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Application of grinding roller bearing in coal mill in thermal power plant
Source: China Bearing Network Time: 2018-07-21
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Anti-wear particle requirements and countermeasures for grinding roller bearings of coal mills <br> It is well known that thermal power professional equipment is one of the most challenging applications of bearings. As a coal-fired machine for auxiliary equipment of thermal power plants; The bearing must be in high dust and low temperature to ensure the operation under the harsh environment of smooth and lacking. In this case, the function and stability of the bearing are related to the stable operation of the whole equipment. Lifespan; it means cutting down the stop; then improving the performance of equipment operations; preventing unnecessary human and material waste caused by unnecessary maintenance.
The grinding roller part is located in the coal mill chamber; it is surrounded by high-temperature coal powder under working conditions. The coal powder particles are very fine; if the sealing of the grinding roller is slightly abnormal; it is very simple to enter the bearing grinding roller through a bad seal. Because the coal mill grinding roller is more immersed in oil smoothing; the smooth oil is replaced once in a while. Once the coal powder enters the inside of the grinding roller; it will stay inside the grinding roller for a long time; become the bearing raceway And the rolling body constitutes the rated wear of the abrasive particles. The presence of such abrasive particles; very simple damage to the bearing is inherently thinner smooth oil film; greatly increase the wear of the bearing surface of the bearing; constitute the bearing early elimination. Figure 1 is abrasive wear An analogy of the bearing damage can be seen in the figure; the bearing is damaged by the seal; the abrasive grain enters the bearing cavity; the entire bearing raceway is worn by the abrasive grain; the ribs and the cage of the bearing are severely worn; Crash damage in the moment.
It is necessary to prevent the occurrence of such bearing damage; the usual practice is to improve the quality of the seal; after sealing the bearing, after a timed view of the smooth oil sample to determine whether there are many abrasive grains entering, the running current of the coal mill is detected. To investigate whether there is a rated frictional attack, etc. In addition to these practices, we also see; because the grinding roller has been operating in a high dust chamber; coal powder will always enter the bearing cavity; if it can Improve the bearing's own anti-wear grain wear function; it will also extend the application period of the bearing.
The reliable product is derived from the reliable data. The purity of the steel used in the bearing, the heat treatment process, etc. will affect the wear resistance of the bearing. The bearing with better steel purity; less self-contamination; In the case; the thinner the outer surface is less; the relative bearing is not simply damaged. Others; the heat treatment process ensures a satisfactory bearing surface hardness; the bearing can be more wear-resistant. If the bearing is selected for carburizing; Its appearance is due to the existence of a certain degree of compressive stress; the effect of the opposite abrasive wear is also obvious.
The combination of coating skill and surface treatment skills can reduce the impact of abrasive particles; then significantly improve the bearing life and extend the protection cycle.
The smooth demand of the grinding roller bearing of the coal mill <br> As mentioned above; the demand for the roller bearing is high; except because it is operated in a high dust environment; also because the bearing is in a high temperature, low speed operating environment; Smooth conditions are difficult to satisfy. We know that the composition of the smooth oil film is related to the viscosity of the smooth oil, the pressure between the two surfaces, the relative speed, and the roughness of the two surfaces. Let's analyze the effects of each element and we will analyze each of them. How to use it in actual operation.
First, the viscosity of the smooth oil is higher; the simpler the oil film is. We know that the viscosity of the smooth oil decreases with the increase of temperature. In the grinding roller; because of the influence of external hot air; the overall temperature is higher. In the coal mill, the oil bath is smooth. The smooth oil does not have circulating cooling when it is used; it only passes through the shaft to dissipate heat; the heat is concentrated in the grinding roller; the entire roller bearing and the oil reach the heat balance at a higher temperature. In this case; a higher viscosity smooth oil is required to ensure that the oil can still ensure viscosity at the operating temperature. Another option is to use a smooth oil with a relatively high viscosity index; for example, some oils. The viscosity of the smooth oil decreases with increasing temperature; it also allows the smooth oil to ensure viscosity at the operating temperature.
Secondly; to form a useful oil film; there must be a certain relative speed and reasonable pressure. In the grinding roller; the bearing is relatively strong; this also makes the roller and the raceway between the two relatively moving touch surfaces The pressure is relatively large. If the pressure is too large; it is very simple to crush the oil mill. So here; from the point of view of the bearing application; we recommend the use of smooth oil with extreme pressure additives; to ensure the smoothness of the bearing under pressure .
Look at the speed. This is actually another major obstacle to the smoothness of the roller bearings. The selection speed of the grinding rolls is relatively low; usually around 35 to 55 rpm. This speed constitutes a useful oil film; the difficulty is even greater. In addition to the smooth oil viscosity at the elevated operating temperature; addition of extreme pressure additives; from the point of view of the bearing; can also be used to improve the smoothing effect.
The role of the oil film is to separate the two touch surfaces; how the separation works; depends on the thickness of the oil film and the sum of the surface roughness of the two touch surfaces. Thus we introduce a parameter λ to characterize the smoothing effect.
When λ is greater than 1, it indicates that the two appearances are useful; the smoothing effect is outstanding. When λ is less than 1, it indicates that there are still touches on both surfaces. Starting from the bearing itself; to make the λ coefficient as far as 1; can pass the appearance of the descending bearing The roughness value is completed. That is to say; in this orientation; the bearing with a reduced appearance roughness can be selected as needed to achieve the intention of improving smoothness.
In summary; in the smoothing problem of the roller bearing; we can open the bow left and right; on the one hand to ensure the smooth oil viscosity; on the other hand, reduce the bearing surface roughness; then reach a better application.
The above is the first analysis of the operating environment of the roller bearing; from the two aspects of anti-wear particles and improved smoothness, the key points of bearing selection and application are analyzed. It is expected that such analysis can help the vast power plant operators to better. Selection and use of bearings; prevent unnecessary stops; improve the overall production power.
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