First, the typical process of aluminum alloy regeneration production
1. Features of recycled aluminum melting process
Recycled aluminum is aluminum ingots that meet the requirements of various types of standards and are manufactured through smelting, using recycled scrap aluminum parts or scraps from the production of aluminum products, scrap aluminum wire as the main raw materials. This aluminum ingot uses recycled aluminum scrap, which has a lower production cost, and it is a re-use of natural resources, and has a strong vitality, especially in the current rapid development of science and technology, the quality of people's lives continue to improve today, product updates The frequency of replacements has accelerated, and the recycling and comprehensive utilization of used products has become an important issue for the continued development of human beings. The production of recycled aluminum has emerged in this form and has excellent prospects.
As the raw materials of recycled aluminum are mainly waste aluminum materials, there are scrap aluminum castings (based on Al-Si alloys), waste aluminum forgings (Al-Mg-Mn, Al-Cu-Mn alloys, etc.), and aluminum profiles. (Al-Mn, Al-Mg and other alloys) Waste materials (mainly pure aluminum) and other materials, sometimes mixed with some non-aluminum alloy waste parts (such as Zn, Pb alloy, etc.), this gives The preparation of recycled aluminum brings great inconvenience. How to formulate such a variety of raw materials with complex ingredients into a qualified recycled aluminum ingot is a core issue in the production of recycled aluminum. Therefore, the first step in the production process of recycled aluminum is the separation and classification process of aluminum scrap. The finer the sorting, the more accurate the classification, the easier it is to realize the chemical composition control of recycled aluminum.
Scrap aluminum parts often have many inlays. These inlays are non-aluminum parts mainly composed of steel or copper alloys. They are not extracted in a timely manner in the smelting process, resulting in some unnecessary addition of recycled aluminum components. Ingredients (such as Fe, Cu, etc.) Therefore, in the early stage of remelting aluminum smelting, that is, when the waste miscellaneous aluminum is just melted, it is necessary to have a process of inserting a tantalum alloy (commonly known as a tantalum iron process). The more timeliness and cleanliness the inserts in the scrap aluminum components are picked out, the more easily the chemical composition of the recycled aluminum can be controlled. The temperature of the molten iron during the yttrium iron should not be too high, and the increase of the temperature causes the Fe and Cu elements in the insert to dissolve into the molten aluminum.
The waste aluminum materials collected in various places are not free from dirt on the surface due to various reasons, and some are also heavily rusted. These dirt and rust surfaces will enter the molten pool during melting to form slag phases and oxidation inclusions, which will seriously damage the metallurgical quality of recycled aluminum. . Removal of these slag phases and inclusions is also one of the important processes in the remelted aluminum smelting process. The use of multi-stage purification means that a coarse purification is performed first, the secondary rare earth is refined after the composition is adjusted, and then the inert gas is further blown to further enhance the refining effect, and the inclusions in the aluminum melt can be effectively removed.
The oil on the surface of the waste aluminum material and the absorbed moisture cause the aluminum melt to contain a large amount of gas. Failure to effectively remove these gases will greatly reduce the metallurgical quality. The degassing step in the regeneration of aluminum production will be strengthened to reduce the gas content of recycled aluminum. The important measures for obtaining high quality recycled aluminum.
Second, the composition and pretreatment of recycled aluminum raw materials
1. The composition of recycled aluminum raw materials
(1) Sources of waste aluminum
At present, the waste aluminum used in China's reclaimed aluminum plant mainly comes from two aspects: first, waste miscellaneous aluminum imported from abroad, and second, domestic waste miscellaneous aluminum.
a. Imported waste aluminum sp;
In recent years, a large amount of domestic waste aluminum has been imported from abroad. In terms of the composition of imported aluminum scrap, most of them are mixed except for a few classifications. Generally can be divided into the following categories:
1 single species of waste aluminum
Such scrap aluminum is generally a certain type of waste parts, such as pistons of internal combustion engines, automobile speed reducers, automobile wheels, and front and rear automobile safety catches. Aluminum doors and windows. These aluminum scraps have been categorized clearly at the time of import, and they are of a single species and are imported in bulk. Therefore, they are high-quality recycled aluminum raw materials.
2 scrap aluminum section
The waste aluminum scraps, also referred to as slices, are high quality aluminum scraps. The reason why it is called slicing is that many developed countries have used mechanical methods to break them into scrap when they dispose of end-of-life automobiles, waste equipment, and various kinds of waste household appliances, and then sort it out by mechanization. The aluminum scrap is aluminum scrap. In addition, when the recycling department reprocesses some large-volume scrap aluminum parts, it is also broken into scraps by crushing. Such scraps are also called scrap aluminum chips. The scrap aluminum chips are easy to transport and easy to sort. The texture is relatively pure and is also a good quality aluminum scrap material. At present, in the scrap aluminum trade in the international market, the slice has the largest amount of possession, and all kinds of slices are undergoing standardized development. As for the components of slicing, it is generally divided into several grades, among which the high-grade slicing is a relatively pure mixture of various aluminum scraps and their alloys. The vast majority of smelting is performed without any treatment, and a small amount of grades The low section contains different amounts of other impurities, generally containing 80% to 90% of waste aluminum, in which the impurities are mainly non-ferrous metals such as scrap steel and scrap copper, and also contain a small amount of waste rubber, etc. After being manually selected, they are purified. Waste aluminum material. Scrap aluminum smelting is also relatively easy. When smelting, it is easy to enter the furnace, easy to get rid of impurities, less flux consumption, high metal recovery rate, low energy consumption, processing costs are low, very popular with users, generally large-scale recycled aluminum plants are sliced main ingreadient.
High-quality aluminum scrap is more expensive than other aluminum scraps, and it is suitable for large-scale modern enterprises. It is difficult to obtain in the international market. Therefore, in China, except for wholly-owned or joint-venture companies, they are rarely used by ordinary aluminum scrapers. .
3 mixed scrap aluminum material
This type of waste aluminum is complex in composition and has different physical shapes. In addition to aluminum scrap, it also contains a certain amount of scrap steel, waste lead, scrap zinc and other metals and waste rubber, waste wood, plastic waste, stones, etc. Waste aluminum and scrap steel machinery are combined together. Such scrap components are complex. A small amount of scrap aluminum is large and the surface is clear and easy to sort. Such scraps must be pre-sorted before being smelted, that is, scraps and other impurities are manually picked.
