VARDHAMAN COLLEGE OF ENGINEERING(Autonomous)Shamshabad, Hyderabad-501218.

DESIGN OF MACHINE MEMBERS-I

LECTURE NOTES by

D.V.RAMANAREDDYASSISTANT PROFESSORMECHANICAL ENGINEERING DEPARTMENTUNIT-VII

SYALLABUS:

SHAFT COUPLING : Rigid couplings Muff, Split muff and Flange couplings. Flexible couplings Flange coupling (Modified).

Instructional Objectives:

The focus is on blending fundamental development of concepts with practical specification of components

The objectives of the text are to:

1. Cover the basics of machine design, including the design process, Engineering mechanics and materials, failure prevention under static and variable loading, and characteristics of the principal types of mechanical elements. (PEO 2)1. Offer a practical approach to the subject through a wide range of real world applications and examples. (PEO 1,2)1. Encourage readers to link design and analysis. (PEO 2)1. Encourage readers to link fundamental concepts with practical component specification. (PEO 2)

At the end of this lesson, the students should be able to understand: 1. Ability to design of shaft couplings2. Ability to understand the stresses in design of shaft couplings

DESIGN OF SHAFT COUPLINGA 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.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 reduced maintenance costs and downtime.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 provide for misalignment of the shafts or to introduce mechanical flexibility. To reduce the transmission of shock loads from one shaft to another. To introduce protection against overloads. To alter the vibration characteristics of rotating units. To connect driving and the driven part

A rigid coupling is a unit of hardware used to join two shafts within a motor or mechanical system. 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. A rigid coupling may also be added between shafts to reduce shock and wear at the point where the shafts meet.When joining shafts within a machine, mechanics can choose between flexible and rigid couplings. While flexible units offer some movement and give between the shafts, rigid couplings are the most effective choice for precise alignment and secure hold. By precisely aligning the two shafts and holding them firmly in place, rigid couplings help to maximize performance and increase the expected life of the machine. These rigid couplings are available in two basic designs to fit the needs of different applications. 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. 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.Clamped or compression rigid couplings come in two parts and fit together around the shafts to form a sleeve. They offer more flexibility than sleeved models, and can be used on shafts that are fixed in place. They generally are large enough so that screws can pass all the way through the coupling and into the second half to ensure a secure hold.Flanged rigid couplings are designed for heavy loads or industrial equipment. They consist of short sleeves surrounded by a perpendicular flange. One coupling is placed on each shaft so the two flanges line up face to face. A series of screws or bolts can then be installed in the flanges to hold them together. Because of their size and durability, flanged units can be used to bring shafts into alignment before they are joined together. Rigid couplings are used when precise shaft alignment is required; shaft misalignment will affect the coupling's performance as well as its life. Examples:Sleeve couplingA sleeve coupling consists of a pipe whose bore is finished to the required tolerance based on the shaft size. 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. Two threaded holes are provided in order to lock the coupling in position.Sleeve couplings are also known as Box Couplings. In this case shaft ends are coupled together and abutted against each other which are enveloped by muff or sleeve. A gib head sunk keys hold the two shafts and sleeve together

Clamp or split-muff couplingA 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.Rigid Sleeve Coupling Suitable for joining any two shafts when flexibility not required Consists of a one piece sleeve, with two set screws Applications include: light to medium duty applications

A Sleeve Coupling consists of a pipe whose bore is finished to the required tolerance based on the shaft size. 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. Two threaded holes are provided in order to lock the coupling in position. Sleeve couplings are also known as Box Couplings. In this case shaft ends are coupled together and abutted against each other which are enveloped by muff or sleeve. A gib head sunk keys hold the two shafts and sleeve together.

These couplings cannot take much misalignment hence are preferred on long shafts which can absorb stress. In sleeve coupling two shafts screw into a single connecting piece. To remove sleeve coupling shaft needs to be moved.Flexible Coupling: Can take shaft misalignments and are of many types. Some are shown below

Rigid CouplingFlange locked onto each shaft. One flange with recess and the other with matching spigot. Flanges bolted together to form rigid coupling with no tolerance for relative radial, angular or axial movement of the shafts.

Muff CouplingLong cylindrical coupling bored and keyed to fit over both shafts. Split axially and clamped over both shafts with recessed bolts. Rigid coupling for transmitting high torques at high speeds

Pin CouplingAs rigid coupling but with no recess and spigot and the Bolts replaced by pins with rubber bushes. Design allows certain flexibility.

Flexible Rubber disc CoupingAs rigid coupling except that a thick rubber disc bonded between steel plates is located between the flanges. The plates are bolted to the adjacent coupling flanges.

DESIGN

design a pin bushed flexible couplingto draw a pin bush flexible coupling the given data will be dia of shaft d to be joined in mm,power P to be transmitted in kw ,no. of revolution N in rpm,bearing pressure pb in n/mm2,allowable shear stress in shaft,keys,flange t in N/mm2 and allowable stress in pin s.STEP 1.

find torqueT=(P*60)/(2*3.14*N) in N-m

cange it in N-mm by multiplying 1000.

Check suitability of shaft dia by

(d')3=[(16*t)/(3.14*t)]

if d'