1. Definition of stripping ratio
Stripping ratio: the ratio of the amount of stripping to the amount of mined ore. In addition to mining ore, open-pit mining also requires a large amount of stripping of rock, which is an important difference between open-pit and underground mining;
Average stripping ratio: the ratio of the total stripping Vp in the mining boundary to the mined volume Ap. Vp/Ap; the stripping ratio of the boundary: after the unit depth is increased by open pit mining, the new stripping amount ΔV and the newly added mined amount △A Ratio ΔV/△A,;
When stripping surface mining or no greater than the cost of not less profit than underground mining, ore generally cost comparison, cost comparison and metal profitability comparison;: economical stripping ratio nj
The essence of open-pit mining: under the premise of ensuring the safety of the formation, that is, the stability of the slope, the stripping ratio is minimized, that is, the mine is mined at the least cost, and the stability of the slope is determined by the nature of the rock;
2. Selection of mining forms
All underground mining, upper open-pit mining underground mining, all open-pit mining (too little ore), under normal circumstances, can use the open air without underground, stripping ratio is the criterion for selecting mining methods;
The maximum depth of open-pit mining is generally determined by the ratio of the stripping ratio of the boundary to the average stripping ratio not greater than the economically reasonable stripping ratio; when the lower part must also use underground mining, the cost is generally determined by nj; The amount is not much, use the profit method to determine nj, that is, as long as there is profit, then another step;
3. Choice of mining methods
The kind of open up the way: roads, railways, tape, adit chute, skip the slopes and joint development; construction period to open up different modes of transport, infrastructure investment, operating costs, system capabilities are different;
The principle of choice of pioneering methods: early production, fast production, low investment, low operating costs; design must include a multi-program technical and economic comparison of development methods;
Influencing factors of development methods: geological and topographic conditions, ore body occurrence status, plant selection location, transportation distance, production capacity, infrastructure construction and infrastructure construction period, loss depletion rate, equipment supply;
Comparison of development plans: infrastructure construction, construction investment, construction period, production capacity, operating expenses, loss depletion, system reliability, infrastructure investment and operating expenses are key indicators; sag open pit mines like stadiums, hillside open-pit mines like terraces;
4. Economic production scale
Iron ore scale: generally refers to the original ore, large-scale open-air is more than 2 million tons, small is less than 600,000 tons, and underground iron ore is more than 1 million tons;
Influencing factors: total amount of recoverable and stratified ore, reasonable service life, number of equipment that can be arranged, depth of mine engineering, equipment ratio (wearing, loading, transporting, discharging and discharging); !
Expansion potential: The mineral bed's own conditions determine its economic scale, not how much it wants;
"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."
Gravity Die Casting
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.
- The heated mould [Die or Tool] is coated with a die release agent. The release agent spray also has a secondary function in that it aids cooling of the mould face after the previous part has been removed from the die.
- Molten metal is poured into channels in the tool to allow the material to fill all the extremities of the mould cavity. The metal is either hand poured using steel ladles or dosed using mechanical methods. Typically, there is a mould [down sprue" that allows the alloy to enter the mould cavity from the lower part of the die, reducing the formation of turbulence and subsequent porosity and inclusions in the finished part.
- Once the part has cooled sufficiently, the die is opened, either manually or utilising mechanical methods.
Advantages
- Good dimensional accuracy
- Smoother cast surface finish than sand casting
- Improved mechanical properties compared to sand casting
- Thinner walls can be cast compared to sand casting
- Reverse draft internal pockets and forms can be cast in using preformed sand core inserts
- Steel pins and inserts can be cast in to the part
- Faster production times compared to other processes.
- Once the tolling is proven, the product quality is very repeatable.
- Outsourced Tooling setup costs can be lower than sand casting.
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