Product Introduction

NF Type Cylindrical Roller Bearings is a single-row Cylindrical Roller Bearing designed for unidirectional axial location. Structurally, it features integral ribs on both sides of the inner ring and a rib on only one side of the outer ring. The bearing consists of two main parts: an inner ring assembly (comprising the inner ring, cylindrical rollers, and cage) and the outer ring. The inner ring assembly is a self-contained unit where the rollers and cage are axially retained by the ribs on both sides of the inner ring. The outer ring features a single rib, allowing the inner ring assembly to slide out independently from the side without a rib.

This configuration—ribs on both sides of the inner ring and a single rib on the outer ring—enables the NF-type bearing to provide unidirectional axial location. The ribs on the inner ring securely retain the rollers. When the shaft is subjected to an axial force directed toward the side of the outer ring that has the rib, the inner ring moves with the shaft, and the roller end faces press against the outer ring's rib, thereby transferring the axial force to the bearing housing. Conversely, in the opposite direction, the absence of a rib on the other side of the outer ring allows the inner ring assembly (along with the rollers) to slide out relative to the outer ring, meaning no axial restraint is provided in that direction. Therefore, while both NF-type and NJ-type bearings are classified as semi-locating bearings, their rib configurations are exact opposites, resulting in distinct axial force transmission paths and separation characteristics.

Operating Principle

During operation, the cylindrical rollers of the NF-type bearing undergo pure rolling motion between the inner and outer ring raceways. Radial loads are transmitted through the line contact areas between the rollers and the raceways; consequently, the radial load-carrying capacity is essentially the same as that of N-type and NJ-type bearings of identical dimensions.

The core mechanism for axial location lies in the single rib of the outer ring. When the shaft is subjected to an axial load directed toward the side of the outer ring with the rib, the force transmission path is as follows: the shaft drives the movement of the inner ring; the rib face of the inner ring pushes against the end faces of the rollers; the rollers transfer the axial force to the single rib of the outer ring; and finally, the outer ring transfers the force to the shoulder of the bearing housing. In this configuration, the double ribs on the inner ring ensure there is no relative axial displacement between the rollers and the inner ring; the entire axial force is borne by the single rib on the outer ring. Consequently, the rib on the outer ring and the corresponding shoulder on the bearing housing must possess sufficient strength and rigidity.

When the shaft is subjected to axial force in the opposite direction, the inner ring drives the rollers to move outward. Since there is no rib on that side of the outer ring, the rollers can slide directly out of the outer ring raceway, meaning the bearing provides no axial restraint. Therefore, NF-type bearings can reliably support axial loads in only one direction; when using them, one must ensure the direction of the axial force aligns with the side of the outer ring that has the rib.

It is important to note that with NF-type bearings, axial force is borne by the outer ring and transmitted to the housing. While this appears similar to the NJ type in terms of the final load-bearing component (where axial force is borne by the inner ring rib but ultimately transmitted to the outer ring and housing), the load transmission path differs. The double-ribbed inner ring structure of the NF type provides greater rigidity for the inner ring assembly and more reliable roller positioning; however, the single-ribbed outer ring has lower overall rigidity compared to a double-ribbed outer ring, placing higher demands on the machining precision and coaxiality of the bearing housing bore.

Model and Series

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

NF: Indicates a single-row cylindrical roller bearing with double ribs on the inner ring and a single rib on the outer ring.

Dimension Series: Common series include NF2 (light, narrow), NF3 (medium, narrow), and NF4 (heavy, narrow).

Bore Diameter 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, NF308 denotes an NF-type, Series 3, single-row cylindrical roller bearing with a 40mm bore diameter. In the suffix codes, M denotes a solid copper alloy cage, J denotes a pressed steel cage, P6 and P5 indicate precision classes, and C3 and C4 denote larger internal clearance groups.

In the market, the NF series typically consists primarily of the NF2 and NF3 types; the NF4 and NF10 series are less common and usually require custom ordering. This is linked to the relatively narrow application scope of the NF type—the NJ type is preferred for most applications requiring unidirectional axial location, whereas the NF type is used only in specific industries and mounting configurations.

Key Advantages

Inner ring assembly is removable as a unit: Double integral ribs on the inner ring retain the rollers and cage, allowing the inner ring assembly to be mounted or dismounted as a single unit—similar to the separation method of the N type. This is highly convenient when the inner ring has an interference fit with the shaft and frequent removal is required: the outer ring remains in the housing bore while the inner ring assembly is removed intact, resulting in high maintenance efficiency.

