Yan Li, 'In years in the total', Yu Yu's characteristics and manufacture of ceramic bearings, Jiang Yiping (School of Materials Science and Engineering, Shandong University, Jinan 250061), introduced the means and application prospects, and demonstrated the use of engineering ceramics for bearing manufacturing. Feasibility and Importance Engineering ceramics is a new type of engineering material that has been developed in recent years. Because it not only has the characteristics of high temperature resistance, wear resistance, and corrosion resistance of traditional ceramics, but also has excellent properties such as high strength and high tenacity, it can be used in aerospace industry. There are broad application prospects in fields such as advanced national defense and machinery, metallurgy, and chemical industries. At present, industrialized countries in the world are investing a large amount of manpower and funds to research various new types of engineering ceramic materials. Ceramic bearings are among them creative. One of the inventions Due to the excellent performance of ceramic bearings, it has become a hot spot for the development and application of high-tech in the world and has become one of the hallmarks of the material technology revolution in the mechanical industry. 1 The characteristics of engineering ceramics Engineering ceramics are polycrystalline materials. The valence bonds, ionic bonds, or a mixture of the two form the different crystal lattice structures of the material. It is determined that it has special properties that metals and other materials do not possess, namely high temperature resistance, high hardness, wear resistance, corrosion resistance, low coefficient of expansion and light weight, etc. 1.1 Hardness, strength General engineering ceramics are harder than metals The hardness is more than twice as high, this characteristic determines that it has good wear resistance. The strength of the ceramic material is affected by the organizational factors such as porosity, grain size, and grain boundary phase content to increase the strength of the ceramic material in addition to the control In addition to the above organizational factors, composite and toughening methods can be used to improve the strength of ceramic materials. The greatest feature of engineering ceramics that can be changed is that the high temperature strength is much higher than that of metals, and its compressive strength is extremely high, which is almost that of metal materials. More than a dozen times of 1.2 heat-resistant engineering ceramic materials generally can withstand 1200 ~ 1500 high temperature, but also can maintain high hardness and strength under high temperature conditions, and has a good thermal shock resistance. Therefore, this feature is very advantageous for bearings used in high temperature environments.
1.3 Density Compared with metal materials, the density of ceramic materials is only 1/2~1/3 of that of ordinary steel materials. This feature of density makes the bearing weight less, and the bearing can inhibit the rolling caused by the centrifugal force when it rotates at idle speed. Increase in body load: 1.4 elastic model The engineering ceramics have a much higher elastic modulus than metal, about 1.5 times that of bearing steel, so the relative elastic deformation of the load is small, and the relative rigidity of the load is high. If the ceramic bearing is used for the machine tool In the spindle, the high rigidity is a very important characteristic: 1.5 corrosion resistance, non-magnetic, insulating chemical, food, marine and other departments of the machine, the corrosion of steel bearings is a big problem, such as: railway vehicle traction motor The use of bearing steel bearings will produce electrical erosion, in the magnetic environment using steel bearings, the micro-powder wear from the bearing itself is adsorbed between the rolling body and the roller surface, will become the bearing peeling damage and increased noise The main reason is that all-ceramic bearings made of engineered ceramics can work in these environments due to their corrosion resistance, non-magnetic properties, and insulation properties. Conventional applications include: water, acid, and alkali media (for example, the performance of various common ball bearing materials is shown in Table 1. Medical and pharmaceutical equipment, printing and dyeing, and fishery equipment, etc. In these areas, the performance material density linear expansion coefficient elastic modulus M dimension Hardness strength Fracture toughness Thermal conductivity Resistivity Polyaldehyde Plastic bearing steel Stainless steel used to be plastic or unheated stainless steel bearings, such as polyamide cages, glass or stainless steel balls. However, plastic or stainless steel bearings have certain weaknesses. That is, they can only be used in low temperature, low load situations, while ceramic bearings can withstand higher loads than expected, and ceramic bearings will play an irreplaceable role under special conditions. Ball bearings made of bearing steel are still widely used today, and they still have certain advantages when used without special requirements.
3 Manufacturing of Ceramic Bearings The manufacturing process of ceramic bearings is: raw material mixing, forming one, sintering one, roughing one, finishing one, inspecting one, assembling one, finishing one, producing ceramic bearing parts, and making blanks, regardless of the use of any ceramic materials. To manufacture bearings, it is necessary to add a certain amount of other materials as sintering aids in the base member to change the shape of the crystal grains to generate a microstructure that has a significant effect on the mechanical properties of the materials.
There are many sintering methods for ceramic bearing-related ceramic components, such as reaction sintering, hot-pressing sintering, gas pressure sintering, and secondary reaction sintering, and it is desirable to use hot isostatic pressing in order to obtain a completely dense blank material.
The process is: in the preparation process, the required ceramic powder and the sintering aid are first mixed and formulated into a raw material powder in a certain proportion. The powder is put into a mold according to a required amount, is isostatically pressed, and then is formed. The green body is filled with graphite crucibles and sintered under a certain temperature regime to achieve full densification. 3.2 Processing of ceramic bearing components 3.2.1 Processing of bearing inner and outer rings Bearing inner and outer ring Machining, such as surface and channel grinding, is generally done with resin bonded diamond wheels. The coarse grinding generally has a large grain size, and the fine grinding generally has a small grain size. In the channel grinding, a grinding wheel with a certain radius is used for forming grinding. During the grinding process, a large amount of material is removed during rough grinding, and then the precision grinding is performed by micro-feeding to achieve the required accuracy. Because the grinding precision is very high, the diamond grinding wheel needs to be repaired in a relatively short period of time. 3.2.2 Ceramic Balls The processed ceramic ball and the bearing steel ball are basically similar in terms of grinding principle. Generally, they must be rough ground and Lapping and other processes. A batch of ceramic balls from the installation to the end of the lapping process is generally divided into three stages.
