The Mechanical Handling and Storing of Material

AUTOMATIC FEEDING DEVICES 203 thus increasing the maximum angle of the shoot and causing the material to flow more quickly. The screw-conveyor feeder, illustrated in Fig. 272, will deliver a constant stream of material, but in this case the material must be of such a nature that it will flow by gravity to the screw. The capacity can be changed only by altering the speed of the screw shaft. This type of feeder has a large field in the handling of pulverised mate- Fig. 272. Screw-Conveyor Feeder, rial, such as coal, cement, etc. The roll feeder, shown in Fig. 273, is extensively used in the mineral industries for handling both large and small materials. The roll is so located under the hopper that the material will not flow when the roll is stationary, but when rotated it will carry the material forward. The capacity is determined by the speed and width of the roll, and the thickness of the stream, as fixed by the adjust- able gate. The roll feeder has been successfully used in handling iron ore, coke, and stone from the bins to the Fig. 273. Roll Feeder. weigh cars for furnace charg- ing. Edison used this type for feeding ore and stone from bins to crushing rolls. The disadvantage is the head room required, owing to the large roll necessary to satisfactory operation. For handling mine- run material the roll should be 6 ft. to 8 ft. in diameter, and in many cases it is not possible to obtain this space. The rotatory - paddle feeder, Fig. 274, acts not only as a feeder, but as a measuring device. It is used for fine material which flows readily from the blades. The capacity is fixed by the speed of the paddle shaft. The revolving - plate feeder, shown in Fig. 275, is used mostly for feeding stamp-mills. The inclined plate driven by gears, placed either above (as shown) or below, moves the material out of the hopper where it is scraped off by the skirt-board. When the skirt-board is made adjustable, sticky material may be handled by this feeder, because the curved plate will scrape the material off the