Brazing Cast Iron

A while back a question was asked about welding cast iron. Several reply's said that brazing was better than welding. I remember a couple of M Farmall's that the centers of the rear wheels had cracked and were brazed. OK, how do you braze cast iron?? I have a cutting torch that runs on propane, will this make enough heat , or do you need acetylene? How much do you preheat and how do you keep it hot so it cools down slowly?? I have successfully welded cast iron, not very pretty, but functional, I would like to try brazing if I had a clue what I was doing. Thanks, Chris

first of all, i'm 99% sure the "cast" wheel centers on your M are cast STEEL, very very different than cast iron. the exhaust manifold would be cast iron.

cast steel is not all that difficult to weld with whatever your favorite machine might be. at the risk of a stern rebuke, i'll admit to having welded cast steel with 6011 and while that may not be "right," it's been a functional, reliable repair for several years now.

cast iron is very tricky. pre heat, post heat, brazing or nickel rod, all that.

I think nickle welding is better than brazing. The parts should be clean and free of oil. Then it should be pre-heated then welded and then either put in an oven and gradually reduce the temperature cooling it or if the part is large buried in sand to keep it from cooling too fast. Still cast is fickled. You could have two identical parts from the same equipment and one could weld easily and the other could be your worst nightmare.

If you do a search at the welding sites for "brazing cast" you'll get a zillion hits. Short story, just enough heat, warm the whole item, cool slowly.

Propane usually does not work very well for any type of brazing.

I have also found that using propane even for cutting does not save as much as guys think. You cut slower and use more oxygen.

The other posters have covered the actual brazing issues.

I disagree with pouring sand on a part to slow cool it, even tho I know it's done a lot. Unless you preheat the sand you are effectively quick cooling it to half the difference between the sand temp and part temp. As far as I understand it, it's the upper temps that need to be slow cooled so cool sand does little good. You would be better off to throw a leather and then a blanket over it since they won't touch as much and won't transfer the heat out as much but will insulate fairly well.

Brazing cast iron requires a different flux also, doesn't it?

(quoted from post at 12:00:00 11/16/14) Brazing cast iron requires a different flux also, doesn't it?

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I don't think so Don, it's all borax based. What some heavier cast requires is cleaning the surfaces with a file rather than a grinder. The grinder tends to bring the graphite out of the alloy and lay it on the surface which gives adhesion issues. Filing cuts rather than abrades is reputed to give better results. At least that the way I was told! :lol:

I would ask me self How expensive is this part? Worth a try to fix? What stresses is the part going to be under ? Will I get enough preheat to bring the part up past the point of being brittle. Can I slow cool it somehow in my own shop.Am I going to try to grind and hide the repair?Would it pay to have a welding shop make the repair for me.? If it does crack is it the type of part where the weld will hold and a few smears of J-B weld will seal any leaks from the stress cracks that do occur ,then get painted.

Those should be pretty common, I would just find used replacements.

I can't immediately think of what would be wrong with welding cast steel with 6011. I'd say it was a good choice, and if your welder was an AC buzz box, I'd call it the best choice. Partly that's because I've never cared for 7018AC, but that's just my own opinion.

Stan

I've never brazed using propane, so I can't speak to that part of the question.

As far as the actual brazing, it's usually just a matter of preheating the part, if it's large enough to need it, and then using an appropriate sized tip. What you'll want is for the area your brazing to get hot (usually red hot or nearly so)to the point that as the rod melts it flows just like it would if you were soldering. From there you use the distance from the tip to the material, and in some cases you can let the rod stay in the puddle to help it cool, to keep the area your brazing hot enough, and the puddle fluid enough to do the job, without getting too hot or too cold. Believe me, it's not as difficult as it sounds with a little practice.

As far as flux, I almost always use rod that is already flux coated. If the rod doesn't want to flow and runs off the piece instead of sticking and flowing, then you can get additional flux to use. Something else I often do, if all else fails, is to use some muratic acid to clean the part before brazing it.

As far as cooling, it depends on the part. Usually I will just let the part air cool naturally. Now if it's an intricate piece that has a lot of bends, thick and thin parts, etc, etc, I usually bury the piece on cat litter/oil dry and let it cool that way.

Like I have said in past posts, I've brazed everything from axel housings to transmission housings, to exhaust manifolds. I'm sure there are 'by the book' ways to do everything, but when in the field you do what you have to do to get the job done. That said, I have never had problems with the end result of any of the repairs I have done.

Have you done those axle and tranny housings overhead too?

There is a triangular shaped Oxy-acetylene welding rod, used with a separate can of dry flux that does an an excellent job on cast iron especially building up missing sections of an intake manifold. I have also had excellent results stick welding and brazing cast, always preheating and cooling slowly. Find a cast piece(s) to practice on.

