The manufacturing process of silica bricks is generally similar to that of clay bricks. The difference is that the former increases the preparation system of lime and mineralized.

The choice of particle composition

The loosening and sintering ability of the siliceous body when heated depends on the nature and number of the coarse and fine particle sizes in the particle composition.

When the brick body composed of fine particles is used, it is beneficial to reduce compression during firing, reduce cracks and volume changes in the brick body, improve the yield, and also increase the content of tridymite in the finished product, but the fine particles of the mud will also lead to silicon dioxide. Advances in brick porosity.

Generally, the critical particle size of silica brick is 2-3mm.

Manufacturing process of silica bricks

1. Forming:

The siliceous billet is a barren material with low hardness, low cohesion and plasticity, so its ability to be compacted under pressure is low. The molding machine of siliceous blanks is affected by its particle composition, moisture and additives. Adjusting these components can improve the forming performance of the blank. For any composition of the blank, increasing the molding pressure will increase the density of the silica brick. In order to ensure the dense brick body, the molding pressure should not be lower than 100 ~ 150MPa.

2. Firing

Silica bricks undergo a phase change during the firing process, and there is a large volume change. In addition, the amount of melt formed by the brick at the firing temperature is small (about 10%), making it more difficult to fire than other refractory materials. Much more valuable. The firing system of silica bricks has nothing to do with a series of physical and chemical changes during the firing process of the bricks, the number and properties of the components, the shape and size of the green body and the characteristics of the firing kiln.

3. The physical and chemical changes of silica bricks during the firing process are below 150℃. When the residual water is squeezed out of the bricks at 450℃, Ca(OH)2 begins to decompose. The combination of silica particles and lime is damaged, and the strength of the green body is greatly reduced. In the range of 550-650 °C, -quartz changes to α-quartz, because the change process is accompanied by 0.82% volume compression, so the quartz crystal will show microscopic cracks with different densities.

Between 600 and 700 °C, the solid phase response of CaO and SiO2 begins, and the brick strength increases. The response formula is:

2CaO+SiO2→-2CaO·SiO2

2CaO·SiO2+SiO2→2(CaO·SiO2)

To 1000 ~ 1100 ℃, there are solid solution α-CaO·SiO2 and FeO·SiO2 born.

α-CaO·SiO2+FeO·SiO2→[GaO·SiO2—FeO·SiO2]

From 1100°C, the rate of change of quartz increases greatly, and the density of adobe also decreases significantly. At this time, the volume of adobe increases greatly due to the change of quartz to a low-density variant. Although the amount of liquid phase is also increasing at this time, cracks are still prone to occur in the range of 1100-1200 °C.

At 1300-1350 °C, the density of the adobe is much lower due to the increase in the number of tridymite and cristobalite. At this time, the viscosity of the liquid phase is still large, the resistance to internal stress is still weak, and the possibility of natural cracks exists. When heated to 1350 ~ 1430 ℃, the change level of quartz and the resulting compression of the brick body are greatly enhanced. In this temperature range, the slower the heating, the more tridymite produced by the quartz dissolving in the liquid phase and recrystallization, the less natural amount of cristobalite, the less likely the brick body is born with cracks. If the heating is too fast, especially in an oxidizing atmosphere, the quartz will be changed into cristobalite, which will loosen the adobe and cause cracks.

4. Burning rail system

Below 600°C, it can be fired at a faster and average heating rate. In the temperature range above 700 ° C to 1100 ~ 1200 ° C, due to the small change in the volume of the brick, the strength gradually increases, and there will be no excessive stress. It is only necessary to ensure that the brick is heated evenly, and the temperature can be raised as soon as possible.

In the high temperature stage from 1100 to 1200°C to the final firing temperature, the density of the silica brick is significantly reduced, and the crystal change and volume change are concentrated in this stage. It is the critical stage that determines whether the adobe is cracked or not. At this stage, the heating rate should gradually decrease, and the average heating should be slowed down.

In order to make the temperature slow and evenly rise in the high temperature stage, the weak recovery flame is usually used for firing during production. At the same time, it can evenly distribute the temperature in the kiln, reduce the difference between high and low temperatures in the kiln, prevent the high temperature flame from hitting the bricks, and achieve the firing requirement of "soft fire" (average intense fire firing).

The maximum firing temperature of silica brick should not exceed 1430℃.

After the silica brick is fired to the highest firing temperature, sufficient heat preservation time is usually given according to the shape and size of the finished product, the characteristics of the kiln, the difficulty of changing the silica, and the required density of the finished product. The cooling after firing of silica brick can be rapidly cooled at high temperature (above 600-800 °C). At high temperature, due to the rapid crystal form change of cristobalite and tridymite, volume compression occurs, so it should be cooled slowly.

When determining the firing curve, in addition to meeting the above requirements, it should also consider:

1) The heating property of the material;

2) The number and nature of the participants;

3) The shape and size of the bricks. Other factors such as the layout, size, installation method of the kiln, and temperature distribution in the kiln are all affected.

The firing heating rate can generally be divided into the following stages;

Temperature scale, °C Heating rate °C/h

20～600              20

600～1100         25

1130～1300      10

1300～1350       5

1350～1430       2