HT Kiln Building

Brian Stucker

Brian Stucker

Joined
Apr 20, 2016
Messages
147
Has anyone used fiberboard to build a HT oven ? I done an experiment with a scrap piece of 2" I had left over from a project. When you initially introduce heat to it it will turn black and smoke. But after it burns out it will be white. It doesn't hold near as much heat as bricks. I finished my kiln build and it turned out great but I have to let it run about an hour so the temps will level out. I have 3 thermocouples in it. Its 27" long. I can get it down to 18-30° temp. variance between the front and back. I am thinking about relining it with this fiberboard so it won't take near as long to level out. What do you guys think?20191213_215059-574x765.jpg
 
Sounds like a reasonable idea to me, but I always think more insulation is better, and I'm not an expert in electric kilns...
 
I would use Ins-board.

When you say "fiberboard", what exactly are you referring to? Can you show a link to the supplier/seller?
 
I think he use ceramic fiberboard but with organic binder /that s way they get black and smoke/ not vacuum formed one ....
 
A.McPherson said:
Sounds like a reasonable idea to me, but I always think more insulation is better, and I'm not an expert in electric kilns...
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I built mine too insulated. It holds way too much heat. It's good for annealing but for multistep processes when the temp goes up and lowers. It doesn't lower fast enough and will abort the firing program. And I would also like to be able to use my kiln for tempering. But It will not lower fast enough for that. I think the new Paragon knife kilns are using fiberboard instead of bricks. They are much lighter and will raise and lower in temp much faster. Making them more versatile.
 
I have used some Ceramic Fibre Board in HT ovens. Mainly because it seemed a lazy way to do things. I have not grooved it for elements though.

I first used the board, 1" thick, for the roof and backed it up with 2” Calcium Silicate board. It meant that I could bridge a full 9” width, which would not have been easy with 9” IFBs, enabling me to build a quick-and-dirty sword-length (42") oven without needing to cut bricks. The door used the same construction and for the same reason. Prior to that oven, I had built 3 smaller ones using all IFBs. I have since built 3 more ovens and used 2" Ceramic Fibre Board for the doors. Everything else is IFBs.

The floor used IFBs because ripping up ceramic fibres while putting stuff in and out seemed like a potential health hazard and I don't have the skill/experience to be sure I will not rip the floor up in use. The walls were also IFBs because the easiest way to cut grooves for the elements, in my experience, is to use a router. Routing board seemed unnecessarily hazardous in terms of creating airborne fibres. I do not have the equipment to capture and remove 100% of the dust generated when routing IFBs and fibres seemed much more likely to pose a long-term hazard.

I tried a porcelain floor tile, cut with a wet diamond tile saw, as a floor liner on the next (IFB) oven I built, just to see if it would hold up well enough to use to protect a Fibre board floor on future builds. It was not a great success. It survived a couple of heat cycles before cracking longitudinally, It still offered pretty good floor protection at that point but I don't know how well it stood up to further use or whether the new owner kept it in.
 
timgunn1962 said:
I have used some Ceramic Fibre Board in HT ovens. Mainly because it seemed a lazy way to do things. I have not grooved it for elements though.

I first used the board, 1" thick, for the roof and backed it up with 2” Calcium Silicate board. It meant that I could bridge a full 9” width, which would not have been easy with 9” IFBs, enabling me to build a quick-and-dirty sword-length (42") oven without needing to cut bricks. The door used the same construction and for the same reason. Prior to that oven, I had built 3 smaller ones using all IFBs. I have since built 3 more ovens and used 2" Ceramic Fibre Board for the doors. Everything else is IFBs.

The floor used IFBs because ripping up ceramic fibres while putting stuff in and out seemed like a potential health hazard and I don't have the skill/experience to be sure I will not rip the floor up in use. The walls were also IFBs because the easiest way to cut grooves for the elements, in my experience, is to use a router. Routing board seemed unnecessarily hazardous in terms of creating airborne fibres. I do not have the equipment to capture and remove 100% of the dust generated when routing IFBs and fibres seemed much more likely to pose a long-term hazard.

I tried a porcelain floor tile, cut with a wet diamond tile saw, as a floor liner on the next (IFB) oven I built, just to see if it would hold up well enough to use to protect a Fibre board floor on future builds. It was not a great success. It survived a couple of heat cycles before cracking longitudinally, It still offered pretty good floor protection at that point but I don't know how well it stood up to further use or whether the new owner kept it in.
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I have some matrikote 90. I was going to coat the floor with that. I grooved mine with a razor knife and I rounded a chisel and scraped the channels. Then vacuumed it up with my shopvac.
 
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That sounds like it should work.

Something that I didn’t get to test was how well the board takes the staples that hold the elements in the grooves.

Let us know how it goes.
 
timgunn1962 said:
That sounds like it should work.

Something that I didn’t get to test was how well the board takes the staples that hold the elements in the grooves.

