What is the efficiency of screw jacks?

A key parameter that determines the energy efficiency, heat generation and performance of the drive.

The efficiency of a screw jack describes how efficiently the input drive power (rotation) is converted into usable lifting power (linear motion).

• High efficiency → little energy is lost due to friction, heat generation is low.
• Low efficiency → a large proportion of the drive power is converted into heat, which increases thermal loading and thus limits the permissible duty cycle.

The overall efficiency essentially consists of two components:

• Efficiency of the worm gearbox
• Efficiency of the screw drive (trapezoidal or ball screw) / The screw drive in particular has a dominant influence.

Efficiency of trapezoidal screw drives (TR)

Screw jacks with trapezoidal screw work with sliding friction – a type of friction that is inherently more lossy than rolling friction.

• Typical efficiency: Depending on gear ratio, screw lead and lubrication, the overall efficiency of a screw jack with trapezoidal screw is typically in the range of approx. 25% to 50%.
• Implications:
  • Higher drive power required: A noticeable share of the motor power is needed to overcome internal friction.
  • Significantly higher heat generation: Around half to three quarters of the input energy is converted into heat. This limits the permissible lifting speed and duty cycle (ED).
  • Self-locking: The relatively low efficiency is at the same time the basis for (conditional) self-locking – an important advantage when loads are to be held in position without an additional brake.

Efficiency of ball screw drives (KGT) / screw jacks with ball screw

Screw jacks with ball screw drive use rolling friction: balls run in a closed circuit between nut and screw. As a result, friction losses are very low.

• Typical efficiency: The efficiency of the ball screw drive alone can reach up to ≈ 98%. The overall efficiency of a screw jack with ball screw (incl. worm gearbox) is typically around 80% to 90%, depending on the design.
• Implications:
  • Lower drive power: For the same lifting work, significantly less motor power is required. This allows smaller motors and reduces energy costs.
  • Low heat generation: As only a small proportion of the energy is converted into heat, the gearbox heats up significantly less. This permits higher lifting speeds and – with suitable design – continuous operation (up to 100% ED).
  • No self-locking: The high efficiency makes the drive very easy-running – a load cannot be held safely without an additional brake. In practice, a motor brake or holding brake is therefore required.

Conclusion

The choice of gearbox type has a direct impact on the energy balance, installation space and thermal load capacity of the entire system:

• Screw jacks with ball screw / KGT version: Ideal where energy efficiency, high speed, high duty cycle and dynamics are the main priorities – e.g. in automation, handling or fast adjustment axes.
• Trapezoidal screw drives / TR version: The right choice when self-locking, simpler peripherals and lower system costs are decisive and the duty cycle remains comparatively low – for example in occasional adjustments, clamping or positioning tasks.

In practice, efficiency is therefore not just a figure in the data sheet, but a central criterion for selecting the right screw jack – with a direct influence on motor size, energy consumption, thermal behaviour and the safety concept of the entire system.