|
|
Post by pinhead on Jun 20, 2017 12:43:48 GMT -8
The problem of spanning the "roof" of the bell in a rocket stove has always been something I've worried about. I've used Matt's half-barrel bells with success for low benches. However, barrels are difficult to find in usable condition in my area and are much more useful as the "primary" bell above the heat riser. They're also a bit difficult to cut due to their thick and sturdy construction. This led me to another resource that is plentiful in our area as it is replaced with its more modern equivalent. When I built my most recent rocket stove this summer, I discovered how I'll be building the ceiling/roof of the bells from here on out. It's a lot simpler and much stronger than I expected. I don't know what the limit would be on load bearing vs span, but it will absolutely work for a self-supporting bell ceiling. More testing will have to be made with regards to span vs weight bearing abilities. It's very simple: we call it "corrugated steel" in the US.  I quickly cut it to shape with a jig-saw (cuts through it like a hot knife through butter), laid it down flat and cobbed over the top of it. With a good clay/sand/straw cob mix at about 2- 1/ 2 inches thick, it is surprisingly strong; in my particular stove, it spanned approximately 4 feet and will support me standing on it (180 lbs). If I were making a four-foot "deep" bench I'd simply make the cob thicker with plenty of straw. Just wanted to share another "eureka" moment with everybody! |
|
|
|
Post by pigbuttons on Jun 20, 2017 18:42:08 GMT -8
Excellent discovery, thanks for sharing.
A couple of questions:
Was this the galvanized type?
Did you pre-burn off any coatings?
Thanks
|
|
|
|
Post by pinhead on Jun 21, 2017 10:52:51 GMT -8
Excellent discovery, thanks for sharing. A couple of questions: Was this the galvanized type? Did you pre-burn off any coatings? Thanks Yes, it was galvanized. No, I didn't burn off the coating; the temperature at which galvanizing coats vaporize is closer to the temperature of welding steel which is much higher than even a rocket stove can produce within the heat riser. Since this is used at the roof of the bell - where temperatures are drastically reduced, there is absolutely no risk of vaporization. EDIT: Zinc oxide fumes are produced at 1663°F (907°C). While these temperatures are often seen inside the heat riser and possibly inside the burn tunnel of a J-tube and the firebox of a PBB, nowhere post-riser does the temperature come close to this temperature. |
|
|
|
Post by fzurzolo on Jun 22, 2017 7:32:38 GMT -8
Great idea pinhead!
Now that you mention this I realize that I see this a lot in large construction projects. It's a very common floor type where a corrugated steel floor is overlain with poured concrete. Obviously the steel is much heavier gauge in that case. I think if you needed larger spans for the bell roof, you could pour some concrete in place (with or without reinforcing depending on the span) instead of the cob. If the span is very large you'd obviously have to temporarily support the steel while the concrete is poured, but for most cases I think you wouldn't need it. |
|
|
|
Post by pigbuttons on Jun 24, 2017 15:06:48 GMT -8
Pinhead, the reason I asked about the galvanized was because of the unusual color in the picture, and I haven't encountered any non-galvanized since the 1970's. I was confident that you knew what you are doing and I know that the bell isn't going to be an issue with off gassing.
Fzurzolo, the stuff for concrete floors is a bit different, yes slightly heavier gauge, and the roofing stuff is rigid 90 degrees to the ridges, but will curl up if bent with the ridges. For most applications, I would think 2 to 4 inches of standard concrete would require reinforcement at 90 degrees to the ridges every two feet or so. You'd probably want to lay a layer of expanded lathe down to help limit cracking as the constant heating and cooling will reek havoc on standard concrete.
|
|
|
|
Post by ronyon on Jun 25, 2017 11:00:43 GMT -8
Neat idea. I have been looking at using metal studs layed side by side to build a "pan" and pouring into that.
Sheet metal would work, but it would need support until the concrete set.
Narrow benches could be capped with stainless steam table pans,which could then be filled with concrete.
One could even build a wooden form so you could pour in place, but, that would be complex to craft, install and remove.
|
|
|
|
Post by pinhead on Jun 29, 2017 8:50:09 GMT -8
Pinhead, the reason I asked about the galvanized was because of the unusual color in the picture, and I haven't encountered any non-galvanized since the 1970's. I was confident that you knew what you are doing and I know that the bell isn't going to be an issue with off gassing. The stuff I used was old rusty galvanized stuff that had been taken down by the wind years ago. It was literally in a pile in the corner of a junk silo. |
|
|
|
Post by Orange on Oct 1, 2017 2:26:00 GMT -8
how about classic steel from old ovens? you have easy openings for inspection and cleaning.  |
|
