Furnace construction process for improving lining life of intermediate frequency furnace
One. Foreword:
The high temperature performance of the medium frequency coreless induction furnace lining depends mainly on the physical, chemical properties and mineral composition of the refractory materials used. Under the premise of selecting the raw and auxiliary materials, the sintering process is to make the furnace lining obtain a good microstructure to fully exert its resistance. The key process of high temperature performance. The degree of densification of the lining sintering is related to the chemical composition of the refractory material, the particle size ratio, the sintering process and the sintering temperature. Through more than 20 years of continuous exploration and production tests, our factory has summed up a reasonable furnace-knotting process and baking and sintering process, which has greatly increased the age of the furnace, and the furnace age of the 2T intermediate-frequency furnace dry-type knotting furnace lining A medium repair) has reached 1157 heats and achieved remarkable economic benefits.
two. Furnace construction process:
3.1 Remove the mica paper when building the furnace.
3.2 The following treatments are applied to the crystal quartz sand for furnace construction:
3.2.1 Hand selection: mainly removes bulk and other impurities;
3.2.2 Magnetic separation: magnetic impurities must be completely removed;
3.2.3 Dry ramming material: It must be slowly dried, the drying temperature is 200 °C-300 °C, and the temperature is kept for more than 4 hours.
3.3 Selection of binder: Boric anhydride (B2O3) was used instead of boric acid (H3BO3) as binder, and the amount added was 1.1%-1.5%.
3.4 Selection and proportioning of furnace materials:
3.4.1 Selection of furnace material: It should be noted that not all quartz sand with SiO2 ≥ 99% can be used as the lining material of the induction furnace. The important thing is the size of the quartz crystal. The coarser the crystal grains, the less the lattice defects are. (For example, crystal quartz sand SiO2 has high purity, white appearance and transparency.) The larger the furnace capacity, the higher the requirement for crystal grains.
3.4.2 ratio: quartz sand ratio for furnace lining: 6-8 mesh 10%-15%, 10-20 mesh 25%-30%, 20-40 mesh 25%-30%, 270 mesh 25%-30% .
3.5 Knotting of the lining: The quality of the lining of the lining is directly related to the quality of the sintering. When the knot is evenly distributed, the sand particle size distribution is uniform and does not cause segregation. The density of the sand layer after knotting is high, and the probability of cracking after sintering is lowered, which is beneficial to improve the service life of the induction furnace lining.
3.5.1 Dry type knotting furnace lining (take 2t medium frequency coreless induction furnace as an example): Application of coil insulation clay: The induction coil of 2t medium frequency coreless induction furnace is coated with insulating clay layer. Compared with insulating materials such as mica and glass cloth, which are commonly used in induction roads, the use of coil insulation clay has the following advantages: First, after drying, the coil insulation layer with a thickness of 8-15 mm has good insulation properties and can be completely replaced. Mica and glass cloth act as an insulating protective layer between the coil and the lining; the thermal conductivity of the cement material is high, and there is no need to worry that the relatively thick cement layer will affect the three-layer knot of the hot lining. Second, the cement layer is located between the coil and the insulation layer. Under normal circumstances, the ambient temperature is very low (<300 ° C. Occasionally, when the molten metal approaches the surface, the cement layer will release a small amount of residual moisture, so that the insulation resistance is lowered, the system Provide early warning. Third, the use of the cement itself is higher than 1800 ° C refractoriness, when occasional metal liquid leaks to its surface, the cement can provide a protective barrier to the coil, when the alarm occurs, the cement layer can provide a certain The accident handling time. Fourthly, for the furnace with bottom ejector type, the clay is made into a tapered shape, which avoids the friction between the lining and the coil, and at the same time fixes the coil by its strength, avoiding the coil The deformation during the use, construction and demolition process prolongs the service life of the coil. Fifth, the coil and the rubber layer serve as the permanent lining of the furnace. Although the one-time cost is high and the construction period is long, the service life can be compared with the coil. In the same way, partial repair can also be carried out, thus reducing the cost of building the furnace as a whole.
Before the dry knotting furnace lining, firstly lay a layer of asbestos board and a layer of glass cloth in the insulation layer of the furnace coil. In addition to manual flattening and compacting the layers of materials, the spring ring should be tightened up and down to tamper the quartz sand. When moving the coils one by one from top to bottom until the lining is finished.
3.5.2 Knotted bottom: The bottom of the furnace is about 280mm thick, and the sand is divided into four times. When the knot is artificially knotted, the uneven density is prevented. The lining after baking and sintering is not dense. Therefore, the thickness of the feeding must be strictly controlled. Generally, the thickness of the sand filling is not more than 100mm/time, the wall of the furnace is controlled within 60mm, and the operation of multiple people is divided into 4-6 people per shift. Each time the knot is changed for 30 minutes, the furnace is surrounded. Slowly rotate the position and apply even force to avoid uneven density.
When the bottom of the furnace is knotted to the required height, the mold can be placed. In this regard, care should be taken to ensure that the die is concentric with the induction coil, and the vertical adjustment is vertical. The pattern is closely combined with the bottom of the furnace. After adjusting the peripheral clearance, the three wooden wedges are clamped, and the middle weight is pressed to avoid the furnace wall. The quartz sand is displaced when knotted.
3.5.3 Knotted furnace wall: The thickness of the lining is 110-120mm, and the dry type of knotting material is added in batches. The cloth is evenly distributed, the thickness of the packing is not more than 60 mm, and the knot is knotted for 15 minutes (manual knotting) until it reaches the upper edge of the induction coil. Flush. After the knotting is completed, the die is not taken out, and induction heating is performed during drying and sintering.
3.6 Baking and Sintering Specifications: In order to obtain the three-layer structure of the lining, the baking and sintering process is roughly divided into three stages:
3.6.1 Baking stage: The dies are heated to 600 ° C at a rate of 25 ° C / h and 50 ° C / h, respectively, for 4 h, in order to completely eliminate the moisture in the lining.
3.6.2 Semi-sintering stage: heat up to 900 ° C at 50 ° C / h, keep warm for 3 h, heat up to 1200 ° C at 100 ° C / h, keep warm for 3 h, must control the heating rate to prevent cracks.
3.6.3 Complete sintering stage: When sintering at high temperature, the sintered structure of niobium is the basis for improving its service life. The sintering temperature is different, the thickness of the sintered layer is insufficient, and the service life is significantly reduced.
The 2T intermediate frequency furnace adds about 950 kg of iron material to enhance the heating effect of the induction coil during the baking process. As the baking and sintering continue, a relatively stable electromagnetic force is used to stir the molten iron through low-power transmission, which is uniform heating up and down the furnace lining. . Strictly control the temperature of the three phase change zones of quartz sand, promote the phase change of quartz sand, and improve the first sintering strength of the lining.
three. summary
For the life of medium and power frequency furnace lining, in addition to ensuring a complete and reasonable three-layer furnace lining, it should also pay attention to the usual operation. The furnace is made of high quality and clean furnace building materials, reasonable ratio, meticulously knotted, scientific baking With the sintering specification and strict operation process, the service life of the furnace can be extended.
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