A slag removal and purification process in gray cast iron production

Abstract

The present application relates to the field of metal casting, and discloses a slag removal and purification process in gray cast iron production, which comprises the following steps: obtaining a metal liquid stream with a tapping temperature of 1450 DEG C to 1480 DEG C, and spraying a mixed material composed of asymmetric particle size graded ferrosilicon inoculant particles and silicon-based slag remover powder in the pouring runner, using discrete liquid phase droplets formed by melting of the slag remover to capture micrometer-sized inclusions, and using latent heat released by dissolution of the inoculant to establish a micro area temperature gradient, inducing micro thermal capillary convection to shear and strip the viscous fluid layer on the surface of the inclusions, pumping the dispersed inclusions into the droplets to aggregate into large particle slag clusters, and removing the slag clusters by standing, so that the present application uses endogenous latent heat compensation mechanism to solve the contradiction between purification kinetics and heat dissipation, makes the inclusions change from random collision to directional enrichment, and improves the quality of the castings.

Description

Technical Field

[0001] This invention relates to a slag removal and purification process in the production of gray cast iron, belonging to the field of metal casting technology. Background Technology

[0002] In the current production process of gray cast iron machine tool basic components, the purity of the molten metal directly affects the mechanical properties and processing quality of the castings. The industry generally adopts the technical approach of induction furnace melting combined with ladle slag removal, which mainly utilizes the natural buoyancy of non-metallic inclusions in the melt and the collision mechanism induced by macroscopic turbulence to achieve slag agglomeration and floating.

[0003] However, in the production of high-rigidity precision castings, the high-viscosity fluid boundary layer adhering to the surface of micron-sized composite oxide inclusions in the melt constitutes a physical barrier. Macroscopic mechanical turbulence is insufficient to overcome the viscous resistance generated by this boundary layer, leading to a physical limit on the collision probability of small inclusions. The physical flow channel morphology and macroscopic flow state are limited, and the methods for controlling the molten metal purification process and the use of auxiliary materials also have shortcomings. For example, Chinese invention patent application CN106367555A discloses a high-strength molten iron purification and slag removal covering agent for gray cast iron and ductile iron. This agent uses a mixture of various mineral components that expand upon heating to form a slag-aggregate layer to assist in slag removal. However, in the dynamic filling of large and heavy castings, this type of covering agent acts on the static surface of the molten metal, and its purification efficiency is insufficient to reach the deep microscopic inclusions in the melt. The technology lacks the microscopic shear force against the viscous boundary layer on the surface of the inclusions, making it impossible to effectively remove slag from the melt. The internal induced directional migration mechanism creates a technical antagonism between the deep purification of fine inclusions and the filling capacity of molten metal under strict temperature drop constraints. In pursuit of higher purity, the industry's common practice is to extend the settling time of molten metal before pouring. However, this leads to significant heat loss from the melt. Once the temperature drop exceeds the control range, it will induce the molten metal to become supercooled, resulting in cold shuts or uneven microstructure in the casting. Thus, while attempting to solve the inclusion problem, it introduces thermodynamic risks that affect the stability of casting performance. Linear improvement methods, such as simply increasing the amount of slag remover or increasing the stirring frequency, not only cause secondary slag formation on the melt surface due to excessive slag remover, but also fail to solve the boundary layer's constraint on inclusion agglomeration at the micro-dynamic level. Achieving deep removal of fine inclusions within the temperature window required to maintain the filling capacity of molten metal has always been a difficult trade-off in the field of metal casting.

