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1 Background Introduction
The heating of the 7th bearing of the second gear supporting wheel in a certain production line of a certain company's rotary kiln forced production reduction. After adjusting the process operation and taking a series of cooling measures such as opening the external discharge of circulating water, fan blowing, and pouring cold lubricating oil, the equipment resumed normal production. To check whether the supporting wheel bearing has been damaged during the heating process, an outsourced team for supporting wheel maintenance was invited to inspect it during off peak production time, and the bearing was scraped and ground. However, after the kiln was opened, the supporting wheel bearings experienced high temperature heating, which caused the rotary kiln to be unable to reach normal speed. In addition, the supporting wheel bearings were subjected to emergency cooling measures by directly pouring water due to high temperature (around 90 ℃), resulting in significant damage to the supporting wheel bearings. This equipment malfunction not only consumed a large amount of manpower and material resources, but also seriously affected the production and quality of clinker. In actual production, the heating of the supporting wheel bearing of the rotary kiln is mainly related to its lubrication state and the load it bears. The following article will mainly analyze the causes of the heating of the supporting wheel bearing and the corresponding preventive measures from these two aspects.
2 Analysis of the main reasons for the heating of the supporting wheel bushing
2.1 Poor lubrication condition
a. There are too many impurities in the cooling circulating water of the rotary kiln, which causes blockage of the cooling water pipe and hinders the flow of circulating water, resulting in ineffective cooling of the lubricating oil; The internal circulating water pipe ruptured, causing water leakage and emulsification of lubricating oil. Due to the deterioration of oil quality, the temperature of the bushing increased.
b. Failure to change the lubricating oil in a timely manner due to the failure of the supporting wheel bearing, resulting in a decrease in the viscosity of the lubricating oil, oil deterioration and emulsification.
c. Poor sealing of the supporting wheel axle leads to severe oil leakage, resulting in a decrease in oil level or detachment of the oil spoon. Insufficient lubrication causes the temperature of the supporting wheel bearing to rise.
d. The surface of the supporting wheel shaft is rough or the shaft is heavily brushed (the area between the shaft and the bushing is equivalent to point contact), which is not conducive to the formation of an oil film.
e. The relative movement between the shaft and the bushing causes re grinding, resulting in heating.
f. If the tile mouth is too small or the scraping method is incorrect, a good wedge-shaped space is not formed between the supporting wheel shaft and the bushing, and an effective oil film cannot be formed.
g. After long-term use, the contact angle between the bearing and the shaft becomes larger, and the contact gap between the bearing mouth and the shaft also becomes smaller. When it becomes too small, the lubricating oil cannot smoothly enter the bottom of the bearing, resulting in high temperature heating of the bearing.
2.2 Abnormal Load Bearing
a. Improper adjustment of the supporting wheels in each gear or excessive temperature difference in the inner and circumferential directions of the kiln can result in a significant deviation between the actual center elevation of each gear and the standard elevation, causing the centerline of the kiln to bend and resulting in excessive force fluctuations in each gear. When the original bearing capacity is exceeded, it is highly likely to cause heating of the shaft bearings.
b. The wear gap between the tire and the pad is too large, causing the deformation ellipticity of the tire to exceed the normal range, or causing changes in the contact surface between the tire and the supporting wheel, resulting in uneven stress on the bushings at both ends of the supporting wheel, causing high temperature heating of the supporting wheel bushings.
c. The clearance between the side of the supporting wheel bearing and the thrust plate is too small (the normal value is generally 3-5mm), which causes friction between the thrust plate of the bearing and the shaft shoulder, resulting in heating of the bearing.
d. If the upward and downward movement speed of the kiln is too fast, and the upward speed of the hydraulic stop wheel is too slow and unstable, while the downward speed is too fast, a downward thrust will be generated in the axial direction. This force can also cause relative buckling and friction between the supporting wheel bearings, resulting in excessive force on the end face of the supporting wheel bearings and damage to the oil film.
e. The use of refractory bricks in the kiln results in varying thermal conductivity types, uneven or detached kiln skin thickness, frequent adjustment of the position and flame of the coal injection pipe, leading to large temperature differences outside the kiln barrel. The radial temperature difference of the kiln barrel is also too large. When the barrel deforms or the external temperature is high, it causes high temperature radiation to the supporting wheel, resulting in high temperature heating of the supporting wheel bearing.
f. The sinking of the kiln foundation or the loosening of the foundation or top wire can cause changes in the position of the supporting wheel, and uneven stress can easily cause the bearing to heat up.
