SPRINGS & SHOCK ABSORBERS FEATURE
SMOOTH SOLUTIONS: A guide to modern industrial couplings
Offering features such as vibration damping and
protection against shock loading, modern industrial couplings can help to ensure the smooth running of machinery and equipment. Renold Couplings explains
M
odern industrial couplings usually do much more than simply joining
two shafts – they are, in fact, vital, hi-tech components that ensure the optimum performance of the power transmission system and the driven equipment. They can provide features such as fail-safe operation, reduced maintenance and downtime, vibration damping, elimination of backlash and torque amplification, misalignment solutions, soft starting, protection against shock loading, torsional vibration and resonance. With so many coupling types
available that meet the demands of different applications, correct selection and installation is essential. Not only could incorrect coupling selection result in increased maintenance, more frequent downtime and higher operating costs, but it could mean coupling failure – leading to lost production, unplanned maintenance and even catastrophic consequences.
CONSIDERATIONS So, before the most suitable coupling can be selected, a number of points need to be considered: • The power to be transmitted, whether normal or high, continuous or intermittent
• The characteristics of the drive, the type of prime mover and the characteristics of the driven equipment • Speed, including the speed at which maximum power is transmitted, as well as the maximum speed
• The dimensions of the shafts to be connected including keyway details. It’s more than likely that more
than one type will be suitable for the application, so it’s worth thinking in advance about what you want or need the coupling to do. For instance, if the couplings are located somewhere that is difficult to access then low or zero maintenance couplings would be beneficial, even if there is a lower-cost type that is also suitable.
It’s also essential to ensure that the coupling selected is the right size for the application in terms of drive power, speed of operation and suitability for the shaft sizes of the motor and driven equipment. An incorrectly sized coupling will cause problems, whether too big or too small, and it’s important to consider all of the forces the coupling will be exposed to during normal operation, including peak torques and shock loads. Another factor to consider
is misalignment. A wide range of flexible couplings is available that provide perfect solutions for different misalignment conditions. These are essentially of two basic types – elastomeric and metallic. Elastomeric couplings incorporate non-metallic elements, such as rubber or plastic, through which the coupling is driven. These are either low maintenance or maintenance free as they do not normally require lubrication. This type of coupling also has the benefit of providing excellent vibration damping, noise reduction, protection against shock loads and backlash free operation. Metallic couplings
derive their flexibility through components that slide or move against each other, or through the flexing of a membrane or disc. These are torsionally stiff and generally well suited to high temperature applications. In addition, they can be selected with good resistance to chemicals and are suited to high speed and high power applications with large shaft sizes. When considering alternative coupling types it’s always worth being aware of
Couplings offer features such as fail-safe operation, reduced maintenance and downtime, vibration damping, elimination of backlash, etc.
their weaknesses and modes of failure as well as the strengths and benefits they offer. For instance, elastomeric couplings are not usually suitable for high temperature applications and can break down as a result of chemical contamination or when the internal temperature of the elastomeric element exceeds its limits. High temperature elastomers and ones that offer chemical resistance are now available but do not come as standard, so it’s important to discuss your requirements with your coupling supplier. Failure in
metallic couplings is due primarily to wear, as a result of the moving parts, and they therefore require regular lubrication.
Overloads in the system shorten
their life as a result of increased wear rather than sudden failure. Couplings
with membrane technology are generally more expensive but require no lubrication and little if any maintenance – their mode of failure is fatigue and they can fail quickly if overloaded.
SELECTING A SOLUTION Most coupling manufacturers offer selection guides that go into more detail than it is possible to do here, but the basic initial principles of coupling selection are always the same. Employing the correct selection procedures will result in the identification
of the best coupling solution for any given
application and will pay huge dividends in the smooth running of
equipment, reduced maintenance and the lowest possible lifetime costs.
Renold Couplings
www.renold.com
DESIGN SOLUTIONS | APRIL 2016 35
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