This paper presents comparative theoretical results regarding the computational estimation of operational magnitudes of hydrodynamically lubricated finite journal bearings which…
Abstract
This paper presents comparative theoretical results regarding the computational estimation of operational magnitudes of hydrodynamically lubricated finite journal bearings which are either smooth or of negligible roughness and waviness. Results are obtained using various calculational simulation methods. It is concluded that various modern mathematical models used to determine journal bearing properties lead to similar results and support further investigations via the calculational code developed by the author on rough and wavy journal bearing tribosystems for determining their behaviour via an efficient and accurate approach.
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C.N. Pandazaras and G.P. Petropoulos
A study of piston ring‐cylinder tribological behaviour under mixed lubrication mode is usually based upon data regarding surface contact magnitudes, fluid film characteristics and…
Abstract
A study of piston ring‐cylinder tribological behaviour under mixed lubrication mode is usually based upon data regarding surface contact magnitudes, fluid film characteristics and resultant mixed friction forces. The present paper introduces a Fisher‐Pearson statistical model to describe elastic deformation of piston rings and liners’ asperities in order to derive more realistic functions that represent the aforementioned functional quantities considering real surfaces of used and worn liners. The hypothesis that the microtopography follows Gaussian law overestimates critical contact magnitudes such as: minimum film thickness‐surface separation distance, deformed asperities supported load, number of contacts and contact area. Increased time of use and wear of liners decreases transverse geometrical anisotropy. Correction contact integral functions in cases of used liners’ surfaces may be calculated through surface profile measurements. Theoretical and experimental results are in good agreement for the configuration considered.
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C.N. Pandazaras and G.P. Petropoulos
Presents theoretical results regarding the computational estimation of the critical rotational speed in smooth or of negligible roughness and waviness hydrodynamically lubricated…
Abstract
Presents theoretical results regarding the computational estimation of the critical rotational speed in smooth or of negligible roughness and waviness hydrodynamically lubricated journal bearings. Results were provided using a developed calculational simulation code adapted to modelling of hydrodynamic lubrication regime encountered in the operation of various conventional or unconventional configuration finite journal bearings (j‐b). It is concluded that empirical formulae of general character used to determine j‐b rotational speed critical domain may either considerably underestimate or overestimate operational magnitudes. This fact leads to the necessity of use of high values for rotational speed safety factors in order to assure liquid lubrication and to avoid j‐b contacts during operation. Relevant diagrams resulting from the present investigation show a direct estimation of critical j‐b operational magnitudes.
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Jun Cheng, Xianghui Meng, Youbai Xie and Wenxiang Li
The purpose of this paper is to study the real-time change of surface roughness at different small regions of piston rings during running-in process. Meanwhile, the effects of…
Abstract
Purpose
The purpose of this paper is to study the real-time change of surface roughness at different small regions of piston rings during running-in process. Meanwhile, the effects of real-time change of the rough surface topography on the lubrication and friction of piston rings are investigated.
Design/methodology/approach
An uneven wear model has been developed to research the running-in behavior at the different small regions of piston rings. The model is verified by comparing the simulation results with the experimental results on a reciprocating friction and wear test rig.
Findings
This research shows that the wear process of piston ring surface is uneven during running-in. At most time of the operating cycle except the vicinity of top dead center and bottom dead center, the minimum oil film thickness ratio increases while the friction force and power loss decrease after the running-in period.
Originality/value
Through this research, the running-in behavior of piston rings is investigated in detail. The interaction between the running-in and the lubrication and friction of piston rings is understood more deeply.
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C. Pandazaras and G. Petropoulos
This paper aims to introduce an innovative methodology for the determination of operational characteristics of journal bearings (j‐bs) through using new type charts based upon a…
Abstract
Purpose
This paper aims to introduce an innovative methodology for the determination of operational characteristics of journal bearings (j‐bs) through using new type charts based upon a numerical solution of the Reynolds equation.
Design/methodology/approach
The present paper proposes the mapping of the behaviour of a smooth, isothermal and hydrodynamic (j‐b) as a first step towards a future representation of the behaviour of j‐b's with limited length and high lubricating clearance with or without macro or micro topographic features operating under high loads, high temperatures and low linear velocities leading to conditions of mixed or boundary lubrication.
Findings
The derived analytical relationships between dimensionless quantities lead to the development of high precision synthetic operational charts regarding sliding j‐b of any given geometry and varying operational characteristics.
Originality/value
By considering the iso‐operational curves which are of a hook form relevant to comparative data becomes directly and rapidly clarified.
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G. Petropoulos and C. Pandazaras
The real profile length constitutes a hybrid parameter in surface metrology which is rather neglected in literature, albeit it affects or controls sometimes surface functional…
Abstract
The real profile length constitutes a hybrid parameter in surface metrology which is rather neglected in literature, albeit it affects or controls sometimes surface functional properties like corrosion resistance, adhesibility, wear, lubrication etc. Real profile length values are assessed here in turning of different carbon steels under a wide range of cutting conditions variation leading to a variety of relevant textures. Useful quantitative information for evaluation and modeling of the turning process is provided, as well as correlation is sought with other topography parameters and the statistical distributions over the turned surfaces are determined. Also, possibilities of turned profiles discrimination are discussed.
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J. Paulo Davim and Francisco Mata
Surface roughness, normally defined by the Ra and Rt/Rmax parameters, is an important topic in the manufacturing engineering, for controlling produced components. This paper…
Abstract
Surface roughness, normally defined by the Ra and Rt/Rmax parameters, is an important topic in the manufacturing engineering, for controlling produced components. This paper presents a study of the influence of cutting parameters on surface roughness in turning of glass‐fibre‐reinforced plastics (GFRPs). A plan of experiments was performed on controlled machining with cutting parameters prefixed in workpiece. A statistical technique, using orthogonal arrays and analysis of variance, has been employed to investigate the influence of cutting parameters on surface roughness in turning GFRPs tubes using polycrystalline diamond cutting tools. The objective was to obtain the contribution percentages of the cutting parameters (cutting velocity and feed rate) on the surface roughness in GFRPs workpiece.