[TheForge] Chip forge

[Rich Maynard]

I think this isn't too far off the mark. I suspect the heating of the bar
due to the hot gases is minimal - think about playing a propane flame over a
piece of steel bat for a few minutes, not much happens or we'd all be using
torches to forge.

The setup is perhaps all about making sure that the bar can't lose any heat
while it is being heated. Surrounding it with orange-hot ceramic chips is a
good way to have that happen.

A lot of thermal mass means the environment you poke your steel into doesn't
cool down so much when you do. You need to add the same amount of heat back
into the system whatever the thermal mass of the chips - enough to raise the
temp of the bar to forging temp - but a higher thermal mass means the temp
of the chip pile drops less, so less heat is lost from the bar while its
heating (or alternatively, the temp of the chips next to the bad stays
higher, so the thermal gradient is bigger and heat moves quicker)

Maybe I should try different chips on my forge, but if they shatter and take
someone's eye out it's my job on the line!

Rich M.

> -----Original Message-----
> From: theforge-bounces at mailman.qth.net 
> [mailto:theforge-bounces at mailman.qth.net] On Behalf Of Jeffrey Polaski
> Sent: 06 March 2006 21:57
> To: Sponsored by ABANA
> Subject: RE: [TheForge] Chip forge
> 
> 
> I'm just curious, but does anyone have any experience to say 
> how what the effects are? Has any one tried a forge with 
> different chips?
> 
> I'm not sure, but this is how I think of what's going on in a 
> chip forge. It's purely conjectural, but these are my working 
> assumptions:
> 
> 	1.) Start with a running and heated forge
> 	2.) Cram some metal in it. 
> 	3.) Chips near metal cool down as they radiate heat 
> into cooler metal 
> 	4.) Metal starts to heat up
> 	5.) Hot gas swirling by heats the metal, too
> 	6.) The cooled-off chips around the metal start to heat up
> 	7.) As chips heat up they (mostly) radiate more heat 
> into the metal
> 	8.) Most of the heat put into a piece is from:
> 		a.) Hot gas swirling by
> 		b.) Radiated from the chips
> 		c.) Physical chip-to-metal contact plays a fairly small
> role (not a lot of contact, due to chip size (i.e. 1/2") and, 
> because we're talking about heat flowing *from* an 
> *insulator*, it's not going to deliver a lot of heat all at once. 
> 
> Given this, I think that a *lot* of thermal mass would be a 
> drawback. That is, the column of cooled-off chips (from when 
> you just crammed in a metal bar) would take *longer* to heat 
> up with more thermal mass. I think this would make it take 
> longer for your bar to heat up, too.
> 
> Just a thought, but has anyone put a flat "clamshell half" 
> over a chip forge to radiate heat back into the pile
> 	
> 
> Jeff Polaski
> Research and Graduate Studies Webmaster
> University of California, Irvine
> http://www.rgs.uci.edu/
> 949.824.6363
> 
> -----Original Message-----
> From: theforge-bounces at mailman.qth.net 
> [mailto:theforge-bounces at mailman.qth.net] On Behalf Of 
> xlch58 at swbell.net
> Sent: Monday, March 06, 2006 1:01 PM
> To: Sponsored by ABANA
> Subject: Re: [TheForge] Chip forge
> 
> Rich Maynard wrote:
> 
> >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.
> >
> Shape does have a major effect on heat transfer.   Since the 
> heat is in 
> the gas and the goal is to use the chips to absorb the heat 
> from the gas
> 
> and feed it back to the metal, therby avoiding sending such a large 
> percentage up the flue, the heat transfer plays a big role.  
> I suspect 
> the thermal storage aspect would be important if the heat supply was 
> variable, but it is not. 
> 
> Charles
> 
> 
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