1 Introduction:
Copper has become the first choice and main material in the electronics and power industry due to its good electrical and thermal conductivity. In order to achieve the required performance standards, almost all of the high purity copper is used. This article mainly discusses the reasons for this, but also pays special attention to some fundamental principles of smelting. The aim is to further discuss the relevant developments in the copper field over the past decade.
2. Conductor requirements:
In recent years, the interpretation of precious metals (ie copper, silver and gold) on the electronic properties has made tremendous progress. These elements show high electrical conductivity because their conducting electrons have little resistance to the motion of the electric field. Copper is especially an excellent conductor because there is a lot of free space between the outermost electrons so that no collision occurs. And its resistivity is inversely proportional to this large space. There are several types of conductive metals that are lighter than copper, but deliver the same amount of current, and they require a larger cross-section, so these metals are not desirable if space savings are required. (Example: in some small electric motors). So when overweight became a problem, people started using aluminum . Copper has the best performance characteristics required for commercial applications, so silver is not used because of its high price.
3. Application:
Copper is one of the most widely used rare metals in its pure form rather than in alloy form. The minimum copper content in about fifty different forging alloys is 99.3%, although only a small portion is used industrially as an electrical conductor. The most commonly used of these low alloys is electrolytic tough copper, which is composed of a metal of this purity which is alloyed with oxygen in the range of 100-650 ppm. However, it is recommended not to use ETP copper in a hydrogen atmosphere because it is subject to hydrogen embrittlement when exposed to these temperatures. In such an environment, either oxygen-free copper or oxygen-free electronic copper is used. Applications in power supply voltages with silver-containing copper are quite limited because of their higher strength and weaker resistance at elevated temperatures.
4. Production of copper rods and copper wires:
Before the 1970s, almost all copper was produced by batch method. The specific steps of the batch method were: pouring and solidifying molten copper into a special ingot called "wire ingot", and then slightly The restricted protective atmosphere reheats the rod and then decomposes the cast dendritic structure into a rod form in the air by hot pressing. Next, it is placed in 10% sulfuric acid to remove the oxide above, and a longer coil is formed by butting one end to the other end. Now, virtually all copper rods are made by continuous casting and rolling procedures. The benefits of continuous casting are: small separation of impurities, reduced copper oxide particles on the surface, reduced steel content during contact with the rolls, virtually elimination of all welds, and reduced overall processing costs. Oxygen and copper are intentionally alloyed as a scavenger for dissolving hydrogen and sulfur to form two gases, H2O and SO2, in the melt. If the oxygen component is controlled to some extent, then small bubbles will form, and under appropriate conditions, these bubbles will offset about 4% of the shrinkage during the transition from liquid to solid. If the pores formed are not very large, they can be completely eliminated during hot pressing. Most of the continuously cast and rolled products are equipped with non-destructive equipment, which is often used in-line applications to detect defects such as cracks and oxides. For some high-quality applications, mechanical finishing is usually used to remove a good surface layer of metal. Most round and square copper products are produced by drawing with conventional artificial polycrystalline dies or natural single crystal dies. Copper has good formability, and copper rods can be easily fabricated into relatively thin copper wires without any intermediate annealing process. Despite its desirable characteristics, the general practice in the magnet wire industry is to reduce the rate of reduction to about 90% during the drawing process, followed by annealing. In addition to the reduction rate, the metallographic structure may also change, thereby weakening the mechanical properties of the copper wire. Magnetic wires are often produced by so-called "on-line processes", which include: "slow" drawing followed by continuous annealing while coating. The final copper wire product was improved by reducing the reduction ratio between anneals to 90%.
5. The role of impurities:
Chemical properties are one of the most important variables in the formation of high conductivity. The most harmful of these ingredients can reduce electrical conductivity, increase the mechanical strength of the annealing line, avoid recrystallization, and sometimes cause hot brittleness during the hot pressing process of producing copper rods. Numerous studies have shown that a very small amount of dissolved matter will increase the resistivity of copper at one time. Many impurities will increase their semi-hard recrystallization temperature step by step. However, when impurities are mixed with precipitates or oxides rather than dissolved substances, the detrimental effect on conductivity is minimized. Table 2 shows the effect of various single elements added to high purity ETP copper containing only 200 ppm oxygen. In general, the first half of each millionth of the impurity is more influential than the second half of the same dose. However, it should be noted that since the copper power standard established in 1913 was expressed by 100% IACS conductivity, the purity of commercial copper has been greatly improved. Today, most commercial copper anodes have a conductivity of more than 101% IACS.
