View Full Version : Making hotface liner, screwed up

12-11-2008, 04:20 PM
I tried making a 1/2-3/4" hotface for my furnace to be. Will be using some of Jammer's blanket around the hotface to line it.

I bought Mizzou 3000, mixed with 10% water per instructions. Mixed it was the consistency of greensand, so I had to pack it in the form.
(see my blog for the process pics)
I waited for about a week to start removing the forms due to work, rain, etc.

This is what i find.
nice break all the way down and through. I would think refractory would be kinda hard like concrete once it dried, but this is crumbly and fragile I guess because its so thin.

Is it salvagable, or do I just need to set it aside and start over?

I haven't been able to do any work on the furnace lately due to cold weather and work (wife won't let me mix in house), and I can't work on the dasifier till after xmas waiting on my compressor present.

12-11-2008, 04:34 PM
sorry, I can't get the pic to show, it was huge, but here is the link

last pic

12-11-2008, 04:51 PM
I have never used Mizzou but it may have cracked due to shrinkage.

It should be like concrete when dry and fired.


12-11-2008, 05:02 PM
I think you didn't used enough water.

I spoke to a Harbison Walker representative when I purchased my stuff from them, and he explained to me that the best way to test for water content is to make a ball, and throw it 2-3 feet in the air. If it crumbles apart when it comes back in your hand, there isn't enough water, if it flattens out like a liquid pancake then you have too much water. It should maintain a nice ball shape.

I'm not sure if it's salvageable or not. However, it wouldn't hurt to try.

12-11-2008, 07:06 PM
Not nearly enough water.

I'd try misting it heavily several times, waiting for the water to soak in in between. That should let it finish setting, I'd think. Then you can glue it back together with some that's mixed right (a lump held in the hand should sit as a flattened ball and hold together when tossed 1 foot in the air: if it doesn't flatten out, it's too dry; if it runs through your fingers, it's too wet). It will be fairly weak until it's fired, at which point it becomes harder and tougher than the hardest concrete, but not that weak.

12-11-2008, 08:13 PM
Thanks for the replies.

Kinda confusing about the water, seeing as when i checked out the instructions, it said not to use over 11% water. I mixed up 10 cups of refrac with 1 cup of water. It was very crumbly, almost the same as what flour/shortening should be for pie crust. I don't see how anyone could "pour" this at that consistency.

I haven't attempted to take off the form of the top section yet, as it has been too cold/wet to get out in the shed. Driving me crazy, supposed to mix at 50-70degrees, and only been getting that temp when it rains.

I will probably just start over, and make the form more to the shape I wanted to begin with. This was just a hotface tube that I was going to attach to a flat section on bottom with drain hole, ring at top to cover blanket at opening.
I see why most people don't use the blanket/hotface that often. Its more difficult than just packing in dense. But money is always tight, and took enough penny scraping to just get 1 bag of refrac.

I havent gotten to firing any of the pieces yet, as the only thing i could currently do would be lighting a charcoal fire on top of the pieces, seeing as I don't have a burner done yet.

12-11-2008, 08:17 PM
Not sure about this, but they might mean 11% by weight, not volume.

12-11-2008, 09:18 PM
I'm sure they do.

I've always gone by texture, and it sounds like I've been mixing it a tad too wet. Still seems to hold up pretty well, though.

If my math is right you'd want about 11 cups of water for a 50 pound bag of Mizzou, assuming that you want the weight of the water to equal 11% of the dry weight of refractory. (I'm not clear whether "11%" means that 11% of total weight is water, or that the weight of the water is 11% of the dry weight. The latter seems easier to calculate, which suggest to me that it's probably what they mean.)

Later: OK, I was right. They mean water weight as a percent of the dry solids. http://www.hwr.com/products/mixingv1/MIZZOU%20CASTABLE%20Plus.pdf

But 11 cups of water is for the maximum of 11% moisture, which they don't recommend you start with.

12-11-2008, 10:31 PM
I have been considering a method for making a bonded hotface foam mix insulation. I mentioned it before it think but it keeps coming back to me a great way to form up a furnace. Note I have not tried this so I could well be off my rocker.

My idea is to take a cardboard or wood form sized for the finished bore and coat it repeatedly with a suitable refractory material until it is built up to the desired thickness. Place this into the outer shell and fill with a foam refractory mix then after it is dry burn it out.

In my experience with the castable I have used thorough drying is not necessary and a candling fire could be used to drive off remaining moisture while the inner form burns out. I would think this would make for a great bond between the insulating layer and the hotface and also be easy to put together, only problem is that not having actually done it cannot say with certainty how it would come out.


