1.Oxygen Free Copper

01. Overview

No. 1 and No. 2 oxygen-free copper plates TU1 and TU2 are copper with very little oxygen content. They have the characteristics of high purity, high conductivity and high thermal conductivity. Oxygen-free copper with very low phosphorus content has good sealing property with glass, good processability, weldability, corrosion resistance and cold resistance. Oxygen-free copper is mainly used in electric vacuum instrument parts, widely used in bus bar, conductive bar, waveguide, coaxial cable, vacuum seal, vacuum tube, transistor parts and so on.

02. Oxygen Free Copper Physical Chemistry

TU1, copper content: 99.97, the summation of impurities ≤0.03

TU2: Copper Content: above 99.97, summation of impurities ≤0.051 oxygen-free copper thermal performance 

melting point: 1082.5 ~ 1083 °C. Thermal Conductivity: 391W/(m °C) at 20 °C. Specific Heat capacity: 385J/(kg °c) at 20 °C.

 quality characteristics of TU1 OXYGEN-FREE COPPER: at 20 °C, the shrinkage and density of oxygen-free copper are 4.92% and 8.94 G/CM respectively.

3 The conductivity of oxygen-free copper is g = 101.4% IACS at 20 °C, annealed at 700 °C and measured after 30 min. The resistivity is 0.0171 M at 20 °C. 4 MAGNETIC PROPERTIES OF OXYGEN-FREE COPPER: oxygen-free copper is diamagnetic, the room temperature magnetic susceptibility is-0.08510-6 m3/kg. 5 OXYGEN-FREE COPPER CHEMICAL PROPERTIES OXIDATION RESISTANCE: Copper Oxidation rate at high temperature significantly increased in the atmosphere, and at room temperature that is slow oxidation.

 Corrosion Resistance: oxygen-free copper in the atmosphere, pure fresh water, low flow rate of seawater are corrosion resistance, non-oxidizing acid also has good resistance, but to oxidizing acid kind, wet ammonia, wet halogen, sulphide and contains the ammonium ion solution anti-corrosion very low.

03.Specification for thermal processing of oxygen-free copper

Specification for hot working and heat treatment of oxygen-free copper: annealing temperature: 375 ~ 650 °C.

 HOT WORKING TEMPERATURE: 750 ~ 875 °C.

04.Mechanical Properties of Oxygen Free Copper

According to the provisions of Gu/t14953-1994, the test standard for the repeated bending performance of wire rod with diameter not less than 0.3 mm is repeated bending test after hydrogen annealing, and the number of bending test is not less than 10 times. Hardness: room temperature hardness: HBS35 ~ 45(M state) , HBS85 ~ 95(Y state) . 2 tensile properties: The tensile properties of TU2 copper sheet at room temperature are: B = 350 ~ 390MPA, = 3% ~ 5% (Y state) b = 220 ~ 235MPA, = 45% ~ 55% (m state)3 impact property: IMPACT TOUGHNESS: Ku = 1560 ~ 1760 Kj/m 24 torsion and shear property: Shear Strength: = 210 MPA (Y state) : = 150 MPA (m state)5 fatigue property: High Cycle Fatigue Strength Limit: TU2 PLATE, cold deformation 50% . The number of cycles was 108 weeks, D = 119 MPA. 6 ELASTIC PROPERTIES: MODULUS OF ELASTICITY: e = 117.2 GPA. SHEAR MODULUS: G = 44.1 GP at present, with the development of vacuum electronic devices, electrical, microelectronics and other high-tech fields in China, the market demand for oxygen-free copper is increasing, and the demand for materials is also increasing. How to produce high-quality oxygen-free copper (TU0, TU1) to meet the needs of the market is a major issue faced by copper processing enterprises.

2.The main factors affecting the quality of oxygen-free copper

01.Main factors 1 the quality of raw materials 2 the influence of Oxygen 3 the production of sealed oxygen-free copper in smelting equipment follows the technological principle of "concentrate, seal and refine" , strictly controls the quality of raw and auxiliary materials, and strictly controls the technological system and operating rules, it is a feasible and effective control method to improve the quality of oxygen-free copper by adopting effective detection means.

 02.Influencing factors and control of oxygen content in oxygen-free copper

Oxygen content is a very important index of oxygen-free copper, there are many factors that affect oxygen content of oxygen-free copper, the following are the main factors and control measures: 

(1) the oxygen content of raw material cathode copper does have a big difference (the lowest 3ppm, the highest 90ppm) . High Quality (TU0, LC1011, TU1) oxygen-free copper production of raw material cathode copper high requirements, generally should choose high-purity cathode copper. 

