Tools and Machinery of the Granite Industry

Later, black powder was manufactured in paper tubes (or sticks) that could be easily placed in the drilled holes. Some quarries "rolled their own" black powder in paper cartridges. Also, DuPont made cylindrical cakes of compressed black powder. For the first hole, a whole stick was placed in the back of the hole, a half stick in the middle, and a whole stick near the front. The next hole loaded was six or eight holes over and had a half stick in the back, a whole stick in the middle, and a half stick near the front. This process would be repeated until the end of the line of holes was reached. Sand in cylindrical bags was tamped in behind each stick (Figure 32). Today, electrically-fired primer cord explosive is loaded into every other lift hole.

Blasting caps were introduced as a much more reliable way to fire the charge. Blasting caps were initially non-electric with a fuse. Electrical detonation was a great improvement since it was safer and more holes could be shot at the same time. An electric blasting cap is fired by a blasting machine (Figure 33). There are a number of types of blasting machines, but all strive to produce every time a sufficient amplitude electric pulse. When there is an insufficient or marginal electrical pulse and blasting caps in series, the most sensitive caps detonate first and the remaining caps do not fire causing a misfire. The powderman must then deal with the remaining and dangerous unexploded powder-not knowing exactly where it is located. With the pushdown plunger type blasting machine, the handle is pushed down as hard as possible-spinning a dynamo. When handle reaches the bottom, a switch made of a strip of brass under the handle is closed and an electric pulse is sent to the blasting caps. The pull-up plunger type works similarly, except that the handle is pulled up to spin the dynamo. The condenser discharge type blasting machine consistently produces a sufficient electrical pulse. A crank is turned to build up an electric charge on condensers and when a red light comes on the condensers are fully charged. The condensers can be discharged, by pushing a button, only after the red light comes on. Blasting caps can be wired in series, in parallel, or in series-parallel. For series-parallel wiring, the blasting caps are divided into groups in series with wires coming back to the blasting machine from each serial group. For example, there may be ten groups each with one hundred caps in series. Some blasting machines can handle up to a thousand blasting caps in series-parallel, which is an order of magnitude greater than was possible with non-electric blasting caps.

Splitting Out Saw Blocks