Copper rod is the main raw material of cable industry, and there are two main ways of production - continuous casting and continuous rolling method and up-drawing continuous casting method. There are many production methods for continuous casting and rolling low-oxygen copper rods, which are characterized by the melting of metal in shaft furnace, the copper liquid enters the closed mold cavity from the pouring pipe through the insulation furnace, chute and tundish, and the cooling intensity is large to form the casting blank, and then the multi-pass rolling is carried out. The produced low-oxygen copper rods are hot-working structures, and the original casting structures have been broken. Oxygen content is generally between 200 and 400ppm. Oxygen-free copper rod is basically all the domestic production of up-lead continuous casting method, the metal is melted in the induction furnace through the graphite mold for up-lead continuous casting, and then cold rolling or cold processing, the production of oxygen-free copper rod is the casting organization, the oxygen content is generally below 20ppm. Due to the different manufacturing processes, there are great differences in many aspects such as organizational structure, oxygen content distribution, form and distribution of impurities.

1. Drawing performance

The drawing performance of copper rod is related to many factors, such as impurity content, oxygen content and distribution, process control and so on. The drawing performance of copper rod is analyzed from the above aspects.

1. The effect of melting method on impurities such as S

The production of copper rod by continuous casting and rolling is mainly through the combustion of gas to melt the copper rod, in the combustion process, through oxidation and volatilization, part of the impurities can be reduced into the copper liquid to a certain extent, so the continuous casting and rolling method has relatively low raw material requirements. In the production of oxygen-free copper rod, because it is melted by induction furnace, the "copper green" and "copper beans" on the surface of electrolytic copper are basically melted into the copper liquid. The molten S has a great effect on the plasticity of the oxy-free copper rod, which will increase the wire breaking rate.

2. The entry of impurities in the casting process

In the production process, the continuous casting and rolling process needs to transfer copper liquid through the insulation furnace, chute, tundish, which is relatively easy to cause the peeling of refractory materials. In the rolling process, it needs to pass the roll, resulting in the loss of iron, which will cause external inclusion to the copper rod. The rolling of oxide on and under the skin during hot rolling will have an adverse effect on the drawing of low oxygen rod. The production process of up-drawing continuous casting is short, the copper liquid is completed by the latent flow in the combined furnace, the impact on the refractory is not large, and the crystallization is carried out by the graphite mold, so the process may produce less pollution sources and less opportunities for impurities to enter.

O, S, and P are elements that produce compounds with copper. In molten copper, oxygen can be partially dissolved, but when the copper is condensed, oxygen is almost not dissolved in the copper. The dissolved oxygen in the molten state is precipitated as copper = cuprous oxide eutectic and distributed at the grain boundaries. The appearance of copper-cuprous oxide eutectic significantly reduces the plasticity of copper.

Sulfur can be dissolved in molten copper, but at room temperature, its solubility is reduced to almost zero, and it appears at the grain boundaries in the form of cuprous sulfide, which significantly reduces the plasticity of copper.

3. Oxygen distribution form and its influence in low-oxygen copper rod and no-oxygen copper rod

Oxygen content has obvious influence on the drawing performance of low oxygen copper rod. When the oxygen content is increased to the optimum value, the breaking rate of copper rod is the lowest. This is because oxygen acts as a scavenger in the process of reacting with most impurities. Moderate oxygen also helps to remove hydrogen in copper liquid, generate water vapor overflow, and reduce the formation of pores. The optimum oxygen content provides the best conditions for the wire drawing process.

Low oxygen copper rod oxide distribution: In the initial stage of solidification in continuous casting, the heat dissipation rate and uniform cooling are the main factors determining the oxide distribution of copper rod. Uneven cooling will cause the essential difference in the internal structure of the copper rod, but the subsequent hot processing, the columnar crystals are usually destroyed, so that the cuprous oxide particles are fine and evenly distributed. A central burst is typical of the accumulation of oxide particles. In addition to the influence of oxide particle distribution, the copper rod with smaller oxide particles shows better wire drawing characteristics, and the larger Cu2O particles are easy to cause stress concentration points and fracture.

