The chairs, fastenings, and sleepers employed on this line of railway are entitled to the particular attention of the engineer, on account of the good judgment and skilful execution displayed in the details of the work; combining, as they appear to do, durability of structure with economy of material. A description of this permanent way was furnished to the Institution of Civil Engineers, by Mr. John Pope, Grad. Inst. C. E. from which we shall make such few extracts as we have room for.
On either side of the bank of ballast, and below the level of its bed, there is an open drain, three feet in width, extending throughout the line, which ensures perfect draiuage frombeneath the sleepers. The sleepers are placed transversly, and differ in shape from any hitherto employed. They are of Baltic fir, and are formed by a square balk being diagonally divided so as to cut out four triangular sleepers, which are laid with the right angle c downwards, which form (a b c) has as much bearing surface as one of twice the cubic content cut out as a half balk in the usual manner. The advantages arising from this form in the economy of timber, the facility of packing, and the improved drainage of the ballast in contact with the sleepers, are obvious. The chairs are of a peculiar form, designed by Mr. Cubitt to combine lightness with strength; they are cast on a plan invented and patented by Messrs. Ransome & May, of Ipswich, whereby the inward inclination of the rails, instead of being made to depend merely upon the rail layers, (as is usually the case) is effected entirely by the shape of the cavities, which are all cast- with peculiar accuracy.
The uniformity of inclination attained by this improvement greatly diminishes that lateral motion of the carriage which is commonly observed on other lines of railway. The chairs are placed horizontally on the sleepers, and are fastened down with treenails of oak, compressed by the patent process of Messrs. Ransome & May. The wedges employed to secure the rails in the chairs are similarly compressed. The rails are parallel, with their upper and lower tables of equal breadth, the sectional form of which is shown in the previous figure.
Square balk divided to form four sleepers.
Triangular sleeper a b c, contrasted with half a balk.
The subjoined four figures (p. 422,) exhibit the end elevation and plan of a joint chair, and the end elevation and plan of an intermediate chair, which, considered in connexion with the preceding side elevation of the chair, will, it is hoped, render the peculiar form understood.
Mr. Cubitt's object has been to lay a railway entirely upon transverse sleepers, of such a form as would expose the largest amount of bearing surface for the least portion of timber; that the bulk of the ballast should be beneath the bottom of the sleeper, where alone it is useful; to use only the best foreign timber; to have the rails rolled uniform and sufficiently heavy; the chairs simple in form, possessing great regularity, and giving the inward inclination to the rail within the chairs, instead of depending upon the rail layer doing so when fixing them on to the sleepers; and that the fastenings should he simple, but firm, and not liable to breakage, or to be detached by the passage of the carriages.
Elevation of Chair, showing the incli-nation of the Rail.
With these views he had directed four sleepers to be cut out of each square log of foreign timber, giving about 2 1/2 cubic feet to each sleeper; to place them with the right angle downwards, so that the ballast could always be consolidated by ramming, without lifting the sleeper, or digging around it, as with square, or other formed sleepers; two places are planed to receive the chairs, and one fastening-hole bored in each sleeper: they are then Kyanised in close tanks, completely filled with the prepared solution, under a pressure of 80 lbs. per square inch. When placed upon the ballast, the joint chairs are first put down 15 feet apart, and the intermediate chairs three feet apart; "cramp gauges embracing the inside and outside of the rails, are then fixed between each pair of sleepers, and the wedges along one side driven up - one treenail being driven in each chair, the hole for which is previously bored in the sleepers byagauge, to insure an equal projection on each side of the rail.
Rails, Chair;; and Sleepers, with the cramp gauge fixed.
A "guide tube" of an internal bore to fit the spiral auger for boring the treenail holes, with the external lip tapered to correspond with the hole in the chair for the head of the treenail, is then used, and by its agency the holes are pierced with great accuracy, concentric with the hole in the chair, at the same time protecting the tool from being injured by the cast-iron. The intermediate chairs are then fixed in the same manner, and the operations are repeated for the opposite rails; the ballast is then consolidated by ramming. In this manner the work proceeds very rapidly; the ballast supports the sleepers throughout, and has no tendency to fall away from them; the water drains away freely; and the passage of the ballast waggons (though without springs) over the new made portion of the line was found to be productive of benefit, rather than injury. .
The inclination of the rail being given by the shape of the chair, insures so much accuracy, that after one day's traffic over it, the surface of the rail is rubbed equally throughout, and not alternately on either side, as is commonly the case.
The uniformity of surface produced is, we think, in a great measure due to the surpassing excellence of Messrs. Ransome & May's castings, which appear to be executed in the highest style of the foundry art, presenting externally a highly finished appearance; and the dye-like accuracy of their internal form is obtained by the introduction of nicely fitted metallic cores. Mr. Pope describes the mode adopted by the patentees of casting these chairs to be "by placing an iron plate on each side of the pattern, ramming them up in sand and using an iron core, which being sustained in its position by a projecting tongue falling into a groove in the side plates, preserves an uniform inclination of the rails in the chairs." Extraordinary precision is thus obtained, and only about 2 per cent. of waste castings are made, although they are subjected to a rigid test; for if the bearing points allow the rails to vary 1-16th of an inch from the required inclination, they are broken up. The iron cores do not unduly chill the metal, and the average strength is retained.
The iron used is chiefly "Welsh Cold Blast."
The peculiarity of the system of the compressed wooden wedges and treenails as fastenings to railways consists (as explained by Mr. May) in subjecting the fibre of the timber to compression equally from the circumference to the centre. The pieces of wood for the wedges are cut out with parallel sides, and forced by hydraulic presses into tapering moulds; whilst in those moulds they are subjected to the action of heat, applied through the medium of low pressure steam; after being allowed to cool, they are forced out of the moulds, and so long as they are kept dry they retain their compressed form; but as the operation simply contracts the dimensions of the sap vessels without crushing the fibre, the power of capillary attraction is not destroyed, and when the wedge is driven into the chair and exposed to moisture they swell so as to become and remain perfectly tight. There is this difference between wedges so compressed and all others; that a true wedge is obtained from a piece of wood cut parallel on all sides, whilst all former modes produced not wedges but parallel pieces.
Guide Tube, and Spiral Auger, in use.
The diminution of the bulk of the treenails by this process of compression, is from 100 to 63, and of the wedges from 100 to 80. It is found that the wood does not swell until it is placed in a damp situation, as in the sleepers. Even the most solid woods, such as African teak, can be compressed without sustaining injury. Perfectly seasoned timber will not shrink after compression, but green wood will shrink after the process. One of the principal advantages of the compressed treenails is the firmness with which they hold into the sleepers. Around the iron spikes generally used, a sheath of rust is formed by the damp sleeper; the shaking of the carriages tends to draw them upwards; and the elasticity of the fibre around the hole in the sleeper being impaired, it is of no use to drive them down again in the same place, and the chairs eventually become loose.
It is proper to add that Mr. Cubitt disclaims the invention of the angular formed sleeper, as Mr. Reynolds used it before him for his longitudinal bearing rails; but he believes transverse sleepers of that form had not been used previously.
Uncompressed treenails for fastening down the chairs to the sleepers were used in the Hull and Selby railway; in the Dublin and Drogheda and many other lines; and it is well known that these frequently become loose. Yet the difference in the cost between these and Messrs. Ransome & May's must be so trifling as not to be worth a moment's consideration, when compared with the advantages of the latter.