![Blasting Machine
A typical "capacitive discharge" blasting machine works
by charging a capacitor from a battery, then discharging
the capacitor through an external circuit, called the
firing line, to fire the blasting cap.[1]
While the machine is idle, an "internal shunt" is
connected across the output terminals so that any stray
voltages induced in the external circuit, for example by
nearby radio transmitters, are harmlessly short-circuited
without triggering the blasting cap.
The machines also typically include an "abort" feature to
discharge the internal capacitor without firing the cap.](https://image.slidesharecdn.com/lecture5blastinitiation-231016114008-bf72eba1/85/Lecture-5-Blast-Initiation-pdf-26-320.jpg)
Lecture 5 Blast Initiation.pdf
- 1. Presented by: Dr Clement Kweku Arthur
- 2. Learning Objective Having worked through this chapter, the student will be able to: Know and understanding the various initiation systems
- 3. Initiation Systems An initiation system is a combination of explosive devices and component accessories designed to convey a signal and initiate an explosive charge from a safe distance when properly configured and activated. The signal function may be either electric or non- electric.
- 4. Initiation Systems Electric initiation systems use electrical power source with associated circuit wiring to convey the needed energy. Non-electric systems use various types of chemical reactions ranging from deflagration to detonation to convey the impulse to the non-electric detonators, or in the case of detonating cord.
- 6. Initiation Systems The initiation systems commonly employed in surface blasting are: Safety fuse with caps (mainly in quarries for secondary blasts), Detonating cord, Electric caps or detonators Non Electric (NONEL) assemblies, Electronics detonators and Wireless Electronic Blasting Systems (WEBS)
- 8. Capped Fuse (Safety Fuse) SAFETY FUSE is a ductile cord twined of cotton threads and coated with black polyethylene plastic. The core of the fuse contains black powder. Throughout the mining world today, the capped fuse has been superseded by the other three systems for primary blasts due primarily to safety hazards, slow burning rates and poor water-resistance properties. Safety fuse is primarily used in quarrying and in small blasts with detonating cord caps.
- 9. Detonating Cord Detonating cord (detonating fuse) resembles safety fuse but contains a high explosive instead of black powder. The first successful one, patented in France in 1908, consisted of a lead tube, about the same diameter as safety fuse, filled with a core of TNT (Trinitrotoluene). It was made by filling a large tube with molten TNT that was allowed to solidify. The tube was then passed through successively smaller rolls until it reached the specified diameter. PETN (pentaerythritol tetranitrate) is another explosive used in the detonating cord
- 10. Detonating Cord Detonating cord is a flexible but strong continuous detonator that can be several hundred meters long. A length of detonating cord is required to initiate a detonator which cannot be normally initiated by fire. Detonating cords are available with a variety of charge weights, tensile strengths and protective coatings, depending on the application. Their energy release depends on the amount of PETN in the core, which generally varies from 1.5 g/m to 70 g/m. (Detonating cord is rated in explosive mass per unit length) However, 10 g/m is the PETN weight of standard detonating cord whose VOD is about 7000 m/s.
- 11. Electric Initiation Systems Designed to be detonated by a pulse of electrical energy. Hence, susceptible to accidental initiation by extraneous electricity such as stray currents, static electricity, Radio Frequency Energy (RFE), electrical storms, and high- voltage power lines. This constitute a major disadvantage of the system. This therefore, suggests that due consideration must be given to the potential hazard from extraneous electricity when using electric detonators or when choosing electrical initiation system for blasting operations.
- 12. Electric Initiation Systems Electric detonators may be classified into 3 main groups according to their inherent timing properties. These are: Instantaneous detonators. These are employed mainly for boulder or stone blasting and presplitting, where no delay interval between the different charges is desired. Millisecond detonators. These are mainly used in bench and tunnel blasting. Half-second detonators. These are exclusively for tunnel blasting where longer delays are required to prepare space for the movement of the blasted rock masses.
