Introduction: pure copper and copper alloys for casting are an important class of Non-ferrous metal and are widely used in practical production. Copper alloys in common use can be divided into two main classes according to their composition: cast brass and cast bronze. Both sand casting and investment casting, smelting is a crucial link in the production of casting. There are similarities and differences in the smelting of various copper alloys. In Years of production practice, we summarized the smelting process experience of pure copper and copper alloys (mainly bronze and brass) for your reference. The melting equipment used: medium frequency induction furnace, thermocouple, pouring ladle, graphite crucible and so on. 

1. Smelting of pure copper (1) the crucible is preheated to dark red and a layer of dried charcoal or covering agent (Borax 63% + broken glass 37%) about 30-50 cm thick is added to the bottom of the crucible. In turn, scrap, scrap and bar are added, and finally electrolytic copper is added. (2) the added Alloy Element can be preheated on the hearth, and the cold material is forbidden to be added into the liquid metal. Charge should be moved frequently throughout the melting process to prevent bypass. (3) heating causes the alloy to melt completely. After the alloy is fully melted, when the temperature reaches 1200-1220 °C, 0.3%-0.4% copper phosphate is added to deoxidize the alloy. The following reaction takes place between phosphorus and Cuprous oxide: 5Cu2O + 2P = P2O5 + 10Cu and Cu2O + P2O5 = 2cupo3. The resulting tetraphosphorus decaoxide gas escapes from the alloy, the copper phosphate can be floated on the surface of the liquid, and the slag can be removed so as to achieve the goal of deoxidation. The deoxidization process requires constant agitation. (4) the casting temperature of the alloy liquid is 1100-1200 °c when the slag is finally removed from the furnace.

 2. Brass smelting zinc as the main alloy element of copper-based alloy for brass, brass is divided into two categories: ordinary brass and special brass. Brass is a two-component alloy of copper and zinc, mainly used for pressure processing. The addition of other alloying elements (such as silicon, aluminum, manganese, lead, iron, nickel, etc.) to ordinary brass makes it a special brass. Most of the cast brass is special brass. (1) in the process of burden calculation, the proper burden composition should be selected according to its performance requirement, because the main composition of copper alloy has a wide range of change. The chemical composition of the alloy shall be in accordance with GB1176-87. The composition of several commonly used brass smelting ingredients shall be carried out according to Table 1.

