Anyone
who uses a microwave knows that metals, such as aluminum foil, should not be
placed in these ovens, but a team of Penn State material scientists is microwaving
a wide range of powder metals and producing machine components with improved
properties.
Now, Dennis Tool Co. -- a leading manufacturer of polycrystalline diamond (PCD) products based in Dallas, Texas -- has teamed up with Penn State researchers to use this technology. Equipment and tools made of PCDs are used in a wide range of industrial and consumer applications -- primarily electronics, communications, data storage and optics. Machine parts made of PCDs are wear-resistent and extremely hard.
Dennis Tool Co. and Penn State have developed and patented a commercial furnace, heated by microwave energy, to produce these hard metal carbides and diamond/carbide composite materials. Valentine, a major producer of tungsten carbide cutting tools and wear parts, has joined Dennis Tool Co. and Penn State to bring tools produced by the new process to market.
"Solid metals cause problems in microwaves because they reflect, rather than absorb, the microwave radiation," said Dinesh K. Agrawal, professor of materials, senior scientist and director of Penn State's Microwave Processing and Engineering Center. "Powder metals absorb microwave radiation and can be heated and sintered, using microwaves."
Sintering is used to manufacture many parts made from ceramics, metals and combinations of materials. Sintering causes the metal powder particles to bond together forming a solid dense material after the microwave treatment. Powdered metals are commonly used to make parts for automobiles, power tools, lawn and garden appliances, firearms, business machines and medical equipment -- particularly those parts that are irregularly curved or have holes or recesses in them that cannot be easily made by machine.
The Penn State research team took commercial powder metal components, including small gears, rings and tubes, and compared them with microwaved products. What the team found is that microwave sintering takes less time, uses less energy and is more cost effective.
Field tests in commercial applications show superior performance at a much lower cost to produce. Sintering times are in minutes instead of hours.
The Penn State research team includes Agrawal; Rustum Roy, Evan Pugh professor emeritus of solid state; Jiping Cheng, post-doctoral research associate; and Shalva Gedevanishvili, former research associate, now with Phillip Morris. They published their results last year in the journal Nature.
The key to microwave sintering of powder metals is the specialized insulated sintering cavities. In conventional thermal sintering, the sintering oven is heated and this heat is transferred to the greenware, but microwaving does not heat the chamber, just the greenware.
Without insulation, the heat generated in the greenware would be lost to the inside of the microwave cavity and it would take an enormous span of time to reach the required temperatures. The insulated chambers trap the heat and allow temperatures to rise rapidly.