SIEMENS
2/6
Siemens MD 50.8 · 2017
Configuring guide
Configuring a gearbox
2
■
Service factor
Determining the required service factor
The operating conditions are crucial in determining the service
factor and for selecting the geared motor. These are taken into
account by the service factor
f
Btot
.
In standard operation, i.e. with a uniform load provided by the
driven machine, small masses to be accelerated, and a low
switching frequency, the service factor of
f
Btot
= 1 can be
selected.
For different operating conditions, the service sector can be
taken from the tables. When the motor power and the gearbox
output speed are known, a gearbox type is selected with a
service factor that meets the following condition:
f
Btot
=
f
B1
f
B
The gearbox size or rated gearbox torque and the resulting ser-
vice factor are not standardized and depend on the manufacturer.
Determining the load classification
The service factor of the driven machine
f
Btot
is determined from
the load classification, switching frequency, and operating
period per day.
The operating conditions can vary greatly. To determine the ser-
vice factor, empirical values can be derived from the configura-
tion of other similar applications. The driven machines can be
assigned to three load groups according to their load classifica-
tion. These groups are assessed based on their mass accelera-
tion factor
m
AF
.
Load groups of driven machines
Fig. 2/1
Service factor
f
B1
Note:
When selecting and dimensioning drives with the following
special application conditions, please contact Siemens.
•
Frequent reversing
•
Short-time and intermittent operation
•
Abnormal temperatures
•
Reversal braking
•
Extreme and/or circulating radial forces at the gearbox output
shaft
•
Fluctuating loads
Mass acceleration factor
The mass acceleration factor
m
A
F
is calculated as follows:
All external moments of inertia are moments of inertia of the
driven machine and the gearbox, which are to be reduced to the
motor speed.
The calculation is made using the following formula:
In most cases the relatively insignificant moment of inertia of the
gearbox can be ignored.
The mass acceleration factor
m
A
F
is calculated as follows with
reference to the gearbox and the adapter:
Load
classifi-
cation
Mass
acceleration
factor
Driven machine
(examples)
I
Almost
shock-
free
0.3
Electric generators, belt conveyors, apron
conveyors, screw conveyors, lightweight
elevators, electric hoists, machine tool feed
drives, turbo blowers, centrifugal compres-
sors, mixers and agitators when mixing
materials with uniform density
II
Moderate
shock
loads
3
Machine tool main drives, heavy elevators,
slewing gear, cranes, shaft ventilators, mix-
ers and agitators when mixing materials with
non-uniform densities, reciprocating pumps
with multiple cylinders, metering pumps
III
Heavy
shock
loads
10
Punching presses, shears, rubber kneaders,
machinery used in rolling mills and the iron
and steel industry, mechanical shovels,
heavy centrifuges, heavyweight metering
pumps, rotary drilling rigs, briquetting
presses, pug mills
G_D087_EN_00156
1.5
1.4
1.6
1.7
1.3
1.2
1.1
1.0
1.7
1.6
1.8
1.5
1.4
1.3
1.2
1.5
1.4
1.6
24 h
16 h
8 h
1.3
1.2
1.1
1.0
0.9
0.8
Operating period per day
Number of starting operations per hour
Load classification III
Load classification II
Load classification I
Service factor
f
B1
1500
1250
1000
750
500
250
0
Code
Description
Unit
i
Transmission ratio
-
J
2
Moment of inertia of the load referred
to the output speed of the gearbox
kgm²
J
AD
Moment of inertia of the adapter referred
to the input speed
kgm²
J
B
Moment of inertia of the brake
kgm²
J
G
Moment of inertia of the gearbox based on
the input speed
kgm²
J
mot
Moment of inertia of the motor
kgm²
J
X
Moment of inertia of the load referred
to the input speed
kgm²
J
Z
Additional moment of inertia of
a high inertia fan
kgm²
m
AF
Mass acceleration factor
-
n
1
Input speed of the gearbox
rpm
n
2
Output speed of the gearbox
rpm
m
A
F
J
x
J
mot
J
B
J
Z
+
+
-----------------------------------------
=
J
X
J
2
n
2
n
1
-----
2
J
2
i
2
--------
=
=
m
A
F
J
x
J
G
J
+
AD
+
J
mot
J
B
J
Z
+
+
-----------------------------------------
=
© Siemens AG 2017