It is required that the charge should be dry and clean, and any dirt corrosion should be cleaned by blowing sand. (2) according to the general casting practice, the proportion of new material in the total weight of charge should be more than 30% , return charge less than 70% . But in actual production, we take into account that there are more recharges of copper alloy, when the mass percentage of recharges is more than 90% , the melting quality is still very good, and the chemical spectrum analysis proves that the composition of the casting is qualified. It is necessary to consider whether the impurity in the alloy exceeds the standard when returning more burden. (3) preparation before melting. 1 PREPARATION OF METAL CHARGE: return charge is the same grade of waste casting, pouring riser and remelting Ingot, it needs to have clear chemical composition. The electrolytic copper is cleaned by sand blowing and the surface dirt is removed by preheating and then charging after preheating (the first batch of cold furnaces can be melted and preheated with the furnace) , can Be installed furnace (the first batch of cold furnace melting can be preheated with the furnace; pure metal elements into the furnace before the furnace can be preheated in the furnace. The maximum size of the charge shall not exceed 1/3 of the diameter of the crucible and the length shall not exceed 4/5 of the depth of the crucible. Sentence is too long, please supply a shorter sentence. (4) preparation of covering agent and flux. 1 Charcoal shall be baked in a sealed oven at not less than 800 °C for 4 hours to prevent moisture absorption. 2 covering agent consists of Borax 63% , broken glass 37% , also can use dry charcoal as covering agent. Covering agents require drying and removal of impurities. (5) alloy melting process 1 the crucible is preheated to dark red color and 20-40cm thick charcoal is added at the bottom. 2 Add electrolytic copper, melt quickly and then add intermediate alloy in the order of first high melting point and then low melting point (if any) , then add back the charge, and add charcoal at the same time to ensure that the alloy surface is not exposed to air. 3 deoxidization is also needed in brass smelting. When all copper is melted, phosphorus copper (calculated as 0.04%-0.06% of the weight of copper liquid) is added to deoxidize when the temperature reaches 1150-1200 °C. The surface quality of the deoxidized casting is better than that of the non-deoxidized casting. 4 adding alloy elements according to the component requirements of each alloy: adding al-cu master alloy at 1100-1120 °C, adding pure zinc and pure aluminum in batches and stirring at 1100-1150 °C during power cut. When melting silicon brass should first add silicon, then add zinc; when melting lead brass should first add zinc and then lead. The adding temperature of zinc element should be controlled. If the temperature drops after adding zinc, the electricity can be sent in the middle. When the alloy liquid temperature is higher than 1200 °c, the adding zinc is not allowed. 5 tapping slag, adjusting the alloy liquid to the casting process card required temperature, quickly out of the furnace pouring. The pouring temperature of the alloy is one of the factors that affect the properties of the castings. The general furnace temperature is ZCuZn38:1100-1130 °C; ZCuZn40Pb2:1080-1100 °C; ZCuZn31Al2:1120-1140 °C; ZCuZn16Si4:1100-1140 °C. 6 when melting two kinds of alloy of different grade, its chemical composition has influence, should carry on washing furnace in the middle. For example, a crucible and a tool used to smelt aluminum bronze would be used to melt tin bronze. The crucible and the tool would contain aluminum, which is a good ingredient in aluminum bronze but is the most harmful element in tin bronze. After deoxidization of copper alloy, qualified castings can be obtained. But for aluminum bronze, aluminum brass, silicon bronze and so on, it is easy to oxidize to produce high melting point oxide Al2O3 and SIO2, which can make the casting form slag, and can only be removed by refining.

3. The melting and casting of bronze bronze bronze can be divided into tin bronze and non-tin bronze according to their composition. Tin Bronze is a copper-based alloy with tin as the main alloying element. It has good wear resistance, corrosion resistance, good strength and plasticity. There are no tin bronze aluminum bronze, lead bronze, silicon bronze, etc. , contain different major elements, such as aluminum bronze is the main alloy element of copper-based alloy. (1) the alloy burden and the metal burden require the composition of several commonly used bronze alloy smelting burden to be carried out according to Table 2.

