Top's A10 furnace Project

I decided to go for it with items on hand at home. I also made a Venn diagram:



Seeing Kelly's table made me want to improve my setup. As the air chisel worked before, I decided not to try the reciprocal saw method.
Seeing the table above with the polymer bushings reminded me of changing suspension bushing on the old Jeep to fight the 'death wobble'.
Thinking of that reminded me that I had some reclaimed screen printing squeegee material in the basement, sort of a low durometer polymer material about 3/8" (9mm) thick., softer than a Jeep bushing.
I cut one of those into 8 piece approx 2 x 3" (50x75mm) and clamped my molds in between them and to the table, so there would be a small degree of freedom to shake but not so much as to move or fall off the table.
So not a pure loose mold and not a pure vibration table, somewhere in the middle so to speak. Before I either worked on the floor or clamped wood around the mold to keep it from walking off the table.
Things seem to shake out fine, other than needing earplugs for the chisel and the splinters caused by the chisel hitting the sacrificial wooden block.
The cylinder seemed to fill faster than anticipated, I think I neglected to minus out the 4 x7 x 3/4" (100 x 175 x 19mm) 'knockout' panel from the overall needed amount.
I did a re-calc based on the third and final layer being 3" (75mm) deep rather than 4 1/8" (103mm) and ended up right at the brim.
Having a flange on the top of the outer form would have made for less spills loading in the refractory.



I appreciate all of the input, thanks!

 

Thanks Kelly.

I am starting to think about a dryout procedure. I have yet to do this at scale, so far I have only cured out a thin Mizzou lining on Kaowool type material and tempered crucibles.
Here is what I found do far for the refractory:


Would starting out with light bulbs in porcelain sockets be the way to go for getting through the 100-200F (40-95 C) range?

After that I thought I could use the burner from the small furnace. I don't have anything with a controller so it's going to be by thermocouple readings and burner adjustments.

 

+1 to pouring in 1" courses and vibrating them each in turn, as Jeff said. I did the same thing and it worked out really well. It's a lot easier and less failure-prone than trying to do the whole thing with makeshift equipment. Also, not to state the (hopefully) obvious: Don't let the refractory set between courses, try to get each poured and vibrated w/in the working-time of the previous one

 

This is what I did and it worked out well. After that I switched to a small burning charcoal pile, built that up bigger and bigger over hours, eventually running it with forced air, then at the end switched to my oil burner.

 

The lid piece and the top and bottom of the cylinder were all done as single pours.
The cylinder was split into 3 sections with about 8 pounds (3.63kg) mix and 17% by weight water each section, applied wet on wet. The mix took up about a gallon ice cream pail in volume dry and so I mixed in the water in a 2 gallon bucket. The last section did not need all 8# so I re-figured and mixed the last batch short.

 

In my excitement to move forward, I tried de-molding the big doughnut after 30 hours...failure.
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That's frustrating to say the least, can you make it thicker next time?.

 

Yeah, sorry that happened At least you learned on a cheap-to-redo part though.

I'd second that. I may have the concept wrong, but I.I.U.C. because the volume is growing by a power-of-three, adding a bit more thickness brings significantly more strength than simply the extra thickness would suggest.

As for curing, assuming this is a cement binder:

1. You're doing the right thing by very carefully controlling your water mix by weight.
   1. "Too Much" water in this situation is a bad thing.
   2. You may consider using a little less. Remember the mix probably absorbed some humididty from the air while sitting in the bag.
   3. You only need just enough water so it's minimally flowable. Since you're vibrating, that means you can probably get away with less than what's on the instructions.
2. You can significantly increase the strength by letting it cure air-tight-ish (keep it wrapped in plastic) and wet (mist it occasionally).
3. It takes about 26-days to get near it's max-strength I'm guessing it would be good to keep it wrapped and wet the whole time if you can.
4. Ceramics (in general) have terrible tensile-strength compared to compression. Consider adding something that behaves like re-bar:
   1. Furnace/kiln/boiler supply companies (and amazon) sell these (approx.) 1" deformed/crimped stainless steel "needles" purpose-made for this. This is what I used, I think it was 2% by weight (maybe 4).
   2. I've seen others embed a simple steel mesh, like bent-up coat-hangers and the like. I can't speak to this method, or if it's compatible with refractory and the expected environment.
   3. Perhaps there's a clever way you can not put it under any tensile-strength. Like figure out a way to add a steel skin w/ strapping that carries all the load when moving the lid.

HTH

 

Thanks Guys. I appreciate the input.

I originally designed at 3/4" (19mm) but ended up making both flat pieces 1" (25mm) after Razortoe (r4z0r7o3) mentioned the same. I will have to think more about that.

I checked again this morning, the green strength is slightly better 12 hrs later at room/garage temp but still seems in the realm of uncured. I have not applied any additional heat, will work towards that to save the cylinder. I also noticed that the refractory seems to be sticking more to the wax fillets and paste wax than expected. So I may have gone backwards in mold prep rather than forward. The one that released nicely under similar conditions was 2 days cure, no wax, and only shelf paper and epoxy fillets as the release media. I also purposely destroyed that mold during de-mold, I tried not to destroy this last one, hoping that my 'improvements' in draft and coatings would make the part release much easier. I ended up tapping some carpenters' wedges between the foam and plywood and those caused the cracking to start. Once I saw that the broken parts were not releasing cleanly, any hopes to patch up what was there while still green went out the window.

