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Example:<br />
duration necessary in hours = 20.000<br />
output speed of the gearbox = 25 rpm<br />
20.000 [h] 25 [n2] = 500.000 [n2 • h]<br />
therefore a gearbox with a torque of 500.000 n2 • h corresponding to the torque required by the application<br />
will be selected. The same procedure is applied to diagrams of external loads, whilst knowing the application<br />
point of the load and its entity.<br />
n1 • h = input duration index:<br />
is the product of the input speed and the duration expressed in hours.<br />
It is used to calculate the duration of the bearings of the input supports.<br />
If you know velocity n1, the loads applied and the application point,<br />
the duration in hours can be obtained.<br />
Indicative values of the durations required for different applications<br />
Application Hours of life required<br />
Agricultural machines 300-3.000<br />
Machines which operate intermittently or forbrief periods (building machinerie) 3.000-8.000<br />
Machines which operate intermittently or forbrief periods with a high operative reliability (hoists) 8.000-12.000<br />
Machines which operate for 8 hours per day, but not fully utilised (various industrial machines, rotating crusher) 10.000-25.000<br />
Machines which operate for 8 hours per day, fully utilised (various industrial machines, conveyor belts) 20.000-30.000<br />
Machines operating continually (rolling mills, textile machines) 40.000-50.000<br />
1.8 Power<br />
Pt = thermal power:<br />
maximum mechanical power that the gearbox can transmit while operating continuously, with plash<br />
lubrication, without exceeding the thermal limit (oil temperature not greater than 90°C). Greater powers<br />
can be transmitted by using an appropriate cooling system. The value refers to a continual operation<br />
with mechanical effi ciency of 0,97 for each reduction stage, input velocity of 1500 rpm, ambient<br />
temperature of 20°C, altitude 0 / 500 m, application to the cover.<br />
For different conditions, the thermal power value must be multiplied by the thermal factors shown<br />
in the following table. For limited operating periods, followed by rest periods that are suffi ciently long to<br />
guarantee an adequate cooling of the gearbox, the thermal power loses its signifi cance and can be<br />
disregarded.<br />
Room temperature<br />
Thermal factors<br />
working time<br />
100% 80% 60% 40% 20%<br />
www.jahns-<strong>hydraulik</strong>.de<br />
10°C 1,2 1,3 1,4 1,6 1,8<br />
20°C 1,0 1,1 1,3 1,4 1,6<br />
30°C 0,8 1,0 1,1 1,3 1,4<br />
40°C 0,7 0,8 1,0 1,1 1,3<br />
50°C 0,5 0,7 0,8 1,0 1,1<br />
altitude input speed<br />
400 800 1000 1500 2000<br />
0 1,2 1,1 1,1 1,0 0,7<br />
500 1,2 1,1 1,1 1,0 0,7<br />
1.000 1,1 1,0 1,0 0,9 0,6<br />
1.500 1,1 1,0 1,0 0,9 0,6<br />
2.000 1,1 1,0 1,0 0,9 0,6<br />
Page B. 7<br />
H Y D R A U L I K
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