Long-distance Localization of 4Cr13 Stainless Ball-pocket in Radiative Region

Radiation caused by high-energy particles would speed up the damage of accelerator equipment. The high residual radiation from equipment affects staff health as well. Intelligent robots receive various limits to replace human in completing complex and time-consuming maintenance in radiative region because of high sensitivity to radiation. The 4Cr13 stainless ball-pocket was designed in the study of localization in long distance with the advantages of the conical fit technology. Moreover, the 4Cr13 stainless ball-pocket and bearing ball combine and form a locating structure, which has good performance on automatic aligning, self-locking and rapid dismantling. The comprehensive mechanical properties of 4Cr13 stainless ball-pocket were studied and optimized based on three heat treatment methods of martensite steel containing chromium alloy. The study of machining conditions states that compared with the design accuracy of localization, the machining error retains definite allowance. The 4Cr13 stainless ball-pocket successfully exhibits sufficient supporting strength, wearing reducing and radiation resistance. This study shows that 4Cr13 stainless ball-pocket has better fitting precision than 0.2 mm in practice. This study could offer a reliable strategy and measure for long-distance localization in other dangerous regions.

The Crack Propagation Trend Analysis in Ceramic Rolling Element Bearing considering Initial Crack Angle and Contact Load Effect

Silicon nitride ceramic bearings are widely used for their excellent performance. However, due to their special manufacturing method, cracks will occur on ceramic ball surface, and this initial surface crack will propagate under the action of cyclic stress, which will lead to material spalling. This will greatly limit its service life in practical applications, especially under heavy load at high speed. Therefore, it is necessary to study the surface crack propagation of silicon nitride ceramic bearings. In this paper, the effect of initial crack angle and contact load on crack growth is analysed by the finite element method (FEM). A three-dimensional finite element model of a silicon nitride bearing ball containing an initial crack is created by the FEM. The cracks are initially classified based on the angle between the crack and the bearing ball surface, and the location of the most dangerous load for each type of crack is known by theoretical analysis. The stress intensity factors (SIFs) are calculated for the crack front to investigate the effect of load position on crack growth. Subsequently, the SIFs are calculated for each type of crack angle subdivided again to investigate the effect of crack angle on crack propagation.

Experimental Analysis of Friction and Wear of Self-Lubricating Composites Used for Dry Lubrication of Ball Bearing for Space Applications

Lubricating space mechanisms are a challenge. Lubrication must be sustained in different environments, for a very long period of time, and without any maintenance possible. This study focuses on the self-lubricating composite used in the double transfer lubrication of ball bearing. Ball/races contacts are lubricated via the transfer of materials from the cage that is made of the composite. A dedicated tribometer has been designed for the study. A specificity of the tribometer is to not fully constrain the composite sample but to let it move, as the cage would do in the bearing. Four composites (PTFE, MoS2, glass or mineral fibers) where tested in ultrahigh vacuum and humid air environments. Transfer was achieved with morphologies and composition similar to what is observed on real bearings. Adhesion measurements performed on composite materials before and after friction allowed one to explain the differences in tribological behaviors observed (transfer quality and contact instabilities). Beyond strengthening the composites, fibers are shown to be critical in trapping mechanically and chemically the transferred material to lubricate and prevent instabilities. Equilibrium between internal cohesion of transferred material, and adhesion to counterparts must be satisfied. Mass spectrometry showed that water appears also critical in the establishment of stable transfer film, even in vacuum.