Tin bronze horizontal continuous casting production line is composed of melting furnace, insulation 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 related factors on bar quality and take corresponding measures, it is necessary to analyze the crystallization process, characteristics and mechanism of horizontal continuous casting, so as to adopt reasonable technological system and obtain high quality products. [/BR/]2.1 When the casting is stopped, the slab stress in the mold (see Figure 1) [/BR/] When the casting is stopped, the slab in the mold is subjected to the following forces: ① The hydrostatic pressure generated by the molten metal in the furnace, P=HPG (h is the height of the liquid column; P is liquid density; G is the acceleration of gravity) : P 1> P 2; (2) The gravity of slab, because horizontal continuous casting is closed continuous casting, casting liquid, cavity and charge are connected, direct heat transfer. As a result, there is no condensation on the graphite plates 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. The condensation gradually thickens towards the exit direction until it solidifies into copper rods. Due to condensation and shrinkage, the gap between the condensing shells in the graphite is conducive to the casting billet, but due to the thin condensing shells and the static pressure of the liquid metal column, some condensing shells (L1 and L2 regions) do not leave the inner surface of the sleeve, only in the thick condensing shell slab (mold height 16mm, mold outlet copper bar thickness about 0.5mm, mold width 456MM, The crystallizer outlet copper bar shrinks by about 7mm) at static pressure P1 (p1> P2) The contact area between the lower part of the casting side and the graphite made by the metal shell under the double action of the condensate and gravity; Upper contact area L2; In addition, due to the non-uniformity 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 drawing, in order to facilitate the solidification process and stress analysis of the molten metal in the mold, it is assumed that the upper and lower crystals crystallize on the vertical interface. The condensation process in the drawing process is shown in Figure 2. [/BR/] When stretching begins, part of the melt will be released between the melt and the solid. Under the static pressure of the metal liquid, the metal behind will be replenished immediately. The closer the longitudinal distance between melt and graphite, the greater the cooling strength, the lower the metal temperature and the poorer the liquidity, while the higher the temperature of the intermediate metal, the faster the flow speed. According to the principles of fluid mechanics, the faster the flow in a liquid, the lower the pressure, so from the graphite wall to the longitudinal center, the pressure on the melt decreases, creating a pressure difference inside the melt, which forces the metal to flow in the direction of the arrow. Due to the pulling action of the metal bond, the shell condensed part is formed, but the static pressure of the surface is greater than that of the upper surface when the drawing is stopped, so the curvature of the lower surface is less than that of the upper surface. [/BR/] With the increase of the drawing distance, the new area of s gradually increases, and the arc length of the condenser shell keeps increasing. When the friction force is small enough and the strength of the condensation shell is high enough, there is no fracture, forming a curved surface (groove), but the curved surface is rough. In most cases, as the drawing distance increases, the copper water in the crystallization zone gets hotter and the condensing shell gets thinner, which is the weak one of the condensing shells, and a new small flow of liquid spills out of the crack and fills the concave part of the condensing shell. If this happens to be the end of the drawing, the metal crystallizes instantaneously during the stopping process and connects to the rest of the curved solidified shell. When 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 grain size is 100-150 times that of the fine crystal. See metallographic photos 3 and 4. [/BR/] FIG. 3 is a macroscopic diagram of H65 profile during crystallization, and FIG. 4 is a partial schematic diagram of the profile (contact area with the mold), that is, the metallographic structure diagram of the interface between the small liquid flow and the original condensate shell (X100). As can be seen from the figure, the fine grains and columnar crystals that are later filled have distinct separations and staggered shielding from each other, and the junction should contain rich metals, which must be ground away when the surface is milled during oxidation and solidification. [/BR/] FIG. 5 is a picture of the macro-structure milling to 0.4 mm at the bottom of the plate surface. In the figure, the coarse crystal area is the part of crystallization, and the fine crystal area is the part of filling after fracture. (To measure the thickness of the fine crystal, the surface on the left side is milled so that there is an extra part, marked by a distinct longitudinal arc). [B/B] From the crystallization principle and related photos, it can be seen that the old and new shell is oxidized due to the periodic change of temperature difference and non-uniformity, forming ring spots to characterize the asphalt. The determination and operation of the process conditions, the pouring temperature is 100-105℃ higher than the metal liquid temperature, it requires 30-40℃ higher than the pouring temperature. To avoid heat loss as the melt flows through the chute. The casting temperature of H65 is 1040-1060℃, and the fluctuation range of the insulation furnace is controlled within ±10℃. [/BR/]3.2 Pull-stop system [/BR/] Casting adopts reverse push-pull-stop procedure. The push-back function is as follows: (1) Prevent adhesion between the shell surface in the direct contact area with the mold and the mold wall (there is needle copper adsorption on the graphite in the crystallization process, and the feeling of binding when contacting the removed graphite). (2) Clean the zinc oxide and zinc attached to the graphite mold (in the area where there is a gap between the slab and graphite) to reduce the friction between the mold and the casting. ③ Vibration refining grains. [/BR/] The affinity of zinc oxygen is greater than that of carbon oxygen. In zinc-rich HPb59-1, oxygen does not react with graphite, and the graphite in the liquid phase is relatively flat, smooth and without pits. However, the friction resistance of graphite plate combined with Zn0 and Zn in solidification zone is higher. In order to avoid the superposition of Zn0 and Zn in the same region, with the development of the casting process, crystallization can be achieved by making the region move inward towards the volume direction through appropriate deceleration, thus improving the surface quality of the billet and the service life of the graphite. [/BR/] From the point of view of horizontal continuous casting, the role of intermittent casting is to obtain sufficient thickness and strength at the stop of the shell to avoid cracks or leaks, so the choice of pull-stop system is very important. [/BR/] Drawing and stopping are two mutually restrictive factors. Long stopping time - drawing time - drawing distance can be increased, short stopping time - drawing distance can be shortened. Due to the wide H65 two-phase area and developed dendrite, the gas released in the solidification process slowly diffuses to the liquid phase area. Generally, medium-low stroke, medium-instantaneous speed and medium-high frequency drawing casting are adopted to ensure that the outlet temperature of the copper bar reaches 30% ~ 35% of the solid phase line (for the copper bar with a thickness of 16mm), and the dark red surface of the copper bar at the crystallization outlet is better. [/BR/] Good billet quality is the result of the comprehensive action of billet temperature, billet temperature and cooling strength. Under the condition of determining the temperature and drawing system, the water pressure is usually 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 solid phase line temperature. In order to ensure the actual cooling intensity, reduce the thermal resistance, add secondary cooling water, so that the liquid cavity becomes shallow and dense. In the actual production, the matching gap between graphite and water-cooled copper sleeve shall not exceed 0.02mm. The copper cold sleeve shall be polished regularly, and the inner wall of the scaling cooling water cavity on it shall be removed regularly. [/BR/]4. Common quality problems, influencing factors and control measures of horizontal continuous casting. [/BR/] Mainly through 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 breaks.
