Product Introduction

NUP Type Cylindrical Roller Bearings is a single-row Cylindrical Roller Bearing designed for bidirectional axial location. Structurally, it features integral ribs on both sides of the outer ring; the inner ring has an integral rib on one side and a detachable flat rib ring (or "loose rib") on the other. The bearing assembly consists of three main components: the outer ring assembly (outer ring, cylindrical rollers, and cage), the inner ring, and the flat rib ring. The flat rib ring snaps into a groove on the side of the inner ring that lacks an integral rib; together with the inner ring's integral rib, it provides axial constraint on both sides of the inner ring.

This configuration—combining integral ribs on both sides of the outer ring with an integral rib and a flat rib ring on the inner ring—enables the NUP-type bearing to withstand axial loads in both directions. It is the only single-row cylindrical roller bearing model capable of bidirectional axial location without requiring additional components. The detachable flat rib ring is the defining feature that distinguishes the NUP type from other models; it provides bidirectional location capability while maintaining the convenience of separable inner ring mounting.

Operating Principle

During operation, the cylindrical rollers of the NUP-type bearing undergo pure rolling motion between the outer and inner ring raceways. Radial loads are transmitted through the line-contact zones between the rollers and the raceways, resulting in a radial load-carrying capacity essentially identical to that of NJ-type and NU-type bearings of the same dimensions.

Bidirectional axial location is the core function of the NUP type, with force flow paths operating in two directions:

When the shaft is subjected to an axial force directed toward the side with the inner ring's integral rib, the shaft causes the inner ring to shift. The face of the inner ring's integral rib presses against the roller ends, transferring the axial force to the corresponding integral rib on the outer ring, which ultimately transfers the load to the bearing housing. This path is identical to the unidirectional location mechanism of the NJ type; the load-carrying capacity is determined by the strength of the integral rib, ensuring reliable performance. When the shaft is subjected to an axial force directed toward the side with the loose rib, the shaft drives the inner ring to move; the sidewall of the inner ring's groove pushes the loose rib, and the end face of the loose rib bears against the end faces of the rollers, which in turn transfer the axial force to the integral rib on the corresponding side of the outer ring. Along this load path, the axial force is transmitted via the sequence "inner ring groove → loose rib → roller end face." As the loose rib is a separate component, there is a slight clearance at the interface with the inner ring groove, and the rib itself has less thickness and strength than an integral rib; consequently, the axial load-bearing capacity in this direction is lower than that on the side with the integral rib. This is a critical characteristic to note when using NUP-type bearings: the axial load-bearing capacities in the two directions are not equal, with the loose rib side representing the weaker link.

Loose ribs are typically manufactured from the same bearing steel as the rings; they undergo heat treatment and grinding, with their end faces super-finished to minimize sliding friction against the roller end faces. During installation, the loose rib is snapped into the groove on the side of the inner ring that lacks an integral rib, where it is secured by the axial positioning provided by the groove. During disassembly, the loose rib can be removed first, allowing the inner ring to slide out of the roller assembly, thereby enabling the inner ring to be removed or installed independently.

Common Model Designations

The model designation format is: NUP + dimension series + bore diameter code. Suffix codes indicate parameters such as cage material, precision class, and internal clearance group. NUP: Designates a single-row cylindrical roller bearing with two integral ribs on the outer ring and one integral rib plus a loose rib (flat retaining ring) on the inner ring.

Dimension series: Common series include NUP2 (light/narrow), NUP3 (medium/narrow), NUP4 (heavy/narrow), and NUP10 (extra-light/wide).

Bore code: 00=10mm, 01=12mm, 02=15mm, 03=17mm; for 04 and above, multiply the code by 5 to obtain the bore diameter in millimeters.

Example: NUP2310 indicates an NUP-type single-row cylindrical roller bearing with a 23 dimension series (wide series) and a 50mm bore diameter. Suffixes include: M (machined brass cage), EM (reinforced brass cage), P5/P4 (precision classes), C3/C4 (increased internal clearance), and W33 (outer ring with lubrication groove and holes).

Application focus varies by series: NUP2 series is suitable for moderate loads and high speeds (e.g., small-to-medium gearboxes and pumps); NUP3 series offers higher load capacity and is widely used in speed reducers and construction machinery transmissions; NUP4 series is used for ultra-heavy-load, low-to-medium-speed equipment in mining and metallurgy; NUP10 series is used in precision transmissions and machine tool spindles where radial space is limited and high rigidity is required.

Key Advantages

Integrated bi-directional location: A single bearing can simultaneously support radial loads and axial loads in both directions, eliminating the need for additional angle rings or thrust bearings; this simplifies the shaft system design and reduces the number of components.

