China Metallurgical Encyclopedia: Mining

Author: Chief Editor: Lin Cong
Publisher:
Publish Date: 1999-01-01
Features:
Segment: The initiating system consists of a gas tank, mixing chamber, igniter, gas explosion tube, connecting elements, and non-electric millisecond detonators. Before blasting, the air pipeline is checked using an air pump, then air is replaced with nitrogen, and finally nitrogen is replaced with a mixture. After the pipeline is fully pressurized, the connection between the mixing chamber and the gas tank is cut, and the igniter is operated to initiate the blast. This system has excellent electrical safety, reliable operation, accurate delay timing, and has been used in some mines in the United States. The disadvantages are the need for special equipment and complex operation, so it is not widely used. (3) The low-energy detonating cord initiating system is composed of detonating cord with a charge of 0.8g/m, transmission elements, and non-electric millisecond detonators. The detonation velocity of the low-energy detonating cord is 6200m/s, and its detonation wave ignites the delay element of the detonator to initiate it. The detonators are placed in the blast holes. When the low-energy detonating cord is initiated, it transmits the blast through connecting elements to small detonators, which then initiate the branch detonating cord, ultimately igniting the detonators in the blast holes. The advantages are excellent electrical safety and accurate and reliable multi-stage millisecond delay blasting, widely used in the United States and Canada. Industrial explosives, ammonium nitrate explosives, have largely replaced nitroglycerin-based explosives, significantly improving the safety of blasting operations. These explosives are much less sensitive to impact, friction, heat, and flame compared to traditional explosives. Some varieties cannot even be initiated by detonators and require intermediate blasting charges. Due to their high safety, low cost, and suitability for modern engineering blasting, they have been rapidly adopted. Modern ammonium nitrate explosives are divided into water-containing and dry types, and intermediate blasting charges are specialized blasting materials developed to their use. Water-containing ammonium nitrate explosives include slurry explosives, water-gel explosives, and emulsion explosives, each representing representative products of different development periods. (1) Slurry Explosives Ammonium nitrate is highly soluble in water, and dry ammonium nitrate explosives often degrade due to moisture absorption and caking. The invention of water-containing slurry explosives was a breakthrough in understanding, as it adds 9%–13% water to increase density, improve water resistance, and enhance transmission performance. Slurry explosives, both domestically and internationally, contain ammonium nitrate solution, fuel, sensitizers, surfactants, gelling agents, crosslinking agents, and density regulators. Depending on the formulation, their density ranges from 1.1 to 1.54g/cm3, detonation velocity from 3500 to 5800m/s, and they exhibit good water resistance. Slurry explosives in some countries have been series-developed, suitable for deep-hole and small-diameter shallow-hole blasting. China primarily develops slurry explosives suitable for deep-hole blasting with diameters greater than 150mm. (2) Water-Gel Explosives Developed based on slurry explosives, water-gel explosives replace solid explosives like TNT in slurry explosives with water-soluble sensitizers, such as ammonium methyl nitrate. Since both the sensitizers and oxidizers are in solution phase, they are easier to mix and exhibit better transmission performance. (3) Emulsion Explosives Emulsion explosives are water-containing ammonium nitrate explosives prepared using emulsification technology. They replace explosive sensitizers with fuel oil emulsified in an ammonium nitrate solution, further improving safety. Due to their superior water resistance, detonation performance, and sensitivity, as well as adjustable energy density, they are suitable for various blasting projects. The use range and development prospects of emulsion explosives are better than those of slurry or water-gel explosives. Dry ammonium nitrate explosives include ammonium nitrate-fuel oil explosives and ammonium-TNT explosives. The