Industrial Lubrication and Tribology

Yu, Rufei ; Li , Pei ; Chen, Wei

2016 Industrial Lubrication and Tribology

doi: 10.1108/ILT-03-2015-0028

Purpose – This paper aims to study the impact of surface texture on grease-lubricated journal bearing, load-carrying capacity, friction and friction coefficient. Design/methodology/approach – The paper opted for a basic application research using the commercial CFD software FLUENT 14.0. Findings – The load-carrying capacity can be enhanced if the surface texture is introduced from a suitable position. The textural shape has a more significant effect on the friction and load-carrying capacity than the friction coefficient. The rheological parameters of grease affect the load-carrying capacity in the same way, i.e. the load increases with the increase in the rheological parameters. With the decrease in the value of cavitation pressure, the cavitation area reduces but the dynamic pressure area gets enlarged. Research limitations/implications – Because of the chosen research method, the research results may lack the analysis of experiments. Practical implications – The research results can be applied to the domain in the high-speed spindle and lubricated multibody system. Originality/value – The investigation on the performances of grease-lubricated journal bearing with surface texture would be significant.

Zhang, Yali ; Zhang, Xiaogang ; Wu, Tonghai ; Xie, You-bai

2016 Industrial Lubrication and Tribology

doi: 10.1108/ILT-05-2015-0063

Purpose – The piston ring-cylinder liner pair is one of the most important tribological systems of an internal combustion engine. The friction loss of the piston ring-cylinder liner pair accounts for the largest portion of total efficiency losses. Therefore, improving the tribological system design of the piston ring-cylinder liner pair can reduce friction losses and bring tremendous economic benefits to society. This paper aims use surface texturing, which is proving to be an effective method, for improving the tribological performance of sliding surfaces. Design/methodology/approach – In this paper, an experimental study using a pin-on-disk tribometer was carried out to evaluate the effects of surface texturing on friction reduction of piston rings under various loads and sliding velocities. Rectangular- and circular-shaped textures with different depths and area densities were produced by a Femtosecond laser. Comparison experiments were conducted with un-textured rings. Findings – The results indicate that the friction performance of the ring surface was significantly improved by surface texturing, and the running-in stage was also shortened. More specifically, it was found that the rectangular-shaped texture had a better effect on friction reduction than the circular-shaped texture. Results also indicate that an optimum texture density existed for the rectangular-shaped texture. Additionally, it was observed that the average friction coefficient reduction of the textured ring decreased with increasing load and increased with increasing sliding velocity. Originality/value – Consequently, these findings provide a more in-depth understanding of the relationship between micro-textures and tribological properties of piston rings in lubricating sliding.

Gao, Fei ; Miao, Jia ; Han, Xiaoming ; Fu, Rong ; Chen, Jiguang

2016 Industrial Lubrication and Tribology

doi: 10.1108/ILT-06-2015-0077

Purpose – Since the multi-component of powder metallurgy was dispersed, and each component sheared flow and tiered under the action of friction force, it was difficult to disclose the evolution characteristics of each component. Meanwhile, third body mixing with particles of each component covered on the friction surface, which further increased the difficulty of understanding evolution of each component and the corresponding third body in the friction process. To solve this problem, this paper aims to propose a mechanical assembled method which compact several component sheets in order. Design/methodology/approach – Pure copper, aluminum and artificial graphite sheets with thickness 0.5, 1 and 2 mm, respectively, were assembled into a jig by mechanical compact method. The relationship between arrangement patterns of the components and its friction coefficient was studied by using fixed speed friction test machine, the speed range from 200 to 2,000 r/min and the pressure range from 0.25 to 0.64 MPa. Findings – The testing results showed that when the distribution of same components was congregated, friction coefficient dropped from 0.6 to 0.4. While the distribution of different components was dispersed, friction coefficient dropped from 0.6 to 0.25. The friction coefficient decline was caused by performances changes of third body fluidity. The sufficiently mixed third body made third body adhesion weaker and increased third body fluidity. That provoked friction coefficient decreasing obviously at high speed. On the contrary, with the high congregation of same components, strong third body adhesion led to a rougher surface which contributed to a higher friction coefficient. Originality/value – By means of the mechanical-assembled multi-layer components to reveal the influence mechanism of every component on friction properties, will provide a new test approach for tribology.

