A gearbox does not only transmit torque; its bearings also carry the forces coming from the output shaft. These forces are considered in two directions:

  • Radial load: a force perpendicular to the shaft. Belt tension, chain pull or gear mesh force are of this kind. A small-diameter pulley or sprocket produces a larger force for the same torque.
  • Axial load: a force along the shaft. The thrust of a screw conveyor or the weight or pull of an agitator impeller on a vertical mixer are examples.

The radial force can be estimated as F ≈ 2000 × T / d (T in Nm, d pulley or sprocket diameter in mm, F in newtons). For example, with 435 Nm torque and a 150 mm sprocket, F ≈ 5,800 N; tensioning allowance for belts and chains increases this value.

Where the force acts on the shaft also matters: as the pulley moves towards the shaft end its effect on the bearing grows, so mount the pulley as close to the housing as possible. Permissible radial and axial loads vary by frame and are given in the catalogue; if exceeded, a larger frame or additional bearing support is needed.