EM 113 Drilling and Blasting subject presentation

1. Chapter 7
Blasting accessories
Mary Kassel T. Blanco

2. Outline
7.1 INTRODUCTION
7.2 POWER SOURCE FOR ELECTRICAL FIRING
7.2.1 Exploders
7.2.2 Sequential blasting machine
7.2.3 Mains firing
7.3 BLASTING CIRCUIT TESTING

3. 7.1 INTRODUCTION
Blasting accessories
- Various products that are used in blasting, in
addition to explosives and initiating devices.
- Few are consumed in the blast, but most of them
are designed to be used in blasting repeatedly.

4. tools and equipment normally
required include:
• Power source
• Non-metallic measuring tapes equipped with
lead or non-sparking weights
• Lowering ropes
• Non-sparking lowering and retrieving hooks
• Tamping poles

5. tools and equipment normally
required include:
• Blasting knives
• Connecting wire
• Lead line
• Blasting covering material
• Crimper
• Lightning detector

6. • The substitution of steel nuts or bolts for
weights, steel pipe or length of drill steel for
tamping poles, lengths of detonating cord as
measuring tapes or lowering ropes, reclaimed
leg wire as connecting wire, improper test
instruments must not be permitted.

7. 7.2 POWER SOURCES FOR ELECTRICAL FIRING
Electric blasting circuits are energized by
exploders or by powerlines through special
arrangements.
Storage in dry cells batteries are not
recommended for blasting operations because
they cannot be dependent on for consistent
output.

8. 7.2 POWER SOURCES FOR ELECTRICAL FIRING
• 7.2.1 Exploders
• 7.2.2 Sequential blasting machine
• 7.2.3 Mains firing

9. 7.2.1 Exploders
Two types of exploders:
- Generator type
- Condenser discharge type

10. Generator type
Rack bar:
- Operated by vigorously pushing down a rack
bar which, through a set of gears, spins the
rotor in a DC.
- The electrical energy from the generator is
connected to output terminals when the rack
bar reaches the bottom in its downward travel
where it closes a switch.

11. Generator type
- capable of blasting 30-50 caps in single series

12. Generator type
Key-twist type:
- A spring is first wound and with the help of key, it
is suddenly released. This through a set of gears
spins the rotor in DC generator.
- Operated by a quick twist of the handle with one
hand while the machine is held firmly in the other
hand.
- Capacity of 250 to 400 shots

13. Condenser type
- The capacitor discharge (CD) machine a
condenser is charged to a high voltage and
discharged later through the external firing
circuit.
- The basic source may be a low voltage dry
battery or an electromagnetic generator.

14. Condenser type
• One button or switch is activated to charge
the capacitors and a second button or switch
is activated to fire the blast.
• Some are capable of firing 100 caps in parallel
series.

15. • The capacity of the exploder must be more
than sufficient to fire all the detonators, it
should be too much higher than what is
needed.
• A good rule of thumb is to use an exploder 1.5
- 2 times the needed capacity.

16. 7.2.1 Sequential blasting
• SB machine is a unit containing 10 capacitor
discharge machines that will fire up to 10
separate circuits with a preselected time
interval between the individual circuit.
• This can be useful in improving fragmentation
and in controlling ground vibration and
airblast.

17. 7.2.3 Mains firing
• Powerline blasting is often carried out with
parallel circuits where the capacity of available
blasting machine is inadequate.
• Power blasting should not be carried out
unless precautions are taken to prevent
arcing. Arcing can result in erratic timing or a
misfire.

18. 7.3 BLASTING CIRCUIT TESTING
• Blasting procedure can be successfully
executed only if proper care is exercised in
planning and connecting the blasting circuit.

19. 7.3 BLASTING CIRCUIT TESTING
A list of possible circuit weaknesses is given
below:
1. Discontinuity
2. Current leakage
3. Stray electricity

20. 7.3 BLASTING CIRCUIT TESTING
• Discontinuity or shorts in:
– detonator circuit and
– the total or any part of the blasting circuit;
• Current leakage
– can occur when damage to a leg wire insulation
allows the bare wire to make a contact with the
rock specially under conditions or conducting ore
body.

21. 7.3 BLASTING CIRCUIT TESTING
• Stray electricity
– Current leakage from extraneous sources.

22. 7.3 BLASTING CIRCUIT TESTING
Two type of blasting circuit testers:
- Blasting galvanometer
- Blasting multimeter

23. 7.3 BLASTING CIRCUIT TESTING
• Blasting galvanometer
– Is used only to check the circuit resistance.
• Blasting multimeter
– Can be used to check resistance, AC and DC
voltage, stray currents, and current leakage.