Form Kastolite using Styrofoam?

Trying to gather more information about molding/forming a Kastolite hot face body and lid using Styrofoam, as I have a bunch of it in block form and I am comfortable cutting it with a hot wire and gluing it back together as needed. I saw a video of Kelly making a crucible hat with XPS and a vibrating tabletop. Wondering if the same concept would work for something about 14" ID x 16" OD x 20" high [355mm x 405mm x 500mm).

https://forums.thehomefoundry.org/index.php?threads/yet-another-keg-furnace.401/

Thanks!

 

That video offers an important message, one we can all agree on: Properly mixed refractory doesn’t act like you think it will.
A guy needs to find out the Mfg’s exact instructions and follow them to a tee including the right amount of clean water, etc no matter what his “gut” tells him. Harbison Walker knows what they’re talking about. It’s an un-asked-for comment, but one worth making.
I take it you’re using solid refractory and no wool? If so the correct refractory will be kastolite30-i. You’ll need 2 bags for these dimensions. Others may want to talk you out of foregoing the koawool and they’re not wrong in doing so, but I have a solid refractory furnace and it runs fine once the rock is hot. If the need ever arises to build another furnace though, I would use koawool.
So there’s a lot of ways to skin this cat. The bore your talking about will weigh about 55lbs if I’ve done my math right so your forms will have to stand up to the weight as well as whatever method you use to place it - whether it’s vibe or ramming or both. If you think a foam assembly will withstand it, then have at it.
Say for instance you’re doing this in a hot water tank and just using solid kastolite. You could take the tank’s original sheet metal skin, form a 14” diameter cylinder with it, rivet it, and make 3 or four 14” disks to shove down in it for support, and go ahead and place your refractory. That’s my abbreviated input.

Thats my 2 cents for the morning.

Pete

 

Thanks Pete.
55 gallon (200L) barrel cut down, 3" (75mm) ceramic fiber sides and lid, firebricks on floor, all lined with Kastolite 30i. Still mulling over whether to make Kastolite faces 1" (25mm) or 1.5" (38mm) thick. At 1"(25mm) the design takes about 1 CF or 90# including the lid. The warehouse associate at the firebrick shop gave me a nod and a paraphrased "that'll be snug with so much blanket" comment...

Thanks Kelly. I had thought about CNC'ing layers of foam and gluing them back together. I will consider the concrete tube and forces that may conspire against me. The tips about a foam tuyere is brilliant. I had been thinking about a 3.5" square section as a placeholder in the casting process and then mold the real one as a 2 piece split ala Denis with a slight flare and tangential face to the bore and remaining diameter to fit the burner tube.

Pics of design and loot below. Design is normal top lid, drawn 'open' for visualization purposes. Cut barrel and start of roller base, brick, refractory, mortar and wash coat.

 

Thanks Kelly for the top tips on the refractory. I have gone back and forth on height. Here it is as numbers:

 

Here is where I am at so far.
Full disclosure, I had a gyro for dinner recently and I can see that influence in the design... Opa!

1-Start with the bricks in the barrel and drill in a centering hole.
2-Make the mold pieces hot-wired using templates from EPS aka Styrofoam, tuyere piece may be CNC routed in layers and glued.
3-Coat them with latex paint and possibly another mold release (does anything inhibit Kastolite?)
4-Insert armature shaft and spacer and lower outer mold that kisses barrel on the points of the octagon
5-Insert lower inner mold, mark tuyere location on barrel, remove molds, drill tuyere pilot holes in barrel, replace lower outer mold
6-Add first layer of Kastolite just up to bottom of tuyere, liquify with vibration
7-Insert lower inner mold, add more castable, liquify with vibration
8-add upper inner and out molds
9-set upper armature support, weight down inner molds, add more castable, liquify with vibration
10-let cure x days at 65-70F
11-demold in reverse order, destroy Styrofoam if needed, fill in hole from shaft and spacer
12-fire hot face shell before (?) adding ceramic blanket

 

Thanks Kelly. I have the foam and my local does not stock the right sizes tubes so both diameters would involve some rework. I will think on it, will look at the tubes first, and I appreciate the other tips. I could easily see myself overworking the settling of the refractory without your warning.

 

If you do find and decide to use sono tubes, note that they ship to stores nested inside each other, so the sizes are nominal and different for almost every tube. So bring a tape measure (or borrow one from another aisle) if you need one with a precise diameter.

I used sono tubes and styrofoam for the formwork in my oil furnace. If it helps, pix and details are in the build thread, link is in my signature.

Good luck!

Jeff

 

Thanks Jeff, I had no idea they made them vary in size to ship that way. I will check out the link...again

 

I went forth, tape measure in hand, and found a 16" x 48" tube that was really 16.5" ID, my original target OD. (419mm ID x 1219mm long)
Thinking I will pull ID in to 14" even instead of 14.5" as 5/4's thick sounds 'oh so much' better to me than 1". (355mm ID @ 31mm thick vs 367mm ID, @ 25mm)
Thanks for insisting, sometimes I can be taught
Next question will be tuyere height off inside of hot face. Seems like I have headroom, would it make sense to design some 'bottomroom' to survive a crucible failure without drowning the burner in molten metal? Make it look like a Jell-O ring? Or better to have an open or stoppered drain?

PS-Tube takes Highlighter and Sharpie marker without beading up, suspect there is no coating on either surface.

 

I started work on the forms. This tube can be cut easily with the large shears that I used to use for fiberglass. I CNC's some flanges for the OD form to keep it 'in the round' and to help center during assembly.
I was planning to cast the hot face on top of insulating fire bricks that are mortared together and top coated with HWI Sair Set right in the barrel that is on a rolling base.
-Do I need to seal the tube or flange to the bricks or suffer leakage of the refractory? Is latex caulk OK? Or just use mortar and/or ???
-Would I be better off trying to cut the tuyere holes in barrel and forms and leveling in the pipe and sealing before casting rather than attempt half before (forms) and half after (barrel)?
Thanks!

 

Thanks Kelly, I really appreciate the montage as I am having issues viewing the old 'http://' threads with my current browser.
That is some awesome design and execution!
I totally forgot about molding in a tunnel or a space for a separate tuyere insert.
I'd better coffee up and go back to the drawing board.


PS-I went to size the inner form tube and mixed up on ID and OD circumference. I cut the tube to length and circumference, and... because of pi times delta in diameter...it is 17/32"(13.5mm) too short of lining up at the seam around a correctly sized ID template. I'll be adding that back in and using more tape.

 

Here are the concrete forming tubes, cut to length and re-sized for diameter and located in the barrel. I will cast the hot face outside the barrel per Kelly's recommendation. This furnace is being put on hold for something one size smaller. Planning to do the smaller one in this same fashion.

 

I have switched efforts to the medium format and cast the lid refractory today with Kast-o-Lite 30i Plus. The expanded polystyrene was scrap from another project off the CNC so I did not have to prep it to go back on the CNC.
All the advice upthread was useful and helped me not to second guess the material, thanks.
-How long should it stay in the mold?-
HWI also emailed me some sheets but this detail is missing.

 

Thanks Kelly. It did flow when vibrated, even the tail ends I made into a plinth. I was expecting a more 'concrete' like reaction with heat, etc. but plinth still seems soft at 3 hrs. Temps were about 70 F / 21 C and I used lukewarm water to mix. I moved the works into the house to keep warm overnight. I am not in a hurry but wanted to make some forward progress this weekend. I should be able to remove the top part with the wooden disk, leaving the majority supported from the bottom and sides. The outer chimney has a splitable seam.