Industrial Lubrication and Tribology

Cheng‐Chi Wang

2011 Industrial Lubrication and Tribology

doi: 10.1108/00368791111154922

Purpose – This paper employs a hybrid numerical method combining the differential transformation method (DTM) and the finite difference method (FDM) to study the bifurcation and nonlinear behavior of a rigid rotor supported by a relative short gas lubricated journal bearing system with herringbone grooves. The analysis reveals a complex dynamic behavior comprising periodic, subharmonic and quasi‐periodic responses of the rotor center. The dynamic behavior of the bearing system varies with changes in the rotor mass and bearing number. The current analytical results are found to be in good agreement with those of other numerical methods. This paper discusses these issues. Design/methodology/approach – In this paper, DT is used to deal Reynolds equation and is also one of the most widely used techniques for solving differential equations due to its rapid convergence rate and minimal calculation error. A further advantage of this method over the integral transformation approach is its ability to solve nonlinear differential equations. In solving the Reynolds equation for the current gas bearing system, DTM is used for taking transformation with respect to the time domain τ , and then the FDM is adopted to discretize with respect to the directions of coordinates. Findings – From the Poincaré maps of the rotor center as calculated by the DTM&FDM method with different values of the time step, it can be seen that the rotor center orbits are in agreement to approximately four decimal places for the different time steps. The numerical studies also compare the results obtained by the SOR&FDM and DTM&FDM methods for the orbits of the rotor center. It is observed that the results calculated by DTM&FDM are more accurately than SOR&FDM. Therefore, the DTM&FDM method suits this gas bearing system and provides better convergence than SOR&FDM method. Originality/value – This study utilizes a hybrid numerical scheme comprising the DTM and the FDM to analyze nonlinear dynamic behavior of a relative short gas lubricated journal bearing system with herringbone grooves. The system state trajectory, phase portraits, the Poincaré maps, the power spectra, and the bifurcation diagrams reveal the presence of a complex dynamic behavior comprising periodic, subharmonic and quasi‐periodic responses of the rotor center. Therefore, the proposed method provides an effective means of gaining insights into the nonlinear dynamics of relative short gas lubricated journal bearing systems with herringbone grooves.

Dewan Muhammad Nuruzzaman; Mohammad Asaduzzaman Chowdhury; Mohammad Lutfar Rahaman

2011 Industrial Lubrication and Tribology

doi: 10.1108/00368791111154931

Purpose – The present paper seeks to report the effect of duration of rubbing on friction coefficient for different polymer and composite materials. Variations of friction coefficient and wear rate with the normal load are also investigated experimentally when stainless steel (SS 304) pin slides on different types of materials such as cloth‐reinforced ebonite (commercially known as gear fiber), glass fiber‐reinforced plastic (glass fiber), nylon and polytetrafluoroethylene (PTFE). Design/methodology/approach – A pin on disc apparatus is designed and fabricated. During experiment, the rpm of test samples was kept constant and relative humidity was 70 percent. Findings – Studies have shown that the values of friction coefficient depend on applied load and duration of rubbing. It is observed that the values of friction coefficient decrease with the increase of normal load for glass fiber, nylon and PTFE. Different trend is observed for gear fiber, i.e. coefficient of friction increases with the increase of normal load. It is also found that wear rate increases with the increase of normal load for all the materials. The magnitudes of friction coefficient and wear rate are different for different materials. Practical implications – It is expected that the applications of these results will contribute to the design of different mechanical components of these materials. Originality/value – Within the observed range of applied normal load, the relative friction coefficient and wear rate of gear fiber, glass fiber, nylon and PTFE are experimentally investigated.

Sudipto Ray; S.K. Roy Chowdhury

2011 Industrial Lubrication and Tribology

doi: 10.1108/00368791111154940

Purpose – The paper's aim is to predict numerically the contact temperatures between two rough sliding bodies and to compare with the experimental results. Design/methodology/approach – An elastic contact algorithm is used to analyze the normal contact between two nominally smooth surfaces. The algorithm evaluates real contact area using digitized roughness data and the corresponding contact pressure distribution. Using finite element method a steady state 3D temperature distribution at the interface between the sliding bodies is obtained. Using infrared (IR) imaging technique, experiments were carried out to measure the contact temperature distribution between rough rubbing bodies with a systematic variation of surface roughness and operating variables. Findings – Contact temperature distributions over a wide range of normal load, sliding velocity and surface roughness have been obtained. It was seen that the maximum contact temperature expectedly increases with surface roughness (S a values), normal load and sliding velocity. The results also indicate that the “hot spots” are located exactly at the positions where the contact pressures are extremely high. Temperatures can be seen to fall drastically at areas where no asperity contacts were established. The temperature contours at different depths were also plotted and it was observed that the temperatures fall away from the actual contact zone and relatively high temperatures persist at the “hot spot” zones much below the contact surface. Finally it is encouraging to find a good correlation between the numerical and experimental results and this indicates the strength of the present analysis. Research limitations/implications – Experimental accuracy can be improved by using a thermal imaging camera that measures emissivity in situ and uses it to find the contact temperature. The spatial resolution and the response time of the camera also need to be improved. This can improve the correlation between numerical and experimental results. Practical implications – One of the major factors attributed to the failure of sliding components is the frictional heating and the resulting flash temperatures at the sliding interface. However, it is not easy to measure such temperatures owing to the inherent difficulties in accessing the contact zone. Besides, thermal imaging techniques can be applied only with such tribo‐pairs where at least one of the contacting materials is transparent to IR radiation. In practice, such cases are a rarity. However, the good correlation observed between the numerical and experimental results in this work would give the practicing engineer a confidence to apply the numerical model directly and calculate contact temperatures for any tribo‐material pairs that are generally seen around. Originality/value – A good correlation between the numerical and experimental results gives credence to the fact that the numerical model can be used to predict contact temperatures between any sliding tribo‐pairs.

