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#21 Pres

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Posted 19 May 2013 - 10:17 AM

A tip or two for ya' on kiln building and design............

One of the common causes of cold floors on kilns revolves around the mistaken understanding that so many people have that "heat rises". That preception being some sort of a "law" comes from our experiential understanding of our lives....where we experience that HOT GASES rise (like in heated structures). Hot gases rise when suspended in colder gases. Heat energy....... not true.

This mis-understanding is a core concept that I deal with in my Kiln Design and Construction classes.

Heat energy ALWAYS moves from areas of higher concentration to areas of lower concentration. Basic law of thermodynamics. Entropy. Water flows downhill. (Yes... a heat pump can move heat energy seemingly "uphill",...... but that is a separate subject.)

If you want the kiln to fire as evenly as possible using as little fuel to accomplish that feat as possibe........ make sure you don't under-insulate the floor. Otherwise you'll have to adjust the heat DISTRIBUTION pattern in the unit to send more of the overall energy into the floor area than otehrwise necessary.... some of which to also be lost out of the underinsulated floor..... and costing you money in every firing.

So if you decide that the walls and roof structure of a kiln has to have a specific insulation value (heat loss in BTS/ Sq. Ft. / hr.) then the FLOOR should have the same level of insulation. (See * note below also) So if your walls are 9" of brickwork compoised of a 4 1/2" hard brick hot face layer, backed with a 4 1/2" insulating brick layer (of some specific use temp rating) then the floor should also have about this same rating overall.

This can be a little different due to the typical layout of floor bricks being set in the 2 1/2" high layer and the walls being in the 4 1/2" format..... but you CAN lay floors with the brick set in the same (or similar) configuration. The common choices to "match" up to a 9" wall section oftten comes to a decision between a 7 1/2" thick floor and a 10" thick floor. If you understand the insulating values of refractories, you can achieve the SAME insulating value (BTU / Sq. Ft / Hr. conductivity) out of a thinner floor wall section than the side wall structure using DIFFERENT materials........ so the thickness is actuall irrelevant.

The important concept is that the INSULATING value be similar.

The old Rhodes book showing so many 5" thick hardbrick floors in kilns is responsible for SO many kilns with cold bottoms it is amazing. This is something that I commonly end up fixing on a kiln when I am called in to troubleshoot some kiln firing issues.

And if you decide to use fiber in the floor area........ make sure not to compress the fiber too greatly (difficult in a load bearing situation). The more you compress the dead air spaces... the more the loss of insulating value. There is an optimum level of compression for fiber...... used in stuff like Z blocks. Best (easiest) to use "hard versions" of fiber for floors....like board forms.

best,

......................john

(*NOTE: Because there is typically less free air circulation across the cold face of the floor structure, technically the amount of heat energy disappated into the surrounding environment off the cold face is lower than on the vertical wall surfaces and off the roof or arch. So the BTU /Sq,. Ft. / Hr. loss values there is slightly less than the same construction in a wall or roof. But this factor is so small in the overall picture ...as to be inconsequential.)


The old Rhodes book showing so many 5" thick hardbrick floors in kilns is responsible for SO many kilns with cold bottoms it is amazing. This is something that I commonly end up fixing on a kiln when I am called in to troubleshoot some kiln firing issues. I have the old Rhodes book, and have read it a couple of times. I always wondered about the floors as many later books take the approach you mentioned as top, sides and bottom being equal. Thank you for clarifying something that has always bothered/mystified me. At one time I had thought about building a gas kiln, but my present circumstances would not allow it. I wondered about the same approach to electrics, as I have the habit of using a double floor(old floor or lid under new one) in my electrics, with a slightly thicker than original lid.

Simply retired teacher, not dead, living the dream. on and on and. . . . on. . . .                                                                                 http://picworkspottery.blogspot.com/


#22 Biglou13

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Posted 17 August 2013 - 10:36 AM

moving forward with kiln build...... finally buying a pyrometer and thermocouple, to go with build,    so far the ultimax from axner is #1 on list.  and yes i plan on using cones in addition to pyro.   (inexpensive is important,  a $400 pyro/thermo  is out of budget)

 

any suggestions or alternatives for (decent inexpensive) pyrometer/thermocouple?

 

ive seen on videos where they slop some "mud" on wood fire kilns to cover leaks,and where they brick up....  its also not permanent. Any  formulas for this "mud"?


