Consolidation freight locomotive of the Pennsylvania
In recent years, the rather graceful custom of giving names to the classification of locomotives has been extended to the passenger motive-power. In 1895, the Baldwins created the Atlantic type of four-driver locomotive for high-speed service both on the Atlantic Coast Line and on the Atlantic City Railroad, from Camden to the ocean—and the name has stuck. The Brooks plant of the American Locomotive Company at Dunkirk similarly developed the Pacific type for passenger locomotives with six drivers instead of four. The Prairie type was appropriately enough sponsored by the Burlington system. It is like the Pacific type save that the forward or lead truck (the Englishman would blandly call it the “bogey”) has but two instead of the conventional four wheels.
Your locomotive-builder is apt to be more systematic about these types of engine, and he falls back on what is generally known as Whyte’s classification. The basis of this simple system is in the number of wheels of the engine itself. Each type is described by a series of three numbers, the first of these being the number of wheels in front of the drivers, the second the number of drivers, and the third the number of wheels to the rear of these. The eight-wheel American type, the simplest for illustration here, would thus be described as “4-4-0.”
The trailer, which is described by the third number in this series, is a recent addition to the locomotive family in this country. It came from the constant lengthening of the fire-box, due to the necessity of providing greater steam-power for engines of increasing weight and cylinder capacity. When the fire-box began to overhang too far, the trailer-wheels were introduced, and a device was affixed to the locomotive by which they might receive its weight for hill-climbing purposes. This last device has not proved particularly successful. But the trailer itself has become a fixed device in locomotive construction. When the third figure in Whyte’s classification is a cypher it simply means that there are no trailers. Similarly the first figure a cypher, indicates the absence of a forward truck or even wheels, which is common in some forms of switch-engines, where the weight is entirely concentrated on the drivers for better gripping power upon the rail.
Such, in brief, is the development of the locomotive. It has been development rather than change, for while some designers have fretted about whether the engine’s cab should be in the middle of the boiler or at its end and others have recently developed the Walsheart gears upon the outside of the engine frame, where it is of easier access than the old-style links, the general design of the iron-horse remains practically the same as that given it by our grand-daddies. They planned carefully and they planned for the long years. The essential features of their designs have not been questioned. It has simply been a problem of growth.
From out of the fiery womb of steel comes the locomotive. If you would better understand the iron horse, find your way to any of the great plants in which he is being built. Begin at the beginning in a factory, which seems, with dozens of shops and great yards, to be almost a miniature city. Begin at the draughting-rooms where each locomotive is given a whole ledger page—sometimes two or three—for specifications. From those specifications, the young draughtsmen take their instructions. They work out their charts and elevations, their detailed plans; and the ink is hardly dry upon their drawings before they are being whisked away to the blueprint rooms. The blueprints are still damp, when in turn they are hurried to the different construction shops of the plant.
You see these shops, one by one, in care of an expert guide. You see the wooden patterns going to the blast furnaces at the foundries and to the sullen tappings of the trip-hammers. You leave the blacksmiths and stand for a moment—not long—under the terrific din of the boiler-makers. The boiler, the great trunk of the locomotive, is built of steel plate—plate that is the very pride of the rolling-mills. In some foreign lands, copper fire-boxes are demanded; but the real American locomotive has these also of steel.
The steel plates are rolled to form the boiler itself, flanged by angle-workers into the square fire-box. Finally the boiler and the fire-box are riveted together, section by section—made as fast by steel thread as man’s ingenuity can make them. Together they form a unit. Another unit is being formed in an adjacent shop, the solidly welded steel frame in which the boiler shall yet set, and to which truck and drivers will be firmly fastened. Forward on this frame will sit the cylinders; in another corner of this shop they are being made ready. Cast-iron still remains the best material for the cylinders and the steam-chests. These are cast in one piece and the rule holds good where there are two cylinders, as in the case of the compounds. The cylinders, and steam-chest for one side and half the “saddle” of the locomotive, upon which the forward end of the boiler rests, are nowadays generally made in a single casting. After that it is a simple enough matter to smooth down the outer surface, bore the cylinders to perfect surfacing, and line the steam-chests with a bushing that can be readily removed once it is worn out.
The driving-wheels are an important detail of the construction of the locomotive. They are made in rough castings—of steel for fast passenger engines, and of iron for other forms of motive power—and are then made true in giant lathes. The steel tires are shrunk on the wheels, a work of astounding nicety; and in turn the wheels themselves are heated and shrunk upon the axles—of the best steel that man can forge. To place these wheels upon the axles is hair-line work. A 9-inch hub receives an axle just 8.973 inches—no more, no less—in diameter. It is keyed and then under the slight expansion of a gentle heat it is rammed upon the axle-end. It goes on to stay, and stay it must.