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Old 03-17-2004, 02:51 PM
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For the wire furnaces...

This information likely exists in various other threads, but I thought it would be nice to make a bit of a summary in one place.

For those with wire furnace, a few questions:

1. What is the longest continuous stretch you run your furnace in hours?

That is, if you run it for 2 weeks, then turn it off, then fire it up a month later, this is 2 x 7 x 24 = 336 hours.

2. What size/type wire are your elements, and how are they configured?

3. What is the longest life you get out of your elments (hours if you have it)?

4. What is the highest temperature you run?

5. Cullet or batch? Anything of interest?

6. Noticed any problems (i.e. element fatigue before they die, etc.) Details?



Here's my numbers so far:

1. I started the furnace up Feb 8, and it's never been below 1850 since. (yet). Counting initial heating, that's 900 hours so far - all between 1850 and 2250.

2. 14 Ga. Small by melter standards. Kanthal A-1. Two elements, in parallel 240V power. Designed to 2400W (20A), but run 4.5 A at 1850.

3. Don't know yet. First set died because I bent them during a rebuild - only 420 hours. This set is 900+ hours so far.

4. Cook cycle is 2250F for 17 hours (5 hour "thermal equilibration" plus 12 hour cook. Squeeze and hold at 1850F, blow at 2060F. Charged at 1850 or 2060 or 2150 or (once) 2250 depending on what else is going on.

5. Spruce Pine. Started with 50/50 cullet/batch (3 charges), now 100% SP batch (3 charges). So far 6 charges on the current elements.

6. No problems so far.

-Richard
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Old 03-18-2004, 10:43 AM
Brice Turnbull Brice Turnbull is offline
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100 pound crucible, freestanding with wire elements 1" away, surrounding pot. lid is flat hinged which lifts up like pac-man, and rests aprox. 1 1/2" above crucible rim when closed.

1 - est. 6500 hours (24/7 for 9 months). Will be longer when I can figure out how to hook up SSRs I hope. Only reason it's this short is the elements' life.

2 - 11 gauge Kanthal A1, two sets of three elements in series per set. Each set runs on a mechanical relay of 25 Amp capacity.

3 - see (1)

4 - Holy Crap! You are either running a big furnace, or are overcooking your batch I think. My melt cycle for SP87 is - 2115 work temp. Throw in batch at work temp. After full & flat, soak at work temp for 6 hours, up to 2170 for 2 hours, up to 2265 for 4 hours, down to 1700 for 5 minutes, up to work temp.

As to highest temp possible, now I only go to 2265, but I used to run this setup up to 2350 for 8 or 10 hours, and have actually been to 2400 a couple of times, back before I realized it was a waste of energy & elements (and made the glass a little shorter). By the way - if 2400 sounds impossible, don't blame me - 'S' type thermocouple centered vertically in chamber said 2400, and when I opened it a little, it looked like the sun. That was back when I listened to gas melters who told me you had to hit "at least" 2400 to melt batch. Who knows? Maybe with a big invested crucible and the burner in the top of the crown, 30" away you do need to, but if you tuck your elements in the walls around the crucible, it's apparently not the same.

5 - SP 87

6 - Before the elements go out they fade - longer recovery times when throwing in batch, etc.
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Old 03-18-2004, 11:28 AM
Steve Stadelman Steve Stadelman is offline
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I have a set of 11ga Kanthal a-1 that are now 18months old, melting cullett, only going to 2150f, very low watt density, fired with a Phase angle S.C.R.

The phase angle fired unit is not the best choice, a burst fired unit would be better.

The info about 2400f is what Tom Littleton put out for just the scenario that you described Brice, Invested pot and gas burner system.

Electric freestanding pots are different.
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Old 03-18-2004, 11:44 AM
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Brice,

WOW! Those are shorter cook times (and squeeze times) for sure.

I'll have to try that.

Anyone: Where do you get your 11Ga Kanthal wire? The local fellow here will wind me anything, but he only buys the 10,000 ft roll of 14Ga. If I can bring up some 11Ga, he'll wind that for me.

Thanks,

-Richard
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Old 03-18-2004, 11:46 AM
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Oh - and 2400... it's doable. I had mine up to 2400 on the first set of elements (for 10 hours!). It does glow like the sun at that temp, but you must watch the expansion of the glass at those temps. I didn't, and my pot overflowed, prompting the rebuild.

-Richard
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Old 03-18-2004, 11:58 AM
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Quote:
Originally posted by Richard Huntrods
Anyone: Where do you get your 11Ga Kanthal wire?
I suggest that you contact Steve Stadelman. I hear he winds elements like those.
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Old 03-18-2004, 01:05 PM
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Kanthal A1 - 11 gauge - $32.00 per pound

http://www.resistancewire.com/mainpage.php

Use the "inventory" link on the left side to locate the wire.

