Warner Electric SFPBC-500, SFPBC-650 - Manual (Page 22)

22 Warner Electric • 800-825-9050 P-202-01 • 819-0482
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
fac to ry with the friction material slightly undercut
to assure good initial contact.
Normally, the desired wearing-in process occurs
nat u ral ly 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 and cycle duty.
If maximum torque is required immediately after
in stal la tion, the unit should be burnished by
slipping the friction surfaces together at reduced
voltage. It is rec om mend ed that the burnishing 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 volt age 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 sem bled 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 mend ed. 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 lat ed as efficiently as
possible, especially if the ap pli ca tion requires fast,
repetitive cycle operation.
Foreign Materials: If units are used on machinery
where fine, abrasive dust, chips or grit are dispelled
into the at mo sphere, shielding of the brake or clutch
may be nec es sary if maximum life is to be obtained.
Where units are used near gear boxes or
transmissions requiring frequent lubrication, means
should be pro vid ed to protect the friction surfaces
from oil and grease to pre vent 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
ef fec tive. 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 field as follows:
90-Volt Series: Connect a DC voltmeter with a range
of 0-100 or more directly across the magnet or field
terminals. With the power on and the potentiome-
ter turned up, a normal reading is 90 volts, although
85 to 95 is satisfactory. The reading should drop as
the potentiometer control is ad just ed
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 in di cate 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
read ing 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 op er at ing condition and properly
installed.