DIAGNOSTICS OF ROLLING EQUIPMENT SLIDING BEARINGS

Peculiarities of rolling bearings operation are analyzed. Methods of diagnostics of general purpose sliding bearings and rolling equipment are considered. Direct control of the maximum allowable wear of plain bearings during operation is proposed. It is advisable to provide remote information and consulting services to technical services of metallurgical enterprises for maintenance, repair and operation of crankshaft bearings. Bearings of electric machines of drives of rolls of rolling mills work in extremely difficult conditions with considerable overloads in the environment of the increased vibration. This leads to premature wear of the liner and its fatigue failure. The technical condition of bearings of electric machines of drives of rolls of rolling mills for the purpose of an exception of an emergency stop of production is carried out by indirect control of temperature and vibration. However, these controls do not guarantee an avoidance of an emergency. All problems with working plain bearings can be grouped into three groups: insufficient bearing capacity of the lubricating layer, unregulated clearance between the shaft and the liner, unsatisfactory technical condition of the bearing surfaces. Insufficient bearing capacity of the lubricating layer is more often associated with loss of lubricant properties due to improper maintenance of the lubrication system. The discrepancy between the size of the gap between the shaft and the liner to the normalized value arises from design, technological and operational reasons. Key words: plain bearing; failure; rolling equipment; direct wear control; remote information and consulting services

Numerical analysis of a radial hybrid lobe bearing with gas lubrication

В работе рассмотрены результаты численного исследования модели радиального гибридного подшипника с газовой смазкой. Установлено наличие оптимальных значений параметров, определяющих форму смазочного зазора, получены их значения и закономерности влияния на них различных характеристик подшипника. Рассмотрено распределение давления в смазочном слое при различном количестве секторов лепестков. Подтверждено предположение о наличии оптимальных значений параметров, определяющих форму смазочного зазора. И опровергнуто предположение о том, что оптимальные значения этих параметров будут зависеть от значений других параметров подшипника. Выявлен положительный эффект от совместного воздействия газодинамического и газостатического эффектов. Относительно газостатических параметров – выявлен параметр, имеющий оптимальное значение (расстояние от выбранного торца подшипника до линии сетки, на которой располагаются питатели ряда с номером р), которое сохраняет постоянное значение. На основе полученных результатов разработаны основы методики расчета и оптимизации радиальных гибридных подшипников с газовой смазкой, имеющих профилированную рабочую поверхность. The paper considers the results of numerical study of gas-lubricated hybrid radial bearing model. The presence of optimal values of parameters determining the shape of the lubrication gap is established, their values and regularities of influence of different bearing characteristics on them are obtained. Pressure distribution in the lubricating layer at different number of lobe sectors has been considered. The assumption of optimum values of parameters determining the form of the lubrication gap is confirmed. And the assumption that the optimal values of these parameters will depend on the values of other bearing parameters is refuted. The positive effect of the combined effect of gas-dynamic and gas-static effects has been revealed. Concerning gas-static parameters - the parameter which has optimum value (distance from the chosen end face of a bearing to a grid line on which feeders of a row with number p are located) which keeps constant value has been revealed. On the basis of the obtained results the bases of calculation and optimization methodology of radial hybrid bearings with gas lubrication, having profiled working surface, are developed.

Dynamics of marine diesels when using motor oils with different structural characteristics

