Want to prevent unannounced motor downtime? Installing bearing isolators will greatly help your cause.
There's no doubt about it. Motors are wonderful pieces of machinery. Thanks to modern design and manufacturing technologies, today's motors feature significantly improved efficiency and energy savings. Despite these improvements, maintenance is still critical for enhanced performance. This means you shouldn't take bearing maintenance lightly.
Historical evidence over the last half century conclusively shows that proper bearing lubrication and maintenance result in improved motor reliability. One of the best ways to maintain your bearings is to install bearing isolators. Simply put, these devices keep the rolling element clean and well lubricated.
Typical bearing isolators are mechanical devices that permanently isolate the bearing from its operating environment - keeping humidity and moisture from entering the bearing enclosure during stop and start cycles. Basically, these isolators contain grease lubricant within the bearing enclosure while keeping external contaminants such as sand out. But for the bearing lubrication system to work properly, the bearing enclosure must remain intact.
Here's a list of guidelines to help you maintain your motor bearings:
- Make certain the bearing isolator you're working with is a modern labyrinth-sealing device recommended by the motor manufacturer for the specific motor.
- Ensure that the type of grease placed into the bearing and its enclosure is of the type and temperature rating recommended by the manufacturer for the specific motor in question. In mill and chemical duty motor applications, the grease may vary, depending upon the chemical environment in which the motor operates.
- Be careful when replacing the grease, and don't exert enough pressure to force grease past the grease seal and into the motor. The amount of hydraulic force a common grease gun can create is surprisingly large and can be much more than needed to blow out most bearing isolator seals. This is because these seals are normally just tapped into place with an interference fit. So, if you simply attach a grease gun to the grease fitting and start pumping (as you might do when lubricating the steering arm on an automobile column), you may impair the integrity of the bearing enclosure. Worse yet, the grease may enter the bell housing of the motor, get slung around the interior during motor operation, and prevent normal air circulation and cooling of the windings. The loose grease would then coke into a carbonized solid, which would catch particles that could cause short circuits within the motor windings.
- Follow a specific procedure that removes the old grease while charging the bearing enclosure with new grease. You can accomplish this by removing the grease plug and the grease fitting from the bearing enclosure, and then inserting the fitting into the bottom opening in the housing. Then, as you begin to pump the new grease in, watch for the old lubricant to flow out through the top hole. You'll recognize the new grease by its consistency and color. After you're done, remove the fitting, place it into the top hole in the bearing enclosure, and reinstall the plug into the bottom hole. Be careful: Do not overtighten the grease fitting and plug, because they're tapered and they can act as a wedge, causing the enclosure to crack.
With this kind of careful maintenance approach for your motor, you can expect your rolling elements to stay clean and well lubricated. By thinking ahead and taking bearing maintenance seriously, you can expect an average bearing life of 150,000 hr (about 17 years).
The physical characteristics of the grease you use are critical. For example, some motors require conductive grease, which prevents the charging of the rotor capacitance. The arcing associated with the discharge of this rotor charge causes degradation of the rolling bearing contact surfaces.
Other motors may require high-temperature grease, which will not decompose when subjected to the heat produced by the motor. The temperature rise of the motor (together with the motor cooling system design) will determine how hot the bearing lubricant can get. If the grease does get too hot, it will separate within the bearing enclosure. Then, oil will rise to the top of the bearing enclosure and residuum will slump to the bottom. The resulting loss of lubricating qualities will lead to additional heating, coking, and eventual bearing failure.