Soldering Cast Iron?

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GlennW
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Re: Soldering Cast Iron?

Post by GlennW »

Well, this project finally floated back up to the top when I found a O/A torch set with cylinders and a cart a couple of weeks ago on Craigslist that was just a few miles from my home.

I had a cast iron lever from a machine that had broken in three pieces from shipping about ten years ago, so I brazed it up with standard old flux coated brass to see what that was all about. It went great, and after a coat of paint, is hardly noticeable.

Cleaned up the cylinder head, peeled the old lead off, broke the pieces loose, and aluminum oxide blasted the pieces and head inside and out. Beveled the edges a bit with a grinder and fit it all back together. Dug out the Muggy silver brazing rod and gave it a try. The first try didn't go too bad, but cracked in a couple of places when it cooled, as the head varies in thickness right where the breaks are. Next try I put it in the furnace and pre-heated it, then re-brazed it, then back in the furnace to stabilize the temp and cool slowly. Still a crack on one joint along the edge of the braze. Tried it again tonight and found that I may have been putting too much heat into it. I found that the rod acts the same with too much heat as it does with too little and forms a poor bond, so with a bit of finesse and less heat, it flowed right in nicely, looked completely different, and cooled off without cracking by just throwing a blanket over it for a half hour.

Did the Muggy rod work? Sure did!

Would I buy more? Probably not, due to too many more experiments with cast iron!

TIG brazing/welding cast iron is next, trying Phosphor Bronze, Silicone Bronze, Ni99, and 308ss, and probably a couple others for filler rod.

Got another similar crack/repair on the other side of the head.

I may go to an antique engine show this weekend so I can pick up some old, broken, cast iron junk to weld on. :)
Glenn

Operating machines is perfectly safe......until you forget how dangerous it really is!
scmods
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Re: Soldering Cast Iron?

Post by scmods »

Glenn,

My experience with cast iron has centered around control of the carbide layer that develops at the root of the applied material. Brazing appears to be less prone to this problem than welding, possibly because of the generally lower working temperature, but also, I feel, to the general use of a torch to supply the heat. Using a torch uses a lower intensity (softer) heat than an electric arc and applies it slower than the arc. This allows the heat to diffuse into the metal to a greater degree and lessen heat induced stresses. Pre and post heating works for the same reason. The fellow that spoke about his father building a firebrick chamber for containing motor blocks for welding/brazing was controlling the same factors.

Because of strength and operating temperature considerations I usually weld rather than braze cast iron. I believe the filler I use is MG290 with the associated flux and a slightly reducing torch flame. I build a muffle out of firebrick atop my plumber's pot heater and get the part dull red. This is still a long way from the melting point of the part, but significantly reduces the torch time and improves the application process. The flux forms a heavy crust and the whole process takes place out of sight under it. You can have a lot of fun with it while you are gaining skill. The filler rod is part of the tool system and by pushing in or out on the filler you move the semi-liquid metal inside the blob of flux around to where you need it and leave some excess to machine off. For cast iron gears and clutch jaws and the like, the broken off part is of lesser importance as it is easier in the long run to build up new metal and machine it out than to align a broken piece and stick it back on.

On the subject of crack repair, I am sure you are aware of the old trick of drilling a hole at the end of the crack to arrest further cracking, but I will mention it so others may benefit. The end of the crack is where all the stress is concentrated and by spreading the end out from a point to a curved face, the stress is reduced. It is kind of like a crack in one of your fingers where the thickened skin, often callous, concentrates opposing forces on the root of the crack, causing pain and difficulty healing. Beveling the edges of the crack back with a nail clipper increases the flexibility of the adjacent area and reduces the stress concentration. Because you have stopped irritating the root of the crack, it heals up. Next time you are polishing a round part with a burr on it by placing it on a piece of rod and letting it spin while it is against the belt and it comes up the rod and bites the heck out of your thumb, try it. Not that any of us would be so unprofessional to attempt anything like that. Just hand in those hundred attaboys.

Don't sell the torch short or think of it as "old fashioned". The TIG is a great process for certain applications, especially aluminum and stainless, but it is only one of the tools in the arsenal. After all, that's why we keep buying tools isn't it?

Just remember CARBIDE CONTROL.

Bill Walck
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GlennW
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Re: Soldering Cast Iron?

Post by GlennW »

Hello Bill,

Thank you very much for the informative post!

I hope that I did not leave the impression that I was abandoning the O/A torch in favor of the TIG welder. My comment was to the effect that I may just not use the silver brazing rod any more as just plain old flux coated brazing rod seems to work well. I am just curious about the different methods and filler rods available, as different types of repairs may warrant different methods. Welding or brazing two pieces back together of a broken rod the size of your finger can differ from welding/brazing up a crack in the middle of a casting. I just enjoy tinkering with this sort of thing!

Thanks!!
Glenn

Operating machines is perfectly safe......until you forget how dangerous it really is!
f350ca
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Re: Soldering Cast Iron?

Post by f350ca »

Glen I've had good luck arc welding cast with using stainless rod. There are special alloys for cast that can work wonders. I cut out the crack with a carbide burr, (was told the fragments from an abrasive disk will contaminate the weld and cause cracks), not sure if its true. Preheat the casting and weld short beads, peen the weld and surrounding area with a chipping hammer. Continue with more weld, maybe 1/2 to inch bead at a time. Have welded a few exhaust manifolds that should have been tossed. but they held up well. The only on I had no luck with was a water jacketed marine manifold, expect it was some odd alloy to resist corrosion, you'd lay a bead and it would crack ahead or to the side of the weld instantly.
Greg
JTiers
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Re: Soldering Cast Iron?

Post by JTiers »

As far as soldering..... you can do it with regular plumbing solder, or even electronics solder. But the joint has to be one that solder is good for... doesn't get hot, doesn't need to be strong in tension, etc.

I've used it for putting wear strips on things like shaper crank blocks, etc. Basically it functions as glue.

The key is cooking out all the old oil, and burning off some of the carbon on the surface. heat it and brush it a few times, and then the solder should actually work as it should.

Solder that peels right off was improperly done to begin with.
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rudd
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Re: Soldering Cast Iron?

Post by rudd »

I need to silver braze some cast pieces to make a "casting" - I read where the cast should be bead blasted just prior to brazing to get the graphite particles out of the surface, is aluminum oxide media OK or would I be better off with ground glass or something else?

I tried the "searing the surface" trick, I get mixed results, plus, since I'm going to be machining this stuff afterward, I *really* don't want to turn the grey iron into white iron.. or pearlitic iron. That's the reason for using silver braze rather than brass, hold the temp below the critical point.

I'm actually getting much better flow with the white safety silv paste as opposed to the black flux.
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GlennW
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Re: Soldering Cast Iron?

Post by GlennW »

This is where I'm heading. (A hundred pounds of lathe tailstock) Hence the experimentation.

I really don't want to bring the entire housing up to glowing red.
P2260019.JPG
It was like that when I got it as it had been dropped.
Glenn

Operating machines is perfectly safe......until you forget how dangerous it really is!
f350ca
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Re: Soldering Cast Iron?

Post by f350ca »

Glen, I'd gouge the crack out with a carbide burr and electric weld it with a nickel rod for cast iron.

Greg
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GlennW
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Re: Soldering Cast Iron?

Post by GlennW »

Thanks Greg.

Got the Ni99 rod sitting on the table.
Glenn

Operating machines is perfectly safe......until you forget how dangerous it really is!
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