The Application of Dense Zircon Brick in Glass Furnaces

Zircon is chemically inert with good erosion resistance to high temperature molten glass and slag solution. High dense zircon brick made of zircon powder as the main raw material has good high temperature strength and strong resistance to glass liquid, so it is widely used as the bottom paving block and back lining structure in the glass furnaces and the lining of the glass furnaces for producing glass fiber.
During the use, some parts of the glass furnace are required to have good thermal shock resistance. Since the thermal shock stability of the dense zircon brick is bad, it reduces the service life of glass furnaces and increases the repair cost of glass furnaces.
Zircon can improve the properties of dense zircon brick. The dense zircon brick is made of zircon powder by adding high pure industrial zirconia, fused stabilized zirconia and desilicated zirconia. After Formulating according to the amount of the added zirconia, wet-mixing, spray granulation, isostatic pressing and sintering at 1530 ℃ and 12h insulation, 69% dense zircon brick is made.
Research about these three different samples of zirconia on the apparent porosity, bulk density, firing shrinkage and thermal shock stability and a scanning electron microscope (SEM) on the microstructure and fracture surface samples are carried out.
The results showed that: compared to 65 dense zircon brick without ZrO2 added, the samples with ZrO2 added have higher apparent porosity, bulk density, firing shrinkage and thermal shock stability.

Applications of Fused Cast AZS Block

Fused cast AZS block is made of high pure raw materials in a special electric arc furnace by the casting process of long arc melting and oxidation treatment. There is almost no carbon contamination from the electrodes.
Due to the casting process and high pure materials, fused cast AZS block has super strong corrosion resistance to the glass liquid and low potential of pollution.
Fused cast AZS 33# block has great advantage in preventing the pollution from glass liquid. It can generate stones in glass and has low potential of glass precipitation and bubbling. It is suitable to the upper structure of the melting zone, the sidewall of the work tank, the paving blocks and the forehearth.
Fused cast AZS 36# block is the standard fused cast AZS block made by the oxidizing method. It has special high corrosion resistance to the glass liquid and has low potential of pollution. It is suitable for the areas that are in direct contact with the glass liquid, such as the sidewall of the melting zone, paving block and feed port.
Fused cast AZS 41# block is the highest grade fused cast AZS block. It has the best corrosion resistance to the glass liquid and low pollution potential. It is suitable for the parts that require super high resistance such as the electric melting furnace, throat, kiln dam, bubble block and the corner block of the feed port.

Chemical composition of fire clay bricks

Fire clay brick is the refractory brick containing 30-46% SiO2. It is made of clinkers calcined from refractory clays as the oxidant and bond clay as a binder agent.
The main raw material is refractory clay. Clay is an earthy mineral. It can form plastic mud pie when mixed with water and maintain the shape after drying. It has rock-like hardness after fired at high temperature.
Additionally, the clay contains a certain amount of impurities such as quartz, mica, pyrite, feldspar and organic substances. The impurities, especially iron, can reduce the quality of clay and are harmful to the fire clay bricks.
Alkalis such as Na2O and K2O exist as mica. It can improve the sintering properties of clay and form dense products after sintered. It should be fewer than 2%.
The content of CaO is generally under 11.5% and distributed evenly. So, it will not affect the refractory properties of raw materials.
There is a certain amount of TiO2 in the bond clay. It exists as diamond. When it is less than 1%, it has no big effect on the quality of bond clay. In the chemical analysis, its content is not tested alone but counted in the content of A1203 + TiO2.
When the impurities in the clay exceed 6%, the refractoriness of clay will decease and cannot be used as the raw materials. The content of organic substances in the clay is fluctuated greatly, up to 5%.

