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Old 10-16-2017, 03:42 PM
Jordan Kube Jordan Kube is offline
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Custom Wire Furnace Bricks

This is sort of a continuation from the electric metering thread but I thought breaking it out into something new was appropriate.

The furnace in that thread got fired up and tested but did not perform well. Denver has their elements spec'd differently in two different places on their website, one with a 35 amp draw and one with a 28 amp draw. My intention was to put 208v through the 240v elements and get 30 amps. Instead, I ended up putting 208 through the 28 amp elements and just didn't get the power I needed. Shame on me. Additionally, I feel like that castings I made ended up with too much mass and really sucked the life out of what power was going in. This was a result of compromises made trying to use off the shelf parts.

After a bit of head scratching trying to figure out how to proceed I settled on a custom modular solution I've had on the shelf for awhile. I didn't want to make a mess with brick and I really needed to wind the elements to do exactly what I needed them to do.

And so, the wire furnace brick was born. One of the challenges of wire furnaces is getting all the wire in there to get the watt loading low enough for decent element life. Brick is a great material for insulation, but can be a pain to groove and end up very delicate after all the groves are in. Additionally, they don't hold up to glass attack very well. Castable refractory is better for glass and fume attack but also has its challenges including mold set up, insulation value, and mass.

A couple of years ago I tried to come up with a nice compromise and machined some models of a brick that could be cast out of Kastolite 30. The idea was to keep the brick to the minimum of material needed to be structurally sound and then back with frax. I also wanted them to be modular. Get glass on the bottom brick? Just un-stack and replace only what you need. It's easy to have a few laying around, no need to set up a brick grooving operation.

Each brick is 2" wide and 1.5" tall. The bricks make a ring with a 15" ID and 19" OD. After firing to 1200, per the recommended Kastolite heat up schedule, the bricks weighed about 1.5# each. The full stack weighs 36 pounds. They fit a 12 gauge element wound on a 1/2" mandrel. Each three stack of bricks with elements wired in series makes a 14.5 amp bank at 208v with a watt loading of 9.25 watts per square inch of wire surface area. The stretch comes out to about 2.5 times the wire diameter. A 240v or 220v bank would end up with a bit more wire. Wire passages are either made with additions to the mold to block out space prior to casting or cutting them out with a masonry disc or tile saw afterwards.

I machine the molds out of sheets of pink foam and cast in large batches. If this design works well I might be able to make the molds for people pretty economically. This particular stack took less than a bag of Kastolite to make. Something a little taller or wider, for an 80# pot for instance, would probably still use less than 2 bags.

Wire melters are what they are and it's a bit of a fun engineering challenge to find a ways to get a little more out of them. Everyone who has posted their experiences here has been a big help. I've built a few, and made a hundred different drawings over the past 15 years of reading what people are doing here.

I will update my progress here in the next couple of weeks.
Attached Images
File Type: jpg 40# furnace brick 5 resize.jpg (78.7 KB, 59 views)
File Type: jpg 40# furnace brick 4 resize.jpg (84.4 KB, 60 views)
File Type: jpg 40# furnace brick 3 resize.jpg (86.0 KB, 43 views)
File Type: jpg 40# furnace brick 2 resize.jpg (40.3 KB, 61 views)
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Old 10-16-2017, 03:57 PM
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Pete VanderLaan Pete VanderLaan is offline
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wasn;t it Zocar that made pressed material with inlaid elements years back?
Seems to me this is the direction Hetland was going in as well but look out for sacred geometry.

I really like your inventive spirit on this Jordan.
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Old 10-16-2017, 04:13 PM
Eben Horton Eben Horton is offline
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Beautiful!!! Well done Jordan.
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Old 10-16-2017, 05:31 PM
Steve Stadelman Steve Stadelman is offline
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I like it!
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Old 10-16-2017, 09:23 PM
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Franklin Sankar Franklin Sankar is offline
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very neat Jordan. did you consider using green cast or will that also suck up too much of the heat.
Franklin
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Old 10-17-2017, 03:36 AM
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This is brilliant. Now add some kind of sacrificial gutter for spills and cracked pots and you'll have licked the most annoying parts of wire melters. Kudos.
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Old 10-25-2017, 02:57 PM
Jordan Kube Jordan Kube is offline
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I just got the new base out of the oven and I was able to take 150# out of the weight of the castings. The new sidewalls and base weigh about a third each of the old ones.
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Old 10-25-2017, 03:29 PM
Jordan Kube Jordan Kube is offline
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Another little progress pic. I would consider this thing over insulated at this point. I would have preferred to shrink the exterior size as opposed to adding more insulation but that's how it goes sometimes.
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File Type: jpg 40# furnace resize.jpg (83.8 KB, 54 views)
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Old 10-25-2017, 03:56 PM
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that insulation looks to be really efficient to me Jordan. I recall when Joe Clearman had this little electric unit about the size of a lunchbox and he would take it to demos, plug it in to 115V and drop color rods in it. He had clor all thru the demos. I don't think it could have cost more than 150 bucks.
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Old 10-26-2017, 04:10 AM
George Vidas George Vidas is offline
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I like what you're doing here, Jordan. It makes me excited to build a little oven.

I always really liked the idea -- I picked it up around here somewhere, dunno where -- of using 500W or 1000W quartz lamps as a heating element around a tiny crucible, e.g. an unglazed ceramic mug.

The quartz should be survive glass temps. They're pretty cheap -- $1.50 for 500 watts at harbor freight right now. Most of the energy comes off as heat anyway, and only a bit of that is in the visible spectrum. You should have it on a door switch anyway, so the blinding light isn't a huge issue.

What I ran into quickly was a simple physical construction problem -- how do you hold the quartz lamp/heater tight enough to have a good electrical connection, while also making something mostly out of fiber or other light fluffy insulation?

A shitty dangerous mockup of mine got a mug up to red heat. I never considered machining foam to make nice molds for refractories. That seems like a really nice approach to holding funky high temp objects.
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