The Xarod Pulverizer, similar to the Griffen mill, consists of a shallow, heavy cast iron mortar or pan, surmounted by a conical sheet-iron ease, in which are revolved three iron rolls, carried loosely at the end of vertical shafts. The shafts are fixed in an iron cast ing at the top of the machine, having, individually, a radial play in order to allow for centrifugal motion, and the whole is rotated by a horizontal pulley at the top of the ma chine. The rollers, being loose on the shafts, are free to turn. The ore is fed into the machine at one side, just above the rollers, and is crushed against the side of the mortar. Each shaft is covered by a sleeve, fixed to the roller, and extending to the top of the shaft. On each sleeve. just above the roller, are two spiral fans which, according to the makers, take up the material after preliminary grinding, and keep it in self-frictional agitation until rendered fine enough to discharge through screen in the base of the machine. The sleeves on the verti cal shaft serve as oil chambers for the rolls, and the main or central shaft, which is hollow, serves as oil chamber for the main journal. The main shaft is driven at 140 revolutions per minute, This machine has been used for pulverizing phosphate rock, etc., but, like the Griffen mill, does not seem to be adapted for anything but fine grinding.
Tustires Rotary Pulverizer consists of a cast-iron cylinder, or barrel, hung horizontally upon two hollow trunnions. Within the barrel is a ring, of somewhat smaller diameter than the barrel itself, composed of chilled-steel bars, placed longitudinally and a small distance apart, like grate bars. Within this annular grate-bar ring are two heavy cast-iron rolls, which are nearly as long as the cylinder itself, lying loosely. The cylinder is turned slowly upon the trunnions. Ore is fed into a hopper at one side of the cylinder, and passes into the latter by means of a tube projecting through one of the hollow trunnions. The ore falls onto and under the rollers, and is crushed between them and the grate-bar ring. The crushed ore falls between the bars, and, if fine enough, sifts out through the screens in the outer shell of the barrel. If not fine enough, it slides down over the screen until stopped by one of the ribs which support the grate-bar ring, and is carried upward by the rotation of the barrel until nearly overhead, when it drops back to the interior through the apertures in the crushing (grate-bar) ring, and .again falls between the rollers. The rollers lie naturally at the lowest point in the circumference of the barrel, and if the machine is properly fed, they remain ap proximately in that position. If the feed is scant, however, they oscillate right and left, like a pendulum ; in so doing they strike a horizontal yoke, fixed at the end of a shaft passing through the hollow trunnion opposite the feed trunnion, and by a pointer at the other end of this shaft, outside the barrel, give warning to the attendant ; or, this pointer may be con nected with an automatic feeder, and regulating the latter, insure absolutely constant feed. The best work clone by this mill is on rock broken to 1i in. size, or smaller. The makers claim that, owing to the free escape of the crushed ore through the slotted dies, and the ample screen surface, it is almost impossible for the rollers to run more than once over a grain small enough to pass the screen, and that for that reason a high percentage of the ore grains are nearly of the same size as the screen, and but very little slime is made.
ORE FEEDERS.—Regular feeding is an essential in securing the maximum efficiency from any crushing machine, and where possible this is accomplished by automatic devices. It is
usually necessary to hand-feed coarse-crushing machines, such as the Gates or Blake crushers, where the lumps of rock are of large and irregular size; but to the fine-crushing machines— stamps and Huntington mills, which are invariably run on rock broken previously to a comparatively small and uniform size, automatic feeders are well adapted and are almost a necessity. Not only is the efficiency of the crushing machine increased by this means, but there is a saving in labor, as one man can attend to a greater number of stamps or machines fed automatically than if fed by hand only. Nearly all ore feeders in common use are of the same general type, consisting of a sheet-iron hopper from which the ore is discharged regu larly by some device actuated by one of the stamp stems, or some other regularly moving part of the crushing machine.
The Challenge Ore Feeder consists of a hopper, below which is fixed a cast-iron plate, the latter being inclined at an angle to the receiving aperture of the crushing machine. The plate is rotated by a bevel gear, which in turn is moved by a lever, which is struck by the tap pet on the stamp stem, the motion being communicated to the gear through an ingenious friction device. At each partial rotation of the plate a small quantity of ore is scraped off by stationary wings, projecting from the hopper, which rest upon it. One feeder is used for each battery of five stamps. This feeder is an especially good one for wet ores.
The Fulton Ore Feeder has a roller with wide, shallow, spiral corrugations, placed below a sheet-iron hopper. The ore slides down in a shallow stream onto the top of the roller, which discharges it regularly and continuously. Just enough pitch is given to the corruga tions of the roller to have one commence discharging at one end of the roller when the pre ceding one has finished at the other. The roller is turned by an adjustable pawl movement, actuated by a lever struck by a stamp tappet, as in the Challenge feeder.
The Ore Feeder consists of a similar hopper, below which is suspended an in clined tray, by four short iron rods, from the same frame that supports the hopper. The tray is swung backward and forward by a system of levers actuated by one of the tappets of the stamp battery, just as in the Challenge feeder. The back of the hopper has an adjustable scraper, and at each motion of the tray a portion of the ore is scraped forward to the battery.
Krom's Ore Feeder (Fig. 15), de signed for feeding crushing rolls evenly and regularly, consists of a hopper discharging over a slowly re volving cylinder, the flow of ore over the latter being regulated by a gate at the bottom of the hopper. The re volving cylinder is driven by a large geared wheel and pinion, and the pin ion shaft being driven by a cone pulley, its speed can be adjusted thereby.
The minimum speed required is about 4 revolutions per minute ; the maxi mum, 10 revolutions. In front of the revolving cylinder is an electro magnet, before which the stream of falling ore passes. Any pieces of iron or hard steel mixed with the rock or ore, such as drill points, which might damage the rolls, a-re thus caught. The eleetro-magnets are drawn back at intervals, and the pieces of iron and steel collected are dropped by cutting off the electric current. A regular feed for rolls is an essential point not only for prolonging the life of the shells, but for securing the maximum efficiency in crushing, and this feeder has given excellent results.