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CHAPTER V.

CONSTRUCTION OF CARRIAGES ADAPTED TO
RAILROADS.

§ 1.-Coal Waggons, and Wooden Wheels. Ir is very obvious, that the form of carriages for rail, roads, will depend, in a great measure, upon the nature of the goods to be conveyed in them; different kinds of goods, and various species of traffic, requiring different descriptions of carriages. There are, however, some parts of the carriages common to all the varieties, viz. the wheels, the axles, and the bearings, in which the axles run. We shall, therefore, at first, describe the different forms of wheels, and axles, or other parts, which, the nature of the road requires, should be always of the same form and construction; and then give drawings, of some of the different kinds of carriages used on railroads.

The body of the carriages, or, as they were termed, "waggons," used at the first introduction of railways, was, (and still remains, where employed in conveying coals,) in the form of the frustum of a pyramid, or in the shape of a hopper, being much broader and longer at the top, than at the bottom. The railroads, almost universally, descending towards the depôt, the forewheels were made of greater diameter than the hindwheels, according to the angle of the road, the object being, to keep the framing, or body of the waggon, in a horizontal position. The end of the waggon, resting on the large wheels, was also made to project considerably

farther, beyond the perpendicular line of the axles of the front, than the hind-wheels; so that the centre of gravity of the load was not midway between the wheels, but much nearer the large wheels than the smaller, and, consequently, a greater weight was laid upon them, than upon the latter. This form of the waggon has gradually given way to wheels of the same size, and the body of the carriage is square, and placed equally upon the two axles, as shewn in Figs. 1, 2, and 3, Plate VII.

The wheels were, for a long period, made of wood, composed of one entire piece, or of two or three pieces, fastened together. The mode of making the latter, was, by joining the pieces together by wooden pins, and securing them by flat slips of iron, in the shape of an s s, nailed upon the line of the joining. The periphery of the wheels was hewn into the proper shape, by the workmen, with a projection on one side, to keep them upon the rail. The axles were made of wrought iron, and fixed firmly into the centre of the wheels, and, consequently, turned upon the bearing with the wheels. From the very probable inaccuracy of the workmanship, it is not likely the periphery of the wheels would be perfectly circular, which would cause considerable jolting, or an undulatory motion, to the load, and thus increase the draught.

§ 2.-Cast-iron Wheels.

It seems uncertain at what precise period cast-iron wheels were first introduced. In a Dictionary of Arts and Sciences, published in 1754, a drawing is given of a cast-iron wheel, used upon carriages to convey stones from a quarry near Bath, said to be "a great improvement in some carriages and waggonways, made use of at the coal-mines, near Newcastle;" from whence we may suppose, that cast-iron wheels had not been used

at the latter place at that period. How long after this they were adopted, we cannot learn; but in 1765, two wooden and two cast-iron wheels were mostly in use, the wooden ones being retained for the application of the brake, or convoy.

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Great reluctance was shewn, even down to a very recent date, to relinquish the employment of wooden wheels; many objections were urged against castiron, their liability to break, to cut the rails, their insufficiency to present an adequate hold to the brake. At first, sufficient attention does not appear to have been paid, to avoid the contraction, in cooling of cast-iron wheels, and they frequently broke in pieces. Increased knowledge of the properties of cast iron, and of the utility of that kind of wheel, soon, however, produced a general acquiescence in their use. When cast-iron rails came into use, the wooden wheels could no longer be used, so that the introduction of the former would accelerate the discarding of the latter; and, therefore, in 1767, the date of the introduction of cast-iron rails, we may suppose wooden wheels were little used.

A B C, Fig. 1, Plate VI., shews the form of the castiron wheels, for an edge rail; ff, is the nave; a a, the rim; and bb, the spokes. The rim is made sometimes nearly, or often quite, cylindrical, with a projection at one side, called the flanch, to keep the wheel upon the rail; c is a square hole, through the nave, for the axle.

This is the form which was generally used for edge rails, for many years after their introduction, the whole being cast in one piece; the spokes being about half an inch thick, and four inches broad; the rim, one inch thick, and the flanch, one inch deep. For the plate rail, the spokes were tapered away, from the nave, to about two inches broad, forming a rim of that breadth,

perfectly cylindrical, to run upon the rails; or, in some cases, the middle portion, between the nave and rim, was cast of one entire piece, with circular holes, to make it lighter.

A very formidable objection to the use of iron wheels, was, that the rails, especially when their surfaces were narrow, tended to form, or wear an indented groove around their rims; which groove, when of moderate depth, not only caused considerable friction, but was liable to break the rails by a side pressure. The edges, also, of the top of the cast-iron rail, suffered much by the action of the sides of the groove thus formed, and were frequently broken off, on the interior side, for the whole length of the rail. To remedy this, the breadth of the surface of the rails was increased, which diminished the evil to a certain extent; but the expense of repairs was still considerable.

§ 3.-Cast-iron Wheels, Case-hardened.

A complete remedy was, however, effected a few years ago, by what is called, "case-hardening" the rim of the wheels. This is done by placing a massive ring of cast iron, around the mould for forming the casting of the wheel; and running the metal, which forms the exterior surface of the rim of the wheel, against this cold cylindrical piece of iron. The rapid abstraction of heat by the cold iron, produces such a degree of compactness, and hardness, to the superficies of the wheel in contact with the cold iron, that the file has no effect upon it, and this hardness effectually prevents the action of the rail from wearing the wheel into grooves.

Previous to this, the cost of wheels was a very serious charge, in the annual repair of the carriages; but the wheels now, when properly case-hardened, and where the speed is moderate, work for many years without

wearing away. Several, which have been in use for eight years, are still in good order; and, from their appearance, are likely to remain so for a considerable time to come. The operation of case-hardening was, at first, attended with great difficulty; the rapidity, with which the cold iron caused the rim to cool, produced an unequal contraction of the metal, in all the several parts of the wheel, and made them frequently fly in pieces. The rim, being first cooled, would not yield to the contraction of the spokes in cooling; and, therefore, when the spokes cooled, if the contraction did not cause them to separate immediately, it left such a tension upon them, that the shocks they received, when brought into use, soon made them crack, and thus rendered the wheel useless. Many plans were devised to remedy this, in some, the rim was made considerably thicker than the spokes, that the spokes might cool more rapidly, and thus compensate for the more rapid cooling of the rim by the iron ring; the spokes, in this case, being more

numerous.

The plan now mostly used, where the wheel is entirely formed of cast iron, is, to cast the nave in two pieces, as is shewn in Fig. 1, Plate VI., e c e, being the division; two hoops of wrought iron, i i, i i, being laid around the nave, to secure it.

In Messrs. Losh and Stephenson's patent, to which we have before alluded, there is described a mode of forming the wheels, with wrought-iron spokes, in such a way as to yield to the unequal contraction, occasioned by the case-hardening of the wheels.

ABC, Fig. 2, Plate VI., represents the form of their wheel; ccccc c, are the arms, which are of flat malleable iron, dovetailed at the ends. The iron arms being laid in the mould, the cast iron is run around them, and thus forms one entire wheel; the contraction

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