Production process and classification of aluminum ingots
Time : 2023-03-07
Production process and classification of aluminum ingots

What is the production process of aluminum ingots?

The production of aluminum ingots is composed of bauxite mining, alumina production, aluminum electrolysis and other production links.

The bauxite is mined first, and the aluminum ore powder is produced through processes such as washing and grinding, and then alumina is obtained through four complicated processes such as roasting. 

There are three main types of bauxite for the production of alumina: gibbsite, diaspore, and boehmite. 

Among the proven global reserves of bauxite, 92% are weathered laterite-type bauxite, which belongs to the gibbsite type. These bauxites are characterized by low silicon, high iron, and high aluminum-silicon ratio, and are concentrated in Africa. Western, Oceania and Central and South America. The remaining 8% is sedimentary bauxite, which belongs to boehmite and diaspore type, with medium and low grades, mainly distributed in Greece, the former Yugoslavia and Hungary. 

Due to the different characteristics of the three kinds of bauxite, each alumina production enterprise adopts different production processes in production, mainly including Bayer method, soda lime sintering method and Bayer-sintering combined method. 

Usually, high-grade bauxite is produced by Bayer method, and medium and low-grade bauxite is produced by combined method or sintering method. Due to its simple process and low energy consumption, the Bayer method has become the most important method used in the current alumina production, and its output accounts for about 95% of the world's total alumina production.

Under the action of strong current, aluminum oxide is electrolyzed to produce aluminum metal. This process is called electrolytic aluminum; 

How many types of aluminum ingots are there?

Aluminum ingots can be divided into three types: aluminum ingots for remelting, high-purity aluminum ingots, and aluminum alloy ingots according to their composition;

Several common aluminum ingots:

Aluminum ingot for remelting--15kg, 20kg(≤99.80%Al):

T-shaped aluminum ingot--500kg, 1000kg(≤99.80%Al):

High-purity aluminum ingot--l0kg, 15kg (99.90%~99.999%Al);

Aluminum alloy ingot--10kg, 15kg (Al--Si, Al--Cu, Al--Mg);

Plate ingot--500~1000kg (for plate making);

Round ingot - 30~60kg (for wire drawing). 

What are the common defects of aluminum for remelting?

① stomata. The main reason is that the casting temperature is too high, the aluminum liquid contains more gas, the surface of the aluminum ingot has many pores (pinholes), the surface is dark, and thermal cracks occur in severe cases.

② Slag inclusion. The main reason is that one is that the slag is not clean, resulting in slag inclusion on the surface; the other is that the temperature of the molten aluminum is too low, resulting in internal slag inclusion.

③ Ripple and flash. The main reason is that the operation is not fine, the aluminum ingot is too large, or the casting machine is not running smoothly.

④ cracks. Cold cracks are mainly caused by the low casting temperature, which makes the crystallization of aluminum ingots not dense, resulting in looseness and even cracks. Hot cracks are caused by high casting temperature.

⑤ composition segregation. It is mainly caused by uneven stirring when casting alloys.

Shangang has been committed to researching and improving the quality of steel. The aluminum produced for remelting has fewer pores, basically no slag inclusions and cracks, and the composition is uniform. We are proud to strive to provide customers with high-quality aluminum ingot products. 


The process flow of casting aluminum ingots is roughly as follows:

(1) Aluminum tapping—slag removal—weight inspection—ingredients—furnace loading—scouring—casting—aluminum ingots for remelting—finished product inspection—finished product inspection—storage

(2) Aluminum tapping - slag removal - weighing - batching - furnace loading - refining - casting - alloy ingots - casting alloy ingots - finished product inspection - finished product weighing - storage

Commonly used casting methods are divided into continuous casting and vertical semi-continuous casting


Introduction to the continuous casting method of cast aluminum ingots:

Continuous casting can be divided into two ways: mixed furnace casting and external casting. Both use continuous casting machines.

Mixing furnace casting is to pour aluminum liquid into the mixing furnace, and then pour it from the mixing furnace. It is mainly used to produce aluminum ingots and casting alloys for remelting.

