Specifications

81
Baking and varnishing : After the armature has been wound, soldered and banded and tested,
the next operation is varnishing. This process makes it moisture-roof and also prevents vibration
of the coils of wire in the slots. Vibration has a tendency to impair the insulation on the wires and
cause shorts. Moisture will also cause the insulation on the wires to deteriorate. Before varnishing
the armature, it must be reheated to drive cut the moisture on it. Armatures may be varnished by
either baking varnish or air-drying varnish. Air-drying is applied to the armature when baking is
undesirable or inconvenient. Baking varnish is more effective because the moisture can be
eliminated fully only by baking.
Balancing the armature: Armatures should be tested for mechanical balancing after they are
varnished. This is very important; otherwise undue vibration and unusual noises may be produced
due to the imbalance of the armature. Ultimately it may lead to repeated bearing problems,
loosening of nuts etc. Hence the armatures are balanced before assembly. Balancing of armature
is mainly done, using dynamic balancing machines. Anyhow for small armatures static balancing
can be done, when dynamic balancing machines are not available.
Static balancing: A balancer, similar to the balancing grinding wheel in machine shops, may be
used. These balancers are built in various sizes. The method of balancing an armature using
this type is as follows.
Place the armature on the balancing ways, as shown in Fig. 6.12 and roll the armature
gently. When the armature comes to a shop, the heavier portion of the armature will be at the
bottom. Mark this point (portion) with a chalk piece. With such successive rolling, if the armature
stops at different positions, the armature is balanced, and if it stop in a particular position, it is
necessary to counterbalance it with weights diagonally opposite to the heavy portion.
This is accomplished by lacing a lead or a small metal piece on the banding of the armature.
In small armatures, this weight may be laced in the lace of the wedge, under the banding.
Experience will determine the amount of metal necessary to balance the armature. This method
of balancing is called
static balancing
.
Fig. 6.12