Cracked cast iron frame

On Sun, 11 Aug 2013 19:01:05 -0400, snipped-for-privacy@snyder.on.ca wrote:


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
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On Sun, 11 Aug 2013 16:37:38 -0700, snipped-for-privacy@whidbey.com wrote:

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-)
--
Ed Huntress

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On Sunday, August 11, 2013 8:22:24 PM UTC-4, Ed Huntress wrote:

First my recommendation is to repair the press as a learning exercise. Rep airing it will take too much time to be really worthwhile.
But here is something that some one might try. Using a neon sign transform er to generate plasma to clean the surface of cast iron that has be abraded . It is not something that I have tried. I just have not needed to weld o r braze any cast iron since I thought of using plasma. But the plasma from a neon sign transformer ought to oxidise both grease and grapbite. Using plasma to clean grass surfaces before mirror coating is well known. But I have not heard of anyone using it to clean cast iron surfaces.
If anyone tries this, please post your results. It should work, but one ex periment is worth ten thousand conjectures.
Dan
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On Sun, 11 Aug 2013 20:22:24 -0400, Ed Huntress

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
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On Mon, 12 Aug 2013 08:58:31 -0700, snipped-for-privacy@whidbey.com wrote:

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=XSGaKuYQLjIC&printsec=frontcover&source=gbs_ge_summary_r&cad=0#v=onepage&q&f úlse
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

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On Sun, 11 Aug 2013 16:37:38 -0700, snipped-for-privacy@whidbey.com wrote:

I've grazed castings too, with mixed results - and silver brazed things as critical as distributor drive gears. Until we figured out we needed to use a wooden alignment pin to install the head on the R12 rallye car we broke 3 didtributor drive gears - and there were no more available locally - so I ground the parts of 2 damaged gears to fit and silver brazed them together. It stood up for 3 years of competetive rallye driving and another 3 years of my brother thrashing it as his every-day whipping boy. It didn't break.
The "drawing out" is more than capilliary action - it is actually "alloying" the puddle, making a maleable transition from the base metal to the weldment and back to the base metal which takes the shock better than the base cast and "absorbs" the shock - preventing the brittle cast from breaking as easily under shock. Brass doesn't appear to do this as well. I've ended up grinding out brazed repairs and redoing them with stainless (tigged) on several parts - and stainless welding even permanently repairs cracked exhaust manifolds - which are often high nickel castings to start with and do not last long when brazed..
Welding with mild steel rod causes a brittle zone on both sides of the weld, where the carbon has been "drawn" out of the casting, which makes the part succeptible to breakage under even low levels of shock (and even vibration in some cases).
Just my experience, going back 45 years and proven as recently as last year.
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snipped-for-privacy@snyder.on.ca wrote:

Less likely to warp something and also more fuel efficient is the technique I was taught by the Ag Eng welding shop in college. Cold Welding with Nickel.
Grind it out to a V (leaving enough broken cast to register it (or the threads, and a little bit, in this case), drill the ends if a crack. Lay a short bead of nickel rod (55 or 99 Ni) and peen it as it cools. Lay more short beads elsewhere (not continuous nor contiguous at least until you return to the area later in the process and fill in between older sections to connect them), peening each time. The peening stretches the nickel so it does not pull the casting as it cools. If the work gets warm enough that you can't leave your hand on it, go have a cup of coffee, or lunch. Keep at it until you have filled the whole thing. Slow, but not as slow as preheating a large casting, and does not required stripping parts away from the immediate work zone as preheating does.
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I don't know why everybody says to vee the crack. The depth of the vee will be so much less than the frame thickness that it can't be significant. And the braze will wick into the crack without needing a funnel.
The link Ed posted in the "Joining Stainless Wire" thread about silver brazing (http://www.aws.org/wj/amwelder/9-00/fundamentals.html ) had a chart showing joint strength versus joint width. The maximum was for a joint .0015 thick!! That thickness joint had a much higher tensile strength than the silver itself (3X). Joint strength fell off dramatically with increasing thickness. Thus a vee will be much weaker than a close joint.
Bob
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On Sun, 11 Aug 2013 13:57:46 -0400, Bob Engelhardt

Bronze brazing (actually, it's brass) is a little different. It has a higher bulk strength and works better in fillets. But it doesn't have the high *joint* strength of silver in close joints.
I saw that graph and I don't doubt it, but it's a little sharper than others I've seen in the past, and the usual recommendation for silver brazing is to have joints of 0.002" or slightly less. That's in close agreement with the graph from H&H, which AWS re-published.
There are silver braze materials (and special bronze brazing alloys) formulated for use in fillets but their ultimate strength isn't quite as high. The maximum joint strength for silver brazing that's usually quoted is 120,000 psi, for close-fitting joints. As you say, that's close to three times the bulk strength of the material.
When you silver-braze wires, and when they're in contact in a parallel joint, enough of the joint is within the high-strength range that the overall joint strength is quite high.
Keep in mind that there's a distinction between silver-brazing that's done like soldering, wherein the braze wicks into a close-fitting joint, and what is sometimes (inaccurately) called "braze-welding," which is mostly a matter of wetting the material on both sides of a joint and building up a fillet. That's how Brit race-car builders made their tubular space frames back in the '50s and '60s. In that case there may be some wicking but you don't count on it.
Too bad Jim Rosen isn't around these days. He's pretty knowledgable about silver-brazing.
--
Ed Huntress

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On Sun, 11 Aug 2013 13:57:46 -0400, Bob Engelhardt

Greetings Bob, It is very hard to get brazing to wick into cast iron. Even silver brazing alloys. I thick it is because of all the free carbon (graphite) present at the surface. I have brazed a lot of cast iron and it is always a bit of a chore to get the brazing alloy to wet the cast iron. Brazing rod typically has at least as high tensile strength as cast iron, and typically more, in thick sections. Eric
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On Sun, 11 Aug 2013 13:21:24 -0700, snipped-for-privacy@whidbey.com wrote:

Wetting is a big issue, and graphite flakes or smeared graphite on the surface is a major cause of trouble.
But it's only one issue of several, when it comes to brazing cast iron. Here's an article from the British journal _Welding and Metal Fabrication_ from 1980 that I remember using as a source for an article I wrote a year or two later:
http://tinyurl.com/k8fzynj
It covers it well, although it doesn't address repairs. You probably could find an alloy available in the US that has the same properties as the one discussed in the article.
A few notes: This casting is almost certainly gray iron. Where the article discusses nodular iron, that's what we mostly call "ductile iron" in the US.
And, finally, I think this particular job is a waste of time and money, as others have commented. <g> It could be a worthwhile learning experiment, however. But don't count on finding any brazing alloy or flux that could allow the braze to wick into that crack without opening it up first.
--
Ed Huntress

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On Saturday, August 10, 2013 6:12:15 PM UTC-7, snipped-for-privacy@gmail.com wrote:

check out http://atbayappliance.com/news-and-tips/ for appliance repair news and tips from a reliable company in California.
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snipped-for-privacy@gmail.com wrote:

It didn't have enough paint to keep it from cracking. ;-)
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