Protected flange coupling
The Protected Flange Coupling has two similar cast iron flanges, (left & right ) with the shape similar to the flanges in the 'flanged pipe joint'. But these flanges have keyways in the hubs, so that the ends of the shafts to be connected can be keyed to the flanges with separate rectangular sunk type keys.
Even the shafts also have keyways, which are assembled at right angles, so that the key of one shaft does not slide into the other. These keys are usually driven from inside faces of the flanges for easy fitting.
Here also, the faces of the flanges are kept at right angles to the axis for proper alignment. Now, to get the perfect alignment of shafts, one of the flanges may have a projected circular extension on the outside and thus the other flange will, have a corresponding slot / recess. This gives the flanges a perfect fit and this kind of arrangement being similar to the spigot and socket joint is termed as 'spigot and socket centring'. There may also be some clearance (gap) between this kind of fit, to adjust the shaft. The faces of the two flanges are then held together with the help of bolts and nuts (4 or more). These may be square headed or hexagonal headed. The bolts should be an exact fit, so that the power can be transmitted properly from one shaft and flange to another.
It can also be noticed, as shown in Fig. that the bolt and nuts lie inside the projected ring (shroud), that is why this flange coupling get the name as Protected Flanges Coupling.
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