This document is based on the joint paper presented by Cober Electronics, Inc. and Crompton Corporation, Uniroyal Chemical Division at an Annual Meeting of the Rubber Division of the American Chemical Society and at the June 2002 Symposium of The Connecticut Rubber Group. It presents updated information that is the result of the cooperative effort between Cober Electronics, Inc. and Compton Corporation, Uniroyal Chemical Division in the area of systems, techniques, materials and chemistry for rubber processing.
With 85% of the homes in the U.S. containing microwave ovens, most people have experienced the speed and the penetrating effect of the microwave heating and also some of the disadvantages. The intent of this booklet is to explain the principles of microwave heating in a practical and non-mathematical way and illustrate how these principles are used to increase productivity and quality in industrial processing applications. The rubber industry is used as an example since microwave continuous vulcanization of automotive weather stripping used worldwide, wherever automobiles are manufactured.
Conventional and traditional technology for applying heat to rubber during the vulcanization process has relied on labor intensive steam autoclaves (a batch system), long and inefficient hot air tunnel ovens, and environmentally unfriendly high temperature liquid salt systems. These are now being replaced by highly efficient, high speed microwave curing ovens automated with electronic controls and sensors, producing rubber weather stripping of the highest quality to seal passenger car doors from noise and rain thereby providing user comfort. Steam, hot air and molten salt are yielding to the benefit of microwave electronics in factories on a worldwide basis. The authors estimate that there are approximately 1,000 rubber curing systems worldwide that rely on microwave technology.
Microwaves are invisible radio frequency or electromagnetic waves which have properties that enable them to be generated and sent through space and received or absorbed at a distance. Electromagnetic waves are basically identical to the familiar radio and TV transmissions which we receive daily and to aircraft radar (Figure 1). All electromagnetic waves are similar. They differ only in the number of alternatives or oscillations of their field per second. These oscillations are measured in megahertz or millions of oscillations per second (abbreviated MHz). Each electromagnetic wave has a characteristic spatial dimension called wavelength. The higher the frequency of a radio wave, the shorter the length of the wave.