Page:The New International Encyclopædia 1st ed. v. 12.djvu/436

* LOCOMOTIVE. 386 LOCOMOTIVE. roads led to the development of the sand-box as a requisite appliance. Co.NSTiiUCTioN. Structurally a locomotive con- sists of a. frame, the boiler and engine suiiporled by it, and the running pear on wiiich tlio whole travels alonj; tin; track. Since the boiler at present sets the limit of power that a locomotive is capable of cxertinfr, a description of modern locomotive construction may projjcrly begin with this im])ortant part. The boilers used upon locomotives are of a dis- tinct type. They consist of an approximately cylindrical barrel or shell filled with longitu- dinal tubes and having an internal fire-box or furnace at one end and an attached smoUe-box and stack at the opposite end. Kig. 7 is a LO.VdlTUDlXAL SECTIOS OF LOCOMOTIVE BOILER. longitudinal section of such a boiler with the attaclicd parts indicated. The fire-box is sur- rounded on all sides except the bottom by the boiler water, and to support and maintain in place its top and four sides they have to lie at- tached to the adjacent sheets of the boiler shell by stay-bolts, tiluij-bolls are of various forms. An ordinary form is a round steel rod threaded at its ends, one end being screwed into a hole in the fire-box sheet and the other end into a hole in the adjacent sheet, and the two ends then riveted over or lieaded. Usually a small hole is drilled into the fire-box end of each stay-bolt, which serves as a warning, if the bolt becomes broken, by allowing a small stream of water to escape into the fire-box. The form of stay- bolt just des.Tibed is known as a rigid stay-bolt. Flexible stay-bolts are also employed; these are hinged at one end. usually by means of a ball and socket joint, so that unequal expansion of the two sheets connected is possible without bending the stay. To support the top or crown sheet of the fire-box, two means are employed; one is to use long radial stays from the ci-own sheet to the boiler shell, and the other is to suspend from the shell l)y means of sling stays a number of crown bars which are stay-bolted to the crown sheet. Various combinations of these methods of support and of the several forms of stay-bolts are also employed. The staying of the crown and side and end sheets of locomotive fire-boxes is one of the most ditneult and important details of locomotive boiler construction. The enormous warping effect of the fire-box sheet due to the fierce fire on one side and the water on the other side would soon destroy the- sheets were they not securely bolted in position. The stays are con- sequently put in very close together and only the best material and workmanship is countenanced. Even when all these precautions are taken much trouble results from broken and leaky stay-bolts and from warped sheets. The boiler shell is nearly always made of sheet steel ; the tubes are sometimes made of steel, but are more often of wrought iron. Wrouglit iron is the preferred material for stay-bolts also. In outer form locomotive boiler.s are either btraight-to]) boilers or wagon-top boilers. The straight-top boiler is one who.sc shell is a recti- linear surface from front to rear; a wagon-to]) boiler (Fig. 7) is one whose shell is cyliiidrieal for part of its length from the front end and then bulges up and outward to a considerably larger diameter at the rear end. Sonic fornix of boiler have received special names. The lid piiire boiler is one in which the crown sheet ami side sheets are rectilinear planes instead <if curved surfaces. The LvnU boiler has a cylin- drical corrugated fire-bo.x and requires no stay- bolts. A ^'uott€n boiler has a wide shallow fire- box with the grates above the tojis of the driving wheels; it is designed for burning anthracite, which requiies more grate area than does bi- tuminous coal. Generally speaking, the locomotive fire-box is rectangular in plan and is I'oughly of balloon shajie in vertical transverse section. The top sheet is called the crown sheet, those at the two sides are called side sheets, those at the two ends are called the front and rear tube sheets. For- merly it Avas the practice to make the fire-box narrow, so that it would sit between the engine frames, but the more common practice now is to set it on toj) of the frames and thus obtain greater width and length. The bottom of the fire-box is formed by a grate. (Iratcs are of various forms. For burning wood a stationary grate, consisting of a heavy cast-iron plate per- forated by narrow slats arranged in rows, is used. For burning bituminous coal movable or rocking grates are invariably employed. For anthracite coal similar rocking grates are used, and use is also made of water-grates. In water-grates the grate-bars are hollow tubes connecting with the front and rear water-legs of the fire-box and are consequently kept filled with water. (Irnerally all the grate-bars are not water-tubes, but a few of these are alternated with solid liars which can be moved to shake and dump the fire. Many engines are now constructed for burning oil fuel, and the fire-boxes are adapted to its use with but few changes. Brick arches are commonly used in locomotive fire-boxes to improve the combustion and the distribution of the heat through the tubes. They consist of an arch of fire-brick whose front end connects with the tube sheet just below the low- est tubes, and whose rear end terminates near the rear end of the fire-box a short distance below its top. The sides of this arch are com- monly supported by lugs or brackets fastened to the side sheets or by water-tubes placed at in- tervals underneath the arch and connecting the crown sheet and the tube sheet. Ash-pnns are suspended beneath the fire-box for the purpose of catching and carrying the ashes and coals that may drop between the grate-bars; they are made of sheet steel. The smohe-hox is the chamber in the front of the lioiler into which the gases of combustion flow from the tubes. There are two types of smoke-boxes in use. but the extension front shown by Figs. 7 and 8 is the type now almost in- variably applied to new locomotives. In this box the gases issuing from the tubes either strike I