6. The effect of oxygen components:
Oxygen is an alloying component used to improve the robustness of cast copper by controlling the vapor-metal reaction. Equally important, oxygen acts as a scavenger in the reaction with most of the impurities, and these impurities have a large effect on their properties and annealing reactions as they dissolve in the copper matrix. Conversely, when these impurities are mixed with insoluble oxides, these bad effects are offset. As can be seen from Table 3, the maximum value of the ETP copper conductivity is 200 ppm. Thus, the oxygen content of the ETP copper is approximately between 175 and 450 ppm. Since the dispersed impurities are liable to cause thermal cracking, low oxygen values ​​are usually avoided as much as possible. Conversely, oxygen values ​​that exceed this optimal limit are not common because they have an effect on formability. The actual oxygen content should be both a good annealing process and a possible plasticity problem.
7. The importance of thermomechanical tunable variables:
In addition to the oxide formed by the metal impurities, the oxide can also dissolve or precipitate the oxide from the copper matrix by changing the heat history. These solid reactions may affect the final particle size because the copper oxide component helps to form uniformly sized particles during recrystallization. However, secondary recrystallization (abnormal particle growth) is usually associated with a dual particle structure that is formed by the dissolution of oxide during high temperature annealing. Particle coarsening and twinning occur mainly because the solution temperature exceeds 500 degrees Celsius and the oxygen concentration is less than 600 ppm. The coarse particles formed prior to drawing are not eliminated after the subsequent low temperature annealing. The cooling rate from high temperature cooling also affects high temperature mechanical properties, especially when the impurity composition is relatively large. Rapid quenching can result in high concentrations of non-uniform impurities in the solid solution. On the other hand, slow cooling enhances the interaction between impurities and oxygen, which in turn facilitates the precipitation of impurities from the solid solution. Cold working by wire drawing or rolling during annealing is limited for commercial magnetic wires. In order to obtain better compliance (i.e., the ability of the copper wire to retain its shape with minimal resilience during forming or bending) prior to final cooling, it is desirable to limit the amount of cold working. Both high modulus and low yield strength are desirable because they are the hallmark of minimum resilience.
8. Annealing process:
The annealing properties of copper are a very complex property that consists of a series of other properties that vary with deformation, thermal history, metal purity and oxygen composition. When the impurities are precipitated, their effect on the annealing process is relatively small, which is quite different from the situation in solid solutions. The annealing temperature has a certain relationship with the difference in atomic size between the solvent (herein referred to as copper) and the solute (herein referred to as impurities). The valence of solute elements is also an important parameter affecting annealing properties. However, due to the complexities of thermodynamic interactions between multiple materials, annealing is not simply related to some possible parameters, such as the atomic weight or the valence of the solute.
9. Surface effects:
At ambient temperatures, the copper wire always has a residual oxide film that is formed from the high temperature, continuously cast copper rod as it enters the hot rod rolling stage. It has become a relatively standard practice to measure the thickness of residual surface oxide film in a copper industry by means of a power analysis control method. Oxide films can be quite detrimental because they can cause many defects during the drawing process, excessive wear of the wire drawing film, poor solderability, and weak adhesion between the enamel film and the bare conductor. The defects of the copper rod are often derived from the continuous casting process and the rolling process, including: residue, copper oxide inclusions, hot cracks, cracks, and the formation of oxidized particles on the surface of the copper rod. Most of the intermetallic inclusions are relatively brittle and thus become the site of cracking and propagation during the drawing process. Thinner magnetic wires and forming wires are the most important production products relative to defects. The single largest surface defect stems from drawing, often in the form of die scratches, mechanical damage, arc chisels or lobes on the surface of bare conductors. The lobes formed by the drawing problem are often not much related to the captured oxide. Surface damage is usually caused by misalignment of the moving wires in the wire drawing machine or by the excessive pressing force of the copper refining in the furnace opening of the wire drawing film.
