Inspection and Maintenance of Points and Crossings

Points and crossings should be inspected in detail, as the quality of a train ride greatly depends on their maintenance. The following important points should be checked.

Condition of tongue rails and stock rails There should be no wear on the top as

well as the gauge face side of the tongue rail. Badly worn out rails should be replaced. It should be ensured that the turnout side stock rail is provided with the requisite bend ahead of the toe of the switch; otherwise the alignment at this spot is bound to be kinky.

Condition of fittings of tongue and stock rails The fittings should be tight and the spherical washers must be placed at their correct locations. The slide chairs should be cleaned and greased with graphite for smooth operation of the points. The fish plates should be provided with the correct amount of bend at the loose heel joint. A gauge tie plate should be added if provisions for the same have not been made.

Gauge and cross level at switch assembly The gauge and cross levels should be checked for correctness at the following locations: (i) the stock joint, (ii) 150 mm (6") behind the toe of the switch, (iii) the mid-switch for the straight track and for the turnout side, and (iv) the heel of the switch for the straight track and for the turnout side.

Clearance between stock and tongue rails at the heel of the switch The correct divergence to be provided at heel of the switch should be as follows:

1 in 16 or 1 in 12 1 in 8.5

BG133 mm (5.25") 120 mm (4.25")

MG117 mm (4.65") 120 mm (4.75")

Throw of the switch The throw of the switch should be as follows

Recommended Minimum

BG 115 mm (4.5") 95 mm (3.25")

MG 100 mm (4") 89 mm (3.5")

Condition of crossing and tongue rail The condition of the crossings and of the fittings should be checked. The maximum vertical wear permitted on a point or wing rail is 10 mm and these should be reconditioned when the wear is 6 mm. The burn burrs should also be removed and the fittings should be tightened. The maximum vertical wear permitted on a tongue rail is 6 mm, whereas the permitted lateral wear is 8 mm for 90 R and 52-kg rails and 5 mm for 60 R and 75 R rails. The tongue rail should be replaced or reconditioned before this value is reached. The Railway Board has recently decided that the maximum vertical wear on wing rails and the nose of the crossings should be limited to 4 mm on the Rajdhani and Shatabdi routes and 6 mm on all other routes. The wear limits for CMS crossings are, however, 5.5 mm for Rajdhani and Shatabdi routes and 7.5 mm for all other routes.

Gauge and cross level of crossing assembly The gauge and cross level should be checked at the following locations and should always be correct: (i) 1 m ahead of the nose on straight tracks and on turnouts, (ii) 150 mm (6") behind the ANC on straight tracks and on turnouts, and (iii) 1 m behind the ANC on straight tracks and on turnouts.

Check rails The condition of check rails should be ascertained. Check rail clearances should be as follows:

Maximum Minimum

BG 48 mm 44 mm

MG 44 mm 41 mm

Lead curvature The curvature should be checked either by the offset method or by the versine method. The curvature should be correct and uniform.

Cross levels on straight tracks and turnouts The cross levels on straight tracks and turnouts should be checked to see that they are correct at all places.

Sleepers The condition of the sleepers and their fittings should be checked and unserviceable sleepers should be replaced. The squaring and spacing of sleepers should be proper and they should be well packed.

Ballast and drainage Enough quantity of ballast should be available so as to provide an adequate cushion. The drainage should be proper.

Any other defects If there are any other defects in the layout, these should be checked and corrected.

Special attention is required to ensure that the sleepers are well packed, all fittings are tightened, gauge and cross levels are properly maintained, and the wear on the tongue rail as well as on the crossing is within permissible limits. It should also be ensured that proper distance blocks are provided at correct locations. The schedule of inspection followed on Indian Railways is given in Table 14.7.

PWI (permanent

Once in 3 months in rotation for passenger lines and once in

way inspector)

6 months in rotation for other lines. The interval between two

III and PWI

inspections for passenger lines of the same turnout should not

(in charge)

exceed 4 months

AEN (assistant

Once in 12 months for all passenger lines and test checking of

engineer)

10% of other points and crossings

DEN (divisional

Test checking of certain number of points and crossings,

engineer)

particularly in running lines and those recommended for renewals

Summary

A turnout is an integral part of a railway track. It is a combination of lead rails and points and crossings. These are provided when two tracks are to be connected or when a branch line is to be introduced. The various features and designs of a turnout have been discussed in this chapter. Design examples have also been included. It is possible to have various types of track junctions with different combinations of points and crossings. These are described in Chapter 15.

