Flexible couplings are one of the major types of couplings. They find use to connect two shafts, end-to-end in the same line to transmit power that is torque from one shaft to another, thereby causing both to rotate in unison, at the same rpm. The other purpose is to compensate for small amounts of misalignment and random movement between the two shafts. Several factors should always be taken into consideration when looking to specify flexible couplings.
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These are torsional stiffness, backlash, torque, life, and attachment system. All of these have bearing on coupling selection. Specific details vary depending on the different types and their functions. In this article, we review the different types of flexible coupling in all aspects. Follow this new blog in Linquip to find out more about these types of couplings.
Most Flexible couplings are characterized as belonging to one of four main categories:
Mechanical Flexible Couplings
Elastomeric Couplings
Metallic Membrane Couplings
Miscellaneous Couplings
The mechanical flexible coupling generally obtains its flexibility from loose-fitting parts by rolling, sliding, or from both with some flexure of material. Flexible mechanical couplings provide a flexible or movable connection that accommodates misalignment between the shafts. This flexible feature reduces the forces or loads caused by the reaction to the misalignment. The mechanical nature of these types of flexible coupling allows for nearly unlimited horsepower and torque capabilities.
They maintain high torsional rigidity and allow a considerable degree of angular misalignment; however, they are not maintenance-free and require occasional lubrication unless one moving part is made of a material that supplies its own lubrication needs. Several different types of mechanical flexible couplings are as follow:
A common type of mechanical flexible coupling is gear coupling. Each coupling consists of two hubs with crowned external gear teeth. The hubs mesh with two internally splined flanged sleeves that are bolted together. They are called gears as a result of the generally huge size of the teeth. These couplings are commonly constrained to precise misalignments of 4° to 5°.
The gear coupling provides good torque characteristics. Gear couplings transmit the highest amount of torque and the highest amount of torque in the smallest diameter of any flexible coupling. Gear couplings require periodic lubrication depending on the application. These couplings have a service life of 3 to 5 years and in some cases, they can last for decades.
High torque density
All types of misalignment (angular, parallel, axial)
High torque at high speeds
Sensitive to lubrication failures
Application: Metal industry such as steel or wire mills, large industrial machines such as pumps, blowers, compressors, mixers, etc.
Grid couplings are multi-piece mechanical couplings used to transmit torque and rotation between shafts in mechanical power transmission assemblies. Grid couplings are comprised of two radially slotted hubs, a grid spring element, and a split cover kit. These types of flexible coupling are a popular option where both high torque levels and dampening requirements exist.
Grid couplings have a unique ability to reduces vibration by as much as 30%, and cushions shock loads to safeguard driving and driven power transmission equipment. They are available with either a horizontal or vertical split cover design. Grid couplings transmit torque and accommodate angular, parallel, and axial misalignment from one hub to the other through the rocking and sliding of a tapered grid in the mating hub slots.
Interchangeable components
High power density
Relatively straightforward
Simple installing
Good resistance to environmental conditions
Available for both inch and metric bores
Not maintenance-free
Require periodic lubrication
Application: Motors, pumps, reducers, conveyors, etc
Roller Chain type couplings consist of two radially sprocketed hubs that engage a strand of double pitch roller chain. These couplings find a use for low to moderate torque and speed applications. The meshing of the sprocket teeth and chain transmits torque and the associated clearances accommodate angular parallel, and axial misalignment. These couplings are also able to accommodate up to 2 degrees of misalignment. They have flanges that are linked with duplex roller chains, giving them a high level of strength. Roller chain couplings are considered an economical way to transmit power between shafts.
High levels of torque
Requires frequent lubrication
Not suitable where slip and precise motion is required
Not affected by temperature and environmental conditions
Easy to install
Application: Transportation industry, woodworking machinery, agricultural machinery, oil well drilling rigs, building construction, material handling equipment, lifting load
Oldham&#;s couplings consist of three discs, one coupled to the input, one coupled to the output, and a middle disc that is trapped by 90° displaced grooves between the tongue and groove. These couplings can accommodate lateral shaft misalignments up to 10% of nominal shaft diameters and up to 3 angular misalignments. Some manufacturers claim an ability to tolerate up to 5-degree angular misalignment through the use of cylindrical, rather than rectangular, sliders. Lubrication is a problem but can be overcome by choosing a wear-resistant plastic or an elastomer in place of steel or bronze floating members.
