. Cement and concrete. onsists of a steel cylinder 15to 30 feet long and about 5 feet in diameter, lined with chillediron or with stone, and mounted on trunnion bearings aboutwhich it is slowly revolved. (See cut.) The tube is at least half full of flint or steel balls, the formerbeing a natural product imported from Europe, while thelatter are made in this country. As the tube revolves the ballsare carried up the rising side, but before reaching the highestpoint of revolution they drop to the bottom of the tube, im-pinging upon each other and crushing the product betweenthem. The material is
. Cement and concrete. onsists of a steel cylinder 15to 30 feet long and about 5 feet in diameter, lined with chillediron or with stone, and mounted on trunnion bearings aboutwhich it is slowly revolved. (See cut.) The tube is at least half full of flint or steel balls, the formerbeing a natural product imported from Europe, while thelatter are made in this country. As the tube revolves the ballsare carried up the rising side, but before reaching the highestpoint of revolution they drop to the bottom of the tube, im-pinging upon each other and crushing the product betweenthem. The material is fed in at one end and gradually workstoward the other; the fineness of grinding is regulated by therate of feed, and no sieving is necessary. The capacity of atube mill 5 feet by 22 feet is said to be from 8 to 20 barrels perhour when working on the product of a ball mill, and the power GRINDING 29 consumed is variously stated at 30 to 70 The renewingof the flint pebbles forms one of the heaviest repair items, and. THE DAVIDSEN TUBE MILL, F. L. SMIDTH & CO. the cost of these has been estimated as high as one-half centper barrel of cement. 29. The Griffin Mill is an American invention that hasfound much favor for grinding clinker. A heavy steel crush-ing roller is rigidly attached to the lower end of a steel shaftwhich is suspended by ball and socket joint at its upper shaft is thus free to swing in any direction within a casewhich incloses a ring or die surrounding the crushing the shaft is revolved rapidly by means of a horizontalpulley at the top, the roller presses by centrifugal force againstthe inner surface of the ring where the grinding takes place, andthus runs around the ring in a direction opposite to thatin which the pulley is revolved. The material which dropsbelow the roller is thrown up again by steel blades attachedto the bottom of the shaft, and above the roller are fans whichcreate a draft, forcing the finished product through the scree
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