How To Operate IF Induction Furnace（Intermediate Frequency Induction Melting Furnace） Efficiently And Safely?

  Intermediate frequency induction furnace (frequency: 150~2500Hz) has been widely used in the metallurgy and casting industry due to its advantages such as low investment, long service life, high electric efficiency and low single consumption of electric energy, easy operation, small burning loss of smelting alloy elements, little brittle inclusion and high purity.

  With the demand for metal smelting quality is getting higher and higher. The application requirements of intermediate frequency induction furnace are also higher and higher, mainly reflected in the requirements of longevity technology; High-efficiency production requirements; Reduce the smelting energy consumption, and other aspects. Our company USES the intermediate frequency induction furnace as the roll production equipment. By exploring and summarizing the technical points of use, we can realize the long life, energy saving, high efficiency, and necessary accident prevention, which is of great reference significance to the casting industry.

Longevity technology of acid medium frequency induction furnace

1. Raw material requirements

  Quartz lining material requires wSiO2 > 99%, wCaO < 0.5%, wMgO < 0.5%, wFeO < 0.5%, wAl2O3 < 0.5%, wH2O < 0.5%;Refractory > 1700℃, softening temperature > 1650℃.Lining materials shall not conduct electricity at high temperature.Boric acid (H3BO3) or boron anhydride (B2O3) are generally used as additives in silica sand materials, mainly to reduce sintering temperature.

2. Furnace building process

  The furnace lining USES pneumatic knotting, the bottom is knotting with the bottom builder first, then the mold is put in, the material is added between the mold and the insulation layer, and the vibrator is used to vibrate the mold to make the material compact. The furnace material is silica sand.

3. Oven technology

  The oven should be strictly according to the oven sintering process.

(1) The feeding characteristics in the baking and initial sintering stage can generally fill the furnace with charge, after the metal begins to melt, add 50 ~ 200 kg charge in small batches each time (depending on the specification), until the final metal liquid level is 50 ~ 100 mm away from the edge of the furnace.

(2) The general principle of heating characteristics in the baking and sintering stage is “slow heating and long duration in low-temperature stage”, and the temperature in the sintering stage is 50 ~ 80℃ higher than the maximum iron temperature at ordinary times.

  Baking stage: 50 ℃ for 4 h/h slow warming, the purpose is to eliminate the moisture from the furnace lining, and the crucible mode at a speed of 100 ℃ / h heated to 600 ℃, 4 h, completed in 573 ℃ of silica sand phase transformation for the first time, namely to alpha-beta quartz transformation, phase variation will expand about 0.82%, to 577 ℃ when boron anhydride melting and powdered crystalline silica sand glass phase formation, make the lining surface of the glaze is changed.

  Semi-sintered stage: the second phase transition of silica sand was carried out at a temperature of 50 ° C/h to 900 ° C for 3h, and at a temperature of 100 ° C/h to 1200 ° C for 3h with a temperature of 870 ° C or above: the transition rate from -quartz to -scale quartz was very slow. Due to the volume expansion rate of 16%, the temperature rise rate must be controlled to prevent cracks.

  Complete sintering stage: heating to 1470℃ at 50℃ / h, holding temperature for 1h, at 1470℃, -scale quartz transforms to -calcarine, and the third phase transition occurs, with the volume increasing by 4.7%.The sintering temperature is low, the sintering layer thickness is insufficient, and the service life is obviously reduced. The temperature should not be heated too fast to prevent the crack and porosity of the sintered layer due to the huge phase transition stress.

(3) Formation of sintering layer High-temperature sintering is conducive to the formation of the sintering layer, transition layer, and loose layer, each accounting for 1/3 thickness, from inside to outside on the radial of furnace lining, as shown in the figure below. The sintering temperature should be higher than 1500℃ to ensure the quantization of the sintered layer and reduce surface cracks.

4. Maintenance requirements

(1) Feeding charge should be added in small batches, small lumpiness, and multiple batches, not the canopy, in order to reduce the impact of the charge on the furnace wall and bottom.

