Repairs to cast iron

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Izzy

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I have a few cast iron parts that I would like to attempt repairing. I have little experience working with cast iron and I'm not sure what method would be best for repairing certain parts.
I've got 2 things I need repaired
1. Is a cast iron cover that broke in half it is a clean brake though and fits together nicely
2. I have a few gears that need a new tooth or 2
So what method would u guys recommend for each part and why? I'm just trying to learn so the more info the better! Also if anyone has any links to some guides for the method recommended that would be great to!
 
Disclaimer: I'm no expert at welding cast. My two cents:

You can weld or braze cast iron. Cast iron comes in various forms. White cast is commonly used for decorative pieces and cookware. It is called white because a fresh break looks silvering color. The large percentage of carbon in the cast makes it brittle and, in my experience, difficult to weld. The repair usually breaks adjacent to the weld. Brazing will work on it. Grey cast is white cast iron that has been heat treated, much like annealing carbon steel. It is somewhat ductile and will weld with proper technique. Nickle rod is often used to weld cast as it is ductile and a better match for thermal expansion coefficient. Even so, a common practice is to peen the nickle weld immediately after laying a bead to physically expand the weld to relieve some of the tension in the cooling cast. For very simple welds, I have successfully welded cast with mild steel rod. The weld area was small and not subject to a large amount of thermal stresses as the weld cooled. Welding studs into an exhaust manifold come to mind.

I guess that I would try brazing in both your examples. After brazing, I would heat the entire work to something short of the brazing temperature and cool it slowly in a bed of ashes. This will tend to minimize any hardening which may have occurred during the repair process.
 
Hi Izzy,

Lots of info here:
http://www.hobby-machinist.com/threads/welding-cast-iron.42577/
I read that whole thread before doing my own repair:
http://www.hobby-machinist.com/threads/found-a-sheet-metal-shear-that-needed-a-small-repair.48881/

I decided to braze with ox-acetylene, my basic method was:
1) grind a vee shape deep enough for penetration, but leaving a clean edge for alignment of the pieces
2) work from one end and move along the crack filling as you go, do not worry about adding too much material
3) grind down the bumps that are too high, fill any spots to low, repeat step 3 as required

Here's a Keith Rucker video where he replaces a missing gear tooth by brazing in material and then re cutting the gaps.

-brino
 
Pretty much what RJ said, again Im not an expert but have had good luck in most cases.
For the covers if they're thin I'd braze them.
I preheat the cast with a propane weed burner, big flame so you get an even heating. Preheat seams to reduce the stress from the weld shrinking, then cool slowly.
If stick welding I use an alloy for cast iron and as said peen the heck out of it with a dull welding hammer. Short maybe inch long welds, one at a time then fill in.
Groove the joint out with a carbide burr, I've read a grinding disk leaves traces of the wheel in the weld and can affect it. Don't know I use a burr.

Greg
 
Thanks guys I was hesitant to go down the welding path I've welded cast iron manifolds in the past but didn't have much luck (they cracked again a month later) and I've never brazed before at all so I wasn't sure if that would be sufficient for what I'm doing. All I have is a MIG welder so I'll have to bust out the torches and give it a go!
 
Are the repairs to expensive parts? Welding/brazing cast iron is not a walk in the park, things can go wrong fast! I understand your eagerness for a challenge. But, if things go wrong, will the parts be too hard to replace? Maybe find someone with a good back ground in welding cast iron. It might be cheaper in the long run…Dave.
 
It's for the McKenzie lathe I have, the company doesn't exist anymore so parts availability is 0 lol I've never brazed but I've torch soughtered and I'm pretty good with an oxy/acet torch. I've tried finding someone around here who has do e this before so I could get some tips but can't find anyone. It's a bit of a dying art I guess and part of the reason id like to learn myself. The way I look at it is the part is already broken so it's not like it could get any worse either the brazing works and I have a fixed part or it doesn't work and I'm left with what I started with, no biggie. I gonna give it a shot though just gotta prep the material get some flux and some ni99 rod (correct me if I'm wrong) and I should be good I also have a needle scaler for peening :) thanks to @brino for the idea!
 
This is the part its just a cover for the change gears absolute worst case scenario I could live without it or just the top half lolIMG_20170118_182649.jpg
 
Izzy, the NI99 rod is for stick welding, if your looking at welding it with the torch all you need is brazing rod. Don't think it needs to be peened, at least I've never. I'd preheat the whole part to 4 or 500 f with a propane torch first, but may not be necessary.

Greg
 
I have stick welded Cast Iron several times but I'm no expert. I pre heat, peen, weld short beads and allow it to cool slowly. Most times I had very good results but on a couple of castings I had to weld more cracks that formed from the welding than the original repair...
 
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