I tries welding some cast steel with 6011 once, it kept cracking. Switched to 7018 and it worked great and held forever.

First rule of cast iron repair for me... is ask myself if I can buy the part reasonably and in the time frame I need before I even think about repairing it. Having said that... if it must be repaired, my preference is with nickel rod (Sodel 35) if it's something not too intricate that will not crack when it cools. If it is likely to crack or is intricate, has think/thin/variable pieces to it... then I'll try brazing it. Those fancy parts NEED to be preheated. Last large pulley I brazed the hub back into I preheated on the BBQ and brazed it right there with the heat on full blast.. As far as my torch goes... I've used propane for years now. Standard welding tips to not work with LP so I just use my cutting tip that has an LP tip... for fine work it sucks. For big and ugly it will suffice. I've never much worried about extra O2 usage. I find it insignificant. I do run the LP pressure at upwards of 10 psi tho.. Give it gas and it will make flame. Beyond that, if you can braze steel, you can probably braze cast iron. The difference is in the cooling. Make sure you keep the casting warm after you're done and slowly cool it. I just turn the heat to low on the BBQ or whatever preheat source you're using and allow it to back off slowly, then turn the heat off and mabey throw a blanket over it or just close the lid and give it time..

Rod

I did a lot of brazing years ago. Not so much any more.
Brazing is a tried and true way to repair cast iron.
It is inexpensive and does not require special skills, technique, equipment or exotic alloy rods - all of which I have and know how to use.
I brazed a crack in the cast iron end frame on an old cultipacker this fall. Just because I didn't have any special welding rod on hand and hadn't done any brazing for a while.
It was easy and I am confident it will last for a long time.

They actually make a welding rod for cast iron i have used it. Brazing process just takes a little time but i prefer it. You still need to preheat where you going to work. What i do is grind a V in the crack to be welded from end to end and about a inch past each end of crack.When to heat it up youll be able to see the crack alot better. preheat with torch (not Propane) I use a brass rod with the flux on outside. Important keep the work hot. when finished cool down is important dont let it cool quickly.

Hi Russ;

I don't want to give you the impression I'm arguing about this. There's no arguing with results. If it worked, then it worked. I am interested in this subject, though, so I'd like to ask if you formed an opinion about why 6011 made it crack, and 7018 didn't? Do you think it might have been cast iron rather than cast steel? I think cast steel might be difficult to distinguish from regular mild steel because they are the same in a spark test, but cast iron sparks clearly different from steel. I can't remember having heard of any particular welding process that makes steel crack, but cracking after being welded is the number one problem of welding cast iron. However, I have also heard people talk of having successfully welding cast iron with 7018. So it's kind of a muddle, but the circumstantial evidence, you might call it, kind of suggests to me that the part you repaired might have been cast iron rather than cast steel---unless you know of sure that it wasn't, of course.

Stan

I've welded upside down, backwards, sideways, and even had to use a mirror on occasion.....but never have I had the need to braze overhead, as such. I have found it necessary to braze item where there might be a short section that was inverted, and I don't mind saying that getting the upside down part to flow out and not drip was a royal PITA. That said, fortunately, I do my best to insure that any brazing I need to do is positionable to allow all work to be done in a horizontal position as, like most other welding processes, everything simply works better when gravity is working for you instead of against you.

There is brazing flux to use with brazing rod. I use plain old Borax that can be found in any grocery store in the laundry detergent isle. I've used it for 40 years and know it works very well. Also if you want to keep your braze edges in a straight line, just scribe a line down each outside edge with a good heavy carbon line (lead pencil). The same thing for brazing around a hole, fill the hole with carbon (I've used the carbon piles from D cell batteries). Just what I've done for years that works, take it for what it's worth or not. Keith

7018 is more ductile than 6011. As it cools either the weld or the parent material needs to stretch. Nickel is easier to stretch than 7018, which is easier than 6011, etc.

Good explanation, but doesn't it still support the premise that it's more likely to have been cast iron than any common variety of steel? My experience is far from unlimited, but I've seen a lot of welding. Cracking of the weld, the base metal, or the interface between the two is not a problem I can remember seeing with mild steel---and I've probably seen more bad welds than most people see in a lifetime. I'm not saying it never happens, only that it doesn't happen often or I would have seen some of it.

Stan

When brazing overhead, you will know you are getting a good bond because the liquid brass has to flow & adhere against gravity & not just flow by gravity. In my younger days, it was a challenge & I felt good when I could do it. But no more.

The way it was explained to me is the rod needs to have a similar carbon content of the welded material. Reason being if you weld a high carbon steel with a 6011 the softer metal will pull carbon out of the welded material, and then it will crack around the weld. That's what a welding instructor told me and it seemed like that was what was happening to my welds. Ground it all out and rewelded it with 7018 and no cracks.