My Attempt at an IFB Domed Furnace Lid

Well, my satanite/insulating wool lid has worn out largely because of the chimney and its associated load on the lid and the diversion of hot gas caused by the chimney. Since seeing OIF's lid a while back I have been toying with giving it a try. Here are some pics of the beginning of that quest. I am using 2600 degree brick as that is the best I can get locally and hope I can protect them with satanite and a better lid design with the chimney being part of the design rather than a make-do afterthought.

So far, so good.



More to come.

Thanks to OIF for his original post and design.

Denis

 

Easier than it looks, isn't it?

I think you'll find it to be very durable. I did not use mortar between bricks so they could grow and rise without pressing against the cold outside rim. I was concerned they would grind against each other with each rise and fall but after 320 melts I can't see any sign of that.

Congratulations on a great fit!

 

Looks great so far! Doesn't look THAT easy to me though... Good job setting everything up to make nice accurate angles and cuts.

Jeff

 

Yah, “easy” would not be the first word that comes to mind. I spent likely 4 to 5 hours thinkin, measuring, thinkin, cutting, fitting roughly, thinkin, refining fit etc. This looks like a basic CAD design problem that could be calculated to thousandths of an inch and angles to degrees, minutes, and seconds. In my shop not exactly... the welded can is quite accurately tacked and welded, but there is still a 1/8” variance in diameter which has a significant effect on fits. So, not only are the blocks numbered, but their position as to how they clock in the can is marked as well.

Next, fitting the wedges will be challenging since all three fitting surfaces have to be pretty accurately made. (In the large blocks there is some leeway as the end that terminates where the chimney will be can “run wild” and will be trimmed to a circle as a last step. ). Doing wedge fitting with the blocks in the can would be really hard. So I’m going to layout a 20” circle on a piece of plywood and secure 8 wood blocks at 45deg intervals. I’ll prop the refractory blocks in position and the fit the wedges. Still those fits will vary a bit from the actual in-the-can fit. So, I’ll leave the a bit plus in the mock-up and true them up in the can.

A 10” disc grinder with a tilting table has been essential to doing final fits. Hand block sanding results in some unavoidable rocking and rounding of sanded faces. I would estimate that 10 thou increments or less are ground off for final fitting.

Denis

 

That's the interesting part, it really is pretty easy. Just take your time and measure carefully. I did calculate my angles on Fusion360 but my ring is more out of round than his, and I had to selectively fit everything several times to find the best fit. In the end it really didn't matter much because the errors in fit just does not affect the serviceability much.

The little wedges were quite easy for me. I just measured each side (they were all different), ripped them on the table saw with the blade tilted the right amount, then dropped them in. I had a few short ones, they got mortar against the ring to hold them up and snug but that was just a couple.

Initially I did not coat my brick walls with Satanite, I coated the floor and underside of the arch. The flue opening is the most important area on mine. The Satanite in the flue is hard enough at temperature I've taken to rapping my tools against it to clean them back into the crucible. Seems kind of stupid thing to do but does not seem to damage the Satanite.

I have no idea how thick I put it on. I mix it thin and brush on a coat, let it dry a couple of hours, brush on a second coat and after a couple of hours start using the furnace. Touchup is a breeze for me but I don't do it often. Said it before but the best thing about Satanite is you can let it dry in the bucket then add a little water months later and mix it up to brush more on.

 

In progress as we speak... this setup makes life easier. Allows the outside end of the wedge to run wild. Flipping block bottom up so its top is on top of the gap and scribing is pretty slick. Finish the cut on the disc sander.





Mark the outside end with pencil line as a target for final cutting but it was only a guideline not a precise cut-to line. It’s going pretty smoothly.


Denis

 

Its a bit like a jigsaw puzzle.
I sort of accidentally got mine cut right.

.

 

Like this?



So happy to have the fitting done with 1.5 bricks left over. Phew!

Denis

 

That disc sander was cheating. Nice job!

How long is the cure cycle?

 

Thank you!

If you are not good you have to cheat.

I hope the "cure cycle" will be brief. I'd like to fire this up by the end of the week. But there is a fair bit of welding and metal fitting yet to be done as well as some machining on a few sold straight edges.

I took a few measurements to help the next victim I mean person who decides to do this. The angles will vary slightly from brick to brick or wedge to wedge due to final fitting.

Tail end of brick side angle.



Wedge side angle



Nose of full brick.


Denis

 

I just noticed that I had failed to post this tip. So here it is in photo form in case it is of some use to “the next guy.”

 

Great tip! I just measured the angle of the adjacent brick and cut everything based on top dimensions. I got lucky.

 

Too much damn math gives me a headache..... nice fancy lids.

 

Yabut, I didn’t use no stinkin math. I just propped up a quarter of the circle of bricks and used a square to scribe the cut angles on the bricks. (Carpenters generally don’t use trig to layout trusses etc either, but do some pretty cool stuff). Those angles got me close. But, final fitup required tweaking things here and there since the lid shell was not a perfect cylinder. I just tried to take my time was careful. All the bricks were cut to approximate size on the bandsaw but were final shaped on the disc sander.

Denis

 

Did you fire it yet?

 

Noooo..... I worked on the lid lifter mechanism today and will continue tomorrow. Lots of other stuff has kept me from spending a lot of time on finishing up the lid. Helped my son by welding up an aluminum diamond plate lid for his house, three straight edges machined and shipped, grand kids, yard....the list seems to go on and on. But, it will get done and in the next few days. I am very anxious to fire it and pour some more straight edges. Will soon be working on the pattern for a 48" 50 pounder which should be interesting.

Also starting to pipe dream about a precision right angle pattern. And then there is always the larger heat treat oven.

Denis

 

Denis,
If you get round to the Right angle....Let me know I'm currently on the lookout for some right angle plates for my mill.

 

It should be noted that a fire brick can be cut in half on its diagonal, and this eliminated the small pieces that may be prone to falling out, and there are no wasted pieces associated with this method.

Why not just cut the bricks on the diagonal with zero waste and zero chance of dropout?

Melterskelter's brick layout/cuts are precision made, unlike mine, and his fit is much better than mine, but my bricks sit on top of 1" of cast Mizzou, and so they don't have to be exact.

But the question still stands.








.

 

Are you suggesting there is a risk of dropout in the way I cut the bricks? Not sure about the above post.

Your lid looks like it is 18" diameter and mine is 20". If you lay it out you can not cut on the diagonal down the center of the brick to achieve the greater outside diameter and fill the center. you have to offset the cut to be diagonal but leaving an inch or so off the corner-to-corner diagonal. That also means you have an array of 1" or so wide butts (fragile) making up the vent edge. I did not spend the time to lay it out precisely, but I think you might get buy with 11 bricks so cut. Mine took 12. I liked the idea of having nice beefy pieces of brick surrounding the vent rather than twice as many and twice as small pieces at that vulnerable location.

Denis