1. Crucible Furnace Concept:

　　A crucible furnace is a simple melting device mainly used for melting non-ferrous metals with relatively low melting points, such as copper, aluminum, zinc, tin, magnesium, and their alloys. In this type of furnace, the alloy is melted inside the crucible, and heat is transferred from the crucible to the charge. The charge does not directly contact the combustion products; therefore, the alloy's chemical composition is almost unaffected by the furnace gas, and the alloy liquid temperature is relatively uniform. This is its main advantage. Its disadvantages are lower thermal efficiency, high fuel consumption, smaller crucible capacity, and poorer working conditions. For high-volume production, a melting pool furnace should be selected, such as a melting pool aluminum furnace or a melting pool copper furnace.

　　2. Fuel Selection for Crucible Melting:

　　During melting, the metal is placed in a crucible container, which is placed in the furnace and heated using diesel, heavy oil, gas, or coke as fuel. Depending on the requirements, crucibles can be made of different materials such as graphite or cast iron. The furnace body comes in several types: pit-type, fixed-type, and rotating-type. There is also an electric resistance crucible furnace, which generally has a very small capacity and cannot achieve mass production.

　　Crucible furnaces are simple in structure, require low investment, and have a fast production start-up time. They are widely used in the casting workshops of small and medium-sized non-ferrous alloy processing plants and machinery manufacturing plants. However, crucible furnaces have low thermal efficiency, low output, and poor working conditions, making them unsuitable for large-scale production.

　　Crucible furnaces have always been used for melting copper alloys. Currently, a large proportion of copper alloy melting uses crucible furnaces. The current heat sources are heavy oil, gas, electricity, and coke, in that order. To save energy and protect the environment, and to improve efficiency, some heat sources have been changed from heavy oil to gas, and some to induction furnaces.

　　The same trend is observed for crucible furnaces used to melt light alloys such as Al and Zn. Melting equipment has switched to reverberatory furnaces, rotary furnaces, and induction furnaces. Small-scale production or small-scale insulation furnaces for casting still use crucible furnaces. Due to improvements in heating methods, the future development trend is to use clean light oil and gas; small-scale insulation furnaces may achieve energy saving through ceramic fiber furnace linings and multi-layer furnace wall structures.

　　3. Types and Capacity:

　　(1) Types of Crucible Furnaces, Classified by Operating Method:

　　① Fixed Crucible Furnace: In the structure of a fixed crucible furnace burning heavy oil, the combustion system includes primary air and secondary air. The secondary air enters the burner brick through an air regulator.

　　② Tilting Crucible Furnace: Tilting crucible furnaces are roughly divided into two categories based on the tilting pivot position: center tilting and front tilting.

　　Except for center tilting pivots that use manual operation, others use electric motors, hydraulics, etc. For example, there are front pivot hydraulic tilting types and center pivot electric tilting types.

　　The tilting state of the front pivot hydraulic tilting crucible furnace shows that, in terms of furnace discharge operations, the front pivot type is better because it ensures that the copper liquid discharge ratio remains constant. The discharge position of the center pivot type varies too much, significantly worsening the operating conditions.

　　③ Fixed Insulation Furnace for Melting Light Alloys: In the furnaces mentioned in ① and ② above, the upper part of the furnace cover is open, and the material is preheated by the sprayed flame. However, insulation furnaces do not need to do this; instead, they try to reduce exhaust from the top by changing the operating conditions and use a chimney exhaust method.

　　(2) Combustion Device:

　　Crucible melting furnaces are divided into gas-fired crucible melting furnaces, oil-fired crucible melting furnaces, and crucible resistance furnaces according to the fuel used. Zhengzhou Zhongwei Environmental Protection Equipment Co., Ltd. has many years of design and manufacturing experience.

　　(3) Controlled Atmosphere Inside the Furnace During Melting:

　　When melting copper alloys, the furnace atmosphere has a significant impact on the molten metal, especially its susceptibility to absorbing hydrogen, which reduces the quality of the molten liquid.

　　The air excess coefficient of heavy oil furnaces is slightly larger than that of gas furnaces; otherwise, complete combustion cannot be achieved. However, understanding the characteristics of various furnaces is crucial, especially fully understanding the characteristics of the furnace atmosphere, which is essential for producing high-quality products.

　　4. Oil-fired Crucible Furnace:

　　Oil-fired crucible furnaces often use heavy oil and diesel as fuel. The fuel oil is sprayed into the furnace chamber through a fuel burner. Due to the different fuel oil and wind pressure used, there are various types of nozzles: commonly used low-pressure fuel oil nozzles. This type of nozzle uses compressed air to atomize the oil. The oil tank is placed more than 3 meters above the nozzle, and the oil is sent into the nozzle using its own weight and the pressure of the compressed air. The oil is impacted multiple times by the flowing air as it passes through the nozzle, so the atomization effect is good. This nozzle has a simple structure, with air directly impacting the oil flow for atomization, resulting in a long flame. Improved nozzles have a swirl device installed inside the nozzle, which can change the atomization conditions.

　　Zhengzhou Zhongwei Environmental Protection Equipment Co., Ltd. undertakes domestic and international projects for gas, oil, and electric crucible melting aluminum furnaces, zinc melting furnaces, tin melting furnaces, copper melting furnaces, and magnesium smelting furnaces.