[China Aluminum Industry Network] 1. Foreword With the development of society and the improvement of people's living standards, the use of aluminum and aluminum alloys has increased significantly. As the main smelting equipment of aluminum and aluminum alloys, induction furnaces have attracted more and more attention. Therefore, the refractory materials used in induction melting furnaces have become one of the technical problems that casting operators are very concerned about.
Here, the research work done by the Institute in this area over the years is described as follows:
2.Features of Refractory Materials for Induction Fused Aluminum Furnaces 2.1 Characteristics of Working Frequency Core Induction Furnaces The heat source of the cored induction furnace comes from a trench-type inductor located in the lower part of the furnace body. The molten aluminum is induced in the fused trench. Heating, and then through the circulation or one-way flow heat exchange with the molten aluminum in the furnace. The large-tonnage heartfelt induction melting furnace uses a jet-type sensor developed by Ajax. This sensor not only greatly reduces the temperature difference between the molten metal in the frit and the metal liquid in the furnace, but also prevents the accumulation of chemical reaction products on the frit wall, which changes the clogging of the frit to a certain extent, but due to Increased electromotive force, increased flow rate of molten aluminum, and complex fused channel shapes increase the wear and structural stress of the lining refractories; the thinning of the fused groove walls and the setting of the water-cooled jacket increase the heat that the refractories withstand. stress.
The low energy consumption of the centered induction furnace lies in its continuous operation method, which undoubtedly increases the time and opportunity for reaction between the refractory material and the molten bath, and the possibility of blocking the ditch is always present.
2.2 Working Characteristics of Centerless Induction Furnace The commonly used centerless induction furnaces are divided into two types: industrial frequency and medium frequency. From the current development trend, the intermediate frequency furnace is more promising. The common point of the two is that the intermittent or continuous operation mode can be adopted as required, and the furnace lining is subjected to a large thermal stress due to the continuous repetition of the “adding-melting-removing†operation process. The liquid metal furnace in the furnace is more powerful than the intermediate frequency furnace, that is, the lining is subjected to more severe erosion, while the intermediate frequency furnace has a higher specific power (double the power frequency furnace), high power density, and high melting speed. Hot and cold alternating faster. Due to the high turn-to-turn voltage (about 2 to 4 times that of industrial-frequency furnaces), the possibility of overheating the molten metal that penetrates the lining through cracks and causing damage to the coil is greater.
2.3 Refractory materials should meet the requirements Refractory lining, whether for induction furnace, or centerless induction furnace, should meet the following requirements.
(1) Good chemical stability Metal aluminum and aluminum alloys have not only high chemical activity but also excellent fluidity of the melt. The viscosity of aluminum melt at 750°C is only 1.04 centipoise, which is close to the viscosity of water at 20°C (1.0 centipoise). This is the main reason for the easy penetration into the lining and the chemical reaction. At temperatures where the molten aluminum comes into contact with the refractory, the aluminum acts as a reductant. SiO2, TiO2, FeO and other oxides in the refractory material are reduced by aluminum. The reaction between the molten aluminum and lining refractories not only affects the quality of the product, but also causes the lining surface to nodule, bulge and deposit debris, and there is a risk of cracking at the interface between the liquid impregnated part and the original brick. It will also cause flaking. Therefore, the lining material that comes into contact with the molten aluminum must have high chemical stability and as little impregnation as possible.
(2) Good resistance to erosion Generally, in order to make the furnace have higher electrical efficiency, the material of the furnace wall is designed to be very thin, but during the operation of the furnace, due to the effect of electromagnetic force, the molten metal in the furnace continuously churn and Stirring, constantly scouring and fraying the lining. For the induction furnace, due to the use of jet-type fused channels, the fused refractories are more subject to erosion and wear. Therefore, it is required that the refractory material used must have high mechanical strength and hardness.
(3) High density and volume stability As refractory materials for smelting furnaces, in the case of a certain material, it is desirable to obtain a high density and volume stability. The level of body density reflects the amount of pores in the molded body, especially the degree of sintering. The higher the volume stability of the material, the smaller the possibility of cracking during sintering and use, and the smaller the width of cracks produced, the stronger the resistance to permeation.
(4) Not easy to produce furnace knobs. Very rare furnace knobs may be formed due to impurities (for example, Al2O3) present on or in the melt. Because the furnace knob significantly reduces the furnace capacity and the metal tumor itself is dense and tough, removal is very difficult.
(5) It is not easy to be wetted and infiltrated with molten metal. It is known that refractories are brittle materials and cracks are inevitably generated during heating and cooling. However, one of the key factors determining its lifespan is the size of the crack and the speed of crack propagation. The crack propagation is related to the wetting and penetration capacity of the molten metal to the contacted material. The worse the wetting ability, the better.
(6) The resistance to quenching and rapid heating is particularly important for non-induction furnaces. Because the non-hearth furnace operation mode is the continuous cycle of "Feeding-melting-pulling out" process, the lining material is repeatedly subjected to thermal shock. If the thermal shock stability of the refractories is not good, cracks and cracks are prone to cracking, and the molten metal will permeate the coils in a short period of time, causing the entire lining to be scrapped.
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