subject: Connecting The Shafts For Transmission Of Power: Couplings [print this page] What is coupling? What is coupling?
Coupling is a device that connects two shafts together at their ends with the purpose of transmitting power. Couplings normally do not allow disconnection of shafts during operation, however there are torque limiting couplings which can slip or disconnect when some torque limit is exceeded.
To join two pieces of rotating equipment while permitting some degree of misalignment or end movement or both is the couplings primary purpose. By careful selection, maintenance and of installation couplings, substantial savings can be made in reduced maintenance costs and downtime.
What is gear coupling?
A gear coupling is a mechanical device for transmitting torque between two shafts that are not collinear. It consists of a flexible joint fixed to each shaft. The two joints are connected by a third shaft, called the spindle.
Each joint consists of a 1:1 gear ratio internal/external gear pair. The tooth flanks and outer diameter of the external gear are crowned to allow for angular displacement between the two gears. Mechanically, the gears are equivalent to rotating splines with modified profiles. They are called gears because of the relatively large size of the teeth.
Gear couplings and universal joints are used in similar applications. Gear couplings have higher torque densities than universal joints designed to fit a given space while universal joints induce lower vibrations. The limit on torque density in universal joints is due to the limited cross sections of the cross and yoke. The gear teeth in a gear coupling have high backlash to allow for angular misalignment. The excess backlash can contribute to vibration.
Gear couplings are generally limited to angular misalignments, i.e., the angle of the spindle relative to the axes of the connected shafts, of 4-5. Universal joints are capable of higher misalignments.
Single joint gear couplings are also used to connect two nominally coaxial shafts. In this application the device is called a gear-type or flexible coupling. The single joint allows for minor misalignments such as installation errors and changes in shaft alignment due to operating conditions. These types of gear couplings are generally limited to angular misalignments of 1/4-1/2.
What is half gear and full gear couplings?
It is generally observed that even with the most exacting precision in the original installation, subsequent misalignment can rarely be avoided over a period of time, foundations may settle, bearings ultimately wear and dimensions change with temperature.
The misalignment also takes place due to vibrations. These Flexible Geared Couplings are available in two configurations Full Geared and Half Geared Half Rigid.
Full Geared Coupling : Here both the halves of the Coupling are identical and consist of two Hubs and two outer Flanges Sleeves bolted together.
This type of Coupling is capable of accommodating both Offset as well as Angular misalignment.
Half Geared Half Rigid Coupling : Here instead of two identical halves one half is geared and the other half is rigid.
There is a single Hub in this type of Coupling since the other side is rigid. This type of Coupling is used for taking care of only Angular misalignment.
