In-line surface and subsurface crack detection in ceramic tiles and pavements by ultrasound

In this work the use of ultrasonic techniques was investigated in order to determine their relevance for the detection of surface and subsurface cracks in ceramic tiles. The requirements for effective and automatic quality control, in addition to the shape and thickness of such products, has led to the development of a system based on ‘pitch and catch’ angled probe configuration as the most effective to the proposed goal. The ultrasonic inspection system has been designed to detect all cracks independently of their position and orientation with respect to the probes. The results are excellent for tiles with either flat texture or presenting a low degree of roughness. The equipment only requires calibration when the tile size is changed. The sorting of the tiles is done in an automatic way, making use of a pen marker mounted on the tip of a pneumatic cylinder. The tests have demonstrated that the inspection system is very reliable and effective; however, some improvements are necessary concerning the coupling material used between the probes and tiles. The important aspect to solve here deals with the high temperature of the ceramic tiles after the firing process which reduces considerably the life-time of the rubber tyres used s ultrasonic coupling media.