Annotation – The influence of the structural characteristics of engine lube oil on the dynamics of a marine diesel engine is considered. It is indicated that micron layers of marine engine lube oils separating the contact surfaces of marine diesel engines acquire the properties of liquid crystals and are characterized by an ordered molecular structure. The qualitative indicator of this structure is the degree of ordering of the molecules, and the quantitative indicator is the thickness of the ordered (boundary) lubricating layer. It is proposed to determine the structural characteristics of marine engine lube oils (the degree of ordering of the molecules of the boundary layer and its thickness) using the optical method of absorption dichroism. A diagram of an experimental setup is presented that allows such studies to be carried out. It has been experimentally established that for Shell Rimula X15 and Castrol TPL 123 engine lube oils (used in the oil system of the Caterpillar CatC18 marine diesel engine), the thickness of the ordered (boundary) lubricating layer is 14.3 ... 14.7 microns and 16.4 ... 16.6 microns, respectively. The degree of ordering of molecules in the boundary layer for Shell Rimula X15 engine lube oil is in the range of 0.56 ... 0.58, for Castrol TPL 123 engine lube oil – in the range of 0.63 ... 0.64. The results of studies of the dynamics of the CatC18 marine diesel engine by Caterpillar, carried out in the starting mode, as well as at various increases and decreases in load, are presented. As indicators, which were used to assess the dynamics of the diesel engine, the overshoot of the rotational speed and the time to reach a new steady state mode were taken. Experiments have confirmed that Castrol TPL 123 engine lube oil, which has a higher molecular structure in the boundary layer compared to Shell Rimula X15 lube oil, ensures the transient processes of the Caterpillar CatC18 marine diesel engine with less overspeed and less time to reach a new state work. The proposed technology for determining the structural characteristics of engine lube oils can be used for any type and grade of oil (mineral or synthetic, high and low viscosity, used both in circulating and cylinder lubrication systems). The proposed method for assessing the dynamic characteristics of marine diesel engines (by overshoot of the speed and the time to reach a steady state of operation in the event of a change in load) can be used for any types of internal combustion engines (low-, medium- and high-speed; as well as performing the functions of both main and auxiliary engines).

Modelling the thermal state of a turbocharger bearing housing when calculating the rotor dynamics at transient modes

Purpose The reliability of various mechanisms and machines is determined by the durability of tribo-units, which must ensure operation at high temperatures and an extended range of rotor shaft speeds. The best performance of the bearing assembly is achieved with hydrodynamic lubrication, which depends on optimal operating conditions and temperature conditions. The purpose of this paper is determining the thermal state of the turbocharger (TCR) bearings. Design/methodology/approach The simulation was carried out in the ANSYS Fluent software package. The boundary conditions for the calculation were obtained from experimental data. The experiments were carried out at a specialized stand created at the scientific and production association “Turbotekhnika”. Findings The result of the simulation was the determination of temperatures and thermal fields in the TCR housing. The data obtained testify to the uneven thermal loading of the bearings. When calculating the dynamics of the rotor, transient modes are considered. The results are the trajectories of the rotor in the space of the bearing clearance. The thickness of the lubricating layer was calculated as a parameter that determines the hydrodynamic friction regime. The thermal state of the TCR elements was evaluated at all the considered rotor speeds. The flexible axis of the rotor was obtained at different speeds. Originality/value The paper presents a model of heat transfer in a TCR housing and rotor dynamics, based on numerical methods, which will help in the design of TCRs and journal bearings.

Development of methods for evaluation of lubrication properties of hydraulic aviation oils

A method for evaluation of the lubricating and rheological properties of hydraulic oils in tribological contacts has been developed, which consists in online studying samples of commercial batches of oils on a software and hardware complex with visual evaluation of the kinetics of changes in the main tribological indicators of friction contact. Using a roller analogy, the operation of gears in the conditions of rolling with 30% sliding is simulated. Samples of AMG-10 oil from two producers are analyzed. It is established that with increasing temperature of lubricant for Sample 2 (“Kvalitet-Avia” AMG-10), a long-term restoration of protective boundary films of oil is observed and the period of their formation increases by 2.5 times, causing the implementation of a semidry mode of lubrication at start-up. The total thickness of the lubricating layer is 1.27 times less as compared with Sample 1 ("Bora B" AMG-10 oil), regardless of the lubricant temperature. Also, the rheological properties of the oils have been determined. Sample 1 exhibits low shear stresses at the level of 9.4 MPa and high effective viscosity, 4249 and 5039 Pa·s, at a volumetric oil temperature of 20 and 100 ºС, respectively. For Sample 2, with increasing oil temperature to 100 ºC shear stress increases by 1.15 times and the effective viscosity in contact decreases by 1.53 times. Additives present in Sample 1 are characterized by more effective antiwear properties and thus increase the wear resistance of contact surfaces in the conditions of rolling with sliding thanks to strengthening of the surface metal layers during operation, while Sample 2 undergoes strengthening-softening processes which reduce the wear resistance of friction pairs

