Marks Kiln build

[dnalot]

I just realized that you could actually put the molds over a catch pan in the oven

I have already made a S.S. drip pan to catch any dripping wax. I will be doing mostly lost 3D resin. It doesn't melt, it turns to a gas and gets vented out. The small amount of wax used for the spur is not worth recovering.

Mark T

 

[dnalot]

Naturally, I can't see what is under that, but it doesn't look like it is supported except on the edges. Does the hi temp silicon stop it from sagging?

It is very well supported by the silicon and the bricks have a deep slot cut into them where they touch the cast refractory. Allowing some of the cast refractory to engage the bricks. You will be able to see this detail when I cast the top. I should have taken more photos when I mounted the bottom to the frame.

Mark T

 

[dnalot]

After almost two weeks of freezing weather the snow is starting to melt off my shop's roof. Icicles are 36" long.

Mark T

 

[Tug40]

Randoo, yes i live in Castle Rock area.
I suspect U got hammered with snow & ice too.
Looks like Mark really got it.
We haven’t had any mail delivery since last Tuesday.
Lunch with you & Mark sometime would be good. Richard also, he sounds like a wild & crazy guy.
Stay warm & outa the ditch's.

 

[Richard Hed]

Randoo, yes i live in Castle Rock area.
I suspect U got hammered with snow & ice too.
Looks like Mark really got it.
We haven’t had any mail delivery since last Tuesday.
Lunch with you & Mark sometime would be good. Richard also, he sounds like a wild & crazy guy.
Stay warm & outa the ditch's.

I may have been wild in my younger days, but I'm just crazy now.; Yeah, and I would luv to be invited for lunch, but it is too far to go over there on such a wild errand.;

 

[abby]

A well constructed build Mark , may I suggest that you include a venting facility.
My own burn-out kiln , although very similar in construction , is much larger and can accomodate 4 flasks which are 6" diameter and 12" high.
A full kiln load equates to about 21 lbs of water , which eventually leaves the kiln as steam so an exit is required.
In addition it is important to have sufficient oxygen enter the mould cavities to complete the burn-out , residual wax or resin cannot burn without oxygen.
I have experienced moulds that showed the existence of wax even after casting.
If I may tell you of one or two discoveries I have since made ;
My kiln was built in the days when programmable controllers were financially out of my reach .
I wrote a programme for an Apple II which I had lying about , this simple program switched solid state relays on/off according to input from a thermocouple .
The kiln had an inner box core about an inch thick with grooves in the side walls for the heating elements , which totalled 5 Kwatts.
The inner box was encased in a 4" thick layer of ceramic fibre blanket ( rescued from a dumpster at a local tile manufacturer ).
Again because I was setting up a business with restricted finances I saved money by using a piece of 9" dia steel pipe 18" long as a flask .
I had several 14 hour long un-eventful firings , normally overnight.
Then finally disaster , an overnight power cut swiched the computer off, when the power came back on everything fired back up.
When writing the programme I included a line of code which requested an input for the final casting temperature , the programme would wait for this input , but the output to the kiln would be high , elements switched on but no control !
Anyway to cut a boring story the kiln fired to an unknown temperature causing a chemical reaction between the investment cement and the steel pipe.
When we managed to open the door after 24 hours cooling the pipe and contents had disappeared leaving a pile of slag burned into the kiln floor.
One side of the kiln had a hole burned though an inch of high temperature refractory cement , only the ceramic blanket , acting as a barrier , prevented the reaction melting through the steel outer casing and possibly setting fire to the building.
Needless to say the rebuild incoporated safeguards to prevent such an occurence and eventually I was able to buy a proper controller and nimonic investment flasks , I also changed the heating elements to encased ones which , although limiting the temperature to about 850°C , is more than enough for a wax burn-out.
My castings range from hundreds of tiny ones

to single large pieces

Dan.

 

[dnalot]

may I suggest that you include a venting facility.

Thanks for the input Dan. I really appreciate it. I have provided a .5" vent hole it the top of the kiln and will be adding a smaller hole or two in the bottom. I had thought the door would not fit tight and provide a way for air to get in. But as luck will have it the door fits snugly and the spring-loaded latch keeps it tight. Any suggestions as to vent hole size? I have thought about using an aquarium air pump to supply the air through a hole in the bottom, any thought on that? I completed the kiln a week ago and have been testing it a little. I have no investment plaster yet as I have been snowed in since Christmas eve.

Your castings look great. I hope to be able do at least half as well.

Mark T

 

[dnalot]

Next step, the walls are fitted into place and the groves the element will ride in were drilled for the hooked pins that will hold the element in place. Also the hole for the thermocouple was drilled into the floor and the holes for the element's leads were drilled into the back wall.

I drilled a hole through the top brick nearest the front of the oven to run a couple of piano wires that will help hold the ends of the cast horse shoe shaped brick in place. Four wood legs will support the top bricks while the collar is cast. Like the floor I reinforced the corners with some piano wire in the cement. I fully expect the corners to crack but that isn't a problem as long as the wire holds the parts in alignment. I cast the top and the door at the same time.

I bought 30 pounds of refractory cement and I have about 3 pounds left over. 41 pounds of bricks and 27 pounds of refractory cement. That will put the total weight of this oven at nearly 95 pounds. Guess that's why the store bought furnaces cost so much to ship.

