Nondestructive testing of refractories for glass melting by microwaves

The melting, finig and processing of glass requires a broad variety of refractory materials which have a strong influence on the quality of the final product. During the last years nondestructive testing techniques have been developed and tested for refractories. A microwave setup with variable frequency of 20 - 40 GHz was built up and with a broad variety of refractories the absorption dependent an the local position was measured. With lenses it is possible to improve the recognisation of faults and cracks. We examined different systems of lenses and reach a fault dissolution in the region of millimeter, If the water content of unfired bodies is too high there are difficulties with microwaves because of absorption The microwave method has several advantages against ultrasonic methods.