[0004] Therefore, the technical problem to be solved by this invention is how to disintegrate the inclusion boundary layer by reconstructing the micro-flow mechanism inside the melt and synergistically utilize the heat of reaction to compensate for heat consumption, thereby achieving efficient purification under a narrow temperature difference window. Summary of the Invention

[0005] To address the problems mentioned in the background art, the technical solution of the present invention is as follows: A slag removal and purification process in gray cast iron production, comprising the following steps: Step S1: Obtain gray cast iron molten metal with a furnace exit temperature of 1450℃ to 1480℃, and control the flow of gray cast iron molten metal through the pouring channel. Step S2: Using carrier gas, a mixed additive is simultaneously injected into the gray cast iron molten metal flow in the pouring channel. The mixed additive is composed of ferrosilicon inoculant particles and silicon-based slag remover powder mixed in a mass ratio of 3:1 to 5:1, wherein the particle size of the ferrosilicon inoculant particles is 1.5 mm to 3.0 mm, and the particle size of the silicon-based slag remover powder is 0.1 mm to 0.3 mm. Step S3: The highly dispersed liquid droplets formed by the melting of silicon-based slag remover powder in gray cast iron molten metal capture micron-sized inclusions, and the latent heat of phase change released by the silicon-iron inoculant particles during the dissolution process are used to establish a local temperature gradient in the micro-region of molten metal around the silicon-iron inoculant particles. Step S4: The local temperature gradient is used to induce the interfacial tension gradient flow in the micro-region of the molten metal. The interfacial tension gradient flow shears and peels off the high viscosity fluid boundary layer on the surface of the micron-sized inclusions, and pumps the dispersed micron-sized inclusions into highly dispersed liquid droplets to aggregate into slag agglomerates. Step S5: Pour the gray cast iron molten metal into the casting ladle and let it stand. Utilize the density difference between the slag clump and the gray cast iron molten metal to complete the floating and slag removal.

[0006] Preferably, in step S2, the amount of mixed additives added is adjusted according to the furnace exit temperature of gray cast iron molten metal; when the furnace exit temperature drops by 5°C, the mass ratio of ferrosilicon inoculant particles in the mixed additives is increased by 2% to 3%, and the total amount of latent heat of phase change dissolution released by the ferrosilicon inoculant particles is used to compensate for the heat loss in the micro-region of the molten metal, so as to maintain the adsorption intensity of the interfacial tension gradient flow.

[0007] Preferably, step S2 includes the following sub-steps: step S21, coating the surface of the silicon-based slag remover powder with a flux film of 5μm to 10μm thickness; step S22, placing the coated silicon-based slag remover powder and ferrosilicon inoculant particles in a sealed mixing chamber, and performing high-frequency vibration mixing under a nitrogen purging pressure of 0.2MPa to 0.4MPa.

[0008] Preferably, the ferrosilicon inoculant particles contain, by mass percentage, 72% to 78% silicon, 1.5% to 2.5% barium, 1.0% to 2.0% calcium, less than 1.5% aluminum, with the remainder being iron and unavoidable impurities.

[0009] Preferably, the silicon-based slag remover powder comprises, by mass percentage: 60% to 70% silicon dioxide, 10% to 15% aluminum oxide, 3% to 5% sodium oxide, 2% to 4% magnesium oxide, 1% to 3% sodium hexafluoroaluminate, with the balance being unavoidable impurities, and the silicon-based slag remover powder has a dynamic viscosity of less than 0.5 Pa·s at 1450°C.

[0010] Preferably, in step S1, the Reynolds number of the gray cast iron molten metal is limited to below 2000 by adjusting the valve opening at the outlet end of the pouring channel, so that the gray cast iron molten metal enters the pouring ladle involved in step S5 in a laminar flow state.

[0011] Preferably, in step S5, a negative pressure environment with a vacuum degree of 0.05MPa to 0.08MPa is established above the liquid surface of the casting ladle, and an argon gas flow of 2L / min to 5L / min is introduced into the bottom of the gray cast iron molten metal to assist in the enrichment of slag clumps by utilizing the drag force generated by the rising argon bubbles.

[0012] Preferably, the flux film in step S21 has a melting point of 1100°C to 1200°C and is composed of calcium fluoride, borax and sodium carbonate in a mass ratio of 2:1:1.

