Subject: wanted: refractory for carbon-arc melting

From: C++ Freak <[email-masked]>
Date: 22 Jul 1996 14:10:51 GMT

I am experimenting with carbon arcs with a 150 amp electric welder.
I attach a carbon rod from a 4.5 V battery to the clamp terminal and another
rod via a thick copper wire to the welder's handpiece.
In a chamotte brick I carved a little crater of about 25 mm (1") diameter
and put some iron into it.
After starting the arc at 80 amps the irom melted within seconds.
But the chamotte too. I did the same (with or without iron) with a piece
of ordinary concrete, 1650 C rated refractory concrete, pumice or a Hessian
crucible. All of them melted easily close to the arc within seconds.
Using a cuttlefish bone (virtually pure CaCO3) which would result in
decomposing
to CaO which is 'unmeltable' resulted in vaporizing the CaO (bp 3000 C) and
glassy traces of melting (mp 2700 C). Not an option either. I might try
marble which I don't have at the moment which is more 'solid' CaCO3.
Graphite itself cannot be used as some metals dissolve the carbon.
Is there any refractory for such temperatures which does not
melt of vaporize too quickly ?

Klaas

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From: [email-masked] (James P. Riser)
Date: 22 Jul 1996 16:09:52 GMT

> melt of vaporize too quickly ?

Have you tested porcelain crucibles?  How about copper coated carbon
electrodes? If not, in about a month I could send you a couple small
crucibles to test.
Jim

-- 
James P. Riser
Home page:  http://www.azstarnet.com/~jriser

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From: [email-masked] (Carl)
Date: Mon, 22 Jul 1996 14:34:11 GMT

On 22 Jul 1996 16:09:52 GMT, [email-masked] (James P. Riser)
wrote:

>> After starting the arc at 80 amps the irom melted within seconds
>> But the chamotte too.

snip
 
>> melt of vaporize too quickly ?

   The problem is that there are likely,  no substances that will
stand up to the direct heat of an electric arc.

   The key is to keep the arc from impinging directly on the
refractory, and keep the iron from getting so hot that it destroys the
refractory.

   If you can use a larger crucible and more iron then you should be
able to heat the iron without bringing the arc itself near the
refractory.

  I work in a steel Minimill ( we melt scrap steel then cast and roll
it into medium size structural bars).  Our DC furnace melts up to 90
tons of steel scrap using an arc at up to 65,000 amps and 900 volts.
The furnace shell is 16 feet in diameter to keep the sidewalls away
>from  the arc, and above the slag line we use water cooled panels to
carry away the heat radiated from the arc and the bath.  We also use a
water cooled roof to contain the gasses so that they can be drawn off
through water cooled ductwork to a baghouse where the dust is
captured.  Below the slag line the furnace is lined with refractouy
brick to contain the bath of molten steel.  the brick wears partly
because of the high temperatures but mostly because almost anything
that is heated to a temperature in excess of 3000 degrees farenheit is
very active chemically.

   We worry about the life of the brick lining for economic reasons.
You probably wouldn't have quite the same worries unless you decided
to use your furnace commercially.

   If you will look in the phonebook under refractories you might find
some help selecting what you need.

I hope this answers your questions or at least points you in the right
direction.

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From: "Paul Passarelli" <[email-masked]>
Date: Tue, 23 Jul 1996 19:41:47 GMT

C++ Freak <[email-masked]> wrote in article
<[email-masked]>...
> melt of vaporize too quickly ?

  I would try MgO mp 2852 C bp 3600 C  and a bigger hole.

-- 
--Paul
------------------------------------------------------------
Continuum Systems (203)846-2500
[email-masked]

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From: [email-masked] (Reg H. Beardsley)
Date: 24 Jul 1996 18:56:01 GMT

This is where a call to the nearest refractory dealer comes in.  
Carbon arc furnace service is pretty severe duty and requires very
high temperature materials.

Limestone is NOT a refractory, in fact it melts at very low temperatures.
(relatively speaking for rocks;  for years no one believed in molten
 calcium carbonate until a volcano started spewing it in Africa.  It
 became VERY difficult for those who denied the existence of carbonatite
 to argue with an active carbonatite volcano :-)
(marble is simply metamorphosed limestone, there is a recrystallization
that takes place, but no significant chemical changes)

National sells several castables for service to 3400 F.  They are all very
high alumina (~99%) and very low Ca.  Ca is apparently detrimental to
the refractory properties.

-- 

------------------------------------------------------------------------
               I am solely responsible for the contents...

Reginald H. Beardsley                                      [email-masked]

                       Consultant/Programmer 
------------------------------------------------------------------------

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From: Chris Allen <[email-masked]>
Date: 26 Jul 1996 03:18:38 GMT

Don't want to spoil the party but this could KILL or MAIM if not handled carefully. 
Water and hot metal in inexperienced hands join to make extremely nasty explosions.

-----------------------------------------------
All opinions here are mine, not my company's.

Chris Allen     [email-masked] 
Senior Project Geologist   BHP Steel LPD, Whyalla SA  5600 Australia
Lance Ryan <[email-masked]> wrote:

>C++ Freak wrote:
snip
> Implying this to your 
>process one cold suggest that  you immerse your crucible in a water tub 
>and provide enough area so as to obtain an interface of powdered iron to 
>molten iron.(maybe)

snip

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From: [email-masked] (Art Devonshire)
Date: 25 Jul 1996 05:45:45 GMT

Klass. Sounds like you are having fun. I think the alumina or magnesia 
based refractories should do the job for melting iron base metals. I have 
bought my small high temp crucibles at local rock hound or chemical 
laboratory supply shops. I am interested on how your arc furnace project 
turns out. I used to operate melting melting arc furnaces while I was in 
the navy. I have pacthed  and relined these furnaces many times. By the 
way a few years ago I built a very small BOF (basic oxygen furnace) to 
melt a small amount of steel. I cast a small anvil about the size of my 
thumb out of steel. I carved the anvil out of a bar of dial soap. I 
rammed the mold up in sand. I took a small crucible and put in three bars 
of drill rod, a half inch in dia & six inches long. Then I took a oxy-
acetylene torch and the drill rod to about 1500F ,at that temp I squeezed 
the oxygen lever on the torch. This melted the steel (a lot of slag) upto 
about 3000F. I skimmed the slag back and stirred in the deoxidizers, a 
small amount of ferro silicon,ferro manganese and pure aluminum. The 
small steel anvil turned out gas free. The carbon content went from 90 
points down to 50 points.                                    Art       
San diego

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From: [email-masked] (Art Devonshire)
Date: 26 Jul 1996 15:28:06 GMT

rec.crafts.metalworking
[1] wanted: refractory for carbon-arc melting
[email-masked]

Don't want to spoil the party but this could KILL or MAIM if not handled 
carefully. 
Water and hot metal in inexperienced hands join to make extremely nasty 
explosions.

snip

snip