Why Microwave Heating?
The Nature of the Phenomenon
Microwaves are a form of electromagnetic energy.
Polar molecules and free ions in receptive materials respond to these fields by creating a molecular friction which results in heat throughout the mass of the material.
Microwave frequency is measured in Megahertz (MHz). The FCC has reserved 915 MHz and 2450 MHz, among other frequencies, for industrial applications. At present, most microwave ovens in use operate at 2450 MHz, which is a wavelength of 4.8" in air. 915 MHz is about 13" in air. Microwave power is usually measured in kilowatts.
At room temperature, and 1 atmosphere pressure, 1 kilowatt of microwave energy will evaporate approximately 2.5 pounds of water in 1 hour.
Turning Up the Heat
Materials differ in their reaction to microwave fields. Metals tend to reflect microwaves, a quality that enables them to be used as conduits, called waveguides, and as containers to hold, direct and apply microwave fields. Some non-polar compounds, for example, many plastics, are transparent to microwaves, a quality that allows them to be used as containers for material to be heated or as process control windows.
Materials that respond to and, therefore, can be processed by microwave energy are composed of polar (e.g., water), ionic, or conductive (e.g., carbon black) compounds.
Quite often, material which is only weakly receptive to microwave energy can still be effectively processed as a result of careful oven design and consideration of the chemistry and process methods.
The Cober team provides total process response.
The key to the effectiveness of microwave heating is that the process is one of direct energy conversion within the material being treated.
The need to heat a container, such as an oven, is eliminated and process speeds can be very high.
The Advantages of Microwave Heating
Microwave heating offers numerous advantages in productivity over conventional heating methods such as hot air, steam, etc.
Save space, reduces scrap and saves labor.
Microwave energy penetrates to generate heat internally as well as at the surface of the treated material. Other methods apply heat only to the surface and temperature must be limited in order to avoid burning.
Conventional processing time is slow due to thermal conductivity. Microwave energy overcomes those time and temperature limitations and produces a very high quality product even when the materials being processed are fairly thick.
Selective Energy Absorption
Some material absorbs microwaves readily, others do not...a characteristic used to advantage in the microwave process.
Pharmaceuticals, for example, can be pasteurized within their packages without burning the packaging material.
Instantaneous Electronic Control
Most conventional heating systems (e.g., hot air ovens), require appreciable amounts of time to effect temperature changes.
Microwave power levels can be adjusted electronically in a fraction of a second...a characteristic that makes microwave equipment readily adaptable to automated systems and to data logging programs.
High Efficiency & Speed
Microwave processing requires fewer BTU's for the same or better results than conventional equipment.
Microwave Processing is Clean
Microwave processing -- an inherently dry and fumeless process -- is environmentally clean...particularly in comparison to processes which require additional media for heat transfer.