Yasar Totik; Akgun Alsaran; Ayhan Celik; Ihsan Efeoglu

2011 Industrial Lubrication and Tribology

doi: 10.1108/00368791111154959

Purpose – This work aims to investigate the wear behavior of manganese phosphate coating on plasma nitrided AISI 5140 steel. Design/methodology/approach – Prior to manganese phosphate coating, plasma nitriding of substrates was performed at gas mixture of 50 percent H 2 and 50 percent N 2 , for the different treatment parameters. The structural, mechanical and tribological properties of the substrates were determined using hardness test, optical microscope, scanning electron microscopy , X‐ray diffraction and pin‐on‐disk tribotester. The wear behavior of untreated, nitrided and duplex treated substrates was evaluated under dry sliding conditions. Findings – The results indicated that the duplex treatment improved the wear behavior. It was also observed that manganese phosphating of the nitrided substrates at low temperature (450°C‐2h‐N) resulted in a decrease of the wear rate and yielded a reduction in the friction coefficient by forming a transfer film at the counter face. Originality/value – This study can be a practical reference and offers insight into the effects of duplex treating on the increase of wear resistance.

Erol Feyzullahoğlu; Nehir Şakiroğlu

2011 Industrial Lubrication and Tribology

doi: 10.1108/00368791111154968

Purpose – The purpose of this study is to develop new Al‐based bearing alloys which have better properties than classic commercial bearing materials and to analyze tribologic properties of these alloys under dry sliding conditions experimentally. Design/methodology/approach – Four different aluminium alloys were produced with casting method and tested on pin‐on‐disc wear testing machine. Friction coefficients and weight losses of the samples were determined under various working conditions in consequence of the experiments. Hardness, surface roughness, and surface temperatures of the samples were measured. Findings – The results of the experiment show that friction coefficients vary by surface pressure and sliding speed. Al15Pb3.7Cu1.5Si1.1Fe and Al15Sn5Cu3Si alloys have lower friction coefficient values than other alloys. Al8.5Si3.5Cu alloy has the biggest wear resistance. Al15Pb3.7Cu1.5Si1.1Fe and Al15Sn5Cu3Si alloys are the most worn materials. Al8.5Si3.5Cu alloy has the lowest wear rate. Research limitations/implications – When the comparison was done between commercial Al alloys and developed Al alloys in this study, it was seen that Al15Sn5Cu3Si and Al15Pb3.7Cu1.5Si1.1Fe alloys have lower friction coefficient values than other commercial alloys. Practical implications – The effects of the elements except aluminium composing alloys upon tribologic properties were analyzed. Some of the alloy elements were seen to improve tribologic properties whereas some downgrade. When the results are evaluated, Al15Sn5Cu3Si and Al8.5Si3.5Cu alloys containing Si and Sn can be preferred among the aluminium alloys that will work under dry sliding. Originality/value – This paper reveals new bearing materials. These alloys can be used in journal bearings.

Mumin Sahin; Ceyhun Sevil

2011 Industrial Lubrication and Tribology

doi: 10.1108/00368791111154977

Purpose – The aim is to provide detailed mechanical and metallurgical examinations of ion‐nitrided austenitic‐stainless steels. Design/methodology/approach – Austenitic‐stainless steel was the material chosen for the present study. Ion nitriding process was applied to fatigue and tensile samples prepared by machining. Process temperature was 550°C and treatment time period 24 and 60 h. Then, tensile, fatigue, notch‐impact, hardness tests were applied and metallographic examinations were performed. Findings – High temperature and longer treatment by ion nitriding decreased fatigue and tensile strengths together with notch‐impact toughness. Scanning electron microscopy and energy dispersive X‐ray spectroscopy analysis revealed formation of nitrides on the sample surfaces. Surface hardness increased with an increase in process time due to diffusion of nitrogen during ion nitriding. Research limitations/implications – It would be interesting to search the different temperature and time intervals of the ion nitriding. It could be a good idea if future work could be concentrated on ion nitriding on welded stainless steels. Practical implications – Surfaces of mechanical parts are exposed to higher stress and abrasive forces compared to inside mechanical parts during the time period that mechanical components carry out their expected functions. When stresses and forces exceed the surface strength limit of the material, cracks begin to form at the material surface leading to abrasion and corrosion. Therefore, surface strength of materials needs to be increased to provide a longer service life. Ion (plasma) nitriding is a possible remedy for surface wear. Originality/value – The main value of this paper is to contribute and fulfil the detailed mechanical and metallurgical examinations of ion‐nitrided austenitic‐stainless steels that are being studied so far in the literature.

