The horizontal continuous casting production line is composed of melting furnace, holding furnace, mold (copper water jacket and graphite lining), lead casting machine (tractor), sawing machine, and auxiliary chip collection mechanism. [/BR/] In order to find out the influence of relevant factors on the quality of bar and take corresponding measures, it is necessary to analyze the horizontal continuous casting crystallization process, characteristics and mechanism in order to adopt a reasonable process system to obtain high-quality products . [/BR/]2.1 When the casting is stopped, the stress of the slab in the mold (see Figure 1) [/BR/] When the casting is stopped, the slab in the mold is subjected to the following forces: ①Still water generated by the molten metal in the furnace Pressure, from P=HPG (h is the height of the liquid column; P is the density of the liquid; G is the acceleration of gravity): P 1>P 2; The cavity is connected with the charge to transfer heat directly. Therefore, there is no condensation on the graphite plate near the furnace. Condensation is formed on the inner wall of the graphite plate and enters the alloy crystallization temperature, that is, the liquid-solid two-phase zone, and the condensation gradually thickens toward the outlet direction until it solidifies into a copper rod. Due to condensation and shrinkage, the gap between the condensing shells in the graphite is beneficial to the casting, but due to the thin condensing shell and the static pressure of the liquid metal column, some condensing shells (L1 and L2 areas) do not leave the inner surface of the sleeve. Thick condensed shell slab (mold height 16mm, mold outlet copper row thickness is about 0.5mm, mold width 456mm, mold outlet copper row shrinkage is about 7mm), under static pressure P1 (P1>P2) and gravity affect condensate Under the dual action of the lower part of the mold, the contact area between the lower part of the casting side and the graphite is L1>the upper part contact area L2; in addition, due to the unevenness and adhesion of the contact interface, the precipitation resistance of the lower part is much greater than that of the upper part. [/BR/]2.2 In the process of stopping the drawing, in order to facilitate the analysis of the solidification process and stress of the molten metal in the mold, it is assumed that the upper and lower crystals crystallize on the vertical interface. The condensation process during the drawing process is shown in Figure 2. [/BR/] After stretching begins, part of the melt will be released between the melt and the solid. Under the action of the static pressure of the metal liquid, the metal behind will be replenished immediately. The closer the longitudinal distance between the melt and the graphite, the greater the cooling strength, the lower the metal temperature, the worse the fluidity, and the higher the intermediate metal temperature, the faster the flow rate. According to the principle of fluid mechanics, the faster the flow rate in the liquid, the lower the pressure, so from the position of the graphite wall to the longitudinal center position, the pressure on the melt gradually decreases, forming a pressure difference inside the melt, which forces the metal to follow the arrow The direction flows. Due to the pulling action of the metal key, a thin shell-like condensation part is formed, but the static pressure of the lower surface is greater than that of the upper surface when the drawing stops, so the curvature of the lower surface is smaller than that of the upper surface. [/BR/] With the increase of the draw distance, the new area of s gradually increases, and the arc length of the condensing shell continues to increase. When the friction force is small enough and the strength of the condensed shell is high enough, there is no fracture and a curved surface (groove) is formed, but the curved surface is rough. In most cases, as the draw distance increases, the copper water temperature in the crystallization zone becomes higher and the condenser shell becomes thinner. This is the weaker one in the condenser shell. A new stream of liquid overflows from the crack. Fill up the recess of the condensate shell. If this happens to be the end of the drawing, this part of the metal crystallizes instantaneously during the stopping process and connects with the other parts of the arc-shaped solidified shell. When it is cast again, it is pulled out together. The metal of the solidified shell should grow in the center to form a large columnar crystal whose crystal grain size is 100-150 times that of the left and right fine crystals. See metallographic photos 3 and 4. [/BR/] Figure 3 is a macroscopic view of the longitudinal section of H65 during the crystallization process, and Figure 4 is a partial schematic diagram of the longitudinal section (contact area with the mold), that is, the metallographic structure of the