally during normal use.

I tried TIG a few times but due to the concentrated heat it doesn't work
well for castings. The localized HAZ is so small that it is hard to
equalize the stresses even with pre-heating to equal temps.

Well, you have experience with the whole gamut. Did you just learn it
all on the job, or did you go for some training? It seems like
learning to weld c.i. must involve some testing to destruction, or
maybe just seeing what holds together?

--
Ed Huntress