Silicon nitride ball processing
2019 11/04
1 Silicon Nitride Blank Ball Forming Like most ceramic products, silicon nitride balls are also made from powder. At present, the commonly used silicon nitride blank ball manufacturing processes include: reaction sintering, hot pressing sintering, hot isostatic pressing, and the like. In the production of bearing parts, the hot isostatic pressing method is currently considered to be the best process for the manufacture of silicon nitride blank balls, because the process is directly applicable to a part of the sealing pre-forming or sintering production method, and can produce a density close to 100%. material. Brief description of the hot isostatic pressing process: The hot isostatic pressing method is to heat the silicon nitride material in an argon atmosphere at a pressure of 250 MPa and a temperature of 750 ° C for 2 h to prepare a sample ball. The glass blank is then used to spray the blank to form a porous shell, which is then heated in a special vacuum furnace to remove the trapped air from the material and melt the glass. After the cooling is controlled, the glass layer is changed. Become a sealing layer. After the hot pressing phase is completed, the pressure is reduced and the glass is removed from the ball. The manufacturing technology of silicon nitride blank ball has great influence on the subsequent processing of silicon nitride ceramic ball. The dimensional tolerance and surface quality of the blank ball will determine the final quality of the ceramic ball and the post-processing cost. 2 Abrasive selection Ceramic ball processing includes rough grinding, fine grinding, lapping, and super-finishing, among which coarse grinding removes 95% of the ceramic ball. After each process is completed, the ceramic balls are cleaned to ensure good cleanliness of the ceramic balls. Because the surface of the ceramic ball in the previous process must have a large amount of abrasive particles, it must be cleaned, especially in the lapping and superfinishing processes. The grinding process of silicon nitride balls should be based on different types of abrasives with different types and hardness. The abrasive grain size is from coarse to fine. If the abrasive is used too much or too little, the grinding efficiency and the surface precision of the ball can be reduced. The desired ratio can be achieved by using an abrasive ratio that is coordinated with the corresponding processing steps. The coarse grinding and fine grinding processes use different sizes of silicon carbide, and silicon carbide can also be used for grinding; the finishing process uses boron nitride or chromium oxide for grinding; • the superfinishing process uses diamond ointment or Grinding is carried out with a superfine mortar made of chromium trioxide, mechanical oil and stearic acid. 3 Rough grinding process The rough grinding process can eliminate various defects on the surface of the blank ball, including sintering oxide layer, pores and surface micro cracks. Before grinding, the groove of the grinding disc is rolled with the same size steel ball and Run-in, the ceramic ball and the grooved track are well matched to improve surface accuracy and geometric accuracy. Rough grinding: When the silicon nitride ball is ground in the groove of the concentric grinding wheel, the ball moves in a grinding wheel groove concentric with respect to the axis of the grinding wheel, and is grounded by a relative pressing force with a spherical surface and a grinding wheel. Part of the ball. 4 Fine grinding process The finishing grinding process is basically the same as the rough grinding, which can further eliminate the defects of the machining of the previous process and improve the dimensional accuracy and surface quality of the ball. Finishing: The fixed and rotating discs used are cast iron discs. The hardness of the disc should be greater than 220HB. 5 The lapping process of the silicon nitride ball is carried out in the V-shaped groove of the rotating cast iron ball and the plane of the fixed grinding plate, forming a three-arc contact state, in the role of grinding pressure Under the driving of the rotating and grinding disc, the silicon nitride ball is continuously rolled and rotated along the groove. The abrasive is extruded by a silicon nitride ball and embedded in the grooved surface of the grinding ball to form three circular arc-shaped abrasive tools. 6 Super-finishing processing Silicone ball super-finishing processing is processed by a single-disc multi-ditch sealing method on a vertical ball-making machine. Ultra-finishing processing, because the ball is circumferentially ground in the respective grooves in the grinding disc, the groove of the groove is quite consistent with the ball, thus avoiding collision and friction such as cycle grinding, and the surface quality can be processed better. High-precision ball with higher geometric accuracy and dimensional accuracy and small vibration value. Finished Ball Inspection The ceramic ball processing process consists of two stages of forming and machining. Accidental surface defects can occur in every process of ceramic ball production. Due to the brittleness and defect sensitivity of ceramic materials, surface defects reduce the reliability of ceramic balls and affect the wide application of ceramic bearings. In order to ensure the quality of the finished ball, various methods such as radiation detection, ultrasonic inspection, penetration detection and laser scattering are used at home and abroad to study the surface defect detection of ceramic balls. Since the ceramic ball surface defects are diverse and the spherical surface is not expandable, there is still no perfect non-destructive testing method.