Simulation of the thermal process and friction diagnostics in a system of nonlubricated sliding bearings on a common shaft

The development of a method of thermal diagnostics of friction allowing evaluating friction torque in a system of sliding bearings on a common shaft by temperature data under the assumption of uniform temperature distributions on the cross section of a shaft and along the length of bearings in the case of dependence of thermal properties of materials on temperature is described. The resistance of the obtained solutions to errors in temperature data is shown.     

Thermal diagnostics of friction in sliding bearings with account for propagation of heat and movement of shaft

A method for the thermal diagnostics of friction in a sliding bearing is considered for the case when a three-dimensional mathematical model of the thermal process taking into account the motion of the shaft is used. Basic relations for restoring the specific power of the frictional heat generation in the friction zone of the bearing using temperature data and results of computational experiments are presented, which show the stability of a solution of the corresponding inverse boundary problem to errors of the temperature data.     

Thermal diagnostics of friction in slip bearings

A quasi-three-dimensional thermal mathematical model is proposed for a slip bearing made of polymer composite, in which with the shaft’s cross section varies over its length. The algorithm proposed for solving the inverse boundary problem permits the derivation of the frictional torque from temperature data. Numerical calculations demonstrate the efficiency of the algorithm and its robustness with respect to errors in the temperature measurements. The practical applicability of this method is confirmed experimentally.     

Thermal diagnostics of friction in plain bearings with account for speed and mode of shaft motion

The paper discusses the method of thermal diagnostics of friction in plain bearings at low speeds of rotation and reciprocating motion of the shaft, in which case the assumptions that simplify the mathematical simulation of a thermal process are inadmissible. The results of a computational experiment on the recovery of the power of frictional heat generation by temperature data are presented.     

Vibration monitoring of bearings at low speeds

Some experimetnal observations and results are given comparing acceleration shock pulse transducer, acoustic emission and jerk measurements from slightly damaged bearings at medium to low speeds. Additional results showing defects at very low speeds with an acoustic emission transducer are not easily explained     

Performance of impregnated bronze bearings at low speeds

The performance of bronze bearings impregnated with graphite and MoS₂ was studied and the effects of speed, pressure and running time are discussed in detail. A performance chart is provided to aid the selection of bearings for practical use.     

Stick-slip of rotors in fluid bearings at very low speeds

The stick-slip phenomenon which occurs at very low speeds with rotors in fluid bearings was studied analytically and experimentally to improve understanding of the phenomenon and to identify the controlling factors. A flexible rotor in fluid bearings was studied at low speeds. The function describing the coefficient of friction versus the linear velocity was found to have a concave form and to be strongly dependent on the bearing load. Polynomial expressions were used to obtain an exponential law. The system stability was investigated by means of numerical integration of the equations of motion. Areas of instability predicted by the analytical model are in close agreement with the experimental results. Damping was found to have a strong influence on the stability of the system.     

Thermal diagnostics of friction in self-lubricating radial plain bearings of swinging movement. Part 2. Accounting for shaft mobility in the mathematical model

The thermal process in a plain bearing is simulated taking into account the shaft motion. Examples of the analysis for the dynamics of temperature fields are given; on the basis of these examples, the kinematic conditions for applicability of the simplified models are determined.     

Consideration of the multizone hydrodynamic friction,the misalignment of axes,and the contact compliance of a shaft and a bush of sliding bearings

The second version of the original Bearing Builder Finite Element Method (BBFEM) software and its application for analyzing the hydrodynamics of cylindrical sliding bearings has been briefly described. The two-dimensional problem of the lubricating fluid flow in a bearing clearance taking into consideration the different types of deviations in the contact surface from a cylindrical shape has been solved by the finite element method. The bearing design that leads to the formation of several hydrodynamic friction zones (fluid wedges) has been considered. The role of the contact compliance of a shaft and a bush and the operation factors that cause the deviation from the initial cylindrical shape of a bearing, including the deformations and the misalignment of the shaft and bush is shown by citing specific examples of antifriction composites of different compositions.     

