The general smelting process involves several key steps to ensure the production of high-quality alloy. First, based on the specific alloy grades outlined in the casting technical requirements, the chemical composition range is determined, and an appropriate composition is selected. Next, the ingredients are calculated according to the element's burning rate and the required composition. The charge materials are then selected, and if any contamination is found, they must be treated. It is essential that all charge materials are clean, free from rust, and preheated before being fed into the furnace.
Before melting, the equipment, tools, and furnace must be inspected and prepared. This includes painting and preheating to prevent contamination from gases, inclusions, or harmful elements. The feeding sequence typically starts with return charges, followed by intermediate alloys and metal materials. Low-melting-point and easily oxidized metals like magnesium are added after the initial charge has melted.
To minimize oxidation and pollution, the alloy should be melted as quickly as possible, avoiding overheating. If necessary, a covering agent can be used to protect the molten metal. After melting, refining treatments are performed to purify the alloy and test the effectiveness of the process. Further modifications may be made to improve the microstructure and mechanical properties, followed by temperature adjustment and casting.
Some alloys require stirring before pouring to prevent density segregation. The smelting method varies depending on the type of metal. For example, steel is often melted using converters, open hearth furnaces, electric arc furnaces, or induction furnaces. Cast iron is typically processed in cupola furnaces, while non-ferrous metals such as aluminum and copper alloys are melted using specialized equipment like the Komatsu A furnace.
Aluminum alloy smelting requires careful control due to its low melting point, susceptibility to oxidation, and the volatility of elements like magnesium and zinc. Smelting is usually carried out in electric or gas-heated furnaces, such as graphite crucibles or iron-based ones. The process involves precise calculation of ingredients, drying of materials, and controlled heating to avoid gas content issues.
Refining agents like hexachloroethane are commonly used to remove impurities and gases. Proper degassing techniques are crucial, as excessive gas content can lead to defects like blowholes. After refining, modifiers may be added to enhance the alloy’s properties. The final step involves pouring the molten metal into molds, ensuring smooth flow and proper solidification.
To achieve high-quality aluminum alloys, it is essential to manage gas content, minimize contamination, and follow strict process controls. Techniques such as "defense," "discharge," and "dissolution" are employed to reduce porosity and improve casting quality. Preventing moisture and gas ingress, removing inclusions through refining, and controlling solidification rates are key strategies in achieving defect-free castings.
In addition, sand mold preparation plays a critical role in preventing defects. Controlling the moisture content, improving air permeability, and enhancing exhaust capabilities help reduce gas-related issues during casting. Proper core design and baking also contribute to better casting outcomes. Overall, attention to every detail in the smelting and casting process ensures the production of high-performance aluminum alloy components.
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