Grease Couplings and Coupling Grease

Rusting Coupling

The photo shows a coupling during construction of a new plant. The grid is rusting, shroud is oxidized, seals are degrading, keys are too long, and the hubs are dirty, chances are the coupling will not last it’s designed life.

I have read over 70 coupling installation procedures with some differences to each and all from the same manufacture. So, always read the specific instructions for your application and follow them.

As my friend Heinz Bloch would say lets discuss “best of class” tips for most grid and gear couplings.

  • Bore couplings to a 0.000” or 0.0005” tight fit (some mills will be 0.0005” per inch of shaft diameter tight)
  • Heat coupling interference fit hubs the same way you heat your bearings for best results.
  • Don’t file or sand the shaft fit, use Scotch-Brite to remove residue, it want change the contact area as much.
  • Keys fit under the hub and extend half way in the keyway beyond the hub (with rounded keyway ends extend the key 5% less).
  • Keys are to fit snug side to side and about 0.005” loose top to bottom.
  • Grease quantity is specified by the manufacture and never exceeds 90% of the fill area.
  •  Grease life is dependent on type, quality, temperature, rpm, load, environment, alignment, and more, so to determine the correct life we must inspect the lube over time and once life is determined schedule maintenance accordingly.
  • Use only coupling grease, most #2 grease will last 2 months on average.
  • Fill the setscrew hole to the top with setscrews to maintain balance.
  • Clean the hubs, grids, shrouds, seals, gaskets, and all internals to get the maximum coupling life.