emergence of ammonium nitrate-fuel oil explosives provided the blasting industry with a safe, economical, and medium-power blasting agent, composed of fuel oil and ammonium nitrate. The application of porous granular ammonium nitrate improved caking properties, making on-site mixing of ammonium nitrate-fuel oil explosives possible. Like on-site mixed emulsion explosives, all raw materials are non-explosive before loading into blast holes, significantly enhancing safety. Ammonium-TNT explosives have the of moisture absorption and caking, often leaving residual explosives after blasting, and TNT is toxic, increasing toxic gas emissions upon detonation. China's developed ammonium-TNT explosives have completely solved caking issues by adding composite surfactants. China's research and development of TNT-free ammonium-resin explosives are also used in production. Reference Books DuPont Company, translated by Long Weiqi, Blasting Manual, Metallurgical Industry Press, Beijing, 1986. Wang Xuguang, Emulsion Explosives, Metallurgical Industry Press, Beijing, 1986. (Xu Tianrui)
Safety Platform (Safety Berm) A platform on the final bench of an open-pit mine to maintain bench stability and intercept falling rocks. It is often alternated with a cleaning platform, with a width generally one-third of the bench height. In large open-pit mines in China, the safety platform width ranges from 4 to 6m, while in medium and small mines, it ranges from 2 to 4m. In open-pit mines in countries like the United States and Canada, the safety platform width is generally 6 to 8m. (Cai Hongqi)
Safety Signal Device Devices for various communication, indication, and warning signals to ensure mine safety production. In addition to mine railway signals, the following eight types are commonly used.
Slope Mine Signal Devices In inclined mines used for transporting personnel by train, signal devices must meet the following requirements: (1) At any point during operation, each carriage can signal the driver. (2) For multi-stage systems, signals from each stage must be distinguishable to the driver. (3) All signal-receiving and transmitting locations must display clear signal signs.
Shaft Signal Devices The hoisting system in shafts must have signal devices capable of transmitting signals from each stage to the surface signal operator, who then relays them to the hoist operator. The shaft signal must be locked with the hoist's startup, and auxiliary signal devices, as well as telephones or microphones, must be provided.
Cage Hoisting Signal System The following signals must be provided: (1) Operational execution signal; (2) Hoisting stage indication signal; (3) Hoisting type signal; (4) Maintenance signal; (5) Accident signal; (6) Contact inquiry signal when no telephone communication is available.
Skips Hoisting Signal System The above (1), (2), (5), and (6) signals must be provided.
Level Crossing Signal Devices At level crossings between railways and highways, and at underground motor vehicle transport intersections, level crossing signal devices must be installed to ensure traffic safety. When a vehicle approaches the crossing, audible and visual signals must be issued in the relevant directions. Level crossing signal devices are either manual or automatic.
Underground Slope Road Highway Signal To ensure the safe operation of vehicles and loaders on underground slope roads, prevent collisions on single slopes, and ensure safe passing at meeting points.
Blasting Safety Signal Devices During surface and underground blasting, sentries and markers must be set up at the boundaries and routes of hazardous areas. Before blasting, simultaneous audible, visual signals, and corresponding organizational measures must be used to ensure personnel in hazardous areas can evacuate to safety in time. Signals include advance warning signals, blasting signals, and warning removal signals. After blasting, a warning removal signal can only be issued after a safety check confirms it is safe.
Ropeway Signal Devices At loading stations, intermediate transmission stations, and unloading stations of aerial ropeways, start/stop communication signals, tension car over-position, and accident signals must be provided.
Fire Signal Devices When a fire occurs underground, it must notify all personnel at work locations to evacuate from hazardous areas promptly.
