Allowable NSK bearing space
The allowable space for a NSK rolling bearing and its adjacent parts is generally limited so the type and size of NSK bearing must be selected within such limits. In most cases, the shaft diameter is fixed first by the machine design; therefore, the NSK bearing is often selected based on its bore size. For NSK rolling bearings, there are numerous standardized dimension series and types, and the selection of the optimum bearing from among them is necessary. The picture below shows the dimension series of NSK radial bearings and correcponding bearing types.
Load capacity and NSK bearing types
The axial load carrying capacity of a NSK bearing is closely related to the radial load capacity in a manner that depends on the bearing design as shown in picture below. This figure makes it clear that when NSK bearings of the same dimension series are compared, NSK roller bearings have a higher load capacity than ball bearings and are superior if shock loads exist.
Permissible speed and NSK bearing types
The maximum speed or NSK rolling bearings varies depending, not only the type of NSK bearing, but also its size, type of cage, loads, lubricating method, heat dissipation, etc. Assuming the common oil bath lubrication method, the NSK bearing types are roughly ranked from higher speed to lower as shown in picture below.
Misalignment of inner/outer rings and NSK bearing types
Because of deflection of a shaft caused by applied load, dimensional error of the shaft and housing, and mounting errors, the inner and outer rings are slightly misaligned. The permissible misalignment varies depending on the NSK bearing type and operating conditions, but usually it is a small angle less than 0.0012 radian (4').
When a large misalignment is expected, bearings have a self-aligning capability, such as self-aligning ball bearings, spherical roller bearings, and certain bearing units should be selected.
Permissible bearing misalignment is given at the beginning of the dimensional tables for each NSK bearing type.
Rigidity and NSK bearing types
When loads are imposed on a NSK rolling bearing, some elastic deformation occurs in the contact areas between the rolling elements and raceways. The rigidity of the NSK bearing is determined by the ratio of bearing load to the amount of elastic deformation of the inner and outer rings and rolling elements. For the main spindles of machine tools, it is necessary to have high rigidity of the bearing together with the rest of the spindle. Consequently, since NSK roller bearings are deformed less by load, they are more often selected than ball bearings. When extra high rigidity is required, NSK bearing are given a preload, which means that they have a negative clearance. Angular contact ball bearings and tapered roller bearings are often preloaded.
Noise and torque of NSK various bearing types
Since NSK rolling bearings are manufactured with very high precision, noise and torque are minimal. For deep groove ball bearings and cylindrical roller bearings particularly, the noise level is sometimes specified depending on their purpose. For high precision miniature ball bearings, the starting torque is specified. NSK deep groove ball bearings are recommended for applications in which low noise and torque are required, such as motors and instruments.
Running accuracy and NSK bearing types
For the main spindles of machine tools that require high running accuracy or high speed applications like superchargers, high precision bearings of class 5, 4 or 2 are usually used.
The runnign accuracy of NSK rolling bearings is specified in various ways, and the specified accuracy classes vary depending on the NSK bearing type. A comparison of the inner ring radial runout for the highest running accuracy specified for each NSK bearing type is shown in picture below.
For applications requiring high running accuracy, NSK deep groove ball bearings, angular contact ball bearings, and cylindrical roller bearings are most suitable.
Mounting and dismounting of NSK various bearing types
Separable types of NSK bearings like cylindrical roller bearings, needle roller bearings and tapered roller bearings are convenient for mounting and dismounting. For machines in which bearings are mounted and dismounted rather ofter for periodic inspection, these types of NSK bearings are recommended. Also, self-aligning ball bearings and spherical roller bearings (small ones) with tapered bores can be mounted and dismounted relatively easily using sleeves.