Compact axial footprint: The loose rib is contained within the bearing assembly and does not occupy external axial space. Compared to the "NJ type + HJ angle ring" combination, it saves the axial length otherwise taken up by the angle ring, making it ideal for applications with limited axial installation space.

Separable inner ring installation: With the loose rib removed, the inner ring can be mounted on or dismounted from the shaft independently, and the outer ring assembly can be removed as a unit. This facilitates installation and maintenance, making it suitable for operating conditions requiring an interference fit between the inner ring and the shaft. The loose rib can be replaced independently: If the loose rib wears due to excessive axial load or poor lubrication, it can be replaced without scrapping the entire bearing assembly, thereby reducing maintenance costs.

Limitations

Unequal bidirectional load-carrying capacity: The axial load-carrying capacity on the side with the loose rib is significantly lower than on the side with the integral rib; the direction of the maximum axial force must be verified during design to ensure the primary axial force is borne by the integral rib side.

Clearance fit between the loose rib and the groove: High-speed operation may result in fretting wear and noise, necessitating stringent lubrication conditions.

Complex structure and higher cost: The machining and assembly of the loose rib increase manufacturing costs, resulting in a price typically higher than that of NJ and NU types of the same size.

Unsuitable for heavy axial loads: The strength and rigidity of the loose rib are limited; excessive axial loads can cause deformation, wear, or even fracture of the rib. Consequently, the NUP type is suitable only for bidirectional locating applications involving moderate or light axial loads.

Application Scenarios

NUP-type bearings are utilized in applications requiring "compact, bidirectional axial location" combined with "moderate axial loads." Typical scenarios include:

Gearboxes and speed reducers: High-speed and intermediate shafts in spur gear reducers and planetary gearboxes; they provide bidirectional location within limited axial space while withstanding radial forces from gear meshing and bidirectional axial force components.

Pumps and compressors: Rotor support for multistage centrifugal pumps and screw compressors; the compact bidirectional locating structure limits axial rotor displacement while handling axial forces generated by fluid flow.

Construction machinery transmissions: Gearboxes and travel drives for loaders and excavators; these applications involve variable loads and impacts, alongside strict requirements for compact dimensions.

Machine tool spindles and drives: Spindle supports or feed drive shafts in certain lathes and milling machines; they offer high radial rigidity and bidirectional location where radial space is limited.

Railway and rolling stock: Axle boxes for certain railway vehicles and wheelsets for metro trains; the bidirectional locating capability allows them to withstand axial forces acting in both directions when traversing curves.

Mining and metallurgical equipment: Drive shafts for conveyors and crushers; they provide compact bidirectional location under moderate axial loads.

In these applications, NUP-type bearings can be used either independently as the bidirectional locating bearing or paired with N-type or NU-type floating bearings—with the NUP type serving as the locating bearing and the N/NU type as the floating bearing to form a complete shaft support system.

Differences Between NUP-Type and Other Types

The five basic types of single-row Cylindrical Roller Bearings share the same rolling element and raceway designs; the core differences lie in the rib configuration and axial locating capabilities. As the only type with built-in bidirectional locating capability, the NUP type differs from the others as follows:

NUP type vs. N type: The N type is a pure floating bearing with two ribs on the inner ring and no ribs on the outer ring, meaning it cannot withstand axial forces at all; the NUP type is a bidirectional locating bearing featuring two ribs on the outer ring and a combination of one rib and a loose rib (flat ring) on the inner ring, allowing it to withstand axial forces in both directions. The separability of the two types also differs: for the N-type, the inner ring assembly can be removed as a single unit; for the NUP-type, the outer ring assembly can be removed as a single unit, whereas the inner ring requires the prior removal of a flat retaining ring before it can be taken out separately. In shaft system design, the N-type serves only as a floating end, while the NUP-type serves as a bidirectional locating end; the two are frequently used in combination.

NUP-type vs. NU-type: The NU-type is a pure floating bearing featuring an outer ring with two integral ribs and an inner ring with no ribs; it has the simplest structure and lowest cost. The NUP-type builds upon the NU-type's outer ring design but modifies the inner ring to include one integral rib and a flat retaining ring, thereby adding bidirectional axial locating capability—though this increases the cost. The NU-type is suitable for floating ends requiring no axial location, while the NUP-type is suitable for locating ends requiring compact bidirectional location.

