[TheForge] Chip forge

[Jerry Frost]

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