only to abnormal strains caused by the acci dental passage through the rolls of uncrush able substances, such as broken drill points, etc. The rolls may be adjusted to a nicety by screwing or unscrewing the nuts on the adjust ing bolts, which are attached by a °key colter° to the movable journal and are held in place by lock nuts which rest against the heavy brackets cast on the main frame.
The size of rolls ranges from 24" X 15" to 60" X 24", and ranges in weight from 14,000 to 60,000 pounds. Their operative speed ranges from 100 revolutions per minute for the larger and from 100 to 175 revolutions per minute for the smaller machines.
Fig. 4 shows an Allis-Chalmers steam stamp designed for the reduction of copper ores. This stamp is driven by a vertical steam cylinder with valve gearing arranged to keep the steam port freely open during the downward stroke, thus adding the power of the steam to the weight of the stamp. The mortar has four dis charge screens and rests on a heavy anvil or bed plate, and is held in place by angle guide pieces cast upon the massive framing of iron columns. The upper and lower guides for the dies. Fig. 6 shows a sectional view of the same battery, with automatic feeders in place. From the ore bin down to the stamp die within the mortar the various devices and their movable stamp-stem are detachable bronze bushings in which the stem is slowly revolved by a hori zontal pulley on a sleeve between the upper and lower guide brackets. The sleeve contains two feathers which fit into corresponding slots in the stamp-stem, by which the latter is rotated. The steel piston-rod is connected to the steam stem by a circular disc which is encased in a cast-iron bonnet bolted to the flange of the stem, the space between being filled with pure gum-rubber packing, so as to relieve the shock on the piston and to permit its removal for repairs without disturbing the stamp. These stamps have a capacity of several hundred tons per day. Other forms used chiefly on copper ores are the Kraus Atmospheric Stamp and the Tremain Steam Stamp.
Fig. 5 shows the general aspect of a 10-stamp battery operating gravity stamps. The screen and a portion of one of the sectional mortars is removed so as to reveal the stamps and the parts, which comprise the battery, are illustrated by the following figures: Fig. 7, ore-bin gate and spout. These are built in sizes ranging from 18 to 24 inches, or in special sizes as may be required. Fig. 8, a °Challenge° ore-feeder.
This is an automatic arrangement which may be used with wet or dry ores. Its operation is simple and regular: The cast-iron plate placed at an aii6le below the hopper is rotated by bevel gears actuated by a friction device in the shape of a tappet-rod or forked lever, which engages a feed collar placed on the central stem of the battery. The entire apparatus is about feet in height, 3 feet 9 inches in width and weighs about 845 pounds. Other types of feeders are the "movable suspended," and the "fixed sus dashed up against the screens by the falling stamp. Amalgamation takes place within the mortar by the pulp being splashed up on the copper lining plates. Fig. 10 is an example of a deep straight-back mortar not provided with copper lining plates, amalgamation being ef fected outside. It is provided with steel lining, and a steel wearing plate, and is so propor tioned that it affords unusual facilities for the quick discharge of the pulp through the screen. Fig. 11 illustrates a double-discharge mortar pended,' automatic feeders. The principal ad vantage of using the suspended type of feeder is that it gives an unobstructed floor space behind the battery, and thereby facilitates the work of "clean up,* repairs, etc. When they are used for feeding "Huntington' mills or other pulverizing mills, they are usually ar ranged to be driven by belting.
Mortars are made in a great variety of forms, and are designed for both wet and dry crushing. Fig. 9 is an example of the deep single dis designed for use in wet crushing silver, in con centrating or in combination mills where large crushing capacity is desired. The pulp dis charged through the back screen flows toward the centre at the back of the mortar, and pass ing through an opening in the base of the mor tar proper joins the pulp from the front screen. Fig. 12 is an example of the mortars designed for dry crushing. All of them are made double-discharge, with the dies so placed that the dry pulp will easily reach the screens when it is dashed up against them by the action of the stamps. A peculiar feature is the fastening of the die by a dove-tail flange at the bottom. Fig. 13 illustrates a general view and cross-sec tion of a sectional mortar. Its construction in sections adapts it for mule-back transportation in mountainous countries.