Steel Mill Facing Nine Motor Rebuilds a Year Due to Premature & Severe Commutator Wear

A customer from the metal industry was pulling multiple motors from service within eight months or less due to severe commutator wear. At that time, D.I.E. was not the chosen repair partner, but was asked to help. Our experts, in order to reduce the commutator wear and attain better and longer motor life between rebuilds, engaged in root cause failure analysis techniques.

After our initial inspection, we found two main issues at play:

1.       Blowers were running backwards, allowing for the possibility that heat could be a contributing factor.

2.       Motors were not running at anywhere near nameplate load ratings.

After identifying these problems, we worked with the brush manufacturer to come up with a brush that would be better suited to the lower amp draw (load). At the next planned maintenance check, our technicians ensured the new brushes were installed and seated properly. We also made sure the blowers on all units were running in the right direction to assure good air flow through the motor.

By reducing the commutator wear, we expect to double the time between reconditioning of the motor, saving them downtime and dollars.

Does this sound familiar? Run a motor to failure. Buy a new motor. Rinse and repeat.

When a motor runs until failure it causes unplanned production downtime and emergency maintenance. At that point, the cost to repair the motor is generally not economical and a new motor has to be purchased.  As the preferred vendor for this customer, we instituted a tracking spreadsheet to note when a motor was removed prior to failure and the cost to repair versus running a motor to failure and the cost to replace.  The difference in cost proved how predictive and preventative maintenance practices offered through Decatur Industrial Electric can extend motor life and increase reliability.

Part of our protocol with this customer now includes vibration analysis on critical equipment to identify areas of concern, lubrication program, and energy efficiency analysis of motors serviced against replacement motors. Contact a reliability specialist to see how we can implement a predictive maintenance program at your facility.

Decatur Industrial has taken the lead in helping the reliability of a regional paper mill and their (DC) preventative maintenance program. As part of our value-added services, we perform a visual inspection of the motors prior to any scheduled plant outage.

Visual inspection is often overlooked as an effective preventative maintenance tool. Our specialists are trained in recognizing signs of deterioration or developing problems through a visual inspection while the motor is in operation.

During inspection, Decatur Industrial, along with the brush manufacturer who supplies the brushes for the DC motors, found an 800 HP DC motor showing major issues on the brush/commutator – it was about to fail and needed to be changed out as soon as possible.

This discovery saved unnecessary production downtime as a proactive scheduled replacement was able to be installed during a routine machine outage. This proactive inspection also prevented a catastrophic run-to-failure, very expensive repair.

A cement company recently learned how costly it can be when a manufacturer is not supplied with the correct motor drawings. Unfortunately, it’s a common and preventable mistake.

This particular customer had ordered a custom base upon which to mount a Flender gear reducer and 250hp electric motor.  Unfortunately, the base was manufactured with the wrong motor design drawing, so the new base this customer received did not work. It is unknown how the wrong motor drawing was supplied, but the customer did know they had a serious problem and they needed to start production.

At this time, Decatur Industrial was engaged in the project and helped to find the error. The manufacturer said a new base could be made over several weeks and for an additional $15,000. Plus, the motor and gearbox were 360 feet off the ground, which would have required extensive man hours and crane costs.
After Decatur Industrial’s team reviewed the equipment, the mounting base, and the application; we found a speedy and great solution!

Before Decatur Industrial got involved, this large grain processing company had suffered two bearing failures in less than two years. They called us in to fix their 450HP motor, which was driving a large fan in their feedhouse, and they told us the story of their repeat catastrophic failures. They wanted to know why it kept happening!

Diagnosing the problem:  When we arrived on scene the motor was still in place running and our reliability specialist could hear bearing fluting as the motor had an audible howl to it.  With our SKF Arc meter and vibration analysis we verified the existence of electric current at both motor bearings and also at both driven fan bearings. Once the motor was able to be brought to our service center, we verified the bearings were indeed suffering from classic bearing fluting. Current discharge from voltage passing through the bearings as long been associated with large electric motors; however, the increased use of variable frequency drives (VFDs) has since resulted in shaft voltages in small low voltage machines.

The fix:  We insulated the ODE bearing housing and installed an AEGIS grounding ring – this motor has now been in place and running for four years with no subsequent bearing failures.  It operates noise free and vibration readings show no bearing issues. The customer has saved approximately $80,000 in repair costs over what they had been spending in repairs – plus no more downtime due to motor issues.