Furnace heating element

After perusing posts about the Gingery furnace and visiting
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'%20Bertha.shtmlI have bought myself a nice little thermocouple and controller kit on
e-bay with the intention of constructing a small tempering and
annealing furnace and maybe doing some enameling.
Nothing so ambitious as a melting furnace for metal casting.
Anyhow, the question of what to use as a heating element arises. Where
does one buy suitable heating coils, and how do you calculate how much
you need with respect to the volume of the furnace? Would a stove
element do? Or some other clever substitute for expensive purpose
built oven elements? I have both 115 and 240 volts available at up to
50 amps.
Reply to
John Ings
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How about calrod elements (used in ovens?).
Best regards, Spehro Pefhany
Reply to
Spehro Pefhany
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'%20Bertha.shtml> I have bought myself a nice little thermocouple and controller kit on
I have often thought that toaster oven elements would work for this application. Readily available at yard sales and the like. Ken.
Reply to
Ken Davey
The nichrome wire is readily available from pottery supply places. Haven't bought any for years but $15 or $20 should get your pleny for a small heat treating furnace. Trying to reclaim the wire is dicey, it get real brittle. Example of elements and prices:
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Ken Davey wrote:
Reply to
Roy J
Got mine (kanthol) here-
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This is actually buried on Dan's website somewheres, that's how I came across it. Theres also some discussion there somewheres of what you can use as elements & what you shouldn't use, or maybe it's in the plans ( IMHO well worth the nominal cost).
Howard.
Reply to
Howard Eisenhauer
Ken I use clothes dryer coils. You can get them at you local applaince parts store for around $10 or used ones will work fine to.If you use new ones thet come coiled tight so you have to strech them out a little so the coils won't touch.Then take an ohm meter and cut the coil down untill it reads 6.5 ohms from end to end for 120 volts 13 ohms for 220 volts. I use 120 volts on my Heat treat oven ,here are some pictures of it.
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Reply to
TLKALLAM8
I find lots of listings for them with a Google search, but I couldn't find any that gave a maximum temperature.
Reply to
John Ings
How did you arrive at these figures? Trial and error? Run the elements up until they got as hot as you dared?
Interesting. The device on the right is an SCR switch?
Elements at a white heat? How long do they last?
I wanted to try for a furnace with a side load rather than a top load, but maybe that's too fancy to be practical?
Reply to
John Ings
You can find some useful info at
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regarding element design criteria also
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. Kanthal has good information regarding temp limits of alloy type, environment effects, element forms. I think you may find some info at
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. Joppa and glass notes are glass related but Joppa at least list some temperature range for normal glass application so may give you a good guide to power required for temperature and size.
In the US I have seen
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as suppliers. Farnell electronics
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sell sheathed elements like used in ovens which can be bent as required. From the UK catalogue a part number is 322-5203 and these have an upper limit of 800C listed.
John >After perusing posts about the Gingery furnace and visiting
Reply to
David Billington
The Chinese seem to make a lot of these too. Probably not as good quality but it's an attractive idea. Easier to position inside the oven than coils of nichrome.
Did you see this gem?
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about diabolical ingenuity!
I was afraid of that. Not quite hot enough. I like the silicon carbide heating element idea better.
Reply to
John Ings
I presume you mean the sheathed elements. I haven't used these as the temp limit of 800C was a problem. I got lots of info regarding element design criteria from kanthal in PDF format and have now bought the wire to wind my own elements. I am building a furnace for melting glass and it'll have an upper limit of 1200C but normally will be used at about 1100C. High spec FeCrAl wire such as Kanthal A1 will do this and they have 1 better but the limit is about 1300C for wire. Pottery kilns do this often but they don't sustain it. As I understand it they reach the max temp then shutdown or go into a cooling cycle.
Seen it but its just so difficult to get US post boxes in the UK.
