Ceramic wool compressed?

T

Tehemton

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Sep 6, 2016
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Hi, I'm the the process of building my HT oven and have sourced all the parts and grooved the bricks (I got 9x9x3 k23 bricks). Also, I got 2'x24' of ceramic wool roll for a good price so I picked it up for secondary insulation around the bricks.

the wool is 1" thick, but I plan on having 3-5 layers around my bricks and compress them into a nice tight seal to prevent any heat loss and keep everything packed.
My question is, can ceramic wool be compressed and still work well? It's only for secondary insulation so I'm not worried too much. But I would still like to avoid some fundamental error if possible.
Thanks.

Regards
Tehemton
 
To some degree the air gaps between the wool fibers are part of its insulation value. But, yes, it works fine if compressed. With multiple layers, you will certainly have no heat loss.
I would think 2 layers would be more than sufficient, though.
 
Before you possibly waste that much ceramic insulation, I would STRONGLY suggest you contact the manufacturer to get their thoughts on your idea. I don’t know this for certain, but it’s my guess that a single layer that hasn’t been compressed could offer better insulative value than a whole heap of the stuff that’s been pressed down. Again, I don’t know this, and I highly doubt anyone here will, either, which is why contacting the manufacturer is your best course of action.

As a rule, we tend to think that more of something is always better, but that might not be the case, and you may just end up squandering a whole lot of material without finding the right answers, and never know it. Good luck with your build!
 
Matthew Gregory said:
Before you possibly waste that much ceramic insulation, I would STRONGLY suggest you contact the manufacturer to get their thoughts on your idea. I don’t know this for certain, but it’s my guess that a single layer that hasn’t been compressed could offer better insulative value than a whole heap of the stuff that’s been pressed down. Again, I don’t know this, and I highly doubt anyone here will, either, which is why contacting the manufacturer is your best course of action.

As a rule, we tend to think that more of something is always better, but that might not be the case, and you may just end up squandering a whole lot of material without finding the right answers, and never know it. Good luck with your build!
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I spoke to him about this and he said that packing it into layers like that would increase it's density and make it equivalent to a higher density blanket. And apparently, higher the density more insulation it provides. Though he didn't sound quite sure over the phone.
Is there some way that I can test it on the gas stove? I don't own a propane torch and have been using a basic coal fire.
 
Hey man, by 'he' who are you referring to? The person that sold it to you, or someone at the company that MAKES the ceramic insulation?

Did they explain what percentage or increase in efficiency or lessening of loss that multiple layers would provide?
 
Im probably wrong but here goes.

Compressed you will lose r value but gain thermal density and mass

Un compressed you have higher r value but it will change temps easier as i belive the one with more thermal mass will take.more fule to heat to the same temp but will maintain it better ?
 
Guys, my friend in his workshop has industrial quality /Germany made I think / HT oven .Inside was completely covered with ceramic panel , you can not see HT elements/Kanthal/ inside . . . .
Refractory ceramic fibre board is a vacuum formed product that resists higher gas velocities than ceramic fibre blanket. Ceramic fiber board is ideal for furnace, boiler duct and stack lining due to its low thermal conductivity and low heat storage allowing shorter cycle times and quicker access for maintenance.
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http://www.vitcas.com/ceramic-fibre-board
 
Matthew Gregory said:
Hey man, by 'he' who are you referring to? The person that sold it to you, or someone at the company that MAKES the ceramic insulation?

Did they explain what percentage or increase in efficiency or lessening of loss that multiple layers would provide?
Click to expand...
Yeah I spoke to the guy who sold it to me.
I did speak to another vendor as well about this and he said the same thing, that by compressing it, the fibers are more tightly packed and provide better insulation. I doubt if anyone in Mumbai might be able to give me numbers as to how much better it actually is.
It's anyways only for secondary insulation around my firebricks since I'm not using any mortar. So it shouldn't hurt I suppose. What T Teppojutsu said does make sense and aligns with what the vendors have mentioned so far.
Thanks guys
 
This is a total peanut gallery comment but.

Cut one square of the material. Put a piece of paper ontop of it. Now hit the bottom with a flame and see how long it takes for the paper to catch fire. (Hold the material with tongs or something)

Now stack a few compressed sheets and repeat the experiment. Which caught faster?
 
Several things here are not quite as simple as it seems they ought to be.

My understanding (and it may be completely wrong) is that the main heat transfer mode through ceramic fiber is essentially radiative heat transfer to/from the fibers by the other fibers in their line-of-sight: in effect, there are lots of steps. Increasing the density by packing the fibres tighter over the same distance just means that there are more steps, each with a smaller drop. Because the rate of heat transfer across each step is dependent on the height of the step (the temperature difference across the step), more smaller steps mean that less heat is transferred.

Shielded elements tend to be more of a safety feature than anything else. Although using a muffle* tube in a forge tends to help to even out the temperature, it does so by effectively averaging out the temperature at different points on the outside. For an oven that already has an even temperature distribution, there is very little to be gained.

Whilst the shielding of the elements does have some theoretical advantage in that it works like a muffle and reduces the small temperature variations still further under steady-state conditions, this tends to be offset by the delay it introduces between applying power/heat to the elements and that heat reaching the interior of the oven. The "lag" needs to be factored into the controllers tuning and generally results in having a slower approach to the set point following a disturbance to steady-state conditions.

There is therefore a tradeoff between the steady-state stability offered by shielded elements and the rapid recovery offered by unshielded elements. For most knifemakers, who will be putting stuff in and taking it out every so often, the rapid recovery tends to win.

Other factors like ease of maintenance also play a big part in the choice. Exposed elements tend to be easier to change and much easier to fault-find. Smiths and knifemakers seem more inclined than many other groups to undertake maintenance on their own equipment, making this a more significant consideration than in many industries.

* "Muffle" has several meanings. In this case, I am referring to a tube, usually steel, placed in a forge (or occasionally oven) into which the workpiece is placed for heat-treatment.
 
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