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Selection calculation of slewing bearing

Views: 560     Author: Mickey Sun     Publish Time: 2018-03-06      Origin: Site


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1.The bearing capacity curve of the slewing bearing

Each type of slewing bearing of product samples has a corresponding load-carrying capacity curve, and the graph can help the user to select the slewing bearing preliminarily.

There are two types of curve, one is the static curve (①line), the maximum load that slewing bearing can bear when it keeps static. The other one is bolt load limit curve (8.8, 10.9,      12.9), it is decided when the bolt’s fixture length is 5 times as the bolt’s nominal diameter, and the preload is 70% of the bolt material’s yield limit.

2.Calculation method of slewing bearing’s selection

 1)The selection process

Make sure the maximum load the slewing bearing can support when it remains static (axial load Fa, radial load Fr, overturning moment M). Set the maximum load as the static rate value. Static rate value must consider the existed maximum load on principle, which must conclude the additional load and experimental load.


Make sure the static security coefficient fs according to the type of the main engine(application situation), whose numerical value see table 1.


 Preliminarily choose the type of slewing bearing, make sure the calculation method of static reference load Fa and M.


Calculate Fa and M


Static load limit curve corresponds to the selected type of slewing bearing among the samples, and mark out (Faˊ,M ˊ)


Check whether the coordinate point(Faˊ,M ˊ) is under the static load limit curve


No  or  Yes


Checking calculation of bolt’s bearing capacity (see this section 5.2.4)



No  or  Yes


Complete the preliminary selection of slewing bearings type


 2) type selection in static

Calculation method of static reference load Fa 'and M'

Method I(a=60°)

The selection calculation of the single-row four point contact ball slewing bearing process by load support angle 45° and 60° respectively .

Methods I (a = 60 °)


M ′=M×fs

Method II(a=45°)


 M ′=1.225×M×fs

In the formula: Fa '-slewing bearing equivalent center axial force (104  N )

M '- slewing bearing equivalent overturning moment (N. m)


fs—safety factor in the static working conditions of slewing support (see table 1) 

Then find the above two points on the curve, one of them is below the curve.

Single-row crossed roller type




Double-row ball type


The selection calculation of the double-row different diameter ball slewing bearing ,when Fr<=10%Fa,the change of the pressure angle inside raceway must be accounted,please contact us about its calculation.

Fa′= Fa×fs

M ′=M×fs


Three row roller type

When select the triple-row roller slewing bearing , only calculate the interaction of the axial raceway load and overturning moment.

Fa′= Fa×fs

M ′=M×fs

3) Dynamic selection


Please contact our technical department for the application of continuous operation, high speed rotation and other applications for the service life of rotary support.

4) Checking calculation of the bolt’s bearing capacity


The maximum load (no static safety factor fs) is used to load the rotary support. Check whether the load is below the limit load curve of required grade bolts;

If the bolt bearing capacity is not sufficient, we may choose slewing bearing again or contact our technology department.

The factory can provide information according to the product sample, using the static bearing capacity curve, according to the rotary bearing type selection calculation method of preliminary selection slewing bearing, and technology with my company to confirm. Can also provide information on rotary bearing to our company, when carrying on the design selection by my company , please ask for the 《rotary bearing selection of technology parameter table 》(including the annex A and annex B in the parameter table), and fill in, so that we can submit to you as soon as possible accurate rotary bearing selection plan of economic and practical.


Safety factor of rotary support for various applications

Application situation



  On principle, the static maximum load that the slewing bearing support must be used as a computation value, which must include additional load and test load.
Not included in the application in the table, the static safety factor fs can be selected by reference to the similar working conditions and applications in the table.

*)Rotation upward crane

Mf=Reverse overturning moment on empty load

M= The overturning moment of maximum amplitude is used for the application static safety coefficient fs to take 1.45, because of the high average load and heavy working conditions, it is preferable to choose the multi-row rolling slewing bearing.

