The effect of lubricant viscosity on the performance of full ceramic ball bearings

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.

Si3N4 Ceramic Ball Surface Defects’ Detection Based on SWT and Nonlinear Enhancement

In order to improve the detection accuracy and efficiency of silicon nitride ceramic ball surface defects, a defect detection algorithm based on SWT and nonlinear enhancement is proposed. In view of the small surface defect area and low contrast of the silicon nitride ceramic ball, a machine vision-based nondestructive inspection system for surface images is constructed. Sobel operation is used to eliminate the nonuniform background, and the silicon nitride ceramic ball surface image is decomposed by SWT. And frequency-domain index low-pass filtering is used to modify the decomposition coefficients, and an adaptive nonlinear model is proposed to enhance defects; finally, the image is reconstructed and segmented by the stationary wavelet inverse transform and the dynamic threshold method, respectively. The enhanced algorithm can effectively identify surface defects and is superior to traditional defect detection algorithms.

Tribological Properties of ZrO2 Coating on the Ball Joint of an Axial Piston Pump in High Water-Based Emulsion Medium

This paper studies the tribological properties of the ZrO2-coated spherical joint pair of the axial piston pump in a high water-based emulsion medium. Firstly, atmospheric plasma spraying was used to prepare the ZrO2 coating on the surface of the spherical joint pair. Secondly, the tribological characteristics of the steel-steel pair and ceramic-ceramic pair were analyzed by the friction and wear testing machine under the conditions of a high water-based emulsion concentration, load size, and load frequency. White light interference three-dimensional surface profiler and scanning electron microscope were used to analyze the original and worn surfaces of the samples, and then the friction and wear of the different material pairs were discussed. The results show that the friction reduction and wear resistance of the ceramic ball joint are superior to those of the steel ball joint. When the load is 100 N, the frequency is 1 Hz, and the emulsion concentration is 5%, and the friction coefficient and wear loss of the ceramic-ceramic ball joint pair are the lowest. The emulsion concentration and load have great influence on the friction coefficient and wear amount, while the frequency has little influence on them. With increasing concentration of the emulsion, the friction coefficient decreases and tends to be stable, but with increasing of load, the friction coefficient and wear increase. The friction coefficient and wear loss of the ceramic-ceramic ball joint in pure water are 0.25 times higher than those of the steel ball joint under the same working conditions. Therefore, when the concentration of the high water-based emulsion is 5%, 100 N load, 1 Hz frequency, the ceramic-ceramic ball joints display the best friction and wear resistance of the two. The research results provide a theoretical basis for the design, manufacture, and application of the ceramic coating hydraulic components in a high water-based emulsion medium.

Raceway Defect Frequency Deviation of Full-Ceramic Ball Bearing Induced by Fit Clearance in Wide Temperature Ranges

Full-ceramic ball bearings are widely applied in wide temperature ranges due to their excellent thermal shock resistance, and the condition monitoring and fault diagnosis are mainly conducted through the spectrum analysis based on the defect frequencies. However, the outer ring has a spinning motion in the temperature-related fit clearance, which leads to the deviation of raceway defect frequencies, and is not conducive to the fault diagnosis. In this paper, the temperature-related fit clearance is considered in the dynamic model, and defects are added on the inner raceway and outer raceway. The motions of the rings are calculated and analyzed in the frequency domain, and the trends of peak frequencies with temperature are investigated. Simulation and experimental results show that the spinning speed of the outer ring increases with temperature, and the defect frequencies exhibit obvious deviation in wide temperature ranges. In a temperature range of 500 K, the defect frequencies exhibit deviations of over 3%, which is obvious in the defect frequency identification. The results provide insights on the full-ceramic ball bearing dynamics and help with the fault diagnosis and status monitoring of the relevant devices.