Rigid couplings are the most basic but often the most cost-effective types of couplings. These couplings are used to connect two aligned shafts at their ends to transmit power. In the case of these couplings the shafts provide a fixed union between each other where torsional flexibility is not required, shaft alignment is maintained and proper bearing support is provided. They have many advantages, including simple structure, easy assembly, convenient maintenance, low cost, high torque capacity, torsional stiffness, and zero backlashes. Rigid couplings are available in different configurations. In this article, we are going to discuss the different types of rigid couplings. Follow this new blog in Linquip to find out more.
Types of Rigid Couplings
Rigid couplings are characterized as belonging to one of the following categories:
- Flange Couplings
- Sleeve / Muff Couplings
- Sleeve Couplings With Taper Pins
- Clamp / Ribbed / Split Muff / Compression Couplings
- Ring Compression Couplings
- Set Screw Couplings
- Spline Couplings
Flange Couplings
Flange couplings are widely used rigid couplings to connect shafts of the same or different diameters. The flange-style couplings consist of two separate flanged hubs, bored and keyed to fit their respective shafts and joined by bolted pattern. On one flange there will be a projected part called a pilot or spigot on the other flange there will be a corresponding recess to make the perfect alignment for both flanges. Some may include removable bushing or spacer to allow for the removal of a mechanical seal and easier replacement.
These couplings can be helpful to bring the shaft to maintain the alignment and are also capable to adopt heavy loads. Flange couplings are normally utilized in pressurized piping systems and funneling frameworks where two pipes or tubing closes need to meet up.
- Usually are made of carbon steel
- Available to over 8” in diameter
- Mostly designed for heavy-duty applications
- Can be used on the large shafts
- Suitable for alignment accuracy, for example, marine applications
- The gasket is used to eliminate leakage
Sleeve / Muff Couplings
Sleeve or muff couplings are the simplest type of rigid couplings. These couplings consist of a hollow cylindrical sleeve keyed to the shafts to be connected.
There is a keyway in the sleeve to couple the drive shaft with the sleeve and to the driven shaft with the help of a gib-headed key. Shaft keys transmit torque from the shaft to the coupling hubs, and the sleeve transmits the torque from one shaft to the other. It is important to design the sleeve and the key properly. The key design is usually based on shear and bearing stresses.
The outer diameter of the sleeve should be 2 times the diameter of the shaft + 13mm additional on diameter and the length of the sleeve should be 3.5 times the shaft diameter. There is an important thing to note that to install this coupling, the drive shaft or the driven shaft position needs to be changed.
These couplings are used when the two shafts are perfectly aligned. For high power transmission or high speeds, these sleeves coupling are not recommended. The sleeve coupling transmits low to medium torque between connected equipment in shear through an elastomeric insert.
- Simple and compact construction
- General-purpose applications
- Cannot accommodate any misalignment
- Cheaper compared to other types of couplings
- Cannot absorb shock and vibration
- Difficult to assemble and dismantle
- Torsional dampening
- End float with slight axial clearance
- Safe to use since it has no projecting parts
Sleeve Couplings with Taper Pins
Sleeve Coupling with Taper Pins
Torque transmission from one shaft to another is done using pins.
This device finds a use for applications that involve repairing gears pulleys on the shaft. The taper allows to align or locking pulleys, sprockets, or toothed couplings to a transmission shaft, quickly and without the use of equipment.
These types of rigid couplings feature simple axial and radial shaft positioning, and slot elimination. The taper allows an elastic recovery of tolerances and can be re-used after a replacement. No re-boring is necessary, as a broad range of both inch and metric bores are available. On light-duty applications, pins are not needed. Tapers with short lengths enable and allow for maximum bore increase.
- The taper is equipped with a bore and keyway.
- Easy to install and remove
- Simple maintenance requirements
- Maximum angular misalignment: 3°
- Maximum offset misalignment up to .04″
- Space required to remove bushing with short key
Clamp / Ribbed / Split Muff / Compression Couplings
Clamp couplings also called Ribbed coupling Split Muff coupling or Compression coupling, are used to connect shafts of the same diameter. Ribbed rigid couplings are axially split to clamp (two half-cylinders) on the ends of the shafts, coupled and held together by the mild steel studs or bolts. The coupling uses one key over the entire length.
- Quick and easy installation and removal
- Can be used for heavy-duty and moderate-speed applications
- No need to change the position of the shafts for assembling or disassembling
- The number of bolts may be 4, or 8 (Multiples of four)
- The bolts are placed in recesses formed in the sleeve halves
- Can be applied to inline shaft in power transmission
Ring Compression Couplings
Rigid couplings are also available in a ring compression configuration. These couplings consist of two cones that are placed on the shafts to be coupled and a sleeve that fits over the cones. Three bolts are used to draw the cones towards each other and thus wedge them firmly between the shafts and the outer sleeve.
Set Screw Couplings
These couplings consist of a cylinder that is secured to the shaft by set screws that impinge upon the shaft. Set screw couplings are also available with a keyway for keyed shafts for additional torque capacity. They are designed to provide torque transmission and alignment. Compared to other types of rigid couplings, set screw couplings are the most cost-effective option.
The precise design of bores on the set screw is important for applications such as servo systems and mixers because it allows for more surface contact with the shaft and higher torque transmission capabilities. With set-screw couplings, keyways are necessary for torque transmission, thus the phase relationship between coupled shafts cannot be changed.
- It can loosen under vibration
- Set screws can leave dents or dimples in the shaft or keyway
Spline Couplings
The spline couplings are similar to the sleeve or muff coupling but instead of the keyway, they have a number of slots on the inner diameter of the sleeve. The sleeve inner side and the shaft outer side will have the same profile slots with the same number of them. Spline couplings are often used in power transfer systems to connect mechanical components such as shafts, flanges, brakes, clutches, pulleys, sprockets, and gears.
- Equally distributed load along the circumference
- Small installation size
- Transfer of rotational concentricity
- A little Angular misalignments accommodation
- Can allow for radial misalignment accommodation
- Suitability for high rotation speeds
- Relatively insensitive to overloading