Efficient Plant March 2020 - 17

feature | lubrication strategies

Properly
Lubricate

Electric
Motors

Follow these practices to maximize electric-motor performance and longevity.
Mark Barnes, PhD, CMRP
Des-Case Corp.

TREATED CORRECTLY, ELECTRIC motors can last a long,
long time. In many cases, motors fail prematurely not because of
any design, manufacturing, or installation issues, but from the
most fundamental of root causes: poor lubrication. Studies by the
Electric Power Research Institute (EPRI, Palo Alto, CA, epri.com)
reveal that 95% of motors fail prematurely. Of those, 53% are due to
bearing failures. Put simply, we are killing our motors through poor
lubrication practices.
Electric-motor lubrication is not complicated. You simply need to
select the correct lubricant, apply the right amount each time, and
do so at the required frequency. So why do so many companies get
it wrong?

LUBRICANT SELECTION
It all starts with selecting the correct lubricant. For the purposes of
this article, we'll only focus on motors equipped with rollingelement bearings, though some larger-horsepower motors use jour-

MARCH 2020

EP2003flube.indd 17

nal bearings, in which lubricant selection is just as important.
Three dominant factors-load, speed, and bearing dimensions-
determine lubricant selection.
The purpose of any lubricant is to separate moving surfaces with a
film of oil. The amount of separation is referred to as film thickness.
Too low a film thickness and metal-to-metal contact will occur.
Too great a film thickness and internal churning will result in fluid
friction and elevated temperatures. Largely, the viscosity of the oil,
relative to the load and speed of the bearing, governs film thickness. As viscosity increases, film thickness increases. Conversely as
viscosity decreases, fill thickness and the separation between metal
surfaces decreases.
Most electric motors are lubricated with grease, not oil, which
is where the first mistake often occurs. Many people simply do not
understand how grease works. A grease is nothing more than an oil
bound together with a thickening agent and appropriate additives.
It is not the "thickness" of the grease, more correctly called
EFFICIENTPLANTMAG.COM |

17

2/17/20 11:43 AM


http://www.epri.com http://www.EFFICIENTPLANTMAG.COM

Efficient Plant March 2020

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