Copper Melt is the soul of copper processing, how to handle the purity of copper water, how to handle the internal quality of copper melt by chemical reaction, why do all kinds of auxiliary materials have to be added in the traditional copper smelting process, we can only understand it in theory, in order to guide them in practice.

1. Modification treatment is called modification treatment for the purpose of improving the crystalline structure or some properties of the Ingot by modifying the alloy melt. Addition of modifier and crystallization under vibration are common modification methods. The main effects of modification are as follows: (1) refining the crystal structure of the Ingot, coarsening the columnar crystal to fine equiaxed crystal. (2) reducing or spheroidizing some low melting point materials at grain boundary. (3) to change the distribution of some harmful elements in the crystallized structure of Ingot. (4) both deoxygenation and degassing. (5) improving the high temperature plasticity of ingot.

The principles for selecting and using modifiers are as follows (1) to form a compound with at least one component of the alloy, E. G. by peritectic reaction to form a large number of compound particles. The modifier element can form compound with the main component in the alloy, which is ideal. (2) the melting point shall be higher than that of the alloy when the crystal nucleus is formed or the compound is formed. Dispersed particles should be uniformly distributed in the melt prior to crystallization. (3) it has strong metamorphism ability to avoid causing negative effects. (4) proper adding time and method can reduce the loss of ignition. Application example of copper and copper alloy melt modification

2. In degassing refining (1) large amounts of copper will be oxidized when oxygen is introduced into the melt by oxidation and degassing. The reaction formula is: 4CU + O2 = 2cu2o Cuprous oxide is first dissolved in the copper solution, the Cuprous oxide then reacts with hydrogen in the Liquid Copper, Cu2O + H2 = 2cu + H20, resulting in the reduction of copper and the Escape of water vapor from the melt. As the reaction continues, the hydrogen content in the liquid copper will decrease. Cupric oxide method: Air Pipe is used to transport Compressed air or mixed gas of oxygen and nitrogen into the Molten Pool; oxidizing flux is used, etc. . During the oxidation process, samples should be taken continuously to check the degree of oxidation of the melt, and the oxidation should be stopped immediately when the oxygen content in the liquid copper is determined to meet the requirements. The oxidized copper liquid should be deoxidized to remove the excess oxygen before it comes out of the furnace.

(2) The vapor pressure of boiling degassing zinc increases with the increase of temperature, and the pressure at the boiling point of 907 °C is equal to one atmospheric pressure. The evaporation intensity of zinc will increase several times under reducing atmosphere, at this point, the volatile zinc is not the usual oxidation atmosphere can be about. The decomposition pressure of ZnO was 5.4 × 10-21 MPA at 1127 °C. When the molten metal overheats to 1250 °C, the decomposition pressure of Zno does not exceed 1.4 × 10-17 MPA. The decomposition pressure of Zno is so small that rapid oxidation of Zinc vapor is inevitable. When brass is smelted by induction furnace with iron core in power frequency, the temperature is high and zinc vapor bubbles float up. With the increase of bath temperature, the vapor pressure of zinc increases gradually. When the bath temperature rises to near or above the boiling point, a large amount of steam is ejected from the bath, which is the phenomenon of flame injection. The more intense and frequent the flame, the more hydrogen in the melt goes into the vapor bubble, and the better the degassing effect. Due to the uniform distribution of steam bubbles from bottom to top, the effect of boiling degassing is better. Brass containing less than 20% zinc can not be degassed by boiling.

(3) the partial pressure of hydrogen in the bubble is zero, while the partial pressure of hydrogen in the melt near the bubble is much greater than zero, based on the difference of the partial pressure of hydrogen inside and outside the bubble, the hydrogen dissolved in the melt is diffused to the bubble continuously, and is expelled into the atmosphere with the rise and escape of the bubble, so as to degassing. The smaller and more bubbles are, the better for degassing. It is not easy to completely degassing by this method because of the fast speed of bubble floating, the short time to pass through the melt, and the inhomogeneous distribution of bubbles in the melt. In order to improve the degassing refining effect, the gas purity should be controlled. The results show that the oxygen content of refining gas should not exceed 0.03% (volume fraction) and the moisture content should not exceed 3.0 g/l. If the oxygen content in nitrogen is 0.5% and 1% , the degassing effect decreases by 40% and 90% respectively.

(4) the main characteristics of vacuum degassing and vacuum melting are as follows: (1) the oxidation loss and gettering of alloy elements can be avoided, and good conditions are created for the gas precipitation in the melt; (2) the Melt is free from pollution; To some extent, it can improve the purity, which is helpful to obtain the metal and alloy with higher purity, and to improve some physical or mechanical properties of the material. Small vacuum induction furnaces are usually lined with a graphite crucible to avoid contamination of the melt by other Refractory and to take advantage of the good deoxidation of carbon. The main disadvantage of vacuum melting is that it can cause a lot of volatilization loss of some alloy elements with lower boiling point and higher vapor pressure. As a result, a melting process has been developed in which a vacuum is pumped first and then an inert gas, such as Argon, is pumped into the chamber. Vacuum melting furnace and vacuum casting equipment installed in the same vacuum chamber, limited by the capacity of equipment suitable for small batch production of some high purity, or some high copper alloy, copper-nickel alloy. The pressure on the surface of the molten pool is very low under the vacuum condition, and the hydrogen and other gases dissolved in the liquid copper are easy to escape. The degassing rate and degree of vacuum degassing are higher. The degassing effect of active refractory metals and their alloys, heat-resistant and precision alloys is better by vacuum melting casting.