4 Incineration of aluminum-containing materials
This type of aluminum material is a kind of aluminum-containing waste material with a relatively low grade, and is mainly a crushed material of various kinds of scrapped household appliances, etc., and sorts out a part of the scrap material and then burns it to form a material. The purpose of incineration is to remove combustible materials such as waste rubber and waste plastics. Such aluminum-containing waste generally has an aluminum content of about 40% to 60%, and the rest are mainly non-ferrous metals such as garbage (bricks and stones), scrap steel, and extremely small amounts of copper (copper wires). Aluminum is generally less than 10 cm in size. During the incineration process, some aluminum and low-melting substances such as zinc, lead, and tin are melted, forming glassy materials with other materials, which are difficult to distinguish with the naked eye and cannot be classified. . p;
5 mixed shredded aluminum scrap
This kind of scrap is the lowest grade aluminum scrap, its composition is very complex, including various scrap aluminum in 40% to 50%, the rest is scrap steel, a small amount of lead and copper, a lot of garbage, stones and soil, waste plastics, Waste paper, etc., soil accounts for about 25%, scrap accounts for 10% to 20%, and stones account for 3 to 5%.
b. Domestic recycled shredded aluminum scrap
Most of the waste aluminum scraps recovered in China are pure and basically free from impurities (except for man-made impurities), which can be basically divided into three major categories, namely the waste-cooked aluminum, waste raw aluminum, and scrap-alloyed aluminum, which are often referred to in the recycling department. It is scrap aluminum and scrap alloy aluminum. More waste machinery parts (such as waste auto parts, waste molds, waste cast aluminum pots, internal combustion engine pistons, etc.). Waste aluminum generally refers to waste aluminum with aluminum content above 99% (such as waste cables, waste household cutlery, kettles, etc.). Scrap aluminum alloy (such as waste aircraft aluminum, aluminum frame, etc.). As far as the production sector is concerned, it can be divided into domestic waste aluminum and industrial waste aluminum.
1 Waste aluminum produced in the field of life such as waste household cutlery, kettle cast aluminum pots, waste aluminum parts in waste household appliances, scrap wires, waste packaging, etc. Waste scrap parts of aluminum and its alloys in mechanical and electrical equipment (such as waste auto parts, aluminum waste airplanes, waste dies, waste internal combustion engine pistons, waste cables, waste aluminum pipes, etc.
(2) Aluminium scraps produced by production enterprises Such scrap aluminums are generally called new scraps and mainly include aluminum scraps produced during the production of aluminum and its alloys, scraps and scraps produced during the processing of aluminum, and mechanical processing systems. The scraps of aluminum and its alloys, aluminum scraps and waste products, the waste aluminum cables of cable plants, and the pouring risers and waste castings produced in the foundry industry are the same as those of the new scraps, except that the new waste is sticky with oily crumbs. Higher waste aluminum materials can be clearly classified and stored if the waste is generated by the enterprise, and the utilization value is extremely high.
3 Smelting scum generated during the smelting of aluminum and aluminum alloys This type of waste is commonly referred to as aluminum ash. Wherever molten aluminum is present, aluminum ash is generated, such as in the production, smelting, processing and scrap aluminum regeneration of aluminum. A large amount of aluminum ash will be produced in the middle, in particular, the aluminum ash produced during the regeneration and smelting of waste aluminum will be more. The composition of the waste aluminum is complicated, the more impurities are, the more serious the surface contamination is, the more aluminum ash will be. The aluminum content of aluminum ash is related to the selected covering agent and smelting technology. Generally, the aluminum content is below 10%, and the high aluminum content is up to 20%.
2. Composition features of waste aluminum
The main sources of scrap aluminum are industrial waste, recycled materials, and cast slush systems. Its composition is relatively complicated. In most cases, it contains a lot of foreign impurities, including various organic substances such as plastics, moisture, etc. If such substances are not cleaned before the smelting process is carried out, it will result in serious inhalation of the alloy melt and subsequent solidification. During the process, defects such as blowholes, loosening, etc. are generated. In addition, the incorporation of some non-aluminum metals will also cause the composition of the material to be unacceptable and the performance to deteriorate. Non-metallic inclusions caused by the incorporation of various non-metallic minerals can also degrade the quality of the material. Because of this characteristic, the first important step in the production process of recycled aluminum is the pretreatment of waste aluminum, in order to purify the raw materials as much as possible, and minimize the factors that are not conducive to the quality of recycled aluminum.
(1) Pretreatment of waste aluminum R> a. Basic principles of domestic waste aluminum pretreatment
Because the composition of the waste aluminum is quite complex, the secondary processing of the alloy as its main raw material must carry out the necessary pretreatment of the raw materials.
In theory, all impurities should be completely removed. The actual industrial process takes into account the cost factor and can only solve the main contradiction. The usual processing principles are:
The raw materials are classified according to the composition of the materials, and the classification is based on the composition of the aluminum alloy. The necessary disassembly of the classified aluminum alloy scrap is performed to remove large non-aluminum metal or organic impurities.
Necessary cleaning of raw materials, including cleaning with water or organic solvents, sandblasting, etc.
The above-discussed waste aluminum can be used as a basic raw material for alloy smelting.
b. Status of waste aluminum pretreatment
The purpose of the pretreatment of the waste aluminum is to remove other metals and impurities contained in the waste aluminum, and to classify the waste aluminum according to its composition, so that the alloy components therein can be utilized to the maximum degree. The third is to dispose of oil, oxides, and coatings on the surface of waste aluminum. The final result of the pretreatment is to treat the scrap aluminum into charge that meets the furnace conditions, and the fourth is to make the aluminum (aluminum oxide) contained in the aluminum-containing scraps most economically and most reasonably utilized.
Domestic waste aluminum pretreatment technology is still very simple and backward. Even in large-scale reclaimed aluminum plants, there is no advanced technology for the pretreatment of waste aluminum. From the current point of view, the following pretreatment techniques are mainly used.
1 A kind of scrap aluminum that is single or almost free of other impurities is generally not subjected to complex pretreatment, but is classified according to the type and composition of the waste, and is piled separately. When a single type of scrap aluminum is used, only one component can be sampled and tested to determine whether or not it can be known. The batch ingredients are high quality recycled aluminum raw materials that are generally smelted without any pretreatment. When smelting a certain alloy, waste aluminum with the corresponding components and types is often directly added to the large-scale reverberatory melting furnace, so that it can be easily smelted into the corresponding aluminum alloy. Some copper-containing, high zinc-containing scrap aluminum can also be used as an intermediate alloy for adjusting components. Enterprises using small reverberatory furnaces or crucible furnaces are required to crush bulk aluminum scrap into pieces that meet the furnace specifications as required.
