For
#7000: 120 Vac Nichrome Heating Element - 1400 °F Max
#7000 SPECIFICATIONS:
If you are building Dave Gingery's "Lil' Bertha" foundry furnace, you will need a source of electric heating elements. BCS #7000 offers the required 120 Vac, coiled wire electric heating element for the project. These elements are suitable for a furnace that can be used to melt metals that have melting points lower than about 1400 deg F. This means typically aluminum and zinc. Anything above this will melt the element.
#7101: 120 Vac Kanthal Heating Element - 2300 °F Max
#7101 SPECIFICATIONS:
If you are going to be working with Brass or Bronze in addition to aluminum you may want to consider using these high temperature Kantal Elements. The element material is rated to 2300 °F.
#7103: 240 Vac Kanthal Heating Element - 2300 °F Max
#7103 Specifications:
This Kanthal element provides a lot of power in a compact space. It's perfect for furnaces or heat treat furnaces that don't have a lot of room inside yet still need to get to higher temperatures.
The question then is how much power do you need for your furnace design? Unfortunately I can't tell you. It mostly depends on how much insulation the refractory provides and how hot you are trying to run the furnace. Other variables include the wall thickness, the chamber height, the sealing between the body and the top and bottom, the room air temperature, how hot you trying to run the chamber, etc. For specific furnace design information I will refer you to books by David Gingery and others who have designed furnaces and know how much power is required.
Stretching the element provides a gap between each turn to prevent shorting of one turn to the next. I have also noted that the elements tend to shrink slightly with the first firing and cooling cycle. It's better to have them stretched a bit on the long side so they stay in place.
The connections to the elements need to be mechanically and electrically secure. Stainless steel screws, washers and nuts have proven to be a good choice. It is also important to use between the outside connection of the furnace wall feed thru and the controller. This helps dissipate the heat from the wire so it won't damage the controller. Also standard wire insulation will melt when used at higher temperatures.
I have used my furnace for 3 years with the original elements, but have friends who have had to replace their elements after only 6 melts. I have a hunch that the secret is to treat the heaters carefully by SLOWLY increasing the furnace temperature to the operating point over a period of 45 minutes to an hour each time. I think that this avoids damaging thermal shock. The same for cooling down afterwards. Let the furnace slowly cool, with the top on. Also don't stretch the coils after they have been fired. The heating and cooling creates a hard scale on the element surface that will fracture if the element is stressed after the first use.
Another factor in element life may lie in the installation. I was careful about stretching out the coil to fit. Try to evenly stretch the element so that the coils are spaced about the same over the length. A bunch of coils closely spaced will create hot spots that may cause a burn out.
If you need precise temperature control, consider the BCS "Hot Box"©™ Digital Temperature Controller.
These heating elements are NOT INSULATED. The heating elements and wiring can be "live" even though the control is in the off position. NEVER come in contact with the heating element or other wiring while the power is connected. Unplug the power before coming near any part of the circuit. This unit MUST be operated from power that is protected by a Ground Fault Interrupter (G.F.I.) unit. Consult with a licensed electrician prior to applying power. You may be shocked, burned or killed by contacting electrical circuitry that is connected to the power source.
Heating Element Safety and Tech Data
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Nichrome Heater Element, 120 Vac, 1800 W, 1450 °F Max | |
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Nichrome Heater Elements, 120 Vac, 1800 W, 1450 °F Max | |
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Kanthal Heater Element, 120 Vac, 1550 W, 2300 °F Max | |
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Kanthal Heater Elements, 120 Vac, 1550 W, 2300 °F Max | |
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Kanthal Heater Element, 240 Vac, 3120 W, 2300 °F Max | |
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Kanthal Heater Elements, 240 Vac, 3120 W, 2300 °F Max | |
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Revised: 4-21-10
