turned and key-seated to receive the following flange, the two flanges being bolted together with through bolts.
The stamp guides are made of wood; wood bushings in iron frames; or entirely of iron. They are made either solid or sectional, the latter form being preferable as a considerable saving in time can he effected by their use, especially when the guides require dressing down.
The stamps range from 840 to 1,200 pounds as for concentration and speedy amalgamation, the tube mill has become increasingly popular, and has been greatly improved by being enlarged as to diameter and shortened. This gives a greater force to the falling balls, and the cost of grinding has been reduced to seven cents per ton of ore, for the larger sizes. The progressive treatment of ore has thus become the Blake or gyratory crusher for the primary work, the stamps, disc crushers or rolls for secondary and the tube mills for finishing— a conical mill for a 90-mesh product for amalgamating or concentrating and a cylindrical mill for a 200 mesh product for the cyanide and flotation in weight each, and are usually operated through a mean space of six inches at rates ranging from 105 to 110 drops per minute. Their crush ing capacity ranges from 6 to 40 tons for 24 hours according to the milling quality of the ore.
processes. One of the advantages of the tube mill is the capability of grinding in any desired size. This type of mill, however, is not an economical crusher for hard quartz ores, but is best adapted to those of moderate hardness. In the case of the hard ores, the stamp mill has no rival. In the gold mining plants it is now the practice to use one tube mill for regrind ing to each 10 stamps in the battery. The type of mill to be used depends upon the character of the ore; the harder the ore the larger diameter required. In the Marathon tube mill a series of rods from one-half inch to two inches in diameter replace the balls or pebbles of the usual type.
Pulverizers.—Perhaps the best representa tives of this class of, machines are the °Hunting ton" and the °Chilian" mills. Fig. 25 shows a general view of a Huntington mill of the latest pattern. In operation, the ore and water fed into the mill through the hopper is thrown by the rotating rollers and scrapers against the ring-die where it is crushed to any degree of fineness desired by the centrifugal force of the rollers as they roll over it. The water and pulverized ore are thrown against the screens through which they are discharged when ground sufficiently fine to pass the mesh, which ranges in fineness from 60 to 120. Very little slime results from the operation, and the pulp or pul verized ore is delivered in good condition for concentration. The rollers are suspended so as to leave a space of about one inch between them and the bottom of the mill, thus allowing them to pass freely over the quicksilver and the amalgam without grinding it or throwing it from the mill, while at the same time the agita tion of the pulp is sufficient to make amalgama tion perfect.
They are built in sizes ranging from three and a half to six feet in diameter, and from 7,000 to 44,500 pounds in weight. They require from 5 to 15 horse power to drive them at pulley speeds ranging from 120 to 150 revolu tions per minute, to give capacities ranging from 10 to 75 tons of ore for 24 hours.
The principal machinery used in the proces ses of separation are of the following classes: Preliminary washers, which are employed for the purpose of disintegrating and floating off the adhering fine clayey substances from the coarse particles, by the use of running water aided by some form of stirring device.
Sieves and screens are used for separating the finer from the coarser particles of ore. They are of two classes, (1) °stationary screens," which include the wire-cloth gravel screens, and the perforated plate screens, and (2) °moving screens," which include the oscil lating bar screens, the plain shaking screens or riddles and the revolving screens or trommels.
Classifiers are used for obtaining a series of products of diminishing size by means of cur rents of water.
When the process of separation is accom plished by °hand-picking" methods, the work of separating the valuable ore from the waste material is usually done on °tables," of which there are at least five classes in general use: (1) Stationary horizontal tables; (2) station ary sloping chutes; (3) shaking tables; (4) belt, rope or plate conveyors, and (5) revolving circular tables.
Other methods of separation employ °hy draulic jigs," which perform their work through the alternating upward and downward action of two currents of water upon a bed of sand supported by a screen; “vannersp or endless belts which are shaken rapidly either endwise or sidewise, and have a continuous slow motion up hill; °bumping tables"; "film sizing tables,'" and various forms of magnetic separators.
Fig. 26 shows an ore-grizzly, which repre sents the various forms of metal bar screens. See AIR-COMPRESSOR; BLOWING MACHINE; POWER TRANSMISSION; PULSOMETER ; PUMPS.
Bibliography.— Del Mar, A., 'Tube Mill ing> (New York 1917) ; Engineering and Min ing Journal, 'Who's Who Among Manufactur urers of Mining Machinery' New York 1911) Ihlsen, M. C., and Wilson, E. B., 'Manual of Mining' (New York 1911) ; Richards, R. H., 'Ore Dressing' (New York 1909) ; Whitcomb, G. D., 'Mechanical Methods of Mining' (Chi cago 1911) ; Young, C. J., 'Elements of 1/fin ing' (New York 1916).
Revised by RICHARD FERRIS.