2 For the higher-grade scrap aluminum chips, the main components are cast aluminum alloy, alloy aluminum, pure aluminum, etc., among which the first two are of many brands, and it is difficult to classify them according to brand numbers. In large-scale recycled aluminum plants, generally only Screening removes mixed soil and the like, that is, directly into the furnace smelting. In small-scale reclaimed aluminum plants, such scrap aluminum is to be manually divided into cast aluminum alloys, alloyed aluminum, and pure aluminum, and then used separately.
3 For the low-grade slicing and incineration of scrap aluminum material (which is not normally used in large-scale recycled aluminum plants), complex sorting is required due to its complex composition, including scrap copper, scrap, and lead scrap in addition to aluminum scrap. Wait for metal and contain other waste. The sorting of such wastes depends mainly on labor. First, the soil and garbage are sieved out and then manually separated. Most manual sorting operations are carried out on the operator's desk. They rely mainly on the visual inspection and experience of the workers to sort out the non-metal scraps and then sort the scrap metal. Among them, the selection of scrap copper and scrap pure aluminum is particularly meticulous, because the scrap copper can be To increase production value, pure aluminum scraps, such as scrap aluminum wire, are high-grade raw materials that are used to adjust components in smelting. Separated waste aluminum is mixed and generally no longer subdivided.
At present, the pretreatment of waste aluminum in China has not basically achieved mechanization and automation, mainly relying on labor, and the tools used are magnets and steel boring, which are based on experience. This sorting method has low efficiency, poor quality, high cost, and waste. Most of the non-ferrous metals such as copper in aluminum are contaminated, and manual sorting is difficult and has fallen far behind. There is an urgent need to study advanced waste aluminum pretreatment technology.
3. Advanced waste aluminum pretreatment technology
The purpose of the advanced waste aluminum pretreatment technology is to realize the mechanization and automation of waste aluminum separation, to remove metal impurities and non-metallic impurities to the utmost extent, and to effectively classify the waste aluminum alloy according to the alloy composition classification. The sorting method is based on the main alloy composition of scrap aluminum into several categories, such as alloy aluminum, aluminum-magnesium alloy, aluminum-copper alloy, aluminum-zinc alloy, aluminum-silicon alloy. In this way, it is possible to reduce the impurity removal technology and adjust the composition in the smelting process. It is also possible to comprehensively utilize the alloy components in the scrap aluminum, especially the aluminum scraps containing zinc, copper, and magnesium, which must be stored separately and used as smelting aluminum alloys. Adjust the composition of the intermediate alloy raw materials. The current advanced waste aluminum pretreatment technologies mainly include:
1Wind separation separation of waste paper, waste plastics and dust. All kinds of waste aluminum contain more or less waste paper, waste plastic film and dust, and the ideal process is the winnowing method. The process of the winnowing method is simple and it can separate most of the light wastes efficiently. However, the wind-sorting method needs to be equipped with a good dust collection system to avoid dust pollution to the environment, sorting out the waste paper, and waste plastic film. It is generally not appropriate to continue sorting. It can be used as fuel.
2 Magnetic separation equipment is used to sort scrap magnetic waste. Iron is a harmful substance in aluminum and its alloys, and has the greatest impact on the mechanical properties of aluminum alloys. Therefore, it is necessary to maximize the sorting of waste steel in the mixed aluminum in the pretreatment process. For scrap aluminum and low grade aluminum scrap. The preferred technique for sorting scrap steel is magnetic separation. This method has been widely adopted in foreign countries. The magnetic separation method is relatively simple. The magnetic source comes from an electromagnet or a permanent magnet. The design of the process is various and the cross-cutting method of the conveyor belt is relatively easy to realize. The waste aluminium on the conveyor moves in a lateral direction. After entering the magnetic field, the waste steel is sucked up and left the transverse belt and immediately taken away by the longitudinal belt. After the running longitudinal belt leaves the magnetic field, the scrap steel loses its gravity and is automatically grounded and collected. . The magnetic separation process is simple and has low investment and can be easily adopted. The volume of the waste aluminum material treated by the magnetic separation method should not be too large, and general chipping and scrap aluminum scraps are suitable. Large pieces of waste materials must be broken before entering the magnetic separation process.
The waste steel separated by magnetic separation method must be further processed. Because there are some non-ferrous metal components that are mechanically combined with aluminum in the scrap steel devices, it is difficult to separate them, such as nuts, wires, and keys on aluminum scraps. , Plumbing, pinions, etc., are necessary for the sorting of this part, because the separation of non-ferrous metals can increase the value and improve the grade of scrap steel, but the sorting is more difficult, generally manual dismantling and distribution Selected, but inefficient. In order to increase production efficiency, the most effective way to sort out the hard-to-disassemble aluminum and steel joints is to heat them in a dedicated melting furnace to melt the aluminum and remove the scrap steel.
3 Water-based flotation method Light-weight materials such as waste plastics, waste wood, and waste rubber mixed in lightweight impurities, waste aluminum, etc., can be sorted by water flotation. The main equipment is a screw-type propeller. Scrap aluminum is introduced with the screw propeller. During the entire process, most of the remaining soluble materials such as dirt and dust are dissolved in water and washed away by water and enter the sedimentation tank. The sewage is returned to the circulation after it is clarified by multiple sedimentation, and the sludge is cleared regularly. This method can completely separate lightweight materials with specific gravity smaller than water, which is a simple and easy method.
4 Sorting of heavy non-ferrous metals such as copper from scrap aluminum. The non-ferrous metals such as copper in scrap aluminum are basically contaminated by oil. It is more difficult to separate non-ferrous metals from waste by manual sorting. The effective method is parabolic ore dressing. This method utilizes the principle that different objects of substantially the same volume fall differently when the same force is thrown. It is possible to separate various waste non-ferrous metals with different densities in scrap aluminum. When objects of different densities and substantially the same volume are ejected along a straight line with the same force, various objects move in the direction of the parabola and fall at different points when landing. The simplest test can be carried out on a horizontal conveyor belt. When the mixed waste material runs at high speed along the conveyor belt, when the conveyor belt runs to the end, the waste aluminum is thrown along the straight line, and the gravity of the various wastes is different. Point to landing, so as to achieve the purpose of sorting. This method can evenly separate scrap aluminum, scrap copper, and other wastes. Equipment designed on this principle has been adopted abroad, but the price is prohibitively expensive. Domestic is in the research stage.