High inner ring rigidity and reliable roller guidance: Double ribs on the inner ring provide more stable axial guidance for the rollers; rollers are less prone to tilting or skewing during high-speed operation, ensuring superior running accuracy and stability.

Unidirectional axial location: While retaining the radial load-carrying advantages of Cylindrical Roller Bearings, it offers axial location capability in one direction, which can simplify the shaft system design and reduce the need for additional locating components.

Limitations

Insufficient rigidity of the single-ribbed outer ring: With a rib on only one side, the overall rigidity of the outer ring is lower than that of a double-ribbed outer ring. It places higher demands on the machining accuracy and coaxiality of the housing bore; insufficient housing rigidity can easily lead to outer ring deformation and vibration.

Narrow application scope: Although the NF and NJ types share similar functions, their rib configurations are reversed. The NJ type, featuring a double-ribbed outer ring, offers superior rigidity and a wider range of applications. Consequently, market demand for the NF type is significantly lower than for the NJ type; some sizes and series require custom ordering, resulting in longer lead times.

Restricted axial force direction: It can only accommodate axial forces directed toward the side with the outer ring rib. Correct orientation during installation is critical; reverse installation will cause the axial locating function to fail completely. Incompatibility with L-shaped thrust collars: Unlike the NJ type—which allows for bidirectional locating capabilities by adding an L-shaped thrust collar to the inner ring—the NF type features a single integral rib on the outer ring. Consequently, the NF type is limited to unidirectional locating and cannot be upgraded to bidirectional locating through simple accessory additions.

Application Scenarios

Automotive and construction machinery transmissions: Used for countershafts and reverse gear shafts in certain manual and construction machinery transmissions. The separable inner ring assembly facilitates gearbox maintenance, while the outer ring's single rib withstands the unidirectional axial force generated during gear shifting.

Agricultural machinery: Used in drive shafts and gearboxes for tractors and harvesters. Given the harsh operating environments and frequent maintenance requirements, the separable inner ring assembly allows for quick replacement in the field.

Textile machinery: Used in drive shafts for spinning frames and looms. These applications involve high rotational speeds and moderate radial loads; the stability provided by the inner ring's double ribs enhances operational precision.

Light industry and food processing machinery: Used in drive shafts for packaging machines and conveyors. These applications prioritize simple structures and easy maintenance, and the NF type's unidirectional locating capability is sufficient to meet operational needs.

Specific motors and pumps: Used at the non-locating end of certain small-to-medium-sized motors and single-stage pumps where axial movement needs to be restricted in only one direction.

Speed reducers and worm drives: Used for worm gear shafts in certain worm gear reducers, where the NF type withstands the unidirectional axial force component generated by worm meshing.

In these applications, the NF type typically serves as the unidirectional locating bearing, paired with an N-type or NU-type floating bearing at the other end to form a complete shaft support system. It is important to note that the NF type is often selected not because it outperforms the NJ type, but due to specific installation and maintenance requirements: the NF type's inner ring structure (with double ribs) is more convenient when the inner ring assembly needs to be frequently removed from the shaft as a unit while the outer ring remains in the housing bore.

Differences from 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 configuration of the ribs. The NF type is a single-direction locating bearing featuring a single integral rib on the outer ring; its distinctions from other types are as follows:

NF vs. N: Both feature inner rings with two integral ribs, allowing the inner ring assembly to be removed as a unit; their separation methods are identical. The difference lies in the outer ring: the N type has no ribs on the outer ring, making it a purely floating bearing incapable of handling axial loads, whereas the NF type has a single rib on the outer ring, allowing it to support axial loads in one direction. The N type offers a simpler structure and lower cost, making it suitable for floating-end applications requiring no axial location; the NF type is suited for applications requiring single-direction location and frequent removal of the inner ring assembly.

NF vs. NU: The NU type is a purely floating bearing with two ribs on the outer ring and no ribs on the inner ring, differing significantly from the NF type. With the NU type, the outer ring assembly can be removed as a unit while the inner ring separates independently; conversely, with the NF type, the inner ring assembly can be removed as a unit while the outer ring separates independently. Their separation methods are exact opposites, as are their axial locating capabilities: the NU type is fully floating, while the NF type provides single-direction location.

