Engineers and designers working on power transmission applications can face a daunting task in specifying the most appropriate drive coupling for the task in hand. Detailed consideration must be given to both the input and output sides of the drive equation, with regard to torque, shock loads, starting frequency, temperature and environmental conditions. David Proud, general manager of Reich Drive Systems UK, explains how to navigate through what can sometimes be seen as a technical minefield for designers and engineers.
Drive couplings vary greatly in their design and capabilities, so for any given application engineers must specify the drive coupling correctly to be sure of reliable, efficient, and, in the more challenging applications, safe operation.
A detailed review of what the coupling will be subjected to in use is an essential starting point. Factors such as torque transmission, speed ranges, running start/stops and potential shock loadings are just some of the key elements in the selection of the coupling. However, the designer must also consider alignment between the various components, the environmental operating conditions – which could include high temperatures or moisture, for example – and any maintenance requirements or restrictions. There may be potential limitations on available space, size or weight which will have to be taken into account. The prime mover, diesel or gas engine or hydraulic or electric motor, will also be influential in the specification and selection of the drive coupling.
Get it right, and the coupling will provide years of uninterrupted service, requiring little or no maintenance in its own right, while protecting mating components from undue stresses and keeping downtime to a minimum.
Mistakes can be costly
There are a number of commonly made mistakes which result in the wrong coupling being specified. This can have serious consequences both for the coupling and the other elements in the drivetrain. Often, it does not take long before these issues rise to the attention of maintenance engineers in the form of a catastrophic failure of the coupling and hours of unplanned downtime. Other, less visible, effects will be undue wear on bearings, shafts and gears, which will ultimately affect motors or gearboxes.
Before making a final decision on selecting the drive coupling the specifier must fully evaluate and understand the forces and loads that will be applied to the coupling in use. Making an educated guess at these values is not an option and could result in either a coupling being specified which is not fully up to the job, or design overkill, resulting in an unnecessarily large and more expensive solution to the application.
The specific application will dictate whether the component required is a disc coupling, shaft-to-shaft coupling, auxiliary coupling or other variant. However, it is essential that consideration is given to factors such as the torque rating and torsional stiffness required for the task. Generally, couplings with a higher torque rating will be larger and less flexible. In addition, the degree of axial, radial or angular misalignment that the coupling will be required to compensate for will influence choice. It is essential that the coupling to be used is able to meet these criteria, but has the capacity to accommodate a level of unexpected deflection while in service without failing.
Another factor which will influence success is how the coupling is mounted. In applications where there are minimal shock or reversing loads, keyways and taper bushes will be a reliable solution. For applications where there may be high shock loads it may be preferable to avoid a keyway solution and instead opt for a taper bush fixing, or couplings with shrunk discs, which will also provide backlash-free operation.
From a maintenance perspective, the time required to remove or replace a coupling or change parts is a major consideration. Therefore the selection of a coupling which not only meets all the technical and application requirements, but is either maintenance-free or has the ability to have parts replaced in-situ will bring significant benefits for uptimes and efficiency.
If there is any doubt on the part of the individual responsible for specifying and selecting the coupling, seeking expert advice from the manufacturer will eliminate risks and ensure longevity and reliability in operation. With a history spanning over 70 years, Reich Kupplungen has built up unrivalled expertise in the design and manufacture of drive couplings for use in a wide range of industries and applications. The company embraces a D2C (design to customer) principle, which allows the creation of customised high-quality and long-lasting power transmission products in collaboration with the customer and their specific requirements.
David Proud + 44(0) 161 714 4191
d.proud@reich-uk.com
www.reich-uk.com