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Old 09-03-2009, 02:01 AM
Doug Harroun
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Furnace build thread

So if it's all right with everyone I'm going to document my furnace build here. Feel free to comment, add notes, etc... this is a work in progress.

I'm building a freestanding pot furnace essentially as depicted in Glassnotes as the Penland Pot Furnace.

Years ago I obtained a Dyson pot 18" OD, I am going to keep it as my standby pot and order one to build around. Probably the 19" EC, unless otherwise guided.

Furnace dimensions, approx: 50" tall, 50" OD, 24" ID.


Wall will be 3" Kast-o-lite 30: 2.945 cu ft. Surround that with 10" of frax, and some sheet metal.

Crown will be ...dunno what yet. Phlocast, Mizzou? ~2 cu ft. With similar frax over lay and a very artistic metal shell.

base will be Kast-o-lite, IFB and hard brick....

Cast various parts from what I have left....

Need advice on burner heads.

will add more as needed, including pics if they'er allowed

-Doug
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Old 09-03-2009, 06:38 AM
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I would recommend the 19 inch pot from High Temp in Portland. It's a better pot for less money and you don't have to wait for it.

Don't ask them about horseshoes either. They know nothing about them.
Put the ten inches of frax on the crown and eight around the outside. More is simply unnecessary. I would suggest recuperating it. Wake up Hugh! If you do recuperate, the burner needs special consideration and Hugh does sell them I think. I've seen them work and they do it well.
Phlocat will work fine as a crown. Morco 95 would be better but it's hard to get.
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Old 09-03-2009, 08:48 AM
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i agree with Pete, recuperate. my furnace is a lot like my v-10 F-250 and that's getting old
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Old 09-03-2009, 10:31 AM
Eben Horton Eben Horton is online now
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Quote:
Originally Posted by Thom Kennedy View Post
i agree with Pete, recuperate. my furnace is a lot like my v-10 F-250 and that's getting old
same here...
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Old 09-03-2009, 11:37 AM
Doug Harroun
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Recuperation will be part of the furnace as well. I'm not entirely sure which scheme I want to go with yet. I can fabricate stainless steel parts pretty easily, but the designs that seem to work well are cast refractory, correct?
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Old 09-03-2009, 11:45 AM
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Both. Get together with Hugh. Pay him. You won't regret it.
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Old 09-03-2009, 07:36 PM
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You can PM me and I'll reply. I'm on the road for the next two weeks.
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Old 09-04-2009, 12:29 AM
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Quote:
Originally Posted by Doug Harroun View Post

Furnace dimensions, approx: 50" tall, 50" OD, 24" ID.


Wall will be 3" Kast-o-lite 30: 2.945 cu ft. Surround that with 10" of frax, and some sheet metal.

Crown will be ...dunno what yet. Phlocast, Mizzou? ~2 cu ft. With similar frax over lay and a very artistic metal shell.

base will be Kast-o-lite, IFB and hard brick....

Cast various parts from what I have left....

Need advice on burner heads.

will add more as needed, including pics if they'er allowed

-Doug
Welcome to the board! It's think it's great your documenting your build. I always learn a little more with everyone.

Kast-o-lite 30 make sure there are several varieties.

You need to think about your floor. It will see glass and kast-o-lite won't hold it back. Some use mizzou or a ramable clay I used a few inches of mizzou over 2800 brick on our last build (only because they are salvage). Don't forget to cast a drain port this to will need to be resistant to glass attack. You also want to angle your base towards the drain. I placed mine on the back of the furnace with a fiber plug. I do think most have the cleanout in the front.

I used kast-o-lite 30 for my crown and never had a problem. If you want extra strength you can cast a dome shape on the top. I also used it for my door. For a sill I like to use a large clipper brick but there are several castables you can use. .

Burner. I would scrap that idea and go with electric. Seriously you may want to look at gas prices and compare to what you pay a kilowatt hour.
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Old 09-04-2009, 05:18 AM
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Start up costs on electric are high but the convenience is incredible, as is the safety, particularly in a hot town, which Albuquerque is. While I vastly prefer, and would advocate for moly, SiC has the advantage of not needing a transformer. New Mexico has pretty reasonable electric rates, so it would cost a good deal less to run.

