Developing a Motor Bearing Regreasing Strategy

Tags: electric motor lubrication, greases

Question
You have just been hired as a maintenance engineer for a large manufacturing plant. The plant has a history of never greasing electric motor bearings, believing that this practice does more harm than good. The plant has a mix of motors, some of which have been in service for 10 years, others just a few months. Depending on motor manufacturer, speed and horsepower, there is everything from sealed and shielded bearings to open bearings. How would you go about developing a regreasing strategy for these motors?

The Winning Answer
First, establish a way of tracking each motor as an asset. Develop a preventive maintenance (PM) program in your computerized maintenance management system (CMMS) package to track these motors. Now it is time to be a detective and find as much information on each motor as possible. Look for date of installation, horsepower (hp), rpm, bearing type, type of duty, volts and frame size. Also, find out which vendor last repaired the motor, what type of grease was used, what type of bearing was used, and if there’s a warranty. This may sound like a lot of work but it will pay off. Start with your most critical motors and new replacements.

Now separate the sealed, shielded bearings into one group and the open bearings into another group.

Perform a vibration analysis on the sealed and shielded motor bearings. Trend the vibration until replacement. On motors of 15 hp or less, stay with the sealed bearings. We tend to replace the motors and not repair them. Use your own formula for replacement vs. rebuild. On larger motors, when vibration shows bearings near failure, we rebuild the motor with open bearings and bring them into the grease program.

Establish a PM practice for open motor bearings. It is best to develop your PM frequency on runtime. We use 6,500 hours (nine months continuous duty). We like to relubricate the bearings with the motor at operating temperature with the motor running when possible.

  1. Clean top grease fitting, remove the bottom grease relief valve.
  2. With a manual grease gun, pump grease into the bearing and listen to the bearing using an acoustic grease gun adapter. Follow the manufacturer’s directions. Note: AVM Technology (1-800-667-5325) offers a free Ultrasonic Lube Training CD-ROM.
  3. Watch for grease coming out the bottom port. If you pump excessive grease into the motor and none comes out the bottom port, stop and check for hardened grease in the bottom passage.
  4. Allow the motor to run for one hour to expel any excess grease before installing the bottom grease relief valves.
  5. Clean any excess grease from the exterior of the motor.
  6. You must know if the original grease is compatible with new grease. We supply the grease to our rebuild vendors. On new motors you will need to contact the manufacturer.

When you send out a motor for repair, evaluate the bearings and determine how well your program is working. Start with your more critical motors or your most frequent failures. We also conduct vibration analysis on our critical motors. Your strategy should depend on your plant’s ability to run a motor to failure and how much downtime it can withstand.

Jeff Stegemiller, Maintenance Planner/Scheduler, Gallatin Steel

Editor’s Note
For bearings two years old or older in which the grease fitting attaches to a pipe or tube via a supply tube, the supply tube should be removed and swabbed clean. Grease can become caked in these supply tubes over time. Be sure to fill the supply tube with grease after cleaning.

Other Answers Received
Create a Team
At my plant this was a real problem. Most bearings that were being greased were based on guesswork. Many were not greased at all. I decided to form a team consisting of our lubricator, his supervisor, a vibration technician and myself.

We started with our most critical machines. We then collected the bearing sizes and used the SKF formula G = [(0.114)X(D)X(B)] to determine the amount in ounces of grease needed for relube (D = bore diameter, B = bearing width). We then determined the speed of the bearing and the bearing type (ball, roller, etc.) and used an SKF bearing chart to determine the relube interval.

At that point, we were able to determine how much grease we needed and how often. We set up PMs with the proper frequency and listed the amount to add for each machine. (In many of the bearings we were lubricating, we found that we had been adding four to 10 times too much grease.) For this to work, the lubricator needed to know how much grease his grease gun was putting out.

We measured the amount in two ways. First, we determined the weight per stroke. (The lubricator’s grease gun puts out .062 ounces per stroke). Secondly, we made up a grease block to determine how many strokes are in a cubic inch. Many times the motor manufacturer will give you a specification such as: add two cubic inches of grease every six months. Now we know how many grease gun strokes make a cubic inch - 11 pumps per cubic inch.

