Top's A10 furnace Project

Preamble:

After failing at bronze the 2nd time with the small propane (1 burner naturally aspirated) Amazon special, I found myself looking longingly at a bigger, shiny stainless Vevor 2-burner version...even though I have 2 furnace shells and about as many burners started in the garage. One of the shells has a completed frame with wheels and a lid w/ cast and fiber insulation and lift mechanism and a firebrick base, so like 1/2 done. Last week has been gorgeous early fall weather with it holding for a few more days...maybe it is time to make some forward progress before the refractory casting needs to be an indoor sport?

Here are the threads so far:

https://forums.thehomefoundry.org/index.php?threads/form-kastolite-using-styrofoam.2504/
https://forums.thehomefoundry.org/index.php?threads/resizing-55-gallon-200l-drum.2490/

Next step: I am a little concerned about getting my Kast-o-Lite 30i hot faces cast in good working order.
My plan was to cast a 'top hat' with a tuyere hole, now I am thinking it might be better to make it into 3 pieces, along with a separate tuyere.
What do all-y'all think about this? I was thinking of doing the floor casting a bit bigger round than the main cylinder, then the cylinder, followed by the tuyere and the upper brim.

 

Having done something similar as a one-piece, your idea is superior. Are you at all worried about the 3/4" top-lip cracking? I don't think increasing it to 1" thick would hurt anything, and it would provide a substantial increase in strength. Nice drawings BTW.

 

Thanks Razor.
I could make the top and bottom pieces 1" for sure.
I am not sure if I could do that with the main cylinder of hot face, if reducing my outer bore to inner shell spacing to 1 3/4" will still work with 2 layers of 1" blanket.

 

I started in on the bottom hot face mold, digging deep in my scraps for plywood and expanded polystyrene and keeping things low-tech while the CNC is still taken apart for the spindle issue. This one is 2 layers of EPS , cut on the small hot wire, and epoxied to cheap plywood as a base. The interior surfaces of the mold have a coat of epoxy and some small strips of epoxy-soaked paper to keep the EPS layers from de-laminating. My plan is to coat the interior surfaces with either mold release wax and/or self-stick shelf paper to make a non-stick surface for the Kast-o-Lite 30i.

 

I took the mold above and covered it bottom and sides in the finest discount store wood-grained shelf paper (self stick vinyl) and molded the lower disk.
I stirred the mix with a drill and an old battery strap j-bolt as the paddle.
The refractory acts like a reverse Newtonian fluid, dry-looking and solid at rest but moves like a liquid under vibration. I used the air hammer on wood on the rig as I did last time.
The plastic container contains my 10% extra and will make a nice small plinth.
I sourced the concrete tube (12" checked for 11.5" ID) and some foam to make the rig for the upper disk, which will have the hole for tongs and crucible.


Q: Would it make sense to mold the main bore with a blanked-out area for the tuyere and mold the tuyere in place?

 

If you know the position and shape of the tuyere, then yes mould it in place. If vibrating refractory then the slightest leak will flow, so a solid block of styrofoam or something solid would be handy. I used a split PVC tube with tape and it filled with refractory during the vibrating and filling.

 

Thanks Mark. I think I'd like molding the bore better with an oversized hole and then use the tuyere to take up all the differences with the burner in position rather than trying to mold the bore with the burner in place, which would mean trying to mold it in the shell, on top of the bottom disk, with the burner hanging off the side.

The bottom disk (hot face floor) is out of the mold along with the leftovers.
The piece was stubborn to release so I scored the plywood backer to the inner layer (only 3 ply) and bent it at the scores until it released.
Turns out the few places I tapped the inner surface with the air chisel did not like being bothered, tore the vinyl, and allowed the mix to reach the wood and gain a toehold. The rest is quite smooth. The leftovers did not do as well, many air bubbles and breakouts. I don't think I shook it soon enough to mold correctly. I de-molded that at one day, because of its issues I did not de-mold the disk until almost 2 days. The leftover mold had draft, the disk mold really did not, but did have a small epoxy fillet between flat and side. I may try to add a degree or two to the upper disk edges and perhaps wax fillets.



