Marks Kiln build

[dnalot]

Here are some photos of the completed furnace ready for action. I made an exhaust hood for it that directs the exhaust to the inlet of the exhaust fan in the hood above my bench.

Mark T

 

[dnalot]

The element turns out to work perfectly. And it heats the oven far faster than what you would want, but the PID controller takes care of that. The controller will turn the current on and off to the element to control the rate of climb to whatever you want. And the 3300 Watt element can easily heat the oven up to the max 2200 degree F. I had hoped for. On my first use I slowly ( over 8 hours) brought up the temp in timed stages to 1200 F. and then let it cool down naturally. 8 hours later it was still 120 F inside (shop was 60 F.). Inspection showed there to be do damage to the refractory or anything else.

As you can see in the photo (element is just turning on) the element heats up faster where the coils are closer together. It turns a uniform color after about 10 seconds. I sorted this out by stretching the hot areas out a bit more. After getting hot the wire is much stiffer and I suspect more brittle.

The second go I did the same thing only I took it up to 2000 F. over 10 hours and held it there for 3 hours. After cooling down everything still looked good.

I made a drip pan for burning out wax. The grate is S.S. But the pan is mild steel. I will make a stainless tray when the material arrives. The photo of the pan shows two 4 inch flasks and one 3.5” flask. The drip pan is elevated above the floor by .5”. I have a long heavy duty spatula that I can remove the pan with when needed.

I have been doing some early tests burning 3D resin printed parts just lying on the drip tray and it is extremely stinky. Its the kind of stink that hangs in the air for days. The hood works great collecting the smoke and directing it to the overhead hood vent but the slightest breeze will let some smoke escape. My shop can be drafty so I plan to add a curtain made of fire prof felt that will attach to the back and sides of the hood with magnets.

“Abby” in a previous post suggested I needed a much larger vent hole in the top. I think I will start with a bit larger (tan planed) top vent hole and air provided by a controllable aquarium air pump to a couple of holes in the kiln's floor. After I put my furnace through a few test runs I will let you all know what I finally end up with.

My original budget was $600 and I came close at $660. The hood, the drip pan and a spare element put me over the original budget. I also plan to protect the floor with a “kiln shelf” and expect to spend another $20 there. I don't know what it will cost to operate but my area of Washington State enjoys one of the lowest electrical rates in the country. The Hydro-power dam is only seven miles away.

To avoid electric shock I plan to add a micro switch that interrupts the signal to the relay if the door is open. And I plan on making myself a ceramic coffee cup and a beer mug.

Mark T

 

[awake]

Mark, this is an exceptional build; I suspect the quality exceeds much of what is commercially available in a similar size. So much so, that I hate to quibble with one small point:

The PID controller I bought was made by RoHS.

RoHS is similar to UL Listing - a certification, not a brand name; analogous to, but with a different focus from, UL or CE: The Differences between UL, CE, EMC, CSA, RoHS Certifications

Of course, I suppose someone could try to use it as a brand name ...

 

[dnalot]

RoHS is the similar to UL Listing

Nice to know. It was the only marking on the box that looked like it might indicate who made the unit. Must be a generic knock off of some kind.

Mark T

 

[awake]

For so many electronics items, even if it has a "brand name" on it, it is probably a generic knock off!

Again, magnificent work on your kiln - a work of art, and lots of useful information for those of us that keep thinking we might build one some day ...

 

[dnalot]

Again, magnificent work on your kiln - a work of art, and lots of useful information for those of us that keep thinking we might build one some day

Thanks Andy. And thanks to all of you that have been following along.

I will post updates as I figure out how to use the furnace for use as a burnout oven..

News Alert. I have been watching the deployment of the mirror of the James Web Telescope all morning. The mirror was just successfully deployed.

Mark T

 

[ddmckee54]

From us nerd type EE's:

RoHS compliance means that a product has been tested for 10 banned substances by an independent authority, and that the tests confirmed levels of the substances below the RoHS threshold. Under RoHS 3, the latest version of the RoHS directive, the 10 substances restricted are:

• Cadmium
• Lead
• Hexavalent chromium
• Mercury
• Polybrominated biphenyls (PBB)
• Polybrominated diphenyl ethers (PBDE)
• Bis(2-ethylhexyl) phthalate (DEHP)
• Benzyl butyl phthalate (BBP)
• Dibutyl phthalate (DBP)
• Diisobutyl phthalate (DIBP)

All of these substances must be limited to 1,000 ppm except cadmium, which has a limit of 100 ppm.