5 Pretreatment of surface coatings of scrap aluminum A lot of scrap aluminum surfaces are coated with a protective layer such as paint, especially aluminum waste packaging containers, the largest number being waste cans and other packaging containers and toothpaste. In a small smelter, the waste is generally smelted without any pretreatment, and the paint is re-burned during the smelting process. However, these types of waste materials are thin-walled, and the paint will oxidize part of the aluminum during the combustion process and increase the impurities and bubbles in the aluminum. The more advanced recycled aluminum process generally treats the coating before it is smelted. The main techniques are dry and wet methods. Wet method is to soak waste aluminum with a certain solvent, so that the paint layer falls off or is dissolved by the solvent. The disadvantage of this method is that the amount of liquid waste is large and it is not easy to handle. It is generally not suitable for use. The dry method is the fire method. Rotary kiln roasting method is generally used.
The main equipment for the roasting method is a rotary kiln. Its greatest advantage is its high thermal efficiency, which facilitates the separation of aluminum scrap from carbides. The heat from the calcination comes from the hot air from the furnace and the heat generated during the charring of the aluminum paint layer. During production, the rotary kiln rotates at a certain speed, and the lacquer layer on the waste aluminum surface is gradually charred at a certain temperature. Due to the rotation of the rotary kiln, the materials collide with each other and vibrate, and finally the carbonized material falls off from the scrap aluminum. Some of the fallen carbon is collected at one end of the rotary kiln, and some of it is recovered in the dust collector.
The pretreatment of waste aluminum is an important part of the recycling process of waste aluminum. With the improvement of the level of recycled aluminum technology, pretreatment technology will become more and more important. The non-aluminum material is completely separated from the waste aluminum and its alloys, and the aluminum scrap is classified according to the grade of the alloy with high efficiency, and the most comprehensive utilization of the waste aluminum is achieved. This is the research direction of the pretreatment technology in the recycled aluminum technology.
Third, the smelting of recycled aluminum
1. The purpose of smelting
The basic task of metal alloy smelting is to put a certain ratio of metal charge into the furnace, and the melt is obtained by heating and melting. Then the composition of the molten melt is adjusted to obtain the desired alloy liquid. And in the smelting process to take appropriate measures to control the content of gas and oxide inclusions, in line with the provisions of the composition (including the main component or impurity element content), to ensure that the castings are properly organized (grain refinement) high-quality alloy liquid.
Due to the characteristics of aluminum, aluminum alloys have a strong tendency to produce pores and are also prone to oxide inclusions. Therefore, preventing and removing gas and oxidizing inclusions are the most prominent problems in the smelting process of aluminum alloys. In order to obtain high-quality aluminum alloy liquid, the smelting process must be strictly controlled and measures must be taken to control it from all aspects.
2. Smelting process
The aluminum alloy smelting process is as follows:
Furnace → melting (add copper, zinc, silicon, etc.) → slag → Magnesium, yttrium, etc. → Stirring → Sampling → Adjustment of components → Stirring → refining → Slag → Converter → refining and standing still → casting.
The correct furnace installation method is very important to reduce metal burnout and shorten the melting time. For the reverberatory furnace, an aluminum ingot is placed on the bottom of the furnace, placed in a burnable material, and then pressed onto the aluminum ingot. The lower melting point of the reflow material is installed on the upper layer to make it melt the earliest and flow down to cover the following burnable material, thereby reducing burn-in. All kinds of charge should be evenly distributed.
Melting and melting processes and smelting speeds have important effects on the quality of aluminum ingots. When the charge is heated to stay softened, the flux should be properly covered. During the melting process, care should be taken to prevent overheating. After the charge liquid level of the charge is leveled, the melt should be properly agitated to make the temperature consistent, and at the same time it is also conducive to accelerated melting. The long smelting time not only reduces the production efficiency of the furnace, but also increases the gas content of the melt. Therefore, the secondary refining of the melt should be performed when the smelting time is long.
The slag can be slagged when the charge is completely melted to the smelting temperature. Before the slag dross should be sprinkled with powdered flux (sodium-free flux should be sprinkled on high-magnesium alloys). The slag should be as thorough as possible because of the presence of scum when it can easily contaminate the metal and increase the gas content of the melt.
After adding magnesium and adding slag, magnesium ingot can be added to the melt, and flux should be added for coverage. For high-magnesium alloys, 0.002% to 0.02% niobium should be added to prevent magnesium burning. Niobium can be obtained from sodium hypofluorite by a metal reduction method, and sodium hypofluorite is added by mixing with a flux.
Stirring There should be sufficient time for stirring before sampling and after adjusting the ingredients. The stirring should be stable without destroying the oxide surface oxide film.
After the sample melt is fully stirred, it should be sampled immediately for pre-furnace analysis.
Adjusting ingredients When the ingredients do not meet the standards, they should be fed or diluted.
After the converter composition of the melt is adjusted, when the melt temperature meets the requirements, the surface scum is pumped out.
The refining and metamorphic components of the melt are different, and the purification and modification methods are also different.
3. Composition adjustment
In the smelting process, each element in the metal is reduced by their own oxidation, and how much they are oxidized depends not only on the size of their own affinity for oxygen but also on the concentration of the element in the liquid alloy. (degrees), the nature of the resulting oxide, and the temperature at which it is located. In general, the elements with higher affinity for oxygen have more losses, and aluminum, magnesium, boron, titanium, and zirconium have strong affinity for oxygen; carbon, silicon, and manganese are secondary; iron, cobalt, nickel, copper, and lead, etc. weak. Therefore, the elements that have a stronger affinity for oxygen in the smelting alloy will be preferentially oxidized to cause excessive loss; on the contrary, those elements that have a weaker affinity for oxygen can be relatively "protected" and less depleted. . After smelting, the content of an element in the alloy is increased or decreased due to oxidation loss, which should be determined by the relative loss of the element and the base metal element. Relatively depleting elements will be reduced in content, known as “burningâ€; elements with less relative loss will increase in content and can be called “burn-inâ€; in order to properly control the chemical composition of the melt, when the metal charge is selected Should take into account the changes after smelting, the corresponding compensation in the amount of each element added.
In actual smelting, the degree of burn-in of the elements in the alloy is also affected by the quality of the raw material, the flux and slag, the handling technology, and in particular the nature of the oxides produced.
