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Patrick

Used fire brick changed my plans

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This arch is really a high arch. I'm wondering are you going to have burners coming in the back or from walls to the sides. All My catanarys I ever made where wider and less tall. Most had burners coming in the sides into bag walls. My guess since this is so skinny the burners are front or rear walls -forced air.

 

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The interior floor space ended up being 36" x 40".  My plan is to have 4 forced air burners - the first of which I am am finishing up. If it goes well - which I don't see why it shouldn't - I'll build the second, install them in the front wall, and try a bisque fire without insulation just to see how things go.  7/32" orifice + a 50 cfm blower at 7" WC (water column gas pressure) should yield 171k btu per burner.  Each blower will move enough air for up to 300K btu max worth of combustion, so if I need a little more heat, I can drill a larger orifice.

I will allow 6" of space (give or take, depending on curve) between the arch walls and the kiln shelves. A la Abernathy, I will have two burners (the first two I finish) on the front wall a few inches off the floor (2.5 inches) with the center of the burner 3" from the arch wall (and 3" from the shelves) with 40" of room to blow.  I will also have 2 burners coming in the rear wall of the kiln somewhere between 1/2 and 2/3 of the way up the wall.  Same 3" center-of-burner-off-the-wall placement as the front 2.   The exhaust will come out of the front wall 2.5" above the floor in the center of the wall - I'll have to work on the size, but I'm going to start with about 5" x 5" or something in that neighborhood.

The arch is tall - I couldn't go any higher without getting uncomfortably close to my rafters. I'll be putting a 4 inch insulating castable layer over the brick and, if my memory serves me correctly, that will leave a little less than 2' to the rafters at the rear of the kiln.

Gas company placed meter yesterday, and I hooked up a free standing gas fireplace/stove with a thermostat in the shop - NO MORE FROZEN CLAY!!!  I find myself going out there and turning up the thermostat just to watch it turn on and off.  I'll leave thermostat at 40 or so degrees just to keep everything liquid.  I'll be able to heat up my throwing water too. ... Feeling kinda spoiled.

Been stacking the arch yesterday and today. The weather has been unusually warm.  Should finish up tomorrow.   I'll throw a pic up if I remember.

Regarding shelves: 12x24 for the bulk (will leave me my 6" on each side).  Depending on how I end up loading it I may need a few odd-ball sizes to keep my desired space from the side walls, but that's no big deal.  I'll fine tune that as I go. 

Thanks for all the pointers and ideas, guys and gals. I really do appreciate it.

Edited by Patrick

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Since your layer is 4,5 inches of hard brick how about instead of cartable how about a better insulated coating?Cheaper lighter homemade.

I have done a few arches with these ideas-a few have been  my own mix of fireclay/vermiculite-that worked great as it had tons of vermiculite which made it it a great insulator. Since your arch will expand and contract plan on that. You could also cover with lower grade ceramic fibers a number 4 pound or #6 pound. Its light and moves and is cheap as it does not have to be dense or high temp-no need for 2300 fiber less will do that far away from the hot face-that could be covered with metal or a layer of homemade mix above to give it a great look.

If you make your own use a wheelbarrow an mix it as dry as you can for less shrinkage.  Or mix hot wet than add the last dry stuff to dry up the mix(this is easier to do)

No need for expensive castabes that  are that far away from hot face.Besides castlables are heavy and dense and you do not need that 4.5 inches away from hot face.

just some ideas outside the box

Good to see you using standard 12x 24 shelves-not everyone works around the standard size which is the best and cheapest and by far the most available in all types.I decide shelve size and build the kiln around that.

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1 hour ago, Mark C. said:

Since your layer is 4,5 inches of hard brick how about instead of cartable how about a better insulated coating?Cheaper lighter homemade.

I have done a few arches with these ideas-a few have been  my own mix of fireclay/vermiculite-that worked great as it had tons of vermiculite which made it it a great insulator. Since your arch will expand and contract plan on that.

I am too tight ... cheap ... stingy ... broke ... conscientious to shell out for commercial insulating castable. I have found several recipes and am planning on a fire clay/sand/sawdust (wood flour, actually) mixture.  I plan on forming blocks up along the arch about 4" x 4" x (how ever long I need them) with corresponding V grooves so the expansion and contraction can happen, and they will stay well-behaved (hopefully). 

