This document discusses lubrication of electric motor bearings. It emphasizes that lubricant is critical for electric motors to reliably operate at high speeds. It recommends following proper lubrication practices and staying informed of lubrication technology advances. The document then discusses regreasing procedures and highlights the benefits of a polyurea-based grease as a suitable lubricant choice, noting its high temperature resistance helps extend relubrication intervals and bearing life.

1. Electrical Motor Bearing Lubrication
Lubricant is the lifeblood of electric motor bearings.
As industry continues to demand higher operating
speed and performance from electric motors and
their bearing components, it becomes increasingly
important for maintenance personnel to stay abreast
of advancements in lubrication technology and to
continue following sound lubrication practices. In
the end, it will be the lubricant and the lubricant
technician that enable electric motors to run reliably
at high speeds in day-to-day operation.
Electric Motor Grease Selection
Motor Bearing Regrease Procedures
Key Factors to look at:
Most large electric motors are equipped with a Molykote G-0100 Multi-purpose
1. NLGI Grade 2-3, ISO VG 100-150 motor bearing grease has been
grease fitting and a drain plug. When
2. High drop point > 400ºF min. developed to meet the increasing
relubricating, thoroughly clean the grease
3. Low oil bled characteristics demands of the industry. It’s a
fitting and the area around it to avoid
4. Excellent resistance to high mineral oil grease thickened by an
contaminating the grease. Then pump new
temperature oxidation urea system that offers a wide
grease into the bearing through the fitting
5. Good low temperature torque temperature range, low noise
while allowing the old grease to exit through
characteristics performance, with excellent
the open drain. After injecting the
6. Good anti-wear performance but corrosion and oxidation preventive
recommended amount of grease, run the
not EP (causes corrosion in properties.
motor with the drain open until the bearing
windings).
has a chance to purge all the excess grease.
When the grease stops exiting the drain, plug With a service temperature range of
Examples are lithium complex or +338ºF and drop point in excess of
the drain securely.
polyurea thickener greases. 482ºF, the product was tested for the
Although proper relubrication procedures are application for over a decade before
Recently, SKF selected an advanced rust- now generally standard practice, there is its commercial introduction.
inhibiting, polyurea-based grease as the always the chance for error. When done
standard fill for its U.S. electric motor improperly, relubrication can introduce solid It can extend relubrication intervals
bearings. Polyurea greases have all the or liquid contaminants into a bearing’s cavity, vis-à-vis the conventional greases
advantages that is important in the selection causing lubricant breakdown or damage to used by the industry for electrical
of a right electric motor bearing greases. bearing raceways and rotating elements. Also, motor bearings, and extend bearing
technicians may inadvertently overgrease life by preventing prevent premature
Polyurea greases provide superior shear and bearings, causing a condition called churning. failures.
oxidation stability. This is particularly Churning results in a higher operating
important in motor bearings, making them temperature within the bearing and eventually Along with its high temperature
more s more suitable vis-à-vis other soap leads to lubricant breakdown. performance, Molykote G-0100
bases. provides all key requirements that is
Even the lubrication procedure itself can have required by an electric motor bearing
With polyurea as a base, a mineral oil grease unintended consequences. Recently, for greases: excellent low torque
can offer high temperature resistance example, technicians at a power plant characteristics, low oil separation,
characteristics, making the use of a synthetic relubricated a shielded motor bearing using a high speeds capability (DN value
grease unnecessary. However, where grease gun. The entry of new grease caused 600000 = bearing avg.dia x rpm). low
bearings must continuously operate under increased pressure inside the bearing and evaporation loss, etc.
high temperatures as in rolling mills and forced the bearing’s shield into its rolling
furnace areas, a choice of polyurea base with elements. Subsequently, the relubricated The product is available in 1 kg and
a synthetic oil would be desirable. bearing failed prematurely 25 kg packs from Dow Corning.
Molykote® Greases can significantly extend your equipment life and reduce failures. Trusted by all OEMs and Maintenance
Engineers for nearly 60 years now. To know more about Molykote, log onto www.molykote.com or write to Project Sales Corp,
channel partners for Dow Corning’s Molykote products in this region at sales@projectsalescorp.com.