4. Prevention of gases and oxides during smelting
As mentioned earlier, the main source of gas and oxide inclusions in aluminum liquids is H2O. H2O is from the surface oxide film stirred into the aluminum liquid, the surface of the charge (especially the charge that is corroded by moisture), melting and casting tools, and refining. Agents, modifiers into the liquid aluminum. The oxide film stirred into the aluminum liquid and the low-grade charge (such as slag splashing, scrap remelting ingot) containing many inclusions will form oxide inclusions in the aluminum liquid. For this reason, the following points should be noted from the smelting and pouring process:
1 crucible and melting pouring tools
Before use, dirt, oxidized slag, old paint layer, etc. adhered to the surface should be carefully removed, then coated with new paint, preheated and dried before use. The crucibles that melt the casting tools and transport the aluminum liquid should be fully preheated before use.
2 charge
The charge should be stored in a dry place before use. If the charge has been corroded by moisture, sand is blown prior to batching to remove the surface corrosion layer. Sand (SiO2) is often adhered to the surface of the return charge, and some of the SiO2 and aluminum liquids react as follows: 4 Al + 3 SiO2 → 2 Al2O3 + 3 Si
The generated Al2O3 and the remaining SiO2 form oxidized inclusions in the aluminum liquid, so it should be used after blowing sand before adding this type of material. The three-stage return material produced by re-melting chips, splashing slag, etc., often contains more oxidizing inclusions and gases. Therefore, the amount of oxidized inclusions and gases used should be strictly limited, generally not exceeding 15% of the total amount of charge, and should be used for important castings. Not used at all. The surface of the charge should also be free from oil contamination, cutting coolants, etc., because various oils and greases are hydrocarbons with complex structures, and the oil is heated to bring hydrogen.
The charge must be preheated to 150-180°C when adding the molten aluminum. The purpose of preheating is on the one hand for safety, to prevent the molten aluminum from colliding with the moisture on the surface of the cold charge and cause an explosion; on the other hand, Prevents the introduction of gases and inclusions into the liquid aluminum.
3 Refining Agents and Modifiers
Some of these constituents are easily deliquescent due to the absorption of moisture in the atmosphere, while others contain crystal water. Therefore, it should be fully dried before use, some substances such as ZnCl2 need to be re-melted to remove moisture before use.
4 Operation of melting and pouring process
Melting and stirring the aluminum liquid should be stable, so as not to stir the surface oxide film and air into the aluminum liquid. The number of injections of liquid aluminum should be minimized. Drops of liquid flow and splashes should be reduced during injection. When pouring, the pouring nozzle should be as close as possible to the sprue cup to reduce the falling height of the liquid flow, and should be poured at a constant speed to minimize the spatter and eddy current of the aluminum liquid. After pouring the castings, the remaining liquid in the spoon should not be poured back into the crucible and poured into the ingot mold, otherwise the oxidation inclusions in the aluminum liquid will increase continuously. A large amount of Al2O3 and other inclusions are deposited in the aluminum liquid at a depth of about 50 to 100 mm at the bottom of the crucible, and thus cannot be used for pouring castings.
5 Melting temperature, duration of smelting and pouring process
Increasing the temperature will accelerate the reaction between aluminum liquid and H2O and O2. The solubility of hydrogen in molten aluminum will also increase sharply with the increase of melting temperature. When the temperature is higher than 900°C, the oxide film on the aluminum surface will not be dense. The above reaction is significantly increased, so the melting temperature of most aluminum alloys generally does not exceed 760°C. As for the aluminum-magnesium alloy with a loose protective oxide film on the surface of the aluminum liquid, the reaction between the aluminum liquid and H2O and O2 is more sensitive to the temperature increase, so the melting temperature limit of the aluminum-magnesium alloy is more strict (generally not exceeding 700°C). .
The longer the duration of the smelting and casting process (especially the time from refining to completion of pouring), the higher the content of gas and oxide inclusions in the aluminum liquid. Therefore, the duration of smelting and pouring should be shortened as much as possible. In particular, the time from refining to pouring should be shortened as much as possible. The general requirement in the factory stipulates that the smelting should be completed within 2 hours after refining, and if it is poured, it should be re-refined in the weather. In regions and castings that require high levels of pinholes or alloys that are prone to blowholes and inclusions, the casting time should be limited.
Fourth, the refining of recycled aluminum
When the metal melting component is adjusted, the next step is the aluminum refining process. The purpose of aluminum alloy refining is to obtain high cleanliness and low gas content alloy liquid after degasification and impurity removal measures are taken. Refining has the following methods:
Add chlorides (ZnCl2, MnCl2, AlCl3, C2Cl6, TiCl4, etc.);
Ventilation (pass N2, Cl2 or N2 and Cl2 mixture);
Vacuum treatment method;
Add non-toxic refining agent method;
Ultrasonic treatment
According to its principle, the refining process has two functions: for dissolved hydrogen, it mainly relies on diffusion to remove hydrogen from the aluminum liquid; for oxide inclusions, it is mainly removed through the addition of flux or bubbles to the surface of the media.
Degas
In general, the floatation method is used for degassing. The principle is that a certain hydrogen-free gas is introduced into the aluminum liquid to generate bubbles, and these bubbles are used to take dissolved hydrogen out of the aluminum liquid during the floatation process and escape into the atmosphere. In order to obtain a better refining effect, the iron pipe that introduces the gas should be pushed into the depth of the molten pool as far as possible. The lower end of the iron pipe is 100 to 150 mm away from the bottom of the crucible, so that the stroke of the air bubble rises longer, and at the same time it does not sink The inclusions on the bottom of the aluminum liquid stir. When the gas is introduced, the iron pipe should be slowly moved laterally in the aluminum liquid so that air bubbles pass through the molten pool. Use lower ground pressure and speed as much as possible, because the smaller bubbles thus formed enlarge the surface area of ​​the bubbles, and because the bubbles are small and the float speed is slow, more inclusions and gases can be removed. At the same time, in order to ensure a good refining effect, the selection of the refining temperature should be appropriate. If the temperature is too high, the generated bubbles are large and float quickly, and the refining effect is deteriorated. When the temperature is too low, the viscosity of the aluminum liquid is relatively large, which is not conducive to the full discharge of the gas in the aluminum liquid, and also reduces the refining effect.
