Power Transmission

Definition:- Power transmission is the movement of energy from its place of generation to a location where it is applied to perform useful work.

For power transmission, many of the mechanical devices can be used which are as follows:-

  1. Belt drive
  2. Gear drive
  3. Rope drive
  4. Chain drive

In the coming section we shall be discussing on the belt drive and gear drive extensively.

Belt drive

Belt drives are called flexible machine elements. Flexible machine elements are used for a large number of industrial applications, some of them are as follows.
1. These are used in the conveying systems for example Transportation of coal, mineral ores etc. over a long distance
2. Also used for the transmission of power. Mainly used for running of various industrial appliances using prime movers. like electric motors, I.C. Engine etc.
3. Replacement of rigid type power transmission system. A gear drive may be replaced by a belt transmission system.

Types of Belt drives

Depending upon the shape of the cross-section, belts are classified as-

  1. Flat belts– Have narrow cross section
  2. V-Belts-Have trapezoidal cross section

Flat Belts

Two types of belt drives, an open belt drive and crossed belt drive are used. In both the drives, a belt is wrapped around the pulleys. Let us consider the smaller pulley to be the driving pulley. This pulley will transmit motion to the belt and the motion of the belt in turn will give a rotation to the larger driven pulley. In open belt drive system the rotation of both the pulleys is in the same direction, whereas, for crossed belt drive system, opposite direction of rotation is observed.

Nomenclature of Open Belt Drive

NPTEL
figure-Open belt drive

dL – Diameter of the larger pulley
dS – Diameter of the smaller pulley
αL– Angle of wrap of the larger pulley
αS – Angle of wrap of the smaller pulley
C- Center distance between the two pulleys

Basic Formulae
αL = 180ο + 2β
αS = 180ο – 2β

Where angle β is,

β=sin-1(dL-dS)/2C

L0 = Length of open belt

L0=π/2  (dL+dS) +2C +1/4C  (dL-dS)2

Nomenclature of Cross Belt Drive

NPTEL
Figure-Cross belt drive

dL – Diameter of the larger pulley
dS – Diameter of the smaller pulley
αL– Angle of wrap of the larger pulley
αS – Angle of wrap of the smaller pulley
C- Center distance between the two pulleys

Basic Formulae
α L = α S = 180ο + 2β

Where angle β is,

β=sin-1(dL-dS)/2C

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