Shaft Coupling Types
A shaft coupling connects a driving shaft to a driven one and carries the torque across the joint. The types differ in how they carry it: gear, grid and chain couplings transmit through hardened steel parts and must be greased; disc, elastomeric and jaw couplings transmit through a flexing member and need no lubrication; a rigid coupling has no flexible element at all. This guide sets out what each type tolerates in torque, misalignment, speed and maintenance, where each is used, and which coupling lines we carry from Kop-Flex, Ameridrive, Jaure, Browning and Morse.
How is a coupling selected?
A coupling is selected on torque, then checked for speed and bore. Application torque in lb-in is horsepower times 63,025 divided by rpm; that figure is multiplied by a service factor for the prime mover and the driven machine to give the selection torque, and the coupling chosen must have a continuous torque rating greater than it. The application speed must not exceed the coupling's maximum speed rating, and the bore capacity must cover both shafts.
The service factor accounts for uneven or shock loading and increases with the severity of the application: a smooth motor or turbine adds nothing, an engine adds one, a centrifugal pump adds one and a rock crusher adds three, and the two are added together. The information needed to make a selection is the horsepower and rpm, the type of application, the prime mover and driven equipment, the distance between shaft ends, the shaft sizes, and any special requirement such as high start-up torque, limited end float, balancing or high temperature. Long spacer and floating shaft couplings also have a lateral critical speed to check, and gear and disc couplings each have a balance chart that says whether the coupling can be used as manufactured or must be dynamically balanced at the application speed. Send those details through the support form and we will confirm the size before you order.
Lubricated or non-lubricated: which coupling types need maintenance?
Gear, grid and chain couplings are lubricated: their working parts slide under load, so they need coupling grease and have wearing parts, in exchange for the highest torque capacities. Disc, elastomeric, jaw, Max-C and Morflex couplings are non-lubricated: the flexing member is a stainless steel disc pack or a rubber or urethane element, so there is nothing to grease. The table lists each type's strengths and limitations as the manufacturer states them.
| Type | Lubrication | Strengths | Limitations |
|---|---|---|---|
| Gear | Lubricated | High torque, rugged, good misalignment capability, slide capability, medium relative cost; interchangeable by half coupling with competitive designs | Lubrication required, wearing parts, assembly backlash |
| Grid | Lubricated | Shock loading, medium torque capacity, interchangeable by part with competitive designs, low relative cost | Lubrication required, wearing parts, lower torque capacity than gear couplings, cannot be balanced |
| Chain | Lubricated | High torque capacity, low initial cost, covers available for extended life | Lubrication required, wearing parts, limited size ranges, cannot be balanced |
| Disc | Non-lubricated | High torque capacity, long life, minimal maintenance, excellent balance, zero backlash | Higher cost, limited misalignment capacity |
| Elastomeric (rubber in compression) | Non-lubricated | Rubber element removed without moving equipment, some shock absorption, low maintenance, easy element replacement, low to medium relative cost | Limited torque capacity (less than jaw), speed limitation |
| Jaw | Non-lubricated | Low cost, no lubrication, interchangeable with competitive designs | Equipment must be moved to change the element, low misalignment capability, small applications only |
| Max-C resilient | Non-lubricated | Shock absorption, low maintenance, urethane elements drive in compression | Large coupling, medium torque capacity, high cost; not for severe reversing applications |
| Morflex | Non-lubricated | High misalignment capacity (up to 10 degrees), no lubrication, simple assembly, resilient | Limited torque (13,300 lb-in) and bore capacity (3.50 in) |
What is a gear coupling and where is it used?
A gear coupling transmits torque through external gear teeth on two hubs meshing with internal teeth in a sleeve, and the tooth mesh is what absorbs misalignment. It is the choice where torque is high: gear couplings are rugged, have good misalignment capability and slide capability, and sit at a medium relative cost. They must be greased, they have wearing parts, and the assembled mesh has backlash.
