Technical Physics最新文献

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.

A drum-type installation for humidifying finely dispersed material is proposed. When implementing the installation concept at the stage of design and technological calculations, an important role is played by determining the rotation angle of the nozzle that sprays the humidifying liquid and the spraying time required to apply the liquid to the surface of the finely dispersed material layer. In order to implement the installation, mathematical calculations were performed, according to which, for a prototype humidifying installation with a drum with a diameter of 480 mm and a depth of 250 mm, a drum angular velocity of 1.256 rad/s, and a height of the humidified material layer corresponding to an angle of 0.42 rad, the calculated nozzle rotation angle was 0.39 rad. The liquid spraying time with the probability of droplet–particle interaction P = 0.95 was 126.9 s. To automate and simplify calculations when designing technological humidification lines, a program in Visual C# has been developed which allows calculating the nozzle rotation angle and liquid spraying time based on the characteristics of finely dispersed material and the geometric parameters of the drum. The calculation results obtained from the models are to be further verified by experiments.

The purpose of the work is the development, software implementation, and testing of algorithms designed to find resonant frequencies in an inhomogeneous dielectric ball coated with graphene. The relevance of the task is due to the widespread use of graphene in engineering due to its unique properties. The Galerkin method is applied to discretize a vector integrodifferential equation; piecewise-constant basis vector functions are determined on a three-dimensional body and on its surface, and a parallel algorithm for solving the problem is developed using the MSMPI library. The effectiveness of the parallel algorithm, which makes it possible to detect the sought resonances under specified conditions, has been confirmed. An effective parallel algorithm has been created for discretizing the integrodifferential equation, finding the determinant of the matrix, and searching for resonant frequencies.

The reliability and efficiency of equipment depend, among other things, on the operation of the cylinder–piston group (CPG)—the most frequently repaired unit in automotive and tractor engines. The quality of the CPG assembly is ensured by group interchangeability methods (selective assembly). In mechanical engineering, the human-readable marking of parts based on color schemes is insufficiently informative, so it is advisable to move from human-readable to machine-readable marking. In order to implement digital marking for spare parts and digital transformation of repair enterprises, the main quality indicators of CPG spare parts of engines and selective assembly of piston–liner joints of ZMZ-402 engines in 10 groups are considered. To improve the accuracy of the basic assembly conditions when implementing the method of intergroup interchangeability of CPG engines and automate the assembly process, it is proposed to use machine-readable marking based on a QR code or radio frequency tags. The advantages of a QR code are low cost of creation, fast readability of information, the ability to create a redundant QR code, high capacity, and the ability to read several tags simultaneously. Marking using radio frequency tags (RFID, NFC) allows encoding and reading information without direct contact. It is more resistant to mechanical impacts compared to a QR code. Significant disadvantages of radio frequency tags are the difficulty of reading when shielding the signal and the high cost of implementing this marking system. Digital marking of spare parts will help to forecast demand, improve automation, ease of use of warehouse databases and transparency of operations, and more accurately predict the timing and cost of repairs. Using a QR code together with the information environment (Internet catalog) of an enterprise will improve collection during selective assembly and reduce the likelihood of personnel errors.