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#23 neilestrick

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Posted 17 August 2013 - 01:51 PM

It is usually a mixture of fireclay and other non-clay and organic materials, kind of like adobe. People use sawdust, straw, sand, grass clippings, etc. Some also include a bit of portland cement to harden it. Straight clay or mud will shrink and crack off, so the other materials are very important.


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#24 Biglou13

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Posted 29 August 2013 - 08:20 PM

moving forward with kiln build...... finally buying a pyrometer and thermocouple, to go with build,    so far the ultimax from axner is #1 on list.  and yes i plan on using cones in addition to pyro.   (inexpensive is important,  a $400 pyro/thermo  is out of budget)
 
any suggestions or alternatives for (decent inexpensive) pyrometer/thermocouple?
 ]


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#25 Mark C.

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Posted 29 August 2013 - 09:56 PM

Back in the day we made this mud with fireclay- vermiculite-a pinch of sand and water with a minor amount of sawdust-mixed with water in tub -mix till workable but not to wet.

Mark


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#26 Marcia Selsor

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Posted 29 August 2013 - 10:08 PM

Back in the day we made this mud with fireclay- vermiculite-a pinch of sand and water with a minor amount of sawdust-mixed with water in tub -mix till workable but not to wet.
Mark


Biglou,
I made mud with scrap clay and cellulose insulation from Home Depot on a salt kiln door when I was at he Bray. it worked reall well. Add some Potland cement to the mix for a good protective /insulating cover for the arch. sounds like you're getting I done.Good job!
Marcia

#27 JBaymore

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Posted 30 August 2013 - 09:04 AM

any suggestions or alternatives for (decent inexpensive) pyrometer/thermocouple?


Biglou,

I think that the terms "inexpesnive" and "decent" here are mutually incompatible. Don't by a cheap analog unit....they are "expensive" to have.

If the pyrometer allows you to fire more successfully..... how many screwed up loads / pieces would it take to pay for a decent pyrometer system to start with? On fuel alone..... knowing the information that the pyro can give you will likely result in savings every firing.

Check out Flukes or my preference ...Omega Engineering.

best,

.............john
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#28 MDJones

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Posted 30 August 2013 - 08:08 PM

A tip or two for ya' on kiln building and design............

One of the common causes of cold floors on kilns revolves around the mistaken understanding that so many people have that "heat rises". That preception being some sort of a "law" comes from our experiential understanding of our lives....where we experience that HOT GASES rise (like in heated structures). Hot gases rise when suspended in colder gases. Heat energy....... not true.

This mis-understanding is a core concept that I deal with in my Kiln Design and Construction classes.

Heat energy ALWAYS moves from areas of higher concentration to areas of lower concentration. Basic law of thermodynamics. Entropy. Water flows downhill. (Yes... a heat pump can move heat energy seemingly "uphill",...... but that is a separate subject.)

If you want the kiln to fire as evenly as possible using as little fuel to accomplish that feat as possibe........ make sure you don't under-insulate the floor. Otherwise you'll have to adjust the heat DISTRIBUTION pattern in the unit to send more of the overall energy into the floor area than otehrwise necessary.... some of which to also be lost out of the underinsulated floor..... and costing you money in every firing.

So if you decide that the walls and roof structure of a kiln has to have a specific insulation value (heat loss in BTS/ Sq. Ft. / hr.) then the FLOOR should have the same level of insulation. (See * note below also) So if your walls are 9" of brickwork compoised of a 4 1/2" hard brick hot face layer, backed with a 4 1/2" insulating brick layer (of some specific use temp rating) then the floor should also have about this same rating overall.

This can be a little different due to the typical layout of floor bricks being set in the 2 1/2" high layer and the walls being in the 4 1/2" format..... but you CAN lay floors with the brick set in the same (or similar) configuration. The common choices to "match" up to a 9" wall section oftten comes to a decision between a 7 1/2" thick floor and a 10" thick floor. If you understand the insulating values of refractories, you can achieve the SAME insulating value (BTU / Sq. Ft / Hr. conductivity) out of a thinner floor wall section than the side wall structure using DIFFERENT materials........ so the thickness is actuall irrelevant.

The important concept is that the INSULATING value be similar.

The old Rhodes book showing so many 5" thick hardbrick floors in kilns is responsible for SO many kilns with cold bottoms it is amazing. This is something that I commonly end up fixing on a kiln when I am called in to troubleshoot some kiln firing issues.

