Application of SiC Bearing

As one of the modern engineering ceramics, SiC ceramic is a new artificial kind of inorganicnonmetallic materials. Its hardness is next only to diamond. It has variety of characteristics, such as good chemical corrosion resistance, abrasion resistance, high temperature resistance, high mechanical strength, excellent self-lubricating, anti-creep under high temperature, low friction coefficient, high thermal conductivity, and low thermal expansion coefficient. It can be widely used in petroleum, metallurgy, chemical, machinery, aviation, and aerospace fields. It usually be used as material of friction pairs. A lot of experiments show that SiC is the most excellent material for friction pair, especially Pressureless SSiC and hot sintering SiC.

Currently, the main performance indicators of Pressureless SSiC produced domestically has beenclose to the level of similar foreign products. Although the hot pressing sintering SiC has the best performance, the cost of manufacture is very high. Thus, it has not yet been applied totally. Due to the excellent characteristics of SiC, it has been applied in the shielded electric pump and magnetic pump fields. From 2001, Dalian Sifang electric pump Co. started to do research and development of SiC friction pairs. Bearing, bearing sleeve and thrust plate are made of Pressureless SSiC. From 2002, it has been applied in products and the company achieved good results. At the beginning of 2003, based on the original results, the improvements were carried out:

1.Improve the torsion structure of bearing sets, solve the stress concentration caused by theopening of the bearing sets and increase the reliability.

2.Add an elastic automatic compensation sleeve, have the ability to automatically compensate the material expansion difference caused by temperature rise, and make pump operate normallywithin the temperature range of 0℃-250℃.

3.Unique thrust collar structure makes it more reliable.

As a shielded electric pump bearing, the problems of SiC, such as thermal expansion coefficient is small, material is more brittle, and it` s easy to be broken, need to be solved.

The thermal expansion coefficient of SiC is 1/4 of stainless steel, when the medium temperature is higher, and its stainless steel parts to produce a gap or interference and lead to bearing damage;its fracture toughness is 1/50 of stainless steel, the material is brittle, and it is easy to be broken subjected to impact force, especially the edges and corners.

The elastic coefficient of SIC is the 1/50 of stainless steel, the mechanical property is more fragile,and easily damaged. The thermal expansion coefficient is the 1/4 of the stainless steel, which should be paid attention to when combined with stainless steel.

Problems of structure

If a rotor shaft (made of stainless steel) with diameter of 50mm is applied in the pump of liquid temperature of 100℃, it will have the following problems: the gap between shaft sleeve and rotor shaft will reach 0.052mm,that is, the gap will be decreased by 0.052mm compared at room temperature (20℃). To obtain the gap at room temperature, the gap between shaft sleeve and rotor shaft needs to be largen. Thus, shaft sleeve is easy to be damaged when it operates at room temperature, and more prone to be broken if it is used in high temperature.

Through continuous improvements, the stress concentration caused by the opening of the bearingsets has been solved, the reliability has been increased, an elastic automatic compensation sleeve has been added and the material expansion difference caused by temperature rise has beenautomatically compensated. All of these make SiC bearing be successfully applied in the shieldedelectric pump and make pump operate normally in the temperature range of 0℃-250℃. SiC bearing has been completely applied in shielded electric pump, such as basic type PB, reverse cycle type PBN, water cooled high temperature type PBG, slurry type PBLK, self-priming type PBZ ,insulation type PBB, high power type PBGL and little capacity type PBX. Its use power is within the range of 0.75-75Kw, and the temperature is within the range of 0℃-250℃. The main application conditions include: a. its useful life should be longer; b. medium should have strong chemical corrosion; c. medium should have low density and be easy to be vaporized; d. high temperature; e. there are traces of fine and soft particles in medium; f. there is not mixed with power from friction pairs wear, such as pure water industry and working conditions with high purity requirements.

Characteristics of SiC bearing:

1.Bearing is made of Pressureless SiC crystal, name: SSiC, purity: ≥99.5%.

2.With unique structure, it can automatically compensate the differences of material expansioncaused by increase in temperature and make pump normally operate in the temperature range of 0℃-250℃.

3.Its useful life is 10 times more than the ordinary graphite bearing.

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