Wednesday, March 28, 2018

Short Welded Rail

Definitions –

(1)Short Welded Rail (SWR) is a welded rail which contracts and expands
throughout its length.

Note – Normally the length of SWR is 3X 13 M.for Broad gauge and 3X12 M. for

Metre gauge.

(2) Rail temperature is the temperature of the rail as recorded by an approved type of rail thermometer at site. This differs from the ambient temperature which is the temperature of air in shade at that place, as reported by the meterological department. The Indian Railways have been divided into four rail temperature zones.
(3) Mean annual rail temperature {tm} is the average of the maximum and minimum rail temperature recorded during the year. tm will be fixed locally wherever rail temperature records are available for a reasonable period of five years. Where rail temperature records are not available tm can be read from the rail temperature map.

(4) Installation temperature (ti) is the average rail temperature during the process of fastening the rails to the sleepers at the time of installation of SWR.

Track structure for SWR –

(1) Formation – SWR shall be laid generally on stable and efficiently drained formation.
(2) Rails – The minimum section of rail shall be 90-R for Broad Gauge and 60-R for meter Gauge. Only new rails and second hand rails conforming to the standards laid down in relevant cause of the Code of practice for welding of Rail Joints by the Alumino Thermite process and the Code of Practice for Flash Butt Welding of rails shall be welded into SWR.

(3) Sleepers – The sleepers approved for use with SWR shall be as under –

(a) Wooden sleepers with anti-creep or elastic fastenings.

(b) Cast iron sleepers and steel trough sleepers with key type or elastic fastenings. Wooden sleepers with mild steel bearing plates and rail free fastenings may preferably be used at all fish plated joints when SWR is laid on metal sleepers. Concrete sleepers should be used in cases where SWR is likely to be converted to LWR/CWR immediately. In such cases the fish-plated joints shall have concrete sleepers at uniform spacing in addition 1m long fish plates be provided at fish plated joints.(Cs.No 102)

(4) Sleeper Density – (m+4), (m+7) etc.

(5) Ballast: – Only stone ballast shall be used. The recommended depth of ballast
below the bottom of sleepers is as indicated ,the minimum in no case being less than 200 mm. both for Broad Gauge and Metre Gauge. 100 mm. extra width of shoulder ballast over and above the standard ballast section on tangent track shall
be provided on outside of curves upto 875 metres radius in Broad Gauge, 600 metres radius in Metre Gauge. In the case of sharper curves, the extra width shall
be 150mm. On existing SWR lengths, where this width is not available, this may
be provided on a programmed basis. In the case of 60 kg. Rails LWR profile shall be adopted.

Laying Short Welded Rail

Condition of laying:

(1) Alignment - SWR shall not be laid on curves sharper that 500 meters radius in both Broad Gauge and Meter Gauge. However, on PSC Sleepers, SWR may be laid on curves with radius not less than 440 meters. Existing SWR laid on sharper curves may, however, be allowed to continue if there is no difficulty experienced in maintaining these lengths. Chief Engineer’s approval should be taken in such cases.

(2) Junction with insulated joints and points and crossings – SWR shall not butt against insulated joints, heel of crossing and stock rail joints. Two standard length rails (13M./12M.) shall be interposed to isolate the SWR from such locations. These standard length rails shall be anchored effectively to arrest movement in either direction.

(3) Junction with standard length rails on wooden sleepers – When SWR track butts against track laid with standard length rail (13M. for Broad Gauge and 12 M. for Meter Gauge) on wooden sleepers, the latter shall be adequately anchored for at least six rail lengths to check the creep of rails. These six rail lengths shall have a sleeper density of M+7. Additional shoulder ballast should also be provided. Laying of short welded rails (SWR) – The gaps to be provided for SWR at the time of laying shall be in accordance with Table 1 depending on the installation temperature (ti) and the Zone in which the rails are laid –

(4) Regarding laying of SWR in Level Crossings and Bridges, Para 921 of Chapter  on Level Crossings.

Track Structure on Bridges may be referred to.

Laying of short welded rails (SWR) – The gaps to be provided for SWR at the time of laying shall be in accordance with Table 1 depending on the installation temperature (ti) and the Zone in which the rails are laid –

TABLE 1

Initial laying gaps for SWR for various installation temperatures 
(C. S. No. 125 dated 21 . 02. 2011)

If the laying has to be done outside the temperature range given in table above, or whichever joint gaps could not be provided as per the table, readjustment of gape shall be carried out within two days of laying before the track consolidates. Along with the gap adjustment, any re-spacing of sleepers, if required, must be carried out.

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