Abstract: This paper introduces the concept of sliding bearing friction and wear, and improves the surface structure of the existing sliding bearing to ensure that boundary friction is formed at the initial stage. When the shaft rotates at high speed, the oil supply of the oil pump rapidly enters the liquid friction. The shaft is not in contact with the sliding bearing. The annular oil groove plays a role of cooling, flushing and lubricating, and the generated debris is significantly reduced, extending the service life of the sliding bearing.
Key words: polymer injection centrifugal pump; Sliding bearing; Technical innovation; Field application
1 Overview
There are 4 polymer injection stations and 188 polymer injection pumps in Lamadian Oilfield of No. 6 Oil Production Plant. The top clearance of sliding bearing is greater than 0.3mm, and the side clearance is greater than 0.2mm.
2 Sliding bearing and friction loss analysis
Bearing is a component that supports the journal, sometimes also used to support the rotating parts on the shaft, the rotor of the motor and the rotor of the multi-stage ground pump, etc. According to the friction and nature of the bearing parts, the bearing can be divided into sliding friction bearing (referred to as sliding bearing) and rolling friction bearing (referred to as rolling bearing). Sliding bearing: if a lubricating film can be formed on the surface of the sliding bearing to separate the surface of the moving pair, the sliding friction can greatly reduce the friction coefficient of the surface of the moving pair, and the sliding friction can be greatly reduced. Since the surface of the moving pair does not contact directly, wear can also be avoided. The sliding bearing has large bearing capacity, high rotation accuracy, good lubrication effect, and impact resistance. Therefore, it has been widely used in oil fields. The formation of the lubricating oil film is the basic condition for the normal operation of the sliding bearing. The factors affecting the formation of the lubricating film include the lubrication mode, the relative motion speed of the moving pair, the physical properties of the lubricant and the roughness of the surface of the moving pair. The design of the sliding bearing should determine the structural type of the bearing and select the lubrication and lubrication method according to the working conditions of the bearing.
3 Wear mechanism analysis
Adhesive wear. When the micro convex bodies of the friction surface of the moving pair interact with each other at rest, and the points are embedded together, that is, the phenomenon of "cold welding" occurs. During relative sliding, the material is transferred from one surface to another surface or separated from the attached surface, forming free particles, which is called adhesive wear.
(2) Abrasive wear. Free hard particles (such as dust, or metal particles caused by friction) or hard micro-convex that enter between the friction surfaces from the outside, and the grooves on the soft material surface. The stripped material forms new free particles, and such micro-cutting process is called abrasive wear.
4 Analysis of sliding bearing mechanism
The bearing supports the shaft. When the shaft rotates in it, there must be strong friction between the shaft and the sliding bearing. The general sliding bearing material shall meet the following requirements: first, it shall have sufficient strength and hardness at working temperature. So as to withstand the unit pressure exerted by the journal and wear resistance; Second, it has enough plasticity and toughness to ensure a good fit with the shaft and resist impact and vibration; Third, it has good running-in ability, good corrosion resistance, good thermal conductivity and small expansion coefficient; Fourth, the friction coefficient with the shaft is the minimum and the lubricating oil can be kept.
5 Problems and improvement of sliding bearing in operation
The sliding bearing works in the environment of heavy load and high speed rotation. The lubricating oil is forced to circulate to the surface of the friction pair by the oil pump to form an oil film. Because the oil film is very smooth and the resistance is very small, the friction force is greatly reduced. Due to various reasons, the sliding bearing cannot be fully lubricated. When the pump shaft is statically pressed on the bearing, the side clearance between the bearing and the shaft is only 0.08mm, and the top clearance is 0.17mm, while the bearing bottom and the shaft are in direct contact with each other and there is no clearance. It is difficult for the lubricating oil to bypass the pump shaft to form a 360 ° annular radial flow, and it is difficult to achieve the ideal lubrication effect. When the pump is started and stopped immediately, the lubricating oil does not form centrifugal force, Not enough buoyancy can be generated, and the pump shaft and bearing can only be driven by the motor to friction and rotate. At this moment, most of the bottom of the bearing will generate dry friction with the shaft, forming high temperature, and the generated high temperature will scorch and harden the bearing black gold surface to form carbon deposit. This blackened and hard high point will cause the most serious damage to the pump, causing the pump shaft to have grooves, the bearing to have pits, denudation, and this kind of repeated starting and stopping of the pump for a long time will cause secondary damage, In serious cases, the bearing bush is damaged, the surface of the pump shaft is rough, and the service life is too short. This causes dry friction between metals, which produces high temperature in a short time, burns out the sliding bearing, and causes major mechanical accidents.
The accident causes are analyzed as follows: first, when the pump is stationary. The shaft presses the sliding bearing tightly to make the clearance between the sliding bearing and the shaft small. When the pump is started, dry friction will occur, resulting in wear and alloy falling debris; The second is that the pressure at the inlet and outlet of the pump is unstable, the fluid impact force in the pump is uneven and the vibration occurs, the sliding bearing has fatigue deformation, the clearance increases, and the vibration occurs, and the shaft impacts the sliding bearing; Third, the sand and dust in the air floated between the shaft and the bearing bush, and the bearing appeared pear grooves and chips; Fourth, when the debris falls off seriously, the bearing cannot be flushed, which blocks the oil inlet of the bearing bush and interrupts the lubrication.
According to the above analysis, when starting and stopping the pump, dry friction has the greatest wear probability on the sliding bearing. We adjust the surface structure of the sliding bearing, and the lubrication of the shaft changes from dry friction, boundary friction and mixed friction to liquid friction.
First, turn and mill two 4mm wide and 2mm deep oil grooves on both sides of the sliding bearing in the axial direction, so that the lubricating oil can form 360 ° lubrication flushing and cooling effect in the sliding bearing. Drill through hole φ 4mm each, so that the lubricating oil containing sundries flows out here, which not only strengthens the cleaning of debris and the cooling of the pump shaft, but also accumulates the additional amount of oil on the bearing surface in the oil grooves on both sides. Second, in the middle of the sliding bearing in the axial direction, mill two oil grooves with a width of 2mm and a depth of 2mm on average, and drill the diameter evenly on the bearing surface φ There are 9 oil storage pits with a width of 2mm and a depth of 2mm. When the pump is started and stopped, there is sufficient lubricating oil supply to improve the dry friction condition. Because the oil film between the shaft and the sliding bearing is kept below 0.01 when the pump is running at high speed, the boundary friction can be ensured. When the shaft is running at high speed, the oil supply from the annular oil groove quickly enters the liquid friction. The shaft does not contact with the sliding bearing, and the generated debris is significantly reduced, extending the service life of the sliding bearing.
6 Benefit analysis
The surface processing of the sliding bearing is not large, and its cost is very low, such as power consumption, equipment wear, labor, etc., less than 50 yuan. The price of one pair of bearings for each pump is 5000 yuan, and the service life of two pairs of sliding bearings can be extended by 20000 hours after improvement. A pump can save 10000 yuan per year. If applied to 188 high-pressure water injection pumps in the whole plant, the cost will be saved by 1.8 million yuan. At present, the new technology has won the second prize for new technology promotion in the Sixth Oil Production Plant, and was gradually popularized and used in the Sixth Oil Production Plant area in July 2010. The service life of the improved sliding bearing has been extended by 2 overhaul times compared with that before the improvement, saving the country millions of yuan in maintenance costs.
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