Abstract: This article introduces the structural characteristics of SA type circulating pump, analyzes the reasons for oil leakage in the pump bearing shell, and proposes technical solutions.
Keywords: circulation pump; Bearing shell; Oil leakage; analysis; handle
Henan Provincial Gas Group Co., Ltd. Yima Gasification Plant is equipped with 8 sets of 28SA-10J circulating water pumps for the circulating water system. Since its installation and use, the pump has been plagued by oil leakage and seepage issues, resulting in oil stains on the equipment foundation and surrounding ground. This not only increases the consumption of lubricating oil, but also poses a hidden danger of bearing burnout, pollutes the environment, and increases the workload of on-site operators. It has been a problem that has plagued the lubrication work of workshop equipment for more than a decade.
1. Introduction to 28SA-10J circulating water pump
Structural type: SA type pump is a single-stage, double suction horizontal open centrifugal pump. The pump is installed horizontally, and the pump casing is horizontally separated from the axis line. The upper part is the pump cover, and the lower part is the pump body. The suction and discharge ports are both located on the pump body below the pump axis, and the center line is perpendicular to the axis line. During maintenance, the pump cover can be removed and the rotor components can be taken out without disassembling the inlet and outlet pipelines. The pump shaft seal adopts soft packing sealing, and the bearing oil seals at both ends adopt labyrinth sealing. Pump parameters: flow rate 3600m3/h, head 52m, speed 742r/m, shaft power 555kW, mass 5800kg, manufactured in September 1998.
2. Analysis and Handling of Fault Causes
From the structure of the pump bearing shell, it can be seen that the areas of oil leakage are: first, the static seal of the bearing shell end cover is leaking oil; second, the dynamic seal of the oil tank oil seal is leaking oil; third, the connection pipe joint between the oil tank and the oil cup is leaking oil. The structure of the bearing shell is shown in Figure 1.
1. Upper bearing end cover 2. Dynamic ring fixing screw 3. Pump shaft 4. Dynamic ring A 5. Lower bearing end cover 6. End cover bolt 7. Sealing gasket 8. Bearing 9. Bearing seat 10. Adjusting washer 11. Oil slinger 12. Moving ring B 13. Shaft sleeve 14. Bearing shell cover 15. Observation hole cover plate
Figure 1 Structural diagram of bearing shell
2.1 Analysis and Treatment of Oil Leakage Causes of Bearing Shell End Cover
The bearing end cover and bearing housing are sealed with a flat seal using an oil resistant rubber asbestos gasket. This sealing material will seep out after being soaked in mechanical lubricating oil for a long time, accumulating and flowing onto the equipment foundation, causing pollution and waste.
Using PTFE board instead of oil resistant rubber asbestos as a sealing gasket can solve the problem of oil leakage in this static seal. Teflon plate is a new type of sealing material. The material of Teflon plate is polytetrafluoroethylene. It has good mechanical strength, corrosion resistance, aging resistance and non-conductive properties between -100 and 100 ℃. It has good pressure resistance. Z can withstand 10MPa pressure. Although PTFE plates have many good properties, they are not resistant to high temperatures, and the temperature of the circulating pump bearing shell generally does not exceed 80 ℃, which can meet the requirements when used here. During installation, apply 704 sealant on both sides of the PTFE pad and evenly press it together with the bearing end cover, which can achieve very satisfactory results. After long-term operation, the oil leakage at this sealing point has been completely eliminated after the modification.
2.2 Analysis and Treatment of Oil Leakage Causes of Fuel Tank Shaft Seal Dynamic Seal
From the structural diagram of the SA type pump bearing shell, it can be seen that the bearing oil seal of the pump is a simple labyrinth seal composed of a dynamic ring fixed on the pump shaft and a static ring integrated with the bearing end cover. Due to the fact that the dynamic ring is directly fitted onto the pump shaft, there is no gap between the two that is relatively stationary when sealed with sealing material. When the equipment is running, the lubricating oil splashed onto the bearings by the oil slinging ring to provide lubrication conditions. Part of the lubricating oil on the journal surface flows back to the oil tank, while the other part leaks out of the oil tank through the gap between the dynamic ring of the labyrinth seal and the pump shaft. The treatment of this leakage point can be solved using 704 sealant, which is to apply a sealing ring at the joint between the dynamic ring of the labyrinth seal and the pump shaft. When applying sealant, rotate the rotor of the pump while applying the sealant, forming a triangular cross-section with a right angle of 3-5mm. Be careful not to leak the sealant into the flow gap and expansion cavity of the labyrinth seal to avoid affecting the sealing effect. To ensure this, keep the pump rotor rotating during the process of applying sealant until the 704 sealant solidifies. If any sealant flows into the bearing shell or intercepts the gap and expansion cavity, it must be cleaned thoroughly.