The oxygen content of oxygen free copper exceeds the standard, the copper rod becomes brittle, the elongation decreases, the tensile pattern port appears dark red, and the crystal structure is loose. When the oxygen content exceeds 8ppm, the process performance deteriorates, which shows that the break bar and break rate of the casting and drawing process are extremely increased. This is because oxygen can form a brittle phase of cuprous oxide with copper, forming a copper-cuprous oxide eutectic, which is distributed in the boundary with a network structure. This brittle phase has a high hardness and will be detached from the copper body when it is cold deformed, resulting in a decline in the mechanical properties of the copper rod, which is easy to cause fracture in subsequent processing. High oxygen content can also lead to a decrease in the conductivity of copper rods without oxygen. Therefore, the casting process and product quality must be strictly controlled.

4. The effect of hydrogen

In the upper casting process, the oxygen content is controlled low, the side effects of oxides are reduced, but the effect of hydrogen becomes a more significant problem. There is an equilibrium reaction in the melt after inhalation: H2O(g)=[O]+2[H];

Gas and porosity are formed by the precipitation and aggregation of hydrogen from supersaturated solution in the process of crystallization. The hydrogen precipitated before crystallization can also reduce cuprous oxide and form water bubbles. Because the top casting is characterized by the crystallization of copper liquid from top to bottom, the shape of the liquid is approximately cone. The gas precipitated before the liquid copper crystallization is blocked in the solidification structure during the floating process, and pores are formed in the casting rod during crystallization.

When the upper gas content is low, the precipitated hydrogen exists in the grain boundary, forming loose. When the gas content is too much, it gathers into pores, so the pores and porosity are formed by both hydrogen and water vapor.

Hydrogen comes from various process links in the up-drawing production process, such as the "patina" of raw copper electrolytic, the auxiliary charcoal, the climate environment, and the graphite crystallizer is not dry. Therefore, the surface of the copper liquid in the melting furnace should be covered with baked charcoal, and the electrolytic copper should be removed as far as possible, such as "copper green", "copper bean" and "ear", which is very important to improve the quality of the oxygen-free copper rod. In the process of continuous casting and rolling, moderate oxygen content is often used to control hydrogen. Cu2O+ H2= 2Cu+ H2O

Since the copper liquid is crystallized from the bottom up during the casting process, the water vapor generated by the oxygen and hydrogen in the copper liquid is easy to float out, and most of the hydrogen in the copper liquid can be effectively removed, so the impact on the copper rod is small.

2. Surface quality

In the process of producing products such as electromagnetic wires, the surface quality of copper rods also needs to be required. The surface of the copper wire needs to be drawn without burrs, less copper powder and no oil pollution. The quality of surface copper powder is measured by torsion test and the recovery of copper rod after torsion is observed to determine its quality.

In the process of continuous casting and rolling, from casting to rolling, the temperature is high and it is completely exposed to the air, so that the surface of the casting blank forms a thick oxide layer. In the rolling process, with the rotation of the roll, the oxide particles are rolled into the surface of the copper wire. Because cuprous oxide is a brittle compound with a high melting point, for deeper rolled cuprous oxide, when the strip-like aggregates are stretched by the mold, the outer surface of the copper rod will produce burr, causing trouble for the subsequent painting.

The oxygen-free copper rod manufactured by the up-drawing continuous casting process is completely isolated from oxygen due to casting and cooling, and there is no hot rolling process thereafter, and the surface of the copper rod is not rolled into the surface of the oxide, and the quality is better, and the copper powder is less after drawing, and the above problems are less.

Anaerobic copper rod is also divided into imported equipment and domestic equipment, but the current imported products have no obvious advantages, the difference between copper rod products is not very big, as long as the copper plate is selected well, the production control is relatively stable, domestic equipment can also produce copper rod that can be stretched 0.05. Imported equipment is generally the equipment of Finland's Otto Kunpu, the best domestic equipment should be Shanghai's naval factory, the longest production time, military enterprises, reliable quality.