They currently have about 120 pounds on hand.
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Old 03-18-2004, 01:23 PM
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i use kanthal a1 14 gauge wires, three 5 ohm elements in series. it pulls about 16 amps at 240v. i melt 4c cullet and never go higher than 2150F. my crucible kiln is shut down totally cold during the work week. i charge it cold, and start heating up on friday and start ramping down sunday afternoon. i estimate about 50 hours of hot time per weekend. this set of elements is at 1300 hot hours right not, with no end in sight. i use an electromechanical relay controlled by my rampmaster ii controller. this was standard equipment from evenheat, the manufacturer of the kiln.

as for problems, i used to use a 40 pound flat bottom crucible, and i had 2 of them crack. the last time it was a very bad spill. i redesigned the kiln now and i use a 30 pound round bottom crucible. it has thicker walls and just works better all around. there are no signs of cracks, so right now, i have no problems

Last edited by Mark Wilson; 03-18-2004 at 01:34 PM.
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Old 03-18-2004, 01:38 PM
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I built mine based on the elements that Brice was using
which I have been buying from jen ken kilns for the past
3 years. They are 20 bucks a piece.

12.7 ohm 15 gauge 63" long elements run 2 each in series.

The way it used to be set up is descibed in detail on my site.
http://www.kurtwalrath.com/largeglassstudio/furnace.htm

I now run 4 sets of 2 on 240V single phase in my new shop.

Brice, I'm curious if you switched to a different element
because you mentioned 11 gauge in your post above.

My grooved brick has me locked in to this small element
but if I had it to do over I'd use a beefier gauge. the 11
gauge is almost twice as thick.

I think the best life I had was 7 months or so on the 1st set
of elements. Its been degrading though and I don't keep
close track of it anymore. Where the element fries it leaves a
mark on the brick and I think that they tend to give out in the
same place. my groove is just big enough to shove the elements
in it and I would make them bigger for a loose fit if I was
doing it again.

I use SPB and charge like brice at my working temp of 2100
filling up the pot to the rim each time and adding more as soon
as it is flat till full. I step to 2070 now and hold for 5 hours
then step to 1900 to squeeze. with my level of insulation
it takes 3 hours or so to get to 1900. then it sits there
until an hour or so before I 'm ready to blow and I send
it up to 2100.

I fire with a SSR set to 80% maximum heat, I use the EC
16" round bottom 100# crucible, s type thermocouple,
Eurotherm controller.

Richard, you don't say what size pot you have but I suspect
you can use a drastically shorter melt cycle. I started melting
much hotter and longer but I keep cutting it back and it keeps
working just as well.

I doubt if it matters if you shut down or leave it on in terms
of element life. There have been many times in the past
3 years that I'd turn mine off every 2 weeks to go to a show.

if my pot is empty I can just pull the plug. no ramping down,
the insulation takes care of that. also if I go out of town I can
program my controller to have it ready to charge whenI pull
in after a show. I ramp up at 150 degrees an hour after
stepping to 250 when I bring it up. I don't do anything fancy
around 1000 for inversion and I've had good life out of my pots.

The absolute worst mistake I made in my design was a soft brick
floor! You know I was going to be carefull and never have a
pot break which has not happened to me but.....
over time it has gotten eaten up by overflow from my careless batching and the fact that 100#s is just not enough
glass for me so I always try to get it as full as possible ( read
too full). The last time I changed elements I chipped out the
remains of the grungy soft brick and replaced it with about 3"
of sand. I opened it up after trucking it 6 hours to my new
studio to discover that the pot seems to be fused in place in
the sand bed. I suspect that when I need to pull it to replace
elements I'll have to bust the pot apart and rebuild the floor
with some castable.

I think I have come up with a new design for a wire melter that
will utilize hot swapable heavy gauge elements that will make
maintaining a wire furnace a simple thing and allow you to get
as many Kilowatts in there as you need to melt quickly.

Basically it would be an wound element that slips over a hollow
quartz or mullite tube, one of the leads would pass down the
middle of the tube and you would pass these tubes through
holes in your furnace where they would rest in a notch that
would support it in the back. You could briefly fire the element
on the supporting tube to preheat the tube so it doesn't thermal
shock when you slip it in the hot furnace.

I think this type of setup would be a big improvement over
grooved brick because the elements would run cooler as the
heat could radiate away from them easier than when they
are in the brick grooves.

I probably will go with waste oil when I build my
next furnace though. I like the sound of cheap energy.