Ultrasonic treatment of liquid aluminum can also effectively degas. Its principle is that by introducing elastic waves into the aluminum liquid, a "hole" phenomenon is caused in the aluminum liquid, thus destroying the continuity of the aluminum liquid structure and producing countless microscopic holes, which are dissolved in the aluminum liquid. Hydrogen rapidly escapes into these cavities and becomes a bubble core, and as it grows up, it escapes as a bubble to escape the aluminum liquid, thereby achieving a refining effect.
2. Removing impurities
For non-metallic inclusions, the use of gas refining methods can be effectively removed, and for the more demanding materials can also be used in the casting process using a filter method or the melt through the molten flux layer mechanical filtration, etc. to remove.
For metallic impurities, the general treatment method is to turn harmful factors into favorable factors. That is, it becomes a beneficial second phase by the alloying method so as to facilitate the performance of the material. If it must be removed, in most cases it is the high-temperature and low-pressure selective distillation using different boiling points of different elements to achieve the purpose of removing metal impurities.
Aluminum alloys smelted from aluminum-containing scrap often contain excessive metal elements that should be removed as much as possible. Selective oxidation can be used to remove various metal impurities having a higher oxygen affinity than aluminum and oxygen from the melt. For example, elements such as magnesium, zinc, calcium, and zirconium accelerate the oxidation of these impurity elements by stirring the melt. These metal oxides are insoluble in molten aluminum and enter the slag, so that they can be melted from the aluminum by slagging. Removed from the body.
Metal impurities in the alloy can also be removed by utilizing the difference in solubility. For example, an aluminum alloy contaminated with impurities is co-melted with a metal that can dissolve aluminum without dissolving impurities, and then the aluminum alloy liquid is separated by filtration, and then the added metal is removed by vacuum distillation. Iron, silicon and other impurities in aluminum are usually removed by the addition of magnesium, zinc, mercury, and then these added metals are removed by vacuum distillation. For example, if an aluminum alloy contaminated with impurities is eutecticized with 30% magnesium, the alloy is allowed to stand for a period of time at near-eutectic temperature, and the precipitated crystal phase containing iron and silicon is removed by filtration, and is then vacuum-removed at 850°C. In the case of magnesium, impurities with high vapor pressure, such as zinc and lead, are also removed together with magnesium, and the pure aluminum alloy after magnesium removal can be ingot-cast.
In order to further improve the liquid quality of aluminum alloys, or when certain brands of aluminum alloys require strict control of hydrogen content and inclusions, a combined refining method may be used, that is, two refining methods may be used simultaneously. For example, chlorine salt-filter combined refining and argon-flux combined refining can achieve better results than single refining.
V. Organization control and degeneration
1. Metamorphic treatment of hypoeutectic and eutectic Al-Si alloys
The silicon phase in the aluminum-silicon alloy eutectic grows into flakes in a self-growth condition, and even a thick, polygonal plate-like silicon phase appears. These forms of silicon phase will severely split the Al matrix at the tip and corners of the Si phase. At locations where stress concentration occurs, alloys tend to crack along the grain boundaries, or plate-like Si itself cracks to form cracks, making the alloy brittle, and the mechanical properties, particularly the elongation, are significantly reduced, and the cutting function is not good. In order to change the existing state of silicon and improve the mechanical properties of the alloy, modification techniques have been used for a long time.
The metamorphic effect elements of eutectic silicon include: Na, Sr, S, La, Ce, Sb, and Te. At present, the research mainly focuses on several kinds of metamorphic agents such as sodium, strontium, and rare earth.
1 sodium metamorphism (Na)
Sodium is the earliest and most effective metamorphic element of eutectic silicon. It can be added in three ways: metal sodium, sodium salt and sodium carbonate.
The initial modifier of metal sodium is metal Na. The sodium has the best metamorphic effect. It can effectively refine the eutectic structure and add a small amount (about 0.005% to 0.01%) to get the eutectic silicon phase from the needle. The metamorphoses into a completely uniform fibrous form. However, there are some disadvantages in the use of metal Na metamorphism. First, the metamorphic temperature is 740° C., which is close to the boiling point of Na (892° C.). Therefore, the aluminum liquid easily boils and splashes occur, which promotes the oxidation and absorption of the aluminum liquid, and the operation is not safe. Secondly, the Na specific gravity. Small (0.97), enriched in the surface layer of molten aluminum, the upper layer of aluminum fluid deterioration, the bottom is deficient in metamorphism, metamorphic effect is very unstable. At the same time, Na easily reacts with the water vapor to generate hydrogen, increase the content of aluminum liquid Gas volume. Na is chemically very active. It easily reacts with oxygen in the air. It is generally stored in kerosene and must be removed before use. This is also a difficult task, but it will not be removed in the molten aluminum. Bring gas and inclusions.
The commonly used modificator in the production of sodium salt is a mixture containing a halogen salt such as NaF, which reacts with sodium to produce sodium and metamorphose. However, these sodium salts can easily bring moisture into the air, which increases the oxidation tendency of the alloy. At the same time, these sodium salts have a corrosive effect on the environment and cause damage to the health of the body.
The sodium carbonate-based metamorphic agent is a non-environmental damage modifier that should be developed to overcome the environmental problems of the above sodium salt deterioration. In other words, sodium carbonate and aluminum and magnesium react at a high temperature to produce sodium and undergo metamorphism. The reaction process and reaction products are non-toxic. Similarly, such pollution-free modifiers also have the problem of water absorption and increase the tendency of the aluminum alloy to inhale and oxidize.
Another shortcoming that can not be ignored is the use of sodium metamorphism. It is a short-term maintenance of the metamorphic effect, that is, a non-long-lasting metamorphic agent. The effective period of Na salt modifier is only 30-60min. After this time, the effect of metamorphism disappears on its own. The higher the temperature, the faster the failure. Therefore, the molten aluminum that must be degraded must be used within a short time. When remelting, it must be Renewed. Moreover, it is difficult to precisely control the sodium modification process. Therefore, in many occasions, sodium deterioration is gradually being replaced by some long-term metamorphic methods.
2 锶 metamorphism (Sr)
Strontium (Sr) is a long-lasting metamorphic agent, and its metamorphic effect is equivalent to that of Na, and does not have the disadvantage of Na metamorphism. It is a promising metamorphic agent. In the United Kingdom, the Netherlands, and other countries began to promote the use of Sr modification methods from the early 1980s. At present, many studies have been conducted at home and abroad for metamorphic metamorphism. The scale of using Sr instead of Na or Na salt is also increasing in China. Sr metamorphism has the following advantages: 1 good metamorphic effect, long effective period; 2 metamorphic operation, no smoke, non-toxic, no environmental pollution, no corrosion of equipment, tools, does not harm health, easy to operate; 3 easy to obtain satisfactory mechanical properties; 4 Reloading materials have certain remelting and metamorphic effects; 5 castings have high yields and significant overall economic benefits. However, practice has shown that metamorphic alloys tend to produce shrinkage, increase the pinhole degree of the castings, reduce the compactness of the alloy, and exhibit a mechanical deterioration.
