On account of the vast influence of the machinery developed for unloading vessels on the problem of stocking and reclaiming ore at the blast-furnace, it will not be amiss to illustrate here some of the equipment by which these results are achieved. Fig. 6 shows a fast plant, designed and built by the Brown Hoisting Machinery Co., and may be considered the legitimate development of the first mechanical equipment built for this purpose by the same company twenty-odd years ago.

Where greater stocking capacity is required than the fast plant trolley travel will cover, traveling bridges are used, as shown in Fig. 7. In these the trolley travels on the straight member of the bridge, which is carried on the two traveling towers shown. One of these runs on a double set of rails near the dock front, spanning one or more standard gauge tracks, the other on a single rail at the rear end. The bridge is pivoted to the towers or legs so that it can be slewed at a considerable angle. The runway is carried beyond the line of the traveling legs on cantilevers, the outer one of which is hinged so that it can be raised up out of the way to permit the bridge to pass the spars of vessels. Equipment of this type is used particularly where the furnace plant is at the lake front. Where the stocking capacity required is so great as to necessitate the employment of bridges and where rapid unloading capacity for the vesels is also required a combination is made of the two styles of equipment. Several fast plants remove the ore from the vessels and dump it within reach of the bridge, which picks it up again and stocks it as required, as shown in Fig. 8. This system will be described more in detail in conjunction with the Hoover & Mason and the Wellman-Seaver-Morgan apparatus.

Fig. 6. Brown-hoist fast plant.

Fig. 9 shows in diagrammatic style a Hoover & Mason unloading and stocking apparatus. This consists of two distinct parts. First, a gantry crane with cantilever extensions; one side of it is carried on wheels running on the top of the left hand wall of the ore trough, the other on wheels running outside the railroad tracks close to the dock face. This gantry supports a horizontal runway for a trolley from which hangs a grab bucket, shown in its open position after descending into the ship's hold, at the extreme right.

The method of suspension of this grab bucket is such that it may be rotated at any angle, for the reason that it can only go through the hatches when turned with its long axis parallel with the hatch. But in order to reach out beyond the hatch line and get the ore between the hatches, it is necessary for it to be able to rotate so that its long axis is at right angles to the line of the hatch.

The operation of unloading is carried on as follows: The grab bucket is lowered into the ore, closed, turned parallel with the hatch and elevated to a position alongside the cab hanging from the trolley. The whole trolley is then traversed back to one of two positions and there dumped. The first position is just to the left of the center of the gantry; the other on the left-hand extension of the cantilever outside the gantry. In the first position it discharges into a small hopper and from there the ore is loaded into railroad cars for direct shipment. In the second case it discharges into a concrete trough, from which the ore is reloaded by the second portion of the apparatus.

This consists of a traveling bridge one hundred and eighty-seven feet from center to center of supporting legs, with cantilever extensions on each end, running its total length up to four hundred and ninety-five feet. This bridge is also equipped with a trolley and grab bucket, the later being of more than twice the capacity of the one which goes into the ship's hold, which is of six tons' capacity, the one on the main bridge being of fourteen tons.

Fig. 9. Hoover and Mason unloading and stocking apparatus.

This bridge travels on tracks laid on concrete walls raised up well above the level of the ore yard, so that the ore will not run down on the tracks even when the yard is filled about to its capacity. The trolley and grab bucket on the main bridge use the ore in the trough as a source of supply, and taking it out of this trough carry it back . to any one of the three piles under the three portions of the bridge and there dump it.

The drawing is so plain as not to need much detailed explanation. Means are provided whereby ore may be shipped out by rail from two or three points. At the left of the drawing is the bin system for the furnace itself, this plan having been prepared for a furnace plant located just back of the dock line on the lake front, but a plant of the same general type would be used if the ore were merely stored in the yard and shipped out as required through the winter.

It will be seen that the gantry unloaders are relatively inexpensive as compared to the main ore bridge, and it is therefore commonly possible to have five or six of these all working on a vessel at the same time, and delivering their ore into the concrete trough. The large bridge follows these and keeps the trough sufficiently clean for them so that they are free to dump in it when they move, as required by the contents of the hatchways, etc., thus the unloaders can be devoted to the purpose of unloading without much consideration of the question of ultimate disposal.