As one of the modern engineering ceramics, SiC ceramics is a new synthetic inorganic non-metallic material. Hardness is second only to diamond, with excellent chemical corrosion resistance, wear resistance, high temperature resistance, high mechanical strength, good self-lubricating performance, high temperature creep resistance, low friction coefficient, high thermal conductivity and low thermal expansion coefficient. Used in petroleum, metallurgy, chemical, machinery, aviation, aerospace and other fields, commonly used as mechanical friction sealing materials. A large number of tests have shown that silicon carbide is the most excellent material in the current friction pair, especially the performance of pressureless sintered SiC and hot pressed sintered SiC.

At present, the main performance indicators of domestically produced pressureless sintered SsiC are close to the level of similar foreign products. Although the performance of hot-pressed sintered SiC is optimal, it is expensive to manufacture and has not been widely used. Utilizing the excellent properties of SiC, it is widely used in the field of shielded electric pumps and magnetic pumps. Dalian Sifang Electric Pump has been conducting research and development of all-silicon carbide ceramic friction pair since 2001. The bearing, bearing sleeve and thrust disc are made of pressureless sintered SSiC material. Since 2002, it has been applied to products and achieved good results. At the beginning of 2003, based on the original results, improvements were made:

1. Improve the bearing sleeve torque transmission structure, solve the stress concentration caused by the end of the bearing sleeve, and improve the reliability.

2. An elastic automatic compensation sleeve is added, which can automatically compensate for the difference in material expansion caused by the temperature rise in the radial direction, so that the pump can operate normally in the temperature range of 0 °C ~ 250 °C.

3. Unique thrust disc structure, more reliable.

When silicon carbide is used as a shielded electric pump bearing, it needs to be solved due to its characteristics of small thermal expansion coefficient, brittle material, and easy cracking.

The thermal expansion coefficient of silicon carbide is 1/4 of that of stainless steel. When the temperature of the medium is high, it will cause gap or interference with the stainless steel parts. The fracture toughness is 1/50 of stainless steel, and the material is brittle and impacted. It is easy to break when the force acts, especially in the corners.

The modulus of elasticity is 1/50 of that of stainless steel, which is mechanically brittle and easily broken. The coefficient of thermal expansion is 1/4 of that of stainless steel, and care should be taken when it is combined with (stainless steel).

Structural problems

If a pump with a diameter of d = 50 (mm) is used on a pump with a liquid temperature of 100 (°C), the following problem will occur: the clearance between the sleeve and the rotor shaft will reach 0.052 mm, ie the sleeve and rotor shaft The gap between them is 0.052 mm smaller than that at normal temperature (20 ° C). To obtain the gap at normal temperature, the gap between the sleeve and the rotor shaft becomes large. Therefore, when the temperature is running, the sleeve is easily broken, and when it is used for the high temperature liquid, it is more likely to malfunction.

Dalian Sifang Electric Pump Co., Ltd. has solved the stress concentration caused by the end of the bearing sleeve through continuous improvement and improvement, improved the reliability, and added an elastic automatic compensation sleeve, which can automatically compensate the difference of the material expansion due to the temperature rise due to the temperature rise. The silicon carbide bearing has been successfully applied on the shielded electric pump, and the pump can operate normally in the temperature range of 0 °C to 250 °C. Silicon carbide bearings are used in our company's basic PB, reverse cycle PBN, water cooled high temperature PBG, mud type PBLK, self-priming PBZ, thermal insulation PBB, high power vertical PBGL, small flow PBX and other shielded electric pump products. The actual application has been fully realized. The power consumption is between 0.75 and 75 KW, and the temperature range is from 0 °C to 250 °C. The main application conditions are:

a. requires a long life,

b. The medium is extremely chemically corrosive,

c. Low density, easy to vaporize the medium,

d. high temperature,

e. There are traces of fine soft particles in the medium.

f. The medium is not allowed to be mixed with the powder worn by the friction pair, such as the pure water industry, or the working condition with high purity requirements.

Characteristics of SiC bearings developed by Dalian Sifang Electric Pump Co., Ltd .:

1. The bearing adopts pressureless sintered crystal SiC, grade: SSiC, purity: ≥99.5%.

2. The unique structure can automatically compensate for the difference in material expansion caused by the temperature rise in the radial direction, so that the pump can operate normally in the temperature range of 0 °C ~ 250 °C.

3. The service life is more than 10 times that of ordinary graphite bearings.