The Mechanical Handling and Storing of Material

BLAST-FURNACE HOISTS 347 is also essential that the feeding device which admits the material into the furnace should be so arranged as to distribute the material evenly, and at the same time to do so without allowing the gas to escape. The general construction of these elevators consists of an inclined iron-trussed bridge upon which the rails for the ascent and descent of the trucks are laid, whilst the hoisting gear for the manipulation of the trucks is laid on the ground level. The rails, when they reach the upper terminus, are generally bent into a more or less horizontal position, so as to tilt the truck for unloading purposes. In addition to this, the back wheels are supported either by rails that are bent at the terminus, or else they have a different diameter on either side of their flanges, so that during the ascent the tiuck runs on its normal wheels, whilst at the terminus the larger diameter wheel engages with short lengths of extra rails and thus assists the automatic clearance. To balance the dead weight of the bucket or car a counterweight may be used, or a double track may be employed, so that the empty car will descend on the one track whilst the loaded car is being drawn up on the other. In such a case the distributing hopper on top of the framework must have an elongated form, so as to take the charges alternately from, buckets on either track. Another plan which has been recommended is to lay the two tracks above each other, and to run one car on the upper and the other on the lower rails. The two cars will pass each other at about the centre of the bridge, where there will be plenty of room for them to clear each other. At the terminals, that is to say, at the loading and discharging points, both will be in a suitable position for filling and discharging. The difference in the capacity of the cars, of course, depends a great deal on the system on which the furnaces are worked and on their capacity. In the Brown Hoisting Machinery Co.’s apparatus the capacity of the carriers is generally 2 tons of ore or 1 ton of coke, while the cubical capacity is 110 ft., and the hoisting speed 300 ft. per minute. The time occupied in raising the load to a furnace 80 ft. high would be 20 secs., discharging it takes 4 secs., and returning it 10 secs., or 34 secs, altogether for each turn. The speed at which the bucket travels is 5 ft. per second, which, if no counter- weights are used, would require a motor of about 100 H.P. Another estimate is for a motor of about 150 H.P. for a truck of about 150 cub. ft. With a car of a capacity of 240 cub. ft., intended to serve a furnace of 550 tons daily capacity, the service would require ninety charges (which would each take two truckfuls of ore and lime and as many of coke) in twenty-four hours; therefore the car would have to make 360 ascents, and only four minutes could be given to each turn, including the filling of each truck. Furnace Hoists of the Brown Hoisting Machinery Co.—Fig. 486 represents a typical installation of a furnace elevator as designed by The Brown Hoisting Machinery Co. The stock of iron ore, coke, etc., required for use during one day is kept in large silos or bins, constructed of iron and wood, at the foot of the elevator. The main stock pile is kept on the open ground in the store yard, and from this the silos are served with the material to be used immediately. Ihe material which has been bi ought by rail or from a distant part of the works is conveyed along an elevated railway and dow n an incline into the store hoppers. The trucks which are used for this purpose are hoppered to both sides, and discharge their load through two longitudinal hinged doors on each side of the truck. One of these trucks can be seen in position on top of the silos in the illustration.