Warner Electric SFC-120, SFC-170, SFC-250, SFC-400 Bearing Mounted, Flange Mounted - Manual (Page 11)

11 Warner Electric • 800-825-9050 P-200
• 819-0481
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
assembled 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 com-
ponents be replaced at the same time.
Remachining the face of a worn armature is not
recommended. 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 .001" - .003" below the metal poles.
Heat: Excessive heat and high operating temperatures
are causes of rapid wear. Units, therefore, should be
ventilated 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 accidentally 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 counterclockwise.
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 normally are 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.