3 锑 metamorphism (Sb)
Sb can change eutectic silicon from acicular to lamellar. In order to obtain a lamellar sheet, the optimum addition range is usually 0.15% to 0.2%. Its metamorphic effect is inferior to Na and Sr. A prominent advantage of twisting metamorphism is a long time of deterioration (more than 8 hours). The melting point of niobium is 630.5°C and its density is 6.68g/cm3. Therefore, the niobium content is relatively easy to control, and it is not easy to cause deterioration or deterioration. It does not increase the tendency of inhalation and oxidation inclusion of aluminum liquid, but its metamorphic effect is affected. The effect of cooling rate is relatively large. It has good metamorphic effect on metal type and rapid cooling castings, but it is not obvious on slow cooling of heavy-walled sand type castings, so the use is subject to certain restrictions.
4 碲 metamorphism (Te)
Radon is a domestic research metamorphic agent. The effect of metamorphism is similar to that of metamorphic metamorphism. Its role is to promote silicon to be refined in the form of flake-like branching, but not to become fibrous, but the metamorphic effect is more reluctant. The metamorphic effect has a long-lasting effect and does not change after 8 hours or remelting. Similarly, its metamorphic effect is also greatly affected by the cooling rate.
5 metamorphism
Ba has a good metamorphic effect on eutectic Si. Compared with Na, Sr, and Sb, the metamorphic effect of Ba is relatively long-lasting, and a wide range of addition amounts to 0.017% to 0.2% Ba to obtain a good metamorphic structure. After Ba was added, the tensile strength of the alloy was significantly improved, continuous remelting was performed, and the metamorphic effect was still maintained, and its metamorphic effect was satisfactory.采用Baå˜è´¨çš„ä¸è¶³ä¹‹å¤„是对铸件的å£åŽšæ•æ„Ÿæ€§å¤§,对厚å£é“¸ä»¶çš„å˜è´¨æ•ˆæžœå·®ï¼Œä¸ºäº†èŽ·å¾—良好的å˜è´¨æ•ˆæžœ,必须快冷。åŒæ—¶ï¼ŒBa对氯化物æ•æ„Ÿï¼Œä¸€èˆ¬ä¸ç”¨æ°¯æ°”或氯ç›æ¥ç²¾ç‚¼ã€‚
⑥稀土å˜è´¨
The countries where rare earths were used in aluminum and aluminum alloys were earlier in Germany, and Germany had successfully used rare earth-containing aluminum alloys during the First World War. Rare-earth elements can achieve similar metamorphic effects as sodium and strontium, which can change eutectic silicon from flakes into short rods and spheres, improving the properties of the alloy.而且稀土的å˜è´¨ä½œç”¨å…·æœ‰ç›¸å¯¹é•¿æ•ˆæ€§å’Œé‡ç†”稳定性，其å˜è´¨æ•ˆæžœå¯ç»´æŒ5～7å°æ—¶ï¼Œå¼ å¯è¿ç‰äººå¯¹Laå˜è´¨å¯¿å‘½è¿›è¡Œæ£€éªŒï¼Œå«La0.056%çš„å˜è´¨åˆé‡‘，ç»åå¤ç†”化-å‡å›º10次ä»æœ‰å˜è´¨æ•ˆæžœã€‚
稀土由于其化å¦æ€§è´¨çš„活泼性，æžæ˜“与O2 ã€N2ã€H2ç‰å‘生å应，从而起到脱氢ã€è„±æ°§ã€åŽ»æ°§åŒ–çš®ç‰ä½œç”¨ï¼Œå› 而å¯ä»¥å‡€åŒ–é“液。
总之，稀土在Al-Siåˆé‡‘ä¸å…¼æœ‰ç²¾ç‚¼å’Œå˜è´¨çš„åŒé‡æ•ˆæžœï¼Œå˜è´¨æ•ˆæžœå…·æœ‰ç›¸å½“长效性和é‡ç†”稳定性.ç¨€åœŸå…ƒç´ çš„åŠ å…¥æ高了åˆé‡‘çš„æµåŠ¨æ€§,改善了åˆé‡‘çš„é“¸é€ æ€§èƒ½,优化了åˆé‡‘的内在质é‡ã€‚ Another major advantage is that the addition of rare earth does not produce smoke, does not cause pollution to the environment, and complies with the needs of the development of the times.
â‘´å˜è´¨å‰‚的选择
At present, the most widely used aluminum alloy casting production is the sodium salt modifier, which consists of sodium and potassium halide salts.这类å˜è´¨å‰‚使用å¯é ，效果稳定。 In the composition of the modifier, NaF can be metamorphic.与é“液接触åŽå‘生如下å应：
3NaF + Al → AlF3 + 3Na
å应生æˆçš„é’ è¿›å…¥é“液ä¸ï¼Œå³èµ·å˜è´¨ä½œç”¨ã€‚ Since NaF has a high melting point (992° C.), NaCl and KCl are added to the modifying agent in order to reduce the metamorphic temperature and reduce the suction and oxidation of the aluminum liquid at high temperature. Add a certain amount of ternary ternary modifier composed of NaCl and KCl. The melting point is below 800°C. Under the general metamorphic temperature, it is in the molten state, which is conducive to the deterioration and improves the speed and effect of metamorphism. In addition, the metamorphic agent in the molten state easily forms a continuous coating layer on the liquid surface, which improves the covering effect of the modifying agent.为æ¤ï¼Œ NaClã€KClåˆç§°ä¸ºåŠ©ç†”剂。
有的å˜è´¨å‰‚ä¸åŠ 入一定é‡çš„冰晶石（Na3AlF6）， è¿™ç§å˜è´¨å‰‚具有å˜è´¨ã€ç²¾ç‚¼ã€è¦†ç›–作用，一般称为“通用å˜è´¨å‰‚â€ã€‚ This modifier is often used when pouring important castings or when the metallurgical quality of the molten aluminum is high.