No velocity variation as with universal joints
High lateral misalignments possible
High torque capacity
Oil resistance and electrical insulation
Suitable for small transmission torque occasions and connecting two coaxial transmission shafts
Sliders Can be chosen with different materials
Requires periodic lubrication due to relative sliding motion unless nylon or rubber construction is employed.
Possible loss of loose members during disassembly
Application: Robotics, printers, copy machines
Beam couplings are one-piece metal beam cylinders with spiral slots that are cut to form a spring-like flexing portion. Beams are shaped to allow torque transmission in either direction. They are considered miniature and used in small-sized equipment applications where and easy installation is important. The beam couplings are classified into two series: helical beam coupling and parallel slit coupling.
These couplings can accommodate parallel misalignments up to 0.025 inches and angular misalignments up to 7 degrees. They are used primarily for motion control applications where torques are typically below 100 inch-lbs. Zero backlash designs available ensure positioning accuracy between driving and driven shafts. These types of flexible coupling generally feature excellent flexibility and a lower price, as well as zero need for maintenance.
Good misalignment capabilities
No need for lubrication
Torsional stiffness for accuracy
Strong for carrying torque loads
Not suited for extreme operating environments with extreme temperatures and harsh chemicals
Identical clockwise and counterclockwise rotation characteristic
Application: CT scan, laser marking device, confectionery equipment, automatic rotation stage, matching box for RF power, 3D printer, food processing equipment, index table, encoders, tachometers, and other instrumentations
Bellows couplings are single-piece flexible shaft connectors that are used to couple driving and driven shafts in mechanical power transmission assemblies. They consist of two hubs connected by a flexible bellows section. Typical bellows couplings tolerate angular misalignment of 1° to 2° and parallel misalignment from 0.01 to 0.02 in. Bellows couplings are known for their exceptional torsional rigidity to accurately transmit velocity, angular position, and torque.
They are used where precise rotation, high speeds, and dynamic motion must be transmitted. They exhibit zero-backlash and a high level of torsional stiffness, offering distinct performance advantages. Unlike other mechanical flexible shaft couplings, these generally need no lubrication.
Bellows couplings are often selected in place of low-cost jaw couplings and disc couplings by engineers looking to benefit from their well-documented performance advantages. It is also used in some heavy industry applications, where its ability to accommodate axial thermal growth makes it useful for installations with large temperature swings.
Able to run at speeds up to 12,000 to 32,000 rpm
Offers high rigidity
Suitable for sensitive motion-control applications
Capable of handling high accelerations and dynamic motions
Withstands high speed and thermal growth
Low tolerance for misalignment
Application: Bar feeder encoder, laser engraving machine, grinding machine, linear and ball screw actuators, robots, step motors, light-duty pumps, tube production machine, motor test bench, laser cutting machines, radars, etc.
The universal couplings are mechanical joints used for connecting two rotating shafts or rods whose axes are inclined at an angle to each other. They consist of a pair of hinges or fork shapes yokes oriented at 90° to one another and connected by a cross shaft. The universal coupling is also known as a Universal joint, U-joint, Cardon Joint, and Hooke&#;s joint.
They compensate for the angular misalignment and allows the shafts freedom of movement in any direction while transmitting rotary motion. These couplings operate at 250 rpm with an operating angle of 10°. The universal joint is mainly used for the lengthy shaft linings supported by bearings. They are used to transmit motion, power, or both. Universal joints can also be used in series to eliminate velocity fluctuations, to connect offset (non-intersecting) shafts, or both.
Large angular displacements are possible
High torsional stiffness
High torque capacity
Negligible backlash
Corrosion resistance
Capability for high-speed operation
Velocity and acceleration fluctuation increases with the operating angle.
Shafts must lie in precisely the same plane
Application: Automobiles, aircraft applications, driveshafts, stone crushers, control mechanisms, belt conveyors, metal forming machinery, control mechanisms, electronics, instrumentation, medical and optical devices, ordnance, radio, sewing machines, textile machinery, and tool drives.
