Humidity And Brush Wear - Baldor MN605 Installation And Operating Manual

Humidity and Brush Wear

This curve represents 2 grains of water per cubic foot of dry air or 4.6 grams per cubic
meter of dry air.
Zone of Safe Brush Operation
Caution: Be very careful when repainting a drip proof motor. Do not get any paint on the commutator. Paint on
the commutator will show up as black marks in brush tracks. Also, excessive brush sparking or erratic
operation can be caused by paint or other material on the commutator.
Commutator
After several hours of operation, the commutator surface under the brush should take on a darker bronze
color. This is due to self-generated film caused by normal commutation. This coloration should be even,
without blotches or black areas. A shiny copper color or black streaks in the brush tracks are signs of improper
commutation or contamination by a foreign material. Contact Baldor for assistance in correcting these problems.
If the commutator becomes rough and burned, or becomes black, it should be cleaned of dirt and carbon
particles. This can be done by wiping it with a dry, lint-free cloth. Also vacuuming or blowing out the motor with
a dry air supply are suitable cleaning methods. Do not use solvents or cleaning solutions on the commutator.
To remove spots or contamination that will not wipe off, wrap a strip of coarse (60# grit) sandpaper around the
commutator. Then rotate the armature back and forth by hand. Do not use emery cloth as this contains electrically
conductive materials.
Another method of commutator resurfacing is to use a commercially available commutator dressing stone.
This should only be done by trained and experienced people. This stone should be taped or attached to the end
of a stick made of electrically insulated material. The motor should be run at about half speed and the stone
applied lightly to the commutator surface. This operation must be done with no load on the motor.
The surface of the commutator should be smooth and round. This can be checked while the motor is running at
low speed. Press lightly on one brush with an insulated stick. Do not use a lead pencil as this contains electrically
conductive graphite. If you feel movement of the brush, it suggests a worn or uneven commutator. The armature
must be removed from the motor and the commutator machined by a qualified repair shop.
Rapid Commutator Wear
Light electrical loads and contamination are the usual causes of rapid commutator wear.
Light loading may require the removal of some brushes on motors with multiple brushes per pole.
Sometimes a low current density brush grade is used. There are also brushes that have a mild polishing action.
These prevent certain chemicals, especially chlorine and silicone, from attacking the commutator.
Brushes, are available for use in plastic extruder applications where PVC is present. Usually, you do not have to
change the design or grade of the brushes on new motors unless special operating conditions exist.
Do not change brush grades or the number of brushes per pole. Doing so may void the warranty and make
the motor unsafe. Contact your local Baldor district office or an authorized Baldor service center for technical
assistance.
Blowers & Filters
Do not use silicone RTV around DC motors as commutator surface damage can occur. Intake filters on blowers
and louvers of drip proof motors should be cleaned to remove any dust or foreign matter.
Canister type filters should be replaced when dirty. Failure to keep air intakes clear will cause overheating and
premature failure of the insulating system.
3-4
110
100
90
80
70
60
50
Danger Zone
Too Low Humidity
40
30
10 20 30 40 50 60 70 80 90 100
Percent Relative Humidity
45
40
35
30
25
20
15
10
5
0
MN605