Abbildungen der Seite
PDF
EPUB

Scientific Notices.

REPORT OF TRANSACTIONS OF THE INSTITUTION

OF CIVIL ENGINEERS.
(Continued from page 459, Vol. XX.)

March 1, 1842.

The PRESIDENT in the Chair.

"Description of the Permanent Way of the South-Eastern Railway." By John Pope, Grad. Inst. C. E.

This communication commences with a general description of the slopes of the cuttings and the embankments of the line, and explains the mode of ballasting and the quality of the materials employed. On either side of the bank of ballast, and below the level of its bed, there is an open drain, 3 feet in width, extending throughout the line, which ensures perfect drainage from beneath the sleepers. The different works connected with the laying of the rails are then successively noticed. The sleepers are placed transversely, 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

[graphic][merged small]

sleepers, which are laid with the right angle C downwards, which

Triangular sleeper A, B, C, contrasted with a half balk.

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 pointed out, and the apparent dis

advantage of the tendency to act as a wedge, is combated by showing that the inclination of a right angle exceeds the limits within which the principle of the wedge obtains. The chairs are

Elevation of Chair, showing the inclination of the Rail.

of a peculiar form designed by the engineer to combine lightness with strength; they are cast on a plan invented and patented by Messrs. Ransome and 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 of the chairs, which are all cast with peculiar accuracy. The uniformity of inclination attained by this improvement greatly diminishes the lateral motion of the carriages, observed on almost all other lines of railway. The chairs are placed horizontally on the sleepers, and are fastened down with trenails of oak compressed by the patent process of Messrs. Ransome and May. The wedges employed to secure the rails in the chairs are similarly compressed. Details are then given of the rails, which are parallel, with their upper and lower tables of equal breadth of the amount of compression of the wedges and trenails, their dimensions, shapes, &c.

The author concludes by stating, upon the authority of Mr. Barlow, the resident engineer of that part of the line, that the passage of 70,000 tons of ballast over several miles of the " permanent way" already completed, has not rendered the slightest repair necessary, although the weather has been very unfavourable.

The paper is accompanied by a Drawing showing the construction of the permanent way, and it was illustrated by the exhibition of a pair of sleepers with two pieces of the rails placed in the chairs, which were fixed down with the compressed trenails, complete as on the railway; all the tools employed in laying the permanent line; and specimens of teak, oak, mahogany, hornbeam, walnut, and other timber, compressed and cut so as to show the subsequent form of the sap vessels.

In answer to questions as to the compressed fastenings, Mr. May explained that the peculiarity of the system consisted in the fibre of the timber being compressed equally from the circumference to the centre. The pieces of wood for the wedges were cut out with parallel sides and forced by hydraulic presses into tapering moulds; whilst in those moulds they were subject to the action of heat applied through the medium of low pressure steam, and after being allowed to cool, they were forced out of the moulds, and so long as they were kept dry would retain their form; but as the operation simply contracted the dimensions of the sap vessels without crushing the fibre, the power of capillary attraction was not destroyed, and when driven into the chair and exposed to moisture they swelled so as to remain perfectly tight. There was this difference between wedges so compressed and all others; that a true wedge was formed from a piece of wood cut parallel on all sides, whilst all former modes that he was acquainted with, produced, not wedges, but parallel pieces. The diminution of the bulk of the trenails, by the from 100 to 63, and of the wedges from 100 to 80. 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 trenails, is the firmness with which they hold into the sleeper. 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.

is

process, It is found

The mode of casting the chairs was described 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 rail 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 rail to vary th 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."

[merged small][merged small][graphic][graphic][merged small][merged small][graphic][graphic][merged small][merged small]

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 uniformly and sufficiently heavy; the chairs simple in form, possessing great regularity, and giving

[graphic][subsumed][merged small]

Guide Tube and Auger.

the inward inclination to the rail within the chairs, instead of depending upon the rail-layer doing it in fixing them; and that the fastenings should be simple, but firm, and not liable to breakage, or to be detached by the passage of the carriages.

[ocr errors]

With these views he had directed four sleepers to be cut diagonally out of each square log of foreign timber, giving about 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 planned to receive the chairs, and one fastening hole bored in each sleeper; they are then kyanized 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 loosely placed 3 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 trenail being driven in each chair, the hole for which is previously bored in the sleeper by a gauge, to insure an equal projection on each side of the rail. A "guide tube" of an internal diameter, to fit the spiral auger for boring the trenail holes, with the external lip tapered to correspond with the hole in the chair, for the head of the trenail, 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. It is found that the work proceeds very rapidly; the ballast supports the sleepers throughout, and

« ZurückWeiter »