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how many stages for casting aluminum?

Casting is the process of melting aluminium in a furnace, pouring it into a mould and freezing it to form aluminium rods. The process may be divided into five main stages: charging of the furnace, smelting of billets, pre-heating of the filter and cast table, casting, and removal of aluminium rods.

Charging the furnace (from top and from bottom)
The first step is to charge the furnace. Charging is usually done from the top of the furnace. The roof and the electrodes are lifted up and moved aside to enable the crane to deliver a batch of scrap metal over the furnace. The bucket of scrap may open up when it is directly over the opening of the furnace so the scrap can fall in without any human intervention. Otherwise, the scrap may be loaded manually by hand. After loading the scrap metal, the roof is lowered and the electrodes are also lowered to create an arc with the scrap.

Smelting of billets
The billets are smelted within the electric arc furnace which can heat up the aluminum to about 1,200 degrees Fahrenheit (the temperature at which the aluminum will melt). The smelting of the aluminum continues until all the aluminum has been completely liquefied. After the aluminum has been heated beyond 1,200 degrees, the slag and other impurities are removed from the molten aluminum. At this stage any additional elements needed to make various aluminum alloys are added to the molten aluminum.

Heating the casting table
It is important to heat up the metal mold where the aluminum rods or billets will be formed. Heating the mold helps to prevent the uneven cooling of the aluminum as it passes into the mold. It also heats up the air in the mold and facilitates the release of air in the mold as the molten aluminum flows out of the furnace. An oxy-acetylene flame may be used to heat up the mold just before the molten aluminum is released.

Pouring of the molten aluminum
After heating the mold, the aluminum is poured into the mold. The molten aluminum settles in the mold and gets cold rapidly. Cooling is usually achieved by circulation of water around the mold. Cold water takes away the heat from the mold and becomes hot. Then fresh cold water is allowed to flow around the mold again to take away more heat from it.

Casting
As the aluminum gets cooled, it changes from liquid to solid. The aluminum takes the shape of the mold and becomes hardened. In this case, the aluminum solidifies to become a long rod that will be used later in the extrusion process. This solid aluminum will be passed through an extrusion machine to form the shape of the long cylindrical rod.

Lifting and arrangement of billets
Each aluminum rod or billet is removed from the mold and taken to the storage area. The billets are removed with the aid of a chain that is tied around them. This chain is then attached to a crane that moves the billets to the place where they are stacked together. From the stacking area, they may be moved by a forklift or conveyor to the place where they will be used for extrusion.

Casting is an efficient process for making the aluminum rods that are used to produce the aluminum profiles. It ensures that the right type of aluminium or alloy is produced and used for the extrusion process.