Silicon brick molding process and production considerations
Author: haloong Time: 2019-03-12 14:19
Silica brick belongs to the acid refractory material, good resistance to acid corrosion performance, its function of thermal conductivity, high load hardening temperature, generally above 1620 ℃, only 70 ~ 80 ℃ lower than the refractoriness.The thermal conductivity of silica brick increases with the increase of working temperature without residual compression. In the process of drying, the volume of silica brick increases with the increase of temperature.
The raw material for making silica brick is silica stone.The higher the SiO2 content of silica, the higher the refractory.The most harmful impurities are Al2O3, K2O, Na2O, etc., which seriously reduce the fire resistance of refractory products.Silica brick is made from silica with SiO2 content of not less than 96% by adding mineralization agent (such as iron scale and lime milk) and binder (such as molasses and sulfite pulp waste liquid), through mixing, molding, drying and burning processes.
The production process of silica brick is similar to that of other refractory bricks in general. The difference is that the former increases the preparation system of lime and mineralizing agent.
Ⅰ.Selection of particle composition
The porosity and sintering ability of siliceous body depend on the nature and number of particle size.
The use of fine granule composition of the brick, when burning is conducive to reduce the contraction, reduce the brick body crack and volume change, forward product rate, but also forward products in the content of quartz scale, but fine particles, will also lead to the silica brick porosity forward.
The critical particle size of silica brick is 2 ~ 3mm as usual.
The characteristics of silica brick forming are as follows: the blank forming characteristics of silica brick, the complicated appearance of silica brick and the great difference in quality. Silica billet is hard, joint and low plasticity of fine materials, it is compressed and the ability to low. The shaping machine of the silicon billet can be affected by its grain composition, moisture content and its components. The adjustment of these factors can improve the blank forming machine. For any blank formed, increasing the molding pressure affects the density of the bricks. In order to produce fine bricks, the forming pressure shall be no less than 100 ~ 150MPa.
In the process of firing, the phase transformation of silica brick occurs, and there is a large volume change, and the amount of molten liquid formed by the brick at the firing temperature is less (about 10%), which makes it much more difficult to be fired than other refractories.
The physical changes in the firing process of silica brick show different states at different temperatures, and the firing system should be strictly followed to reduce the generation of cracks.at the same time,In drawing up the firing curve, in addition to the above request should be consistent, should also be considered
1)Heating properties of materials
2)The number and nature of the participants
3)The overall size of the brick. Other such as the layout of the kiln, size, method of kiln installation, kiln temperature distribution are affected.
Like most sintered refractory bricks, silica bricks are produced by semi-dry process and fired in tunnel kilns. In the next article, the author will analyze the types and causes of cracks in the finished silica brick, and show that the formation of cracks can be reduced and the product quality can be significantly improved by strictly controlling the main mechanical molding and firing processes in the production of silica brick.