The Mechanical Handling and Storing of Material

42Ö THE MECHANICAL HANDLING OF MATERIAL The shears support the bridge span on sliding bearings under the top chords. The cantilever extensions from the dock end of the two-span bridges are supported from the top of masts over the pier (see Fig. 597). Attached to the cantilevers are hinged aprons that can be raised and lowered. '1'he moving gear for each bridge crane is operated by a motor in a house over the pier support. This motor is controlled from the operator’s cab on the man trolley, when the trolley is brought to a point immediately under the moving gear house. The man trolleys are so designed that the operator can turn the bucket through an angle of 90°. In general the operation of the screening apparatus at the rear is as follows : The coal is first placed by the grab bucket in a 30-ton receiving bin. It is then passed over a shaker screen to a pivoted conveyor for delivering it into cars. The coal going through the shaker screen passes into a small bin beneath, delivering to an elevator, by which it is either delivered to revolving screens for preparing small sizes, or directly into the screening bin for delivering it to a belt conveyor discharging on a screenings stock pile. By this arrangement, when lump coal is being loaded, a car load each of stove, nut, and screenings may be taken at the same time. In case lump coal is being loaded and there are no orders for the smaller sizes, the screenings can be delivered from the elevator direct to the screening bin, which in turn will deliver the screenings to the belt conveyor for the stock pile. When taking general screenings from the stock pile for sizing and loading, they are dumped by the grab bucket into the receiving bin and handled as described. The bins are of parabolic form. The 30-ton bin is equipped with a large recipro- cating gate operated by power. The screening apparatus for handling the coal passing through the shaker screen has a capacity of 200 tons an hour. The other rear pier is equipped with a 30-ton bin, gate, and chute for unloading coal into gondola cars, a screening bin and elevator for screenings, and chutes for unloading screened coal into box cars in connection with box-car unloaders. Beneath the screening chute is a 50-ton bin for catching the screenings. In connection with this screening equipment is a bucket conveyor for raising the screenings to a point from where they are discharged by gravity to a screenings pile on the water side of the pier, or carried by a belt conveyor and discharged in cars on the second track on the other side of the pier. The electrical equipment is arranged to operate on 440-volt, 3-phase, 25-cycle, alter- nating current. The motor equipment includes the following, in addition to the motors in connection with the screening apparatus, all furnished by the General Electric Co.: three 112 H.P. motors for moving the three two-span bridges and a 112 H.P. motor for operating the single-span bridge that has the extensive screening equipment; one 50'H.P. motor for moving the other single-span bridge; one 225 H.P. motor in each of the four trolleys for hoisting; two 112 H.P. motors in each trolley for the trolley travel; one 5 H.P. turntable motor in each trolley for rotating the grab buckets; one 2 H.P. clutch motor in each trolley, and one 15 H.P. continuous running motor for operating the screening elevator and conveyor in the pier of the single-span bridge not containing the extensive -screening equipment. The travel motor on each bridge is operated by a general electric drum-type controller. The hoist motor on each trolley is operated by a master-operated magnetic controller. The trolley travel motors on each trolley are operated by a master-type controller. During tests of the plant the steamer “J. S. Ashley,” with 8,983 tons of lump coal, was unloaded in ten hours and fifteen minutes, and the cargo of the “J. E. Upson,” 8,747 tons of the same grade, was taken out in ten hours and fifty-five minutes actual working time. While working in free coal, each bucket averaged nearly 6 tons to the lift.