[0013] Preferably, after the slag removal in step S5 is completed, the gray cast iron molten metal is controlled to be filled into the cavity of the sand mold at a flow rate of 0.5 m / s to 1.2 m / s, and the total mass ratio of non-metallic inclusions in the gray cast iron casting matrix after filling is less than 0.005%.

[0014] Compared with the prior art, the beneficial effects of the present invention are: 1. In gray cast iron production, by constructing an asymmetric particle size distribution between the inoculant and the slag remover during the flow stage, and utilizing the thermodynamic dissolution difference between millimeter-sized coarse inoculant particles and sub-millimeter-sized fine slag remover powder in the molten metal, a local microscopic temperature gradient field is induced inside the melt. This microscopic thermorheological coupling mechanism causes strong thermocapillary convection around the incompletely dissolved inoculant particles, thereby effectively tearing the high-viscosity fluid boundary layer attached to the surface of micron-sized non-metallic inclusions. This mechanism realizes the essential transformation of inclusions from traditional macroscopic random physical collisions to microscopic thermocapillary directional enrichment, significantly compressing the time scale required for slag agglomeration and ensuring that deep purification of the molten metal is completed within a narrow operating window before solidification.

[0015] 2. The latent heat of phase change released during the dissolution of a specific ratio of ferrosilicon inoculant is converted into a built-in compensating heat source to resist external heat dissipation during the settling stage. This establishes a dynamic interlock between the inoculation reaction and heat dissipation at the physical mechanism level. This heat balance logic enables the molten metal to maintain the interface slag removal within the target temperature range during a short settling period. This solves the technical antagonism between deep purification and molten metal undercooling in the production of high-rigidity castings. By linearly compensating and controlling the spray flow rate of the slag remover and the real-time temperature at the furnace outlet, secondary slag formation or local viscosity surges caused by excessive additives are avoided, ensuring excellent fluidity of the molten metal during the subsequent filling process.

[0016] 3. By synergistically utilizing a high-preheating-temperature casting ladle and a vacuum pressure-holding constraint system, along with constant mass flow rate control, the purified high-temperature molten metal enters the sand mold cavity in a laminar flow state. This controlled flow environment eliminates the vortex disturbances and liquid surface turbulence commonly found in traditional open casting processes, and blocks the formation chain of secondary oxidation inclusions and air entrapment defects. This whole-process physical quantity coupling management from smelting and purification to casting reduces the micro-stress concentration sources inside the gray cast iron matrix, enabling the final casting to achieve a stable distribution of tensile strength and Brinell hardness within a precise range while possessing a high pearlite content, thus meeting the engineering requirements of high-precision machine tool core components for extreme uniformity of metallographic structure. Attached Figure Description

[0017] Figure 1 This is a flowchart of the slag removal and purification process driven by thermocapillary convection and compensated by endogenous latent heat according to the present invention. Figure 2 This is a diagram of the architecture of the multi-dimensional working condition perception and material feeding dynamic feedback control system of the present invention.

[0018] The objectives, features, and advantages of this invention will be further explained in conjunction with the embodiments and with reference to the accompanying drawings. Detailed Implementation

[0019] The technical solutions of the embodiments of this application will be clearly described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of this application, not all embodiments. All other embodiments obtained by those skilled in the art based on the embodiments of this application are within the scope of protection of this application.

