Single Row Full Complement Cylindrical Roller Bearings
Full complement cylindrical roller bearings incorporate a maximum number of rollers and are therefore suitable for very heavy radial loads. However, they cannot operate at the same high speeds as caged design cylindrical roller bearings. The standard SKF range of single row full complement cylindrical roller bearings consist of the NCF and NJG designs.
NCF design bearings have two integral flanges on the inner ring and one integral flange on the outer ring and can thus support axial loads acting in one direction and provide axial shaft location in one direction. A retaining ring at the flangeless side of the outer ring holds the bearing assembly together. The axial internal clearance in the bearing is provided in the product table and is designed to permit small axial displacements of the shaft in relation to the housing, e.g. as a result of thermal expansion of the shaft, to be accommodated in the bearing.
Single row full complement cylindrical roller bearing,NCF design
NJG design bearings comprise the heavy dimension series 23 and are intended for very heavily loaded, slow speed applications.
Single row full complement cylindrical roller bearing, NJG design
These bearings have two integral flanges on the outer ring and one integral flange on the inner ring and can thus support axial loads acting in one direction and provide axial shaft location in one direction. In contrast to the other full complement bearing designs, NJG design bearings have a self-retaining roller complement. The outer ring with its two integral flanges together with the roller complement can therefore be withdrawn from the inner ring, without having to take any precautions to prevent the rollers from falling out. This simplifies mounting and dismounting.
The outer ring with its two integral flanges together with the roller complement can be withdrawn from the inner ring
The boundary dimensions of SKF single row full complement cylindrical roller bearings are in accordance with ISO 15:1998.
SKF single row full complement cylindrical roller bearings are produced to Normal tolerances. The values for the tolerances correspond to ISO 492:2002.
SKF single row full complement cylindrical roller bearings are produced with Normal radial internal clearance as standard. The majority of the bearings are also available with the greater C3 radial internal clearance. The values correspond to ISO 5753:1991. The clearance limits apply to unmounted bearings under zero measuring load.
The ability of single row full complement cylindrical roller bearings to accommodate angular misalignment of the inner ring with respect to the outer ring is limited to a few minutes of arc. The actual values are
- 4 minutes of arc for bearings of the narrow dimension series 18
- 3 minutes of arc for bearings of the wide dimension series 22, 23, 28, 29 and 30.
The above guideline values apply provided the position of the shaft and housing axes remains constant. A larger misalignment is possible, but may result in reduced bearing service life. In such cases, please contact the SKF application engineering service.
Influence of operating temperature on bearing material
SKF single row full complement cylindrical roller bearings undergo a special heat treatment. They can operate at temperatures of up to +150 °C.
To achieve satisfactory operation, single row full complement cylindrical roller bearings, like all ball and roller bearings, must always be subjected to a given minimum load, particularly if they are to operate at relatively high speeds (n > 0,5 times the reference speed) or are subjected to high accelerations or rapid changes in the direction of the load. Under such conditions the inertia forces of the rollers and the friction in the lubricant, can have a detrimental effect on the rolling conditions in the bearing arrangement and may cause damaging sliding movements to occur between the rollers and raceways.
The requisite minimum load to be applied to single row full complement cylindrical roller bearings can be estimated using
Frm = minimum radial load [kN]
kr = minimum load factor (see product data)
n = operating speed [r/min]
nr = reference speed [r/min] (see product data)
dm = bearing mean diameter
= 0,5 (d + D), mm
When starting up at low temperatures or when the lubricant is highly viscous, even greater minimum loads may be required. The weight of the components supported by the bearing, together with external forces, generally exceeds the requisite minimum load. If this is not the case, the single row full complement cylindrical roller bearing must be subjected to an additional radial load.
Dynamic axial load carrying capacity
Single row full complement cylindrical roller bearings with flanges on both the inner and outer rings can support axial loads in one direction only. Their axial load carrying capacity is primarily determined by the ability of the sliding surfaces of the roller end / flange contact to support loads. Factors having the greatest effect on this ability are the lubricant, operating temperature and heat dissipation from the bearing. When applying axial loads to full complement cylindrical roller bearings, lubrication by oil only is recommended.
Calculating the dynamic axial load carrying capacity
Under normal operating conditions the axial load carrying capacity can be estimated using the equations below. Conditions that are considered typical for normal bearing operation are:
- a certain temperature
There is a difference of 60 °C between the bearing operating temperature and the ambient temperature.
- a specific heat loss from the bearing
There is a flow of 0,5 mW/mm2 °C; with reference to the bearing outside diameter surface (A = π D B).
- adequate lubrication
Oil lubrication only is recommended. A viscosity ratio K ≥ 2 is required (see the section Lubrication conditions - the viscosity ratio K). If K is less than 2, friction and wear will increase. These effects can be reduced at low speeds, for example, by using lubricants with AW (anti-wear) or EP (extreme pressure) additives.