Bekir Sami Yilbas; Mazen Khaled; Sohail Akhtar; Cihan Karatas

2011 Industrial Lubrication and Tribology

doi: 10.1108/00368791111154986

Purpose – Laser bending is a good candidate to replace the flame bending process. The electrochemical response of laser bending region changes due to the microstructural modifications and high level of residual stress developed in the laser‐irradiated region after the bending process. Consequently, investigation into laser bending and microstructural changes in the irradiated region as well as the electrochemical response of bending section becomes essential. This paper aims to focus on the laser bending process. Design/methodology/approach – The laser bending of steel sheets was carried out. The microstructural changes in the bending region are examined using the scanning electron microscopy and X‐ray diffraction. The electrochemical response of the bended sections is investigated through potentiodynamic tests. Findings – It is found that laser‐irradiated surface is free from cracks and cavitations. However, deep pit sites due to secondary pitting are observed in the bending sections. Research limitations/implications – The experiment is limited to certain thickness of the steel sheets. Increasing workpiece thickness reduces the bend angle. However, introducing high‐intensity laser beams improves the bend angle on the expense of high surface roughness in the bend section. Practical implications – Laser bending process is involved with non‐mechanical tooling with low cost and precision of operation. Moreover, laser bending is a good candidate to replace the flame bending process. Consequently, laser bending finds application in industry. However, under the corrosive environment care should be taken. Originality/value – The work presented is original and has not been published anywhere before. The findings will be useful for researchers and engineers working in the sheet metal forming area.

H.C. Garg

2011 Industrial Lubrication and Tribology

doi: 10.1108/00368791111154995

Purpose – This paper aims to describe the theoretical study concerning the effect of non‐linear behavior of the lubricant on the performance of symmetric constant flow valve compensated hole‐entry hybrid journal bearing. The bearing performance characteristics have been computed for various values of non‐linearity factor, land width ratio, aspect ratio and external load. Design/methodology/approach – The analysis considers the generalized Reynolds equation governing the flow of lubricant having variable viscosity in the clearance space and equation of flow of lubricant through constant flow valve restrictor. The non‐Newtonian lubricant is assumed to follow the cubic shear stress law. Findings – The study indicates that for generation of accurate bearing characteristics data, the inclusion of non‐linear effects of lubricant in the analysis is essential. Originality/value – The performance characteristics in terms of minimum fluid‐film thickness, fluid‐film stiffness and damping coefficients, critical mass and threshold speed for a wide range of values of the non‐linearity factor and external load are presented. The results presented are expected to be quite useful to bearing designers.

U. Soy; A. Demir; F. Findik

2011 Industrial Lubrication and Tribology

doi: 10.1108/00368791111155002

Purpose – The main goal of the present study is to investigate the friction and wear behaviors of aluminum matrix composites with an A360 matrix reinforced with SiC, B 4 C and SiC/B 4 C particles. Design/methodology/approach – Un‐reinforced aluminum casting alloy, Al/SiC, Al/B 4 C and Al/SiC/B 4 C aluminum composites were prepared for the present study. Friction and wear tests of aluminum and its composites versus AISI316L stainless steel were carried out for dry sliding condition using by a pin‐on‐disc arrangement. Tests were realized at the sliding speed of 0.5, 1.0 and 1.5 ms −1 and under the loads of 10, 20 and 30 N. The microstructures of the present composites were examined by scanning electron microscopy and energy dispersive spectroscopy analysis. Findings – The coefficient of friction of the composites is approximately 25‐30 percent lower than that of the un‐reinforced aluminum. The specific wear rate of the aluminum and its composites decreases with the increase in load and increases with the increment of sliding speed. Un‐reinforced aluminum has specific wear rate value of 1.73×10 −13 which is the highest specific wear rate, while Al+17%SiC has specific wear rate value of 2.25×10 −13 m 2 N −1 which is the lowest specific wear rate among the tested materials. The average specific wear rates for Al+17%B 4 C, Al+17%SiC/B 4 C and Al+17%SiC composites are obtained about 49, 79 and 160 percent lower than aluminum wear rate under the same test conditions, respectively. Originality/value – In the present study, composites were prepared by pressured infiltration technique. The employed composites are important in industry due to their higher wear resistance, light in weight and less thermal distortion comparing to conventional composites. Also, wear behavior of Al/B 4 C, Al/SiC/B 4 C and Al/SiC composites produced by pressured infiltration technique were not studied very much earlier, therefore more explanation about these composites were proposed.