10. Future challenges:
The demand for better surface quality and larger packaging models is steadily increasing, and it is increasingly desirable to produce a copper rod that has no flaws and is less broken (ie has good pullability). The driving force to meet these needs will be: better energy efficiency, increasingly fierce global competition, more home applications, small motors used in the event of rising land prices, such as motors used in cars. Therefore, people will be more and more willing to use smaller gauge sizes. With the advent of electro-metallurgy and the continuous progress in electrolytic refining, the purity of commercial copper anodes seems to have reached a level acceptable to everyone, and there is no need to further limit the amount of impurities. However, in the free-cutting brass industry, niobium has been used to replace lead as an alloying element. Because niobium has a great toxic effect on electric copper conductors, it is required that the brass fragments should be completely separated from the copper fragments. One problem faced by the copper wire industry is that many defects in the surface are caused by grinding or delamination during the drawing process. In order to solve this problem, Guan Jian is to improve in the following aspects: the surface texture of the copper rod, the drawing lubricant, the filtration of solid particles, the production of a single synthetic crystal diamond wire drawing film. A very important future challenge is to develop more sensitive sensors that detect non-destructive defects on copper rods, copper rods, and copper wires by using a non-contact detection method. Most of these defects are too small to be detected at all by the current eddy current testing equipment. In addition, there is a need to develop an in-line inspection device to easily detect large pores and other internal defects. The factors affecting the performance, processing and operation of linear power copper conductors are largely based on existing smelting principles. However, the relationship between impurities and annealing temperature and resistivity also needs to be further improved in number.
11. Summary:
Often used as wire conductors are pure copper, not copper alloys. At the same time, a small amount of oxygen is usually added to control the impurities and improve the conductivity. The final properties and processing are closely related to impurities and oxygen components, and are completely explained by some basic smelting principles. trend. The ASTMB370 specification, the copper and copper blocks used in engineering construction, is the basis for specifications and purchases in a variety of models and thicknesses. The competitive amount of copper metal and confidence in copper continue to drive the development of this healthy market. The most recently approved specification is ASTMB882, a pre-rusted copper used in construction. Architects and engineers have long expected to produce this product because they are eager to develop this praiseworthy green with copper roofing and building crossbars.
12. Low lead and lead free forged and cast copper alloys:
The effect of lead leaching into the water on human health has led to a rethinking of existing copper alloys and the development of a new alloy for drinking water. Tightness of the pressure casting and fine machining of forged and cast components provided by the lead appendages are necessary to achieve the requirements. Forged and cast lead-free tantalum containing alloys must have the following characteristics: Meets ANSI/NSF61 health requirements and water system component health requirements. Now people have started using an acidified sodium acetate detergent to remove lead stains from the machine. However, some sectors of the industry have raised concerns about mixed crumbs because they believe that in these mixed crumbs, traces of niobium can cause hot brittleness of the metal during processing. The Institute of Debris Recovery Industry (ISRI) and the Brass and Bronze Foundry Manufacturer (BBIM) are working on a strict control program and segmentation procedure for debris recovery.
13. Household products:
In household products, people choose copper because copper has the following characteristics: beautiful shape, reliable quality, high reputation, good design factors, good material and mechanical properties for a long service life. Electric lighting equipment and stove equipment together become the main category of household products.
14. Service:
The traditional method used to determine the sensitivity of copper materials to stress corrosion cracking is the mercury nitrate test. (ASTMB154) In response to requests from ASME Boiler and Pressure Vessel Code and US Coast Guard, the B-5 Commission converted the IS06957 copper alloy ammonia test for stress corrosion immunity to the ASTM form. This is entirely due to their consideration of test solutions and sample handling. ASTMB858M, a method of determining the sensitivity of a ammonia vapor to a stress corrosion cracking in a copper alloy, is now an official method. This test method stimulates the development of service conditions under which stress corrosion cracking may occur and overcome the shortcomings of the mercury nitrate test.
15. Future Outlook:
The world economy has become more and more global. With the advent of the 21st century, third world countries are establishing telecommunications links, becoming the main consumers of electricity, building homes, factories and commercial buildings, which requires a large amount of copper to meet their needs. Copper has been used as a raw material for engineering for 10,000 years, and its contribution to humanity is pyramidal and growing. If there is no copper, I can't imagine what the future world will look like.
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