Bearing selection

General

The binding selection of a slewing bearing is generally carried out by thyssenkrupp rothe erde. This allows us to ensure the correct dimensioning of the bearings’ raceways, the gearing and bolt connection.

Please communicate to us the information needed to select a bearing via the company standard, KD 100. The request form can be downloaded as a PDF from the bottom of this page.

The most important information for selecting a bearing is:

1. Loads
2. Load spectra with corresponding time proportions in %
3. Speed or number of swivel movements and swivel angles per time unit with corresponding load spectrum
4. The circumferential force to be transmitted from the gearing
5. Bearing diameter
6. Other operational conditions

Provided the KD 100 has been filled in in full, we can largely cater to your requests and work out a technically suitable and economical bearing suggestion. The filled in KD 100 is to be sent to us as early as possible in the project work but at the latest when the order is placed, so that a confirmation of the bearing can ensue

Bearing selection on the internet

An estimated bearing selection can be made during the project development phase. The rothe erde® slewing bearings are assigned maximum load curves for static load-carrying capacity and service life curves. For each application, load factors are taken into consideration for the specified loads to determine the load-bearing capacity necessary. Except for type 13 and type 21 from the KD 210 series. For applications which are not listed, comparable applications must be selected based on the type of operation. The bearing is suitable if the loads lie below the static maximum load curve, the bolt curve and the service life curve.

Static load-carrying capacity

The determined loads are multiplied by a factor assigned to the application f_stat. The product, F_a' or, M_k' must lie below the static maximum load curve of the selected bearing.

For radial loads in load combinations

F_a = axial load

F_r = radial load

M_k = tilting torque

are determined for the “static” selection of bearings, the “reference loads” as an estimate for the series KD 210, type 110 and KD 600 in accordance with I and II, as follows:

Load combination I

F_a' = (F_a + 5.046 · F_r) · f_stat

M_k' = M_k · f_stat

Load combination II

F_a' = (1.225 · F_a + 2.676 · F_r) · f_stat

M_k' = 1.225 · M_k · f_stat

For types 13 and 21, I and II apply analogously but without a factor f_stat.

The bearing is statically suited if one of the two load combinations (I or II) lies below the static maximum load curve.

For the RD 900 series, radial loads do not influence the reading of the maximum load curve.

Theoretical service life

In the engineering of rolling bearings, theoretical service life is a well-known term. Given the many influencing factors, the nominal service life in accordance with DIN/ISO 281 cannot be used as an absolute value in practice, but as a comparative value and design parameter. Not all bearings necessarily reach their theoretical service life, but the majority generally exceed this, even many times over in some instances. The criteria for theoretical service life cannot be easily applied to slewing bearings, especially those which perform swivels or slow rotations.

Service life

In most applications, the velocity of circulation in the rolling wheel is relatively low so that the smoothness and precision are not negatively impacted by wear or isolated pittings. Thus, it is not common to categorise slewing bearings for swivel and slow rotational movements by theoretical service life. The term “service life” was introduced here. A slewing bearing’s service life has been reached if the rotational resistance rises progressively or the wear is so advanced that the bearing no longer functions (see wear measurement).

Slewing bearings are used for the most diverse of operational requirements. Depending on the type of operation, for example, pivoting movements with different pivoting angles and different frequencies, continuous pivoting movement or continuous turning, when selecting a bearing, the expected service life from the dynamic load is to be taken into consideration in addition to static aspects.

The service life determined using the curves is only to be used for bearings with pivoting and slowly rotating movements. For example, this procedure is not applicable for:

• bearings for the absorption of high radial forces,
• bearings with high rotational speeds
• bearings which must meet high precision requirements.

In these cases, the calculation is carried out by thyssenkrupp rothe erde based on the load spectra with corresponding speed and duty cycle durations. Consequently, a distinction must be made here between the machine's operational time and the actual rotational or pivoting time. The different loads are to be taken into consideration in load spectra and proportions. When considering the service life, the loaded pivot angle without a load is a factor not to be overlooked.

In addition to the static maximum load diagrams, “service life curves” are available to approximately estimate a service life. Type 13 and type 21 profile bearings are excluded.

These curves are based on a service life of 30,000 rotations under full load. They can be used to determine the service life of diverse load spectra or for selecting a bearing with a specific service life.