Analysis on the Aging Mechanism and Conditions of Brick-making Raw Materials | Brick and Tile Technology
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The meaning and principle of aging. In the natural environment, the excavated brick-making block raw materials are weathered by wind, sun, rain and accumulation of "stuffy hair", so that the process of further dredging the large blocks is the first step of aging. The raw materials are forcibly crushed by machinery, and the raw materials are further reduced from large particles. After being mixed with water, they are placed in a silo for static storage. At the same time, the particles are forcibly damaged by external force, the stress of the particle itself and the existence of cracks, under the action of water molecules, the stress concentration is "expanded" by water molecules through capillary action and cracking, the large one becomes smaller, and gradually becomes smaller. At the same time, the particle itself is moistened by water. Mechanism is due to the water O-H bond bond energy is slightly stronger than the mineral crystal intermolecular force between the destruction of the crystal connection; the smaller the individual particle size, the larger the surface area, and the water molecules of the contact surface is also larger, the number of hydrogen bonds of water molecules and the number of crystal molecules in contact with the more, so the object is ease.
Why does the viscosity of raw materials increase after aging? Because the internal molecules of mineral crystals are affected by the force of surrounding molecules, the energy is low; and the surface water molecules are less in contact with the surrounding molecules, but the energy is higher, so the surface energy is large, the adsorption force is stronger, and the viscosity increases.
Necessary Conditions for 2. Aging
Grain size gradation of raw materials into the warehouse, moisture content (moisture) of raw materials into the warehouse, static time in the warehouse, and indoor temperature of the aging warehouse.
Based on the mechanism and practical experience of material aging, the author thinks that the selection basis of the grain size of raw materials into the warehouse is: firstly, according to the types of raw materials and the varieties of bricks, when shale is the main type and load-bearing bricks (blocks) are produced, more large particles should be used as the skeleton; When raw materials with higher hardness are used as the leading raw materials and non-load-bearing bricks (blocks) are produced, less large particles are required, relative increase in the number of filled particles (about 1mm), the number of bonded particles strive to increase (the pursuit of the particles will increase the wear and power consumption of the equipment; reduce production). After crushing and mixing with water (mud), some larger particles become smaller particles after absorbing water, and gradually form bonded particles, which is conducive to the production of molding.
The water content of the material after crushing and mixing is the mud material, and its moisture content is determined by the requirements of the molding production process, and is not greater than the moisture content of the molded product. In particular, the current process requirements of the hard plastic brick extruder, when the moisture content of the clay is higher than the molding requirements, the product is deformed, especially the brick (bottom layer) blank of the layer directly in contact with the kiln car table is seriously deformed, forming waste products and residual bricks. According to practical experience, the moisture content of the mud is 2-3 percentage points lower than the moisture content required for molding, which can meet the capillary action of the water when the mud is "stuffy.
The rest time of the raw material in the silo. The principle of determining the best aging time of raw materials, by determining the relationship between the deformation ratio and time (days, hours) of brick-making raw materials after aging, when the time T (days, hours) is the abscissa axis, the deformation ratio a is the ordinate axis, and the connecting points are drawn into the time-deformation ratio curve. The maximum deformation ratio point is found from the curve, and the time corresponding to the cover point is the best aging time. Through the determination of different regions and raw materials, most of them are between 40 hours and 72 hours. Some materials represented by soft shale have shorter aging time after full weathering in natural environment.
The indoor temperature of the aging warehouse. According to the working practice, I realized that the mud in the aging warehouse of the same brick factory in summer is better than that in winter. When mixing, heating water is better than adding cold water, which is beneficial to molding production. The principle is that under the condition of high temperature, the movement speed is accelerated and the material particles are more fully combined. Therefore, in the design of the aging library, the indoor temperature is different according to different geographical locations, and the winter temperature in the north usually requires 10-15°C.
There are two brick factories in a certain place, one of which is an individual brick factory and the other is a state-owned brick factory. The two brick factories are 7 kilometers apart. There are state-owned brick factories first and then individual brick factories. The raw materials used are consistent. It is mainly coal gangue, supplemented by shale.
Production process of individual brick factory:
Tearing and mixing → coarse breaking → fine breaking, sieving → forming and extruding → drying → roasting → finished product.
state owned brick factory production process:
Retaking and mixing → coarse breaking → fine breaking, sieving → adding water and stirring → belt conveying into aging warehouse → forming and extruding → drying → roasting → finished product.
The two processes are different: one has an aging library, and the other has no aging library to save money. The effect is that the state-owned brick factory has reached the standard of production, while the individual brick factory has repeatedly visited the state-owned brick factory to ask for advice and tell: the same raw materials have also secretly employed your post workers, and the molding output cannot be increased. even if there are bricks, the finished bricks burned after drying are not as good as yours; in order to increase the molding output, the replacement frequency of hammers is increased from the particle size of raw materials, and the aperture of the screen is reduced. Only the molding output is increased, but the cost of raw materials is increased by 5 yuan/ton. Billet quality: the appearance of the upper corner, rotten core; The bottom brick of the kiln car is deformed. Cracking after drying; The finished brick has low weatherability and compressive strength. Later, in order to strengthen the relationship between land and enterprises, he was told that an additional aging warehouse should be added to change the material performance. After the addition of its furnishings, the output and quality have been improved and the cost has been reduced.
In a word, when the raw materials are aged through the aging warehouse, the particles are disintegrated, the mud mass is loose, and the water content is homogenized, so that the water content on the surface of the particles penetrates into the inside of the particles, so that the raw materials with uneven dryness and wetness or insufficient stirring can achieve uniform water content through mutual penetration, and then the performance of the raw materials is further improved through physical and chemical changes, which is beneficial to extrusion molding production, drying and roasting, and improve the yield and quality.
