The knowledge of loads and working conditions is necessary to allow us
to design and dimension the "BEARING" function of the slewing ring
i.e. : movement type, speed, accelerations, temperatures, environment etc.
The transmission of loads from one raceway to another varies according to
the nature of applied loads.
In order to calculate the ideal dimensions of the raceway,
we define the load equivalent to all external efforts in the most stressed areas.
These loads are corrected by factors according to the application, the usage, etc.
We distinguish between :
• The application factor KA
• The usage factor KU
• The safety factor KS
THE APPLICATION FACTOR KA is a coefficient taking into account the application specifity in relation with the slewing ring element.
This factor is established from ROLLIX experience. It is defined in the table "APPLICATION FACTORS".
THE USAGE FACTOR KU is defined according to the particular operating conditions : vibrations, shocks, occasinal or accidental overloading, etc. If no other value is specified, then the nominal value is taken as 1.
THE SAFETY FACTOR KS is defined from standardized criteria for applications which must specific regulations such as : FEM, LLYODS, API... This generally has the value 1, as the designer of the machine must include the regulation factors in the calculation of the loads applied on the bearing.
APPLICATION FACTORS
| MACHINES |
Average
speed
Rpm |
Applications
factors
K A |
| Armament turret |
1.5 |
1,5 |
| Bucket |
1,5 |
1,65 |
| Cable shovel |
2 |
1,65 |
| Compacter |
2,5 |
1,80 |
| Concrete mixer |
5 |
2,40 |
| Concrete pump |
1,5 |
1,65 |
| Dragline |
1.5 |
1.65 |
| Dock crane |
1 |
1,65 |
| Fairlead |
0,8 |
1,35 |
| Fork-lift truck |
1 |
1,35 |
| Fork-lift wheel |
1,5 |
1,50 |
| Grabbing crane |
1,5 |
1,80 |
| Heavy winch |
2 |
1,65 |
| Hydraulic lift platform |
1 |
1,50 |
| Hydraulic shovel |
2,5 |
2 |
| Loading dock crane |
1 |
1,65 |
| Merry-go-round |
5 |
2,40 |
| Mine digging machinery |
1,5 |
2 |
| Mobile fixed boom crane |
1 |
1,5 |
| Mobile grappe crane |
1 |
1,80 |
| Mobile telecospic crane |
1 |
1,65 |
| Offshore crane |
1 |
1,8 |
| Post jib crane |
1 |
1,35 |
| Railway crane |
1 |
1,50 |
| Rapid rotation radar |
5 |
2 |
| Rapid rotation scanner |
3,5 |
1,65 |
| Robotics |
3,5 |
1,65 |
| Service deck crane |
0,8 |
1,35 |
| Settler (water & sewage treatment) |
0,6 |
1,35 |
| Slow rotation radar |
1 |
1,35 |
| Slow rotation radiology |
1 |
1.35 |
| Tpwer crane, slewing jib type |
1,5 |
1,65 |
| Tower crane, slewing tower type |
1,5 |
1,80 |
| Track hook crane |
1,5 |
1,80 |
| Truck crane |
1 |
1,50 |
| Turntable |
1 |
1,35 |
| Vibrating compacter |
2,5 |
2 |
| Welding positionner |
0,8 |
1,35 |
|
Windturbine |
0,8 |
1,65 |
These factors are determinated statistically and are based on a large number of observations for each type of application.
The standard parameters retained are as follow :
• Theoritical service life : 6000 hours
• Work under normal weather conditions.
• Conventional application (and not specific).
Selection of the ring according to capacity
The load capacity of the slewing ring is calculated according to its performance in function of :
• its geometric envelope,
• the nature of the raw materials,
• the heat treatment carried out,
• the nature, the number and the dimension of the rolling elements,
• the contact parameters of the rolling elements.
The ring size is determinated by plotting the representative point of loads onto this curve. This point called "application point" has the following coordinates :
• on the horizontal axis : Px = Feq . KA . KU . KS
• on the vertical axis : Py = MT . KA . KU . KS
In any case, the application point P must be under the limit curve.
Service life
Many external factors have a very important influence on the service life of the bearing. Among others, we can cite :
• geometric quality of supports,
• structure deformation under load,
• climatic conditions and environment,
• quality of operating maintenance,
• conditions of use :
repeated exposures to shocks, vibrations or sudden or intermittent movements can considerably reduce the theorical service life.
KT = OL / OP
An estimate of the theorical service life can be obtained by comparing the application point to the limit curve : the ratio OL/OP is called K T .
An estimate of the service life D can be obtained using the graph :
. The curve indicated the estimated service life (hours) directly from the K T value on the horizontal axis.
Service Factor
Rotational speed influence
The service life D, estimated on the graph is only valid for the applications having a low rotational speed 1 rpm. The value obtained mudt be multiplied by the speed factor K V indicated on the graph when speed differs from this.
Speed Factor
D(n) = K V x D
For applications having oscillating movements, the following formula applies :
n average = 0,60 x n real
Selection of the ring according to capacity
The load capacity of the slewing ring is calculated according to its performance in function of :
• its geometric envelope,
• the nature of the raw materials,
• the heat treatment carried out,
• the nature, the number and the dimension of the rolling elements,
• the contact parameters of the rolling elements.
The ring size is determinated by plotting the representative point of loads onto this curve. This point called "application point" has the following coordinates :
• on the horizontal axis : Px = Feq . KA . KU . KS
• on the vertical axis : Py = MT . KA . KU . KS
In any case, the application point P must be under the limit curve.
Service life
Many external factors have a very important influence on the service life of the bearing. Among others, we can cite :
• geometric quality of supports,
• structure deformation under load,
• climatic conditions and environment,
• quality of operating maintenance,
• conditions of use :
repeated exposures to shocks, vibrations or sudden or intermittent movements can considerably reduce the theorical service life.
KT = OL / OP
An estimate of the theorical service life can be obtained by comparing the application point to the limit curve : the ratio OL/OP is called K T .
An estimate of the service life D can be obtained using the graph :
. The curve indicated the estimated service life (hours) directly from the K T value on the horizontal axis.
Service Factor
Rotational speed influence
The service life D, estimated on the graph is only valid for the applications having a low rotational speed 1 rpm. The value obtained mudt be multiplied by the speed factor K V indicated on the graph when speed differs from this.
Speed Factor
D(n) = K V x D
For applications having oscillating movements, the following formula applies :
n average = 0,60 x n real
