Seepex BN 5-12 Series, Operation & Maintenance Manual

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Manual of Electric Motors 83
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Motors designed with sleeve bearings have 3 (three) marks on the shaft end. The center mark is the indication
of the magnetic center and the 2 (two) outside marks indicate the allowed limits of the rotor axial movement, as
shown in Figure 6.9.
The motor must be so coupled that during operation the arrow on the frame is placed over the central mark
indicating the rotor magnetic center. During start-up, or even during operation, the rotor may freely move
between the two outside marks when the driven machine exerts an axial load on the motor shaft. However,
under no circumstance, the motor can operate continuously with axial forces on the bearing.
6.4.1. Direct coupling
Direct coupling is characterized when the Motor shaft is directly coupled to the shaft of the driven machine
without transmission elements. Whenever possible, use direct coupling due to lower cost, less space required
for installation and more safety against accidents.
6.4.2. Gearbox coupling
Gearbox coupling is typically used where speed reduction is required.
Make sure that shafts are perfectly aligned and strictly parallel (in case of straight spur gears) and in the right
meshing angle (in case of bevel and helical gears).
6.4.3. Pulley and belt coupling
Pulleys and belts are used when speed increase or reduction between motor shaft and driven load is required.
6.4.4. Coupling of sleeve bearing motors
Remove or fix the shaft key firmly when the motor is operated without coupling in order to prevent
accidents.
Do not use roller bearings for direct coupling, unless sufficient radial load is expected.
Excessive belt tension will damage the bearings and cause unexpected accidents such as breakage of
the motor shaft.
Motors designed with sleeve bearings must be operated with direct coupling to the driven machine or a
gearbox. Pulley and belts can not be applied for sleeve bearing motors.
Axial clearance
Figure 6.9 - Axial clearance of motor designed with sleeve bearing
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