Arch Grates

[RC Maple]

9914

I have question about arch grates. I have never boiled on anything but my barrel evaporator so I haven't seen anything else. My grate in the firebox gets mis-shaped every season. It is made of square tubing and it tends to sag in the middle to the point I don't think it would make it through 2 seasons. Is this because the ashes and coals can't fall through the grate and away from the metal and so the metal stays hotter and bends? I don't see others on here ever talk about replacing grates and can't imagine they are made much different than mine. I have just had a new grate made every year and it isn't a big expense but it is one I could do without. Here is a picture of my grate. You can see the coals can't fall through there very far

[Super Sapper]

A lot of people use angle iron instead with the point down to allow the angle to fill with ashes which will insulate the metal. I used the same concept with unistrut that I had laying around and they are as straight as the day I put them in 2 seasons ago. I put in Air Under Fire this last season and got the fire hot enough to have flames come out the top of the stack when I fired but it did not affect the grate at all.

[psparr]

The angle iron is probably the best solution. I use sections from a cast iron radiator and they hold up well.

[DoubleBrookMaple]

My $.02 worth...

Research on this site will back up the angle iron "V" system as long lasting... but...

With the small distance from the floor a lot of heat must be captivated, and the large cross section (area) creating low air flow across the metal, are a perfect storm of intense heat. Another noteworthy item is your long distance across, creating a long moment arm in the middle of the cross members. Just like building a deck without any posts supporting the center.

My plan, given the existing dimensions, would be to use angle (minimum 3/16 thick, 1/4 is available), and definitely add a center angle "V" perpendicular to the cross members, and put 2-3 "feet" under it to support the center from sagging.

I could not have this problem with mine, as it is only 14 inches across, and I have a blower.

9916

[Super Sapper]

I would space the cross pieces closer together to keep larger coals from dropping through and cutting off air flow. I used a piece of 3/8" or1/2" rebar tacked on the side to space mine out. You may also have to watch out for the incoming air short circuiting under your grates and straight up the stack. Air will take the easiest path and I have noticed that if I do not keep the coals and wood spread out that the forced air goes right around and up the stack. With not much space under your grates you will need to remove the ashes often to keep air flow.

[RC Maple]

Thanks everybody for the replies. It looks like angle iron for the cross pieces should be the plan for the grates. If the metal shop hasn't already made them I will see if they could do that.

[RC Maple]

10191

I just got my grates back from the shop. I thought I would try the angle iron with the point down. My of grates have some life left in them so I will use them to start the season. Everything should be ready to go now - just a few more weeks.

[brookledge]

The best option is to look around scrap yards for cast iron grates or radiators that can be cut to make grates. Normal angle etc is only mild steel and will sag under the weigh of the wood
keith

[maple flats]

The angle iron should be spaced about 1/4" max. Then you should use firebrick to close off the open space behind the grates, to force the air thru the grates.
super sapper, you are likely seeing the flame re-ignite and do not have flame the entire length of the arch and stack. I had that before I added AOF (air over fire), I would get a ball of flame at the top of the stack. After adding AOF I no longer got it. What was happening is that the oxygen for combustion ran out before the wood gases were all consumed. As the super heated gases go to more oxygen they burst into flame. That is heat you could use under your pans. Try adding high pressure air in the firebox, that will mix and burn the gases so you get the heat where it is needed. You will boil faster, use less wood and see lower stack temperatures. Read about how to add AOF.

[Swampmapleman]

I made this grate out of schedule 80 2 inch black pipe. with 1/4 inch holes and a high pressure bounce house blower under the ramp it mixes the gasses quite well. Only test boiled so we'll see what happens. Dont want to cool the pans with too much air. What does come out of the holes is very fast so maybe its mixing all the gases before heading up stack. i have the blower intake covered up so its not getting tons of air. I have angle iron pointed down in between the pipes to trap ash and help insulate. No air can come from under the grates unless i remove the angle. The pic was taken before bricking. I have never uploaded pics so i dont know if it will work. also i drilled too many holes in first pipe. i have welded every other one up for now.


matt

[maple flats]

Let use know how well it works. I think it will help, but my guess is not as well as a HP air that is directed down into the fire from above. However I hope my guess is wrong. If that does work well it is simpler than the way the original plans were for HP over fire air. The plans show a HP nozzle every 6" and aimed from 6" below the pans at an angle of 12-15 degrees. Good luck on your design.

[Swampmapleman]

I don't think it would ever be true gasification like your setup just trying to improve the air through grates style. Just trying to be different. Will post how well it works as soon as the season arrives.

Matt

[lpakiz]

It been my experience that you need relatively little air under the fire to make it burn as fast or faster than you want. You are on the right track to have a method of restricting the air. You will need it.

[Super Sapper]

maple flats you are correct with the combustion after it hits the air. This only happens for about a minute after adding wood and then quits as I use pallet wood that is very dry. I was just using it to show how hot the firebox is and not have any warping of the grates. I'm not sure if AOF would help for me with the low moisture wood that I use as most recommend higher moisture for it to work.

[maple flats]

My wood is very dry until I use up the first stack along the side of the sugarhouse (5' high x 24' long) and it works very well. After that my well seasoned wood is brought from stacks in the field and put beside the sugarhouse for additional drying but it does not get as dry as what was there since the previous season. Since I got my RO I move a lot less wood, Last season I never even finished off the older wood, but at just over half way gone I had it refilled from the field but continued to use the drier wood. With AOF I never get that ball of flame I got before adding my AOF.