|
Post by Karl L on Jun 22, 2020 9:32:10 GMT -8
I did the first burn today, in the open air.
The combustion seemed good - no smoke after a while, and 'damp charcoal' smelling exhaust.
When I pulled the core out of the bell after the burn, I noticed that some edges of the ceramic fibre board were 'fluffy' and disintegrating. I noticed this on one of the two very small pieces to either side of the top box exit port (the piece on the other side was OK). I didn't notice this damage in the heat riser, which I guess might be hotter?
I am using Superwool HT board, which was rated at 1300C by the seller.
The datasheet says Classification Temperature: 1275C Continous use temperature: 1177C
Anyone got any experience of using Superwool HT board in a batch rocket or DSR2?
|
|
|
Post by Karl L on Jun 27, 2020 9:20:23 GMT -8
After the first burn I pulled the core box out of the bell while it was still quite hot. I noticed the sides of the core box (2mm mild steel, 570 x 550mm) were bulging ~10mm, because of differential heating of the centre of the panels compared to the rim. (I thought this wouldn't be a problem, but clearly it was.) One long piece of Superwool board, in the top box, was broken by the bulge (because it bulged inwards). After some thought I decided to cut some vertical slits into the box, to eliminate the bulging. This seems to have worked perfectly - no bulging at all this time, and the burn seemed fine. The core box seemed to remain strong and rigid enough, even with the slits. I also cut the unbroken long piece of Superwool board (~550mm) into two lengths, as there was some differential bending in them. I chose to place the cut at the Stumbling Block, so it could hold the pieces in place. Here's a photo of the slits: drive.google.com/file/d/1CDvk0gzGVhH3rfIhCmQl4r4LX8t3ezua
|
|
|
Post by Orange on Jun 28, 2020 5:44:11 GMT -8
that's good to know that 2mm steel will bend even after firepbrick and vermiculate insulation. And that CFB bends too. If you can please post mor photos.
|
|
|
Post by Karl L on Jun 29, 2020 2:05:12 GMT -8
I'll try to post some more photos, but first, to clarify:
I'm only using one 25mm layer between the hot side and the 2mm steel sheet, except in the heat riser, where I am using 2 x 25mm layers.
In the fire box this is 25mm Skamolex (i.e. compressed Vermiculite board) blocks, cut to the exact size of a firebrick split. This is so I can selectivly replace Skamolex with firebrick if I need to decrease the insulation value and increase the thermal mass (based on Peter's observations a few months ago). My thought is that I don't have to replace all the Skamolex blocks, but just some of them, to allow fine adjustment. Currently it seems to be burning just fine with the Skamolex.
In the heat riser and top box, I am using Superwool HT board.
The firebox ceiling/topbox floor, and the firebox/heat riser port wall are Superwool board. This is very fragile, but the ceiling doesn't get too much contact with firewood, and the port wall is quite well protected by the foor channel's vertical tube. If these prove to be too fragile I can replace them with firebrick, or perhaps insulating firebrick. Hopefully the loss of insulation value won't matter too much because both sides are hot (even if not the same temperature).
CFB bending The bending was mostly very small, but in the ~550mm long piece it was around 2-3mm. I can't post photos of this because I've already cut it into two.
|
|
|
Post by Karl L on Jun 29, 2020 3:45:31 GMT -8
|
|
|
Post by ahansen on Jun 29, 2020 23:02:58 GMT -8
can you adjust primary and sekondary air individualy? superwool in the back of fire box look a bit fragile
|
|
|
Post by Karl L on Jun 30, 2020 12:53:14 GMT -8
can you adjust primary and sekondary air individualy? I don't intend to have separate adjustments. I want it to be very simple to operate: Open or Closed. But it is possible to change the primary air CSA, as a 'build option'. The primary air flow restriction is not shown in the photos: I use some very thin Aluminium sheet, inside the 'door frame' (which I call the cowl), to create the same CSA as Peter's door frame. I may also experiment with directing the primary air flow: direct it onto the door glass (to pre-heat the primary air), or away from the door glass. (In a previous stove I could adjust the primary and secondary air independently. I used this during the charcoal phase to restrict the secondary air to a small flow. This reduces the amount of 'ballast' air flowing, but also keeps the steel floor tube cool. I was trying to collect as much heat as possible from the charcoal. I don't know how effective this was.) superwool in the back of fire box look a bit fragile Yes, I mention that in a prevous post. I don't think it will be a problem because the vertical steel tube will protect it a lot. But if it is a problem it's very easy to change it.
