If you need a mechanical power transmission coupling, the device used to connect facing ends of two shafts together or flange to shaft to transmit mechanical power from the driver to the driven, there are two main options. Rigid shaft couplings are used in applications where the two shafts are more precisely aligned, but flexible shaft couplings allow for issues such as angular, axial and parallel misalignment which are more common in many industrial applications.

The three different types of mechanical power transmission shaft misalignment.

Axial misalignment can be caused by different tolerances or by thermal expansion of shafts and components that the shafts are in contact with.
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Radial misalignment can be defined as a measure of the offset distance between the centre lines of the driving and driven shafts. This type of misalignment causes the highest stress due to the forces involved.
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Angular misalignment can be defined as a measure of the angle between the centre lines of the driving and driven shafts, where those centre lines would intersect approximately halfway between shaft ends.

Shaft misalignment is the result of displacement during assembly and operation and where machines constructed with two radial bearings each are rigidly coupled causing high loads to be applied to the bearings. Elastic deformation of base frame, foundation and machine housing will lead to shaft misalignment which cannot be prevented, even by precise initial setup alignment. Furthermore, because individual components of the drive train heat up differently during operation, heat expansion of the machine housings causes shaft misalignment. Poorly aligned drives are often the cause of seal, rolling bearing or coupling failure. Alignment should be carried out by specialist personnel in accordance with operating instructions.

Flexible shaft couplings are designed to relieve the effects of mechanical power transmission shaft misalignment. Rigid shaft couplings are able to transmit higher torque than flexible shaft couplings, due to the cushioning effect of flexible coupling elements adsorbing some of the torque when using flexible shaft couplings.

Read and download the guide to correct coupling selection for your application found via this link: selecting-the-correct-coupling
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‍jbj Techniques hold in stock a wide range of mechanical power transmission coupling types in a wide range of sizes for quick despatch. jbj Techniques also have the technical expertise to assist you in the specification of the best coupling for your needs and extensive machine shop services, all in-house to enable prompt despatch of those more bespoke couplings, large or small in size and quantity.

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Understanding Coupling Elastomer Element Failure Due to Torsional Vibration

This image shows a classic elastomer coupling element failure due to torsional vibration.

Torsional vibration is an occurrence that can have a negative effect on coupling elastomer elements. It can also have a catastrophic effect on couplings and drive systems. The graph shows a calculated torque spike in a drive, at the point the spike goes off the chart at around 1200rpm, the value is infinite and will go on adding energy to the system until something breaks. In other words, if the machine that this chart represents were allowed to run continuously at any of the speeds shown, the coupling elastomer would melt and fail. If the elastomer was sized well enough to survive, the failure point would be the next weakest point, perhaps a shaft with a machined sharp corner or stress raiser.

Consider an electric motor driving a device such as a high pressure piston water pump using a flexible shaft coupling. As the water in each cylinder opens the outlet valve, it can deliver a torque spike or torque reversal back into the drivetrain. The greater the number of cylinders and the higher the speed, the greater the quantity of torque spikes. We now don’t have a shaft rotating at a steady speed. Every time there is a torque spike it slows momentarily then speeds up again only to be hit by another spike and so on.

This continuous pulsing in the drive train will usually be damped by the coupling element however if the level increases above the thermal capability of the elastomer then problems result.

Think of the elastomer as a plastic spring; at a molecular level when the plastic is compressed the molecules subjected to this compression rub together generating heat. The element has a thermal limit of the amount of heat it can dissipate into the air and coupling drive material in contact. If this heat input value is within the element’s capability all is well, however, if the heat input exceeds this thermal rating the plastic inside the affected areas will melt, as the coupling is rotating centrifugal force causes this melted plastic to extrude from the outer surfaces, when the molten plastic comes into contact with cooler air it solidifies into the string like tails you can see in the picture.

As the surfaces of the affected areas are in contact with the coupling drive mechanism they remain cool and may not melt which can produce hollow sections.

There are many circumstances that can generate torsional vibration, not just piston water pumps. Engine drives can be susceptible especially if there is a large inertia differential either side of the coupling, or perhaps an engine misfiring.

Torsional vibration is the responsibility of the machine builder, however, we are able to advise and examine systems by the use of one of our many specialist partners but be warned, the amount of data required to perform a torsional vibration analysis is considerable. For engine drives, a mass elastic diagram will be essential, driven equipment inertia and stiffness values to name just a few more.

Critical speed due to resonance:

Select coupling stiffness so that the system does not run at high resonance as well as the normal running and idle speeds are not at or near critical speeds.

