We may now consider the bins which serve for storage of the raw materials going immediately into consumption.

These bins are of many types, bins having had a development covering many decades. Substantial and well designed wooden bins were in use at a few plants thirty, forty and fifty years ago. But the great storage required for modern plants necessitates one and frequently three or four tracks on top of the bins, all of which must carry the most heavily loaded railroad equipment. This, with the excessive maintenance of wooden structures, has gradually forced the introduction of steel bins, built as an integral part of the structure which supports them and the railroad tracks at the same time. Recently concrete bins also have been introduced.

It is useless to try to illustrate all the types of bins which have been used, and I shall therefore show only four of the best known types, three of which are brought out by the three concerns whose ore-handling machinery has previously been described.

It is necessary to explain that at the large modern plants where equipment of the highest type is used, mechanical filling is now practically universal, and these bins are not therefore designed to discharge into filling barrows, but into the modern successor of the filling barrows, the scale car.

The design of gates for bins is a matter, the difficulty of which in practice is as great as its simplicity appears to be on cursory examination. The material to be handled is irregular in size, irregular in shape, rough, as likely as not to be sticky, and more likely than not to have its coefficient of friction greatly altered by change from dry to wet. If the gate opens and closes from above, guillotine fashion, it may just happen to catch the largest lump passing, which may be too strong to be crushed, and holding the gate open will leave room for a rapid flow of finer material under it. If the shape of the chute be not right the material will jam and bridge, exercising apparently almost human, not to say devilish, ingenuity, in building an arch which quickly cuts off the flow of material from the bin, and which cannot be broken outward because the material is under compression, nor inward except with the greatest difficulty because the pressure of all the material in the bin lies against it.

More than one case is on record where an engineer or furnace manager has designed a new type of gate for a bin, taken a guest out to see how beautifully it operates, and then had it fail so completely that the filling barrow, or even the scale car, would be buried up because the material could not be shut off when the "improved" gate was brought into play.

Even if these fundamental difficulties be overcome great care is necessary in placing the spouts on the bins and bringing them sufficiently close together so that material does not build on the space between them and in time almost fill up the bin. This may seem like an extreme statement, but I have seen bins of the very best construction and most carefully designed, which looked to be full of ore, but on closer examination two holes, three or four feet in diameter, were to be seen running down from the top to the two chutes blow. These holes would represent almost the only free-flowing capacity of the bin. The ore being plastic and sticky, had built up upon the base of the bin and the bridge between the spouts, until the capacity of the bin was almost gone. This is likely to happen to some extent with any design, and the only way to meet the situation is to dig the bin out at frequent intervals, as the rapidity with which the ore builds is increased as it gets a larger and larger foothold.

It was with the object of overcoming these various difficulties and furnishing bins whose flow would be under the absolute control of the operator that the four designs now to be described were brought out.

Taking the designs of the three builders mentioned in the same order as before, Fig. 16 shows a "parabolic" bin designed by the late Alexander E. Brown, of which the principle is taken from the fact that when a liquid or semi-liquid is suspended in a trough of flexible material, the cross section assumed by the trough is a parabola, therefore by giving the bin this shape, stresses tending to deform it are eliminated, and only its weight needs to be considered. These bins are suspended from heavy girders, which in turn are supported by steel columns. The complete parabola at the left is for ore. The incomplete one of greater width, on the right, joined to the ore bin at the left, is for coke.

The spouts on these bins with their gates in the form of cylindrical quadrants are plainly shown at the bottom as is also the scale car beneath them. A locomotive crane standing on an adjacent trestle, and in a position to discharge ore into the railroad car standing on the bin trestle, is also clearly shown.

The construction of the bins is well shown by the photograph Fig. 17.

Fig. 18 shows the bottom of the bins with their chutes, also the scale car and its operator. It will be seen that the quadrant gates are operated by a pair of connecting rods attached to crank pins, carried on a heavy gear shaft, supported at the top of the chute. The large gear is driven by a pinion which in turn is driven by a pair of bevel gears. From the vertical shaft of the driver of these depends a shaft carried by a universal joint and carrying a socket at its lower end. The scale car carries a square-headed shaft, which can be thrown up by the operator to engage with the socket for any chute. After this is done a small motor is started and the gears are revolved until the crank pins come to the bottom, in which position the gate is wide open. When the required amount of stock has been drawn the gate is raised by revolving the large gear shaft through another half revolution.