The Mechanical Handling and Storing of Material

424 THE MECHANICAL HANDLING OE MATERIAL and there is a 35-ft. cantilever extension from the rear end of each of the single-span bridges. Each man trolley is designed to carry a load of about 10 tons, to hoist the full load of the bucket at the rate of 225 ft. per minute, and to travel along its runway at 1,200 ft. per minute. Each bridge, when carrying a loaded bucket, can propel itself along its own runway at a speed of 60 ft. per minute. The front or water end of each two-span bridge, Fig. 597, is carried on a portal pier equipped with bins for loading coal into hopper or gondola cars. The centre and rear end of the two-span bridges and the forward end of the single-span bridges are carried on shear legs, each shear leg running on a single line of rail. The shear leg rails are supported on trestles constructed of steel girders carried on steel A frames. There is one single rail trestle or ■S runway, and one double rail trestle. The 'S former is for the shear leg at the centre of the two-span bridges, and the latter is for the rear ■g shear leg of the two-span bridges, and the shear E legs of the single spans. The distance from h3 the foundations to the top of the rail on the trestles is 35 ft. 6 in. The rear ends of the E single-span bridges are carried on inverted piers. 1 The piers for the two-span bridges are each u supported on four equalising trucks, each truck ® being mounted on four 24-in. double-flanged, cast iron, chilled-tread wheels. The wheels on each pier are connected by a train of gearing and shafting to the moving gear mechanism located on the bridge span, near the bridge support. Each inverted pier at the rear end of the single spans is carried on two sets of equalising trucks, each truck supported on eight similar wheels. In addition the rear pier that carries the screening apparatus has for partially carrying that apparatus one equalising truck supported on six 24-in. wheels, each truck travelling on two lines of rails spaced 2 ft., centre to centre. The six-wheel truck acts as an idler only. All of the wheels in each of the eight-wheel trucks are driven, being connected by a train of gearing and shafting to the moving gear mechanism located at the top of the pier. Under the other rear pier one half of the wheels are similarly connected to the moving gear mechanism. Each shear support in the bridges is mounted on two single-rail equalising trucks, each truck being supported by four wheels.