CH_11_BME_Couplings.pptx used for design and analysis

Couplings , bme, function and application

1. Couplings & Flanges

2. Introduction Couplings : A coupling is a device used to connect two shafts together at their ends for the purpose of transmitting power. The primary purpose of couplings is to join two pieces of rotating equipment while permitting some degree of misalignment or end movement or both. 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.

3. Uses Shaft couplings are used in machinery for several purposes, the most common of which are the following. To provide for the connection of shafts of units that are manufactured separately such as a motor and generator and to provide for disconnection for repairs or alterations. To reduce the transmission of shock loads from one shaft to another. To provide for misalignment of the shafts or to introduce mechanical flexibility. To introduce protection against overloads.

4. Requirements of a good shaft coupling A good Shaft coupling should have the following requirements: 1: It should be easy to connect and disconnect. 2: It should transmit the full power from one shaft to the other shaft without losses. 3: It should hold the shaft in perfect alignment. 4: It should reduce the transmission of shock loads from one shaft to another.

5. Types Shaft couplings are divided into two main groups, as follows: 1: Rigid Couplings 2: Flexible Couplings 1: Rigid Couplings: these are used to connect two shafts which are perfectly aligned. It may be used to connect two separate systems, such as a motor and a generator, or to repair a connection within a single system. Rigid couplings do not offer any kind of relative misalignment between the shafts.

6. Merits & demerits of rigid couplings Merits 1: Rigid couplings are the most effective choice for precise alignment and secure hold. 2: Rigid couplings help to maximize performance and increase the expected life of the machine . 3: These type of couplings are easy to manufacture. Demerits: 1: They do not allow any relative motion b/w the two shafts. 2: They can only be used for co-axial shafts.

7. Types of rigid couplings Sleeve or Muff Couplings : Sleeve-style couplings are the most affordable and easiest to use . They consist of a single tube of material with an inner diameter that's equal in size to the shafts. The sleeve slips over the shafts so they meet in the middle of the coupling . Based on the usage of the coupling a keyway is made in the bore in order to transmit the torque by means of the key. A series of set screws can be tightened so they touch the top of each shaft and hold them in place without passing all the way through the coupling.

8. Clamp or split muff coupling A clamp coupling is different from the sleeve coupling in that the sleeve used in this type is split from one side. The shafts are entered and keyed to this sleeve and then split sides are screwed together . This coupling is also called compression coupling because the two halves of the sleeve compresses the shaft

9. Flanged Coupling A flange coupling is usually applies to a coupling having two separate cast iron flanges. Each flange is mounted on a shaft end and keyed to it. The faces are turned up at right angles to the axis of shaft. One of the flange has a projected portion and other flange has a corresponding recess. This helps to bring the shaft into line and to maintain alignment. The two flanges are coupled together by means of nuts and bolts. The flange couplings are used where the shafts are acted upon heavy loads because they provide a very good strength

10. Flexible Couplings As clear from the name, a flexible coupling is used to join the shafts which are not in exact alignment i.e. when there is a clearance is required for axial misalignment. Flexible couplings can accommodate varying degrees of misalignment up to 3° and some parallel misalignment . In addition, they can also be used for vibration damping or noise reduction . Merits: They allow some angular misalignment of shafts which reduces the chances of breaking of shaft. They can absorb the shocks more effectively as compared to rigid couplings due to their flexibility.

11. Types of flexible couplings A  beam  coupling, also known as  helical  coupling, is a flexible coupling for transmitting torque between two shafts while allowing for angular misalignment, parallel offset and even axial motion, of one shaft relative to the other . This design utilizes a single piece of material and becomes flexible by removal of material along a spiral path resulting in a curved flexible beam of helical shape.

12. Oldham’s Coupling 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 and groove on one side is perpendicular to the tongue and groove on the other. The middle disc rotates around its center at the same speed as the input and output shafts. Its center traces a circular orbit, twice per rotation, around the midpoint between input and output shafts.

13. Universal Joint A universal or Hooke’s coupling is used to connect two shafts whose axes intersect at a small angle. The inclination of the two shafts may be constant, but in actual practice , it varies when the motion is transmitted from one shaft to another. The main application of the hooke’s coupling is found in the transmission from gear box at one end and the differential on the other end. As shown in figure, body 1 can rotate about axis 2 and body 2 can rotate about axis 1.

14. A Universal Joint

15. Flanges Introduction: A   flange  is an external or internal ridge, or rim (lip), for strength, as the flange of an iron beam such as an I-beam or a T-beam; or for attachment to another object, as the flange on the end of a pipe, steam cylinder, etc., or on the lens mount of a  camera ; or for a flange of a rail car or  tram wheel . Thus flanged wheels are wheels with a flange on one side to keep the wheels from running off the rails. The term "flange" is also used for a kind of tool used to form flanges. Pipes with flanges can be assembled and disassembled easily.

16. Uses They are used to increase the strength of a joint because they provide an extra contact area for the joint. They are easy to connect or disconnect in comparison of direct abutted joint. They prevent leakage more effectively in applications where a gas flows through pipelines.

17. Types of flanges Weld neck flange: This flange is circumferentially welded into the system at its neck which means that the integrity of the butt welded area can be easily examined by radiography. The bores of both pipe and flange match, which reduces turbulence and erosion inside the pipeline. The weld neck is therefore favored in critical applications.

18. Slip on flange This is a simple kind of flange in which pipes are connected directly by slipping it into the flange and welding it. This flange is slipped over the pipe and then fillet welded . Slip-on flanges are easy to use in fabricated applications .

19. Threaded Flange This flange is referred to as either threaded or screwed. It is used to connect other threaded components in low pressure, non-critical applications. As there are Threads cut on the inside surface of the flange, no welding is required.

20. Blind Flange Blind Flanges are manufactured without a bore and used to blank off the ends of piping, Valves and pressure vessel openings. From the standpoint of internal pressure and bolt loading, blind flanges, particularly in the larger sizes, are the most highly stressed flange types. However , most of these stresses are bending types near the center, and since there is no standard inside diameter, these flanges are suitable for higher pressure temperature applications.  

21. Application of Blind flange in piping

22. Lap Joint Flange Lap Joint Flanges have all the same common dimensions as any other flange named on this page however it does not have a raised face, they used in conjunction with a "Lap Joint Stub End“. A Stub End always will be used with a Lap Joint flange, as a backing flange. This flange connections are applied, in low-pressure and non critical applications, and is a cheap method of flanging.

23. Thank you! 