These types of flexible coupling use a resilient material to transmit torque between two metallic hubs. Elastomeric couplings obtain their flexibility from stretching or compressing a resilient material such as rubber, and plastic. Some sliding or rolling may take place, but it is usually minimal.
The design of elastomeric couplings means that the elastic material is meant to wear out before any metal components. This not only saves time and money on maintenance but also means that the couplings do not require lubrication. A few advantages of this coupling are the high vibration dampening, shock absorption abilities, and toleration of a high degree of misalignment. They are also inexpensive and of lighter weight than mechanical couplings. The elastomeric element is sufficiently resistant to fatigue failure to provide an acceptable life compared to the cost of the coupling.
Exposing elastomeric couplings to high temperatures and UV light will reduce the coupling&#;s lifecycle. Due to the limitations of the flexible element, this type of coupling is used up to 37 kW and rpm.
Popular elastomeric couplings are as follows:
Tire Coupling
Jaw Coupling
Pin and bushing Coupling
Torsional Coupling
Tire-type couplings resemble the tires on a car. These couplings consist of two flanged hubs equipped with clamping plates, which grip the coupling&#;s hollow, ring-shaped element, by its inner rims. Tire coupling elements are rubber or polyurethane derivative elastomers with layers of cord, such as nylon, vulcanized into the tire shape. The coupling transmits torque through the friction of the clamp applied to the inner rims of the tire and the shearing of the element.
When the coupling fails, usually only the elastomeric part is replaced. Axial forces on the shaft caused by centrifugal forces working on the elastomer, restrict the speed of these couplings. Additionally, their bulky size limits what applications they could be applied to, although there is a variant with the tire inverted to reduce the coupling&#;s size.
High misalignment capacity
Easy assembly w/o moving hubs or connected equipment
Wide range of torque capacity
Easy installation
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Virtually maintenance-free
Can accommodate angular, parallel, and axial misalignment
Application: Centrifugal compressors and pumps, machine tools, metal presses, mills, winches, and fans
The jaw coupling or Spider coupling is a general, all-purpose industrial power transmission device. Jaw coupling is a material flexing coupling that transmits torque through the compression of an elastomeric spider insert placed between two intermeshing jaws. These couplings have two hubs with projecting jaws that mate with a one-piece elastomeric spider insert. For higher power applications, individual load cushions can be substituted for the spider. Torsional stiffness and torque capacity vary with the number, width, and shape of the jaws.
They operate in a range of temperatures, handle angular misalignment and the accompanying reactionary loads, resist chemicals, and have good speed and dampening capabilities. They are not extremely tolerant of misalignment as compared with other types of flexible coupling. The design of the jaw coupling is considered to be fail-safe, which could be a positive or a negative factor, depending on the application.
Useful in high acceleration/deceleration motion control applications
Electrically isolates the motor from the driven equipment
Continues driving upon loss of the flexible element
Application: Conveyors, blowers, mixers, winders, compression pumps, propeller pumps, printing presses, shredders, excavators, stone crushers, hammer mills, welding machines, etc
They are simple types of flexible coupling with two flanges bolted with the help bolt and nuts covered by a bush made up of rubber. Pin and bushing couplings consist of two hubs that can be made of different materials and are fitted with pins where rubber bushes are attached. Relative movement is accommodated by the compression of steel-bonded bushings. This type of coupling can handle misalignment of 0.5 mm laterally and 1.5° angular misalignment.
These couplings are mainly used as flexible links in applications where reliable link transfer is required under severe operating conditions. Because of their simple design, these are less expensive. They are widely applied to hoisting applications.
More radial space is required compared to other couplings
Easy to assemble & disassemble
Application: Fans, line shafting, alternators, pulp grinders, shakers, rotary dryers, wire mills, cement mills, pulverizes, cranes, mechanical shovels and dredges, winding gears and drums, prolonged and reversing drives
Torsional couplings are mostly to accommodate the torsional vibration. Most of these are rubber coupling which can dampen the vibrations moving from one shaft to the other and also accommodate the misalignments. Spring torsional couplings are available as torsional couplings.
The goal of torsional coupling is to tune the system above or below its natural frequencies. Both torsionally soft (incorporating soft rubber) and torsionally hard (often incorporating hard plastics) are available to tune the system. These are very stiff couplings designed to shift critical speeds well above the operating range.