REQUIREMENTS: 0.7% ~ 0.9% NI and 0.3% ~ 0.4% mn can be added into ZCuAl10Fe3 alloy to improve the mechanical properties of the alloy. (2) burden ratio. The composition of the new burden should be more than 30% of the total burden weight, and the return burden should be less than 70% . (3) preparation before melting. The preparation for bronze smelting is the same as that for brass smelting. Charcoal should be packed into a sealed oven, in not less than 800 °C baking 4 hours, to prevent moisture absorption when waiting. Straw ash should be ground into powder, remove moisture, thoroughly drying, stand-by also pay attention to moisture. Covering agents require drying and removal of impurities. (4) alloy melting process. There are many kinds of cast bronze. Only a few typical alloys are discussed here. Other copper alloys of the same kind can be used for reference. Smelting of ZCuSn10Pb1, ZCUPB10SN10:1 The crucible is preheated to a dark red color, and 20 cm-40 cm thick charcoal is added at the bottom. (2) adding electrolytic copper, quickly heating and melting, then adding back charge, at the same time adding charcoal to ensure that the alloy surface is not exposed to air. 3 after melting, adding phosphor copper (usually 0.5% of burden weight, all phosphor copper used in melting phosphor tin bronze can be added) . Add Zinc, tin and lead in turn (according to the ingredient) , after the first charge is melted, add the next one, and keep stirring the alloy. 5 adjust the alloy liquid temperature between 1100 °C and 1150 °C. 6 blast furnace slag, add phosphor copper (generally 0.1% of burden weight) , deoxidize, evenly mix, spread a layer of rice straw ash on the surface of the alloy liquid, adjust the alloy liquid to the required temperature of the casting process card (generally 1130-1180 °c) , then pour it out quickly. Smelting of ZCuAl10Fe3 and ZCUAL10FE3MN2:1 these two alloys can not be melted with a crucible which has been used to melt other grades of alloys. Preheat the crucible to dark red and add the prepared flux. Flux composition: cryolite 20% (WT%) , sodium fluoride 60% , calcium fluoride 20% . 3 The low carbon thin steel sheet preheated to about 200 °C and the returned charge are added at the same time, the alloy is melted and stirred, and the temperature is raised to 1150-1180 °C. 4 adding 0.3% phosphorus copper deoxidization by alloy weight and adding flux. 5 pure aluminum and pure manganese (by ingredient) , preheated to 200 °C, are added in batches, and each batch is pressed in with a stirring rod for rapid melting and constant stirring to homogenize the composition. Finally, the temperature of the alloy liquid is adjusted between 1120-1220 °C. 6 cover the slag with the straw ash, adjust the alloy temperature (usually 1160-1200 °c) according to the casting process card, then adjust the pouring rapidly. Safe production is the basic requirement of the foundry industry, the smelting of pure copper and copper alloy must be: (1) the operator should wear protective articles, the working place should be kept clean and tidy, no water and Sundries are allowed. (2) check whether the equipment is in good condition before the furnace is opened. If there is any unsafe factor, it should be eliminated in time. (3) preheating shall be carried out only after careful inspection and confirmation that there are no explosive or dangerous substances in the charge. (4) melting and pouring tools, such as stirring bars, iron spoons and slag removal tools, shall not be in contact with the alloy liquid without pre-heating. (5) the remaining alloy liquid during pouring should be poured into the preheated ingot mould and should not be poured directly on the ground or poured back into the furnace. The melting time should be controlled from the beginning of feeding to the end of melting time is called melting time. The melting time not only affects the productivity, but also obviously affects the casting quality. Because the melting time increases, will cause the alloy the element to burn the loss rate to increase, the inhale the opportunity to increase. Therefore, the melting should be completed in the shortest possible time. Under the permitted condition, the preheating temperature of charge should be raised as much as possible, the operation should be compact and the action should be rapid. (2) the stirring rod used for melting should be some elements of carbon rod copper alloy, such as iron and lead, which exist in the form of mechanical mixture when melting. Some elements, due to the density of different, there is a tendency to specific gravity segregation stratification. Practice has proved that these elements in the smelting and pouring process, easy to cause the chemical composition of the unqualified, resulting in mechanical properties unqualified. To overcome this phenomenon, we must use the role of stirring, which is an indispensable link in melt pouring. But in the temperature and cooling period, generally do not need to stir. And the material ingredient of the agitator that uses, appropriate uses graphite commonly. This is because the chemical composition of the alloy is affected by the melting of the iron bar during mixing if other agitating materials such as iron bars are used. At the same time, if the iron bar is preheated at a higher temperature in the furnace or stirred for a longer time, the oxide on the iron bar will enter the alloy liquid and become an impurity, this can be observed in production. (3) the use of covering agents in smelting for smelting copper alloys, the amount of covering agents used is generally 0.8%-1.2% of the charge weight in the case of glass and Borax, as the thickness of the covering layer is kept at 10-15 cm; The amount used is about 0.5%-0.7% of the burden weight, and the cover thickness should be kept at 25-35 cm. Stripping time of covering agent, usually before pouring, too early will increase the copper alloy oxidation and inhalation. If is uses the charcoal as the covering agent, and when the blocking slag effect is good, also may not remove the covering agent, lets it also play the blocking slag effect in the pouring process, the effect is more ideal. 

Source: MCC nonferrous technology platform

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