- 13. Electric Initiation Systems Electric detonators may be connected in anyone of the following ways: i. In series ii. In parallel, or iii. In parallel-series. The series circuit is generally preferred because of its simplicity. However, it requires larger current than that for firing a single detonator.
- 14. Electric Initiation Systems In general, exploders providing DC currents are suited for series blasting. Research has shown that minimum current requirements for straight series circuit is 1.5 amperes for Dc or 3.0 amperes for AC; and for parallel-series circuits the minimum DC or AC current should be 2.0 amperes in each series circuit. Similarly, for straight parallel circuits the recommended minimum current per detonator is 1.0 ampere.
- 15. Non-Electric Initiation Systems Non-electric initiation systems available for open pit and other surface blasting operations combine the advantages of electric and detonating cord systems and are generally referred to as NONEL DETONATORS. They consist, basically, of a cap similar to an electric blast cap or detonator and having a tube that extends from the cap similar to those of the leg wires in the electric detonator or cap. Inside the tube is a powdery material that propagates a mild detonation, which activates the cap. The systems are incorporated with delay periods
- 16. Electronics Initiation Systems Electronic detonators have an electronic counter on a microchip in place of the pyrotechnic delay charge, and a capacitor to supply the discharge energy for ignition. Advantages compared to regular electric or NONEL detonators: Higher timing precision (10 µs instead of 1-10 ms delay scatter). Same high timing precision at long delay times (10 µs at 5 second delays). Increased control over time delay Greater safety against accidental ignition (coded firing signal).
- 17. Electronics Initiation Systems Current disadvantages include: i. Higher price because of chip and capacitor cost ii. Back to electric wiring – risk of ground faults or poor contacts
- 20. Wireless Electronic Blasting Systems Orica Mining Service’s Next Generation of Electronic Blasting Systems is the culmination of 20 years of laboratory testing and 15 years of in-field use. At the heart of their systems is the electronic timing module. Offering up to 1000x greater accuracy and significantly more timing flexibility than traditional pyrotechnics, it provides greater control of energy. In the right hands, significant productivity gains are possible through: fragmentation improvement, muckpile shaping, vibration control, larger blasts, improved wall/face conditions, and reduced overbreak, damage and ground support.
- 21. Wireless Electronic Blasting Systems
- 22. Firing Methods Safety Fuse and Detonating Cord A safety fuse may be lit by using matches or, better, special igniter torches. When several fuses are lit, a control fuse, the length of which is 0.6 m shorter than the shortest fuse of the round, may be lit and carried around as an extra safety measure. When the control fuse has burnt out, the blasting crew should evacuate the blasting site immediately.
- 23. Firing Methods
- 24. Electric Firing The introduction of electric firing gave a higher degree of safety for the people involved in blasting operations. The blaster became able to fire the blast from a protected area and could have the moment of firing completely under control. As it became possible to check with instruments that all the detonators were connected, the risk of misfires decreased.
- 25. Blasting Machine A blasting machine or shot exploder is a portable source of electric current to reliably fire a blasting cap to trigger a main explosive charge. It is mostly used in mining and demolition. The use of the term "machine" dates from early designs that used an electrical generator operated by winding a rotary handle or pushing down a T-handle. Modern blasting machines are battery-powered and operated by key switches and push-buttons, and do not resemble the older designs.
- 26. Blasting Machine A typical "capacitive discharge" blasting machine works by charging a capacitor from a battery, then discharging the capacitor through an external circuit, called the firing line, to fire the blasting cap.[1] While the machine is idle, an "internal shunt" is connected across the output terminals so that any stray voltages induced in the external circuit, for example by nearby radio transmitters, are harmlessly short-circuited without triggering the blasting cap. The machines also typically include an "abort" feature to discharge the internal capacitor without firing the cap.
- 27. Blasting Machine
- 28. Blasting Machine