Continuous Welded Rails
On Indian Railways, the length of long welded rails has been limited to only 1 km taking into consideration the convenience of laying, destressing, and maintenance. Welded panels longer than 1 km have also been tried and are known as continuous welded rails. Such rails have been laid from station to station, but the conventional insulation joints and turnouts have been left out and isolated by switch expansion joints. Trials for LWR/CWR passing through points and crossings are also in progress.
The theory behind continuous welded rails is the same as for long welded rails. Once the concept of locking up of longitudinal thermal forces is accepted, there is no reason why the length of LWR should be limited to only 1 km. However, the switch expansion joints or buffer joints that are provided after every 1 km of LWR. have been a source of weakness in the track, requiring heavy maintenance. It was to avoid this effort that continuous welded rails were laid from station to station. In fact, on European Railways, particularly on German and British Railways, LWR or continuous welded rails have been laid for several miles together, without the inclusion of any SEJ, which pass through stations, yards, etc. The important features of SWR, LWR, and CWR are presented in Table 17.4.
Table 17.4 Comparison of SWR, LWR, and CWR
Item |
SWR |
LWR |
CWR |
Definition |
A welded rail, which expands and contracts through out its length |
A welded rail, the central portion of which does not undergo any thermal expansion |
A welded rail like the LWR, which has to be destressed in stages |
Length |
3-5 rail lengths |
0.5-1 km |
Above 1 km |
Expansion arrangement |
Expansion gap |
Switch expansion Joint |
Switch expansion joint |
Relevant theory and occurrence of stresses |
Normal expansion/ contraction theory |
Theory of locked up stresses in the rail with no stresses |
Same as LWR |
Destressing of rails |
Not required |
Can be done in one stage |
Has to be done in stages |
Maintenance precautions |
Can be maintained any time in any way |
Regulated maintenance in specified temperature ranges |
Same as LWR |
Cost of laying |
Minimum |
More than SWR |
Almost the same as LWR |
Comfort in travelling |
Minimum due to a large number of joints |
Better than SWR |
Best |
Type of maintenance |
Manual |
Both manual and mechanized |
Same as LWR |
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