Nono Junang

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since Jul 14, 2017
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Recent posts by Nono Junang

Peter van den Berg wrote:The construction as in the Mallorca build is used a dozen of times now and works well. Done in a number of different materials for the outer skin, raw stabilized bricks, mud bricks, normal building bricks, solid concrete bricks and hollow bricks filled with cob.
Anything above the riser in double skin with an expansion joint between the skins is what I would recommend. That said, a bit more won't hurt anybody.
The same construction is used in the Brussels build, see http://batchrocket.eu/en/applications#opensystems and scroll down to the second item.

Keep in mind that the top half of the bell will be slower to heat up and cool down this way as compared to the lower half.

The phenomenon of opening cracks on the outside during heating up is due to the inside of the bricks heating up too fast so the outside is lagging behind. Ultimately, those bricks could "walk apart" in time so the cracks won't close again when cooled off. Mark however, it's still quite normal to see a few hairline cracks in some places.



Thanks Peter. I've looked at the skp from the Brussel build and will make the changes accordingly, starting a bit lower than the top of the heat riser. I have assumed that the expansion gap is 10mm filled with ceramic fibre blanket. Is that correct?
Is there any drawback if I have the bell a bit higher at say 2400mm instead of currently 2130mm? That would bring the top of the bell to about 800mm from the top of the heat riser, but still within the 9sqm recommendation.
5 months ago
I have found this video from a build from Peter:


It looks like somewhere around the top of the heat riser he uses a double skin with insulation in between to complete the bell.
The top of my heat riser is five rows below the top of the bell and this is exactly the area where I have the cracks.

So my idea now is to remove the top 7 rows of the bell to be well below the heat riser and use a double skin in that area as Peter did.
The double skin will be 40mm fire brick on the inside, 10mm ceramic fibre blanket and 75mm of the old chimney bricks.
Or do you think the double skin should be all the way down to the bottom of the bell?

What are your thoughts?
@Peter van den Berg, any suggestions?
5 months ago

Glenn Herbert wrote:I don't really have an opinion, other than making the slabs thick enough relative to their height and width that they will not be fragile to handle. You can tell best, being there with the material. I think 25mm would be adequate for heat tempering, though handling strength is an unknown for me.



here is an image of how the crack patter looks like
5 months ago

Glenn Herbert wrote:I don't really have an opinion, other than making the slabs thick enough relative to their height and width that they will not be fragile to handle. You can tell best, being there with the material. I think 25mm would be adequate for heat tempering, though handling strength is an unknown for me.


Yeah, I have spoken with a guy who is in the refractory industry and he said that handling 25mm slabs is tricky and he would go at least 50mm. And even at that thickness the slab could crack.

He suggested another solution which would consist of adding a 10mm expansion gap horizontally at the top of the bell and a 5mm one vertically every 1m of height. What do you think?
5 months ago

Glenn Herbert wrote:In the US, masonry heater building code requires a double skin for pretty much the reason you are experiencing. Thermal expansion is obviously the culprit. Is the bell made of ordinary brick? Firebrick is recommended for at least the top half of a bell with the heat riser in it, because firebrick is formulated to not expand when heated (and to resist very high temperatures).

Adding refractory slabs or bricks inside the bell would probably completely solve the problem. An insulating blanket would be counterproductive.



Thanks Glenn for the input. I have used old chimney bricks (about 230mmx115mmx75mm laid on flat) for the bell. Only the top row of the bell is done with firebricks and even there I can see the mortar open up.
How thick do you think the inside lining should be? 25mm? 50mm? 75mm?

I would like to use refractory slabs the following size (thickness x width x height):
25mmx650mmx435mm (10 pieces) and 25mmx990mmx435 (10pieces) and just dry stack them inside the bell in such a way that they interlock. And also would leave a small air gap between both skins.
And if one slab fails it is easier to replace.

What do you think?

5 months ago
Hi @all,
I have now fired the heater a few times and each time I noticed that after about an hour into the fire the lime mortar between the clay bricks of the bell starts to open starting from the top row of bricks down to about half the high of the bell. At that time I have the batch box about half-full.
And the hotter the fire gets the wider the crack in the mortar gets. At that point I have to remove some pieces of wood to reduce the heat inside the bell and pevent leakage.
Interestingly as the bricks cool down, those cracks also gets smaller and almost close.

I am wondering why this happens, is it because I am heating the bell too fast? If so any suggestions on the amount of wood to add per hour?
Is it because the bell is not high enough? It is currently at 2160mm, about 500mm above the top of the heat riser.