Another leakage point is the leakage between the dynamic and static rings of the labyrinth seal, mainly caused by the inappropriate flow gap and expansion cavity gap between the dynamic and static rings. During installation, pay attention to adjusting the position of the dynamic ring and tightening the top screw. When adjusting, use the three-point positioning method to level the outer machining plane of the labyrinth seal static ring of the bearing shell as the reference, and level the outer end face of the moving ring with it, with an error not exceeding 0.3mm. At this point, apply an appropriate amount of 704 sealant to the top screw hole of the moving ring and tighten the top screw to ensure that the lubricating oil does not leak out while positioning. Apply an appropriate amount of 704 sealant around the intersection gap between the outer side of the moving ring and the pump shaft, then use a 4F tape to roll a 1mm diameter rope around the gap and embed it into the previously applied 704 sealant for 3 weeks. Use a straight screwdriver to trim it to form a right angled triangular sealing ring, ensuring that lubricating oil does not leak between the moving ring and the pump shaft.
Maze seal is a non-contact seal with no solid phase friction, low power consumption, easy maintenance, and long service life. It is suitable for high temperature, high pressure, high speed, and large-sized sealing conditions. However, labyrinth seal has the characteristic of large leakage. Increasing the number of labyrinth stages or using suction assisted sealing methods can reduce the leakage, but it is difficult to achieve complete non leakage. Due to the fixed structure of the SA type circulating pump (model 28SA-10J) currently used in our factory, increasing the number of labyrinth stages, using suction assisted sealing, or replacing it with a skeleton rubber oil seal to reduce leakage would incur high renovation costs, with each unit costing tens of thousands of yuan, which is not economically feasible. After long-term observation and research, it has been found that the leakage of labyrinth seals is related to the level of lubricating oil. The higher the oil level in the bearing shell, the greater the amount of lubricating oil thrown up by the rotating oil slinger. The lubricating oil flowing down the inner wall of the bearing shell flows out along the flow gap between the dynamic and static rings of the labyrinth seal, causing lubricating oil leakage. To achieve this goal, it is crucial to lower the level of lubricating oil in the bearing shell to ensure good bearing lubrication and minimize leakage. To achieve this, it is necessary to visually observe the amount of oil spilled in the bearing shell. Therefore, the metal cover plate of the observation hole on the oil tank was replaced with a transparent organic glass plate with a thickness of 4mm, and 704 sealant was applied to the observation hole, so that the oil spill situation in the bearing shell can be observed at any time. During the test drive, adjust the height of the intelligent oil cup while ensuring that the oil slinger is functioning properly. Observe and adjust until the labyrinth seal no longer leaks or leaks slightly.
2.3 Analysis and Treatment of Leakage Causes in Oil Pipe Connections
The connection from the bearing housing to the oil cup is through joints and oil pipes, with a total of 5 static sealing points. If not handled properly, oil leakage may occur. The connection between the oil pipe joint, bearing shell, and oil cup is a threaded connection. In the past, 4F tape was wrapped around the external thread of the joint and directly screwed into the corresponding threaded hole. Once the threaded connection is not handled properly, oil leakage will occur. To solve this problem, first apply 704 sealant on the external thread of the joint, then wrap it with 4F tape, apply 704 sealant on the corresponding internal thread hole, and tighten the threaded joint. The joint is connected to the rubber oil pipe, and replacing the socket joint with a sleeve joint connection can avoid the occurrence of oil leakage caused by the softening of the connection due to temperature rise when using socket connection for polyethylene transparent plastic pipes.
3. Conclusion
By accurately selecting existing new materials, parts, and changing installation techniques, the problem of long-term oil leakage in SA type circulating pump bearings has been effectively eliminated with minimal investment. The circulating water pump can achieve automatic oil supply without oil leakage at each static sealing point, and the labyrinth seal without leakage or slight leakage. Cleaning once per shift can ensure the cleanliness of the equipment environment. The oil slinger can be directly seen from the observation window, ensuring the reliability of the equipment lubrication system and keeping the production environment clean on site. Not only does it reduce the consumption of lubricating oil, but it also reduces the labor intensity of operators. It is easy to observe the lubrication status of bearings during equipment inspection, thereby reducing the difficulty of inspection technology and eliminating the safety hazards of bearing burnout caused by oil leakage and untimely oil replenishment.
2024 September 4th Week VAFEM Product Recommendation:
A linear-motion bearing or linear slide is a bearing designed to provide free motion in one direction. There are many different types of linear motion bearings. Motorized linear slides such as machine slides, X-Y tables, roller tables and some dovetail slides are bearings moved by drive mechanisms. Not all linear slides are motorized, and non-motorized dovetail slides, ball bearing slides and roller slides provide low-friction linear movement for equipment powered by inertia or by hand. All linear slides provide linear motion based on bearings, whether they are ball bearings, dovetail bearings, linear roller bearings, magnetic or fluid bearings. X-Y tables, linear stages, machine slides and other advanced slides use linear motion bearings to provide movement along both X and Y multiple axis.
2024-09-29