Underground Mining Equipment List | Mining Technology

In this article we will discuss about the equipment used in underground mining. The equipments are: 1. Safety Fuse 2. Detonating Fuse 3. Nonel 4. Raydet 5. Detonating Relays 6. Cord Relays 7. Circuit Tester 8. Crimper 9. Shot Firing Cables 10. Exploder 11. Magneto (or Dynamo) Exploder 12. Battery Condenser Exploder 13. Condenser Dynamo Exploder.

Equipment # 1. Safety Fuse:

A safety fuse which looks like a cord consists of a core of fine grained gunpowder wrapped with layers of a tape or textile yarn and waterproof coatings. The burning speed is usually 100 to 120 sec/metre. ICL manufacturers a range of safety fuses to suit various conditions, e.g., Double Bull brand for dry conditions, Blue Sump for damp conditions, OCPS (orange coloured plastic sheathed) and Blue Plastic for wet and very rugged conditions.

IDL also manufactures safety fuse (yellow). When one end of the fuse is ignited, it carries the flame at a uniform rate to ignite gun powder or to detonate an ordinary detonator which is turn can detonate a high explosive.

Equipment # 2. Detonating Fuse:

For shallow depths, say less than 3 m, and for small number of holes, a detonator is inserted in the cartridge itself and detonated by ignition of safety fuse or in the case of elec. detonator, by an exploder. For a large no. of holes blasted at a time in mechanised quarries and in U/G coal mines electric detonators are used.

A deep hole in a quarry needs a long length of detonator leads and to avoid this it is common to use a detonating fuse like cordtex trade name of ICI. The fuse consists of a core of PETN enclosed in a tape which is wrapped with cloth.

The fuse is then completely enclosed in a tubular cover of plastic material which is white for Cordtex and orange for Geocord detonating fuse (ICI). The detonating fuse looks like a plastic cord; its external dia. is about 5 mm and weight about 20 g per metre length. It has a velocity of detonation of 6500 m/sec. and it is practically instantaneous in its action.

A large number of shots connected with detonating fuse can be blasted by a single detonator. A detonating the fuse through the plastic cover. Water may however penetrate into the core through the cut ends which can be guarded against by sealing them with tape or water-proofing compound. A detonating fuse is often used for demolition operations.

Equipment # 3. Nonel:

The Nonel system of detonation is developed by Nobel AB of Sweden. Primers of explosives with Nonel detonators inserted in them are charged in the blast-holes and the Nonel tubes are bunched for convenience of connection to the mains blasting system.

Upon initiation, the shock wave passes down the plastic tubes, the insides of which are coated with reactive substance that maintains the shock wave at a rate of approx. 2000 m. per second which has sufficient energy to initiate the primary explosive or delay element in a detonator. Since the reaction is contained in the tube, this has no blasting effect and acts as a signal conductor.

Nonel means non-electric detonator. The flexible plastic tube has 3 mm external and 1.5 mm internal diam. The tubes are available in pre-cut lengths. One end of the tube is fitted with a non-electric delay detonator which is crimped to it in the factory while the other end is sealed. The end having detonator is lowered down into the blast hole while the sealed end projects outside the hole. The sealed end is initiated by a detonator or detonating cord.

The advantage of the Nonel system lies in its extreme resistance to accidental initiation by static electricity, stray current, radio transmission, flame, friction and impact. It is also immune to misfires caused by current leakage in conductive ore bodies and eliminates the need for complicated electrical circuit testing and shot-firing equipment. Raydet manufactured by IDL Chemicals, is just like Nonel.

Equipment # 4. Raydet:

Raydet is a non-electric initiating device combing the versatility and advantages of electric detonator and detonating cord. It consists of a plastic tube carrying a very small quantity of explosive material on its inner surface. A high strength no. 8 instantaneous or delay detonator is crimped to one end of the ray tube.

When initiated, a low order shock wave travels through the tube and initiates the detonators. Raydet can be initiated by a detonator or a detonating cord. A tag indicates the delay number of raydet and a tape fastening the tube in a coil indicates the tube length. Length of tube varies from 3 m to 45 m. The delays are from no. 0 delay to no. 15 delay; No. 0 delay is instantaneous No. 1 delay is 50 ms and No. 15 delay is 625 ms.

When using the raydet, do not cut factory sealed end of ray tube and do not connect two ray tubes. One ray tube will not initiate another.

Equipment # 5. Detonating Relays:

In opencast workings, detonating relays using detonating fuse for initiation provide a non-electric delay firing system. This method avoids the electrical connections which are required when using delay detonators. A detonating relay is essentially an assembly of two open-ended delay detonators coupled together with flexible neoprene tubing in an aluminium sleeve suitable for crimping into a detonating fuse.

Inside the detonating relay, the construction is symmetrical with the delay element at either end so that the detonation wave may pass in either direction. The delay interval for each detonating relay varies from 15-45 millisecond.

In sue, the main or branch line of detonating fuse is cut at the point where a delay is required, and the detonating relay is then crimped between the two cut ends of the line. By judicious selection of the points at which the detonating relays are inserted, any delay firing sequence can be arranged. Being nonelectric in nature, detonating relays are insensitive to stray current and static electric.

Equipment # 6. Cord Relays:

Delays detonating relays manufactured by IDL Chemicals are known by the trade name Cord Relays.

