| One of the keys to heavy ingots casting technology is how to guarantee the order of ingot solidification and the full feeding of ingots, which is the important condition for controlling casting defects effectively and getting heavy ingots of high quality. In order to get high-quality ingots needed in forging, we must control the ingot solidification process. It’s difficult to observe and control directly as ingot solidification is proceeded under high temperature. However, the numerical simulation technology can make us observe and understand the ingot solidification process intuitively and control the solidification process effectively by adjusting the correlation coefficients.This article first researched the influence of water velocity, the ingot mold thickness and gap on heat-transfer coefficient during ingot solidification process. The study shows that,1) The thinner the water cooled wall thickness of ingot mould can reduce thermal resistance, combined with the actual production status, the water-cooled ingot mould thickness is confirmed.2) The solidification rate of ingots is0.04mm/s when water velocity is2m/s. The solidification rate of ingots increases with the increase of water velocity under the confirmed thickness of the ingot mould when water velocity is below2m/s. However the effect on ingots becomes unobvious when the thickness of the ingot mould is5mm and water velocity is above2m/s.3) Gap has less effect on heat-transfer coefficient. We can calculate the heat-transfer coefficient between gap and the ingot mold as well as between gap and the ingot.Secondly, simulation study was conducted on the original mould process, The study shows that the liquid core region is longer in the longitudinal direction and has narrow distribution range. The phenomenon of bridge appears at the top of the ingot in the late stage of solidification, which causes that the riser of the ingot does not have enough feeding to the central area and then the shrinkage defect is formed at the center of the ingot, which is500mm from the bottom,1900mm in longitudinal direction, and the diameter is107mm,Thirdly, numerical simulation was conducted on the water-cooled mould process. The study shows that, as the cooling capability of the water-cooled ingot mold is much stronger than that of the ordinary ingot mold, the liquid core area of ingots becomes narrower and narrower over time, which causes that the riser of the ingot doesn’t have enough feeding to the central area and then the shrinkage defect is formed at the center of ingots which is300mm from the bottom and2000mm in longitudinal direction,15mm in radial direction. Compared with ordinary mould process, the location of shrinkage cavity is200mm lower, the longitudinal length increases by100mm and the radial length shrinks by92mmThen, the numerical simulation study was conducted on self-feeding process. The study shows that the solidifying velocity of the ingot becomes smaller in self-feeding process than in the original process, which makes the ingot core maintain the liquid state for a long time. However, shrinkage cavity still appears in the late stage of solidification, mainly distributed in the area of600mm above the bottom. The longitudinal length is about1800mm, and the radial length is10mm. Compared with water-cooled mould process, the location of shrinkage cavity is300mm higher, the longitudinal length shrinks by200mm and the radial length shrinks by5mm.At last, gradient feeding process is put forward by analyzing research results of three processes above, and is numerically simulated. The research result shows that, at different places between the ingot and the ingot mold and at different time appropriate cooling intensity should be given to make the cooling time at the bottom of the ingot earlier than that on the top to form a top-down temperature gradient, and then make the solidification interface present the shape of "V" pushing upward in the longitudinal direction to suppress the appearance of shrinkage cavity. |
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