Kurt
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Old 03-18-2004, 05:11 PM
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Steve,

When you say very low watt loading, what do you mean?

Have you actually calculated the watt loading at working and fining temperatures?

The reason I ask, is that the wire melter I built last year uses 11 gauge A1, and your figures would help me decide when to replace the elements, once they have already gone for a considerable length of time.

In regard to winding elements, I wound my own on a small bench lathe. The first one took an hour, the last one 10 minutes.
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Old 03-18-2004, 06:39 PM
Steve Stadelman Steve Stadelman is offline
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Mine are about 8 watts per square inch cold. A1 increases resistance as it heats up, so the resistance is higher at temp, but not a whole lot.
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Old 03-18-2004, 09:38 PM
Brice Turnbull Brice Turnbull is offline
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Howdy Kurt,
moved to a new studio, eh? You sound like an energetic guy each time you make a comment!

I switched to 11 gauge last year after talking to an engineer at duralite & having them design elements that would not burn out my mechanical relays so fast. I think the main problem is still the relays, but I'm out of money to try and rework that for the time being.

I'm only on my 2nd set of elements, and to be fair, I lost the first set when one touched the stainless skin of the furnace - it was all downhill from there.

I check this set for the odd movement every week or two now, so we'll see how it does.

That insertable element tube sounds interesting - good luck, and post something if you get it working!
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Old 03-18-2004, 10:11 PM
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Quote:
Originally posted by kurt walrath


I think I have come up with a new design for a wire melter that
will utilize hot swapable heavy gauge elements that will make
maintaining a wire furnace a simple thing and allow you to get
as many Kilowatts in there as you need to melt quickly.

Basically it would be an wound element that slips over a hollow
quartz or mullite tube, one of the leads would pass down the
middle of the tube and you would pass these tubes through
holes in your furnace where they would rest in a notch that
would support it in the back. You could briefly fire the element
on the supporting tube to preheat the tube so it doesn't thermal
shock when you slip it in the hot furnace.

Kurt
In general, I like the idea - no more brick grooving

However, when the suckers get hot they sag in the grooves. What's to keep these vertical ones from just sliding down the support tube?

- Randy
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Old 03-19-2004, 12:39 AM
Greg Frankhouser Greg Frankhouser is offline
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Randy, I would guess that they are mounted horizantaly, for just that reason.

All: Since Annealer design is fresh in my mind, and my EXTRA GOOD GAS Handouts are filed in a pile, Is there a Watts per Cu ft figure for the Thumbesque melters? And do you include the pot and glass area in that figure?

Just to throw something back in trade for the expected return.

I'm told annealers ( Blown work) need to be around 500 watts per cu ft, for good heat response. Casting ovens up to a blazing 1000 watts per cu ft. 650, for a decent combo.

Thanks for the info folks

Greg
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Old 03-19-2004, 02:30 AM
Durk Valkema
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cub.ft/kW

Good to hear hands on experience on these figures.
A lot depends on how the annealer/kiln is build up and how much shelving you have in your annealer.
.5 kW per cubic foot sounds a bit underpowered, go for the 1 kW/cuft.
for temperatures up to around 2300 F its more like 2 kW/cuft
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Old 03-19-2004, 10:57 AM
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hey Brice-
I had talked to Duralite about this myself a few years back but
never took the time to pursue it. do you have the specs for
these 11 ga elements? how many ohms each, what's the
outside diameter? I grooved my brick at 3/8" and I'm
curious if your new ones would fit my unit. I had 9 sets of
grooves in my melter to start out but I lost the bottom set
from overfilling early on so now I have 8 and use them all
in my current set up. Also how much are they from duralite?

I'd be happy to try to help you set up the SSR. It was easy
and I picked mine up surplus. you need a controller that can
talk to them, switched dc output, they are available on ebay
and maybe someone here know if those inexpensive fuji
controllers can be set up like that . I would think so.

On my controller you tell it the percentage of power output,
( I use 80 ) and the switching time, I think mine goes every
second, 8 tenths on, 2 off.
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Old 03-19-2004, 11:28 AM
Brice Turnbull Brice Turnbull is offline
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Hiya Kurt,

If you want to order the ones I used to get (started winding my own - cheaper, but much more work), the invoice from Duralite is Part ID "DURA004722"

Each element (I use 6 at a time) cost $31.25

Description says - 11GA-875CMF-FECRAL .520 OD,
10 SIDED 17.5X 11D 240V 45A

If you were to wind them (buy them - it will make me feel good for referring sales to them, and it will save you hours of non-glassmaking work, unless you've wound heavy gauge wire before), they are 63" of coiled length, averaging 346 coils, and the inner diameter is 5/16", outer diameter is 1/2". I had to rebuild my furnace due to operator error, so making the grooves bigger was not a problem.