Liu, De-Liang ; Cao, Shu-hua ; Zhang, Shi-feng ; Xu, Jiu-jun

2016 Industrial Lubrication and Tribology

doi: 10.1108/ILT-04-2015-0057

Purpose – The purpose of this study is to solve this problem. Different lubrication states play a huge role in friction, wear and service life of parts. To ensure the reliability and power of the internal combustion engine, it is necessary to ensure that the friction pair has been in the best lubrication state. One of the key problems of lubrication state and transformation characteristics is to achieve real-time measurement of lubrication state. Design/methodology/approach – Previous studies show that the contact resistance method is very effective in the qualitative analysis of lubrication state test. The circuit is simple and does not require expensive test equipment. But this method could not accurately reflect the film thickness ratio. Through a combination of experimental and theoretical analysis methods, the limitation of the contact resistance method could be overcome. Findings – The relationship between the point contact film-thickness ratio and contact resistance was established, then the film-thickness ratio could be obtained through the contact resistance, thus providing the basis for determining the point contact lubrication state. Research limitations/implications – According to existing research, the lubrication state of the friction pair mainly was determined through two methods, the friction coefficient and film-thickness ratio. But there are limitations on either using Stribeck curves or optical interference methods. The method used in this paper not only provides a verified way of design theory and model, but is also beneficial to the formation of a new design theory. Originality/value – A new real-time measurement method of lubrication state based on contact resistance is established and its practicability and veracity are verified by series experiments.

Huang, Xingbao ; Wang, Youqiang

2016 Industrial Lubrication and Tribology

doi: 10.1108/ILT-05-2015-0061

Purpose – This paper aims to investigate the mechanism of spur gears running-in and to solve the lubrication problems of teeth running-in. Design/methodology/approach – The elastohydrodynamic lubrication (EHL) model considering solid particles was established by applying multi-grid and multiple-grid integration methods to the numerical solution. Findings – In the region where debris settle, transient pressure increases sharply, and a noticeable increase in the running-in load causes a remarkable increase in both the centre and maximum pressures and a slight increase in the minimum film thickness. Roughness wavelength makes a considerable difference to the minimum film thickness at double-to-single tooth transient. A considerable increase in rotation velocity can cause a remarkable reduction in both the centre and maximum pressures but an amazing increase in the minimum film thickness. The effects of roughness amplitude on the maximum pressure are considerably distinct. Research limitations/implications – Research on EHL of spur gears in the running-in process considering solid particles, surface roughness and time-variant effect is meaningful to practical gears running-in. Thermal effect can be included in the next study. Practical implications – The analysis results can be applied to predict and improve lubrication performance of the meshing teeth. Social implications – The aim is to reduce gears’ manufacture and running-in costs and improve economic performance. Originality/value – The EHL model that considers solid particles was established. The Reynolds equation was deduced taking the effects of solid particles into account. The EHL of spur gears running-in was investigated considering the time-variant effect, surface roughness, running-in load and rotation speed.

Tian, Xinli ; Wang, Long ; Wang, Wanglong ; Li, Yongdong ; Ji, Kaiwen

2016 Industrial Lubrication and Tribology

doi: 10.1108/ILT-04-2015-0051

Purpose – The cutting and extruding processing technology for ceramics based on the edge-chipping effect is a new contact removal machining method for hard, brittle materials such as engineering ceramics. This paper aims to provide an important reference to understand the tool wear mechanism and the wear law of this new processing technology. Design/methodology/approach – The real-time temperature monitoring and the observation of micro-morphology are used to analyse the wear characteristics of the tool face. In addition, the research focuses on the influence of three processing parameters (axial feed rate, thickness of flange and depth of groove) on characteristics including tool wear. Findings – The temperature variation shows that the new processing technology improves the tool temperatures condition. The tool is worn mainly by mechanical friction including abrasive wear, and the flank face also suffers the sustained scratching of residual materials on the rough machining surface. With increased feed rate, the wear of the rear face of the major flank initially decreased and then increased. As the depth of the retained flange increases, the wear became worse. The wear initially decreased and then increased with increasing depth of groove. Research limitations/implications – Study on the new processing technology is still in its early stages. Therefore, researchers are encouraged to test the proposed propositions further. Practical implications – The machining process itself destroys materials, albeit a controllable manner: based on this principle, the authors proposed a new machining technology based on cracks driven by edge chipping. In this way, the surface of such ceramics is removed. Therefore, the research provides a new method for reducing processing costs and promoting the extensive application of engineering ceramic materials. Originality/value – The cutting and extruding processing technology based on cracks driven by edge-chipping effect makes full use of the stress concentration effect caused by prefabricated defects, and the edge-chipping effect which occurs during machining-induced crack propagation. The wear mechanism and law of its tool is unique than other machining ways. This paper provides an important reference to understand the tool wear mechanism and the machining mechanism of this new processing technology. With the application of this study, the ceramics could be removed with less energy consumption and the tools with the hardness of lower than its own one. Therefore, it could not only reduce the processing costs but also promote the extensive applications of engineering ceramic materials.

