Requirements that refractory materials should meet

The refractory material for furnace lining, whether used in a cored induction furnace or

a coreless induction furnace, should meet the following requirements.

(1) Has good chemical stability

Metal aluminum and aluminum alloys not only have high chemical activity, but also have

excellent fluidity of their melt. The viscosity of aluminum melt at 750 ℃ is only 1.04

centipoise, which is quite close to the viscosity of water at 20 ℃ (1.0 centipoise). This is

the main reason why it is easy to penetrate and undergo chemical reactions inside the

furnace lining. At the temperature at which aluminum liquid comes into contact with

refractory materials, aluminum acts as a strong reducing agent. Oxides such as SiO2,

TiO2, and FeO in refractory materials need to be reduced by aluminum. The reaction

between molten aluminum and lining refractory not only affects the quality of the

product, but also makes the lining surface nodulate, bulge and precipitate sundries.

The interface between the part impregnated with molten aluminum and the original

Fire brick is in danger of cracking, which will also cause peeling when the furnace is

shut down. Therefore, the lining material in contact with aluminum liquid must have

high chemical stability and as little impregnation as possible.

(2) Has good erosion resistance

Generally, in order to make the furnace have a high Electrical efficiency, the furnace wall

materials are designed to be very thin. However, during the operation of the furnace,

due to the effect of electromagnetic force, the molten metal in the furnace constantly

churns and stirs, scouring and wearing the furnace lining. For the induction furnace with

a center, due to the use of a jet type melt groove, the refractory material in the melt

groove is subjected to more severe erosion and wear. Therefore, it is required that the

refractory materials used must have high mechanical strength and hardness.

(3) Has high density and volume stability

As a refractory material for smelting furnaces, it is hoped to achieve high density and

volume stability when the material is certain. The density of the body reflects the content

of pores in the formed body, especially the degree of sintering. The higher the volume

stability of the material, the less likely it is to produce cracks during sintering and use,

the smaller the width of the cracks generated, and the stronger the anti permeability ability.

(4) Not prone to furnace nodules

It is rare to form furnace nodules due to impurities present on the surface or inside of the

molten material (such as Al2O3). Because furnace nodules can significantly reduce the

capacity of the furnace, and the metal nodules themselves are dense and tough, it is very

difficult to remove them.

(5) Not easily wetted and penetrated by liquid metal

As is well known, refractory materials are brittle materials that inevitably produce cracks

during heating and cooling processes. But 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 permeability of the metal liquid to the material in contact. The poorer

the wetting ability, the more advantageous it is.

(6) Good resistance to rapid cooling and heating

This is particularly important for heartless induction furnaces. Because the operation mode

of coreless furnace is the continuous cycle of "feeding melting discharging" process, furnace

lining materials are repeatedly subjected to Thermal shock. If the thermal shock stability of

refractory materials is poor, cracks and crack propagation are highly likely to occur, and the

metal liquid will penetrate into the coil in a short period of time, leading to the scrapping of

the entire furnace lining.