The first stage is the rough grinding stage. At this point, the abrasive grain size is relatively coarse, and the abrasive material performs the functions of cutting, scraping, squeezing, and peeling on the surface of the ceramic ball, and continuously removes the amount of ball abrasion of the ceramic to change the dimensional accuracy and spherical precision of the ball. The second stage is the finishing stage. The abrasive grain size used in this stage is small. The dimensional precision, spherical precision, and surface defects after lapping generally meet the technical requirements that are close to the finished product. The third stage is the superfinishing stage. The abrasive grain size used in this stage is smaller than the abrasive grain size used in Pan 2nd stage. The abrasive grains in the liquid film between the ceramic ball and the grinding disc groove have very little grinding ability, making the ceramic ball surface roughness and The waviness is gradually improved until it reaches the finished product requirements: 3.2.3 Assembly of ceramic bearings As we all know, the general bearing is composed of four main components, namely the outer ring, the inner ring, the rolling elements and the cage. The choice of cage material depends on the operating conditions (ie speed, temperature, load, corrosiveness of the surrounding liquid or lubricating oil, etc.). Bearing assembly can basically be completed in 2 steps. The first step is to combine the inner ring, outer ring and a set of ceramic balls to ensure a certain cooperation relationship between them, such as to ensure that the bearing should have a certain radial travel The gap value or the nominal width of a certain tolerance value; the second step is to rivet the cage. Ensure that the ceramic ball is fixed in the bearing ring so that it can be rotated flexibly without scattering, so as to facilitate the installation and use of the ball bearing in various machines. Due to the large number of ball bearings, different types of bearings use cages. The form varies, so the bearing assembly method is not the same.
4 Nondestructive testing technology of ceramic bearing components The production process of ceramic bearing components determines that it is more prone to occasional surface material defects than steel bearing components. The surface defect may be a problem of the material itself, or it may be generated during the grinding process. Therefore, to ensure the quality of the finished product, it is necessary to adopt different detection means and detection methods according to the size and use of the component.
4.1 Ultrasonic Detection Technology The defect detection of ultrasonic components is the use of the material's discontinuous surface to reflect the nature of the ultrasonic waves. During flaw detection, surface waves (Rayleigh waves) and transverse wave angle flaw detection probes are used from the vertices of the parts to be measured. After the offset compensation is fixed, since the speed of sound is determined by the density and elastic constant, the speed of sound of the transverse wave and the speed of sound of the surface wave should be calculated according to the values ​​provided by the ceramic manufacturer. The surface flaws should be detected by the surface wave. Transverse waves detect internal defects.
4.2 Fluorescent coloration detection Although the operation of fluorescence staining penetrating technology is simple, it is very effective for inspecting the surface defects of ceramic parts. Through careful operation and special inspection methods, it can detect very small, visually undetectable cracks.
4.3 Optical Microscopy Inspection of bearing components using standard brightfield or darkfield luminance techniques can be used as a supplement to fluorescent coloration inspections. Because of the relatively low magnification of oblique illumination, it is easy to distinguish between large-particle impurities and post-combination fracturing defects. In addition, due to the small surface roughness of the lapping, other conditions of the material quality can be observed using a high magnification microscope.
5 Ceramic bearing materials with broad prospects As can be seen from the above table, the most promising material is silicon nitride, but zirconia, alumina, etc. are also worth noting, especially the density, linear expansion coefficient, elasticity of zirconia materials. Modulus, Poisson's ratio, etc., are basically similar to those of bearing steels and stainless steels, and their hardness is nearly double that of bearing steels, and they have good wear resistance. Therefore, it is more suitable to manufacture balls for mixed ceramic bearings (ie ceramic balls and Steel inner and outer ring assembly bearings). In addition, from the cost point of view, the price is 15%~52% cheaper than silicon nitride. Therefore, when using ceramic materials to manufacture bearings, they should be selected according to their structure and application.
Because ceramic materials are inexhaustible on the earth, they have low density, low friction coefficient, high hardness, high temperature resistance, strong corrosion resistance, moderate impact toughness, and high fatigue life under low and medium contact stress. Therefore, in the high-precision, high-speed, vacuum, low friction torque, strong wear state of the bearing, select the ceramic material is the best, especially in high temperature, strong acid, strong alkali, magnetic, no oil lubrication and other special circumstances It has an irreplaceable role.
Therefore, with the needs of social progress and the rapid development of science and technology, the diversification of the environment and conditions for the use of bearings makes ceramic bearings have a wide range of use and market prospects.
Sodium Tert-Butoxide Chemical Information
Density 1,104 g/cm3
Boiling Point 180°C/1mmHg
Melting Point 180 °C
Molecular Formula C4H9NaO
Molecular Weight 96.103
Flash Point 12°C
Storage condition Flammables area
Water Solubility reacts
Sodium tert-butoxide Structure
Sodium Tert-butoxide Application
1. Used as an intermediate for organic synthesis and Pharmaceutical Intermediates
2. As a strong base, it is widely used in the condensation, rearrangement and ring opening reactions in organic synthesis such as chemical, pharmaceutical and pesticide.
Sodium Tert-butoxide CAS No.865-48-5
Sodium Tert-Butoxide,Sodium Tert Butoxide Cas No,Sodium Tert Butoxide Synthesis,Sodium Tert-Butoxide Mechanism
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