Starting build with 30 gallon barrel

I like the diamond wheel on the grinder for thin steel because it lasts for a long time. There's alot of friction though and it leaves a heck of a burr. It looks like you used it to your advantage!

 

Kinda like the jelly roll. Once in place, just run a few wires through the wool. Wool stays where it's placed.

 

I think the intended use of your furnace has a lot to do with the style of lid you make. Some of the folks here do elegant builds for furnaces used only at aluminum temps. That means they can run their furnaces much cooler and for much shorter times than if you are doing iron melts and I suspect smelting iron, a goal you stated in your first post, will be even tougher on the furnace than simply melting iron stock. It seems clear to me that prolonged heat is a significant factor as it seemed like 2 one-hour iron melts were much less damaging than one 2-hour melt. This likely has to do with the whole system reaching a higher equilibrium temp and the shell being heated more (both are damaging) than in the shorter melts.

Based on my prior 4 lids two of which were wool and one cast monolithic refractory, none of them hold up for a long time. The monolithic refractory was the most durable, the flat pancake-style wool was the least durable. Book stacking helped the durability of the wool lid. Using IFB dome-stacked worked pretty well and might have been fairly durable, but I have to include a chimney on my furnace and that adds some complications as well. It might have helped if I had domed up the book-stacked lid. I did not domne it very much and with time it sagged some and that contributed to its failure. It held up pretty well for 5 or so melts and then started to flake Satanite. I repaired large or small flakes every burn after that. Eventually it just started to burn worse and the steel shell that was holding it became weakened too. That shell warped some from heat and that caused distortion of the wool----not good.

My most recent build is based on those experiences. I am using segmental plastic (castable segments would likely work as well) refractory in a way that does result in a dome whose segments can move some without cracking and the shell is designed to minimize heat-related warping. Time will tell as it has only had one melt. But, this much I know, the other three styles will fail in twenty to 40 melts. I am very hopeful that the segmental style will be better.

I would be very cautious about building a book-stacked or jelly roll style lid for your intended purpose. They are proven for aluminum and bronze, but not for iron. I would also try to include some sort of joints in any refractory/wool lid. I would also avoid a flat lower surface lid design.

Just one guy's perspective.

Denis

 

@Melterskelter, really appreciate your comments!

I will be using the top part of the steel barrel that I cut off yesterday for lid shell. It’s 11 inches deep. I was thinking about cutting that down. However, sounds like it might actually be better to use the entire 11 inch depth and install wool and refractory in a domed shape on inside of lid. I have 25 feet x 2 feet of 1 inch thick wool on hand, which should hopefully be enough to do whatever I want. Need to be more careful with castable refractory. Have enough on hand but not much wiggle room. Worst case, I just go buy some more, I suppose.

In a way, happy to hear that lids tend to fail pretty quickly. Was the case for my first furnace. I thought that I just screwed up lid when making it.

After lid failed, I used fire brick. Was suboptimal. Bricks didn’t last too long either. Even managed to melt one of them.

 

I am not sure if you mean you might make a lid that is a total of 10 or 11 inches thickness. I don't think that is what you mean. But, making the lid very thick may not be helpful at all. Mine have failed at the hot face first and eroded from there. It looks like uneven heat may be a big factor in the failure and the reason monolithic lids don't fare well in iron furnaces. You can see the uneven effect of hot gases on the segmental lid I recently uploaded where the dark areas are those subjected to highest heat. It is asking a lot of any ceramic material to stretch and bend to accommodate such uneven heating. How much better segmental ones may work is still an open question. But there has to be a good reason for Mifco using segmental refractory.

Denis

 

lol, definitely not. Given that the lid shell is currently 11 deep, I have room to create a domed hot-face in that space.

@Melterskelter, the segmented design is really interesting. Do you have any issues with heat escaping through the segment joints?

I’ve been ruminating over lid design for a few days. One option that I’ve considered is creating segments that are essentially boxes with inch to half inch walls. Each segment is filled with a couple inches of wool.

 

No trouble with heat escape as the wool backing prevents any jets of gas that might like to occur and the fit is actually pretty good anyway. As long as hot gas does not flow over wool, it won’t melt. When it deadends on wool, nothing happens.

Boxes? Not sure what you mean exactly. You might try it, but refractory in closed loops does not do well regarding cracking.

Denis

 

The idea was outside of each segment, on all sides except top was casted refractory. Inner part of each segment was wool.

I realized that it wasn’t the best idea I’ve ever had once I mocked up segment form using construction paper.

 

To remove a cardboard form from the inside of a furnace is not differcult. Use fire! I made a round wooden form when I cast the hot face of my furnace, and just burnt it out.

 

So, Kelly, given your furnaces are very gentle and uniform in their heating characteristics due to them being resistance-heated, I am supposing they are not inclined to crack? Also, how hot do you estimate the walls and lid of your furnace become when melting aluminum? Dull red, bright red, white?

Denis

 

I see you were replying while I added a couple lines to my above post. How hot does your furnace get?

