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The limit speed, the required service life and the scheduled working load, which are the three performance requirements that the selected NSK bearing selection must meet. The limit speed is the high allowable working speed of NSK bearing. Beyond this limit, the operating temperature of the bearing will continue to rise, the lubricant will dry up, and the bearing will be stuck.
Therefore, the limit speed of the selected NSK bearing selection should be 10% higher than the predetermined high working speed of NSK bearing. When the bearing type has not been selected, it is advisable to calculate the average diameter DM of NSK bearing by the sum of the shaft and seat hole diameter in the part where NSK bearing is scheduled to be installed. Multiply DM by the predetermined high working speed n of NSK bearing, and the obtained DMN value shall not be 10 / 9 times higher than the limit speed of the selected NSK bearing.
But directly related to the lubrication mode. For example, the limit speed of NSK bearing selection under the oil lubrication condition listed in the bearing sample is N0, the limit speed of the same NSK bearing under the grease lubrication condition is 0.8n0, and it is 11.5n0 under the oil mist lubrication condition; Under the condition of constant volume non repetitive circulating oil lubrication, it is 0.85n0 for continuous operation of small oil tank and 0.95n0 for intermittent operation of large oil tank.
The lubrication method equivalent to N0 value is the repeated circulating oil lubrication with filter and heat sink. Note that instead of adopting this lubrication method or other lubrication methods with the same effect, the above N0 value in the bearing sample cannot be taken as the actual limit speed of NSK bearing selection, but N0 should be multiplied by a proportional constant according to the specific lubrication method and the above example, Take the obtained value as the actual limit speed of NSK bearing;
Although the actual limit speed of NSK bearing can be improved by improving lubrication, the equipment cost and maintenance cost due to improving lubrication and the space occupied by lubrication equipment should be taken into account to comprehensively weigh the gains and losses and make a choice. In fact, when considering the limit speed of NSK bearing selection, not only the type of NSK bearing, but also the components of the bearing, such as the material, form, design and process factors of cage
but also the sliding friction inside NSK bearing selection, the storage and maintenance of lubricant, the stability of rolling element operation, etc, Sometimes it becomes the key to whether the bearing can reach the limit speed. The life requirements and reliability requirements of NSK Bearings are considered uniformly. Generally, the reliability coefficient is 90%, which means that 90% of NSK Bearings operating under the same working conditions still maintain normal state when reaching the predetermined working life L10.
Such as 96%, you must reduce the required life of NSK Bearings selection, for example, you must reduce the life of L10 to L4. Generally speaking, for the main shaft bearing, the high requirement is that it has the same or slightly higher service life as the whole machine, and the low requirement is that the service life is longer than the overhaul period of the main shaft components. In fact, the comprehensive consideration scheme that can meet the performance requirements of the main engine without causing the main shaft system to be too large and cost-effective is mostly adopted.
For most machines, There are quite successful precedents for reference. It should be emphasized that the failure forms of NSK Bearings selection, as well as wear, lubrication failure and fretting abrasion, shall also be considered in the type selection calculation.Among them, the wear life must be checked, and other failure forms must also be considered if involved. Note that the expected fatigue life and wear life of NSK bearing are not only related to lubrication, but also directly related to the installation position of the bearing,
NSK bearing itself and the cleanliness of the lubricant used by NSK bearing, but also related to the form and effect of sealing.The rated life of the selected NSK bearing selection must adapt to the conditions of lubrication, cleanliness and sealing provided, Improving these conditions can also improve the actual service life of NSK Bearings.
It should be noted that the service life of the bearing is more sensitive to the load than the speed. Therefore, for multi-stage transmission shaft, if possible, the larger deceleration should be placed in the later stage; For the main shaft bearing, if possible, properly adjust the distance between the external load action point and the NSK bearing selection fulcrum, strive to reduce the load of the main shaft NSK bearing, and strive to ensure that the load transmitted to the main shaft NSK bearing is stable and avoid impact and vibration
which requires that the shape and position accuracy of the bearing installation position are high enough, and the clearance and fit of NSK bearing selection are selected correctly, NSK bearing has good installation accuracy.The more the NSK bearing calculation load selected in the type selection design can represent the actual load of the bearing, the more correct the calculation result is. Therefore, it is necessary to study the actual load of NSK bearing extensively and deeply. If NSK bearing not only bears great load, but also stands still and does not rotate, this state is more unfavorable.
A small indentation will be formed between the rolling element and the raceway and will soon develop into pitting corrosion, resulting in early failure of the bearing. In this case, it is necessary to verify whether the rated static load of the selected NSK bearing selection can exceed the equivalent static load of the NSK bearing.
Just the opposite. The NSK bearing operates at high speed but does not bear load. In this way, the rolling element often slides on the raceway without rolling, resulting in the rapid rise of NSK bearing selection temperature, decomposition and deterioration of lubricant, and the NSK bearing will also fail quickly. Therefore, NSK bearing needs a small load to prevent slipping. In some cases, the axial force and radial force generated by the equipment itself, the weight of parts such as gears and even the weight of the shaft, and the stress of relevant parts must also be considered.
They are all calculated in the afterload and load borne by the bearing, which are often easy to be ignored and omitted. In many cases, the actual load of NSK bearing selection increases significantly due to the influence of vibration. When the coaxiality error of NSK bearing is large (misalignment), it will also increase the actual load of NSK bearing. Therefore, the calculated load value must be corrected.