PRESSES.
Presses assume a great variety of forms in different mechanical pro cesses. They arc employed (i) to compress bodies into small space, as in the packing-press; (2) to increase their dimensions in a particular direc tion, as in the roller-press or roller-mill; (3) to divide substances either wholly or partially, as in the cutting-press; or (4) to impress substances with figured designs, as in the stamping-press, etc. The machines by which these several operations are effected can be better explained in con nection with the different manufactures. Custom, however, has so lim ited the term press that it does not apply to all the machines in the above classification, but, as a rule, only to those which act by means of a lever or a screw, and to the hydraulic press of Bramah (q. v.). We shall there fore describe those machines, not elsewhere noticed, which are employed for compressing materials for purposes of extraction, as wine-, oil-, and cider-presses, and those for compacting substances, or formative presses, such as baling-presses, etc., of which examples will be given illustrating the acting principle of the lever-, screw-, toggle-, and hydraulic press.
IIThe-presscs.—Most races of mankind have possessed the secret of making some kind of intoxicating drink. The Biblical wine-press was simply a vat, usually about 8 feet square and 4 feet high, with a grated opening near the bottom, through which the juice of the fruit ran into a vessel beneath. The juice was expressed by the bare feet of one, two, three, four, or even five, men, who tramped the fruit in the vat, staining their legs and garments with the color of the "must." The wine-presses of the ancient Egyptians, as depicted on their tombs, were of various kinds: in one form the grapes were put in a bag and squeezed by twisting the bag in opposite directions; another plan was to place the fruit in a cloth, which was twisted and strained by means of a pole at each end in the hands of a number of workmen (pi. 9, jig. I). The Romans employed several methods for expressing the juice. The grapes were usually crushed beneath a wooden beam or in a press whose platen (prehem) was driven down upon the bed (torcular) by wedges. Sometimes a lever was used for the purpose, and iu a Pompeian painting there is seen a press having a pair of screws. The treading operation was also common, and is repre sented in a mosaic of the temple of Bacchus at Rome; it .is substantially the same as that of the Syrian wine-press of modern times exhibited in Figure 2. In some parts of France and other wine-producing countries of Europe the old plan of treading out the grapes is still in vogue.
In the vineyards of California presses of great power are employed. One form consists of a press-box, 6 feet square by 4 feet deep, iu the sides of which small interstices occur for the escaping of the must. The follower or platen is moved by an iron screw 6 feet long and 5 inches in diameter, having a slow pitch, which is said to exert a pressure of 282,00o pounds. The press is filled with alternate layers of crushed grapes and 3-inch wooden cubes, every 6 inches of grapes being followed by a laver of cubes. Figure 3 (pl. 9) represents a simple toggle wine-press which is operated by two ratchet hand-levers for the flexion of the toggles.
Cider-presses.—Figure 4 shows the simplest type of cider-press, which is a lever-press consisting of a long beam (lever), a press-box, and a bed. The lever, which is fulcrumed at one end to heavy posts, imparts the pres sure by means of heavy weights placed on the other end, or, as in the Fig ure, by movable bars and pins, alternately actuated by a short hand-lever. The press-box, which is provided with interstices for the escape of the juice, is substantially made, and is supported on a solid bed of sufficient height to allow a vessel to be placed under the press to receive the expressed juice. The crushed fruit receives at first a gradual pressure; as the pomace becomes compacted or the action of the lever becomes inoperative the latter is raised, and heavy blocks of wood are laid on the press-cover or platen, whereupon the lever is again lowered and the press ing is completed. The modern hand cider-press usually combines a grinder and a press in one frame, the platen being operated by a direct acting screw (Jig. 5). Until within a very recent period cider-presses have been worked almost exclusively by hand. Hand-presses have largely been supplanted by power-presses of the knuckle-joint, or direct acting-screw, type. For heavy and continuous work the latter press has four vertical screws, one at each corner of the press-frame. The pressure beam is operated from each end by screw-nuts actuated by spur-wheels that receive their motion from a cog-wheel on a vertical spindle, which engages with two spur-wheels and is turned by a bevel-wheel gearing at the top of the press. It has three rates of speed—fast, medium, and slow —which enables the operator to run the head clown rapidly until it strikes the cheese, then to shift to the medium motion, until most of the cider is extracted, and to finish on the slow speed, the power increasing as the speed decreases.