I have calculated the heat losses of the house to be heated to be 2.1kW based on the heat loss calculator sheet. On my 200mm system that would mean 1 fire per 24h with 14.2kg of wood.
During my test firing I never use all the 14.2kgs because the cracks in the mortar occurs well before.

I have the following ideas in mind:
1- Line the inside of the bell with some additional material that would absorb the heat and prevent the bricks/mortar to heat up too fast, for example 25mm thick plates of refractory castable, wide and high enough to limit the amount of joints. That would provide additional mass to store heat. There would be a small air gab between the lining material and the clay bricks.
2- Line the inside of the bell with 10mm thick ceramic fibre blanket to achieve the same without adding extra mass to the system.

But before I do anythign I would like to have your opinion.

Any suggestion is welcome.
Thanks
5 months ago

Peter van den Berg wrote:

Nono Junang wrote:What do you think about using 25mm of ceramic fibre board instead of the steel plate and cross weld? I have used some for the bottom of the heat riser. They are rated 1260degC, come in 1000mmx500mm size and cost NZD30 and are also rigid enough to close the top of the bell. So since my opening is 1070mmx700mm, I would need max. 3 pieces glued together. I still have some leftover of ceramic board glue.
I wouldn't get much immediate heat release, but that would be ok. And that would be a lot cheaper and lighter than a steel plate.


Yes, temperature-wise this would do the job. I don't have any experience with the ceramic board glue you mention. Of course you could try it and see whether it leaks and how to solve that. Is it possible to build your bell a little smaller so it can be done with just two boards?
Hmmm... Actually, it should be bigger instead because the top plate doesn't extract heat in this case.



Ok I will give it a try. I have used the same ceramic glue to stick the heat riser together. When getting hot for the first time it expands to fill any gaps and then hardens. I got it from a furnace components supplier.
Later on I could go higher with the bell if I find the exhaust temperature to be too high.
6 months ago

Graham Chiu wrote:What temperatures are you recording at the top of your riser, and at the point where the top of the bell is?
I see that Fox James is recording less than 600 deg C at the top of his riser ( not batch though ) even with ceramic blanket and so is able to use Neoceram glass https://permies.com/t/120/86886/Rocket-stove-hot-plate#797952



Good question. I haven't measure yet what temperature is at the top. Only thing I measured was the temperature at the bottom of the heat riser. And I stopped at 943DegC after I got burned. And I was probably about 30cm above the top of the heat riser. See here: https://www.youtube.com/watch?v=RQg0X1eReUk

I will put some sensor at those places to measure the temperatures.
6 months ago

Peter van den Berg wrote:

Nono Junang wrote:The second thought is doable and works, just one inch (25 mm) of superwool would be enough to take off the high heat. I am not sure this will prevent warping but since the 5 minutes riser is a lasting solution, shielding the top of the bell on the inside with superwool should be working. The only problem you are facing then is the need for a heat resistant adhesive to glue the superwool to the steel.



Hi Peter,
What do you think about using 25mm of ceramic fibre board instead of the steel plate and cross weld? I have used some for the bottom of the heat riser. They are rated 1260degC, come in 1000mmx500mm size and cost NZD30 and are also rigid enough to close the top of the bell. So since my opening is 1070mmx700mm, I would need max. 3 pieces glued together. I still have some leftover of ceramic board glue.
I wouldn't get much immediate heat release, but that would be ok. And that would be a lot cheaper and lighter than a steel plate.

6 months ago

Satamax Antone wrote:At what height will be the top of your bell?


The top row of the bell is at 2130mm. You can have a look at pictures here: https://drive.google.com/drive/folders/1TTte8ubv0mXUnUykzTdTiDUk3rx4VqcT

Satamax Antone wrote:Because, besides cooking, a steel plate doesn't serve much purpose, except if you want to heat a room above. Two over dimensioned metal I beams, supporting firebrick slabs is easier to do. Or a poured single slab.


The steel plate is not for cooking but I wanted a cap solution that allows for easy removal just to be able to look inside the bell. So I am happy with any other alternatives.

Regarding the two over dimensioned metal beams supporting firebricks, do you have any pictures so that I can see what you mean?
I have thought of a poured slab with handles to lift it. But I was not sure what material to use to pour it and also had some concerns regarding the weight. The opening of the bell is 1070mmx700mm. I am also a bit concerned that it might crack and I wouldn't want to handle a cracked slab when the fire is burning

So I am open to any suggestions.
6 months ago