| With the development of national economy, our country has entered a new economic "Transitional period". During the period of “13th Five Year Plan”, premier Li keqiang, proposed the requirements of "green production, saving energy and reducing consumption" in the government work report. The national economy from the period of extensive economic industry pattern has experienced more than half a century transition to the energy saving, intensive industry pattern in the 21 st century. This historic industrial revolution proves the comprehensive strength of China got great progress; meanwhile also proposes the way for the development of science and technology.It has been taken almost 60 years for the development of our country’s coal industry from small individual stages of disordered mining to building large coal group for planning, orderly mining stage. However, compared with the same foreign industries, the efficiency of coal mining, resource utilization and anti-fouling ability are still far behind. Search to the bottom, it can be still blamed for the backward ideas and the not advanced research technology of mining machinery equipment. After decades of struggle, the level of our country science and technology development has reached a new height. Mining machinery equipment is continually replaced by new ones. Compared to before, the existing mine equipment operate more intelligent and become more compact. As the main mining machinery equipment, the energy consumption and operation cost of belt conveyor has always been the focus of the industry and the key point to the structure design. As the main energy consumption component of belt conveyor(especially for long distance, large capacity conveyor), the rotation characteristic of roller is directly related to the running cost of conveyor. As the main index to estimate the performance of roller, its rotation resistance mainly includes the frictional resistance of rolling bearings, the frictional resistance of labyrinth seals filled with grease and frictional resistance between the outer cover and roller. Where the frictional resistance of rolling bearings is the main component of roller rotation resistance, accounted for 80% ~ 90%. Therefore, it has an important significance to investigate the frictional characteristics of roller bearing on improving the performance of roller and the conveyor running efficiency.In this paper, the correlation between the various factors affecting the roller under the actual working conditions and the bearing frictional torque characteristics will be investigated after field surveying and browsing a large number of relevant literatures. After a great deal of experiments and analysis, the main influence factors can be divided into three aspects which includes grease filling volumes, interference assembly and radial load. It is a significance to investigate the correlation between the three aspects and the roller bearing for finding the optimum ranges of grease filling volumes, fitting dimensions and weight of conveying materials. Based on that, the specific research work are as follows:(1) Based on the Hertz contact theory, geometry features and parameters of micro-contact between the bearing rolling elements and raceways will be analyzed and derived;On the basis of Hertz elastomers point contact theory, the calculating methods for the ellipse geometric parameters including the elliptical major semi- axis, minor semi-axis and area between the bearing rolling elements and raceways will be analyzed and deduced. Meanwhile, explanation and calculation methods of relevant concepts including: the first and second kind elliptic integral functions, curvature of contact point, sum function of curvature were proposed. Through the analysis of Taylor’s series expansions for the basic parameters of the rolling bearing point contact, a numerical iterative calculation method by setting the minimum control amount through the computer numerical analysis software will be proposed. Through the analysis of the rolling characteristics of rolling bearing, the calculation formulae of revolution and spinning angular velocity of the rolling elements and kinematics equation will be derived. Meanwhile, the concepts and calculation methods of stress cycle times and contact cycle times will be proposed. Based on the analysis of rolling bearing quasi statics, the bearing quasi dynamic analysis method considering inertia factors can be established. Meanwhile, through the computer numerical analysis soft wares, several simple and convenient solve methods will be proposed. Through the quasi dynamic analysis of rolling bearings, several interaction equations will be established between the rolling element and cage pocket holes, cage and guide rings, lubricant and bearing components. In addition to that, the inertia force and inertia moment equation of high-speed rolling bearings and the kinetics equations of rolling elements will be derived.(2) All calculational methods and formulae of friction sources on the rolling bearing will be analyzed and investigated;Combining with the quasi dynamic analysis of the rolling bearing, bearing friction sources can be divided into five components including: rolling friction caused by the elastic lag, friction caused by the roller differential sliding, friction caused by rolling element spinning, friction the lubricant viscosity(including the friction caused by oil film shearing and friction caused by the flow resistance of oil and gas mixture), and relative sliding friction among the cage, roller and rings. To accurately calculate the total friction torque of the bearing, the theoretical analysis and torque calculation formulae above most friction components will be proposed, respectively. For the friction caused by the material elastic lag of bearing rings, the length of minor semi-axis of point contact ellipse between the rolling elements and raceways will be needed, moreover, when considering the energy elastic hysteresis curve of rings material before and after the contact, elastic lag coefficient αh is also be introduced to ensure the calculation accuracy of torque value. Differential sliding is a special frictional characteristic to the rolling bearings, which can be understood as: the contact ellipse area between the rolling elements and raceways can be divided into three components because of the speed in a different direction, the friction direction of elliptic area between the two pure rolling points is opposite to the ones of elliptic areas from the two pure points to the ellipse semi-major axis