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CASEY EQUIPMENT CORPORATION
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PHONE: (412) 963-1111
 

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MOTOR REBUILDING PROCEDURES


* NEMA FRAME SQUIRREL CAGE/INDUCTION MOTORS

* SLIP RING MOTORS (WOUND ROTOR)

* SYNCHRONOUS MOTORS

* DC CRANE AND MILL DUTY MOTORS

* DC GENERAL PURPOSE MOTORS


NEMA FRAME SQUIRREL CAGE/INDUCTION MOTORS:

Nema frame motors are available in frame sizes 48 through 505 in both drip proof and totally enclosed fan cooled (tefc) enclosures with the largest motor being typically about 25' high and around 48' not including the shaft. Tefc motors are usually easier and quicker to rebuild than drip proof motors because the inside is not exposed to moisture and corrosion. To insure a quality rebuild both drip proof and fan cooled motors should be subjected but not limited to the following procedures. (1) Preparation (A) All surfaces (inside and out) to include stator, end bells, rotating assemblies and parts, will be completely cleaned. (B) All parts will be fully inspected. (C) All parts will be epoxy primed and painted with a hard enamel finish. (2) Electrical & Mechanical (A) The motor windings will be fully reconditioned to include cleaning, additional dips and bakes in a high tensile strength varnish treatment, and fully tested. Winding will be tested by: (1) D.C. hi-potential tests in accordance with NEMA standards (2) Coil surge comparison tests (3) Polarization index tests (B) The rotor will undergo the following: (1) Tested for soundness (2) Checked for concentricity (3) Dynamically balanced in accordance with NEMA standards (4) On TEFC motors, fans are balanced separately of rotors (C) All mechanical fits will be checked to insure proper tolerances (D) All ball bearing units will have new bearings (3) Final Assembly & Test Procedures (A) Run-in test all full voltage (B) Vibration analysis tests (C) Phase balance amperage checks, starting and unloaded (D) Bearing temperature checks (E) Magnetic center shaft scribe (F) Shaft run-out checked

SLIP RING MOTORS (WOUND ROTOR):

Slip ring motors are similar to squirrel cage/induction motors except the rotor has windings imbedded into the rotor connected to shaft mounted rings and the frame is equipped with brushes and brush holders to complete the connection of the rotating windings to external resistors. When rebuilding a slip ring motor use the squirrel cage/induction motor procedure with addition of the following steps: (A) Clean dip and bake rotor in a high tensile strength varnish treatment as needed, and test. (B) Glass bead blast brush holders and replace brush springs. Replace brushes.

SYNCHRONOUS MOTORS:

Synchronous motors are the same as slip ring motors but they are equipped with rotating dc field coils mounted to the rotor and connected to shaft mounted rings and the frame is equipped with brushes and brush holders to complete the connection of the rotating fields to an external field application panel. There are no windings imbedded into the rotor. When rebuilding a synchronous motor use the slip ring motor procedure with addition to the following steps: (A) Clean dip and bake rotating fields in a high tensile strength varnish treatment as needed and perform ac potential drop test on dc field coils. (B) Glass bead blast brush holders and replace brush springs. Replace brushes.

DC CRANE AND MILL DUTY MOTORS:

These motors are for heavy duty service applications usually found in steel mill auxiliary and crane applications. Frames are horizontally split (like a suitcase) in a manner to allow armature removal by a straight vertical lift. Rebuild using the following 21 step procedure. 1. All motors are match marked and disassembled 2. All mechanical parts are sandblasted to remove paint and other contaminates 3. All electrical parts are steam cleaned and baked dry in gas fired ovens 4. Insulation and meggar tests are taken and recorded 5. AC potential drops are taken on the DC fields to detect shortened turns 6. Armature slot wedges are checked for condition and tightness, then replaced or repaired as needed 7. The headers on the main poles and interpoles are checked and replaced or repaired as needed 8. New field frame wiring is installed using ethylene propylene, flexible type wire 9. The brush holders and springs are glass bead blasted, inspected, and repaired or replaced 10. A bar-to-bar test is made on the commutator to detect shorts, high resistance connections, and in the larger lap-wound machines, faulty equalizers 11. The armature is placed in a lathe, and the commutator is turned and undercut. Measurements are then taken and recorded to assure the diameters meet manufacturers' allowable tolerances. 12. the armature is glass banded 13. The bearings are checked and replaced as required 14. All electrical parts are heated and then dipped in class H varnish. The parts are baked dry at approximately 250 degrees fahrenheit for 24 hours to cure and dry the varnish 15. The motor frame is shot blasted, primered, and painted on the outside with Rustoleum paint. The inside is painted with an orange, epoxy-type insulating compound. 16. The armature, field coils, and interpoles are painted with an orange varnish-type oil resistant air-drying insulating compound. A preservative is also added to the shaft extension 17. The machine is assembled on the test floor 18. New brushes are installed 19. The air gap around the periphery of the armature is checked for uniformity 20. Each machine is operated throughout its speed range. Each is dynamically balanced, and the data is recorded. These tests are implemented with electronic balance equipment. 21. Test data including final meter readings, field resistance, field current, dynamic balance readings, etc., should be recorded and stored for future reference.

DC General Purpose Motors:

DC general purpose motors are nema frame dc motors 1 hp -500 hp designed for adjustable speed operation usually from SCR controls. Unlike crane and mill (suitcase) motors the armature is removed horizontally once an end bell removed. The above 21 step crane and mill motor rebuild procedure may be used to rebuild DC general purpose motors.






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