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What causes motor seizure?
Motors can seize up due to a variety of reasons. The most common causes of motor seizure include:
Lack of lubrication
Lubrication is essential for allowing parts in motors to move freely. Without enough lubricant, friction between moving parts increases leading to overheating and potentially seizure. Common causes of lubrication problems include:
– Oil leaks leading to low oil levels
– Using the wrong viscosity oil for the application
– Infrequent oil changes allowing contaminants to build up
– Oil breakdown from excessive heat or operation beyond recommended service intervals
Rust and corrosion
Exposure to moisture can cause rust and corrosion on internal motor components like bearings and the rotor. Rust and corrosion increase friction levels leading to potential seizing. Common causes include:
– Water ingress due to damaged seals or improper storage
– Operating in damp or wet environments
– Condensation buildup inside the motor during storage or idle periods
Overheating
Excessive heat is one of the most common causes of motor failure. Several issues can cause overheating:
– Operating above the motor’s rated capacity
– Inadequate ventilation or clogged air intakes
– Mechanical problems like misalignment or worn bearings
– Electrical issues like unbalanced voltages or excessive starts/stops
The extreme heat can glaze and breakdown lubricants, damage insulation, and expand or distort motor components leading to seizure.
Foreign object damage
Debris sucked into the motor can jam the rotor, damage windings, or scratch shafts and bearings. Common foreign objects include things like rocks, sand, dirt, paper, rags, hardware, and bits of metal. Air intake filters, covers, and regular maintenance help prevent foreign object damage.
Electrical faults
Electrical issues like phase loss, unbalanced voltages, frequent starts/stops, and overloads can all contribute to overheating and motor failure. Burned out windings or excessive resistance in squirrel cage rotors can cause hot spots leading to seizure.
How to unseize a motor?
If a motor does seize up, taking prompt action can sometimes get it operational again. Here are some steps to attempt unseizing a seized motor:
1. Disconnect power
Immediately disconnect all electrical power to the motor to prevent any further damage to windings or other components. Do not restart the motor until the seizure cause has been identified and resolved.
2. Allow the motor to cool
Let the motor cool completely before attempting to turn or dismantle it. Forcing a hot seized motor can cause further damage and complicate disassembly. Cooling for 24 hours is recommended for badly seized motors.
3. Check for obvious causes
Inspect the motor installation for any visible causes of the seizure like:
– Low oil level
– Broken or loose hardware
– Misalignment issues
– Damaged drive components like pulleys or belts
– Debris buildup around the motor
– Evidence of overheating like bluing or discoloration
Rectifying external factors like these before attempting disassembly improves your chances of freeing the motor.
4. Remove debris/foreign objects
If foreign objects are visible externally or internally through fan covers, carefully remove them. Debris can jam between the rotor and stator causing excessive friction.
5. Add lubrication
If the motor appears under lubricated, adding the proper oil type and amount can help free a seized rotor. Note that forcing oil into a seized motor can damage seals. Go slowly and monitor for leaks.
6. Break loose the rotor
The next step is to attempt freeing up the rotor by turning the shaft by hand or with a wrench. Apply gradual turning force in both directions while rocking the shaft back and forth. Applying heat to the stator or penentrating oil around the rotor shaft can help break loose the rotor.
7. Disassemble if needed
If the rotor remains seized after the above steps, the motor will need to be disassembled to remedy the problem. Dismantling and inspecting will reveal where and why seizure occurred. Typical actions include:
– Cleaning components of rust and debris
– Polishing the shaft and bearing surfaces
– Replacing damaged bearings or windings
– Filing burrs or high spots on the rotor or stator
Extensive repairs or replacements may be needed for badly seized motors. Reassembly with proper alignment and lubrication should allow the rebuilt motor to run smoothly again.
How to prevent motor from seizing up?
Prevention is the best approach to avoid seized motor problems. Here are key seizure prevention measures:
Proper lubrication
– Use the recommended oil type and viscosity
– Check oil level regularly and top up as needed
– Perform oil changes per the maintenance schedule
– Ensure seals are in good condition to prevent leaks
– Keep breather vents clear to prevent pressure buildup
Cooling system maintenance
– Clean air intake screens and fins regularly
– Ensure fan covers are installed properly
– Check fan operation and blades for damage
– Keep minimum motor air gap clearances
Electrical system maintenance
– Test for and correct unbalanced voltages
– Inspect connections for tightness and corrosion
– Ensure wiring is properly sized for the application
Application review
– Verify the motor is sized appropriately for the load
– Make sure operation stays within nameplate ratings
– Consider adding a drive for variable speed control
Environment protections
– Add enclosures, filters, drip covers to prevent contamination
– Avoid washdowns that could introduce moisture
– Keep storage areas clean and dry
Preventive maintenance program
A comprehensive preventive maintenance program tailored to the application and environment is key to avoiding motor failures. Typical PM tasks include:
| Frequency | Maintenance Task |
|---|---|
| Daily | Check oil level and top up as needed |
| Weekly | Inspect for leaks, odd noises, or odors |
| Monthly | Check mounting, alignment, wiring, and ventilation |
| 3 months | Test insulation resistance |
| 6 months | Change oil and lubricate bearings |
| Annually | Check balance, resistance, and performance |
Conclusion
Motor seizure can often be avoided through proper maintenance and operating practices. When seizure does occur, cooling then lubricating the motor may help free up the rotor if acted upon quickly. For stubborn cases, disassembly and rebuild of the motor is needed to get it running smoothly again. Implementing a comprehensive PM plan tailored to the motor and application is the best way to prevent costly downtime due to seized motors.