The highest engineering skill is required for the design and construction of the huge locomotives which haul heavy trains at high speeds across the North American continent
IN THE ERECTING SHOP of a locomotive works at Philadelphia, Pa., a huge boiler is suspended from the overhead travelling crane, ready to be lowered on to the locomotive frame. The boiler shown is for a streamlined engine of the New York, New Haven and Hartford Railroad.
THE North American continent has presented the railway locomotive engineer with a twofold problem. This problem involves the hauling of enormous loads and the elimination of vast distances.
A freight train in the United States may represent a dead weight of some 4,000 tons, and the run from New York to San Francisco is more than 3,000 miles. Coupled with load and long distance is a not unreasonable desire for speed, even across the Rocky Mountains and the great range of the Sierras.
In solving the problem the American engineer has presented his country with the largest locomotives in the world, steel monsters of amazing size and power.
The building of these giants of the railroads calls for a special technique and provides an interesting contrast to the methods adopted in locomotive construction in Europe. Basically the principles of operation and building are the same for all locomotives, but North American construction furnishes many interesting variations in detail to cope with abnormal size and weight. A Mallet type locomotive in the United States in working order may weigh 435 tons and have a length of 118 feet over the couplers. That vast mass of metal is expected to pound along at all speeds up to and over a mile a minute and constructional methods must necessarily conform to this standard.
The frames, that is the foundation on which the railroad engine is built, are of the most massive proportions. The plate frames of rolled steel that yield excellent service on British railways would scarcely be regarded as adequate in the United States or in Canada, where locomotive frames are of the “bar” type, resembling girders built up of rectangular-section steel bars. This variation in practice comprises one of the main differences, apart from size, between locomotives of the Old World and the New.
The development of the American bar frame has led to an astonishing method of locomotive building that is now accepted as standard practice in many railroad shops. The frames, with the cylinders, two or more according to type, the cross-ties or stiffeners and the horns or slots that carry the axle boxes are all comprised in one enormous steel casting.
PASSENGER EXPRESS LOCOMOTIVE built in 1937 for the New York, New Haven and Hartford Railroad. The cylinders have a diameter of 22-in and a stroke of 30-in. Driving wheels are of 6 ft 8-in diameter. The total evaporative heating surface is 3,815 square feet and the superheater heating surface 1,042 square feet. Working pressure is 285 lb per square inch. Ten engines of this class were ordered in 1937 for express trains between New Haven (Conn.) and Boston (Mass.).
The first requirement in casting one-piece frames and cylinders is the making of a pattern, built up section by section, in wood. The pattern is a little bigger than the casting, to provide for the necessary shrinkage as the molten metal cools. A modern American locomotive foundry is a large hall having a concrete floor with numbers of large pits containing special moulding sand.
The pattern is used to make an impression in the sand, an extremely complicated impression requiring remarkable skill. The sections of the pattern are then, removed piecemeal and cores of sand are inserted in cylinder and valve chest bores and other portions of the mould where the casting is required to show a hole or cavity.
The stage is then set for one of the most spectacular operations in the building of a locomotive. We can visualize the huge mould, completed after days or even weeks of anxious toil, ready for the metal. High overhead, spanning the great foundry from wall to wall, is a powerful travelling crane propelled at the touch of a switch by electric motors. Suspended from the crane, shimmering in its own terrific heat, is a giant ladle full to the brim with molten steel. The crane slowly manoeuvres the ladle into position over the mould. A gate is opened and out flows a brilliant stream of white-hot liquid fire casting dark shadows across the foundry. The molten cascade of finest vanadium steel seeks out every nook and cranny in the fashioned sand, and there it solidifies, tough and immensely strong.
Slowly the mass of metal cools and after long hours, perhaps even days, the upper part of the mould is removed and the overhead electric crane is called upon to take up the huge casting for the next operation. This consists of a thorough cleaning with revolving steel wire brushes driven electrically or by compressed air. Portable grinders also are used to clean off any excrescences on the casting. Again the casting is picked up and is now removed to the machine shop for the boring of the cylinders and valve chests. Hundreds of bolt and bearing holes have to be drilled also, and many of these have to be tapped to receive screwed studs. Studs, short rods threaded at both ends, are used to secure the covers at the ends of the cylinders and valve chests.