3. deoxidization refining (1) diffusion deoxidization the deoxidization reaction of the surface deoxidizer is mainly carried out on the surface of the molten pool, and the deoxidization of the internal melt is mainly realized by the continuous diffusion of the Cuprous oxide to the surface of the molten pool. The Cuprous oxide is less dense than copper and tends to float towards the surface of the bath. The Cuprous oxide on the surface of the molten pool is continuously reduced and the concentration is constantly reduced. As a result of the concentration difference, the internal Cuprous oxide of the molten pool is constantly raised. Under the cover of charcoal at 1200 °C for 20 min, the content of Cuprous oxide in copper solution can be reduced from 0.7% to 0.5% . The deoxidization reaction of charcoal is: 2Cu2O + C = 4Cu + CO2 in addition to charcoal, some Cuprous oxide fluxes with much less density than copper, such as magnesium borate (Mg3B2) , calcium carbide (CAC2) and Boron slag (Na2b1o Mgo) can be used as surface deoxidizers. (2) precipitating deoxidizers commonly used for precipitating copper and copper alloys are phosphorus, silicon, manganese, aluminum, magnesium, calcium, titanium, lithium, etc. . The main reactions are as follows

5CU2O 2P=P2O5 10cuCu2O P2O5=2CUPO3Cu2o Mg =Mgo(S) 2cuCu2O Li=Li2o(S) 2Cu deoxidation reaction produced fine solid oxides, so that the viscosity of the metal increases or become uneven distribution of inclusions in the metal. When using this kind of deoxidizer, the amount should be controlled. Precipitation deoxidation can be carried out in the whole molten pool, the deoxidation effect is remarkable. The disadvantage is that deoxidizer residue may form inclusions. Specific analysis of the commonly used phosphorus copper deoxidation:

Phosphorus is the most widely used deoxidizer except pure copper used in electrical materials, phosphorus is added in the form of phosphorus-copper master alloy, Cu + Cu3P eutectic is formed in P-Cu binary phase diagram at 8.4% p, the melting point is 714 °C, after more than 14% P, phosphorus escapes as vapor, therefore, the commonly used phosphorus copper content of less than 14% . After the phosphor copper is added into the copper liquid, the deoxidation reaction is carried out in the whole molten pool. (3) the partial pressure of hydrogen in the bubble is zero, while the partial pressure of hydrogen in the melt near the bubble is much greater than zero, based on the difference of the partial pressure of hydrogen inside and outside the bubble, the hydrogen dissolved in the melt is diffused to the bubble continuously, and is expelled into the atmosphere with the rise and escape of the bubble, so as to degassing. The smaller and more bubbles are, the better for degassing. It is not easy to completely degassing by this method because of the fast speed of bubble floating, the short time to pass through the melt, and the inhomogeneous distribution of bubbles in the melt. In order to improve the degassing refining effect, the gas purity should be controlled. The results show that the oxygen content of refining gas should not exceed 0.03% (volume fraction) and the moisture content should not exceed 3.0 g/l. If the oxygen content in nitrogen is 0.5% and 1% , the degassing effect decreases by 40% and 90% respectively.

(4) the main characteristics of vacuum degassing and vacuum melting are as follows: (1) the oxidation loss and gettering of alloy elements can be avoided, and good conditions are created for the gas precipitation in the melt; (2) the Melt is free from pollution; To some extent, it can improve the purity, which is helpful to obtain the metal and alloy with higher purity, and to improve some physical or mechanical properties of the material. Small vacuum induction furnaces are usually lined with a graphite crucible to avoid contamination of the melt by other Refractory and to take advantage of the good deoxidation of carbon. The main disadvantage of vacuum melting is that it can cause a lot of volatilization loss of some alloy elements with lower boiling point and higher vapor pressure. As a result, a melting process has been developed in which a vacuum is pumped first and then an inert gas, such as Argon, is pumped into the chamber.

Vacuum melting furnace and vacuum casting equipment installed in the same vacuum chamber, limited by the capacity of equipment suitable for small batch production of some high purity, or some high copper alloy, copper-nickel Alloy. The pressure on the surface of the molten pool is very low under the vacuum condition, and the hydrogen and other gases dissolved in the liquid copper are easy to escape. The degassing rate and degree of vacuum degassing are higher. The degassing effect of active refractory metals and their alloys, heat-resistant and precision alloys is better by vacuum melting casting. 

Source: Copper Alloy Casting