The Mechanical Handling and Storing of Material

 WHW 410 THE MECHANICAL HANDLING OF MATERIAL powerful vertical rods. The lower large piston closes the jaws, whilst the upper is for the purpose of withdrawing the former, and thus opening the jaws. Both pistons are connected together by rods, and the stuffing boxes are easily accessible. This apparatus is said to be satisfactorily at work in the United States. Electrically Driven Grab.—Grabs have lately been fitted with electro-motors, so that all the work the crane has to perform is to lower the grab on to the material to be raised, in an open condition, when the current is switched on to the motor which closes the Fig. 580. Hydraulic Grab. grab, and similarly opens it after it has been conveyed to its destination. As the capacity of the grab depends to some extent upon its own weight, it is obvious that a grab so fitted will have an increased weight, which adds to its efficiency. The rope cannot lessen the hold of such a grab on the material as it does not come into action until the grab is closed. This seems an ideal solution, but the construction presents several difficulties, one of which is the reduction of speed from the fast running motor to the very slow closing action of the grab; the gearing which transmits the power is, therefore, necessarily very heavy. 1 his appliance is especially suitable where a heavy grab is neces- sary. Figs. 581 and 582 show an example of the application of the principle to a Continental grab built by the Augsburg- Nürnberg A. G. This is particularly applicable for heavy ores, and the closing power is exceptionally great. This grab has been used for handling Thomas phosphates, which is one of the most difficult materials to deal with, and for which a heavy grab is particularly suitable. The weight of the grab alone is 6 tons, and it has a capacity of approximately 2 cub. yds.; the grab actually lifted in one operation over 3 tons of this material. The electro-motor is of 15 H.P., and the transmission of power from this to the jaws is effected by worm and worm wheel, two pairs of spur wheels, and a chain drive. Appliances Similar in Principle to Grabs.—These take the form of huge tongs and are frequently used in the iron and steel industry for handling large single loads. An interesting example of a similar appliance for unloading short lengths of timber out of barges has been described by Professor Buhle.1 I he timber handled is used for manufactur- ing wood pulp, and the pieces, which are very similar to mining props, are about 6 ft. long and do not exceed 1 ft. in diameter. Figs. 583 and 584 show this appliance open and closed. The action very much resembles that of a grab, with the difference that the appliance must not be opened until the timber has been lowered on to the ground or on to the timbers already accumulated, so as not to disarrange them. The weight of the appliance is close upon tons and it will handle on an average 1^ tons of timber at each grip, which is equal to about 3 cub. yds. It is used in connection with a man telpher, and installed on a long bridge crane which spans the store yard, and makes thirty to thirty-five journeys per hour. The Lifting Magnet.—Although this latest and most useful appliance cannot, strictly speaking, be called a grab, it so nearly fulfils the same essential functions that it must be included in this chapter. 1 Zeitschrift des Vereins deutscher Ingenieure, 15th May 1909.