Abstract: The article presents the course of the calculations and conclusions from the analysis of a bevel gear motion transmission using FEM. The motion transmission graphs show the angular variation of the driven gear in the case of a driving pinion that rotates with a constant angular velocity. In contrary to the classical Tooth Contact Analysis, which is carried out on stiff bodies, FEM analysis includes deformations of mating gears. Thus, it brings more realistic information on dynamic behavior and noise characteristic of analyzed gear drive.
Abstract: In the paper findings are discussed on the issue of dynamic characteristics of a tribometer as a factor influencing the result of the tribological experiment. An advanced approach to tribo-testing is attempted with integrated dynamic analysis of the tribometer and the sliding pair. The fundamental idea is explored of the tribometer being regarded as any machine in which friction is inflicted with all the resulting consequences such as e.g. wear, vibration, fatigue etc. The research described is concentrated around friction induced vibration and it’s potential consequences to the results obtained in a tribological experiment. General methodology used for the task described is presented.
Abstract: First gas-lubricated compliant foil bearings (CFBs) were built in the 1950s. Due to their significant advantages, such as oil-free operation, good tolerance to bearing misalignment and very low maintenance, they have been penetrating the bearing applications for high speed compressors, air-cycle machines and gas turbines. The work presented here investigates a novel idea of water-lubricated compliant foil bearings, which could be used in applications where environmentally friendly lubrication is desired, for example in hydroelectric turbines or water pumps. Experimental results collected for three prototype water-lubricated foil journal bearings are presented. The tests were conducted under steady radial load and with the sliding speed varied incrementally. A sequence of design improvements is presented, with the best bearing demonstrating friction coefficient of about 0.01 at the sliding speed of about 4 m/s and the radial load of about 300 kPa. Encountered difficulties, research methodology and the testing equipment are also described.
Abstract: In many machines and devices there are hydraulic drives. They should operate well in various weather conditions, also in low ambient temperatures. Some malfunctions may occur during operation of hydraulic system in a so called “thermal shock condition”, which happens when frozen hydraulic component (e.g. hydraulic pump, motor or directional spool valve) is suddenly supplied with hot oil. Transient thermal state emerges in these conditions. Particular elements of component warm up differently. This results in different thermal expansion of components during warm up, which is changing the size of clearance between cooperating elements. Experimental tests of hydraulic components in low ambient temperatures were conducted in the hydraulic laboratory of the Faculty of Mechanical Engineering of Gdansk University of Technology. They concerned: orbital motors, satellite motors, gear pumps, spool valves (also proportional), piston pumps, and hydraulic cylinders. It was proved, that in thermal shock conditions some malfunctions may occur, especially with large temperature differences between oil and component. Based on results of the tests of hydraulic components and systems start-up in low ambient temperatures, one can perform a change in components design, change the type of material of components elements, and even prepare a proper procedure to be followed during start-up of cold hydraulic components and systems. In the article discusses some designs of hydraulic components resistant to thermal shock, and how to prepare components to work in low temperatures, e.g. by providing system with an additional heater to ensure uniform heating of elements in components. Change in design of hydraulic components resistant to thermal shock conditions can be obtained through computer simulation method. Analytic and computer simulation methods can be used by engineers who design machines and devices that work in low ambient temperatures.
Abstract: Structure and basal application of magnetorheological fluids as well as their application in rotary shaft seals, have been presented in this study. As the application of magnetorheological fluid in seals is relatively purely known, the conducted studies were aimed at defining their operational parameters. The most essential was manner of the MR fluid delivery into oil gap, mostly the applied fluid volume. Not sufficient volume of the MR fluid often results in non-uniform oil gap filling what in turn decreases the seal efficiency. Results of studies on MR fluid-based seal burst pressure, conducted on specially designed testing stand, have been presented. The results comprise three oil gap sizes of d=0,15mm, d=0,3mm and d=0,5mm, for tests conducted with various volume of MR fluid applied on single sealing stage. Comparative values of the seal burst pressures obtained for three oil gap sizes of multi-stage seal, with the same apparent volume of MR fluid (the same fluid and oil gap volume ratio), were also presented.
Abstract: Hydropower industry increasingly frequently uses water lubricated bearings in turbines. This stems from the lack of negative impact of such solution on the environment. The paper presents an analysis of the influence of shaft misalignment in a turbine with water lubricated main shaft bearing on its hydrodynamic capacity. The theoretical analysis was based on the results of calculations for experimentally verified elastohydrodynamic lubrication (EHL) model. The obtained results showed impact of the stiffness of bush material and the degree of misalignment on bearing's hydrodynamic capacity.
Abstract: The references concerning the strength analysis of gears include a few methods of calculating the value of the face load factor (KHβ). In the paper, discussed are the C2 ISO method [1, 2, 3] and a method presented in [4, 5]. The two methods differ mainly in the way the bending and torsional deformations in the shafts and gears are calculated. On the example of the calculations of the first stage in a two-stage helical gear presented schematically in Fig.1, the influence of the these two different approaches on the value of the safety factors for pitting (SH) and tooth breakage (SF) has been analysed. The influence of four accuracy classes used in the manufacture of gearing (5, 6, 7 and 8) on the value of the safety factors SH and SF has also been evaluated.
Abstract: Serious problems arise when the magnetic fluid seal technology is needed to use in assemblies working in water or other liquid environment. Some efforts have been up to time made to design hybrid, two stage sealing structures with shields or mechanical seals used as protection measures to the magnetic fluid seal. Anyway, earlier or later there is always problem with direct contact between magnetic fluid and the environmental liquid. In the paper are presented results of experiments carried out with one stage rotating magnetic fluid seal operating in an direct contact with utility water. The special test procedures have been elaborated and practically used, with the aim to define main characteristics of magnetic fluid seals and to simplify experiments. These characteristics were: critical pressure, critical motion velocity and working life of the seal. Four grades of commercial, silicon based magnetic fluids of hydrophobic properties were tested in a single stage sealing system. The results of tests are presented in the form of tables and diagrams. It is concluded that hydrophobic commercial magnetic fluids could be efficiently used in rotating shaft seals however within limited and rather low range of motion velocity.
Abstract: The working unit of the hydraulic gerotor machine consists in cycloidal gears. In the paper, ways of increasing the load limit for the plastic cycloidal gears have been presented . The objective has been achieved by means of structural and material methods. The modifications have been introduced on the basis of the theoretical analysis of stress and deformation that are generated in the cycloidals gears while in operation. The analysis has been carried out with the use of the finite elements method. The outcome of the analysis is determination of the maximum working pressure value at which the hydraulic gerotor machines featuring the plastic cycloidal gears can operate.
Abstract: In slewing bearings, a great number of contact pairs are present on the contact surfaces between the rolling elements and raceways of the bearing. Computations to determine the load of the individual rolling elements, taking into account the flexibility of the bearing ring, are most often carried out using the finite element method. Construction of a FEM full model of the bearing, taking into account the shape of the rolling elements and the determination of the contact problem for every rolling element, leads to a singularity of stiffness matrix, which in turn makes the problem impossible to solve. In FEM models the rolling elements are replaced by one-dimensional finite elements (linear elements) to simplify the computation procedure and to obtain an optimal time for computations. The methods of modelling the rolling elements in the slewing bearing, in which balls have been replaced by truss elements with a material non-linear characteristic located between the raceway centres of the curvatures in their axial section, are presented in the paper.