Insulate your hood. Mine is six inches thick, all steel and insulation. It's very cool in my shop, almost too cool.
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Old 09-04-2009, 09:46 AM
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The guys at Hi-Temp Refractories in MO. supplied me with their Morocast 60 HS (60% alumina) product as a substitute for Mizzou to replace the 3-4" of floor that had gone to mush from pot leaks over the last 12 years. The old floor was unstable at melting temps but hard as rock at room temp. Had to use a rented electric jack hammer to get the old stuff out.

But I have listened to Pete & others long enough to decide to go Moly for the sake of lower fuel bills among other things. Just my maxon blower running 24/7 consumes $100.0 plus a month in electric charges. Now it'll only run while I'm blowing (glory).
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Old 09-04-2009, 02:01 PM
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Ya know what, it might be a good idea to start a thread for guys that are just starting to build or are doing a total rebuild.

We could offer some precepts to follow, for example if you don't have to be in a city, moving to a spot where building standards are easyier to deal with is a good plan. Nice little backyard studio.

Also figure out how many pounds you use a week and designing your equipment around that.

I way overbuilt my studio when I started, I made a huge glory hole and a 150 pound electromelt. This cost me big bucks over 20 years.
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Old 09-04-2009, 05:12 PM
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At first I considered electric elements. Being electrically inclined the wiring and power is a non-issue for me. SiC was out of the question. I know a few people using them and the replacement cost of shot elements would run higher than the cost of gas. Moly elements look better, but the _VERY_ high initial investment was the factor that pushed me back towards gas.

Also, unless you live near a wind farm or hydro plant you power is most likely coal/gas/oil based anyways, why deal with a loss in conversion?

Right now I pay about $0.015-$0.02 per kWh for gas. For electricity it's $0.1085 per kWh.

So I'm still pretty sure I'm building a gas furnace.

...unless someone knows a source for moly elements for less than $100 each.
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Old 09-04-2009, 09:15 PM
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Quote:
Originally Posted by Doug Harroun View Post
Recuperation will be part of the furnace as well. I'm not entirely sure which scheme I want to go with yet. I can fabricate stainless steel parts pretty easily, but the designs that seem to work well are cast refractory, correct?
Yeah, Doug...if you recuperate you will need a completely different burner setup. Its a surface mix burner as opposed to a premix burner.

Charlie Correll also builds and sells them as complete units: the recuperator and the burner.

http://www.correllglassstudio.com/recupburner.htm

http://www.correllglassstudio.com/recuppaper.htm
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Old 09-04-2009, 09:37 PM
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Quote:
Originally Posted by Lawrence Ruskin View Post
Ya know what, it might be a good idea to start a thread for guys that are just starting to build or are doing a total rebuild.

We could offer some precepts to follow, for example if you don't have to be in a city, moving to a spot where building standards are easyier to deal with is a good plan. Nice little backyard studio.
**************************

I think thats a great idea Lawrence. I will take this thread and make it sticky so it's always at the top. as long as it keeps getting added to, I'll leave it there. If it winds up being really good, I'll move it to antiques and classics and stick it there.
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Old 09-05-2009, 07:04 AM
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I do think that the floor of the furnace never gets the attention it deserves. First, its walls are the foundation upon which you will build a heavy thing and secondly that glass is the universal solvent and will eat through pretty much anything you stick down there short of rammable coarse grog clays. I don't think a 60% alumina castabe will last that long down there. Kastolite 30 will simply be dissolved wherever glass gets to it. So will IFB. Once you have a glasscrete down there you will have no insulation. The walls have 8 inches of fibre, the crown 10. Consider the floor if you want to look at heat loss.
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Old 09-05-2009, 08:46 AM
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Good point on the floor...My furnace was built by Charlie Correll & we installed in 1997. To be clear about the floor - From the steel up, the layers are 4" of Insblock 19, one course of G20 softs, one course of G26 softs, then the original floor was 3" of Mizzou. When I excavated with the Jack Hammer, pretty much all the Mizzou strata was glassy but fortunately very little of the next layer of G26 was eaten. The old glassy Mizzou peeled away from the ins. brick layer pretty cleanly so I could put in about 4" of the Morocast.
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Old 09-05-2009, 10:57 AM
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I have never been satisfied with Mizzou as a refractory for actual glass contact and a floor inevitably has glass contact. It just turns to mush and when it does, heat is really scooting right through it to the steel plate and you never appreciate how much heat is being lost down there since you can't see it. Eight inches in the floor sounds good to me.
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Old 09-05-2009, 10:46 PM
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[quote=Doug Harroun;82268]At first I considered electric elements. Being electrically inclined the wiring and power is a non-issue for me. SiC was out of the question. I know a few people using them and the replacement cost of shot elements would run higher than the cost of gas. Moly elements look better, but the _VERY_ high initial investment was the factor that pushed me back towards gas.


