Maintenance and baking system of refractory prefabricated blocks
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2024-05-27
The flowability of castable materials is generally better than that of rammed materials. Therefore, most castables can be made into prefabricated blocks by simply pouring or vibrating the mixture to tightly arrange and fill the model with components.
After the casting material is formed, appropriate measures must be taken for curing according to the hardening characteristics of the binder to promote its hardening. Calcium aluminate cement should be cured under appropriate temperature and humid conditions. Ordinary high alumina cement should first be covered at a lower temperature (less than 35 ℃), and then watered or immersed for 3 days after solidification; Low calcium and high aluminum cement curing for 7 days, or steam curing for 24 hours. Some metal inorganic salts need to be dried and baked. If combined with water glass, it should be stored in the air at 15-25 ℃ for 3-5 days without being damp, and can also be baked below 300 ℃. However, it must not be cured in wet conditions, let alone watered. As the silicic acid gel absorbs water and expands, it loses its cohesiveness. After the water dissolves, its strength will decrease sharply. Phosphate producers can first be cured in air above 20 ℃ for more than 3 days, and then baked at 350-450 ℃. Before baking, it is also not allowed to be damp or soaked in water.
When precast blocks of castable are placed on the inner lining and furnace body of thermal equipment, they should generally be baked before the first use to gradually remove physical and crystalline water, so that their volume and certain properties can reach a stable state during use and achieve a certain degree of sintering. The proper sintering system has a significant impact on the service life. The basic principle of formulating a baking system is to adapt the heating rate to the possible dehydration and other phase changes and deformations that may occur. During certain temperature stages where the above changes occur rapidly, the temperature should be slowly increased or even kept warm for a considerable period of time. If the baking is improper or not done properly, it is easy to quickly heat up and put into use, which can cause serious cracks, even loose collapse, and even explosions in extremely thick areas. The baking speed of hardened bodies varies depending on the size of the binder and the cross-section of the structure. In terms of cement castables, it can be roughly divided into three stages:
(1) Discharge free water. Heat up from 10-20 ℃ to 110-115 ℃ for 24-48 hours and then keep it warm.
(2) Exclude crystalline water. Heat up to 350 ℃ at a temperature of 15-30 ℃/h and keep it warm for 24-48 hours.
(3) Uniform heating stage. Heat up from 15-20 ℃/h to 600 ℃ and keep it warm for 16-32 hours. Then raise the temperature to the working temperature at 20-40 ℃/h. For structures with larger cross-sections, the heating rate is set to the lower limit, while for insulation, the upper limit is set. For smaller cross-sections, the opposite is true.
Through this article, I believe everyone has learned about the precautions for maintenance and baking of prefabricated blocks made of casting materials. The prefabricated blocks are made of suitable materials and poured into shape. They are then lifted or installed by other methods on site, making construction convenient. Nowadays, many heating furnace roofs use the method of lifting prefabricated blocks made of casting materials for construction.
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