Bearing Failure – The Facts

Motors don’t fail just because of age or operating hours. 51% of failures are bearing related. And here are the reasons why:

1. Insufficient lubrication

Re-greasable bearings need regular maintenance… don’t fit and forget. For example:

TECHNICAL – Insufficient Lubrication

Refer to the manufacturer operation and maintenance annual for specific re-lubrication intervals for your motor.

TIPS – Insufficient Lubrication

Look for this plate on your motor. It gives you the detail you need to re-grease your motor bearings.

FAQ – Insufficient Lubrication

Do I have to re-grease sealed for life bearings?

No, these bearings are permanently greased (sealed for life) and can not be re-greased

2. Excessive greasing

Yes this can overheat bearings and lead to failure.

TIPS – Excessive greasing

  • Ensure grease relief valves are open during the re-greasing process to allow excess grease to purge from the bearing housing.
  • A bearing lip seal will typically fail at 500 psi, yet grease guns can produce up to 1500 psi
  • Add each shot of grease slowly to avoid pressure build-up

FAQ – Excessive greasing

What is the best way to control over-greasing?

  • Always make sure relief valves are cleaned out of any dirt or hardened grease
  • Remove grease outlet plug or open outlet valve where fitted
  • Slowly pump grease into the bearings every few seconds
    (avoid quick-lever actions as pressure will build and damage seals)
  • Discontinue greasing if any abnormal back pressure is felt

3. Wrong lubricant

Check that you are using the right grade or type of grease.

TECHNICAL – Wrong lubricant

When re-greasing, use only special ball bearing grease with the following properties:

  • Good quality grease with lithium complex soap and with mineral or PAO-oil
  • Base oil viscosity 100-160 cST at 40°C
  • Consistency NLGI grade 1.5 – 3

Temperature range -30°C – +120°C, continuously.

TIPS – Wrong lubricant

  • Do not mix different types of grease.
  • Incompatible lubricants may cause bearing damage.

FAQ – Wrong lubricant

Are there any specific greases I need to use in specific applications?

Yes, there are specific greases you need to use for say high temperature or hygienic applications. Refer to the lubricants section of your motor operation manual.

4. Misalignment

It’s essential that the motor and load are correctly aligned under actual operating temperatures and conditions. Machines that are correctly aligned at room temperature may become badly misaligned due to deformation or different thermal growth associated with temperature change. The alignment must be checked, and corrected, if necessary, after the motor and driven machine have reached their maximum temperature under load.

TECHNICAL – Misalignment

Soft foot is one of the main causes of misalignment.

The 2 types of Soft Foot are:

  • Angular soft foot
  • Parallel soft foot

Common Causes of Soft Foot:

  • Bent or deformed shim
  • Bolt hole with a burr
  • Bent motor foot
  • Deformed machine base

TIPS – Misalignment

When torqueing the holding-bolts of your motor, use a cross-torque pattern to ensure an even secure fit.

FAQ – Misalignment

How often should I check the alignment of a motor?

  • ABB technicians recommend a motor should be checked approximately every 2,000 hours.
  • Both operating and non-operating alignment should be checked.

5. Shaft overload

  • Excessive loading through the shaft of your motor may cause failure.
  • Belt driven pulleys often put high load directly onto the shaft bearing.

TECHNICAL – Shaft Overload

Pulley diameter

When the desired bearing life has been determined, the minimum permissible pulley diameter can be calculated with FR (right).

TIPS – Shaft Overload

For motors in frame sizes 160 and above, on belt driven applications fit roller bearings.

FAQ – Shaft Overload

How do I tell if an existing motor is suffering from shaft overload?

  • Rapid wear of belts is a simple visual sign of an overloaded shaft.
  • Check how often your belts are bottoming out – if it is happening a lot – shaft overload could be the cause.

6. Vibration

  • Excessive vibration can lead to premature bearing failure.
  • Check motor mounting bolts are secure as vibration may cause them to become loose during operation.

TECHNICAL – Vibration

Motor vibration causes can be:

  • Electromagnetic
  • Mechanical imbalance
  • Rubbing parts
  • Bearing failure
  • Resonance

Measure vibration on all 3 planes:

– Vertical

  • Horizontal
  • Axial

TIPS – Vibration

  • Vibration causes are often in one of two areas:

– Shaft vibration

– Housing vibration

  • Check vibrations with a combination of

– Magnetic accelerometers (ensure they are mounted correctly)

– Proximity probes  (commonly known as Eddy probes)

FAQ – Vibration

How do I tell if the vibration on my motor is normal?

Stringent specifications for Motor vibration call for:

  • A maximum velocity level of 0.1 in./sec on the housing
  • 1.5 mm of displacement vibration on the shaft

7. Over-heating

  • Make sure your motor is designed to cope with the heat it is subjected to
  • Bearings have different clearances to allow for thermal expansion in operation.

TECHNICAL – Over-heating

Keep an eye on your bearing temperature and ensure you use the correct grease for high temperature applications.

TIPS – Over-heating

  • For every 15°C cooler you typically double the re-greasing interval / bearing life!
  • Keeping the motor operating environment as cool as possible will greatly increase motor life.

FAQ – Over-heating

How do I tell if the motor bearings are overheating?

  • Use a temperature probe or thermal imaging camera to test bearing temperature.
  • Make sure the readings are within the tolerances of the installed bearing.

We provide 24/7 Technical Support to engineers, our dedicated Support line is available 8am – 5pm every day, manned by one of our fully qualified engineers.

If you need further assistance on how to prevent your motor from failing, call us, day or night, on 0330 9000 247.