(2) Measures to protect the furnace collar Add a round cast iron protective pressure ring on the edge of the furnace. The position of the upper plane of the last layer is 20 ~ 30 mm lower than the edge of the furnace, which can play a good protective role on the collar part.

(3) Grasp the furnace condition at any time to strengthen the daily spot inspection, pay attention to the lining erosion, crack condition, with special measuring tool to measure the total height and different height of the diameter of the site, do a good job of regular maintenance is an important factor to improve the service life of lining materials.

(4) Under the condition that the furnace bottom corrosion is less than 50mm, the material of the furnace shall be properly dampened, and the impurities in the furnace bottom shall be removed and then tamped with a tamping hammer for “hot repair”. Generally, the furnace bottom shall be repaired no more than twice.

(5) It is necessary to consider stopping the furnace and dismantling the furnace when stopping the furnace and dismantling the furnace wall. Horizontal ring cracks, lining erosion, and peeling are obvious to the naked eye in the circumferential direction of the furnace wall, the power, and current reach or even exceed the rated 5% ~ 10%, and the molten iron in the furnace is significantly more violent than usual.

(6) Check the inductor regularly

For fine cracks or local leakage to cause enough attention, and timely repair, to avoid the deterioration of serious accidents.FCAR-H copper crack – repairing agent can be used as far as possible without affecting production.

If the insulation layer on the surface of the inductor blackens or falls off, it must be repaired as soon as possible to prevent lighting or arc breaking caused by insulation damage. If the insulation is damaged in a large area, the inductor shall be removed for overall insulation treatment. Insulation paint selection must be suitable for intermediate frequency furnace production conditions, especially to be able to withstand high temperature, tsC-L ultra-high temperature insulation paint, or APC-H+ high-temperature arc insulation enamel.

5. Smelting operation

(1) Smelting temperature system Avoid high temperature smelting in the smelting process.In the high temperature state, SiO2 + 2C → Si + 2CO, the higher the temperature, the higher the C, the lower the Si, the lining erosion will be intensified, especially in the new furnace is more obvious, so no high temperature smelting is a good way to improve the furnace life, reduce power consumption.

(2) Avoid lining overheat burden “bridging” phenomenon will make lining appear local high temperature even more than lining refractoriness, resulting inlining melting and corrosion, reduce the service life of the lining.

(3) The influence of molten iron on the lining life is mainly reflected in the following aspects: the stirring force generated by molten iron under the electromagnetic effect, washing the lining; SiO2 in the furnace lining is reduced by C in the molten iron at high temperature.

(4) Influence of slag on lining Rust in the charge and return charge contain FeO slag, which reacts with SiO2 in the lining to form a slag of low melting point. A large amount of slag seriously corrode the lining, and slag will cover up the real crack of the lining. Therefore, timely slag removal is a factor to prolong the lining life.

(5) Iron and steel materials shall be strictly prevented from adding materials containing too much Zn and Pb. As the melting point of the above two elements is relatively low compared with iron, it penetrates the whole furnace lining in the form of vapor before iron melts, resulting in ablation holes and cracks in silica sand furnace lining.

High efficiency production and energy saving technology

  According to the metallurgical characteristics of medium frequency induction furnace establishment reasonable melting process, from the loading, temperature control, adding alloy at different temperatures, carburant, slagging agent, and the tapping temperature of each link strict control, strive to use the shortest melting time and minimum alloy oxidation burning loss and, microstructure control and stability and purpose of improving the quality of the roll.

1. Proper ingredients

Scientific management and good use of charge, to achieve the main chemical components meet the requirements, harmful impurity elements content as little as possible, to avoid the adjustment of the composition and delay smelting time, to prevent unqualified components and scrap.

In the process of feeding, the metal should be kept as compact as possible to fill the whole furnace chamber, so as to ensure the maximum utilization of thermal efficiency and improve melting efficiency.

