The furnaces for melting gold and silver generally use round pits. Gas and diesel are mostly used as fuel. Or use the usual coke furnace, gas or diesel furnace, mostly made of magnesia bricks or refractory clay bricks. The size of the furnace is mainly determined by the size of the crucible used. Under general conditions, the diameter of the clearance section of the 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, crucibles of several specifications are often used for casting in the same furnace. Low-pressure nozzle holes for burning gas or diesel are mostly located on the wall near the bottom of the furnace, with a furnace cover on the furnace mouth, and the flue gas is discharged from the center hole of the furnace cover or an underground flue near 100mm below the furnace mouth. There is also an underground flue set on the wall near the bottom of the furnace, while the combustion nozzle hole is left 100mm below the furnace mouth. After the furnace is built, place two refractory bricks in the center of the furnace bottom, and place the crucible on the refractory bricks with coke powder during smelting to prevent sticking to the bottom.Graphite crucibles are mostly used for crucibles, which can withstand the highest temperature of about 1600℃, and graphite crucibles of size 50-100 are usually used. In view of the hygroscopicity of graphite crucible, it must be heated and baked slowly for a long time before use to remove water, and then slowly heated to red heat (dark red). Otherwise, the damp crucible will burst and be damaged when exposed to high temperature and sudden heat.
In modern times, resistance furnaces or induction furnaces are also used to cast gold or silver ingots. The resistance furnace is composed of carbon or graphite crucible (or lining refractory clay crucible for smelting metal), and usually adopts single-phase AC power supply. After the low-voltage current is turned on, the crucible acts as a resistor and heats the metal to the required temperature. Calculated on the basis of 20kg of metal baked 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 crucibles, in addition to graphite crucibles or graphite crucibles lined with (or outer) refractory clay crucibles alone, there are also refractory clay crucibles used alone for smelting.
When using a crucible furnace to melt pure gold and silver, the loss of gold (including the recoverable in the smoke and dust) is generally 0.01% to 0.02%, and silver is 0.1% to 0.25%. When smelting gold-silver alloy or gold-copper alloy, the loss is even greater. When melting in an electric furnace, the loss rate of gold and silver can be reduced by about 70% to 90%.
Post time: Nov-17-2020