When considering suitable geared motors for a given application, the thermal capacity of the unit is often considered second to service factor ratings or even overlooked entirely. This is a mistake. Thermal capacity can limit selection of a gearmotor – even when it is less than the nameplate rating of the motor.
The thermal rating of a gearbox determines the power that can be continuously transmitted at a predetermined ambient temperature without resulting in the damage of the inner workings, or the degradation of the lubricant.
Most gearmotor manufacturers base their thermal capacity designs on an ambient temperature of 20 degrees Celcius, which is then adjusted based upon the duty degree of intermittence.
In Bonfiglioli’s C Series of gearmotors, units featuring more than two reductions and/or a gear ratio greater than 45:1 do not normally require the thermal limit to be checked. In these instances, the thermal rating usually exceeds the mechanical rating.
Different Gear Types
Input Speed Matters
As the below chart for Bonfiglioli C Series in-line helicals demonstrates, 2 pole motor inputs reduce the thermal capacity of gearboxes significantly.
If there is no avoiding a drive design that does not adhere to the thermal capacity of the gearbox, external cooling can be utilised to assist in increasing capacity. The different cooling techniques usually employed are:
- Air cooling
- Water cooling
- Oil cooling
The method of cooling chosen is determined by unit accessibility, serviceability and cost.