Fired the last of the blocks with the seed mix

It's been a while. A few interesting things have happenned.

First off, a mouse or two discovered the clay blocks with implated seed and started eating them. After a two day excursion in garage emptying cleaning and putting back the garage is free of mouse bait and the remnants of the mice. On the upside the garage is organized better now and we got a bunch of crap thrown out.

This included the partially fired block. They made a small hole in the side of it nad hollowed out the unfired core. I have not figured out how to use this little phenomina. However, it did give me an idea for an alternate approach I would like to try. That is slip casting hollow blocks. Basic idea would be this:

• Mix the clay / sawdust or poly styrene dust mix with enough water to make it into slip, very thin clay.
• Pour the slip into a simple plaster mold & allow to set until a 3/8" +/- wall forms, pour our the rest of the slip. This is just like alot of ceramic products are made.
• Dry & fire.

Perhaps this has been tried. I've not seen hollow refractory products like this on the market. There may be a very good reason why ... right? Often times yes.

Next, I took the remaining blocks and fired them.

• I did a ramp to 900 and held that for about eight hours to accomplish as full a burn out as possible.
• Then I took them to cone 8 with a tow hour hold at the top. Took about 10 hours with my kiln.
• I kept the bung in to minimize the oxygen present and the burn rate. My thinking was that it would limit the fracturing in the blocks.

The results were interesting.

• The transitioin through to 900 and the hold created the same results as below but eventually all the black goo burned off. Did not smell good. Burnt popcorn would be about right. Fortunately it was breezy. The smell blew away.
• The blocks remaining pretty much in tact.
• The blocks did crumble once I tried to pick them up.
• This time there were regions that retained some strength. Not much. Maybe 20 psi. That gave me some hope the clay mix might have enough strength.
• Last but not least, in the middle there was still a lot of carbonized material left. That tells me that after all that time in there at ~ 2300 F the core was probably not more than 600 degrees F.

Conlcusions:

1. The seed idea is not going to work. I think the combination of the large voids / thin walls and the expansion of the organics during burn out is destroying the structural ingerity to the point where even a pretty high fire will not allow any fusing to occur.
2. A smaller particle size on the combustible material should yield a stronger matrix.
3. The insulating properties are great!
4. I don't need 1 1/2 inch thick slabs. 3/4 inch will probably do it. Assuming a similar ratio of burn out material.
5. The hollow slip casting method is worth a shot.

I don't expect another shot at this for a few months. I'm back on the road consulting again. My weekends are shot. Eventually I will come up with a workable and very specific process for this. My objective is to publish something that anyone with access to the raw materials can do. Access to the raw materials is pretty straight forward in most areas or with a little shipping cost.

Later,
John

Oozing Black Crud

So, what really happened? This is a close up of the side of the test block. I originally thought, as I posted, that the seeds had popped. Nope. It looks like as they got to the temp where the oil started to plasticize and char. Then it began to expand and ooze out of the pores and cracks. Obviously it did not all ooze out so it broke the clay apart.

The black material at this point is dry, crunchy, and porous. It's almost like carbon foam. It's got no strength at all. It crumbles with a very small amount of pressure. So it doesn't serve to really hold the clay together at all either.

The whole thing looks a little like a chocolate cake with some funky black frosting. My daughter, the art major, said I could put it in a gallery. Maybe I can recover some costs. I can make five more of these tomorrow ...

It's a bust!

  Yeah, it's a bust. So I ramped it to 300 F. It soaked for another 2 hours. Did the mirror test with the kiln lid cracked about 20 minutes from the end of the soak. (You hold a mirror next to the opening to see if you get any vapor condensing on the mirror.) Good to go.

I went about my business chasing down some screwed up wiring in the house. About 45 minutes later I start to smell the seeds burning. Okay, that's about right I'm thinking. Checked it out.

Temp is at 554 F. Smoke is oozing out the crack between the lid and the kiln body. I got my welding gloves, opened the door to what you see in that picture. Hmmm ...

