Author Topic: Casting iron using Thermite instead of a furnace  (Read 24744 times)

Offline bhowden

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Casting iron using Thermite instead of a furnace
« on: January 26, 2013, 02:35:12 PM »
Another topic ("a Light Light") went well off topic and I helped push it further by posting about using Thermite to cast iron.  In the intersts of letting that thread get back on topic and exposing the idea to a more relevant audience I am reposting my original reply here:

This thread, now thoroughly off topic, has given me an interesting idea.  I wonder if the home foundry type could use thermite to cast iron.  Make up the normal green sand flask but instead of a furnace and crucible, scoop out a funnel in the sand and fill it with a mixture of thermite and cast iron bits.  In theory you could work out how much extra cast iron it would take to absorb the surplus heat released by the thermite and make the process much more efficient and regulate the temperature of the pour.  Not sure how well it would mix but, in theory you could add other elements to make all sorts of alloys.  Add high carbon steel and get a low carbon steel mix.  The major snag I can see is what happens to the aluminum oxide released by the thermite.  Anybody know if it stays in the melted iron released or if it boils or floats off?  There must be something in all the smoke!

Has anybody heard of this or tried it?  While it would be quite spectacular and make lots of smoke I think it would be fairly safe if done in an open area.  The thermite reaction is not quick (as in explosion quick) and you could be well away from the hot bits, unlike wandering around with tongs and a crucible of molten iron.

Brian

Offline Fergus OMore

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Re: Casting iron using Thermite instead of a furnace
« Reply #1 on: January 26, 2013, 02:58:34 PM »
Try :-

The London Blitz 1940#
Dresden
Hamburg
Coventry etc etc

I've actually put out an incendiary bomb. I was all of about 10 or 11.

It'll be a lot easier- yours will not be associated with  8x 500kg HE's and one of them,  a time bomb.

Really, what is this forum allowing?

Offline spuddevans

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Re: Casting iron using Thermite instead of a furnace
« Reply #2 on: January 26, 2013, 03:01:48 PM »
Somewhere in the back of my mind ( a dark and dangerous place, I don't like going there  :lol: ) I seem to remember that the railways used to use such a mix to weld the rails together. Also I know that heavy duty copper earthing points are welded using the same method.


Tim
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Offline bhowden

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Re: Casting iron using Thermite instead of a furnace
« Reply #3 on: January 26, 2013, 03:21:17 PM »
Yes, it is used industrially to weld all sorts of heavy steel items.  Wikipedia has quite a bit of info on its uses.  While I suppose it makes sense, I was not aware of its use in incendiary bombs although that makes sense.  The wiki article indicates that the most common military use was to disable your own equipment in a hurry if it looked like it was going to be captured.  Melted field guns don't work very well.

Brian

Offline dsquire

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Re: Casting iron using Thermite instead of a furnace
« Reply #4 on: January 26, 2013, 03:32:55 PM »
Fergus OMore

Thanks for your concern. Just because termite can be used for bad things does not mean that everything it is used for is bad.

Take for example fertilizer. Better Homes and Gardens talk about it all the time and give details on how to use it as well. Now we all know that fertilizer can also be used to make explosives but that does not stop people talking about it for other purposes.

If it comes to the point that a product or material can not be talked about on the forum because someone has or might use it for bad purposes then it is time to burn all the books (encyclopedias and dictionaries included) and turn off the internet. In other words, stick our heads in the sand and wiggle our toes.

Cheers  :beer:

Don
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Re: Casting iron using Thermite instead of a furnace
« Reply #5 on: January 27, 2013, 04:00:16 AM »
Hi Brian

I suppose its possible ,you would end up with a steel casting ,not cast iron . Had a quick look through my foundry books and the only reference to the  use of Thermite  in a foundry was to raise the temperature of a ladle of molten steel to make it more fluid for casting thin sections .This was done by plunging a canister of Thermite into the molten steel . 

Rob 

Offline Pete.

