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Tech Tips: Repairing a Crack in Cast Iron

Hi, I’m Joe Kolasa. I’m the welding instructor at the Lincoln Electric welding school. We are here in Cleveland Ohio at the Lincoln Electric corporate headquarters, and I’m here to help you with some welding tips on cast iron. Most of the problems that we have with cast iron is due to its high carbon content. That creates cracking problems, which creates a lot of thermal control versus mild steel welding. In mild steel, you have very low carbon. Generally, they’re classified as a 1015 or a 1020 carbon steel. What that means is that their carbon content is around .20 In cast irons, cast irons have around two-to-four percent carbon with a lot of silicon. The more carbon content you add to your metals, the harder the steel gets, and the more carbon content you add to your metals, the stronger your steel gets. But also it’s very crack sensitive, so when we’re working on anything of a cast iron with a very high carbon content, we have to start really following rules of welding and not just striking an arc on the material. I have an oxy-propane setup here with Harris products. Then over here I’m going to be using an AC/DC 125/225 welder and it’s going to be sent on DC positive and I’m going to be running about 85 amps and I’m going to be using a 1/8 nickel 55 Softweld electrode. Most of the time there’s several different ways you can repair castings. One of the ways is stick welding, and they make several different types of consumables. We make a Ferroweld, we make a nickel 55 Softweld, and we also make a nickel 99 Softweld. The difference between them is that the Ferroweld is basically a steel electrode designed to weld castings but it will not be machinable so if you have to do any machining you have to not make sure you use Ferroweld The nickel 55 has a lower end nickel, which actually gives it more strength in thicker sections. And then the nickel 99 has almost 100 percent nickel and the reason for that is that it is a non-ferrous alloy, which does not absorb any carbon into the weld so it is very good for single pass welds, also for castings that need to be machined. So make certain that you’re very aware of the selection of the material
you were going to use to weld your casting. On this casting i have an area that is ground out. This crack is in the casting but it’s not all the way through the casting. So first of all, I have to take a grinder or a carbide drill, anything of that nature that can take and remove the material, and I’m going to V it out into around a 30 degree bevel and I want to remove all of the crack. Once I get that done, I’ll take and clean the material and then I will have to take and add preheat to the casting. What that does is that the preheating in the casting will allow the casting not to cool very fast. Therefore, we’re going to limit or hopefully not have any cracking problems. If I would just weld on this casting without any preheat, it would cool too fast. You would actually hear a slight pinging sound, which means it’s cracking again. You have to control the preheating in the casting, so what we have here is a temple stick. And the temple stick, they are marked with
celsius and fahrenheit. They are various degrees that they melt at. So I am going to take and preheat this up and when I touch the temple stick to the casting, when this melts means that that’s when I
come weld on the casting. It has enough heat into a to keep it
from cracking. I’m also going to limit
myself in a parameter of thermal. I will take a 300 degree temple stick, 500 degree temple stick, and maybe have an 8 or 900 degree temple stick and I can stay within that range of
temperature to keep the casting as is where it doesn’t
get a lot of stresses. Therefore, when I’m done with the casting I can take and slow cool. Either wrap the casting in a fireproof blanket and/or put the casting in an oven and drop it down 50 degrees an hour. Generally, that will allow the casting to stress relieve itself. However, we don’t have all the options of doing that at home, so the best thing is you can bury it in sand if you have to. All we need to do is control the slow cooling of the casting. So one of things that I do is I put charcoal in a grill, let it burn out. When I’m working on a
casting, after the charcoal has burned out I’ll throw more charcoal in it. I’m done with the casting welding on it
for two hours, I throw the casting in a charcoal grill and let it come down for two days and it’s still warm when I get done. That’s more or less something that we
can do to control thermal care when we’re trying to repair things at home. So what I’m going to be right now is
show you the preheating technique that we do and how I actually
use the temple sticks. And then I’m going to show you some of
the techniques we do welding. First thing I’m going to do is I’m going to light the oxy-propane torch system. And what I’m going to do is take and then
preheat the casting. And while preheating the casting I’m going to
take this temple stick and I’m going to start scraping it along the
casting then when it melts, that’s when I can start doing my welds
on the actual casting. So let’s go ahead and light the torch here. As you noticed that I kept checking on the casting in
different areas to make sure that the heat is localized. I want to make sure that everything is
going into the casting at an even rate. I have my welder set to go at 85 amps, I’m on DC positive. I am running as I said before the 1/8 nickel 55 Softweld. And before you proceed with your welding, you’ve got make certain of a few things. You want to make certain you have the
right safety gear on. The safety gear that I’m wearing here are big heavy gloves. Make sure you have a correct helmet on. Make sure you cover your head because of the sparks. You want to protect yourself from getting burned. Most importantly, you want to make certain you have some way of eliminating the fume exposure. Right here I have a portable fume extractor that I’m going to turn on before I weld. And it actually takes away the fumes out of
your breathing zone. So make certain that you follow
these instructions and also make certain you have your safety glasses on under
the hood. Sparks can fly everywhere. What I’m going to be doing is I’m going to start my beads in the casting. I’m going to weld approximately about one inch of weld. Then I’m going to stop welding, take my chipping hammer, clean the slag off, but at the same time I’m actually doing what they call peening the weld. It’s basically a mechanical type of stress leaving. What you can do is also use a very small ball-peen hammer to do the same thing. But you want to make certain that you
don’t over-peen the weld because you can re-harden it. All we’re doing is trying to relieve the
stresses out of the weld. And then after I do that I’m going to skip around on the casting itself and repeat the same procedure. If you noticed that when I was welding, I kept skip welding, and take the chipping hammer and clean the slag off but at the same time I’m basically peening the weld. You want to stagger and stop your starts as to localize the heating. so you’re going to put a little bit of heat here, a
little bit of heat hear, a little bit here, you’re going to move it around so we don’t
get one area of localized heating. So therefore you have a uniform bead, you’re going to make very small beads. and you follow that sequence all the way
out through welding to make sure until your casting is actually completed. Following these rules, you should have quite a
bit of success in your castings. If you like to learn anything more about
the products that we used today, you can visit our website at

