The rolling element is a radial rolling bearing made up of cylindrical rollers.
The internal structure of a cylindrical roller bearing consists of rollers arranged in parallel, with spacers or separators placed between them to prevent tilting or friction between the rollers. This arrangement effectively prevents any increase in rotational torque.
Overview
Cylindrical rollers and raceways are types of line contact bearings that have a large load capacity and are mainly designed to bear radial loads. The rolling element produces very little friction with the ferrule rib, making it suitable for high-speed rotation.
Based on the presence or absence of ribs on the ferrule, cylindrical roller bearings can be divided into single-row bearings such as NU, NJ, NUP, N, NF, and double-row bearings such as NNU and NN.
These bearings consist of separable inner and outer rings. Cylindrical roller bearings without ribs on the inner or outer ring allow for relative movement in the axial direction and can be used as free-end bearings. On the other hand, cylindrical roller bearings with a single rib on one side of the inner and outer rings can withstand axial loads in one direction.
Steel stamping cages or solid copper alloy cages are commonly used, although some designs may incorporate polyamide-shaped cages.
Bearing characteristics
The rollers and the raceways are in contact with the wire or repaired, and have a high radial load capacity, making them suitable for bearing heavy and impact loads.
The friction coefficient is small, making them suitable for high speeds, with a limit speed close to that of a deep groove ball bearing.
N-type and NU-type bearings can move axially, which allows them to adapt to changes in the relative position of the shaft and the housing caused by thermal expansion or installation error, and can be used as free-end support.
The shaft or seat hole’s machining requirements are high. After installation, the relative deflection of the outer ring axis should be strictly controlled to avoid contact stress concentration.
The inner or outer ring can be separated for easy installation and removal.
Features
Cylindrical roller bearings have the advantage of being in line contact with the raceway, providing them with a large radial load capacity. They are suitable for heavy and shock loads and can also handle high-speed rotation.
The raceways and rolling elements of cylindrical roller bearings have a geometric design. With improved structural design, they now have even higher carrying capacity.
The new rib and roller end face design enhances the axial bearing capacity and lubrication conditions of the contact area between the roller end face and the rib. These enhancements improve the overall performance of the bearing.
Structural type
- The N0000 type of cylindrical roller bearings has no rib on the outer ring, while the NU0000 type has no rib on the inner ring. These bearings can accept large radial loads, have a high limit speed, do not restrict the axial displacement of the shaft or housing, but cannot withstand axial loads.
- Cylindrical roller bearings with ribs on both the inner and outer rings (NJ0000 and NF0000 bearings) can displace the shaft or housing in one direction and accept small one-way axial loads.
NU0000+HJ0000, NJ0000+HJ0000, and NUP0000 bearings can displace the shaft or housing in the axial clearance of the imported bearings and accept small bidirectional axial loads.
Bearing classification
Cylindrical roller bearings are bearings that can be easily installed and disassembled. They are capable of withstanding large radial loads and are suitable for use in high-speed applications.
These bearings allow for a small angular error (inclination) of only 2′ to 4′ between the inner ring axis and the outer ring axis. Therefore, the machining accuracy of the shaft and the bearing housing needs to be relatively high to prevent uneven load or stress concentration at the contact portion of the raceway. However, stress concentration can be reduced by correcting the roller or raceway contact busbar.
Cylindrical roller bearings can be divided into different structures, including single row, double row, and multi-row cylindrical roller bearings, depending on the number of rows of rolling elements. Different structural bearings are also designed with different ribs.
Cylindrical roller bearings are commonly used in various forms, including:
Single row cylindrical roller bearing
Single-row cylindrical roller bearings are designed to be separable, making them easy to install and disassemble. These bearings can be installed with a tight fit on both ferrules, and the modified roller’s contact line with the raceway helps reduce stress concentration.
Double row cylindrical roller bearing
Double-row cylindrical roller bearings are floating bearings, and their separability makes installation and disassembly convenient. Both ferrules can be fitted tightly.
Double-row cylindrical roller bearings have almost no inclination angle.
Single row bearing
N, NU type
The N-type bearing’s outer ring lacks ribs, while the inner ring has them on both sides. As a result, it can accommodate shaft displacement in the axial direction concerning the bearing housing.
On the other hand, the NU type bearing’s outer ring has ribs on both sides, whereas the inner ring has none. This design allows for shaft displacement in both axial directions concerning the bearing housing.
