What is a coupling?
A coupling is a component which joins two shafts and transfers torque from a driven shaft (driving force) to a driven shaft component. An example of this is a propeller – the motor shaft drives a coupling, which is then attached to the propeller blades – and thus the motor can turn the blades.
Why do you need a coupling? Can’t things just be built as one unit?
The main purpose is this drive function – connecting things to turn power into motion. Another purpose, though, is to absorb misalignment. This means that where there are mounting errors or the driver and component to be driven aren’t quite aligned in height or parallel plane, there would be additional pressure and wear in the misaligned areas and component parts. A coupling absorbs the impact of this, and prevents that damage. Often different components will have small fluctuations in size, dimension, fitting etc. and it can be very difficult to assemble with flawless precision – so the inclusion of a coupling in the design allows for those small fluctuations without impacting the final output of the application.
Another reason for couplings is to protect components from vibration or impact; motors often vibrate, and this can mean small incremental movements in the component – and that could cause damage and wear in the driven component. The coupling absorbs this vibration and any shock loads from emergency braking or stopping and prevents the potential for any resulting damage.
Yet another reason, again to protect driven components, is that the motor or drive creates heat and some static charge, and the coupling will absorb that heat and prevent it from reaching the application where it might cause damage. Special conductive couplings can also eliminate static and risk of sparks in hazardous areas.
What kinds of coupling do we sell?
There are many different kinds of couplings, and they come in a vast range of sizes and lengths and with additional factors which help to protect your application from impact, misalignment, vibrations, movement and any factors which could cause damage to components without that protective aspect.
To ensure that our customers have a wide selection we offer many different kinds of coupling, all of which are suited to different uses – and if you’re unsure which is the best choice for your needs do give us a call, our technical engineers can guide you in the right direction.
Some of the options are:
These have what is referred to as ‘high torsional stiffness’ and are backlash free; this means that there is very little twist in the couplings, and the full torque and precision of the drive system will be transferred to the driven component. They are the best choice when you require high positional accuracy of rotation and multidirectional movement. The metal bellows also can allow for high misalignment if used correctly and requires no maintenance.
Our elastomer couplings include an elastomeric polymer insert – available in a range of torque and hardness capacities – and this is a lubrication free way to transfer torque and absorb vibration and misalignment without damaging the components, thus significantly reducing maintenance requirements. R+W elastomer inserts are oven cured to set the material properties and ensure the inserts are a good fit with no play or backlash in the coupling.
The purpose of these elastomer inserts is that they absorb the impact, and they are designed to wear quicker than the metal parts. Replacing the insert is significantly less difficult or expensive than replacing the whole coupling, and keeps maintenance costs and timescales to a minimum, meaning less down-time for the application. They are also an excellent way to protect against damage from misalignment, allowing for quicker and less precise manufacturing and fitting for the other components.
A line shaft is a longer, usually hollow, aluminium or other material tube which attaches the driver to the driven component over a longer distance (for example in wind turbines) and we supply self-supporting line shafts up to 6m long; these convey drive over a more significant distance and are designed to convert that drive energy over the specified distance without buckling or whipping. Each line shaft has 2 couplings, 1 each end and can be either elastomer or metal bellows depending on the alignment and torque to be transferred.
Flexible gear couplings are a universal coupling designed for any applications where there’s a possibility of misalignment or large axial moments. They protect against these additional forces and reduce the risks of damage or wear, reducing or eliminating the need for maintenance. The joints between the driving and driven components and the coupling itself are flexible, which allows for consistent transference of torque without damage or any loss of energy or force.
Similarly to the elastomer coupling, the disc pack coupling contains an added component – the disc pack – which use friction to transfer torque from a driver to whatever you want to be driven; as opposed to one single elastomer insert there is a pack of discs of high torque capacity which absorb misalignment, vibration and impact, and bring slip-free torsional stiffness, avoiding stress concentration and micro-movements. They have almost infinite life and provide high torsional stiffness. These don’t come as one single unit but are in parts which need to be assembled as part of the installation process. Using 1 or 2 disc packs per coupling allow for varying misalignment properties on high torque applications.
As above, the servo disc pack couplings are based on the same disc pack technology designed to be torsionally stiff with zero backlash and low inertia – but they are a smaller solution for servo applications. These are ready assembled as a complete coupling rather than requiring assembly.
These are – as the name would indicate – designed to function in the same way as the metal bellows couplings, but are smaller and best suited for small motors and micro applications. Despite their small size, these miniature couplings provide backlash free power transfer and are maintenance free.
There are occasions when you need to protect a component or design from torque overload; these limiting couplings absorb that overload and prevent damage from this excess of force and impact, and allow for effective and efficient drive motion. The limiters can be integrated into either an elastomer or bellows coupling or be a direct drive for pulley or sprocket shaft applications. Each limiter has a torque range and can be easily adjusted to suit the application to find the correct safety cut off torque point.
How to choose which kind you need.
The decision about which kind of coupling is best suited to your needs requires consideration of various factors – the torque and output of your driver, the positional accuracy and rigidity of your desired end result, the potential misalignment and impacting factors like vibration, and the potential wear and maintenance opportunities.
If you aren’t sure which would be the best solution for your design give our team a call, and we can discuss your needs and guide you towards the best choice. Call today on 01234 360689 or fill your details in on our contact form and we’ll give you a call.