The piston is made of steel and fitted with bronze packing-rings, and is easy of access for packing and repairing when necessary, The water is fed in through the two nozzles shown on the top of the mortar, and from the circular chamber is thrown against the stamp-stem from every side, preventing it from being cut and worn by the sand. The ore-feed, or spout, is placed on top of the mortar, and is covered over to prevent any pieces of ore from falling outside around the mortar. The speed of the stamp averages 90 blows per minute. The ca pacity of the 15 x 30 in. stamp averages about 150 tons tine-crushing, and about 230 tons coarse crushing, per 24 hours. A stamp of this size weighs 70 tons. The new stamps at the Tamarack mill, Lake Superior, crush 225 tons per 24 hours, from 3-in. size to running at 90 to 92 strokes per minute ; from 34 to 36 tons of ore being crushed per ton of coal consumed. Although the steam stamp makes a greater percentage of slimes than careful crushing by rolls, by its rapid and enormous delivery it makes less slimes than gravitation stamps, as has been proved by crushing the same kind of ore in both ways for pan amalgamation—a steam stamp having been used for the latter purpose by the Anaconda Mining Co., at Anaconda, Mont.
Gravitation Stamps are still the means generally in use for crushing gold and silver ores for amalgamation and lixiviation. The tailings from the amalgamating plates in gold mills are frequently concentrated to recover the auriferous pyrites, but stamps are never used now iu well-designed dressing-works, except, perhaps, for re-crushing middlings, unless it is necessary to crush all the ore to the condition of meal or pulp. When ore is to be crushed to the size of fine sand only, even the best stamp-batteries are objectionable. because they reduce by far the greatest proportion of the ore—frequently over 90 per cent.—to a much finer condition than is required. Some important improvements have been made in the wearing parts of stamps, particularly shoes, dies, and guides.
Fraser f Chalmers' stamp-shoes are cast of two kinds of iron at the same operation, by a patent process. The body of the shoe is made of white-iron of the hardest quality, while the neck, or stem, forming the upper part of the shoe, is made of iron possessing almost the tenacity of malleable or wrought-iron. The two qualities of iron are thoroughly united when in an incandescent state, the point of union being below the bottom of the stem. The com bination of extreme toughness where the strain is greatest, with exceeding hardness and durability of parts exposed to wear, makes these it is claimed, far more lasting and reliable than those made in the ordinary manner.
The chrome-steel shoes and dies, made of chrome-steel prepared by a special formula and process, which is kept secret by the manufacturers, have given excellent results. At the Utica mill, Angel's Camp, Cal., where chrome-steel dies and iron shoes are used, the wear of shoes, according to the Eighth Anneal Report of the Slate Mineralogist, was 19 lbs., or cents, per ton, of ore crushed, and 55 lbs., or 2'5 cents, of iron dies per ton of ore, making a total wear of but 4 cents per ton.
Broughall Stamp Guides.—These consist of a series of wrought-iron clamps and links enclos ing wooden bushings, completely filling the space between the battery posts, being rigid, but fully adjustable. These guide clamps consist of two or more arms pivoted to keys, which are firmly secured to the guide rail. At their free ends each is connected by a link, having an outwardly movable part provided with a locking or pressure device, which is simply a clamp screw and lock nut bearing upon a plate, which protects the guide blocks from injury by the point of the clamp screw. By this arrangement any one set of the clamps can be loosened or tightened to properly adjust the bushings without interfering at all with the others. There is no wear on the iron clamps or links, nor are they shaken out of place or loosened by the regular, recurring blows of the stamps—a source of great annoyance, demanding constant attention, with the ordinary guides. By removing the upper bushings, the tappet can be taken off or put on any stein without stopping any other. By removing both upper and lower bushings, any stem can be taken out without removing either tappet, stamp head, or shoe, and without disturbing any other stem, and if desired the battery can be run with one or more stamps out for re pairs.
The Fargo sectional stamp guides (Fig. 9), for which are claimed the same advantages as the Broughall, consist of a series of iron keys enclosing wooden bushings, completely filling the space between the battery posts. The keys for each stem are arranged in pairs, connected at the outer end by iron bars, and at the inner end by the guide rail of the battery. The inner faces of each pair are inclined to each other with a broad bearing of each side of a hush ing, and by tightening the nut on the inner end, will take up all wear in the bushing. Their outer edges are parallel, and tongued and grooved together. This admits of each pair of keys being moved, and its bushing lightened, without interfering at all with any other pair.