A cord relay has a dia. of 11.5 and length of 152 mm. They are available with two delay periods, 15 ms and 25 ms.

Under the Explosives Rules, the various explosives and accessories are classified under the following headings:

Class 1 – Gun powder.

Class 2 – Nitrate mixture (e.g. GN/1, Power flow, Godyne, Pentadyne, etc.)

Class 3 – Nitro compounds, e.g. Blasting Gelatine, Special Gelatine, O.C.G. permitted explosives, Permex, Gelanite, Powex 80, TNT, gun cotton, PETN, etc.

Class 4 – Chlorate mixtures.

Class 5 – Fulminate.

Class 6 – Ammunition safety fuse, detonating fuse, detonators, and delay detonator relays, etc.

Class 7 – Fireworks.

Class 8 – Liquid Oxygen Explosives

Equipment # 7. Circuit Tester:

In electric shot firing before any attempt is made to fire the shots, the circuit is sometimes tested to make sure that there is not open or short circuit. Such testing should be done by approved apparatus and it is important that the current passed during testing should be limited, so that there is no possibility of accidental explosion of the detonators. In addition, all testing must be done from a safe a place and safe distance from the blast site.

An instrument to test continuity of an electric circuit for blasting is the blastometer manufactured by IDL chemicals Ltd.

It is an electronic solid state circuit tester and is available in two ranges:

(a) 0 to 100 ohms for underground coal mines.

(b) 0 to 100 ohms for other applications.

Equipment # 8. Crimper:

A crimper is a paid of pliers to crimp or press the end of a plain detonator tube on a safety fuse inserted into it so that the fuse cannot come out of the detonator. It is dangerous to crimp the tube end with teeth.

Equipment # 9. Shot Firing Cables:

During electric shot firing the leads for the detonator are connected to long shot firing cables (not less than 30 m in length) to fire the shots from a safe distance. The cables are twin- core and insulated to withstand at least 250 V.

Other accessories for shot firing include.

i. Wooden stemming rod to stem the holes.

ii. A wooden dolly weighted with lead or brass for deep holes in mechanised quarries.

iii. A scraper made of brass to clean the holes and detect cracks.

iv. A pricker made of brass, aluminium or wood to prick the cartridge prior to inserting the detonator or detonating fuse.

Equipment # 10. Exploder:

Electric shot firing is safer, quicker, and more convenient than ordinary fuse firing by flame or ignition as it provides safety to the shot firer and his helpers. Tapping of electric power from lighting or signaling lines is not permitted by the Regulations.

The portable apparatus which provides the current necessary for firing electric detonators is called an exploder.

The types of exploders than are currently used in India.

Equipment # 11. Magneto (or Dynamo) Exploder:

The magneto exploder consists essentially of a permanent steel magnet between the poles of which revolves an armature rotated through gearing by rotary handle or by a rack and pinion. The value of the voltage depends upon the speed at which the armature revolves and the flux created by the magnets.

A low tension exploder gives a voltage of about 15 volts. A.H.T. exploder gives about 125 volts. The magneto exploder fires only 1 or 2 shots at a time with single shot exploder and upto 6 shots in series with a 6-shot exploder.

The exploder for U/G coal mines should be intrinsically safe. The armature is actuated by a special twist action detachable key which should always be with the shot firer.

Equipment # 12. Battery Condenser Exploder:

The current is provided from a battery of 4 or more dry primary cells connected in series, each giving an e.m.f. of 1.5 V per cell. It is operated by a detachable key. Rotation of the handle through half a revolution first winds up a time up a time switch against the tension of a spring and then trips the mechanism which is controlled by a centrifugal governor so that the battery is connected to the condenser during a predetermined interval of time (a small fraction of a second).

The Rhino exploder is the market is an example of battery condenser exploder. It in battery operated condenser discharge type exploder capable of firing upto 3 shots at a time in Rhino 3 model (and upto 25 with Rhino-25). When using the exploder, the two wires of shot firing cable are connected to the terminals on the exploder.

Insert key and rotate one step clockwise. The action charges a 150 microfarad electrolytic condenser and a small neon lamp glows very brightly. To fire, turnkey anticlockwise to “Off” position. This action explodes the detonator and also discharges the residual charge instantly. In Rhino-25 the firing current is 1.5 amps, input D.C. volts 6, output D.C. volts 600 and firing current duration 3^:4 millisecond.

The exploder uses only one P-276 Eveready battery. Rhino exploders are permitted only in degree 1 and degree 2 gassy mines of coal.

Equipment # 13. Condenser Dynamo Exploder:

These are manufactured by Narendra & Co. The machine is suitable for operations in places where inflammable gas does not constitute a hazard. Three types are in the market.

CNT 50 to fire 5.0 detonators connected in series.

CNT 100 to fire 100 detonators in series.

CNT 200 to fire 200 detonators in series.

All the three are suitable where the circuit resistance is 160 ohms. The CNT-100 exploder has an output voltage of 750 V.D.C. The duration of current impulse to the line varies from 5 to 6 millisecond.

It has got one visual neon indicating lamp to indicate that the exploder is ready to fire. To operate – connect the shot firing cable to the exploder terminals. Place handle on to the unlocking shaft; rewind until the moon light comes on and then fire; switch off and disconnect.