How to install a torsionally soft coupling

Edited by Mike Santora

*This is an excerpt from a Design World Webinar presentation by Ed Cole of Ringfeder Power Transmission.

 …Our TNR series torsionally soft coupling is typically installed on the flywheel of a diesel engine. The TNR is usually installed on pump packages, compressor packages, gen-sets, other specialty packages and fire-pumps. The primary function of the coupling is to eliminate resonance problems in the system. In addition to eliminating the resonance problems, this coupling will also accommodate small amounts of misalignment.

The TNR will require the laser alignment and dial indicators used during typical installation processes. It is important to install all couplings with care from the beginning because as time goes on, things change. Floors settle. Bearings wear. Parts heat and cool and they expand and contract at different rates. The coupling will need to handle this misalignment and you don’t want to use up all the alignment capability. Typically, you should install the coupling using less than one-third of the total permissible misalignment that the coupling can handle. The better then installation, the longer the coupling life.

Eventually you’re going to need to replace the elastomeric elements in any coupling due to wear, temperature, exposure to environment, ozone and chemicals. Unlike many other torsionally soft couplings, as in the older style design, you can remove or install the elastomer elements easily without having to move the motor, engine or driven component. This will save you a considerable amount of time. In addition, you can easily change the performance characteristics of the coupling by removing the elastomeric elements and replacing them with ones that are harder or softer, depending upon what your needs are.

In a typical diesel engine,  the flywheel is right in front. This is where the coupling mounts. The engine will support the coupling on one side. The driven component, however, cannot hang on the coupling. There must be bearing support on the driven component. If there’s a heavy weight that’s hanging on a TNR coupling, you will prematurely wear out the elastomeric elements; it’s not designed to take the weight, so you must have bearing support.
So basically you put the coupling in and install it in halves. The flange and the outer elastomeric elements, they bolt to the flywheel of the engine. The hub and inner elastic elements mount on the shaft of the driven component. In most cases, the shaft on the driven component is attached with a bore and key weight, but some customers prefer using our shrink disc technology, which is an external clamp that clamps on a round shaft. The shrink disc connection is similar to an interference fit, except in with a shrink disc you use a torque wrench; interference fits, instead of a torch in interference fits.

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