From: dwilkins@northernnet.com (Don Wilkins)
Newsgroups: rec.crafts.metalworking
Subject: Re: Cast Iron Crucibles, was Cutting Cast Iron?
Date: Tue, 16 Jan 1996 15:13:35 GMT

On 15 Jan 1996 19:59:27 GMT, Andrew Werby <drewid@lanminds.com> wrote:

>>>In article <4crgip$fmh@news.cis.nctu.edu.tw>, hagemann@persoft.com (John
>>>P. Hagemann) wrote:
>>>
>>>> I've got a cast iron saucepan that I need to cut the rim off of.  I plan
>>>> on using it for a crucible in my homemade blast furnace.  It would be
>>>> the perfect size if I could just get the top 1" cut off.  Is it feasible
>>>> to cut cast iron?

It may be hard enough so that both sides of your band saw blade look
the same.

>>>> Is there a special process required to cut it?  Also, what is cast iron 
>>>> composed of? 

There is more than one cast iron but in general an iron-carbon alloy
with between 2.25 and 4.5 % carbon. Some contain sulfur, silicon,
manganese and/or phosphorous or a lot of other elements which modify
the properties.

Nodular cast iron contains magnesium or cerium in sufficient
quantities so that graphite precipitates as spheres instead of flakes.
This product resembles a malleable iron or mild steel depending on the
heat treatment.

Gray cast iron-- The carbon is largely not combined with the iron.
Properties depend on heat treatment.

White cast iron-- All of the carbon has combined with the iron. Often
produced by sudden cooling of the molten iron. This stuff is very hard
and almost impossible to machine.

malleable cast iron-- white cast iron which has been heat treated
after casting to decompose the carbides.

Cast iron alloys-- Any of the above with added chrome, copper,
molybdenum, nickel or other steel alloying elements.

>[Being cheap is not always its own reward. 

Cast iron is not necessarily cheap. Some of the heat treatments add
substantially to the cost.

>Cast iron is not what 
>crucibles are made from- there is too much danger of it failing 
>catastrophically.

Doesn't it depend a bit on which cast iron you are using and what you
are melting?

>GET A REAL CRUCIBLE. They are made from silicon 
>carbide in the larger sizes, which takes heat shock much better than 
>cast iron. 

Over the years I have used platinum crucibles, nickel crucibles,
porcelain crucibles, clay crucibles, vicor crucibles, quartz crucibles
and iron crucibles (and probably others). I never realized that they
weren't real crucibles. That being said I would be hesitant to use
some discarded cooking pot to melt up a large quantity of something I
didn't want running all over the floor.

>Believe me, there are few things worse than splashing molten
> metal on yourself. The silicon carbide crucibles may seem expensive,
> but they are a real bargain compared with a hospital stay.]

>P.S. Cast iron is composed of iron, which is cast into a mold.

Cast iron is really a bit more complicated than this.

  _               _   _                  Für d' Flöh gibts a Pulver 
 (_|   |   |_/o  | | | |  o              für d' Schuach gibts a Wix, 
   |   |   |     | | | |      _  _    ,   für'n Durst gibts a Wasser
   |   |   |  |  |/  |/_) |  / |/ |  / \_  bloss fuer d' Dummheit gibts nix.
    \_/ \_/   |_/|__/| \_/|_/  |  |_/ \/