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Coupling Failure Identified As Being Result Of Wrong Selection

01 April 2005

Torque, speed and duty cycle are important factors when selecting an
appropriate coupling, but they are not the only parameters that need to
be taken into consideration, as Huco discovered when it recently supplied
a US manufacturer of rail track maintenance machines. These machines are
used to grind sections of track to remove surface cracks that might
otherwise propagate. Routine grinding has been found to extend track life
and reduce downtime when track needs to be replaced.

Able to travel at speeds of up to 8mph, the machine is equipped with a
number of grinding units, each with 16 grinding wheels mounted to match
the profile of the track. Originally, a Huco size 34 Uni-Lat coupling was
chosen to complete the connection between the vehicle axle and an
encoder, mounted outside the wheel. However, this failed and the client
requested a size 41 Uni-Lat, which started to ring alarm bells at Huco.
When the size 41 began to show signs of wear and was replaced with a
section of rubber hose and two jubilee clips, the company decided to

The cause of the failure was identified as being simply a case of
incorrect selection. While the torque and speed were well within the
capabilities of the Uni-Lat coupling, in this application it was being
subjected not only to axial, but also lateral movement, a combination
that it is not designed to accommodate. The inertial mass of the encoder
bouncing on its rubber mounts created an excessive loading that caused
the coupling failure. Huco quickly suggested an alternative in its Flex-P
product, which features a tough, moulded elastomeric element that
tolerates up to 18o of angular misalignment. The problem was solved, but
it does highlight the need to be aware of all the dynamics of your
application before finalising your specification.

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