[0020] A slag removal and purification process in gray cast iron production includes the following steps: Step S1: Obtain gray cast iron molten metal with a furnace exit temperature of 1450℃ to 1480℃, and control the flow of gray cast iron molten metal through the pouring channel. Step S2: Using carrier gas, a mixed additive is simultaneously injected into the gray cast iron molten metal flow in the pouring channel. The mixed additive is composed of ferrosilicon inoculant particles and silicon-based slag remover powder mixed in a mass ratio of 3:1 to 5:1, wherein the particle size of the ferrosilicon inoculant particles is 1.5 mm to 3.0 mm, and the particle size of the silicon-based slag remover powder is 0.1 mm to 0.3 mm. Step S3: The highly dispersed liquid droplets formed by the melting of silicon-based slag remover powder in gray cast iron molten metal capture micron-sized inclusions, and the latent heat of phase change released by the silicon-iron inoculant particles during the dissolution process are used to establish a local temperature gradient in the micro-region of molten metal around the silicon-iron inoculant particles. Step S4: The local temperature gradient is used to induce the interfacial tension gradient flow in the micro-region of the molten metal. The interfacial tension gradient flow shears and peels off the high viscosity fluid boundary layer on the surface of the micron-sized inclusions, and pumps the dispersed micron-sized inclusions into highly dispersed liquid droplets to aggregate into slag agglomerates. Step S5: Pour the gray cast iron molten metal into the casting ladle and let it stand. Utilize the density difference between the slag clump and the gray cast iron molten metal to complete the floating and slag removal.

[0021] Preferably, in step S2, the amount of mixed additives added is adjusted according to the furnace exit temperature of gray cast iron molten metal; when the furnace exit temperature drops by 5°C, the mass ratio of ferrosilicon inoculant particles in the mixed additives is increased by 2% to 3%, and the total amount of latent heat of phase change dissolution released by the ferrosilicon inoculant particles is used to compensate for the heat loss in the micro-region of the molten metal, so as to maintain the adsorption intensity of the interfacial tension gradient flow.

[0022] Preferably, step S2 includes the following sub-steps: step S21, coating the surface of the silicon-based slag remover powder with a flux film of 5μm to 10μm thickness; step S22, placing the coated silicon-based slag remover powder and ferrosilicon inoculant particles in a sealed mixing chamber, and performing high-frequency vibration mixing under a nitrogen purging pressure of 0.2MPa to 0.4MPa.

[0023] Preferably, the ferrosilicon inoculant particles contain, by mass percentage, 72% to 78% silicon, 1.5% to 2.5% barium, 1.0% to 2.0% calcium, less than 1.5% aluminum, with the remainder being iron and unavoidable impurities.

[0024] Preferably, the silicon-based slag remover powder comprises, by mass percentage: 60% to 70% silicon dioxide, 10% to 15% aluminum oxide, 3% to 5% sodium oxide, 2% to 4% magnesium oxide, 1% to 3% sodium hexafluoroaluminate, with the balance being unavoidable impurities, and the silicon-based slag remover powder has a dynamic viscosity of less than 0.5 Pa·s at 1450°C.

[0025] Preferably, in step S1, the Reynolds number of the gray cast iron molten metal is limited to below 2000 by adjusting the valve opening at the outlet end of the pouring channel, so that the gray cast iron molten metal enters the pouring ladle involved in step S5 in a laminar flow state.

[0026] Preferably, in step S5, a negative pressure environment with a vacuum degree of 0.05MPa to 0.08MPa is established above the liquid surface of the casting ladle, and an argon gas flow of 2L / min to 5L / min is introduced into the bottom of the gray cast iron molten metal to assist in the enrichment of slag clumps by utilizing the drag force generated by the rising argon bubbles.

[0027] Preferably, the melting point of the flux film in step S21 is 1100°C. Up to 1200 It is composed of calcium fluoride, borax and sodium carbonate in a mass ratio of 2:1:1.

[0028] Preferably, after the slag removal in step S5 is completed, the gray cast iron molten metal is controlled to be filled into the cavity of the sand mold at a flow rate of 0.5 m / s to 1.2 m / s, and the total mass ratio of non-metallic inclusions in the gray cast iron casting matrix after filling is less than 0.005%.

