Audio - 5 Minute Maintenance Tip - Rules of Thumb for Maintenance and Reliability Engineers

In follow up to SDT’s tip around grease fittings with tubes.

It would be a best practice to ‘charge ‘ the tube - that is pump grease into the tube before installing. It ensures that grease gets to the bearing quicker, when necessary and if you pump a little extra grease and discard you will get rid of any contaminant that may be in the tube.

Reader tip provided by Cliff Williams
Operations Maintenance Manager
ERCO Worldwide
Toronto ON Canada

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Typically there are two options of maintenance concerning electric motor bearings

One is to re-lubricate them and other is to change them. Monitoring electric motor bearing condition is paramount to insure reliability. Electric motors are an asset that must be managed and prolonging their life will insure more contribution to the bottom line profit. Preventing collateral damage caused by electric motor bearing failure is true cost avoidance. Because lubrication is the first line of defense for prolonging bearing life it is imperative that the lubrication film thickness between the rolling elements and the raceways be measured and monitored. Standard foot mounted motors that are mounted in the vertical position must have special consideration related to lubrication.

The normally mounted bearing in a horizontal motor is supporting load/overhung load in the radical direction. If the motor is mounted in the vertical position the bearing will see more thrust loads and the lubrication will run out through the opening of an open or shielded bearing. A sealed bearing will hold the lubricant longer in the lower half of the bearing because the bearing is lying on its side in this application.

This position will also force all of the balls of a ball bearing to one side of the raceway thus placing them all in a more loaded situation both radial and thrust directions. Load affects the lubrication film thickness. Normally a motor mounted in this position will need lubricating more often with less lubricant than what is recommended.

Find out how SPM can measure the film thickness of lubrication between the rolling element and the raceway of a bearing

“Unbalance Will Not Reduce Even Though I Keep Adding Weights”

CAUSES (match the number of the cause with its solution below)

1. The phase readings are unstable.
2. You are adding weights WR (with rotation) when the instrument is set to AR (against rotation) or vice-versa.
3. The trial weight used is too light.
4. You are not accurate enough when placing correction weights at specific angles.
5. The correction weights are inaccurate.
6. You are placing correction weights at a different radius than your trial weight was placed.
7. You are placing correction weights at a different plane relative to your trial weight.
8. You are not measuring from the same weight reference mark for the trial and correction weights.
9. You have the left channel sensor plugged into the vbSeries ® instrument on the right side and vice versa. (This only applies if you happen to change the left/right sensor during the balancing process.)
10. There is another vibration source nearby which is close to the 1X frequency (e.g. drive belt of balance stand).
11. The machine is running at slightly different speeds during each run (initial/trial/balance/trim).
12. You may be attempting a dual plane balance on a machine which has a severe static unbalance.
13. The machine is running near a natural resonance frequency (for its current mount or stand).
14. The machine is not ‘rigid’ i.e. it is flexing significantly at its normal running speed, or it may be running above its first critical speed.
15. The machine being balanced is an overhung rotor.  These often have characteristics such as Disk Skew and Gyroscopic Effects that can make them hard or impossible to balance with standard single or dual plane balancing techniques.