I still have a ways to go learning the ins and outs of casting refractory. Working up more courage to go after the bore...

 

I did this and found it a bit hard to fixture, but it can be done and is probably a good idea despite the complexities. IMO it's really really hard to bore a hole like this after-the-fact and have it come out decent. One tip: As the refractory is curing, rotate the tuyere model 1/4-turn periodically. That will help the model de-mold easier and you'll end up with a more round hole.

Also, in case it helps. I had good luck using Vaseline as a release. It's really messy, but it's cheap and compatible with just about everything.

 

Thanks RT.

Is there any sort of rule of thumb or initial guidance on how far the end of the metal burner tube should go into the tuyere? I am thinking it needs to stop short of the inner bore...but by how much?

 

I insert mine just short of the bore. If you stick it in too far it will self-adjust.lol

Pete

 

Thanks Pete.
I got the two molds put together. Epoxy is setting on the upper disk mold. I tweaked the hot wire just a hair so the shapes have a little draft.
The cylinder bore is also done. Tubes cut, inner re-sized, support rings made for inner, inner mummified with packing tape, outer waxed (coating look thin on the inside of the outer tube) and all hot glued to a base with a 'knockout' (piece of foam) for the tuyere buried in the mold. About the time I got done I saw another 12" concrete tube in the garage. If all goes well than one can go back.

 

PS/Edit Pictures as promised, see post above ^^^

The hero tool for cutting the tubes was a small Harbor Freight Japanese-style saw. I also used a yardstick, framing square, a stiff piece of plastic film, and a large compass to measure and mark most of the work.
The inner support rings were marked with the laser and cut and sanded to fit by hand (CNC is still down, bearing is on order and for some reason it made sense for it to be shipped from Ohio to California to arrive back in Minnesota. It is due it later today so I soldiered on with hand tools yesterday to take advantage of the nice weather).
I may add a flange to the the cylinder outer tube before molding. The 3 small white foam bits were to center the tubes and will be removed. The green tape is where the hole for the tuyere is being molded (excluded), I may run some screws through there so it does not become 'buoyant'.
The upper disk mold needs a few touch ups at the joints, the as-glued epoxy fillets did not form as nice as they did with the EPS foam on the other mold. I roughed up the back of the XPS foam with 40 grit for better tooth with the epoxy.

 

I'm afraid this is the world we live in now. It's somehow cheaper for airlines to burn tens of thousands of extra fuel, over and over again, then it is to pay a room full of engineers to fix their 1970's software

I once took a flight from NC to MI, that went through FL, then a wormhole above Disney, then back down from the moon right to the Detroit airport

This is a wise idea. I wish I added more structure and made sure it was all level when I did this. Instead I ended up with a tuyere at a slight upward angle (so oil dribblings come back toward me, smoking all the live-long-day)

 

I ended up doing wax fillets, shelf paper, and #2 paste wax on the XPS foam mold today.
I made some more homemade fillets. Today's mix was 2 parts beeswax and 1 part not-so-natural. I did learn that heavier angle iron works better than my previous drywall corner bead and possibly better than the machined aluminum plate. I ended up splitting most of them in half as I poured them too large. I applied these using my homemade ball tools (Michaels mandala paint daubers) and scrapers (used shipping and receiving steel banding shaped to suit) and an online-purchased lamp.

I just added a couple screws and fender washers to help the hot glue keep the tuyere knockout in place.

 

Thanks Jeff. Wondering if I should try the reciprocal saw trick instead the air chisel for the cylinder. Did you work your way up as you filled the forms in with castable?

 

Thanks Kelly, I had a look at the table in your link and saw the picture with the circles and springs.
I found a commercial one that uses bushings instead of springs:

And they offer instructions on how to make one with a discarded tire:


Too bad I don't have either a discarded tire or valve springs at home. For valve springs, do you remember what make/model/intake or exhaust you got them from?

 

I just sat my beer keg on a doubled up foam yoga mat with the vibration source ratchet strapped to the keg.