The dynamic and static pressure combined lubrication bearing with double arc surface rocker is used to replace the dynamic pressure bearing with frequent Bush burning.
Abstract: dynamic pressure bearings are used in DTM287/ 470 steel ball mills of 50 MW unit boilers in Jiangyou Power Plant. Due to the aging of the equipment, the tile burning accidents are frequent, which seriously affects the safe operation of the boiler. After transforming the dynamic pressure bearing into the dynamic and static pressure bearing with good centering performance, the problem has been solved, the high failure rate of the steel ball coal mill has been reversed, and the safe and economic operation has been achieved.
Key words: steel ball mill; Dynamic pressure bearing; Dynamic and static pressure bearing
Jiangyou Power Plant 4 × 50MW high-pressure units were put into operation successively in the middle and late 1960s. Among them, three boilers (No. 3 boiler, No. 4 boiler and No. 6 boiler) adopt intermediate storage type pulverizing system, each boiler is equipped with two sets of pulverizing systems, and two DTM287/ 470 steel ball mills are equipped. The output of each unit is 16 t/ h, and its bearings adopt dynamic pressure bearings with 180 ° wrap angle.
Due to the extended service of the boiler, serious aging of the equipment and frequent bearing bush burning accidents of the ball mill, the safe and full power generation of the unit is seriously restricted. Especially around 1993, two steel ball coal mills had bearing bush burning accidents at the same time, which was difficult to repair, and the safety production of the whole plant was faced with a severe test.
1 Reasons for frequent bearing bush burning of steel ball mill
The DTM287/ 470 steel ball mill of No. 3 boiler, No. 4 boiler and No. 6 boiler in Jiangyou Power Plant adopts the dynamic pressure bearing with 180 ° wrap angle, and the lubricating oil film can be established only after it is operated by the journal. Therefore, there are high requirements for the smoothness and concentricity of the Journal at both ends of the cylinder, and at least two contact points per square centimeter between the bearing bush and the journal. At the same time, the bearing bush is required to have certain centering performance, Otherwise, the lubricating oil film is difficult to establish or easily damaged. It can be seen that the requirements of the hydrodynamic lubrication sliding bearing are relatively harsh.
Due to the aging of the overdue equipment, the cylinder of No. 3 boiler steel ball pulverizer and the end covers of No. 4 and No. 6 boiler steel ball pulverizers have been cracked for many times, which has greatly damaged the concentricity of the two shaft journals matching the two ends of the cylinder and the bearing. Due to the limitation of site conditions, it can only be repaired each time, and it is unable to solve the problem that the concentricity of the two journals exceeds the standard. In addition, the back of the bearing bush of the steel ball coal mill is spherical, which has a certain centering ability but is very small. In addition, the joint part between the back of the bearing bush and the bearing seat is exposed in the external environment, which is neither dustproof nor lubricant, resulting in the loss of centering ability of the bearing. Due to the above two reasons, the operating conditions of the bearing have changed, which makes the original dynamic pressure bearing unable to work under the new situation, so the bearing bush burning accidents are frequent.
Since the concentricity of the two shaft journals at both ends of the ball mill cylinder exceeds the standard, it is impossible to solve the problem. At the same time, according to the actual situation of the power plant, it is difficult to replace the key and key components of the ball mill - cylinder, end cover, etc., which requires a huge amount of money. Of course, it is difficult to solve the problem by simply relying on the maintenance of bearings.
2 Discussion on the scheme of eliminating ball mill bearing fault
In view of the above situation, Jiangyou Power Plant actively organized engineers and technicians to conduct comprehensive investigation and investigation, repeatedly demonstrated, and sought a scientific and reasonable scheme to eliminate the frequent Bush burning fault of ball mill bearings. It was agreed that:
1) It is unrealistic to replace the cylinder and end cover of the ball mill.
2) The original dynamic pressure bearing has unreasonable structure and poor centering capacity. Although the capital investment is small, it has high requirements on the concentricity of the two journals and the contact rate of the bearing pads, poor environmental adaptability and low reliability.
3) Shenyang Heavy Machinery Factory designed the 120 degree wrap angle double arc surface rocker type dynamic and static pressure combined lubrication bearing, which has extremely strong centering performance, and is suitable for working under harsh working conditions due to the characteristics that the high-pressure jacking oil system forces the establishment of lubricating oil film when the steel ball pulverizer is not started. The maximum different centrality of the journal at both ends of the cylinder is 2 mm. Moreover, the maintenance and repair workload of the bearing is small, and the grinding of the bearing bush and journal The requirements for scraping accuracy and contact rate are not high. The high-pressure and low-pressure oil systems form a "double insurance", which works stably and reliably. It can skillfully solve the contradiction that can only be solved by replacing the end cover of the ball mill or even the cylinder. It can be used as a solution to eliminate the frequent Bush burning failure of the bearings of the steel ball mills in the above-mentioned extended service.
3 Retrofit scheme of steel ball coal pulverizer dynamic pressure bearing
From 1994 to 1996, on the premise of maintaining the original ball mill dynamic pressure bearing foundation and bearing pedestal foundation bolt hole size, bearing center elevation and bearing bush width, Shenyang Heavy Machinery Factory was entrusted to redesign and manufacture the double arc surface rocker type dynamic and static pressure combined bearing with 120 ° wrap angle and double arc surface (arc surfaces with different radii along the axial and radial directions of the ball mill) with double arc surface (furnace 4, furnace 6 Transformation and replacement of dynamic pressure bearings of ball mills of 3 boiler.
1) Maintain the low-pressure lubricating oil spray system above the journal unchanged, set the jacking lubricating oil channel in the center of the bearing bush, add a high-pressure jacking oil system with an oil pressure of 6 MPa, and set low oil pressure thermal protection in the electrical control circuit to ensure that the coal mill can be started only when the jacking oil system operates and the oil pressure is higher than 4 MPa, and the coal mill trips when the jacking oil pressure is lower than 4 MPa.
2) The original way of cooling the bearing bush tire was changed to directly cooling Babbitt alloy, and the cooling water copper pipe was directly buried in Babbitt alloy to enhance the cooling effect.
3) Set the bearing shell to seal the bearing bush as a whole.
4 Conclusion
After the transformation of the main bearing of the ball mill, the problem of frequently burning the bearing bush was solved. There was no bearing bush burning accident again. All ball mills can operate safely and stably for a long time. After the equipment transformation, the old equipment is rejuvenated, the reliability is greatly improved, and the safe and economic power generation is effectively guaranteed.
It is successful and economical to replace the dynamic pressure bearing with double arc surface rocker type dynamic and static pressure combined lubrication bearing, which is frequently burned due to the poor concentricity of the journal and other reasons. It is worth using for reference in the design and manufacture of new steel ball mills and the transformation of old steel ball mills that have been in service for a long time.
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