Silicon carbide ceramics, as one of the modern engineering ceramics, is a new type of artificially synthesized inorganic non-metallic material. The hardness is second only to diamond. It has excellent chemical corrosion resistance, wear resistance, high temperature resistance, high mechanical strength, good self-lubricating performance, high temperature creep resistance, small friction coefficient, high thermal conductivity coefficient, low thermal expansion coefficient, etc. It can be widely used It is used in petroleum, metallurgy, chemical industry, machinery, aviation, aerospace atomic energy and other fields, and is often used as friction material for mechanical seals. A large number of tests have shown that silicon carbide is currently the best material for friction pairs, especially pressureless sintered SiC and hot-pressed sintered SiC with the best performance.
At present, the main performance indicators of domestically produced pressureless sintered SiC are close to the level of similar foreign products. Although hot-pressed sintered SiC has the best performance, its manufacturing cost is expensive and it has not yet been widely used. Taking advantage of the excellent characteristics of SiC, it is widely used in the fields of canned electric pumps and magnetic pumps. Dalian Sifang Electric Pump has been researching and developing full silicon carbide ceramic friction pairs since 2001. The bearings, bearing sleeves and thrust plates are all made of pressureless sintered SiC materials. It has been applied to products since 2002 and has achieved good results. In early 2003, based on the original results, improvements were made:
1. The torque transmission structure of the bearing sleeve was improved to solve the stress concentration caused by the end opening of the bearing sleeve and improve reliability.
2. An elastic automatic compensation sleeve is added, which can automatically compensate for the radial material expansion difference caused by temperature rise, so that the pump can operate normally within the temperature range of 0°C to 250°C.
3. Unique thrust plate structure, more reliable.
When silicon carbide is used as a canned electric pump bearing, problems caused by its small thermal expansion coefficient, brittle material, and easy rupture need to be solved.
The thermal expansion coefficient of silicon carbide is 1/4 that of stainless steel. When the temperature of the medium is high, gaps or interference will occur with the stainless steel parts that match it, causing bearing damage; the fracture toughness is 1/50 that of stainless steel, and the material is brittle and susceptible to impact. It is easy to break when force is applied, especially at edges and corners.
The elastic coefficient is 1/50 of stainless steel, which is mechanically brittle and easy to break. The thermal expansion coefficient is 1/4 of stainless steel, so care should be taken when matching it (stainless steel).
Structural problems
If a rotor shaft (stainless steel) with a diameter of d=50 (mm) is used on a pump with a liquid temperature of 100 (℃), the following problems will occur: the gap between the sleeve and the rotor shaft will reach 0.052mm, that is, the sleeve and the rotor shaft The gap between them is 0.052mm smaller than that at normal temperature (20°C). To obtain the clearance at normal temperature, the gap between the sleeve and the rotor shaft becomes larger. Therefore, the bushing is easily damaged when running at room temperature, and it is more likely to malfunction when used with high-temperature fluid.
Through continuous improvement and perfection, Dalian Sifang Electric Pump Co., Ltd. has solved the stress concentration caused by the end opening of the bearing sleeve, improved reliability, and added an elastic automatic compensation sleeve, which can automatically compensate for the radial material expansion difference caused by temperature rise. , silicon carbide bearings have been successfully used in canned electric pumps, and the pumps can operate normally within the temperature range of 0°C to 250°C. Silicon carbide bearings are used in our company's basic PB, reverse circulation PBN, water-cooled high-temperature PBG, slurry PBLK, self-priming PBZ, thermal insulation PBB, high-power vertical PBGL, small flow PBX and other canned electric pump products. Has been fully applied in practical applications. The operating power is 0.75~75KW, and the temperature range is 0℃~250℃. The main application conditions are:
a. Long life is required;
b. The medium is highly chemically corrosive;
c. The medium has low density and is easy to vaporize;
d. The temperature is high;
e. There are trace amounts of small soft particles in the medium;
f. The medium does not allow powder from the friction pair to be mixed in, such as the pure water industry, or working conditions with high purity requirements, etc.
Features of SiC bearings developed by Dalian Sifang Electric Pump Co., Ltd.:
1. The bearings are made of pressureless sintered crystalline SiC, brand: SiC, purity: ≥99.5%.
2. The unique structure can automatically compensate for the radial material expansion difference caused by temperature rise, allowing the pump to operate normally within the temperature range of 0°C to 250°C.
3. The service life is more than 10 times that of ordinary graphite bearings.