interface between the small liquid stream and the original condenser shell (X100 ). It can be seen from the figure that the fine grains and columnar crystals to be filled later have obvious separation and staggered shielding from each other, and the junction should be rich in metal. When the surface is milled, the gas must be generated during the oxidation and solidification process. Was ground away. [/BR/] Figure 5 is a photo of milling the macrostructure at the bottom of the board surface to 0.4 mm. In the figure, the coarse crystal area is the crystalline part, and the fine crystal area is the filled part after fracture. (In order to measure the thickness of the fine grains, milling was performed on the left side surface to make one more part, and the marked longitudinal arc was used as the milling mark). [B/B] It can be seen from the crystallization principle and related photos that this new and old shell is oxidized due to the temperature difference and the periodic changes of inhomogeneity, forming a ring-shaped spot that characterizes the asphalt. The process conditions are determined and operated. , The pouring temperature is 100-105℃ higher than the molten metal temperature, and it is required to be 30-40℃ higher than the pouring temperature to avoid heat loss when the melt flows through the chute. The casting temperature of H65 is 1040-1060℃, and the fluctuation range of the holding furnace is controlled within ±10℃. [/BR/]3.2 Pull-Stop System[/BR/]The pull-casting adopts reverse push-pull-stop procedure. The reverse thrust function is: ①Prevent adhesion between the shell surface of the area in direct contact with the mold and the mold wall (the graphite in this area has needle-shaped copper adsorption during the crystallization process, and the hand is tied when it touches the removed graphite). ②Clean the zinc oxide and zinc attached to the graphite mold (the area where there is a gap between the slab and the graphite) to reduce the friction between the mold and the casting. ③Vibration refines the grains. [/BR/] The affinity of zinc and oxygen is greater than that of carbon and oxygen. In the zinc-rich HPb59-1, oxygen does not react with graphite, and the graphite in the liquid phase region is relatively flat, smooth and without pits. But the graphite plate in the solidification zone is combined with Zn0 and Zn, and the frictional resistance is relatively large. In order to avoid the superimposed force of Zn0 and Zn in the same area, with the development of the casting process, the area can be moved inward in the volume direction through appropriate deceleration to achieve crystallization, thereby improving the surface quality of the cast slab and the service life of graphite. [/BR/] From the perspective of horizontal continuous casting molding, the function of intermittent casting is to obtain sufficient thickness and strength when the shell is stopped to avoid cracks or leakage. Therefore, the selection of the pull-stop system is very important. [/BR/]Drawing and stopping are two factors that restrict each other. The parking time is long-the drawing time is long-the drawing distance can be increased, and the parking time is short-the drawing distance can be shortened. Due to the wide two-phase zone of H65 and developed dendrites, the gas released during solidification slowly diffuses into the liquid zone. Generally, medium and low stroke, medium instantaneous speed, medium and high frequency drawing casting are used to ensure that the outlet temperature of the copper rod reaches the solidus line. 30% to 35% (for 16mm thick copper rods), the surface of the copper rod at the exit of the crystallization is better with dark red. [/BR/]3.3 Cooling Intensity[/BR/] Good cast billet quality is the result of the combined effect of billet temperature, billet temperature and cooling intensity. Under the conditions of determining the temperature and drawing system, the water pressure is usually selected as 6bar, and then the cooling intensity is adjusted by adjusting each outlet to ensure that the outlet copper bar temperature reaches 30-35% of the metal solidus temperature, in order to ensure the actual Cooling strength, reduce thermal resistance, increase secondary cooling water, make the liquid cavity shallower and denser. In actual production, the matching gap between graphite and water-cooled copper sleeve should not exceed 0.02mm. The copper cold sleeve should be polished regularly and knotted on it. The inner wall of the cooling water cavity should be cleaned regularly. [/BR/]4. Common quality problems, influencing factors and control measures of horizontal continuous casting. [/BR/] Mainly by controlling the gas content of the molten metal, reducing the false resistance, improving the strength of the shell, and reducing the repair welding depth of the small liquid flow when the shell is broken.
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