Worm Gear Reducers (MRT) - Rotor UK

4. GEAR UNIT SELECTION
General
The wide range of ratios specified in the catalogue enables to solve any requirements resulting from the operation of various
equipment. The following data are necessary to specify a suitable gear unit:
a) input and output speed determining the gear ratio i
b) required torque M k
or input power P 1
The data given in the tables 7.1 to 7.4 enable easy selection of a suitable gear unit. Should a non-standard unit be required please
contact your distributors for the technical support.
Gear Ratio i
Gear ratio is a relation between input speed n 1
[rpm] and output speed n 2
[rpm].
n
i = 1
[-]
n 2
Gear ratios from 5 to 100 are used at worm-gear units. The use of squirrel cage asynchronous motors is recommended to drive
the equipment as their speed n 1
[rpm] is almost constant even if under load. The following speed can be used for 50 Hz:
2-pole motor n 1
= 2800 rpm
4-pole motor n 1
= 1400 rpm
6-pole motor n 1
= 900 rpm
8-pole motor n 1
= 700 rpm
Two-pole motors are usually suitable for short-time operation. Their use should be consulted with the manufacturers. When
60 Hz supply frequency is used the increase of the input as well as output speed by 20 % need to be taken into consideration.
Torque M 2
The required torque M k
is determined by the load applied on the gear unit. It can be described as force F applied at certain
distance of the arm r.
M k
[Nm] = F [N] × r [m]
The output torque M 2
can be calculated from the following formula:
M 2
[Nm] = 9550 × P [kW] × η [%] × i
1
100 × n 1
[rpm]
The output torque M 2
need to be selected at a higher value than the required torque. Output torque related to individual gear
ratios is specified in the Gear Unit Selection Table 7.4.
Input and Output Power P 1
and P 2
Motor input power can be calculated from the general relation between torque M and speed n:
P [kW] =
M [Nm] × n [rpm]
9550
The efficiency η of a gear unit is given by the ratio of the output power P 2
and the input power P 1
, see Table 7.1 to 7.3.
P 1
[kW] =
M k
required [Nm] × n 2
[rpm]
9550 × η [%]
5. SERVICE FACTOR
Operation factor S m
In order to guarantee operation safety at various loads and operation conditions the type of the gearbox (and motor) must be
specified through the operation factor S m
. The values of operation factor S m
can be found in Table 5.1 taking the type of load,
the average daily operation, the number of starts per hour into consideration. These values are applicable when the gear unit
is used in conjunction with an electric motor. Should a brake motor be used the operation factor S m
needs to be multiplied by
a coefficient of 1.15.
When selecting an actual gear unit the operation factor S m
must be lower than the gear unit service factor S f
or the required output
torque M p
must be increased as per the following formula:
M 2
= M p
× S m
prior to alterations
6