3 Emergency response plan for idler bearing after heating up
When there are signs of heating in the supporting wheel bearing, the on-site equipment management personnel should carefully analyze the cause and take effective measures to quickly cool down according to the temperature rise of the bearing, in order to avoid the occurrence of burning and locking of the supporting wheel shaft and bearing. The specific emergency response measures for the heating of the supporting wheel bearing are as follows:
（1） Check if the temperature of the on-site bearing is consistent with the central control temperature, and confirm if the temperature of the on-site bearing is too high.
（2） When the temperature reaches 50 ℃ or above, use a trachea to cool the hot spot and install a cooling fan on the supporting wheel seat for cooling.
（3） Check the oil film on the supporting wheel shaft and the oil level in the oil spoon, it is advisable to fill the cup with oil from the oil spoon.
（4） Check if the oil on the oil pan is flowing smoothly.
（5） Check the hot spot. If the hot spot is caused by friction due to a small gap between the thrust plate and the end face of the supporting wheel tile, promptly check whether the kiln is at the lower limit position. If this is the reason, manually open the hydraulic stop wheel to lift the kiln upwards.
（6） When the temperature reaches 55 ℃ or above, turn on the external circulating water and observe the oil film on the supporting wheel shaft. For high-temperature points with poor oil film, use a small pointed oil can to add oil.
（7） If the tile temperature is not high and the oil temperature is high (over 55 ℃), compressed air can be turned on appropriately to cool the idler oil. Stop using air when the temperature drops below 55 ℃.
（8） When it is found that the heating of the supporting wheel bearing exceeds 65 ℃ and there is still an upward trend, the surface temperature of the shaft is high. The kiln speed can be reduced first, and cool lubricating oil can be continuously added until the temperature of the supporting wheel bearing returns to normal.
（9） Observe the contact between the wheel belt and the supporting wheel, as well as the contact between the thrust plate at the shaft end and the side of the bearing. If there is abnormal contact and the bearing temperature continues to rise, consider making slight adjustments to the supporting wheel (do not easily adjust the position of the supporting wheel until the cause of the heating of the supporting wheel and bearing is identified).
4 The main prevention and solution measures for the heating of the supporting wheel bushing
The emergency response measures for the heating of the supporting wheel bearing can timely and effectively reduce the temperature of the bearing and restore it to normal bearing temperature in a short period of time. But if effective prevention and solution measures are not taken for the cause of heating, the heating problem of the supporting wheel bearing will recur, and even emergency cooling measures cannot restore the bearing temperature to normal. Therefore, corresponding preventive measures should be taken to address the root causes of the analyzed problems.
4.1 Poor lubrication condition
Shortage of oil supply or damage to the oil film can cause direct contact between the supporting wheel and bearing, resulting in increased friction and high temperature heating of the bearing. Therefore, based on the analysis of the reasons, it is recommended to take the following measures:
a. During maintenance and installation, ensure that the tile seat is clean and free of impurities, and use compressed air to blow the cooling water pipe of the bushing to ensure unobstructed flow. At the same time, filter and remove impurities from the cooling water, and regularly check whether there is return water in the return pipe.
b. Use specialized lubricating oil for supporting wheel bearings. In summer, when the ambient temperature is high, choose lubricating oil with higher viscosity to increase compressive strength and facilitate the formation of an oil film; Choose lubricating oil with lower viscosity in winter to prevent accidents such as "tile flipping" and hanging off oil spoons. Lubricating oil requires regular replacement, and overheated bushings require thorough replacement of lubricating oil once a year; For bearings that have not overheated, it is required to completely replace the lubricating oil within two years.
c. Replace the sealing ring according to the usage cycle and usage situation, ensuring that the sealing ring can maintain elasticity and integrity during use. It is recommended to replace the rubber sealing ring once a year, and the usage time should not be too long to prevent equipment oil leakage caused by wear or aging; In daily inspections, the integrity of the oil supply system of the supporting wheel bearing group should be checked, and the oil spoon should be observed for looseness or detachment. The oil spill pan should be checked for smooth oil leakage. If any abnormal situation is found, on-site personnel should be organized to handle it in a timely manner.
If the surface of the supporting wheel shaft is found to be rough, it should be dealt with in a timely manner. Generally, it is ground with an oilstone during slow rotation of the rotary kiln. In severe cases, it is recommended to replace the supporting wheel directly.
d. Adopt the correct method of scraping and grinding the bushing to form a good oil film between the shaft and the bushing. At the same time, after scraping and grinding and replacing the bushing, pay attention to the standardized process operation when reopening the kiln. When increasing the kiln speed, it should be raised by 0.05r/min each time to prevent the shaft and bushing from overheating due to too fast a speed increase and short running in time. Before scraping and grinding the bearing, check the contact between the back of the bearing, and then scrape and grind the spherical surface and the bearing according to the requirements of the "Construction and Acceptance Specification for Cement Machinery Equipment Installation Engineering" JCJ/T3-2017.
e. Explore suitable external circulation cooling devices for lubricating oil, and provide emergency cooling for the idler oil when the idler bearing heats up or the oil temperature is high (the viscosity of idler oil is high, and the selection of external circulation cooling devices should ensure the normal flow of idler oil).
