M. S. Morrow, Microwave Synergy, Inc., Chattanooga, TN; H. E. Huey, Micramics, Inc., San Jose, CA
As discussed in the companion symposium on energy efficiency, microwave furnaces for the melting and holding of metal melts are energy efficient (and environmentally green). But the major difference is the use of new types of crucibles. Gone is the necessity to use painted refractory coatings on graphite crucibles. Gone are the flaking, spalling, and recoating of graphite crucibles. By using the advantage of microwave heating, sintered ceramic crucibles are significantly less prone to problems leading to inclusions. Proper selection and handling of crucible material for the metal will permit numerous reheats. In the microwave environment, the use of nitrogen, and inert gases can be used to avoid oxidation or other chemical reactions. Gas absorption can also be minimized by microwave heating in a vacuum. Examples of dud and cast melts will be on display.
The reduction of impurities in the new microwave furnace reduces metal loss and provides a better product with fewer inclusions or chemical reactions. Samples of aluminum alloy molten and cast in a microwave furnace illustrates the new paradigm for microwave heating of crucibles for metal melting freeing the user from the use of painted refractory coatings. This reduces inclusions and the formation of carbides. Controlling the atmosphere/vacuum also reduces chemical interaction and/or gas absorbtion.
