Drake's 38" Oven

[DrakeRemoray]

Good idea on the aluminum foil and the plastic....

I am building a 20" high dome. More of the Tuscan design...

Drake

[arevalo53anos]

Drake:

I realize that I could attach some pictures that I taked in the vanes phase.

Luis

[mrpbjnance]

Drakes oven size?

Drake - What is the size of the oven you built. It looks HUGE. Or is that just the perspective from the picture?

[DrakeRemoray]

Drake - What is the size of the oven you built. It looks HUGE. Or is that just the perspective from the picture?

It is a 38" oven. It looks huge to me too... but the interior is not that large.

Drake

[Marcel]

Things are not always what they seam.

It is a 38" oven. It looks huge to me too... but the interior is not that large.

Drake

(M) "Although the moon is smaller than the Earth, it is farther away!"

(M) Astronomy is my specialty.

Ciao,

Marcel

[DrakeRemoray]

Casting the Lintels

Hi All,

I chose to cast a lintel instead of using an angle iron. I chose to do this mostly because I am planning on casting a vent, so I had the material.

These three pictures show the empty forms, the filled forms and a closeup of the filled forms.

I used "Insulcast", a castable insulating refractory concrete from a company called pryor giggey. It looked a lot like the perlcrete, but it is supposed to be strong structurally up to 1800 deg f.

I have to let these cure (and cure them by baking at increasingly hot tempratures for a couple of hours according to the instructions...), the I will put them in place.

Drake

[Marcel]

Did you add Re-Bar to your Lentil soup?

(M) If you didn't add re-bar to your lentil soup you may not be getting enough iron.

(M) If you didn't add re-bar to your Lintel form, you may not be getting enough strength.

Ciao,

Marcel

[christo]

rebar and expansion

i'm a little curious about the rebar in the lentils. Long time ago I worked with industrial boilers and mostly insulation type refractory cements. So I do not claim to know what I am talking about in this instance.

Rebar has a different coefficient of expansion than most masonries.

I'd have to wonder how many heat cycles it would take to break the lentils apart. That may be why Marcel put only a single piece of relatively small diameter rebar in his cast. That way the overall strength of the casting was superior to the force the rebar could exert???

Here's where I need to ask the collective wisdom of the list - Does the chimney throat get all that hot? Does it exceed 600 degrees - i.e. does the soot burn away during firing? I like the casting ideas that are going on here - I want to make sure they are a lasting solution.

also might get away with very small diameter wire in place of rebar to avoid any thermal expansion differences.

Drake and MArcel - nice looking stuff!!!

Christo

[Marcel]

Marcel cast no lintels, nor dispersions.

[QUOTE=christo]i'm a little curious about the rebar in the lentils. <snip>

Rebar has a different coefficient of expansion than most masonries.

(M) That's likely to be correct, but steel may need to get a lot hotter than 700F before it expands enough to crak a casting.

I'd have to wonder how many heat cycles it would take to break the lentils apart.

(M) Maybe I was wrong in suggesting re-bar, but another builder put some in his vent manifold.

That may be why Marcel put only a single piece of relatively small diameter rebar in his cast.

(M) You must be confusing me with another builder. I made no cast.

That way the overall strength of the casting was superior to the force the rebar could exert???

(M) I doubt that. If freezing water can crack stone, then steel expanding can crack masonry. But perhaps the masonry expands more than the re-bar? Then you should have an air space around the re-bar inside the brick. Who said "A little knowledge is a dangerous thing" ? Let's get Luis, or other thermal engineers to clarify the effect of heat on rebar inside a masonry casting.

(M) I believe that steel starts to glow only around 2,200 F. and probably doesn't start to measurably expand before then. Though our ovens get hot, they don't get nearly that hot. Anyway, I'm through guessing, but I havent heard anyone complain of re-bar cracking a casting.

Ciao,

Marcel

[DrakeRemoray]

I did add 1 peice of small diameter rebar with each lintel. I painted it first per the instructions on the concrete...You can see it in picture 1 above...


Drake

[Marcel]

Paint on re-bar may be a &quot;slip plane&quot;

(M) Thanks, Drake for pointing out the Re-Bar in Pic. #01. I hadn't noticed it before.

(M) In my previous post I said I was through guessing but the paint precipitated this thought: In addition to slowing any possible internal rust, perhaps the paint might also serve as a slip plane. ?

(M) Keep up the good work!

Ciao,

Marcel

[DrakeRemoray]

Hi All,
I built the form for the vent area and cast it (after work today...not bad...). It is 22" wide at the widest by 14" deep and 12" tall. The walls are approx 2" thick, so the interior vent space is 18"x10" at the bottom tapering to about 10"x10" at the top.

The refractory concrete is pretty light, so I hope it won't be too hard to handle.

Drake

[DrakeRemoray]

Tragedy...hopefully minor

Quite a disappointing evening last night.

I came home and unmolded the vent, only to crack it all the way through on one corner when removing the inside mold. Advice to others: Think about how you are going to get the mold out, and be gentle! I think it is still going to be OK, it stands up just fine and with a little mortar it should be fine. (crossing fingers).

THEN, I needed to start curing the lintels per the refractory concrete manufacturer's instructions. I heated them to 350 on my grill (they didn't fit in my oven so I put some thick tile down on my grill to moderate the heat). 350 def F for 1 hour, then I raised it up to 450 for another hour, it got hotter than that for a while when I was distracted and when I came back out...they had cracked.

I wonder if what Christo said about the coefficient of expansion could have been the problem or if I got them too hot too quickly.

They still seem to be pretty sturdy, but I am worried. When I cast the vent, I had some extra concrete mixed, so I poured 1 lintel without rebar. I think I will cure that and see if it cracks. I may also used the cracked lintels if I can satisfy myself that they will hold together...but a big bummer. Pictures of the cracks attached.

Drake

[Marcel]

lintel spans, but vent &quot;compresses&quot;

(M) I spent about 20 minutes constructing a detailed response to your post about the cracks and then lost it during a "preview". Argh!

(M) Consider looking at my posting with images from a long time ago. If you go this route, be prepared to notch your plywood for pouring the hearth slab.


http://www.fornobravo.com/forum/showthread.php?t=294


Best of luck,

Ciao,

Marcel

[jengineer]

Aaaaaaaaarrrrggggghhh

Blcak Pirate Marcel -

I have had this happen too. Gets under 'ye skin. I have resorted, when making long replies or doing the dreaded "preview" to cut and paste my response to either a text file or a MS Word file. This way if the system loses it you still have it on another platform. I am sure that the members of the forum appreciate it when I use Word as I then fix my numerous typos.