How to read a gear reducer datasheet: thermal vs mechanical power

The datasheet is a reducer's "identity card". Reading it avoids oversizing or, worse, undersizing. There are two limits to tell apart: the mechanical one and the thermal one.

Torque and mechanical power

Mechanical power (or rated power) is the limit set by the strength of gears, shafts and bearings: the power the reducer transmits without damage for its design life. On the sheet it appears as rated torque M₂n or power P₁ at the various ratios.

Thermal power

Thermal power (Pt) is the limit set by the ability to dissipate heat: beyond it the oil overheats and lubrication degrades, even if the reducer would hold up mechanically. It is typically critical on large reducers, in continuous duty and at high ambient temperature.

Always choose the lower limit

The real permissible power is the lower of the mechanical and thermal values, each corrected by its factors. If the thermal one is lower, either reduce the continuous load, or add cooling (fan, cooling coil) or a suitable oil.

The thermal factor (ft)

Thermal power is corrected by a thermal factor that depends on ambient temperature, duty type (continuous or intermittent) and ventilation. Intermittent duty allows higher thermal power because it leaves time to cool down.

The service factor

On the mechanical side the service factor comes in, increasing the required torque by load type. Find all the data on the Rossi catalogue datasheets or start from the selector.