Month: December 2019

# Switch Angle in Railway & Depends On What?

## Switch Angle in Railway

Switch angle or angle of switch divergence is defined as the angle formed between the gauge lines of the stock rail and tongue rail(Switch rails).

If the switch angle is more, the entry of the train will not be smooth and consequently, the speed of the train will have to be reduced. On the other hand, a small switch angle will increase the overall length of the turnout.

Hence, small switch angles are provided in the case of fast-moving trains. But, in the case of slow-moving trains or station yards, a greater switch angle is recommended.

The switch angle depends on the length of tongue rails and heel divergence, which is given below:

Case:1 When the thickness of tongue rails at toe = 0

Let,

• d = Heel divergence
• D = Length of tongue rail
• $\theta$ = Switch Angle

Now, from the above Fig.

$\sin \theta$ = (heel divergence / Length of tongue rail) = $\frac{d}{D}$

Switch Angle = $\theta$ = $\sin ^{-1}\frac{d}{D}$

Case:2 When the thickness of tongue rails at toe = t

Let,

• t = Thickness of tongue rail at toe
• $D_{1}$ = Actual length of tongue rail
• $D_{2}$ = Theoretical length of tongue rail
• x = Difference between $D_{1}$ and $D_{2}$

From the above equation and fig, we can write

• Actual Length of tongue rails $D_{1}$= $\frac{ ( d – t ) }{ \sin \theta }$
• Theoretical Length of tongue rails $D_{2}$ = $\frac{d}{ \sin \theta }$

Now, x = ( $D_{2}$ – $D_{1}$ ) = $\frac{t}{ \sin \theta }$

Types of Rails

Bending of Rails on Curves

# Bending of Rails on Curves – Railway Engineering

## Bending of Rails on Curves

Curves of less than 3 degrees are considered to be flat curves and in this case, rails can be kept in curved position by sleepers which are maintained in place by the ballast.

The curvature greater than 3 degrees are considered to be a sharp curve. In order to correct the curvature, it is desirable to bend the rails.

Otherwise, the side thrust on ballast at the ends of the sleepers due to the rail which acts as a spring, that is sufficient to form elbows and disturb the alignment of the track.

The amount by which the rail is to be bent can be easily found out as shown in Fig.

• AB = v = Rise of rail at center
• PB = BQ = c = One-half of the chord length
• R = Radius of the curve

Now we can write,

AB ☓ BZ = PB ☓ BQ

v ☓ (2R-v) = c ☓ c

2Rv – v2 = c2

v = c2 / 2R [ Neglecting v2 , as this will be very small]

### Mathematics Example:

Example: For a 12 m rail length to be laid on a 4 degree curvature

Solution: Here, 12 m rail length means the total length of the chord. So, the value of c will be 6 m ( c = One-half of the chord length).

v = c2 / 2R

Where, R = (1719/4)

v = 0.0418 m = 4.18 cm = 42 mm (approximately)

Creep of Rails

Types of Rails

# Size and Section of Ballast in Railway

## Size of Ballast

The size of the ballast used in railway tracks varies from 1.9 cm to 5.1 cm. A stone of size larger than 5.1 cm is not preferable due to its poor interlocking property.

The best-recommended ballast is that which contains stones ranging in size from 1.9 cm to 5.1 cm.

The size of the ballast mainly depends upon the type of sleeper used and the location of the rail track. The following sizes of ballast are used in Indian Railway:

## Section of Ballast

The section of the ballast layer consists of depth of ballast below the sleeper and the width of the ballast layer.

### Depth of Ballast

The depth of the ballast section is an important factor as the load-carrying capacity and distribution of traffic load on formation depend much on it. The more the depth of ballast under the sleeper more will be the load-carrying capacity of the track.

For curves tracks, more ballast is required than straight tracks, because of providing superelevation. The minimum depth of ballast is calculated from the following equation:

Minimum Depth of Ballast = D = (S-W)/2

Where S = Sleeper Spacing and, W = Width of Sleeper

The minimum depth of ballast prescribed on Indian Railway is 20 mm

### Width of Ballast

The width of the ballast section is also an important factor as the lateral stability of the track depends partly on the quantity of ballast at the end of sleepers.

The lateral stability increases with the increase in width of the ballast section up to a certain limit(380 to 430mm from the end of the sleeper).