Furnaces that melt gold and silver are generally round furnaces. Fuel multi-purpose coal gas, diesel. Or using a conventional hearth coke, gas or diesel hearth, the use of magnesium brick or clay brick refractory, the furnace size is mainly employed in accordance with the size of the crucible may be. Under normal conditions, the diameter of the clearance section of the earth furnace is 1.6 to 1.8 times the outer diameter of the crucible, and the depth is 1.8 to 2.0 times the height of the crucible. However, in actual production, it is often used in the same furnace to cast a few specifications of crucible. The low-pressure nozzle hole for burning gas or diesel oil is mostly disposed on the wall near the bottom of the furnace, and the furnace cover is provided with the furnace cover, and the flue gas is discharged from the central hole of the furnace cover or the underground flue around 100 mm below the furnace mouth. There is also the installation of the underground flue on the wall near the bottom of the furnace, and the combustion nozzle hole is left at 100 mm below the furnace mouth. After the furnace is built, put two refractory bricks in the center of the furnace bottom. When smelting, place the enamel on the refractory brick with coke powder to prevent sticking.
Many graphite crucibles are used, which can withstand a maximum temperature of about 1600 ° C, usually using graphite crucibles of 50 to 100. In view of the hygroscopicity of the graphite crucible, it is necessary to heat and bake for a long time before use to remove moisture, and then slowly heat up to red heat (dark red). Otherwise, the wetted heat will burst and damage if it is hot.
In modern times, gold or silver ingots are cast by using an electric resistance furnace or an induction furnace. The electric resistance furnace is composed of carbon or graphite crucible (or refractory clay crucible for lining the metal), and is usually powered by single-phase alternating current. After the low-voltage current is turned on, å©åŸš acts as a resistor and heats the metal to the desired temperature. According to the calcination of 20kg metal per furnace, the power consumption per kilogram of gold is 0.5kW·h, and the power consumption of silver is slightly less.
In the selection of tantalum, in addition to graphite crucibles or linings (or outer lining) refractory clay crucibles, refractory clay crucibles are also used alone.
When melting pure gold and silver in a crucible furnace, the loss of gold (including recoverable from soot) is generally 0.01% to 0.02%, and the silver is 0.1% to 0.25%. And when smelting gold and silver alloy or copper alloy, the loss of even bigger. When melted in an electric furnace, the loss rate of gold and silver can be reduced by about 70% to 90%.
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