Torsional couplings are made to adapt to shafts, flywheels, or universal joints.
Low weight, low moment of inertia
Short profile for tight engine housing, or shaft-to-shaft requirements
Easily assembled, no special bands, tools, or time-consuming assembly procedures
Oil, heat, and corrosion-resistant elements
Fail-safe operation
Applications: Diesel engine generators, marine applications, crawler tractors, manlifts, compactors, skid steer loaders, excavators, and lift trucks
Metallic membrane couplings rely on the flexure of metallic elements to accommodate misalignment and axial movement in shafts. These flexible couplings obtain flexibility through the bending of a membrane within the coupling. They have been around longer than the other three major types of couplings. These couplings require low maintenance and no lubrication, however, they may be more expensive than mechanical flexible couplings.
Metallic membrane couplings are somewhat expensive flexible couplings that, do not usually permit offset misalignment. These types of flexible coupling obtain their flexibility from the flexing of thin metallic, disc, or diaphragms. Classified as metallic membrane couplings, disc, and diaphragm couplings transmit torque and accommodate the slight misalignment anticipated between most equipment shafts.
The disc couplings have a thin sheet of discs laminated as the main part of the coupling for the flexibility to accommodate the misalignments. They consist of two hubs on each side and a spacer as a center member joined by the discs on both sides. The disc coupling&#;s principle of operation has the torque transmitted through flexing disc elements. It operates through tension and compression of chorded segments on a common bolt circle bolted alternately between the drive and driven side. A single-disc pack can accommodate angular and axial misalignment. Two-disc packs are needed to accommodate parallel misalignment.
A true limited end float design
A zero-backlash design
High-speed rating and balance
Finds use on fractional to 100,000 hp drives
Application: Hydrostatic application (Gearbox to hydraulic pump), turbomachinery, blower, compressor, mixer, servo motor applications, stepper motors, high-speed machine tools, semiconductor manufacturing equipment, actuator, surface chip mounting, and packaging machine
Diaphragm couplings also use thin sheets as a flexible element like disc coupling. These couplings handle misalignment through the use of a single or a series of flexing metal plates or diaphragms in parallel for the flexible members. It transmits torque from the outside diameter of a flexible plate to the inside diameter, across the spool, and then from inside to outside diameter.
The outer diameter side of the diaphragm will be bolted with the hub and the inner side diameter portion of the diaphragm disc will be fitted into the slots of the spool portion also known as a spacer. On the other end of the spool will be again joined by a diaphragm disc with a hub. Diaphragm couplings can accommodate all three misalignments. It can accommodate more range of misalignment axially.
Diaphragm couplings were originally introduced to service very high speed, high horsepower applications in the petrochemical industry and have since progressed to other extreme applications such as helicopter drives. Diaphragm couplings are known for their large outside diameters, and, generally, very high cost. Diaphragm couplings are generally sold as custom solutions, and there are a wide variety of options to consider.
Used in high torque, high-speed applications
Finds use been used from fractional to 100,000 hp drives
Application: Turbomachinery, high power water pump, chemical pump, fan, compressor, hydraulic machinery, petroleum machinery, printing machinery, textile machinery, chemical machinery, mining machinery, metallurgical machinery, aviation, and high-speed power transmission system of ships
These types of flexible coupling obtain their flexibility from a combination of the mechanisms described above or through a unique mechanism like Spring and Schmidt couplings. Many of these designs require lubrication.
Consist of one or more square-wire springs that are concentrically wound and connected to hubs at each end of the spring. They are available in standard and miniature sizes and different lengths. The spring coupling can have many different hubs or flanges fitted to the ends and are available in. Spring couplings have been a part of powertrains for more than 80 years.
Multistage stiffness for optimized system tuning
Lubricated and non-lubricated environments
Drop-in replacement for original drive plates, no spacers required
Minimal impact from the temperature on performance or durability
Performance can be optimized for a given application
Space-efficient design
Application: Agriculture vehicles, construction equipment, industrial equipment, marine, mining equipment, gearbox, pump drive, hydrostatic drive, hybrid transmission,
Schmidt couplings are designed specifically to operate on shafts that are offset and to adapt to various drive conditions. They consist of an arrangement of links and discs. Three discs rotate in unison and are interconnected in series by three or more links between each pair of disks. These couplings offer great flexibility in shaft displacement while maintaining undisturbed power transmission at a constant angular velocity and torque in a wide range of parallel shaft misalignment. They use precision sintered parts for the hubs which are connected to the shafts.
