SKF CYLINDER ROLLER BEARING NNU 4956 BK/SPW33

SKF cylindrical roller bearings are available in many designs, series and sizes. The major design differences between the bearings presented in this section are in:- the number of roller rows (one, two or four) - the type of cage (with, without or special designs) - Bearings with cage can accommodate heavy radial loads, rapid accelerations and high speeds. - Full complement bearings (without cage) incorporate a maximum number of rollers and are therefore suitable for very heavy radial loads at moderate speeds. - SKF high-capacity cylindrical roller bearings combine the high load carrying capacity of a full complement bearing with the high speed capability of a bearing with cage. - the configuration of the inner and outer ring flanges (position and number of guide flanges)

This SKF cylindrical roller bearing series with two rows of rollers was developed for high-precision applications and combines high radial load capacity with precise running accuracy. The optimized design eases mounting while helping to reduce vibrations and heat generation.

Explanation:
• NNU: two-row bearing with three flanges on the outer ring and without flanges on the inner ring. Allows axial displacements in both directions without taking up axial loads
• K: tapered bore 1:12 for mounting by progressive press fitting and precise adjustment of the radial internal clearance
• B: two-piece brass cage in comb-type design for high mechanical stability and suitability for high speeds
• SP: precision class for spindle applications with very low runout deviation and high dimensional stability
• W33: lubrication groove and lubrication holes for simplified relubrication and improved lubricant distribution

Features:
The two-row configuration enables efficient distribution of radial loads while providing high stiffness. Because there are no flanges on the inner ring, the inner ring can displace axially in both directions, while the outer ring flanges guide the rollers precisely. This feature is particularly advantageous for bearings exposed to thermal expansion or position changes. Furthermore, the brass cage increases mechanical stability and reduces vibration-induced influences.
The separable and replaceable inner ring facilitates mounting and dismounting operations, especially when both bearing rings must be fitted with high precision. The tapered bore 1:12 supports mounting through controlled press fitting and allows fine adjustment of the radial internal clearance.
The integrated lubrication system with lubrication groove and lubrication holes ensures even lubricant supply. In addition, the low cross-sectional height of the bearing makes it ideal for compact machine designs.

Maintenance:
Controlled lubrication of the bearing is essential for reliable operation. Thanks to the integrated lubrication holes, relubrication can be performed easily and regularly. Regular inspection of the lubricant condition is recommended to limit wear and temperature rise.
Monitoring vibrations and noise enables early detection of potential malfunctions. Additionally, visual inspection should be carried out as part of maintenance to check the condition of the raceways and the cage. Cleaning must be performed with suitable, compatible products to avoid contamination.

Strengths:
• Ensures high running accuracy in spindle applications and sensitive precision systems
• Facilitates mounting and dismounting through the separable design, especially for tight fits
• Allows axial displacements of the inner ring and thereby reduces stresses caused by thermal expansion
• Reduces vibrations and noise and thus contributes to overall system stability
• Optimizes lubrication management through even lubricant distribution
• Ideal for compact designs thanks to low cross-sectional height

Applications:
The typical application area for these bearings is the machine tool industry: turning, milling or grinding spindles where running accuracy and shaft stiffness are decisive for the surface quality of manufactured parts.
In addition, these bearings are used in measurement and precision engineering as well as in drive systems that require stiff guidance at high speeds. In heavy industry, the W33 version facilitates integration into systems with centralized lubrication. This is particularly advantageous in continuous production environments where maintenance downtime must be minimized.
The separable design also simplifies replacement in hard-to-reach bearing positions — a concrete advantage for maintenance departments that service production plants in continuous operation.