With the development of society and the improvement of people's living standards, the amount of aluminum and aluminum alloys has increased significantly. Induction furnaces, as the main melting equipment of aluminum and aluminum alloys, have received more and more attention. Therefore, refractory materials for induction melting furnaces have become one of the technical issues of great concern to casting operators.

Here, the research work done by the Institute in this respect over the years is described as follows:

2. Characteristics of refractory materials for induction melting aluminum furnace

2.1 Working characteristics of power frequency cored induction furnace

The heat source of the induction furnace comes from the grooved sensor located in the lower part of the furnace body. The aluminum liquid is inductively heated in the molten groove, and then exchanges heat with the aluminum liquid in the furnace through circulation or one-way flow. The large-tonnage induction induction melting furnace uses a jet-type sensor developed by Ajax. The inductor not only greatly reduces the temperature difference between the molten metal in the molten groove and the molten metal in the furnace, but also prevents the accumulation of the chemical reaction product on the wall of the molten groove, and changes the clogging of the molten groove to some extent, but The electric power is increased, the flow speed of the aluminum liquid is increased, and the shape of the molten groove is complicated, which increases the wear and structural stress of the lining refractory; the thinning of the molten groove wall and the setting of the water cooling jacket increase the heat of the refractory material. stress.

The low energy consumption of the heart-shaped induction furnace lies in its continuous operation mode, which undoubtedly increases the time and opportunity for the reaction between the molten refractory and the melt, and the possibility of blocking the groove always exists.

2.2 The working characteristics of the heartless induction furnace

The commonly used centerless induction furnaces are divided into two types: power frequency and medium frequency. From the current development trend, the medium frequency furnace is more promising. What the two have in common is that intermittent or continuous operation can be adopted as needed. The furnace is subjected to a large thermal stress due to repeated "feeding-melting-out" operation. The metal liquid in the power frequency furnace is more powerful than the tumbling in the medium frequency furnace, that is, the lining is more severely washed, while the intermediate frequency furnace has a larger specific power (twice the power frequency furnace), high power density, and fast melting speed. Hot and cold alternates faster. Since the inter-turn voltage is high (about 2 to 4 times that of the power frequency furnace), the metal liquid that penetrates the lining through the crack is overheated and the coil is likely to be damaged.

2.3 Refractory materials should meet the requirements

Furnace lining refractories, whether for heart induction furnaces or centerless induction furnaces, should meet the following requirements.

(1) has good chemical stability

Metallic aluminum and aluminum alloys are not only chemically active, but also have excellent fluidity of the melt. The viscosity of the aluminum melt at 750 ° C is only 1.04 centipoise, which is quite close to the viscosity of water (1.0 centipoise) at 20 ° C, which is the main reason for its easy penetration into the lining and chemical reaction. At a temperature at which the aluminum liquid is in contact with the refractory material, the aluminum acts as a strong reducing agent. The oxides of SiO2, TiO2, FeO and the like in the refractory material are to be reduced by aluminum. The reaction between the aluminum liquid and the lining refractory material not only affects the quality of the product, but also causes nodulation, bulging and sedimentation of the surface of the lining, and there is a risk of cracking at the interface between the impregnated portion of the aluminum liquid and the original brick. It can also cause spalling. Therefore, the lining material in contact with the aluminum liquid must have high chemical stability and as little impregnation as possible.

(2) Good anti-scourability

Generally, in order to make the furnace have higher electric efficiency, the material of the furnace wall is designed to be very thin, but during the operation of the furnace, due to the action of electromagnetic force, the molten metal in the furnace constantly churns and stirs, and the lining is continuously washed and worn. . For the heart-shaped induction furnace, the refractory material of the gully is more severely washed and worn due to the use of the jet-type melting groove. Therefore, it is required that the refractory material used must have high mechanical strength and hardness.

(3) High density and volume stability

As a refractory material for a smelting furnace, it is desirable to obtain a high density and volume stability in a case where the material is constant. The level of compactness reflects the amount of pores inside the molded body, especially the degree of sintering. The higher the volume stability of the material, the less likely it is to crack during sintering and use, the smaller the width of the crack produced, and the stronger the resistance to penetration.

(4) It is not easy to produce a bell tumor

It is rare to form a furnace due to impurities (such as Al2O3) present on the surface or inside the melt. Because the furnace tumor will significantly reduce the furnace capacity, and the metal tumor itself is dense and tough, it is very difficult to remove.

(5) Not easily wetted and infiltrated by molten metal

It is well known that refractory materials are brittle materials which inevitably generate cracks during heating and cooling. But one of the key factors determining its life is the size of the crack and the rate at which the crack propagates. The crack propagation is related to the amount of wetting and penetration of the molten metal to the material being contacted. The worse the wetting ability, the better.

(6) Good resistance to quenching and rapid heat

This is especially important for heartless induction furnaces. Because the unburning furnace operation mode is the continuous circulation of the "feeding-melting-out" process, the lining material is repeatedly subjected to thermal shock. If the thermal shock resistance of the refractory material is not good, cracks and crack propagation are likely to occur, and the molten metal will penetrate into the coil in a short period of time, resulting in the entire lining being scrapped.