The slewing ring, being the link between a mobile element and a fixed base, must have a capacity to transmit the stresses of the mobile part towards the base. It is necessary to accurately define all the actual stresses applied so that a suitable slewing ring with adequate capacity can be selected. This should include the effects due to masses and inertias of the payloads and structures. It is necessary to distinguish the fixed loads and the variable loads as well as the effects due to dynamic loads, the latter constituting "fatigue" stresses. The direction of forces affecting the slewing ring must be well defined so that the active tilting moment can be established.
We distinguish :
• The AXIAL LOADS
whose direction is parallel to the slewing ring rotation axis. The resultant of these loads is called FA.
• The RADIAL LOADS
contained in planes perpendicular to the rotation axis. The resultant of these loads is called FR
• TILTING MOMENTS
(bending) : in planes parallel to the rotation axis. The resulting moment working in the plane containing the rotation axis is called MT.
• SLEWING TORQUE CD controls the slewing rotation.
CALCULATION OF THE EQUIVALENT LOADS
For the calculation, the resultant of the radial loads FR is transposed into an equivalent axial load using a factor KR as follows :
For standard bearings
if: FR/FA < 0.25 then KR = 0.5
if: 0.25 < FR/FA < 1 then KR = 1.5
if: FR/FA > 1 then KR = 2.4
For light series and solid sections, KR = 3.225.
The equivalent loads Feq can be obtained by the following formula :
• For the horizontally mounted slewing rings : vertical rotation axis Feq = FA + KR*FR
• For the vertically mounted slewing rings : horizontal rotation axis Feq = FA + 1.2*KR*FR