Design of the reducer

All the gear pairs inside these reducers are designed according to the rules of the AGMA Standards (American Gear Manufacturers Association): the helical pairs are designed according to the AGMA 2001 Standard, while the bevel pairs are designed according to the AGMA 2003 Standard.
The tabulated values are the nominal powers of the reducers, defined as the minimum powers among the pitting and bending allowable powers of all the gear pairs inside the reducer. Hence, these values must be intended as powers calculated with a service factor of 1 (one).
On this catalog the listed powers are calculated at three different rotating speeds of the high speed shaft (1500, 1000 and 750 rpm); for speeds within this range it is possible to interpolate the value of the nominal power, while for speeds well outside this range, please contact our technical-sales department for the necessary power calculation and for the check of the operating parameters (lubrication, cooling, bearings life, ...).

Depending upon the reducer application and its actual operating conditions, the required service factor can be determined; this factor corresponds to the ratio between the reducer nominal power (listed on the catalog) and the power actually absorbed by the reducer during operation.
In practice, increasing the service factor means increasing the safety margin of the application with respect to the reducer design limits.
Table 1 lists the service factor values suggested for the different operating conditions, and is completed by the indications of table 2, which refers to the frequency of the start-ups, and of table 8, which refers to a number of different reducers applications.

 

For any reducer size, the values of the thermal ratings are listed in the three conditions of: natural cooling, cooling by means of a fan fit onto the high speed shaft, cooling by means of a cooling coil submerged into the oil bath inside the reducer.
The thermal rating of a reducer is defined as the mechanical power, applied to the reducer input shaft, which generates such a dissipated heat flow that the reducer reaches an equilibrium temperature of 95°C with an ambient temperature of 20°C.
In fact, for any value of mechanical power applied to a reducer a correspondent value of thermal power is generated inside the reducer itself (the complement to one of the mechanical efficiency multiplied by the applied power), which causes the increase of the reducer temperature until an equilibrium is reached between the thermal power generated inside and the power dissipated towards the surrounding environment.
The equilibrium temperature increases as the applied power increases, and when it reaches 95°C, the corresponding applied power is called the reducer thermal rating, representing the maximum allowed limit for continuous operation.
The adoption of devices (fan, cooling coil) for increasing the heat exchange capability between the reducer and the surrounding environment allows the application of higher power for the same equilibrium temperature, and therefore increases the reducer thermal rating.
Thermal rating reduction and increase factors are provided for the case of intermittent operation, when the ambient temperature around the reducer is different from 20°C (table 3) , when the duration of operation is intermittent (table 4) and when the temperature of the water for the cooling coil is different from 20°C (table 5).
To calculate the thermal rating of reducers equipped with a cooling coil, taking into account all the correction factors, the following expression should be used::

In this way, the correction correspondent to the cooling water temperature is applied only to the thermal rating related to the presence of the cooling coil, while the correction correspondent to the air temperature is applied only to the natural thermal rating.
Whenever the reducer is directly exposed to sunlight or to any other source of radiant heat, this thermal power input shall be accounted for in the reducer heat balance, and the necessary measures to avoid overheating shall be carried out.
Besides, please be sure to install the reducer without hindering the air passage around the casing, so as to avoid detrimental effects on the heat exchange capability.
Obviously, the thermal ratings listed in the relevant tables are referred to reducers in optimum conditions as far as the outer surfaces cleanliness is concerned.
In the end, when it is foreseen that the reducer temperature may get lower than 0°C, the whole cooling water circuit must be completely drained, so as to avoid damages to the coil and to the piping.
 

In case that the connection between motor and reducer or between reducer and driven shaft is performed with the interposition of devices introducing significant load components other than the transmitted torque (pulleys, pinions, chains, drums, brakes, ...) it is necessary to transmit the relevant data to our technical-sales department for the calculations of shafts strength and bearings life.