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I am suggesting you use denser homemade mortar for your wedge material between bricks to get the angles. This must be made to hold up to high heat as its right near the hot face.

but a much lighter mix on outside of bricks as an outer coating was what I'm talking about over the whole brick structure. If you could spend some $ on that cheap fiber and coat over  with skip coat of light mix it will insulate way great.Since your brick will suck up the BTU this outer coating will keep them hot and insulated well.

Are your bricks going to be laid in the long sides so they are 4.5 inch out off form (wall will be 4.5 icus thick) or the 9 inch out of form with the 4,5 edge touching form(wall will be 9 inches thick)?? which one?

Edited by Mark C.

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7 hours ago, Mark C. said:

I am suggesting you use denser homemade mortar for your wedge material between bricks to get the angles. This must be made to hold up to high heat as its right near the hot face.

but a much lighter mix on outside of bricks as an outer coating was what I'm talking about over the whole brick structure. If you could spend some $ on that cheap fiber and coat over  with skip coat of light mix it will insulate way great.Since your brick will suck up the BTU this outer coating will keep them hot and insulated well.

Are your bricks going to be laid in the long sides so they are 4.5 inch out off form (wall will be 4.5 icus thick) or the 9 inch out of form with the 4,5 edge touching form(wall will be 9 inches thick)?? which one?

We're on the same page. Brick angle mortar is fire clay + sand.  The insulating layer will have the burn out material.   Hard brick walls are stacked 4.5 thick.  I have about 500 lbs of dry fire clay, so I'm planning on using that up on the insulating layer before I go buy anything else (fiber). 

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How long or until what event should I leave the arch form in place?  I am at least thinking until the mortar is dry. ... The last batch I mixed up was a little too wet, thinking about getting the propane weed burner after it to speed things up just a tad - nothing crazy. Just warm it up a bit.

 

Edited by Patrick

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Where will you mount 4 burners? With forced air, there's no need for more than 2 burners. You just use larger orifices and larger blowers to get the btu you need. It's much simpler and cheaper than building and plumbing 4 burners. That's the beauty of forced air over venturi. When I worked for Alpine, even the 40 cubic foot kilns only used two burners.

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3 hours ago, neilestrick said:

Where will you mount 4 burners? With forced air, there's no need for more than 2 burners. You just use larger orifices and larger blowers to get the btu you need. It's much simpler and cheaper than building and plumbing 4 burners. That's the beauty of forced air over venturi. When I worked for Alpine, even the 40 cubic foot kilns only used two burners.

Fabbed up one burner and will test it next week.  If it is ok, I'll make burner #2 and get them on the kiln.

My plan is 2 burners on the front flat wall at floor level and 2 on rear flat wall a little more than half way up.  It's more of an even-heating/fuel-saving issue as opposed to hitting required btu's.  If I read the (albeit, limited) studies correctly, Abernathy-style kilns experienced about a 30% fuel cost savings on 3 different kilns by spreading the btu's around (read: thinking about convection and chamber flow) as opposed to just worrying about getting the required btu's into the kiln.  The image in my head makes sense - blower on bottom and another blower opposite and higher up would create (in my mind) a circulation on the side wall.  Would that not equate to more even heating? Again, it makes sense in my head, but whether that will correspond to reality...?

I'll start with 2 on the front wall on the floor and see what happens. Do a few firings with cone packs around the kiln.  My guess is I'll get a temp differences between top and bottom - but I may not. We'll see. ... And I am open to ideas/input.

+1 on larger blowers and orifices. On each burner I've got a 50 cfm blower (at a 10:1 air to nat gas ratio) can support a max of 300k btu's wide open on a good day.  I am planning 172K btu's (7/32" orifice at 7" WC) per burner. That will give me plenty of wiggle room and room to play with oxidation/reduction.  If I need need more heat, it's there.  If I wanted to max out the blower (which I don't see why I would), I'd go with (2) 13/64" orifices per burner and that would give me around 300k. ... ... But I quit doing burn-outs in my car when I was about 25 years old. Tires cost money! LOL!

What are your thoughts?

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I think it's definitely worth a try. If it ends up making things too goofy, then you've got a second set of burners for your next kiln. I think it may very well be a good thing on your kiln since it is a fairly tall and narrow as cats go. It may help to even things out. I'm thinking that you won't need to run the upper burners as high as the lower burners. It'll be fun to play with.

