A coupling connects two rotating shafts to transmit power while allowing for some misalignment. There are many types of couplings including sleeve, flange, gear, and flexible couplings. A bearing supports rotating machinery and reduces friction by facilitating only the desired motion. Common types of bearings include ball, roller, thrust ball, and roller thrust bearings.

1. Coupling
A coupling is a device used to connect two shafts together at their ends
for the purpose of transmitting power.
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2. 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.
In a more general context, a coupling can also be a mechanical device
that serves to connect the ends of adjacent parts or objects.[1]
Types of coupling:
1-Sleeve or muff coupling
It is the simplest type of rigid coupling, made of cast iron.
It consists of a hollow cylinder whose inner
diameter is the same as that of the shaft. It is fitted over the ends of
the two shafts by means of a gib
head key. The power is transmitted from one haft to the other shaft
by means of a key and a sleeve. It is, therefore, necessary that all
the elements must be strong enough to transmit the torque.

3. 2- flange coupling:
A flange coupling usually applies to a coupling having two separate cast iron
flanges. Each flange is mounted on the shaft end and keyed to it. The faces are
turned up at right angle to the axis of the shaft. One of the flange has a
projected portion and the other flange has a corresponding recess.

4. There are three type of flange coupling:
a-Unprotected type flange coupling
b- protected type of flange coupling

5. c- Marine type flange coupling
3- Gear coupling
Gear couplings transmit the highest amount of torque and the highest
amount of torque in the smallest diameter of any flexible coupling.
Each coupling consists of two hubs with crowned external gear teeth. The hubs
mesh with two internally splined flanged sleeves that are bolted together. Gear
couplings accommodate angular and axial misalignment by the rocking and
sliding of the crowned gear teeth against the mating sleeve teeth. Parallel
misalignment is accommodated by having two adjacent hub/sleeve flex points.
Gear couplings require periodic lubrication depending on the application.

6. 4- flexible coupling
a flexible coupling is used to join the abutting ends of shafts when they are not
in exact alignment. In the case of a direct coupled drive from a prime mover to
an
electric generator, we should have four bearings at a comparatively close
distance. In such a case and
in many others, as in a direct electric drive from an electric motor to a machine
tool, a flexible
coupling is used so as to permit an axial misalignment of the shaft without
undue absorption of the
power which the shaft is transmitting. Following are the different types of
flexible couplings
a-Bushed pin flexible coupling
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

7. 2- Oldham coupling
It is used to join two shafts which have lateral mis-alignment. It consists of two
flanges A and B
1with slots and a central floating part Ewith two tongues T
2and T
3-Universal (or Hooke’s) Coupling
A universal or Hooke’s coupling is used to connect two shafts whose axes
intersect at a small
angle. The inclination of the two shafts may be constant, but in actual practice,
it varies when the
motion is transmitted from one shaft to another. The main application of the
universal or Hooke’s
coupling is found in the transmission from the gear box to the differential or
back axle of the
automobiles

8. Bearing
A bearing is a machine
element that constrains relative motion to only the desired motion, and
reduces friction between moving parts. The design of the bearing may, for
example, provide for free linear movement of the moving part or for free
rotation around a fixed axis; or, it may prevent a motion by controlling the
vectors of normal forces that bear on the moving parts. Most bearings
facilitate the desired motion by minimizing friction. Bearings are classified
broadly according to the type of operation, the motions allowed, or to the
directions of the loads (forces) applied to the parts.
Types of Rolling Contact Bearings:

9. 1- Ball bearings
ball bearing is a type of rolling-element bearing that uses balls to maintain
the separation between the bearing races.
The purpose of a ball bearing is to reduce rotational friction and support
radial and axial loads. It achieves this by using at least three races to
contain the balls and transmit the loads through the balls. In most
applications.
2- Roller bearing
•Roller Bearings, in which cylinders are used instead of spheres, increasing the
contact area so that it holds a greater radial load.
Suitable for high radial loads and medium to high speeds
3-Thrust ball bearing
The thrust ball bearings are used for carrying thrust loads exclusively and at
speeds below 2000

10. r.p.m. At high speeds, centrifugal force causes the balls to be forced out of the
races. Therefore, at
high speeds, it is recommended that angular contact ball bearings should be used
in place of thrust ball bearing.
•4-Roller Thrust Bearings
•which can support large thrust loads. Tapered Roller Bearings can
support large radial and thrust loads.