I looked at these and if you can justify the cost like you are doing it commercially then these may be a good option. They can operate to higher temp and should last longer but are quite pricey for amatuer use. Factor in requirements for a phase angle controller to limit the power and it adds up even more. SiC elements increase in resistance considerably over their lifetime so you need to factor this into the control system. FeCrAl wire increases about 5% so the difference is small and a SSR and temp controller make a simple and cheap control solution. A benefit of SiC is that they can be hot swapped if this is an issue and you design allows it.
Reply to
David Billington
Aha! As a result of David's mention of Kanthal, and Kanthal's ad for silicon carbide heating elements I just found this
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the interest of anyone else with the same intentions.
Reply to
John Ings
Good find I never did in my searches. Another source of SiC elements produces under the name "StarBar" try this link
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John >>
Reply to
David Billington
The dryer element & other coiled wire elements will work well, as will oven type clad heating elements so long as the oven temperature doesn't exceed about 1850F.
If you plan to exceed that temperature very often, you'll want Kanthal up to 2300F.
I just built an annealer for a glassblowing shop that is designed to reach 18-1900F. I used oven type clad heating elements I got from McMaster.com. You can also buy elements at your appliance repair shop.
The McMaster elements are straight but can be bent however you like. The main benefits of the clad type elements are:
1) the cladding isolates them electrically and chemically so you don't need to worry about touching them when they are hot. Exposed elements are easy to ruin if garbage falls on them; scale for example. Also it is easy to electrocute yourself or short circuit them while using metal tongs in the hot furnace if you use exposed elements.
2) It is easy to make connections to commercial clad elements. The McMaster elements have ceramic insulators with high temperature alloy stud & nut type connectors on them. You can just poke the end of the element through the furnace wall & tighten the nut on your electrical supply wire.
That said, I've used a lot of exposed elements for ceramic kilns; they are easy & inexpensive to buy or make.
Quartz clad radient heating elemnts also work well below 1800F. They (and other types) are usually availible thru surplus outlets like C & H.
Reply to
dave martin
Depends on what max temperature you'll want, the total surface area (not volume) of your furnace, and the thickness and effectiveness of the insulation.
A.P. Green Kast-O-Lite castable refractory has conductivity of 0.5 watt/( m*degC). So, for example, if your furnace is 9" ID x 9" deep (about 2.5 gallon volume BTW) and your wall thickness is 2" of Kast-O-Lite, MathCAD sez you'd need about 1300 watts to get to 1000F.
You can buy an 1100 watt hotplate from Wal-Mart for under $15. I have a 2000 watt (220v) stovetop element I think I paid less than $20 for. I don't know how these elements would stand up to temps above 1000F, though they glow orange in normal service so they can clearly stand 1600F - 1700F at their surface. I keep meaning to try these in my Pyramid furnace but I haven't gotten around to it yet. If using elements like this, it might be a good idea to put a thermocouple right on the element and limit current so they never exceed orange heat regardless of furnace temp.
Kilns and foundry furnaces typically use Kanthal (coiled wire) elements that can withstand temps of 2550F but you'd need to devise support for the coil(s).
See ,
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for more info.
Keep us posted on your progress,pls!
Reply to
Don Foreman
Do you know if MathCad can take into account the temperature of the insulation at a given point from the heat source. To clarify that all the insulation I have looked at such as IFB, fibre board and fibre have decreasing insulation properties as the temperature goes up. What maybe very good at 20C doesn't perform anywhere near as well at 1200C. Makes for some more complicated calculations.
D>>
Reply to
David Billington
That mailbox has gone postal..? ;-)
Tim
-- "That's for the courts to decide." - Homer Simpson Website @
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Reply to
Tim Williams
Well it's pretty damn hot under the collar sometimes!
Reply to
John Ings
Try the Salvation Army for stove elements. Seattle Pottery has Kanthal elements and does mail order.
Dan
Don Foreman wrote in message Would a stove
Reply to
Dan Caster
It's a bit over the top as a way to get rid of junk mail
Mark Rand RTFM
Reply to
Mark Rand

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