Motion System Design

Don't forget your lubes 'n greases

All lubricants minimize friction and result in lower heat generation. However, oil provides the best lubricating properties for gearmotors and is typically used in 1/10 hp and larger gearmotors designed for industrial service. Increasing the service life (over 10,000 hrs) can be accomplished with a circulating fluid lubrication system. The fundamental characteristic of oil is its free flow and constant presence at the tooth surfaces of a gearhead during operation. The oil needs to provide a consistent and continuous lubricating film at the load zone, while withstanding dynamic forces such as centrifugal forces or severe loading that can prevent the lubricant from doing its job.

Lubricants used in parallel shaft gearmotors (which usually employ spur or helical gearing) are relatively less critical than those for right angle worm-gear types. Usually, mineral-based oils with EP additives suffice if the proper level is maintained. Some fractional hp gearmotors use hydraulic-type oils to decrease gearshaft or journal wear. Right-angle gearmotors with worm or other sliding-contact gearing require careful attention because the lubricants reach higher operating temperatures due to lower inherent efficiency. Such lubricants generally have higher viscosity and contain protective additives to prevent oxidation and to enhance “oiliness.”

Despite its advantages, oil is not commonly used in smaller gearmotors because of sealing issues. Smaller gearmotors usually do not have large gasket surfaces and may not have sufficient power to withstand the increased friction of a contact seal on the rotor shaft. Therefore, grease is used as a compromise in most gearmotors under 1/4 hp. Compared with oil, grease provides less consistent lubrication to the gear teeth under load and gear life can be reduced by up to 50%. However, grease provides mounting flexibility, minimizes leakage risk, and eliminates visual oil level inspections.

With regard to operating conditions, lubricant life in gearmotors is directly related to temperature. Generally, within normal operating ranges, lubricant life doubles for every 25° F decrease in temperature. Gearmotors operating in high or low ambient temperature ranges require special lubricants such as synthetic lubricants, or a lubricating system. Gaskets, motor insulation, and lubricant life may be seriously affected by temperature extremes. When other than normal ambient temperatures (32° to 104° F) are expected, consult the motor manufacturer.

Information courtesy of Bodine Electric Co.

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