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Re: Casting iron using Thermite instead of a furnace
« Reply #6 on: January 27, 2013, 04:33:28 AM »
Somewhere in the back of my mind ( a dark and dangerous place, I don't like going there  :lol: ) I seem to remember that the railways used to use such a mix to weld the rails together. Also I know that heavy duty copper earthing points are welded using the same method.


Tim

They still use thermite for welding rail over here.

Online NormanV

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Re: Casting iron using Thermite instead of a furnace
« Reply #7 on: January 27, 2013, 06:52:30 AM »
I produced a thermite reaction and was suprised to find that the resulting lump of metal was not magnetic. Can anybody tell me why?

Offline Lew_Merrick_PE

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Re: Casting iron using Thermite instead of a furnace
« Reply #8 on: January 27, 2013, 12:52:51 PM »
Tim & Pete -- And thermit is still used in rail welding here in the U.S.  It is losing ground to capacitive-discharge welding using super-capacitors, but it is still in use.

Norman -- Magnetic materials become non-magnetic when structural orientations change at temperatures higher than the Curie point.  In theory (and I am unaware of anybody turning this into practice) you could create a non-magnetic version of otherwise magnetic alloys by a near-instantaneous cooling from a thorough soak above Curie point temperatures.  This was one of the industrialization of space experiments (using the solar forge) back in SkyLab days.  I was working on analyzing data from other experiments, but it was my understanding that this particular experiment failed.

Brian is correct in terms of military usages of thermit.  It is often used as an igniter charge in incendiary devices, but the primary distribution of fire is a different fuel mixture because of the way it concentrates its exothermic reaction.

Offline raynerd

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Re: Casting iron using Thermite instead of a furnace
« Reply #9 on: January 28, 2013, 04:24:38 PM »
Norman, when we carry out the thermite the vast majority of the product is not magnetic despite what looks to be some nice balls of iron (we do it over water so it forms balls). Our understanding is that our mix is not perfect and consequently the iron formed is contaminated with so much iron oxide, aluminium powder and various unreacted ignition materials that you can`t detect the magnatism from the produced steel. I could be miles away from the truth, but it seems very possible. It also rings true since the balls crumble easily, so they are clearly not pure iron - that said, some lumps are magnetic so it is working to a degree....and besides, it looks good!

I`d love to see a video of them actually using the thermite reaction practically. We have to teach that it is used to "repair railways lines" but have no video showing it and in all honesty, no proof that this actually is done other than me being told to say so!

good luck and stay safe....

Chris

Offline philf

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Re: Casting iron using Thermite instead of a furnace
« Reply #10 on: January 28, 2013, 04:37:49 PM »

I`d love to see a video of them actually using the thermite reaction practically. We have to teach that it is used to "repair railways lines" but have no video showing it and in all honesty, no proof that this actually is done other than me being told to say so!

Chris

Chris,

Plenty of vids on YouTube e.g:



Phil.

(Have you had a go at cutting a pinion yet?)
« Last Edit: January 28, 2013, 04:55:12 PM by dsquire »
Phil Fern
Location: Marple, Cheshire


Rob.Wilson

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Re: Casting iron using Thermite instead of a furnace
« Reply #12 on: January 28, 2013, 04:40:44 PM »
I have a 25Kg bag of Iron Oxide powder (dont ask)  if anyone wants to play  :zap:


Rob

Offline John Rudd

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Re: Casting iron using Thermite instead of a furnace
« Reply #13 on: January 28, 2013, 04:56:23 PM »
I've seen 'Cadweld' welding whuch is a similar type of process used for attaching large earth lugs to cables...Quite a sight to see but not with the naked eye...
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Offline raynerd

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Re: Casting iron using Thermite instead of a furnace
« Reply #14 on: January 28, 2013, 05:18:12 PM »
Andrew/ Phil, thanks for the links!  Great stuff


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

Offline philf

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Re: Casting iron using Thermite instead of a furnace
« Reply #15 on: January 28, 2013, 05:52:26 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

