8/10/2019 Coupling and application.docx

http://slidepdf.com/reader/full/coupling-and-applicationdocx 1/4

2. COUPLING: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.2.1 PURPOSE OF COUPLING:

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 reducedmaintenance costs and downtime.

2.2 TYPES OF COUPLING:

Rigid Couplings Flexible Or Compensating Couplings

2.2.1 RIGID COUPLING:

A rigid coupling is a unit of hardware used to join two shafts within a motor ormechanical system. It may be used to connect two separate systems, such as a motor and agenerator, or to repair a connection within a single system. A rigid coupling may also be added

between shafts to reduce shock and wear at the point where the shafts meet.

2.2.2 FLEXIBLE COUPLING:

. Flexible couplings are used to transmit torque from one shaft to another when the twoshafts are slightly misaligned. Flexible couplings can accommodate varying degrees ofmisalignment up to 3° and some parallel misalignment. In addition, they can also be used forvibration damping or noise reduction.

Fig 2.1

8/10/2019 Coupling and application.docx

http://slidepdf.com/reader/full/coupling-and-applicationdocx 2/4

The aim of the flexible coupling is to transfer motion between two shafts on the same axis whilstaccounting for possible misalignments.

2.2.2a FUNCTIONS OF FLEXIBLE COUPLING:

The two basic functions of flexible coupling are, To transmit power. To accommodate misalignment.

TRANSMIT POWER

Couplings are used primarily transfer mechanical power from one machine to another so thatuseful work can be done. To the coupling, the power is in the form of mechanical torque atoperating speed, or work per unit of time, so the coupling is being “twisted” as it is spin at somehigh rpm. Torque is transferred into and out of the coupling at the equipment connection, usually

by shaft fits or flange fits.

MISALIGNMENT:

There are three types of misalignment and which the coupling must accommodate: angular,offset and axial. This is commonly caused by thermal growth of the machine casing and rotors asthey change between ambient and operating temperatures.

Angular misalignment is produced when the centre lines of the two equipment shafts thecoupling connects are not parallel and they intersect at an angle. Offset misalignment commonlycalled parallel offset, is when the two shaft centerlines are parallel and they do not intersect, theyare offset by some distance. Axial misalignment is caused by changes in the axial position of theshafts which moves the close to each other or further apart.

2.2.2b Types of Flexible Coupling:

The different types of flexible couplings are,

Flanged Pin Bush Couplings

Bibbly Coupling

Gear Tooth Coupling

Tyre couplings Elastomeric Couplings – This consists of jaw type and S-flex couplings.

Oldham’s Coupling

Universal Coupling or Hooke’s Coupling

Bellows Coupling.

8/10/2019 Coupling and application.docx

http://slidepdf.com/reader/full/coupling-and-applicationdocx 3/4

8/10/2019 Coupling and application.docx

http://slidepdf.com/reader/full/coupling-and-applicationdocx 4/4

crowned to allow for angular displacement between the two gears. Mechanically, the gears areequivalent to rotating splines with modified profiles. They are called gears because of therelatively large size of the teeth.

Fig 2.3

2.2.2d OLDHAM:An Oldham coupling has three discs, one coupled to the input, one coupled to

the output, and a middle disc that is joined to the first two by tongue and groove. The tongue andgroove on one side is perpendicular to the tongue and groove on the other. The middle discrotates around its center at the same speed as the input and output shafts. Its center traces acircular orbit, twice per rotation, around the midpoint between input and output shafts.

Fig 2.4a Oldham coupler, assembled Fig 2.4b Oldham coupler, disassembled