My first furnace

I visited a crematorium about a half dozen times before building my furnace. That's where I got my brick from. I was there when they were pouring the lid. The lid was the only thing they poured. I was literally shocked by how thick they poured it out of the cement mixer.

Pretty much as soon as the dust stop flying they would pour it out in clumps into a wheel barrel. Small buckets were lifted into the form and dumped. It was vibrated into place with a mini jackhammer for about each 2 gallons dropped in. 4 men were work working nonstop for over 3 hours. The owner told me it would take almost a week to cure. 24 hours after the pour he would slowly ramp up temperatures for seven days, Without interruption. The furnace for the next seven-ish years will never drop below 400°F.

I was told, Most of the cracking will be in the ceiling refractory, that is dome shaped and would occur in the first six months of operation. The ceiling was vibrated flat and then a three-quarter inch (19mm) fibre board, with 2 inches(50mm) of ceramic wool, and then a steel box. The ceiling thinnest part was well over 4 inches thick. The operating temperature will never exceeded 2200°F. The fuel they used was natural gas.

 

Ah like that, that makes it very clear, thank you! I have one and a half bag of refractory left, i don't need to recycle anything, sorry for the confusion. My refractory has grains/chunks in it, and i feel like crushing them would make it easier to handle without (maybe) changing the refractory's composition by sieving it.

Those guys must have some decent experience. We have a special concrete vibration rod tool that's used to flow the concrete and get the air out, but with the recommended refractory/water mix even a jackhammer would have no effect. The refractory would not even clump together. So i figured i would be better of adding more water to make it easier to pour.

Greetings, Job

 

From memory, I had 76 millilitres of water per kilogram of refractory. With that ratio it was completely solid until vibration was applied and then it was a rubbery fluid as soon as vibration was turned off it became a solid again. I was able to apply a powerful vibration to the entire furnace mould (beerkeg) using an out of balance electric motor.

The refractory manufacturer suggested using an industrial bread dough mixer to mix the water in thoroughly.

 

First time mixing the refractory i emptied a whole bag in a big bucket and added 2,5 L of water as listed, then i used one of these on a handdrill, and from what i remember, the refractory it still was dryer/crumblier than the refractory in your video. Or could that be because of the chunks/grog ?
This afternoon i took some refractory and sifted it, then crushed the bigger chunks or grog to make it quite a bit finer. After crushing the chunks some of it became as fine as the sifted refractory, It also looks the same as the sifted refractory, and i'm not so worried about the composition anymore.
Then added some of the sifted refractory to the crushed refractory (so it's not only grog) and slowly added water to both, still quite wet because i didn't have a scale to measure how much i should add . But both are indeed easier to work with than the refractory straight out the bag with all the big pieces in there.

This is what's left after sieving.


When i go and patch up the cracks i will carefully measure how much water i should add and while doing that film how the refractory handles and hopefully close the water mixing ratio discussion (because my refractory is already cast and cured, and i don't feel like it's going anywhere. That might be my fault, but still).

Anyhow, thanks for the info!

Greetings, Job

 

Phosphate or phosphoric acid is required for the reaction to set high alumina refractory, a very different beast to portland cements. Worth a read up.

I'd say patch the cracks with a thin slurry and see how it holds next couple of heats.

 

before i started building, i read that portland cement has silica in it which melts or crystalizes around 1400(?) degrees celsius, and that i needed alumina refractory.

I have been busy with school and will be for the coming few weeks, so i might not get too much done. But i did chisel out two cracks last weekend.

As pete suggested i went in about 10mm, i didn't fill them in yet because i would like to hear what you guys think of my chiseling job .
I also found a place where i can get a sheet of stainless relatively cheap, i still have make an order.
this idea came up to me last week: what if i weld a few pecies of stainless around the bottom where the insulation blanket sits on, just high enough to leave a small gap underneath the insulation to prevent it from getting soaked in the case oil will still leak through cracks ? I'm curious to what you guys think about that idea.

 

Modern commercial furnace cements 1650 deg C are usually calcium aluminate cements made by roasting bauxite and lime in a cement kiln. You can also chemically react the mineral rock Wollastonite with 85% phosphoric acid to make a paste that gets hot and sets solid in ten minutes. The pottery people use it to patch their furnace walls and you can buy powdered Wollastonite from the pottery supply places. I've used it and it's not particularly strong but strong enough and I think it's temperature limit is pretty high too.

 

I'm not able to see your pictures from the post above.

 

x2

 

Oh that's very annoying, i hope it works now, i have edited the post with the pictures uploaded. I had copy pasted them in before.

 

They're working for me now.