ABSTRACT: through the analysis of annealing technology, the bell-type furnace technology of B19 for Cupronickel was studied, and the brush type selection experiment was used to get the result that 3m brush with 500 Mesh was used for brushing on the pickling equipment, which can effectively solve the problem of burning and sticking on the surface of the strip, the product with smooth surface and stable property is obtained.

Key Words: B19 cupronickel; Annealing; burning and sticking; brushing, author: Fan Xianyong ZHONGTU classification number: TG339 document identification number: A article number: 1002-5065(2019)05-0013-2

Cupronickel is a copper alloy with nickel as the main additive element. copper-nickel alloy has good electrical conductivity, thermal conductivity and mechanical properties. At the same time, it has the advantages of beautiful color, strong corrosion resistance and so on, and is widely used in industrial production. With the development of science and Technology, metal alloys are widely used in the manufacture of various kinds of mechanical tools, cupronickel is used more and more in the fields of shipping, instrument, medical instrument, craft decoration and so on because of its excellent physical chemistry performance. Its excellent performance has been tested in engineering practice, which is both reliable and stable, it is also an important alloy for resistance and thermocouple.

1. Composition and manufacturing process of cupronickel strip

Cu and Ni form a continuous solid solution with face-centered cubic structure. In Cu-Ni alloy, when the NI content exceeds 16% , the CU-NI alloy will appear white, and the higher the NI content, the whiter the color will be. In B19 Copper Alloy, Ni content is about 19% and it is white. The alloy mainly contains Fe, MN, Zn and so on. Table 1 shows the elemental composition of B19.

The cold working property of B19 white copper is good. When cold deformation, the processing rate can reach over 80% . The technological process design of B19 white copper is shown in Fig. 1.

B19 Copper Alloy Strips are annealed in a bell-type furnace. The main parts of the bell-type furnace include the hearth, the spray-type cooling cover, the thermocouple heating cover, the convection plate, etc. , the whole annealing process consists of heating up, continuous heat preservation and cooling. The main process is shown in Fig. 2.

In actual production, when B19 is annealed by bell-type furnace, the temperature is usually controlled at 600 °C ー750 °C, in the annealing process, it is easy to appear the phenomena of bumping, heating delay, heating speed or cooling speed too fast, and it is easy to cause burning and sticking on the surface of the Strip, which affects the production schedule and the economic value of the Strip.

2. Product Improvement Responses

In industrial applications, users will be white copper B19 product quality restrictions, and the general requirements of soft products HV in 90 or less, and requires the product surface to be bright, can not be dark, can not have burning and printing. In view of the problem of bell back burning and sticking, combined with the status of equipment, this paper discusses the solution. The effect of annealing temperature on HV of B19 band is shown in Table 2. When annealing temperature is 600 °c, the vickers hardness of B19 band is up to 95, when the annealing temperature is 650 °c, the vickers hardness of the product can be reduced to 85.

That is, when the annealing temperature of the bell-type furnace is 650 °c, the B19 white copper strip can be softened to less than HV90. But the annealing temperature of bell-type furnace is too high, it is easy to burn and stick the surface of the Strip, so that the surface color of the strip is dark, there is burn and stick printing, it is difficult to meet the user's requirements. In order to improve the surface quality of B19 heavy strip product, a series of experiments were carried out. After the production of the bell-type furnace, the pickling process is carried out, and the dense NI2O and Nio are formed on the surface of B19 white copper after heat treatment. The effect of pickling is improved by adding a small amount of nitric acid (HNO3) to the solution of nitric acid or sulfuric acid:

NiO+H2SO4—NiSO4+H2O

Ni2O+2H2SO4—2NiSO4+H2O+H2

Ni+2HNO3—Ni(NO3)+H2

In order to remove the burning layer on the surface of the Strip, the pickling process consists of brushing step, using nylon brush, 200 Mesh 3m brush, 500 Mesh 3m brush, 1000 Mesh 3m brush and 2000 Mesh 3m brush, the brush-making technology is that the strip-like nonwoven material is uniformly bonded to the roller shaft made of Bakelite pipe material to form the radial structure of outer loose and inner tight. The effects of different brush types are shown in table 3. From the test results, using a 3m brush with 500 Mesh on the pickling equipment can completely remove the burning adhesion layer on the surface of the strip. Fig. 3 shows the surface of the strip before and after brushing. The surface of the Strip after brushing is bright and the test results are good.

3. Conclusion

1 The annealing process and mechanical properties of B19 white copper are explained and studied systematically, and the operation process of the bell-type furnace is obtained according to the actual production, you can get a smooth surface, bright color, stable performance, non-burned adhesive products. 

Source: Chinanews.com, by Fan Xianyong

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