Swing Nose Crossing
IMPROVED DESIGN OF SWING NOSE CROSSING
Fixed nose crossings are normally used in turnouts in railway tracks to enable wheels to cross the rail of an intersecting track. In such crossings, the tread of the moving wheel drops by about 3 mm while traveling between throat and actual Nose because of 1:20 cant of the wheel-tread. During further onward movement of the axle, the wheel-tread suddenly climbs up by 3 mm while moving from actual Nose to the Vee of crossing within a short distance of about 100 mm. Such sudden climbing within a very short time causes severe vertical accelerations in the axles. Correspondingly, it results in large vertical reaction in the Crossing-Nose region. The magnitude of the vertical load on the nose of crossing depends on the square of the speed of vehicle and the static axle-load.
For instance, the axle of a vehicle running at 75 kmph will be subjected to a vertical acceleration of 26.5 g while climbing 3 mm in a distance of 100 mm. With higher speeds, the vertical accelerations will increase in geometric progression as under:
|Speed in Kmph||75||120||160|
|Acceleration in g||26.50||67.90||120.80|
Such high accelerations/ loads lead to severe impacts and result in heavy wear and fatigue damage to the nose and wing rails in the proximity of actual nose. While the wear is visible to the naked eye, the fatigue damage continues to remain unnoticed. Therefore, its full significance escapes the attention of several permanent way engineers.
The surfaces of nose and wing rails which suffer heavy wear have to be routinely resurfaced/ rebuilt by welding at intervals of about 6 to 9 months. Though such rebuilding of worn surfaces is possible, there is no known process for healing the internal fatigue damage suffered by the crossing material under severe impacts. As such, the entire crossing has to be scrapped within 3 to 4 years of service (after resurfacing about 4 to 6 times).
Increase in train-speeds is absolutely unavoidable for Railways which are required to carry increasingly larger volumes of traffic in order to remain financially viable. With higher speeds the accelerations in the nose region increase in geometric progression. These will in turn give rise to much higher impacts and heavier localized wear. Therefore, the crossings would necessarily have to be scrapped at even greater frequency. However, with increased volumes and speeds of traffic, availability of traffic blocks to permit frequent replacements of worn-out crossings also becomes difficult. High cost of procuring larger number of crossings and the labour costs for replacing the worn crossings together with the high hidden costs of traffic blocks needed for such replacements make this matter a crucial one meriting serious consideration.
In order to tackle the effects of the above vicious circle created primarily by high accelerations in the nose region, a new design of Swing Nose Crossing (SNC) has been invented by Bina Metal Way Ltd (BMW). In this crossing, the wheel-tread runs on a continuous surface of rail-head without encountering any vertical drop in actual nose region. As a result, vertical accelerations and resultant rapid wear/ fatigue damage are almost totally eliminated. It would be logical to assume that the service life of such a crossing would increase manifold.
The first 1:12 Broad Gauge 60 kg SNC as per BMW's design was laid on Indian Railways on 29th July 1997 near Tatanagar railway station. This line carries predominantly freight traffic of 20.3 t axle-load, with the traffic density being approximately 40 Gross Million Tonnes (GMT) per annum. Measurements taken in March 2004 showed less than 2.0 mm wear on actual nose after a service-duration of about 80 months. No resurfacing of the SNC was carried out during this entire period. On the other hand, bolted fixed nose crossings laid earlier at the same location used to develop 6-7 mm wear in 6 months time. Thus, resurfacing/ replacement of fixed-nose type of crossing at least on 13 occasions have in fact been avoided while using the new design of SNC at this location. Cast Manganese Steel (CMS) crossings used earlier at this location used to be scrapped after being in service for about 18 months (resurfacing of CMS crossings has not yet been found practical or advantageous on Indian Railways). So even in comparison with CMS crossings the use of SNC of BMW make has avoided at least 4 renewals.
100 Sets of SNC crossings were supplied by BMW to Central, Eastern, Northern, South Eastern and Western Railways. The SNCs laid are performing to the satisfaction of field-staff of Engineering Department. Necessary point-locking equipment and ground connections for the SNCs were also evolved and supplied by BMW as desired by Indian Railways.
BMW's design of SNC has potential for wear up to 6 mm before it becomes due for resurfacing and reuse, as per extant wear-norms stipulated by Indian Railways. There being very little fatigue damage (due to near-absence of impact caused by vertical accelerations), the new crossing can possibly be reconditioned several times more before final scrapping unlike fixed nose crossings which are presently reconditioned hardly 4 to 6 times. The benefits from deferred replacements and longer life of the new type of crossings laid on heavy-traffic lines can, therefore, be readily visualized.
BMW's invention has been found to be a superior one for use on high speed & heavy duty track line. The minimum thickness of the 'actual nose' in BMW's invention is 72 mm which is the same as full head thickness of 60 kg rail. The thickness of 'actual nose' is about 20 mm in currently used designs of SNCs on advanced foreign railway systems. Indian Railways had procured 20 Nos. of foreign turnouts with SNC at much higher cost in comparison with the SNC developed by BMW. Experience gained during field trials with foreign design of SNC (with 20 mm thick actual nose) on Indian Railways has shown that they need resurfacing at intervals of 3 to 4 months. On the other hand, BMW's design has not needed resurfacing even once in 80 months of service. Considered in this light, BMW expect that their design of SNC will give longer service life than fixed nose crossings, CMS crossings or foreign SNCs at lesser overall cost.
BMW is in a position to design, produce and supply Swing Nose Crossings tailor-made to suit any crossing angle and any rail section.