1、Coupling,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.,Shaft couplings are used in machinery for several purposes the most common of which are following:1. To provide for t
2、he 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 anoth
3、er.4. To introduce protection against overloads.5. To alter the vibration characteristics of rotating units.,Shaft couplings will be used under the following conditions:1. With shafts having collinear axis, that is, axis in the same straight line, rigid or flexible couplings of various form are used
4、.2. With shafts having intersecting axis, a Universal Coupling is employed.3. With shafts whose axes are parallel and at a relatively small distance apart, the double slider crank principle ofmechanism is used.A shaft coupling should have the following requirements:1. It should be easy to connect or
5、 disconnect.2. It should transmit the full power of the shaft.3. it should hold the shafts in perfect alignment.4. It should have no projecting parts.,Sleeve Coupling It is the simplest type of rigid coupling, made of cast iron. It consists of a hollow cylinder whose inner diameter is the same as th
6、at of the shaft. It is fitted over the ends of the two shafts by means of a jib head key. The power is transmitted from one shaft 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.,Sleeve coupling,Rigid C
7、ouplings provide a connection between two perfectly aligned shafts.,Flange Coupling 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
8、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 two flanges are coupled together by means of bolts and nuts. The flange coupling is adopted to heavy loads and hence it is used on large shaftin
9、g.,Unprotected type flange coupling,Protected type flange coupling,It is nearly impossible completely to eliminate all chance misalignment between the shafts of separately built machines, and such misalignment of shafts always leads to eventual failure of bearings or fatigue failure of shafts. The r
10、elative position of the connected shafts, inaccurate at the outset due to inevitable errors of manufacturing, is in course of time aggravated by deformations caused by the working load, temperature fluctuations, the uneven sinking of foundations or supports, etc. In such cases ineffective rigid coup
11、lings are replaced by flexible couplings. Therefore the purpose of a flexible coupling is to allow for imperfect alignment of two joining shafts, or to absorb impact from the fluctuation of torsional moment or of angular speed.(因此，一个弹性联轴器的目的是允许两个连接轴的不完美的对齐，或吸收扭矩或角速度波动的冲击力。)These couplings are rigid
12、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,This flexible-disk couplin
13、g contains at least one disk attached at its outside to one of the two rotary parts connected therewith and is splined adjacent its inside periphery to the other of said parts. The splines let the disk expand naturally under centrifugal stress, independently of said other part. They have preferably
14、straight radical profiles, so that the increased expansion of the disk avoids backlash. The couplings may be used in pairs, as common-place, or also singly.The flexible disks are subjected to various stresses, of which the stress set up by centrifugal inertia is a major component. It is customary to
15、 rigidly weld the disks at their inner portion to one of the two parts connected by the coupling. The invention departs from this custom. It lets the disks expand naturally without being tied to the expansion of said one part. As this decreases the stress on the disks it enables them to carry increa
16、sed load.,Metallic Disk coupling,In cases where the angular or offset misalignment of the shaft reaches values which cannot be accommodated by flexible couplings, a different type, known as Hookes coupling or universal Flexible coupling can be applied to good advantage. It is named after Robert Hook
17、 , who developed the device. The universal coupling is used for two shafts whose center lines form a large angle , as 5 to 15 degrees, or even 30 degrees. The joint itself has no torsional flexibility nor can it accommodate any parallel misalignment. This coupling is widely used in agricultural mach
18、inery, machine tools and automobiles. It consists of two fork mounted on the shaft end, either with the help keys or screwed on the shaft ends. There is a center piece through which pass two pins whose axes are at right angles to each other.,Universal Flexible Couplings/ Hookes Couplings,A jaw coupl
19、ing is a type of motion control (servo) coupling designed to transmit torque (by connecting two shafts) while damping system vibrations, which protects other components from damage. Jaw couplings are composed of three parts: two metallic hubs and an elastomer insert called an element, but commonly r
20、eferred to as a spider. The three parts press fit together with a jaw from each hub fitted alternately with the lobes of the spider. The curved jaws of the hubs reduce deformation of the spider to maintain the zero backlash fit.,Jaw Type Couplings,Jaw Type Couplings,Jaw Type Coupling,Multi Jaw Coupl
21、ings, light duty couplings have spider-ring design with a special elastomer insert.,Three-Jaw Insert couplings are used to provide quieter running and to minimize vibration.,Doughnut Couplings,Elastomeric doughnut coupling, unclamped,Elastomeric doughnut coupling, clamped or restrain,Understanding c
22、oupling designs and limitations can help us to make a good selection. Every coupling has its limitations, which is why various coupling types are offered to fit industry applications.For example, if an application has high misalignments, then a flexible coupling would be required to compensate for a
23、nd absorb the anticipated misalignments without risking performance issues. Each coupling has permissible misalignment ratings that can compensate for difficult applications that cannot be fully aligned 100 percent. Motor and pump shaft end play is crucial and should not exceed the permissible axial
24、 misalignment rating of the chosen coupling. The fluctuation of axial misalignment can gradually fatigue the coupling and result in premature failure.,Understand the Coupling Design Needed,In vertical applications, evaluation is needed to ensure that the coupling is capable of supporting vertical we
25、ight. Special inserts can be designed to support such loading and prevent excessive compressive forces on the coupling. Distance Between Shaft Ends (DBSE) is the gap between the drive and driven shafts. Coupling spacers not only bridge larger DBSE gaps, but can also add misalignment capacity to the
26、coupling.Proper shaft engagement into the coupling hub is also critical whether it be a keyless frictional connection or keyed connection. Premature shearing of keys or hub slippage on keyless shafts can cause extensive damage and costly re-work.Choose a coupling with caution when using variable frequency drives. Checking maximum and minimum speed ratings is critical to ensure proper performance and longevity of the coupling.,
