PLAIN DETONATOR AND ELECTRIC DETONATOR || LOW TENSION & HIGH TENSION DETONATOR

PLAIN DETONATOR AND ELECTRIC DETONATOR -- LOW TENSION & HIGH TENSION DETONATOR.

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PLAIN DETONATOR : 

✓ It is a Aluminium tube having diameter 6mm and 32mm to 50mm in length, it is made out of a 0.3mm thin section aluminium plate closed at one end.

✓ The tube is filled with two types of explosive. i.e Base charge (PETN - Penta -erythritol-tetra-nitrate) and Prime charge A.S.A composition ( The A.S.A composition consist a mixture of lead azide, lead styphnate and small quantity of aluminium powder.

✓  The ⅓ portion of the tube is filled with  A.S.A composition (0.35 gm)  and PETN (0.25 gm)

✓  TheBase charge PETN present at the bottom of the tube and above the base charge there is a primed charge (A.S.A) , and the top portion of the tube is filled with saw dust, during the use of detonator the saw dust is remove by tapping before inserting the safety fuse.

✓  Then the safety fuse is placed in the tube and the top portion of the tube is crimped.

✓ The safety fuse must be projected minimum 1.2mt outside the hole.

✓ When the safety fuse is ignited it explodes the A.S.A priming composition which initiates the base charge of PETN which is a much more powerful explosive.

✓ Plain Detonator is a non - electric. type of detonator. And use of detonator is prohibited in underground mine.

ELECTRIC  DETONATOR:

There is two types of electric detonators which are as follows.

1) Ordinary ele. Detonator or instantaneous detonator.

2) Delay detonator.

Note: the electric detonators will be either low tension detonator or high tension detonator. The ordinary or instantaneous detonator will be low tension or high tension detonator. But in appearance and composition the delay detonator is like low tension detonator.

ORDINARY ELECTRIC DETONATOR : 

✓ It is a copper or aluminium tube of 6mm diameter and 32 mm to 52mm in length, the tube is made out of 0.3mm thin plate and closed at one end.

✓  Thetube is carrying a main charge at base called as PETN which act as a detonating medium.       

✓ Above the base charge there is a prime. charge The prime charge called as A.S.A which is a mixture of lead azide, lead styphnate mixed with small percentage of aluminium powder. 

✓  These detonators are produced as No.6 and No.8  ,The No.6 detonators contain 0.25gm of PETN and 0.35gm of A.S.A . While No.8 detonators contain 25% more charge as compared to No.6 detonators.

Note : In India IDL company manufactured No.6 and No.8 instantaneous detonators. And No.6 contain 0.30gm of PETN while No.08 contain 0.60gm of PETN, and the length of the leading wires is 2,3 or 4mt long.

✓  The mouth of the Detonator is sealed with neoprene plug (polymerised dichlor buta diene) . This is a water sealing synthetic rubber with low inflammability. This neoprene plug carries two leading wires (copper) or tin coated iron wire of length 1.8mt or more outside the detonator.

✓ The  other end of these leading  wire inside the detonator are connected to the fuse head. The fuse head is above the priming charge and contain inflammable mixture.

✓ When the electric current is passed this flashing mixture get flashed and the flashing mixture ignites the priming charge which causes increased detonation impulses through detonating medium, this gives the shattering effect which initiates the detonation of high explosive.

On the basis of the composition of the flashing mixture and the electric circuit used in the flashing mixture (fuse head) the electric detonator classified into two types.

1) Low tension electric detonator

2) High tension electric detonator

While the priming charge and base charge of the both detonator is same (unchanged)

LOW TENSION ELECTRIC DETONATOR :

✓ In low tension detonator there is two brass foil of unequal length. These two brass foil is separated by hard board. The one end of the brass foil is soldered to leading wires and the other end is connected by a bridge of thin Nickel-chromium wire.

✓ The Ni-Cr bridge is then dipped in the adhesive mixture (flashing mixture) which formed of lead - mononitro - resorcinol. (LMNR) + Potassium chlorate + charcoal + colloidal cotton.

✓ The globule is formed around the brass foil and the bridge.

✓ The internal resistance of the circuit including internal resistance of the leading wire is less than 1 ohm and the current required for the blasting is 0.5 amp.

✓ The total resistance of the firing circuit including the resistance of blasting cable is approx 7 ohm and voltage required for blasting is 3.5 volt.

✓ The exploder used for blasting in such detonator are of  capacity to produce 1.5 amp current at 5 volt.

✓ The Numbers of hole can be blasted at one time using low tension detonator with series connection.

✓ The LT detonator circuit is also used in delay detonator.

HIGH TENSION DETONATOR :

✓ In High tension electric detonator there is two brass foil of equal length, the one end of these brass foil are soldered to leading wires end, and another end of the brass foil is open.

✓ There foil is separated by hard card board, The open end of the brass foil are dipped in the flashing mixture.

✓ In this case the flashing mixture contains Lead-mono-nitro-resorcinol (LMNR) + potassium chlorate + charcoal + Nitro cellulose + graphite powder and copper acetylide.

✓ The graphite powder used in the flashing mixture act as a semi-conducting medium or chemical bridge between the ends of the two brass foil in the flashing mixture.

✓ The internal resistance of such detonator is very high, i.e it vary from 1500 ohm to 30,000 ohm and the internal resistance of the detonator is not equal.

✓ The resistance of the shot firing cable is comparatively negligible and the resistance of the blasting cable is ignored.

✓ The high tension electric detonator required 0.025 amp current but voltage required is 50 volt.

✓ The HT detonator cannot be tested for continuity because of variable and very high resistance. Moreover when numbers of HT detonator when connected in series the voltage required will be very high which may causes shot circuit in the blasting cable.

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