Fig. 16. Furnace with Brown skip hoist and parabolic bins.

Fig. 17. Parabolic bins.

The style of bin and chute designed by Hoover & Mason is shown in Fig. 19. No attempt is made in this bin to use the parabolic shape, which is open to the objection that its angle changes, so that while it may be steeper than necessary in some portions it is flatter than necessary in others, and the latter condition prevails near the bottom, where the flow should take place most freely.

The bottom of the bin is formed by a horizontal roller five feet in diameter which lies close to the bottom edge of the chute, so that no material can get between the two. This can be rotated at the will of the operator in the direction shown by the arrow. The angle from the top of the chute opening in the bin to the top of the roller is considerably less than the angle of repose of the material, so that no material can possibly get out of the bin when the roller is stationary. On the other hand, when it is rotated the material is carried forward by the roller to a point at which its slope is greater than the angle of repose of the material, which then slides off. When the roller is stopped the flow of material instantly ceases.

The front of the bin is built with louvres with a reverse slope, through which it is impossible for the material to make its way out, but through which it is very easy for the operator to thrust in a bar and break any bridge or arch that may form" to obstruct the flow.

The roller is driven by means of gearing thrown in by a clutch worked by the operator. The gearing is actuated by a line shaft or driving shaft, which runs continuously. There is a separate roller for each discharge, the equivalent of each chute in the older type of construction, and the design is such that the ends of these rollers come very close together, leaving a miminum of space between them, so that the bin is practically open at the bottom all the way along. This to a great extent prevents the formation of accumulations of ore, as these have no foothold on which to begin to form, the bottom of the bin being kept clean by the continuous sliding of the material over it, and no bridges between chutes existing. For the coke bin the roller is perforated, and by an ingenious arrangement made to serve as a screen for the removal of the fine material from the coke. This action is always complete and automatic because the roller cannot run as a feed device without also acting as a screen.

Fig. 18. Bottom of Brown hoist bins with their chutes, and scale car with operator.

The transfer car used in bringing the ore from the bridge to the bin is shown in dotted lines above, as is also the overhanging end of the ore bridge with its grab bucket and trolley.

A gate has been introduced by the Wellman-Seaver-Morgan Company, which is on the same principle in all particulars as that of Hoover & Mason except that the former uses instead of a roller, an endless belt made of overlapping metal slats mounted on sprocket chains, as shown in Fig. 20. The pressure of the stock on top of this is taken by beams lying inside the endless belt, on which its upper half slides. Owing to the location of this apparatus up underneath the bottom of the bin, the construction is not as clearly shown by the photograph as might be desired, but the overlapping metal slats and the sprocket chains are visible, and the operation will be understood from the description of the Hoover & Mason apparatus. The metal belt acts as a bottom to the bin and carries the material bodily forward until it drops over the driving-sprocket end into the scale car.

Fig. 20. Wellman-Seaver-Morgan Gate. Endless belt made of overlapping metal slats on sprocket chains.

It will be noted that all three of these designs which jointly have probably been applied to a greater tonnage of bin capacity than all other types combined used power for the operation of the gates.

This is because of the difficulty that has often been met in operating hand gates quickly and positively, to which I have already alluded. At the same time it must be understood that many hundreds of bins are in successful use with hand-operated gates, which have the advantage of greater simplicity and lower first cost than any of the power-driven gates.

Fig. 21 shows an outline drawing of the Baker suspension type of bin built by Arthur G. McKee, Contracting Engineer, Cleveland, Ohio. The gate in this type of bin is a quadrant of a cylinder, but in the reverse position to that used on the Brown bin. The axis of the cylinder is so located that the flow of the material tends to close the gate, so that it is not liable to be opened accidentally. The gate is operated by the scale-car operator through the lever shown in the drawing.

Owing to the ab-sence of machinery these gates are only separated from one another by the small space necessary for clearance, so that the opening in the bottom of the bin is continuous and the formation of bridges and building up of the ore inside the bins is thereby prevented to a great extent.

These bins are, like the Brown, of the suspension type, but instead of their cross section being that of the true parabola it is made up of four tangents thereto, which give to a large extent the same freedom from distortion that comes from the use of a true parabola, any minor stresses of this nature being taken up by the transverse partition plates and the rigid bottom.

A considerable tonnage of these bins is in successful operation at various plants and there are many others with other types of hand-operated gates, some of which are entirely successful.