1 basic coupling, 3 application ideas

The Zero-Max CD(R) Coupling is a unique hybrid coupling, combining the best features found in both steel-disk and elastomeric couplings. Through its patented open-arm design and use of rugged composite materials, the coupling offers the high misalignment capacity found in many elastomeric couplings, but with higher torsional stiffness.

The primary function of these couplings is to transmit power from one section of a machine to another section. The floating shaft coupling described here connects together gearboxes that are located at distances on the order of 12 inches or more.

The standard floating shaft coupling can be modified easily to meet the requirements of many different kinds of applications. This article describes three applications in detail.

High torque, small footprint

Design application: M1A2 Abrams Main Battle Tank

Coupling function: Floating shaft coupling for auxiliary drive for an enhanced air-filtration system for the M1A2 Battle Tank.

Design challenges: Increase speed and torque to intake scavenger fan in the same space/size envelope as the original coupling. Specifically, increase power from 5 to 18 hp, which imposed higher operating loads on the connecting coupling between the oil cooler fan on one end and the scavenger fan on the other. A larger, torsionally soft coupling could have been used to handle the increased torque requirements. However, a larger coupling would require major changes to the ductwork of the entire cooling system, including potentially expensive changes to both right angle gear box assemblies. The work envelope for the coupling assembly could not be altered.

Design solution: Engineers developed a customized version of the Zero-Max Model 22 CD coupling with a 21/4-inch overall diameter, a 7/8-inch bore, and a disk pack at each end of the coupling. They also thickened up each of three disks that make up each disk pack from 0.050 to 0.070 inches. The added disk thickness improved coupling stiffness and strength. To reduce stress at the bolt hole locations on the disk arms, engineers also redesigned the bushing/bolt interface to carry the increased torque. The disks themselves are left unfinished to facilitate required decontamination washdowns in case of nuclear exposure.

High power and oscillating loads

Design application: Wind turbine generator

Coupling function: Floating-shaft coupling for giant wind turbine drive train delivering 2,000 kW power. Operating life for the wind turbine is projected at 20 plus years.

Design challenges: Achieve high strength and accommodate up to 2 degrees misalignment in a high-power application with maximum coupling reliability and longevity. Absorb changing torque and misalignment transmitted to the drive train by the wind. Provide a maintenance-free coupling in a size 50% smaller and lighter than elastomeric designs and at a 25% lower cost.

Design solution: A customized, larger version of the Zero-Max CD Coupling using two 8-bolt disk packs in a spacer-coupling configuration. Overall disk diameter is 460 mm with a coupling length of 578.5 mm. The coupling mounts to diameters of 150 mm on each end. By increasing disk arm length, more flexibility was added to the coupling thereby absorbing the oscillating aerodynamic loads. Disk material is not affected by changing climate conditions and requires no maintenance.

Minimal torsional deflection, maximum torsional rigidity

Design application: Multiple station offset printing press

Coupling function: A floating-shaft coupling used to connect a series of print stations. The coupling must provide minimal torsional deflection and maximum torsional rigidity to maintain print registration. The press prints 2,000 fpm of a continuous stream of paper.

Design challenges: The coupling requirements for torsional stiffness were 5.5 times higher than the highest rated catalog coupling. The coupling also was required to withstand a corrosive environment created by the inks and other chemicals used in the printing process. Maintaining torsional rigidity while using an extended coupling spacer was an added challenge.

Design solution: Zero-Max developed a CD Coupling that would utilize a 12-bolt disk pack and a larger diameter spacer. In order to have a zero backlash connection between the coupling hub and gearbox shaft, use of a shrink disk was required. A special isotropic disk pack material was required to transmit the torque and maintain torsional rigidity. The fibers of the disk pack are orientated at 0, 30, 60, 90 degrees , etc. (Standard Zero-Max coupling disk pack fibers are orientated at 0 and 90 degrees ). The coupling also employs a special spacer, enhancing the coupling's torsional stiffness. To design this coupling for maximum performance, Zero-Max used finite element analysis.

For more information

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Customized and standard versions of the Zero-Max CD Coupling: Enter 550 or e-mail author Brian Onkst at bonkst@ zero-max.com