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With Venturi burners and a chimney it makes sense for more burners but for a forced air kiln it feels Overkill since you're operating at positive pressure (unless you install a draft style chimney).  I've only read a few books on kilns but the idea of forced air is overcoming the problems with natural draft by forcing air and gas through the space.  Luckily you can build burner ports into the back wall and if the front burners don't cut it you can always add after.  So envious of this project! Looks like a lot of fun

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Here's a pic of the brick on the form.

To help anyone messing around with the idea of a similar project, here's a few things I learned/settled for:

(1) In using old (as opposed to new) fire brick, there was a lot of culling of not-good-enough bricks. Lot's of beating old mortar off so bricks would lay somewhat flat and/or flush.  Some brick were unusable, some were ok, and a few were great.  Had I purchased new fire brick, I imagine this part of the process would have been a entirely different type of satisfying.

(2) It didn't take long before I realized keeping my lines "straight" was going to be a concern. 1/16th of an inch off x 4 times of that = a lot - for some. Perfect lines would have taken a lot more mortar (1 part fire clay/1 part sand) than what I was wanting to mix up or a lot more scraping and beating.  So I adjusted my rows with a little mortar where needed to keep everything pretty level.  Once at the top of the kiln, it wasn't that big of a deal because more mortar was being used anyway - just made sure the inside edges of the bricks were in contact with the brick below.  Didn't want any floating only on mortar.  The front and rear faces of the arch are a whole different story - my thoughts here were "It'll be getting a layer of insulating clay anyway..." 

(3) Hand splitting brick versus saw cutting brick. I hadn't run across many who recommended hand splitting brick as opposed to cutting with a tile/brick saw.  I don't own said saw, and was thinking about purchasing one, and then I recalled all the talk of going through diamond blades (not cheap), so I settled for hand splitting. A mason's chisel is about $5, and I have an angle grinder with masonry cut off wheels.  This left an imprecise, jagged face, which I made sure was placed to the outside (toward front or rear of kiln).  No biggie. If I had had new brick, I would guess this eye-soar would have been aesthetically more problematic for me.  To hand split, I simply scored the brick all the way around where I wanted the split to occur with an angle grinder about 1/8 - 1/4 inch deep (I was just cutting bricks in half), laid half of the brick on a solid surface (another brick) leaving the score to overhang a smidgen,  stuck a 4" mason's chisel in the score, and smacked it a couple of times.  They all fell apart nicely.  Worked better than what I was expecting, but again, it leaves a jagged, uneven face.

(4) Keystone. I thought about splitting brick for the keystone. After about 20 minutes of considering that, I decided to use a castable. I used fire clay/EPK/sand. I went a little lighter on the sand than in the mortar, remembering Rae Reich's lamentations of crunchy additions to her glazes from falling crumbles.  Might make a difference, might not.  I may just end up having to create a crunchy line of porcelain something-or-others.

That's about it for right now. Gonna let everything set up until dry and pull the form out.  I'll probably fire it a time or two before I put the insulating layer on, if for nothing else to see where my gaps are that need some attention.

ArchFinished.jpg

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Harbor freight sells a really cheap diamond wet saw-I would suggest that.

I did hand cut bricks like you but only once-never again.

Cleaning old bricks is just part of the old brick deal.

Keeping them straight is important -nice straight batter board works good.

The keystone made from straight mortar could be an issue thru time when it weakens-consider cutting one on a saw from bricks-you will still need mortar but much less.There is a lot of force on the keystone.

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Hmm.  Not sure how to respond except by sharing my deliberations. I am no physicist or engineer - so pardon the slaughtering of certain concepts if I screw this up.

Every row holds the arch together - which is ultimately held together by gravity, being a catenary arch.  And if gravity quits working, well... that'll be an interesting time.

There are several types of forces that can affect the keystone: tensile (pulling apart - doesn't apply here), flexure (bending/twisting - negligible), and compression (crushing - here is where the money is, I think).

Abrasion is a concern also with the expansion/contraction of each firing, (which I think what Mark was getting at by "weakens").

I can't say I understand how a soft brick keystone would be better than a castable keystone if the forces we are dealing with are either primarily compression or abrasive.

