Railway operation and control

Railway operation and control

POINTS AND CROSSINGS

• Points, crossings, turnouts and cross-overs are arrangements by which different routes either parallel or diverging are connected
• Allows the trains to move from one track to another
• also used in marshalling and shunting work in station yards.

• Turnout is a simplest combination of points and crossings which enables one track to takeoff to another track

NECESSITY OF POINTS AND CROSSINGS

• Points and crossings provide flexibility of movement by connecting one line to another
• Also helps in imposing restrictions over turn outs

Heel divergence or heel clearance

• Distance between the running faces of the stock rail and gauge face of the tongue rail when measured at the heel of the switch
• Kept equal to flange way clearance plus tolerance for the wear plus the width of head of rail

• B.G Heel clearance = 13.7 cm to 13.3 cm
• M.G Heel clearance = 12.1 cm to 11.7 cm
• N.G Heel clearance = 9.8 cm

Flange way clearance

• Distance between adjacent faces of the stock rail and the tongue rail

Flange way depth

• Vertical distance between the top surface of the running rail (or stock rail) to the top surface of heel block used between the stock rail and the tongue rail

Flare

• Gradual widening of the flange way which is formed by bending or splaying the end of a check rail or wing rail away from the gauge line.
• This is provided to guide the path so that the flange wheels enter and leave the track smoothly.

Crossing

• Device which provides two flange ways through which the wheels may move, when two rails intersect each other at an angle
• Flange wheels of the train jump over the gap from throat to the nose of crossing.

Requirements of good crossing

• The assembly of crossing has to be rigid
• In order to prevent the wear, nose should be made of special steel alloy
• Crossing body should be rigid and long
• Nose of the crossing should have some thickness, varying from 6mm to 8mm components of a turnout

Types of crossings

1.Acute angle crossing or V crossing

2.Obtuse angle crossing or Diamond crossing

3.Square crossing

Switch angle

• Angle of switch divergence
• Angle between running faces of the stock rail and tongue rail
• Switch angle= heel divergence/Length of tongue rail

Throw of switch

• Distance through which the toe of the tongue rail moves sideways (with heel of tongue rail as the centre of rotation) to provide a path for the desired direction over the turn out
• 9.5 cm for B.G.
• 8.9 cm for M.G and N.G.

• Point of intersection of the running face of the splice rail and the point rail is called the nose of the crossing
• The actual intersection of both the rails is called the T.N.C
• The nose of crossing provided in the rail in practice is called A.N.C

Distance between ANC and TNC

n = N x t

where n is the distance between ANC and TNC

N is the crossing number

t is the thickness of the nose of crossing

Crossing Number (N)

• Crossings are designated in terms of the distance required in spreading the point and splice rails by 305 mm.
• Spread is measured between the gauge faces of the rails and the distance is measured from theoretical nose of crossing.

Crossing Angle

• Angle formed between the gauge faces of the crossing

Methods to determine N

1.Right angle or Cole’s method

• Used by Indian Railways
• Main line and branch line form a right angled triangle with angle of crossing as α
• tan α = 1/N

i.e. N = cot α

2. Isosceles triangle method

• Main line and branch line is expressed in form of an isosceles triangle with angle of crossing as α
• sin (α/2) = 1/2N

i.e. 2N = cosec (α/2)

3. Centre line method

• The horizontal distance is N
• tan (α/2) = 1/2N

i.e. 2N = cot (α/2)

Switch lead (SL)

• It is the distance from the springing of the crossing curve to the heel of the switch, the distance measured along the straight

Different type of leads

• Switch lead
• Curve lead
• Lead

Curve lead (CL)

• It is the distance from the springing of the crossing curve to the theoretical nose of the crossing, the distance being measured along the straight

Lead (L) = curve lead (CL)- switch lead (SL)

• It is the distance from the heel of the switch to the theoretical nose of the crossing, distance measured along the straight.