The chain short-wall machine (Fig. 10) is an improvement of the breast machine, and is designed to avoid the labor and loss of time of the breast machine in withdrawing the coal ing and unloading of the machine is effected by its own winch.
The manner in which the short-wall ma chines are operated is shown in Fig. 11. At (a) the machine has been unloaded; (b) shows it in lace for making the sumping cut; (c) is the position taken for the same purpose where the roof is bad and the props are set close to the face; at (d) the sumping is finished and the cutter and shifting the frame at each cut. The short-wall machine, like the disc and bar ma chines, is designed for continuous work. The machine is provided with a winch or drum and machine is ready to travel across the face; (e) shows the machine cutting across the face; (f) the cutter arm is advanced for hard cutting; (g) shows how the machine is manipulated where a nodule of hard pyrite is encountered; (h) the cutting arm is turned out to set the bits and (i) returned to continue the cut; (k) the under cutting is finished; (1) machine is ready to widen out a room; (m) cutting along the side; (n) moving and loading the machine on its truck. The above illustrations show the ease with which the short-wall machines are manipulated.
Short-wall machines as now constructed weigh about two and one-half tons and are provided with 30 horse-power motors, either electric or compressed air. The cutter bars are from 5 to 10 feet long. Long cutter bars in creased greatly the capacity of the machine and diminish the cost of cutting per square yard and per ton of coal. They can be used, how ever, only where conditions are favorable.
As short-wall machines are used for under cutting the coal in entries and rooms, their capacity is greatly reduced by the time in going from one working place to another, and in unloading and loading the machine and starting work at each place. Under average conditions from six to eight working places can be undercut in a shift of eight hours.
The endless chain long-wall machine (Fig. 12) differs from the short-wall type in that the cutter bar is pivoted so that it can be swung through an arc of 180 degrees. In cutting the bar is at right angles to the machine. This permits the machine to travel in a narrower space, so that props can be set within three feet of the space. The short-wall machine requires a space of six or seven feet.
The arc wall or turret type of chain ma chine (Fig. 13) represents the latest develop ment in coal cutting machinery. It is mounted on a self-propelling truck, and is operated from the track without the delay of unloading. The cutter bar swings through a semi-circle and the machine is mounted on three standards and can be raised or lowered about one foot. By the
use of different sized offset brackets, or by attaching the cutter bar without offset, the machine can be built to cut the kerf at the floor or roof of the coal seam or at any desired level between. This permits the kerf to be made in a dirty or slaty seam. The machine weigns six to seven tons and is provided with powerful motors. With a seven and one-half-foot cutter bar it commands a width of 20 feet. For rooms of greater width the track must be shifted or laid along the face. Two tracks may be used. It can be operated in an entry of ordinary width. The capacity of the machine is said to be about double the short-wall machine and three times that of the breast machine.
The loading of mine cars by hand is a slow operation. Fig. 14 shows a shoveling machine in successful use in the metal mines, which is now coming into use in the coal mines as well. These machines have a loading capacity of one to two tons of coal per minute. They are built to work in coal seams as thin as four feet and can be used in narrow entries, rooms or long wall workings. The machines weigh from 5 to 10 tons, and require PA to 12 horse power. They are driven by compressed air or electric power, and are generally equipped with motors 50 per cent above actual power requirements. The shovel should have sufficient lifting power to break up coal which has fallen in large blocks.
In long-wall mining the rapid loading of the coal from the long working face is difficult. The use of convey-ors, extending along the faCe. to move the coal and load .it on cars in the haulage entries greatly Jacilitates this work Face conveyors are particularly useful in thin or inclined coal beds. These conveyors are of three types: (1) Small cars run back and forth by mechanical means, singly or in trains. These can be used in thin coal beds and at any in clination, but do not provide for continuous loading. (2) Shaking troughs, used in inclined workings. The trough of sheet metal is given a combined reciprocating and up and down motion, and can be operated at a small inclina tion. The breakage of coal is sometimes a serious objection. (3) Continuous mechanical conveyors either endless belt or scraper lines. The endless belt type conveys the coal with min imum power and minimum breakage. These conveyors are loaded by hand or a shoveling machine may be used for the purpose. The remarks at the beginning of this article on the importance of keeping mining machines steadily at work by effective organization applies with especial force to loading and conveying ma chinery. The haulage system must be well designed and equipped and efficiently operated that there may be no failure to supply mine cars as they are needed at any given point in the mine.