hydraulic cylinders
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Relevance. Agricultural machines widely use hydraulic cylinders for various auxiliary and working movements. Operation in harsh field conditions leads to the failure of the hydraulic cylinder mirror and, as a result, to the loss of force on the cylinder rod. The development of technological solutions for the restoration of the inner surface as a more appropriate solution in repair production is relevant.Methods. Studies of the heat flow using the “Fluke Ti32” thermal imager and ofthe influence of gas-dynamic spraying (GDS) modes on the adhesive and cohesive strength when using a new design of the nozzle part of the GDS equipment were carried out.Results. The suitability of usage of new nozzle design for GDS in order to restore the inner surface of the hydraulic cylinder body has been established. The elongated and curved nozzle for installations of the “Dimet” type practically does not change the temperature regime of spraying. The adhesive and cohesive strength of the coatings obtained with the new nozzle design is sufficient to operate under conditions characteristic of the inner surface of the hydraulic cylinder body.

Reducing friction in the coaxial sealing systems of hydraulic cylinders is one of the solutions for increasing the energy efficiency of industrial actuations. This is a requirement, particularly in the case of small velocities that carry the risk of eigen-vibrations and/or stick-slip. The authors discuss the experimental research conducted on three coaxial sealing systems made from thermoplastic polymer and polyurethane type materials. The paper presents the equipment and method used for the experimental determination of static and kinematic friction coefficients and discusses the subsequent results obtained to test different working parameters. The experimentally determined friction coefficients yielded a range of materials recommended for coaxial seals such as to minimize the occurrence of jerky operation.

The publication discusses the issues of mathematical modeling of dynamic processes occurring in a complex hydromechanical system of the hydraulic drive of the wide-cut cultivator sections with consistent wear of the hydraulic cylinders. The analysis of known designs of wide-cutting tools and agricultural units is carried out. It is noted that one of the tendencies in the development of domestic agricultural engineering is an increase in the width of coverage of tillage machines. In this regard, hydraulic drives for decomposition and assembly of sections of these machines are widely used. The use of this type of drive is due to its compactness, speed and power. The basic schematic diagrams of hydraulic drives for decomposition of wide-cut tillage machines are considered. On the basis of the analysis, a schematic diagram of the hydraulic drive for assembling (decomposing) sections of a wide-grip cultivator with sequential actuation of hydraulic cylinders is proposed and the principle of its operation is described. A mathematical model has been developed for the hydraulic drive of the wide-grip cultivator sections in the working and transport position. The mathematical model consists of the equations of the continuity of the flows of the working fluid, which describe the processes occurring in the hydraulic drive, and the equations of moments and forces, from which it is possible to determine the force factors acting on the elements of the system. It is difficult to obtain an analytical solution to the resulting system of equations, therefore, to find solutions, numerous methods were applied, namely the Runge-Kutta-Feldberg method with an automatic change in the integration step. On the basis of the obtained dependencies, an analysis of the operation of the hydraulic drive with sequential wear of the hydraulic cylinders was carried out and recommendations were proposed on the design device and directions for improving the hydraulic drive of the tillage unit sections.

Honing processes are currently employed to obtain a cross-hatched pattern on the internal surfaces of cylinders that favors oil flow in combustion engines or hydraulic cylinders. The main aim of the present paper is to optimize the machining conditions in honing processes with respect to surface roughness, material removal rate and tool wear by means of the desirability function. Five process variables are considered: grain size, density, pressure, linear speed and tangential speed. Later, a sensitivity analysis is performed to determine the effect of the variation of the importance given to each response on the results of the optimization process. In the rough and semi-finish honing steps, variations of less than 5% of the importance value do not cause substantial changes in the optimization process. On the contrary, in the finish honing step, small changes in the importance values lead to modifications in the optimization process, mainly regarding pressure. Thus, the finish honing phase is more sensitive to changes in the optimization process than the rough and the semi-finish honing phases. The present paper will help users of honing machines to select proper values for the process variables.

