Back-to-back Rigs

The contact fatigue strength of gear steels and the performance of gear lubricants can only be determined by running gears at sufficiently high torque to cause contact fatigue or lubricant breakdown. This often results in the need for high power and long test durations. For this reason, all contact fatigue testing of gears at Design Unit is carried out on back-to-back, or ‘power recirculating’ test rigs. 

Two test gearboxes of identical gear ratio and centre distance are joined by torsionally compliant shafts (torsion bars), with a servo-hydraulic torque actuator in one shaft.  This rotates the shafts to induce equal and opposite torques in the test gears at each end.  A small variable speed motor drives both gearboxes, the power required being only equal to the total mesh friction, windage and churning losses of the gears.

Such an arrangement is relatively inexpensive to run, and can be used economically to test gearing at any speed and power.

All Design Unit rigs are characterised by

  • Servo-hydraulic control of test torque, which can be varied while the test rig is running.
  • Test gear geometries that can be optimised for maximum performance (not to generate failure).
  • Spray lubrication with large oil tanks, operating temperature controllable to ± 2°C between 50°C and 90°C, oil filtration to 10mm.
  • The ability to test helical gears.
  • Two test gearboxes rather than a slave and test gearbox.

Rig specifications: