Papers by Author: Hong Liang Zheng

Abstract: This paper presents the relationship between the carbon atom diffusion coefficient in the austenite and the temperature during the nodular cast iron solidification under different cooling rates or with different carbon contents. Pouring the wedge-shaped casting explores the influence of cooling rate on the diffusion coefficient. The other part explores the change of the diffusion coefficient with different carbon contents by water quenching to save the organization in the solidification. Results show that both the cooling rate and the carbon content can affect the diffusion coefficient, and it decreases as the cooling rate increases. More attempts were also done to correlate the diffusion coefficient with the temperature in different carbon content. It has been found that the diffusion coefficient decreases as the temperature increase.

Abstract: Based on the source code of 3D modeling software called Sinovation, the user interface is developed by Visual Studio 2005, then 3-demensional computer aided design (CAD) module of gating system for iron castings is built by the Script language of SINOVATION. The CAD module has a friendly interface, quick and accurate calculation, and is able to design complicated gating system. As the efficiency and accuracy for gating system designing are improved,

Abstract: The liquid structure of Ni₂Sb₉₈ eutectic alloy is studied with the method of X-ray diffraction and measurements of viscosity in this paper. Covalent bonding structures, which are characterized by the shoulder on the high- Q side of the first peak of structure factors, are observed over the full measuring temperature range. And the split of second peak of the pair correlation function suggests that the chemical short-range order structure exits in the melt. Correspondingly, variation of the viscosity obeys the Arrhenius law except the abrupt point near 1025K and the electrical resistivity changes abnormally at about 1020K. In addition, the coordination numbers prove that the A7-like structure is almost destroyed in liquid Ni₂Sb₉₈ alloy. This research is aim to provide new insight into the structure evolution of liquid alloys during the cooling process.

Abstract: Two S-type thermocouples connected to paperless recorder are used to record the temperature change during solidification of the wedge spheroidal-graphite casing. The cool-down time and eutectic temperature are obtained from the cooling curves which are calculated by Pro CAST software. Aided by the image-pro plus software, graphite nodules’ mean diameter and amount can be obtained. Carbon diffusion coefficient of graphite nodule is calculated according to the spherulite growth model. The result is in good agreement with the reference date which shows the validity of parameters. It could provide the parameters for simulation of casting solidification.

Abstract: The residual Mg content ,spherodize ratio and nuclei of spherodial graphites(abbreviated SG) were studied by casting a series of similar composition ductile iron rods and white samples with different holding time of spheroidizing. The results indicate that the residual Mg content in the ductile iron was less and less as the holding time grows ,which causing the morphology of graphites transfer from spherodial to oval. Spherodize ratio change law is not continuous as increasing the residual Mg content which is divided at the 0.02%. The morphologies of nuclei of SGs core are typical examples of the highly magnified structure of spherical and irregular polygons; the diameters are about 0.5~2μm, consisting of (Mg, Ca)S along with CeO₂ and MgO. Disregistry δ between the nucleus compounds and graphite are low,which indicates that nucleus compounds are good nucleating site for SGs.The Mg element in nuclei of SG just act as nucleation substrates.it is the Mg which maybe simple substance in the metallic matrix that act as the role of spherodizer determines the graphite shape.

Abstract: Shrinkage porosity is often found in Spheroidal graphite iron (S. G. Iron) castings because of the mushy zone and special volume change during their solidification. Although the volume expansion is very important to the shrinkage porosity simulation of S.G. Iron castings, conventional methods for predicting the porosity defects do not consider it. A Series of macro-micro models such as macro heat transfer calculation and microstructure formation simulation are proposed to simulate the solidification of S. G. Iron castings. The nucleation and growth models are employed to calculate the accurate latent heat and volume change especially graphite expansion during the solidification. The pressure induced by graphite expansion is introduced as a parameter to predict the shrinkage porosity and a new shrinkage porosity criterion is developed. Cooling curves and solid fraction of each phase are compared with experimental castings. At the same time, the porosity area ratio of castings is compared with the results calculated by several porosity criterions. The results show that the new shrinkage porosity simulation criterion of S. G. Iron castings based on macro-micro models is accurate on shrinkage porosity shape, size and distribution simulation.

Abstract: It is very important to predict the hot spots of castings properly, which is known as a criterion for riser design. In this paper, an improved geometric model for hot spot prediction is proposed, and subsequently, its application to hot spot analysis is presented. As we know, the heat dissipation potential of a location in a casting depends on its distance to the heat transfer surfaces. In a meshed casting, the reciprocal of distance from a certain cell to surfaces is calculated at all the six orthogonal directions, by which the heat dissipation potentials of every cell will be evaluated considering the influences of the neighboring grids. With the improved geometric model, there is no iteration during calculation, and only twice of cell traverse is required. The first traverse gets the distance reciprocal and the second focuses on the heat dissipation potential. The result of this model, which turns out similar to that of procedures based on heat transfer equations, reflects solidification sequence in a casting, hence the hot spots will be known instantaneously. Obviously this geometric model ignores many conditions during solidification process. However, messages like locations of hot spots are shown much faster and more conveniently than that of procedures based on heat transfer equations. Therefore, it is believed that it will shorten much time for casting technology design.