ОПРЕДЕЛЕНИЕ КОНТАКТНЫХ НАПРЯЖЕНИЙ И ЗАЗОРОВ В ШАРНИРАХ ЦЕПНЫХ ПЕРЕДАЧ

The article considers the questions of determination of contact stresses in the chain transmission hinges that need to be known for assessing their wear resistance, because the wear and tear of hinges is the most common type of damage to the chain gears. In this context the main attention was paid to determining the required clearance between the bushing and the pin of roller chain drives. This gap largely determines the character of the distribution and magnitude of contact stresses in the hinge, and, consequently, the durability of chain drives. A method of calculation of the maximum contact stresses in the chain transmission hinges is developed. It is shown that decreasing clearance in the hinges increases the contact angle between the pin and the bushing and reduces the maximum contact pressure. However, for the actual angles of contact the contact stress greatly exceeds the allowable average unit pressure, causing increased wear of the hinges. One of the possible solutions to this problem is the use of transition fits in hinges, in which the gaps and interferences are relatively small. When pressing the pins into in the bushings, due to cutting microasperities from the contact surfaces, the interference in the connection virtually disappears. Examples of determining gaps and contact stresses in the chain transmission hinges are provided.Контактные напряжения в шарнирах цепных передач необходимо знать для оценки их износостойкости, поскольку износ шарниров является наиболее распространенным видом повреждения цепных передач. Определен необходимый зазор между втулкой и валиком цепных передач. Зазор в значительной степени определяет характер распределения и величину контактных напряжений в шарнире, а следовательно, и износостойкость цепных передач. Разработана методика расчета максимальных контактных напряжений в шарнирах цепных передач. Показано, что с уменьшением зазора в шарнирах увеличивается угол контакта между валиком и втулкой и снижаются максимальные контактные напряжения. Однако для реальных углов контакта контактное напряжение сильно превышает допустимое среднее удельное давление, вызывая повышенный износ шарниров. Один из возможных путей решения данной задачи - использование в шарнирах переходных посадок, в которых зазоры и натяги сравнительно невелики. При запрессовке валиков во втулки за счет срезания микронеровностей с контактных поверхностей натяг в соединении практически исчезает. Приведены примеры определения зазоров и контактных напряжений в шарнирах цепных передач

Разработка методики расчета круговых прерывистых сварных швов на кручение

The main criterion for the performance of welds is the strength. The least durable are the corner joints used to perform various types of welded joints. In the literature, the methods of calculating the strength of welded joints with solid seams are considered in sufficient detail. Methods of calculation of connection interrupted sutures absent. In this case, the greatest difficulty is the calculation of connections using circular intermittent seams, which are often performed in welded drums and pulleys. They work on torsion. Therefore, the development of methods for calculating circular intermittent seams for torsion is quite important. Shear stresses in welds from torque are determined depending on the value of the polar moment of resistance of its dangerous section. When determining the polar moment of resistance of the dangerous section of a circular discontinuous seam, it was represented by a set of sections in the form of a sector of a circular ring. The method of calculation of the polar moment of resistance of the rotated dangerous section of a circular discontinuous weld, which takes into account the relative length of the weld areas and their number, is proposed, as well as the method of accurate and approximate calculation of shear stresses in the weld.Основным критерием работоспособности швов сварных соединений является прочность. Наименее прочными являются угловые швы, используемые для выполнения различных видов сварных соединений. В литературе достаточно подробно рассмотрены методы расчета на прочность сварных соединений сплошными швами. Методы расчета соединений прерывистыми швами отсутствуют. При этом наибольшие трудности представляет расчет соединений с помощью круговых прерывистых швов, которые довольно часто выполняются в сварных барабанах и шкивах. Они работают на кручение. Поэтому разработка методики расчета круговых прерывистых швов на кручение имеет достаточно важное значение. Касательные напряжения в сварных угловых швах от крутящего момента определялись в зависимости от величины полярного момента сопротивления его опасного сечения. При определении полярного момента сопротивления опасного сечения кругового прерывистого шва оно представлялось совокупностью участков в виде сектора кругового кольца. Разработана методика расчета полярного момента сопротивления повернутого опасного сечения кругового прерывистого сварного шва, которая учитывает относительную длину участков шва и их количество, а также методика точного и приближенного расчета касательных напряжений в данном сварном шве