Review Questions

1. Design a turnout for a BG track if the number of the crossing is 12 and the heel divergence is 114 mm. Assume a simple circular curve from the toe of the switch to the TNC.

2. Draw a neat sketch of a right-hand turnout taking off from a straight broad gauge track and name thereon the various component parts and important terms connected with the layout. Show the disposition of the sleepers.

3. A turnout is to be laid off a straight broad gauge track with a 1 in 12 crossing. Determine the lead and radius for the turnout given the following data heel divergence d = 133 mm, the straight length between the TNC and the tangent point of the crossing curve, h = 1.418 m, crossing angle a = 445 '49", and switch angle b = 19'00".

4. Draw a neat sketch of a left-hand turnout and name its various components. Describe any one method of designing a turnout and give the detailed procedure for calculating the (a) lead, (b) radius, and (c) heel divergence.

5. Calculate the elements required to set out a 1 in 8.5 turnout taking off from a straight BG track, with its curve starting from the heel of the switch and ending at a distance of 864 mm from the TNC, given that the heel divergence is 136 mm and the switch angle is 1 34'27". Make a freehand sketch showing the values of the calculated elements.

6. Explain with the help of neat sketches the points and crossings used in railways, indicating the precautions to be taken while laying the same.

7. On a straight broad gauge track a turnout takes off at an angle of 6 42'35''. Design the turnout when it is given that the switch angle is equal to 1 34'27'' and the length of the switch rails is 4.73 m. The heel divergence is 11.43 cm.

The straight arm is 0.85 m long.

8. Draw a neat sketch of a crossover between two parallel straight MG tracks spaced at 5 m centre-to-centre distance. Show the position of the switches as they would be when trains would be diverted from one track to the other. Also show the following particulars on the sketch of the crossover: (a) overall length of turnout, (b) overall length of the crossover, (c) any two wing rails, (d) any two check rails, (e) any two stock rails, (f) any two switch rails, (g) two heel blocks, (h) one pull rod.

9. Calculate all the necessary elements for a 1 in 12 turnout taking off from a straight BG track, with its curve starting from the toe of the switch, i.e., tangential to the gauge face of the outer main rail and passing through the TNC, given that the heel divergence is 11.4 cm.

(a) Find the crossing angles of the 1 in 12 crossing using the right angle method.

(b) Draw a labelled section for the points at the toe of the switch.

10. A crossover is to be laid connecting two BG parallel tracks spaced 4.5 m apart. Assuming that 1 in 8.5 crossings are to be used, work out the various details required for setting out the crossover.

11. Calculate the principal dimensions required to connect a parallel siding to a main line with the help of a 1 in 8.5 turnout, the spacing between these BG parallel tracks being 6 m c/c. For a 1 in 8.5 crossing the detailed dimensions are as follows: theoretical length of switch rail = 4950 mm, actual length of switch rail = 4725 mm, heel divergence = 136 mm, distance between the ends of the switch and stock rails = 840 mm, distance between TNC and the first distance block (tangent point) at the toe of the crossing = 864 mm. Draw a detailed dimensioned sketch for this turnout connecting two parallel tracks and label therein the various parts of the turnout.

12. Find the crossing angles for a 1 in 12 crossing using the centre line method.

13. What are the standard turnouts prescribed on Indian Railways? What are the special fittings that are provided with turnouts and what are their functions?

14. When is it necessary to recondition worn out crossings? Describe in detail one of the methods of reconditioning a crossing.

15. What are the various points required to be checked during the inspection of points and crossings? Give the schedule laid down by Indian Railways for the inspection of these points and crossings.

16. Describe the main constituents of a crossing. Draw neat sketches to show a point rail and a splice rail.

17. What is a CMS crossing? Describe its advantages.

18. Differentiate between the following.

(a) Stud switch and split switch

(b) Stock rail and tongue rail

(c) Flangeway clearance and heel divergence

(d) Flat bearing plate and anticreep bearing plate

(e) Slide chairs and grade-off chairs

CHAPTER

15

Trends in Turnout Design on Indian Railways | RAILWAY ENGINEERING | Track Junctions and Simple Track Layouts