Warner Electric PCBC-500 Clutch_Brake Coupling - Manual (Page 23)

Burnishing and Maintenance
Burnishing
Intimate metal to metal contact is essential between the
armature and the metal rings (poles) of the magnet or
rotor. Warner Electric clutches and brakes leave the
factory with the friction material slightly undercut to
assure good initial contact.
Normally, the desired wearing-in process occurs
naturally as the surfaces slip upon engagement. The time
for wear-in, which is necessary to obtain the ultimate
torque of the unit, will vary depending on speed, load, or
cycle duty.
If maximum torque is required immediately after
installation, the unit should be burnished by slipping the
friction surfaces together at reduced voltage. It is
recommended that the burnishings be done right on
the application, if at all possible.
Burnishing at high speed will result in a smoother wear-in
pattern and reduce the time for burnishing. The voltage
should be set at approximately 30% or 40% of the rated
value.
The unit should be cycled on and off to allow sufficient
time between slip cycles to prevent overheating.
When a Warner Electric brake or clutch is properly
as sembled and installed, no further servicing,
lubrication, or maintenance should be required
throughout the life of the unit.
Maintenance
Wear Pattern: Wear grooves appear on the armature
and magnet surfaces. This is a normal wear condition,
and does not impair functioning of the unit. Normally, the
magnet and armature, as a mating pair, will wear at the
same rate. It is the usual recommendation that both
components be replaced at the same time.
Remachining the face of a worn armature is not
rec om mended. If a replacement armature is to be used
with a used magnet, it is necessary to remachine the
worn magnet face. In refacing a magnet: (1) machine
only enough material to clean up the complete face of
the magnet; (2) hold the face within .005" of parallel with
the mounting plate; and (3) undercut the molded facing
material .002" - .004" below the metal poles.
Heat: Excessive heat and high operating temperatures
are causes of rapid wear. Units, therefore, should be
ven ti lated as efficiently as possible, especially if the
application requires fast, repetitive cycle operation.
Foreign Materials: If units are used on machinery
where fine, abrasive dust, chips or grit are dispelled into
the atmosphere, shielding of the brake may be
necessary if maximum life is to be obtained.
Where units are used near gear boxes or transmissions
requiring frequent lubrication, means should be provided
to protect the friction surfaces from oil and grease to
prevent serious loss of torque.
Oil and grease accidently reaching the friction surfaces
may be removed by wiping with a rag dampened
with a suitable cleaner, which leaves no residue. In
performing this operation, do not drench the friction
material.
If the friction materials have been saturated with oil or
grease, no amount of cleaning will be completely
effective. Once such a unit has been placed back in
service, heat will cause the oil to boil to the surface,
resulting in further torque loss.
Torque Loss: If a brake or clutch slips or loses torque
completely, the initial check should be the input
voltage to the magnet as follows:
90-Volt Series: Connect a DC voltmeter with a range of
0-100 or more directly across the magnet terminals. With
the power on and the potentiometer turned up, a normal
reading is 90 volts, although 85 to 95 is satisfactory. The
reading should drop as the potentiometer control is
adjusted counter clock wise.
24-Volt Series: Use a DC voltmeter with a range of
0-30 volts or more. A normal reading is approximately
22-26 volts.
6-Volt Series: Use a DC voltmeter of approximately
0-15 volt range. A normal reading is from 5.5 to 6.5
volts.
The above checks are normally sufficient. Further checks
may be made as follows: a low range ammeter, when
connected in series with one magnet lead, will normally
indicate approximately .40 amperes for the 90 volt units,
1.0 ampere for the 24 volt, and 3.5 amperes for the 6
volt series. These readings are with the power on and
the potentiometer control in the maximum position.
Ohmmeter checks should be made with the power off
and the circuit open (to be certain, disconnect one lead
to the magnet). Average resistance for the 90 volt series
is 220 ohms; for the 24 volt, 20 ohms; and for the 6 volt
series, 1.5 ohms. A very high or infinite resistance
reading would indicate an open coil.
If the above checks indicate that the proper voltage and
current is being supplied to the magnet, mechanical
parts should be checked to assure that they are in good
operating condition and properly installed.
Warner Electric • 800-825-9050 819-0484 23