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When charging and smelting, the order and method of loading the charge are not only related to the smelting time, metal burning loss, and heat energy consumption, but also affect the quality of the metal melt and the service life of the furnace. The principle of loading is: 1. The order of loading the furnace materials should be reasonable. The correct charging depends on the nature and state of the charge added, and should also take into account the fastest melting speed, the least burning loss and accurate chemical composition control. When loading, small pieces or flake scraps are loaded first, aluminum ingots and large pieces are loaded in the middle, and finally the intermediate alloy is loaded. The intermediate alloy with a melting point that is easily oxidized is installed in the middle and lower layers. The loaded charge should be evenly distributed in the molten pool to prevent it from being too heavy. Small pieces or thin sheets are installed in the lower layer of the molten pool, which can reduce burning loss and also protect the furnace body from damage caused by direct impact of large pieces of material. Some intermediate alloys have high melting points. For example, the melting points of AL-NI and AL-MN alloys are 750-800°C. They are installed on the upper layer. Because the upper temperature in the furnace is high, they melt easily and have sufficient time to diffuse. ； Making the intermediate alloy evenly distributed is beneficial to the composition control of the melt. The charge is loaded flatly, and the melting speed is similar everywhere. This can prevent local metal overheating caused by heavy loading. The charge should be fed into the furnace at one time. Two or more additions will increase the non-metallic inclusions and gas content. 2. For the furnace materials of products with high quality requirements (including forgings, die forgings, hollow beams and beam profiles, etc.), in addition to the above charging requirements, 20-30kg of powdered flux must be sprinkled into the molten pool before charging. During the furnace loading process, powdered flux must be sprinkled on the furnace materials in layers. This can improve the purity of the furnace body and reduce losses. 3. When charging the electric furnace, it should be noted that the distance between the highest point of the furnace charge and the resistance wire must not be less than 100mm, otherwise it will easily cause a short circuit. After the melting charge is loaded, the temperature can be raised. Melting is the process of changing from solid to liquid state. The quality of this process has a decisive impact on product quality. A. As the temperature of the charge increases during the covering and melting process, especially when the charge begins to melt, the oxide film covering the outer surface of the metal is easily broken and will gradually lose its protective effect. Gas can easily invade at this time, causing further oxidation of the internal metal. And the melted liquid or liquid flow will flow to the bottom of the furnace. When the droplets or liquid flow enter the bottom and gather together, the oxide film on the surface will be mixed into the melt. Therefore, in order to prevent further oxidation of the metal and reduce the oxide film entering the melt, when the charge softens and collapses, a layer of powdery flux should be appropriately sprinkled on the metal surface to cover it. The dosage is shown in the table. This also reduces metal outgassing during the melting process. Covering agent type and amount Furnace type and product covering agent amount (accounted for input amount)/% Covering agent type Electrical melting ordinary products 0.4-0.5 Powder flux special products 0.5-0.6 Gas furnace melting ordinary products 1-2 Kcl: Nacl press 1: 1 Mixing special products 2-4 B. Add copper and zinc. After the charge is partially melted, zinc ingots or copper plates can be evenly added to the liquid. It is appropriate that the melt in the molten pool can just sink the zinc ingots and copper plates. It should be emphasized at this time that the melting point of the copper plate is 1083°C. Within the aluminum alloy melting temperature range, copper is dissolved in the aluminum alloy melt. Therefore, if the copper plate is added too early, the melt will not cover it, which will increase the burning loss of the copper plate. ； On the contrary, if it is added too late, the copper plate will not have time to dissolve and diffuse, which will prolong the melting time and affect the control of the chemical composition of the alloy. When smelting in an electric furnace, try to avoid replacing resistance ribbons to prevent dirt from falling into the melt and contaminating the metal. C. When stirring the melt, attention should be paid to preventing overheating of the melt. Especially when melting in a natural gas furnace (or gas furnace), the furnace temperature is as high as 1200°C. At such a high temperature, local overheating can easily occur. For this reason, when the charge is melted, the melt should be stirred appropriately to make the temperature uniform throughout the molten pool, which will also help accelerate the melting. Slag removal and stirring When the charge has been fully melted in the molten pool and the melt temperature reaches the melting temperature, a large amount of oxidized slag floating on the surface of the melt can be removed. A. Before slag removal, powdery flux should be evenly sprinkled on the melt to separate the slag from the metal, which is beneficial to slag removal and can bring out less metal. The slag removal needs to be smooth to prevent the slag from being involved in the melt. The slag removal must be thorough because the presence of scum will increase the gas content of the melt and stain the metal. B. After adding magnesium and beryllium and removing the slag, magnesium ingots can be added to the melt. At the same time, they should be covered with No. 2 powdery flux to prevent burning loss of magnesium. For high-magnesium aluminum alloys, in order to prevent the burning loss of magnesium and change the properties of the oxide film on the surface of the melt and ingot, a small amount (0.001%-0.004%) of beryllium must be added to the melt after adding magnesium. Beryllium is generally prepared with Al-BeF4 and No. 2 powdered flux at a ratio of 1: 1. Mix and add. Stir thoroughly after adding. Na BeF Al→2NaF AlF Be To prevent beryllium poisoning, a mask should be worn when adding beryllium. In addition, the waste removed after adding beryllium should be accumulated in a special storage area or treated specially. C. Stirring Before sampling and after adjusting the chemical composition, stirring should be carried out in time. Its purpose is to make the alloy components uniformly distributed and the temperature in the melt tend to be consistent. This may seem like an extremely simple operation, but it is a very important step in the process. Because some alloying elements with higher density easily sink to the bottom, and the addition of alloying elements cannot be absolutely uniform, which results in uneven distribution of alloying elements between the upper and lower layers of the melt and