[TheForge] Chip forge Crucibles

Sat Mar 11 14:14:44 EST 2006

Since I'm less than enthusiastic about regular chip forges, it naturally 
follows that my warped brain keeps coming up with ideas about them. This 
week a Clay-graphite Crucible from an ebay seller arrived. What does it have 
to do with chip forges?
    The outer walls of standard chip forges are very much crucible shaped. 
Clay-graphite crucibles are notoriously rugged (and usually-argh-it-hurts 
expensive). However, there is an ebay store specializing in them, who is 
even now having their final sale--they are going out of business after two 
years of totally satisfying customers). Dan Brewer has been using their 
crucibles for bronze casting and none of them has been flawed yet.
    So, as the main outer body of a chip forge, they would probably last 
forever (anyway, longer than the user). Especially those of you in driving 
distance of LA should consider buying one, although my shipping costs were 
only a dollar a pound UPS for a twenty pounder. Next weekend will be too 
late, so think and act NOW! Harbor Freight sells cheap carbide encrusted 
hole saw kits, and most big hardware stores also carry them. Even a worn out 
hole saw will penetrate ceramics with a little patience, so changing them 
over takes care of a huge share of the work of building a regular chip 
forge. I've got mine, but your clock is ticking, ticking, away.
Mikey
----- Original Message ----- 
From: "Jerry Frost" <frosty at customcpu.com>
To: "Sponsored by ABANA" <theforge at mailman.qth.net>
Sent: Friday, March 10, 2006 9:32 PM
Subject: Re: [TheForge] Chip forge


> Thanks Bruce:
>
> Good idea for texturing spheres, maybe use the "grippy" gloves with the 
> little bumps to roll spheres?
>
> In a perfect world "chips" would have a high specific heat, very high heat 
> conductivity and be excellent black body radiators. (I'm using "chip" as a 
> generic term for whatever shape media we use, it's short and easy to type. 
> I'm lazy that way you know. <grin>)
>
> It's kind of like heating with a wood stove. A lot of manufacturers say 
> their stoves hold heat as if that's a good thing. I want my heat stove as 
> close to thermally transparent as possible. Look at any other commercial 
> heat exchanger, they're as thin as safely possible.
>
> Same thing with forge chips, while a high specific heat will let them give 
> up heat without losing as much temp themselves I don't want them holding 
> heat. I want them to shed heat readily even eagerly to a piece of cold 
> steel. Likewise I want them to absorb heat from the flame greedily. So, if 
> I have to choose I'll take good conductivity over high specific heat.
>
> I certainly don't want an insulating refractory for chips.
>
> As I think you mentioned, graphite would be wonderful were it not flamable 
> itself. While it's a pretty good insulator it more than makes up for it by 
> having a high specific heat and being an excellent black body radiator.
>
> The #1 (in my opinion anyway) factor once suitable heat exchanging 
> characteristics are met is breathing. Letting the fire move through the 
> chips as restriction free as practical is what's going to make these 
> things possible for a naturally aspirated burner. This is easier than it 
> sounds and isn't very dependant on chip shape; size is what counts. To be 
> specific uniform size counts. While large chips have large spaces between 
> them the ratio of surface to volume is less so the fire can have less 
> effect. Also, for a given weight, the smaller the particle size the 
> greater the volume, meaning the more space between particles.
>
> There is a practical limit though because every time the flame has to go 
> around another particle it meets resistance meaning back pressure which is 
> bad for naturally aspirated burners. For myself this is why I intend to 
> start with 1/2" chips and tune the size from there.
>
> Back to ideas for shapes and how to make them without taking forever. I'm 
> thinking rounded cubes with a hole or two through them might work well. A 
> life saver shape might be even better. Yeah, I know, these shapes might 
> get hung up on small work (ring toss dontchaknow <grin>) but they 
> shouldn't key together, pack or be difficult to get work in or out and 
> they should transfer heat in and out well.
>
> Frosty
> -------------------------------
> If it ain't forged
> it ain't real.
> Wrought iron is.
> The FrostWorks
>
> Meadow Lakes, AK.
>
> http://www.artmetalradio.com/
>
>
>
> From: "Bruce Freeman" <FREEMAB at pt.fdah.com>
>
>
> 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
>
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