Crtical speeds are related to the system natural frequency and the number of pulses or excitations generated per revolution ‘I’ (order). For analysis, if possible, reduce the application to a 2-mass system and apply the following equations:

n_R = critical resonance speed of the system (rpm).
C_Tdyn = dynamic torsional stiffness of the coupling.
J_A = mass moment of inertia for the drive side.
J_L = mass moment of inertia for the load side.
i = number of oscillations generated per revolution.

The coupling will be modelled as the spring controlling torsional oscillations of the engine and the flywheel on one side and the driven equipment on the other:

Use the dynamic torsional stiffness values (C_Tdyn) from the performance data tables which are found in representative coupling catalogues. Mass moment of inertia values may be obtained from the respective engine and equipment manufacturers.

*Note: System steady-state operating speeds should be 1.5 to 2 times the major critical speed for safe, low-resonance operation.

See page 5 of our Pump Drive Components catalogue for torque ratings for the Spidex Couplings^®

See page 1 of our Torsional Couplings catalogue for further information about torsional vibratory load.

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Windup and Backlash

The functional requirement to interconnect rotating shafts across a wide range of machinery has driven the development of an equally broad spectrum of flexible coupling designs. At the lower end, this includes economical, lightweight couplings suited for shaft diameters as small as 4 to 5 mm. At the upper end are high-capacity, multi-element couplings engineered for heavy-duty applications with shaft diameters in the 150 to 500 mm range. Across this spectrum, the unifying design objective is the ability to accommodate angular, parallel, and axial misalignments while simultaneously satisfying application-specific demands for torsional rigidity, permissible backlash, and dynamic performance.

Shaft coupling windup and backlash are fundamentally different types of mechanical error, although both can cause inaccuracies in a rotational system. They are related in that they both cause lost motion, but they arise from different physical phenomena.

Key differences between Windup and Backlash summarized

Advantages of Couplings that Prevent Drive Windup

Couplings that prevent drive windup offer superior precision, repeatability, and system stability by eliminating unwanted rotational deflection between the driving and driven shafts. This prevention is critical for high-performance applications where any play or angular lag can cause significant errors or system damage.

What is drive windup?

Drive windup, also known as torsional windup, occurs when a torque load causes a coupling to twist elastically like a spring. This causes a difference in the angular position between the motor and the load. While the coupling may return to its original position when the load is removed, this elastic deformation is unacceptable in many motion control applications.

Advantages of couplings that prevent windup.

Enhanced precision and positioning accuracy.

» Ensures exact motion: By eliminating the "give" of torsional windup, these couplings guarantee that the driven shaft's rotation perfectly matches the driving shaft's rotation.

» Improves repeatability: They ensure that a system will return to the exact same position every time, which is essential for robotics, CNC machines, and automated inspection systems, for example.

Increased system stability and performance

» Faster settling times: In applications involving rapid acceleration and deceleration, windup causes the system to oscillate before settling. Couplings with high torsional stiffness prevent this by ensuring a more immediate and stable response.

» Reduces overshoot: Torsional windup can cause a system to overshoot its target, which can be detrimental in sensitive applications. Couplings that prevent windup provide a more predictable and controlled movement.

Prolonged service life and reliability

» Reduces wear and stress: The elastic twisting of windup puts stress on the coupling and connected components like bearings and seals. By maintaining a more rigid connection, anti-windup couplings reduce this stress and extend the lifespan of your equipment.

» Minimizes backlash: Couplings that prevent windup are also designed to be backlash-free, meaning there is no lost motion or play when the direction of rotation is reversed. This prevents wear and protects against cumulative positioning errors.

Better for high-tech and dynamic applications

» Ideal for servo systems: High-gain servo systems are particularly susceptible to the performance degradation caused by windup. Zero-backlash, anti-windup couplings are a necessity for these systems to achieve their intended accuracy and responsiveness.

» Essential for high-speed use: In applications with high rotational speeds, even small amounts of windup can cause significant instability and vibration. Couplings with high torsional stiffness maintain a more balanced and stable drive, even at high RPMs.

Common couplings that prevent windup

Several types of couplings are designed to minimize or eliminate drive windup by maximizing torsional rigidity:

» Beam and helical couplings: These are machined from a single piece of material, and the cuts provide flexibility to accommodate misalignment while maintaining high torsional stiffness.

» Bellows couplings: Featuring a thin, flexible, metallic corrugated section, these couplings offer high torsional stiffness and precise torque transmission.

» Disc couplings: These use one or more flexible metal discs that allow for misalignment while transmitting torque with high torsional rigidity.

» Oldham couplings: Using a central disc between two hubs, these couplings transmit torque with zero backlash and are designed for high precision.

Advantages of Backlash Free Couplings

Backlash is the unwanted movement between coupling components which can compromise the performance of systems requiring exact motion control. Zero backlash couplings such as the Flender Bipex-S and the Trasco-ES spider couplings eliminate this issue by ensuring that torque is transmitted immediately and directly without any lag. This is achieved using an elastomeric ring available in various hardness levels, which acts as a buffer while maintaining rigidity under load.