[0029] Example 1: In the production scenario of gray cast iron for high-precision machine tool bed castings, the tapping temperature of the gray cast iron molten metal is controlled at 1475℃ to meet the fluidity requirements of large-volume castings during the filling process. The purification treatment operation window is limited to a specific temperature drop gradient. During the flow of the gray cast iron molten metal through the gating channel, a mixed additive consisting of ferrosilicon inoculant particles and silicon-based slag remover powder is simultaneously injected into the liquid flow by carrier gas. The particle size of the ferrosilicon inoculant particles is selected as 2.0mm, and the particle size of the silicon-based slag remover powder is selected as 0.15mm, through asymmetric particle size classification. When the silicon-based slag remover powder comes into contact with the molten metal, it forms dispersed liquid droplets. Due to the thermodynamic hysteresis dissolution characteristics of the ferrosilicon inoculant particles, they continuously release latent heat of dissolution during the dissolution process, establishing a local temperature gradient within the micro-region of the molten metal surrounding the ferrosilicon inoculant particles. In the initial stage of this physical dissolution, when the high concentration of silicon on the surface of the ferrosilicon inoculant particles transiently diffuses into the gray cast iron molten metal, a localized exothermic reaction accompanied by local component supercooling is triggered at the solid-liquid interface between the particles and the melt. The heat flux density released by this interfacial reaction is higher than that of the surrounding high-temperature molten iron within a microsecond timescale. The thermal conductivity and diffusivity of molten cast iron overcomes the transient heat dissipation of fluids with low Prandtl numbers. Within a fluid boundary layer with a thickness of only a few micrometers close to the particle surface, a non-equilibrium microscopic thermodynamic temperature field is briefly constructed, with the inoculant particles as the thermal centers. The maintenance of this non-equilibrium microscopic thermodynamic temperature field depends on the transient chemical potential difference generated when iron and silicon atoms dissolve at the solid-liquid interface. When ferrosilicon inoculant particles with a diameter of 1.5 mm to 3.0 mm enter the high-temperature molten metal flow, a silicon-rich, high-viscosity transition film rapidly forms on their surface. This film constitutes a barrier to thermal conduction. The barrier layer slows down the absorption of sensible heat by the internal core. At the same time, the local exothermic reaction triggered by the spontaneous diffusion of high-concentration silicon atoms into the molten iron matrix continues to occur on the outside of the transition film. In the micro-region space of 5 to 25 micrometers away from the particle surface, the exothermic rate is significantly greater than the bulk thermal conductivity of the molten metal in the initial 0.01 to 0.5 seconds. This non-equilibrium energy input at the microscale keeps the local temperature difference between 2.5°C and 4.0°C, thereby stably maintaining the high-gradient micro-region temperature field within a micrometer-thickness and blocking the transient heat dissipation of the high-temperature melt.

[0030] Local temperature gradients induce interfacial tension gradient flows in micro-regions of molten metal. These flows generate shear forces to peel away the high-viscosity fluid boundary layer on the surface of micron-sized composite oxide inclusions, pumping the dispersed inclusions along the viscosity gradient into adjacent molten droplets. This causes the inclusions to switch from a random collision mode to a directional thermocapillary agglomeration mode, forming slag agglomerates. A physical wettability difference exists between the inclusions and their surface high-viscosity fluid boundary layer. The interfacial tension gradient flows form micro-vortices along the temperature gradient in local micro-regions. The streamlines of these micro-vortices cause abrupt changes in normal strain rate at the inclusion boundaries, leading to the peeling of the high-viscosity boundary layer under hydrodynamic shear. Simultaneously, the surface tension of the molten droplets formed by the melting of the silicon-based slag remover is lower than that of the surrounding area. In the molten cast iron with edge gray, the exposed inclusions after the boundary layer is stripped are physically driven by the Marangoni effect. Following the local viscosity decay path established by the latent heat of phase change within the fluid, they are directionally transported and spontaneously adsorbed into the interior of the molten droplets of the slag remover with lower surface energy. The local latent heat of phase change is easily dissipated by transient conduction in fluids with low Prandtl numbers. A flow stabilizing grid and an alternating electromagnetic generator are sequentially connected in series along the flow direction of the molten metal in the casting channel. The multiphase turbulent flow induced by the jet is transformed into a parallel flow stream by the flow stabilizing grid. The alternating electromagnetic generator radiates an alternating magnetic field to the parallel flow stream at a frequency of 50Hz to 200Hz. Although the incompletely dissolved ferrosilicon inoculant is a non-magnetic millimeter-sized entity, when its high concentration of silicon on the surface is released outward, it will establish a local resistivity physical gradient in the conductive molten metal around the particles.

