On Mon, 12 Aug 2013 08:58:31 -0700, wrote:

On Sun, 11 Aug 2013 20:22:24 -0400, Ed Huntress
wrote:

On Sun, 11 Aug 2013 16:37:38 -0700, wrote:

On Sun, 11 Aug 2013 19:01:05 -0400, wrote:

On Sun, 11 Aug 2013 10:05:35 -0700, wrote:

On Sat, 10 Aug 2013 18:12:15 -0700, wrote:

I bought a small press in a junk shop for $20. I mounted it on a 2x6
and let it collect dust for a year before I started to use it to
flatten sections of copper pipe. It did very well until today: There
was an ominous sound and the frame cracked:

http://www.flickr.com/photos/2768312...7635013299389/

No way will I admit using a cheater bar and even if I did I barely
leaned on it. Anyway...Can this be repaired or is this thing done for?
My understanding of welding cast iron is that it is not a free lunch.

Thanks,

Michael Koblic,
Campbell River, BC
Greetings Michael,
I have experience with this type of repair that worked well. At wotk
someone pounded on the large vise and it broke through the ram that
encloses the screw. I was taking a welding class at the time so I
brought it into class to fix it. I built an open top "oven" out of
firebrick and set the vise part into it. I then heated the veed out
part to nearly red heat with a big torch. Using flux and brazing rod I
wetted the cast iron vee with the brazing rod. Once I had the surfaces
completely wetted I just filled with brazing rod. I did this repair in
about 1.5 hours and used a lot of welding gasses. This repair was done
over 20 years ago and I still use the vise. Frankly, I did the repair
for the experience, your press may not be worth it. It may just crack
somewhere else.
Eric
A similar method, but likely stronger, is to pre-heat as above and
then weld with "ni-rod" (high nickel) or stainless steel wire. Makes
a very strong and permanent repair - the weld and the absorption layer
around it are stronger than the base casting, as the alloy from the
Ni-Rod or stainless "draws out" into the casting. Let it cool slowly
and naturally when finished. I've used this method on numerous
machine (agricultural) and tractor parts over the last several decades
and I'm not aware of any of the repairs failing.
Greetings Clare,
Your method described above will certainly result in a repair that is
stronger than the parent metal. Brazing rod is as strong as or
stronger than the cast iron parent metal. I'm talking tensile
strength. In a wear or impact situation welding with ni-rod is
certainly a better solution. When you say "draws out" I assume you
mean the capillary action where the melting metal penetrates the
casting between the crystals. This also accurs when brazing and silver
soldering and is one of the reasons why silver soldering and brazing
can result in such strong joints. When brazing cast iron I'm not sure
how well the brazing metal penetrates into the casting.
Eric

FWIW, and I don't want to obscure the practical issues with
technicalities, neither brazing nor soldering involve any penetration
between crystals of the parent metals. Unless you're dealing wth
something that's porous to begin with, such as sintered powder metal,
the action occurs within a few microinches of the parent metal's
surface.

Cast iron and the other metals that are usually brazed or soldered are
not porous. The bonding occurs at the boundary, where the parent metal
and molten braze metal form an extremely thin layer of alloy (in broad
terms) by diffusion, usually. This "alloy" is either a solid solution
(brazing, with a few exceptions) or intermetallic compounds
(soldering, with a few exceptions). Solid solutions are atomic-level
alloys that typically are very strong. Intermetallics are alloys that
generally have a different atomic lattice structure than the parent
metal or the braze or solder, and they can be hard-crystalline and
very brittle. In general, you want to avoid them, and you can minimize
them by avoiding overheating the joint.

This gets complicated, obviously, but it's probably a good idea to
dispell the idea that there is any "drawing" into the parent metal
going on. Of course, the capillary action of the liquid braze or
solder flowing into the joint can be thought of as "drawing," but it
ends at the parent metal surface.

There is a misconception about cast iron being porous because it *can*
be porous at the very surface, where graphite flakes are exposed. As
they wear away, pockets are left in the surface and they can hold oil.
But these pockets do not penetrate the metal. They're just microinches
deep, on the exposed surface. Keep in mind that 2% or 3% carbon
content by weight, which is typical of gray iron, means that, by
volume, the material is 10% graphite. That's a lot of flakes, and they
leave a lot of surface pockets as they're worn away. But cast iron
does not "wick" braze, solder, or even oil, into the parent metal.

When you abrade an oily cast iron surface, such as when you grind or
sand it to clean it, you smear both the oil and the graphite around on
the surface. You can't just abrade cast iron and expect to get a good
solder or braze bond because of that.

Anyway, we now return you to practical issues. d8-)
So Ed, when I see silver solder or brazing rod in the steel when I
mill away the silver solder or brazing rod at the surface I am not
seeing the result of capillary action but instead a sort of alloy? I
have done this more than once, milled away a joint that had been
silver soldered or brazed. With silver solder especially I have seen
where the solder appears to penetrate below the surface by wicking.
And When I have had to weld on a jointg that had been previously
brazed or silver soldered I had to remove metal below the original
surface in order to get the solder or braze that is below the original
surface. And it is obvious when this hasn't been accomplished, the
puddle starts to boil. I learned years ago that this was because of
capillary action pulling the soldering alloy into the parent metal. I
guess it's time for more learning. Or you could be wrong. Which
doesn't seem to happen very often in your posts here. Either way I'll
find out.
Eric

My memory is not completely reliable these days, and I studied brazing
over 30 years ago, but I think I've explained it correctly. Also, from
memory, anything more than an extremely thin (like, maybe a thou or
so) alloyed depth produces a weaker joint. That's the result of
overheating or soaking for too long at the brazing temperature.

I'll look it up for you if you want, because it wouldn't hurt me to
refresh my memory, but I think you can find enough in _Brazing_, the
AWS's technical bible on the subject, to satisfy your question. I used
to talk to the author a lot when I was writing about it and there's no
doubt that Schwartz is The Man on brazing.

Unfortunately, the book costs $140. Fortunately, most of it is
available on Google Books. The questions you're asking are answered in
the first dozen pages or so, which appear to be contiguous. To see
what Schwartz says about capillary action on the visible pages as well
as the invisible ones, search on "capillary" in the search box.

Here's the full URL, which will be worth keeping:

http://books.google.com/books?id=XSG...page&q&f=false

Here's a Tiny URL of the same:

http://tinyurl.com/k543xzm

Brazing is simple and reliable, and much stronger than most people
realize. But it also is very tricky when you work with materials other
than the usual standards: steel, copper, brass, etc. Cast iron and
aluminum are tricky. And there are many special brazing materials for
special applications, which _Brazing_ covers quite well.

One last point: There are occassions when you get intergranular
penetration. It is a bad thing, and it's limited mostly to special
diffusion-bonding brazing materials that contain bismuth. That's out
of our realm -- it's an aerospace thing, mostly -- but I don't want to
confuse you by saying it doesn't happen. It just isn't something we're
likely to encounter. And when it happens, the joint often is shot.

Good luck, and let me know if you want me to do any more digging.

--
Ed Huntress