In production, the deterioration process is generally performed after refining and before casting.å˜è´¨æ¸©åº¦åº”ç¨é«˜äºŽæµ‡æ³¨æ¸©åº¦ï¼Œè€Œå˜è´¨å‰‚的熔点最好介于å˜è´¨æ¸©åº¦å’Œæµ‡æ³¨æ¸©åº¦ä¹‹é—´ï¼Œè¿™æ ·ä½¿å˜è´¨å‰‚在å˜è´¨æ—¶å¤„于液æ€ï¼Œå¹¶ä¸”å˜è´¨åŽå³å¯è¿›è¡Œæµ‡æ³¨ï¼Œå…å¾—åœæ”¾æ—¶é—´é•¿ï¼Œé€ æˆå˜è´¨å¤±æ•ˆã€‚ In addition, after the modification process is completed, the degraded slag has become a very thick solid, which facilitates skimming, so that the residual flux is not poured into the casting mold to form flux slag.
When selecting a modificator, the melting point and metamorphic temperature of the modificator are generally determined according to the required pouring temperature, and then the appropriate modificator component can be selected according to the selected mordant melting point.
⑵å˜è´¨å·¥è‰ºå› ç´ çš„å½±å“
The main factors of deterioration process are: metamorphic temperature, metamorphic time, type and amount of modifier.
å˜è´¨æ¸©åº¦
温度高些，对å˜è´¨ååº”è¿›è¡Œæœ‰åˆ©ï¼Œé’ çš„å›žæ”¶çŽ‡é«˜ï¼Œå˜è´¨é€Ÿåº¦å¿«ï¼Œæ•ˆæžœå¥½ï¼Œä½†å˜è´¨æ¸©åº¦ä¸èƒ½è¿‡é«˜ï¼Œå¦åˆ™ä¼šæ€¥å‰§å¢žåŠ çš„é“液的氧化和å¸æ°”，并使é“液ä¸é“æ‚è´¨å¢žåŠ ï¼Œé™ä½Žå©åŸšçš„使用寿命。 In general, the metamorphic temperature should be chosen to be slightly higher than the pouring temperature. This avoids the high metamorphic temperature, can reduce the time to adjust the temperature after deterioration, and is conducive to improving the metamorphic effect and the metallurgical quality of the aluminum liquid.
å˜è´¨æ—¶é—´
The higher the metamorphic temperature and the better the contact of the molten aluminum with the modificator, the shorter the required deterioration time. The deterioration time should be determined on the basis of the experiment according to the specific circumstances. If the metamorphic time is too short, the metamorphic reaction will be incomplete; if the metamorphic time is too long, the burning of the modificator will increase and the inhalation and oxidation of the alloy will increase.
The metamorphic time is composed of two parts: the variator covering time is generally 10 to 15 minutes, and the pressing time is generally 2 to 3 minutes.
å˜è´¨å‰‚ç§ç±»åŠç”¨é‡
The type and amount of modificators should be selected according to the type of alloy, the casting process, and the specific requirements for the control of the structure. Selecting non-toxic, non-polluting and long-lasting metamorphic effect modifiers is the current development direction of aluminum alloy melting process. In the production practice, it should be considered that the mutator reaction may be incomplete, so the amount of modificator should not be too small, otherwise the effect of deterioration is not good.但å˜è´¨å‰‚用é‡ä¹Ÿä¸å®œè¿‡å¤šï¼Œå¦åˆ™ä¼šäº§ç”Ÿè¿‡å˜è´¨çŽ°è±¡ã€‚å› æ¤ï¼Œå˜è´¨å‰‚用é‡ä¸€èˆ¬è§„定为å 炉料é‡é‡çš„1～3%。 In production, usually adding 2% can guarantee good deterioration. For metal castings, the amount of modifier can be reduced.当采用通用å˜è´¨å‰‚时，除了考虑å˜è´¨æ•ˆæžœå¤–，还è¦è€ƒè™‘对这ç§å˜è´¨å‰‚的覆盖ã€ç²¾ç‚¼èƒ½åŠ›çš„è¦æ±‚，通常其å˜è´¨å‰‚用é‡ä¸ºé“液é‡é‡çš„2～3%。
⑶å˜è´¨å¤„ç†çš„炉å‰æ£€éªŒ
Cast the sample, knock it open after cooling, and judge the effect of deterioration according to the shape of the fracture.
è‹¥å˜è´¨ä¸è¶³ï¼Œåˆ™æ™¶ç²’粗大，æ–å£å‘ˆç°æš—色，并有å‘亮光的硅晶粒å¯è§ã€‚
è‹¥å˜è´¨æ£å¸¸ï¼Œåˆ™æ™¶ç²’较细，æ–å£å‘ˆç™½è‰²ä¸ç»’状，没有硅晶粒亮点。
è‹¥å˜è´¨è¿‡åº¦ï¼Œåˆ™æ™¶ç²’也粗大，æ–å£å‘ˆçŽ°è“ç°è‰²ï¼Œæœ‰ç¡…的亮晶点。
2.过共晶é“ç¡…åˆé‡‘å˜è´¨å¤„ç†
Hypereutectic Al-Si alloy due to the large amount of silicon, so that the alloy's thermal expansion coefficient decreases, increased wear resistance, suitable for internal combustion engine piston and other wear parts.过共晶Alï¼Siåˆé‡‘组织ä¸å˜åœ¨æ¿çŠ¶åˆæ™¶ç¡…和针状共晶硅。åˆæ™¶ç¡…作为硬质点å¯æ高åˆé‡‘å¾—è€ç£¨æ€§ï¼Œä½†å› 为它硬而脆，对åˆé‡‘机械性能ä¸åˆ©ï¼Œå¹¶ä½¿åˆé‡‘çš„åˆ‡å‰ŠåŠ å·¥æ€§èƒ½å˜åï¼Œå› æ¤ï¼Œè¿‡å…±æ™¶Alï¼Siåˆé‡‘ä¸çš„共晶硅和åˆæ™¶ç¡…都è¦è¿›è¡Œå˜è´¨å¤„ç†ã€‚
For a long time, the refinement of primary silicon has been studied in depth. Ultrasonic vibration crystallization method, quenching method, superheat melting, low temperature casting can achieve certain results. However, the effect is the most stable, and the most useful value in the industry is to add a modifying agent.
At present, the modificator actually used for production is phosphorus monolith.èµ¤ç£·ä½¿ç”¨æœ€æ—©ï¼Œå½“åŠ å…¥é‡ä¸ºåˆé‡‘é‡é‡çš„0.5ï¼…æ—¶