Can adapt to very wide variations in radial displacement while running under load
Allows radial displacement greater than twice the radius of the disks
zero-backlash
Application: Papermaking machine, packaging machine, printing machine, wood processing machines, roll forming machines and, food industry
For the applications being compared, mechanically flexible gear coupling is most often considered because of torque, misalignment, speed, and environmental requirements.
Taking time to determine the right type of flexible coupling is worthwhile. Selecting a flexible shaft is fairly easy once you understand its basic operation and performance limitations. It might lead you to something different that will work better and last longer. The right flexible coupling design may also prevent shafts fretting, minimizing noise and vibration, and cutting long-term maintenance costs.
So, there you have every single fact about different types of flexible coupling. If you enjoyed this article in Linquip, let us know by leaving a reply in the comment section. Is there any question we can help you through? Our experts will be happy to assist you in finding the best flexible coupling needed for your technical challenge. Feel free to contact us on our website to get the most professional advice and answer your questions.
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In the power transmission field, there are many different types of couplings that can be used in order to transfer power from the gear side to the machine. Taking into consideration that each specific application has its own features, it is extremely important to analyse and check what characteristics should our coupling have, to ensure a long-life cycle and a successful performance of our machinery.
We should take into account the following factors in the coupling selection process:
It is important to analyse the area, the temperature where the coupling is going to be exposed, and also if the device is going to be in a corrosive environment or not.
The space might be an issue when placing the coupling. In some applications there is a limited or a difficult access to locate the coupling. Therefore, this is also another key aspect to take into consideration for the coupling selection.
The type of shafts should be checked, as well as the diameter and the length.
As an example; considering the access, space required, and the shaft types, we have to analyse what size would apply best to our installation from our range of products.
The operator should check what types of misalignments should be corrected; parallel, torsional, axial, angular or lateral.
The main target consists on understanding what kind of performance we want to have with our coupling; high torque, high speed, repeatability or high level of flexibility and cushioning.
Decide which type of coupling will be most appropriate depending on the above aspects.
In order to determine the type of coupling to be used the following formula should be applied:
M = N hp/ n. . K
M = N kW/ n. . k
M = Nominal torque
N = Driving-motor power (CV or KW)
n = Minimum speed of the connected axles (rpm)
k = Multiplying co-efficient
The value obtained on applying the formula should be less or equal than the indicated in the tables of sizes and powers that refer to the corresponding coupling in the column &#;nominal torque&#;.
k = Multiplying co-efficientElectric motorNotes:
The values indicated in the above table are by no means applicable to every case. If, for example, one of the machines to be coupled displays such a degree of irregularity that it is judged necessary to carry-out technical investigations of the oscillations, then it is recommended to proceed to the selection of the multiplying co-efficient using the enclosed questionnaire.
K-coefficient calculation guidance for different groups of machines.
The elevator bucket is driven by a motor of 16 kW; n=1.450 rpm., by means of a reducer whose outlet axle rotates at a speed of n= 180 rpm. The motor and reducer are protected by a UNE-FLEX flexible axle coupling.
1. COUPLING BETWEEN MOTOR AND REDUCER
N = 16 kW
n = rpm
M = NKw/n. . k
Elevator buckets figure in group 2 of the classification. Under &#;variable load machinery&#;. The multiplying co-efficient k = 1,5 figures in the k value table under heading 2 and in the classification of machines driven by &#;electric motor&#;.
M = 16/ x x 1.5 = 158.07 Nm
Then, according to the power table. the appropriate coupling for a torque of 158 Nm. is model M-5.
2. COUPLING BETWEEN REDUCER AND ELEVATOR, BUCKET MECHANISM
N = 16 kW
n = 180 rpm
M = NKw/n. . k
M = 16/180 x x 1.5 = Nm
Then, according to the power table, the appropriate coupling for a torque of Nm is the model M-9.
Note: to carry out the correct selection of a coupling, an indication of power and speed is generally sufficient. However, it&#;s better to have the following information as well:
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