Shrunk by Liquid Air
Modern locomotive shops have their own methods of machining castings, but in most instances the job is taken to a machine, such as a boring mill, planer, drill or other device that saves labour and ensures accuracy. The giant casting we are considering, however, does not lend itself to movement from one machine to another, even were it economical to build machines big enough to tackle so large a job. United States engineers have solved the problem in a simple manner. They place the great steel casting on a special steel floor provided with inverted T slots for holding-down bolts. Then the drilling and boring machines are rigged up alongside the casting and are set to work. These portable machines are sometimes driven by compressed air but are generally electrically operated. Their armoured cables trail away to power points in various parts of the shop.
To bore the casting with one of these machines, a long boring bar is set up with its axis coinciding with that of the cylinder or valve chest. The interiors of these have been left hollow, or cored out, in the casting. When in its correct position, the boring bar with high-speed steel cutters set to the required diameter is rotated and fed forward at the same time. The result is a perfectly smooth cylindrical bore. Similar methods are adopted to face the ends of the cylinders ready for the covers. The valve chests are fitted with steel “liners” or tubes, ground to size, that are forced into place by hydraulic pressure after having been shrunk by immersion in liquid air. Having regained their normal temperature after the intense cold of the liquid air, the liners swell slightly and become firmly fixed in the bores of the valve chests.
ERECTING THE SUPERHEATER in the boiler of a mammoth American freight locomotive. The men inside the smokebox are bolting the superheater units to the header. The flanged connexion for the steam pipe leading to the right-hand cylinder can be seen in position.
With the finishing of the cylinders and the valve chests that will ultimately supply them with steam, the great bedplate casting is ready for the addition of the many components that complete a locomotive chassis. Not all American locomotives, however, are built with one-piece cylinders and frames. Locomotive frames are often cast separately, with separate spacers or cross-ties, a separate cast cradle for the trailing bogie and separate cylinders. Valve chests are always incorporated in the cylinder castings and these are generally arranged to include also half the saddle that carries the boiler smokebox. With separate cylinders the methods of machining differ from those described above. A cylinder casting is mounted with the bore vertical on the turntable of a large boring mill, a machine sometimes referred to in the United States as a vertical lathe. On a bridge above the turntable is mounted a slide carrying a vertical boring bar. The bar is equipped with cutting tools and, as the turntable is revolved by its electric motor, the interior of the cylinder is bored out. The exact diameter of the finished bore is determined by the setting of a graduated sleeve and the feed or downward movement of the bar is carried out automatically at a predetermined speed.
The boring mill is used also to prepare the valve chests for their liners and for facing the ends of the casting. The faces of the cylinder castings that have to be bolted together are trued up by yet another type of machine, the plano-miller, of which a British example is described and illustrated on page 397. This machine comprises a long steel table provided with inverted T-slots for holding-down bolts and driven backwards and forwards on massive slideways by an electric motor. Flanking the table are two standards that carry an overhead bridge somewhat similar to that of the boring mill. Carried in housings on the bridge are electrically driven revolving cutters and, as the table is driven slowly beneath them, the top surface of the casting is machined true. Machines of this type are used extensively also for shaping the shoes and wedges that are fitted to the axle box horns. The wedges are used for taking up wear.
Roller Bearings
With the enormous weight and power involved in designing American locomotives, axle boxes constitute highly important items and a noteworthy development in this direction is the increasing use of roller bearings for locomotive work.
While the cylinders, frames and axle shoes and wedges are being cast, the wheel shop is busy with the wheels. The first part of the job involves foundry work again, and castings are made for as many wheels, of different types, as will be required for the engine, or series of engines, under construction. The methods of locomotive wheel manufacture in the United States differ but little from those used in Great Britain. Size and weight show increases in American engines and the wheel counterbalance weights are generally of massive proportions to suit the large connecting rods, which in the States are known as driving rods. The connecting rods of American practice are those that link the wheels on either side of the engine and permit them to serve as drivers. In Great Britain these rods are called coupling rods.
