Analysis on How to Effectively Reduce Casting Loss in Aluminum Casting

[China Aluminum Industry Network] Aluminum is a group III A element in the periodic table of elements and is an active metal after K, Ca, Na, and Mg. It can interact with oxygen, nitrogen, and water vapor in the air at high temperatures. Carbon dioxide and other interactions [2].

Aluminum casting is the conversion of liquid aluminum into aluminum ingots, bars, or other shapes of finished and semi-finished products through batching, mixing, standing, refining, slag slag, and other processes. Aluminum and aluminum alloys have different degrees of loss due to oxidation, refining, slagging and other reasons during the casting process.

The so-called aluminum cast loss is aluminum and aluminum alloy in the smelting process due to oxidation, volatility and the interaction with the furnace wall, refining agent caused by the non-recoverable metal loss and aluminum slag contained in the metal in general [1].

The general formula for cast loss is: (amount of primary aluminum - volume of finished product) Aluminium quantity of primary alumina × 100%. The higher the cast loss, the smaller the quantity of finished products. If the aluminum production enterprise with an annual output value of 100,000 tons, if the cast loss is reduced One thousand points, no additional investment, it will produce 100 tons of aluminum products (ie reduce the loss of 100 tons of aluminum products), which will be considerable social and economic benefits, so how to effectively reduce the loss is very important.

Analyze the cause of cast loss

The main external manifestation of cast loss can be divided into two parts: one is in the form of pure aluminum ash, and the other is in the form of bulk aluminum and defective aluminum, aluminum slag

I conducted data statistics in the casting shop of Henan xx Aluminum Co., Ltd., in which non-recyclable pure aluminum ash accounted for about 90% of the cast loss (oxidation burned slag forming), other factors accounted for about 10%, other factors for possession of 10% The statistical analysis of further data is mainly caused by the secondary reheating of large aluminum and defective aluminum, and the aluminum content in aluminum ash (the main raw material of aluminum, aluminum and aluminum). Therefore, the main cause of the internal cast loss is oxidation. Secondary damage such as burnout, defective aluminum, and aluminum content in aluminum ash.

The principle of aluminum oxide burnout can be further understood by the following chemical equation:

4Al+ 3O2=2Al2O3

The study of metal oxidation thermodynamics shows that the tendency of metal oxidation, oxidation sequence of each alloying element and oxidation degree are all determined by the affinity of metal and oxygen, and are related to the composition, temperature and pressure of the alloy. The greater the affinity between metal and oxygen, the greater the trend of oxidation, the higher the degree of oxidation; the higher the temperature, the greater the affinity of metal and oxygen, the greater the trend of oxidation, the higher the degree of oxidation; the smaller the decomposition pressure of oxides The greater the affinity of metal and oxygen, the greater the trend of oxidation, the higher the degree of oxidation [1, 3].

In the range of smelting temperature, aluminum and oxygen have great affinity and are easy to be oxidized. After oxidation, Al2O3 film forms on the surface. When it is higher than 500°C, it is metastable r-Al2O3. This kind of metastable oxide film is stable. During the oxide film transition, volume shrinkage occurs and further oxidation and cracking occur. With the increase of the temperature and time of the aluminum liquid, the oxide film grows faster, and the amount and thickness of oxidation also increase significantly [1, 3].

The factors that affect cast loss are:

1) liquid aluminum temperature; 2) contact strength of aluminum liquid with oxygen; 3) aluminum content in aluminum slag; 4) aluminum liquid with slag; 5) how much defective aluminum and large aluminum; 6) other causes Loss

Ways to reduce cast loss

Control the temperature of liquid aluminum

The melting point of aluminum is 660°C. In general, the casting temperature of primary aluminum is controlled at about 730°C or even lower, and the aluminum alloy has better fluidity and the casting temperature is lower than that of primary aluminum, about 710°C-730°C, for direct use. The unit of liquid aluminum in the electrolytic cell, when the high-temperature aluminum liquid enters the mixing furnace, should be promptly mixed into the cold material, that is, adding inferior products such as aluminum, aluminum slag, etc. to the mixture maintaining furnace, and some of the intermediate alloys (industrial silicon) can also be advanced Into the furnace to form a pressure melt state, both to increase the actual yield and reduce the temperature. The surface of the cold material added at the same time must be clean and free from oil contamination, etc. Otherwise, it may burn exothermic and promote burning. In short, the temperature of the aluminum liquid is effectively reduced to the corresponding casting temperature, which can reduce the great influence of the temperature on the cast loss.

Reduce the contact of aluminum liquid with air, the greater the contact strength between liquid aluminum and oxygen, the more serious oxidation burnout, the greater the loss of cast

1) Reduce the contact time between liquid aluminum and oxygen: 1 Under the conditions of meeting the production requirements, turn the liquid aluminum in the furnace into finished products as quickly as possible, preferably on-shift production of on-duty ingredients, and do not make liquid aluminum stay in the furnace for too long; 2 Reasonably install the casting equipment and shorten the length of the runner as much as possible to reduce the exposure time of the liquid aluminum in the air. At the same time, the aluminum silicate insulation board can be covered in the upper part of the runner, which can not only have certain insulation but also reduce the oxygen content in the runner. .

