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In order to improve the processing accuracy of silicon nitride ceramic balls and to investigate the mechanism of forming ceramic balls by flexible support grinding method, a new cone-type flexible support grinding method with controlled deflection motion of grinding disc is proposed. Based on the new grinding method, a simulation model is established to deeply analyze the influence of the deflection motion of the grinding disc on the grinding trajectory and force state of the silicon nitride ceramic balls. Orthogonal experiments were conducted on a new cone-type flexible support grinding platform built to further analyze the effect of grinding disc motion characteristics on ball formation. Simulation and experimental results show that under the flexible support grinding method, As the increases of grinding disc deflection angle, the standard deviation of ball trajectory uniformity decreased from 43.58 to 35.49, the maximum contact force increased to 4 times the initial value, the average ball diameter variation increased from 1.466 μm to 2.382 μm, and the batch diameter variation increased from 4.98 μm to 10.27 μm. The lower grinding disc deflection motion is beneficial to optimize the grinding trajectory, but increases the unevenness of the ball force, which is not conducive to improving the average ball diameter variation and batch diameter variation of silicon nitride ceramic balls. In the actual process, the angle of deflection of the grinding disc must be controlled to within 0.02°.

A silicon nitride ceramic bearing has good self-lubricating characteristics. It still has a good operational status under the condition of a lack of oil. However, the temperature distribution of a silicon nitride ceramic bearing during its operation is unclear. To clarify the thermal distribution of a full-ceramic ball silicon nitride ceramic bearing under self-lubricating conditions, the changing trend of the rolling friction temperature between the rolling elements and channels with different accuracies is analyzed using the friction testing machine. The bearing heat generation model based on the silicon nitride material coefficient is established, and the life test machine measures the temperature of the bearing to verify the accuracy of the simulation model. The results show that the friction temperature between the ceramic ball and channel decreases with the increase in ceramic ball level. With an increase in the ceramic ball pressure and temperature, the friction temperature rises. Under self-lubrication, when the bearing bears a heavy load, the influence of the rotating speed on temperature rise tends to decrease. Under the condition of high speed, with the increase in load, the change range of temperature rise shows an upward trend. The important relationship between the bearing’s heat and bearing’s load and speed is revealed. It provides some theoretical guidance for the thermal analysis of a silicon nitride ceramic ball bearing under the self-lubricating condition to improve the service life and reliability of full-ceramic ball bearings.

Compared with metal ball bearings, full ceramic ball bearings have more outstanding service performance under extreme working conditions. In order to reveal the lubrication mechanism and improve the operation performance and service life of full ceramic ball bearings, in this paper, the friction, vibration, and temperature rise characteristics of 6208 silicon nitride full ceramic deep groove ball bearing, under the condition of oil lubrication, are studied experimentally. Based on the test results, and through theoretical calculation and simulation analysis, the distribution of the lubricating oil film in bearing contact micro-zone under different working conditions was simulated. After that, the surface of contact micro-zone of full ceramic ball bearing was analyzed. It was found that there is an optimal oil supply for full ceramic ball bearing oil lubrication in service. Under the optimal oil supply lubrication, full film lubrication can be achieved, and the bearing exhibits the best characteristics of friction, vibration, and temperature rise. Compared with the load, the rotational speed of the bearing has a decisive influence on the optimal oil supply. When the rotational speed and load are constant, the minimum oil film thickness and oil film pressure in the contact area of the rolling body decrease with the increase of angle ψ from the minimum stress point of the rolling body. Under the action of high contact stress, thin oil film will be formed in the bearing outer ring raceway. In the field of full ceramic ball bearings, the research content of this paper is innovative. The research results of this paper have an important guiding significance for revealing the oil lubrication mechanism of full ceramic ball bearing and enriching its lubrication theory and methods.

Working conditions such as lubrication, preload, and rotational speed have important influence on vibration and temperature rise of the spindle motor. In this study, controlled variable experiments are carried out on the silicon nitride (Si3N4) full-ceramic ball bearing and steel bearing of the same type, and the vibration signal characteristics and temperature rise of the spindle motor are tested and analysed, by changing the lubrication conditions, preloads, and rotational speeds of the spindle motor. Through the research, it is found that as the rotational speed increases, the vibration velocity of the Si3N4 full-ceramic bearing spindle motor under different preloads and lubrication conditions shows an overall increasing trend; kurtosis generally presents a downward trend and gradually flattens, indicating that although the vibration velocity increases at high speeds, the vibration signal shows a relatively stable state. As the rotational speed increases, the difference of vibration velocity under the condition of applying preload and no preload decreases, indicating that the influence of preload on the vibration of full-ceramic bearing spindle motor decreases with the increase in rotational speeds. At the same time, it is found that fr and 5fr have greater impact on the vibration of full-ceramic bearing spindle motor, where fr is the frequency of the bearing in normal operation, and 5fr is 5 times of the normal operating frequency. Lubrication conditions have little effect on the temperature rise of full-ceramic bearing spindle motor, and the temperature rise under nonlubricated conditions is even slightly lower than that under grease lubrication conditions. The research results show that the vibration velocity and temperature rise of Si3N4 full-ceramic bearing spindle motor are less than those of steel bearing with the same type, indicating that full-ceramic bearing has better performance than steel bearing under the same working conditions.

