Load carrying capacity and life
The size of a monorail guidance system is determined by the demands made on its load carrying capacity, life and operational security.
Load carrying capacity
The load carrying capacity is described in terms of the basic dynamic load rating C, the basic static load rating C0 and the static moment ratings M0x, M0y and M0z, ➤ Figure.
Load carrying capacity and load directions
Calculation of basic load ratings according to DIN ISO
The calculation of the basic dynamic and static load ratings given in the dimension tables is based on DIN ISO 14728-1 and 2.
Differences between DIN ISO and suppliers from the Far East
Suppliers from the Far East frequently calculate basic load ratings using a basic rating life based on a distance of only 50 km in contrast to 100 km according to DIN ISO. This results in comparatively higher basic load ratings.
Conversion of basic load ratings
The conversion factors are applied as follows:
Linear recirculating ball bearing and guideway assemblies
Linear recirculating roller bearing and guideway assemblies
| C100 | N | Basic dynamic load rating in accordance with DIN ISO 14728-1 (based on 100 km) |
| C50 | N | Basic dynamic load rating in accordance with DIN ISO 14728-1 (based on 50 km). |
Dynamic load carrying capacity and life
The dynamic load carrying capacity is described in terms of the basic dynamic load rating and the basic rating life.
The basic dynamic load rating is the load in N at which the guidance system, with a survival probability of 90%, achieves a distance of 100 km (C100 ).
ACHTUNG
The data for the basic dynamic load rating C in the dimension tables correspond to the basic dynamic load rating C100 in accordance with DIN ISO 14728-1.
Basic rating life
The basic rating life L and Lh is achieved or exceeded by 90% of a sufficiently large group of apparently identical bearings before the first evidence of material fatigue occurs.
ACHTUNG
In accordance with DIN ISO 14728-1, the equivalent dynamic load P should not exceed the value 0,5 · C. If lateral forces are present, the frictional locking of the fixing screws must be checked. Ideally, locating edges should be provided.
Equivalent load and velocity
The equations for calculating the basic rating life assume that the load P and the velocity vm are constant. Non-constant operating conditions can be taken into consideration by means of equivalent operating values. These have the same effect as the loads occurring in practice.
Equivalent dynamic load
Where the load varies in steps, the equivalent dynamic load is calculated as follows:
Where the load varies in steps and the velocity varies in steps, the equivalent dynamic load is calculated as follows:
Mean velocity
Where the velocity varies in steps, the mean velocity is calculated as follows:
Combined load
If the direction of the load acting on an element does not coincide with one of the main load directions, an approximate value for the equivalent load is calculated as follows:
If an element is simultaneously subjected to a force F and a moment M, an approximate value for the equivalent dynamic load is calculated as follows: 
Symbols, units and definitions
| C100 | N | Basic dynamic load rating in accordance with DIN ISO 14728-1 (based on 100 km) |
| C0 | N | Basic static load rating in the direction of the force acting on the element |
| F | N | Force acting on the element |
| Fy | N | Vertical component |
| Fz | N | Horizontal component |
| H | m | Single stroke length for oscillating motion |
| L, Lh | km, h | Basic rating life in km or in operating hours |
| M | Nm | Moment acting on the element |
| M0 | Nm | Static moment rating |
| nosc | min–1 | Number of return strokes per minute |
| P | N | Equivalent dynamic load |
| p | Life exponent: Monorail guidance systems based on balls: p = 3 Monorail guidance systems based on rollers: p = 10/3 | |
| qz | % | Duration as a proportion of the total operating time |
| vz | m/min | Variable velocity |
| vm | m/min | Mean velocity. |
Operating life
The operating life is defined as the life actually achieved by monorail guidance systems. It may differ significantly from the calculated life.
The following influences can lead to premature failure through wear or fatigue:
- excess load due to misalignment as a result of temperature differences and manufacturing tolerances (elasticity of the adjacent construction)
- contamination of the guidance systems
- inadequate lubrication
- reciprocating motion with very small stroke length (false brinelling)
- vibration while stationary (false brinelling)
- overloading of the guidance system (even for short periods)
- plastic deformation.
Static load carrying capacity
The static load carrying capacity of the monorail guidance system is limited by:
- the permissible load on the monorail guidance system
- the load carrying capacity of the raceway
- the permissible load on the screw connections
- the permissible load on the adjacent construction.
ACHTUNG
For design purposes, the static load safety factor S0 required for the application must be observed, see tables. If lateral forces are present, the frictional locking of the fixing screws must be checked. Ideally, locating edges should be provided.
Basic static load ratings and moment ratings
The basic static load ratings and static moment ratings are those loads under which the raceways and rolling elements undergo a permanent overall deformation corresponding to 1/10 000 of the rolling element diameter.
Static load safety factor
The static load safety factor S0 is the security against permanent deformation at the rolling contact:
| S0 | Static load safety factor | |
| C0 | N | Basic static load rating in the load direction (for KUSE: C0I, C0II, C0III) |
| P0 | N | Equivalent static bearing load in the load direction |
| M0 | Nm | Static moment rating in the load direction (M0x, M0y, M0z) |
| M | Nm | Equivalent static moment rating in the load direction. |
ACHTUNG
The static load safety factor S0 for the design of linear guidance systems must be observed, see tables.
Application-oriented static load safety factor
For the design of linear guidance systems, the static load safety factor S0 according to the following tables must be taken into consideration.
Standard arrangement
Preconditions | S0 | ||
|---|---|---|---|
High dynamic loading (such as vibrations) is present, Severe contamination is present. Actual load parameters are not defined. Catalogue specifications for accuracy of adjacent construction are not observed.. | 8 | – | 12 |
Not all load parameters are completely known.. Loads are estimated from the performance data of | 5 | – | 8 |
All load parameters are known.. | 4 | – | 5 |
All load parameters are known and definitely correspond | 3 | – | 4 |
ACHTUNG
In the field of machine tools, safety factors of S0 ＞ 10 are normal for reasons of rigidity. For the precise design of the guidance system, Schaeffler offers BEARINX or design by the Schaeffler Technology Center in conjunction with Application Engineering. In precise design, the displacement of the tool point can also be analysed.
Utilisation in general applications Overhead arrangements**
Preconditions | S0 | ||
|---|---|---|---|
Not all load parameters are known | 20 | ||
Not all load parameters are known All load parameters are known | 8 | – | 12 |
All load parameters are known | 5 | – | 8 |
**If the guidance system is in a suspended arrangement, a drop guard is recommended.
Strength of guidance systems
If the fixing screw threads are of a sufficient size, monorail guidance systems can be subjected to loads up to the static load carrying capacity C0 and M0.
ACHTUNG
The load must be transmitted via locating surfaces. The basic load ratings can only be achieved if the whole thread length is utilised.