Composite Alternatives for Floating Shaft Couplings

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A lighter option for easy installation and longevity

Composite shafting for long span applications isn’t new. Especially within cooling tower applications, composite shaft couplings, such as Addax disc couplings, have been widely accepted as the standard for years. However, because of concerns about strength, they haven’t been widely adopted for applications in industries such as oil and gas, pulp and paper, wastewater treatment and general industry.
But, by dismissing composite shafting you could be missing out on opportunities to simplify installation and maintenance, and extend the life of connected equipment, without sacrificing strength and longevity.
Benefits of composite shafting include:
  • Reduced need to upsize: Have you ever needed to upsize a coupling to meet span requirements? Switching to a composite shaft makes that a thing of the past. Using lightweight, composite spacers, our advanced long-span couplings can be “right-sized” for your application, which allows them to effectively operate at higher speeds with greater maximum span capabilities. In fact, when compared to steel, composite shaft couplings can be up to 25% longer.  
Additionally, an increased bore capacity of up to 10 in./260 mm with standard, XL, and XXL options keeps you from needing to upsize. By not needing to upsize based on span or bore capacity, you save money on your coupling purchase.
  • Increased longevity: The lower weight of the composite shaft reduces coupling inertia and overhung bearing loads, resulting in lower vibration and extended service life of connected components.
  • Simplified Installation: Long-span steel couplings are heavy and require a crane – and some time – to install. Our lightweight composite solution makes it quicker to install and with less hassle. Drop-in spacer assembly also makes installation easier.
Thomas XTSRLS-C disc couplings can help you realize these benefits with their lightweight composite construction and robust, field-tested adhesive joints. They provide an effective solution for a variety of applications, including vertical pumps, industrial fans and blowers, paper machinery and centrifugal compressors.
But what about the joint? Is it as strong as a welded joint?
It’s not uncommon for OEMs to shy away from adhesive joints because they don’t believe an adhesive joint can hold up to the same stress as a welded steel joint. But the real story is that when compared side by side under similar conditions, our strong, field-tested adhesive performs as well or better than swage joints, welds, or rivets, with superior reliability.     
The maximum shear stress a bonded joint can endure is a function of the adhesive used, materials to be bonded, bond joint design, and type of load. Because we’re talking about rotating equipment, when designing composite couplings our engineers were primarily concerned with torsional loading. That is, introducing a torsional load to a composite tube from an end fitting so the adhesive bond is under shear stress and not tensile stress. As part of testing, we simulated the life of a coupling, including ensuring that it can withstand peak startup torque, which can be about 3 times operating torque with an electric motor. In the fatigue tests, the eventual failure mode was never the bonded joint, but rather the flexible element or the bolts. The design intends for the flexible elements and bolts to be the points of failure both to protect connected equipment and reduce downtime, as these are easy, inexpensive components to replace. To date, tens of thousands of Rexnord couplings with adhesive joints have been sold with no recorded joint failures.
The bottom line is that if you are looking for a way to improve longevity and simplify installation and maintenance, you should take a second look at composite shaft couplings.
For technical specifications, or to find out more about our Thomas XTSRLS series of long-span composite couplings, click here.

Jonah Mrozinsky

Jonah Mrozinsky is the application engineering manager for general purpose Regal Rexnord couplings. Jonah previously served as the coupling specialist for disc couplings assisting with technical expertise in selection, design, installation, and troubleshooting of cooling tower composite driveshafts.