Power transmission couplings are used to connect two shafts that turn in the same direction on the same centerline. There are three principal types of couplings; rigid, flexible, and special purpose.
Rigid couplings are used in applications where misalignment is not a factor, where flexibility is not required, and where the coupling is not required to absorb load shocks or torque changes. Rigid couplings connect shafts using bolted flanges, keyed sleeves or ribbed clamps bolted together over the shaft ends with keyways. Rigid couplings are used primarily for vertical drive systems. Lubrication is not required, but larger couplings, or those running at high speeds, may require balancing to reduce vibration.
Flexible couplings also connect two rotating shafts but are designed to dampen vibration, absorb some shock loading, and provide some axial movement or end float of the shafts, as well as compensate for minor misalignment.
There are three fundamental categories of flexible couplings; “mechanically flexible,” such as gear and chain couplings, “material flexible,” such as disc, spring, diaphragm, elastomeric and bellows and “combination,” such as metallic grid couplings, that provide a combination of mechanical and material flexibility.
Special purpose couplings include such devices as mechanically flexible “U joints” and “constant velocity joints” used for automobile applications, “magnetic couplings,” such as magnet to magnet and eddy current couplings, and “fluid couplings,” such as liquid, silicone, and shot filled types. Magnet and fluid couplings provide “no contact” between drive and driven elements, offer low maintenance and both are capable of absorbing shock loads.