| The change of liquid metal structure is very sensitive to the change of the electrical resistivity. So, the structure information of liquid metals are deduced by observing the change of the electrical resistivity. In addition, the electrical resistivity of liquid metals is also very important for many technological processes, such as steel-making in the electric furnace and steel refining, electromagnetic stirring of the melt, aluminum extraction from electrolytic Al2O3 and so on.In this paper, many methods for measuring the molten metal electrical resistivity are reviewed and analyzed. Based on these, a new method named"negative pressure sampling"is proposed to rapidly measure the molten metal electrical resistivity. In this method, the molten metals are inhaled into the double-column conductivity cell by a negative pressure system, and the electrical resistivity will be measured rapidly. The most important advantage of this method is that the measurement speed is very fast and the electrical resistivity can be measured the moment the metals are inhaled.The simple measuring device based on the negative pressure sampling method has been developed, and it is composed of double-column conductivity cell, negative pressure system, and precious constant current source and so on. The double-column conductivity cell is constituted of two parallel cylindrical quartz tubes, high-temperature electrodes, and port sealing materials. The negative pressure system consists of the vacuum pump and buffer container, and by which the molten metals can be smoothly and quickly inhaled in the double-column conductivity cell. Precious constant current source with high stability is mainly composed of the operational amplifier REF102, OPA277 and OPA602. The measured voltage can be acquired by digital potentiometer UJ33D-2 with maximum resolution 1μV, which can meet the measuring requirement.The electrical resistivities of liquid mercury, aluminum alloy and cast iron have been measured, and the experimental results have shown that the electrical resistivity can be got quickly by the negative pressure sampling method, and this method has the advantages of fast measurement and high accuracy. Because the length of the conductivity cell will change at high temperature and will affect the measuring accuracy, the formula of calculating the thermal expansionis introduced to revise it. Comparative experiments of the dipping depth of the conductivity cell show there is an appropriate dipping depth, and the conductivity cell can not be dipped near the bottom or the liquid surface. Because the thermoelectricity will lead to the inaccuracy of measuring the voltage of the conductivity cell, both positive and negative current sources are used to stimulate the molten alloy.According to practical measuring results, a device composed of auto-lifting mechanism, probe locking mechanism, negative pressure units and computer measurement and control system was designed to automatically measure the electrical resistivity of the molten metal. Under the control of computer, the device can carry out various movements and data acquisition and processing by I/O card and analog-input card respectively.
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