Product Introduction

NJ Type Cylindrical Roller Bearings is a semi-locating single-row Cylindrical Roller Bearing. Its structural design features integral flanges on both sides of the outer ring and a flange on only one side of the inner ring. The bearing consists of two main parts: an outer ring assembly (comprising the outer ring, cylindrical rollers, and cage) and the inner ring. The outer ring assembly axially retains the rollers and cage via its double flanges, allowing it to be separated and handled independently. The inner ring features a single flange, allowing it to slide out freely from the side without a flange. is a semi-locating single-row cylindrical roller bearing. Its structural design features integral flanges on both sides of the outer ring and a flange on only one side of the inner ring. The bearing consists of two main parts: an outer ring assembly (comprising the outer ring, cylindrical rollers, and cage) and the inner ring. The outer ring assembly axially retains the rollers and cage via its double flanges, allowing it to be separated and handled independently. The inner ring features a single flange, allowing it to slide out freely from the side without a flange.

This configuration—double flanges on the outer ring and a single flange on the inner ring—enables the NJ-type bearing to support radial loads while providing axial location in one direction. Because the single inner-ring flange supports axial loads in only one direction, the NJ type is classified as a "semi-locating bearing." It falls between the fully floating N and NU types and the fully locating (bidirectional) NUP type, offering a unidirectional locating solution.

Operating Principle

During operation, the cylindrical rollers of the NJ-type bearing undergo pure rolling motion between the outer and inner ring raceways, with radial loads transmitted through the line-contact zones between the rollers and raceways. This line-contact structure gives the NJ-type bearing a radial load-carrying capacity comparable to that of N and NU types of the same size, and significantly higher than that of deep-groove Ball Bearings.

Its axial locating mechanism is a defining characteristic of the NJ type. When the shaft is subjected to axial force in a specific direction, it drives the inner ring to move in that same direction. The flanged face of the inner ring presses against the ends of the rollers, which then transfer the axial force to the corresponding flange on the outer ring, ultimately transmitting the load to the bearing housing. This force transmission path allows the NJ-type bearing to reliably support axial loads in one direction. Conversely, in the opposite direction, the absence of a flange on the other side of the inner ring allows the shaft and inner ring to move freely relative to the outer ring assembly, providing no axial restraint.

It is worth noting that NJ-type bearings are frequently used in conjunction with HJ-type angle rings. An angle ring is an annular component with a flange; it is fitted onto the shaft against the side of the inner ring that lacks a flange, effectively serving as a detachable second flange for the inner ring. When paired with an angle ring, an NJ-type bearing can withstand axial loads in both directions, enabling bidirectional axial positioning; however, its primary axial load-carrying capacity remains on the side with the integral inner ring flange, while the capacity on the angle ring side is relatively limited. This "NJ+HJ" combination is widely used in equipment such as gearboxes and speed reducers, offering a cost-effective way to achieve bidirectional positioning while retaining the radial load-carrying advantages of Cylindrical Roller Bearings.

Model and Series

The model designation format for NJ-type bearings is: NJ + Dimension Series + Bore Code, followed by suffixes indicating parameters such as cage type, precision class, and internal clearance.

NJ: Indicates a single-row cylindrical roller bearing with two integral flanges on the outer ring and one integral flange on the inner ring.

Dimension Series: Common series include NJ2 (light/narrow), NJ3 (medium/narrow), NJ4 (heavy/narrow), and NJ10 (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.

For example, NJ2310 denotes an NJ-type, single-row cylindrical roller bearing with a 23 dimension series (wide series) and a 50mm bore diameter. Among the suffixes, M indicates a machined brass cage, J indicates a pressed steel cage, P5 and P4 indicate precision classes, and C3 and C4 indicate greater-than-normal internal clearance groups.

Each series is suited to specific applications: the NJ2 series is suitable for gearboxes and electric motors operating under moderate loads and high speeds; the NJ3 series offers higher load-carrying capacity and is widely used in speed reducers, crane travel wheels, and railway axle boxes; the NJ4 series is used for ultra-heavy-duty applications such as mining machinery and rolling mill auxiliary rolls; and the NJ10 series is used in precision drive units where radial space is limited but high rigidity is required. 