To prolong the lifetime of hydraulic cylinders, a wear-resistant low-friction surface is required. Until now, hard Cr coatings were the best materials for this. However, in recent years, there has been an increasing pressure on the manufacturing of hard Cr plating and plated products, because of environmental and health hazards. The replacement of these coatings by alternatives has not been highly successful yet, because it requires extensive component testing, which is costly and time-consuming and thus not appropriate for material development. For this reason, there is a high need to develop tribological methods that simulate hydraulic cylinders’ component-testing closely. In addition, these new methods should also provide additional information (e.g., friction evolution) that can assist in the further development and optimization of alternative coatings. Having the above in mind and building on an existing method from the American Society for Testing and Materials (ASTM G133), a new test method that allows users to test directly on hydraulic cylinders was developed. This method can provide a relative ranking of both the wear resistance and frictional performance of alternative coatings in direct comparison to state-of-the-art hard Cr. Importantly, the method is repeatable and has a much shorter test duration than full-scale component tests, thereby accelerating material development significantly.

Abstract The operating conditions of magnetic fluid seals during reciprocating motion are so different from those observed in rotating motion that the use of their conventional structures for reciprocating motion seals yields no good results. The analysis of the sealing mechanism of magnetic fluid seals in reciprocating motion shows that the operation of these seals is affected by the carry-over phenomenon and magnetic fluid film deformation in the sealing gap, which depends on the velocity of the reciprocating motion. The reduced amount of magnetic fluid in the sealing gap caused by the reciprocating motion of the shaft is the main reason for seal failures. The paper presents a short characterisation of magnetic fluid sealing technology, the principle of sealing, the operation of the magnetic fluid and the seal failure mechanism in linear motion of the shaft. Moreover, some new structural designs of hybrid seals, being combinations of typical hydraulic seals with magnetic fluid seals for reciprocating motion, and some examples of magnetic fluid sealing structures for hydraulic cylinders and piston compressors which have practical application values are presented.

Features of the operation and typical damages of standard hydraulic systems’ elements of road-building machines have been analyzed. The occurrence reasons of defects and the elimination ways of them were determined. Methods for eliminating the defects were analyzed, and it is shown that one of the most promising methods for eliminating the defects in liners of hydraulic cylinders and hydraulic lines is the use of polymer composite materials with a fibrous or dispersed filler for the repair.

Hydraulic systems fed by fixed displacement pumps driven by frequency-controlled electric motors can replace conventional throttling systems due to their ability to control the speed of hydraulic cylinders regardless of the value and direction of the load. These systems can improve the energy efficiency of the drive or even provide the possibility of energy recuperation during lowering. This paper presents experimental studies of the new drive system with volumetric control of the speed of the lifted/lowered payload using the example of a scissor lift. The system uses a reversible gear pump driven by an asynchronous motor fed by a frequency inverter operating in field-oriented control mode. Comparative studies of the mapping of the assumed speed of the hydraulic cylinder and platform are presented, as well as studies of the influence of the load change on the speed and positioning of the mechanism driven by the open-loop controlled system.

Abstract Currently, the ordering of standardization objects and their properties, optimization of the parameters of standardization objects, normalization of requirements for objects are the most important areas of standardization as a science. In this regard, the issues of choosing parametric series are very relevant. In order to increase the level of interchangeability and reduce the range of products and standard sizes of blanks, overall cutting tools, tooling, productivity, speed, speed, power, etc., used in a particular industry, as well as to create conditions for effective specialization and cooperation of plants, reduce the cost of products, the principle of preference is used in the unification and development of standards. There are two methods for choosing parametric series: the method of technical justification and the method of economic justification. The technical method is easier to use and is used to expand the technologies of unification of standard sizes of parts of homogeneous products. This method was used to calculate a number of diameters of hydraulic cylinders of broaching machines of the same series based on the mathematical dependence between the force developed on the hydraulic cylinder rod, which is formed by the initial parametric series laid down by the designers. As a result of technical optimization of the choice of the parametric series, a number of diameters of hydraulic cylinders R20/2(45-224) mm was installed, fully corresponding to the main functional parameter - a number of forces on the rod of broaching machines R10/2(0.63-16.0) kN.