What‘s the reasons for pores in fused zirconium corundum bricks

What's the reasons for pores in fused zirconium corundum bricks?


Introduction to fused zirconium corundum bricks:

Fused zirconium corundum brick is also called AZS fused zirconium corundum brick, AZS brick, fused cast AZS brick, etc. The English abbreviation is AZS, which is based on the three chemical components of the Al2O3-Zr02-Sio2 ternary system phase diagram, according to its content Arranged in some order, Al2O3 takes A, Zr02 takes Z, and Sio2 takes S. The standard uses this abbreviation. For example, No. 33 fused zirconium corundum brick is abbreviated as AZS33#, No. 36 fused zirconium corundum brick is abbreviated as AZS36#, and No. 41 fused zirconium corundum brick is abbreviated as AZS36#. Zirconium corundum brick, abbreviated as AZS41#. Among them, 33, 36, and 41 are named according to the content of alumina (Al2O3). For example, fused zirconium corundum brick AZS41# refers to fused zirconium corundum brick with an alumina content of 41%, and fused zirconium corundum brick AZS36# refers to is a fused zirconium corundum brick with an alumina content of 36%, and the fused zirconium corundum brick AZS33# refers to a fused zirconium corundum brick with an alumina content of 33%.

It is normal for ordinary cast AZS castings to have shrinkage cavities, but if a lot of pores are found, this is obviously a problem with product quality, because the presence of any pore will directly reduce the quality of the casting.

There are two types of pores in castings. One type is microscopic pores, which can only be seen when made into thin sections under a microscope; the other type is macroscopic pores, which are visible to the naked eye, which is what we often call pores. They mainly come from four aspects: charge, melting process, casting materials, and casting process.

Here we discuss the impact of casting mold on pores.

Porosity caused by casting material

There are two common types of pores on the edges of castings that are in contact with the mold:

1) Dense subcutaneous honeycomb pores perpendicular to the mold wall - this is caused by moisture on the sand mold working surface. Water is a gas-generating substance. When a unit volume of water is heated to 1000°C, it turns into water vapor. When the pressure remains constant, the volume increases by 1700 times. If heated to the casting temperature, it may reach nearly 10,000 times. Therefore, the water on the surface of the sand mold suddenly generates so much gas that it will form a high pressure, causing the gas to invade the solidifying edge melt and extend in the direction of small resistance, thus turning into a long shape. Therefore, it is forbidden to use wet molds during casting operations.

 

2) Subcutaneous circular pores are mostly single circular bubbles within 10 mm from the edge. This is because the sand mold adhesive decomposes when in contact with the melt to produce a large amount of gas, part of which escapes from the sand mold gap, and part of which is due to transient The cavity exhaust is not smooth, which generates pressure and invades the melt. Therefore, it is very important to pay attention to the exhaust of the cavity during casting. Of course, it is necessary to improve the air permeability of the sand mold (for example, use round sand to clean the dust in the sand. The air permeability on the back side should be greater than that of the workpiece. surface, etc.), which means that it is more important to continuously expand from the inside out.

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