Specifications

164
Frequency of Lubricating Oil Analysis
Disk lubrication method One year 6 months
Oil bath or splash lubrication 6 months 3 months
Circulating lubrication 9 months 1 to 3 months
Severe operating
conditions
Lubrication
system
Inspection interval
Normal operating
conditions
Checking the alignment of a directly coupled motor
The alignment is easily checked by laying the edge
of a steel foot rule against the sides of the two flanges
and checking whether the steel edge sits fully against
the sides of the two flanges or if there is any gap. Any
variation in levels is corrected by suitable steel shims.
The alignment should not only be correct in the vertical
and horizontal planes but the axis of both the shafts
should be in the same line and not make an angle with
each other. This can be checked by measuring the gap
between the flanges faces at four points, i.e. top, bottom,
front and back. Fig-2 shows the two types of
misalignment, in an exaggerated way for clarity.
Fig.15.2 - Misalignment - 2 types
15.7 Balancing
However carefully constructed, a motor armature shaft will have some unequal distribution
of weights in its body, which results in its axis of gravity being slightly off centre and out of line
with the axis of rotation. Therefore, when the armature rotates, centrifugal forces are created
which set upon the bearings. This causes the whole machine to vibrate. Its intensity varies
at different speeds and becomes maximum at some critical speeds due to the effects of
resonance. The amount of unbalance determines the degree of vibration. For smooth running
and long useful life, the rotating parts should be properly balanced. Balancing consists of re-
adjusting the distribution of masses in the body in such a way as to bring the axis of gravity to
coincide with the axis of rotation. This is done by placing a counter-weight on or removing some
weight from some part of the armature in such a way that the unbalanced centrifugal force is
cancelled out. To do this it is necessary to determine precisely where the counter-weight is to be
placed or removed, and also the weight of material to be removed. Balancing consists of two
types. They are Static Balancing and Dynamic balancing.
Static balancing : In static balancing, the rotor is supported on a pair of perfectly horizontal
knife edges. If the armature is in perfect balance, the rotor should rest in any position. If, on the
other hand, the rotor is not well-balanced and has uneven distribution of weight, the rotor will