Double row cylindrical roller bearings with cage can absorb very high radial forces due to the linear contact between rolling element and bearing ring. They are classified into two general designs which differ in flange position on the inner or outer ring. Double row cylindrical roller bearings can be disassembled and are easily installed or uninstalled. They are suitable for medium to high speeds, but they are rigid and cannot compensate angular misalignments.
KRW supplies double row cylindrical roller bearings with normal tolerance (PN) in accordance to DIN 620-2 (Tolerances for roller bearings) and ISO 492 (Radial bearings - Dimensional and geometrical tolerances). All other deviating or special tolerances must be specified with the order.
Double row cylindrical roller bearings with cage are dismountable and non-latching bearings that are available in the standard designs NNU and NN.
The outer ring of NNU bearings has three integral flanges while the inner ring is designed without flanges. For NN bearings, the three integral flanges are located on the inner ring and the outer ring has no flanges.
Double row cylindrical roller bearings with cage are suitable for the absorption of very high radial forces and offer especially high rigidity. Cylindrical roller bearings can be delivered with cylindrical or tapered bore.
The ball race type without flanges of both designs facilitates clearance in axial direction of the housing. The compensation of misalignment or linear expansion of the shaft occurs unrestrained in the bearing so a sliding fit in the housing or on the shaft is not necessary.
By default, cylindrical roller bearings by KRW are designed with optimised contact areas between rolling elements and raceways. Due to the logarithmic profiling of the cylindrical rollers, damaging edge tension is avoided even with very high loads.
Roller profiling and tension distribution of cylindrical rollers in comparison: Left without profiling, right with profiling
By default, double row cylindrical roller bearings by KRW are equipped with a roller-riding solid brass cage (suffix: M). Other cage designs are available on request or chosen for specific applications and labelled accordingly on the bearing.
Double row cylindrical roller bearings are not suitable for compensation of misalignments. Misalignments cause edge stresses between rolling elements and raceways and produce additional stresses in the bearing which reduce its operating life.
The kinematic limiting speed nG is a practical mechanical limit value and is based on the mechanical fatigue strength of the rolling bearing as a function of its installation situation and lubrication. The limit speed must not be exceeded even under optimum operating conditions without prior consultation with KRW.
The DIN ISO 15312 (Rolling bearings - Thermal speed rating) does not specify a thermal speed rating nth for these bearings.
Admissible Operating Temperatures
The admissible operating temperature of a bearing is limited by cage material, dimensional stability of the bearing components (ball race and rolling elements), as well as lubrication. By default, KRW bearings are stabilised up to 200°C (S1). KRW provides roller bearings for higher operating temperatures on request.
For dynamically loaded bearings
The service life formula according to ISO 281 L10 = (C/P)p for dynamically loaded bearings requires an equivalent load (P) from constant direction and size. To calculate P, calculation factors and the ratio of axial and radial load are required. This is shown in the following equations.
Equivalent Dynamic Bearing Load P
For a purely radially loaded cylindrical roller bearing acting as a floating bearing, the following applies:
|P||equivalent dynamic load||[kN]|
|Fr||dynamic radial force||[kN]|
For statically loaded bearings
Dynamic dimensioning loses its validity for bearings rotating at very low speeds (n x dm ≤ 4000 mm/min). The static load safety factor S0 is calculated as follows:
|S0||static load safety factor||[-]|
|C0||static load rating (from bearing chart)||[kN]|
|P0||equivalent static bearing load||[kN]|
|dm||mean bearing diameter [dm = (D+d)/2]||[mm]|
Static load capacity
A minimum load is required for the reliable operation of a rolling bearing. If the minimum load is not reached, slippage may occur. The minimum radial load for double row cylindrical roller bearings is roughly assumed to be 1.67% of the static load rating C0 of the bearing. If the value falls below this value, please consult KRW Application Technology.