IMPROVED DESIGN OF INTEGRATED CROSSING
In the Indian Railway's design of built-up crossings, IRS:T -23 grade bolts are used to fasten the wing rails with the Vee through nose blocks. It is common knowledge that this arrangement is not quite satisfactory. Due to severe impact near the nose of crossing under traffic, heavy play develops between the contact surfaces of rails and nose-blocks. Further, the bolts get loosened frequently, they get bent and the bolt-holes get elongated. As a consequence, the play increases further in a vicious circle. As a result, the point rail and the wing rails suffer severe fatigue damage in addition to rapid wear near the actual nose of crossing.
Presently the worn crossing is superficially rectified by depositing weld-metal. However, the internal fatigue damage suffered by the rail-material does not get healed. Unlike the surface-wear which is quite visible to the naked eye, the internal fatigue damage to rail material remains invisible. Consequently, the life of the crossing progressively decreases even after successive resurfacing operations. While such wear damage is considerable in the nose-region of the crossing, the remaining portion of IRS built-up crossing suffers relatively little fatigue or wear damage. However, because of heavy damage near the nose, the railways are compelled to scrap the whole crossing.
BMW have designed an improved built-up crossing to minimize the wear and fatigue damage suffered by IRS built-up crossings and also to improve the built-up crossing's overall life and maintainability. The targets kept in view while developing the new design were five-fold as under:
- There should be no need for frequent re-tightening of bolts near the nose of crossing or anywhere else unlike in IRS crossings.
- BMW's improved crossing should eliminate the need for frequent resurfacing.
- It should eliminate the need for scrapping the whole crossing because of local wear and damage only near the nose of crossing.
- The improved crossings should not be expensive to procure, lay and maintain.
- They should be capable of being resurfaced in-situ without entailing their removal from track, transportation to a depot, resurfacing and reinsertion in track as in the case of Cast Manganese Steel (CMS) crossings.
The salient design features of the Improved Built-up Crossing of BMW make are as under, which show how they will meet the targets aimed at in the previous paragraph:
- The web of the point rail is not terminated at actual nose as in Indian Railway's standard crossings but is extended by 500 mm towards throat. The extended web is fastened to the web of each wing rail independently using two-holed C.I. fishing-fit blocks, HTS bolts and synthetic-resin coated fiber-glass layer. As a wheel advances on any wing rail and depresses the wing rail, it also depresses the point rail since wing rail and point rail function integrally. These steps will arrest the high-frequency vibration of the nose presently observed under traffic in Indian Railway standard crossings.
- Again, at the actual nose, the web of point rail is fastened to one wing rail using two-holed fishing fit block, high tensile bolts and synthetic-resin coated fiber-glass layer. A short distance away, the webs of point rail, splice rail and the other wing rail are also similarly fastened. These steps are expected to make the crossing Vee function as an integral unit similar to CMS crossings thus arresting the high-frequency vibrations of the Vee.
- The heads of point rail, splice rail and wing rails in the proximity of nose are hardened to 320 ± 20 BHN using special pearlitizing process. This will reduce the rapid wear and fatigue damage observed in Indian Railway's crossings.
110 Nos. of such improved Built-up Crossings have been supplied by BMW to Indian Railways. Of these, 50 Nos. were consigned to Northern Railway and 60 Nos. to Western Railway.
BMW's design of improved Built-up Crossings can be used on wooden sleepers, steel sleepers and also on PSC sleepers in replacement of Cast Manganese Steel (CMS) crossings.