Ways to improve the age of medium frequency induction heating furnace

(1) Induction heating furnace structure. The structure of the induction heating furnace is the basis for ensuring the age of the furnace. The strength and stiffness of the furnace shell, coil, and furnace cover, as well as the stable assembly between them, are important factors that affect the age of the furnace. The strength and rigidity of the furnace shell and furnace cover purchased by the author's unit are obviously insufficient, the casting quality is poor, and it is easy to produce cracks and deformations; the insulating columns around the induction coil are not strong enough. Such an induction furnace structure will cause the furnace to produce It is elastic and cannot be tightened. High-temperature molten metal can easily penetrate into the gaps between the furnace lining materials. During operations such as smelting and furnace tilting, since the furnace structure cannot provide strong support, the lining is prone to cracks, eventually leading to premature failure of the furnace lining. Therefore, the original furnace body was improved, and high-strength aluminum alloy furnace shell and furnace cover were made, and stainless steel plates were used to reinforce the easily cracked parts of the furnace shell; the induction coil was re-reinforced; insulation boards, asbestos boards, and special furnace bottoms were used Bricks and furnace mouth bricks can basically ensure the stability of the furnace structure.

(2) The impact of furnace lining materials on furnace age. Quartz sand + 2% boric acid is used as furnace lining material to smelt high chromium cast iron, medium and low alloy cast steel and high alloy heat-resistant steel. The results show that due to the low strength of the sintering furnace lining, it is difficult to withstand the static pressure of the molten metal and the feeding of materials. The furnace lining is prone to failure early due to impact; in addition, when smelting heat-resistant steel, a higher furnace temperature is required, and the refractoriness of quartz sand is relatively low, making the furnace lining prone to erosion during the smelting process. Quartz sand is used as the furnace lining material, and the average furnace age is only 18 furnaces, indicating that it is not suitable for the lining material of the 1.5t intermediate frequency furnace. A mixture of 50% metallurgical magnesia + 50% fused magnesia and 2% boric acid was used as the furnace lining material. It was found that it has good resistance to high temperature corrosion, but has poor resistance to rapid cooling turbidity, large expansion and contraction, and is prone to cracks and furnace wear. The average furnace age is only 38 furnaces, which cannot meet production requirements. The use of magnesia shaped furnace bladder brings some convenience to operations such as furnace opening and oven sintering. The shaped furnace bladder is pressed by high pressure, has high density, and has better stamping performance and corrosion resistance. However, the furnace lining is prone to cracks and various horizontal and vertical cracks during use. The problem is more prominent especially in the discontinuous production mode. After cracks appear, it is difficult to repair them. It uses a fixed furnace with an average furnace age of 52 furnaces. When selecting furnace lining materials, in addition to meeting the melting quality requirements of various casting materials, the price and performance of the selected furnace lining refractory materials must also be comprehensively assessed to achieve better overall benefits. After a long period of comparison and practice, it was finally decided to use magnesia-aluminum spinel material for ramming. On this basis, through the control and improvement of other factors that affect the furnace age, the average furnace age has been increased to more than 120 furnaces, and the maximum furnace age is 153 furnaces.

(3) The impact of smelting materials and production on furnace age. The quality of the furnace charge has a great influence on the age of the furnace. The furnace charge with a lot of rust and dirt and the large amount of sand adhering to the recycled charge will intensify the erosion of the furnace lining. It should be pre-treated as much as possible before use. Among the furnace lining materials, high chromium cast iron has the least erosion effect on the furnace lining due to its low melting temperature. However, special attention must be paid to the feeding method of the recycled materials. High chromium cast iron has poor thermal conductivity and high brittleness. Cold materials are suddenly added to the molten iron. Explosion is prone to occur, especially when the material block is large, and the impact caused by the explosion is enough to cause cracks in the furnace lining. Alloy cast steel, heat-resistant steel and stainless steel require high furnace temperatures, long reduction and refining processes, and greater erosion of alkaline furnace linings, especially when smelting steel with high silicon content. During intermittent production, repeated opening and closing of the furnace causes the furnace lining to withstand alternating expansion and contraction, and the furnace lining is prone to cracks.

(4) The impact of operating methods on furnace age

① Furnace opening operation: When adding materials, pay attention to prevent debris from being mixed into the furnace lining material. Use correct tamping methods to discharge the air between the furnace materials and make it compact and dense.

②Oven sintering operation: Strictly operate according to the oven curve and control the heating rate. When the oven temperature is about 1000°C, add clean and regular furnace materials to prevent the furnace materials from tearing the crucible when adding materials. In the first 2 to 3 furnaces, cast steel with a high melting point is melted as much as possible and kept at high temperature for 2 hours to completely sinter the furnace lining.

③Smelting operation: Pay attention to the feeding method when feeding, and it is forbidden to throw large pieces of furnace material directly into the furnace. Observe the melting conditions in the furnace frequently, replenish the furnace materials in time, take timely measures to deal with the occurrence of shedding, and discharge the steel (iron) liquid in the furnace in time when it reaches temperature. When a power outage or intermediate frequency power supply failure occurs and cannot be restored in a short period of time, the liquid steel (iron) in the furnace must be poured out in time to prevent the furnace from freezing and then leaking.

④Maintenance. After the smelting is completed on the same day, some charge is added to the furnace and the furnace cover is covered to avoid cracks in the furnace lining due to rapid cooling. After the furnace has been used for a period of time, the charge expands and the furnace mouth is higher than the furnace cover. The unsintered layer becomes loose and the furnace lining cracks. It is necessary to tighten the unsintered layer with pins, repair the cracks in the furnace lining, and re-tie the furnace mouth.

In short, in order to improve the service life of furnace lining materials, in addition to correct furnace opening, baking, and sintering methods, we must also constantly explore and sum up experience in practice to achieve better results.