Selection must be three major factors to consider is the speed limit, the service life of the predetermined requirements and work load, which is three performance requirements of the selected NSK bearing must meet.
The speed limit is the maximum operating speed of the bearing, beyond this limit, the operating temperature will be bearing continues to rise, the lubricant dry, so that the bearing is clamped, the speed limit so the selected bearing and bearing a predetermined maximum operating speed is 10% higher for. In the bearing type has not been selected cases, desirable predetermined installation of bearing parts, shaft and hole diameter and half for NSK bearing calculation of the average diameter of DM, DM is multiplied by a predetermined maximum operating speed of N bearing, 10 / 9 times the DMN value should not be higher than the speed limit of the selected bearing.
But NSK bearing limit speed is not immutable and frozen, but directly related to lubrication. Such as bearing sample listed under oil lubrication bearing limit speed is N0, the same bearing in grease lubrication condition and its speed limit is 0.8n0, in the oil mist lubrication condition is 11.5n0; the volumetric non repetitive circulating oil lubrication conditions, for the small tank work continuously for 0.85n0, and for intermittent working big fuel tank is 0.95n0. Lubrication and N0 values is repeated circulating oil lubrication device with filter and heat dissipation, pay attention not to take this lubrication or other lubrication effect is the same, is not the N0 bearing sample values as the actual speed limit of the bearing lubrication, and should be based on specific, according to the above example N0 took the last ratio constant, is taken as the actual limit speed numerical bearing; secondly, the actual speed limit bearing although could improve lubrication and improved, but consider to improve the lubrication and pay for the cost of the equipment and maintenance cost, space and other factors accounting for the and lubrication equipment, integrated weigh the pros and cons, make the best choice.
In fact, in considering the NSK bearing limit speed, not only to take into account the bearing type, sometimes must also take into account the components such as bearings, cage material, form, print design and technological factors, and the bearing sliding friction, lubricant storage and maintenance, operation stability is closely related to the rolling body, sometimes will become the key bearing can reach the speed limit on the bearing life and reliability requirements are unified consideration, usually take a reliability coefficient of 90%, which means a lot in the bearing in the same working condition in running, bearing 90% remained normal at the working life of the L10 when a predetermined. If you want to get higher reliability, say 96%, we must reduce bearing life, for example, the L10 must be life reduced to L4.
Speaking for the main shaft bearing, the highest requirements is the life is the same or slightly higher and the whole machine, the minimum requirement is to overhaul period longer than the spindle, in fact, the use of both the host can meet the performance requirements and does not cause the comprehensive consideration of spindle system is too large and the economy is more cost-effective the scheme, for most machines, have a successful precedent for reference.
It should be emphasized that, the selection and calculation of bearing failure form should also be considered, and wear, lubrication failure and fretting wear, the wear life is to check the other forms of failure, if involved must also be considered.
Note that the fatigue life of NSK bearings can be expected and wear life not only with lubrication, but also directly related to clean lubricant three for mounting parts, bearings, bearing itself, is also concerned with the form and the sealing effect, the rated life of bearing must be provided by lubrication, cleaning and sealing condition to adapt, and improve these conditions can also improve the service life of bearings.
Considering the load factors should be paid attention to when the NSK bearing life is more sensitive to load matching speed, so for the multistage transmission shaft, if possible, should be the great series of the deceleration in later; for the main shaft bearing, if possible, the appropriate allocation between external load bearing pivot point and the distance, and strive to reduce the spindle bearings load, and strive to the spindle bearing load is stable, to avoid the shock and vibration, which requires the shape and position accuracy of the installation position of the bearing is high enough, the bearing clearance and choose the correct installation of precision bearings, the good.
Load bearing selected in the selection and design of the actual load calculation, more representative of bearing during operation, the calculation result more correct, so extensive and in-depth study of the actual load bearing.
If the NSK bearings can bear large load, and still and does not rotate, this state is worse, a rolling body and a micro indentation will be formed between the raceway and soon become the pitting corrosion, so that the early failure of bearing. In this case, the static load must check the bearing rated, can overcome the bearing static equivalent load.
Contrary to the other extreme, bearings operating at high speed, but does not bear the load, so that the rolling body often in the raceway on sliding without rolling, the bearing temperature rise rapidly, the lubricant will rapidly decomposed metamorphic, bearing failure, so the bearings require a minimum load for preventing slip.
In some cases, must also consider the equipment itself, axial force and radial force, gear and other parts of the weight and the weight of the shaft, stress related parts, they are calculated under NSK bearing, load, and these are often ignored and leakage.
In many cases, NSK bearings due to the influence of vibration and the actual load increased significantly, the actual bearing installation of coaxiality error is larger ( in ) the actual load will also increase the bearing, so it must be a necessary correction for numerical computation load.