With the continuous expansion of the mining industry, large mechanical equipment has been introduced into the operation of the mine, which has promoted the efficiency of the mine. Many large hoist motors use rolling bearings, which can be better applied to the mining industry. However, the hoist motor with sliding bearing is also often used in mining industry, which can prolong the service life of sliding bearing and hoist motor. Of course, the maintenance of the sliding bearing is difficult, and is restricted by many factors, resulting in restrictive negative effects on the operation of the hoist motor in coal mining. Therefore, it is very important to maintain and repair the sliding bearing of the large hoist motor.
1. Conditions of sliding bearing liquid friction
The lubrication form of sliding bearing is liquid, and its formation conditions are relatively harsh. The suspension state formed by the rotating shaft supported by the dynamic pressure of lubricating oil forms liquid lubrication, which becomes the friction condition of bearing. The thickness of the liquid lubricating oil is more important. If the amount of lubrication is small, it will aggravate the roughness of the shaft diameter and the friction surface of the bearing, causing the deviation of the shaft diameter rotation axis, affecting the sliding of the bearing, and damaging the thickness of the minimum oil film, leading to the lubrication failure between the shaft diameter and the bearing.
The sliding bearing can only drive the rotation direction of the journal to move and form the floating eccentricity under the friction condition of liquid lubrication. The eccentricity is the center distance between the journal and the bearing hole that is less than the static environment. It is related to the speed of the bearing. The faster the bearing speed is, the smaller the eccentricity will be. At this time, the dynamic pressure effect is produced in the bearing, which can enlarge the wedge clearance, thus reducing the sliding capacity and bearing capacity of the bearing journal. Therefore, the dynamic pressure of the sliding bearing is directly proportional to the running speed of the journal, and the dynamic pressure effect is inversely proportional to the eccentricity, which sums up the conditions for the liquid friction of the sliding bearing: first, the wedge-shaped clearance and sufficient running speed; Second, enough continuous lubricating oil; Third, the coaxiality between journal bearings.
2. Structure and material of sliding bearing
The structure of the hydrodynamic sliding bearing of the mine hoist motor is divided into two types, one is integral type and the other is split type. The bearing materials are also divided into two categories, one is tin-based babbitt alloy, and the other is lead-based babbitt alloy. These two materials have the advantage of low friction coefficient and can increase the adsorption of lubricating oil, thus reducing the friction of bearings and improving the heavy-load capacity of hoist motors.
3. Maintenance of sliding bearing of large mine hoist
3.1 Maintenance process of sliding bearing of large mine hoist
According to the practice, the maintenance process of the sliding bearing of the large mine hoist mainly includes the following seven aspects: first, the skip will be suspended at the right time, and then the power supply of the drum and the motor will be locked and cut off, and then the gap between the motor rotor and the stator will be measured; Second, remove the coupling shell and measure its end clearance; Thirdly, remove the motor stator shell and slip ring, motor bearing cover, oil pipeline and bearing upper bearing bush, and then measure the bearing clearance and shaft level; Fourth, use magnetic particle to detect the wear condition of the shaft circumferential surface at the bearing seat, and then deal with it according to the results; Fifth, remove the bearing bush, check its wear and correction, and then clean the bearing seat; Sixth, install the bearing lower bush and motor rotor in place according to relevant specifications, and then measure whether the shaft levelness meets the standard. After reaching the standard, install the upper bearing pad and measure whether the distance between the upper and lower bearing pads is qualified. If not, adjust it; Seventh, reset and install the hoist components removed in the above maintenance one by one, restore the hoisting system at the same time, and finally conduct commissioning to ensure its normal operation.
3.2 Maintenance of sliding bearing in operation
3.2.1 Temperature detection
The common problem of the running bearing is that the clearance of the sliding bearing is reduced due to the high temperature, which is not conducive to the operation of the sliding bearing. At this time, the heating resistance is added at the temperature measuring hole of the sliding bearing, and the thermal resistance is used to detect the online temperature of the sliding bearing. If the temperature is too high, the thermal resistance will automatically transmit the alarm function, which will be reflected to the main interface through the standard interface of the PC to remind the timely detection of the fault with high bearing temperature, Reduce bearing failure caused by serious grinding and holding.
