Overhaul
Process of restoring and maintaining an equipment, machine, or system in a serviceable condition. Overhaul involves
(1) partial or complete disassembly of the item,
(2) inspection to detect damaged, defective, or worn parts,
(3) repair or replacement of such parts, and
(4) reassembly, testing, and trial-run prior to returning the item to its full operating level.
PPE
Safety goggles and hand gloves
TOOLS:
Hammer brass, steel or soft mallet and center punch
Magnetic stand with dial and Vernier caliper digital
V - block
SKF bearing kit
Bearing puller.2 arm and 3 arm
Bearing heater
Multi meter, Megger, Clamp on meter
Basic tools
MAJOR PARTS OF A MOTOR
Stator
-The stator is the stationary portion of the motor and delivers a rotating magnetic field to interact with the rotor. One or more copper windings make up a "pole" within the stator, and there is always an even number of poles within a motor. The electric current alternates through the poles, resulting in a rotating magnetic field.
Rotor
-The rotor is the central component of the motor, and is fixed to the shaft. The rotor is generally constructed of copper or aluminum strips attached at each end to a circular fixture. This configuration is called a "squirrel cage rotor" because of its appearance.
-The magnetic field generated by the stator induces a current in the rotor, which then creates its own magnetic field. The interaction of the magnetic fields in the stator and rotor results in a mechanical torque of the rotor. In some induction motors, the copper bars are replaced with slip rings and copper windings that behave in the same way.
Shaft
-The motor shaft is fixed within the rotor, and rotates with it. The shaft extends outside of the motor casing, and allows a connection to an outside system to transmit the rotational power. The shaft is sized to the amount of torque the motor puts out to avoid breaking the shaft.
Bearings
-The rotor shaft is held in place by bearings at either end of the motor casing. The bearings minimize the friction of the shaft connection to the casing, increasing the efficiency of the motor.
Casing
-The casing of the induction motor contains all of the motor components, provides electrical connections and allows for ventilation of the motor parts to reduce heat buildup.
Carryout visual external examination
-Record Machine Nameplate & Serial Number of the motor.
-Check for any missing parts & record.
-Check insulation resistance of the winding and record.
-Remove all dirt & dust from motor body. Motor to be cleaned externally, preferably in a de-dusting chamber with dry compressed air.
Removal of Rotor:
Before and after dismantle take reading by using magnetic stand with dial for Axial play as found must be required and record for future references. All parts must be marked.
Remove both stator & rotor together to a separate work place & place it on a pre-arranged stool. Care is to be taken to ensure that the load is absolutely balanced. The rotor to be lifted with the crane hook while taking precaution that the sling does not damage the overhang winding.
Wooden piece of suitable thickness to be given as packing. While threading out/in the rotor from/into the stator it must be leveled to avoid damage inside the motor.
Depending upon the size of the motor, a balance beam with a ratchet hoist may be deployed. Otherwise the job can be completed with the help of any kind of Crane.
INSPECTION OF INTERNAL PARTS
Stator & rotor to be cleaned thoroughly by dry compressed air in a de-dusting chamber. Where such chambers are not available, it should be done in an open space, so that the dust does not enter into other motors.
Then apply suitable solvents (the recent advance methods of cleaning using steam/hot water/dry ice and recyclable cleaning agents can be adopted as per available facilities) to remove settled oil, dust & grime.
Check insulation resistance of the windings.
Check overhang portion of the windings.
Check looseness of the slot wedges.
Check for hot points (loose connections) in end connections. Check condition of connecting leads & terminal arrangement.
Check condition of the terminal insulators.
Use bearing puller for taking out the bearings. After measurement of bearing gap of the new bearing, compare the observed data with respect to allowable limits.