diy kiln DIY Kiln Built opinon

[neilestrick]

28 minutes ago, lbispo said:

The concrete brick is there.

Ah good. I thought it was a metal stand. Good to go.

[Bill Kielb]

1 minute ago, lbispo said:

12.2kWh of energy consumption

I think this is great, one of my pet peeves is the large losses in most kilns  and a competitive market that has kept them the same for many many years. I read of an L&L model now using interior refractory coating for the UK market I believe. Just reviewed Skutts interesting electrically approved solid state relay solution  using single leg switching and economical isolation relays for safety so things with kilns are changing for the better.

Probably not a good time to wonder why perforated fire brick has not been produced or any other number of whacky ideas In my head. Keep working till your happy, I think there are quite a number of thermal gains to be had pretty easily.

[neilestrick]

1 hour ago, Bill Kielb said:

Just reviewed Skutts interesting electrically approved solid state relay solution  using single leg switching and economical isolation relays for safety so things with kilns are changing for the better.

Skutt, L&L, Evenheat, Paragon, others, all have solid state relays available. While I personally think they're great, the problem from a sales standpoint is that they drive up the initial purchase cost considerably, on an appliance that is already one of the most expensive things people will own. And when you consider how inexpensive the cost per pot is to run the kiln, it's difficult to justify paying so much more for a kiln that will function just fine without the SSR upgrade. I've only sold one kiln with the SSR upgrade in the past couple of years, because there was a big sale on it. Usually I can't justify the cost to my customers. For folks who like to tinker and have the slickest electronics, it's very cool.

1 hour ago, Bill Kielb said:

I think this is great, one of my pet peeves is the large losses in most kilns  and a competitive market that has kept them the same for many many years.

Extra insulation is good from a n efficiency standpoint, but backup fiber insulation makes replacing bricks more difficult, and dangerous due to inhaling fibers. I'll charge extra to replace bricks on kilns with backup insulation. Luckily for me, it's very rare that I see kilns built that way at all. Fiber board/blanket backup insulation tends to degrade over time as the bricks expand and contract and compress and rub against it, making a real mess during repairs. The other issue is that at some point added insulation makes it harder for the kiln to fire accurately, as the elements continue to radiate heat even when they cycle off, and the controller has to try to compensate for that. That's why L&L build their crystalline kilns with only 2.5" of brick- the controller can be more precise without the lag, and have better control over controlled cooling rates.  Thicker insulation also means slower cooling times and a longer wait between firings.

Just my thoughts on this from a sales and repair standpoint. I'm all for more efficiency in kilns, but unfortunately it has to be more cost effective before it will be commonplace. I had a long conversation with L&L a couple of months ago when I was considering having them build me a square top-loader kiln with 4.5" thick walls, for better durability. The slower cooling rates were the thing that made me decide against it, as I need more flexibility in my schedule.

[Bill Kielb]

3 hours ago, neilestrick said:

Skutt, L&L, Evenheat, Paragon, others, all have solid state relays available. While I personally think they're great, the problem from a sales standpoint is that they drive up the initial purchase cost considerably, on an appliance that is already one of the most expensive things people will own. And when you consider how inexpensive the cost per pot is to run the kiln, it's difficult to justify paying so much more for a kiln that will function just fine without the SSR upgrade. I've only sold one kiln with the SSR upgrade in the past couple of years, because there was a big sale on it. Usually I can't justify the cost to my customers. For folks who like to tinker and have the slickest electronics, it's very cool.

Extra insulation is good from a n efficiency standpoint, but backup fiber insulation makes replacing bricks more difficult, and dangerous due to inhaling fibers. I'll charge extra to replace bricks on kilns with backup insulation. Luckily for me, it's very rare that I see kilns built that way at all. Fiber board/blanket backup insulation tends to degrade over time as the bricks expand and contract and compress and rub against it, making a real mess during repairs. The other issue is that at some point added insulation makes it harder for the kiln to fire accurately, as the elements continue to radiate heat even when they cycle off, and the controller has to try to compensate for that. That's why L&L build their crystalline kilns with only 2.5" of brick- the controller can be more precise without the lag, and have better control over controlled cooling rates.  Thicker insulation also means slower cooling times and a longer wait between firings.