between various areas in the furnace. If the stirring is not thorough (the time is not guaranteed to be long enough and dead corners are not eliminated), it is easy to cause uneven chemical composition of the melt. Stirring should be carried out smoothly and should not cause too big waves to prevent the oxide film from being involved in the melt. Adjusting the composition During the smelting process, the composition of the alloy may change due to various reasons. This change may cause a large deviation between the actual composition of the melt and the calculated value of the ingredients. Therefore, it is necessary to take samples for rapid analysis after the charge is melted, so as to determine whether the composition needs to be adjusted based on the analysis results. A. Sampling After the melt is fully stirred, samples should be taken for rapid analysis in front of the furnace to analyze whether the chemical composition meets the standard requirements. The melt temperature in the furnace when sampling should not be lower than the middle limit of the melting temperature. The sampling locations for rapid analysis samples must be representative. For natural gas furnaces (or gas furnaces), take one set of samples from the center of the two furnace doors. For electric furnaces, take two sets of samples from the center of one-half of the melt. The sample spoon must be preheated before sampling. For high-purity aluminum and aluminum alloys, in order to prevent contamination of the sample spoon, a stainless steel sample spoon should be used and coated with paint for sampling. B. Composition adjustment When the rapid analysis results do not match the alloy composition requirements, the composition should be adjusted - dilute or supplement. (1) Feeding. When the rapid analysis results are lower than the alloy chemical composition requirements, additional materials are required. In order to make the feeding accurate, calculations should be made according to the following principles: 1) Count those with smaller quantities first and then those with larger quantities. ； 2) Calculate impurities first and then alloy elements ； 3) Calculate the low-component master alloy first, and then calculate the high-component master alloy. ； 4) In the final calculation of new metal, the amount of additional material required can generally be calculated approximately by the following formula, and then calculated. The formula is as follows: X= In the formula, ； b——Analyzed amount of this component, % ； cc - the amount of other metals or master alloys added respectively, kg; d - the content of this component in the master alloy for supplementary materials (if pure metal is added, d=100), %. 2) Dilute. Rapid analysis results are higher than those of chemical composition * * The upper limits of standards, delivery standards, etc. need to be diluted. During dilution, alloying elements that are higher than the chemical composition standard must be diluted to the upper limit of the alloying element content that is lower than the standard requirement. Based on production practices over the years, my country's aluminum processing plants have formulated in-plant standards for aluminum alloys so that these alloys can obtain good casting properties and mechanical properties. For this reason, when diluting, the required chemical composition is generally diluted to a level close to or lower than the upper limit of the factory's chemical composition standard for the element. When diluting, the required dilution amount is generally calculated according to the following formula. X=Q(ba)/a where b——the analytical amount of a certain component, % ； a——The required content of the (in-factory) standard upper limit of this ingredient, % ； Q——Total amount of melt, kg; The reason why the sample is not representative is because some elements have a high density, slow dissolution and diffusion, or are prone to segregation and stratification. Therefore, it should be stirred thoroughly before sampling to evenly distribute its components. Since the surface temperature of the molten pool in the reverberatory furnace is high and the furnace bottom temperature is low, there is no convection heat transfer effect. Stir multiple times before sampling, and each stirring time should not be less than 5 minutes. (2) The sampling location and operation method must be reasonable. Since the reverberatory furnace molten pool is large and deep, despite multiple stirrings before sampling, there is still a certain deviation in the composition of various parts of the molten pool. Therefore, the sample should be taken out from one-half of the deepest part in the middle of the molten pool. The sample mold should be fully heated and dried before sampling. The operation method when sampling is correct to make the sample meet the requirements. Otherwise, the sample has pores, slag inclusions or does not meet the requirements, which will bring certain errors to the rapid analysis. (3) The temperature should be appropriate when sampling. For some dense elements, their dissolution and diffusion speed accelerates as the temperature increases. If the melt temperature is low before sampling, the dissolution and diffusion rate is still very slow despite repeated stirring, and the sample taken out at this time is still unrepresentative. Therefore, the melt temperature should be controlled to be appropriately high before sampling. (4) Master alloys are generally used when feeding and diluting. New metal materials with higher melting points and more difficult to melt should be avoided. (5) The amount of feed and dilution should be as small as possible while ensuring the requirements of alloy elements. When diluting, the capacity of the smelting furnace and whether it is convenient for dilution operations should be considered. (6) If the amount of dilution is large, other alloying elements should be added so that the content of these alloying elements is not lower than the corresponding standards or requirements. Most of the aluminum alloys produced in the refining industry no longer have a gas refining process in the smelting furnace, but mainly rely on stationary furnace refining and online melt purification. Some aluminum processing plants still have smelting furnaces for refining, with the purpose of improving the purity of the melt. These refining methods can be divided into two categories: That is, gas refining method and flux refining method. After the melt has been refined and the surface scum is removed, when the temperature is suitable, the metal melt can be poured into the static furnace to prepare for casting. Furnace cleaning is to completely remove the remaining slag from the furnace. Every time metal comes out of the furnace, it must be cleaned. When the alloy is converted, ordinary products are produced continuously for 5-15 furnaces. Every time a furnace of extraordinary products is produced, a furnace cleaning is generally required. When cleaning the furnace, you should first spread a layer of powdery flux evenly into the furnace, raise the furnace temperature to above 800°C, and then use a triangular shovel to completely remove the remaining slag everywhere in the furnace. This post was last edited by yutr on 2009-3-11 13:14 ]