This was clipped off from an RoHS compliance site. In most cases it just means that they didn't use lead solder when building the electronics.

Don

 

[Richard Hed]

From us nerd type EE's:

RoHS compliance means that a product has been tested for 10 banned substances by an independent authority, and that the tests confirmed levels of the substances below the RoHS threshold. Under RoHS 3, the latest version of the RoHS directive, the 10 substances restricted are:

• Cadmium
• Lead
• Hexavalent chromium
• Mercury
• Polybrominated biphenyls (PBB)
• Polybrominated diphenyl ethers (PBDE)
• Bis(2-ethylhexyl) phthalate (DEHP)
• Benzyl butyl phthalate (BBP)
• Dibutyl phthalate (DBP)
• Diisobutyl phthalate (DIBP)

All of these substances must be limited to 1,000 ppm except cadmium, which has a limit of 100 ppm.

This was clipped off from an RoHS compliance site. In most cases it just means that they didn't use lead solder when building the electronics.

Don

Thank you for that info. Just so you all know: 1000ppm is one out of a thousand or .1% which, when dealing with poisons, is actually a lot. If dealing with carcinogens, it's too much. I suspect some of those chemicals mentioned are carcinogens. It's funni how we all fall into that trap of seeing 'ppm' and we thimpfks it is automatically a small amount. It's how someone trying to sell you something leaves out pertinent information.

 

[JLaning427]

Thank you for that info. Just so you all know: 1000ppm is one out of a thousand or .1% which, when dealing with poisons, is actually a lot. If dealing with carcinogens, it's too much. I suspect some of those chemicals mentioned are carcinogens. It's funni how we all fall into that trap of seeing 'ppm' and we thimpfks it is automatically a small amount. It's how someone trying to sell you something leaves out pertinent information.

Yes, 0.1% is a large amount for some poisons, and negligible for others. And in the case of most electronics, 1000 ppm is probably acceptable, as I doubt Mark will be using his controller as a hot beverage container anytime soon. But as a complementary example, the USDOT haz-mat limit for transporting Benzene in water is 5 ppb, (5 parts per billion) which is more appropriate because you could end up drinking that contaminated water down the road (say, if it gets mixed into a municipal waste stream, or spilled from an overturned truck). Different horses for different courses....

James

 

[dnalot]

UPDATE

After struggling for days trying to figure out how to use the no-brand PID controller. I bought a new one. The first controller came with the most pathetic manual I have encountered. Before buying a new one I went to the companies web sight and downloaded their manual. Complicated yes, its a complicated device. But their manual was easy to understand and I was quickly up and running. The controller I bought is Auber Instruments SLY-353P. See link above.

I have added a short skirt to the edges of my exhaust hood. It is a welders felt blanket rated at 1500 degrees F. The curtain keeps drafts in my shop from letting smoke or vapors from escaping the hood. And I added an aquarium air pump with two outlets and a volume control knob to supply air for a clean burnout. The air lines are silicon rated for 500 Degrees F and the air is introduced through the bottom of the kiln. My first burnout of a flask with a wax based resin went smoothly (as far as the controller was concerned) with the controller doing its job very well and the hood took care of the fumes.

At 1360 degrees for 4 hours the door face came up to 500 degrees F. The sides were 250 F degrees and the bottom was at 350 degrees”. And that's where the story took a sour note. My element got to hot and came lose from one of the pins that keep it in place. To many coils to close together allowed the wire to get to hot (white hot). (I error-ed on my original calculation thinking I had a 220 volt service to my shop but when I checked it was actually 240 volts). To try and remedy this problem I went from 240 Volts to 120 volts and installed an element with 6.5 Ohms resistance. The kiln now has a 2200 Watt element and now glows with a bright orange color perhaps bordering on yellow. That will only let me heat up the kiln to 1150 degrees F. I have used all the available amps on my 120 outlet so will have to go back to the 240 volt outlet. I have now ordered some 20 gauge wire (used 18 gauge originally) With that I can make an element that should yield 3100 watts, down from 3600 watts of the first one I made. Somewhere I will find the sweet spot. If you are building a kiln cut more groves for the element to sit in. When I get this sorted out I will post another update.

I have also doubled the number of pins securing the element and have enlarged the top vent to 1”

I built this kiln for my exploration of investment casting. You can view the results of my first pour here

Mark's First investment casting

Mark T

 

[dnalot]

Update 2: I installed a new 240 volt element that draws 13 Amps with a resistance of 18 ohms, yielding 3100 Watts. I used 20 gauge wire wrapped around a .42" rod to create the coils. It can take the furnace up to 1400 degrees F quickly. I don't think it has much power to spare but it reaches the temperatures I need. Shortening the element would result in higher temps with an increase in amperage draw. I used 23' of 20 gauge wire to make the element I am testing now. 25' spool of wire only cost $8.

