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

Railway operation and control
Railway operation and control

 

  • 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.

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