12-11-2008, 10:42 PM
I thought something similar and may try but my knowledge of clay is not what I thought it was before I joined this forum. :? I was thinking along the lines of Anon's kaolin/silica hotface and try to get it plastic enough to roll out like dough( :roll: probably not a simple feat,) cut it rectangular to get the circumference and height to then make a tube. :idea:

I figuring if the kaolin cracks while trying to form it, it can be patched up with slip???

12-11-2008, 11:55 PM
Oh, it works pretty well. That is how I constructed my last two furnaces, I actually rolled the hotface material out to the correct thickness and then wrapped it around the inner form using wax paper to help support it. I placed this in the center of the shell, and packed the foam/grog/clay/sand insulating layer in behind it(after removing the wax paper). This gives a very good bond between the insulation and the hotface. I left the form (just a sonotube on my big furnace) in place and burned it out. I didn't let mine dry at all, I fired it while it was still damp. Seemed to work okay, both furnaces i have done this way are holding up fine. the nice thing about using the roll it out method is that you can get a very dense and uniform hotface that is thinner than one you can ram in place.
On my big furnace the hotface is only about 1/4" thick (wanted it to be more, but I ran short on hotface mix and didn't have the alumina processed to make more... :oops: )

12-12-2008, 12:28 AM
Hey, I have a cardboard concrete form in my basement right now that I bought for exactly this purpose. But I was planning to put the clay on the inside of the form, because it seemed like it'd be more likely to crack during drying if I put it on the outside. Figured I'd fire the hotface first (and simultaneously burn off the cardboard), then add the rest of the insulation.

12-12-2008, 12:38 AM
Any time there's something rigid inside wet clay, there's a large chance of cracks as the wet clay shrinks.

Ideally, you would roll the hotface out over a form, ram the insulation layer behind it, and pull the form out before the drying cycle, possibly leaving a layer of newspaper or other non-rigid material on the inside of the hotface. This can act as parting and won't interfere with drying.

Even if you don't have problems with the shrinkage of the insulation layer around the fired hotface, I'm not sure it'll adhere well. Then again, adhesion isn't too necessary.

12-12-2008, 12:57 AM
Thanks for the confirmation oddduck, from what I have experience so far I thought this would be a good route. I was thinking a little different approach though by mixing the refractory a little wet and actually painting it on. Your suggestion of keeping it somewhat plastic and using wax paper to help it around the form sounds much better as far as keeping the water content down to avoid cracking.


12-12-2008, 01:26 AM
It also allows you to smooth the seam down to the point that it is not noticeable. When I re-did my big furnace I also did it upside down, and put the cap for the insulation layer in at the same time and rammed it up from the bottom. Of course this will only work if your shell doesn't have a bottom.
I cut out a piece of blue foam the same size as the inside diameter of the sonotube and hot-glued it to a smooth piece of board, and glued chunks of foam around the outside of the shell to locate that as well. that way it didn't move around when I rammed the liner mix in. I attached the bottom after I had it all rammed up and flipped it over (very carefully) with the locator board still attached. Worked pretty slick. I realise that it is probably against every ceramic rule to do so, but I think firing a clay/foam structure like this wet may have some advantages in preventing shrinking. I actually got very little shrinkage overall, I did get a few cracks but they were all small and don't seem to be affecting strength. I did get some flaking of the hotface, but I wonder if it is because I didn't thoroughly mix the clay, sand, and alumina and got layers somehow.

12-12-2008, 01:38 AM
When you guys make the hotface separately, how do you deal with properly locating the tuyere hole in it?

With my next furnace I'm planning to cast a separate hotface with HWR versaflow 60 plus and use inswool ceramic blanket for the insulation, but am still puzzled over how to deal with the tuyere.

I've also been puzzled as how to deal with the tuyere itself in that I don't think I should have any of the inswool exposed to the burner. I can't decide between steel pipe, or perhaps casting a tube out of refractory. I saw Jammer used mullite for his, but I don't have any mullite.

12-12-2008, 01:46 AM
I'd cast the hotface around an inner form or between forms (you can do that with castable, because it doesn't shrink), with tuyere form stuck on as a piece of foam. You can extend that all the way to the furnace wall, or cast a tube with in-built flare and burner, and mortar them together. Castable should stick to itself pretty well.

With clay, you can do the same thing minus the inner form, or cut the hole out at the plastic stage. With either, you could potentially make a hole after firing, but that's dicey and not a good idea.

12-12-2008, 02:05 AM
When you guys make the hotface separately, how do you deal with properly locating the tuyere hole in it?

With my next furnace I'm planning to cast a separate hotface with HWR versaflow 60 plus and use inswool ceramic blanket for the insulation, but am still puzzled over how to deal with the tuyere.

I've also been puzzled as how to deal with the tuyere itself in that I don't think I should have any of the inswool exposed to the burner. I can't decide between steel pipe, or perhaps casting a tube out of refractory. I saw Jammer used mullite for his, but I don't have any mullite.