4.2 Abnormal Load Bearing
If the load borne between the supporting wheel and the bushing of the rotary kiln is unevenly distributed, it will lead to an increase in local stress, making it difficult to form a complete oil film on the contact surface, resulting in boundary friction or dry friction, ultimately causing the bushing to heat up or burn out. Therefore, based on the analysis of the reasons, it is recommended to take the following measures:
a. Ensure that the installation deviation of the supporting wheel and kiln body assembly meets the standard requirements; Ensure that the radial runout of the cylinder center during the replacement of the rotary kiln is within the specified requirements; After the rotary kiln is stopped, it should be kept in a slow rotating state to prevent the kiln body from deforming and bending due to heat.
b. Use specialized high-temperature lubricating oil for spraying to regularly lubricate the cylinder gasket and tire, reducing the wear caused by direct friction between the gasket and the tire. When the wear gap is too large, it is recommended to thin the gasket or replace it with a new one to restore the initial installation gap; Air cool the high-temperature areas of the belt and cylinder to control the surface temperature of the kiln body and belt within the normal range.
c. If the clearance between the supporting wheel thrust plate and the side of the bushing is too small or even under contact force, observe the temperature change of the bushing, check whether it is caused by excessive upward or downward movement of the kiln, and make corresponding adjustments. If it is necessary to adjust the idler, it should be fine tuned according to the idler adjustment requirements, so that a certain gap is formed between the idler bearing and the thrust plate.
When the upward or downward movement of the rotary kiln is too large, the oil supply speed of the hydraulic stop wheel oil station oil pump and the oil discharge speed of the throttle valve should be adjusted in a timely manner to restore the uniform upward and downward movement of the rotary kiln cylinder. It is recommended to control both the upward and downward time cycles of the rotary kiln within 8 hours, and to reasonably control the working pressure of the hydraulic stop wheel. The working pressure of the Φ 4.8 × 74m rotary kiln should be controlled at around 6.0MPa (upward pressure 5-7.5MPa, downward pressure 4-6MPa), while other small rotary kilns should be controlled at around 5MPa.
d. In some cases, the heating of the bushing is caused by uneven distribution of kiln skin and other process reasons. When improper process operation causes the bushing to heat up, efforts should be made to prevent the temperature rise of the bushing while identifying the specific cause, so as to adjust the process data and operation plan in a timely manner to restore normal operation.
e. Strengthen inspections and promptly prevent and restore any changes in the position of the supporting wheels caused by foundation sinking or loose feet or top threads on site.
5 Conclusion
There are many factors that can cause high temperature heating of the supporting wheel and bearing of the rotary kiln. How to quickly identify the cause and deal with it in a timely and effective manner is the key to testing the comprehensive ability level of on-site equipment technical management personnel. As on-site equipment technical management personnel, firstly, it is necessary to enrich on-site practical experience, understand the potential causes of high temperature heating in the supporting wheel bearing, and be good at summarizing and analyzing, making correct judgments, and proposing reasonable prevention and solution measures; Secondly, it is necessary to frequently visit the site and assist on-site workers in carrying out daily maintenance work of the rotary kiln. At the same time, timely understanding of the operation status of the rotary kiln and the wear and tear of various components should be done, and records should be kept. Using the planned maintenance time, abnormal situations should be maintained and repaired in a timely manner to avoid accidents such as overheating, burning, and overturning of the supporting wheel bearings.
2024 August 2nd Week KYOCM Product Recommendation:
Rotary bearings consist of an inner ring and an outer ring, one of which usually contains a gear. Together with the connecting holes in the two rings, they enable optimized power transmission through simple and fast connections between adjacent machine parts. Bearing raceways are designed with rolling elements, cages or gaskets to accommodate loads acting individually or in combination in any direction.
Features and advantages:
High carrying capacity
High stiffness for rigid bearing applications
Low friction
Long service life
Surface protection and corrosion resistance
Integrate other features including:
Driving mechanism
Control device
Lubrication system
Monitoring system
Sealed cassette tape
https://www.kyocm.com/products/Slewing-Bearing/745.html
2024-08-09