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DEPARTMENT OF MECHANICAL ENGINEERING VIi-semester MACHINE DESIGN- III CHAPTER NO.1 COUPLING & FLYWHEEL

CHAPTER 1:- SYLLABUS . Types of shaft coupling, design of flange coupling 1 Flexible bush coupling , Flywheel 2 Coefficient of fluctuation of energy and speed 3 Energy store in flywheel 4 Stresses in flywheel, design of flywheel 5 DTEL 3

CHAPTER-1 SPECIFIC Objective / course outcome The student will be able to: The function of couplings in machinery. 1 Different types of couplings: rigid and flexible couplings. 2 Types of rigid couplings such as sleeve, clamp, ring compression type and flange couplings. 3 DTEL 4

Introduction LECTURE 1:- COUPLING Couplings are used to connect two shafts for torque transmission in varied applications. It may be to connect two units such as a motor and a generator or it may be to form a long line shaft by connecting shafts of standard lengths say 6-8m by couplings. Coupling may be rigid or they may provide flexibility and compensate for misalignment. They may also reduce shock loading and vibration. A wide variety of commercial shaft couplings are available ranging from a simple keyed coupling to one which requires a complex design procedure using gears or fluid drives etc. However there are two main types of couplings: Rigid couplings Flexible couplings. 5 DTEL 5

Introduction LECTURE 1:- COUPLING Shaft couplings are used in machinery for several purposes, the most common of which are the following : 1. To provide for the connection of shafts of units that are manufactured separately such as a motor and generator and to provide for repairs or alternations. 2. To provide for misalignment of the shafts or to introduce mechanical flexibility. 3. To reduce the transmission of shock loads from one shaft to another. 4. To introduce protection against overloads. 5. It should have no projecting parts. 6 DTEL 6

Fig-Types of misalignments in shafts LECTURE 1:- COUPLING RIGID COUPLINGS Since these couplings cannot absorb any misalignment the shafts to be connected by a rigid coupling must have good lateral and angular alignment. The types of misalignments are shown schematically in figure. Fig-Types of misalignments in shafts DTEL 7

THANK YOU LECTURE 5:- FLYWHEEL LECTURE 1:- COUPLING DTEL 8

LECTURE 2:- COUPLING Flange coupling DTEL Flange coupling - It is a very widely used rigid coupling and consists of two flanges keyed to the shafts and bolted. This is illustrated in figure. FIG-FLANGE COUPLING DTEL 9

Design procedure of rigid flange coupling LECTURE 2:- COUPLING Design procedure of rigid flange coupling Consider a flange coupling as shown in above Fig. Let d = Diameter of shaft or inner diameter of hub, D = Outer diameter of hub, d1 = Nominal or outside diameter of bolt, D1 = Diameter of bolt circle, n = Number of bolts, tf = Thickness of flange, τs, τb and τk = Allowable shear stress for shaft, bolt and key material respectively τc = Allowable shear stress for the flange material i.e. cast iron, σcb, and σck = Allowable crushing stress for bolt and key material respectively. The flange coupling is designed as discussed below : DTEL 10

Design procedure of rigid flange coupling LECTURE 2:- COUPLING Design procedure of rigid flange coupling 1. Design for hub The hub is designed by considering it as a hollow shaft, transmitting the same torque (T) as that of a solid shaft. The outer diameter of hub is usually taken as twice the diameter of shaft. Therefore from the above relation, the induced shearing stress in the hub may be checked. The length of hub (L) is taken as 1.5 d. 2. Design for key The key is designed with usual proportions and then checked for shearing and crushing stresses. The material of key is usually the same as that of shaft. The length of key is taken equal to the length of hub. 3. Design for flange The flange at the junction of the hub is under shear while transmitting the torque. Therefore, the torque transmitted, T = Circumference of hub ×Thickness of flange × Shear stress of flange × Radius of hub The thickness of flange is usually taken as half the diameter of shaft. Therefore from the above relation, the induced shearing stress in the flange may be checked. DTEL 11

Design procedure of rigid flange coupling LECTURE 2:- COUPLING Design procedure of rigid flange coupling 4. Design for bolts The bolts are subjected to shear stress due to the torque transmitted. The number of bolts (n) depends upon the diameter of shaft and the pitch circle diameter of bolts (D1) is taken as 3 d. We know that From this equation, the diameter of bolt (d1) may be obtained. Now the diameter of bolt may be checked in crushing. We know that area resisting crushing of all the bolts = n × d1 × tf and crushing strength of all the bolts = (n × d1 × tf ) σcb DTEL 12

