Research on the pre laying technology of converter bottom

　　1、 Classification of converter, furnace type and bottom

　　Converter is a vertical cylindrical smelting furnace that does not need external heat source and mainly uses liquid pig iron as raw material to make steel. According to the properties of lining refractory, it can be divided into acid converter and alkaline converter. According to the position of gas blowing into the furnace, it is divided into bottom blowing, top blowing, side blowing and top bottom combined blowing converter.

　　Converter is a vertical cylindrical smelting furnace that does not need external heat source and mainly uses liquid pig iron as raw material to make steel. According to the properties of lining refractory, it can be divided into acid converter and alkaline converter. According to the position of gas blowing into the furnace, it is divided into bottom blowing, top blowing, side blowing and top bottom combined blowing converter. The bottom of the bottom blowing and top bottom composite converting converter is designed with breathable bricks, and the position of the breathable bricks needs to be positioned during masonry. The bottom of top blowing and side blowing converter is not designed with breathable bricks, and the bottom masonry is relatively simple.

　　The converter is composed of three parts: furnace cap, furnace body and furnace bottom. Because the shape of furnace cap (truncated cone) and furnace body (cylindrical) has not changed. The furnace types are divided into three types: cylinder ball type, cone ball type and truncated cone type.

　　(1) Tube ball type, the molten pool is composed of sphere and cylinder. The furnace shape is simple, bricklaying is convenient, and the furnace shell is easy to manufacture. It is widely used by large and medium-sized converters at home and abroad.

　　(2) Cone ball type, the molten pool is composed of spherical defect body and inverted truncated cone. Compared with the cylinder ball type with the same capacity, the cone ball type molten pool is deeper, which is conducive to the protection of the furnace bottom. With the same depth of the molten pool, the diameter of the molten pool can be larger than that of the cylinder ball type, which increases the reaction area of the molten pool and is conducive to the removal of phosphorus and sulfur. This type of converter is widely used in small and medium-sized converters in China.

　　(3) Truncated cone type, the molten pool is an inverted truncated cone. The furnace structure is relatively simple, and the flat molten pool is easier to build than the spherical bottom. When the loading amount and the diameter of the molten pool are the same, the molten pool is the deepest, so it is not suitable for large capacity furnaces. Converter below 30t is widely used in China.

　　There are two common types of converter bottom, namely, flat bottom and truncated ball bottom (commonly known as arc bottom)

　　The flat bottom converter bottom brick is a standard brick type, and the masonry is simple. This paper mainly introduces the pre masonry of truncated ball bottom with refractory bricks.

　　2、 Preliminary preparation for furnace bottom pre laying

　　According to the drawing of converter bottom, arrange to produce magnesia carbon bricks for furnace bottom. Each brick type is produced with allowance. The center brick of furnace bottom is processed brick. According to the physical and chemical indicators of the design material, select appropriate magnesia carbon bricks for bonding processing. After processing, a cross reference line must be engraved on the upper surface of the center brick, so as to provide a reference for positioning breathable bricks and determining the positions of steel tapping side and steel facing side during subsequent pre laying.

　　Breathable bricks need to be made in advance. The model is generally made of wood. If the size is too small, it can be replaced by magnesia carbon bricks and other materials. When processing breathable bricks, special attention should be paid to the technical indicators such as sharpness, diagonal ruler difference, twist, etc. The size deviation of permeable bricks directly affects the masonry of steel plants. When making permeable brick mold, the dimensional tolerance should be controlled as negative ruler as far as possible. If the positive ruler is out of tolerance, there is likely to be a large gap around the permeable brick during the masonry of the steel plant.

　　In addition to the appeal materials, it is also necessary to prepare auxiliary materials such as sand cushion at the bottom of the furnace (the sand cushion granularity is 3mm-1mm is preferred), grinding tools, cutting machines, rubber hammers, etc.

　　3、 Accurate positioning of center brick

　　When the furnace bottom is pre laid, the positioning of the center brick is particularly important. The accuracy of the positioning of the center brick directly affects the subsequent laying of the furnace bottom brick, breathable brick, and even the inverted flat area. The central point shall be located and determined by the cross method, and its eccentricity shall not be greater than 10mm. Due to the different radians of the converter bottom in different steel plants, the masonry radian of the bottom working layer design is also different, but the size of the false bottom used in the internal pre masonry of the fire-resistant company is fixed, which requires corresponding adjustment according to the specific furnace bottom radian, that is, whether the bottom of the center brick needs to be padded. If the radian of the steel plant furnace bottom is greater than that of the pre built false furnace bottom, the center brick needs to be padded, and the cushion height is calculated, otherwise, it is not needed.

