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8.1 INTRODUCTION

Power is transmitted from one end to the othercommonly by means of shafts. If the distancebetween the two ends is large (say 810 m), itwould be inconvenient and expensive to have onesuch long length of shaft both from manufacturingand transport point of views. Hence, it is

recommended to connect a number of pieces bymeans of suitable couplings to transmit powerfrom one end to the other.

Shaft couplings may be broadly classified as1. Rigid or fast couplings.2. Flexible couplings.

3. Loose or disengaging couplings.

4. Couplings for shafts out of alignment.

8.2 RIGID OR FAST COUPLINGSThis type of couplings provide rigid connectionbetween the two shafts without permitting anyrelative motion between them. The importanttypes of rigid couplings are1. Unprotected type flanged coupling.

2. Protected type flanged coupling.

3. Solid or forged flanged coupling.4. Muff couplings.

5. Compression coupling.1. Unprotected Type Flanged CouplingIt consistsof two similar cast iron flanges to which the shafts

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are keyed with the help of taper keys. After drivingthe keys the flanges are turned up true with the

shaft axis by turning on a lathe. The machined

flanges are then tightly held together by exactfitting bolts in the holes. Fig. 8.1 shows a typicalrigid unprotected type flanged coupling.

2. Protected Type Flanged Coupling

Hereeach flange is provided with annular projection forcovering bolt heads and nuts. This prevents boltsand nuts from catching the clothes of workmen

and thus ensures their safety. A spigot and socketis provided in the middle of the flanges for exactcentring. Such a coupling is shown in Fig. 8.2.

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4. Muff CouplingIn muff or sleeve couplingshown in Fig. 8.4, the ends of the two shafts to becoupled butt against each other and a cast iron

muff or sleeve envelops them. A gib

headed sunkkey is provided to hold the sleeve and the shaftstogether, thus forming a rigid coupling.

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In halflap muff coupling shown in Fig. 8.5, theends of the two shafts overlap each other for a

small distance. The taper of the lap is 1:12. A

hollow saddle key is used to keep the muff andshafts in position. This is an efficient coupling butis expensive.

In the splitmuff coupling shown in Fig. 8.6, themuff is splitted up in two semicylindrical halveswhich are held together by means of square

headed

bolts and nuts. Two halves of the muff arerecessed to accommodate the bolt

heads and nuts. The coupling is done by a featherkey. The adyantage of this

coupling is that it can be placed directly anywhereon the shaft.

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5. Compression CouplingThis coupling shownin Fig. 8.7 does not require any key for holding theshafts and the coupling together. It consists of a

steel sleeve of double conical form which forms thecasing for the two ends of the mating shafts. Thesleeve has six saw-cuts equally spaced round its

circumference, one saw-cut running from one endto the other while the other cut runs alternatelyfrom either end to within 25 mm of the opposite

end. Over the sleeve is mounted cast iron flangedcoupling having the same taper as the sleeve. Thegripping of the couplings is brought about bymeans of bolts and nut and in turn the split sleeve

grips the shaft tightly.

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8.3 FLEXIBLE COUPLING

Flexible couplings are used where slight relativemovement is required or the axis of shafts runslightly out of line. Pin-type coupling shown in Fig.8.8 is the most commonly used flexible coupling.

Here the motion from one half of the coupling to

the other half is imparted with the help of drivingpins rigidly bolted to one flange and loosely fitting

corresponding holes in the other. Brass bush andrubber covering is provided on the driving pins forabsorbing shocks and as insulators.

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8.4 LOOSE OR DISENGAGING COUPLINGIn these couplings the shafts may be coupled

together or disengaged when required, even duringrotation.

1. Claw CouplingA three jaw claw coupling is

shown in Fig. 8.9. These are often used for

slow running main driving shafts. One of theshafts is keyed fast to one flange of thecoupling while the other flange slides along afeather on the second shaft. It has a groove in

the boss in which the forged end of a leverfits. The engagement of the two halves of thecoupling is easily brought about by means ofprojecting jaws.

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1. Cone Friction ClutchIn this coupling shown in Fig. 8.10, the shafts are coupled togetherdue to friction between two conical surfaces of the flanges. The engagement ordisengagement is done by sliding the flange on the driven shaft.

1. Dog ClutchIt is another type of clutch suitable for slow machinery as shown in Fig. 8.11.Here power is transmitted due to the engagement of dogs.

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8.5 COUPLINGS FOR SHAFTS OUT OF ALIGNMENT1. Oldham CouplingThis coupling shown in Fig. 8.12 is used for connecting shafts whose axes areparallel but not in one line. The ends of the two shafts are

keyed to their respective cast iron flanges. The flanges have grooves cut across their inner faces. Acylindrical piece having two projections, generally known as tongues, situated at right angles to eachother is inserted in between the flanges. The tongues slide in the recess across the flanges andtransmits power.2. Hookes or Universal CouplingThis type of coupling is used to connect two shafts whose axesintersect. In this coupling shown in Fig. 8.13, to each end of the shaft is secured two similar forks.The coupling consists of a central block having two arms at right angles to one another. The forksare pin jointed to this central block.

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Example 8.1 Fig. 8.14 shows the two views of an unprotected type flanged coupling. Draw thefollowing views on full scale:

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1. Right half sectional front view (b) Side view

Solution : The views are shown in Fig. 8.15.

Example 8.2 Fig. 8.16 shows the two views of a protected type flanged coupling. Drawthe following views on full scale:

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(a) Front view lower half in section (b) Side viewSolution: The views are shown in Fig. 8.17.

Example 8.3: Fig. 8.18 shows the two views of a pin type flexible coupling. Draw thefollowing views on full scale

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1. Right half sectional front view (b) Side view

Solution : The views are shown in Fig. 8.19.

Example 8.4 From the orthographic detail of Fig. 8.20 of two jaw claw clutch, drawfollowing views..

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1. Front view full in section. (b) Right end view.

Solution : The views are shown in Fig. 8.21.