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in the cooling, draws the dovetailed spokes firmly into the rim and nave; and, by the use of a little borax, an union is formed, between the wrought and cast iron, which produces a degree of combination, that prevents the possibility of their working loose. The spokes were first made straight, as shewn in the drawing, and were six in number, but experience has since shewn that a greater number is preferable; and they are, also, now made of a slightly serpentine form, so as to yield to the contraction of the rim in cooling. In this wheel, the nave is cast entire.

This system of case-hardening the rim of the wheels, aa before stated, has been found to be of very great utility, reducing the wear and cost to a comparatively trifling amount. The hardness, certainly, renders them more liable to crack, or break, by sudden jerks or blows; but this tendency is partly overcome, by the rims being made a little thicker now than formerly; the malleableiron spokes also tend, in a certain degree, to obviate this objection.

It has been urged, against case-hardened wheels, that their hardness makes them liable to cut the rails; this might apply to narrow rubbing surfaces, but cannot have any application to one surface, rolling over another, when the hard surface is the rolling one, and also the broader. We have often examined, very carefully, their action upon the rails, but could never find any tendency in them to cut the rails; whereas, when the common wheels are indented, on the surface of the rim, they are very liable to injure the rails, from the periphery, thus grooved, breaking the sides of the bearing surface of the rails off, and leaving only the middle section. This may be seen, on all those railroads upon which the common wheels have been long used.

The universal adoption of case-hardened wheels, on

all the railroads where a slow rate of travelling is practised, in preference to the common wheels, is, however, the best criterion, which can be adduced, of the general belief of their superiority.

We are also inclined to think, that casting the wheel against a perfectly cylindrical piece of iron, tends to form it more perfectly cylindrical, than casting in the ordinary way, and this will likewise lessen the resistance, arising from the undulatory motion, produced by the imperfect circular form of the rim.

§ 4.-Cast-iron Wheels, with Wrought-iron Tires.

The very great rapidity of travelling, which is now adopted upon public railways, causes the subject of wheels, to be a most important object in railway travelling. The rapid motion, very materially, increases the liability of case-hardened wheels to break, not only from the brittle nature of the material, but, also, by the friction of the wheels upon the rails, at such great velocities, heating and expanding the rims, and thus causing them to crack, and fly to pieces; and various plans have, therefore, been devised, to obviate this objection.

The wheels of the locomotive engines, up to 1826, were formed of common cast iron, the case-hardening being deemed objectionable, as diminishing the adhesion upon the rails. Finding the wear of those wheels very great, I had a rim, or tire, of wrought iron, put upon one set of wheels, of one of the Killingworth engines. This tire was made by the hammer of the workman, and, not being of uniform thickness, produced considerable resistance to the engine. The experiment was, however, pursued a sufficient length of time to prove, that, with regard to common cast iron, the wear was very much less. The trial being so very satisfactory, the Bedlington

Iron Company were induced to erect a pair of rollers, to roll them by machinery, by which means, a uniformity of thickness was preserved. Since that time, the use of malleable iron tires has gradually increased, and is now adopted upon all the public lines, where rapid travelling is practised, not only for engine wheels, but also for the common carriages.

In forming this wheel, the nave and spokes were the same as the common, or case-hardened wheels, but the rim was cylindrical, without the flanch. The rim was then turned, to clear it of all sand, or loose particles, and to make it perfectly cylindrical. The tire, being previously turned into a cylindrical shape, and welded, is then heated to a certain degree of temperature, and the contraction in cooling, causes it to embrace the rim of the wheel sufficiently tight, to prevent it from coming off; experience having shewn, that, when the carriages do not travel at a velocity, which heats the tire, such a mode of laying them on is sufficient.

At very rapid rates of travelling, for locomotive engine wheels, and for the wheels of passenger carriages; cast-iron spokes and rims, have not been found of that degree of safety, as to ensure perfect confidence in their use. Mr. George Stephenson, therefore, on the Liverpool and Manchester railway, adopted cast-iron naves, with wooden spokes and rim, on which the wrought-iron tire was laid. Square boxes are cast in the nave, to receive one end of the spokes, the other ends being inserted into the fellies, in the same manner as in coach wheels. A thin wrought-iron rim is laid around the fellies, upon which the outside, or flanched tire, is laid. This description of wheel ensures perfect safety, but the expense of construction is very considerable.

Mr. George Stephenson has obtained a patent for a wheel, with cast-iron nave and rim, and hollow cast

iron spokes; ABC; Fig. 3, Plate VI., represents this form of wheel. The wheel in this plate shews the dimensions of one of the engine wheels, those for common carriages being made lighter. This wheel differs little from those previously described, except that the spokes are made of hollow wrought-iron tubes, or what is called "gun-barrelled spokes." These spokes are laid into a mould, and the cast iron forming the nave and rim, is run around them in the usual way; but a composition of borax is applied, upon the ends of the tubular spokes, for the purpose of causing a more perfect union between the wrought and cast iron; and the spokes, thus united, are found, in practice, not to work loose. The nave is cast of one entire piece, and the rim is cast cylindrical; the latter is then turned, and a tire of wrought iron, with a flanch rolled upon it, is laid upon the cylindrical rim of cast-iron.

These wheels, being much less expensive than the wheels with wooden spokes, have been extensively used upon the public railways, where rapid travelling is practised. There still, however, exists the objection to the rim being formed of cast iron; and though the risk of breaking is greatly obviated by the adoption of wrought-iron spokes, and the malleable-iron tire, still there is certainly some risk, resulting from the use of cast iron being used as a rim for wheels, which are to travel at very rapid rates of speed. The rim is, generally, made very heavy, to still further guard against the risk of breakage; notwithstanding which, cast iron, used as a rim for such very rapid rates of travelling, as from twenty to thirty miles an hour, is certainly objectionable.

Messrs. Jones, of London, have a patent for a kind of wheel with wrought-iron spokes and rim, which is much used for heavy carriages, on the common roads, and

which has been tried, in some places, on railways. The rim and spokes of this wheel are of wrought iron, and the nave of cast iron; the spokes are formed of round bars, screwed at one end, and dovetailed at the other; holes are made through the rim, which are bevelled outwards, and into which the dovetailed spokes are inserted; holes are cast in the nave of the wheel, through which the other ends of the spokes pass; this end of the spoke is screwed downwards into the nave, thus screwing the dovetailed ends into the rim of the wheel. The spokes, therefore, do not rest upon or within the nave, as in other wheels, but are suspended around the rim; the nave, and, consequently, the axle and carriages, are, therefore, suspended from the rim, the spokes being in a state of tension, and not of compression, as in the ordinary wheels. These wheels have not, however, been much used on railways.

§ 5.-Wrought-iron Wheels.

Mr. William Losh, of Walker, has produced a wheel, with wrought-iron spokes and rim, which has been very extensively used on railways, both public and private, being of such a construction, that economy is combined with safety. This wheel was the subject of a patent, in August 1830, previous to the introduction of which, no more perfect wheels had been used, than those with castiron rims, hooped with wrought iron.

ABC, Figs. 4 and 5, Plate VI., shew different forms of these wheels. The spokes are formed of flat iron bars, one end of which is cast into the nave, in the same manner as shewn in Fig. 2. In the wheel, Fig. 4, the spokes are a little bent; but this is not necessary, aș they may be made quite straight. The outer ends of the spokes are bent, according to the different modes of construction, into a circle, so as, when joined together,

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