| Surface tension is one of the important physicochemical features of the molten alloy. Not only is it the foundation of studying the interface reaction dynamics of the molten alloy, but also plays very important roles in metal solidification process and forecasting parameters of the casting alloy, such as fining and inoculating effect, gas isolation, graphite shape, modification effect, filling mould ability and surface roughness of castings and so on. Therefore, it has very important theoretical value and practical significance to study and test surface tension of the molten alloy. Although many methods had been developed, they cannot fit for fast testing surface tension of the molten alloy in front of the furnace. On the basis of studying new method for testing surface tension, a apparatus of fast testing equivalent surface tension in front of furnace has been developed and new methods for evaluating quality parameters of the molten alloy has been put forward. The research includes theoretical analysis of surface tension and experimental studying of the new testing method, the development of the apparatus and establishment of the model of calculating equivalent surface tension, methods and models of evaluating graphite shape, modification effect, mold-filling potential in front of furnace by equivalent surface tension. The investigation results have proved that the apparatus based on the new testing method can fast test equivalent surface tension of the molten alloy in front of furnace and can fast evaluate the quality parameters before casting.Through further analyzing the principle and testing process of maximum bubble pressure method, it can be concluded the dipping depth of capillary must be measured exactly and the rate of gas blowing out must be slow, so, it can not fit for fast testing surface tension. Consequently, a new method, Amplitude and Frequency Equivalent of Bubble Method, for fast testing equivalent surface tension can be studied synthetically by author, which establishes the technology foundation of fast testing equivalent surface tension of the molten alloy in front of furnace. On the basis of analyzing and experimentally studying the affecting factors of bubble pressure curve, information parameters and mathematical model form have been determined and the requirements of capillary are that inner diameter of capillary is 1.8-2.2mm, outer diameter is 3.5-4.0mm, the rate of blowing out bubbles is 2-3 per second and the dipping depth can be alter at 10-20mm.Equivalent surface tension and temperature of the molten alloy can be tested in 10 seconds by the apparatus that had been developed based on the new method and the high precision methods of testing the information parameters ahd been studied by author. Because the capillary is one-off, a special mechanism is designed to carry out the functions of crimpling detector automatically and driving detector forward or backward. By experiments the model calculating equivalent surface tension has been obtained and programmed in the computer, and it has been testified that the absolute error and relative error of testing equivalent surface tension are below±15.0mN/m, 3.0% respectively, and that the absolute errors of testing temperature are cast iron≤±2.5℃, Al-Si alloy≤±1℃.According to crystal growth theory and interfacial tension theory, the relationship between graphite shape and surface tension has been analyzed and it really exists, which supplies the theoretical foundations of evaluating graphite shape by surface tension. The model evaluating graphite shape has been got by many experiments on cast iron, namely,σe≤990mN/m, graphite shape is complete flake; 990≤σe≤1108mN/m, flake and vermicular; 1108≤σe≤1283mN/m, many vermicular and little nodular; 1283≤σe≤1385mN/m, many nodular and little vermicular;σe≥1385mN/m, complete nodular. The accuracy of evaluating results is higher than 95%.Feasibility of evaluating modification effect by surface tension of Al-Si alloy has been analyzed theoretically; experiments have proved that modifier content is the major factor of varying equivalent surface tension and that temperature effect on equivalent surface tension is faint. The model of evaluating modification effect in front of furnace has been achieved through experiments on binary eutectic Al-Si alloys, namely,σe≥530mN/m, under modification, including unmodified and partial modification, equals AFS1-2; 400≤σe≤530mN/m, moderate modification, equals AFS3-4;σe≤400mN/m, perfect modification, equals AFS5-6. The accuracy of evaluating results is higher than 96%. Through analyzing the general model of alloy Cessation flow, the relationship between mold-filling potential, including the length of filling mold and the ability of filling taper angle, and surface tension really exists and when mold conditions, pouring conditions and casting structure kept invariable mold-filling potential can be evaluated by equivalent surface tension. The device measuring the length of filling mold has been improved to keep the pouring temperature and static pressure constant and the new device measuring the ability of filling taper angle has been developed and its parameter has been put forward. Took as examples of HT200 and ZL102, the practical relationship between the length of filling mold, the ability of filling taper angle and equivalent surface tension has been found and mold-filling potential can been evaluated by equivalent surface tension by means of table lookup. The absolute errors oft he length of filling mold and the ability of filling taper angle are below±10mm and±3mm-1 respectively.
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