The bearings of papermaking machinery have various requirements in a series of processes, including corresponding heat resistance and high-speed.
Rolling bearings used in papermaking machinery often fail during operation, and bearing failure will cause equipment failure or downtime. Most of the reasons for bearing failure are caused by improper selection, configuration, installation, lubrication, and maintenance. The sum of these reasons may exceed 90% of the total failure. Therefore, correct observation, analysis, finding the reasons, and taking corresponding countermeasures are the fundamental means to improve the stable operation of paper machinery bearings.
①Bearing arrangement
Paper machines generally use self-aligning roller bearings, which can withstand radial loads and certain biaxial loads. When the shaft is deflected and the bearing seat is inclined, the internal self-aligning contact angle can be automatically adjusted to prevent the bearing from being unilateral. overload. In general roller systems, the transmission side is usually used as the fixed end for the axial positioning of the rollers; the operation side is used as the floating end to compensate for thermal changes and position adjustment of the shaft. Generally, the end faces of the inner and outer rings of the fixed end need to be positioned; the floating end only needs to be positioned for the inner ring, and the outer ring retains the momentum in both directions.
If the thermal changes of the shaft cannot be compensated axially, the bearing will be subjected to a large additional axial load on one side, causing the bearing to fail.
②Bearing installation
The installation quality of paper machinery bearings will directly affect the accuracy, life and performance of bearings. Most bearings have tapered holes and are directly mounted on the tapered shaft or transition sleeve, so the inner ring not only needs to be fastened axially, but also should pay attention to the change in the radial clearance of the bearing during the tightening process, which cannot reach the preload. , the bearing has a large clearance, which will lead to reduced vibration and life; too tight will cause the bearing to heat up during use, especially the dryer bearing. And once the inner ring exceeds the due amount of elastic deformation, high tensile stress will be generated on the bearing surface, which is very likely to cause premature fatigue or sudden fracture, so it should be strictly preloaded according to the working conditions and standards.
Taking the drying cylinder standard bearing 22344CCK/W33C3 as an example, by looking up the table, the original C3 standard clearance is 0.25~0.32mm, and the actual testing product assumes that the clearance is 0.28mm, then the table shows that the clearance reduction is 0.1~0.14 mm, according to the maximum reduction, the clearance after installation is 0.14mm, which is greater than the minimum clearance after installation "0.12mm" specified in the standard table, and the installation is judged to be qualified.
When installing, first unpack the bearing, carefully check the model and observe that there is no obvious defect in the appearance, clean the bearing with kerosene, and clean the surface of the shaft. After putting the bearing on the shaft, hydraulically remove the bearing. Install the hydraulic nut on the shaft at a constant speed, and check the change of radial clearance at any time. When installing a particularly large and thick inner ring, when the required clearance is not reached and the nut cannot be pushed forward, the pressure should be maintained for a period of time. Time, let the inner ring expand and deform first, and then move forward after it is stable; when the hydraulic nut can continue to move forward, but the clearance does not change, it should be stopped immediately, and the inner ring should be checked in time for cracks.
If the preload is not enough, the bearing is easy to slip with the shaft, which will cause the bearing to break and the shaft head to wear; Fatigue spalling and other failures occur.
If it is a bearing with a straight bore, it is generally necessary to use a heating method to heat the inner ring of the bearing to make it thermally expand, and then install it on a straight shaft. Heating generally adopts the method of hot oil bath or induction heating. However, the following should be noted:
1. The heating temperature of the bearing should be kept within 120 ℃, and it should not be in direct contact with the open flame, and the heating should be uniform;
2. If the oil bath is used, the cleanliness of the oil should be ensured, and foreign matter in the oil cannot be brought into it;
3. If it is induced, be careful not to heat with high power for a long time, which will cause the local temperature to rise too high and too fast;
4. The installation should pay attention to the operation time to avoid the bearing not installed in the position, and the shrinkage will lead to scrap;
5. When the bearing is cooled, it will not only shrink in the radial direction, but also shrink in the axial direction. It needs to be preloaded in the axial direction to prevent the gap with the shaft shoulder.
③Bearing lubrication
The lubrication of paper machine bearings is extremely important in the operation of equipment, because modern paper machines are high-speed paper machines, and the bearings are always in a state of high-speed rotation. If the lubrication is improper, the bearings will quickly have problems, resulting in serious equipment failures or accidents. For the lubrication of paper machine bearings, the main purposes are as follows:
1. Reduce frictional heat and contact wear;
2. Through the action of the oil film, the service life of the bearing is prolonged;
3. Use the flow of lubricating oil to take away frictional heat and cool the bearing;
4. The lubricant can effectively cooperate with structures such as seals to prevent the entry of foreign matter, water vapor, etc., as well as the corrosion and rust caused by foreign pollutants to the bearing.
The paper machine adopts different lubrication forms and lubricants according to different rolls and sections, and the following should be noted:
1. Cadres with high temperature should choose grease with higher viscosity, such as 3# lithium-based grease, while the water vapor in the pressing and wire parts is large, generally choose calcium-based grease with strong water resistance;
2. When using a pneumatic grease pump or a manual grease pump, you should pay attention to the amount of grease added each time. Too much grease is not conducive to the heat dissipation of the bearing, and it is easy to cause oil rejection, paper pollution or paper breakage and other problems; Adding lubricating grease should strictly follow the equipment maintenance instructions, and add it regularly. Failure to inject grease in time will easily lead to problems such as bearing heating or fatigue failure;
3. For oil lubrication, the lower the rotational speed, the lower the viscosity of the lubricating oil; the higher the load, the higher the viscosity of the lubricating oil used. If the viscosity is too low, the oil film cannot be effectively formed, and the inside of the bearing cannot be well lubricated, resulting in serious wear and adhesion, and even early fatigue spalling. Conversely, if the viscosity is too high, the resistance will be higher, which will also cause the bearing to generate too much heat.
E-ASIA BEARING has been committed to the research and development and production of paper machine bearings for a long time. The products adopt high-quality imported raw materials and advanced design concepts and processing technology. Through strict quality control, the reliability of products has been improved to an unprecedented height. The long-term use of ten domestic papermaking enterprises has won unanimous praise from customers, which has made a certain contribution to the localization of imported bearings for paper machines and to the reduction of costs and efficiency of the majority of paper enterprises.
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