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Annealer Calculator
Spiral Arts Annealer design calculator
What's an annealer? An annealer is a large oven used to relieve the stress in glass. Soda lime glass anneals at about 900° F and at about 50° above that it begins to slump. Annealers usually have two or more doors that open allowing you to place a piece of glass inside, either on a shelf or the floor of the annealer. The process of designing an annealer involves both a mechanical design as well as an electrical design. The purpose of this calculator is to help you calculate your electrical requirements based on the interior size of the annealer. How to use this calculator Start by entering interior dimensions. As a rule of thumb the annealer should be deeper than it is tall. This will help keep the heat inside. If your annealer is taller than 24" inside, be aware that a temperature gradient from top to bottom of more than 20° F will make annealing large pieces extremely difficult. When dimensioning the interior, take into account material sizes. Fiber board is commonly available in 24"x36" dimensions. The most available insulating firebrick size is 2-1/2" x 4-1/2" x 9". Enter watts per cubic foot. This number will determine your annealers responsiveness. Typically you should enter a number between 450 and 600 watts per cubic foot. This is a good number for annealers that go no higher in temperature than 1,000° F. Enter number of coils per leg. For single phase annealers this will be the total number of coils since single phase wiring only involves a single power leg. For three phase annealers, the total number of coils will be three times the number of coils per leg. While it's possible to design “unbalanced” three phase wiring schemes, this calculator assumes a simple balanced schematic. Enter the incoming voltage. It is important to note that if you build a single phase annealer that is sized for 240 volts and it gets run on a 208 volt circuit, it may not get to temperature quickly enough. Enter the wire dimension. It's possible to get Nichrome or Kanthal wire in a large variety of gauges. Make sure you know what gauge wire you are using before winding your own coils. Changing the wire size has a big effect on the watts/sq. ft. as well as the OD of the coil and the length. Enter a mandrel size. The size of the mandrel the coil is wound on will determine the OD of the coil as well as the “close wound length”, which is the length of the coil before it gets stretched out. You will want a coil that is at least 2 times longer than the close wound length to assure that it doesn't short itself out. If you are hanging the coil on a tube or rod, make sure you wind the coil on a mandrel larger than the tube OD. Run the calculation. You should be looking for a watts per square inch on your coils between 15 and 20. The number must be between 10 and 40 for Nichrome, the recommended wire for annealers that operate under 1000°F. Notes and assumptions
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