A load profile describes the totality of all loads experienced by a component or system during operation, including their magnitude, duration, frequency, and sequence over time. It thus provides a realistic representation of the actual stress conditions and serves as a key basis for the design, service life, and safety calculations of mechanical components such as ball screws, bearings, spindles, and drive units.
The load collective goes beyond considering a single maximum load and takes the following into account:
- alternating tensile and compressive forces
- different rotational speeds and velocities
- Acceleration and Braking
- Downtime
- Varying Load Levels During Operation
This enables a realistic assessment of wear, fatigue, and service life.
A correctly determined load group is crucial for:
- Proper sizing of the spindle and nut
- Selection of Appropriate Bearings and Drives
- Service Life Calculation According to Standards
- Avoiding Oversizing or Undersizing
- Safe and Cost-Effective Design
Components of a load pool
- Load Levels
e.g., 20%, 50%, 100% of the rated load - Duration or Cycle Ratios
how long or how often a specific load level is active - Direction of Movement
Compression or tensile load - Rotational Speed or Speeds
Effect on friction and heat generation - Operating mode
Continuous operation, intermittent operation, standby operation
Presentation
- Load profiles are often represented as:
- Table (load level – time percentage – speed)
- Histogram (frequency of specific loads)
- Time series (load over time)
Example
A ball screw operates under the following load conditions:
- 60% of the time at 2 kN
- 30% of the time at 4 kN
- 10% of the time at 6 kN (maximum load)
This load combination is used to calculate the equivalent dynamic axial load, which in turn determines the service life of the KGT.