Just my thoughts on this from a sales and repair standpoint. I'm all for more efficiency in kilns, but unfortunately it has to be more cost effective before it will be commonplace. I had a long conversation with L&L a couple of months ago when I was considering having them build me a square top-loader kiln with 4.5" thick walls, for better durability. The slower cooling rates were the thing that made me decide against it, as I need more flexibility in my schedule.

Yes, I know we have had this conversation and I understand first cost and competition and your argument actually.  We had many of the same arguments when I was driving a car that got six miles to a gallon. Heck I  made some of those arguments because I wanted to go fast. To me kilns are huge energy wasters for the last fifty years. Precision in heating is way better with SSR’s, residual heat in elements is really not an issue especially from a mass or controller standpoint, definitely not a heat exchanger and definitely does not store a bunch of heat, it’s just not, period. In industry we control the same elements and processes far far more accurately when we have to. Depending on something to cool by making it wasteful and leaky is far far inferior than controlling the cooling. Rigid insulation is a thing, not necessarily soft cheap fiber and not necessarily space shuttle tiles (which are more than 20 years old now). 

So all reasons I have heard before, very similar to emission controls on a car, R11 insulation in the attic, vapor barriers, 80% efficient furnaces, 10 seer air conditioners, 100 watt incandescent light bulbs instead of 13 watt LED’s, etc... to me and this is just my opinion, all driven by the competition and first cost. When something does not evolve in efficiency  significantly over fifty years there is truly something wrong with the model in my mind.

To me potters pay the price in operation and maintenance. Who designs something that needs replacement after 10% wear and accepts it? Tires used to  be worse, but not that bad. I get it, kilns are a niche market and individuals pay the cost for their inefficiency over time, but honestly is there any real reason they waste so much energy and still rust away? It was acceptable for car quarter panels and rocker arm panels to rust away within a few years, couldn’t be fixed without making a car far too expensive. Guess what, that went away when quality cars started to come from other sources. To me I can counter every single point made with accurate examples of how we do this right now, far better because we have to, for the process,  and have done so for at least twenty years. Is it ok to run your cement kiln like we run pottery kilns? The answer is no, the energy and process precision becomes a financial disadvantage.

So again, I have heard all the reasons, personally I find them extremely thin and mostly feel that potters have gotten the short end of the stick and there is no real good reason to be still using the incandescent light bulb of kilns. On the manufacturing side, In defense of them, I really like them all about equally and understand that competition is a guide they cannot afford to ignore ........ but still it is coming slowly. It’s ironic that  we just got a kiln to fire way better on 2300 watts by adding 1” of insulation in the crudest of ways yet these arguments still exist?

Just a personal pet peeve of mine though, so no worries. I do see positive change though so it is coming. Single pole ssr (vs double pole) is interesting and the safety they chose ends up Economical and reasonably safe. Refractory coatings finally making it into pottery kilns even though they have been in existence for twenty years. All positive signs that it’s coming though.

[lbispo]

Great insights. From my personal test, I see the relay cycling not very often, thus a SSR would add very few benefit, and it would dissipate an awful amount of heat, meaning that the enclosure will need to be different.

 

@Bill Kielb
 Is perforated insulation brick a thing ? It it's just an idea? The guy selling bricks in Denmark have a powdered insulating brick version that I could cast a perforated brick and test... I like that idea

[Bill Kielb]

28 minutes ago, lbispo said:

 Is perforated insulation brick a thing ? It it's just an idea? The guy selling bricks in Denmark have a powdered insulating brick version that I could cast a perforated brick and test... I like that idea

Perforated bricks and hollow blocks are an old idea  (very old) used in structures. It was a way to reduce material cost and weight but still leave sufficient structure for for the use which was mainly to maintain compressive strength. Anyway a very old construction idea that might translate to use in kilns with respect to thermal conductivity and mass.  It may not be worth doing with IFB, not sure just one of those ideas that pops into my head wondering if anyone has tried it.

