Casting iron using Thermite instead of a furnace

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philf:

--- Quote from: raynerd on January 28, 2013, 05:18:12 PM ---
Phil, not had a shot at cutting the pinion yet. Borrowed mums deep fat fryer and it went only to 180! Father in law is going to put them in his temp controlled industrial oven tomorrow night! I'm all set up ready, just waiting to temper. I'm very excited ... By the way, did you cut from silver steel?

Chris

--- End quote ---

Hi Chris,

Yes, I used silver steel. I've cut some 8 tooth pinions tonight.

I tried the ground up soap method to prevent scale when I heat treated them but it wasn't too successful. A 15 minute dunk in dilute HCl shifted most of it.

Phil.

awemawson:
I have some stainless steel foil that I use to prevent scale when hardening & tempering. Just like cooking foil but stainless steel not aluminium. Works a treat but is lethal, vicious stuff that cuts your hands as soon as you look at it. Wrap the piece up in it like a pastie, ie fold over the edges to make a seal. Include a little sliver or two of pine shavings to adsorb the oxygen from the air inside as it is cooked, and bits come out pretty clean and unscaled.

Andrew

philf:

--- Quote from: awemawson on January 29, 2013, 03:14:49 AM ---I have some stainless steel foil that I use to prevent scale when hardening & tempering. Just like cooking foil but stainless steel not aluminium. Works a treat but is lethal, vicious stuff that cuts your hands as soon as you look at it. Wrap the piece up in it like a pastie, ie fold over the edges to make a seal. Include a little sliver or two of pine shavings to adsorb the oxygen from the air inside as it is cooked, and bits come out pretty clean and unscaled.

Andrew

--- End quote ---

Hi Andrew,

I've heard of this before. How thick is the foil you use? Where do you get it from?

I just did a quick search and the only prices I could find were horrific.

I also read that borax works well in preventing scale but that you can have as much trouble removing the borax as you do the scale. I wonder about using silver solder flux.

Cheers.

Phil.

Fergus OMore:
Phil,
But silver solder flux is essentially borax.

Probably the cheapest way is to paint it with a fireclay or a chalk. I believe that Tubal Cain( T.D.Walshaw) did write up how he overcome the problem.

Worth a try?

Cheers

Norman

philf:

--- Quote from: Fergus OMore on January 29, 2013, 04:44:12 AM ---Phil,
But silver solder flux is essentially borax.

Probably the cheapest way is to paint it with a fireclay or a chalk. I believe that Tubal Cain( T.D.Walshaw) did write up how he overcome the problem.

Worth a try?

Cheers

Norman

--- End quote ---

Hi Norman,

Easy Flo flux usually falls off in water. It is rated to 750 deg. C. I can't control the temperature that well with a propane torch so may exceed it and then the residue gets glassy. I agree silver solder flux does contain borax but I don't have any borax so can't try it neat. Tenacity flux copes better with higher temperatures (up to 900C) but is harder to remove (10% NaOH at >40C).

I have read somewhere that wrapping in iron wire and then coating in soap should work as the wire keeps the soap in place as the part is heated.

I do have a small electric furnace in which I could try Rob Wilson's method of putting a few pieces of charcoal inside to consume the oxygen but these parts are so small they'd have cooled down by the time I'd got them out of the furnace and into the quenching oil.

I'll do some experiments later.

Cheers.

Phil.

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