(1) Coal mine water damage Any flood that affects production, threatens mining face or mine safety, increases the cost per ton of coal, and partially or completely inundates the mine. It is called coal mine water damage. According to statistics, since the founding of the People's Republic of China, a major accident in which more than three people died in a coal mine in China, Water damage ranks third; the average number of deaths per accident is 7.06, second only to gas and fire accidents. For the city, water damage is a major factor that is particularly likely to cause serious accidents. There are several types of mine water damage: 1. Surface water damage: The water source is atmospheric precipitation and surface water bodies (rivers, rivers, lakes, reservoirs, ditches, pits, etc.). The water source enters the mine through the wellhead, the mining caving zone, the karst ground collapse or the cavern, the fault zone and the old borehole with poor sealing of the coal seam roof and floor. For example, in 1998, a sudden flood in the northern part of the country, a coal mine located near a river, was flooded due to the surge of river water, causing huge economic losses. 2, old water and water damage The water source is the accumulated water in ancient wells, water kiln, waste alley and goaf. When the mining face is approaching or communicating, the old empty water enters the roadway or work surface, causing an accident. This is the main type of water damage in coal mines in our city. For example, on July 23, 1997, the mined area of ​​the small coal kiln in the upper part of Yongding Mine was permeable and killed three people. 3, pore water and water damage The water content of the coal seam strata in Longyong coalfield is weak-medium, but it is obviously affected by atmospheric precipitation. It is affected by the seasonal increase of water inflow from April to September. 4, karst water damage There is no limestone in the coal-bearing strata of Longyong Coalfield, but it is directly affected by the structure of the Qixia limestone. The fault is connected with karst water and enters the mine to cause water damage. For example, a certain infrastructure in Longyan was seriously affected by karst water and had to invest more than 13 million yuan and was forced to dismount. 5, crack water damage The water source is sandstone , conglomerate and other fissure aquifer water, which is often replenished by surface water or other aquifers. It passes through the caving zone, the fault zone, the mining roadway exposes the sandstone water of the roof or floor, or the old drilling water with poor sealing. Enter the roadway or work surface. Second, the "Safety Regulations for Coal Mines" on the main provisions of mine water control 1. The coal mining enterprise shall ascertain the hydrogeological conditions of the mining area and the mine, prepare a medium- and long-term water prevention plan and an annual water control plan, and organize the implementation. Coal mining enterprises must regularly collect, investigate and check the situation of adjacent coal mines and abandoned old kiln, and mark the location of the wells, mining years and water accumulation on the upper and lower engineering comparison maps. 2. For mines with complicated hydrogeological conditions, a groundwater dynamic observation system must be established for the main aquifers (segments), groundwater dynamic observation, water damage prediction analysis, and corresponding “inspection, exploration, prevention, blocking, interception, drainageâ€, etc. Comprehensive control measures. 3. Coal mining enterprises must conduct a comprehensive inspection of water prevention and control work before the rainy season every year. Mines threatened by water during the rainy season should formulate measures to prevent and control water during the rainy season, and should organize rescue teams to reserve sufficient flood prevention and rescue materials. 4. Coal mining enterprises must check the water supply and leakage of the surface water flow system in the mining area and its vicinity, the hydrophobic capacity and related water conservancy projects, and master the local precipitation and the highest flood level data to establish a hydrophobic, waterproof and drainage system. 5. Waterproof coal pillars must be left at the boundary of adjacent mines. When the mine is demarcated by faults, waterproof coal pillars must be left on both sides of the fault. Mines that have been interconnected must construct a waterproof wall of sufficient strength in the connected areas. The size of the waterproof coal pillar shall be specified in the mine design according to the geological structure, hydrogeological conditions, coal seam occurrence conditions, surrounding rock properties, mining methods and rock movement laws of adjacent mines. According to the Regulations on Mine Hydrology and Geotechnical Regulations, the minimum vertical distance between the roadway and the water body shall not be less than 10 times the height of the roadway in the flooded area or under the water accumulation area. The size of the waterproof coal pillar shall not be less than the water guide. The sum of the maximum height of the fracture zone and the thickness of the protective layer should generally be greater than 30 times the thickness. 6. The mine must make a good analysis and forecast of water damage, and insist on the principle of exploration and release of water. Before exploring water or near the water accumulation area, before flooding or discharging water accumulated in the flooded roadway, it is necessary to prepare the exploration and drainage water design and take safety measures such as preventing gas and other harmful gas hazards. The advanced distance of the arrangement of the water-seeking eye shall be specified in the design of the exploration and drainage water according to the height of the water head, the thickness and hardness of the coal (rock) layer, and safety measures. Correctly determine the water line, the water line is the starting point of water exploration, should be determined according to the location, extent, hydrogeological conditions and reliability of the data, as well as the damage of the goaf and roadway affected by the mine pressure. Water line.
"Gravity Die Casting. A permanent mould casting process, where the molten metal is poured from a vessle of ladle into the mould, and cavity fills with no force other than gravity, in a similar manner to the production of sand castings, although filling cn be controlled by tilting the die."
Sometimes referred to as Permanent Mould, GDC is a repeatable casting process used for non-ferrous alloy parts, typically aluminium, Zinc and Copper Base alloys.
The process differs from HPDC in that Gravity- rather than high pressure- is used to fill the mould with the liquid alloy.
GDC is suited to medium to high volumes products and typically parts are of a heavier sections than HPDC, but thinner sections than sand casting.
There are three key stages in the process.
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Gravity Die Casting
First, coal mine water damage basics