Insulating fire brick on picture, for heat riser ?

[novicerocket]

Hi to all, 
I am in process of buying bricks for building 15cm batchrocket. 
So i have question. Can IFB (isolating fire brick) from picture be used in heat riser. 
I am concerned that flame will erode/destroy brick if used in heat riser. 

 
Second question. I would like to get as clean burn as possible.
I  have limited width,  but i can build higher heat riser.I would like to build 1.4-1.6m heat riser. 
Is it too much for 15cm batchrocket ? Default is 1,1m. 
Thanks for help.

[fuegos]

hello & welcome to the forum.Can you get a technical specification sheet for the bricks ? the 23 stamped on the brick might mean G 23 = grade 23 rated at 2300 F or 1260 C I'm sure someone else will be able to advise you about their suitability & durability in a riser where you could see temperatures of 1200 C.It's not just the maximum temp. that the brick needs to last but its ability to survive thermal shock & lots of cycles so maybe a higher rated brick might be better ?
"I would like to get as clean burn as possible" then you need to stick to the exact sizes as stated on batchrocket.eu

[novicerocket]

Thanks for advice and for welcome.

I think that markings are C23/76 HBU5.

I searched by HBU 5 and found single url with similar data.

www.refrasil.cz/english/produkty/insulating-products/

HBU 5 - up to 1350 C

C23 - 230mm

76 - by shapes table it should be 76mm wide but that i can't confirm.

At first i planed to use normal firebrick for riser with stone wool for isolation, but then i found that stone wool binder evaporate/burn above 250C so it is not adequate for riser.

After that i planed to user ceramic wool, but it is very expensive.

Last choice is isolating with isolating firebricks.

After that i found that they can be used for riser, and then you don't need extra isolation.

But  i found that it is not recommended to use it on flame path.

So i search for information if someone use it and what are results.

[martyn]

Where do you live? Ceramic matting should not be that expensive in most populated areas.

[novicerocket]

Hi, I live in Croatia. I found a ceramic wool, but problem is that it can't be bought by the meter, only whole package (4m^2) And that package is over 200 euros. Isolating brick I can get  0.7 euro per brick. It is cheaper to use firebrick and isolating fire brick behind it instead of ceramic wool, that is the safest option if I can't use just IFB for riser.

[peterberg]

Insulating firebrick with the specification you mention is safe for the riser. Highest temperature I measured in there has been 1173 ºC, so those bricks are suitable. In case those are soft, use hard firebrick (i.e. non-insulating) for the firebox.

[novicerocket]

Those are soft brick. So riser only from those bricks, and (firebox) place for wood from clasic dense firebrick.

Thanks for advice.

[Jura]

Oct 15, 2021 0:50:11 GMT -8 novicerocket said:

Hi, I live in Croatia. I found a ceramic wool, but problem is that it can't be bought by the meter, only whole package (4m^2) And that package is over 200 euros.

damn expensive!
I obtain it for €50

Oct 15, 2021 0:50:11 GMT -8 novicerocket said:

Isolating brick I can get  0.7 euro per brick.
It is cheaper to use firebrick and isolating fire brick behind it instead of ceramic wool, that is the safest option if I can't use just IFB for riser.

Insulative perlite brick are not to be used in flame area.
Those based on Mullite can. but they cost €3,5
alnmost the same with vermiculite.

[novicerocket]

After your post I tested one insulating brick with a gas burner for 5 minutes.

Brick glowed red under direct flame, and a place where where little cracks after flame expand little.

So  classic fire brick as core is my  only option with normal price.

One other question, can i use high temperature sealant 1500C to connect insulating and normal fire bricks.

Will thermal expansion two different material destroy the sealant ? Sealant in not elastic after curing by manufacturer.

I have limited width so i would use 3cm wide normal fire brick and 78mm wide insulating one.

Other option is to saw insulating bricks but without enough insulating material i have potential fire hazard around rocket.

I don't know how wide insulating brick is enough. 

And 3cm normal fire brick is to thin to stand alone, so it must be glued with sealant.And better insulating rocket is better rocket. Lots of compromise/problems  for few missing centimeters.

Thanks for advice.

 

[Orange]

does IFB smell after being burned? CFB does.

That sealeant should work but I prefer to user sand/clay mortar.

[fuegos]

1+ for the sand/clay mortar. use sharp sand, 3 parts to 1 part clay & about 5% wood ash.I think a build of just dense firebrick would be much easier but it will compromise performance - perhaps someone could put some numbers on this ?

[novicerocket]

Oct 30, 2021 12:15:53 GMT -8 Orange said:

does IFB smell after being burned? CFB does.

That sealeant should work but I prefer to user sand/clay mortar.

I noticed smell only on magnesite heavy dark red brick (best for heat acumulation).

I will try with clay/sand mortar first.

[novicerocket]

Nov 1, 2021 3:22:58 GMT -8 fuegos said:

1+ for the sand/clay mortar. use sharp sand, 3 parts to 1 part clay & about 5% wood ash.I think a build of just dense firebrick would be much easier but it will compromise performance - perhaps someone could put some numbers on this ?

Thanks for recipe. I used wood ash and mud before for closing gaps on pipe/chimney for current central heating stow. Worked ok but clay would be muck better.

[fiedia]

Hi,

I just bought class 23 bricks, soft, porous and insulating. I then read this thread which is quite worrying about using such bricks.

...Personally, I recommend using a surface sealant on the "hot-face" of BOTH exposed ceramic fiber AND insulating firebrick (the more insulating and lighter-weight the insulative firebrick, the more porous its surface will be, and the more susceptible to disintegration it will be.) After your first firing, those coated surfaces will essentially form a hard, glazed surface which will resist woodash flux penetration and thus low-fire crystalline conversion and decomposition.

 I will coat them with sodium silicate before mounting them.