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.
Phil Fern
Location: Marple, Cheshire

Offline awemawson

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Re: Casting iron using Thermite instead of a furnace
« Reply #16 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
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Offline philf

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Re: Casting iron using Thermite instead of a furnace
« Reply #17 on: January 29, 2013, 03:39:32 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

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.
Phil Fern
Location: Marple, Cheshire

Offline Fergus OMore

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Re: Casting iron using Thermite instead of a furnace
« Reply #18 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

Offline philf

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Re: Casting iron using Thermite instead of a furnace
« Reply #19 on: January 29, 2013, 06:40:52 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

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.
« Last Edit: January 29, 2013, 07:14:16 AM by philf »
Phil Fern
Location: Marple, Cheshire

Offline awemawson

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Re: Casting iron using Thermite instead of a furnace
« Reply #20 on: January 29, 2013, 06:40:52 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

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.

I cannot remember where I got it - possibly JLA - I know that it was horrendously expensive, and there was a minimum order so I ended up buying two rolls but that was maybe ten years ago. It's probably about half a thou thick maybe less.

If you can find a tin with a slip over lid (as opposed to a press in lid so not pressure tight), and cook your parts in it but add wood shavings to absorb the oxygen you can get a similar result. You could also fill the tin with argon if you have a welding set - all you are trying to do is heat the item in an oxygen free atmosphere to stop the metal oxidising. Salt baths are another way of achieving the same thing but more fiddly to set up for a one off.

Andrew
Andrew Mawson
East Sussex

Offline philf

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Re: Casting iron using Thermite instead of a furnace
« Reply #21 on: January 29, 2013, 06:47:14 AM »
I cannot remember where I got it - possibly JLA - I know that it was horrendously expensive, and there was a minimum order so I ended up buying two rolls but that was maybe ten years ago. It's probably about half a thou thick maybe less.

If you can find a tin with a slip over lid (as opposed to a press in lid so not pressure tight), and cook your parts in it but add wood shavings to absorb the oxygen you can get a similar result. You could also fill the tin with argon if you have a welding set - all you are trying to do is heat the item in an oxygen free atmosphere to stop the metal oxidising. Salt baths are another way of achieving the same thing but more fiddly to set up for a one off.

Andrew

Thanks Andrew,

I found some SS foil at Goodfellows but the cost wasn't just horrendous it was unbelievable.

As I just said in my reply to Norman I'll do some experiments later on scrap pieces rather than on my delicate pinions.

I realise I'm off-topic with this subject!

Cheers.

Phil.
Phil Fern
Location: Marple, Cheshire

Offline Fergus OMore

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Re: Casting iron using Thermite instead of a furnace
« Reply #22 on: January 29, 2013, 07:51:48 AM »
I was giving the old grey matter a jolt following your comment about soap- and I seem to recall LBSC using   soft soap( whatever that is  or is still available) but  if that is the case( pun) any decent oil based paint or varnish should  have much the same ingredients- vegetable oils    etc.
My  experiences tie in with welding /silver soldering and using pencil lead /graphite to limit  runs. My wife taught me :wack:
It all seems to tie in with casting and using graphite between the greensand and the   casting .

Worth a try on something on  a dummy run?

Meantime
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Offline Pete.

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Re: Casting iron using Thermite instead of a furnace
« Reply #23 on: January 29, 2013, 04:58:51 PM »
I have a 25Kg bag of Iron Oxide powder (dont ask)  if anyone wants to play  :zap:


Rob

You must be scraping it off all that rusty old stuff you keep posting pictures of here!

Rob.Wilson

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Re: Casting iron using Thermite instead of a furnace
« Reply #24 on: January 29, 2013, 05:02:49 PM »
I have a 25Kg bag of Iron Oxide powder (dont ask)  if anyone wants to play  :zap:


Rob

You must be scraping it off all that rusty old stuff you keep posting pictures of here!


 :lol: :lol: :lol: :lol: :lol: you got me Pete  :lol: :lol: :lol:

Rob