Two Kop-Flex designs cover most of the range. FAST'S gear couplings, sizes 1 1/2 through 30, use a lifetime all-metal end ring instead of a perishable lube seal; the end ring gives up to 300 percent greater lubricant capacity, so longer periods between relubrication can be scheduled, and it is the only coupling designed to use oil lubrication. The FAST'S Model B covers sizes 1 through 3 1/2. The Series H, sizes 1 through 30, is the most economical gear coupling design: it seals with a Buna-N O-ring, its sizes 1 through 7 compensate for up to 1 1/2 degrees of static angular misalignment per gear mesh through crowned hub teeth, and its bore capacity reaches shafts up to 10 5/8 inches. Both are interchangeable by half coupling with competitive designs, so one half can be replaced without changing the other. A 1 1/2F EB FFis a FAST'S full flex coupling with exposed bolts.
Beyond Kop-Flex, we carry Ameridrive Amerigear gear couplings in the F, FS and C series as complete couplings, hubs and sleeves, and Jaure MT-series gear coupling halves, hubs and sleeves. All of them are listed under gear couplings. A lubricated coupling is filled with a coupling grease, not a bearing grease: Kop-Flex KSG standard and KHP high performance greases are in coupling grease and lubricants.
What is a grid coupling?
A grid coupling transmits torque through a tapered, shot-peened steel grid laid into grooves across the tapered teeth of two hubs. The grid flexes under load, so the coupling damps torsional vibration and cushions shock; it has a medium torque capacity, lower than a gear coupling of the same size, and a low relative cost. It must be lubricated, has wearing parts and cannot be balanced.
Under a light load only the outer edges of the grid touch the hub teeth, leaving a long span free to flex; as the load rises the span shortens, and under an extreme load the whole grid bears on the teeth and the full load passes straight through. The grid slides in its lubricated grooves to allow parallel misalignment and end float on both shafts, and rocks in them for angular misalignment. In an extreme overload the grid can shear, which protects the connected machinery in the way a shear pin does. Kop-Flex Kop-Grid couplings are interchangeable with other tapered grid couplings and are used in petrochemical and refining, material handling, pulp and paper, and food and textile plants. Grid couplings are supplied on request; send the size and application through the support form.
What is a disc coupling?
A disc coupling transmits torque through flexible packs of stainless steel discs connecting shaft-mounted hubs to a spacer or sleeve assembly, and the discs flex to take angular and axial misalignment. It has a high torque capacity, long life, minimal maintenance with no lubrication, excellent balance and zero backlash. It costs more than a gear coupling and its misalignment capacity is limited.
Kop-Flex KD disc couplings run from size 053 through 905 and are designed for general purpose drives: centrifugal pumps, compressors, generators, cooling towers, machine tools, printing and pulp and paper machines. Most disc packs are unitized and, with self-locking nuts, reduce the number of loose parts; the coupling is self-centering, so no separate provision for limited end float is needed, and the stainless discs give good corrosion resistance. The styles are KD1, KD10 and KD11 close coupled; KD2, KD20 and KD21 spacer; KD33 cooling tower; KD4 single flex; and KD41 and KD42 floating shaft. A 404 KD 10 SS is a size 404 KD10 close coupled coupling, rated 215,000 lb-in with a 4.75 inch bore capacity.
Jaure LAMIDISC steel disc couplings were introduced in the 1990s as an alternative to gear couplings. They are torsionally stiff and backlash free, need no greasing, come in 6, 8 and 10 bolt designs, and can be inspected in operation with a strobe light without disassembly; they are used in pulp and paper, pumps, marine, cooling towers, winches, mining and cranes. We carry LAMIDISC spare disc packs such as the LAMIDISC SX 090-6 disc pack. Kop-Flex and Jaure disc couplings and components are listed under disc couplings.
What is an elastomeric coupling?
An elastomeric coupling transmits torque through a rubber or urethane element between two hubs, and the element flexes to take misalignment, cushions shock loads and damps torsional vibration. It needs no lubrication and the element can often be changed without moving either machine. Its torque capacity is limited and it has a speed limitation, so it is chosen for its resilience rather than its capacity.
Kop-Flex ELASTOMERIC couplings carry the rubber in compression, which the manufacturer states can be loaded 5 to 10 times as high as rubber in tension or shear. The flexible element is a split wrap-around insert: the hubs are mounted and the shafts aligned first, then the element is installed and can be replaced later without disturbing foundation bolts or alignment. Hubs are stocked in aluminum, steel and stainless steel, and the coupling accepts parallel, angular and axial misalignment under continuous operation. Typical uses are pumps, conveyors and mill runout, entry and exit tables. Kop-Flex Max-C K2 and UB resilient couplings drive through urethane elements in compression and are used on overhead cranes, conveyors, fan drives, feed rolls and pumps; they absorb shock and need little maintenance, but the coupling is large, its torque capacity is medium and it is not for severe reversing applications.