There are two main types of imported equipment, one is the United States south line equipment, English is SOUTHWIRE, the domestic manufacturer is Nanjing Huaxin, Jiangxi Copper Industry, the other is Germany CONTIROD equipment, the domestic manufacturer is Changzhou Jinyuan, Tianjin Seamless.

Anaerobic and low oxygen rod from the oxygen content is easy to distinguish, anaerobic copper oxygen content is below 10-20 PPM, but at present some manufacturers can only achieve 50 PPM below. Low oxygen copper rod in 200-400 PPM, good rod oxygen content is generally controlled at about 250 PPM, anaerobic rod is generally taken up method, low oxygen rod is continuous casting and rolling, the two products are relatively low oxygen rod enamelled wire can be more adapted to some, such as softness, rebound Angle, winding performance. However, the hypoxic rod is relatively harsh on the drawing conditions, the same stretch 0.2 of the wire, if the extension line conditions are not good, the ordinary anaerobic rod can be pulled and the good hypoxic rod will be broken Line, but if placed in good extension conditions, the same rod, low oxygen rod may be able to pull to double zero five, and ordinary anaerobic rod can only be stretched to 0.1 at most, of course, the thinest such as double zero two has to rely on imported anaerobic copper rod. At present, some companies are trying to use the peeling method to deal with the low oxygen rod to extend the 0.03 line. But I don't know much about that. The sound line generally prefers to use an anaerobic rod, which is related to the fact that the anaerobic rod is single crystal copper and the low oxygen rod is polycrystalline copper.

Low oxygen copper rod and no oxygen copper rod due to the different manufacturing methods, resulting in differences, have their own characteristics.

First, the inhalation and removal of oxygen and its state of existence

The oxygen content of cathode copper for the production of copper rods is generally 10-50ppm, and the solid solubility of oxygen in copper at room temperature is about 2ppm. The oxygen content of the low-oxygen copper rod is generally 200 (175) -400 (450) ppm, so the entry of oxygen is inhaled under the liquid of copper, and the upper method of oxygen-free copper rod is on the contrary, oxygen under the liquid copper for a considerable time, is reduced and removed, usually the oxygen content of this rod is below 10-50ppm, the lowest can reach 1-2ppm. From the perspective of structure, the oxygen in low-oxygen copper, in the state of copper oxide, exists near the grain boundary, which can be said to be common for low-oxygen copper rods but rare for oxygen-free copper rods. The presence of copper oxide in the grain boundary in the form of inclusion has a negative effect on the toughness of the material. The oxygen in anaerobic copper is very low, so the organization of this copper is uniform single-phase organization, which is favorable for toughness. Porosity in anaerobic copper rods is uncommon, while it is a common defect in low-oxygen copper rods.

Second, the difference between hot rolled structure and casting structure

Low oxygen copper rod due to hot rolling, so its organization is hot processing organization, the original casting organization has been broken, in the 8mm rod has recrystallization form, and oxygen free copper rod casting organization, coarse grain, which is why, oxygen free copper recrystallization temperature is higher, the need for higher annealing temperature inherent reasons. This is because the recrystallization occurs near the grain boundary, the oxygen-free copper rod has a coarse grain size, and the grain size can even reach a few millimeters, so the grain boundary is less, even if it is deformed by drawing, but the grain boundary is relatively less than the low-oxygen copper rod, so a higher annealing power is required. The successful annealing requirements for anaerobic copper are: the first annealing when the rod is drawn, but the line has not yet been cast, and the annealing power should be 10-15% higher than that of low-oxygen copper in the same situation. After continued drawing, the annealing power in the later stage should be left enough margin and the low oxygen copper and the oxygen free copper should be effectively different annealing processes to ensure the softness of the product in process and the finished wire.