In the old days we would remove pump rotors and machine them smaller to save pump horsepower as after balancing the exact flow was known. The relationship with flow and horsepower is cubic so reducing flow by 10% reduces horsepower by 30%. Cost very little to do. Nowadays we have variable frequency drives that allow one to slow the speed and save similar horsepower minus the switching losses in the frequency drive. Old way was very productive and inexpensive, new way easy, productive and mildly expensive.

Old brick idea still might be a good idea, but just something that strikes me as simple to perfect for a maker......... if it’s worth the production cost. 
In the US energy is very cheap and perceptions can be skewed. It’s fashionable to go to grocery stores with your own cloth bag and not use plastic or paper which is good but when I was a kid we often walked to the store and had grocery carts and reused the paper bags to cover our rented school books. Very few had two cars, wash was hung out to dry saving 225 cfm of air horsepower and  infiltration and  plenty of gas or electric to heat the clothes. In fact, very few had clothes dryers and automatic dishwashers so sometimes old ideas are still good ideas even though we practiced them out of necessity.  Convenience  has a cost.

If four or six holes could be put in the K28’s without material affecting their strength and they became the density of k23’s then I would say it probably is worth it. Old concept though and less is more not always accepted or thought about as it’s a low tech solution. That reminds me, gotta find my green bags to throw in my 50k SUV to get groceries tomorrow. Just kidding

[lbispo]

From the glaze firing, cone 04

 

[Bill Kielb]

Basically perfect 04, nice work! 
kwh? Any data?

[lbispo]

On 2/13/2021 at 9:25 AM, Bill Kielb said:

Perforated bricks and hollow blocks are an old idea  (very old) used in structures. It was a way to reduce material cost and weight but still leave sufficient structure for for the use which was mainly to maintain compressive strength. Anyway a very old construction idea that might translate to use in kilns with respect to thermal conductivity and mass.  It may not be worth doing with IFB, not sure just one of those ideas that pops into my head wondering if anyone has tried it.

I received the datasheet from the castable IFB (that is how they call it) and the thermal conductivity is:

• 400C/750F -> 0.38W/mK;
• 600C/1110F -> 0.40W/mK;
• 800C/1470F -> 0.42W/mK;

At this level, I do not see a benefit of making it perforated, unless there's another castable, or brick recipe.

[Bill Kielb]

The purpose of the perforations would be to reduce the mass and total volume of the the brick so a significant improvement in conduction and a real reduction in conductive mass. Only an idea in my head but what I know for sure is if I take any traditional IFB and perforate it removing let’s say 1/5th of its mass, I improve its conduction considerably using less materials. Very likely an overall thermal improvement in excess of 20% actually. As long as the mechanical properties remained suitable, just wonder if anyone has tried it.

With respect to casting your own, depends on the light weight insulating castable I would guess. One thing for sure, casted with holes it will be less dense and conduct less heat. Refractory coating the perforations has some very interesting potential as well. Don’t know, can I make a K28 perform thermally better than a solid K23, probably. Is it worthwhile? So far it seems not.

Super light castables seem more attractive though. It’s entirely possible that the current porosity of the current IFB’s is optimal in production which always makes me ask, can we cast these with holes?

 

[lbispo]

Making holes on IFB was an option that i had not have considered, I was thinking about casting, in order to reduce waste and freight cost (for my personal purpose). The table you shared, is the temperature, for example Super lights... 950C the maximum temperature?

Apparently the information is somehow standard, as the table you shared, CB-10 = 0.35W/mK ... pretty close to mine, which is this one btw: https://shop.vitcas.com/insulation-refractory-castable-1300ins.html

[Bill Kielb]

Yes, truth be told I don’t know the accuracy of any of these sheets from the web and casting your own seems very difficult for sure. Most of the current higher efficiency kilns (watts/ sf)  seem to be utilizing  rigid or blanket insulation, ceramic fiber rope to minimize infiltration etc..... 