We noted in the PM that only the lubricator’s grease gun may be used. All of our grease guns must be checked in this way. The grease gun is marked with this information. After setting up the PMs, our vibration analyst closely monitored the bearings for problems. If he noticed that a bearing consistently needed grease, we updated the PM amount.

The formula is accurate; we had to update only three PMs and they required only one extra pump. We did this in 1997 on more than 100 pieces of equipment. As far as we have been able to determine, we have not had another lubricant-related failure. We also noted that this is for normal operations. Vertically mounted motors or motors subjected to dirty environments or other adverse conditions must be evaluated separately.

Note
We understand that the proper way to grease a bearing would be to shutdown the machine, remove the bearing, clean and repack. However, this is not possible in our business, so we must lube with the unit running.

Wayne Ferguson, Reliability Engineer, Eli Lilly and Company

Gain Management’s Approval
I would begin by prioritizing equipment. Starting with “critical path” machinery, I would look up histories on failure modes to determine bearing-related failures. I would present my findings to management in dollars and cents (loss of equipment utilization due to premature bearing failures). Sponsorship or support from the top of an organization is crucial for any change in strategy to succeed. We are not just dealing with what’s right or wrong for a motor bearing. We are dealing with a change in behavior according to a faulty belief system (greasing motors causes more damage than good).

Begin collecting bearing information specific to each motor (run time, load, manufacturer’s grease specs, etc.) Next, determine the correct regreasing cycle and the amount of lube that needs to be added, as well as the type of lubricant for the bearing requirements. The folks responsible for greasing motors in the plant must then be trained on how to correctly grease a motor.

Looking again at critical path equipment first, then on to the rest, I would use vibration analysis and/or ultrasonic testing to determine on which component to begin the new procedure. PMs or repetitive work orders must mandate the cycle of regreasing, including the amount for each application and type of lube. Returned work orders also serve as documentation that the procedure was completed.

Continue collecting failure data on the machinery, using the new data as a metric to indicate the success of the new regreasing strategy. Communicate successes to both management and production personnel to keep the process going. Strategies are necessary for improvement.

Sustaining change needs at least four components; understanding and clearing out as much resistance to the change as possible before implementation, the intervention (change in procedure), measuring the effects of change and reporting results to all concerned.

Randy Widick, Vibration Specialist, Alcoa Inc.

Base Program on Individual Motors’ Needs
The objective is to design a motor relubrication program that will ensure motor maintenance is done on the basis of chronological need. The following relube program is based on the assumption of a simple PM approach rather than predictive or proactive maintenance programs, which the manager can explore later. The main steps for accomplishing this objective are:

  1. Document and identify the motors in a relevant way.
  2. Determine the relube interval and lubricants required.
  3. Determine the last and next scheduled relube dates.
  4. Set up a relube schedule.
  5. Keep the schedule updated.

I would recommend using Excel to tabulate this data, although any good database program could be used. Excel information is easy to manually manipulate; and for those skilled, much of the maintenance of the database might be automated. At a minimum, I would recommend creating the following fields to track data:

  • Motor ID (location, identification, etc.)
  • Motor Information (hp, manufacturer, frame type)
  • Lubricant (recommended bearing lube)
  • Date Installed (if available)
  • Relube Interval (the recommended time between relubes)
  • Last Relube (date motor was last lubed)
  • Next Relube (date of next motor relube)
  • Comments (list any special actions or conditions)

The most critical Excel field for determining the order of the spreadsheet will be the next relube date. When completed, the spreadsheet should list the motors in order of when pending maintenance is required. Maintenance would then simply address the motor relube program in the sequential order of the spreadsheet list.

