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Explosion-proof performance and other properties of castables

Words:[Big][Medium][Small] Mobile Page Two-Dimensional Code 2018-10-15     

          

At present, high-performance castables are generally added with hydraulic cement and some fine powder. About 6% of water is added during the construction process, so that there is a large amount of free water and crystal water in the masonry. How to safely and quickly remove the moisture in the refractory castable has always been a difficult problem in masonry baking. The water in the castable exists in three ways: free water, adsorbed water, combined water. Among them, free water and adsorbed water account for the majority, and free water can be removed when heated to 110 ° C. The adsorbed water is mainly a water film formed on the surface of the fine powder by a water reducing agent, and evaporates at about 180 ° C. The crystallization water is mainly crystal water in CAH10, C2AH8, C3AH6 and AH3 formed by cement hydration, and can be generally removed at about 250 °C. Hydrates, especially gibbsite, emit a large amount of gas during the drying process, which is prone to bursting. In order to reduce the occurrence of bursting, the temperature can be slowed down in the free water stage for a longer period of time, ensuring the formation of fine through pores inside the body to ensure the smooth escape of the adsorbed water and the crystal water.


 The general baking system, particle grading, type of anti-explosive agent and the amount of addition will affect the explosion-proof performance and other properties of the castable.

1. Baking system: In order to improve the operation rate and production efficiency of equipment, some manufacturers reduce production costs, thereby shortening the construction, curing and baking time of castables. If there is no good baking system, the castable is prone to bursting during the baking process. The general low-cement and ultra-low cement castables introduce a large amount of fine powder, which is filled with many small voids, which makes the castables have high compactness and low gas permeability, which makes it difficult to discharge water vapor generated inside the masonry during baking. The inside of the castable forms an environment of high temperature and high pressure. In this environment, a hydration reaction occurs, and AH, which is more difficult to remove water, is formed. If the baking time is shortened at this time, a large amount of water vapor is not discharged, which is absolutely fatal to the castable. Therefore, according to the existence of water in the castable, it is the key to formulate a reasonable baking system. Generally, the baking section of low-cement and ultra-low cement castables is room temperature to 110 ° C, 110 ° C to 180 ° C, and 180 ° C to 250 ° C. In the early stage of free water dehydration, the heating rate should not be too fast, generally increasing at a rate of 10 to 20 ° C / h, separating free water at about 110 ° C, adsorbing water at about 180 ° C, crystal water at about 250 ° C, 110 ° C and 180 ° C. The two time points should be kept for a period of time, and the temperature should be kept at 40 to 50 hours at these two temperature points; in consideration of the heat transfer resistance in the thickness direction, the temperature is raised to 350 ° C to be kept warm again.


2, particle grading: self-flow castables, pumpable castables and vibrating castables have different particle gradations, and the aggregate gradually increases. Since the matrix-aggregate interface is porous and gas permeable, its thickness is comparable to that of the fine material. In the absence of fibers, as the aggregate gradually increases, the air permeability of the material gradually increases.

Hard fiber, softening point is about 105 ° C ~ 120 ° C, poor dispersion. Therefore, PP fibers will be distributed in parallel under vibration, and the bridging effect is not good; the melting point is high, the free water stage, the fiber shrinks but not completely carbonized, the pores increase but it does not open, the free water is still difficult to discharge; the dispersion effect is poor, so More water must be added to ensure fluidity, and water is added more. The porosity of the castable increases and the performance is reduced. On the other hand, many fibers aggregate together to cause an increase in pores in a certain part, and the performance is also reduced. The PVA fiber produced in Japan has a finer fiber diameter, and the pore diameter left after shrinkage is smaller, which is good for slag resistance. Better dispersion, easy to disperse evenly in the castable. The unique hydrophilicity and water solubility have little effect on the fluidity of the castable. During the free water removal of the castable, shrinkage has begun, and the air permeability has been improved; the amount of dewatering after baking at 110 ° C is increased by nearly 20%, and the baking safety is improved. In the absence of fiber, as the aggregate gradually increases, the air permeability of the material gradually increases.


3, anti-explosive agent In order to reduce the risk of baking in the baking process, the addition of anti-explosive agent is an important way. At present, the explosion-proof agents used in the market are mostly classified into the following categories: metal aluminum powder, organic explosion-proof agent and organic fiber.


