Coupling Grease - Four Things You Should Know

For those who have been working with gear and grid couplings for a while, proper use of coupling grease may seem straight forward... but for those new to installing or maintaining these type couplings there are a few key things to be mindful of.

1. Coupling Grease Is Not Optional - Unless explicitly told otherwise by a manufacturer all metallic gear and grid couplings need to be properly lubricated prior to system start-up. Gear and grid couplings are usually tasked with carrying fairly high torque loads, and, without grease, these couplings would have heavy metal on metal contact... which would result in very high (friction-induced) temperature build-up, and ultimately... very premature coupling failure.

2. Coupling Grease Is Not Bearing Grease - Coupling grease is specifically designed for coupling applications to increase the coupling's life/reducing maintenance time. The grease has a high viscosity base oil and tackifier combine to keep the grease in place and prevent separation. The American Gear Manufacturers Association has a standard for coupling lubrication (AGMA 9001-B97: Flexible Couplings - Lubrication), and it is HIGHLY recommended that the grease you use comply with this standard.

Coupling grease is generally dark brown in color and manufactured with a lithium soap/polymer thickener, which has superior resistance to oil separation when subjected to high centrifugal forces normally found in couplings.

Bearing or general purpose greases tend to separate and lose effectiveness due to high centrifugal forces on the various ingredients at high rotational speeds. These high centrifugal forces encountered in couplings separate the base oil from the thickeners.

Heavy thickeners, which have no lubrication qualities, accumulate in the gear tooth mesh area resulting in premature coupling failure. Coupling grease is designed to be highly resistant to centrifugal separation of the oil and thickener, which allows the lubricant to be used for a relatively long period of time.

One secret to excellent coupling grease is the variable consistency throughout the working cycle of the application. The consistency of great gear coupling grease changes with the operating conditions. Working of the lubricant under actual service conditions causes the grease to become semi-fluid, functionally lubricating the wear surfaces of the coupling. As the grease cools, it returns to the
original consistency, thereby preventing leakage.

3. Couplings Will Need to Be Inspected & Re-Greased Periodically - As a best practice, metallic gear and grid couplings should be inspected regularly and repacked with grease each time. For a new coupling or application, you will want to inspect more regularly to ensure the coupling is behaving properly (i.e. - not leaking much grease). Overtime, application-specific, inspections can be spread out a bit more.

4. Be Prepared for Possible Leakage of Grease - While gear and grid couplings are renowned for their power density (can carry high torques in a small footprint) and ability to handle axial float (in the case of grid and floating shaft gear couplings), no matter the manufacturer, greased couplings are naturally prone to possible grease leakage. Appropriate care must be taken to minimize environmental concerns, and ensure all relevant environmental regulations that may apply are adhered to.

While further advice and council should be sought from your coupling and/or grease manufacturer, remembering these four fundamental steps will keep you headed in the right direction.