Xizhi, Ma ; Gang, Wang

2016 Industrial Lubrication and Tribology

doi: 10.1108/ILT-07-2015-0102

Purpose – This paper aims to study the mechanism of heat generation in a screw, and investigates the heat flux in the connection screw pair under high frequent oscillation along the axial direction. Heat generated in the screw under high frequent oscillation could be observed in a lot of situations and was significant, and it could cause damage of screw joining and transmission. Design/methodology/approach – A heat flux model in a screw pair under high frequent oscillation along the axial direction is established. Bulk temperature field in the connected parts is calculated by means of finite element methods. A testing device aimed to temperature rise measurement in a thread pair under high frequent oscillation is built. Temperature rises under different operation conditions are measured. Findings – The heat flux generated in the screw pair because of friction between the contact surfaces of the screw thread is obtained. The effects of oscillating amplitude and frequency on heat flux are obtained. It is found that amplitude and frequency have a significant influence on the heat generated under high frequent oscillation. The numerical results show good agreement with the numerical results. Research limitations/implications – This study has some limitations; for example, the friction coefficient and the relative sliding displacement between the thread surfaces need further accurate research. Practical implications – Heat generated in a screw under high frequent oscillation is very rarely mentioned in previous research papers. The methods used in this paper could be used to evaluate the heat flux and temperature under high frequent oscillations. The temperature could be used to calculate the thermal stress and expansion in the screw thread under high frequent oscillation. The screw connections need to be protected from the damage because of heat stress and from getting loose because of heat expansion of the connected parts. Originality/value – The mechanisms of heat generation in the screw pair under high frequent oscillation are studied. The model of heat flux in the screw under high frequency oscillation is established, and it could be used to calculate the heat flux under different operating conditions. The transient temperature field of the connected parts is given. A test facility was built and the experiment to measure the temperatures of the bolt and nut was carried out. The results had good agreement.

Lu, Xiaohong ; Hu, Xiaochen ; Wang, Hua ; Si, Likun ; Liu, Yongyun ; Gao, Lusi

2016 Industrial Lubrication and Tribology

doi: 10.1108/ILT-06-2015-0079

Purpose – The purpose of this paper is to establish a roughness prediction model of micro-milling Inconel718 with high precision. Design/methodology/approach – A prediction model of micro-milling surface roughness of Inconel718 is established by SVM (support vector machine) in this paper. Three cutting parameters are involved in the model (spindle speed, cutting depth and feed speed). Experiments are carried out to verify the accuracy of the model. Findings – The results show that the built SVM prediction model has high prediction accuracy and can predict the surface roughness value and variation law of micro-milling Inconel718. Practical implication – Inconel718 with high strength and high hardness under high temperature is the suitable material for manufacturing micro parts which need a high strength at high temperature. Surface roughness is an important performance indication for micro-milling processing. Establishing a roughness prediction model with high precision is helpful to select the cutting parameters for micro-milling Inconel718. Originality/value – The built SVM prediction model of micro-milling surface roughness of Inconel718 is verified by experiment for the first time. The test results show that the surface roughness prediction model can be used to predict the surface roughness during micro-milling Inconel718, and to provide a reference for selection of cutting parameters of micro-milling Inconel718.

Wu, Juan ; Kou, Ziming ; Cui, Gongjun

2016 Industrial Lubrication and Tribology

doi: 10.1108/ILT-05-2015-0060

Purpose – The purpose of this paper is to prepare carbon fiber-reinforced polyimide matrix composites and to investigate the single role of carbon fiber in polyimide composites on tribological performance under distilled water condition. Design/methodology/approach – Three carbon fiber-reinforced polyimide matrix composites were fabricated by using a hot press molding technique. The tribological behaviors of carbon fiber-reinforced polyimide matrix composites sliding against steel ball were evaluated with a ball-on-disk tribotester under distilled water condition. Meanwhile, the effect of different length of carbon fiber on the wear resistance of polyimide matrix composites was investigated during the sliding process. Findings – The friction coefficients and specific wear rates of polyimide composites containing 100 μm carbon fibers were lower than those of other specimens. The wear mechanism of carbon fiber-reinforced composites was delamination under distilled water condition. The interfacial combination between the carbon fiber and matrix became worse with the increase of length of carbon fiber. Originality/value – This paper reported the effect of the different length of carbon fiber on polyimide matrix composites to prepare mechanical parts in mining industrial fields.

Meng, Fanming ; Chen, Yuanpei ; Yang, Yang ; Chen, Zhiwei

2016 Industrial Lubrication and Tribology

doi: 10.1108/ILT-06-2015-0070

Purpose – The severe friction and wear of the spindle in a cotton picker often occur in a picking cotton, which affects the spindle lifetime and its efficiency of picking cottons. This paper aims to investigate the effect of an electroless nick coating on the spindle performances to avoid its abnormal phenomena. Design/methodology/approach – First, it is coated on the surface of the test specimen with the material same as that of the spindle. Then, the friction coefficient and wear for the coating are measured under oil lubrication to evaluate its effect in improving the tribological performances for the spindle. Findings – The stabilized friction coefficient of the electroless nick coating decreases with increasing reciprocating frequency of specimen and increasing applied load. There exists a critical coating thickness yielding the smallest friction coefficient. Moreover, this coating has a property of the smaller friction coefficient in comparison with a hard chromium coating. Originality/value – The research about the electroless nick effect on the spindle’s tribological performances is not found yet to date. To avoid severe friction and wear of the spindle, this paper investigated how the reciprocating frequency of specimen, applied load and coating thickness affect the spindle’s tribological performances. The associated conclusions can provide a reference to enhance the spindle lifetime and its transmission efficiency.