Ультразвуковий метод та засіб для виявлення внутрішніх дефектів залізничних осей

Abstract

The dissertation on obtaining a scientific degree of Ph.D. in specialty 05.11.13 "Devices and methods of control and definition of structure of substances" - National technical university "Kharkiv polytechnic institute". The dissertation is devoted to the development of a new method and means for providing ultrasonic immersion testing with increased sensitivity to the detection of internal defects of minimal size. An analytical review and analysis of modern tools and methods of non-destructive testing and diagnostics of railway axles and their blanks. The influence of various types of noise, technical level of devices and instruments for testing of railway axles, circuit solutions of their power supplies, reception of ultrasonic pulses from products are considered, known advantages, disadvantages and possibilities of their use in research and development are defined. As a result of the information source analysis it is established that ultrasonic contact and immersion methods have their advantages and disadvantages in detecting internal defects and assessing the structure of steel of railway axles and blanks for their manufacture. Technical contradictions for each of them dictate the need to perform research of these methods, followed by their solution. Due to the increasing requirements for the quality of railway axles, the need to increase the sensitivity of ultrasonic flaw detection by calibrating the control device on models of smaller defects, such as flat-bottomed reflector with a diameter of 1 mm or more instead of 3 mm or more [10]. To ensure high sensitivity to the detection of minimal defects, it is necessary to develop methods and means of their implementation. The directions of dissertation research are defined and substantiated. The physical model of product testing in the immersion variant is determined by the results of the analysis of which the minimum thickness of the immersion liquid layer between the combined piezoelectric transducer (PET) and the surface is determined. This thickness must be greater than the spatial duration of the ultrasonic pulse рСt (where р С - the speed of propagation of longitudinal waves in the liquid; t - pulse duration in time). The calculation of the minimum thickness of the layer of immersion fluid between the combined PET and the surface of the workpiece of the railway axis, which must be at least 46 mm with a diameter of the railway axis of 170 mm. A physical-mathematical model of railway axle testing in the immersion variant has been developed. Theoretical calculation of the ultrasonic path for railway axles testing by a longitudinal transducer in the reflection of ultrasonic pulses from models of defects in the form of flat-bottom reflectors of different diameters, taking into account the attenuation of signals in refraction on a curved surface and transformation. An unambiguous relationship between the size of the defect and the frequency of ultrasonic oscillations, which indicates the need to establish a rational value of the frequency of ultrasonic oscillations in identifying the model of the defect specified by regulatory and technical documentation for control. The issue of rational choice of duration of ultrasonic pulses of PET power supply, aimed at increasing the sensitivity of testing, is solved. It is proven that it is possible to significantly raise the sensitivity of testing by increasing the duration of ultrasonic pulses. Such an approach is due to the concentration of signal energy in a narrow range of the spectrum and the wide possibilities of filtering the useful signal from interference. It is advisable to choose the pulse duration of at least 3… 5 periods of signal filling frequency. However, to use pulses of extra duration it is not expedient as at the same time the "dead" (not controlled) zone at a surface of metal increases. It has been theoretically and experimentally proven that the sensitivity of ultrasonic immersion control of railway axles can be increased by feeding piezoelectric transducers with packet current pulses with a given filling frequency and time duration. It is established that to ensure sufficient sensitivity of ultrasonic immersion testing of railway axles (detection of internal defects of an effective size corresponding to a 1 mm diameter flat-bottom reflector), the ultrasonic frequency must be set in the range 4.2… 4.5 MHz with pulse temporal duration of 8 periods of filling of the specified frequency. A method of ultrasonic immersion testing has been developed, which includes immersing a control sample with a model of a defect of a given size into immersion liquid, irradiating a defect in the sample using a singular probe and a singular ultrasonic pulse, which consists of several high-frequency periods, receiving a pulse reflected by the defect with a second probe, adjusting the frequency and duration of the irradiating ultrasonic pulse until obtaining the maximum amplitude of the pulse reflected by the defect, and conducting defectoscopy with the specified parameters of the irradiating pulse. A special generator for powering piezoelectric transducers and a band amplifier for received ultrasonic pulses have been developed. A model of the acoustic immersion unit of the device has been developed, the essence of which is to use two longitudinal PETs located at a certain distance from each other, which is determined by the scattering indicatrix of the defect, the size of which is specified by the normative technical documentation. The use of development made it possible to increase the amplitude of the echo pulse reflected from a 1 mm diameter flat-bottomed reflector, relative to the amplitude of the noise to 15 dB. The efficiency of the results of the performed researches in comparison with the known developments is estimated. The development results are protected by 2 utility model patents.