And if you decide to use fiber in the floor area........ make sure not to compress the fiber too greatly (difficult in a load bearing situation). The more you compress the dead air spaces... the more the loss of insulating value. There is an optimum level of compression for fiber...... used in stuff like Z blocks. Best (easiest) to use "hard versions" of fiber for floors....like board forms.

best,

......................john

(*NOTE: Because there is typically less free air circulation across the cold face of the floor structure, technically the amount of heat energy disappated into the surrounding environment off the cold face is lower than on the vertical wall surfaces and off the roof or arch. So the BTU /Sq,. Ft. / Hr. loss values there is slightly less than the same construction in a wall or roof. But this factor is so small in the overall picture ...as to be inconsequential.)

 

First Post - just found this

Wow , now that was Kiln porn, as I now realize Why I have been stuck for months unable to add another brick to my kiln because I have piles and boxes of half bricks all soft from a kiln I am recycling. I can put 2 layers under the kiln floor and use up a lot of them making a better insulated floor and then tell my wife that I ran out bricks and need to buy more. Plus I may as well move it over a bit since I have to unstack it, add the soft brick floor, start again. I was planning on crushing the broken soft bricks for grog and casting chimney sections with that.  I had already bought 5 bags of Kastolite. I can also now lay some steel tubing under the floor for anchoring the steel supports for the door and the arch clamp system

 

Thanks for that

Mike



#29 Biglou13

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Posted 31 August 2013 - 05:19 AM

John's posts are almost always scholarly. I find my self re reading his (and others) posts, and always extracting a bit more knowledge each time.

I'm planning on hard brick inside and soft out side also old kiln parts. I love that they are easy to cut. I have yet to build it yet . But recently started rethinking my plan. Depending in size of kiln I think soft brick (exclusive) as base layer may be problematic structurally as weight bearing brick. I'm sure someone will reply with science behind this. But I'd be leery of staking heavy hard brick of walls on a base of soft. So at minimum the wall sections will be supported by hard brick, or all hard brick for verticals surfaces. You can still back them soft as I'm planning. It t just be the wall perimeter that won't have soft bricks as floor base.

Are you building with soft brick only? I'm interested in seeing pics of your kiln.

Lou
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#30 Mart

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Posted 31 August 2013 - 05:31 AM

 

any suggestions or alternatives for (decent inexpensive) pyrometer/thermocouple?


Biglou,

I think that the terms "inexpesnive" and "decent" here are mutually incompatible. Don't by a cheap analog unit....they are "expensive" to have.

If the pyrometer allows you to fire more successfully..... how many screwed up loads / pieces would it take to pay for a decent pyrometer system to start with? On fuel alone..... knowing the information that the pyro can give you will likely result in savings every firing.

Check out Flukes or my preference ...Omega Engineering.

best,

.............john

 

I dug up few  form Omega

 

1) TJ36-CAXL-14U-18
2) CASS-18U-12-NHX
3) KMQXL-125U-6

 

150-300 mm length is OK and and 3.2+ mm  diameter sound about right.

It will be used in our experimental CF gas kiln (not a raku kiln!) and we like to fire it at or slightly above 1258 °C (if we can get there :).

 

John, any recommendations?

 

Thank you



#31 Biglou13

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Posted 31 August 2013 - 05:44 AM

Since johns post I've been spending some time at that site also, any suggestions on which model for "thermometer"

http://www.omega.com/pptst/HH500.html

Others were less less expensive with similar features

Does wood fire change needs for thermocouple ?

Since the above links have ultimax sheath does that mean that no additional ceramic sheath is necessary. What features are necessary?
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#32 Mart

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Posted 01 September 2013 - 03:50 AM

Since johns post I've been spending some time at that site also, any suggestions on which model for "thermometer"

http://www.omega.com/pptst/HH500.html

Others were less less expensive with similar features

Does wood fire change needs for thermocouple ?

Since the above links have ultimax sheath does that mean that no additional ceramic sheath is necessary. What features are necessary?


This handheld "thermometer" is nothing more than a overpriced volt meter :) with larger and friendlier numbers.
What if you buy a simple Tester/Volt Meter that can measure millivolts for few €/USD and use it to measure, what is happening at the other end of the thermocouple.

If you think about it, 50.929 mV is as meaningful as 1258C, 2296F and cone 9.

http://www.thermomet...ple-Chart-C.pdf



#33 Biglou13

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Posted 01 September 2013 - 04:30 AM

Since johns post I've been spending some time at that site also, any suggestions on which model for "thermometer"http://www.omega.com/pptst/HH500.html
Others were less less expensive with similar features
Does wood fire change needs for thermocouple ?
Since the above links have ultimax sheath does that mean that no additional ceramic sheath is necessary. What features are necessary?