Everybody keeps bad mouthing SiC for how long the elements last- and I know I have had much better than average luck, but out of the 6 elements that I started with 8 years, 10 months ago, 4 are still running, one is at about 7 and a half years, and one was changed out about 4 years ago and after a trim of the power cable, is ready to go back in as a replacement. So the bottom line is I've bought 9 SiC Starbars total and I still have 2 backups waiting to get installed. That's with running 3 bars in the furnace and 3 in the glory hole.

So what are other people's experiences with Starbar longevity?
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Old 09-06-2009, 08:10 AM
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You're running solid Starbars?

I used two bayonet style elements from I2R and they were 4 plus years old and still going strong when I shut that machine down.

I think those bars will last a long time if you put them in properly in the first place.
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Old 09-06-2009, 11:01 AM
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This board primarily has moly users. Brad Shute's board seems populated with SiC people. Both work and both have advantages and disadvantages. Both in fact seem to be susceptible to moisture issues and I used to think it was just SiC. I used to hear tales of the elements falling apart on SiC for no apparent reason but it seems that with good installations, that really rarely happens. Moly elements break too and probably for reasons associated with installation. SiC doesn't need a transformer which is a big plus but the downside is changing resistivity as they age. So there's good and bad points for each. This board just tends towards moly. There's no basis to be snotty about it though.
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Old 09-06-2009, 12:37 PM
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[quote=Lawrence Ruskin;82294]You're running solid Starbars?

No, the spiral cut Starbars. The one element I lost was due to a pellet popping and landing on the element and eating through it. After that I preheated the pellets and never had the problem again.
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Old 09-06-2009, 02:04 PM
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Now there's a reason to get snotty about Molys! I had forgotten! Somehow using elements that react to glass seems like a less than good idea in a ... ( Oh I know) Glass Furnace! Preheating your glass or batch to avoid element failure doesn't seem like a real solution for me.
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Old 09-06-2009, 02:30 PM
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If you don't preheat your cullet that glass will go winging around the inside of your furnace.

I would expect a good solid hit on a moly element would break it, but I really don't want to find out.

Unless someone can come up with another solution, I will preheat until the sad little day I die.
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Old 09-06-2009, 04:41 PM
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The only time I have ever lost a moly element was due to my own stupidity, of which I have an ample amount. I load cullet as well as batch . It you want to see something really blast around, try throwing in an entire color rod you don't like. My best understanding was that in an SiC, if a piece of cullet sticks to the element, It's toast and that it's not the cullet popping that does it damage at all. It's the chemical reaction.
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Old 09-06-2009, 05:55 PM
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SiC elements do break down in contact with glass. I went to High Density elements 2 years ago as a result of aging after 9 months. We have seen zero aging now for 2 years after going to HD SiC elements. The downside of SiC is also that it becomes brittle at 1200F. We found this to be a problem recently when we had 3 elements within 6 months break at exactly the same spot. All 3 were determined to be a result of prolonged exposure to 1200F. We had idled the furnace at 1700 for a wekk at a time when this happened and the breaks were at the point where it was estimated to be 1200 degrees. Without the cycle of charging and blowing and the 1200 point changing it literally cut the elements at 7" from the end each time. Each element only broke when we fired back up and within a minute of running at full power you could hear a sizzle and pop and the SiC litterally melted at the break point.
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