Tapered Roller Bearings

Single row tapered roller bearings feature angular raceways of inner and outer ring and a resulting force-transferring contact angle. Due to this, an axial load always induces a radial load and the other way around, which is why tapered roller bearings are always combined with a second bearing. Paired, they can in addition to radial forces also absorb axial and combined forces and are particularly suitable for medium to high speeds. Single row tapered roller bearings can be disassembled which facilitates a separate assembly of inner and outer ring.

For combined bearing sets there is a distinction between O-, X-, or tandem arrangement based on pressure line contact. Bearing sets in O-arrangement are very rigid and are excellently suitable for the absorption of moments thanks to their wide support base. The mirror-image X-arrangement is usually used with an additional radial bearing functioning as floating bearing on the opposite end of the shaft. Bearings in tandem arrangement distribute the loads and increase the load capacity. In practice, this option is used very rarely.

Single row tapered roller bearings are of limited suitability for compensation of misalignments. The admissible misalignment between inner and outer ring depends on the bearing size, the internal bearing design, the clearance fit, and the acting of forces and moments. Misalignments cause harmful movement of the rolling elements and produce additional stresses in the bearing which reduce its operating life.

KRW distinguishes between kinematic limiting speed n_G and thermal reference speed n_th. The kinematic limiting speed 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 thermal reference speed represents the equilibrium between the heat generated in the bearing by friction and the heat flow dissipated. It is standardised in DIN ISO 15312 (Rolling bearings - Thermal reference speed).

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.

Equivalent Dynamic Bearing Load P

a) Single bearings and tandem arrangement

b) O- and X-arrangement

The equivalent bearing service life for the tapered roller bearings depends on the ratio F_a/F_r . The equivalent dynamic bearing load can be determined using the following formula:

Resulting axial force for O- and X-arranged roller bearings

Due to the angular raceways, when a radial force occurs, tapered roller bearings generate an axial reactive force which is relevant to the bearing dimensioning. When a shaft is supported by two identical or differently sized tapered roller bearings, the radial load of one bearing produces an axial load for the other bearing. This internal resulting force must be considered when determining the total axial load. The value of the total axial load on a single bearing is determined with the following formulas:

To the formulas applies that the bearings being affected by the outer axial force are marked with A and the counter bearings with B. All bearings are backlash-free and considered without pre-stress.

c) Reduction of dynamic load rating in a bearing set

For identical tapered roller bearings assembled directly side by side in X-, O-, or tandem arrangement, the load rating of the bearing set must be reduced arithmetically. For the dynamic load rating, the following correlation applies:

For statically loaded bearings

Dynamic dimensioning loses its validity for bearings rotating at very low speeds (n x d_m ≤ 4000 mm/min). The static load safety factor S₀ is calculated as follows:

Static load capacity

a) Single bearings and tandem arrangement

For statically loaded single row or tandem arranged tapered roller bearings, the following correlations apply:

b) O- and X-arrangement

For statically loaded tapered roller bearings in X- or O-arrangement, the following correlations apply:

c) Reduction of static load rating in a bearing set

For identical tapered roller bearings assembled directly side by side in X-, O-, or tandem arrangement, the load rating of the bearing set must be calculated. For the static load rating, the following correlation applies:

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 tapered roller bearings is roughly assumed to be 2% of the static load rating C₀ of the bearing. If the value falls below this value, please consult KRW Application Technology.