Flexible Shaft Couplings

Flexible Shaft Couplings

A shaft coupling is a device that connects two shafts so they can transmit power. In ideal circumstances, two shafts are connected by a shaft coupling to form a straight line in order to transmit torque. However, two shafts can become out of line with each other over time as the result of poor installation, thermal growth or shrinkage, foundation movement, or component wear. Therefore, a flexible shaft coupling is needed to connect shafts that are slightly misaligned. There are three types of misalignment: parallel, angular, and axial. In parallel misalignment, two shafts are parallel but offset from one another. In angular misalignment, the shafts intersect at angles to each other. Axial misalignment is a more serious problem because it is a combination of both parallel and angular misalignment. The degree of misalignment a coupling can tolerate depends on its material and its application, but in general, up to 5° of misalignment can be tolerated. Flexible shaft couplings are used to connect drive shafts in automobiles; they isolate driveline vibration, propeller pulse, and gear chatter in motorized boats. Other industrial applications include use in printing machines, paper making machines, roll forming machines, hydraulic pumps, and wind turbines.

The most common materials for flexible shaft couplings in automobiles are stainless steel, which protects against corrosion and increases torque capacity and strength, and aluminum, which is a lighter and less expensive option. Certain types of flexible shaft couplings contain a central disk comprised of plastic or rubber that transmits torque. Flexible shaft couplings are cylindrical in shape, and vary depending on the different types and their functions. The Oldham coupling contains three pieces, two hubs and a central plastic disk. It accommodates slight parallel misalignment, while providing almost zero backlash. Backlash can be described as the amount of lost motion due to clearance or slackness when movement is reversed and contact is re-established. The Bellows coupling has two hubs and a thin walled metallic bellows and can accommodate all three types of misalignment. Single Beam couplings are usually made of a single piece of aluminum and have a system of spiral cuts that allow it to bend in order to accommodate angular misalignment. Multiple beam couplings consist of two to three overlapping beams that address problems of torsional rigidity. Jaw, or spider, couplings consist of two metallic hubs, each with a set of interlocking teeth, and a flexible rubber or plastic piece (the spider), in the shape of a star which fits between them. These couplings have zero backlash and function well at high speeds but do not tolerate a great deal of misalignment. A Single Disc coupling is composed of two hubs that bend to accommodate angular misalignment. The Double Disc coupling has two hubs that are connected by an additional center spacer that allows them to bend in opposite directions to manage offset shafts.