Colliery Engineer by Unknown

Author:Unknown
Language: eng
Format: epub
Publisher: Scranton, Pa.

MINES AND MINERALS

February, 1911

electric fuses, so soon as one started to push down the rack bar. It would be a very weak current at first, gradually increasing with the building up of the blasting machine. Such a current is not well adapted to fire a number of electric fuses simultaneously, because it is impossible to make all of exactly the same degree of sensitiveness, and with the gradually increasing current, the more sensitive electric fuses would fire first, breaking the circuit and causing the less sensitive ones to miss. By employing the shunt, on the other hand, no current is sent out from the blasting machine until there is ample power to fire even the least sensitive. The three-post blasting machine, Fig. 14, contains an ingenious device for increasing by nearly 60 per cent, the number of electric fuses that the two - post blasting machine wovdd be able to fire. When it is desired to take advantage of the three - post feature of such a blasting machine, the electric fuse circuit is arranged as shown in Fig. 17. Three leading wires are used, which divide the blasting circuit into two separate circuits. The great increase

in efficiency is brought about by equipping the contact spring with both an upper and a lower contact, and arranging it so that it will throw the full power of the dynamo first into one circuit and then into the other. While the two circuits do not really fire simultaneously, the interval between them is so extremely short that only one explosion is heard. If it were not

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