(2) melt covering and protection. 2.1 Melt covering charcoal is the best covering agent for oxygen-free copper smelting. Charcoal covered in the melt surface, not only oxygen, anti-getter role, but also play a good role in deoxidation. The deoxidation reaction of charcoal is that the quality of CU2O + C = 2cu + COCU2O + CO = 2cu + CO2 has a great influence on the deoxidation effect of the melt. White Carbon from oak wood should be used as a deoxidizer for oxygen-free copper. In addition, charcoal should be calcined (500 °C ~ 800 °C) and should not be long put, should be roasted immediately.

(2) gas protection: Inert Gas (nitrogen) is introduced into the smelting furnace and the holding furnace (nitrogen should also be introduced into the furnace head) to insulate the air, prevent oxygen inhalation and inhalation, and reduce the loss of charcoal; The melt in the flume flows fast and fluctuates greatly. It is easy to expose the liquid surface with the solid covering agent. The inert gas (nitrogen) or gas should be used for protection.

 (3) there is a certain gap between domestic and foreign oxygen-free copper smelting equipment at present, the key is in the sealing technology. For example, the oxygen content of C10200 oxygen-free copper ingots produced by imported oxygen-free Copper Furnace Group (sealed, only non-calcined ordinary charcoal) below 10 PPM accounts for more than 99% , the oxygen content of C10200 oxygen-free copper ingots produced by other domestic equipment (calcined charcoal) is less than 90% below 10 ppm. This shows how critical is the control of oxygen content in the oxygen-free copper ingot by the sealing condition of the equipment.

 (4) refining Deoxidization in general, even for high purity cathode copper, the base oxygen content is mostly above 10 PPM. To meet the requirement of some customers for oxygen-free copper with oxygen content below 5 PPM, it is necessary to carry out refining deoxidization treatment. In addition to high-quality calcined charcoal deoxidization treatment, adding appropriate amount of CU-P alloy deoxidization to ensure oxygen-free copper content requirements. In addition, in order to further achieve the effect of oxygen removal, a oxygen-free Copper Melt deoxidization technology has been developed in recent years, the aim of removing oxygen from copper liquid is achieved.

(5) heating of ingots to meet the requirement of oxygen content in oxygen-free Copper Ingots, oxygen penetration on the surface of the ingots should be prevented during subsequent processing. In the heating process of oxygen-free Copper Ingot, the heating temperature and time should be well controlled. Figure 1 shows the relationship between the depth of oxygen permeation and the heating temperature and time under the condition of air.

3.Tail shrinkage of oxygen-free copper and its control

1. Oxygen-free copper shrinkage problem high-quality oxygen-free copper (such as LC1011, TU1) rods are mostly used in vacuum switches and other electric vacuum devices. If the rods have shrinkage defects, the quality and service life of these high-vacuum devices will be affected, therefore, the oxygen-free copper material absolutely does not allow the existence of tail shrinkage defects. 

2. Causes of shrinkage tail 1 poor surface quality of INGOT, 2 too fast extrusion speed, 3 not clean extrusion barrel, 4 not enough pressure thickness. 3. The main control measures for tail reduction are:

 (1) grinding the extrusion barrel regularly and cleaning the extrusion barrel one by one when extruding;

 (2) strengthening the overhaul and maintenance of the equipment to ensure the precision of the equipment and the tool and die;

 (3) keeping enough pressing allowance; 

(4) appropriately increasing the amount of skin peeling during extruding;

 (5) the extrusion speed should be controlled properly and not too fast;

 (6) the surface quality of the Ingot should be controlled; 

(7) the inspection by flaw detection should be used.

4. Conclusion

Oxygen content as an important quality index of oxygen-free copper, in the production process, to meet the user's increasingly high requirements for this index, it is necessary to select high-quality cathode copper raw materials, ensure the equipment in a good sealed state, pay attention to the process control of refining deoxidization link, and seek new technology to improve the deoxidization effect The shrinkage tail defect of high quality oxygen-free Copper Bar used in electric vacuum devices seriously affects the product quality of the users, which should be attached great importance to by the relevant technical quality departments, and should be checked in the corresponding shrinkage tail inspection, the most effective inspection methods should be adopted to strengthen the strength of inspectors, strengthen the training and management of inspectors, enhance quality awareness, fulfill responsibility and ensure the quality of oxygen-free copper products. 

Source: "physical and chemical examination-physical volume" wechat public number, selected from: "physical and chemical examination-physical volume. 52,2016.10 by Li Xianghai

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