For casting in a mixing furnace, it must first go through batching, then pour it into the mixing furnace, stir evenly, and then add flux for refining. Casting alloy ingots must be clarified for more than 30 minutes, and the slag can be cast after clarification. When casting, the furnace eye of the mixing furnace is aligned with the second and third molds of the casting machine, which can ensure a certain degree of mobility when the liquid flow changes and the mold is changed. Furnace eye and casting machine are connected by launder, and the launder should be shorter, which can reduce the oxidation of aluminum and avoid vortex and splashing. When the casting machine is stopped for more than 48 hours, the mold should be preheated for 4 hours before restarting. The molten aluminum flows into the mold through the launder, and the oxide film on the surface of the molten aluminum is removed with a shovel, which is called slag removal. After one mold is filled, the launder is moved to the next mold, and the casting machine moves forward continuously. The casting mold advances one by one, and the molten aluminum gradually cools down. When it reaches the middle of the casting machine, the molten aluminum has solidified into aluminum ingots, and then the smelting number is stamped by the printer. When the aluminum ingot reaches the top of the casting machine, it has completely solidified into an aluminum ingot. At this time, the casting mold is turned over, and the aluminum ingot is released from the mold and falls on the automatic ingot receiving trolley. It is automatically stacked and bundled by the stacker to become a finished aluminum ingot. ingot. The casting machine is cooled by spraying water, but the water can only be supplied after the casting machine has turned a full circle. Each ton of molten aluminum consumes about 8-10t of water, and a blower is required for surface cooling in summer. The ingot belongs to flat die casting, and the solidification direction of the molten aluminum is from bottom to top, and the upper middle is finally solidified, leaving a groove-shaped depression. The solidification time and conditions of each part of the aluminum ingot are different, so its chemical composition will also be different, but it meets the standard as a whole. 

External casting is to cast directly from the ladle to the casting machine. It is mainly used when the casting equipment cannot meet the production requirements, or the quality of the incoming material is too poor to be directly put into the furnace. Since there is no external heating source, the ladle is required to have a certain temperature, generally 690-740°C in summer and 700-760°C in winter, to ensure a better appearance of the aluminum ingot.


Introduction of vertical semi-continuous casting method for casting aluminum ingots:

Vertical semi-continuous casting is mainly used for the production of aluminum wire ingots, plate ingots and various deformed alloys for processing profiles.


The molten aluminum is poured into the mixing furnace after batching. Due to the special requirements of the wire, it is necessary to add Al-B in the middle plate before casting to remove titanium and vanadium (wire ingot) from the molten aluminum; the plate ingot needs to be added with Al-Ti--B alloy (Ti5% B1%) for refinement. Make the surface structure finer.

Add 2# refining agent to high-magnesium alloy, the dosage is 5%, stir well, let it stand for 30 minutes, remove the scum, and then cast. Before casting, raise the chassis of the casting machine and blow off the moisture on the chassis with compressed air. Then raise the chassis into the crystallizer, apply a layer of lubricating oil to the inner wall of the crystallizer, put some cooling water into the water jacket, and put the dry and preheated distribution plate, the automatic adjustment plug and the launder, so that the distribution plate The opening is located in the center of the crystallizer. At the beginning of casting, press the automatic adjustment plug by hand to block the spout, cut the furnace hole of the mixing furnace, let the aluminum liquid flow into the distribution plate through the launder, and release the automatic adjustment plug when the aluminum liquid reaches 2/5 in the distribution plate. Adjust the plug so that the molten aluminum flows into the crystallizer, and the molten aluminum is cooled on the chassis. When the aluminum liquid reaches a height of 30mm in the crystallizer, the chassis can be lowered, and cooling water can be sent. The automatic adjustment plug controls the aluminum liquid to flow into the mold in a balanced manner, and keeps the height of the aluminum liquid in the mold unchanged. The scum and oxide film on the surface of molten aluminum should be removed in time. When the length of the aluminum ingot is about 6m, block the furnace eye, remove the distribution plate, stop the water supply after the aluminum liquid is completely solidified, remove the water jacket, take out the cast aluminum ingot with a monorail crane, and press the required size on the sawing machine Saw off and prepare for the next casting.

