NONDESTRUCTIVE TESTING OF CERAMICALLY BONDED REFRACTORIES - APPLICATION OF ULTRASOUND AND MICROWAVES

Quality control on refractory bricks is either mostly destructive or methods are used which require samples with a certain geometry. In a joint project between the University of Erlangen and industry the applicability of non-destructive testing methods for sintered refractory bricks was tested. Various materials with artificial flaws were measured in transmission with ultrasound (500 kc/s) as well as with microwaves (24 to 40 Gc/s) and the results were compared. Despite of good results, the testing with ultrasound proved to be unsuitable for the measurements of greater lots, because the open-pore blocks have to be coupled in water. An excellent alternative is the transmission measurement with microwaves. With both methods structural inhomogeneities as well as density differences or inclusions can be detected.