MINING MACHINERY.
However important the location and development of our mines, and necessary as may be the knowledge and experience to accomplish their development, these requisites are, perhaps, not more important or necessary than the mechanical skill and judgment required in designing or selecting the most available machinery for the place or the purpose. This is evident: we have seen it demonstrated on so many occasions, and in so many places, that we often feel surprised and pained to witness so great a lack of tact where so much mechanical skill exists. The want is not in the ability to manu facture, but to apply the necessary mechanical power. We do not wish to make invidious mention, but within our experience we could point out a hundred cases where the most serious consequences, in increased expenditure and waste of power, have resulted from misapplication and miscalculation.
In mining machinery, two important considerations require the first attention, viz.: simplicity and strength. In colliery engines, the question is not so much economy in the use of fuel, as availability in mining operations; power, durability, and general simplicity of style are the most essential requisites; and, whether designed for hoisting or pumping, the more compact and concentrated their efforts, the more serviceable and permanent will be their duty. But the style of the machinery is also an important consideration. Heavy engines are now generally required, since our mines are in creasing in depth as our colliery establishments increase in proportion; and larger quantities of coal are required as their product in order to compensate for the increase of the original outlay and the general daily expense.
If ten tons of coal, car, cage, and rope are to be lifted 1000 feet per minute, we can form some idea of the size and power of the machinery, taking Watt's calculation of the duty of a horse-power for our guide. At 33,000 pounds lifted one foot high per minute, as the law of a horse-power, it would require 600 horse-power to lift 10 tons 1000 feet per minute; or, by gearing, to lift the same in two minutes, 300 horse-power would be the calculation. But in our mines we always balance the cage and the car:
we have, therefore, on starting, 3 tons less, and 200 horse-power will do the work designed,—that is, lift ten tons 500 feet per minute,—providing the balancing power is equal to one-third of the load.
With machinery of such power it is necessary to calculate the area of the piston-head in proportion to the load to be lifted, since the speed of the piston and speed of the load cannot be varied to the extent they may be in smaller engines. If the drum on which the rope winds is 12 feet in diameter, the pinion on the crank-shaft be 4 feet, and the stroke 5 feet, or the crank 2a- feet, the piston must move at the rate of 413e feet per minute to move the load at the rate of 500 feet per minute, and the number of revolu tions must be 41i per minute,—which is faster than an engine of 200 horse-power ought to move. But by arranging the engines as two 100 horse-power connected link-motion engines, their speed might be increased, and the load moved at the rate of 500 feet per minute, with great facility.
Twenty revolutions per minute would be a fast speed for a 200 horse-power engine with a stroke of 6 feet: therefore, to move a load at the rate of 500 feet per minute, the pinion would be 8i feet diameter. But by the use of two connected 100 horse-power engines the speed may readily be increased to 40 revolutions per minute, and the pinion reduced to 4* feet, while the stroke may be 5 feet or less. This arrangement increases the leverage or power of the engines one-half, and has the advantage of keeping one of the engines continually on the "live centre;" but the amount of steam used is thereby considerably increased. This, however, would be a necessity, under the circumstances of lifting a load of 7 tons, or 14,000 pounds, 500 feet per minute, since a 200 horse power engine would scarcely do the work, while two 100 horse-power connected engines would do it easily, provided the quantity of steam were increased.