Gotta run, Cheers Kurt! Brice
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Old 03-19-2004, 11:55 AM
David Williams
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I'd be happy to try to help you set up the SSR. It was easy
and I picked mine up surplus. you need a controller that can
talk to them, switched dc output, they are available on ebay
and maybe someone here know if those inexpensive fuji
controllers can be set up like that . I would think so.

On my controller you tell it the percentage of power output,
( I use 80 ) and the switching time, I think mine goes every
second, 8 tenths on, 2 off. [/b][/quote]

Yeah you can do that with the fuji pxr3 which is about 125.$. It has percentage-wise output signal control which I would say every smart wire furnace user should utilize. That or the scr. The current limit on the scr does approximately the same thing but for alot more money. Its thumbs gas pedal analogy. Your elements will last alot longer if you just cruise nice and steady rather than flooring it and letting off, flooring it and letting off.... (the scr has other features like soft start which are good) I have my current limit set to the bare minimum I need for reasonable recovery when charging.
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Old 03-19-2004, 12:02 PM
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Hmmm. Digesting all this info... yummy!

Summarizing only the SP Batch melting info posted here:

Brice:
Kanthal 11Ga.
100lb freestanding
Melt cycle for SP87 is - 2115 work temp. Throw in batch at work temp. After full & flat, soak at work temp for 6 hours, up to 2170 for 2 hours, up to 2265 for 4 hours, down to 1700 for 5 minutes, up to work temp.

Brice - only 5 minutes squeeze? How's the glass for seeds?

Kurt:
Kanthal 15Ga.
100lb freestanding
I use SPB and charge like brice at my working temp of 2100 filling up the pot to the rim each time and adding more as soon as it is flat till full. I step to 2070 now and hold for 5 hours then step to 1900 to squeeze. with my level of insulation it takes 3 hours or so to get to 1900. then it sits there until an hour or so before I 'm ready to blow and I send it up to 2100.

Kurt - did you mean 2270 for the cook?

Me:
Kanthal 14Ga.
40lb freestanding (flat-bottom cylinder)
SPB, charge at 2060 (working temp), filling pot to rim BUT the goal is flat 1" to 1.5" below lip. Step up to 2250 for 17 hours, squeeze at 1850 for 12 hours. Blowing at 2060.


YIKES! Looks like I'm spending way too long at 2250, which probably isn't that good for the elements.

Brice, you also mentioned the elements do fatigue before failure. Any info on how long after you notice fatigue before failure?


I'm still "dialing in" this furnace of mine. The long cook times aren't doing me any favors. The elements started to show signs of fatigue on the last charge - I had to bump up the "set point" by 10 degrees to get the same furnace temp.

I could re-wire with 11Ga elements without too much problem. My grooves were cut with at dovetail router bit. The opening is 3/8" but the inner groove is about 5/8". Sounds like the 11Ga. could fit - maybe with a bit of brick filing (make the opening 1/2").

-Richard
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Old 03-19-2004, 04:17 PM
Brice Turnbull Brice Turnbull is offline
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Richard - the 5 minutes sounds short, until you consider that it's all the way down at 1700. It takes hours to drop that far, and then about 2 1/2 hours to get back to work temp. You could probably drop to 1775 and hold for maybe 2 1/2 hours and maybe get the same result.

Actually, this is a good question - I used to squeeze at 1950 for 5 hours, but still found seeds. A couple weekends ago I was at a marble show & talked to Drew Fritts, who recommended a drop to 1500 for the squeeze, but that was in a 15 lb. crucible, and I thought it would take too much power to get back to work temp from there, so I tried my own plan at 1700, and in the two melts since then I've found no seeds down to a depth of about 6" from the surface. First time in a few months I've had glass that clean.

As far as fatigue on the elements, I recall about 4 more melt cycles without too much trouble after the recovery gets slower. I've pushed it to about 7 melt cycles also, but I think it draws a lot of electricity, and it takes a long time.
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Old 03-19-2004, 04:29 PM
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Brice,

Thanks for the great info!


One more question for you (and Kurt). Your larger furnaces - how low do you let them get before you charge? With my 40, it's below 1/4 by the second blowing day, and so I must charge completely. Do you also charge an empty pot, or just when it gets "low"?

