Research On Horizontal Electromagnetic Continuous Casting Of Copper And Copper Alloy Hollow Billets

In recent years, with the development of industry and national economy, the needs of high quality copper and copper alloy tubes and the requirements for the high production efficiency increase quickly. Continuous casting of hollow billets is considered as a profound near-net forming technology with the advantage of high production efficiency and high utilization ratio. But there are many problems for the hollow billets such as poor surface quality, too many casting defects, and coarse grains in solidification structure and poor uniformity of structure in the circumferential direction. How to produce high quality copper and copper alloy hollow billets to satisfy the requirements of succeeding treatment is the key to acquire the high quality tubes. The successful application of electromagnetic field in materials processing provides a chance for producing high quality copper and copper alloy hollow billets.The purpose of the dissertation is to produce high quality copper and copper alloy hollow billets. The technology of horizontal electromagnetic continuous casting of copper and BFe10-1-1 copper alloy hollow billets is studied. The main contents are as follows:ANSYS software is used to compute the influence of the materials of press plate and flange on the active effect of the electromagnetic generator and the distribution of magnetic flux density during horizontal electromagnetic continuous casting ofΦ90×25 mm copper hollow billets. The softwares ANSYS and FLUENT are coupled to simulate the effect of electromagnetic field on the solidification process of copper hollow billets, including velocity field, temperature field and liquid fraction, and the effect of current intensity and casting speed on the solidification process of copper hollow billets with electromagnetic field. The results show that the materials of press plate and flange have great influence on the active effect of the electromagnetic generator. When the materials of press plate and flange are strong permeablility magnetic materials, the active effect of the electromagnetic generator is almost weakened completely. When the materials of press plate and flange are weak permeablility magnetic materials, the active effect of the electromagnetic generator is not nearly weakened. The flange has much greater influence than the press plate on the active effect of the electromagnetic generator. The electromagnetic field obviously changes the flow pattern of the melt in hollow billet. The melt circumrotates in cross section and swirls in longitudinal section of the hollow billet. When the current frequency is 50 Hz, the current intensity is 50 A, the casting temperature is 1150℃, the casting speed is 250 mm/min, the maximum tangential velocity is 0.233 m/s. The electromagnetic field fiercely promotes the temperature field uniform and the temperature gradient is greatly reduced from 748 K/m to 196 K/m. The sump depth decreases from 0.194 m to 0.148 m and the mushy zone enlarges remarkably. When current intensity increases, the tangential velocity increases obviously, the temperature filed and liquid fraction in the sump become even, the temperature and liquid fraction gradient decrease greatly, the mushy zone enlarges obviously and the sump depth becomes significantly shallow. When the casting speed increases, the tangential velocity increases slightly, the temperature and liquid fraction gradient decrease slightly, the mushy zone enlarges slightly and the sump depth becomes slightly shallow.The Sn-3.5%Pb simulation alloy is used to study the effect of rotating magnetic field outside the graphite mold on the movement behavior and the solidification process of the melt in hollow billet. The result shows that the electromagnetic field reduces the temperature gradient and makes the temperature field uniform. The electromagnetic field reduces the sump depth and makes the shape of sump uniform in the hollow billet. The experimental results are consistent with the simulation results.The technology of horizontal electromagnetic continuous casting of copper hollow billets is applied to the industrial production. The difficult problems such as the structure of the crystallizer and the design and installation of electromagnetic generator are solved. The experiments of horizontal electromagnetic continuous casting ofΦ90×25 mm copper hollow billets doing in industrial production line study the effects of magnetic flux density and the imposed pattern of electromagnetic field on the solidification structure and mechanical properties of copper hollow billets and investigate the influence of casting speed, cooling intensity and casting temperature on the active effect of the electromagnetic field systematically. The results show that with the increase of magnetic flux density, the solidification structure is refined correspondingly. But when the current intensity is more than 50 A, the solidification structure turns to get coarse because of the Joule heat. The intermittent electromagnetic field has the same effect as the consecutive electromagnetic field on refining the solidification structure. Increasing the casting speed is helpful for electromagnetic field to refine the solidification structure. Reducing the casting temperature and enhancing cooling intensity are harmful for electromagnetic field to refine the solidification structure. When the current frequency is 50 Hz, the current intensity is 50 A, the casting temperature is 1150℃, the casting speed is 250 mm/min, the cooling intensity is 1 m~3/h, the refined solidification structure of copper hollow billet is better than any others. The inhomogeneous columnar grains change into homogeneous equiaxed grains and the ratio of equiaxed grains is more 98 %. The tensile strength is increased by 15.9 % and the elongation is improved by 63.8 % compared to those without electromagnetic field. The density of copper hollow billet increases from 8.9123 g/cm~3 to 8.9372 g/cm~3, the service life of the graphite inner-mold is increased and the injury points of the copper tubes are deduced because of electromagnetic field.The regular casting defects occuring during horizontal continuous casting of BFe10-1-1 copper alloy hollow billets are studied. The parameters of horizontal electromagnetic continuous casting ofΦ83×21 mm BFe10-1-1 copper alloy hollow billets are optimized to explore new technics. The effect of electromagnetic field on the evolutions of macrostructures and microstructures, the surface quality, solute distribution, the accumulated state and growth morphology of Ni-rich phase, mechanical properties of BFe10-1-1 copper alloy hollow billet is studied systematically. The results show that the macrostructures are greatly refined and the microstructures transform in certain rule by electromagnetic field. The segregations of Ni, Fe and Mn are restrained and the distribution of Ni-rich phase is changed with electromagnetic field. When the current frequency is 50 Hz, the current intensity is 120 A, the casting temperature is 1230℃, the casting speed is 350 mm/min and the cooling intensity is 1.8 m~3/h, the inhomogeneous columnar grains change to homogeneous equiaxed grains which are better than any others and the average grain size reaches to 0.56 mm. The tensile strength is increased by 20.3 % and the elongation is improved by 65.7 % compared to those without electromagnetic field.