L&L seems to be using refractory coating to reduce radiation losses these days, that’s interesting! These have been used successfully in industry for many years. Their use finally made it to pottery kilns.

 

[lbispo]

That makes sense... I believe the coating is made of Zirconium Silicate-ZrSiO4 (at least this one) radiation heat transfer formula is Q/t = σeAT^4 -> As we can see, the only thin that can change the amount of heat transfer is Area or Surface Emissivity:

• Ceramic Produces infrared wavelengths in the 2 to 10 μm range (quick google);
• Concrete, and ceramics, have an emissivity of 0.90 and 0.95 -> https://www.optotherm.com/emiss-table.htm
• from the following document, ZrSiO4 has an emissivity ranging from 0.35 til 0.74: https://www.matec-conferences.org/articles/matecconf/pdf/2016/45/matecconf_d2me2016_02012.pdf

As you mentioned earlier that the big loss at higher temperatures is radiation, if we replace the numbers in the formula considering the following number for simplicity:

• A = constant;
• T differece betweem surface and surrounding = constant
• σ = 5.67 × 10^−8 J/s · m2 · K4 = also constant
• concrete (brick) e = 0.95
• zircon e = 0.74

0.74/0.95 = 19.5% less loss (on the radiation part). This is a quick dirty napkin paper calculation but I'm convinced, and this is the worst case scenario (0.74).

[neilestrick]

1 hour ago, Bill Kielb said:

L&L seems to be using refractory coating to reduce radiation losses these days, that’s interesting!

They've been using the coating for as long as I can remember.

[Bill Kielb]

1 hour ago, neilestrick said:

They've been using the coating for as long as I can remember.

Good to know, makes sense been in industry forever. I just  recently noticed it in a brochure for the fuego kilns for the UK market.

[neilestrick]

3 hours ago, Bill Kielb said:

Good to know, makes sense been in industry forever. I just  recently noticed it in a brochure for the fuego kilns for the UK market.

It appears they're marketing it more now with the new web site.

It would be interesting to see how putting holes in bricks affects the insulating value. Would a series of small holes, say 1/4" diameter, drilled through an IFB to create sort of a honeycomb pattern, insulate as well as a full brick? How many holes could you actually make before the structure of the brick is affected? Could you even drill enough holes to have a real affect on the mass before the brick becomes too weak? How about a brick that mimics SIPs panels, with an IFB type exterior for durability, and a lightweight fiber board interior ?Less mass, better insulating value, but still fast cooling. The durability of IFB with the low mass of fiber board. Lot of interesting possibilities.

[lbispo]

44 minutes ago, neilestrick said:

It would be interesting to see how putting holes in bricks affects the insulating value. Would a series of small holes, say 1/4" diameter, drilled through an IFB to create sort of a honeycomb pattern, insulate as well as a full brick?

Better, Air thermal conductivity at 400C is 0.05W/mK versus K23 which has 0.14W/mK -> accordingly to: https://www.engineeringtoolbox.com/air-properties-viscosity-conductivity-heat-capacity-d_1509.html

44 minutes ago, neilestrick said:

How many holes could you actually make before the structure of the brick is affected?

I guess it can also be calculate as the brick datasheet presents some mechanical number that i have no understanding how to interpret

 

EDIT: it just occurred to me now, differently from double glazed windows, the air inside the brick would be "breathable", otherwise it may expand and explode if too airtight as the air expands...  or not? have no idea

[Bill Kielb]

Yes I think there are a lot of effective ideas but competition is likely just too tight in the marketplace. Drilling holes to reduce mass is an old brute force idea that works by removing mass so it’s just simply works. Can I make a brick that way is probably the real question else drilling probably destroys them. It would be a fundamental I would ask my of engineers that brought their new brick to me saying how light and great it is. My first comment is great let’s cast one that is porous because I know it saves material , reduces mass and traps air. I’m guessing they would have several reason why we can’t though but you never know. Sometimes forest and trees blend and I have an energy mindset.

