Welding/brazing cast iron

[drdoolittle]

Good afternoon!

Have an "opportunity" to weld some cast iron! LOL. In the attached picture is a sprocket off of an older square baler that can apparently only be purchased from the UK. I'm not paying that much for one, so I am going to plan B and plan C.

Plan B - how should I approach trying to weld the three cracks on this? It's small enough that I will be able to preheat it. I have both stick/tig/mig capabilities as well as oxyacetylene. For that route, what rod would be best for stick or oxyacetylene?

Plan C - I have already purchased a new sprocket and universal weld hub so if I "break" plan B it's not going to stop me for long. I was not able to get a sprocket with the exact extended pitch, but a normal 40 chain sprocket with double the amount of teeth fits up real nice.



So, any suggesting a on what to use for Plan B? This will be my first attempt at cast iron and its intriguing to me.

Thanks,
Eric

 

[Shield Arc]

I bought some of these cast iron gas welding rods, but haven't used them yet. They got great reviews.
Cast Iron Flux and Filler Metals for Gas or TIG welding

 

[mrmikey]

Spoked wheels like that are hard to weld because of the inherent stresses pulling every which way. Keep it warm and let it cool slow, keep the better half busy for a few hours and borrow the stove to let it cool in..........Mike

 

[CreekyB]

When I was young we welded a ton of cast pump casings from winter freezing in the panhandle of Texas. They all held, even took to rewelding when someone let them freeze full of water again. Use cast iron welding rods, old timers that taught me called them "trash rods" and even ordered them as such at the welding supply. Heat it, weld heat, keep the heat on it as it cools to keep the temps somewhat uniform.

And yes, I was "torch boy"

 

[Stimw]

My first cast iron repair was a Harley Kick Peddle housing when I was 16 years old in 1964.
The housing was broken all the way around next to the bolt holes like a large "C" from a chain that broke and back lashed.
The drive sprocket ran inside the housing.
I took it to welding shop in high school and brazed it back together.
The housing was still on the bike when I sold it 8 years later!
Your sprocket will be tricky as stated because of the spokes and thermal stresses caused from repairing.
Another thought is if you have the room, installing a plate on one side to beef it up. Or maybe 2 plates with bolts to "sandwich" it.
A cheap excellent heat sink for welded items is Kitty Litter! Preferably unused!!

 

[drdoolittle]

Thanks for the link to those rods, Shield Arc! I'll see if my LWS has those in the morning (I have two fairly close by - one 15mi south of me and one about 20mi east/southeast). If not, I'll fire an online order up.

MrMikey - on the suggestion to use the oven, I do have quite a selection of propane smokers that I've had to 600-650 degrees and could go higher, so I'll probably not take the risk with the missus and just use one of the older ones. :thumbs: Thought about picking some clean sand up and using that as a cool down to save some of the gas. Any issues I need to be aware of in doing that instead of just using the cooker the whole time? Like I said, this "project" is intriguing to me especially because of the different forces that will essentially end up fighting each other if I really goof it up. It's the inherent paradox of the impact of the HAZ in the cast iron being put on three different spokes all at basically 90 degrees to each other yet all tied back together in the outer circle of the sprocket.

Stimw - I did think about a plate or sandwich on the sprocket, may still play with that idea but figured I'd like to see if I can make this "good" again without those. I'll start cleaning the cracks out tomorrow sometime, maybe in the afternoon once it gets to hot to do much else. I'll also take a close look at the top crack as it currently does not appear to be all the way across the spoke - may have to drill a "stop point" on that one.

I do appreciate all the information. Thanks!
Eric

 

[Arc weld]

Brazing is another option but for either gas welding with cast rods like Shield Arc mentioned, you're talking major heat. First the cracks have to be ground out with a die grinder and then you heat it up to about 850 deg's. and the brazing temp is about 1200. Here's an article I found on it on it. You can't use typical grinding wheels because they smear the carbon. Gas welding cast is very similar to brazing and you have to dip the hot rod in the flux about every time you add filler metal to the repair. We had to do both when I went school but that was 30 some years ago. The cast had to break and not the weld or braze. We had square cast iron plates about 1/2" thick and they just used the hydraulic coupon bender to break them. I doubt anybody teaches that anymore.

How to "Braze" Cast Iron --

 

[jwmorris]

I would use silicon bronze filler with a TIG.

 

[flusher]

I used Super Missile rod (1/8" diameter, DC positive, 100-120 amps) and my Hobart Stickmate LX AC/DC stick welder to weld a flange that had broken off completely on my 1948 Farmall Cub tractor.

No preheat. 1" long skip welds. Kept the temperature in the weld zone below 350 degrees F (used one of those IR thermometers from Harbor Freight). Peened the weld during cool down with a pointed air chisel.

Let the work piece cool to 100F or so before laying down the next bead.

Spent time cleaning up the weld area and grinding in the proper bevel. Used silicon carbide abrasive grinding bits (not metal bits) to prevent contamination of the cast iron with other metals.

Good luck.

 

[tjflicek]

As long as you have TIG I would use silicon bronze with the TIG process. Second choice is braze with oxy acet.