A methodology for using the pseudo spectral scheme for the modeling of compliant gas lubricated foil bearings is presented in this work. The pseudo spectral scheme is used to obtain numerical solution of the compressible Reynolds’s equation that models the lubricating gas film. This scheme is coupled to a structural model that models the compliant structure of the foil bearing. The coupled simulation model is applied to both one dimensional and two dimensional cases. The simulation model is validated by comparing its results with analytical solution for short bearing case and to published data for compressible two dimensional cases. The advantages of using this scheme compared to a finite volume scheme for the simulation of foil bearings are presented.
Formation processes of metal-rich tribofilm on the counterface during sliding against metal/diamondlike-carbon nanocomposite coatings have been investigate. The hybridization between DLC matrix and Cu or Ag provides good electric conductivity to solid lubricant films. Metal-rich tribofilms are formed on the counterface of both Cu-DLC and Ag-DLC during sliding, which is important factor to obtain excellent tribological performance as well as good electric conductivity. Such tribofilms are almost pure Cu and Ag. The origin of the tribofilm is the metal clusters in the Me-DLC, and the adhered Cu and Ag clusters on the counterfaces are possibly sintered and refined during iterative plastic deformation in the frictional interface which generates high pressure and high shear rate.
A study was carried out to estimate the thickness of the adsorbed water layer on the surface of austenitic stainless steel (JIS SUS316) in different atmospheric humidity conditions. The purpose of the study is to have a quantitative data on water adsorption that has influences on the tribological phenomena. The mass of stainless steel plate was determined by the weighting method as a function of the relative humidity (RH) in ambient atmospheric air. An experimental device consisting of atmospheric humidity controller and high sensitivity analytical balance with affixed airtight chamber was used for the purpose of the study. The result of water adsorption progression on SUS316 surface has been discussed and schematically demonstrated. It is clarified that the thickness of adsorbed water is significantly large to influence the tribological properties as demonstrated in a schematic model of the interface state of pin-on-disk prior to contact in high RH.
Performance of asymmetric slot-entry hydrostatic and hybrid journal bearings lubricated under micropolar lubricant has been presented numerically. For chosen values of microploar parameters, the effects of micropolar lubricant on both the bearings have been simulated. FEM has been applied for the solution of Reynolds equation for micropolar lubricated asymmetric slot-entry bearings. Micropolar lubrication provides the larger minimum fluid film thickness for hydrostatic bearing than hybrid bearing. It has also been found that values of the coefficient of fluid film stiffness and damping are more for micropolar fluid lubricated hybrid journal bearing than hydrostatic bearing. The presented results of asymmetric slot-entry hydrostatic and hybrid journal bearings under micropolar lubrication are expected to provide the useful information to the bearing designer.
Hard materials were mixed with alloy powders and thermally sprayed at an ultra rapid cooling rate of more than 106°C/s. For example, 65Ni15Cr16P4B at% alloy powder containing tungsten carbide was thermally sprayed. SEM image showed tungsten carbide paticles were scattered in the amorphous alloy coatings. The resulting thermal coatings showed low friction and high wear resistance in a reciprocating-slide-type friction-testing machine because tungsten carbides exhibited cleavage fracture. The stress analysis of an amorphous alloy coating with low friction was also carried out by the finite element method.
In this paper the non-dimensional load, volumetric flow rate, energy flux, oil film temperature and power loss parameters of a tilting-pad thrust bearing are formulated. The objective of the paper is to determine the novel non dimensional thermal, volumetric and power loss parameters in addition to the load and energy flux parameters of the bearing. The computation is done by formulating and numerically solving for the oil film thickness, two dimensional Reynolds’, Vogel-Cameron viscosity-temperature relationship and energy equations at the different nodes of the oil film using a finite difference procedure. The planar film shape polynomial ensures the accuracy of the slider bearing shape and pressure distribution. The numerical procedure evaluates the value of ‘a’ at which the load is maximum. The variation of the bearing centre of pressure with respect to the corresponding values of ‘a’ is studied. From the fluid film temperature equation the rise in bearing temperature corresponding to the range of ‘a’ values is determined. The oil film temperature distribution results are found satisfactory in terms of computer time and convergence criteria. The accuracy of the results is validated in the variation of the load and thermal contours. A mesh independence test is conducted using three meshes of different sizes. The mesh independent solution and convergence is obtained for the smallest mesh that also reduces simulation run time. This data and analysis serves as an input to determine the dynamic stiffness and damping coefficients. It includes the scope to develop a design method for safe operation of the bearing at any speeds in vertical hydro-electric rotors.
Superior tribological properties of mineral oil based nano-lubricants in boundary/thin film lubrication are well established. However, in view of the environmental aspects, vegetable oils are more preferable and studies are being carried out to evaluate the performance of vegetable oils when nanoparticles are added to them. In this paper, behaviour of vegetable oils with the addition of Copper Oxide (CuO) nanoparticles is presented to evaluate their thermo-physical and tribological properties. Experimental studies at elevated temperatures are carried out on two base oils, viz., coconut and mustard oils as well as the nano-lubricants formulated from them by the addition of unmodified and surfactant-modified CuO nanoparticles separately. Enhancement of thermo-physical properties such as viscosity and fire-point is more pronounced for nano-lubricants containing surfactant-modified CuO nano-lubricants than the corresponding nano-lubricants containing unmodified CuO nanoparticles. Similar improvements in friction-reduction and anti-wear properties are also observed based on experiments conducted on a modified pin-on-disc tribometer at ambient and elevated temperatures. From the dispersion analysis it is seen that the nano-lubricant containing unmodified nanoparticles is not suitable for long stationary applications. Analyses of the pin surface before and after sliding with different nano-lubricants at the interface are carried out using Atomic Force Microscopy. The above analyses of the pin surface also show encouraging results with surfactant-modification of CuO nanoparticles in terms of the average surface roughness of the pin surface. The results from the current experimental study envisage the prominence of vegetable oil based nano-lubricants in the foreseeable renewable-based economy.
