104 



STEAM BOILERS 



For the larger sizes of anthracite and bituminous coal, the 

 air space may be from f to f in. wide, and the grate bar may 

 have the same width. For pea and nut coal, the air space may 

 be from f to $ in., and for finely divided fuel, like buckwheat 

 coal, rice coal, bird's-eye coal, crlm ; and slack, air spaces from 

 & to | in. may be used. 



FIG. 2 



The grate bar shown n Fig. 2, and known as the herring- 

 bone grate bar, has in r.iany places superseded the ordinary 

 grate bar, because they will usually far outlast a set of ordi- 

 nary grate bars. Herring-bone grate bars can be obtained in 

 a great variety of styles and with different widths of air spaces. 

 They are usually supported on cross-bars, and, like many 



FIG. 3 



other forms of grate bars, may be arranged with trunnions, so 

 as to rock the individual bars by means of hand levers. 



A form of cast-iron grate bar for the burning of sawdust is 

 shown in Fig. 3. The bar is semicircular in cross-section and 

 is provided with circular openings for the introduction of air. 

 Lugs are cast on each side of the bar to serve as distance pieces 



in providing air spaces between 



the bars. 



Dead Plate. The front ends 



of the grate bars are usually 

 FIG. 4 supported on the dead plate, 



which is a flat cast-iron plate 



placed across the furnace just inside the boiler front and on a 

 level with the bottom of the furnace door. The purpose of 

 the dead plate is twofold: It forms a support for the firebrick 



