TYPICAL SELECTION WITH EXAMPLE

The preliminary selection of an unit can be made from the power ratings specified in the selection chart . Once the preliminary selection has been made the external influencing factors must be taken into consideration. Torque demanded by the application should not exceed the limits specified.

In the case of an electric motor of 4P / 6P / 8P the unit rated for the input speed and the torque can be directly selected from the selection table. The next step is to consider the service factors demanded by the application. Refer table of service factors for the same. Then the unit selected should satisfy the following relation.

Pin . Sf < Pr.

Where

Pin = Input power in kW
Sf = The service factor selected.
Pr. = The rated power of the unit

In the case of a hydraulic motor the following formula may be used to determine the input torque (Tin).

Tin = V . p . h m Nm
        20 p

where

V = Displacement of the hydraulic motor in cc/rev.
p = Pressure in bar.
h m = Hydraulic motor efficiency

The following formulae may be used to calculate the Output torque.

Tout = Tin . i . h Nm

Where

Tout = Maximum torque at the output.
i = Reduction ratio of the gear unit.
h = efficiency of the gear reducer (98% per stage of reduction)

For selecting an ideal gear unit the following relation should be satisfied.

Tr > Tout . Sf.

Tr = Rated output torque of selected gear unit in Nm

 

GEAR BOX SELECTION - EXAMPLE - 1 :
Specification received from customer.
Industry Paper Mill
Application Kiln Drive
Kiln Speed 3
Kiln torque 14500
Input power (Pin) 5.5
Motor speed 1440
Type of prime mover D.C Electric motor
Open gear ratio 3.1
Pinion PCD 300
Bull Ger PCD 930
Face Width 70
Duty Continuous 24 hours
Mounting Horizontal foot
Input To suit above motor
Selection
Overall ratio required 480
Open gear ratio 3.1
Ratio In gearbox ( i ) 155
Output torque from G.Box (Tout) 4677
Recommended Service factor (from page ) (Sf) 1.5
Reqd.Nominal torque of G.Box 7016.129
Selected G.Box Size 3320
Rated torque of selected G.Box (Tr) 7800
Overhang load due to Pinion 33184
Gearbox Overhung Capacity Calculation
Line of action of overhang load from shaft collar 35
Distance Y -47.5
Allowable Overhung at middle of shaft (Frm) 72060
Allowable Overhung at shaft collar (Frc) 99083
Allowable Overhung at load point (Fr) 85483.23
The radial load due to pinion is less than allowable (n2)  
Output speed 9.3
Output shaft bearing life L10a 183815.6

Thermal capacity of the selected unit is more than the applied power. Hence the selection is complete.