At first I thought I didn't let it soak long enough. I thought the big seeds were popping like they did in the toaster oven test. So I shut it down to let it cool. I was going to just let it soak at 300 F longer, write off the edges, and see what I could save.

Once the smoke cleared I noticed the large number of  what looked like popped seeds. The larger seeds in the mix are not that numerous. This had to be the millet. At this point I am sure the seeds near the surface like this are dry too. I mean c'mon, they HAVE to be dry. So what's happening?

A guy at iforgeiron.com who goes by Frosty, mentioned he thought millet had a relatively high oil content. Seeds in general have a good bit of oil as we know. So, what I think is happening is that as the oil is vaporizing and possibly burning, it's acting just like water vapor and causing the seed to expand. It would take a lot more testing to prove this out. I'm not going to do that. So, that's my story and I'm sticking to it.

Anyway, seeds as a burn out filler for a refractory brick are a no-go. Well ... now we know.

So for the next rounds of testing, I will drop the seeds and replace them with perlite. As I mentioned, perlite and "fireclay" are a reported to work just fine. The mixes I've seen don't go as hot as I'd like. I think that's got more to do with the clay than the perlite.

Firing Sample #1

Firing the first sample today. It was dry. I cut it in half with a back saw. It cracked straight through about half way into the cut. The center is totally dry. The other two samples had the same resonance to them when I tapped them. So I am sure they are all equally dry.

Firing program

Ramp at 150 F / hr to 300 F
Hold for 2 hours
Ramp at 1000 F / Hr to 2300 F* - 2300 F is about Cone 9
Hold for 2 hours

*Getting 1000 F / hr past about 1500 with this kiln is impossible. I'll be lucky to get 300.

I'm also going to have to monitor the breaker box. This is the first high fire cycle I've done at this house. I'm using a 10 GA copper cable that is tapped directly into a 30 A breaker. Should be OK. The max draw on the kiln is 1800 watts. That's like running two hair dryers at full heat or every light bulb in the house.

Well, we should have burning seeds before too long!

Dry time note - I think we ended up with ~50 - 60 hours dry time. The first 25% was at 160 F the rest was at 190 F. Starting at 190 F would have been the better way to go.

Cone 11 ?!

Looks like EPK vitrifies at Cone 11. My kiln might get there. Cone is a function of temp and time. To a point, you can get a higher cone at a lower temp. I've gone 1 - 2 cones higher in the past by letting it soak longer.

For the bisque, I should be able to go to cone 9 with a 2 hours soak. We'll see Saturday I guess

Pop Corn!

Did some testing on the seeds. Trying to figure out how hot I should go for the next hold cycle to drive off the remaining water. Here's what I got.

300 for an hour - all the seeds brown a little, no real smell
350 - almost immediately the cracked corn pops, everything else browns pretty dark, smells toasted
400 - some of the other seeds in the mix pop like the pop corn did, everything else gets a lot darker, some of the loose hulls start to char
450 - some more seeds pop, everything starts to char

Note: The millet did not pop at all and it was the last to char badly.

So the answer is 300 F for the max hold temp to drive off the water. If anything in the mix pops, I'm screwed, the whole thing will start to crumble from the inside out.

'Nother induction furnace link.

Hildstrom Engineering ... interesting induction furnace project. Someday ... an induction heater would be handy to have around. It's a lot less BS for probably 80% of what a guy needs. If you could get one built big enough to melt 100 lbs of bronze, you'd have a really nifty foundry. In a DIY setting I am afraid that would probably tax the available power to the house.

"Hello, PG&E, yes I need a service upgrade. What for? Uh ... well ... I have this really big medical marijuana green house I'm building ... what? ... oh yeah totally for personal use. I've got arthritis real bad ... oh ... prescription? Let me find that and get back to ya .... yeah, thanks ... you too ..."

Maybe 25 lbs ...