Copper strip is a very common metal component, which is often seen in electrical components, lamp caps, battery caps, buttons, seals, connectors and other places. Its main function is conductive, heat conduction, corrosion-resistant equipment and so on. There are six areas for copper strip production, namely furnace area, laboratory, cutting area, hot rolling area, water washing area and plate rolling area. Next, Xianji Xiaobian will tell you about the characteristics of cold rolling and hot rolling in copper strip production process and production methods, as well as the solutions to some common problems, such as discoloration and shear indentation. Let's have a look!

Production process flow of copper strip:

1. Embryo making: according to the predetermined production target, different amounts of zinc blocks are added to the waste copper material to prepare copper raw materials of different specifications.

2. Assay: in order to ensure the production of qualified and economic finished products, the accuracy of assay results is still important. The responsibility of the laboratory is to tell the smelter the test results quickly and accurately according to the copper blocks submitted for inspection.

3. Cutting: the complete copper strip is pulled by the lifting rope, placed stably on the special cutting table, cut by the cutting wheel saw, and then the uneven surface of the copper strip is polished and smoothed by the copper strip washing machine, which is conducive to the flatness and smoothness of the surface of the copper strip processed in the later stage.

4. Hot rolling: the cut copper strip is heated at 1000 ℃ and then hot rolled to form a copper strip with a thickness of about 2.3cm.

5. Water washing: after each copper block passes through the blooming step, due to the existence of surface impurities, in order to avoid affecting the quality of finished products, it must go through the sealing furnace again and then go through the water washing procedure. The water washing area is divided into two pools according to different acidity. The high concentration is 6-8 degrees, and the low concentration is 3-5 degrees. Among them, the medium red patches on the surface of copper bars and strips can be washed away by the acid solution of the water washing tank, while the dark red patches are removed by the iron fine bristle brush during the water washing. The copper strips after this series of treatment methods obviously shine the inherent luster of copper itself. Similarly, if there are still red patches and red patches during plate rolling, it is still necessary to repeat the water washing step. The acidity in the water tank shall be checked regularly during water washing, and acid shall be added in time to avoid insufficient water washing due to low acid content.

6. Plate rolling: the plate rolling area is divided into 180 primary rolling and 110 intermediate rolling according to the wheel roll. According to the different sizes of various rollers, the copper strip hot rolled and forged in the sealing furnace is processed from rough to fine through the above two steps.

Characteristics of copper strip production method:

1. Copper strip cold rolling

(1) Plastic deformation.

(2) The pressure in the roll gap area is high and there is pressure distribution, * * * up to 2700mpa.

(3) At the same time, there is friction along the rolling direction and reverse rolling direction.

(4) The instantaneous temperature of roll gap is high, up to 200 ~ 300 ℃.

(5) Rolling and sliding states coexist.

2. Copper strip hot rolling

Advantages of copper strip hot rolling:

(1) Hot rolling can significantly reduce energy consumption and cost. During hot rolling, the metal plasticity is high and the deformation resistance is low, which greatly reduces the hot rolling energy consumption of metal deformation.

(2) Hot rolling can improve the processing properties of metals and alloys, that is, the coarse grains in the casting state are broken, the cracks heal significantly, the casting defects are reduced or eliminated, the as cast structure is transformed into deformation structure, and the processing properties of alloys are improved.

(3) Hot rolling usually adopts large ingot and large reduction rolling, which not only improves the production efficiency, but also creates conditions for improving the rolling speed and realizing the continuity and automation of the rolling process.

Disadvantages of copper strip hot rolling:

(1) After hot rolling, the non-metallic inclusions (mainly sulfide, oxide and silicate) in the metal are pressed into thin sheets, resulting in delamination (sandwich) phenomenon. Delamination greatly deteriorates the tensile properties of metal along the thickness direction, and interlayer tearing may occur during weld shrinkage. The local strain induced by weld shrinkage often reaches several times of the yield point strain, which is much larger than that caused by load.

(2) Residual stress caused by uneven cooling. Residual stress is the internal self balancing stress without external force. Hot rolled sections of various sections have this kind of residual stress. Generally, the larger the section size of section steel, the greater the residual stress. Although the residual stress is self balancing, it still has a certain impact on the performance of metal under external force, such as deformation and stability And fatigue resistance may have adverse effects.

(3) Hot rolling can not control the required mechanical properties of products very accurately, and the microstructure and properties of hot-rolled products can not be uniform. Its strength index is lower than cold work hardened products, but higher than fully annealed products; its plasticity index is higher than cold work hardened products, but lower than fully annealed products.

(4) The thickness dimension of hot-rolled products is difficult to control, and the control accuracy is relatively poor; the surface of hot-rolled products is rougher than that of cold-rolled products, and the Ra value is generally 0.5 ~ 1.5 μ m。 Therefore, hot rolled products are generally used as billets for cold rolling.

Solutions to common problems of copper strip:

1. Solution of copper strip discoloration

(1) Control the concentration of acid solution during pickling. When the oxide layer on the surface of annealed copper strip is washed away, the high acid concentration makes no sense. On the contrary, the high concentration makes it difficult to wash away the residual acid attached to the surface of copper strip, and accelerates the pollution of cleaning water, resulting in high residual acid concentration in cleaning water, resulting in more discoloration of cleaned copper strip. Therefore, when determining the concentration of acid solution, The principle should be followed: on the premise that the oxide layer on the surface of copper strip can be cleaned, its concentration should be reduced as much as possible.

(2) Control the conductivity of pure water. Control the conductivity of pure water, that is, control the content of chlorine ions and other harmful substances in pure water. Generally, the conductivity is controlled at 50 μ It is safer below s / cm.

(3) Control the conductivity of hot cleaning water and passivator. The increase of conductivity of hot cleaning water and passivator mainly comes from the residual acid brought in by the running copper strip. Therefore, under the condition of ensuring the water quality of pure cleaning water, control the conductivity, that is, control the amount of residual acid. According to many experiments, the conductivity of hot cleaning water and passivator are controlled at 200 respectively μ Below s / cm is safe.

(4) Ensure that the copper strip is dry. Conduct local sealing at the coiling outlet of the air cushion furnace, and use dehumidifier and air conditioner in the local sealing device to control the humidity and temperature during coiling of the copper strip within a certain range.

(5) Use passivator for passivation. Now most copper processing plants use benzotriazole, BTA (molecular formula: c6h5n3) as passivator. Practice has proved that it is a convenient, economical and practical passivator. When the copper strip passes through BTA solution, the oxide film on the surface reacts with BTA to form a dense complex to protect the copper matrix.

2. Solution of copper strip shear indentation

To prevent the indentation of the cutting edge, the reasonable outer diameter difference between the round knife and the rubber stripping ring should be selected according to the thickness and hardness of the strip; The hardness of the rubber stripping ring meets the service requirements of the cut strip; When the width of the cut strip is small, the thickness of the round knife shall be reasonably selected to increase the width of the rubber stripping ring.