A short welded rail (SWR) is a welded rail that undergoes thermal expansion throughout its length. These rails are composed of 3, 5, or 10 rails welded together.
It has been experienced on Indian Railways that short welded panels of more than three rail lengths produce excessive thermal forces and it is felt that the extra effort required for their proper maintenance cannot be economically and technically justified. Short welded rails of three rail lengths (3 x 13 m for BG and 3 x 12 m for MG) have, therefore, been standardized on Indian Railways.
Track Specifications for Short Welded Rails
Indian Railways enumerates the following specifications for a track to be laid with SWRs.
Foundation and alignment An SWR should be laid on a stable and efficiently drained formation. It should not be laid on a track curved sharper than 3° on metal
or concrete sleepers and 2° on wooden sleepers in the case of BG tracks. In the case of MG tracks it should not be laid on curves sharper than 5° on metal or concrete sleepers and 3° on wooden sleepers.
Rails Only new rails or good-quality second-hand rails must be used for SWRs. The minimum rail section specified for three rail panels is 90 R for BG tracks and 60 R for MG tracks for all temperature zones. However, 60-kg rails should, however, be laid as 3 x 13 m SWR panels only in temperature zones I, II, and III.
Sleepers and sleeper density Only the following type of sleepers should be used for SWRs.
(a) Wooden sleepers with anticreep or elastic fastenings
(b) Cast iron sleepers with key-type or elastic fastenings
(c) Steel trough sleepers with key-type or elastic fastenings
(d) Concrete sleepers with elastic fastenings
Wooden sleepers should preferably be used at all fish-plated joints when SWRs are to be laid on metal sleepers and these may preferably be provided with MS bearing plates with non-anticreep fastenings.
The minimum sleeper density specified for BG and MG tracks is M + 4, except in the case of 60-kg rails on BG tracks, where it should be M + 7.
Ballast Only stone ballast should be used with SWRs. The minimum ballast cushion below the sleeper should measure 200 mm both on BG and MG tracks. An extra 100 mm width of shoulder ballast over and above the standard ballast section on a straight track should be provided on the outer edges of the curves.
Regular Maintenance Operations of SWRs
Regular track maintenance work including all operations involving packing, lifting, aligning, local adjustments of curves, screening of ballast other than deep screening, and scattered renewal of sleepers may be carried out without restriction when the rail temperature is below tm + 25°C.
All major lifting, major realignment of track, deep screening, and renewal of sleepers in continuous lengths should normally be done when the rail temperature is below tm + 15°C after suitable precautions have been taken. If it becomes necessary to undertake such work at rail temperatures exceeding tm + 15°C, adequate speed restrictions should be imposed.