« VorigeDoorgaan »
enable them to resist the crushing load of the modern locomotive. As in the case of the battle between guns and iron plates, the weight of both has been increased, until at length, unless a new material—the 'adamant' imagined by Mr. Alderson—be employed, it is clear that as regards the locomotive and the iron road, the latter will be vanquished in the contest. The defect is in the material, to which a crushing power is applied which ordinary iron is positively incapable of resisting. The points of contact of the wheels of a 30 ton locomotive with the rail are very minute, and upon these points the whole weight of the engine presses. The effect is to squeeze and crush the iron and roll it off in laminæ as any one may observe who examines a rail laid down on a line of heavy traffic that has borne a fair amount of work under the heavier class of engine.* On some of the metropolitan lines iron rails, especially if placed on sharp curves, will scarcely last a year. Hence the railroad has become even less 'permanent' now, with its rail of iron, than it was with its original rail of wood a hundred years ago. It has thus become absolutely necessary to introduce a new material, and that material is to be found in Steel.
The greatly superior. resistance which steel offers to crushing as compared with iron, may be learnt from the experiments made by Mr. William Fairbairn, with the object of ascertaining their respective strengths in this respect. A piece of cast iron, both ends flat, was crushed by a pressure to which it was subjected of 55 tons to the square inch; and a piece of malleable iron of the same shape was flattened by a pressure of 73 tons to the square inch; while a piece of steel of the same shape resisted a pressure of 120 tons per square inch without being either crushed or flattened.f The result of certain American experiments, quoted by Mr. Mallett, was to a like effect. The mean resistance of cast steel to compression was found to be 295,000 lbs., of cast iron, 125,000 lbs., and of wrought iron, 83,500 lbs. ; while the tensile strength was 40 tons for mild cast steel, 20 to 25 tons for wrought iron, and 10 to 12 tons for cast iron. Thus in cast steel we find a material not only capable of resisting a far greater compressive force than any known metal
* The friction between the driving wheels and the rail, when the engine is thundering along at high speed, is also very great, and the iron is ground off in minute particles, and thrown into the air. Dr. Angus Smith, when once travelling by railway, took the pains to collect some of the particles which floated about him in the carriage and seemed to shine with metallic lustre. On examination they were found to be in reality minute rolled plates of iron, which seemed to have been heavily pressed and torn up from the surface of the rails.
+ • Treatise on Iron Shipbuilding.' By Wm. Fairbairn, C.E. 1865. p. 48.
can do, but also one whose tensile strength is nearly double that of wrought and more than three times that of cast iron.
The comparatively perishable nature of wrought iron when subjected to the crushing load of the modern express locomotive, has necessarily led to a large increase in the annual cost for maintenance and renewal of railways. Thus, while the percentage of locomotive expenses on gross receipts has somewhat decreased on the Great Northern line during the last fourteen years, the cost of maintenance of way has increased during the same period more than 200 per cent. In an excellent practical paper recently read by Mr. R. Price Williams* before the Institute of Civil Engineers, some striking facts were adduced in illustration of this rapid increase in the tear and wear of permanent way of late years. It was shown that during a period of thirteen years, most of the Great Northern up-line between Potter's Bar and Hornsey, where there are heavy descending gradients, has been renewed not less than three times, giving an average of only 3} years' as the life of a rail' under heavy coal and passenger traffic worked at high speeds. That it is the pace that kills' as well as the weight, is obvious from another fact stated by Mr. Williams with respect to the Lancashire and Yorkshire line, where an equal number of trains of about the same tonnage as in the case of the Great Northern line, were worked at low speeds over a portion of railway between Bury and Accrington, but there the rails lasted as long as 74 years.
The heavy cost of maintenance and renewals on the London and North-Western Railway has for some time been a marked feature in the accounts of that Company. As the renewal of the road is properly chargeable against revenue, any large increase of expense on this account necessarily tells upon dividend ; and hence, to relieve revenue against exceptionally heavy charges for renewals, the expedient of a suspense fund has been adopted by some of the larger companies. But, in 1857, the Suspense Renewal Fund of the London and North-Western Company was found to be so heavily in debt, that the only practical mode that could be devised for dealing with it was to write it off direct to capital to the amount of 256,5881.; and since that date 56,0001. has been charged to capital for renewals in like manner. The Great Eastern Company also cut the same knot by charging 86,0001. to capital instead of revenue only two years ago; while the Manchester, Sheffield, and Lincolnshire Company, between the years 1854 and 1861, judging by the accounts, charged
* On the Maintenance and Renewal of Permanent Way. Read by R. Price Williams, M.I.C.E., before the Institute of Civil Engineers, March 12, 1866.
renewals direct to capital, without even the pretence of a suspense account. The charge in respect of renewals is always exceedingly variable. During the first few years of working a railway, while the materials are all new, the cost is comparatively light; no provision is made for replacing them when worn out; but as years pass on, and the rails, sleepers, and chairs have to be renewed, the outlay rapidly increases. Thus in 1847, the charge for renewals on the London and North-Western Railway was 381. per mile ; in the next five
per mile; and in the ten years following, 2001. per mile; the total expenditure of the Company on renewals of way alone, during nineteen years, having amounted to 1,906,8581. The average annual expenditure of the Company "for renewals since 1847,' says Mr. Williams, 'has amounted to 103,0741. This represents something like 73 miles of single way of the main line broken up and entirely replaced annually during the period; chiefly in situations where the traffic was heaviest, and where consequently (owing to the short intervals between trains) the facilities for doing the work are the least, and the danger of accident the greatest.'
