[TheForge] Chip forge

[Rich Maynard]

The porous spheres would heat up quicker, having less thermal mass, but
would also lose their heat quicker when you put the iron in. Part of the
point of the chips in a ceramic forge is to provide a reservoir of heat that
smooths the difference between what can be applied (ie continuous heat) and
what is required (a burst of heat when the iron is in the fire)

I think shape has little or no impact on the heat transfer, as others have
commented, other than by using a shape that packs more densely the thermal
mass is increased for a given material.

It surely impacts on how easy it is to get iron into or out of the fire!

Rich M (who has one, don't forget)

> -----Original Message-----
> From: theforge-bounces at mailman.qth.net 
> [mailto:theforge-bounces at mailman.qth.net] On Behalf Of Bruce Freeman
> Sent: 06 March 2006 13:43
> To: theforge at mailman.qth.net
> Subject: Re: [TheForge] Chip forge
> 
> 
> Frosty,
> 
> I think your ideas on making spheres are good.  Marbles used 
> to be made by cutting marble cubes (yes - marbles actually 
> were made of marble at one time) and rolling these between 
> iron disks with grooves.  The corners of the marble cubes 
> wore off, leaving ... marbles!
> 
> This can be done with clay, allowed to dry to the "leather" 
> stage.  Other sphere-cutting procedures are known as well. 
> But perfect spheres wouldn't be needed for a chip forge - 
> just fairly spherical "chips."
> 
> Now about surface to volume ration.  Seems to me that cuts 
> both ways.  Once a sphere were up to temperature, it would 
> hold that temperature better than an oddly shaped chip.  Is 
> that better or worse?
> 
> But there's a trick used for some years in my industry 
> (chromatography) on the micro scale:  Porous spheres.  These 
> have the shape of spheres, but pores either at the surface or 
> all the way through.  The purpose is specifically to increase 
> surface area.
> 
> Now, I'm reminded of some china cups which have translucent 
> patches where (so I've been led to believe) dry rice grains 
> had been encorporated into the clay and later burned out 
> during the firing.  Maybe some such approach could be used 
> for chip-forge speheres.  Take the clay-like (rammable 
> refractory) sphere and roll it in something organic - pearl 
> barley, radish seeds, poppy seeds, or whatever.  THEN fire it 
> - and the organic burns off, leaving semispherical hollows in 
> the surface of the ceramic sphere.  This would represent a 
> significant increase in surface area.
> 
> To make a fully porous sphere, mix the organic matter into a 
> castable refractory, let it set, then fire it slowly.  The 
> organic matter would burn out, leaving a fully porous sphere.
> 
> The trick here is to make the sphere porous to the desired 
> extent, without making it too fragile.  One way to achieve 
> that would be to combine broken fire brick with the organic 
> matter, then mixing them both in with castable refractory.  
> Let it set, then fire it.  
> 
> I have tried none of these ideas, but get them from my 
> reading about ceramics.
> 
> Bruce
> NJ
> 
> >>> frosty at customcpu.com 3/3/2006 9:04:10 PM >>>
> <snip>
> I've given a couple shapes some thought:
> 
> Spheres will make for the least restriction in flame flow but 
> provides the 
> least surface area/volume ratio of any shape so heat transfer 
> in and out 
> will be minimum. Making spheres will I think be the most 
> hassle as well.
> 
> <large snip>
> 
> 
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