Post on 12-Jul-2016
description
POINTS & CROSSINGS
-Goutham Sarang-
Points and Crossings
To help transfer trains from one track to another
parallel, diverging, or converging
Necessary since wheels train wheels have inside flanges and,
hence require to navigate on rails
Points or switches – divert vehicles
Crossings – provide gaps in rails, for flanged wheels to roll
over them
A complete set of P&C, along with lead rails – a turnout
Terms
Turnout – arrangement of P&C with lead rails, to divert rolling
stock from one track to another Direction – Right Hand TO, Left Hand TO
Tongue rail/ Switch rail – a tapered movable rail, with high-
carbon or -manganese steel to withstand wear.
thicker end (heel) - attached to a running rail
Stock rail – the running rail against which a tongue rail
operates
Terms
Points/ Switches – A pair of tongue and stock rails
Crossing – device introduced at junction where two rails cross
each other to permit wheel flange to pass from one track to
another
Facing direction – from toe of switch towards crossing;
opposite is Trailing direction
Facing point of TO – where trains pass over switches first and
then crossing; vice versa is Trailing point of TO
Check rails – Extra rails bent at both ends and placed parallel
to running rails to guide and provide a path to wheel flanges
Throw of switch – distance by which tongue rails move
laterally at toe of switch, for movement of trains
Turnout
Working
Changing Track
Points or Switches
Stock rails, AB & CD
with medium-manganese steel
Tongue/switch rails, PQ & RS
with medium-manganese steel
Machined to a very thin section to
obtain a snug fit with the stock rail
Tapered end - toe
Thicker end - heel
A pair of heel blocks –
hold heel of tongue rails at standard
clearance or distance from stock rails
Points or Switches
Slide chairs/ Sliding plates support tongue rail and enable its movement towards or away from stock rail
Two or more stretcher bars connect both tongue rails close to toe, for holding them at a fixed distance
from each other
Switch tie plate/ gauge tie plate fix gauges and ensure correct gauge at the points
Types of Switches
Stud switch No separate tongue rail, instead some portion of track is moved
from one side to other side
Simplest type
No more in use in IR
Split switch consist of a pair of stock rails and a pair of tongue rails
Two types on the basis of fixation at heel
• loose heel type and fixed heel type
Two types based on toe
• undercut and overriding
Types of Switches
Loose heel or Articulated type
Tongue rail finishes at heel of switch for movement of free end of tongue rail
Fish plates holding tongue rail may be straight or slightly bent
Tongue rail - fastened to stock rail using a fishing fit block and four bolts
Fish bolts in lead rail - tightened, but kept loose or snug in tongue rail to
allow free movement of tongue
As discontinuity of track at heel is a weakness, NOT preferred
Fixed heel or Spring or Flexible type
Tongue rail not ending at heel of switch, but extends further and is
rigidly connected
Movement at toe of switch due to flexibility of tongue rail
Can be hand operated or by rod from a lever
Types of Switches
Undercut switch Foot of stock rail is planed to accommodate tongue rail
Becomes weak since a flange portion is cut out
Types of Switches
Overriding switch Separate rail sections of stock and tongue rails
Instead of cutting flange – heavy stock rail and lighter tongue rail
sections
Stock rail - full section; Tongue rail - planed to a 6mm (0.25")
thick edge
Tongue rail rides over flange of stock rail
Types of Switches
Overriding switch – Modified
Tongue rail - kept 6mm
higher than stock rail
from heel to point
towards toe where
planing starts
To eliminate possibility
of splitting due to any
false flange moving in
trailing direction
Crossing or Frog Device introduced at point where two gauge faces cross each
other to permit the flanges of a railway vehicle to pass from
one track to another
Gap - from throat to nose of crossing, over which flanged
wheel glides or jumps
Crossing or Frog
Trailing
Crossing or Frog
2 rails: point rail and splice rail machined to form a
nose Point rail ends at nose
Splice rail joins it a little behind the nose
Point rail should end in a point and be as thin as possible, but
would break off
Point rail - fine end slightly cut off to form a blunt nose, with a
thickness of 6mm
Toe of blunt nose - actual nose of crossing (ANC)
Theoretical point where gauge faces from both sides intersect -
theoretical nose of crossing (TNC)
Crossing angle – < b/w gauge faces of point and splice rails
Heel of crossing – line joins ends of point and splice rails
Crossing or Frog
2 wing rails: a right-hand and a left-hand - converge to
form a throat and diverge again on either side of nose Flared at ends to facilitate entry and exit of flanged wheel in the gap
Toe of crossing – line joins ends of wing rails
Throat – narrow space b/w 2 wing rails
A pair of check rails
Guide wheel flanges and
provide a path for them
Prevent them from moving
sideways
Otherwise may result in wheel
hitting nose of crossing as it
moves in facing direction
Types of Crossings
Acute angle crossing or ‘V’ crossing – intersection of
two gauge faces forms an acute angle When a right hand rail of one track crosses a left hand rail of
another track or vice versa
Unlike rail crossings
A and C
Types of Crossings
Obtuse or diamond crossing – intersection of two
gauge faces meet at an obtuse angle When a right hand or left hand rail crosses a similar rail
B and D
Types of Crossings
Square crossing – two tracks cross at right angles rarely used in actual practice
Number and Angle of Crossing
Crossing - designated either by angle b/w the gauge
faces or by number of crossing (N) N = Spread at leg of crossing ÷ Length of crossing from TNC
Design of Turnout – Terms
T – Toe of Switch L – Heel of Switch
E – TNC M – Point on Turnout at heel
Method I – Coles Method
Design of Turnout
T – Toe of Switch L – Heel of Switch
E’ – TNC M – Point on Turnout at heel
Method I – Coles Method
Design of Turnout
T – Toe of Switch B – Heel of Switch
H – Toe of Crossing
Method II – IRS Method