endpoints, respectively, which means the results can be accurately integrated by dividing the ellipse into three components. The rolling elements spinning would happen when the axes of bearing inner and outer ring are misaligned. Moreover, because of the spinning direction of the rolling elements is consistent; therefore, when calculating the friction torque, it can be obtained to integrate the contact stress of arbitrary point on the contact ellipse. Lubricant viscosity friction mainly caused by the shearing stress in lubricant and the resistance torque of gas mixture flow due to the evaporation, eventually leading to bearing friction torque increase, its value can be obtained by experience formula. The relative sliding friction among the cage, rolling elements and rings has nothing to do with the speed, however, related with the lubricant viscosity, the filling amount of grease and the characteristics of bearing materials. Therefore, for the rolling bearing finished the running-in stage, the friction force is a fixed value, and its value can be obtained by experience formula.(3) The influences of grease filling volumes to the bearing friction torque will be analyzed and investigated;Grease lubrication is considered as the most way widely used in rolling bearing lubrication, grease filling volume will directly affect the temperature rise and friction torque of rolling bearing. Therefore, first of all, we need to analyze the friction torque components of grease lubricated bearing. According to the friction characteristics of grease lubricated bearing, its friction torque components can be divided into: the viscosity frictional resistance of the grease(including: drag friction resistance of grease and flow resistance caused by oil and gas mixture), friction resistance caused by rolling elements spinning, friction resistance among the cage, rolling element and inner or outer ring, sliding friction and rolling friction resistance caused by heat generation. In addition, the all above friction sources will be analyzed and calculated, respectively. And, the friction torque calculation model of grease lubricated bearing will be presented finally. It can be seen from the friction torque components of grease lubricated bearing, the last two friction sources are caused by the heat generation due to the grease filling volume. However, the rise of bearing temperature will change the grease rheological properties, therefore, before investigating the correlation between the grease filling volumes and bearing friction torque, experiments for the rheological properties of lithium grease will be carried out. The experiments of Grease rheological properties include the similar grease viscosity vs. temperature and the similar grease viscosity vs. rotation speeds(or shearing rates). Finally, the experimental results will be fitted respectively. Through building the friction torque testing apparatus for grease lubricated bearing, grease filling experiments will be carried out, and the experimental results will be compared with the established model. When verifying the model calculation accuracy, through observing the experimental results, the optimal range of grease filling will be given.(4) The influences of interferential fitting to the bearing friction torque will be analyzed and investigated;In general, the bearing will be applied in the form of interference assembly in the roller. According to the assembly process, the form of interference assembling will be taken between the bearing outer ring and bearing house, bearing inner ring and shaft neck. However, according to the elastic mechanics stress and deformation analysis about a paired thick ring, the interference fitting will inevitably has an impact on bearing friction torque. To analyze the correlation between the assembly stress and the bearing friction torque, it need to analyze the components of friction torque assembled bearing firstly, and establish the friction torque model for assembled bearing. Considering the interference assembly which makes one bearing friction resistance significantly exceed the others, therefore, according to the friction characteristics of assembled bearing, the bearing frictional resistance can be divided into two components: the rolling friction resistance caused by material elastic lag of bearing rings, sliding friction resistance among the cage, rolling elements and rings. The analysis and calculation about two kinds of frictional resistance will be carried out, and the mathematic model of friction torque for assembled bearing will be proposed finally. To simulate the bearing interference assembling, a kind of circular radial loading bearing house will be designed. At the same time, through pressure sensor, the value of load stress can be displayed and recorded. A test rig for assembled bearing friction torque will be built, and experiments will be carried out on the apparatus. Comparing the test results with the theoretical model; meanwhile, through observing the test data the optimal range of fitting size will be given.(5) The influences of radial loads to the bearing friction torque will be analyzed and investigated;In general, the rotation characteristics of belt conveyor rollers changes with weight varying of material conveyed by conveyor, i.e., the resistance of roller rotating is closely related with the material’s weight. Considering the radial loads in the vertical direction changing with the loading weight will affect the bearing friction torque, therefore, according the friction characteristic analysis of radial loaded bearing, the bearing friction resistance will be divided into three components: rolling friction resistance caused by material elastic lag of the bearing rings, differential sliding friction resistance caused by rolling elements, sliding friction resistance among the cage, rolling elements and rings. And analysis and calculation will be carried out for the above three frictional resistance, eventually, the friction torque calculation model for radial loaded bearing will be established. To enable the bearing can be loaded with different radial loads; a bearing radial force loading device will be designed, which can realize the basic function including infinite loading and load measuring. A friction torque test rig for radial loaded bearing will be built, and experiments will be conducted on tit. Comparing the test results with the theoretical model; meanwhile, through observing the test data, the optimal range of radial loads will be given. |
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