It is interesting to note the cone arts seem to use the same crumby insulation from years past. The idea is great but maybe newer rigid panels just too expensive. Controlled cooling is a bit of a misnomer to me as it’s really evolved into controlled reheating of a thermally leaky item. It’s a non energy mindset. Of course perforated brick provides a nice way for me to control cooling evenly.

Lots of ideas, all good actually. Kilns are such a small niche and the operating cost get passed on to many so not as apparent as operating a cement, lumber, or tunnel kiln.

[Bill Kielb]

5 minutes ago, lbispo said:

EDIT: it just occurred to me now, differently from double glazed windows, the air inside the brick w

It expands but the current trapped air is (not really trapped) can move freely enough to be just fine. Current IFB is very porous.

[lbispo]

Back to the math, as I'm still looking for a solution since the insulation wrap on the outside looks ugly, for comparison reasons, K26 + 2" (50mm) blanket = Q = 544 W

I'm now considering drilling hole on the bricks, considering the following:

• Conductive heat formula -> Q = U A dT
• Area = 0.413m2
• dT = 1000K (or Celsius)
• K26 thermal conductivity 0.25 W/mK (@400C)
• Brick is 0.065m (2.5")
• Air thermal conductivity 0.05 W/mK (@400C)
• Convection heat transfer 25 W/(m2 K)
• Will keep the area constant for simplicity

K26 (0.25W/mK and 2.5") brick results in Q = 1433 W

K23 (0.14W/mK and 3") brick results in Q = 782 W

If I replace the brick by air (holes) at a 28%, I get Q = 776 W on my current K26 bricks, which would theoretically match K23 performance. That is kind of 2x 1/2" (12mm) per brick along the longer side.

 

Sounds right?

 

Q (W)	Improv	Hole fill
1433	0%	0%
1369	4%	2%
1310	9%	3%
1256	12%	5%
1206	16%	6%
1160	19%	8%
1118	22%	9%
1078	25%	11%
1041	27%	12%
1007	30%	14%
975	32%	15%
944	34%	17%
916	36%	18%
889	38%	20%
864	40%	22%
840	41%	23%
818	43%	25%
796	44%	26%
776	46%	28%
757	47%	29%
738	48%	31%
721	50%	32%
704	51%	34%
688	52%	35%
673	53%	37%
659	54%	38%
645	55%	40%
631	56%	42%
618	57%	43%
606	58%	45%
594	59%	46%

[Bill Kielb]

It does,........

certainly can test with one brick to see the limits and best pattern for holes. Looks to have  pretty big potential. Thermal storage not accounted for actually. So in a normal firing with 3/4” mullite shelves, we stacked pots every which way and weighed. Our guess is the shelves end up up to be about 40% of the weight of the pots. Given that knowledge looks like over 1/2 the energy in the firing is devoted to heating the shelves and of course the kiln mass. This is pretty big since firing shelves and IFB has no aesthetic outcome. They look the same before and after, pure waste in that respect.

I would not dismiss the weight reduction of the brick as well. Really appreciate your effort here as well, I don’t have the time to explore this anymore and sharing it with the community is great IMO.

[lbispo]

I'm not sure if the number are accurate, but if I used the formula correctly, I have put in a graph Q vs Hole size (need to multiply to area in order to find the real number) as you can see below, it is not linear:

[neilestrick]

Interesting stuff! It would be easy enough to drill out one brick and measure the cold face surface temp and compare it to the neighboring bricks. I think it might be difficult to drill out 28% of a brick and have it maintain structural integrity, though. Nothing to do but start drilling and see how far you get!

[Hulk]

Perhaps a (mostly - allowing for expansion only) captive dead air space would be worthwhile, in terms of insulating value, without much increase in cooldown time, given the space is vented (opened up) when it is time to cool down.

[Bill Kielb]

9 hours ago, lbispo said:

I'm not sure if the number are accurate, but if I used the formula correctly, I have put in a graph Q vs Hole size (need to multiply to area in order to find the real number) as you can see below, it is not linear:

Area  (volume) change is not linear with respect hole diameter so that appears correct what is the change in total mass  vs. diameter?