37 thoughts on “Tech Tips: Repairing a Crack in Cast Iron

  1. very good, you should make some ''how to'' videos for better understanding on welding and don't forget ''tips''

  2. Lot's of good information, but peening should be done with a ball peen. The Chipping hammer is pointed and will add stress. Love your explanation of cooling.

  3. I agree this was informative, all the other I've viewed so far are just testimonial marketing BS,

    Content interests me, I'm not coming here for advertising.

  4. Big Joe is definitely one of the best, and also one of the most knowledgeable welders I have met! Great job!

  5. Great tute, thanks! So THIS is how to do it properly! Years ago, I repaired a 5" bench vise that had broken in half. I used a 230V wirefeed, cranked waaay up, using .035 Innershield (FCAW). I hit that thing with such a vengeance, I think it took hours before I could touch it barehanded! It never did crack and is still good to this day, guess I got lucky. Next time, I can really do it right!

  6. the only thing i would have to comment on, no matter how good of a welder you are, no human can do that kind of work with one arm freely in the air, i would have both arms resting against the bench making sure that i could maximize the steadiness of the electrode

  7. I took your 2 week flux core class couple years back, been welding mainly with NR232-.068 and some times NR203.  I do a lot of heavy equipment repair. Your facility is top notch and now your accredited so if any Veterans have the G I Bill, sign up!

  8. Great working in a welding company most in mold and die repairing and i admire how you present the products and the way how to weld the cast iron properly even its a basic demo.Hope we can meet up oneday.

  9. Good thing that's not a real casting that weighs about 3000 pounds . If you use that method on a heavy casting it will be broken before you're half done. This is a veteran torch welder that's repaired castings for years. Too bad it's a lost trade. Brass or bare cast iron with the proper flux are the only way to go.

  10. I still think all you stick welders should visit a real cast iron welding shop such as Midwest Welding in Casper Wy. and see how it's really done!

  11. When you weld cast iron with any electrode,be sure the price of scrap iron is high so you will have something when you are finished.

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