In recent years, the proportion of unshaped refractories in the whole refractory has been increasing, among which the largest increase is castables. The increase in the use of castables is mainly due to the development of low-cement and ultra-low-cement combined castable technologies.
A low-cement refractory castable with aluminate cement as a binder is usually used. Among the aluminate cement-bonded refractory castable, a considerable number of products are prone to some damage on the surface of the green body during the maintenance process after construction. Phenomenon, ranging from surface pulverization and spalling, in severe cases, it directly causes the green body to lose its bonding strength and pulverize and collapse.
Especially for large castable prefabricated blocks, it is a big loss. For example, the surface pulverization of blast furnace iron trench and slag trench prefabricated blocks is particularly serious. Therefore, in response to this phenomenon, after analyzing the damage mechanism, formulate the practical methods and countermeasures to avoid or reduce the surface damage of the castable are presented.
The solution to the surface damage of the castable
According to the existing analysis of the causes of damage to the surface of the castable, corresponding measures are taken to prevent or reduce the degree of surface damage.
1. Using high-purity raw materials
High-purity, high-density raw materials can reduce the content of soluble alkali metals. For example, refractory bauxite aggregates should be calcined in rotary kilns as far as possible, with few impurities and high bulk density, or dense corundum as aggregates. The refractory raw material is strictly controlled on the impurity content, and the addition amount is controlled as little as possible.
2. Reasonable selection of types of admixtures
Traditional castable admixtures usually use lignin calcium salt and sodium salt, which increases the alkali metal content of the castable and accelerates the reaction of hydration and decomposition. After adjustment, a new type of composite water reducing agent was tested to reduce calcium salts the addition of the admixture was strictly controlled, and the experiment was carried out in the production after the laboratory verification. The type of admixture was changed, and the optimal addition amount was achieved. The phenomenon of surface powdering of the green body was improved. 5 days extended to about a week, while the strength of the green body has also improved. The effects of different additives on the properties of castables. In this way, combined with the control of drying time, drying as early as possible to enhance the early strength, and now the surface powder of the green body has rarely occurred.
3. Control of construction water
The control of construction water quality is strengthened, and water is deposited in a large container before production as much as possible to avoid water turbidity and impurities, so as to reduce the entry of other additives that can increase the speed of cement hydration.
4. Control of construction environment
Enhance early strength in order to reduce and reduce the contact degree between the surface of the castable and the air, the method of surface covering is adopted to close the surface pores, and try to isolate the diffusion of carbon dioxide and water vapor into the castable body, thereby preventing the damage reaction. At the same time, in order to dry the green body as soon as possible, the thermal insulation of the workshop is strengthened, and if necessary, the green body is put into a low-temperature kiln to be dried and then demolded, so that the green body can be hardened within the optimal curing period of 36h to ensure the strength of the casting body.?
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Article Source:Solutions to surface damage of low cement refractory castables
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