- sufficient radial load
The value of the radial load should be at least twice the value of the axial load. A lower ratio (axial versus radial load) is possible, but should be checked by the SKF application engineering service.
- limited misalignment
Where misalignment between the inner and outer rings exceeds 1 minute of arc, the action of the load on the flange changes considerably. Therefore the safety factors included in the guideline values may be inadequate. In these cases, contact the SKF application engineering service.
For bearings with a heat emitting reference surface area Ar ≤ 50 000 mm2, the permissible axial load can be calculated with sufficient accuracy from
For bearings with a heat emitting reference surface area Ar ≥ 50 000 mm2, the permissible axial load can be calculated with sufficient accuracy from
When circulating oil lubrication provides efficient cooling, the permissible axial load can be raised by
ΔFap = k1 ΔTs Vs 15 × 104 / (π (d + D))
Ar = heat emitting reference surface area in accordance with ISO 15312:2003
= π B (D + d) [mm2]
Fap = permissible axial load [kN]
ΔFap = raise for permissible axial load due to cooling [kN]
C0 = basic static load rating [kN]
Fr = actual radial bearing load [kN]
n = rotational speed [r/min]
d = bearing bore diameter [mm]
D = bearing outside diameter [mm]
B = bearing width [mm]
ΔTs = temperature difference between oil inlet and outlet [°C]
Vs = oil flow through the bearing [l/min]
k1 = a factor
k2 = a factor
The values for the permissible load Fap obtained from the equations are valid for a constant and continuous axial load provided there is an adequate supply of lubricant to the roller end / flange contacts. Where axial loads act only for short periods, the values can be multiplied by 2. For shock loads the values can be multiplied by 3, provided the following limits relative to flange strength are not exceeded. A short period can last anywhere from several seconds to a few minutes. It is characterized by a temperature spike of not more than 5 °C after which time the bearing returns to normal operating temperature. As a rule of thumb, a short period is considered as the time it takes for the bearing to make 1 000 revolutions. Values calculated according to the above equations are not hard limits. If higher axial load carrying capacity than calculated is required, contact the SKF application engineering service for detailed analysis.
Axial load limit relative to flange strength
To avoid the risk of flange fracture, the constantly acting axial load applied to the bearings should never exceed
Famax = 0,0023 D1,7
Famax = maximum constantly acting axial load [kN]
D = bearing outside diameter [mm]
Where axial loads act only for short periods, the values for Famax can be multiplied by a factor of 2 while shock loads can be multiplied by a factor of 3.
Requirements for abutments
In applications where single row full compliment cylindrical roller bearings are subjected to heavy axial loads, axial runout and the size of the abutment surfaces of adjacent components can affect flange load and running accuracy. To obtain an even flange load and provide proper running accuracy, use the values provided in the table. For the diameter of the abutment surfaces, SKF recommends supporting the inner ring at a height corresponding to half the flange height. The recommended shaft abutment diameter das can be obtained from the product table.
Abutment diameter for proper flange support
Equivalent dynamic bearing load
For non-locating bearings
P = Fr
If the bearings are used to locate a shaft in one direction, the equivalent dynamic bearing load should be calculated using
P = Fr when Fa/Fr = e
P = 0,92 Fr + YFa when Fa/Fr > e
e = limiting value
= 0,2 for bearings in the 18 series
= 0,3 for bearings in the series 22, 23, 28, 29 and 30 series
Y = axial load factor
= 0,6 for bearings in the 18 series
= 0,4 for bearings in the 22, 23, 28, 29 and 30 series
The appropriate values for e and Y are given in the product table.
Since axially loaded single row full complement cylindrical roller bearings only operate satisfactorily when they are subjected to a simultaneously acting radial load, the ratio Fa/Fr should not exceed 0,5.
Equivalent static bearing load
P0 = Fr
The designation suffixes used to identify certain features of SKF single row full complement cylindrical roller bearings are explained in the following.
|CV||Modified internal design, full complement roller set|
|C3||Radial internal clearance greater than Normal|
|E||Reinforced roller complement|
|HA1||Case-hardened inner and outer rings|
|HB1||Bainite hardened inner and outer rings|
|L4B||Bearing rings and rolling elements with special surface coating|
|L5B||Rolling elements with special surface coating|
|V||Full complement of rollers (without cage)|
|VH||Full complement of rollers (without cage), self-retaining|
Cylindrical roller bearings
Single row cylindrical roller bearings
Double row cylindrical roller bearings
Multi-row cylindrical roller bearings
Single row full complement cylindrical roller bearings
Double row full complement cylindrical roller bearings
Multi-row full complement cylindrical roller bearings
Split cylindrical roller bearings