Step No. 3 is where the greatest difficulty lies in setting up a new program. Some special conditions and exceptions to be considered include:

  • Motors past due for relube: List them at the top of the spreadsheet in order of lateness or criticality so they will be the first to be relubed. In the next relube field, enter the date the motor should have been relubricated, even if that date is past.
  • Motors on which the last relube date is unknown: Assume that half the relube interval has passed and set next relube date accordingly. Consequently, enter the last relube date field with the date that is one-half the previous relube interval (Example: if today’s date is July 21, 2003, and the relube interval is four years, enter July 21, 2001, for the last relube date and enter July 21, 2005, for the next relube date.)
  • Motors that have been installed for a period less than the relube interval: Set the installation date as the last relube date, and schedule the next relube date accordingly.
  • Permanently lubed bearings: Mark “no action.”
  • Special exceptions: Note unusual situations, such as vertical motors that use oil in the bell housing and grease in the shaft bearing.

As mentioned, arrange the spreadsheet in ascending order based on the “Next Relube” field. As each motor is relubricated, update the “Last Relube” and “Next Relube” fields. Then use the Excel sort function on the “Next Relube” field to reorder the spreadsheet. This way, the next required relube items will always be at the top of the list.

After acquiring and tabulating the necessary information to create the schedule, the maintenance manager can begin implementation. After he initiates the program, he needs to be diligent and keep the schedule updated. This will be critical to making the system work. The relube schedule will become a living document because of its frequent updating. It should always reflect the order in which maintenance is to be done from the current date onward.

The schedule should not be clouded by having to wade through previous, closed out maintenance. In other words, the list should have each motor listed only once, in the order of the next scheduled relube. The last lube/relube, the next scheduled relube, and the relube interval, along with other pertinent motor data will be listed.

Establishing what relube equipment is needed is another important part of successful program implementation.

In establishing the program, be careful to ensure that management, maintenance and affected workers are educated about the need of the program and its goals, as early as possible. Many good programs - even those with management blessing - have failed because of ruffled feathers, prejudice or just resistance to new programs or personnel.

H. Ron Elliott, Lubrication Engineer, Castrol North America

Include Vibration Analysis and Lubrication Training
The first thing I would do is get the reliability department together and discuss the scenarios that brought them to the conclusions not to grease bearings in electric motors. I would then send them to a training course on electric motor reliability.

I would evaluate the mean time between failures (MTBF) on the motors and take a look at the latest vibration analysis reports looking for motors with the highest vibration readings at the appropriate bearing defect. I would make a list of motors that were showing cage frequencies and flag them as bearings to beware of when applying grease.

I have had bearings fail right on the spot when they were showing cage frequency and grease was applied. These motors should be shut down and repaired as soon as possible. When the bearing cage fails, it can be damaging to the shaft and rotor.

I would purchase an ultrasonic grease gun and then send one or two of the mechanics to a greasing and oiling training seminar. The next step would be to have the recently trained staff members sit down with the rest of the maintenance team and share what they learned. I believe that by allowing peers to come up with the proper solution as a team, there would be better buy-in by all.

I would set up one or two of my maintenance staff as oilers and make sure that the new program gets off to a good start. I would pick someone who believes in preventive maintenance to take charge of the program. I would determine what grease was put in the bearings during assembly and try to find the best compatible grease available.

I would make sure that all motors with vent ports are purged of the old grease by following proper greasing techniques. I would then set up a PM program based on the recommendation of the motor vendor and make sure the rest of the plant team is aware that there may be a few failures at first, as some of the bearings may already have been at the end of their life. I would determine which bearings have been changed to “sealed for life” and make sure that good reasoning and judgment were used when the decision was made.

I would recommend changing these bearings back to greasable bearings and set up a good greasing program monitoring the MTBF. After a couple of years, I have no doubt the MTBF will be greatly improved.

I would then make sure that all the reports of improvements and successes were shared with all team members and management. I would use a small portion of the money saved to take the plant team out for a victory celebration. With the remaining money, I would set up some good training programs and get the plant on a world-class reliability program which everyone would be proud to be a part of.

KC Hyland, Reliability Technician, BP Canada Chemicals

 

Create your own user feedback survey