Papers by Keyword: Silicon Nitride Ball

Abstract: To research effects of cyclic loadings and the loading magnitude on the crack opening-closing behavior, crack opening displacement evaluations for fatigue cracks on a silicon nitride ball were carried out. The compressive loading magnitude, which was less than 2.7 kN, did not affect crack opening-closing behavior. The crack opened at the early cycles of fatigue during 0 to 10³ cycles.

Abstract: Mode I and Mode II fatigue crack growth on the equator of silicon nitride balls were tested under cyclic compressive loads. The mode I crack propagated in a straight direction along compressive axis. The angle of the mode II crack changed toward the direction perpendicular to tensile stress direction. The effect of mode I on cracks in differential mode II was strong after cycles.

Abstract: For some years ceramic bearing balls based on silicon nitride have been routinely used in technical practice. An important property of bearing balls is their strength, but appropriate testing methods are still missing. In this paper four different methods for strength testing are applied to commercial bearing balls. Each of the tests needs a different type of specimen, their preparation needs a very different effort, and the stress state applied to the specimens is also very different. This causes pros and cons, which are discussed in detail. The conventional 4-point bending test characterises the material in the interior of the balls. The applied stress state is uniaxial. The machining of the bending bars out of the balls is time intensive and costly. The ball on three balls test also characterises interior of the balls. The stress state is biaxial. The machining of the disc shaped specimens out of the balls is less expensive than the production of bending bars, but the finish of the tensile loaded surface needs special care. The data of both types of tests can be converted into each other using Weibull theory. The specimens in the triple ball crush test are as-received bearing balls, which are squeezed together. This causes some kind of contact loading, as will also occur in service. Failure is caused by the creation and growth of contact cracks, followed by a collapse of the compressed and cracked material. A detailed analysis of test results is complicated. It can be speculated that the component’s behaviour is mainly influenced by the toughness of the material and that the flaws in the material or at the component’s surface are of less significance. In the newly developed notched ball test the highest stressed region is a part of the original surface of the balls. Machining of the notch is straightforward. The stress state is almost uniaxial. The strength depends on size of flaws in the surface region. Therefore the notched ball test is a relevant measure to characterize the quality of the bearing balls.

Abstract: To study the sphere-shaping mechanism under dual rotating plates (DRP) lapping mode for ceramic balls, the uniformity of lapping trace distribution is focused in this paper. Methods for simulation and evaluation of the lapping trace uniformity are proposed, and the effect of velocity parameters on the lapping uniformity of ball under DRP lapping mode is analyzed. It is found that the lapping uniformity is dependent not only on the variation range of spin angle θ, but also on the spin angle speed ωb and on the variation form of θ. The analysis results indicate that the effect of amplitude of the speed ratio function on the lapping uniformity is much greater than the effect of phase on that. When the ratio of the inner plate speed to the outer varies from 0 to2, the best lapping uniformity is obtained under the conditions demanded by this paper.

Abstract: Studies on chemical mechanical polishing (CMP) for silicon nitride (Si3N4) balls with CeO2 abrasive carried to investigate the mechanism of chemo-mechanical action between silicon nitride and CeO2. It is found that CeO2 is more effective to obtain smooth Si3N4 balls than other abrasives, and extremely smooth Si3N4 balls with surface Ra 4nm were obtained after polishing. XRD test is used to detect the reaction resultants on the ball surface, and the results show that SiO2 is the main resultant of the chemical reaction between Si3N4 and CeO2, and the test results confirm the correctness of thermodynamic analysis based on Gibb’s free energy of formation. It is also found that water play as a key factor in CMP.

Abstract: To understand the mechanism involved in the lapping process of the silicon nitride balls, the wear mode is investigated in this paper. The abrasion tests were performed on a ball-plate wear test apparatus with different loads (0~2N/ball) and slurry concentrations (5%wt~30%wt W20 B4C3). The abraded surface is observed by optical telescope. A wear-mode map, which defines the regimes for two-body abrasion or three-body abrasion dominating in the micro-scale abrasion test, is plotted with two axes: load and concentration of abrasive. An empirical formula for the wear mode transition is adopted to calculate the transition point S*, which can then used to predict the wear mode in lapping process of silicon nitride ball.