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Your quick guide to couplings, their benefits and uses

3 May 2021

Couplings come in many different varieties and with many benefits for industrial applications. Yet most of us don’t go the extra mile when it comes to selecting the right coupling for our given applications. We’ve made the endeavour a little easier for you, covering the different types, common roles and benefits of couplings – helping you optimally connect the dots – and shafts.  

What are couplings?

Couplings are devices used to connect two shafts at their ends to transmit power. Specifically, couplings are used to join two pieces of rotating equipment while allowing for some degree of misalignment or end movement. By connecting two shafts, the coupling enables the second shaft to also spin. Couplings can also serve to connect the ends of adjacent parts.

The uses of couplings vary, but a primary function is to transfer power from one end to another. Other uses include altering vibration characteristics of rotating units, connecting the driving and driven part, introducing greater protection, reducing transmission of shock loads between shafts and slipping when an overload occurs.

 Benefits and roles of couplings

  •    Transmit power. It’s difficult to manufacture a machine connected with a single shaft instead of using a coupling. Couplings main purpose is its drive function, connecting things to turn power into motion.
  •    Absorb mounting errors. It takes time to align the driveshaft to the driven shaft with precision. If the axes of two shafts are misaligned, extra force is repeatedly applied to surrounding parts, causing vibration and noise. This is where couplings can be used to absorb mounting errors, which can easily occur given errors in machining accuracy. Couplings can transmit power dynamically and accurately even when there is misalignment between shafts.
  •    Absorb vibration. Vibration and shock can be transferred to surrounding parts when using a machine. Couplings absorb vibration and shock to prevent damage and wear to motors and other components. 
  •    Stopping the transfer of heat. Couplings prevent heat transfer from, for example, a motor so that parts are not deformed or shifted from their correct positions from that heat.
Two aluminium coupling for efficient vibration damping
Aluminium couplings for efficient vibration damping on the stepper motors

Different types of couplings

Muff or sleeve coupling

Sleeve couplings are a thick hollow cylinder or pipe called sleeve or muff. The shaft fits perfectly into the sleeve, as it has been manufactured keeping the diameter of the shaft in mind. Both the shafts are then inserted into each side of the sleeve. Two or more threaded holes are provided into the sleeve as well as in the shaft’s end to prevent it from moving in a longitudinal direction when blots are inserted. Sleeve couplings are mainly used when shafts don’t require alignments and load capacity is light or medium.

Split muff coupling

In this type of coupling, the sleeve or muff isn’t a single different part, instead, it’s split into two. The muffs are semi-cylindrical in shape which fit over the shaft. Threaded holes are found on the muffs so that the shafts can be joined with studs or bolts. This type of coupling can be assembled or disassembled without changing the position of the shaft. Split muff couplings are often used in media and heavy-duty load applications with moderate speeds.

Flange coupling

Flange couplings are easy to manufacture and are similar to sleeve couplings. They have flanges on either side of the two sleeves. Both flanges consist of an equal number of threaded holes for bolting. The flanges are joined together with bolts and nuts. To ensure there is no slipping condition, a key section is also provided on the hub and shafts. Flange couplings are used in medium and heavy-duty applications.

Bush pin flexible coupling

This is often seen as an upgraded version of the flange coupling. The difference between them is the use of rubber bushings. Slightly thick rubber bushings are designed so that studs and bolts fit perfectly in the holes provided. This coupling can be used for slightly misaligned shafts. The rubber bushings also add flexibility to the coupling, allowing it to absorb shocks and vibrations. These couplings are used when there is a little angular, parallel, and axial misalignment. Bush pin-type couplings are used in medium-duty applications in machines and electric motors.

Gear coupling

Gear couplings are another modified version of the flange coupling. Here, the flange and hub are separate parts assembled instead of a single part as in a flange coupling. The hubs are externally splined, but they can be regarded as gear teeth due to being thick and deep. The flanges also have internal teeth. Gear couplings are used for heavy-duty applications where torque transmission requirements are higher.

Fluid coupling

Fluid couplings consist of two parts: a pump and a turbine. These have blades mounted inside at a certain angle. The turbine is mounted on the driven shaft whilst the pump is mounted on the end of the driver shaft. Fluid enters into the pump’s centre and when the drive shaft rotates, due to centrifugal force it is pushed outwards. Here the casing diverts the motion of fluid into the turbine and the turbine blades along with the turbine. This way, the turbine and pump make a coupling. Fluid couplings are used in marine and industrial applications where controlled start-up of the power transmission is essential.  

When choosing a coupling, here are some things to consider:

When it comes to finding the right coupling for you, it’s important to find the right type, size and style to help protect your pumps and motors, to avoid unnecessary wear and tear. Having confidence in the coupling you choose is essential as shafts are seldomly perfectly aligned and machines tend to vibrate. Shaft misalignment is one of the biggest factors to consider when choosing couplings for your machinery. 

Your couplings will be affected by other things like changes in temperatures, operating conditions, and movements in machinery. Therefore, you should always consider where your coupling will be working, taking into consideration what may affect them. Think of the operating temperature, the type of run cycles and whether your coupling will be exposed to elements like chemicals or minerals. 

Grid coupling installation showing alignment, grease application, spacing, and torque applied to bolts.
Grid coupling installation showing alignment, grease application, spacing, and torque applied to bolts.

To help you in your search, we suggest you consider these five things:

  1. The total horsepower of the motor
  2. The shaft and keyway size
  3. RPM at the coupling connection 
  4. The distance between the shaft ends
  5. Type of equipment used

Overall, your coupling should be capable of transmitting torque from the driving shaft to the driven shaft. It should align the shafts properly and be easy to dismantle for maintenance if needed, Lastly, it should provide safety to users and your machine in case of coupling failure. 

Popular coupling categories on Marketplace 

There’s a range of different couplings listed on Marketplace. Let the links below guide you or use the simple search tool on the site. Or why not take a short cut? View all couplings currently listed on Marketplace by clicking here.

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Brand or Seller Product name Manufacturer Code
UCIC Rubber Coupling Inse CPLS-FL-55
Tsubaki Tsubaki Coupling 174315
Ducker Ducker PLASTIC COUPLING B42 ART 04 11 1532011952
UCIC PUMP COUPLING FOR BU 18127409032
UCIC TOOTHED RING FOR COUPLING PART 8.74E+08
Rittal Rittal COUPLING OF CP-L RITTA CP 6525.010
Martin Martin STARCH COUPLING COVER  5016COV