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Home > Knowledge > Content
Research on Prefabrication Technology of Converter Hearth
Mar 30, 2018

Abstract: Due to the special dimension of the refractory bricks used in the bottom of the converter, a large number of machining and sanding adjustments are required during the masonry. If the work is carried out directly in the steel converter, it is difficult and the operation is complicated. Therefore, the general refractory company needs to pre-lay masonry (preliminarily referred to as pre-laying) within the company after the furnace bottom brick is produced. The initial processing and adjustment are required to achieve the design requirements of the furnace bottom. This article will focus on the overview of the working process of the furnace bottom pre-laying.

Keywords: Converter, bottom pre-assembly, accuracy control

First, converter and furnace type, furnace bottom classification

The converter is an upright cylindrical smelting furnace that does not require external heating sources and mainly uses liquid pig iron as raw material for steelmaking. According to the nature of the lining refractories, it is divided into two types, acidic converter and alkaline converter. According to the location of the gas blowing furnace, it is divided into bottom blowing, top blowing, side blowing and top and bottom compound blowing converters. Bottom-blown, top-bottom composite blowing converter bottom designed breathable bricks, when positioning, need to locate the location of breathable bricks. Top-blown and side-blown converters are not designed with breathable bricks at the bottom of the converter, and the bottom of the furnace is relatively simple.

The converter consists of three parts: the furnace cap, the furnace body and the bottom of the furnace. There is no change in the shape of the furnace cap (truncated cone) and the furnace shaft (cylindrical). The furnace type is divided into three types: cylindrical ball type, conical ball type and truncated cone type.

(1) Cylindrical type, the molten pool consists of a sphere and a cylinder. Furnace shape is simple, bricklaying is convenient, furnace shell is easy to manufacture, and it is widely used by large and medium-sized converters at home and abroad.

(2) Cone ball type, the molten pool is composed of two parts: bulb absent body and inverted cone. Compared with the same type of cylinder, the cone-shaped bath is deeper and helps to protect the bottom of the furnace. In the case of the same bath depth, the diameter of the bath can be larger than that of the bowl, increasing the reaction area of the bath and favoring the removal of phosphorus and sulfur. China's small and medium-sized converters generally use this type of furnace.

(3) truncated cone, the molten pool is an inverted cone. Furnace structure is relatively simple, flat pool is easier to build than ball bottom. With the same charge and bath diameter, the bath is the deepest and therefore not suitable for large capacity furnaces. China's converters below 30t are used more often.

Basically, the bottom of the converter is divided into two types, that is, flat bottom and cut-off hearth (usually referred to as curved hearth)

Flat-bottomed converter bottom brick is a standard brick type, simple masonry, this paper mainly introduces the pre-laying of fire-brick brick for the cut-off hearth.

Second, the pre-preparation of the bottom of the furnace

According to the drawings of the hearth of the converter, the production of magnesia carbon bricks for the bottom of the furnace shall be arranged, and each brick shall be added with a margin. The center brick of the hearth is a processing brick. According to the physical and chemical indexes of the design material, the appropriate magnesium carbon bricks are used for bonding processing. After processing, a cross reference line shall be scribed on the plane of the center brick mouth to provide a reference for positioning the air-permeable brick during the subsequent pre-assembly and determining the position of the steel-outside and the steel-welding side.

Breathable bricks need to be pre-made models, the general material of the model is wood, if the size is too small, other materials such as magnesium carbon bricks can be used instead. Breathable bricks require special attention to technical indicators such as slightness, diagonal ruler, and distortion. The deviation of the size of the air-permeable bricks directly affects the masonry of the steel plant. In the production of breathable brick molds, the dimensional tolerances are controlled as negative scales as far as possible. If it is positive and negative, the steelyards will likely have large gaps around the breathable bricks.

In addition to the appeal materials, it is also necessary to prepare a bottom sand (grain size of 3mm-1mm), grinding tools, cutting machines, rubber hammers and other auxiliary materials.

Third, the accuracy of the positioning of the center brick

When the hearth is pre-assembled, the positioning of the center brick is particularly important. The accuracy of the center brick positioning directly affects the masonry of the subsequent hearth bricks, air-permeable bricks, and even the anti-flat areas. The cross point method is used to determine the center point, and its eccentricity is not more than 10mm. Due to the different curvature of the bottom of the converter in different steel mills, the masonry curvature of the bottom working layer design is not the same, but the false bottom size used in the internal pre-laying of the refractory company is fixed, which needs to be based on the specific furnace bottom curvature. Make corresponding adjustments, ie whether the bottom of the center brick needs to be lifted. If the curvature of the hearth of the steelwork is larger than the curvature of the false bottom used for prefabrication, then the center brick needs to be lifted, and the height of the cushion is calculated by calculation, and vice versa.