ОПРЕДЕЛЕНИЕ КОНТАКТНЫХ НАПРЯЖЕНИЙ И ЗАЗОРОВ В ШАРНИРАХ ЦЕПНЫХ ПЕРЕДАЧ

The article considers the questions of determination of contact stresses in the chain transmission hinges that need to be known for assessing their wear resistance, because the wear and tear of hinges is the most common type of damage to the chain gears. In this context the main attention was paid to determining the required clearance between the bushing and the pin of roller chain drives. This gap largely determines the character of the distribution and magnitude of contact stresses in the hinge, and, consequently, the durability of chain drives. A method of calculation of the maximum contact stresses in the chain transmission hinges is developed. It is shown that decreasing clearance in the hinges increases the contact angle between the pin and the bushing and reduces the maximum contact pressure. However, for the actual angles of contact the contact stress greatly exceeds the allowable average unit pressure, causing increased wear of the hinges. One of the possible solutions to this problem is the use of transition fits in hinges, in which the gaps and interferences are relatively small. When pressing the pins into in the bushings, due to cutting microasperities from the contact surfaces, the interference in the connection virtually disappears. Examples of determining gaps and contact stresses in the chain transmission hinges are provided.Контактные напряжения в шарнирах цепных передач необходимо знать для оценки их износостойкости, поскольку износ шарниров является наиболее распространенным видом повреждения цепных передач. Определен необходимый зазор между втулкой и валиком цепных передач. Зазор в значительной степени определяет характер распределения и величину контактных напряжений в шарнире, а следовательно, и износостойкость цепных передач. Разработана методика расчета максимальных контактных напряжений в шарнирах цепных передач. Показано, что с уменьшением зазора в шарнирах увеличивается угол контакта между валиком и втулкой и снижаются максимальные контактные напряжения. Однако для реальных углов контакта контактное напряжение сильно превышает допустимое среднее удельное давление, вызывая повышенный износ шарниров. Один из возможных путей решения данной задачи - использование в шарнирах переходных посадок, в которых зазоры и натяги сравнительно невелики. При запрессовке валиков во втулки за счет срезания микронеровностей с контактных поверхностей натяг в соединении практически исчезает. Приведены примеры определения зазоров и контактных напряжений в шарнирах цепных передач

Protection of pipeline systems from water hammer using oscillatory circuits

The issues related to reduction of the amplitude of high pressure waves in long pipes are relevant in connection with the danger of failure of some hydraulic system's sections. The article deals with the reduction of high pressure by simultaneous separation of fluid flow for long hydraulic systems. Numerical experiments are carried out in order to identify the most cost-effective dimensions of the equipment, as well as the most profitable in terms of energy damping locations of this equipment. © Published under licence by IOP Publishing Ltd

Development of methodology for calculation of permissible stresses for evaluation of contact strength of cylindrical gears in case of overload

The article focuses on the development of methods for determining the allowable stresses to check the contact strength of the spur and helical gears under overload. Short-term overloads in gears occur under the action of maximum moments during the start-up of the device or due to the other reasons. The calculation of these loads is performed to check the static strength of the transmission teeth. The analysis of the limiting state of the material in the working area of the gear teeth was performed using the Pisarenko-Lebedev strength criterion, which is one of the most common strength conditions. The method of calculation of allowable stresses was developed. The calculation of limit stresses for normalized, improved or hardened wheels, as well as for the wheels after hardening by chemical-thermal treatment. The calculation results were compared with the values recommended by the standard. It was shown that the permissible contact stress for helical gears is slightly higher than for straight gears. Practically for all heat-treated steels used in the manufacture of gears, the norm of permissible limit stresses recommended by the standard is higher (in some cases significantly) compared to the stresses required from the conditions of contact strength. © Published under licence by IOP Publishing Ltd

Reduction of harmful pressure fluctuations in pipelines by means of introduction of energy damping segments

Problems of water hammer reduction in the pipeline, as well as reduction of the oscillations amplitude of the high pressure wave with a relatively wide front are relevant in our time in the design of pipeline systems, especially for long sections of the pipeline. Dozens of new protective equipment have been developed in the last decade, but interest in the subject has not diminished. This work is devoted to the search for new ideas to achieve the operation safety of modern pipelines. In the article the basic idea of protection is formulated, and also numerical experiments for various schemes of installation of the considered equipment are carried out. The paper provides recommendations on the most appropriate placement of equipment, as well as discusses the issues of economic feasibility. © WCSE 2019. All rights reserved

Water Hammer Decrease by Introduction of Pipes with Low Speed Pressure Waves Propagation

The article presents the results of analysis of pressure fluctuations in a pipe in which the maximum amplitude of the pressure decreases due to the introduction of pipeline sections with low speed of propagation of pressure waves

Influence of the valve-pull-down equipment on the area of high pressure peaks in long pipelines

The pipeline system is usually destroyed by the high internal pressure in the tubes due to development of water hammers. Also the possibility of continuous pressure oscillations causing vibration of external piping is dangerous, because it leads to loosening and destruction of the supports. One of the effective methods to protect a long pipeline is the possibility of removing liquid from the pipeline. The paper deals with the calculation of similar valve-pull-down unit by the numerical method of characteristics. © BEIESP