Let us know how it goes.
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The board actually takes staples well. It hold it in pretty well. I probably won't redo my kiln right away. I'm out of funds due to Christmas but I will eventually get to it. I will report my progress. My chamber size right now is 5.5" x 6" x 27". With the couple pieces of ceramic fiberboard I have I'm gonna make it 9" x 6" x 29". With what I have I will only have to buy one piece to redo the kiln. That ceramic fiberboard is around 140$ for a piece.
 
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I think this is the first time I have seen someone say less efficient oven is better. You know you can turn off the alarm that trips the controller if it doesn’t lower fast enough. Mine use to do that as well. But sign me up for better efficiency any day. My power bill is already enough.
 
JTknives said:
I think this is the first time I have seen someone say less efficient oven is better. You know you can turn off the alarm that trips the controller if it doesn’t lower fast enough. Mine use to do that as well. But sign me up for better efficiency any day. My power bill is already enough.
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As far as efficiency goes I think the fiberboard would be more efficient because it's not holding as much heat as the bricks. Its not acting like a heat sink. The bricks on the other hand are not as efficient. I think using the fiberboard would get to temp much faster and not use as much electricity. But It would also cool alot faster too.
 
Your assumption that the less heat holding the better in a HT oven is backward.
If the oven construction was completely insulating the air would be the only thing heated. That would give HUGE swings in temperature every time the coils switched on and off as well as opening the door would drop the temperature drastically. You WANT the heat absorbtion of the refractory to HOLD the heat and make the oven steady in temperature, That is what the PID figures out and does automatically for your. Opening the door in a fully soaked HT oven will drop the temperature a small amount and it will rebound in less than a minute.

If temperature drops to temper are an issue, either make a tempering oven to move the blades to or wait until the oven cools down. A tempering oven is much simpler and requires less insulation than a HT oven, so your fiber board would work fine for that. PID control at 400F is a breeze compared to 2000F. Also, you can use many commercial heating elements to heat a tempering oven.
 
+1 for Stacy’s comments.

I personally don’t trust high temp heat treat ovens for tempering. It’s not that I think thy are not accurate its just a lot of power for such low temps. Plus I feel these ovens work much better at the high temp ranges thy are built for. I can not advocate enough for the practicality of having a dedicated tempering oven.

From my experience you really need something that circulates the air. I currently have 3 very nice tempering ovens and could not imagine going back to the old days. I am NOT a fan of toaster ovens. Most are small and do not circulate the air. I have found that the bigger the oven the better thy work. With a small oven the hot air rising is what’s circulating the heat. Once you put something in you have now blocked some of that mixing motion. This is not just with small ovens but the small ones are affected much more. The last oven I bought is a gravity convection oven. Very nice lab grade oven with all digital controllers for temp and time. We did a series of tests and noticed once you started loading it up that’s when the temp gradient started showing up. So we added a circulating fan and that went away.

You have better things to do with your time then stand Around waiting for your heat treat oven to drop in temp. With a dedicated oven you already have the first temper done before the heat treat oven even gets close to cooling enough.
 
Stacy E. Apelt - Bladesmith said:
Your assumption that the less heat holding the better in a HT oven is backward.
If the oven construction was completely insulating the air would be the only thing heated. That would give HUGE swings in temperature every time the coils switched on and off as well as opening the door would drop the temperature drastically. You WANT the heat absorbtion of the refractory to HOLD the heat and make the oven steady in temperature, That is what the PID figures out and does automatically for your. Opening the door in a fully soaked HT oven will drop the temperature a small amount and it will rebound in less than a minute.

If temperature drops to temper are an issue, either make a tempering oven to move the blades to or wait until the oven cools down. A tempering oven is much simpler and requires less insulation than a HT oven, so your fiber board would work fine for that. PID control at 400F is a breeze compared to 2000F. Also, you can use many commercial heating elements to heat a tempering oven.
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I was also thinking that. The temperature swings would be to extreme just opening and closing the kiln. The fiberboard does hold heat but it dissipates it much faster than bricks. I'm gonna just leave my kiln alone. I have an oven I'm just going to wire up for a stand alone tempering oven.
 
Brian Stucker said:
I built mine too insulated. It holds way too much heat. It's good for annealing but for multistep processes when the temp goes up and lowers. It doesn't lower fast enough and will abort the firing program. And I would also like to be able to use my kiln for tempering. But It will not lower fast enough for that. I think the new Paragon knife kilns are using fiberboard instead of bricks. They are much lighter and will raise and lower in temp much faster. Making them more versatile.
Click to expand...

Hey mate I am having problems setting up my electric kiln, can you help me out please, I am using REXC100 PID, 2500W heating element, SSR 40 0-32DCV and a LED transformer 20-40DCV....it gets going for a few minutes but then the heating elements stop heating my email is renchasfresh12@gmail.com
 
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