Electric Motor Bearing Grease Selection

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 Key Factors to look at: 1. 2. 3. 4. 5. 6.

NLGI Grade 2-3, ISO VG 100-150 High drop point > 400ºF min. Low oil bled characteristics Excellent resistance to high temperature oxidation Good low temperature torque characteristics Good anti-wear performance but not EP (causes corrosion in windings).

Examples are lithium complex or polyurea thickener greases. Recently, SKF selected an advanced rustinhibiting, polyurea-based grease as the standard fill for its U.S. electric motor bearings. Polyurea greases have all the advantages that is important in the selection of a right electric motor bearing greases. Polyurea greases provide superior shear and oxidation stability. This is particularly important in motor bearings, making them more s more suitable vis-à-vis other soap bases. With polyurea as a base, a mineral oil grease can offer high temperature resistance characteristics, making the use of a synthetic grease unnecessary. However, where bearings must continuously operate under high temperatures as in rolling mills and furnace areas, a choice of polyurea base with a synthetic oil would be desirable.

Motor Bearing Regrease Procedures Most large electric motors are equipped with a grease fitting and a drain plug. When relubricating, thoroughly clean the grease fitting and the area around it to avoid contaminating the grease. Then pump new grease into the bearing through the fitting while allowing the old grease to exit through the open drain. After injecting the recommended amount of grease, run the motor with the drain open until the bearing has a chance to purge all the excess grease. When the grease stops exiting the drain, plug the drain securely. Although proper relubrication procedures are now generally standard practice, there is always the chance for error. When done improperly, relubrication can introduce solid or liquid contaminants into a bearing’s cavity, causing lubricant breakdown or damage to bearing raceways and rotating elements. Also, technicians may inadvertently overgrease bearings, causing a condition called churning. Churning results in a higher operating temperature within the bearing and eventually leads to lubricant breakdown. Even the lubrication procedure itself can have unintended consequences. Recently, for example, technicians at a power plant relubricated a shielded motor bearing using a grease gun. The entry of new grease caused increased pressure inside the bearing and forced the bearing’s shield into its rolling elements. Subsequently, the relubricated bearing failed prematurely

Molykote G-0100 Multi-purpose motor bearing grease has been developed to meet the increasing demands of the industry. It’s a mineral oil grease thickened by an urea system that offers a wide temperature range, low noise performance, with excellent corrosion and oxidation preventive properties. With a service temperature range of +338ºF and drop point in excess of 482ºF, the product was tested for the application for over a decade before its commercial introduction. It can extend relubrication intervals vis-à-vis the conventional greases used by the industry for electrical motor bearings, and extend bearing life by preventing prevent premature failures. Along with its high temperature performance, Molykote G-0100 provides all key requirements that is required by an electric motor bearing greases: excellent low torque characteristics, low oil separation, high speeds capability (DN value 600000 = bearing avg.dia x rpm). low evaporation loss, etc. The product is available in 1 kg and 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 [email protected].