COUPLINGS

ONUR ÇINAR09.11.2010

A coupling is termed as a device used to make permanent or semi-permanent connection where as a clutch permits rapid connection or disconnection at the will of the operator.

COUPLINGS – General Presentation

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Shaft couplings are used in machinery for several purposes the most common of which are following:-

1. To provide for the connection of shafts of units that are manufactured separately such as a motor and a generator, and to provide disconnection for repairs or alterations.2. To provide for misalignment of the shafts or to introduce mechanical flexibility.3. To reduce transmission shock loads from one shaft to another.4. To introduce protection against overloads.5. To alter the vibration characteristics of rotating units.

COUPLINGS – General Presentation

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Shaft couplings will be used under the following conditions:-

1. With shafts having collinear axes, that is, axes in the same straight line. Rigid or flexible couplings of various form used here.2. With shafts having intersecting axes. Universal Coupling is employed.3. With shafts whose axes are parallel and at a relatively small distance apart. Here the double slider crank principle of mechanism is used.

COUPLINGS – General Presentation

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There are two basic classes of couplings:

1.Rigid Coupling

2. Flexible Couplings

Type of COUPLINGS

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1. Rigid Slip Couplings

•This type of coupling has no flexibility or resilience, hence it is necessary for the shafts that are to be connected to be in good alignment, both laterally and angularity, in order excessive loads on the coupling, on the shafts, or on the shaft bearings.• Rigid couplings do not accommodate misalignment and consequently should not be used indiscriminately.

Type of COUPLINGS

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1. Rigid Slip Couplings

There is three types of Rigid Couplings:

1.1 Sleeve or muff coupling1.2 Clamp coupling1.3 Flange coupling

Type of COUPLINGS

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1.1 Sleeve or Muff CouplingsIt is the simplest type of rigid coupling, made of cast iron. It consists of a hollow cylinder whose inner diameter is the same as that of the shaft. It is fitted over the ends of the two shafts by means of a gib head key. The power is transmitted from one haft to the other shaft by means of a key and a sleeve. It is, therefore, necessary that all the elements must be strong enough to transmit the torque.

Type of COUPLINGS

Sleeve or Muff Coupling8

1.1 Sleeve or Muff Couplings

Type of COUPLINGS

Sleeve or Muff Coupling9

1.2 Clamp CouplingsClamp coupling is sometimes called a compression coupling or a ribbed coupling. This coupling is made in two parts which are machined to fit the shaft and are finished off around the periphery and on both ends. The two halves of the coupling are clamped tightly against the surface of the shaft ends by through bolts and the entire torsional moment is transmitted entirely by friction.

Type of COUPLINGS

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1.3 Flange Couplings

A flange coupling usually applies to a coupling having two separate cast iron flanges. Each flange is mounted on the shaft end and keyed to it. The faces are turned up at right angle to the axis of the shaft. One of the flange has a projected portion and the other flange has a corresponding recess. This helps to bring the shafts into line and to maintain alignment. The flange coupling is adopted to heavy loads and hence it is used on large shafting.

Type of COUPLINGS

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1.3 Flange Couplings

Type of COUPLINGS

Flange Coupling12

2. Flexible CouplingsThese couplings are rigid under torsion, but, allow the correction of errors in the alignment of drive shafts. They are widely used in the fields of robotics or automatisms, because they are excellent for very accurate system piloting. They are also known as "precision couplings«Flexible Couplings may be split into two categories from the stand point of design:

2.1 Rigid Slip Coupling2.2 Couplings With Incorporated Flexible Members

Type of COUPLINGS

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2.1 Rigid Slip Couplings

•Couplings whose flexibility is obtained kinematically by the use of rigid members in which constraint is absent in certain directions. This category of coupling can be used for any velocities and loads and cause comparatively small additional loads on shafts and bearings.•Type of rigid slip couplings are:-

– Oldham– Bellows Coupling– Universal Joint Couplings

Type of COUPLINGS

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2.1 Rigid Slip Couplings

Type of COUPLINGS

Oldham Coupling Bellows Coupling

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2.2 Couplings With Incorporated Flexible Member

•This type of coupling anticipates both misalignment and impact.

•Type of incorporated flexible couplings are:– Slip Type– Jaw Type– Bushed Pin Type

Type of COUPLINGS

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2.2.1 Slip Type Flexible Coupling

The object of slip coupling is to permit relative rotation, or slip , between the driving shaft and the driven shaft. A slip coupling is a safety device that prevents damage to rotating parts because of overloading . The slip coupling is adjusted so that it will begin to slip if the transmitted torsional moment exceeds a predetermined value. Usually the slip begins if the load exceeds by 10 to 20 percent the maximum load the shafts and other parts are designed.

Type of COUPLINGS

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Type of COUPLINGS

2.2.1 Slip Type Flexible Coupling

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2.2.2 Jaw Type Coupling

Type of COUPLINGS

Three Jaw Insert Coupling

Multi Jaw Coupling

Three-Jaw Insert couplings are used to provide quieter running and to minimize vibration.

Multi Jaw Couplings, light duty couplings have spider-ring design with a special elastomer insert.

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2.2.3 Bushed Pin Type

•The simplest and commonest type of coupling is the flexible rubber – bushed coupling. In the pin type coupling motion form one half flange is transmitted to the other half by mans of pins or bolts. The pins are rigidly bolted to one flange and loosely fitted in the corresponding holes of the other flange.•In the various designs this type of flexible coupling is extensively used, especially where the driving and driven units are mounted on a common base plate, where excessive misalignment is not likely, for example, a prime mover connected to a generator, a compressor connected to an electric motor, an electric motor connected to a centrifugal blower etc.

Type of COUPLINGS

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Type of COUPLINGS

2.2.3 Bushed Pin Type

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Different types of couplings offer different advantages and disadvantages:

Rigid couplings can accommodate almost no misalignment; should some misalignment occur, from assembly inaccuracy or from thermal expansion during operation, the use of rigid couplings can result in large reactive forces on support bearings.

Oldham couplings can accommodate large radial, small angular, and moderate axial misalignment; they offer good peak torque rating and torsional stiffness, homokinetic transmission (the driven side moves at the same speed as the driving side at all times), very low reactive forces, and low cost, and are a good all-around choice for a flexible coupling in most applications.

Jaw couplings offer the advantage of torsional vibration dampening. They accommodate large torques and small misalignments with low cost. They don't have good torsional stiffness, however, as some windup will occur.

COUPLINGS – General Presentation

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Different types of couplings offer different advantages and disadvantages:

Bellows couplings have a thin-walled flexible metallic element, and can accommodate large misalignments with low reactive forces, but are useful only for low torque, and have low torsional stiffness when measured at torques that approach the peak torque. Like the beam coupling, these are moderate-cost units that will eventually fatigue.

Gear, grid, and chain couplings are very robust designs meant for large shafts (over two inches in diameter), very high torques, and rough applications.

Pin-and-bushing couplings are large-diameter assemblies that accommodate small misalignments and offer small torsional dampening.

COUPLINGS – General Presentation

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