burning cast iron

[Tony]

greets folks!
sheesh.. i turn my back for 10 minutes and this place turns into a madhouse. a madhouse!

strange thing happened today and was hoping to get some insight..

a huge 100#+ cast iron gear came in the door the other day with a fractured bore/keyseat.

plan was to burn out the old hub and bolt in a new (flanged) one.

all went well until i fired the torch up. this cast iron wouldn't burn! it kept peeling back in layers.. like onion skins. i'd preheat, puddle would form, i'd lay in with the oxy, get a shower of molten iron, and i'd lose the burn. i kept repeating this (figuring i wasn't hot enough) but no dice.

i got into it about 1/2" before i gave up and just drilled the whole bore out. (about 60 1/8" holes around the perimeter and a "light tap" with the 5lb hammer

i'm wondering if this cast iron wasn't just so dang old it absorbed alot of dirt/oil?

any thoughts?

-tony

[PTSideshow]

I have never seen one but was told about layered wrought iron hubs on the flywheels and flat drive belt wheels on steam engines verts that where used for building heating and ventilation. It was supposed to be easier to balance them and main thing I think Cheaper LoL.

------------------
Glen
Been there, probally broke it doing that

[JCHannum]

Yup, cast iron will not burn. You can melt and blow it out, or drill a jillion holes and breakit out.

[wierdscience]

Large welding machine and an air arch gouge works,but still not so good.

[torker]

I had to cut an ugly piece of cast like that once. Didn't have the luxury of an air arc so I took some 5/32" dia 6010...soaked it in water for a minute, turn the welder up to 225amps and let er' rip. Was kind of rugged but it got the piece hacked off well enough for the purpose.
Russ

[Tony]

you fellas are shooting me straight? cast won't burn?? i thought anything ferrous would be minced meat under an oxy/act flame.

and i could've sworn i've cut cast before.
i'll have to play a little with a clean piece. torker, i'll give that makeshift gouge a try too.

thanks all.
-tony

[Forrest Addy]

Failed hubs in cast iron gears and pulleys have been repaired since before the Civil War.

You rushed in to a very technical job without researching your options. The usual fix for a busted cast iron hub is to over bore the existing hub and either weld or braze in a steel replacement allowing stock for final machining. Usually the hub is bored out and sleeved but if the spokes are broken away from the hub the repair may be complicated by as-found conditions.

Now that you have the existing cast iron all gouged up it will be more difficult to do a neat repair but one can be done.

Try to bore out and sleeve the existing bore V grooving and weld/braze repairing the spokes back to the existing hub. If the hub is a total loss cut it out using a SawzAll or equivalent cutting as close to the hub as possible. If your butchering with a cutting torch has made hard spots raise them slowly to 1200 degrees and allow them to cool slowly. Bore for registration surfaces if you can.

You will need to round up some heating materials: ceramic fiber blanket and fire brick, a couple of propane weed burners, a steel workbench, Tempilstiks, etc. You'll also need a large acetylene torch or a stick rod that leaves a machinable deposit. Before you start heating, sandblast the cast iron for 3" past the weld joint. If you torch braze use a suitable flux. Decide on a joint prep using standard cast iron repair technique. I suggest you use TIG and silicon bronze to stitch everything together.

Design and make a hub having machine stock on it. Fixture the hub into the iron casting so its centered and in plane with the relevant features. Drape and insulate the casting fixturing and hub to make a furnace of it. Commence heating the whole assembly to the desired temperature. I suggest 800 degrees. When the work is up to temperature procede with welding/brazing skipping around to prevent distortion or excessive movement of the hub within the casting. Undrape and flip the work re-draping to keep the heat so you can comolete the other side.

This will be hot unpleasant work. Wear protective equpment and keep a multi layer sheet metal heat shield between you and the work. Keep a large pitcher of cool water handy and observe fire safety precautions.

Allow the work to cool overnight fully covered in insulation. Blast and clean the welded surfaces. Machine the hub concentric to the castings references.

Go about it right and you'll have a strong, tidy economical repair as strong as the original casting. Take yokel's shortcuts, work dirty, and fail to observe heat and distortion control and you'll end up with a weak, cracked, ugly job.

[This message has been edited by Forrest Addy (edited 01-25-2006).]

[.RC.]

It is the carbon(3%+) in cast iron that stops the oxy from ctting it...Most of the carbon is in the form of graphite...

[.RC.]

It is the carbon(3%+) in cast iron that stops the oxy from ctting it...Most of the carbon is in the form of graphite...

[lathehand]

When I was about 16-17 yrs old we were putting in a drive way. There was a storm drain at the far edge of the new entrance.My dad told me to get the right angle grinder and take the sharp edge off of the curb portion of the drain, so we could blend it into the downward slopeing concrete.I thought I had an easier way, so I dragged the oxy cutting torch out there and proved to myself what he already knew- can't cut cast iron with a torch.