The first operation on a wheel casting, after cleaning, is the preliminary turning and the boring of the axle hole in a boring mill. Then follows the fitting of a pair of wheels to an axle. The axle is turned in a lathe with the seatings a little larger than the corresponding holes in the wheels. The wheels are then placed partly on the axle, with the crank-pin bosses arranged at right angles.
Next, the wheels and axles are placed in a large hydraulic press, a valve is turned and the enormous pressure forces the wheels on to the axle seatings. The wheels on their axle are now placed in an ingenious machine that bores the crank-pin holes exactly at right angles to one another. The reason for placing the crank pins on either side of the engine at an angle of 90° is to eliminate the possibility of stopping on dead centre.
2-6-0 + 0-6-4 SIMPLE ARTICULATED LOCOMOTIVE built for the Norfolk and Western Railway. The cylinders have a diameter of 24-in and a stroke of 30-in. The boiler has a maximum internal diameter of 8 ft 8-in and a working pressure of 275 lb per sq in. The driving wheels have an outside diameter of 5 ft 10-in and the overall length of engine and tender is 108 ft 7¼-in.
At this stage the wheel treads are square, without flanges, and the next process is the fitting of tyres of finest rolled steel. The tyres are first rough turned and then bored, in a vertical mill, to an internal diameter that is just too small to slip over the wheel. This is done so that advantage can be taken of a natural law in relation to metals.
It is only necessary to heat the tyre, thus causing it to expand, to make it large enough to be placed on the wheel. The tyre is therefore placed in a pit in the workshop floor, and upon the tyre are directed a number of gas jets. When the tyre has been heated sufficiently a wheeled axle is placed on end by an overhead crane and lowered so that one wheel enters the tyre, which is then allowed to cool. As the tyre cools it grips the wheel with tremendous force; but to make certain that in no circumstances shall the tyre work loose, it is further secured by bolts and a retaining ring. The second tyre is fixed in similar fashion.
Now follows the final turning of the tyres with flanges and tapered treads, both of which play their part in keeping the locomotive on the track. The special lathes that perform this important work have been brought to a high state of perfection in the United States. Of a typical example, the bedplate is 27 feet long, 36-in deep and 7 feet wide. The machine is double-ended, so that both wheels of a pair are turned simultaneously. The slotted faceplates are 14-in thick and have a diameter of 7 ft 6-in. The maximum distance between the faceplates is 9 ft 8-in. The right-hand faceplate, with its bearings (the tailstock), can be moved back when the wheels are placed in position.
Steam-Driven Bogies
The faceplates are turned, through a system of gearing, by a 50 horsepower electric motor, and the gears of the headstock and the tailstock are coupled by a shaft with a diameter of 6-in. A gearbox is provided that gives twelve different faceplate speeds, and there are five speeds available for the leeding of the cutting tools.
This wonderful machine makes light work of even a pair of driving wheels for a giant passenger engine. The ever useful travelling crane picks up a pair of wheels and lowers them into position between the faceplates, where they are supported on centres. Either wheel is secured to its faceplate by self-tightening driving clamps and a switch is thrown in. As the wheels begin to revolve, two massive tool posts, weighing 6,000 lb each, are moved into the cutting position. Each of the tool posts carries a sliding turret with a number of cutting tools that are brought into operation one alter another as the various contours of the treads and flanges are cut in the solid steel.