Hence, this structure is ideal for use as a swim end bearing.
NJ, NF type
NJ-type bearings feature ribs on both sides of the outer ring, while the inner ring has ribs on only one side. They are capable of withstanding a certain amount of one-way axial load.
On the other hand, the NF type of bearing has a rib on one side of the outer ring and ribs on both sides of the inner ring. It can also withstand a certain amount of one-way axial load.
As a result, this particular structure is well-suited for use as a unidirectional axially oriented bearing.
NUP, NFP type
The NUP type bearing features ribs on both sides of the outer ring, a single fixed rib on one side of the inner ring, and a detachable flat ring on the other side. This type of bearing can withstand a certain amount of bidirectional axial load.
Similarly, the NFP type bearing has a fixed single rib on one side and a detachable flat ring on the other side, with ribs on both sides of the inner ring. It too can withstand a certain amount of bidirectional axial load.
These structural bearings effectively limit the displacement of the shaft in both axial directions relative to the bearing housing. As a result, they are well-suited for use as fixed end bearings.
NH(NJ+HJ) type
The NH type bearing combines the NJ type bearing and the HJ type slanting ring.
The NUP bearing’s inner ring is short and the flat ring is not fixed, making it inconvenient to use.
The NH-type bearing uses the entire width of the inner ring of the NJ-type bearing to maintain a tighter fit with the shaft.
Additionally, the NH type bearing is easier to install and disassemble.
The NH type bearing restricts shaft displacement in both directions relative to the bearing housing, making it suitable for use as a fixed end bearing.
Double row bearing
Double-row cylindrical roller bearings are available with cylindrical inner bores and conical inner bores (indicated by the bearing rear code followed by K). These bearings offer several advantages, such as a compact structure, high rigidity, large bearing capacity, and minimal deformation after being loaded. They are especially suitable for supporting machine tool spindles.
The conical inner bore also allows for slight adjustment of the clearance, simplifies the positioning device’s structure, and facilitates installation and disassembly.
The commonly used double-row cylindrical roller bearings come in the following forms:
NN, NNU type
The NN bearing’s outer ring lacks ribs, while the inner ring has a middle rib positioned at the center.
This design permits axial shaft displacement in both directions relative to the bearing housing.
On the other hand, NNU type bearings feature a middle rib on the outer side of the outer ring, but no rib on the inner side.
This type of bearing is ideal as a swim end bearing, as it also allows for axial shaft displacement in both directions.
Most cages for this bearing type employ a solid cage that is manufactured by a vehicle.
NNF type
The NNF type bearing is a double row, full complement cylindrical roller bearing. The bearing consists of a structure with a middle rib outer ring and two double rib inner rings. The rollers are guided by the ribs of the inner ring, and the two inner rings are fastened together by fastening rings. In addition to being able to withstand large radial and axial loads, the structure can also withstand overturning moments, making it suitable as a fixed end bearing.
Both sides of the NNF type bearing are equipped with contact seals, and the bearing is filled with grease. The working temperature of the grease ranges from -50 °C to +110 °C. However, the operating temperature of the bearing is limited to between -40 °C and +80 °C due to the sealing material’s limitations.
Under favorable working conditions, the sealed NNF bearing does not require maintenance. However, if the bearing is operating in a polluted environment or with water vapor for an extended period while running at medium to high speed, it can be relubricated through the lubricating oil groove and the lubricating oil hole on the outer ring.
Four row bearing
Four-row cylindrical roller bearings are primarily used in rolling mill machinery, including cold and hot rolling mills and blanking machines.
These bearings have a separate structure, and the bearing ring and rolling element assembly can be easily separated, making it convenient for cleaning, inspection, installation, and disassembly of the bearing.
FC type
The FC type bearing is composed of two outer rings and one inner ring, and each of the outer rings has middle rib in the middle of the rib and rib in the inner ring.
FCD type
The FCD bearing type is actually a combination of two NN bearings.
FC and FCD bearings allow for axial displacement in the axial direction relative to the housing, making them suitable as a thrust bearing.
The cage of this type of bearing mostly uses a milled body with a ratio of 13:58.
Bearing applications
- Large and medium motor
- Locomotive vehicle
- Machine tool spindle
- Internal combustion engine
- Generator
- Gas turbine
- Gearbox
- Rolling mill
- Vibrating screen
- Lifting and transport machinery
