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#21
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Right Henry H. did have an idea (or reported an idea) to achieve very
even heating by using compressed air through stainless tubes to set up convective currents in a fusing/casting kiln. Henry is also not a kiln former. In any case, the idea was not to cool down the kiln, but to achieve more even heating. The problem with that idea was the bane of every kilnworker producing gallery quality work--crap landing on your work. Even a slight breeze can stir up refractory dust from the primer or brick and ****ify the piece. Also, convective currents already exist in a kiln naturally when there is an air gap under the shelf. Uneven heating is more a problem when firing fast or when the elements or kiln height are configured wrong. |
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#22
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Nah, that was Ritchie Havens. I believe he was the first performer of the whole weekend. Joe nJb wrote: That's Henry Halem. Henry Havens was that guy that sang at Woodstock. -- Jack Plonked by Native American bobo1148atxmissiondotcom http://photos.yahoo.com/bc/xmissionbobo/ |
#24
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Good point. I hadn't even considered that. It would be a good idea for
annealing. I thought he had mentioned it for heat processes. It seems like we discussed it at one point and he didn't mention it was for annealing. |
#25
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Joe wrote:
Nah, that was Ritchie Havens. I believe he was the first performer of the whole weekend. Joe You're thinking of Richie Valens, the guy that was killed in the skiing accident with Sonny Holly. Richie Havens is a gated community in Florida. -- Jack Plonked by Native American bobo1148atxmissiondotcom http://photos.yahoo.com/bc/xmissionbobo/ |
#26
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wrote:
Good point. I hadn't even considered that. It would be a good idea for annealing. I thought he had mentioned it for heat processes. It seems like we discussed it at one point and he didn't mention it was for annealing. I hadn't either until you mentioned it today. It was only after reading your post that I put the annealing connection to it. I was concerned about the dust also but it dawned on me that in kiln forming, evenivity (that's what they named it) would only be important during annealing larger pieces and maybe certain slumps. All of this is of no concern for the firing of small pieces but could be a real pain in the ass for large slabs. I think Henry lurks here and can point out if I have this all wrong. -- Jack bobo1148atxmissiondotcom http://photos.yahoo.com/bc/xmissionbobo/ |
#27
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"Evenivity" is a Blanthornism. Brian Blanthorn of the Isle of Wight, he
of pebbles and a pioneer in devitrification as design. It actually refers to even firing in a bunch of different ways. Because, kilnformers are very concerned with uniform temperature across the whole range of process temps, not only annealing. Uneven temperature at fusing and slump temps can cause more problems actually than uneven temperature at annealing. For example if you have a 30f difference from the center to the margin of a flat piece, it will still anneal fine. But that difference at fusing temperatures could present big problems in the outcome of the piece. Evenivity at fuseing temperatures is extremely important. |
#28
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nJb wrote: Richie Havens is a gated community in Florida. Nuh-uh, the Gated Community is somewhere near Microsoft HQ. I've noticed *everybody's* English languageing abilitythings have gone to hell in the past 5 years. Might be due to the effects of new-kew-luhr radiationism. Joe |
#29
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Well, at lower temps, one entrains air and keeps it from moving, so you
want a fluffy blanket or other stuff on the outside. If you consider fiber a conductor, I have to say: relative to what? I hope nobody is considering packed fiber all the way out. Packed fiber is supposed to reflect heat, as the specific mechanism, but below the temps that works at (1700F as I recall) volume of non-convective air will work well. The pipe was originally suggested by me because the person wanted to cool the kiln easier. Since kiln work is crash cooled, I assumed the request was for bringing an extra insulated box down through the annealing range. -- Mike Firth No more levees Bury old Orleans Raise New Orleans up if it is worth saving -- wrote in message ups.com... Right Mike,,, Henry Havens? You're drunk, right? At a given thickness (generally agreed to be 7-8" by longtime furnace builders and engineers) Conductive heat loss through packed fiber is not reduced in proportion to the radiant heat loss from the surface. Efficiency proceeds in reverse. That's the theoretical point.The practical point is, yes at some point additional fiber cost begins to outweigh energy savings. But even if fiber were free, it still wouldn't make sense. Remember that fiber is an insulator, but it also conducts heat energy. In general conductive heat transfer is the most efficient form of heat transfer. But don't get the wrong idea, obviously the sheer volume of radiant heat loss per unit area of surface surpasses the conductive heat loss of an insulating material, at some minimum level. Ask a guy with an under-insulated furnace. So, you see we aren't dealing with absolutes, but defined equations. Too much either way, and efficiency is reduced. My point is, the fact that you can't insulate further with a conductive material is not the end of the story. Efficiency can and has been increased by engineering techniques that are used outside the studio glass arena.The trick is to limit heat transfer via conduction, while also limiting the corresponding increase in radiant heat loss per unit area. A hint, air is one of our best insulators, and it is free. It insulates well because of its low heat conductivity. However, it is a great medium for radiant heat loss. Which also fiber is not... and so on, and so on... As a side note, efficiency can also be increased by investing some additional energy in stopping loss from the system.So that, while the overall energy used by the system is increased, the proportion of energy within the system put to work, not lost to the surroundings, has increased. This activity can take different forms. |
#30
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It would be misleading to say that fiber is a "conductor". But, as a
solid it does conduct heat energy. In general we can state that the more dense a material, the better in conducts heat. (Don't ask me if that goes for all material or what exceptions there are.) I.e. a solid is more heat conductive than a gas. However a denser material may be much more effective in stopping radiant heat loss. Which is why as you (sort of) point out, a furnace maker packs fiber insulation: Radiant heat loss is the *primary issue* at higher temperatures. Packed fiber is more effective reflecting heat energy, and limiting radiant heat loss. So Mike in short the question for an engineer is, how does one take advantage of the best qualities of packed fiber (stopping radiant heat loss) while ammeliorating its undesirable qualities (heat conduction). Wrapping your furnace in an outer layer of less dense home insulation is a simple attempt on the right track. But not the best solution. Because, you are increasing surface area dramatically, while still using a (far less dense) solid material. As I said, a gas is going to be the least heat conductive material. So, the least amount of material thickness and resulting increase in outside surface area. And at lower temperatures (near the outside of your furnace) there are also things one can do with emmisivity of materials to combat the tendency of a gas to pass radiant heat energy. |
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