Page:EB1911 - Volume 22.djvu/856

CONSTRUCTION] purposes: they diminish the wear of the sleeper under the rail by providing a larger bearing surface, and they help to support the spikes and so to keep the gauge. On all the accepted forms there are two or more flanges at the bottom, running lengthwise of the plate and crosswise of the rail; these are requisite to give proper stiffness, and further, as they are forced into the tie by the weight of passing traffic, they help to fix the plate securely in place. The joints of flanged rails are similar to those employed with bull-headed rails. Various forms, mostly patented, have been tried in the United States, but the one most generally adopted consists of two symmetrical angle bars (fig. 13), varying in length (from 20 to 48 in.), in weight and in the number of bolts, which may be four or six.

The substitution of steel for iron as the material for rails which made possible the axle loads and the speeds of to-day, and, by reducing the cost of maintenance contributed enormously to the economic efficiency of railways, was one of the most important events in the history of railways, and a scarcely less important element of progressive economy has been the continued improvement of the steel rail in stiffness of section and in toughness and hardness of material. Carbon is the important element in controlling hardness, and the amount present is in general higher in the United States than in Great Britain. The specifications for bull-headed rails issued by the British Engineering Standards Committee in 1904 provided for a carbon-content ranging from 0·35 to 0·50%, with a phosphorus maximum of 0·075%. In the United States a committee of the American Society of Civil Engineers, appointed to consider the question of rail manufacture in consequence of an increase in the number of rail-failures, issued an interim report in 1907 in which it suggested a range of carbon from 0·55 to 0·65% for the heaviest sections of Bessemer steel flange rails, with a phosphorus maximum of 0·085%; while the specifications of the American Society for Testing Materials, current at the same period, put the carbon limits at 0·45 to 0·55%, and the phosphorus limit at 0·10. For rails of basic open-hearth steel, which is rapidly ousting Bessemer steel, the Civil Engineers’ specifications allowed from 0·65 to 0·75% of carbon with 0·05% of phosphorus, while the specifications of the American Railway Engineering and Maintenance of Way Association provided for a range of 0·75 to 0·85% of carbon, with a maximum of 0·03% of phosphorus. The rail-failures mentioned above also drew renewed attention to the importance of the thermal treatment of the steel from the time of melting to the last passage through the rolling mill and to the necessity of the finishing temperature being sufficiently low if the product is to be fine grained, homogeneous and tough; and to permit of this requirement being met there was a tendency to increase the thickness of the metal in the web and flanges of the rails. The standard specification adopted by the Pennsylvania railway in 1908 provided that in rails weighing to the yard 41% of the metal should be in the head, 18·6% in the web, and 40·4% in the base, while for  rails 42·2% was to be in the head, 17·8% in the web and 40·0% in the base. These rails were to be rolled in 33-ft. lengths. According to the specification for rails adopted by the Canadian Pacific railway about the same time, 36·77% of the metal was to be in the head, 22·21% in the web and 41·02% in the base.

Points and Crossings.—To enable trains to be transferred from one pair of rails to another pair, as from the main line to a siding, “points” or “switches” are provided. At the place where the four rails come together, the two inner ones (one of the main line and the other of the siding), known as “switch rails” (b, fig. 14), are tapered to a fine point or tongue, and rigidly connected together at such a distance apart that when one of the points is pressed against the outer or “stock” rail (a) of either the siding or the main line there is sufficient space between the other tongue and the other stock rail to permit the free passage of the flanges of the wheels on one side of the train, while the flanges on the other side find a continuous path along the other switch rail and thus are deflected in the desired direction. The same arrangement is employed at junctions where different running lines converge. The points over which a train travels when directed from the main a branch line are called “facing points” (FP), while those which it passes when running from a branch to a main line are “trailing points” (TP). In Great Britain the Board of Trade requires facing points to be avoided as far as possible; but, of course, they are a necessity at junctions where running lines diverge and at the crossing places which must be provided to enable trains to pass each other on single-track lines. At stations the points that give access to sidings are generally arranged as trailing points with respect to the direction of traffic on the main lines; that is, trains cannot pass direct into sidings, but have to stop and then run backwards into them. In shunting yards the points are commonly set in the required direction by means of hand levers placed close beside the lines, but those at junctions and those which give access from the main lines to sidings at wayside stations are worked by a system of rods from the signal cabin, or by electric or pneumatic power controlled from it and interlocked with the signals (see : § Railway). Crossings are inevitable adjuncts of points. Where a branch diverges from a main line, one rail of the one must cross one rail of the other, and a V-crossing is formed (V). Where, as at a double-line junction, one pair of rails crosses another pair, “diamond” crossings (D) are formed. At both types of crossing, check rails (c) must be provided to guide the wheel-flanges, and if these are not accurately placed the safety of the trains will be endangered. At double-line junctions trains passing over the diamond crossings evidently block traffic going in the opposite direction to that in which they are travelling. To avoid-the delay thus caused the branch line which would occasion the diamond crossing if it were taken across on the level is sometimes carried over the main line by an over-bridge (“flying junction”) or under it by an under-bridge (“burrowing junction”).

Railway Stations.—Railway stations are either “terminal” or “intermediate.” A terminal station embraces (1) the passenger station; (2) the goods station; (3) the locomotive, carriage and waggon depots, where the engines and the carrying stock are kept, cleaned, examined and repaired. At many intermediate stations the same arrangements, on a smaller scale, are made; in all of them there is at least accommodation for the passenger and the goods traffic. The stations for