Floating crane (cargo)



Mobile crane (cargo)

Marine deck crane

welding equipment

Table (continuous operation)

Tower crane


Rotation at top








rotation at base


Rotation crane (cargo load)


Shipping crane

l ship Loader/unloader

Metallurgical Overweight machine



Mobile crane (grab or handle heavy work)


Rotation crane (grab or sucker)

Bridge crane (grab or sucker)

Floating crane (grab or sucker)

· Bucket- wheel excavator



Cantilevered conveyor

Offshore overweight machine

Special standard

In these applications, the working conditions vary considerably, such as the rotary support used for the non-regular rotation, only the static check. For the rotary support used in continuous rotation and intermittent rotation, dynamic life calculation is required.

railway crane


Deck crane (cargo load)



delivery wagon

Rope excavator/cable bucket


Less than or equal to 1.5 M3 hydraulic excavator


More than 1.5 M3 hydraulic excavator

Special standard

ladle turret


Note: fL is the dynamic safety factor. It must be used in combination with dynamic load curve. It comes from experience and experimentation. It is a reference value based on maximum working load.


The portal crane diagram

The calculation method of maximum load is recommended as follows:

Before choosing the rotary support, the static safety factor fs that should be considered for the host should be determined, which can be found in schedule 1. Portal crane:fs=1.45

When the maximum static load is known, the calculation formula of its load is as follows:

1) the maximum working load of an eight-level wind force

axial force Fa = Q + A + O + G

overturning moment M = Q × lmax + A × amax + W × r - O × o - G × g

2)Regardless of wind force, consider the load of 25% test load

axial force Fa = 1.25 × Q + A + O + G

overturning moment M = 1.25 × Q × lmax + A × amax - O × o - G ×


 the working load and amplitude of a clamshell port are known as follows:

Q = 260 kN lmax = 23 m     1max=23m

A = 75 kN amax = 11 m     amax=11m

  O = 450 kN o = 0.75 m      o=0.75m

  G = 900 kN g = 3 m        g=3m

  W = 27 kN r = 6.5 m1)        r=6.5m

Maximum working load of wind power at level 8

Fa = Q + A + O + G

  =260 + 75 + 450 + 900

  =1685 kN

M = Q×lmax + A×amax + W×r - O × o - G× g

 = 260 × 23 + 75 × 11 + 27 ×6.5×450 ×0.75×900 × 3

 = 3943 kNm

3) regardless of wind force, consider the maximum working load of 25% test load

 Fa = 1.25×Q + A + O + G

   = 325 +75 +450 +900

   = 1750kN

  M = 1.25×Q×lmax + A×amax - O×o - G×g

   = 325 × 23 + 75 × 11×45 × 0.75×900 × 3

   = 5566.3 kNm

4)maximum working load regardless of wind force

Fa = 1685 kN

  M = Q×lmax + A×amax - O×o - G×g

= 260 × 23 + 75 × 11×450 × 0.75×900 × 3

   = 3767.5 kNm

Load condition 2 is used as the working load of static calculation

According to schedule 1, the portal crane (grab bucket) should be supported by three rows of roller-type rotary support:

The static reference load of rotary support is:

Fa' = 1750 kN × 1.45 = 2537.5 kN M'= 5566.3 kNm × 1.45 = 8071.1 kNm

The calculation load of bolt is:

Fa = 1750 kN       M = 5566.3 kNm

According to the above calculation results, the selection of the bearing capacity curve can be determined to select the rotary support of 13*.45.2000.002

Xuzhou Wanda Slewing Bearing Co.,Ltd is a slewing bearing manufacturer specializing in slewing bearing can be from 200 mm to 5000 mm,

.Over the years, we keep supplying high quality product & good service to customers. Warmly welcome you contact us with your demand!

Xuzhou Wanda Slewing Bearing Co.,Ltd.
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Xuzhou Wanda Slewing Bearing Co.,Ltd.
 Add: No.8,Dianchang North Road,High-tech Industrial Development Zone,Xuzhou City,Jiangsu Province,China.
  丨 +86-180 2053 7858