Pairs of wheels for locomotive bogies, or “trucks”, as they are termed in America, are built in a similar manner to the driving wheels, but no crank pins are needed. A special feature of the front or leading truck is the use of solid wheels in place of the spoked bogie wheels found on British locomotives. The rear truck of the larger types of American locomotive calls for special comment. First, through the medium of a huge cast cradle attached to the main frames, it carries the cab and the enormous firebox of the boiler. For this reason the rear truck is often of the four-wheeled type and, further, it may comprise a locomotive chassis in itself. Here is sometimes housed the well-known booster, a sturdy type of twin-cylinder steam engine driving a crank-shaft that is geared to one of the truck axles. The booster is an invaluable aid in starting, but after the locomotive has attained a certain speed the auxiliary engine is automatically cut out.
COMPOUND ARTICULATED LOCOMOTIVE built at Roanoke, Virginia, for the Norfolk and Western Railway. This 2-8-0 + 0-8-2 locomotive has an overall length, with tender, of 103 ft 8¼-in. The high-pressure cylinders are of 25-in and the low-pressure cylinders of 39-in diameter; the common stroke is 32-in. The boiler has a total heating surface of 7,431 square feet, including superheater. The working pressure is 300 lb per square inch.
The biggest job of all is making the enormous boiler that must supply steam to the cylinders, of which there may be two, three, four or even six, according to the size and type of engine. Then there are many auxiliaries that demand steam, such as the booster, train heating units, steam reversing gear and sanders, a turbo-generator for the engine headlight, a mechanical stoker and air compressors for the brakes. In no other country in the world is there so wide a range of boiler sizes and steam pressures as in the United States. Grate areas vary from 70 to 115 square feet; heating surfaces are from approximately 4,000 to over 10,000 square feet. Pressures range from 200 lb to 400 lb, and in some instances reach even higher figures.
The boiler of a powerful locomotive in the United States is necessarily of enormous size. A locomotive boiler consists of three main parts: the smokebox, the barrel and the firebox. The smokebox is rolled from steel plate; that is to say, a rectangular plate is “mangled” in a set of enormous electrically driven rollers that bend it to the required curvature. The seam is then riveted, and to the front of the smokebox is riveted a steel pressing resembling a huge steel dish with a central opening that may be oval or circular. Over this opening is fitted a steel door, secured in place by a number of dogs, or screw clamps, spaced round its edge. The holes for the main steam pipes and the chimney (smoke-stack in America) are cut out, generally with a oxy-acetylene blowpipe or torch. The smokebox contains important fittings, such as the exhaust nozzle from the cylinders up which shoots exhaust steam through the chimney, creating the partial vacuum that draws air through the furnace. Inside the smokebox also are a tubular feedwater heater and the fore part of the superheater. This device comprises a nest of tubes bent back on themselves and inserted in the flue tubes of the boiler.
The chimney of a modern American locomotive provides an interesting contrast with those of engines of the early days of railroads in the Western States, when trains were frequently attacked by hold-up men and Red Indians. Then the chimney was a wonderful affair in the shape of an inverted cone, to prevent sparks from setting fire to the prairie. Now the chimney has been almost swallowed up by the enormous smokebox, inside which it is still found as a bell-mouthed tube that assists the action of the blast pipe.
4-8-4 LOCOMOTIVE WITH TWELVE-WHEELED TENDER, built for the Lehigh Valley Railroad. The cylinders have a diameter of 26-in and a stroke of 32-in. The driving wheels are of 5 ft 10-in diameter. The boiler has an inside, diameter of 7 ft 0¼-in and a working pressure of of 255 lb per square inch. Grate area is 883 square feet. The total evaporating surface is 5,441 square feet and the superheating surface is 2,243 square feet. A “booster” is fitted.
Behind the smokebox is riveted the front end of the boiler barrel. This comprises a series of rings, rolled and riveted in the same way as the smokebox. Closing the front end of the boiler shell and forming the rear wall of the smokebox is a circular plate pierced with holes for hundreds of fire tubes that lead back to the inner firebox at the rear end of the boiler. The inner firebox is built of heavy copper plates, flanged in a powerful hydraulic press, and is stayed by hundreds of long bolts to the steel outer firebox, which is riveted to the rear end of the boiler barrel. The firegrate is inside the lower part of the inner firebox. The lower edges of the inner and outer fireboxes are riveted with a mud ring - a huge rectangle of cast steel - between them. The rear end of the outer firebox is closed by a thick steel plate known as the backhead, and a little in front of this is the rear plate of the inner firebox. Through both of these rear plates there is a short tunnel - the firehole door. On the larger American locomotives, however, the firehole door is mainly for inspection purposes. Coal is fed mechanically by chain grates travelling between the tender and firebox, beneath the footplate.
