Grinding
CRUSHING AND PUL- VERIZING MACHINERY. The process of reducing solids from large fragments to small particles may be accomplished by various means which may be classified as under: (1) Breaking, as when a stone is broken by a sledge-hammer. (2) Crushing, exemplified by the crushing of sugar with a rolling pin. (3) Grinding, accomplished by introducing the material between two surfaces, of which one may be stationary and the other rotating, or both of which may rotate but in opposite directions.
GRINDING MACHINERY The surfaces may be smooth, as in the pestle and mortar; abrasive, as in some disc machines; or one or both surfaces may be corrugated and so exert a cut- ting action, as in the ordinary household coffee mill.
On a large scale, all these methods of reducing material to a more or less fine state of division are utilized, and the various mechanical devices on the market merely carry out these processes on a large scale, the particular merit of any machine depending upon the efficiency with which it accomplishes its purpose and the amount of energy it absorbs in doing so. For reducing rocks, coal and similar material from large lumps to fragments of 1 inch mesh breakers are used. These are of various types, the simplest being the Jaw Breaker, which, as the name implies, consists of two jaws, one fixed and the other movable.
The movable jaw is attached to an eccentric, and moves backward and forward as the eccentric revolves. When the jaw moves backward a V-shaped opening is formed, the rock is fed in, and then the V closes, crushing the rock between the heavy jaws. and then the V closes, crushing the rock gyrating head on to which the rock is fed and crushed against stationary con- The gyrating head is attached caves. fed and crushed against stationary con- caves. The gyrating head is attached When the eccentric reat the base. volves, the resulting action is similar to that of a pestle being moved around a mortar by the hand, except that both pestle and mortar are inverted. A modification of the same principle is shown in the Symons Disc Breaker. In this machine, two discs are employed, of very hard steel. The discs are concave, and are set at an angle to each other, with their hollow sides facing.
Both discs are rotated in the same direction and at the same speed, but a gyrating motion is imparted to one of them by means of an eccentric, and owing to the angle at which they are set their outer edges are wider apart at one point, and close together at another. The rock is fed through the center of one disc, and as the discs come together it is crushed and discharged.
Crushers are usually of the roller type and are much used for reducing ores from 2 inch to 14 inch size, or even smaller. The crushers are heavy steel and are much used for reducing ores which is on fixed bearings while the other is supported on bearings which are held in place by heavy springs and therefore have a certain amount of "give." which is on fixed bearings while the other is supported on bearings which are day it is commonly used. The prin- GRINDING MACHINERY of a heavy weight by means of a cane, ciple upon which it works is the raising are usually arranged in a battery of five, the material to be crushed. The stamps are usually arranged in a battery of five, sometimes weigh as much as a ton and
Some of the modern stamping lying on gravity. stamps by means of steam instead of relying on gravity. or more. form of pulverizer is the Ball Mill or Tube Mill in one or other of its many modifications. The principle of all these The mill consists of Tube Mill in one or other of its many modifications. The principle of all these a revolving cylinder, partially filled with mills is the same. as the cylinder revolves the balls or steel balls or flint pebbles. The material as the cylinder revolves the balls or ally fall over one another. The crushally fall over one another. The crushone ball falling against another, partly ing action is partly due to the impact of to the grinding action of the constantly moving surfaces of the balls. Ball mills tube mills are continuous, the coarse matube mills are continuous, the coarse mamaterial discharged at the other. The terial being fed in one end, and the fine Hardinge Conical Mill is a special type of tube mill, and consists of two cones connected by a short cylinder. The feed of tube mill, and consists of two cones cone is of very wide angle, the discharge cone of much smaller angle. Pebbles of mixed sizes are commonly used in this a segregating action on the pebbles, the mill, and the conical shape brings about larger sizes being carried to that part of the mill having the greatest diameter, and vice versa. The same segregation occurs, of course, with the material being ground, and the result is that the coarse particles automatically collect in that part of the mill where grinding action is is of an entirely different type. It depends for its grinding action on revolving rollers, which themselves rotate about a central axis. It also makes use of the principle of air-separation, the away by a circulating current of air, and coarser particles fall back for further away by a circulating current of air, and grinding. By this device a very finelyground product can be obtained, and for the machine. high grinding efficiency is also claimed which finds application a in the paint and drug trade is the Buhr Stone Mill, which consists of two horizontal stone discs, the upper one is stationary. The surthe lower one of which revolves, while the lower one of which revolves, while material is fed through the center of the upper stone and is collected at the pe GRINGORE riphery. The stones are commonly watercooled. These mills are very successful in grinding liquid or semi-liquid mixtures.
GRINGORE (gran-gõr'), or GRIN- (gran-gwär'), PIERRE, GOIRE a French dramatist and satiric poet; born between 1475 and 1480. He early became known as a writer of moral and allegorical poems, next of satirical farces abounding in allusions to the social and political circumstances of the time. He is an important figure in literary history as one of the creators of the French political comedy. In later life he entered the service of the Duke of Lorraine as a herald, and confined his muse to religious poetry alone. He wrote: "The Game of the Prince of Blockheads" (1511), directed especially against Pope Julius II.; "The Foolish Undertakings," "The Hunt for the Stag of Stags," and the famous "Mystery of St. Loys" (about 1524). He died in 1544.