Key Advantages

Combined Radial and Axial Load Capacity: While retaining the radial load advantages of cylindrical roller bearings, this design offers unidirectional axial locating capability; a single bearing can simultaneously support radial forces and axial force in one direction, thereby simplifying the shaft system structure.

Separable Installation: The outer ring assembly and inner ring can be installed independently. For applications requiring an interference fit, the inner ring can be heated and mounted onto the shaft first, followed by the installation of the outer ring assembly into the housing bore. This facilitates assembly and is particularly suitable for conditions requiring a significant interference fit for the inner ring.

Flexible Locating via Angle Rings: By adding an HJ-type angle ring, unidirectional locating can be extended to bidirectional locating. Since the angle ring is replaceable, maintenance costs are low and design flexibility is high.

High Rigidity of Outer Ring Assembly: With integral flanges on both sides of the outer ring, the assembly offers superior overall rigidity compared to designs where the inner ring has the flanges. It maintains good operating performance even when the machining precision of the housing bore is moderate.

Limitations

Provides only unidirectional locating with no axial constraint in the opposite direction; requires pairing with other bearings or angle rings to achieve complete axial location.

The roller ends on the side of the inner ring without flanges lack guidance; consequently, roller stability at high speeds is slightly lower than in designs with double flanges on the inner ring.

Axial load capacity is limited; the contact between the flange and roller ends involves sliding friction. Excessive axial loads can cause flange wear and heat generation, making it unsuitable for applications dominated by axial loads. 

Application Scenarios

Gearboxes and Speed Reducers: High-speed and intermediate shafts in cylindrical gear reducers and worm gear reducers; radial forces from gear meshing are borne by the rollers, while axial force components are borne by the inner ring rib (often paired with an angle ring for bidirectional location).

Railway Axle Boxes: Bearings for freight and passenger railway axle boxes; they withstand the vehicle's weight and track impacts, with the inner ring rib absorbing axial forces generated when the vehicle traverses curves.

Crane Travel Wheels: Travel wheels for bridge cranes and gantry cranes (both bridge and trolley travel mechanisms); they withstand wheel loads as well as axial forces during starting and braking.

Mining Machinery: Drive shafts for crushers, vibrating screens, and conveyors; they withstand heavy radial loads and certain axial impacts.

Transmissions and Gearboxes: Intermediate and output shafts in automotive and construction machinery transmissions; they withstand radial forces from gear transmission and axial forces during gear shifting.

Electric Motors and Pumps: Medium-sized motors and multistage centrifugal pumps requiring unidirectional axial location; the NJ type's unidirectional locating capability is used to limit rotor axial displacement.

In these applications, NJ-type bearings can be used individually as a unidirectional locating bearing, paired with an angle ring for bidirectional location, or matched with N- or NU-type floating bearings—where the NJ type serves as the locating bearing and the N/NU type as the floating bearing—to form a complete shaft support solution.

Differences from Other Models

The five basic models of single-row cylindrical roller bearings (N, NU, NJ, NF, NUP) share the same rolling element and raceway designs; the core difference lies in the rib configuration, which determines their respective axial locating capabilities.

NJ Type vs. N Type: The N type features an inner ring with two ribs and an outer ring with no ribs, making it a purely floating bearing incapable of withstanding axial forces; the NJ type features an outer ring with two ribs and an inner ring with a single rib, allowing it to withstand axial force in one direction. Their separability also differs: for the N type, the inner ring assembly can be removed as a unit, whereas for the NJ type, the outer ring assembly can be removed as a unit. In shaft system design, the N-type bearing serves only as a floating-end bearing, whereas the NJ-type can function as a single-direction locating bearing; the two are frequently used in combination.

NJ-type vs. NU-type: Both feature double-ribbed outer rings, and their outer ring assemblies can be removed as a unit. The difference lies in the inner ring: the NU-type has an inner ring without ribs, making it a purely floating bearing, while the NJ-type has a single-ribbed inner ring, providing single-direction axial locating capability. The NU-type has a simpler structure and lower cost, making it suitable for floating ends requiring no axial location; the NJ-type is suitable for applications requiring some degree of axial constraint.

NJ-type vs. NF-type: The NF-type features a double-ribbed inner ring and a single-ribbed outer ring—the exact reverse of the NJ-type's rib configuration—yet both are single-direction locating bearings. In the NF-type, axial force is borne by the single rib on the outer ring, and its application is relatively limited. In the NJ-type, axial force is borne by the single rib on the inner ring; the double-ribbed outer ring provides greater rigidity to the outer ring assembly, leading to wider application and making it the mainstream single-direction locating cylindrical roller bearing in industry.

