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MAINTENANCE OF POINT AND CROSSING

MAINTENANCE- GENERAL

  • Cess should be low enough to permit efficient drainage and adequate depth of ballast cushion should be provided.
  • Correct spacing of sleepers should be ensured according to the standard lay out drawings.
  • There should be no junction fish plates at stock rail joints or at the heel of crossings. At least one rail on either side of the Points and Crossings should have the same section as the Points and Crossings assembly rail section.
  • The clearance, at the toe, heel of switch, at check rail and wing rail must be maintained within the tolerance prescribed in the schedule of dimensions.
  • Packing under the sleepers must not be loose/defective especially under the crossing and the switch.
  • The chairs and fastenings and all other fittings must be properly secured to control creep and all.
  • Provide gap less joints in xing.
  • Provision of 1 mtr long fish plates in joints.
  • Points and Crossings assembly should be aligned with the rest of the track without kinks.
  • It is desirable to weld stock and lead joints on the Points and Crossings assembly.
  • Examine the condition of slide block (bolted to SR)/switch stops (bolted to TR), spherical washer, and distance block (Connect two different rail at desired distance and/or inclination)

SWITCH PORTION

The length between the toe of switch and heel of switch is called switch length.

  • Replace tongue rail if it is badly worn and/or damaged.

It is defined as badly worn or damaged when:

1) It is chipped/cracked over small lengths aggregating of 200 mm within a distance of 1000 mm from it toe. Chipped length will be the portion where tongue rail has worn out for a depth of more than 10 mm over a continuous length of 10 mm.

2) It has developed knife edged tip(thickness of top edge being less than 2 mm)over a length of more than 100 mm any where up to a distance of 1000 mm from its toe.

3) It has badly twisted or bent and does not house properly against the stock rail causing a gap of 5 mm or more at the toe.

The wear shall be measured at a point with 13 mm head width and at the point where tongue and stock rail are at same level.The wear on tongue rail should not exceed the following limits:

RAIL SECTIONVERTICAL WEAR LIMITLATERAL WEAR LIMIT
For 60Kg8mm8mm
For 52Kg and 90R5mm6mm
For 75R and 60R3mm5mm
  • Replace stock rail if:

1) Burred stock rail, since it likely to obstruct the lock bar.

2) Wear on stock rail exceed the following limits. vertical wear is to be measured at center of rail and lateral wear is to be measures at 13-15mm below rail top table.

VERTICAL WEAR(B.G.)LATERAL WEAR(B.G.)
13mm for 60kg8mm for gr. A&B routes on curves
8mm for 52kg10mm for gr. C&D routes on curves
5mm for 90R6mm for gr. A&B routes on straight
8mm for gr. C&D routes on straight

Corrosion beyond 1.5mm in the web and foot may be taken as the criteria of wear due to corrosion.

  • Minimum throw of switch-Distance between the gauge face of stock rail and non gauge face of tongue rail at toe of switch.
existing works95mm
new and alteration of works115mm
thick web switch(curved switch)upto 160mm

Applicable for thick web switch also.

  • Heel divergence-The distance between the gauge face of stock rail and tongue rail at the heel of switch is called heel divergence.
B.G.(1/12 Curved Switch)PSC Sleeper175mm
B.G.(1/8.5 Curved Switch)PSC Sleeper182.5mm

  • In case of straight switches, correct amount of bend should be given to the stock rail on the turnout side at the theoretical toe of switch, to avoid bad alignment and kink.
  • Rail Gauge ties, rodding etc., hinder proper packing and ordinary beaters become ineffective. Yard gangs therefore, should use tamping bars at such locations.
  • To check the housing of the tongue rail and also the throw of the switch, all non - interlocked points should be operated by hand lever and other points from the signal frame, when traffic permits doing so. If the tongue rail is found to be not housing properly against the stock rail, the defect must be rectified by the Permanent Way Staff in case of non interlocked points and jointly with signal and telecommunication staff,in case of interlocked or partially interlocked points.
  • Ensure the tongue rail rest evenly on all the slide chairs. This will be ensured when all the sleepers are packed properly.
  • Gauge: Uniform gauge to be maintained except just ahead of ATS where
Nominal gaugeif SEA< =0º20’00″
Nominal gauge+6mmif SEA>0º20’00″
  • All bolts on switches should be kept tight.
  • Stretcher bars connected to the pull rod shall be maintained jointly by the Permanent Way Staff and the Signaling Staff. All other stretcher bars shall be maintained by the Permanent Way Inspector. Stretcher bars insulated for track circuit purposes shall not be interfered with unless signal staff are present.