Glue a foam tuyre onto the sono tube inner form and coat the whole mess with your hotface then wrap it with your wool and lower it into the shell. Burn it out and start melting iron :evil:


12-12-2008, 12:59 PM
One of the original questions that didn't get addressed was- can he salvage the mizzou? If unfired clays are similar, I would think so. Experts chime in.

12-12-2008, 03:07 PM
Yes, but it may or may not be practical to. The binding agent (calcium aluminate) may have hydrated without bonding to itself, in which case the shape it's in right now will never get very strong, and it's useful only as grog (or it could be recycled by calcining, ball milling into fine powder, and re-casting it, but this is a bit silly to do on a non-industrial scale). On the other hand, it might sinter together fine as-is, or there might be enough unused binder that a little absorbed water will pull it together.

12-12-2008, 04:08 PM
After reading replies, I'm probably going to just grog it, and start over. I realized that i never made a tuyere hole in that, so it would have been crap anyway.

Now just to wait till overnight temps are above freezing, as I have no elec in my shed to use a heater to keep warm. Been waiting a year to start this, and getting really antsy.

12-12-2008, 10:09 PM
Above freezing?! I hope not :shock:
I'm going fishing this weekend and it's difficult to keep a fire going on the lake when it's melting :)

12-17-2008, 10:28 PM
how was the fishing Todd?

One of the nice things about working at a college, is the 2.5 weeks off for holiday vacation. So, I'm off from job#1, and the low for the next 2 days is 53. YAY!! I told my wife that after I drop off the kids at school tomorrow, and have a pot of coffee, I am unavailable for honeydo list until i make my furnace. It will most likely be the last chance I get the temps to do it till spring, and um, ale no to waiting.

So, hopefully I will be posting pics tomorow.

2 side notes. The kids were begging me to melt some cans yesterday, so I took 2 real big green bean cans i got, took off top and bottoms, stacked them on top of a nice pile of bricks, loaded in some charcoal, and fired it up. I basically made my own charcoal starter, but it surprised me that i didnt need a blower. Wind was only blowing about 10mph, and I melted about 10 cans in a soup tin. Kids loved it, didnt make anything but a flat ingot as i didnt have a mold.

I also stopped by a machine shop and they wanted $30 to make up a steel crucible 1/8"thick 4x6. Is that about right? seemed hi.

12-17-2008, 11:40 PM
Thirty bucks is high but that is what the going rate is gonna be to pay for shop time. You could just about buy a graphite crucible of those dimensions for the same price. Have a look at lmine.com their #8 is about that size and was $40 shipped to me. A case of six combines the shipping and price break to make them about $25 each.

Before I paid $30 for a steel crucible I would make do with cans/cut off fire extinguisher ect... and put the word out and see if there is a friend of a friend who has a welder.


12-18-2008, 02:40 AM
speaking of fire extinguisher shape, what is the best way to cut open the coleman(green) propane cylinders? Friend of mine has a pile of them, as she makes her own glass beads, and will give them all to me. I just have no clue as of how to cut without losing my head.

12-18-2008, 03:27 AM
Step 1: Use the cylinder until it's empty by connecting it to an appliance. Make sure it's empty, not frozen up.

Step 2: Depress the little valve where the cylinder attaches to let the last of the propane out. You should hear a little hiss and smell a nasty odor (the chemical they put in to give propane its smell gets concentrated in the last of the tank, so it'll stink badly). You might want to check the overpressure valve too, just in case there's a blockage in the valve that's concealing a pressurized cylinder. Some people remove the valves entirely and fill with water, but I find it to be a waste of effort with the little cylinders. The big ones have enough gas when at ambient pressure that it's worth the effort to ensure safety.

Step 3: Cut it open. I use a chop saw without problems, but a hacksaw also works and doesn't provide a source of ignition.

12-18-2008, 03:43 AM
They do last fairly well for what they are, make sure you heat it to red hot and let it cool completely once before you melt metal in it, this will make it last a little longer. I have had some last eight or nine melts. Free is also good, and you are doing your friend a favor and ensuring a steady supply at the same time. Granted, you won't be melting iron in them, and brass is pushing it, but they work.

12-19-2008, 02:26 PM
well, change of plans, weatherman lied, didnt get above 50 yesterday, and was so foggy, i couldnt see 20ft away. I did find a nice piece of foam wed night, so I made a form yesterday morning while I could feel my fingers. the fog was so thick that the foam dust stuck to everything due to the moisture. I have to go to my son's xmas party at school, gonna check him out early and get back to play. Today is supposed to be 63, and no rain after 11am. Got to get this done before Sunday, as high will be 35, and i have to work every night this weekend.

thanks for the tip on the bottles, when I try it, I'll have my wife post if I lose anything.