In short, to prevent the aluminum liquid from being stored in the mixing furnace for a long time due to various reasons, to reduce the loss of molten aluminum and oxygen to reduce the loss of the cast.

2) Control liquid aluminum mixing method: whether it is manual mixing or mechanical stirring is carried out in the open state of the furnace door, not only will bring great fluctuations in liquid level, increase the contact area with oxygen, but also increase the oxygen content in the furnace The quantity will inevitably accelerate the above chemical reactions and increase the damage. Electromagnetic stirring can be carried out in a closed state and the fluctuation of the liquid level is small, which effectively avoids the corresponding disadvantages. At the same time, it can also reduce the moisture in the air to enter the furnace and reduce the probability of liquid aluminum absorbing hydrogen.

3) Blowing height when controlling liquid aluminum refining: The general refining method is artificially directly scattering the refining agent into the furnace, and then stirring and refining, but for some of the alloy production requires blowing nitrogen refining (refining time is longer, up to 30 minutes Left and right), there will inevitably be a certain bubbling height and cross to the side, vertical to the head, driving the great fluctuations of liquid aluminum, so better to adjust the nitrogen pressure, the blistering height is controlled at 10-15mm.

Correct selection and use of refining agents to fully separate slag aluminum

In the smelting process of aluminum and aluminum alloys, in addition to its own inclusions, aluminum is prone to generate alumina or hypoaluminum with oxygen, resulting in a layer of scum on the surface of the aluminum liquid, which has a certain degree of wettability with the aluminum melt. A considerable amount of melt is mixed in, so a refining agent is needed to change the wettability of both, increase the surface tension at the slag and aluminum interface, and separate the slag from aluminum.

Aluminum and aluminum alloy flux is generally composed of alkali metal and alkaline earth metal chloride and fluoride, its main component is KCl, NaCl, NaF. CaF2, Na3A1F6, Na2SiF6, etc., but the content of components varies greatly, and the effects are not the same. In addition to using the flux produced by the flux plant, it is preferred to adjust the ratio of flux components based on the composition of the smelted aluminum alloy. At the same time strictly control the refining process conditions, such as the amount of flux, contact time of the flux with the melt, contact area, stirring conditions, temperature, etc., the use of refining agents can effectively reduce the slag with aluminum, reduce casting losses.

Effective treatment of aluminum slag produced during casting

Aluminum slag is an unavoidable part of the melting process. Despite all the relevant measures, a certain percentage of metal aluminum will be brought out and will need to be effectively treated instead of being sold directly to other units. A simpler and more economical method can be The aluminum slag is repeatedly milled and sieved using a roller to effectively recover some aluminum beans.

Reduce the slag slope of the mixing furnace and pull the aluminum slag out of the furnace

The size of the slag slope of the mixing furnace directly affects the amount of aluminum slag discharged. If the slope is too large, most of the slag will not be smashed, resulting in a large amount of aluminum slag and aluminum deposits. The slag and aluminum deposits cannot be recovered in time when the furnace is cleaned. Under the premise of ensuring the capacity of the mixing furnace, the slope of the slag dregs should be reduced as much as possible.

Strictly control the quality of slag to prevent liquid aluminum from being carried out

The existing slag slag operation is basically the manual use of slag to discharge the aluminum slag out of the door of the furnace. In addition to requiring the meticulous operation of personnel during this operation, the aluminum fluid should not be carried out as much as possible. A few rows of small round holes are opened on the surface of the crucible, and the liquid aluminum contained in the aluminum slag can flow into the furnace. Otherwise, excessive liquid aluminum is taken out and then returned to the furnace to cause burning.

Reduce the amount of defective aluminum and bulk aluminum

In the production process, strictly in accordance with the requirements of the process to ensure the production of a furnace, a furnace, in particular, in the production of general aluminum, as far as possible to avoid flash, burrs, ripples, inconsistent with the weight of aluminum and other defective products, while production Before the end, as far as possible, the liquid aluminum in the flow tank is pushed into the mold to form a qualified product to reduce the amount of large aluminum.

Effective treatment of the produced defective aluminum

For a variety of reasons, such as the defective aluminum, aluminum and aluminum slag, aluminum beans, etc. to take the appropriate furnace order to join the mixing furnace, if necessary, the first waste recycling operations to avoid unnecessary burning damage.

Through the above analysis, although the cast loss is unavoidable during the casting process, it is effective in reducing the casting process by controlling the temperature of the molten aluminum, reducing the contact strength of the molten aluminum and air, controlling the aluminum content in the aluminum ash, and reducing the amount of aluminum in the defective product. In the cast loss, it will have a significant effect, it will also bring considerable economic benefits to the company.