  • Wear on switches can be reduced by lubrication of the gauge face of tongue rail.
  • On wooden sleeper layout assembly, the slide chairs should be fixed to timbers by plate screws; Round spikes should not be used for this purpose.
  • Either all the switch stops should bear against the stock rail or all the slide block should bear against tongue rail as the case may be.
  • Proper housing of tongue rails is to be ensured. Burred stock rail likely to obstruct the lock bar, should be replaced, if necessary.
  • Gap between top edge of stretcher bar and bottom of rail foot is 1.5mm to 3mm .
  • Reconditioning of switch: Recondition the stock rail first. A wornout rail shall be reconditioned in closed position i.e. resting against stock rail. In case of broken tip the TR is to be built up initially in the open condition and thereafter it should be closed with SR to attain final profile.

MAINTENANCE OF CROSSING

  • If any damage to the nose of crossing is noticed, its cause must be traced, which may be due to tight gauge or due to excessive clearance at the check rail.
  • If wing rails or check rails are badly worn laterally, it could be due to wide gauge at the crossing. Gauge can be maintained properly by the provision of a gauge tie plate under the nose of crossing, on layout of wooden sleepers.

  • In obtuse crossings, the distance between the throat and the nose must be maintained correctly.
  • In diamond crossings, obtuse crossings should be laid square to each other with respect to the centre line of the acute crossings.
  • Maximum permissible vertical wear on wing rails or nose of crossing shall be 10mm. However, on Rajdhani/Shatabdi routes, as a good maintenance practice, crossing and the wing rails should be planned for reconditioning/resurfacing by welding on reaching the following wear limits:
Built up/welded crossing6mm
CMS crossings8mm
  • In case of CMS crossings, following dimensions should be deducted (to account for slope in casting of wing rails to 1:20 cant) from the observed wear measurements to find out the actual wear.
for 52 kg section2.0mm
for 60 kg section2.5mm

RECONDITIONING OF BUILT UP CROSSINGS:

  • Surface treatment by cleaning and grinding.
  • Welding to be done in flat position.
  • Preheating: the component should be preheated on the surface by to and fro play of oxy-acetylene torch to obtain 250° C to 300°C.
  • Welding to start immediately after preheating, use short arc is length.
  • Care to be taken o fill the crated to the full weld size before breaking the arc.
  • At restart arc should be stuck ahead of crater and then drawn back so as to fill the crater.
  • Inter pass temperature of 250° C to 300°C should be maintained.
  • Each bead should be thoroughly peened with ball pen hammer.
  • While depositing the adjacent layer about 50% of previous layer should be covered.
  • Weld metal to be deposited to provide an excess of 3mm to be finished by grinding.

RECONDITIONING OF CMS CROSSINGS:

  • Surface treatment by cleaning and grinding.
  • Welding to be done in flat position.
  • Preheating not required.
  • The temperature during welding process not to go beyond 150° C.
  • Temperature to be controlled by proper intervals between the runs and by means of compressed air jet or water quenching. Or, the crossing may be kept submerged in water bath with only top 1cm above water level.
  • Welding cycle should be short (2min).
  • Care to be taken o fill the crated to the full weld size before breaking the arc.
  • At restart arc should be stuck ahead of crater and then drawn back so as to fill the crater.
  • Each bead should be thoroughly peened with ball pen hammer.
  • While depositing the adjacent layer about 50% of previous layer should be covered.
  • Weld metal to be deposited to provide an excess of 3mm to be finished by grinding.

MAINTENANCE OF LEAD PORTION

  • Initially, the lead curve correctness should be ensured by measuring offsets from the gauge face of the straight track.
  • During maintenance, stations at 3.0 M intervals should be marked and the versines checked and track attended as necessary.
  • The versines of turn in curves on loops should be recorded at stations at 3.0 M intervals on 6.0m chord length during the inspection of points and crossings to check the sharpness of the curve and rectified as necessary. The turn-in curve should also be checked for condition of sleepers and fastenings.
  • The variation in versines on two successive stations in lead curve and turn in curve portions should not be more than 4mm and versine at each station should also not be beyond ±3mm from its designed value.

CHECK RAIL AT CROSSING

Check rail is required to be provided in front of the actual nose of crossing. This is so as the wheel, when negotiating a crossing has to jump in air at the nose of crossing. In this situation, the wheel can go in either of the two routes on the crossing, if guidance is not provided in the form of check rail. The clearance shall be within 41-45mm. Too tight clearance in check rail will lead to too much stress on the fittings of the check rail and the bolts are likely to snap frequently. Too slack check rail will mean that the wheel will not get guidance from the check rail and can take either route on crossing and accident can result.

TURN IN CURVE

i)In straight alignment,the turn in curves are likely to have built in twist if both the turn outs in a cross over assembly,is not in the same plane. ii)In curve alignment,in addition to be on the same plane,the cant should be same on both turnouts.

 
C:/wamp/www/doku/data/pages/maintenance_of_points_and_crossings.txt · Last modified: 2010/10/31 10:52 by 10.152.8.49