The performance evaluation of ceramic materials mainly includes four aspects, namely mechanical properties, thermal properties, chemical properties and electrical properties. For structural ceramics applied to ceramic shafts, the most important thing is to consider their good mechanical and thermal properties, including strength, hardness, elastic modulus, initial fracture, friction and wear, thermal conductivity, coefficient of thermal expansion, etc. In addition, it also includes performance indicators such as density, heat resistance, thermal shock resistance, fatigue, oxidation resistance, and processability. The table shows the basic performance data comparison of common engineering ceramic materials and steel.
At high speeds, the centrifugal load of the ceramic shaft is reduced, making it possible to work at higher speeds.
It can effectively improve the static and dynamic characteristics of the ceramic shaft system and is conducive to the rapid start, stops and the rapid rise of the shaft.
The larger the elastic modulus of the ceramic material, the stronger the resistance to deformation, which can improve the dynamic stiffness of the ceramic shaft system. But too high elastic modulus will reduce the bearing capacity of ceramic shafts due to the stress concentration of rolling contact points.
The lower thermal expansion coefficient can reduce the sensitivity of the ceramic shaft to temperature changes, thereby greatly improving the working accuracy of the ceramic shaft system.
High bending strength can reduce the bending deformation of the main ceramic shaft, which can effectively improve the static and dynamic characteristics and dynamic stiffness of the main ceramic shaft system. High compressive strength is required for rolling bearings to withstand high stress.
The combination of these two characteristics can obtain better surface roughness and has high abrasion resistance, can prevent damage from external particles and impact. So the ceramic shaft can resist a certain impact load.
During the high-speed operation of the ceramic shaft, this characteristic can quickly dissipate heat.
The biggest difference between the ceramic material preparation process and the metal material preparation process is that the ceramic material is made of the powder raw material which is directly sintered after being pressed and formed.
The properties of the powder, the preparation process, and the molding process have a huge impact on the formation and development of the microstructure during sintering. Therefore, the quality of the microstructure of ceramic materials not only affects the performance of the material itself, but also directly affects the performance of the ceramic shaft for pump, and this effect cannot be improved by subsequent heat treatment processes like metal materials.
In addition, the hard, brittle, and difficult-to-deform characteristics of ceramic materials make the performance of ceramic materials more sensitive to microstructures, especially defects, than metal materials. Therefore, the preparation process of ceramic materials is even more important.
The blank preparation first requires a reasonable formula according to the properties of the structural ceramic material to be prepared, and the materials selection, batching, mixing, granulation and other processes are performed according to the formula requirements. Among them, the ingredients are the most basic part of the ceramic material preparation process and must be accurately proportioned according to the formula.
Dry pressing and isostatic pressing are the two most common forming methods
Dry pressing is suitable for simple shapes, such as large blocks and discs with large cross-sectional areas but small heights. It is not suitable for large rods and other complex shapes. The forming efficiency of dry pressing is very high.
The isostatic pressing method can make up for the shortcomings of dry pressing. It can greatly reduce the uneven stress distribution and density caused by the friction between the mold wall and the powder, and improve the quality of the molded voxels. Its principle is that the ceramic powder is sealed in a rubber mold, and the liquid is used as a pressure transmission medium in a high-pressure container so that the pressure is evenly compressed, and the obtained survival density is high and the uniformity is good. But the efficiency is lower and the cost is higher.
Zirconia and alumina ceramic shafts are generally formed by isostatic pressing or dry pressing. The finished product after the porcelain has the advantages of high toughness, high bending strength and high wear resistance, excellent heat insulation properties, etc. The ceramic shafts are gradually replacing the work of traditional metal shafts.
Ceramic shafts have the following advantages:
1. Due to the strong corrosion resistance of zirconia and alumina ceramics, ceramic shafts are suitable for operation in seawater and some severe corrosive conditions.
2. Because the density of zirconia and alumina ceramic shafts is lower than steel, and the weight is much lighter, the centrifugal effect of the outer ring can be reduced by 50% at high speed, and the service life is greatly extended.
3. The zirconia and alumina ceramic axis expansion coefficient is very low, so when the shaft clearance is constant, the ceramic shaft for pump can be allowed to work in an environment where the temperature difference changes sharply.
4. Zirconia and alumina ceramic shafts have hardness close to that of tungsten steel, which is a highly wear-resistant material. Therefore, zirconia and alumina ceramic shafts' high-speed wear is extremely low, and the service life is more than 10 times that of traditional metal steel shafts. If applied ceramic shafts in the field of reciprocating plungers, the speed of reciprocating motion can be achieved more than 300 times/minute.
5. Since the elastic modulus of ceramic is higher than that of steel, it is not easy to deform when subjected to force. Therefore, this character is conducive to improving the making speed of the ceramic shaft and achieving higher accuracy.
In general, the performance and price ratio of ceramic shafts are much better than all-steel shafts, which can save a lot of downtime and maintenance time, reduce scrap rates, and reduce stock shaft spare parts.
ceramic materials are typically hard and brittle materials. At the same time, ceramic materials are extremely sensitive to defects, and even tiny surface flaws (scratches or gaps) or internal flaws (stomatal, microcracks or inclusions) can cause sudden damage, which is also the fatal weakness of ceramic materials.
Because the physical and mechanical properties of ceramic materials, especially the initial strength are very different from those of metal materials, the material removal mechanism is also very different from that of metals. And the machinability of ceramic material is poor, so it is difficult or impossible for ceramic materials to use ordinary processing.
Although advances in ceramic molding and sintering technology have improved the accuracy of ceramic products, when ceramics are used as structural materials (especially mechanical structures), ceramics must be processed to improve the accuracy of size and shape.
Mechanical grinding is currently the most commonly used method of engineering ceramics processing. This processing method requires expensive diamond grinding wheels and high-rigidity grinding machines. It has high processing costs and low efficiency, and there is a strong force between the grinding wheel and the workpiece during grinding. It is easy to cause micro-cracks on the surface of the workpiece and reduce the service life of the part.
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