Technical Physics最新文献

The parameters of a resonator consisting of two dielectric plates with gratings of strip conductors between the layers in the form of squares, and on the outer surfaces in the form of square meshes having the same subwavelength period, have been determined. The quality (Q) factor of the resonator, which has been measured at the normal wave incidence, is determined by the ratio of the widths of the internal and external conductors. Using electrodynamic analysis of a 3D resonator model, the propagation of plane linearly polarized electromagnetic waves when their angle of incidence φ deviates from the normal to the plane of the layered structure has been studied. It is found that for the parallel polarization of the wave, the Q factor of the observed half-wave resonance with increasing φ first drops to a minimum when approaching the Brewster angle, and then increases as φ → 90°. In the case of the perpendicular polarization of the wave, the Q factor of the half-wave resonance gradually increases with increasing φ, approaching the maximum value at φ → 90°.

Diagnostics of electrical components of hydrotechnical equipment used in agricultural production within the planned maintenance intervals with continuous analysis of residual resource is useful for reducing equipment operation costs. The use of inexpensive universal diagnostic equipment in conjunction with primary analysis of the state of units makes it possible to detect 60 to 80% of prefailure states. To ensure efficient application of the complex approach to primary diagnostics of electrical components of hydraulic equipment used in agricultural production, the authors considered the most common electric motors of pumping units, electrohydraulic distributors, and switching equipment. Complex diagnostics included the use of a thermal imager, vibration signal processing systems, and current signal control systems. The vibrograms of equipment control points were analyzed, and the state of bearing units as well as the cavitation characteristics of pumps were assessed by methods of acoustic and vibration diagnostics; hydraulic equipment leaks were searched, and power cables breakdown zones were detected in accordance with methodical instructions for determining the breakdowns of power cables with a voltage of up to 10 kV (RD 34.20.516-90). The article shows the possibilities of applying the diagnostics methodology based on surface thermograms to determine typical defects. Particularly discussed are the parameters of current signals from the electromagnet coils observed in case of distribution equipment malfunction. The authors give comparative estimation of diagnostics methods with calculated efficiency determination. It is established that the method of combined diagnostics using the analysis of external thermal fields can halve the time of preliminary diagnostics of faults with a stable forecast of the failure time 2–3 months before the critical state. This reduces the expenditures for detection of unit failures and simplifies the planning of maintenance procedures.

Reinforced rubber lip seals are used in bearing assemblies. Their reliable operation is ensured by pressing the lip of the seal against the shaft. The produced contact load prevents the outflow of sealed medium and the penetration of an abrasive and of chemically aggressive substances into the assembly, which reduces the service life of the parts. The contact load in the connection is affected by the force generated by the band spring. The method presented here is used to determine the specific contact load of the seal lip on the shaft imposed by the band spring depending on the parameters of the lip seals and springs. To check the adequacy of the methodology, the authors studied a batch of twenty five 1.1-45x65-1 reinforced lip seals (GOST 8752-79). The theoretically calculated contact force exerted by the spring was 2.64 to 3.804 N, specific contact loads were 0.098 to 0.153 N/mm while those according to experimental data were 2.75 to 3.50 N and 0.102 to 0.141 N/mm, respectively. High convergence confirms the correctness of the presented calculated relationships. It was established that the parameters of the lip seals had a large spread, which hampered accurate calculation of the specific load in the shaft–seal connection. To increase the accuracy of readings, it is necessary to reduce the tolerances on the dimensions of rubber products.

Sickle-bar mowers are mainly employed when harvesting forage. To improve their quality and consumption indicators, it is necessary to study the trajectory of movement, speed, and acceleration of the mower leg under changing terrain conditions. For this purpose, a study is performed to analyze the effect of the offset on the quality and energy indicators of the cutting equipment of the mower, as well as control the parameters and operating modes of the mower knife with an axial knife drive mechanism. The experimental results show that the cutting tool in the process of creating a relief contour changes the angle of inclination relative to horizon within ±15°. In this case, the offset ranges from 0.281 to 0.492 m. A change in the offset entails a change in the stroke, speed, and acceleration of the knife. Using the Artobolevsky analytical method of kinematic study of eccentric crank mechanisms and Excel calculations, we obtained graphic data on the dependence of the stroke, speed, and acceleration of the knife on the angular position of the cutting tool with an interval of 0°, 5°, 10°, and 15°. Changes in the position of the cutting tool of up to 15° leads to unequal speeds of the forward and reverse stroke of the knife, and also increases it from 76.2 to 89 mm, which increases the energy consumption for the knife drive to 17%. Another disadvantage of the eccentric crank mechanism of the knife drive is its dynamic imbalance, which is only partially smoothed out using a counterweight. To eliminate the disadvantages, an experimental mower with an axial arrangement of the crank mechanism on the bar of the cutting tool is proposed, allowing the bar handles to be transformed to the transport position in the working mode of the cutting tool when driving around bushes, trees, or rough irregularities.