Wear of metals at high sliding speeds

High speed sliding wear of AISI 1020 steel, AISI 304 stainless steel and commercially pure titanium (75A) was studied using a pin-on-ring geometry. All the tests were carried out in air without any lubricant. The sliding speed was 0.5–10.0 m s^?1 and the normal force was 49.0 N (5 kgf).The friction coefficient of all the materials tested decreased with the sliding speed; this appears to be a consequence of oxide formation. The wear rate of 304 stainless steel increased monotonically with speed, whereas the wear rate of 1020 steel and titanium first decreased and then increased and again decreased, with a maximum occurring at about 5 m s^?1. The complex variation of the wear rate as a function of speed is explained in terms of the dependence of the friction coefficient, hardness and toughness of the materials on temperature. Microscope examinations of the wear track, the sub-surface of worn specimens and the wear particles indicate that the wear mode was predominantly by subsurface deformation, crack nucleation and growth processes, i.e. the delamination process, similar to the low speed sliding wear of metals. Oxidative and adhesion theories proposed in the past to explain the high speed sliding wear of metals are found to be incompatible with the experimental observations.     

滑动轴承转子系统非线性动力学稳定性研究

采用多尺度法研究了滑动轴承刚性平衡转子系统临界点的稳定性。研究发现，滑动轴承在其线性失稳转速上发生Hopf分岔，系统是发生超临界Hopf分岔还是亚临界Hopf分岔取决于系统参数的设计。给出了通用的公式和程序，为滑动轴承的非线性动力学设计及性能预测提供了有利的工具。     

Refined simulation of friction power loss in crank shaft slider bearings considering wear in the mixed lubrication regime

Friction reduction is a fundamental factor in decreasing fuel consumption of internal combustion engines. During the design stage of the engine the simulation of friction in the crank mechanism plays a vital role to develop optimum solutions. Due to the interaction of oil and elastic structures with rough surfaces in slider bearings, complex simulation models have to be used for representing the relevant physical behavior. The following article is focused on crank shaft slider bearings of large engines.The article describes a procedure evaluated by measurements showing how to model wear profiles of slider bearings to reach a high quality friction forecast. A fundamental influencing factor of bearing friction is given by the mixed lubrication regime and it is considered in the simulation model as part of asperity contact friction and hydrodynamic friction. Further effects result from the compliance in radial and width directions of the bearing structure and the wear of the bearing surface. Furthermore, the specific operating conditions of the slider bearing such as load, temperature, shaft speed and oil characteristics are essential and have to be taken into account.The objective of this investigation is to propose the wear profile of the bearing surface for the simulation model to be treated iteratively, where simulation results for the amount of mixed lubrication are successively assessed. For this purpose an iterative procedure is introduced and validated by measurements on a slider bearing test rig.The applied simulation method is based on elastic multi-body systems; the lubrication film contact is calculated based on Reynolds differential equation via the pressure balance calculated iteratively in the time domain. The model accounting for the mixed lubrication regime is based on the theory of Greenwood and Tripp.     

Tribological study of elastomeric bearings for marine propeller shaft system

Elastomeric compounds, due to their favourable properties like sufficient hardness, toughness and natural resistance to abrasion and corrosion, are commonly used as bearing material for propeller shaft system of Indian Coast Guard Ships. Recently unequal and non-uniform wear of these bearings has resulted in unscheduled lay off of the Coast Guard Ships. To solve this problem of bearing wear, a mixed lubrication analysis of sea-water lubricated journal bearing has been attempted in the present study. A computer code was written to estimate lubricating film thickness for a given set of load and speed condition, and to predict the lubrication regime for the specified surface roughness parameters. To validate the theoretical analysis performed in the present study, the results obtained from the computer simulation have been compared with the established studies on the water lubricated bearing.To understand the uneven wear of marine bearings, actual geometric clearances of new and worn out bearings recorded by the ship maintenance team, and the operational data (load, speed and operating hours), obtained from the log books of ICGS Sangram (AOPV) of Indian Coast Guard, are listed in the present paper. The dynamic viscosity of sea water, surface roughness of propeller shaft and bearings, and particulate contamination has been measured. Finally, the suggestions have been enlisted for proper operation of shaft-bearing system so as to maintain the wear within the permissible limits during ship's operational cycle.     