-Richard
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Old 03-20-2004, 12:17 AM
Brice Turnbull Brice Turnbull is offline
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I don't plan it, but probably get to the bottom every 3rd batch. I don't worry about cleaning it out specifically, it depends more on my schedule for the week. If its a good day tomorrow to work on something besides hot glass, then I'll batch if it's less than 1/4 full.
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Old 03-20-2004, 12:03 PM
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Yeah..step to 2270 for cook.
as for squeeze, I think I recall Pete suggesting 1900 as a
figure to use back on Brads board when I 1st got hot.
Dropping to 1900 and immediately going up to working temp
left some bubbles and if I'm trying to blow asap I need to
hold at 1900 for a couple of hours as I recall. But I just
stop my program at 1900 to save electricity. my furnace
will go from 1900 to 2100 in a little over an hour. About the time
it takes me to cut color bar and set up to blow.

I find that with my pot once the level of glass is below the
straight sides I have trouble with gathering bubbles on the
3rd and 4th gathers. All the heat in my furnace has to pass
through the pot, there's no radiant source on the surface of
the glass, so the glass that trails off tends to trap small bubbles
that would dissapate much faster in a furnace that had heat
coming in from the top. This would be one of the worst flaws in
my furnace design but I did it to protect the elements from
the batch. in my furnace a gather at 2100 feels really cold
compared to glass coming out of a gas fired furnace that runs
colder temps. It's not an issue for regular blowing, but making
an avolio is hard because the bit just isn't as hot. A goblet maker
would probably have fits with my furnace. I tried to raise the
working temp but ran into reboil problems at around 2140 as
I recall.

So anyway I usually charge once I get into the bottom 3rd
of the pot and don't fully empty unless I'm shutting down.
I'm actually going to try to use that last bit tonite when I blow.
I've been working alone making 2 gather pieces and I want to
see if I can get more days out of a pot of glass than in the past.

Kurt
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Old 03-20-2004, 12:18 PM
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Hey Brice-
Thanks for the element info....what's the resistance of one of those so I can figure out the power?

I bought all my annealer elements form Duralite so they do
get some business from me already. I'm interested in making my
own though as part of my continuing program to reduce expenses
and try to make some money at this thing this year, finally, I
hope!
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Old 03-20-2004, 01:32 PM
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Watt Loading for Dummies

I didn't stick through my engineering classes long enough to learn how to figure out the exact science and numbers behind watt loading, but I understand the basic physics pretty well. My understanding tells me that for given x furnace heating chamber space at y temperature I can use the same amount of energy to maintain y and have either one element running hot as blazes (obviously impractical) relative to the furnace temp y or a wall packed thick with elements (equally impractical and unnecessarily expensive) running barely above measured y air temp. My solution to maximizing element life was to get as much heating surface in the furnace as realistically possible (Steve's Watt loading equation tweaks this) to keep the wire temp as low as possible relative to the furnace chamber temp. I tended to run 12 5ohm 13ga 3/8ths OD coils while Steve prefers 12 3.5ohm 11ga 1/2" OD coils. Actually, on the last two furnaces I've sold I've designed them to run off of Steve's elements -- though I'm still trying to talk him into squeezing 4ohms into each element for even more heating surface (Steve's afraid at that point the coils become too tight - I'm going to be the test dummy).

As to suspending the wire inside the furnace to maximize efficiency; what small gains it would produce I fear would be lost because of the extra heat needed to compensate for the added size of the heating chamber (my furnace wall is close enough to the pot that if the elements were outside the wall they'd be nearly touching the pot). What I've done instead is cut a straight edged, square notch in the brick at an upward angle.

Quote:
All the heat in my furnace has to pass
through the pot, there's no radiant source on the surface of
the glass, so the glass that trails off tends to trap small bubbles
that would dissapate much faster in a furnace that had heat
coming in from the top. This would be one of the worst flaws in
my furnace design but I did it to protect the elements from
the batch. in my furnace a gather at 2100 feels really cold
compared to glass coming out of a gas fired furnace that runs
colder temps. - Kurt
This covers at least two reasons why I dislike batch in a wire furnace. If you would cast a Mizu ring (my Thermal Flywheel™ as seen in photo) that sits on the open furnace (the crown and lid then sit on this), and allow a gap of even 1/2 inch between the top of the pot and the bottom of the ring, it will make a great radiant heat source to keep a low pot at temp. The other thing I don't like about batch in a wire furnace is the extra temps people use to fine out. For the last year, using cullet, I've never run the furnace over 2005f. For busy weeks (all of late) I'll toss in 20-30 pounds each night to re-top off the pot, it's fined and good to go the next morning and about once every 10-14 days I'll blow the pot low (1/4 full) and do a full charge. This freshly charged pot sits through the next day -- still at 2005f -- and on the morning after that I'm blowing perfect glass again.

Lather-rinse-repeat.

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