Mark T

 

[Tug40]

My wife has a wood-fired pizza oven she had shipped from Italy, yes shipping these small ovens can be costly.
Her oven will get up to 1000 deg, she actually let me anneal a small engine frame in it “one time”
Mark your workmanship is very professional.
Abby, when you were describing the mishap with the kiln, I had thoughts of The China Syndrome.
Nice castings BTW.

 

[abby]

I suggest a 2 or 3 inch diameter hole in the top and a similar sized hole in the door with a rotatable damper for adjusting the air flow.
I have no chimney fitted and during the summer months the steam is not a problem in my large workshop.
The winter is different , the steam condenses everywhere and any steel quickly rusts. Ideally I should have fitted a chimney to take the steam outside.
I will take a photo to explain as almost all of my pictures are on photobucket and unaccessible to me unless I pay the ransom.
Dan.

 

[dnalot]

The refractory cement requires 6 hours of firing at 350 degrees F. before it comes up to full strength. I was able to do this with the kiln floor and the door by placing them in the wife's kitchen oven. The top of the kiln will get fired in place when the unit is completed. After firing the door in the oven it was ready to be mounted to the door frame of the oven with weld-on hinges. I actually silver soldered them to avoid having the hinges creep around like they would if I used my arc welder. The door is secured with a spring loaded catch. I need to get a bigger spring but improvised with what I have for now. The door swings silky smooth and fits tightly.

Mark T

 

[dnalot]

The piano wire wraps around the furnace sides and over the top to insure the bricks stay in place if the unit is ever tipped over onto its sides or back. I originally thought the sheet-metal shell over a 1/2” ceramic blanket insulation would be all I would need to hold everything together but after further reflection I decided I needed the wire as well.

Mark T

 

[dnalot]

So there you go, the frame is all painted now and the unit is wrapped with ceramic insulation and the sheet-metal shell is installed. And a vent hole has been drilled into the top. The vent hole is required for the burn out process to promote burning and to expel any soot. Soot will conduct electricity and short out your element. My door fits rather tight so I will add a vent hole in the floor to allow air to get into the kiln

That was fun and I am very happy with how it turned out. Time now to install all the parts that make up the heating element and its controls.

Mark T

 

[dnalot]

Here is a link to the Amazon page I ordered the controller from

Ramp Soak Temperature Controller Kiln SSR Thermocouple Programmable Control 60 Segment: Amazon.com: Industrial & Scientific

The PID controller I bought was made by RoHS. Nice unit but the manual if you can call it that was horrid. Even when I went to the sellers web sight and found an updated manual with far less typos and bad info it was still almost worthless. Could find no You Tube videos on this unit. Spent several days farting around before I got it to work and a few more before I got it working smoothly. I recommend looking for a controller that is well covered on You Tube.

In an earlier post “Abby” referenced problems that can arise if the power goes off in the middle of a program. The controller I am using has a lot of variables that can be set. One of them is what to do if the program was interrupted by a power failure. I set it to “end program”.

I think I would have been better off with this one.

Amazon.com: Auber Instruments PID Temperature Controller,W/ 30 RAMP/SOAK,SSR Output, SYL-2352P : Industrial & Scientific

It looks like this unit is easier to program and there are several You Tube videos on how to program it.

Mark T

 

[dnalot]

I stretched my resistance coil out to 54” long and installed it into the groves cut into the bricks and secured it with wire pins with a hook on the end. I used the same wire the element was made from. By design my heating element was to have 14.67 Ohms resistance. I used an Ohm meter and checked to see if I was close and found it to be 15.2 Ohms. The element's pigtails are covered with two layers of ceramic insulation tubing and protrude through the back of the furnace and the sheet metal cover. I cut some slots in the sheet-metal so the cover could be removed without having to straiten out the wire. The element is probably the weakest link and will one day need to be replaced. The wire only cost a little under $20 ($19 for 50 foot roll, only used 28 feet) and was easy to turn into a coil and is very easy to install. I made a spare and put it in a box with some other spares like fuses and screws.

The control box contains the controller, a solid state relay, two fuses for the 220 volt service to the heating element and a 110 volt fuse to protect the controller and an on-off switch. The relay came with a heat sink but it was rather useless as it was painted and the surface the relay was to sit against was very irregular. I stripped the paint off and sanded the surface flat and smooth. A 3” fan was mounted to the back of the controller box for cooling the relay. Wiring was simple and I just followed the diagram that came with the controller kit. At least that part of the controllers manual was clear.

Mark T

 

[Sprocket]

Mark,
In the last picture, is that a fume hood over the oven? Seems like a good idea.
Doug

 

[dnalot]

In the last picture, is that a fume hood over the oven? Seems like a good idea.

It is but you were not supposed to notice until I post a photo of it tomorrow. It collects the fumes and a fan blows them up a 4" duct to a blower that vents to the outside.

Mark T

 

[Chiptosser]

Are you not using a low limit thermo?

 

[Sprocket]

Sorry Mark, but we really do pay attention to your pictures and posts.
Doug

 

[dnalot]

Are you not using a low limit thermo?

I don't know what that is. All I know is that it is a "K" type with a top limit of 2372 degrees F

Mark T