Cold crushing strength of hard fire brick (approximate) = 3500 pounds per square inch

Cold crushing strength of a Morgan K25 insulating fire brick = 200 pounds per square inch

To be conservative, let's say my fire clay/epk/sand keystone mixture (which is solid - not insulating) is right in between the two previous examples = 1650 pounds per square inch cold crushing strength

The entire arch consists of 216 hard bricks. At 8 lbs a brick, if I were to stack the entire pile of bricks one on top of the other, it would ONLY weigh 1728 pounds. 

The area on EACH SIDE of the keystone that comes in contact with HALF of the kiln is about 182 square inches (364 total square inches in contact with all bricks on both sides).

If we could flip the entire arch upside down without it falling apart and put all the weight on just the keystone, we're talking LESS THAN 5 pounds per square inch on the surfaces that contacts another arch brick and ONLY 9.5 pounds per square inch on the part of the keystone that would be sitting on the ground (if you grant the silliness of a catenary arch not falling apart when you flip it upside down.) 

And I know I have assumed uniform distribution of forces AND I used COLD crushing strength - not 2300 degrees crushing strength - etc., but still, the numbers seem on the "it's gonna be just fine" side of it.

Now, here's what I AM concerned about: The clay/sand (no cement, proper) mixture is not yet fired (vitrified), so I will admit I am interested in what will happen through the first firing, it being just bone-dry. If it makes the first firing okay, I will have tons more confidence.  But...  People have been making castable kilns for a while.

I guess what I am saying is I don't understand whence comes the concern.  (I haven't used "whence" in forever. Viva la archaic language!)

 

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I think it's because castable (especially home made) has the tendency to spall over time and once something with that much pressure on it has spalled it could crumble pretty bad.  The castable may also expand and contract at a different rate of the bricks as well causing more spalling.  That's the only negative I can think of, because to repair it you have to put your arch form back in place, it could be a pain in the butt.  The cost of the angled bricks isnt bad, might just buy a few to play it safe?

Edited by liambesaw

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The deal is in your arch or any arch the bricks touch each other and as you noted the compression is 3500#s per inch-a very solid deal. The mortar holds those bricks at the right angle and is not part of that compression much as thats the brick to brick hot face. The whole arch will expand and contract a fair amount each fire. up and down.This will over time make for some loosing goose movement of bricks. The keystone of any arch holds the two 1/2s and is a key element. You have room for another brick-but it sounds like its needs to be shaved some so what I am saying is shave it. The homemade mortar is no replacement for a solid brick especially in this location. If you do not want to cut one row-send me the bricks via USPS flat rate and I'll cut them on my diamond saw for you. I think 5 bricks will fit in a $18 box flat rate as long as its under 70#s-just include the layout(what to cut where)I have sent 50#s of clay in many of these boxes (12x`12 x5.5)

I see this mortar not holding up well at all in this critical location

I think over time that keystone mortar will cause you some big time issues and for 20$ you will not have to suffer this learning curve?

Just offering

You can PM me for my address -I'll cut them same day  received and ship them out same day.I suggest a pice of thin plywood in box bottom to keep box from Turing into a round shape. I shipped 300#s to Hi. a few times in this boxes and filled them with hard bricks myself.

 

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What matters here most is that its a solid brick to brick face-the angle can be mortar -I have used straights in the keystone but not mortar as the hot face just as an angle filler like the rest of arch. I can cut the angel as well if that helps.Just give me any details.

The other cheaper way  to cut these and used brick work well for this as they are less dense is a dry cut diamond saw blades in a  standard skill saw-again you can buy these on the net or harbor freight-not very expensive-you may need two but I think 5 bricks is just a one blade deal-I would have suggested this to cut all your 1/2 bricks but you said you want to spend zero $$ so I did not suggest it.These dry cut blade work well on used bricks.

 

Edited by Mark C.

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I have to agree with the others. The key won't last long.  The kiln is not a static creature.  When the kiln is fired it moves.. expands.. then contracts as it cools causing a noticeable amount of movement throughout the entire firing process.  the key being relatively soft will  inevitably crumble. This being said if it was made with a high alumina cement it would be less susceptible to these forces during firing. Just my 2 cents....

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Another note about the catenary arch: the beauty of this form is that it holds itself up simply by the shape of the arch. True, each row is equally supportive, when complete. However, the keystone is called key for a reason. When this piece fails, all of the the integrity and strength of the arch is lost. 

A keystone is a terrible thing to waste ;)

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