Page:EB1911 - Volume 22.djvu/855

Rh Sleepers, called ties or cross-ties in America, are the blocks or slabs on which the rails are carried. They are nearly always placed transversely, across the direction of the lines, the longitudinal position such as was adopted in connexion with the broad gauge on the Great Western in England having been abandoned except in special cases. Stone blocks were tried as sleepers in the early days of railways, but they proved too rigid, and besides, it was found difficult to keep the line true with them. Wood is the material most widely used, but steel is employed in some countries where timber is scarce or liable to destruction by white ants, though it is still regarded as too expensive in comparison with wood for general adoption. Steel sleepers were used experimentally on the London & North-Western, but were abandoned owing to the shortness of their life. In Germany, where they have met with greater favour, there were over 26½ millions in use in 1905, and they have been tried by some American railways. Numerous forms of ferro-concrete sleepers have also been devised.

In Great Britain, Germany and France, at least 90% of the wooden sleepers are “treated” before they are laid, to increase their resistance to decay, and the same practice is followed to some extent in other European countries. A great number of preservative processes have been devised. In that most largely used, known as “creosoting,” dead oil of tar, to the amount of some 3 gallons per sleeper, is forced into the wood under pressure, or is sucked in by vacuum, both the timber and the oil being heated. In the United States only a small percentage of the ties are treated in any way beyond seasoning in the open air, timber, in the opinion of the railway officials, being still too cheap in nearly all parts of that country to justify the use of preservatives. Some railway companies, however, having a long mileage in timberless regions, do “treat” their sleepers.

Typical dimensions for sleepers on important British railways are:—length 9 ft., breadth 10 in., and depth 5 in. In America 8 ft. is the most common length, the breadth being 8 in., and the depth 6 or 7 in.

There are two main ways of attaching the rails to the sleepers, corresponding to two main types of rails—the bull-headed rail and the Vignoles or flange rail. In the first method, which is practically universal in Great Britain and is also employed to some extent in France and India, the rails have rounded bases and are supported by being wedged, with wooden keys, in cast-iron chairs which are bolted to the sleepers. In the second, method the rails have flat flanged bases which rest directly on the sleepers (fig. 10). The chairs on the British system weigh about 45 or each on important lines, though they may be less where the traffic is light, and are fixed to the sleepers each by two, three or four fastenings, either screw spikes, or round drift bolts entered in holes previously bored, or fang bolts or wooden trenails. Sometimes a strip of felt is interposed between the chair and the sleeper, and sometimes a serrated surface is prepared on the sleeper for the chair which is forced into its seat by hydraulic pressure. The keys which hold the rail in the chairs are usually of oak and are placed outside the rails; the inside position has also been employed, but has the disadvantage of detracting from the elasticity of the road since the weight of a passing train presses the rails up against a rigid mass of metal instead of against a slightly yielding block of wood. The rails, which for heavy main line traffic may weigh as much as per yard, or even more, are rolled in lengths of from 30 to 60 ft., and sleepers are placed under them at intervals of between 2 and 3 ft. (centre to centre), 11 sleepers to a 30 ft. rail being a common arrangement. On the London & North-Western railway there are 24 sleepers to each 60 ft. rail. A small space is left between the end of one rail and that of the next, in order to allow for expansion in hot weather, and at the joint the two are firmly braced together by a pair of fish-plates (fig. 11). These are flat bars of iron or steel from 18 in. to 2 ft. long, which are lodged in the channels of the rail, one on each side, and secured with four bolts passing through the web; sometimes, to give additional stiffness, they extend down below the lower table of the rail and are bent round so as to clip it. Occasionally the joints thus formed are “supported” on a sleeper, as was the practice in the early days of railway construction, but they are generally “suspended” between two sleepers, which are set rather more closely together than at other points in the rail. Preferably, they are so arranged that those in both lines of rails come opposite each other and are placed between the same pair of sleepers.

Flat-bottomed rails are fastened to the sleepers by hook headed spikes, the heads of which project over the flanges. In the United States the spikes are simply driven in with a maul, and the rails stand upright, little care being taken to prepare seats for them on the sleepers, on which they soon seat themselves. The whole arrangement is simple and cheap in first cost, and it lends itself admirably to fast track-laying and to repairs and changes of line. On the continent of Europe the practice is common of notching the sleeper so as to give the rail a slight cant inwards—a result obtained in England by canting the rail in the chairs—and metal plates or strips of felt are put under the rail, which is carefully fastened to the sleeper by screwed spikes (fig. 12). This method of construction is more expensive than the American in first cost, but it gives a more durable and stable track. Such metal plates, or “tie-plates,” have come into considerable use also in the United States, where they are always made of rolled steel, punched with rectangular holes through which the spikes pass. They serve two principal