1) Metal aluminum powder is widely used as an anti-explosive agent and an antioxidant at home and abroad. The principle of explosion protection of metal aluminum powder is:

2Al+2OH-+6H2O→2[Al(OH)4]- +3H2↑

However, once the control is not good, it is easy to cause the casting body to bulge and crack, resulting in a decrease in structural strength. This is because the amount and speed of the reaction of the metal aluminum powder in the castable have a great relationship with the activity, fineness, purity of the aluminum powder, the hardening of the binder, the ambient temperature and other process factors, and it is difficult to produce. control. At present, metal aluminum powder has been gradually replaced by organic fibers.


2) The most commonly used organic anti-explosive agents are azocarboxamide and aluminum lactate. Azoformamide liberates a N2-based gas under the combined action of cement and water. When the gas escapes, fine open pores are formed inside the castable. The specific reaction formula is: C2N4H4O2+Ca(OH)2+2H2O→Ca(C2N2O4)+2NH4OH;3Ca(C2N2O4)+3H2O→2N2↑+3CO2↑+3CaCO3+2NH3↑ aluminum lactate is added to the castable in solution state During the curing process, the matrix gels to produce a turtle-like crack, which improves the gas permeability of the castable.

3) Organic fiber Organic fiber has many excellent properties as an anti-explosive agent, and has gradually replaced metal aluminum powder as the most popular anti-explosive agent on the market. There are two kinds of the most popular organic fibers on the market, one is a conventional polypropylene fiber (PP fiber), and the other is a hydrophilic polyvinyl alcohol fiber (PVA fiber). Both of them are dissolved or melted to increase the micropores in the castable, thereby increasing the permeability of the castable. The PP fiber is a needle-like hard fiber, and the softening point is about 105 ° C to 120 ° C, and the dispersibility is not good. Therefore, PP fibers will be distributed in parallel under vibration, and the bridging effect is not good; the melting point is high, the free water stage, the fiber shrinks but not completely carbonized, the pores increase but it does not open, the free water is still difficult to discharge; the dispersion effect is poor, so More water must be added to ensure fluidity, and water is added more. The porosity of the castable increases and the performance is reduced. On the other hand, many fibers aggregate together to cause an increase in pores in a certain part, and the performance is also reduced. The PVA fiber produced in Japan has a finer fiber diameter, and the pore diameter left after shrinkage is smaller, which is good for slag resistance. Better dispersion, easy to disperse evenly in the castable. The unique hydrophilicity and water solubility have little effect on the fluidity of the castable. Pouring

During the free water removal of the injection, shrinkage has begun, and the air permeability has been improved; the amount of dewatering after baking at 110 °C is increased by nearly 20%, and the baking safety is improved.



       The length of the organic fibers also has an effect on the gas permeability of the castable. For castables with different particle sizes, different lengths of organic fibers should be used. The distance between the particles of the pumpable castable and the particles is long, and long fibers are required to increase the air permeability. The short fibers have little effect on the gas permeability; for the vibration castable, the short fibers can also significantly improve the gas permeability of the castable. Hard fiber, softening point is about 105 ° C ~ 120 ° C, poor dispersion. Therefore, PP fibers will be distributed in parallel under vibration, and the bridging effect is not good; the melting point is high, the free water stage, the fiber shrinks but not completely carbonized, the pores increase but it does not open, the free water is still difficult to discharge; the dispersion effect is poor, so More water must be added to ensure fluidity, and water is added more. The porosity of the castable increases and the performance is reduced. On the other hand, many fibers aggregate together to cause an increase in pores in a certain part, and the performance is also reduced. The PVA fiber produced in Japan has a finer fiber diameter, and the pore diameter left after shrinkage is smaller, which is good for slag resistance. Better dispersion, easy to disperse evenly in the castable. The unique hydrophilicity and water solubility have little effect on the fluidity of the castable. During the free water removal of the castable, shrinkage has begun, and the air permeability has been improved; the amount of dewatering after baking at 110 ° C is increased by nearly 20%, and the baking safety is improved. The length of the organic fibers also has an effect on the gas permeability of the castable. For castables with different particle sizes, different lengths of organic fibers should be used. The distance between the particles of the pumpable castable and the particles is long, and long fibers are required to increase the air permeability. The short fibers have little effect on the gas permeability; for the vibration castable, the short fibers can also significantly improve the gas permeability of the castable. .


       For high-performance castables such as low-cement and ultra-low cements, increasing the air permeability is the principle of improving the explosion-proof performance. Adopting a reasonable baking system, reasonable particle grading, and adding hydrophilic explosion-proof fibers are effective methods to improve the explosion-proof performance of baking.



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