Flood Signal Devices When water inflow signs are detected at excavation work areas or other locations, such as "sweating" at work areas, increased water seepage from the roof, cooler air, fog, "water calling," water inflow from the floor, or other abnormal phenomena, and if the situation is urgent, an alarm must be issued immediately to evacuate personnel at all locations threatened by water. (Yan Weigong)
Ammonite Ammonite is a powder nitrate explosive containing TNT. It is composed of ammonium nitrate, TNT, wood flour, and other materials. In the early 1950s, China began producing ammonite and used it as a major mining explosive. After the mid-1960s, its usage proportion gradually declined. Based on usage conditions, ammonite is divided into: open-pit ammonite, rock (ammonite), water-resistant rock (ammonite), and coal mine ammonium (ammonite). Ammonium nitrate is both an explosive and an oxidizer, making it the basic component of ammonite, with a content of 82%–86%. TNT is a high explosive with high sensitivity, used as a sensitizer, with a content of 5%–14%. Wood flour is a fuel and a loosening agent, helping to prevent caking, with a content of 3%–9%. Coal mine ammonium explosives are safe explosives containing 15% salt as a flame suppressant, suitable for mines with gas or dust explosion hazards. The processing methods of ammonite include grinding and mixing and airflow drying. The density of the explosive is 0.9–1.0g/cm3, brisance 8–12mm, and explosive power 280–310mL. The explosive has poor water resistance and is prone to moisture absorption and caking, degrading blasting performance. It is suitable for medium-hardness and harder rocks and dry blast holes. In the 1980s, rock powder ammonite explosives were developed, adding composite oil phase (1.5%–2.5%) to the basis of ammonite, improving its resistance to moisture absorption and caking, expanding its application range. The nitrogen content in the explosive is 87.5%–90.5%, TNT content 3%–7%, with the remainder being wood flour and a small amount of composite additives. (Gao Mengyi)
Ammonium Nitrate-Fuel Oil Explosive Ammonium nitrate and fuel oil are the main components of this mixed explosive. It includes powder and granular ammonium nitrate-fuel oil explosives. In China, powder ammonium nitrate-fuel oil explosives are more widely used. The explosive performance of ammonium nitrate-fuel oil explosives primarily depends on the particle size, porosity, moisture content of ammonium nitrate, fuel oil type and content, and the degree of mixing. When processing, producing, and using ammonium nitrate-fuel oil explosives, fire prevention, anti-toxic gas, and anti-static ignition safety requirements must be strictly followed. To prevent the risk of static ignition, semi-conductive hoses should be used to transport explosives, and insulated hoses are prohibited. Additionally, manufacturing and loading equipment must be properly grounded, and anti-static detonators must be used. The typical composition ratio of powder ammonium nitrate-fuel oil explosives is 92% ammonium nitrate, 4% fuel oil, and 4% wood flour. Ammonium nitrate serves as the oxidizer, fuel oil as the fuel, and wood flour as both the fuel and a loosening agent to prevent caking. Hot grinding is commonly used for mixing to drive out moisture, keeping the moisture content below 0.3%. Common brands of powder ammonium nitrate-fuel oil explosives include open-pit, rock, and coal mine ammonium nitrate-fuel oil explosives. The density of powder ammonium nitrate-fuel oil explosives is 0.8–1.0g/cm3, explosive power 280–310mL, brisance 9–12mm, and distance 4–7cm. They can be directly initiated by detonators but are prone to caking and cannot be stored long-term, primarily used for small-diameter blast holes.
Granular Ammonium Nitrate-Fuel Oil Explosive A simple mixed explosive that appeared in the late 1950s. It is commonly prepared using porous granular ammonium nitrate, which is more oil-absorbent than ordinary granular ammonium nitrate. Generally, 94% ammonium nitrate is mixed with 6% diesel. Special vehicles can automatically mix and load it into blast holes at the blast site in proportion. This explosive has good looseness, is not prone to caking, and has strong fluidity, facilitating mechanical loading. Granular ammonium nitrate-fuel oil explosives are cost-effective and safe but not waterproof, widely used for open-pit blasting in dry conditions. This explosive has low sensitivity and cannot be directly initiated by detonators; intermediate charges must be used for initiation (see intermediate initiation). (Wang Minglin)
Open-Pit Mine in Rolling Terrain An open-pit mine located below the final boundary closure circle of an open-pit mining area. Its characteristics are: (1) The development and transportation system of open-pit mining gradually forms with increasing depth, and transportation distances continuously increase.