Silica brick is the most commonly used and most important type of brick in various types of glass kilns. Silica bricks are mainly used in the ceiling, parapet, end wall, small furnace and regenerator ceiling of the upper space of the glass melting furnace. The raw material for the production of silica bricks is mainly crystalline quartzite. A small amount of iron oxide and calcium oxide are added as mineralizers to promote tridymite as much as possible and keep it firing in a stable temperature range. The SiO2 content of silica bricks is 93% The lower limit is 96%~98% for high-end products.
Silica brick has high structural strength at high temperature, such as high softening point under load (1640~1700℃) and low creep rate [1550℃-50h-0.2MPa-(6~7)×10-5], and it absorbs a small amount The alkali component does not reduce the structural strength of the kiln roof except for very slight erosion.
The main disadvantage of silica bricks is low thermal shock resistance.
The firing of silica bricks is a key link in the entire production process of silica bricks. During firing, we must strive to complete the phase change process to the greatest extent, to form an ideal microstructure and have better performance.
According to the phase transition characteristics of quartz, the following stages should be controlled during firing:
(1) The 500~700°C stage is the range where β-quartz transforms to α-quartz, and the volume expansion is 0.82%. Calcium hydroxide decomposes and solid-phase reaction with the surface of the quartz particles produces CS.
(2) In the range of 800~1000°C, a small amount of liquid phase can be generated under the action of the mineralizer. According to the measurement result of the electronic dilatometer, there is a slight shrinkage at this stage, and the firing at this stage is still relatively safe.
(3) The temperature range above 1250℃ is the generation stage of metastable cristobalite. For quartz, there will be about 15% volume expansion, and the heating rate will be slowed down as much as possible, but the amount of liquid phase will gradually increase, which will be slightly balanced. Volume effect.
(4) 1350~1450℃ is the massive crystallization stage of tridymite. The transformation from α-quartz to tridymite will have a volume expansion of 16.0%, but quartz cannot be directly converted into tridymite, but it is transformed into tridymite by metastable cristobalite. For tridymite, the volume effect of this phase change is not large. However, the heating rate must be controlled at this stage because: (1) The phase transition from quartz to metastable cristobalite still occurs at this stage. ② Sufficient time should be given to ensure that tridymite crystallizes as completely as possible. Therefore, the firing and holding time at the stage above 1350°C is very important to perfect the formation of the microstructure and obtain the best high-temperature volume stability.
Depending on the production method and use conditions, the performance requirements of silica bricks are different. YB/T 147-2007 Silica brick for glass kiln divides the silica brick for glass kiln into three grades: BG-96A, BG-96B and BG-95 according to the physical and chemical performance indexes. Its physical and chemical indexes, allowable size deviation and appearance are shown in Table 1
The standard also makes the following provisions on appearance:
① When the crack crosses the edge, only one edge is allowed to cross, and the cross-edge cracks are not calculated together.
② Cracks on the silicon brick parallel to the working surface: the length is not more than 1/5 of the length of the common edge between the crack surface and the working surface.
③Spalling: bricks with a unit weight of not more than 20kg are evaluated according to the crack index of the working face; bricks with a single weight of more than 20kg are evaluated according to the crack of the non-working surface.
④For bricks with a single weight of more than 40kg, the technical conditions shall be negotiated between the supplier and the buyer.
Wechat Us 