The consideration of these circumstances led the officials of the London and North-Western Company to direct their attention to the employment of some more durable material than ordinary wrought iron for rails, with the object of providing a more 'permanent' way than any that had yet been adopted. Mr. Woodhouse, the Superintendent of the Permanent Way Department, induced the Directors, in 1861, to order 500 tons of Bessemer steel rails, which were laid down at such parts of the line as were subject to the most rapid destruction, not only by the passage of the regular traffic, but by the starting, stopping, shunting, and making up of trains. Some of these were laid down in the Crewe Station, and others at Camden Station. Perhaps there is no spot on any railway in Europe where the traffic is so great as at the latter place. At Chalk Farm Bridge there is a narrow throat in the line, at which the whole system of rails employed at the London termini of this great Company converges. There all the passenger, goods, and coal trains have to pass, and the shunting of carriages is constantly going on day and night. The iron rails laid down in this throat were rapidly ground to pieces by the enormous traffic. The face of a rail was usually worn away in little more than two months; and the traffic being so unintermitting, its stoppage for the purpose of changing the rails or renewing them was found most inconvenient as well as dangerous. Certainly no better spot could have been fixed upon for determining the durability of the Bessemer material. On the 2nd of May, 1862, two steel rails were laid down precisely opposite two new iron rails of the best quality, so that no engine or carriage could pass over the iron rails without also passing over the steel. When the iron rails were worn as far as the safety of the traffic would allow, they were turned, the lower side upwards, and the second face was worn off in like manner. The old rail was then replaced by a new one, and this process went on until the 22nd of August, 1865, when one of the steel rails was taken up. It was computed by the engineer, that during the period that had elapsed since it was laid down (three years and about four months) not fewer than 9,550,000 engines, carriages, and trucks, weighing 95,577,240 tons, had passed over one face of the steel rail, and worn it evenly down about a quarter of an inch, whilst it was still capable of enduring a good deal more of the same work. During the same time eight iron rails had been entirely worn out on both faces, and the seventeenth face was in use when the steel rail was taken up. The extraordinary endurance of the new material compared with the old was further proved at Crewe Station, along both sides of which steel rails were laid down, and after three years' wear not one of them required turning ; whilst iron rails similarly placed had been removed or turned every few months.
These results were deemed quite conclusive on the subject; and, after mature consideration, the Directors of the Company were so satisfied of the advantages in an economical point of view, as well as on the ground of increased safety to the public, of using the strongest and most durable material, that they wisely resolved on erecting extensive Bessemer steel works at Crewe, which are now in active and successful operation, turning out about 400 tons per week. Mr. Ramsbottom, the Company's locomotive engineer at Crewe, had for some time before been gradually introducing steel in the construction of passenger-engines, wherever great strength and durability were required, as in the case of axles and wheel-tyres; and the results were so satisfactory, that steel is now employed by him in all such cases instead of iron. In designing the machinery and plant of the steel works at Crewe, Mr. Ramsbottom introduced many ingenious modifications and improvements, so that they may be regarded as models of their kind. One of his most valuable contrivances for working up the steel required for engine purposes, is his duplex hammer, which strikes a blow on both sides of the ingot at once, in a horizontal direction, thus rendering unnecessary the enormous foundations required for ordinary hammers. The London and North-Western Company have been very
slowly, slowly, and at a great distance, followed by railway companies generally, who are for the most part content, so long as they can, to go forward on the old iron ways. But it seems to us quite clear that the days of iron as the material for main express lines are numbered ; and that not only considerations of safety, but of economy, will, before long, lead to the general use of steel instead of iron. The Americans, who are quick to discern the merits of any new invention, have already recognised the important uses of Bessemer steel to a much greater extent than English railway engineers have done. They are already substituting steel for wrought iron in almost every department of railway construction, and within the last few months orders have been received by a single Sheffield firm for about 10,000 tons of Bessemer steel rails for the Pennsylvania, Erie, Philadelphia, Baltimore and Ohio, and Michigan Central Railroads.
Another circumstance remains to be mentioned in favour of the substitution of steel for iron, which is, the great deterioration in the quality of modern-made iron. All the earlier experimenters on iron found greater strength in ordinary qualities than is now possessed by the very best. The rails made thirty years since possessed much more durability than those made now. Whether this arises from the greater rapidity of the processes now adopted, -the use of squeezers, by which cinder and sand are pressed into the metal, instead of being beaten out by the tilt-hammer as formerly,—the use of the hot-blast, by means of which inferior ores are capable of being reduced,-or the spirit of competition which induces iron manufacturers to turn out the largest possible quantity of iron at the cheapest possible rate,-certain it is, that the manufacture of wrought iron in this country has undergone a serious deterioration during the last half century.
Dr. Percy raises an important point for discussion, with reference to a supposed deterioration in the quality of iron resulting from the effects of percussion, which applies equally to steel. It has long been a moot point with engineers, whether, under repeated light blows, or rapid vibration of machinery in action, iron becomes disintegrated and consequently brittle. This is undoubtedly the case with brass, which, when subjected to vibration, in a few weeks becomes as brittle as glass. When the frightful accident occurred on the Versailles Railway, some years since, occasioned by the breaking of a crank axle, the best men of science and practice in France were called upon to give evidence on the point ; but they were by no means agreed. The whole subject was again discussed before the Commissioners appointed by our own Parliament, in 1849, to inquire into the appli