This historic book may have numerous typos and missing text. Purchasers can download a free scanned copy of the original book (without typos) from the publisher. Not indexed. Not illustrated. 1901 edition. Excerpt: ...having an effective piston area, after deducting the area of the rifle bar, of 6 square inches; weight of piston and drill steel, 50 pounds. The friction of the pipe and passages, throttling by the valve and back pressure from the exhaust, together with the following of the steam of air pressure for three-quarters of the stroke, will reduce the mean pressure to 40 pounds. Then by the formulas as given for the steam or air hammer, the energy of the blow will be the total mean pressure on the piston multiplied by the stroke in fraction of a foot, plus the stroke multiplied by the weight, or 6 square inches X 40 pounds X fi + X 50 pounds = 120.83 foot-pounds. Then if the drill penetrate the rock of an inch at each 12 stroke the theoretical effect of percussion will be--or 96 X 120.83 = 11.699 pounds, or nearly 6 tons static pressure. A large allowance from the theoretical effect must be made for the actual effect, by the assumed value of the friction of the drill steel on the sides of the hole, and other moving parts, as well as for the resisting effect of water and debris of drilling, which always more or less clog the drill hole. The average running time of drills on open rock work is about five hours per day, and the average of 250 strokes per minute or 75,000 strokes per day is probably a fair average day's work. This at-inch depth of cut and 10 strokes to make a circuit of revolution of the steel to complete the cut will represent 75,OOQ =--! = 78 feet lineal depth of holes for a day's 96 10 work in rock of medium hardness--limestone. In granite from 50 to 60 feet is about an average day's work, owing to the less penetration of the drill per stroke; while in marble, with dry short holes, a very much larger depth of holes, 200 to 250 feet, has bee...
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