Steven Carbone
Technical Education Committee Member
Industrial Electro-Mechanics
In today’s ever-increasing competitive environment, end users are looking for rotating apparatus service centers to increase their offering of value-added support. One of the easiest ways for a service center to achieve this is through a thorough and detailed inspection of items in the shop requiring repair. The results of this type of inspection allow for improved reliability achieved through the results of the evaluation and recommendations the service center offers to prevent reoccurring failures and improve mean time between failure.
Start Painting the Picture
The work scope of an electric motor starts when the first phone call or email occurs. At this point, shops should be asking general questions about the type of motor, the reason it is being sent out, is the motor driving a belted or direct coupled application, how is the motor started, how long has the motor been in service and any other notes that may be available to help aid in the inspection and appropriate repair work scope for the motor. We too often find that customers send us items for repair with no background information. That doesn’t happen when people drop off cars for repair service, so that should not be the case in this critical reliability environment either. All of the general questions can be developed into a simple form that includes both the questions and the answers. The form can then be attached to the motor to allow a manager or shop technician to review prior to scheduling the inspection. This not only helps the internal review process but also shows the customer that you are working as partners with them to improve their process and make sure their items are returned in the best condition. Additionally, we sometimes find the customers know exactly what happened to the motor and it is not necessary for the repair shop to spend resources on the root cause failure analysis when, for example, a starter or fuse failed and caused the motor to fail as a single-phase fault.
Dismantling for Work Scope Development and Analysis
After the shop is off to a good start with preliminary information, it is now time to start the dismantling process. This should be a procedure-driven and documented process to allow for repeatability and a thorough inspection. Pictures during this process are worth a thousand words; they not only help easily communicate the issues to the customer but serve as a tool for shop technicians and management to better analyze after the teardown is complete (Figure 1). The pictures can also be used as reference reminders for assembly or pre-assembly tasks. Almost everyone has a phone camera in their pocket; digital cameras can be given to technicians, or you can go advanced with some of the tablet-based inspection software that is available. The important thing is that these pictures and inspection documents go to a centralized location, so they can be easily shared.
There is a lot of information the technician will gain during the dismantling process, and they will be the best resource to help determine the appropriate work scope and root cause of failure. During the teardown, technicians need to meticulously inspect the items to see how the failure may have occurred. For totally enclosed fan cooled (TEFC) motors with a grounded winding, the technicians may notice that water intrusion occurred and can tell the area where the water entered by seeing a rust pattern. Could that failure have been prevented by simply using room temperature vulcanizing sealant around the rabbet fits? That is a very easy value add to the customer that can increase the mean time between failures. It is important that we communicate big and small problems and the subsequent solutions to show the customer you’re their reliability partner. As another example, sometimes it can be as easy as seeing two different colors of grease in the bearings. This issue may not require any changes to the internal repair process, but it would be very important to communicate that observation to the customer. It also may start the conversation with the customer on what bearing grease they want to use for their repaired items if that hasn’t already been agreed upon.
As the technician continues to dismantle the motor more issues may be found, and everything should continue to be documented. If applicable, additional electrical tests should be performed along with all the mechanical fits being thoroughly inspected. This would include bearing journal and housing measurements using calibrated micrometers capable of measuring to a tenth of a thousandth. In addition, measuring coupling fit dimensions and shaft passage fits is necessary to verify all components are in like-new condition. Checking run-out of the shaft is very important during this process too. Not only do you want technicians to measure those critical components, but visual inspections should also be performed on the rabbet fits to ensure the high integrity of the fit. Some critical assets may require that the shaft be checked for cracks through various options of non-destructive testing, too.
A key component of most motor failures is the bearings; there is a lot of information that can be gained from cutting the bearings in half and doing a thorough visual analysis. Your technicians would see different patterns depending on how the failure occurred, whether it be false brinelling from storage, smearing of the raceways from a lack of lubrication or a wear pattern showing misalignment. Bearing failure caused by electrical fluting is continuing to be more prevalent in the industry, and that pattern is difficult to determine without cutting the bearings in half. It is very easy to see a fluting pattern once the bearings are inspected. This fluting can be a reoccurring failure that requires various types of mitigation; otherwise, the motor will likely continue to fail if the repair shop does not identify it during an inspection. The bearing inspection should be documented with pictures as a confirmation of the repair analysis (Figure 2).
Windings also show signs of failure modes, although sometimes it is more difficult to determine the root cause. For example, inspecting the winding to determine if it failed within a group or between phases is important. It can be as simple as insufficient phase paper on a VFD-driven motor, or something more challenging like an insulation failure to ground within a slot. Top sticks and wedges too should be inspected for possible defects. Sometimes it may be necessary to dissect the winding prior to burning it out in order to better understand where the failure first occurred (Figure 3).
After the teardown is completed and all the existing issues have been documented, inspection results should now be checked by a second technician or supervisor if possible. No matter how skilled someone is with inspection, there can be a risk of tunnel vision, and having that second person check behind is best practice and a great opportunity for additional findings and training.
Analysis of Teardown
Once the inspection is complete, the next step is to develop a workscope for the most reliable repair. Any items out of tolerance, inadequate or defective need to be identified and the addition of opportunities for reliability improvement documented. As an example, finding fly ash in the bearing lubrication that caused it to degrade will warrant a motor having lip seals or bearing isolators added to protect the bearing cavity. The work scope would now include the necessary labor and material for the modification required to add the new seal.
The information obtained in the inspection and analysis should then be presented to the customer. Sometimes, all it takes is a phone call or e-mail, or you may need to develop a full formal report (Figure 4). Either way, show your value and let them know you’re there to support them. If you are sending out formal reports, make sure they reflect a high level of professionalism and are appropriately branded for your business.
This is the type of value-added service our customers will continue to call on us for. They expect us to be experts in our field, and they will find another vendor if a continuous improvement mindset is not within the existing shop's culture.
Utilize Your Resources
Always lean on your available external resources if you ever need help. EASA has a staff of engineers along with technical papers, seminars and training that can aid you in adding value through reliability improvements (
Figure 5). Keep in mind original equipment manufacturers of the machine or components are also available. They too have a staff of engineers and documentation that will aid you in your efforts. The right original equipment manufacturers want their items as reliable as possible and should work with you as a solutions provider.
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