FOR IMMEDIATE RELEASE

September 22, 1995

FROM:

IT IS SMALL BUT IT PLAYS AN IMPORTANT ROLE IN THE BIG PICTURE:
The one piece, flexible (flexured) coupling that makes the difference in successful system operation

by:

Norman L. Paul
Application Engineer
Helical Products Company, Inc.
Santa Maria, CA 93456

A key criterion for a good flexible coupling is that it compensates for misalignments and has a high cycle life with a minimum effect on the shafts and bearings. The wrong coupling can mean a world of trouble.

The "flexured," one piece flexible coupling manufactured from a single, homogeneous piece of metal can help substantially in maximizing system performance. To put you on the right design track, here are some definitions and considerations that can make it easier for you to specify the best one piece rotating flexible shaft coupling or U-joint for your application.

WHY A FLEXIBLE COUPLING?

A "flexible" coupling adjusts for misalignments between two component shafts as torque/motion is transferred between shafts. High side loads may occur on the shaft and bearings should a solid coupling be used. This results in torque loss as it requires more energy to compensate for the higher friction which in turn increases the temperature in the system. These side loads can markedly reduce the life of the system.

IS THERE AN IDEAL FLEXIBLE COUPLING FOR ALL SYSTEMS?

To enhance the ability of all components to work in unison, the flexible coupling should be considered in the early design stages. Then the coupling becomes an integral part of the system. Since requirements differ, there is no such thing as one ideal coupling for all systems. Rather, there is an ideal coupling for a particular application.

The best flexible coupling should:

Accommodate misalignment
Minimize adjacent bearing loads
Absorb shock
Allow for axial motion
Provide the necessary torsional rate
Have a reasonable envelope (outside diameter and length)
Incorporate reliable and easy-to-use attachment
Integrate as many additional functions as possible
Be cost effective

Determining the appropriate coupling should be part of the total design process --as opposed to a last minute selection. When the design is complete, the coupling is an integrated component that works reliably with all components. In production it becomes time consuming and too costly to align shafts perfectly, therefore the flexible coupling is a cost saving device.

WHAT SHOULD ONE KNOW TO BE ABLE TO SELECT THE CORRECT FLEXIBLE COUPLING FOR A GIVEN APPLICATION?

There are a number of things that need to be known to specify the correct coupling. Among them are angular, parallel and skew misalignment, axial motion, RPM, torque, torsional requirements, size constraints, attachment and material requirements.

Angular misalignment occurs when shafts are aligned but are not parallel. Parallel misalignment happens when the shafts are parallel however not aligned. Skew misalignment is when you have both angular and parallel misalignments occurring at the same time. Axial motion compensates for the expansion and extension of the motor shaft. The flexible coupling must help relieve the stress caused by this movement. RPM is another important design consideration as there are limits with respect to rotational speed due to centrifugal forces. Torque considerations should encompass:

Maximum (start up) torque
Working (continuous) torque
Direction of rotation or does it reverse (how quickly)

Torsional requirements may help in the application as well. Is shock absorption needed? System accuracy a primary concern? What is the resonant frequency of the entire system? The flexible coupling must be able to satisfy all of these requirements. Size constraints can be dealt with much easier when the designer considers the flexible coupling early in the design stage. Attachments can enhance the ability to incorporate two, three or more separate pieces into a single piece of material. Materials used depend on the environment in which the system will operate. Temperatures, corrosive atmospheres, magnetic or non-magnetic, higher torque, all must be considered in the coupling's design and material composition.

THE VERSATILE, FLEXURED COUPLING CAN SATISFY A WIDE VARIETY OF DESIGNS

The Helical "flexured" coupling has the inherent potential to more than satisfy the criteria noted above. The remarkable thing about the Helical "flexured" coupling is its versatility. There are so many aspects of it that can be optimized to fit a variety of applications.

The "flexure" in couplings and U-joints can be designed to handle various torque's and misalignments and an infinite number of attachment requirements. Other features, not directly related to the coupling, such as gears or shafts, spline bores, interior/external threads (whatever is needed) can be integrated. In this way, a one piece coupling or U-joint can be created that incorporates the correct torque and misalignment capacity, with attachments that are reliable and easy to use. The net result is reduction in the total parts, and lower total system costs.

Sound remarkable? It really is! The one piece flexured coupling or U-joint, with all of its design options, can incorporate a myriad of features for a particular application -- everything you would want in a coupling and more.

PHOTOS:

Angular misalignment is the easiest form of misalignment for most couplings to accommodate and thus one of the most practical applications of a flexible coupling.

Parallel misalignment is the most difficult form of misalignment for couplings to contain. It can also be the most damaging to shafts, bearings and motors.

When shafts are not in the same plane (skewed), the flexure's ability to compensate are the same as with parallel or angular misalignment - but in the third dimension.

For more information, or for a free catalog, please contact us or fill out our online request form.

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