One of the basic properties of refractory parts determining their fitness for service is heat resistance. Existing methods of measuring heat resistance are laborious, possess low reliability, and involve destruction of the sample and the thermal loading (cooling in water or in air) in the testing does not correspond to the loading of the samples in service in contact with molten metals [i, 2].One of the means of improving the measurement of heat resistance is the use of a method based on recording the acoustic emission accompanying the occurrence and development of cracks in refractories in thermal loading [3, 4]. It is characteristic that the acoustic emission generated in crack propagation correlates with the increase in their area [5]. Therefore, recording of acoustic-emission signals makes it possible to not only reveal the fact of failure but also to evaluate the degree of damage of the material in thermal loading.The block diagram of the instrument used for investigation of the acoustic emission in thermal loading is shown in Fig. i. In the test the sample with the acoustic-emission transducer 1 clamped to it is lowered by a fixed depth (2 mm) into the molten metal 2, which is heated by the specified temperature Tmolt by the heater 3, the supply voltage of which is established by the autotransformer 4 and measured by the voltmeter 5. Cubic samples with an edge of 20-30 mm are used. The temperature difference (Tmolt --20~ determines the amount of the thermal load.The acoustic-emission signals, recorded by the transducer i, are amplified by the amplifier 6 and fed to the amplitude selector 7, which accomplishes twosided amplitude discrimination of the signal with respect to four levels differing from one another by i0 dB and subsequent formation of pulses of standard amplitude and length. The instrument provides recording of signals with an amplitude of 5 ~V and more. The bandwidth of the circuit is 0.02-0.8 MHz.The formed pulses are fed through the main pulse stretcher 8 to the DZ-28 specialized computer 9, which records the counting rate of the acoustic emission, including the number of times the acoustic-emission signals exceed the established level of discrimination in a unit of time (i sec) and the total count of acoustic emission during the time of the experiment in each channel of the amplitude selector. The use of the computer makes it possible to conduct in digital form every-second recording of the counting rate N and the total count of acoustic emission N in the four channels and to provide the necessary mathematical treatment of the measurement results and output of them on a digital printer. To the output of All-Union Refractory Institute. Institute of Strength Problems, Academy of Sciences of the Ukrainian SSR.
In the refractories industry, increasing use is now being made of a method of compacting the material on vibropercussive tables under a dynamic pressure of 1.5-2.0 MPa.An investigation of the process of vibropressing of shaped chamotte products revealed that to obtain a compact material it is necessary to exert a strong dynamic action (about I0 MPa or more). With this aim, at the All-Union Institute of Refractories (VIO) we have developed a method of vibropressing with a powerful dynamic action in a hydroinertial vibropercussive press [i]. A previous report [2] dealt with work on vibropressing of ladle parts of relatively simple shape.In this article we shall give the results of investigations of vibropressingof shaped refractory products made from semidry pastes of various degree of plasticity.In our investigation we used chamotte paste made at the Borovichi Refractories Combine and the Chasov-Yar Combine of Refractory Products, ready-mixed Dinas mixture made at the Krasnogorovka Refractories Works, and also a graphite--chamotte mixture made at the VIO.The graphite--chamotte and Chasov-Yar chamotte pastes were made in a blade-type mixer, which was also used to process the Dinas paste to break up lumps formed during transportation.The Borovichi chamotte paste was made in SM-21A edge runner mills.The specimens were pressed and their characteristics determined by a previously developed method [2]. The power parameters of the process were registered with the aid of tensometers and an N-105 oscillograph.All-Union Institute of Refractories.
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