The present work reports the formulation of castor oil (CO) epoxide as a bio-lubricant basestock. The main objective of this study was to improve the physico-chemical properties and thermo-oxidative stability of CO via structural modification. Epoxidation reaction was carried out at 60°C for 10 h using heterogeneous acidic ion-exchange resin (IR-120) as a catalysts (15mass%), acetic acid (0.5 mol) as an oxygen carrier and hydrogen peroxide (1.5 mol) as an oxygen donor. Product was confirmed by 1H-NMR, FTIR spectral analysis and epoxide content was determined by oxirane oxygen analysis. Further, significant physico-chemical properties such as viscosity, acid value (AV), pour point (PP) was determined for prepared CO epoxide. Thermo-oxidative stability of prepared epoxide and unmodified CO were compared by thermo gravimetric analysis (TGA) technique (in inert and oxygen atmospheres). Modified CO clearly illustrated significant improvement in the required physico-chemical properties and thermo-oxidative stability. Results of this study revealed that the prepared epoxide could be used as a potential bio-lubricant basestock in hydraulic lubricant application.
The condition of machines gradually deteriorates and this gradual quantitative deterioration leads to its failure. When a fault takes place, some of the machine parameters change. Monitoring of these changed machine parameters entail the developing fault. Rolling element bearing is an important part for any rotating machinery. The vibration generated due to bearing fault at slow speed is of low energy and those are mostly absorbed by the structural path. Moreover, the frequency of vibration for such a case falls much below the cut off frequency of normally available sensor. Capturing and processing of this type of signal requires special care to diagnose the incipient fault of the bearing. An attempt has been made to detect the incipient bearing fault operating at slow speed by collecting vibration signal and processing it. The signals are collected using the sensor with sensitivity > 500 mv/g. The signal is processed using enveloping technique along with wavelet transform to disintegrate the signal into different levels.
Copper alloys have been used for plain bearing material in many kinds of engineering machines. In this study typical copper alloys are selected from the view point of strength and thermal conductivity that is proportional to electric conductivity. The aim of this study is to investigate that the thermal conductivity is very important character to keep mild friction with appropriate condition of block-on-ring tests. The results show that the patterns of friction coefficient of time are classified into four types. Type I is stable in low friction. Type II is slightly up in the end part. Type III is less stable and up to 0.4 level of friction coefficient (μ). Type IV is rough waving in more over 0.4 level of friction coefficient (μ). The materials of Type I are chromium copper alloy and Corson copper alloy. The Type II is beryllium copper alloy. These Type I & II alloys have the same properties of high thermal conductivity and characteristic microstructure of dispersed hard particles in copper matrix. High thermal conductivity reveals good tribological performance, i. e., low friction and wear. Moreover after tribological test, the surface of these alloys changes and transformes to rich oxide surface with condensed hard particles. It’s action is simple application of friction steps to escape the severe wear. Especially the copper alloy with ferrous particles dispersed in matrix makes severe mode of friction by the same element of friction.
To meet with the latest environmental regulation, as environmentally acceptable lubricant (EAL) in marine field, biodegradable oils based on synthetic ester oils, have been applied to stern tube bearings of many new building vessels since the end of 2013, when the US EPA∗ effectuated the 2013 VGP∗∗ regulation. These synthetic ester oils are of the same viscosity grade, ISO VG100, as commonly used mineral oil. However, up to now, there has been no report on verification of tribological characteristics to use them for stern tube bearings, including the 2013 VGP regulation. Therefore, physical properties of them were measured in tribological aspects, and load carrying capacities while mooring trial condition were clarified by the tests using 100 mm inner diameter plain bearing, comparing to mineral oil. As the result, the following are derived. 1) There are three major differences in viscosity characteristics of synthetic ester oils depending on temperature, shear stability and pressure, which gives them lower load carrying capacity. 2) Sliding velocities at friction rising points of synthetic ester oils in Stribeck curve are larger than the one of mineral oil by the effects above, which also indicates lower load carrying capacity of them. ∗)EPA: Environmental Protection Agency ∗∗)VGP: Vessel General Permit
Paper-based friction materials used for wet clutches in automatic transmissions require various tribological functions such as a high and stable friction coefficient, good μ-V (friction coefficient-sliding velocity) characteristics, heat resistance, and wear resistance. In this study, microscale texture was formed on the surface of a paper-based friction material using a picosecond pulse laser, and the friction characteristics were investigated using the SAE#2 test system. Stripe-shaped microtexture (microgrooves) with several patterns of depth and pitch were formed on the friction material surface and controlled by the laser processing conditions. The dynamic friction coefficient was particularly improved by the microgrooves under low temperature and low surface pressure conditions. The coefficient changed according to the depth and pitch of the microgrooves, which is related to the volume ratio (microgroove volume per unit volume of paper-based friction material). These results indicate that the dynamic friction coefficient for the wet clutch can be controlled by changing the groove volume ratio according to the laser processing conditions. A new paper-based friction material with a high static friction coefficient (μs) and good μ-V characteristics could be developed by control of the dynamic friction coefficient without changing the pore characteristics of the paper.