Product Introduction

FCD600 ductile iron lost wax investment casting parts main defects

Shrink the holes and loosen them

Due to its paste solidification characteristics, nodular cast iron often produces defects such as shrinkage holes and porosity due to poor feeding. In order to predict these defects before casting production, numerical analogies of casting process have been carried out at home and abroad as early as the printing era. Numerical analogy of casting process is to use numerical analogy technology to simulate the actual casting formation process in a computer virtual environment, including the filling process of metal liquid, cooling and solidification process, stress formation process, to judge the influence degree of main elements in the forming process, to predict the organization, performance and possible defects, and to provide a basis for optimizing the process and reducing waste.

In 1962, Denmark's Forsund was the first to use an electronic computer to simulate the solidification process of castings, and since then the United States, Britain, Germany, Japan, France and other countries have carried out research in this area. In the late 1970s, Dalian University of Technology and Shenyang Foundry Research Institute took the lead in conducting research on this technology in China, and published research reports in 1980 (Guo Keren et al., Digital Analogy of solidification Process of large castings, Journal of Dalian Institute of Technology, 1980 (2) 1-16; Shenyang Foundry Research Institute, Casting Solidification Field Electronic Computer Analogy Casting, 1980 (1) 14-22, since then a lot of manpower in China's universities to carry out this research.

During the "Sixth Five-Year Plan" and "Seventh Five-Year Plan" period, the central part of the national research project has a research project on the application of computers in casting, the "Sixth Five-Year Plan" project is "solidification control of large steel castings", the "Seventh Five-Year Plan" project is "large steel castings casting process CAD", and the joint research of production, science and research has greatly promoted the development of this technology in our country. Tsinghua University and Huazhong University of Science and Technology have respectively been able to provide FT-STAR and Huazhu CAE-INTE 4.0 commercial chemistry software and applied in Sanming Heavy Machinery Co., LTD., and obtained good results.

Computer numerical analogy consists of three parts: pre-processing, intermediate computation and post-processing, including the establishment of geometric model, the division of grid points, the determination of solving conditions (initial conditions and boundary conditions), numerical calculation, the processing of calculation results and graphic display. The basic methods of numerical analogy used are finite difference method, finite element method and boundary element method.

(1) Numerical analogy of solidification process, mainly for heat transfer analysis of casting process. It includes the selection of numerical calculation method, the treatment of latent heat, the prediction and discrimination of shrinkage hole, and the treatment of the heat transfer problem at the interface of castings and moulds.

(2) Numerical analogy of flow field, involving momentum, energy and mass transfer, is more difficult. The numerical solving techniques used include MAC method, SAMC method, SOLA-AOF method and SOLA-MAC method.

(3) Casting stress analogy. This research was carried out relatively late. It mainly carried out elastic-plastic state stress dissociation, including Heyn model, elastic-plastic model, Perzyna model, unified internal variable model, etc.

(4) Organizational analogy is still in its infancy. There are macrovision, mesovision and microvision analogies. It can calculate the number of nucleation, analyze the initial crystal type, dendrite growth rate, analog structure transformation, and predict mechanical properties. There are deterministic models, Monte, Cellular, Automaton and other statistical models, phase field models and so on.

Computer and its application is a rapidly developing technical field, casting as one of the important industrial fields, should strengthen investment. Research and development of the application of computer in the field of casting research and production, completely change the past kind of "open eye type, closed eye pouring" state, the application of computer will also promote the application and development of ductile iron.

Stomatal defect

In the production process of ductile iron parts, after heat treatment, shot blasting or machining, it is often found that some diameter of about 0.5-3mm, the shape of spherical, elliptical or pinhole-like smooth holes on the inner wall, these holes are generally distributed 2-3mm under the skin of the casting, which is the so-called subcutaneous porosity.

The formation of subcutaneous pores is due to the high surface tension of liquid magnesium and iron, which is easy to form an oxide film, which has a certain impact on the obstruction of the discharge of precipitated gases and invading gases, and these gases will form pores when they are trapped under the skin. In addition, the solidification characteristics of ductile iron paste cause the gas channel to be blocked earlier, which will also promote the formation of subcutaneous porosity defects.

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