Denis

 

@Al2O3, lid looks really nice! I can see how that would save a lot of refractory/thermal mass. That was part of the motivation for the design discussed above. However, one of the biggest problems that I encountered with my segmented idea was precision. The form and then the casting would have to be perfect. Otherwise, I'd end up with gaps between the segments. I might have still been tempted to give it a shot, but I'd also have to to calculate the exact amount of shrinkage refractory would experience when drying/curing. Then, I started thinking about potential for expansion/shinking during heating/cooling cycles. In the end, I concluded that a segmented design was a bridge too far for me given that this is my first foray into the world of castable refractories.

I just poured refractory for hot-face last night. Based on outcome, I think that I'll stick to the basics for this project. . Cardboard concrete forms just didn't work well for me.

Thickness of refractory is not consistent around circumference of shell. Had some bulging and form movement while emplacing wet refractory and vibrating it down. I thought that everything was braced well enough. Guess not. Probably, wall thickness varies by as much as 50%. I *think* that shell is still servicable. Thinnest area (that I can see so far) is still 3/4 of an inch, perhaps a bit less.

Was an interesting few hours. Learned a lot. Need to decide if I want to scrap this first attempt and redo. Right now, I'm leaning towards a redo.

I could fix a few things second time around. Biggies are:

1. Build a more ridged form to get more precise pour.

2. Add more vibration. Ended up wasting a lot of time waiting for refractory to settle.

3. Adjust tuyere angle. Ended up with a slight upward tilt. Not too bad but would have preferred it being straighter.

 

Question: are a lot of holes on outside of refractory an indication of a problem, i.e. rest of shell might not be structures sound? This is what I made last night.

see below pic:

 

I agree that there is a reasonable chance that uncontrolled cracks probably would not cause collapse of a well-domed lid. My only caveat is the uncontrolled part. If they are not in such a pattern and at such an angle as to allow fallout of segments of the lid, all is well. Who cares about such cracks. The problem is that the cracks may occur at random and may cause premature failure. I am hoping to control (somewhat) the cracks by pre-making a set. How that will actually work out in practice is part of the point of the trial design. It makes a lot sense to me that it should work. And there is precedent for effective crack control in "expansion joints" in cast materials like sidewalks as an example. That is most of the basis for my hoping it is helpful. BTW, the second 2 hour melt today for 65 pounds of iron showed no "volunteer" cracks or evidence of injury to the segments.

It is true that there are a variety of placement type options in the different refractories available. The plastic I chose to use is a form of refractory intended for high temperature and direct contact with molten iron. I know of no tougher formulation commonly available though my knowledge on the subject is pretty superficial.

Ease of fabrication was a very strong point in favor of this plastic refractory as I had only to make a single dome segment mold. Had I used dense castable (which sits neglected in 3 full bags in a corner of my shop) I would have had to fabricate two dome surfaces and 3 accurately made sides with a clamping system. What I used had one dome segment that was reasonably dome-like and the sides which were very crude serving only as guidelines for dimension. that was a lot simpler form to make. One other favorable aspect was the fact that the plastic was ready to use out of the box.

Your suggestion for making a segmented furnace cavity nearly mirrors one I have in mind. I expect to do that build in the next month or so. I think the segments will be crudely keyed. They will sit on a stepped floor as you suggested. They will be wrapped with 2 inches of wool and then gently banded. That whold works will fit into a shortened 55 gallon drum and will be "back filled" with an inch or two of pearlite. that outer layer of pearlite should not reach breakdown temps and will tend to gradually settle more or less gently packing the hot face and wool into place. I do not think it will compress the wool too much. The cut-down drum also sits neglected in another corner of my shop.

Denis

 

That will certainly not fall apart barring any gross unseen flaws. 3/4" is sufficient. If anyone notices it's off center tell them you employed a special technique to enhance vortex oscillation. Unless your furnace gets dropped or something your walls wont see any structural forces other than expansion. Dont be surprised to see some cracks develop but they will be of no consequence.
This is where patience comes in though. You should be able to remove the cardboard form by now. Let it air dry as long as you can. Days or even weeks if you can.
If you have an old style incandescent light bulb hang it in the bore for at least a couple days before you fire it (after it has air dried as described above). The water has to be removed but it cant be rushed. That will give you plenty of time to get your outer shell together.

Pete

 

@Petee716, lol, gotta keep that vortex oscillating at optimal frequency!

Cardboard forms are gone and main body is drying out. I made the refractory with as little water as I could get away with, so hopefully that will payoff when I start the heat up curing process. Fingers crossed. Will let that sit for a few days in the un-air conditioned top floor of my garage before checking on it again.

I’m a bit annoyed, though. I made the furnace an inch higher than I originally planned. Now, looks like I’ll be a few pounds short of refractory for lid. I need 6 lbs at an absolute minimum.

I really don’t want to buy another 55lbs bag of refractory for just 3 or 4 lbs!

If there is any appropriate refractory that I can buy online in small amounts, I’d appreciate a heads up.

thanks all for your continued help!