Mark T

 

[awake]

Mark, any idea what the maximum temperature is on your setup?

 

[dnalot]

any idea what the maximum temperature is on your setup

It is now around 1500 degrees F. My original element got it up to 2000 degrees but the coils of wire were to closely spaced and the wire got too hot. Using a smaller diameter wire and/or having more groves to house the element would fix that. For my use I need to hold 1350 degrees for 4 to 5 hours so what I have now works for me. I plan to try it out today with a pour at around 10" am tomorrow. It takes about 20 hours to mix and pour the plaster, let it dry and then do the burn-out in the kiln. This time around I have a good vacuum chamber and a much bigger vacuum pump so I am hoping to improve on my first attempt. One thing I have learned doing this is there are no shortcuts.

Mark T

 

[Richard Hed]

It is now around 1500 degrees F. My original element got it up to 2000 degrees but the coils of wire were to closely spaced and the wire got too hot. Using a smaller diameter wire and/or having more groves to house the element would fix that. For my use I need to hold 1350 degrees for 4 to 5 hours so what I have now works for me. I plan to try it out today with a pour at around 10" am tomorrow. It takes about 20 hours to mix and pour the plaster, let it dry and then do the burn-out in the kiln. This time around I have a good vacuum chamber and a much bigger vacuum pump so I am hoping to improve on my first attempt. One thing I have learned doing this is there are no shortcuts.

Mark T

When you say "pour", what are you pouring? I assume you were pouring liquid metal but by your words, it seems you are pouring plaster. I thot you were going to use this for heat treating.

 

[dnalot]

When you say "pour", what are you pouring? I assume you were pouring liquid metal but by your words, it seems you are pouring plaster. I thot you were going to use this for heat treating.

Sorry for the confusion Richard, I'm not the word smith you are. My main purpose in building this kiln is for use in lost wax / resin investment casting. First step is to pour (should have said fill the flask with plaster). Then let stand for a few hours to set . Then into the kiln for about 14 hours to dry out the plaster and then burn out the patterns. The burnout requires lowly ramping up the temperature in several steps to 1350 degrees and then holding that temp for 4 hours before ramping down to the pouring (metal) temperature. I am using brass so pouring temp = 800 degrees F .

Remember I don't really know what I'm doing (yet)

Before retirement I was a fiberglass boat builder. It always burned my *** when people would refer to laminating the hull as "pouring the hull" or other laminated parts. It made it sound like it was easy. My brother and I built boats from 37' and down. The bigger boats were inboard diesel, and the smaller models were outboard or inboard/outboard. Our Big sellers were sold under the C-Dory brand. We also built a line of custom Catamarans.

22' C-Dory Angler and 24' Tomcat

Two 22' Cruisers off to a dealer.

Custom 30' Tomcat . If you think the photo above looks silly, we towed this 10' wide boat on a 5' wide trailer to deliver it to water.


Mark T

 

[jumps4]

off topic: I have dreamed of owning a C-dory 22, a fantasy I will never afford.

 

[dnalot]

I have dreamed of owning a C-dory 22

I just looked at what they are selling for. Remarkable how well they have maintained their value. Whatever you spend on electronics you lose the first day. Motors depreciate rapidly but the C-Dory boat has incredible staying power. They were built to last and the design looks good even if the boat looks a little crusty. The boats I built have a serial number starting with "DOR" I sold the company in early 2000.

Mark T

 

[dnalot]

Update 3

I have added a a false floor to my kiln to house an additional length of element. I was having problems with the element getting to hot and failing. With this extra extra length I was able to fit an element made from 46 feet of 18 gauge wire. The new specs are 2400 watts, 24 0hms, 240 volt drawing 10 amps. I am now able to get the 1400 degrees F. I need without the element getting to hot.

Mark T

 

[abby]

I use sheathed elements in my burnout kiln , these are rated for a maximum temperature of 850°C which is perfect for the maximum requirement of 725°C.
Dan.

 

[dnalot]

I use sheathed elements in my burnout kiln , these are rated for a maximum temperature of 850°C which is perfect for the maximum requirement of 725°C.

How much do they cost? Are they made to fit a particular kiln? The element I have made cost me $10 and it takes me about 3 hours to make and install. It tops out about the same as yours. The investment plaster I have been using works best at 1400F, or 760C. when used with a printed resin pattern.

Mark T