process of repairing a dc motor
TRANSCRIPT
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L&S ElectricEASA AR100 Accreditation
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EASA AR100 Accredited
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EASA AR100 Accreditation
• First company in Wisconsin, Minnesota, and Michigan to earn accreditation.• First company to obtain
accreditation for multiple locations• Providing our customers the
assurance of maintaining efficiency and overall reliability
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DC Motor On-Site Maintenance Practices Related to Commutation
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V - Ring
Commutation Construction
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BONDED COMMUTATOR
RESI-GLASS BINDER
STEEL HUB
INSULATION
SEGMENTS
Bonded
Commutation Construction
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L&S ElectricDC Electric Motor Repair
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Motor Nameplate
• The motor nameplate is a very important part of the repair process• The information from the nameplate is entered onto the job card
that follows the motor throughout the shop• This data is also entered into our data base and is stored so it
can be obtained at a later date if needed• The Model and Serial numbers are
very important when it comes to ordering specific parts for motors
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Job Card
• A final output shaft TIR is taken prior to run out
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Job Card
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Output Shaft TIR Keyseat Check
• All output shafts (if shaft rotates) are checked to insure they are in tolerance with reference to the EASA AR 100 Permissible Shaft Extension Runout document
Shafts .1875 to 1.625 = .002 TIR MaxShafts 1.625 to 6.500 = .003 TIR Max
• Keyseats are checked using a calipers and new non-plated key stock• Keyseats should be true and
accommodate keys to a tap fitWidth of keyseat .188 to .750 (+.002/-.000)Width of keyseat .750 to 1.500 (+.003/-.000)
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Grease Tubes Removed
• On motors that have grease tube extensions the tubes are removed• This insures the grease holes in the bearing housing are able to
be cleaned properly• Generally all grease tubes are
replaced with new tubes
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Brushes Removed
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Brush Springs Inspected
• Brushes are inspected for abnormal wear, fraying shunts, burned shunts• Brush spring pressure is measured prior to removing the
springs. Brush spring pressure should be between 4-6 PSI for most motors• Brush springs are inspected for stretched coils, and any signs of
damage
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Bearing Cap and Housing Bolts Removed
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Housings Carefully Removed
Housings are match marked to the field frame prior to removal to insure they are installed in the correct orientation when it is assembled
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Contaminants
• The motor is also examined for contaminant intrusion• Contaminants such as paper stock as seen
here suggest possible compromised air ducting, plugged filters, or flooding condition
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Bearing Grease Inspected
• Before the grease in the bearing housing is removed the volume and condition is inspected. The grease is examined for contaminants or signs of electrical discharge and noted on the job card• The grease in the bearings themselves
is also examined• This inspection can be beneficial the
motor because if a condition exists preventative measures can be added to the motor during the repair process to remedy the problem
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Bearing Inspection
Bearings are inspected for:• Grease quantity and condition• Visible cage defects• Signs of frosting or fluting from stray voltage discharge
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Bearing Removal
• Bearings are removed using a bearing puller• Shaft center savers are used to preserve the condition of the
centers during bearing removal
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Commutator End Bearing Removed
Some encoder/tach shafts need to be removed prior to pulling bearing to avoid damage to the shaft
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Shaft Grounding
Shaft grounding devices are often utilized where circulating currents are known to be present
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Ceramic Ball Bearings
• Ceramic ball bearings are used to protect bearings from circulating shaft currents• The best combination for a motor is insulation of the Opposite
Drive End bearing (in various fashions) and a shaft grounding device on the Drive End of the motor
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Micrometers Set to Calibrated Standard Prior to Checking Fits
Instruments are calibrated on a scheduled basis
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Bearing Journals are Measured
• Bearing journals are measured during disassembly and the sizes are documented on the job card
• The EASA fit tolerance chart is used to determine if the sizes are within tolerance
• If a journal does not fall within the tolerance and is undersize, it can be metal sprayed and machined back to within tolerance
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Output Shaft and Keyway Checked
• Output shaft extension diameters checked with micrometers to insure they are in tolerance with reference to the EASA Shaft Extension Diameter Tolerance Table in the AR100. If the shaft extension is worn and out of tolerance the shaft can be welded and re-machined• Shaft diameter .1875 to 1.5000
= +0.000/-0.0005• Shaft diameter 1.5000 to 6.500