NJ-type vs. NUP-type: The NUP-type is derived from the NJ-type by adding a detachable flat retaining ring to the side of the inner ring that lacks a rib, thereby achieving bi-directional axial location. The structure on the ribbed side of the inner ring is identical for both; the difference is the addition of the flat retaining ring in the NUP-type. The NUP-type achieves bi-directional location independently without extra components, though the flat retaining ring has limited load-bearing capacity, a complex structure, and higher cost. The NJ-type can also achieve bi-directional location when paired with an angle ring; since the angle ring can be replaced separately, maintenance is more flexible and the overall cost is lower. In practice, the NJ+HJ combination is often selected when axial loads are light and space permits, whereas the NUP-type is chosen when space is restricted or an integrated structure is required.

Installation and Removal

The installation of NJ-type bearings follows the assembly procedures for separable bearings. An interference fit is typically used between the inner ring and the shaft; small bearings are pressed on using a sleeve and a press, while medium-to-large bearings are installed using induction heating—uniformly heating the inner ring to 80–100°C before quickly mounting it onto the shaft journal. The outer ring assembly and the housing bore typically feature a transition fit; they can be installed via press-fitting or cold assembly. During assembly, align the outer ring assembly with the inner ring and push it in steadily, ensuring the rollers are properly centered with the inner ring raceway.

If an HJ-type angle ring is used, it should be mounted flush against the side face of the inner ring that lacks a rib. The fit between the angle ring and the shaft is generally a transition or clearance fit; ensure the end faces of the angle ring and inner ring are in tight contact with no gap. The rib height of the angle ring should match that of the inner ring rib to ensure uniform load distribution on the roller end faces.

During disassembly, the outer ring assembly can be removed using a puller or by pushing it out through the cutout in the housing bore shoulder. The inner ring can be removed using a hydraulic puller or by heating it via induction and removing it while hot. When an angle ring is used, remove the angle ring before disassembling the inner ring. Do not transmit impact forces through the rolling elements, and do not use direct flame heating.

Maintenance Points

Regarding maintenance, the lubrication requirements for NJ-type bearings are the same as for other cylindrical roller bearings: grease lubrication for low-to-medium speeds (filling 1/3 to 1/2 of the bearing cavity) and oil lubrication for high speeds. Due to sliding friction between the inner ring rib and the roller end faces, ensure adequate lubrication when axial loads are high; if necessary, select a model with oil grooves and lubrication holes (suffix W33) to improve lubrication conditions. Regularly monitor temperature, vibration, and noise during operation; abnormal temperature rises or increased noise may indicate rib wear or scoring, requiring timely disassembly, inspection, and replacement.

Summary

NJ Type Cylindrical Roller Bearings is a semi-locating single-row cylindrical roller bearing. Its structural design features integral flanges on both sides of the outer ring and a flange on only one side of the inner ring. The bearing consists of two main parts: an outer ring assembly (comprising the outer ring, cylindrical rollers, and cage) and the inner ring. The outer ring assembly axially retains the rollers and cage via its double flanges, allowing it to be separated and handled independently. The inner ring features a single flange, allowing it to slide out freely from the side without a flange. is a semi-locating, single-row cylindrical roller bearing featuring two ribs on the outer ring and one rib on the inner ring. It can simultaneously support radial loads and axial loads in one direction. It is widely used in applications requiring unidirectional axial location, such as gearboxes, speed reducers, railway axle boxes, and crane travel wheels. Its greatest design flexibility lies in the ability to pair with an HJ-type angle ring to achieve bidirectional axial location, meeting various shaft positioning requirements cost-effectively and with ease of maintenance. Compared to N-type and NU-type bearings, the NJ type offers the additional capability of unidirectional axial location; compared to the NUP type, the NJ type features a simpler structure and lower cost, while providing equivalent functionality when used with an angle ring. When selecting a bearing, one must comprehensively evaluate factors such as the direction and magnitude of the axial load on the shaft system and the conditions for installation and maintenance to determine whether an angle ring is required and to select the appropriate pairing arrangement with the floating-end bearing.