NUP-type vs. NJ-type: This comparison requires careful distinction. Both types feature outer rings with two integral ribs and inner rings with an integral rib on one side; their axial load-carrying capacity on the side with the integral rib is identical. The difference lies in the side of the inner ring without a rib: the NJ-type is completely open and lacks axial load-carrying capacity in that direction, whereas the NUP-type includes a detachable flat retaining ring, providing axial load-carrying capacity in that direction. To achieve bidirectional location with the NJ-type, an HJ-type angle ring must be installed on the shaft; while this externally mounted ring consumes more axial space, it can be designed for greater robustness and load capacity, and its fit with the shaft is more reliable. In contrast, the NUP-type's flat retaining ring is integrated within the bearing, resulting in a compact axial footprint, but the ring has limited load capacity and involves clearance in its fit with the inner ring groove. Simply put, choose the "NJ+HJ" combination when axial space is ample and axial loads are high; choose the NUP-type when axial space is limited and axial loads are moderate or low.

NUP-type vs. NF-type: The NF-type is a unidirectional locating bearing featuring an inner ring with two integral ribs and an outer ring with a single integral rib; it differs significantly from the NUP-type in terms of structure and locating capability. The NF type allows for axial location in only one direction and has limited load-carrying capacity due to the single rib on the outer ring, resulting in less frequent application; the NUP type allows for axial location in both directions, offers greater rigidity due to the double ribs on the outer ring, and is more widely used.

Installation and Maintenance

Special attention must be paid to the assembly of the loose rib when installing NUP-type bearings. An interference fit is typically used between the inner ring and the shaft; small bearings are pressed on using a press, while medium and large bearings are mounted by uniformly heating the inner ring to 80–100°C via induction heating before fitting it onto the shaft journal. The recommended installation sequence is as follows: first, heat and mount the inner ring onto the shaft; next, slide the loose rib onto the journal and seat it into the inner ring's groove, ensuring the face of the loose rib is flush with the face of the inner ring and free from warping; finally, align the outer ring assembly with the inner ring and loose rib, then smoothly push them together to complete the assembly. After assembly, rotate the inner ring by hand to confirm smooth rotation without binding and ensure there is no axial movement of the loose rib.

The disassembly sequence is the reverse: first, remove the outer ring assembly from the housing bore; next, remove the loose rib; finally, remove the inner ring using a hydraulic puller or induction heating. When removing the loose rib, use a specialized tool or a thin copper rod to gently pry it out of the groove; the use of sharp tools for forced prying is prohibited to avoid damaging the loose rib face or the inner ring groove. Transmitting impact forces through the rolling elements and direct flame heating of the bearing are strictly prohibited.

Regarding maintenance, NUP-type bearings have higher lubrication requirements than standard floating bearings because sliding or fretting friction occurs between the loose rib and the roller ends, as well as between the loose rib and the inner ring groove; poor lubrication can lead to wear on the loose rib, abnormal temperature rise, or even scoring/seizure. Grease lubrication is suitable for low-to-medium speeds, with a fill volume of one-third to one-half of the bearing cavity; oil lubrication is recommended for high speeds or heavy axial loads, and models featuring an outer ring with an oil groove and lubrication holes (W33 suffix) are preferred to improve lubrication conditions. During operation, monitor temperature (generally not exceeding 80°C), vibration, and noise regularly; wear on the loose rib ring manifests as periodic vibration and abnormal noise, necessitating timely inspection. During inspection, focus on checking the loose rib ring for wear, scuffing, or bluing (discoloration); the inner ring groove for indentations or deformation; and the roller ends for scratches. If the loose rib ring is severely worn, it can be replaced individually without scrapping the entire bearing assembly.

Regarding internal clearance, NUP-type bearings are more sensitive to clearance variations than floating bearings due to the constraints imposed by the loose rib ring. Clearance reduction caused by interference fits or temperature rises increases friction between the rollers and the ribs; therefore, C3 or C4 clearance classes (larger clearances) should be selected for high-temperature or high-interference applications.

Summary

The NUP-type cylindrical roller bearing is a single-row bearing capable of bidirectional axial location. It features an outer ring with two integral ribs and an inner ring with one integral rib plus a detachable loose rib ring. It can simultaneously support radial loads and axial loads in both directions, making it the only single-row cylindrical roller bearing type capable of bidirectional location without additional components. Its key advantages include compact axial space requirements, integrated bidirectional location capabilities, and separable inner ring mounting. Its primary limitations are weaker axial load-bearing capacity on the loose rib ring side, stringent lubrication requirements, and higher costs compared to NJ and NU types. NUP-type bearings are best suited for bidirectional location applications requiring compact structures where axial space is limited and axial loads are moderate or low; they are widely used in gearboxes, pumps, compressors, and construction machinery transmissions. When selecting a bearing, carefully compare the NUP type with the "NJ type + HJ angle ring" configuration: choose the NJ+HJ combination when axial space is ample and axial loads are high; choose the NUP type when axial space is tight and axial loads are low.