= +0.000/-0.001• The keyway is checked using
standard non-plated key stock. Keyways should be true and accommodate standard non-plated key stock to a tap fit
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Brush Rigging Marked and Removed for Cleaning
• The Brush Rigging is reference marked to the housing before removal• It is inspected for and damage and noted on the job card
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Excess Grease Wiped Prior to Measuring Housing Bores
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Housings Checked Using Inside micrometers
• Bearing bores are measured using a micrometer• The bearing bore size is documented on the job card• EASA Bearing Fit Tolerance tables are used to determine if
housing bearing bores are within tolerance• If the bearing bore is oversize it can
be bored, sleeved and re-machined back to within tolerance
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Insulation Resistance Testing Performed on All Wound Components
• A megohmmeter is used to check the insulation resistance at disassembly• Meg-ohm readings are documented on the job card• Thermostats, heaters and other temperature devices are also
checked during disassembly and recorded on the job card
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AC Voltage Drop Test
• Shunt Fields are voltage drop tested by applying 120 volts AC to the field leads• The voltage between each coil is
measured and should be with +/- 5% of the calculated average• Add the measured voltages for
each coil and the sum should be equal to the input voltage
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Interpoles Tested
Interpoles are tested by using both a high frequency tester and are also tested using a surge tester
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High Frequency Bar to Bar: Testing Armatures
• Using a High Frequency Bar to Bar Tester the armature is tested for any shorts or opens• The filming on commutator surface is also examined.• A chocolate brown color
under the brushes is an ideal filming color
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Washing Components
All components that can be are washed with a mild detergent soap and water
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Components Drying
Components are dried in an oven at 220 °F until completely dry
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Armature Mounted in Lathe
• Bearing journals indicated in to under .001” (As close to zero TIR as possible)
• Armature is checked with a megohmmeter prior to resurfacing• Armature wrapped in
plastic to prevent copper trimmings from entering coil section
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Commutator Resurfacing in Lathe
• The commutator is turned so it is concentric with both bearing journals
• A Resurfaced commutator shall have an indicated runout of less that .001”
• Bar to Bar deviation shall be no more than .0002”
• A resurfaced commutator should have a finish of 40-70 microns
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Polishing Commutator after Turning
A non-metallic abrasive cloth is used to polish the commutator
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Resurfaced Commutator
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Mica Under Cutter Set Up and Ready
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Undercutting Mica Between Commutator Bars
• Under cutter during operation• Depth of undercut to be 1 to 1.5 times the width of the Mica slot
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Deburring BetweenCommutator Bars
• After undercutting the Mica slots, the edges of the commutator bars are deburred to provide a clean smooth edge on each side of the bars.
• The Mica slots are inspected to insure no copper or high Mica is left between the bars
• The armature is checked with a megohmmeter after this step
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Final Indicator Run Out Check
A final indicator runout check is done before the armature is removed from the lathe
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Bar to Bar Test
A high frequency bar to bar test is performed before it is removed from the lathe to insure there are no shorts or opens present
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Dynamically Balancing
• All rotating components receive a two plane ISO G1.0 grade dynamic balance in a calibrated balance stand• Component are balanced to the G1.0 Specification to insure the
assembled motor with perform at the Verso Paper specified vibration limits when test run
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Starting Assembly Process
• Prior to assembly all components are checked with a megohmmeter to insure insulation resistance is acceptable• Readings at assembly are recorded on the job card• Thermostats, heaters and
other temperature devices are checked again prior to assembly and recorded onthe job card• Each component and all
interior surfaces are painted with a red insulating spray varnish
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Bearings and Grease
• SKF or FAG double shielded C3 fit bearings are used• Mobil Polyrex EM grease is used in bearing caps and bearing
housings• Bearings are warmed to 210 ° F by an induction heater equipped
with automatic degaussing for installation• The bearing shield facing the grease
cavity is removed prior to installing the bearing housing• An insulated commutator end bearing
is installed at this time if required• The commutator is also wrapped in
preparation for the bearing housing to be installed
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Preparing Housings for Installation
• The bearing housing grease cavity is filled to ½ capacity• The brush boxes are raised to the highest setting to provide
adequate clearance to for assembly• The Brush rigging is then
installed lining up the match marks that were made at disassembly.
