Preliminary analysis of magnetorheological fluid usability in fluid lubricated bearings has been described in the present study. Results of the study aimed at rheological properties of chosen fluids, which possess magnetic properties (both ferrofluids and magnetorheological fluids) with respect to their application in slide bearings have been presented Preliminary analysis of potential advantages related with the magnetic fluid bearing construction was carried out. Results of measurements of normal force developed within magnetorheological fluid and ferrofluid in result of magnetic field action at various shear rate values have been presented.
The application of magnetic fluids in machine design on an industrial scale has been a fact for over 20 years. In particular, magnetorheological fluids have been used in energy dissipation systems with controlled operating characteristics. The availability of these fluids, connected with the ease of modelling their rheological properties by magnetic fields, contributes to the search for areas of effective use for such substances. Determining the properties and characteristics of magnetic fluid behaviour is one of the key aspects of improving existing and developing new applications for this type of smart material. Some phenomena affecting the behaviour of magnetic fluids have not been fully explained, and a synthetic model to describe their behaviour has not yet been developed, so the research area of this type of substance is still an open chapter for materials science. The paper presents a description of the design of a test stand for examining the behaviour of magnetic fluids working in shear and compression (squeeze) flow modes. Test results are also shown, and attention is given to the problems encountered in developing measurement systems for determining the properties of fluids under magnetic field conditions.
Magnetic fluid seals belong to the class of non-contact seals. They are used as protective seals for vacuum systems, high speed shafts, precision mechanics, and electromechanical devices. The proper functioning of the magnetic fluid seal is related to creating and maintaining the continuity of the fluid ring on the sealing stage. This is achieved by appropriately shaped magnetic field distribution in the region of the sealing stage. Consequently, one of the main issues with the construction of such seals is to determine the distribution of the magnetic field in this region. This paper presents the results of analytical calculations and numerical simulations, based on which the influence of selected geometric parameters on the critical pressure and motion resistance was determined.
Magnetic fluids belong to the class of materials in which rheological properties can be controlled by magnetic fields. Magnetic fluids are suspensions of ferromagnetic particles in a carrier fluid, and the magnetic field can change their internal structure. This phenomenon is fully reversible, almost instantaneously. The test results of a hydrostatic bearing lubricated by magnetic fluid are shown in the publication [L. 7]. It has been shown that the use of MR fluids as a lubricant allows high stiffness of the bearing to be obtained regardless of the height of the bearing gap. The publication [L. 8] presents the results of a thrust bearing lubricated by magnetic fluid with no external feed pump. The load capacity of the bearing was achieved by a self-sealing effect. This effect is associated with the ability to hold a magnetic fluid in a predetermined position through the magnetic field. This is caused by the appropriate geometry of the bearing surface. This effect retains the flow of the magnetic fluid out of the bearing gap as a result of the occurrence of a magnetic barrier, which counteracts the movement of the magnetic fluid. This barrier is a result of a local increase or decrease in magnetic induction similar to magnetic fluid seals. Another phenomenon highlighted in [L. 9, 10, 11] is the generation in the magnetic fluid of additional pressure due to the interaction of the magnetic field gradient. The result is an additional buoyancy force. When selecting a magnetic fluid for application in the thrust bearing, a number of factors should be taken into account. In addition to the parameters describing the typical lubricant, such as lubricity, corrosion properties, and work at high temperatures, the magnetic fluid used in the friction zone should allow a wide range of the rheological properties to be obtained due to changes in the magnetic field intensity. It is also important that the magnetic fluids have the ability to generate the appropriate value of the normal force due to the magnetic field.
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