Air over/under?

[doop]

I am almost done with my 3x8 arch, but have some questions regarding the air under. I have been building it as per the instructions the university of Vermont suggested, but now it says I need to drill 12, 3/4 holes per square ft. Which doesn't leave a lot of metal left in my floor to support my refractory cement and wood. I am wondering if this will bow or bend in after time and heat. I used 5/16 steel for my floor. I'm thinking of laying it out to get as many as I think it can hold and try it out for the year or possibly doubling up on the bottom plate. Any input would be appreciated.

[Paddymountain]

When I did mine over, I took 2" firebrick and drilled them for the floor of firebox. I'm thinking 5/16 steel is going to warp like crazy for you
with the amount of air and fire needed to boil syrup.

[doop]

I'm going to be pouring 3 inches of refractory cement on top of that with tapered holes from 3/8 on top to 3/4 on bottom.

[Russell Lampron]

This is what the inside of my 2x6 arch built by WF Mason looked like before I bricked it. This is what twelve 3/4" holes per square foot looks like. I think the bricks are 3.5"x7" which comes out to 147 sq inches for an area of 10.5"x14" for 6 bricks. 12"x12" is 144 sq inches. It boils like crazy and there was no warpage of the square tubing that supports the bricks.

1932319324

[TapTapTap]

The engineer in me says don't worry about the heat on the plate since the increased combustion heat occurs at some distance above the orifices where the oxygen and fuel combination are optimum. The little devil's advocate in me says to protect the surface with firebrick or refractory cement.

[Paddymountain]

Now I'm on the right page. Yeah , I wouldn't think you will have a problem.
The frame my firebrick set on made of 1/4 angle iron, hasn't warped in 2 years , and
doubt if it will over time.

[DocsMapleSyrup]

Doop

When I built my 2x8 arch, I put 3 - 3/4" holes in each full thickness fire brick for the floor. The second year, I added two more 3/4" holes in the firebrick for a total of 5 holes per firebrick. Last year, I took the two middle firebricks out of the arch floor, and if I had to do it again, I would use 3/16" thick 1.5" angle facing upward in a "V" for the floor in order to allow for ash to insulate the angle iron. It wiill also make the air to move under and through the fire on the AUF. The brick creates obstacles to air flow through the floor of the arch. I also have AOF and use a single 1HP bounce house blower that is split and gated to adjust the air for AUF. We live pretty close so if you want to come over and see what I'm talking about, let me know.

[doop]

Thanks for the responses. Doc it would be great to stop in and check out your setup, just name the time and of course address. I work til 315 mon-fri. Anytime after though I'm available.

[maple flats]

Are you saying you have a 5/16 plate for a grate, or a 5/16 floor. Most commercial evaporators have no floor, they rest on a concrete floor, but then most grates are cast iron. If you go with the refractory with holes approach like offered in the document you reference, it gets supported from below with a few spaced out firebricks on edge.

[doop]

I have 5/16 plate where the grates would be, and I'm going to pour refractory cement over that.

[Mitchell tapper.]

I did something similar on my 2x4. Instead of a plate, I made an angle iron frame to set the refractory on. Then made a wood mold to make the base. Set it on the frame then filled around the edges with more refractory to seal it up. I did add wire so if it cracked it would still hold it together. Doesn’t appear to have cracked though after 4 seasons of use. I fire with a blower, keeping the firebox full of wood as hard as it will run.1938719385

[murferd]

When I did our 30" x 10' conversion from oil to wood, I used fire brick with three or four 3/4 holes in each brick with high pressure blower. Didn't seem to boil good enough to suit us, made a grate system out of 2" angle, V up with 3/4 gap between each & the sides. Wow, wouldn't know it was same machine. Angle has never changed(warped) since we put it in, once full of ashes it's fine. The fire brick thing was a lot of work, save yourself some aggravation.

[mol1jb]

We also use a metal grate of angle iron up vvvvv. Easy and quick to weld up and works great.

[doop]

This is what I'm trying to do, I'm not looking for grates I'm looking at forced air from above and below the fire.Combustion Efficiency for Maple Producers - University of Vermont

PDFUVM.edu › ~pmrc › Combustion

[DocsMapleSyrup]

Doop. Sent you a PM