Improved precision and accuracy

Exact positioning: By eliminating the lost motion inherent in couplings with backlash, these devices ensure that when a motor turns a specific amount, the driven shaft turns precisely the same amount. This is vital for accurate and repeatable positioning, especially in robotics, CNC machinery, for example.

No cumulative error: In systems with frequent starts, stops, and reversals, backlash can cause small errors to accumulate over time. Backlash-free couplings prevent these cumulative errors, ensuring consistent accuracy throughout operation.

Enhanced system performance and stability

Greater repeatability: The consistent, one-to-one transmission of motion enables predictable performance, which is crucial for manufacturing and inspection systems that require repeatable, reliable results.

Better motion control: Backlash-free couplings provide high torsional stiffness, meaning they do not twist under high torque loads. This results in a faster, more responsive system, which is essential for modern servo-driven applications and other dynamic systems.

Reduced vibration and shock: Certain backlash-free couplings, particularly elastomeric types, are designed to dampen vibrations and absorb mechanical shock loads. This reduces noise and extends the life of sensitive system components, such as bearings and actuators.

Increased longevity and reliability

Longer component life: By eliminating impact loads caused by "play” during changes in direction, backlash-free couplings reduce wear and tear on other mechanical components.

Reduced maintenance: Many all-steel disc-pack couplings are wear-free and maintenance-free, offering a long service life when properly installed.

Wider application versatility

Accommodation of misalignment: Many backlash-free couplings are also flexible, accommodating axial, radial, and angular shaft misalignment. Different types, such as Oldham or beam couplings, are optimized for different types of misalignment, allowing engineers to select the perfect fit for their application.

Electrical isolation: Elastomeric spiders in certain couplings can electrically isolate the two connected hubs, preventing the transfer of leakage currents that could damage sensitive electronic equipment.

High-speed operation: Many types, especially disc and bellows couplings, are balanced for use in high-speed applications without causing unwanted vibration.

Conclusion

Windup and backlash represent two distinct but equally important challenges in rotational drive systems. While windup arises from elastic deformation under torque and is generally predictable, backlash stems from clearance between mating components and often leads to inconsistent, cumulative errors. Both phenomena reduce precision, stability, and efficiency, especially in high-performance applications such as robotics, CNC machining, and servo-driven systems for instance.

Modern coupling technologies, particularly zero-backlash and high-torsional-stiffness designs offer effective solutions by minimizing lost motion, improving repeatability, and extending system lifespan.

Selecting the right coupling depends on balancing torsional rigidity, misalignment accommodation, and application-specific performance requirements. Ultimately, understanding and mitigating windup and backlash is critical to achieving reliable motion control, ensuring system accuracy, and optimizing long-term operational performance.

jbj Techniques have the technical expertise to assist you in the specification of the best coupling for your needs and extensive machine shop services, all in-house to enable prompt despatch of those more bespoke couplings, large or small in size and quantity.

If you need assistance with selecting the correct coupling for your application we are here to help. Contact jbj now:

Power transmission couplings; a summary of the different types available from jbj Techniques:

Spider Couplings ~ curved & straight jaw couplings

Torsionally flexible shaft couplings, also known as jaw couplings, enable the connection of shafts or flanges via a polyurethane drive ring.

The flexibility of the drive ring allows the power transmission coupling to compensate for parallel, angular and axial displacements.

Maximum shaft diameters of 145 mm can be accommodated with maximum torques up to 15,000 Nm and maximum speeds of 19,000 rpm.

» Link to Spider Couplings web page

couplings: mechanical power transmission spider coupling

Gear Couplings ~ steel gear hubs with nylon drive sleeve

Torsionally rigid, power transmission couplings which transmit torque between two steel gear hubs and the internal toothing of a nylon drive sleeve.

The gear coupling is designed to release neighbouring shaft bearings from non-controlled additional bearing loads.

Maximum shaft diameters of 100 mm can be accommodated with maximum torques up to 2,400 Nm and speeds up to 8,000 rpm.

» Link to Gear Couplings web page

couplings: mechanical power transmission gear coupling

All Steel Gear Couplings ~ steel gear hubs with steel drive sleeve (ATEX)

Torsionally rigid, power transmission couplings which transmit torque between two steel gear hubs and the internal toothing of a steel drive sleeve.

Gear couplings have the highest power density, offer more variations, a wider size, torque, and bore capacity than any other coupling type.

Easily modified for shear pin service, floating shaft type, vertical applications, electrical isolation, limited end float, and can have a brake drum or disc added.

