Watching Clay Dry ...

Not much to report, really. The slabs are drying. I did cook a sample in the kiln at 200 degrees F for 8 hours yesterday,  no major cracks. That's encouraging!

I did have the idea to make half the slabs with seed and half with saw dust to see which works better long term.

Best,
John

Chile Forge

 Stumbled on these guys last night; Chile Forge. Not at all sure how long they've been around. The forge the size I'm building in their line is $795.00. That's probably about right. These look to be well thought out. There's a good bit of welding on them. I like the work holders.

Right out of the gate I'd be adding something for a door.

It looks like they've added interior protective shelves over the ITC-100 coated Kaowool (or similar ceramic fiber). Good approach. I would ask about what the shelves are made of. Should be a 40% + Aluminum Oxide content clay by what I know.

Even their big one shown here will not work for me as a melt furnace. One of my design criteria was that I had to have enough room to put two #6 crucibles in there. Remember I am going to try to melt iron or maybe steel. So a comercially made crucible is going be e must. I don't have an autoclave to fire A really high temp silicon carbide crucible in.

That said. If one was going to to small aluminum melts, something more like 5 lb. ladle would fit fine in there two burner model, probably.

Anyway, these look like great forges for the buck. We'll see how mine stacks up cost wise once I get done.

Great Burner Safety System Ilustrations

"Great" is relative. The bar is low.

Anyway check out this link.

I live in the lower Oakland hills. 20 years ago, about five miles to the north, there was a huge fire that wiped out 90% of several neighbor hoods. I don't want to be the guy to start the next fire. So, once I get the forge out of the experimental phase, it's getting a safety system.

The same company has a nice burner setup that is essentially a modification of a burner I think I posted earlier. It replaces the bell reducer or taper based flame holder with a lot of little holes in a much larger diameter "nozzle" for lack of a better term. They call it a burner head. Whatever.

If the firebrick works, I can use my mix to fabricate one like it.

Later,
-jd

Need more combustibles

After looking at the clay mix and poking around some more on the 'net, I've decided I need more millet / sawdust, jute or maybe even sisal / hemp.

An article I found indicates that 28% sawdust by weight. I also gives a number I have not seen before called "apparent porosity". This is a quantification of what I was doing visually by comparing my mix to the the IFB (insulating fire brick) my kiln has in it. That article says the apparent porosity is about 70%. 

Apparent Porosity (%) = {(Soaked Wt - Dry Wt) ÷ (Soaked Wt - Suspended Wt)} x 100

A quick read on this is that it's determined by by sectioning a piece of material weighing it dry, soaking it in water, then weighing wet, then pulverizing it and putting into a suspension with water to a specified volume (which I am still looking for right now). So, basically it's the ratio of the water the sample retains divided by a theoretical max. One could then easily equate that to volume given water has a density of 1g / cc. See I DID remember something from my Jr. high metrics blitz and intro to physical science. 

Well, I don't have time to make samples and do destructive testing so I'm going to eye ball it. My clay / sawdust / millet mix looks to be no more than 25% porous right now. So I have to step it up a notch.

Yesterday I wrapped up the clay slabs so they would not dry anymore while I pondered this little problem. Tonight on the way home I'm going to see about getting some big bags of bird seed at the grocery store. How much though?

Well, the dry mix to wet mix volume went down by about 30% - 40%. So I have about 7 - 8 gallons of clay after it's mixed up. There's about 1.5 - 2 gallons of millet & saw dust in there now. So, I need about another 2 gallons worth of millet. I'll get more and do some additional math on this. 

Jute / Sawdust / Sisal / Hemp / Fiberglass?

Two concerns. One is cracking as it dries. The second is max durability during service. I think I'm screwed on the second one. It is what it is. I coud put in glass fibers, but they will just melt. But ... if I get some kind of organic fiber introduced into the wet mix, I can help the cracking while it dries. I think I can get stuff like this at the craft store. I've seen it used in plaster casting. The second benefit here might be that it provides pathways for the burn out gases to escape. 

Okay, that's all the rambling for now.

Making some clay

Stared working on the panels for the forge. Started by getting the proportions right. After half an hour resurecting some algebra skills I came up this this:

EP Kaolin - 31.75 lbs
Aluminum Oxide - 13.25 lbs
Zirconium Silitcate - 5 lbs

I used the bathroom scale for the EPK. I then used a lab scale I have for the smaller weights. The 31.75 lbs of Kaolin filled almost an entire five gallon bucket. The bucket was then split into two buckets by sight. As the Aluminum Oxide & Zirconium Silicate were weighed out they were added to each bucket. Finally the millet and a little sawdust was added. I decided to add the sawdust to give it some strength while it's drying. Hopefully that will help prevent cracking to some extend. In all about 15 lbs of millet and about a pound of sawdust was added.

Adding the millet

Dry clay ingredients before mixing

Adding the sawdust

Drill with mixer

Clay after mixing with drill

Once the dry ingredients were divided and the sawdust and millet were added to the buckets, a drill with a mud mixer was used to blend the dry ingredients. Then water was added until the mix was thick, pliable, and most of the ingredients were combined.

