Acoustic control of the strengthening of building ceramics obtained by extrusion through an ultrasonic die

Abstract

Extrusion through a die, vibrating with an ultrasonic frequency is a promising method for hardening ceramic materials (bricks, tiles, pipes, etc.). We present the results of studying low-frequency acoustic spectra of cylindrical samples of face brick ceramics reinforced by extrusion and addition of fiberglass waste. Correlations between structure changes in the obtained ceramics, parameters of the acoustic spectrum of the samples, and the destructive forces upon their compression (bending) in a press were analyzed. It is shown that ultrasonic extrusion increases the destruction force of the cylinders by 1 – 7 kN (~30 %) and thus shifts the frequency of the fundamental tones of transverse and longitudinal oscillations (6 and 17 kHz) with a coefficient of ~0.1 kHz/kN. The fiberglass particles strengthen the ceramics due to the formation of a needle-like crystalline bond during firing. At the same time, an increased addition of the fiberglass particles reduces the plasticity of the batch thus resulting in formation of the microcracks, cavities and internal stresses in the samples. The occurrence of internal defects shifts the frequency of longitudinal and transverse vibrations to a different extend, which can be used as an indicator of the defects present in the samples and provide the possible of their objective sorting and rejection. The vibration relaxation time (about 0.1 sec) does not change significantly under the described strengthening effects and being characterized by a wide scatter in each series of the samples cannot be considered an informative parameter. Thus, the effectiveness of the presented combined method of ceramics hardening can be accurately tested by the shift in the frequencies of longitudinal and transverse free vibrations of cylindrical specimens. The presented approach facilitates the process of developing new ceramic compositions and extrusion technology in conditions of depletion of sources of high-quality clay raw materials.