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The benefits of elastic jaw couplings with split hubs - ROTEX AH

This article is part a series exploring the various split hub coupling designs of KTR and their respective characteristics and benefits.

In February we introduced a series regarding our split hub coupling designs. As a manufacturer of flexible couplings for rotational power transmission, KTR are finding that requests for these types of designs are becoming more and more frequent. The advantages of  being able to split a hub in half are numerous. But not all split hub designs are the same. First off, we’re going to have a look at our elastomer coupling ROTEX A-H – KTR’s original split hub jaw coupling design.

ROTEX torsionally flexible couplings have long been the most popular coupling design at KTR, ever since it’s conception back in 1967. With numerous designs introduced over the years, including double-cardanic spacers, flange hubs, as well as integrated torque limiters, brake drums and discs, cooling fans, and shiftable linkage for manual release, torsionally flexible ROTEX jaw couplings has proven itself as a very flexible solution provider indeed! 

 

Why use the A-H split hubs?

Shaft coupling with split hubs advantages/benefits:

  • Drop out centre for easy installation
  • Reduced downtimes
  • Intrinsic clamping hub design
  • Capability for radial, angular and axial misalignment

With regards to split hub designs, ROTEX A-H has always featured as an all steel machined option for achieving a drop out centre between drive and driven shaft ends (typically, but not exclusively, pumps and motors). The A-H is machined like any other standard jaw coupling hub, but including two screws for connecting the resultant hub halves. Again, it should be noted that the maximum possible bore of a split hub is reduced due to needing room in the hub for including the connecting screws.

When the desired bore has been machined, the hub is then subjected to two cuts – one from face on which dissects the bore and hub face, and a second from the side of the hub which meets the first cut at a right angle.

Due to the fact that this method features a cut, you end up with a loss of material equivalent to the width of the blade doing the cutting. This loss of material leaves a gap when the hub halves of our half-shell coupling are reconnected, and it is this space between hub halves which allows for a clamping effect when the two halves are reconnected and tightened via the screws. Depending on the application, this can be a beneficial characteristic. However, the extra steps required to machine this type of hub mean extra cost is incurred in production, making the AH more expensive that a standard hub.

ROTEX S-H: Elastic jaw coupling with cracked split hubs

The Elastomer coupling ROTEX S-H on the other hand offers a slightly cheaper alternative to the A-H, as the production method to crack a cast iron hub is typically less costly than cutting steel. But this brings us to the point of material composition. Some applications may not allow for cast hubs, or demand a steel solution. In these instances the all steel jaw coupling ROTEX A-H is a great option to meet application demands yet still enjoy the benefits of reduced downtimes and costs savings inherent to split hubs.

This type of hub features in a wide variety of applications, basically any instance where two open shaft connections occur. A ROTEX A-H jaw coupling offers the same capability of a standard design, with compensation for radial, angular and axial misalignment, and performace flexibility via a variety of spider elements with differing shore hardnesses. However the A-H tends to find it’s real value when used between two large component parts that are better off left in their current positions. The drop out centre of the ROTEX A-H jaw coupling allows the hubs to come away from the shafts by utilising the DBSE (distance between shaft ends). But this means that the DBSE must be sufficient to allow for the removal of the A-H hubs.

 

Retrospective installation considerations

Split hubs can often be supplied retrospectively to help improve maintenance programs, especially in older facilities, and the DBSE of an application may not allow for this type of hub. If not, then repositioning of drive and driven components may be required to achieve the necessary space between the shafts. However, in some cases, repositioning may be opportune as the removal of the pre-existing non-split coupling will already require a pump or motor to be moved… but possibly for the last time!

Ultimately, it is the cost savings over the lifetime of the coupling, or shear ease of use, which is used to justify the higher initial cost of a split hub in comparison to standard hubs.

Hubs are mechanically separated by “cracking”

Next article we’ll explore the details of the elastic jaw coupling ROTEX S-H design and how this type of split hub can offer a slightly different variety of benefits. 

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