Partha Das Sharma’s Technical Diary On EXPLOSIVES & BLASTING a velocity of about 2000 M/sec. without bursting the tubing and therefore having no effect on any Explosives through which is passes. The resulting flame front ignites the top of the delay element with in the detonator tube. These are available in long delay and short delay series. CORD RELAY : These devices permit short delay to be introduced into trunk lines of detonating cords. A cord relay consists of two delay detonators mounted inside a resilient plastic shell. They are bi-directional in operation, Cord Relays are available in the 15 Ms, 17 Ms, 25 Ms, 50 Ms, 75 Ms, 100 Ms, delay time. The shorter delay intervals are generally required for small (65-90mm) dia blast holes drilled on close spacing whereas the longer intervals are suited to larger blast holes drilled on wider spacing. Cord Relays are designed for use with detonating cords, which have core loads of 10 gm/M. No special connecting tool is needed. DETONATING FUSE : It serves the same purpose as detonators and directly initiates the high Explosives while them needing a detonator for initiation. Useful in simultaneous multiple shot firing minimising the use of several detonators. Advantageous in blasting long hole. It comprises of PETN (Pentaerythrol Tetranitrate) train enclosed in a tape wrapped in textile yarn and whole thing covered by plastic. Finished dia 5 mm for the D.F., which contain 10 gm PETN meter (See Sketch).
OHM METER : Used for testing the continuity and resistance of blasting circuits. These are of two types. i) Powered by low voltage hand operated generator. ii) 1.5v dry battery type. EXPLODER : Used for firing shots electrically, these are of two types: i) Generator type :Magneto of dynamo (for large capacity) operated by a quick twist of strong down ward push of handle. ii) Condenser discharge type :- Can be battery of dynamo powered.
6 -----------------------------------------------------------------------------------------------------------------Author: Partha Das Sharma, B.Tech(Hons.) in Mining Engg. (E.mail: sharmapd1@gmail.com) Website: http://miningandblasting.wordpress.com/