Fourth, ring-shaped brick masonry

After the center brick is positioned, masonry tables shall be used to construct ring-shaped bricks, and the bricks must be strictly controlled when the masonry ring-shaped bricks are assembled. The ring peaks shall be ≤1mm and the triangular seams shall be ≤1.5mm. The bricks shall be masonated after the bricks are preassembled and disassembled. There will be some changes in the brick joints, so the brick joint control requirements must be stricter than the steelwork masonry requirements. The thickness of the per-ring door brick is not less than 2/3 of the original brick. In special cases, the thickness is not less than 1/2 of the original brick, and the continuous three-ring seam phenomenon is not allowed. After the single-ring masonry, it is polished according to the specific conditions, and then the next ring is built.

Prior to masonry, the theoretical diameter of each ring should be calculated in advance to calculate the theoretical diameter of each ring, ie the theoretical diameter of each ring after masonry, and the actual diameter of the hole after masonry. The two should be compared according to the difference. Make the next ring of masonry methods to ensure the accuracy of the final bottom. If the design of the anti-flat zone of the working layer of the converter is a U-shaped masonry, the tilt angle of the working layer shall be measured in advance when the bottom of the furnace is pre-assembled. The specific method is not described here in detail.

V. Breathable brick positioning

This process is a special process of bottom blowing and pre-assembly of the top and bottom re-blowing converters. The purpose is to accurately position the air-permeable bricks during pre-assembly and reduce the complexity of steel field construction operations. First, according to the drawings, draw the distribution angle drawings (with reference reticle) of the hearth brick, and then print it out. When positioning the breathable brick, match the baseline of the drawing with the baseline that was previously engraved on the center brick. Ensure that the drawing side of the drawing, the steel side and the center of the brick on the anastomosis. Then use a laser locator (or thin line) to position the breathable brick in the direction of the angle line. After the location is determined, the model of air-permeable bricks shall be built first, then the protective bricks around the air-permeable bricks shall be masoned, and the bricks shall be laid on both sides with the air-permeable brick as the center. Breathable bricks around the protective bricks are not allowed to be polished, nor is it possible to make a brick.

6. When the bottom of the furnace is finished, clean the bottom of the furnace and spray the anti-slip agent. Then draw the bottom cross line according to the center brick baseline. Each tile needs to be numbered, and the numbering method is in the form of 1-1, 1-2,..., 2-1, 2-2. The brick color of the air brick protective brick should be distinguished from the other brick color. The starting position of each ring number should be the same. It is recommended that you use one of the crosshairs as a starting point, and the local position marks the direction of the masonry with an arrow. as the picture shows.

Masonry effect map is as follows

Seventh, packing

When removing the bottom of the furnace, remove the bricks from the outer ring to the inner ring, remove the bricks from the large size to the small number in sequence, and be careful not to damage the bricks. When placed, the trumpet is up and the queen is down. Pallet cracking and other phenomena are not allowed. When packing, it is forbidden to appear large and small inverted trapezoidal phenomenon. The taro sticks in a fixed position inside the stretched film to prevent shedding and wrinkling, and it is strictly prohibited to appear skewed. The bread mark must indicate the range of the brick label of this package. The packing fillers are all made of hot-cut foam as filler, and the size is appropriately enlarged and cut according to the required size to ensure that the packing is fastened and densified. Foams require high strength and no flaking; residual foam must be removed after packaging.

Eight, summary

The pre-roofing of the hearth can be described as the most important task in the lining and masonry construction of the converter. Accurate pre-laying can bring convenience to the operation of the steel works. Conversely, it will bring great work burden to the steel works on site. Pre-roofing of the furnace must go through processes such as production, auxiliary material preparation, positioning, masonry, marking, packaging, etc., grasping the details, and accurate masonry construction can not tolerate sloppy steps. Only in this way can the bottom of the furnace be pre-assembled to achieve the intended purpose. Therefore, prefabrication of the converter hearth is a job that appears to be simple and difficult.