FW: [TheForge] Mineral Wool ,ITC 100 efficacy ?

[Kathy]

-----Original Message-----
From: Kathy [mailto:keporter at comcast.net] 
Sent: Monday, May 28, 2007 10:34 AM
To: 'artgawk at thegrid.net'
Subject: RE: [TheForge] Mineral Wool ,ITC 100 efficacy ?

Pete,
Well, we've danced around the subject long enough, and now it's time to look the
nasty in the eye. I think we both had an ugly suspicion that the coating simply
amounted to "too little, to late." Convection, from all that I have read, is the
big factor in heat transfer within kilns, and they are all designed to promote
it (for the sake of even heat transfer to whatever pottery is being fired).
Unfortunately, convection also moves the heated air over the kiln's walls,
floor, and ceiling with equal thoroughness. Because a kiln has far greater
exterior surface dimensions through which to leak heat via conduction, the IR
coating may amount to "bailing water out of a holed boat." In other words, it is
working, but the problem is so great that the help it provides becomes less than
significant.

Now, we come to the ugly part; dealing with the beast. Pottery kilns sold to
artists and hobbyists have only one course of bricks, which are positioned so as
to cover the maximum space with the least bricks, keeping the cost of
construction low for the manufacturer; they also do the worst possible job of
insulating this way, which is just "tough luck" for the user. Personally, I
can't complain about these facts, since the resulting electric bills and poor
performance causes most of their purchasers to sell or give them away. A
complete stranger gave me two of them in return for just hauling them off.

Naturally, the only effective solution to this problem is secondary insulation.
However, the electrical controls must still remain on the kiln's exterior, which
means that they will have to be moved further out, so as to remain outside of
the second insulation layer...at this point, the few people who have thought
things out this far become discouraged and dump the overpriced (now hated) kiln
into the waiting hands of some despicable unscrupulous dog (arf, arf) Why they
do so is a mystery, as the output for a second layer of insulating bricks is
only about 1/20th the price of the kiln was the first place. Not only are more
insulating bricks the obvious solution, but they are also the most expensive.

Fortunately for such vultures as myself, the poor innocents who are stuck with
this dilemma seldom seek answers from a professional hot glass worker, or they
would find out how easily water glass (sodium silicate) can be combined with
perlite (from the nursery section of Builder's Emporium) to form a moldable
ultra light insulating secondary refractory. Nor, do they spend time on groups
like Castinghobby, where they can hear about calcium board, which they might
purchase for very reasonable prices through some construction supply dealers (it
is used as low cost light weight fire insulation in commercial buildings). No,
poor souls, they never find out how easily the problem can be solved, but you
just did >:-)))

Mikey 
"I can live with the tail, but the fleas are murder!"

-----Original Message-----
From: Peter Fels And Phoebe Palmer [mailto:artgawk at thegrid.net] 
Sent: Monday, May 28, 2007 12:32 AM
To: Kathy
Subject: Re: [TheForge] Mineral Wool ,ITC 100 efficacy ?



Kathy wrote:
> Pete,
> You make good points in your reply. The IR coating does make a significant
> difference in interior temperatures. I have satisfied myself on this point
many
> times. Therefore, you should see a significant difference in s-o-m-t-h-i-in-g.
> The question is in just what?
Hi Mikey;
I thought i would too.
Because Phoebe hasn't been firing uniform loads, ( tiles one 
time, standing sculpture the next, glaze VS bisque etc) ..the 
results are a bit muddied....
But  still, we had to run a firing till 4:30 AM the other 
morning...that was a first. Yawn
> 
> You wrote:
> "Internal distance dissipation losses should be a minor consideration in a
> sealed refractory vessel, and a constant in this instance."
> 
> Agreed; the point I was attempting to make with statements about square of the
> distance losses and the very small size of the target area (the cone) was that
> IR reflection (actually IR generation) would make no difference in droop time
by
> any direct impact on the cone; the gains would have to be from reduction in
> conduction losses through the brick. All an IR reflector coating does is
> generate IR from convection gain and IR gain on the hot face side of the brick
> or other insulation. The generated light returns energy into the internal
> system, slowing conduction losses through the brick. Probably, its most
> significant contribution to heating within a gas forge is that it provides a
> superheated surface area, which acts as a "giant match" surrounding the
gaseous
> contents, and completely upgrading the nature of combustion within a forge or
> furnace. This factor has been thoroughly documented in industry, and is
probably
> beyond dispute. Coatings in an electrical appliance cannot gain from this
> benefit and will only gain from reduced conduction losses. However, I would
have
> thought they would be significant; especially in something as large as a kiln.
> 
> You also wrote:
> "I thought that an increase in IR reflectivity would decrease the 
> amount of heat the walls leaked, leading to shorter firing times.
> The only repeatable indicator we have for internal kiln 
> temperature are the cones."
> 
> You should be getting a reduction in energy loss through the brick, and the
> amount of the reduction should increase with temperature rise, but I don't
> believe the cones, which are only designed to indicate absorbed energy of the
> kiln contents can be used to measure the effectiveness of the coating.

If the coating works, then it should make the most difference at 
the end of the firing where the losses nearly balance the heat 
input, drawing out the firing time to raise it the last couple of 
hundred degrees. I'd expected it to be pretty dramatic. Wrong.

> Electrical use, and time needed to due the firings are going to be your only
> indications of the coating's effectiveness. So, we agree that the coating
should
> have decreased your firing times, supposing that you aren't using automatic
> controls. If you are using automatic controls, it is only going to decrease
your
> electrical consumption. If it does neither, then we have a problem. Does your
> kiln have automatic controls?

Unfortunately not. This was an early Kress kiln and the switches 
are set to a time cycle, no temperature sensing in it.
I put in new elements, switches and wiring, But when i started 
talking about pyrometers, Phoebe chased me away.
I tend to want to get my hands in whatever she is working on way 
too often ( compulsive) and it'd drive her nuts if i'm not real 
careful.
There are an number of uncontrolled variables working here that 
could easily account for theory and practice not meeting up.
For example we are near the end of a funky old powerline that 
runs for many miles along the ocean. We've had a lot of onshore 
winds this spring which loads the poles, the wires, the 
connections and the insulators with salt. Then the fog comes in 
and everything soaks...corrosion and conduction losses yield 
inconsistent power supply, as you might guess....and yes, i did 
apply the ITC about the time of the last rains.
I dunno...certainly not the definitive anecdotal evidence here.. 
( oxymoron?)   pete f

> Mikey
> 
> 
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> 
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