The induction furnace crucible is a simple special smelting equipment, which is made of different raw materials such as high-purity graphite and cast iron. The equipment is not only simple in structure, but also low in cost and fast in production, and can be used for heating with gas or coke as fuel.
An induction furnace crucible is a very simple smelting equipment, suitable for smelting non-ferrous metals with a low melting point, such as copper, aluminum, and alloy. In this induction melting furnace, the alloy is melted in the crucible, and the heat is transferred to the furnace charge through the crucible. The combustion products of the furnace charge are not in direct contact. Therefore, the chemical composition of the alloy is basically not affected by the furnace gas, and the temperature of the alloy liquid is also evenly distributed, which is also its main advantage. Its disadvantages are low thermal efficiency, large fuel consumption, the small storage capacity of the crucible, and poor working conditions.
During smelting, the metal is placed in a container called a crucible. The crucible is placed in the furnace and heated with diesel oil, heavy oil, gas, or coke as fuel. According to different requirements, the crucible can be made of different raw materials such as high-purity graphite, refractory clay, and cast iron. The furnace body includes pit type, fixed type, and rotary type. There is also a resistance crucible furnace, which generally has a small storage capacity and is mostly used in laboratories.
The induction furnace crucible is simple in structure, small in investment, and fast in production. It is widely used in the casting workshops of small and medium-sized non-ferrous alloy processing plants and machine manufacturing plants. However, the heat utilization rate of crucible furnaces is low, the output is small, and the labor conditions are poor, so large-scale production and manufacturing are no longer applicable.
Crucible furnace has always been special equipment for smelting copper alloy. At present, a large proportion of crucible furnaces are used for smelting copper alloys. The heat source of smelting was charcoal in ancient times, but now it is heavy oil, gas, electricity, and coke turn. Recently, in order to save energy, protect the environment and improve efficiency, some heat sources have been changed from heavy oil to gas, and some have been changed to induction furnaces.
The induction furnace crucible for smelting light alloys such as Al and Zn also has the same trend. Large-scale smelting equipment has been converted into reverberators, rotary furnaces, induction furnaces, etc. Small-scale holding furnaces for small-batch production or casting are still crucible furnaces. Due to the improvement of the heating method, the future development trend is to use clean light oil and gas; Small-scale holding furnaces may achieve the purpose of energy saving by ceramic fiber lining and adopting a multi-layer furnace wall structure.
Coke Crucible Furnace
Coke crucible furnace is divided into natural ventilation crucible furnace and artificial ventilation crucible furnace. The fixed crucible furnace with natural ventilation uses coke as fuel. The furnace is built with refractory bricks, and a 60-100mm high refractory filler block is placed on the grate, and a crucible is placed on the filler block. The crucible is covered with a cover made of graphite or refractory material. There is a gap of 300~500mm between the crucible and the furnace wall. A movable metal cover lined with refractory material is arranged on the furnace’s mouth. The smoke outlet is set at the upper part of the furnace, generally, 140~160mm from the outlet.
During smelting, coke is placed around the crucible, and the crucible is heated by burning coke. The coke combustion is related to the air supply mode. During natural ventilation, combustion is difficult to control and furnace temperature fluctuates greatly.
For the crucible with forced ventilation, the furnace temperature control is easier than natural ventilation because the air supply volume can be adjusted.
Crucibles for melting non-ferrous metals include cast iron crucibles, steel crucibles, graphite crucibles, and refractory clay crucibles. Cast iron crucibles are usually made of RT Si-5.5 and RQT Si-5.5 heat-resistant cast iron. Steel crucibles are also divided into cast steel crucibles and steel plate welded crucibles. Cast iron crucibles and steel crucibles are generally used for smelting aluminum alloys and fusible alloys.
Graphite crucibles are made of 20-60% graphite, refractory clay, refractory clinker, and other materials, and are mainly used for melting copper alloys and some alloys with higher melting points.
The crucible should be stored in a dry place. It should be dried at 120~150 ℃ before use. When melting the alloy, the charge should not be too tight to prevent the solid charge from expanding and cracking the crucible when heated.
Oil-fired Crucible Furnace and Gas-fired Crucible Furnace
Oil-fired crucible furnaces often use heavy oil and diesel oil as fuel. Gas-fired crucible furnaces often use gas as fuel. The gas used as fuel is divided into high-pressure gas (pressure is about 70kPa) and low-pressure gas (pressure is 10~20kPa) according to the pressure, and the gas furnace is also divided into high-pressure gas and low-pressure gas crucible furnace.
The combustion oil is sprayed into the furnace through the nozzle. The nozzle also has various forms depending on the fuel used and the air pressure. The commonly used low-air pressure fuel nozzle directly uses the blower to supply air for oil atomization. The oil barrel is placed at a place more than 3m above the nozzle, and the oil is sent into the nozzle by the pressure formed by the weight of the oil itself. When the oil flows through the nozzle, it is impacted by the flowing air many times, so the atomization effect is good. High air pressure fuel nozzle uses about 660Pa of compressed air as the atomizer, and the oil pressure is generally below 260Pa. The nozzle has a simple structure, and the air directly impinges on the oil flow to atomize, but the atomization and mixing conditions are poor, and the flame is long. The improved nozzle is equipped with a swirl device in the nozzle, which can improve the atomization conditions.
Generally, oil-fired crucible furnaces and gas-fired crucible furnaces are made by the factory.
Resistance Crucible Furnace
The resistance crucible furnace heats the crucible with the heat energy generated by the electric heating shell. It is applicable to aluminum, magnesium, zinc, lead, tin, and bearing alloys with low melting points and high-quality requirements
The resistance crucible furnace is made into fixed type and inclined type according to the service conditions.
There are many kinds of electric heating elements used in resistance crucible furnaces, of which Fe-Cr-Al alloy is more commonly used.