NF vs. NJ: This is the most critical comparison. Both are single-direction locating bearings with essentially the same function, yet their rib configurations are reversed. The NJ type features two ribs on the outer ring and one on the inner ring (outer ring assembly removable as a unit; axial load borne by the inner ring's single rib), whereas the NF type features two ribs on the inner ring and one on the outer ring (inner ring assembly removable as a unit; axial load borne by the outer ring's single rib). The key factor in selection is **which ring requires frequent removal**: choose the NJ type if the outer ring assembly needs frequent removal from the housing bore while the inner ring remains on the shaft; choose the NF type if the inner ring assembly needs frequent removal from the shaft while the outer ring remains in the housing bore. Additionally, the NJ type's outer ring (with two ribs) offers greater rigidity, lower housing bore precision requirements, and broader applicability, resulting in higher market prevalence; the NF type's outer ring (with a single rib) has lower rigidity, requires higher housing bore precision, and has a narrower application range. Furthermore, the NJ type can achieve bi-directional location when paired with an HJ angle ring, whereas the NF type cannot extend its locating capability to bi-directional operation through simple accessories. NF and NUP Types: The NUP type is a bidirectional locating bearing featuring an outer ring with two integral ribs and an inner ring with one integral rib plus a loose rib (flat collar); it differs significantly from the NF type. The NUP type can withstand axial loads in both directions; while its outer ring offers high rigidity due to the double ribs, the structure is complex and costly. In contrast, the NF type provides only unidirectional location; although the outer ring has lower rigidity due to the single rib, the structure is simpler, and the inner ring assembly can be removed as a single unit. The NUP type is suitable for applications requiring compact bidirectional location, whereas the NF type is ideal for applications requiring unidirectional location and frequent removal of the inner ring.

Installation and Maintenance

When installing NF type bearings, first verify the orientation of the outer ring's ribbed side to ensure it aligns with the direction of the axial load. An interference fit is typically used between the inner ring and the shaft; small bearings are pressed on, while medium-to-large bearings are mounted using induction heating—heating the inner ring assembly (inner ring, rollers, and cage) as a unit to 80–100°C before sliding it onto the shaft journal. The outer ring usually employs a transition fit with the housing bore and can be pressed in or installed at ambient temperature; ensure the ribbed side of the outer ring sits flush against the housing shoulder, with the non-ribbed side facing outward. During assembly, align the inner ring assembly with the outer ring and push it in steadily, ensuring proper alignment between the rollers and the outer ring raceway.

Since the inner ring assembly is removable, maintenance is convenient; the inner ring assembly can be taken out while the outer ring remains in the housing bore, facilitating inspection and replacement. To remove the inner ring assembly, use a hydraulic puller with the jaws positioned against the inner ring's end face—never hook the cage. If the interference fit is tight, induction heating may be used to expand the inner ring for easier removal while hot. To remove the outer ring, push it out from the side of the housing bore opposite the shoulder using a special tool, or extract it via the removal notches on the housing shoulder.

Regarding maintenance, lubrication requirements for NF 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 outer ring's single flange and the roller end faces, ensure adequate lubrication when axial loads are high; if necessary, select models featuring oil grooves and lubrication holes. Monitor temperature, vibration, and noise during operation; abnormal temperature rises or periodic noise may indicate wear on the outer ring flange, necessitating timely disassembly and inspection. During inspection, focus on checking the outer ring flange face for wear, scuffing, or bluing (discoloration); the inner ring flanges for indentations; and the roller end faces for scratches.

Regarding internal clearance selection, the NF type is more sensitive to clearance variations than fully floating bearings due to the constraint imposed by the outer ring's single flange. For high-temperature or heavy interference fit applications, select C3 or C4 clearance classes to compensate for clearance reduction caused by fits and thermal expansion.

Summary

NF Type Cylindrical Roller Bearings is a single-row bearing featuring double flanges on the inner ring and a single flange on the outer ring, capable of supporting both radial loads and axial loads in one direction. Its most distinctive structural feature is that the inner ring assembly can be removed as a single unit, facilitating frequent disassembly and maintenance. Compared to the NJ type—which shares similar functionality but has an inverted flange configuration—the NJ type offers double flanges on the outer ring, superior rigidity, and a broader application range. In contrast, the NF type features double flanges on the inner ring and a removable inner ring assembly but possesses lower outer ring rigidity and a more limited application scope. Selection of the NF type hinges on installation and maintenance requirements: it is more convenient than the NJ type when the inner ring assembly must be frequently removed from the shaft while the outer ring remains in the housing bore. Otherwise, for most unidirectional locating applications, the NJ type is preferable due to its higher market availability and superior rigidity. NF-type bearings are widely used in automotive transmissions, agricultural machinery, textile machinery, and other applications requiring unidirectional location and frequent maintenance.