- This article describes a mechanical connection between two things. For other meanings, see Coupling (disambiguation).
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 do exist torque limiting couplings which can slip or disconnect when some torque limit is exceeded.
Shaft couplings are used in machinery for several purposes, the most common of which are the following.
- 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.
Types of shaft couplings
Rigid couplings are used when precise shaft alignment is required; shaft misalignment will affect the coupling's performance as well as its life. Examples:
- Sleeve or muff coupling
- Clamp or split-muff or compression coupling
- Flange coupling
Flexible couplings are designed to transmit torque while permitting some radial and axial and angular misalignment. Flexible couplings can accommodate angular misalignment up to a few degrees and some parallel misalignment. Examples:
Torque limiting coupling
Torque limiting couplings, or torque limiters
, protect systems against overtorque conditions.
Requirements of good shaft alignment / good coupling setup
- it should be easy to connect or disconnect the coupling.
- it should transmit the full power from one shaft to other without losses.
- it does allow some misalignment between the two adjacent shaft roation axis.
- it is the goal to minimise the remaining misalignment in running operation to maximise power transmission and to maximise machine runtime (coupling and bearing and sealings lifetime).
- it should have no projecting parts.
- it is recommended to use manufacturer's alignment target values to set up the machine train to a defined non-zero alignment, due to the fact that later when the machine is at operation temperature the alignment condition is perfect
Tools to measure shaft axis alignment condition
- it is possible to measure the alignment with dial gages or feeler gages using various mechanical setups.
- it is recommended to take care of bracket sag, parallaxe error while reading the values.
- it is very convenient to use laser shaft alignment technique to perform the alignment task within highest accuracy.
- is it required to align the machine better, the laser shaft alignment tool can help to show the required moves at the feet positions.