Mig Welding Cast Iron with Stainless Wire (Video)

Lanse

Well-known Member
Hey everyone!!

So, this is one of my newest videos...

As y'all know, I've been exploring my interest in welding cast iron lately, and after running a few different stick welding methods, I turned my focus to Mig Welding...

I just wanted to try something a little bit different, so I got a spool of 308L Stainless-Steel wire, .030" diameter, and tried it out welding up a cracked cast iron exhaust manifold off a V6, and I was pleasantly surprised at how well it turned out...

What I did, was to "Veeee" out the "crack" in the manifold, and then I preheated it with a rosebud until it was just starting to glow... It didnt take long, a thinner casting with a lot of exposed surface area like this will heat up, and cool down, more rapidly than other things, so I gave it a few seconds of "cooling time" while I shut down the torch and grabbed the mig gun...

That wire ran REALLY well... It sounded great, had a very controllable puddle, and even looked pretty nice when it was done.... I'm very happy with how it came out...

Anyway, just thought I'd share the video, and I hope y'all are doing well, I'm just getting over being sick, lol... Anyway, have a nice (early) weekend, everyone!! :)
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Hi Lanse,

Good video, as usual. Watching the beginning of it where you were explaining the prep you did, something occurred to me which I hadn't thought about before. What if drilling holes at each end of the crack doesn't actually make any difference but everybody does it because that's the way it's always done? Even if anyone took the time to try to perform a controlled test, it would be extremely difficult to get two pieces which were exactly the same in all respects.

My reasoning on why the holes might not make any difference is this: You described the crack as if it were an object exerting force on the metal, like a flooding river eroding land as it runs, and that's the way we generally think of it. But the crack is not a thing; it doesn't have substance and mass. It is the result of stresses in the metal which pull the metal apart along a fault line. Drilling holes at the current ends of a crack might help if they do something to relieve the stresses in the metal. Otherwise, can holes really be defeating the force of the crack by imposing a void that it can't cross? What if the holes actually only extend and widen the crack, and if we didn't perform the repair on it right away, we might see the crack continue on the other side of the holes?

People in colonial America didn't eat tomatoes because everyone knew they were poison, so sometimes the collective wisdom is only as sound as our unwillingness to test it. On the other hand, if I have any cast iron repairs to make, I'll undoubtedly drill holes at the ends of the crack because that's how it's done, and I could be wrong.

Stan
 
If you had welded it cross ways rather than length ways you would have likely had different results. SS welds cast well, but has very little flexability. Even with preheating a crack beside the weld would likely happen. The shape of a cast iron piece is the most important fact to take into account when picking a filler material.
 
Drilling a hold at the end of the crack changes the Stress Concentration Factor (SCF) at the crack tip. There are both ductile (iron, steel) and brittle (glass) cracking. The stress at the crack it is theoretically infinite. In a ductile situation, the area around the crack yields reducing the stress and the energy. Cycling through stress ranges slowly propagates the crack as it yields. By drilling a hole, you change the stress distribution and the imperfection size thus eliminating the ability for the crack to propagate.

In order for a new crack to start on the other side of the hole you need an imperfection. Drilling provides and almost perfect surface that resist cracking.

The only other way for the crack to form is from the welding stresses AND imperfections. The preheat and slow cool down eliminate/minimize most of these stresses. In industry Non-Destructive Testing (NDT) (X-ray, magniflux, etc) main purpose is to minimize the imperfections to a size that is small enough that cracking wont be an issue during the design life.
 
The trick is finding the end of the crack and hitting the end with the drill bit. Much easier said than done.
 
I agree, If the manifold had been broken completely off on one cylinder, and that is the way most of them break, and it was welded completely around, when put back in service and it comes up to temperature and cools back off 90% of the time it will crack again in the heat affected zone about 1/4 in. beside the weld. Ask me how I know. BTDT. I do not arc weld manifolds any more.
 
A old gas grill will make preheat and cool down easier.Propane costs less for heating.Grills are junked out instead of repaired.
 

Welding man,

I agree,welding manifolds with any
type of arc is not a good idea. After he gets
15 or 20 years experience , he will want to get
acquainted with a torch cast rod and flux ,and
have a pile of fire bricks to build an oven.

Arc weld is the worst choice for cast repair !

george
 
The holes do help because there is no corner/notch for the crack to progress. A little off topic for cast iron but in school we were taught that the only holes that should go in a semi trailer frame (for a lowboy) have to be round. I have seen other shapes used but the corners always have a big radius rather than square. The holes make the trailer lighter and give more carrying capacity because of the reduced weight. Strange but true they basically make the trailer stronger. Same as a tubular beam can be stronger than a solid bar because the weight of the solid bar.
 
I understand the need for drilling small holes at the ends of a crack if it is not going welded. But does it do any good to drill the holes just before you weld the crack?

Dusty
 
I would like to see it go through some heat and cool cycles to see if the repair will actually hold up. It's all well and good on paper, but until it's tested than I wouldn't consider it a success. Otherwise this video is showing a technique of laying welds on cast iron rather than the correct way to repair a crack in cast iron that is continually stressed after the repair.

I do enjoy your enthusiasm and techniques that you share, but I noticed that especially with your cast iron vids nothing has been actually tested after you laid down your welds.
 
That's why airplane windows have round corners instead of square. Rounded corners don't stress the metal as much and it is less likely to crack. That's true for any hole you put in metal, having a radius instead of an angle is better.
 

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