Thermal diagnostics of friction in self-lubricating radial slider bearings with swinging movement: Part 1. Algorithm for determination of power function of heat generation

It is proposed to find the moment of friction in a slider bearing undergoing oscillatory motion by the solution of the inverse boundary problem of frictional heat generation on the values of temperature measured in the vicinity of a friction zone. Basic boundary value problems and relationships for construction of the algorithm to determine the specific power of heat generation are obtained.     

Development of SiO2 nanolubrication system to be used in sliding bearings

New technology using nanoparticles as an additive in lubricants is recently becoming an attractive topic of study. The performance of SiO₂ nanoparticles in the lubrication system is investigated. Tests were conducted for nanolubrication mixing ratios of 0.0, 0.1, 0.2, 0.5, 0.55, 0.6, and 0.8 wt% with plain bearings rotated by a 2,750-rpm high-speed motor. For each mixing ratio, the frictional temperature and wear rate of the rotating sliding bearings were recorded and compared. During surface testing, the surface roughness values of the sliding bearings were compared and the results showed an improvement in surface roughness after the tests. According to the outcome, the optimum tribological performance of nanolubricant was obtained at 0.5 wt% mixing ratio.     

On the dynamic performance of roller bearings operating under low rotational speeds with consideration of surface roughness

The dynamic behavior of radially-loaded roller bearings operating at high loads and low speeds with different surface roughness values is investigated. The simulations take into account different lubrication regimes (rigid solid–isoviscous, elastic solid–isoviscous, rigid solid–piezoviscous and elastic solid–piezoviscous) in the loaded and unloaded sections of the bearing. The simulation results provide a detailed understanding of the variation of the film thickness, wear rate and heat generation between the rollers and the raceways as the rollers travel in the orbital direction. Simulation results reveal that an increase in the radial load results in a proportional increase in the wear rate and an exponential increase in the heat generation, although it does not affect the film thickness noticeably.     

Calculation of oil‐film thickness in journal bearings running at varying rotational speeds

There are many methods of calculating the properties of lubricated hydrodynamic sliding bearings running at variable loads, but, in some cases, sliding bearings of heavy‐duty machines run under constant load and at variable speeds; this can lead to reduced film thickness in the bearing and boundary lubrication. The minimum oilfilm thickness in such a bearing needs to be calculated so that the proper lubricant viscosity can be selected to reduce solid‐solid contact during machine operation. In this study, a method is presented for calculating the film thickness of sliding bearings operating with alternating rotational directions. The results of the calculations show that the squeeze effect can develop enough load‐carrying capacity to prevent solid‐solid contact between the rubbing surfaces during operation, provided the change of direction of rotation is quick enough.     

Friction and wear characteristics of powder metallurgy copper-graphite brushes at high sliding speeds

Friction experiments using several commercial powder metallurgy copper-graphite brushes against an AISI 4340 steel rotor were conducted at sliding velocities ranging from 20 to 235 m s^?1. The measured wear rates ranged from a minimum of 4.3 × 10^?5 cm km^?1 at a sliding velocity of 100 m s^?1 for a brush with high graphite content to a maximum of 8.4 × 10^?3 cm km^?1 at a sliding velocity of 230 m s^?1 for a brush with high metal content. The coefficients of friction ranged from a minimum of about 0.08 to a maximum of about 0.47 and were greatly affected by the presence of oxide layers at the sliding interface. Almost all the brushes exhibited some degree of edge breaking. The velocity at which edge breaking occurred was dependent on the powder grain size. Brushes with a large grain size seem to exhibit edge breaking at a lower speed than brushes with a fine grain size. High interface temperatures which occur at high sliding speeds result in melting of the lead-tin binders used in most powder copper-graphite brushes.