Following that, the whole bucket was emptied onto the bench and the remaining un-mixed material was hand mixed until it was uniform. I am told this is called wedging. I'm pretty sure what I was doing had no resemblance to actual wedging. At any rate it was mixed.

Then I pressed the clay into the forms I had made the day before. I used some scrap wood to pull across the top of the form. With a slight side to side motion this eventually left a pretty smooth surface. Smooth is not as much the point as it being free of voids that would allow heat to escape.

After a few hours the backs were taken off to let them dry faster. I also added some clay to the backs and pulled them with the scrap wood again to fill in several voids that remained after I molded them in the first place.

Note that I tried to lift the backs off. No go. This just pulled more clay out of the surface. I then took to hitting the bottom sideways to shear it loose.

Now to let them dry. Hope they don't crack! Once they get pretty dry I think I'll put them in the kiln at 200 degrees for several hours to see if we can dry them faster.

I have enough EPK for more. I am going to need another five pounds of Aluminum Oxide and Zirconium Silicate.

Shrinkage

Started building forms for the clay today. In sizing the forms, had to allow for shrinkage. I'm going to assume the EP Kaolin will be the dominant factor so I'm going to use Edgar's data on this. I put that into an Excel file to calculate it and it looks something like this:

	Shrinkage Table for EP Kaolin by Edgar Minerals
	Dry	Fired - Cone 11 (1315 C)
Shrinkage	5.0%	11.8%
Formed 1	2.000	2.125	2.250	2.375	2.500	2.625
	4.750	4.875	5.000	5.125	5.250	5.375
Dry 1	1.900	2.019	2.138	2.256	2.375	2.494
	4.513	4.631	4.750	4.869	4.988	5.106
Fired 1	1.764	1.874	1.985	2.095	2.205	2.315
	4.190	4.300	4.410	4.520	4.631	4.741

The units are inches. The entire table in excel is here.

"The Toaster Project" - New Book

I just ordered a book called "The Toaster Project". This guy decided to build a toaster from raw materials. It got some interesting reviews. Sounds like the dude ended of with toast, but not a very serviceable toaster. It also sounds like he took a pretty extreme approach. Not even the first toaster maker started with raw materials.

It also sounds like he tried to take a bunch of short cuts and failed to study what he was doing very much. For instance there are some pictures of him trying to smelt steel in, as best I could see, a small blast furnace made out of a clay pipe. As anyone looking at the subject knows, just making a serviceable furnace of any type is a big job.

So, I'm thinking maybe it's time for a challenge. I have a pretty remarkable collection of tools at this point. Can I build a working toaster using tools available to me with my budget and using nothing more than stock sheet, rod, tube, pellet, powder, liquid, and wire materials. Modern "raw" materials if you will.

Well, something to think about anyway. First, I need to get this furnace on line.

Recipe Update

Got the stuff at Leslie Ceramics. It was suggested to me to add in some Zirconium Silicate by a friend who is a ceramics guy. So I got 10 pounds of that as well.

Rethought the couscous and went with millet seed instead. It was like $1.50 / pound at Whole Foods Market. I think the millet will expand less as the clay is drying. It still has the consistently round quality of the couscous and will burn out just fine. I'm thinking about 25% by volume right now.

Hopefully will make some molds tonight and get one bottom panel formed up and drying as a test. I'm going to split each side into at least two sections to allow for expansion and mitigate repair problems down the road.

Ward Burner

Ward Burner

http://wardburner.com/home.html

The prices look pretty good considering how much work this takes. Still, I like the challenge. I also like knowing how to fix it when it breaks and never having to worry about getting parts.

DIY Refractory Cement Formula Decision - Couscous

The science content here leaves a lot to be desired. Doing the best I can not to screw this up too much.

I've been stewing over what recipe to use for the insulating refractory panels that will replace the fire brick. After many hours spent reading and dredging up what I remember of chemistry I've come up with some conclusions:

• The chemistry of how alumina (aluminum oxide) behaves when fired is a bit of a mystery even to those who know chemistry really well it seems.
• Aluminum oxide absolutely raises the working temperature of the ceramic.
• There is a clay called Kaolin that has somewhere from 28% - 40% aluminum oxide (alumina) in it that is used in most firebrick recipes and I think many "fire clay" recipes.

Here's the analysis for Lincoln 60 Fire clay

K2O - 2.00%
Al2O3 - 29.00%
SiO2 - 52.00%
Fe2O3 - 2.00%
LOI - 12.40%

Here's the analysis for EPK Kaolin

CaO - 0.18%
K2O - 0.33%
MgO - 0.10%
Na2O - 0.06%
TiO2 - 0.37%
Al2O3 - 37.36%
P2O5 - 0.24%
SiO2 - 45.73%
Fe2O3 - 0.79%
LOI - 13.91%

LOI = "Loss On Ignition" I assume these are organics or hydrocarbons with flash points well below the temperature needed for vitrification. Vitrification is generally used to describe the point at which some of the silicon oxide begins to melt.