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Bearing Housings Installation
• The bearing housing is carefully aligned and slid onto the bearing• In some cases as seen here a crane is needed to assist in the
alignment of the rabbet fits
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Bolting Bearing Housings
• Once the machined rabbet fits are aligned the bolts are started• A crane is once again sometimes necessary to support the
bearing housing depending on size
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Drive End Bearing
• The drive end bearing cap and bearing are installed• If an AEGIS® grounding ring is to be used, a great place to install
it is behind the drive end bearing cap. This keeps it clean and out of harms way.
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Drive End Housing Ready To Go
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Installing Drive End Bearing Housing
• The drive end bearing housing is installed• Care is taken to insure all match marks are aligned so that all
openings are in the correct orientation
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Bearing Cap Bolts Installed
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Checking Commutator TIR Prior to Test Run
The commutator is checked with an dial indicator to insure overall commutator run out is under .001” after motor is assembled
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Setting Brush Box Height
• Each brush box is set to the proper height from the commutator• Normally this height is set at .081” from the commutator surface• Once the box is set to the proper height it is torqued
to the correct value for the bolt used
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Getting Ready to Seat Brushes
• A strip of garnet paper is cut to fit the commutator and applied to the commutator• The brushes are all installed but the shunts are not connected at
this point
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Seating Brushes
• The shaft is rotated several times to sand the brush bevels to match the contour of the commutator• Each brush is checked to insure at least 90% of the brush has
been seated prior to removing the garnet paper• Once the garnet paper is removed
the motor is blown out and the brush shunts are attached and torqued
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Setting Neutral and Checking Interpole to Brush Holder Polarity
• The Neutral position is set and the brush rigging is locked in position using the locking bolts• Checking Interpole to Brush Holder polarity• 20-40 Volts AC is applied to adjacent brush posts• The voltage measured on A1 and
A2 should be less than applied voltage to confirm correct polarity• If voltage measured on A1 and
A2 is higher than applied, all leads going to the brush holder must be moved to adjacent posts
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Final Shaft Run Out
A final output shaft TIR is taken prior to run out
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Motor “No Load” Test Run
Each motor is no load test run at full voltage in both directionsRunning in both directions:• Insures a good neutral
setting by running the same speed in each direction • Allows the technician to
fully seat the brushes by using a light seating stone• Vibration analysis and
bearing temperatures are also taken during this time
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Test Panel Report
• Vibration analysis is taken to insure vibration levels are within EASA or customer’s specific acceptable parameters • Vibration analysis is also
taken to insure no bearing defects are present• The vibration spectrum is
printed for each motor and kept with the job file• A test report from the
panel is generated and stored and a copy is printed kept with the job file
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“Full Load” Test Run
• Once the motor has been run on the test panel at no load and the brushes are fully seated in both directions the motor is run at full load.• This test is done to insure the motor performs as designed under
load• The load test report is
printed and kept with the job file
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Motor is Painted and Prepared for Delivery
• All nameplates, encoder pilots, shafts and openings are masked off prior to painting• New inspection windows and new gaskets are installed on all
covers and junction box• All grease tubes (if applicable) are filled 100% with Mobil Polyrex
EM prior to installation• A light rust inhibitor is applied to
the output shaft• Exterior of motor is painted a
color specified by a Verso paper representative• Grease fittings with caps and grease
reliefs are installed
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Motor is Painted and Prepared for Delivery
• Repaired motors have a metal tag install to identify the repair facility, job number, date and type of repair• A tag is installed that identifies the bearing manufacturer, part
number and if applicable the Inpro Seal part number for each end of the motor• All motor weighing in access of 20 ponds shall have the weight
prominently stenciled in a highly visible area on the motor• All motors equipped with Drive End roller bearing intended for horizontal application shall be tagged with a Red tag marked “Horizontal Belted Application”• All motors equipped with Drive End roller bearing intended for vertical application shall be tagged with a Yellow tag marked “Vertical Belted Application”
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Thank You
We thank you for the opportunityto present this information