in which work passes through the various shops may be gained from Fig. 1, beginning with the raw materials. The latter term may and generally does include a considerable quantity of semi-finished material. Steel castings, axles, and tyres may be mentioned specially in this connection. One or two locomotive works, both of the railway companies and private firms, make their own steel castings, but generally these are purchased from outside manufacturers. The same applies to rough forged axles. Tyres are, in most cases, rolled at the mills of the steel makers who make a speciality of such work.
The diagram Fig. 1 explains itself, but there are considerable variations in the practice at different works. For instance, boiler mounting work is frequently done in an annexe of the boiler shop itself. Of general machine shops there are frequently two or even three, one or two being devoted to the large machines employed upon the heavier parts, and another to the smaller machines for small pieces and repetition work. The diagram does not show the route taken by every part which goes to form the locomotive. To do this would be impossible. For instance, the firebox of a locomotive boiler is stayed with a large number of screwed steel and copper stays. In the latest practice these are screwed in machines which are placed in a convenient bay in the boiler shop itself, but it is more often the case that they are made in one of the machine shops, from which they go to the boiler shop. There are frequently many such cross paths for various details, and to show these would make the diagram unnecessarily complicated. Certain materials coming from the manufacturers have also been omitted, such as the asbestos mattresses or magnesia blocks used for boiler covering, or lagging as it is termed. These are taken from the stores direct to the erecting shop, where the boiler is lagged during the later stages of the erection of the engines.
One department, not shown on the diagram, must be mentioned briefly. This is the template shop, in which thin sheets of metal are cut out to the finished shapes of the different parts of the boiler and engine details in accordance with the drawings. These templates are sent to the forge, boiler and machine shops, where they are laid upon the corresponding parts being manufactured, instead of marking off the latter to measurements by rule. Much time is saved by the use of the templates.
Stores and Costing Accounts All raw materials, or semi-manufactured parts such as steel castings, are received from the makers into the general stores. The works manager issues the necessary orders to the stores for such materials or articles, which are sent to the various shops in which they are required. The cost of these is debited to the particular order, say for ten locomotives, for which they are to be used, each order receiving an order number, against which everything is charged that is required for that particular lot of engines, until they are completed. The cost of labour is determined by means of daily time sheets, on which the number of hours taken by each workman is entered against the order on which he has been engaged. Finally an overall charge is added for general expenses which include rent, rates, taxes, management, unskilled labour, drawing office expenses, power, lighting and depreciation of plant. This charge usually takes the form of a fixed percentage either of the total cost of materials and skilled labour combined, or of the cost of skilled labour alone, generally the latter. The combined total gives the cost of the engines built to the particular order under consideration, which divided by the number of locomotives, gives the cost per engine.
Before the war the cost of an average mainline engine and tender, when say ten were constructed together, would vary roughly from about £2,500 to £3,700 at the works, according to the size of the engine, and the fluctuating prices of materials. Post-war conditions have caused these costs to be from 3½ to 4 times the above amounts.
CHAPTER II
BOILER SHOP
Boiler Plates and Making the Boiler Barrel. The steel plates are delivered into the boiler shop after they have been sheared to sizes about ½ in. larger all round than the finished sizes to which they are put together in the boiler. They must be of the very finest quality, since they have to undergo processes, such as flanging, punching, etc., which would inevitably crack or otherwise injure inferior material.
After their arrival, the plates are first straightened to remove any slight waviness, by passing them through a machine, sometimes known as a “mangle,” which has a number of hard steel rollers, usually four above and three below. By passing the plate through between the upper and lower rollers two or three times the irregularities are removed.
The length of the barrel of the boiler may vary from about 10 ft. to 16½ ft. in British engines. In boiler barrels up to about 12 ft. long, two plates are generally used instead of three plates as in former practice. For longer barrels three plates are usual, though two are sometimes used. Engines have recently been built for the Great Northern Railway, in which the barrel 11 ft. 5½ ins. long is made of a single plate. Such plates have the advantage of dispensing with a transverse riveted seam, and are consequently stronger, but large plates above certain commercial sizes are more expensive per ton weight.
The plates have to be joined together by riveted joints. Each plate is bent round to a true circle, and its edges which come together are covered with narrow plates both outside and inside the boiler. These narrow plates A A (Fig. 2) are called butt strips, and when fixed properly in place are riveted to the main plate to form a joint running longitudinally along the boiler. This forms one ring of the boiler barrel. The second ring is made similarly, and the two rings have then to be united by rivets to form the complete barrel. The latter joint is termed the transverse joint, and may be made from two rings of the same diameter, in which case a narrow weldless ring B must be riveted all round the circumference over this joint. More frequently, however, the front ring is made of smaller diameter than the back ring, just sufficient to allow it to enter telescopically inside the back ring for a short distance, the two then being riveted directly to each other.
The boiler illustrated in Fig. 2 differs from the one mentioned above in that it has three rings of the same diameter, which are united by single-riveted circular butt strips
B
, i.e., there is only one row of rivets on each side of the transverse joints. The longitudinal joints
A
where the ends of each ring are joined together have
Fig. 2.—Sections through Locomotive Boiler
double-riveted butt straps, i.e., there are two rows of rivets on each side of the joint.
Before the barrel rings are made and jointed, the straightened plates are marked off for the rivet holes. In British practice the holes are usually drilled, but in some works, and invariably in American practice, they are punched. Punching boiler plates is injurious to the metal immediately surrounding the holes, and therefore such holes are punched smaller than the finished sizes and afterwards enlarged by passing through them a tool in the form of a round drill with cutting edges, known as a “reamer.” This operation removes the damaged metal.
The exact position of each rivet-hole has to be marked off on each plate when punching is adopted, but when the holes are drilled five or six plates are taken at a time and only the top plate is marked off. The plates are then secured under a radial drilling machine (Fig. 3) and each hole marked
