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Crosshead is used in horizontal steam engines for connecting the piston rod and connecting rod. The figure shows the part drawings of a steam engine crosshead. The crosshead, with the help of slide block 4, reciprocates between two guides provided in the engine frame. The gudgeon pin 3, connects the slide blocks with the crosshead block 1. This acts as a pin joint for the connecting rod (not shown in the figure). The piston rod 2 is secured to the crosshead block by means of the cotter 5. The assembly ensures reciprocating motion along a straight line for the piston rod and reciprocating cum oscillatory motion for the connecting rod.

It is used to prevent loss of fluid such as steam, between sliding or turning parts of machine elements. In a steam engine, when the piston rod reciprocates through the cylinder cover; stuffing box provided in the cylinder cover, prevents leakage of steam from the cylinder. The figure shows the various parts of a stuffing box. At the base of stuffing box body 1, a bush 3 is placed such that the bevelled edge of the bush is at the inner side of the body. Gland 2 is placed at the other end of the body and is connected to the main body by means of studs 4 and nuts 5. The space between the reciprocating rod and the bush and the gland is packed with a packing material such as mineral fibres, leather, rubber or cork.

Non-aligned couplings are used to transmit power between two shafts which are not coaxial. The following are the examples of non-aligned couplings. 1. UNIVERSAL COUPLING (HOOKE'S JOINT):  It is a rigid coupling that connects two shafts, whose axes intersect if extended. It consists of two forks which are keyed to the shafts. The two forks are pin joined to a central block, which has two arms at right angle to each other in the form of a cross. The angle between the shafts may be varied even while the shafts are rotating.

Disengaging couplings are used when power transmission from one shaft to another is intermittent. With this, the shafts can be engaged or disengaged as and when required, even during rotation. A disengaging coupling in general consists of one part firmly fixed to the driving shaft and another one mounted with provision for sliding over the driven shaft. The part that is mounted on the driven shaft, can be made to slide at will to engage or disengage from the rotating driving shaft. The following are the examples of dis-engaging couplings. 1. CLAW COUPLING:  In this, each flange has a number of identical claws which engage into the corresponding recesses in the flange. One flange is firmly fitted to the driving shaft by means of a taper sunk key. The other one is placed over the driven shaft by two feather keys, so that it can slide freely on it. The sliding flange has a groove on the boss, into which the forked end of a lever fits. By operating the lever, the sliding flange m...

Perfect alignment of two shafts is impossible to achieve and difficult to maintain, because of inevitable bearing wear and other reasons. To overcome the trouble, flexible couplings are employed. These permit relative rotation or variation in the alignment of shaft axes within certain limits. The following are the types of flexible couplings. 1. BUSHED-PIN TYPE FLANGED COUPLING:  It is the modified version of a protected flanged coupling. In this, bolts are replaced by bushed pins. The smaller ends of the pins are rigidly fastened by nuts to one of the flanges, while the enlarged ends are covered with flexible material like leather or rubber bushes, in the other flange. The flexible medium takes care of misalignment, if any, and acts as a shock absorber. These couplings are used to connect prime mover or an electric motor and a centrifugal pump.

These are the standard forms of couplings, most extensively used. In a flanged coupling, flanges are either fitted or provided at the ends of shafts. The flanges are fastened together by means of a number of bolts and nuts. The number and size of the bolts depend upon the power to be transmitted and hence, the shaft diameter. There are two types of  Flanged Couplings. 1. FLANGED COUPLING WITH DETACHABLE FLANGES : In this, two flanges are keyed, one at the end of each shaft, by means of sunk keys. For ensuring correct alignment, a cylindrical projection may be provided on one flange which fits into the corresponding recess in the other. In the design shown in figure, the bolt heads and nuts are exposed and liable to cause injury to the workman. Hence, as a protection, the bolt heads and nuts may be covered by providing an annular projection on each flange. A flanged coupling, using these flanges is called a protected flanged coupling.

This is the simplest of all couplings. It consists of a sleeve called muff, generally made of cast iron, which is fitted over the ends of the shafts to be connected. After properly aligning the keyways in the shafts and sleeve, a sunk key is driven-in; thus making the coupling. Instead of a single key running the entire length of the sleeve, it is desirable to use two keys, which may be inserted from the outer ends of the sleeve; thus overcoming the possible misalignment between the keyways. The following are the types of muff couplings along with their animation videos. 1.  BUTT MUFF COUPLING: In this, the ends of the two shafts to be coupled butt against each other, with the sleeve keyed to them, as discussed above. 2. HALF-LAP MUFF COUPLING: In this, the ends of the shafts overlap each other for a short length. The taper provided in the overlap prevents the axial movement of the shafts. Here too, after placing the muff over the overlapping ends of the shafts, a sa...

Shaft couplings are used to join or connect two shafts in such a way that when both the shafts rotate, they act as one unit and transmit power from one shaft to the other. Shaft couplings are classified as four types. Rigid Couplings Flexible Couplings Disengaging Couplings Non-aligned Couplings In this post, I am going to give an idea about each type and few examples.