When all riveting has been done and the boiler has been caulked to make it steamtight and watertight, it is tested hydraulically to a much greater pressure than it will be called upon to withstand in service. Next follows a covering with magnesia or asbestos insulating material and a final cleading (covering) with steel plate to protect the insulation. The boiler is then transported to the erecting shop, where the frames and cylinders await it. Despite its huge size the boiler is secured to the engine chassis at one end only, so that it shall be free to expand when hot. A large American locomotive boiler is more than one inch longer when in steam than when cold. The smokebox is accordingly bolted to the saddle above the cylinders, and the firebox rests on special springs on the cradle at the rear of the main frames. High up on the boiler backhead is the wide footplate, and round this is erected the steel cab for the engine crew.
DRIVING WHEELS of a type recently designed for large American locomotives. A special grade of high-tensile steel is used for the disk centres, which combine maximum strength with a minimum amount of revolving weight. The rim also provides an excellent support for the tyres.
The next operation is “wheeling”. The full set of wheels, comprising the leading truck, the driving wheels and the trailing truck, are all assembled over a track pit in the erecting shop. The shoes and wedges are fitted to the axle slots and the spring gear is rigged to take the load on axle boxes. When all is ready the frames, complete with cylinders and boiler, are lifted by one or more giant electric cranes and lowered carefully on to the waiting wheels.
Mass Attack by Fitters
Then begins a mass attack by a whole army of fitters. The hundreds of components that have been in course of construction during the building of the boiler and chassis are brought to the partly finished engine by mobile electric or petrol-driven cranes that run from shop to shop along concrete roadways laid throughout the works.
The rods that link the wheels and the main driving rods that transmit the thrust of the pistons are placed in position. These components have been shaped on large milling machines and their bronze bushes, after having been turned and bored in a lathe, are forced into the rod holes by a hydraulic press.
There are many fittings on an American locomotive that look strange through British eyes. Viewed head-on from track level the nearest and most prominent feature is the bumper or cow-catcher, a vital necessity because of the unfenced track.
In the centre of the bumper is the buck-eye central coupler that combines the function of draw-hook and buffers. This is the universal method of linking locomotives and coaches in the United States and Canada Another typical fitting is the electric searchlight supplied with power by a small turbo-generator on the boiler. Then there is the bell, one of the most familiar sights on North American engines.
A special feature of these locomotives is the steam power reverse. The valve gear, although carefully balanced, is of such massive proportions that power is essential for reversing and the “notching-up” that regulates the point of steam cut-off in the cylinders.
The brake gear is generally of the Westinghouse type and large steam-driven compressors are fitted, often to the front of the smokebox, to deal with the demand for high-pressure air.
When the locomotive has been completed, the tender is coupled on behind the cab. The modern American tender is a complicated machine of huge proportions, and is generally carried on two six-wheeled trucks often equipped with roller bearings. Sometimes one of the trucks carries the booster engine. All twelve wheels of the tender are equipped with brakes.
In the forepart of the tender are the steam engine that drives the mechanical stoker and the screw conveyer that removes coal from the bunker. Steam for this engine is taken from the boiler through a flexible pipe.
The rear portion of the tender generally comprises a circular water tank holding up to 22,000 US gallons of water. Coal spaces accommodate up to twenty-four tons of coal, or 4,000 gallons of oil, should that method of firing be adopted. An interesting feature of American tenders is the provision of a sprinkler for laying dust on the track.
INSIDE THE CAB of a great American locomotive. The throttle lever, or regulator handle, is at the extreme right, with the automatic and hand-operated air-brake valves below it. The fire-door is pneumatically operated.