THANK YOU DTEL 13

BUSHED-PIN FLEXIBLE COUPLING LECTURE 3:- COUPLING BUSHED-PIN FLEXIBLE COUPLING DTEL 14

BUSHED-PIN FLEXIBLE COUPLING LECTURE 3:- COUPLING BUSHED-PIN FLEXIBLE COUPLING A bushed-pin flexible coupling, as shown in Fig.is a modification of the rigid type of flange coupling. The coupling bolts are known as pins. The rubber or leather bushes are used over the pins. The two halves of the coupling are dissimilar in construction. A clearance of 5 mm is left between the face of the two halves of the coupling. There is no rigid connection between them and the drive takes place through the medium of the compressible rubber or leather bushes. In designing the bushed-pin flexible coupling, the proportions of the rigid type flange coupling are modified. The main modification is to reduce the bearing pressure on the rubber or leather bushes and it should not exceed 0.5 N/mm2. In order to keep the low bearing pressure, the pitch circle diameter and the pin size is increased. DTEL 15

BUSHED-PIN FLEXIBLE COUPLING LECTURE 1:- COUPLING LECTURE 3:- COUPLING BUSHED-PIN FLEXIBLE COUPLING Let l = Length of bush in the flange, d2 = Diameter of bush, pb = Bearing pressure on the bush or pin, n = Number of pins, and D1 = Diameter of pitch circle of the pins. We know that bearing load acting on each pin, W = pb × d2 × l ∴ Total bearing load on the bush or pins = W × n = pb × d2 × l × n and the torque transmitted by the coupling, The threaded portion of the pin in the right hand flange should be a tapping fit in the coupling hole to avoid bending stresses. The threaded length of the pin should be as small as possible so that the direct shear stress can be taken by the unthreaded neck. Direct shear stress due to pure torsion in the coupling halves, DTEL 16

LECTURE 3:- COUPLING LECTURE 1:- COUPLING THANK YOU DTEL 17

LECTURE 4:- FLYWHEEL DTEL A flywheel used in machines serves as a reservoir which stores energy during the period when the supply of energy is more than the requirement and releases it during the period when the requirement of energy is more than supply. In case of steam engines, internal combustion engines, reciprocating compressors and pumps, the energy is developed during one stroke and the engine is to run for the whole cycle on the energy produced during this one stroke. For example, in I.C. engines, the energy is developed only during power stroke which is much more than the engine load, and no energy is being developed during suction, compression and exhaust strokes in case of four stroke engines and during compression in case of two stroke engines. The excess energy developed during power stroke is absorbed by the flywheel and releases it to the crankshaft during other strokes in which no energy is developed, thus rotating the crankshaft at a uniform speed. A little consideration will show that when the flywheel absorbs energy, its speed increases and when it releases, the speed decreases. Hence a flywheel does not maintain a constant speed, it simply reduces the fluctuation of speed. DTEL 18

THANK YOU DTEL 19

The following types of stresses are induced in the rim of a flywheel: LECTURE 5:- FLYWHEEL STRESSES IN A FLYWHEEL The following types of stresses are induced in the rim of a flywheel: 1. Tensile stress due to centrifugal force, 2. Tensile bending stress caused by the restraint of the arms, and 3. The shrinkage stresses due to unequal rate of cooling of casting. These stresses may be very high but there is no easy method of determining. This stress is taken care of by a factor of safety. The following types of stresses are induced in the arm of a flywheel: 1. Tensile stress due to centrifugal force acting on the rim. 2. Bending stress due to the torque transmitted from the rim to the shaft or from the shaft to the rim. 3. Shrinkage stresses due to unequal rate of cooling of casting. These stresses are difficult to determine. DTEL 20

Design of Flywheel Arms LECTURE 5:- FLYWHEEL LECTURE 1:- FLYWHEEL Design of Flywheel Arms DTEL 21

Design of Shaft, Hub and Key LECTURE 1:- FLYWHEEL Design of Shaft, Hub and Key DTEL 22

LECTURE 5:- FLYWHEEL LECTURE 1:- FLYWHEEL THANK YOU DTEL 23

1) Mechanical Design of Machine Maleev, Hartman References Books: 1) Mechanical Design of Machine Maleev, Hartman 2) Machine Design P.H. Black 3) Mechanical Engg. Design Shigley 4) Design Data book B.D. Shiwalkar 5) Design of Machine Elements V. B. Bhandari 6) Design of Machine Elements (Theory & Problems) B.D. Shiwalkar DTEL 24