During casting, the temperature of the molten aluminum in the mixing furnace is kept at 690-7l0°C, the temperature of the molten aluminum in the distribution plate is kept at 685-690°C, the casting speed is 190-21Omm/min, and the cooling water pressure is 0.147-0.196MPa. The casting speed is proportional to the wire ingot with square cross-section:


In the formula, V is the casting speed, mm/min or m/h; D is the side length of the ingot section, mm or m; K is a constant value, m2/h, generally 1.2 to 1.5.


Vertical semi-continuous casting is a sequential crystallization method. After the molten aluminum enters the casting hole, it begins to crystallize on the chassis and the inner wall of the crystallizer. Due to the different cooling conditions between the center and the edge, the crystallization forms a form with a low center and a high periphery. The chassis descends at a constant speed. At the same time, the upper part is continuously injected with aluminum liquid, so that there is a semi-solidified area between the solid aluminum and the liquid aluminum. Since the aluminum liquid will shrink when it condenses, and there is a layer of lubricating oil on the inner wall of the crystallizer, as the chassis descends, the solidified aluminum exits the crystallizer, and there is a circle of cooling water holes in the lower part of the crystallizer, and the cooling water can be sprayed until it has come out The surface of the aluminum ingot is secondary cooling until the entire wire ingot is cast.

Sequential crystallization can establish relatively satisfactory solidification conditions, which are more beneficial to the grain size, mechanical properties and electrical conductivity of crystals. Compared with the ingot, there is no difference in mechanical properties in the height direction, the segregation is smaller, the cooling rate is faster, and a very fine crystal structure can be obtained. 

The surface of the aluminum wire ingot should be smooth and smooth, without slag inclusions, cracks, pores, etc., the length of the surface cracks should not exceed 1.5mm, the depth of slag and edge wrinkles on the surface should not exceed 2mm, and the section should not have cracks, pores and slag inclusions. There are no more than 5 slag inclusions smaller than 1mm. 

Common defects of aluminum wire ingots mainly include:

① crack. The reason is that the temperature of the aluminum liquid is too high and the speed is too fast, which increases the residual stress; the silicon content in the aluminum liquid is more than 0.8%, and the aluminum-silicon melt is formed, and a certain amount of free silicon is regenerated, which increases the thermal cracking of the metal: Or insufficient cooling water. When the surface of the crystallizer is rough or no lubricating oil is used, cracks will also occur on the surface and corners of the ingot.

② Slag inclusion. The slag inclusion on the surface of the aluminum wire ingot is caused by the fluctuation of the aluminum liquid, the rupture of the oxide film on the surface of the aluminum liquid, and the scum on the surface entering the side of the ingot. Sometimes lubricating oil can also bring some slag inclusions. The internal slag inclusion is caused by the temperature of the aluminum liquid being too low, the viscosity is high, the slag cannot float up in time, or the aluminum liquid level changes frequently during casting.

③ cold shut. The formation of cold shut is mainly due to the excessive fluctuation of the aluminum liquid level in the crystallizer, the low casting temperature, the slow casting speed or the vibration and uneven drop of the casting machine.

④ stomata. The pores mentioned here refer to small pores with a diameter of less than 1 mm. The reason for this is that the casting temperature is too high and the condensation is too fast, so that the gas contained in the molten aluminum cannot escape in time, and after solidification, it gathers into small bubbles and remains in the ingot to form pores.

⑤The surface is rough. Because the inner wall of the crystallizer is not smooth, the lubrication effect is not good, and in severe cases, aluminum nodules on the crystal surface are formed. Or due to the iron-silicon ratio is too large, the segregation phenomenon caused by uneven cooling. ⑥ Aluminum leakage and reanalysis. It is mainly an operation problem, and serious ones can also cause tumor crystals.

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