3.2.2 Detection of running vibration
The excessive amplitude of the sliding bearing directly affects the clearance of the sliding bearing and the peeling of the bearing alloy material, resulting in operation failure. At this time, the displacement type sensor is used to detect the online amplitude of the sliding bearing, and a PC standard machine is installed on the bearing pad seat of the sliding bearing, which can automatically alarm the bearing, remind the timely repair of the amplitude fault, and reduce the possibility of bearing bearing bearing peeling.
3.2.3 Periodic ferrographic analysis
Ferrographic analysis can detect the lubricating degree of lubricating oil and the friction debris generated by bearing friction, and determine the size, shape and composition of the friction debris, which directly affects the performance of bearing materials, especially the bad lubrication will have a greater impact on babbitt alloy. Generally, the wear degree of the sliding bearing can be detected by ferrography analysis. When the blue or red spots appear, it indicates that the lubrication is insufficient and the friction is serious, which will remind the maintenance degree of the bearing.
3.3 Maintenance contents of sliding bearing
First, the integrity of the bearing material performance, the friction degree of the alloy and the surface quality performance of the alloy, and the size of the maintenance bearing clearance; Second, the actual contact position and angle of journal and bearing during operation; Third, the matching ratio and quality of the bearing outer circle; Fourth, the wear amount, wear roundness, wear surface thickness and wear cylindricity of the bearing; Fifth, the crack and peeling of bearing alloy and bearing shell, and the combination degree of alloy and bearing shell; Sixth, after installing the lower bearing bush, ensure that the rotor of the motor is in place, measure the horizontal distance of the bearing, and adjust the clearance of the bearing bush; Seventh, the reset of the removed hoist components, and the commissioning and operation of the recovery hoist system.
3.4 Maintenance of bearing alloy and bearing shell
First, knock method: knock the bearing shell, and identify the peeling of the shell according to the knock sound. If the knock sound is clear and clean, it means that the shell is not peeling. If there is a hoarse or obvious knock sound, it means that the surface of the shell is worn and there is the possibility of peeling; Second, oil immersion method: apply powder on the joint between the bearing surface and the bearing shell, soak the bearing shell with kerosene, take it out every half an hour, and observe whether the powder has wet traces of kerosene immersion, which is a warning of poor combination quality; Third, penetrant flaw detection method: flaw detection agent is a kind of detection agent composed of cleaning agent, penetrant and display agent. First, dry the bearing with cleaning agent, spray the penetrant into the bearing bush, and spray the display agent after half an hour of rest. If the color of the display agent changes at the junction of the bearing bush and the bearing, it means that the peeling is not good.
3.5 Scraping repair of sliding bearing
Through the above inspection, the peeling of bearing alloy and bearing shell is normal, and there is no serious bearing shell defect. The operation of sliding bearing can be guaranteed by scraping and repairing; First, the selection of scraping tools: choose triangle scraping or snakehead scraping blade, which can soak oil stone to repair the scraped surface; Second, auxiliary materials: display agent is a commonly used auxiliary material, which can display the contact condition between the scraping surface and the grinding surface. Because the blending material of display agent is red lead powder and engine oil, it can react to the contact point and judge the display condition by the flash condition of the grinding point; Third, the scraping steps of the sliding bearing: first, rough scraping, scraping the scraped surface with the long part of the blade trace to improve the scraping contact point. Next is fine scraping. The working angle of the scraper is smaller than that of coarse scraping. Shorten the blade trace to narrow the scraping point and comply with the scraping direction. Again, fine scraping. The further reduction of the working angle improves the accuracy of scraping and shortens the blade trace, scrapes off the shiny part of the grinding point, leaving light and small grinding points; Fourth, the scraping quality of the bearing: the important reference indicators of the scraping quality include the number of contact points, the contact angle, the top side clearance of the journal bearing pad, etc., and ensure the distribution quality of the contact points on the working surface of the bearing pad. In addition, the range of the contact angle is compressed to 90 degrees to 120 degrees, which can improve the clearance of the bearing pad and improve the lubrication of the sliding bearing.
4. Conclusion
In a word, the maintenance of the sliding bearing of the mine large hoist motor is the daily work of the coal mine production. The sliding bearing is an important component of the hoist motor. Grasp the operation mechanism of the system, solve the common problems of the sliding bearing, and improve the application value of the sliding bearing.
More about Material Specification Sheet–MG-6:
Material specification sheet – MG-6 is Ball and roller bearing steel according to EN ISO 683-17. Ball and roller bearing steel for balls and rollers of any dimension,rings and discs up to 30mm effective thickness.
