[TheForge] Ceramic Chip Forge Workshop?

[keporter at comcast.net]

I will reply to your message point by point, Chuck.

> Hey Mike, 
> I still can't find any information on the maximum temperature a ceramic chip 
> forge can generate.
The only limits on temperature are: 
(1) The maximum temperature of the flame input (and its size being sufficient to account for thermal losses (into the work and into surrounding surfaces). Since there are plenty of fuels capable of reaching 3600 degrees Farenheit without even adding oxygen, this is not a very great problem. Even a properly designed naturally aspirated tube burner can achieve about 3000. With compressed air and special nozzles, this can be increased very near to 3600, which is the theoretical wall, so to speak. Then, there are a number of richer fuels to plunder. Also, this is one case where an oversize burner becomes an advantage, as secondary flame constitutes a good thing in this forge, instead of the usual evil.

> The info on alumna balls shows a 2000 F working temp. 
> The temps that I would like are 2500+ F. I believe most of the material 
> suggested so far would melt at this temperature. 
Not so; both kiln furniture and castable refractories can be bought that are good to far higher temperatures. I will admit that at these temperatures you would be wise to forget simple clay (it will work but will have to be replaced more frequently than a lazy man would like), but kiln furniture is good to +3000 and several common refractories go as high as 3200; there is at least one on the market that will take 4000.
> Another concern is the location and shape of the burner & diffuser cone 
> below the chips. It appears that it would take a radical design change in 
> the burner to prevent fouling and clogging from the flux used in forge 
> welding. 
> The design really appears to me to be more practical for brazing and low 
> temp forging
To begin with, lose the diffuser cone. Ceramic chip forges are quite practical for braze welding, since they provide a secondary heat source, which will allow single gas torches to aproach oxy-fuel in braze welding capability, but it would not be my preference for low temp forging. In fact, you aren't going to find a more practical or economical way to rapidly heat billets, because only a coal forge could equal its ability to transfer energy on all three fronts (conduction, convection, and radiation). Unfortunatly, coal forges have problems of their own. This is why thermal mass has been used for centuries to overcome the need to reach several hundred extra degrees beyond metallic melting points in order to liquify large amounts of metal. 
There is nothing radical about building a ceramic fire chamber (oblong horizontal box), with multiple holes drilled in a heavy kiln shelf slab resting on its top side, and a cast burner portal in which to place the burner, or fan blown nozzle pipe (either kind of burner in horizontal position at one end of the box). This is even simpler to do than building a castable refractory furnace or a Multi-hole (something that hundreds have already copied from book one). In fact, I would say that building a ceramic chip forge would be less actual work than building a tube forge (more expensive though; it will probably take about $100 to buy the ceramic materials alone).
> The 2 main reasons for my using higher temperatures in forge welding are: 
> scale formation, and grain growth in my Damascus steel work. 
Assuming grain growth is tied to heating time--no problem. Scale formation will be largely inhibited by rapid heating and the great reduction of available oxygen within the ceramic media. Secondary flames will suck up oxygen from ambient air  far faster then the heated metal can, and you can slightly choke the burner while your billets are in the chips to increase the fluxing effect of fuel rich flames.
As to mess from the borax flux, you would have to  remove it from the balls (not so much) and kiln shelf burner plate (a lot more here); possibly even from the fire box (unlikely, but the fire box is simply constructed of parts that rest in, and are trapped by, the surrounding insulation). Remember, the KISS formula when constructing heating equipment out of ceramics.
Those daring fellows who don't like KISS will of course build the fire box with double walls and drill extra air holes in the inner fire box walls just above the burner plate, along with one large extra hole (with choke plate),  near the burner collar, through the outer wall, allowing super heating of  controllable secondary incoming air, since a horizontal fire box lends itself so beautifully to heat recouperation (no fan needed because hot air rises through the higher exit holes in the inner fire box walls). 
Mike P.