Motor vehicles and tractors operate in conditions of high dustiness. The main reason for the short service life of precision parts of fuel equipment (FE) is the abrasive wear of working surfaces. The innovative chemical vapor deposition (CVD) method of obtaining coatings by thermal decomposition of chromium hexacarbonyl with subsequent deposition of chromium carbides significantly increases the wear and corrosion resistance of the injector nozzle parts of diesel engines. To increase the service life of the sprayer, the authors propose to apply a hardening coating to both working surfaces of the parts, viz., the needle (steel R6M5) and the inner surface of the housing (steel 12Kh2N4А). In order to minimize costs in the manufacture of new precision parts, the authors determined the critical (minimum) coating thickness, ensuring its load-bearing capacity. They also obtained analytical relationships between the minimum required coating thickness depending on its microhardness and the size of quartz and corundum particles, as well as regression equations and response function graphs. It has been established that in order to ensure the bearing capacity of the hardening coating on the fuel injector nozzle parts of the diesel engine, its critical thickness should be not less than 3 micrometers at a microhardness of 18.9 GPa.

Difficulties in the delivery of machinery, equipment, and spare parts, as well as the limitedness of financial resources for agricultural enterprises, necessitate upgrading of machine maintenance processes and technologies. The damage of radiators in the liquid cooling system of internal combustion engines is one reason for equipment failure. To develop a technique for mechanical damage repair, analysis of the radiator designs has been performed and prevailing defects have been revealed. It has been found that aluminum or copper‒brass radiators are most commonly used in the cooling system of internal combustion engines. Maun in-service defects are mechanical damage of internal combustion engine radiators in the form of leaky tubes and cooling tape (or plate) separation. These defects are most frequently removed by soldering with tin‒lead solders, blanking off leaky tubes, pouring polymer sealants into the cooling liquid, and taping. For the case of radiator mechanical damage, it has been suggested that cold gasdynamic spraying of a metallic layer is applied using a Dimet-405 setup. The surface was subjected to preliminary abrasive treatment by a K00-04-16 corundum powder. Optimal spraying conditions have been suggested: for A-20-11 powder at 100°C (regime 1) or 200°C (regime 2) and for C-01-11 powder at 200°C (regime 2) or 300°C (regime 3). The powder feed rate was 0.3 g/s. The strength of obtained joints was no lower than that of joints obtained using tin‒lead solder. A technique for leakage stopping and cooling tape‒tube contact restoration developed by the authors makes it possible to rapidly and reliably repair damaged radiators. The repair of radiators used in the engine cooling system will allow one to cut the machine down time.

The finishing processes in mechanical engineering are aimed at creating ideal surfaces of parts satisfying specifications, in particular their dimensions, but these processes carried out on actual equipment are subject to deviations from specified values. Statistical methods of quality control and management are a diagnostic tool for analyzing the causes of variations. The diameters of 20 crankshaft main journals of the ZMZ engine were investigated after machining for the repair size. The quality of machining crankshaft journals was evaluated sequentially using quality tools such as the box-and-whisker diagram, Shewhart control charts, and histograms. It was found from the box-and-whisker diagram that after machining for the repair size all the journals had the diameter within the machining tolerance field, but at the same time there was a scatter between journal diameters of the same crankshaft. An analysis of the Shewhart control charts established that the scatter values within one subgroup (crankshaft) and between subgroups were caused by usual reasons, and this scatter pattern can be considered random. Hence, the process can be considered stable and controllable. The histogram helped to determine the probability of 1.95% for recoverable rejects after machining the engine journal for the repair size and the probability of zero for unrecoverable rejects. The calculated reproducibility index of 0.93 indicates a significant wear of the equipment. The index will decrease over time and the risks of rejects will increase. The authors conclude that the quality of setting for machining crankshaft main bearing journals for the repair size is acceptable. It is recommended that the quality of machining crankshaft main journals for the repair size be checked regularly applying successively all three tools to identify the size variation and inconsistencies, which is particularly important for worn equipment.

Quality control is always based on certain physical principles and measurement methods. The parameter that affects any inspection is error produced by measuring instruments and methods. A measurement error may result in good parts being erroneously classified as defective and some defective parts being accepted. When inspecting main bearing diameters of a vehicle cylinder block, it is important to minimize the chance of inspection errors. Erroneous rejection of the main bearing support to the left or to the right of the tolerance limit will result in the need to replace the cylinder block. Erroneous acceptance of the support according to the smallest dimension can result in loose fit of the cap to the bearing and probable break. Erroneous acceptance of the main bearing support according to the largest size can lead to a gap between bearing shells and their subsequent play and rotation. In order to reduce the occurrence probability of these errors during tolerance control, the authors estimated erroneously accepted and erroneously rejected main bearings in detecting defects using NI 100-160 0.01; NI-PT160-0.001; and NIC-PT 160-0.002 inside calipers. Twenty cylinder blocks were analyzed and five main bearings were inspected in each of them. The use of NI-PT160-0.001 in repairs of 1000 YaMZ engines per year is estimated to reduce loss from erroneous rejection by 2.13 times and loss from erroneous acceptance by 1.88 times as compared with NI 100-160 0.01. The use of NIC-PT 160-0.002 is unpractical because of the possibility of increasing loss due to the difference in accuracy readability. The proposed methodology can be applied to detecting defects in other engine parts, for example, for monitoring the inner diameter of the cylinder liners and the big end of the connecting rod.