|
|
|
Post by ahansen on Jun 30, 2020 22:41:48 GMT -8
i would just think that sekondary air only maked sence when you could use it to give some extra air if you but to much wood and wanted to balance the fire killing some burn in firebox by shutting primary or giving some extra air with secondary. now in the DSR2 with visible flame you can keep track of burn
or as i would do, shut primary completely in the last part of burn making some char whit only secondary air open, the char can be used to quick start next fire or to build up soil tructure in garden soil as biochar..
otherwise i cant see why you dont just have primary it all mix up by the port anyway
|
|
|
Post by Orange on Jul 1, 2020 10:14:13 GMT -8
thanks Karl fro the pices. I see now there's no insulation between firebricks and metal, that's why it bended badly.
|
|
|
Post by Karl L on Jul 1, 2020 12:10:41 GMT -8
thanks Karl fro the pices. I see now there's no insulation between firebricks and metal, that's why it bended badly. In my opinion there is insulation :-) -- Skamolex and Superwool board are both sold on the basis of being insulators. But there's not enough insulation to prevent the large, thin sheets from buckling. The size of the sheets compared to their thickness is critical: When I cut slits into the sheets the heating of the steel was the same, but there was no buckling.
|
|
|
Post by Orange on Jul 2, 2020 8:46:53 GMT -8
thanks Karl fro the pices. I see now there's no insulation between firebricks and metal, that's why it bended badly. In my opinion there is insulation :-) -- Skamolex and Superwool board are both sold on the basis of being insulators. I tought those in firebox (not heat riser) are just firebricks.
|
|
|
Post by Karl L on Jul 2, 2020 10:01:41 GMT -8
In my opinion there is insulation :-) -- Skamolex and Superwool board are both sold on the basis of being insulators. I tought those in firebox (not heat riser) are just firebricks. No, in the firebox, currently, it's Skamolex. There is the option to swap out any skamolex 'brick' and replace it with a firebrick. I cut all the skamolex 'bricks' to the exact size of a split firebrick, so it would be easy to replace them, if it seems necessary.
|
|
|
Post by Orange on Sept 26, 2020 11:08:07 GMT -8
I noticed the sides of the core box (2mm mild steel, 570 x 550mm) were bulging ~10mm, because of differential heating of the centre of the panels compared to the rim. (I thought this wouldn't be a problem, but clearly it was.) One long piece of Superwool board, in the top box, was broken by the bulge (because it bulged inwards). Here's a photo of the slits: drive.google.com/file/d/1CDvk0gzGVhH3rfIhCmQl4r4LX8t3ezuaKarl, do you think welding a piece of steel like 5x25mm flat horizontaliy on a 2mm steel sheet would it prevent from bending? I'm not sure if I want to build a steel box just to cut clits on it
|
|
|
Post by Karl L on Sept 26, 2020 13:51:21 GMT -8
I noticed the sides of the core box (2mm mild steel, 570 x 550mm) were bulging ~10mm, because of differential heating of the centre of the panels compared to the rim. (I thought this wouldn't be a problem, but clearly it was.) One long piece of Superwool board, in the top box, was broken by the bulge (because it bulged inwards). Here's a photo of the slits: drive.google.com/file/d/1CDvk0gzGVhH3rfIhCmQl4r4LX8t3ezuaKarl, do you think welding a piece of steel like 5x25mm flat horizontaliy on a 2mm steel sheet would it prevent from bending? I'm not sure if I want to build a steel box just to cut clits on it I guess it might work - I'm not sure. The calculations for bulging are complex, and in the end it's just down to trying it and seeing, I think. The slits worked very well for me, in the end. If I was going to do it again I guess I might try building a frame out of 25 x 25 x 3mm steel angle and fitting 100mm-wide strips of sheet into the frame to form the sides, tack welded at one end only.
|
|
|
Post by Orange on Sept 27, 2020 9:20:07 GMT -8
tnx, good idea!
|
|