Discussion on the phenomenon of melting and boiling in medium frequency induction heating furnace

(1) The difference between boiling furnace and frying furnace

Boiling furnace refers to the phenomenon of violent boiling of liquid steel due to various reasons during the melting process of the medium frequency induction heating furnace. The phenomenon is that molten steel continuously gushes out of the furnace body with a slight explosion. The phenomenon is similar to that of volcanic eruption of molten lava. The reason for the frying furnace is that the added charge contains water. When the charge is immersed in the molten steel, the water vaporizes at a high temperature of about 1000°C, and the gas generated cannot expand in the space of the metal liquid, and then a blast occurs. Explosion takes the molten steel out of the furnace. Frying furnaces are instantaneous, while boiling furnaces last for a long time. Both are destructive and dangerous to a certain extent.

(2) Three boiling furnace phenomena

①The first boiling furnace

a. Phenomenon and causes: When the charge added to the furnace is rusty and has not been baked, it is easy to cause a boiling furnace. Such furnace accidents often occur due to operator carelessness or failure to follow operating procedures. When the corroded and unbaked charge is added, the molten steel immediately boils and continuously gushes out with a slight explosion sound. After the boiling furnace is stopped, more than half of the molten steel in the furnace body is overflowed, and the overflowing molten steel is seriously oxidized. It can be seen that the boiling of molten steel has a huge and long-term power and a large amount of oxidizing gas exists.

We analysis believes that this is because the form of oxygen in the molten steel is different from that of hydrogen and nitrogen. It does not exist in the form of atoms, but in the molecular form of it and iron oxides. In molten steel, there is a certain balance between the carbon content and the ferrous oxide content.

b. Solution: In actual production, the process requirements must be strictly followed, and the charge added must be baked and free of rust. Once such a boiling furnace occurs, the power should be cut off immediately to prevent the overflowing molten steel from short-circuiting the induction coil, causing damage to the equipment or a greater accident. After the power is turned off, add an appropriate amount of deoxidizer into the furnace and cover the liquid surface with slag remover to alleviate the occurrence of this reaction. If the boiling furnace is relatively violent, the molten steel can be poured directly into the furnace pit if necessary.

②The second type of boiling furnace

a. Phenomenon and causes: When the added charge contains low melting boiling point metals and their compounds, it is also easy to cause boiling furnace phenomena. This is because when these low-melting boiling point metals and their compounds are immersed in the molten steel, the temperature of the liquid steel at this time is relatively high (generally 1450~1500°C), which will immediately cause the metal and its compounds to vaporize. Or decompose, thereby producing a large amount of gas and colored flames on the surface of the molten steel. This reaction generally lasts for a short time and occurs on the upper surface of the molten steel, so the molten steel is generally not taken out of the furnace. The materials that cause this kind of boiling furnace are generally small scraps. Since it is difficult to distinguish these materials containing low-melting boiling point metals and their compounds when recycling metal scraps, these materials are easily mixed with small and miscellaneous materials. ingredients. Another situation is that the surface is coated with low-melting boiling point metal profiles, such as galvanized pipes. When this kind of material is returned to the furnace, it is easy to cause boiling furnace.

b. Solution: If you need to melt small materials or scraps during the smelting process of the medium frequency induction heating furnace, you should first place the small materials and miscellaneous materials at the bottom of the furnace body when adding materials. Since heating is relatively slow when melting begins, metals with low melting boiling points and their compounds will slowly decompose or vaporize, and will not cause violent reactions like those that are immediately added to the molten metal.

③The third type of boiling furnace

a. Phenomenon and causes: The third type is boiling furnace caused by furnace penetration, which is rare. When certain parts of the furnace wall are seriously eroded by molten steel, the molten steel can easily penetrate the furnace during the smelting process. The molten steel passing through causes a short circuit between the two layers of induction coils, causing the induction coil to be broken down. Since there is 0.2~0.3MPa cooling water in the induction coil, the cooling water enters the furnace body under such pressure. The temperature of the molten steel in the furnace body is relatively high. The water that has just entered is not enough to cool the molten steel, but is vaporized by the molten steel. A large amount of water vapor is formed, causing a boiling furnace. If the water pressure is not high or the amount is small, it will easily cause the furnace to explode.

b. Solution: Furnace lining should be continuously inspected and repaired during production. During discontinuous operation, before starting the cold furnace, a detailed check should be made on whether the furnace top, walls and bottom need to be repaired. During continuous melting, every time steel is tapped, the furnace top should also be observed to see whether the furnace bottom needs to be repaired. Cracks less than 2mm do not need to be repaired. Cracks exceeding 2mm need to be repaired. First remove the surrounding slag, put the paper containing furnace repair materials at the lower end of the crack, use a U-shaped iron needle to squeeze the material into the crack, and then use The water glass furnace building material is extruded and smoothed on the surface to prevent furnace penetration accidents. The boiling furnace phenomenon is generally caused by unqualified furnace materials or irregular operation. No matter which kind of boiling furnace, it can be prevented in the actual production process. This requires that the process operating procedures must be strictly followed during production. Once the boiling furnace phenomenon occurs, the power should be cut off immediately, a deoxidizer (preferably a strong deoxidizer) should be added, and the liquid surface should be covered with a slag remover. If necessary, the molten steel should be dumped into the furnace pit to prevent larger accidents.