» Link to All Steel Gear Couplings page

couplings: mechanical power transmission all steel gear coupling with ATEX certification on request

JXL Couplings ~ pin and bush style anti-static / flameproof (ATEX)

ATEX certificated to Directive: 94/9/EC II2GD-IM2-T6.

Torsionally resilient couplings, of pin and bush design, comprise of two fully machined steel flanges which are coupled via a series of drive pins and 'hytrel' flexible elements. The elements have the ability to absorb shock loads and dampen vibration.

Maximum shaft diameters up to 400 mm with torques of 300,000 Nm and speeds up to 11,000 rpm can be accommodated.

» Link to JXL Coupling web page

couplings: mechanical power transmission jxl anti-static, flameproof coupling with ATEX certification on request

Grid Couplings

Torsionally flexible and resilient, vibration reduction up to 30%, plus cushion shock loads safeguard driving and driven equipment.

Quick installation and easy maintenance reduces labour and downtime costs. Fully interchangeable with industry standards.

Versatile stock; metric and imperial size cover fasteners available. High tensile, shot-peened alloy steel grids and precision machined hubs ensure superior performance and long life.
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» Link to Grid Couplings web page

couplings: mechanical power transmission grid coupling

Torsional Couplings

Dampen torsional vibrations and tune the system to have critical speeds outside the operating range.

These torsional couplings solve torsional vibration problems typical of those found in diesel engine applications. Torsional couplings dampen torsional vibrations and tunes the system to have critical speeds outside the operating range.

jbj Techniques Ltd can analyse the application with our computer programme and determine the exact torsional coupling needed for almost any application.

» Link to Torsional Couplings web page

couplings: mechanical power transmission torsional coupling

S-Flex Couplings Endurance™

The reformulated S-Flex Endurance™ is the longest lasting and best performing EPDM product available on the market. The simple design of the S–Flex coupling ensures ease of assembly and reliable performance. No special tools needed for installation or removal. S–Flex couplings can be used in a wide variety of applications.

The S–Flex flanges are offered in five models which are made from zinc die cast or cast iron. Sleeves are available in EPDM rubber, Neoprene, or Hytrel® to address a wide variety of application requirements. Thirteen sizes are available with torque capabilities that range from 60 in-lbs (6.78 Nm) to 72,480 in-lbs (8189 Nm).

» Link to S-flex Couplings web page

couplings: mechanical power transmission s-flex coupling

Disc Couplings ~ (ATEX)

jbj Techniques offer a wide variety of superior disc coupling products in models designed to meet the application needs of today’s worldwide power transmission market.

Implementation of Finite Element Analysis, and extensive testing of materials, an innovative disc pack profile design has been developed, revolutionary to traditional disc pack designs found in the market.

Manufactured using high grade stainless steel (AISI-301), for high strength, high endurance to fatigue, and resistance to most environmental conditions.

» Link to Disc Coupling web page

couplings: mechanical power transmission disc coupling with ATEX certification on request

Tyre Couplings ~ (FRAS)

With a flexible body that compensates misalignment and protects other components in the transmission system. UNE-FLEX couplings can be produced in accordance with the requirements of regulation 94/9/CE (ATEX 95) of a group ll device, category 2G or 2D (zone 1) and temperature class T4.

The fundamental element of the tyre coupling is a neoprene rubber tyre reinforced with a synthetic mesh. It adapts itself to the working conditions, absorbing axial, radial, angular and torsional misalignments and prevents vibration via the transmission to the machines to which they are coupled. Compensates for angular misalignments to 3º, radial misalignment by 4 mm, and axial misalignment of 6 mm.

» Link to Tyre Couplings web page

couplings: mechanical power transmission tyre coupling with ATEX certification on request

Torque Limiting Couplings

Protect mechanical equipment, or its work, from damage from mechanical overload.

Torque limiting couplings are designed for machines with chain, gear or belt drives to prevent over-loading of sensitive motors, gearboxes and machine components. High quality torque limiting couplings, fully-machined components with a special rustproof surface coating. This series of torque limiters are completely enclosed to prevent dirt from contaminating the interior.
They allow stepless adjustment of the required slip torque, even when already installed. Torque limiting capacity up to 23,000 Nm.

» Link to Torque Limiting Couplings web page

couplings: mechanical power transmission, torque limiting coupling

A Coupling for the Bloodhound Super Sonic Car . . . 1,000 mph!

The scope of supply was to produce a suitable drive coupling with a maximum diameter of 160 mm which is capable of transmitting 550 Nm @ 10,000 rpm, needed to be as short an assembly as possible and at the same time be able to accept misalignment within the drive-train.

» Link to BSSC coupling page web page

couplings: mechanical power transmission coupling for BSSC

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Mechanical power transmission coupling design types

The engineering expertise to specify & supply the correct coupling to the needs of your system.

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