Use of the ?Zvuk-202? instrument for inspecting the properties of refractory parts

Abstract

The acoustic nondestructive method of determining such important indices of refractory parts as open porosity, apparent density, and compressive strength has obtained wide use in the refractory industry [1][2][3]. The method is based on the correlation relationships between these indices and the frequency of characteristic oscillations of the part. In inspection the frequency of characteristic oscillations of the part and its weight are measured and then the index is determined using previously developed regression equations or nomograms.Measurement of the frequency of characteristic oscillations is possible under conditions of induced (resonant method) or free (impact method) oscillations. With the use of induced oscillations the frequency of characteristic oscillations is called the resonant frequency of the part (from the method of its measurement).In the domestic refractory industry instruments based on the method of induced oscillations are used. Oscillations the frequency of which is changed smoothly are excited in the part by an external source. At the moment of agreement of this frequency with the frequency of characteristic oscillations of the part resonance, characterized by a sharp increase in the amplitude of oscillations, occurs. The frequency of oscillations of the external source at the moment of resonance corresponds to the value of the frequency of characteristic oscillations (resonant frequency) of the part.With the use of the method of free oscillations oscillations are excited in the part by an impact. After finish of the excitation stage the part produces damping oscillations at the base frequency (frequency of characteristic oscillations), which is recorded by an instrument. Despite a number of advantages of the method of free oscillations (lower system error, measuring simplicity, etc.) until recently its practical use has been restricted by the absence of industrial instruments. The development of electronics and digital technology has created the prerequisites for the development of appropriate instruments.Abroad the Grindosonic instrument (Belgium) has found wide use for inspection of ceramic, structural, abrasive, and other parts [4]. In particular, in the Federal Republic of Germany this instrument is used for inspection of refractory parts [5]. In our country production use of the free oscillation method is related to the development by the All-Union ScientificResearch Institute for Abrasives and Grinding of the Zvuk-202 instrument [6].The functional plan of the Zvuk-202 instrument is shown in Fig. i. With application by the striker 1 of an impact on the part being inspected 2, which is located on the soft base 3 (porolon, foam rubber, etc.), mechanical oscillations occur in it and are received and converted into an electrical signal by the microphone 4. The signal is amplified by the amplifier 5 and delivered to the tuneable filter, with which the frequency of characteristic oscillations, measured by the frequency meter 7, is separated. The frequenCy meter is triggered by the synchro...