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Bearing with ideal material - — Silicon nitride ceramics - bearing knowledge

by:Waxing     2020-06-04
As machinery manufacturing industry to develop in the direction of high precision, high speed, bearing application scope is more and more widely, the performance requirements of bearing is becoming more and more high, especially in some special working environment, the metal bearing can't adapt to the demand, or even completely unable to work. And ceramic materials because of the advantages of small density, high elastic modulus, small linear expansion coefficient, wear-resisting, high temperature resistant, corrosion resistance and other excellent properties, become the ideal material of high-speed manufacture precision bearing. One, the characteristics and advantages of silicon nitride ceramics even though the silicon nitride ceramic in the industry is not the most hard, toughness is not the highest, but the requirement of high performance bearing applications, the silicon nitride is thought to have the best comprehensive mechanical and physical properties. Look at the below, silicon nitride compared with other bearing material is excellent. Five kinds of bearing material performance contrast heat-resistant steel bearing generally use the temperature over 120 ℃, the hardness will reduce, rolling life will decline. The silicon nitride has good temperature characteristic, especially suitable for high temperature environment. Centrifugal force density of silicon nitride is about 3. 24 x 103 kg/m3, and the density of bearing steel is about 7. 8 x 103 kg/m3, is only about 40% of the bearing steel density, so when using roller bearings, bearing rotates at high speed to inhibit the increase of the rolling element load caused by centrifugal force effect. The linear expansion coefficient of linear expansion coefficient of silicon nitride is about 1/4 of bearing steel, so the size of the change with temperature variation is small, it is used in the environment of the temperature change is big. Hardness, modulus of elasticity and poisson's ratio for the elastic coefficient of silicon nitride is about 1 of bearing steel. Five times, so the relative load the elastic deformation of small, relatively high rigidity of the payload. Corrosion resistance, nonmagnetic, insulation chemical machinery and equipment, food, Marine and other departments use the machine, using steel bearing, its corrosion is a problem. In strong magnetic environment, the use of steel bearings, powder itself from bearing wear down by adsorption between the roller and the rolling surface, this will be a bearing of the main causes of early spalling damage and increase noise. Second, the preparation of silicon nitride ceramic bearings silicon nitride ceramic bearing preparation process of silicon nitride ceramic powder making bearing parts with silicon nitride powder requirements has the following important features: high purity; High uniformity and fine particles; A high content of alpha. Most conforms to the requirements of the preparation of silicon nitride powder for carbon thermal reduction nitridation method, the equation for: 3 - sio2 + 6 c + 2 n2 = Si3N4 + co, this method get little powder containing metal impurity, high purity, fine grain, high content of alpha, accord with the requirement of bearing parts material. Silicon nitride ceramic bearing related parts molding silicon nitride ceramic bearing the preparation method of a lot of related parts, such as the reaction sintering process, and pressureless sintering, hot-pressing sintering, and the secondary reaction sintering process. In order to get fully dense silicon nitride materials, using the hot isostatic pressing method. Silicon nitride ceramic bearing related parts machining of silicon nitride ceramic bearings related parts basically similar to bearing steel parts processing, grinding mechanism are basically the same. But because of all the properties of silicon nitride and the performance of the steel have bigger difference, so the coefficient of grinding tools in mechanical machining, machining, grinding the mixture has a considerable difference, such as the process of abrasive particle size, type, shape, number, strength, crushing, wear properties and other requirements are different. Currently using abrasive are mainly silicon carbide, boron carbide and diamond powder, etc. Silicon nitride ceramic bearing general assembly of the rolling bearing is composed of four main parts, namely, outer ring, inner ring, rolling element and cage. Because there are as many as ten kinds of rolling bearing, using different types of bearing cage form each are not identical, so the bearing assembly way also is not the same. Silicon nitride ceramic bearing as an important basis of mechanical parts, since it has unmatched by other bearing excellent features, in the material world. In recent years, in the aerospace, Marine, nuclear industry, petroleum, chemical industry, textile industry, machinery, metallurgy, electric power, food, locomotive, subway, high speed machine tools and scientific research and national defense military technology need to be in high temperature, high speed, low temperature, flammable, explosive, corrosive, vacuum, electrical insulation, non-magnetic, dry friction under special conditions, such as silicon nitride ceramic bearing indispensable substitution effect is gradually known by people.
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