# Coupling

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A coupling is a device used to connect two shafts together at their ends for the purpose of transmitting power. Couplings do not normally allow disconnection of shafts during operation, however there are torque limiting couplings which can slip or disconnect when some torque limit is exceeded.

The primary purpose of couplings is to join two pieces of rotating equipment while permitting some degree of misalignment or end movement or both. By careful selection, installation and maintenance of couplings, substantial savings can be made in reduced maintenance costs and downtime.

## Contents

### Uses

Shaft couplings are used in machinery for several purposes, the most common of which are the following.[1]

• To provide for the connection of shafts of units that are manufactured separately such as a motor and generator and to provide for disconnection for repairs or alternations.
• To provide for misalignment of the shafts or to introduce mechanical flexibility.
• To reduce the transmission of shock loads from one shaft to another.
• To introduce protection against overloads.
• To alter the vibration characteristics of rotating units.

### Rigid coupling

Rigid couplings are used when precise shaft alignment is required; shaft misalignment will affect the coupling's performance as well as its life. Examples:

### Flexible coupling

Flexible couplings are designed to transmit torque while permitting some radial, axial, and angular misalignment. Flexible couplings can accommodate angular misalignment up to a few degrees and some parallel misalignment. Examples:

• Universal joint or Cardan joint
• Oldham coupling
• Constant-velocity joint
• Bellows coupling — low backlash.
• Elastomeric coupling
• Bushed pin coupling
• Donut coupling
• Spider or jaw coupling (or lovejoy coupling)
• Resilient coupling
• Disc coupling, by definition, transmits torque from a driving to a driven bolt tangentially on a common bolt circle. Torque is transmitted between the bolts through a series of thin, stainless steel discs assembled in a pack. Misalignment is accomplished by deforming of the material between the bolts.
• Diaphragm coupling transmits torque from the outside diameter of a flexible plate to the inside diameter, across the spool or spacer piece, and then from inside to outside diameter. The deforming of a plate or series of plates from I.D. to O.D accomplishes the misalignment.
• Gear coupling
• Hirth joint
• Roller chain and sprocket coupling
• Fluid coupling