The first change from the primitive arrangement I have described was the introduction of power hoists for taking the material to the top of the furnace. These were of two kinds, vertical and inclined, but irrespective of this, in the majority of cases a platform was used on to which the barrows were rolled by men at the bottom. The platform was then hoisted, whether vertically or on an incline was a matter of detail, and men at the top, known as top fillers, took the barrows off the car, distributed them around the top of the furnace and dumped them.

The introduction of power hoisting as a substitute for the bridge method of bringing the material to the top of the furnace was necessitated by the increase in the height of the furnace from some twenty-five or thirty feet to fifty, sixty and seventy feet. No hill could be found steep enough and high enough to lend itself to filling purposes for furnaces of such heights.

The operation of filling being continuous, and the need for capacity growing rapidly after the introduction of power hoisting, double acting hoists were introduced very early and are used almost universally, with certain exceptions to be noted later. By this means the platforms, cars and filling barrows balance each other on the ascending and descending trips, leaving only the useful load of the charge to be hoisted. This effects the saving of a great deal of power, and permits the use of much smaller hoisting apparatus.

Many styles of hoisting apparatus were tried in the early days of power hoisting, hydraulic, pneumatic, water-balance, and various types of engine-driven hoists were used. Nevertheless this was one of the earliest parts of the equipment to become standardized, and for many years there has been used a very simple type of vertical two-cylinder engine, with cranks at right angles, and the engine shaft geared to the rope drum with either a single or double reduction gear. These engines are not fitted with a link like that used for reversing locomotives and other high-grade engines, but are reversed by running the steam in opposite directions through their ports. One set of openings constitutes the inlet when running in one direction and the exhaust in the other.

In order to operate successfully on this system the valves must be set without "lap" or "lead," the eccentrics being exactly at right angles to the cranks, so that the steam follows the piston full stroke, and is not used expansively, even to the slightest degree. As a result these engines are very extravagant of steam, using about one hundred and twenty pounds per horse-power as against twelve to twenty pounds for ordinarily good engines in power stations.

In the last ten or fifteen years there has been a growing tendency to avoid this great waste of steam by the use of motor driven hoists, these obtaining their current from generators in the power station, driven by an engine using not much more than a tenth of the steam per horse-power that is required for the hoisting engine.

Fig. 1. Steam driven blast-furnace hoist for furnace with vertical hoist tower.

There are, however, problems of control which have had to be met and which have proven rather difficult. With the large masses of material now handled it is very important that the operation of hoisting be started and stopped gradually to eliminate the excessive inertia stresses which would otherwise arise. These problems have been solved successfully with the steam hoisting engine by the use of supplementary throttles thrown in and out of operation by a cam traveling at a suitably reduced speed. In order to accomplish the same result with the electric hoist, sliding contacts and a great multiplicity of switches were at first considered necessary, so that the switchboard for such an apparatus was very large, elaborate and expensive.

This problem has, however, been worked out successfully, and such electric hoists are now articles of regular manufacture, as are the steam hoisting engines previously mentioned. Fig. 1 shows a modern steam-driven blast-furnace hoist for a furnace with a vertical hoist tower, where the ropes are led by guide sheaves from the tops of their respective cages to points vertically over the opposite sides of the drum, so that when the rope from one cage is winding up that from the other is unwinding. The cages are thus balanced through the hoisting drum rather than directly. This hoist is built by the Otis Elevator Company.

Fig. 2. Steam driven hoist for a skip-filled furnace.

Fig. 2 shows a steam-driven hoist for a skip-filled furnace, in which there are two distinct drums, separated by a suitable distance horizontally so that the center of each drum shall be in the central plane of its skipway. This will be more fully explained in dealing with skip hoists. This hoist is also built by the Otis Elevator Company.

Fig. 3 shows an electrical hoisting apparatus with its switchboard, built by the Lidgerwood Manufacturing Company. It will be seen that the rope drums in this are the same type as that shown in Fig. 2, this also being for a skip-filled furnace.