Federal Paper Cuts Pump Failures with Rexnord® Omega™ Couplings
CASE STUDY
Federal Paper Board Co., of Riegelwood, North Carolina, has reduced pump downtime, lengthened the life of motor and pump bearings, and improved overall versatility of replacement coupling parts by converting most of its floating shaft applications to Rexnord Omega couplings with sleeve extensions.
Federal Paper’s Riegelwood mill is one of the world’s largest single-facility producers of bleached paperboard and pulp, with an average production of 1,000 tpd of bleached board and 1,000 tpd of market pulp.
Floating shaft gear couplings between motors and process stock pumps are critical components that also can be the source of major problems. Before converting to Rexnord Omega couplings, Federal Paper crews who were responsible for maintaining dozens of heavy-duty, single-stage, open-impeller process stock pumps had difficulty keeping the units online to transfer pulp as well as corrosive and non-corrosive liquids. Failed gear couplings with floating shafts caused abnormally high downtimes on several of the pumps, the largest running at 400 HP and 900 RPM. Most failed due to pump cavitation, which led to severe bearing vibration and worn bearing surfaces, requiring immediate disassembly and replacement. Process stock pumps at the mill range in size from 12 in X 18 in. X 17 in. to 18 in. X 18 in. X 23 in.
Sleeve extension allows
Federal Paper’s maintenance
crews to use standard Omega
hubs and spacer elements,
even for longer distances
between shaft ends
Repair crews sometimes needed several hours to disassemble the failed gear couplings, match assembly parts, make up correctly sized replacements, and reinstall and relubricate the couplings prior to restarting the pump. A single failed jackshaft gear coupling often meant up to four hours of downtime for a critical process stock pump. In addition, the weight of the all-steel gear couplings exerted a considerable load on pump shafts and ultimately caused bearing failures. The coupling failure rate for certain larger pumps with high torques was particularly excessive, according to Robert Rockwell, area maintenance supervisor at the mill.
Approximately 35 stock pumps at the mill, with 12-1/4 in., 12-5/8 in. and 18 in. between shaft ends now are connected using Rexnord Omega couplings with extended spacers. These couplings transmit torque while protecting the equipment from the damaging effects of misalignment, vibration and gross overload.
The lightweight couplings, with a urethane flex element and no center members or spools, are split in half longitudinally. Their universal flex elements have a unique bolt arrangement that satisfies all standard and non-standard pump/motor shaft separations up to 9.75 in., and by adding sleeve extensions, up to 21 in. The 14 sizes of Rexnord Omega couplings handle torques up to 170,000 lb. in.
Rexnord Omega couplings minimize bearing vibration
and shaft overloading under severe misalignment
conditions without transmitting excessive shock
overloads
The coupling design provides a clear space between hubs. The three-bolt hole arrangement on the element sleeves or metal shoes allows for up to 33 possible connection combinations. These design features simplify installation and also give maintenance crews versatility in spanning unusual or longer distances between shaft ends.
Steel sleeve extensions are provided in standard and custom lengths to meet specifications. They mount to standard Rexnord Omega spacer elements and cast iron or steel hubs of straight-bore or compression-bushed design. Hubs are interchangeable for either the extended spacer or the standard flex element. The elastomer couplings require no lubrication.
NOTE: This application has been featured in an article that appeared in Pulp & Paper.
4-154-MadisonpaperCS/12-10-03
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