The Lincoln 60 analysis very likely omits trace elements below 2%. So if you look at the big hitters here they are aluminum oxide and silicon oxide (silica). The organics are important as they likely provide some of the binding action when water is added. 

The aluminum oxide and the silicon oxide have an affinity for water. I haven't tried it yet, but it must have a role on creating the sticky consistency of the clay. We all know how granular sand tends to stick together when wet, the powdered silica has to be doing nearly the same thing. This affinity for water is called hydrogen bonding. It's a fairly weak bond. It can be broken with a little bit of heat of even just having an imbalance of water in one place as compared to another (air). The water will evaporate off the bond is so weak. 

This affinity for water gives the silica and the alumina the ability to stick together so you can mold or shape the mix. 

Oh, This is NOT cement.

Cement and mortar are based on a combination of calcium oxide reacting with carbon dioxide and other components like aluminum oxide being converted to hydrates like aluminum hydroxide. See this article.

As far as I can tell, this hydration process is not associated with the making of clay based refractories. 

Ok great, so what's the recipe going to be?

• EPK - Kaolin
• Aluminum Oxide (enough by weight to add 3% - 4% to the mix)
• Couscous

The "normal" recipes use saw dust. The saw dust burns out of the ceramic leaving voids that create the insulating properties. The gap don't transmit energy well, and the sheer reduction of mass reduces the thermal conductivity of the ceramic. So why am I using couscous?

If you don't know couscous is a wheat based pasta that is round.

Here's why I think it will work:

• It will burn out like sawdust.
• It is more consistently sized and fairly large so the gaps should be bigger than with sawdust.
• It's round. Round gaps don't have sharp corners that tend to promote crack propagation. So, the resulting part should be stronger. 

So, this week I will make a stop at Leslie Ceramics and Safeway! Maybe this week I'll get to fire some panels. 

Wish me luck!

Hot steel!

Yay! We've got hot steel! This is a shot of a piece of 1 1/4 angle iron on it's 2nd or 3rd trip into the forge. The reheat from it becoming non-plastic to nice and red hot is a couple of minutes at this point. This is 30 - 45 minutes into the first firing.

Work on the forget today started out fitting the lid bricks. I made a 30 degree ramp out of some wafer wood to hold the bricks at the right angle on the tile saw. This tile saw does 90 & 45 degrees only. So I needed something to angle the bricks since the blade could not be set at 30 degrees. About 50 cuts later I had a roof on the forge.

At that point I used a grit edge 2 inch hole saw to bore the burner hole in the side of the forge. The bricks are not grouted in at this point. A piece of wood  was used to back up the brick so the hole saw could push through. Once the hole was bored a bar clamp was used to provide a temporary support for the burner. A vise grip clamp held the burner against the bar clamp. After all the propane was hooked up it was time to fire it up.

Lighting is was a pain in the ass. I used a long propane lighter. It kept going out when I put it in the forge. Either too much gas or something. Only once did I get a small blow out and singed a little bit of arm hair. I did not want to stick burning paper in there because I did not want hot burning paper flying out.

Got it lit. After a couple of flame outs I got the balance of fuel PSI and the opening in front of the forge close. It was darn close to a reduction flame. With two burners it will need a bigger opening. Some of the more successful furnaces I have seen have a chimney.

Temperatures - I've been concerned that the generic fire brick I used was going to be too conductive of heat. It's right on the the edge. The outside temps at peak ran from 80 degrees to 300 +/-. Nothing I could find was over 300. Ok ... so?

Lets put this in perspective. My ceramics kiln will be 1600 - 1700 degrees and the outside will be no more than 250 degrees. I don't have enough experience with this one to see what the outside temp will be as we approach 2000 degrees, but it's going to be a hell of a lot more than 300 degrees. Long term, the fire brick is not going to work. Further it may even vitrify. If so I'll have a pile of really hot glass on my hands.

Next is the question of how to come up with a decent refractory compound that I can get the materials for. There are many formulas. The trick is getting the materials. If getting the materials is too resource intensive then the castables that can be purchased are more cost effective. I would like to over come this because the castable mixes are not cheap. This forge would have cost me $200.00 in castable refractory.

The argument, which I agree with, is that the fuel cost savings make up for the investment many times over. My objective was to simply get a working box of bricks with fire inside at the lowest cost possible. Once I get the 2nd burner in there and working, mission accomplished.

So anyway ... it works and I managed to bend some steel.

Thanks to Teri and Hayley for standing by with the phone, ready to call 911! Fortunately, no problems. Knock on wood!

Oh, forgot to mention the steam. Due to the saw cutting several of the bricks had a good bit of water in them. They steamed off a good bit. I was getting a little concerned. Then I figure these have already been fired. The water got in there via open paths so the steam could follow that paths back out. Fortunately that worked out.