2. Reasonable smelting operation

Power supply: first supply about 60% of the power, when the current shock stops, quickly increase the power to the maximum, in order to speed up the melting of the charge.

3. Reasonably control the temperature of steel output

The short time before casting is used to raise the temperature in accordance with the process requirements, while the rest of the time the molten iron is kept at a low temperature, which can reduce the erosion of furnace lining caused by molten iron at high temperature, extend the service life of furnace lining and reduce the power consumption.

High alloy recovery technology

The burning loss of Si, Mn, Cr, and other easy oxidizing elements in the induction furnace is 3% ~ 5%. Generally occurs in the melting time is too long, and did not pay attention to the slag protection stage. If the amount of scrap steel, light and heavy material, and charge belt rust, the problem is more serious. The way to avoid excessive element burning loss is: the burden as clean as possible, do not branch fork shape, size can not be too large, too thin; Eliminate frame materials;In the early stage of smelting, slag should be made in time, and slag should be covered in the later stage at high temperature. Do not over-tune the frequency modulation in the late melting stage;Do not overheat. Do not keep warm for a long time at high temperature.

When the iron liquid temperature exceeds the equilibrium temperature, the reaction SiO2+2C=Si+2CO will proceed to the right, causing the iron liquid to decrease in C and increase in Si. Therefore, C should be supplemented when batting.In the later stage, the composition shall be adjusted in the order of Mn, Then C, and then Si.

Analysis of the cause of splashing and explosion in induction furnace melting process

(1) The high-temperature decomposition reaction of corroded carbon and oxygen and iron oxide in the induction furnace is continuously carried out in the molten steel, so that the molten steel has the power of constant outflow, and then spillage occurs.

(2) The slag crust is covered on the surface of molten steel to protect alloy elements from oxidation and has certain desulfurization, inclusion adsorption, and heat preservation functions. The main components of slag include the lining materials and impurities carried by a charge which are washed and eroded into slag during smelting. When the heat dissipation rate of slag is higher than the heat transfer rate of molten steel, the surface crust of slag is formed. The lower space of the slag shell forms a closed environment, and the gas produced by smelting cannot be released in time. When the gas reaches a certain pressure, the slag shell will be jacked open, causing the metal liquid and slag to be ejected.

(3) The reason for charging bridge: too much charging at one time, the upper charge is piled up too tight, the charge is stuck and overhead; Unreasonable charge structure, small upper material block, high melting point, large lower material block, low melting point; The furnace wall is not smooth, unfavorable charge line. After the charging bridge is set up, the temperature of the lower molten pool keeps rising, forming a high temperature and high pressure atmosphere in the furnace. The metal liquid corroded the lining refractory material seriously, and even caused the leakage of local metal liquid in the furnace body, causing the cooling water to enter the metal molten pool and causing a big explosion.

(4) the metal liquid leaking medium frequency induction coil, furnace lining material of electromagnetic stirring scour, led to increasing corrosion, some parts of the furnace lining are serious erosion and failure, the liquid steel will wear at the stove, wearing out of the liquid steel adhesion on the induction coil, cause a short circuit between layers of the induction coil, burning through the coil in the cooling water into the furnace explosion.

Conclusion

(1) The economic operation of the intermediate frequency induction furnace is realized through the comprehensive implementation of the above technical management measures.

(2) When medium frequency induction furnace steelmaking, the yield of metal and alloy is significantly increased, the yield of iron and steel can reach 97% ~ 98%, the yield of the alloy is significantly increased by about 1%. Therefore, saving steel and alloy cost advantage is more significant.

(3) It is convenient to adjust the composition of smelting, which meets the requirements of the process on the narrow composition range of molten iron, making the roll more stable in performance and lower in smelting cost. Medium frequency furnace has high power and high temperature raising capacity. It can provide different temperature range for different materials and specifications of rollers to meet the requirements of the casting process.

(4) It is necessary to further study the longevity technology, high-efficiency smelting technology, accident prevention, and other problems of medium-frequency induction furnace, so as to better meet the technical requirements and achieve better economic operation.