[TheForge] Ceramic Chip Forge Workshop?

[Chuck Robinson]

Thanks Mike,
Chuck
----- Original Message ----- 
From: <keporter at comcast.net>
To: "Sponsored by ABANA" <theforge at mailman.qth.net>
Sent: Thursday, July 14, 2005 12:46 PM
Subject: Re: [TheForge] Ceramic Chip Forge Workshop?


>
>
> 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.
>
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