At normal operating temperatures (below 100 °C), the water in the proton exchange membrane fuel cell (PEMFC) is in the form of a mixture of gas and liquid phases. The content of water guarantees that the membrane has good proton conductivity, but it may also block the transmission of the reaction gas to the catalytic reaction sites. Based on the single straight channel of the PEMFC, the water content of the model at various voltages and the water distribution of the different parts are studied. The results indicate that the amount of water in the model generally increases with the reduction in the voltage. When the voltage is set from 1.1 V to 0.7 V, the increase in the amplitude of the water content is higher than 0.7 V–0.4 V, and the water content is highest at 0.5 V. Under each voltage, the largest water content occurs in the gas diffusion layer, the second one occurs in the channel, the third one occurs in the proton exchange membrane, and the water content in the catalyst layer is lowest.

In order to improve the tribological characteristics of Si _3 N _4 friction pairs at high temperature, graphite powder, h-BN powder and MoS _2 powder with excellent lubricating properties were added between the friction pairs. The friction and wear experiments of different powder adding stages (initial adding stage and stable friction stage) and different temperature gradients (25 °C, 100 °C, 200 °C, 300 °C, 400 °C) were carried out on the friction and wear tester. After the experiment, the worn surface was observed by SEM and ultra-depth microscope, and the lubricating powder before and after friction was analyzed by XRD. Combined with the friction coefficient recorded during the experiment, the friction reduction mechanism of powder lubrication under different conditions was analyzed and summarized. The results show that the three kinds of powder all have the best lubrication effect at the initial stage of addition. With the increase of temperature, the film-forming ability of graphite powder and h-BN powder decreases, and MoS _2 powder is little affected. Therefore, the key to lubrication and wear reduction is to form a dense, stable and not easily damaged lubricating film during friction. How to form the lubricating film more easily and how to improve the performance of the lubricating film will become the next research focus.

As a new high-end bearing product, full ceramic ball bearings are favoured in a variety. However, there have been few studies on the lubrication of full ceramic ball bearings. The purpose of this study is to reveal the relationship between the vibration and temperature rise of full ceramic angular contact ball bearings and the lubricant viscosity, and to improve the service life of the bearings. In this study, the effects of lubricant viscosity on the vibration and temperature rise of silicon nitride full ceramic angular contact ball bearings under different axial loads and rotation speeds were tested. Herein, a mathematical model of oil lubrication suitable for full ceramic ball bearings is established and the relationship between the lubricant viscosity, lubricant film thickness, outer ring vibration and temperature rise of the bearing is analyzed. It was found that the vibration and temperature rise first decrease and then increase with the increase of lubricant viscosity. In this range, there is an optimal viscosity value to minimize the vibration and temperature rise of the full ceramic angular contact ball bearing. The contact surface wear of the full ceramic angular contact ball bearing varies greatly under different lubricant viscosities. There is no obvious wear on the contact surface under optimal viscosity, and the service life of the bearing is greatly improved. These results can play an important role in revealing the lubricant mechanism of full ceramic ball bearings and improving their service life under optimal lubrication.

In order to reveal the friction properties and improve the wear resistance of silicon nitride ceramic materials, a calculation model of static friction coefficient of silicon nitride ceramic is established. The influence law of contact surface roughness on friction coefficient under different contact load and friction speed is analyzed. The test and the results verification are carried out by using Friction Wear Testing Machine. Then the dry friction process of silicon nitride ceramic is simulated based on UDEC, and the wear failure form is analyzed. In the dry friction process of silicon nitride ceramics, the coefficient of friction is directly proportional to the contact surface roughness, inversely proportional to the contact load, and directly proportional to the friction speed. There is a critical value for the roughness of friction sub-contact surface. Silicon nitride ceramics can self-lubricate by friction when the contact surface roughness is less than this critical value. In the dry friction process, the oxidation of SiO2 has little effect on the friction. The wear surface of silicon nitride ceramics consists of shear failure units and tensile failure units, and their formation is related to the surface roughness. The results play an important role in revealing the frictional properties of engineering ceramics such as silicon nitride, as well as helpful to improve the wear resistance and service life of ceramic materials.