Effect of Carbon Target Current on Ultralow Frictional Behavior of CrCN Coatings under Glycerol Lubrication

The aim of this paper is to find an effective way to reduce the friction and wear of steel. CrCN coating was deposited on AISI 304 stainless steel by magnetron sputtering technology, and the friction and wear properties of the coating under glycerol lubrication were studied. The hardness of CrCN coatings on stainless steel surface can reach to 17.87 GPa when the carbon target deposition current is 2A. The CrCN coating presents low friction coefficient (COF) under the lubrication of glycerol, a highly efficient green lubricant. When the load is 0.5 N, the lowest friction coefficient is only 0.01. XPS analysis on the wear track suggested that glycerol decomposed during sliding and a fluid lubricating layer was formed, which provides ultralow friction. The paper shows that the glycerol could be used as an efficient lubricant for the CrCN coating.

Designing Self-Sustainable Icephobic Layer by Introducing a Lubricating Un-Freezable Water Hydrogel from Sodium Polyacrylate on the Polyolefin Surface

A convenient, environment-friendly, and cost-effective method to keep anti-icing for a long time was highly desirable. Slippery lubricant layers were regarded to be effective and promising for anti-icing on different surfaces, but the drought-out of lubricants and the possible detriments to the environment were inevitable. By combining super-high molecular weight sodium polyacrylate (H-PAAS) with polyolefin through a one-pot method, a self-sustainable lubricating layer with extremely low ice adhesion of un-freezable water hydrogel was achieved at subzero conditions. The lubricant hydrogel layer could auto-spread and cover the surface of polyolefin after encountering supercooled water, frost, or ice. Due to the reduction of storage modulus in the interface, the ice adhesion of the specimen surfaces was far below 20 kPa, varying from 5.13 kPa to 18.95 kPa. Furthermore, the surfaces could preserve the fairly low adhesion after icing/de-icing cycles for over 15 times and thus exhibited sustainable durability. More importantly, this method could be introducing to various polymers and is of great promise for practical applications.

Caribbean plate tilted and actively dragged eastwards by low-viscosity asthenospheric flow

The importance of a low-viscosity asthenosphere underlying mobile plates has been highlighted since the earliest days of the plate tectonics revolution. However, absolute asthenospheric viscosities are still poorly constrained, with estimates spanning up to 3 orders of magnitude. Here we follow a new approach using analytic solutions for Poiseuille-Couette channel flow to compute asthenospheric viscosities under the Caribbean. We estimate Caribbean dynamic topography and the associated pressure gradient, which, combined with flow velocities estimated from geologic markers and tomographic structure, yield our best-estimate asthenospheric viscosity of (3.0 ± 1.5)*1018 Pa s. This value is consistent with independent estimates for non-cratonic and oceanic regions, and challenges the hypothesis that higher-viscosity asthenosphere inferred from postglacial rebound is globally-representative. The active flow driven by Galapagos plume overpressure shown here contradicts the traditional view that the asthenosphere is only a passive lubricating layer for Earth’s tectonic plates.

Al/Graphene/CNT hybrid composites: Hardness and sliding wear studies

Graphene and carbon nanotubes are two carbon based materials known for their unique wear and friction properties. It would be quite interesting to understand the wear behavior of aluminium hybrid composites when these two nanosize reinforcements are incorporated into it. The hybrid composites with varying weight fractions of graphene (1, 2, 3 and 5 wt.%) and fixed CNT content of 2 wt.% were produced using powder metallurgy technique. The effect of varying graphene content on hardness and sliding wear of hybrid composites was studied. The wear tests were done as per ASTM G-99 standard with fixed sliding velocity (2 m/s) and sliding distance (1200 m) but varying applied load (10 - 30 N). Worn surface analysis was conducted using scanning electron microscope to arrive at wear mechanisms responsible for wear of aluminium and its hybrid composites. Increase in graphene content led to increase in bulk hardness with highest value of 61 RHN for hybrid composite with 3 wt.% graphene content. The wear rate of hybrid composites was found to be decreasing with enhancement in graphene content. Lower wear rate in hybrid composites was due to the formation of lubricating layer on the worn surface.