　　4、 Circular brick masonry

　　After the central brick is positioned, the annular brick shall be built according to the masonry table. When building the annular brick, the brick joint shall be strictly controlled, with the annular peak ≤ 1mm and the triangular joint ≤ 1.5mm. Because the brick joint will change slightly when the furnace bottom brick is pre built and disassembled, and then when it is built in the steel plant, the brick joint control requirements must be stricter than those of the steel plant. The thickness of each ring door brick shall not be less than 2/3 of the original brick, and its thickness shall not be less than 1/2 of the original brick under special circumstances. Continuous three rings with the same seam is not allowed. After the single ring is built, polish it according to the specific situation, and then build the next ring.

　　Before masonry, the theoretical diameter size of each ring in the design of furnace bottom should be calculated and counted in advance, that is, the theoretical diameter size of the upper mouth of each ring after masonry, and the actual upper mouth diameter size should be measured after masonry. The two should be compared, and the construction method of the next ring should be made according to the difference to ensure the accuracy of the final furnace bottom. If the inverted flat area of the working layer of the converter is designed as U-shaped masonry, the inclination angle of the working layer needs to be measured in advance during the pre masonry of the furnace bottom. The specific method is not described in detail here.

　　5、 Breathable brick positioning

　　This process is a unique process of bottom blowing and top bottom combined blowing converter bottom pre laying. The purpose is to accurately locate the breathable bricks during pre laying and reduce the complexity of steel plant site construction. First, according to the drawing, draw the distribution angle drawing of the bottom vent brick (with the reference cross line), and then print it out. When positioning the vent brick, match the reference line of the drawing with the reference line engraved on the center brick in advance, that is, ensure that the tapping side and facing side of the drawing are consistent with the center brick. Then, according to the direction of the angle line, use the laser locator (or thin line) to locate the position of the breathable brick. After the position is determined, the permeable brick model shall be built first, and then the protective bricks around the permeable brick shall be built, with the permeable brick as the center to both sides. The protective bricks around the breathable bricks are not allowed to be polished, and the door closing bricks are not allowed to be made.

　　6、 Furnace bottom masonry

　　After the completion of furnace bottom masonry, clean the furnace bottom, spray anti-skid agent, and then draw the furnace bottom cross line according to the central brick reference line. Each brick needs to be numbered in the form of 1-1, 1-2 ·· 2-1, 2-2. The color of the brick mark of the breathable brick and the protective brick shall be different from that of other bricks. The starting position of each ring number should be the same. It is suggested to take one of the crosshairs as the starting point, and the local position should be marked with an arrow to mark the masonry direction.

　　7、 Packaging

　　When removing the bottom of the furnace, remove the bricks from the outer ring to the inner ring, and from large to small in turn. During handling, pay attention not to damage the bricks, and spray anti-skid agent on the removed bricks. When placing, the small size is above and the large size is below. The pallet shall be free of cracking and other phenomena. When packing, it is strictly prohibited to have the phenomenon of upside down trapezoid. The shipping mark shall be pasted at the fixed position inside the tensile film to prevent falling off and folding, and obvious skew is strictly prohibited. The shipping mark must indicate the range of the brick label of this package of bricks. All packing fillers shall be made of thermal cut foam, and the cutting shall be properly enlarged according to the required size to ensure that the packing is firm and dense. Foam requires high strength and no chips; If there is foam residue after packaging, it must be cleaned up.

　　8、 Summary

　　The pre laying of furnace bottom can be described as the top priority in the construction of converter lining. Accurate pre laying can bring convenience to the operation of steel plant, on the contrary, it will bring great workload to the on-site operation of steel plant. The pre laying of furnace bottom needs to go through the processes of production, auxiliary material preparation, positioning, masonry, marking, packaging, etc., grasp the details, and the accurate masonry can not be sloppy. Only in this way can the pre laying of furnace bottom achieve the expected purpose. Therefore, the pre laying of converter bottom is a seemingly simple but difficult work.