High-alumina bricks can be used in all major high-temperature furnaces. Today, I will introduce the application of high-alumina bricks and other refractory materials in electric furnaces. Box furnace is a kind of electric furnace, with high temperature in the furnace, large changes in atmosphere and short smelting cycle. Furnace lining damage factors Electric arc furnace lining is often in the state of high temperature, slag erosion and rapid cold and heat, and the working conditions are extremely harsh. During the melting period, the charge has a strong heating capacity, and the electric arc is enveloped by the scrap steel for a long time. In the oxidation period, the molten steel boils violently, and the slag molten steel has better heat absorption conditions. Therefore, generally speaking, in these two stages, the furnace lining will not be damaged by high temperature. During the reduction period, the temperature of the steel slag is quite high, and it is directly radiated by the electric arc. Some hot spots of the furnace wall are particularly prominent, and the furnace lining is easily damaged. In addition, the temperature of the furnace lining suddenly drops when the steel is discharged and the material is charged. After the material is charged, the power is transmitted, and the temperature slowly rises. This rapid temperature change is often the direct cause of the furnace lining spalling.
The corrosive effect of slag on the furnace lining is determined by its composition and fluidity. The higher the SiO2 content in the slag, the more severe the alkaline furnace lining will be corroded. In addition to SiO2, Al2O3, Fe2O3, CaF2, etc. in the slag also corrode the furnace lining. The fluidity of the slag also affects the furnace lining. The thin slag has a serious effect on the lining erosion, and the ability to reflect the arc is strong, which will increase the heat load of the furnace lining; thick slag makes it difficult to heat the molten pool, deteriorates the physical and chemical reaction conditions, and prolongs the high temperature action time of the lining (I.e. smelting time). These will accelerate the damage of the furnace lining.
In many cases, the damage of the furnace lining is caused by the impact of mechanical force, such as unreasonable cloth, no small scrap steel protection at the bottom of the furnace, and too high charging tanks. In these cases, the furnace bottom may be smashed into pits by large pieces of scrap steel. The mechanical vibration caused by the lifting of the furnace cover and the opening of the furnace body is also the cause of damage to the furnace lining.
In addition, improper proportion of the furnace charge and incorrect smelting operation, such as direct contact of the high-temperature oxygen stream with the furnace lining during oxygen blowing, will damage the furnace lining.
Therefore, the refractory of the box furnace should have high refractoriness and softening point under load, good thermal shock stability and slag resistance, sufficient high temperature mechanical strength and low thermal conductivity. Siliceous refractories are generally used when building acid arc furnaces, while magnesia refractories are used in alkaline arc furnaces. However, most of the furnace tops use high alumina bricks, and seldom use silica bricks.
Furnace roof damage mechanism The service life of silica bricks on the furnace roof is very low, which is mainly due to the higher smelting temperature. In addition to being subjected to the effects of slag and smoke, the spalling phenomenon is also one of the main reasons for its damage. Due to the appearance of cracks and the peeling of the bricks, the contact between the bricks and the slag is increased, thereby accelerating the penetration of the molten slag into the bricks, forming many channels, which is the so-called deep damage.
After the alkaline furnace top for smelting high-grade alloy steel is changed to high-alumina bricks, the service life is much longer than that of baby bricks. The service life of silica bricks is the furnace age, generally only a few dozen furnaces, while high alumina bricks can reach 80-200 furnaces, and small electric arc furnaces can reach more than 600 furnaces. At the same time, due to the high refractoriness of high alumina bricks, the smelting strength can also be improved.
Proper operation of box furnace:
1. Equipment inspection: Before starting the furnace, make a comprehensive inspection of the equipment to check whether there are tools or other conductive materials in the electrical control box. If there are any forgotten workpieces in the furnace, it should be removed in time, especially the wiring posts of electric heating elements. Ensure that there is no looseness, and the safety shield must be complete and effective. Special personnel should be responsible for the inspection of electrical appliances and instruments. When it is confirmed that there are no hidden dangers in the equipment, the furnace is allowed to start work.
2. Furnace start-up: adjust the temperature control indicator of the temperature control instrument to the position required by the process, then turn on the main power switch of the equipment, turn on the switch of the instrument and the heating furnace, and the furnace begins to heat up to the process temperature. After the heating furnace is raised to the process temperature, the temperature shall be measured and adjusted according to the requirements of the temperature adjustment technical regulations. When adjusting the temperature of the instrument, pay attention to the table temperature=furnace temperature-correction value.
3. Furnace installation: The amount of furnace installation varies according to the structural characteristics of the parts and the batch size. The number of furnaces installed is determined according to the size of the effective heating zone.
4. Out of the furnace: it can be out of the furnace after sufficient heat preservation according to the process requirements. Pay attention to cut off the heater's power when the furnace is out, and remove the parts in the furnace to prevent accidents such as burns.
