Research on the annealing and pickling process technology of white copper B19 strip, interpreting it from annealing, burning, brushing, etc.
White copper is a copper alloy with nickel as the main added element. Copper-nickel alloy has good electrical conductivity, thermal conductivity and good mechanical properties, and also has good hot and cold pressure processing properties. At the same time, it has the advantages of beautiful color and strong corrosion resistance, and is widely used in industrial production [1]. With the development of science and technology, metal alloys are widely used in the manufacture of various mechanical tools. With its excellent physical and chemical properties, white copper is increasingly used in the shipbuilding industry, instrumentation, medical equipment, craft decorations and other fields. , its excellent properties have been tested by engineering practice, it is reliable and stable, and it is also an important resistance and thermocouple alloy.
1. The composition and production process of white copper strip
Cu and Ni form a continuous solid solution with infinite solid solution and a face-centered cubic structure [2]. In Cu-Ni alloys, when the Ni content exceeds 16%, the resulting Cu-Ni alloy will appear white. The higher the Ni content, the whiter the color will be. In B19 copper alloy,
The Ni content is about 19% and it is white in color. The alloy mainly contains Fe, Mn, Zn and other impurity elements. Due to the low impurity content, it has basically no impact on the physical properties and mechanical properties of the product. Table 1 shows the elemental composition of white copper B19.
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Cupronickel B19 products have better cold working performance. During cold deformation, the processing rate can reach more than 80%. The process flow design of cupronickel B19 products is shown in Figure 1.
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White copper B19 strips are mostly annealed in bell furnaces. The main part of the bell-type furnace includes the furnace table, spray cooling cover, thermocouple heating cover, convection plate, etc. [3], which is suitable for the bright annealing requirements of various copper and copper alloys such as red copper, brass, and white copper.
The entire annealing process includes three processes: heating, continuous heat preservation, and cooling. The main process is shown in Figure 2.
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In actual production, when a bell-type furnace is used to anneal cupronickel B19, the temperature is mostly controlled between 600°C and 750°C. Due to the limitations of existing technology and sudden problems at the production site, edges and bumps are prone to occur during the annealing process. Heating delays, excessive heating speed or cooling speed can easily cause the surface of the strip to stick, affecting the production progress and the economic value of the strip.
2. Countermeasures for product improvement
In industrial applications, users will be concerned about the quality of white copper B19 products, while soft products generally require HV to be below 90, and the product surface is required to be bright, not dark, and not have burn-in marks. In view of the problem of bell burning and sticking after retreat, this article discusses the solution based on the current situation of the equipment. When annealing in a bell furnace, a high hydrogen (75%) atmosphere is generally used for bright annealing. Through experimental research, the impact of annealing temperature on B19 zone HV is shown in Table 2. When the annealing temperature is 600°C, the Vickers hardness of the product As high as 95, when the annealing temperature is 650°C, the Vickers hardness of the product can be reduced to 85.
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That is, when the annealing temperature of the bell furnace is 650°C, the white copper B19 strip can be softened and reach below HV90. However, the annealing temperature of the bell furnace is too high, which can easily cause the surface of the strip to burn, resulting in a dark color and burn marks on the surface of the strip, making it difficult to meet user requirements. In order to improve the surface quality of white copper B19 thick strip products, a series of tests were conducted based on the on-site equipment capabilities. After the production of the bell-type furnace is completed, the pickling process is carried out. After the heat treatment of the white copper B19, dense Ni2O and NiO are formed on the surface. Generally, a nitric acid aqueous solution or a small amount of nitric acid (HNO3) is added to the sulfuric acid aqueous solution to improve the pickling effect. The reaction is as follows:
NiO+H2SO4-NiSO4+H2O
Ni2O+2H2SO4-2NiSO4+H2O+H2
Ni+2HNO3-Ni(NO3)+H2
The pickling process includes a brushing step. In order to remove the burnt layer on the surface of the strip, a nylon brush, a 200-mesh 3M brush, a 500-mesh 3M brush, a 1000-mesh 3M brush, and a 2000-mesh 3M brush are used for scrubbing. Among them, the 3M brush material is nylon Silk + abrasive
Al2O3, the brush making process is to evenly bond strip-shaped non-woven materials to rollers made of bakelite tube materials, forming a radial structure that is loose on the outside and tight on the inside. The scrubbing test results of different brush types are shown in Table 3. Judging from the test results, using a 500-mesh 3M brush on the pickling equipment can completely remove the burnt layer on the surface of the strip. Figure 3 shows the results before and after brushing.
The surface of the strip is shiny after brushing, and the test results are good.
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3.Conclusion
① The annealing process and mechanical properties of white copper B19 were explained and systematically studied, and the operating process of the bell furnace was obtained based on actual production; ② By conducting brush selection tests, the problem of strip surface burning and sticking was solved, and the surface was smooth and smooth. Products with bright colors, stable performance, and no burn-in marks.