Third, the difference between inclusions, oxygen content fluctuations, surface oxides and possible hot rolling defects

The drawability of the oxy-free copper rod is superior to that of the low-oxygen copper rod in the wired diameter. In addition to the above organizational reasons, the oxy-free copper rod has less inclusion, stable oxygen content, and no defects that may be caused by hot rolling. The surface oxide thickness of the rod can reach ≤15A. In the process of continuous casting and rolling, if the process is unstable and the oxygen monitoring is not strict, the unstable oxygen content will directly affect the performance of the rod. If the surface oxide of the rod can be made up in the continuous cleaning of the post-process, but the more troublesome is that a considerable amount of oxide exists in the "subcutaneous", which has a more direct impact on the broken wire, so in the drawing of micro-wire, ultra-fine wire, in order to reduce the broken wire, sometimes it is necessary to take a forced approach to the copper rod - peeling, or even the reason for the secondary peeling. The aim is to remove subcutaneous oxides.

Fourth, the toughness of low-oxygen copper rod and oxygen-free copper rod is different

Both can be pulled up to 0.015mm, but low-temperature grade oxygen-free copper in low-temperature superconducting wires has a spacing between filaments of only 0.001mm.

Five, from the raw materials of the rod to the economy of the line is different.

The manufacture of oxygen free copper rod requires high quality raw materials. In general, when drawing copper wire with a diameter of >1mm, the advantages of low-oxygen copper rod are more obvious, and the oxygen-free copper rod is more superior to drawing copper wire with a diameter of <0.5mm.

6. The wire making process of low-oxygen copper rod is different from that of oxygen-free copper rod.

The wire making process of low oxygen copper rod cannot be copied to the wire making process of no oxygen copper rod, at least the annealing process of the two is different. Because the softness of the wire is deeply affected by the material composition and rod making, wire making and annealing process, it cannot be simply said that low-oxygen copper or oxygen-free copper is soft and hard.

Attached: Introduction of low oxygen copper rod and no oxygen copper rod

1. Low oxygen copper rod

Low oxygen copper rod is what copper rod? What is the production process of low oxygen copper rod? What is the introduction of low oxygen copper rod? First look at the definition of low-oxygen copper rod: copper as raw material through continuous casting and rolling method to produce copper rod with oxygen content between 200(175) and 400(450)ppm. The definition of low oxygen copper rod is briefly introduced, and then the relevant content of low oxygen copper rod is introduced.

Low oxygen copper rod introduction - Low oxygen copper rod process flow:

The low-oxygen copper rod is produced by continuous casting and rolling process, and its process is as follows: electrolytic copper → shaft furnace → holding furnace → casting machine → rolling mill → continuous rolling mill → Receiving rod machine → finished (Phi 8mm) electrolytic copper is continuously fed, and copper water is released after continuous melting in shaft furnace, and the trapezoidal ingot with large section is cast by casting machine, and the rolling mill is hot rolled to Phi 8 copper rod billet.

Process defects:

(1) Shaft furnace: A. Due to the small volume of shaft furnace, electrolytic copper is added and melted, and there is no condition for full reduction of copper melting water. The whole melting process and copper water process can not be separated from oxygen, so the oxygen content is very high. C. Molten copper fuel is generally a gas, gas combustion process, will directly affect the copper liquefaction division, the impact of large sulfur and hydrogen and so on.

(2) Casting machine: casting machine crystallizing wheel copper liquid into a solid process, can not be oxygen insulation, so the casting process for the second large amount of oxygen inhalation.

(3) Temperature control: A. copper liquid temperature, due to the large amount of rolling, but also subject to A variety of factors, the temperature is not easy to control. B. Ingot casting temperature of the rolling mill, the temperature is required to be controlled at 850℃, the greater the upper and lower deviation, the greater the impact on the quality of the copper rod, and this temperature is difficult to control. C. The temperature of the copper rod of the rolling mill is required to be controlled at 600℃, and the greater the upper and lower deviation, the greater the impact on the quality of the copper rod. Due to the restriction of the previous process, this temperature is also difficult to control. D. There are many links in the whole process, and some problems in a link will affect the temperature control.

(4) Others: A. Due to the existence of some of the above defects, the quality of the copper rod will be unstable, so the standard stipulates that the torsion test must be done before the continuous casting and rolling low-oxygen copper rod is delivered. But there are production plants