Properties and applications of fused cast AZS

Fused cast AZS block is the most widely used fused cast refractory brick. According to the ZrO2 content, it can be divided into 33#, 36# and 41#AZS.
Fused cast AZS containing 33% ZrO2 is called 33# fused cast AZS; fused cast AZS containing 36% ZrO2 is called 36# fused cast AZS; fused cast AZS containing 41% ZrO2 is called 41# fused cast AZS.
Fused cast AZS is mainly composed of baddeleyite and corundum and their eutectic crystals. High viscosity glass phase is filled in the gaps of crystals. The crystals is directly precipitated from the molten liquid and well developed. So, it has large crystal particles and stable crystal phase. Except the voids, it has compact structure and better density than the common sintered bricks. The pores are mainly closed pores and the crystals are intertwined each other, so it has good mechanical properties and wear resistance. The impurities are difficult to invade the bricks. Therefore, this refractory brick has good corrosion resistance. besides, the transformation of ZrO2 at 900~1150℃ when heating or cooling may cause irregular deformation.
Fused cast AZS block can be used in areas in direct contact with molten metals and molten slags. It is the essential material used in the key areas that suffer from severe corrosion.

How to Store Ceramic Fiber Board

Ceramic fiber board is a high-strength refractory fiber board made of ceramic fiber. It is an essential high temperature refractory material. Ceramic fiber board must be stored properly to fulfill its high temperature properties.
Ceramic fiber board is made of ceramic fiber cotton by vacuum forming. It has tough texture, high strength, superior high temperature performance, excellent support force, good tensile strength and impact resistance. Its strength is better than the fiber blanket and vacuum formed felt. It will be gathered together when contact with water and its hardness will be decreased. In this case, it is easy to fall off when touched. So, waterproofing is very important for the storage of ceramic fiber board.
Ceramic fiber board should be stored in dry circumstances with no water and moisture. The building should be watertight and kept dry. Ceramic fiber board should have waterproof plastic film inside and be covered with cartons and placed on the ground with pallets. It should be placed on pallets without contact with the ground, at least 20 mm away from the ground. In the rain season, ceramic fiber products should be covered with a waterproof canvas. Pay attention to water leakage if it is stored in iron house.

The difference between refractory bricks and insulation bricks

As their names imply, refractory brick is used to withstand high temperature and flame, while insulation brick is used to insulate and reduce heat loss. The insulation bricks seldom directly contact flame, while refractory bricks can directly contact flame. Both have their advantages and are used in different parts of furnaces.
Insulation bricks always have thermal conductivity between 0.2-0.4 w/m.k (350±25℃), while refractory bricks have thermal conductivity above 1.0w/m.k(350±25℃). So, insulation bricks have better insulation performance than refractory bricks. the refractoriness of insulation bricks is usually under 1400 degree, while that of refractory bricks is above 1400 degree. insulation bricks are generally lightweight materials with a density between 0.8-1.0g/cm3, while that of refractory bricks is above 2.0g/cm3.
Refractory bricks have better mechanical strength, long service life and better chemical stability. They do not react with batch materials. They have better high temperature performance and can withstand high temperature up to 1900℃.
Refractory bricks and insulation bricks are quite different. Their applications and functions are quite different. It is important to select the right materials according to the actual conditions.

How to Select Insulation Bricks

The use of insulation bricks in the thermal equipment can greatly reduce the heat loss and the weight of furnaces and improve the thermal efficiency and labor productivity.
For most thermal equipment, in order to save energy and improve the working conditions, insulation is necessary. However, for some equipment, insulation is not necessary, given the pros and cons of insulation. Therefore, the actual conditions and the properties of insulation bricks should be taken into consideration when selecting the right insulation bricks.
The insulation bricks can be divided into the following types:
1) Fire clay insulation brick GB/T 3994-2005
2) High alumina insulation brick
3) Mulite insulation brick
The principles for selecting insulation bricks include:
1) It should not affect the service life of the entire refractory masonry;
2) For continuously working high temperature furnaces, generally large area insulation is reasonable and can reduce the heat loss. However, for some special areas such as the open hearth roof, insulation may reduce the service life. For periodically working furnaces, regenerative heat loss is the main factor of heat loss. Insulation may increase the temperature of masonry and increase regenerative heat loss. So, whether periodically working furnaces should be insulated is determined after calculating the heat storage and heat loss.
3) Since the insulation bricks have high porosity, they cannot withstand too much load and should not directly contact the molten metals, molten slags and high-temperature dust.
4) Insulation bricks have low strength. The brick joints and expansion joints should be properly disposed avoid the damage caused by volume expansion. Insulating firebrick should not be subjected to intense mechanical vibration, shock and friction;
5) Since insulation bricks have big reheating linear shrinkage, the maximum working temperature should be 100℃ less than the firing temperature.