How should you pack the grease in a Grid Coupling?

As completely as possible! Grid couplings are a metal on metal design. Without good lubrication, metal on metal rubbing and flexing will quickly lead to premature coupling failure! (The photo at left shows insufficient lubrication because the grid springs at the bottom are not packed.)

It is also important to note that coupling grease is not bearing grease (see Coupling Grease - Four Things You Should Know). Coupling grease is much thicker, and you will run into problems if you are not using the right type of grease. 

Grid coupling installation videos, highlighting the packing of grease are readily available for  Horizontal Split Cover Grid Couplings, Vertical Split Cover Grid Couplings, Full Spacer Grid Couplings, and Half Spacer Grid Couplings. Formal installation instructions for specific grid coupling types can be downloaded on Lovejoy's Installation Instructions resources webpage. 

An excerpt from one of these instructions can be seen below, with the segments speaking to grease being underlined. For further questions or information regarding grid couplings, please see Lovejoy's grid coupling product page.

Excerpt from Lovejoy's Installation Instructions for Horizontal Split Cover Grid Coupling (Sizes 1020-1220):

6.10  Prior to inserting the grid spring or grid spring segments, thoroughly pack the grooves on each hub with a qualified coupling grease (see Table-2).  If the grid springs consist of two or more segments, assemble the grid springs so that the cut ends of one segment extend in the same direction as the cut ends of the next segment. Spread the grid slightly so that the edge of the spring passes over the grid teeth in the hub.  A flat blade screwdriver can be used to stretch the grid spring.  Insert the blade through the grid spring and into the grid teeth groove a couple loops beyond where the grid spring is to be inserted.  Tilt the screw driver to stretch the spring and the grid loops should drop into place.  Towards the end you may need to switch to a soft face mallet and tap the edges of the spring into the respective grooves.

6.11  Pack the spaces around the grid spring with qualified grease (see Table-2) and wipe off any excess grease flush with the top of the grid spring and grid teeth on the hub.

6.12.1  When using a vertical split grid cover assembly, slide the cover halves over the hubs lining up the bolt holes so that the grease plugs are 180° apart.  Insert the fasteners through the cover holes and tighten to the torque specified in Table-5 using a calibrated torque wrench.

6.12.2  When using a horizontal split grid cover assembly, position the seals on the hubs so they align with the grooves in the covers. Position one cover half under the seals and place the two gaskets in position. Align the second cover half over the seals so that the match marks line up on the same end of the covers.  This ensures the recesses in each of the cover halves that receive the fastener nuts are 180˚ apart.  Insert the fasteners with the nuts fitted in the recesses provided.  Tighten the fasteners to the torque specified in Table-5.

6.13  If additional grease is required, replace one grease plug with a grease fitting and remove the second plug.  With the plugs oriented 180˚ apart in a horizontal position, fill until grease comes out of the second opening.  Then replace the plugs.

6.14  Make sure grease plugs are in place.  Start the equipment and operate with the coupling in place for several minutes. Stop and recheck fastener torques and inspect the coupling for any grease leaks or other abnormalities.

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.