SOLUTIONS

1. Allow phase angles to stabilize before making any corrections.  A stabilized phase angle is considered good when there is no more than a three degree variance in three successive screen refreshes.
2. Make certain that the correction weights are placed in accordance with the way you have the vb instrument set up - either WR with rotation or AR against rotation.
3. When performing the trial weight tests, use a heavy enough weight to offset the angle or amplitude by 30% or more.
4. The placement of the corrective weights is critical.  You should have a tolerance of no more than 3-5 degrees.  Corrections made outside of this parameter will result in the ‘chasing syndrome’.  The use of a magnetic protractor or degree wheel is essential.
5. Your scale is out of calibration and the weights called for are not being applied.
6. You are placing weights at a different radius than the original trial weight.  Use the vb instrument’s recommendation for weight and radius calculations.
7. You are placing your corrective weights at a different reference plane than the trial weights.  If your trial weight was placed on a fan blade support that was 3 inches in from the bearing but your correction was made on the nose of an armature coil that was 5 inches in from the same bearing this will cause inaccuracies.
8. All weight angles should be measured from your chosen weight reference mark.
9. To avoid accidentally switching the sensors during balancing use the green balancing extension cable for the left side position and the red one for the right.  The green (left) cable will plug into CH1 on the instrument and the red (right) cable will plug into CH2.
10. Set the vb instrument to narrow filter bandwidth (+/- 15 RPM) to help cut out the nearby frequencies.  To access this, from the Balancing Menu press [1] Set Balancing Parameters then [7] Advanced Balance Options.  Press [1] to select a bandwidth filter option.
11. Unbalance forces generally vary with the square of the running speed so variations can cause major errors in the balance calculations.  Ensure that the RPM is stable and consistent between runs, certainly within 5% (usually for AC driven machines this is not an issue as they are locked to line frequency).
12. Perform a single plane balance on the worst end first then move on to dual plane balance.
13. Does the machine appear to go through any resonances during run up or down?  You can use the vb instrument to help diagnose this.  If possible run the machine at a different speed, preferably slower.
14. The instrument is designed to balance ‘rigid’ rotors only.  If you can balance the rotor at a much lower speed, the unbalance forces may be reduced to a level where the rotor is effectively rigid at its operating speed.  Try balancing at a slow speed first.
15. Read article Balancing Overhung Rotors, which describes two established and effective techniques for dealing with balancing overhung rotors.

Tip provided by Dennis Shreve
Commtest, Inc.
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This course, delivered by Allied Reliability is designed to teach the principles of improving asset management and maintenance decision making using the fundamentals of reliability engineering principles.

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Detect Cracks in Insulators and Avoid Serious Outages

Hairline cracks in insulators means the insulator no longer functions at 100% allowing electricity to arc and track and producing ionization which further degrades the installation. Meanwhile, moisture, dirt, and other contaminants penetrate the crack and become superheated by the electrical current. The results can vary from minor power loss to a major outage when the insulator finally explodes.

Arcing, tracking, and ionization discharge produce ultrasonic phenomena that are easily detected with an ultrasonic detector. Set your detector in airborne mode and scan in the direction of the insulators using a back-and-forth and up-and-down motion. Good insulators should be quiet. Insulators that are arcing, tracking, or producing corona discharge will have either a steady or intermittent buzzing sound. For long distances use a parabolic dish sensor with a laser sight. For electrical cabinets use the flexible sensor. Scan the edges of the cabinet prior to opening to help decide if there is arc-flash potential.

Tip provided by SDT North America
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RCM - “Communicate, Communicate, Communicate”

Reliability departments within today’s organizations are relatively new. The danger for many can be that they are dragged back to the traditional role of the maintenance department, where fixing today’s breakdown is the priority.

Communicating goals, publishing performance measures and establishing a “culture” of reliability are important elements to help ensure the reliability organization is supported as an important strategic department essential to meeting future plans.
Using modeling tools that takes today’s knowledge and forecasts future performance is a key tool in the Reliability Departments armory. Compare alternative scenarios for shutdown outages, develop zero based budgets, predict plant availability, identify economic end of life; are examples of how a reliability engineer can use modeling tools to communicate likely outcomes.

Tip provided by ARMS Reliability
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AssetPoint Reliability Services uses a tailored approach to develop, install and integrate maintenance best practice programs, systems and procedures.

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Power Factor Correction Capacitor Influence on Current

When performing power and efficiency analysis on an AC induction motor, it is important to identify the location of any power factor correction capacitors in the circuit. Although voltage is unaffected, testing the current upstream of the power factor capacitor will give a higher power factor and a lower current than the motor is actually experiencing. Not knowing the health of the power factor capacitor can negatively affect the distribution power factor, increasing the reactive loading and utility costs.

Tip provided by PdMA Corporation
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The Second Law of Thermodynamics

Energy always travels from areas of higher kinetic energy to areas of lower kinetic energy until the energy levels are equal and a state of thermal equilibrium is achieved and at that point there will be no more energy transfer.

Tip provided by Wayne Ruddock, Reliability Roadmap Web Workshop Instructor
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Tip Sponsored by Academy of Infrared Training
Level 1 and Level 2 On Site Infrared Training