STOKERS, MECHANICAL. The Roney Mechanical Stoker, Figs. 1, 2, and 3, when attached to steam boilers, receives the fuel in bulk, and feeds it continuously and at any desired rate to the furnace.
The fuel to be burned is dumped into the hopper on the boiler front. In small plants it may be shoveled in by hand. In large plants it is usually handled direct from the car to the hopper by elevators and conveyors. Set in the lower part of the hopper is a pusher, to which is attached by a flexible connection the feed plate forming the bottom of the hopper. The pusher, by a vibratory motion, carrying with it the feed 'date, gradually forces the fuel on to the grates over the dead plate. These grates consist of horizontal flat-surfaced bars running from side to side of the furnace, carried on inclined side-bearers extending from the throat of the hopper to the rear and bottom of the ash pit. The grates, therefore, in their normal condition form a series of steps, on to the top step of which coal is fed from the dead plate. These steps at the inclination given would. however, prevent the free descent of the coal. But each bar rests in a concave seat in the bearer, and is capable of a rocking motion through an adjustable angle. All the grate bars are coupled together by a rocker bar, the notches of which engage with a lug on the lower rib of each grate'bar, pin connections being made with two of the grate bars only, for the purpose of holding the rocker bar in position. A variable back-and-forth motion being given to the rocker bar, through a connecting rod, the grate bars necessarily rock in unison. now forming a series of steps, and now approximating to an inclined plane, with the grates partly overlapping. like the shingles on a roof. Assuming the grates to be covered by a bed of coal, and fresh fuel being fed in at the top, it is obvious that when the grates rock forward the fire will tend to work down in a body. But before the coal can move too far, the bars rock back to the stepped position. checking the downward motion, breaking up the cake thoroughly over the whole surface. and admitting a free volume of air through the fire. The rocking motion is slow, being from seven to ten strokes per minute, according to the grade of the coal. This alternate starting and checking motion being con tinuous, keeps the fire constantly stirred and broken up from underneath, and finally lands the cinder and ash on the dumping grate below. By releasing the dumping rod, the clump
ing grate tilts forward, throwing the cinder into the ash pit. after which it is again closed ready for further operation. The dumping grate is made in two parts, so that each half can be dumped separately. The operation of the stoker, therefore, consists of a slow but con tinuous feed, a constant stirring of the fire. and an automatic rejection of the cinder, all performed without opening the fire doors.
All motion is taken from one driving shaft. In a single stoker this shaft may either be driven through a worm gear from a small engine attached to the boiler front and consuming a hardly measurable fraction of a horse-power, or it may be driven by a link belt from any convenient point of the nearest shaft. In large batteries of boilers the driving shaft is ex tended across all the boiler fronts, delivering power to each stoker, and, with the elevators and conveyors, is driven by a small independent engine. The largest stoker can easily be turned over by hand. indicating the nominal power consumed. The worm gear shaft carries a disk and wrist-pin, from which a link couples to the agitator. Through the eye of the agitator passes a stud, screwed into the pusher, on which stud is a feed wheel by which the stroke of the pusher, and, consequently, the amount of feed, is regulated. The agitator hav ing a fixed stroke, it is apparent that if the feed wheel is run down against it in the position shown in the engraving, the pusher will be given its full traverse and the greatest feed. If run back to clear the travel of the agitator, the pusher will, of course, have no motion and the feed will stop, Between these extremes any desired rate of feed can be given.
In like manner, the rock of the grate bars can be adjusted between any limiting angles. and over a range of motion from no movement to full throw, by means of the sheath nut and jam nuts on the connecting rod. By these adjustments the whole action of the stoker is controlled, and the fires forced. checked, or banked at will.
Stone Breaker : see Ore-crushing Machines.