Reading your post now, looks like we are typing at the same time. Thanks for all of the ideas.

Current plan is to eject the remainder of the doughnut out of the mold, clean, and maybe mummify it with packing tape only for the next pour, and see if I can rig a warming system to cure out the new doughnut and the existing cylinder.

 

Yeah, keep the temps warm, I missed that suggestion from Kelly, he's right. Another idea is to wrap it plastic, then in cuddly warm blankets (seriously), so it can keep itself warm and slightly damp at the same time.

Edit: Missed that this is insulating refractory. Forget the SS Needles idea, I think those might be anti-helpful here.

 

Thanks Kelly. I already cleared the mold. I am planning to throw some chunks from that into the bore of the cylinder , add heat, and test them before de-molding the cylinder.

I just got off the phone with HWI. They said the same things as everyone here mentioned about covering, temps, and settling out of product when only using a partial bag. They also suggested different releases besides wax-based (vegetable shortening, PVA, WD-40, automotive grease).

I am at the bottom of the first bag. Trying to decide whether to use it up or setup the next new bag to be broken into 4-5-6 smaller bags with a more uniform mix.

 

IMO all is not lost. I'm optimistic if you can get what you have into a warm-ish place, and keep them mostly air-tight for a few weeks, mist them if you like - they'll be okay. Maybe just handle them a bit more gingerly before firing them.

Someone can correct me, but my understanding is the small amount of cement you're dealing with here is just there to make the thing solid and stable on it's way to firing. During firing the cement is all but blasted away, and it's the refractory-particles sintering together that gives the final strength. But again, maybe I'm wrong about this.

Since I don't remember reading that you mixed up the first bag, let's assume that things did settle. In that case, I wouldn't use the leftover as-is. You should either throw it out, or if it was expensive for you (no judgement) consider dry-mixing it thoroughly into the the new bag, then start taking from that. Either way, definitely dry-mix the new bag before using it. My memory is getting bad, but I think I remember doing this by hand in a 5-gallon pail with a stick or angle-iron. It was labor intensive but also way more than my wee lil drill could handle. If you happen to have (or can borrow) a rotary-hammer drill, it might be strong enough on drill-mode to thrash a dry-mix with a piece of "J" shaped bent up rebar chucked up. Just a guess though.

I don't think it needs to be "perfectly" dry-mixed. Just enough to mostly remove any obvious stratification/settling. The tips given above (minimum water, keeping it warm, moist, air-tight, and given lots of curing weeks) are likely more important long-term.

 

Thanks Razortoe. I do not feel defeated, maybe a bit humbled and afflicted. Perhaps this 'lessons learned' loop will save me or someone else a similar problem in the future.

I think the primary failure was not enough time and too low of temp combined with me trying to horse it out of the mold, which was not using an ideal release. I am not convinced that my problem was induced by stratification. This bag was started for this furnace but there was time between the initial opening and this latest round of molding. I would mix things around a bit but did follow any sort of method to insure a distributed mix. With this failure, I will need to dip into a new bag so I am wondering if I should just use up what is or cross-mix the tail end of this bag into the new bag and then bag it up into smaller sealed bags and use as needed.

Throwing up a few more pictures, sort of like when people play cards together for years and already know what's in each other's hands after they bid. I tried breaking off another piece that had been heated up for 12 hours along with the cylinder. The green strength was better than before and I could feel some #2 paste wax on the smooth surface.

I have the cylinder under an IR lamp and the inner cardboard tube is getting somewhere around 140F / 60 C, very warm to the touch but not at the limit of what a person can hold for any period of time (can't find a thermocouple to confirm exactly). I have some tin foil protecting the edge closest to the lamp, sort of like keeping the edge a pie crust from burning in the kitchen oven. I am planning to have it at that temp for 24 hours and then move the part inside as we are expecting frost next week. The heating surround is made from another concrete tube I had cut for a bigger furnace and the 'lid' is the cutout from the XPS of the mold I am needing to redo.

The doughnut mold has been cleared and cleaned and I re-did the fillets with some painter's caulk that was left over from something else (and was starting to set up in the tube and squirted out the plunger side of the tube...). Where the refractory stuck to the wax and shelf paper was the 30 hours at room temp, where it released better was at 48 hours. Once I figure out my refractory use-as-is or cross-mix thing, I will cast a new doughnut and give it more time and heat before de-molding, probably a destructive de-mold so as not to rely on part strength as Kelly suggested.

 

I did the math and the last little bit from bag#1 would be enough so I went for it.
I used Crisco brand vegetable shortening as a release on the caulk and the foam and left the shelf paper as clean as possible.
I went with 18.5 % water, splitting the acceptable range. It did not seem much different mixing or vibrating into place.
Mold is sitting covered in plastic on the CNC table at 70F/ 21C. I will add some heat at 24hrs and then let this one sit a few days before I de-mold.
I will need to get out the next bag to mold the tuyere, which is stuck away on pallet behind this and that. I should use some of the wait time to re-org the garage before winter (frost last night, tonight, and tomorrow night in the forecast).

 

I removed the forms from the cylinder. Things went pretty good. Again some signs that the #2 paste wax is not the best release for K-30i. The packing tape worked a treat. It will be another couple days before I go after the de-mold of the remold of the upper doughnut.

 

Looks great!