This handheld "thermometer" is nothing more than a overpriced volt meter :) with larger and friendlier numbers.
What if you buy a simple Tester/Volt Meter that can measure millivolts for few €/USD and use it to measure, what is happening at the other end of the thermocouple.
If you think about it, 50.929 mV is as meaningful as 1258C, 2296F and cone 9.
http://www.thermomet...ple-Chart-C.pdf

Are you saying that most "thermometers" / volt meters are less important in reading kiln temp than the actual thermocouple.?
Is this a bad choice for "thermometers"?
I'e spent a few minutes looking at chart and still am no closer on making decision on which to buy. Thermocouple or thermometer.
I'm unclear as to the point of your last post.
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#34 JBaymore

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Posted 01 September 2013 - 07:24 AM

Here's a good starting point for understanding selecting pyrometer systems (thermocouple(s), connectors, extension wires, and meters):

http://www.omega.com...upleSensor.html

Please take note of the upper temperature range limit for Type K thermocouples....... and the output graphs for the upper end of those so that you know the trade off you are getting for using these cheaper thermocouples.

Then you mate it to a corresponding quality meter that gives you the features that you want. Watch the resolution and accuracy numbers for the meters.

Knowledge is power.

Here's another good intro document: ‎http://www.pyromation.com/Downloads/Doc/Training_TC_Theory.pdf


Only you can decide how much accuracy is necessary for what you are attempting to do. The more accuracy in the system, the more information you have to work with in doing your firings and in troubleshooting any issues therin.

best,

................john
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#35 justanassembler

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Posted 01 September 2013 - 10:29 AM

All of what John just put forth is good information, but also remember that the only information a pyrometer is giving you is the temperature at the tip of the thermocouple that it is reading



#36 JBaymore

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Posted 01 September 2013 - 11:21 AM

All of what John just put forth is good information, but also remember that the only information a pyrometer is giving you is the temperature at the tip of the thermocouple that it is reading


SO incredibly true that I spend a LOT of time stressing this point in classes. Ditof for oxy-probes and the like. And DITTO for any cones you are looking at through spy ports.

best,

..............john
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#37 Biglou13

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Posted 04 November 2013 - 09:35 AM

A free brick donation fell through.
(So if anyone has any free brick , soft or hard, even old electric kiln guts.......)

I was planning on using soft brick (electric kiln innards) as inslulative layer in kiln build.
I'm now re thinking. A perlite layer. Then a conventional brick wall?
Also using it as second level floor insulation between support bricks.
How much insulation does perlite provide?
My other option is a layer of (pricer) blanket.

Finally decided on train style cross draft " shoebox " design
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#38 Mart

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Posted 04 November 2013 - 01:10 PM

Get the high temp CF and make your walls at least 10 cm thick. For most inner 50 mm layer, use the one rated for 1430C (what ever the F equivalent). For the second layer (50 mm), use 1260C CF.
If you like or can (have a permanent place for kiln) build a brick wall around it. Will help to slow down cooling. Use second hand hard (heavy) bricks.

Our CF downdraft kiln is doing grate. It has 2 propane burners and can do cone 9-10, no problem.
If you have all the parts, you can build one in a day or 2.

#39 Biglou13

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Posted 01 January 2014 - 07:49 AM

I've seen two schools of thought with kiln building.
1. Perfect sized bricks and appropriate wedges, side skew, key bricks etc etc often mortar-less. (Pricy)
2. Primarily straights with refractory scraps and mortar. (Less expensive, larger, primitive style, anagama etc etc)

With #1 I've read to leave room in build for expansion while hot. But not with #2 how is the expansion dealt with with mortar style build.
How is heat expansion dealt with?

With #2. The refractory mortar will cure unevenly in kiln environment. The mortar exposed to inside of kiln will will be expose to temperature greater than mid point to out side of kiln. So technically the mortar closer to inside of kiln will be more "mature" than outside. Does this cause issues and how.

Sure the kiln will be functional just wondering....... Rambling thoughts.....
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#40 neilestrick

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Posted 01 January 2014 - 09:10 AM

In my experience expansion joints are not necessary in box shaped kilns. In long kilns it can be necessary depending on the type of kiln, but is less of an issue with soft brick kilns. In grad school we had a Train style wood kiln that had such great expansion along its length that it popped the nuts off the all-thread. When it was rebuilt, the firebox, chamber and chimney were built as separate entities to prevent it from happening again.
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