Morse Morflex couplings transmit through Neoprene biscuits between a floating center member and two flanges, and are installed where considerable misalignment is expected: up to 10 degrees, with low spring rates that reduce the reaction at the equipment bearings. Torque is limited to 13,300 lb-in and bore capacity to 3.50 inches. For extreme misalignment the double Morflex series CC uses two center members so four sets of biscuits share the misalignment; a 302 Morflex double coupling is the size 302 double coupling with finished bores. Browning Ever-Flex couplings have a rubber flex member permanently bonded to steel flanges and to steel or cast iron hubs, mount on Browning Split Taper bushings for a wide bore selection from stock, compensate for parallel misalignment up to 1/32 inch and angular misalignment of plus or minus 3 degrees, provide plus or minus 1/32 inch of end float, and operate from minus 30 to 225 degrees F. Kop-Flex, Morse and Browning lines are listed under elastomeric couplings.
What is a jaw coupling?
A jaw coupling is a pair of jaw hubs that drive through an insert between them. It is a low-cost flexible coupling, needs no lubrication and is dimensionally interchangeable with competitive jaw couplings. Its misalignment capability is low, it suits small applications only, and the equipment must be moved apart to change the insert.
Browning Type L jaw couplings offer a choice of four insert materials and are selected by service factor: the load class of the driven machine is read from the manufacturer's table, the factor is raised one class for 16 to 24 hour service, and the motor horsepower times the factor gives the rating the coupling must meet. A coupling is ordered as two hubs bored to each shaft plus one insert. Type J jaw couplings are also offered in finished bore, metric and bushed forms. A CHJS5H is a Browning jaw coupling half; hubs and inserts are listed under jaw couplings, and the full Browning coupling line is on the Browning brand page.
What is a chain coupling?
A chain coupling consists of two sprockets connected by a length of double roller chain. It is a rugged, lightweight and economical way to connect two shafts, with a high torque capacity and a low initial cost, and the two halves are disconnected by removing a single pin and unwrapping the chain. It must be lubricated, has wearing parts, comes in limited size ranges and cannot be balanced; a cover allows continuous lubrication and extends its life.
Morse DRC chain couplings use hardened tooth sprockets and precision roller chain with hardened rollers, permit moderate angular and parallel shaft misalignment, and are furnished as finished bore couplings in 80 stock sizes with bore ranges from 1/2 to 4 1/2 inches and capacities to 708 hp at 1,800 rpm, as reboreable minimum bore couplings, and as Split Taper and taper bore bushing types. Morse Delrin chain couplings use Delrin chain and run quieter than metal couplings: the N400 series is 1/2 inch pitch, rated 0.36 through 31 hp, and the N600 series is 3/4 inch pitch, rated 1.4 through 51 hp; they need no lubrication, resist corrosion and use stock sprockets. An N410 is the N400 series size 410 coupling. Complete couplings, replacement chain and covers are listed under chain couplings, and the rest of the line is on the Morse brand page.
What is a rigid coupling, and when is a sleeve coupling used?
A rigid coupling joins two shafts with no flexible element between them. Browning rigid couplings are machined from malleable castings for use with Browning Split Taper bushings, and a complete coupling is one body plus two bushings. A sleeve coupling is the simplest rigid form: a steel sleeve bored to both shaft ends.
Browning finished bore sleeve couplings, CS-04 through CS-22, are machined from bar steel and fitted with hollow head setscrews; sizes CS-10 and larger are also available with a standard keyseat, indicated by adding K to the part number, as in CS-12K. Bushed type sleeve couplings, CSH, CSP and CSQ, take Split Taper H, P1 and Q1 bushings respectively and are ordered with two bushings. The published torque ratings for both rigid and sleeve couplings are for normal service and are reduced by 50 percent for shock loads; the maximum torque is based on coupling strength, so a smaller shaft within the bore range may not transmit it and the shaft and key stress should be checked. Browning sleeve and rigid couplings are listed under rigid couplings; the Kop-Flex gear coupling lines also offer rigid and flex-rigid halves for floating shaft arrangements.