[0031] When the alternating magnetic field penetrates the resistivity gradient region, according to Faraday's law of electromagnetic induction, the non-uniform induced eddy currents induced inside the gradient melt interact with the original alternating magnetic field, generating an asymmetric Lorentz force precisely pointing towards the particle surface. This macroscopic electromagnetic force counteracts the viscous flow of the molten metal at the microscopic scale, thus physically solidifying a buffer fluid layer of a specific thickness around the particles. The barrier construction mechanism of the macroscopic magnetic field at the microscopic scale lies in the fact that although the electromagnetic skin depth of the 50 Hz to 200 Hz alternating magnetic field in the molten iron is macroscopically 30 mm to 60 mm, the molten metal has been transformed into a laminar flow after passing through the stabilizing and rectifying grid. Therefore, the macroscopic magnetic field distribution exhibits a high degree of spatial uniformity. When the uniform magnetic field passes through the local concentration gradient generated by the disturbance of independent particles, the conductivity difference between the silicon-rich region and the pure molten iron matrix in the melt reaches 15% to 25%. This discontinuity in local conductivity causes the macroscopic induced eddy currents to distort when passing through the particle boundaries. The charge transiently accumulates at the solid-liquid interface, superimposing a microscopic local shear stress component into the macroscopic Lorentz force field. This component is oriented in the opposite direction to the convective disturbance caused by particle dissolution, and its magnitude, within a 50-micrometer range on the particle surface, achieves mechanical equilibrium with the local fluid shear force. This manifests as a strong suppression of local fluid pulsation around the particles, thus indirectly stabilizing the microscopic thermal boundary layer under the influence of the macroscopic field. The magnetic field induces Lorentz forces within the molten metal to maintain a fluid viscosity buffer layer with a thickness of 10-50 μm around the incompletely dissolved ferrosilicon inoculant particles. This fluid viscosity buffer layer constitutes a physical barrier that impedes the instantaneous dissipation of heat from the micro-region to the melt, prolonging the time constant of latent heat of phase change dissipation within the local micro-region, and maintaining the thermodynamic temperature gradient boundary required for thermocapillary convection. The instantaneous mass flow rate of the silicon-based slag remover powder in the mixed additive is compensated and adjusted according to the real-time temperature collected by the sensor, and its calculation formula is as follows: ,in, The instantaneous mass flow rate of the silicon-based slag remover powder. The real-time temperature of the gray cast iron molten metal obtained at the furnace tapping point. The reference mass for gray cast iron molten metal. This is the proportionality coefficient. The temperature compensation coefficient is used. After purification, the gray cast iron molten metal is placed in a casting ladle preheated to 350°C and allowed to stand for 4 minutes. The latent heat of dissolution from the phase change released by the ferrosilicon inoculant particles is used to compensate for the external heat loss. The density difference effect between the slag agglomerate and the gray cast iron molten metal completes the interface slag removal under the premise that the total temperature drop is controlled within 20°C. After slag removal, the gray cast iron molten metal is filled into the cavity of the furan resin sand mold at a flow rate of 0.5 m / s to 1.2 m / s. An alcohol-based graphite coating with a thickness of 0.2 mm to 0.4 mm is uniformly sprayed on the inner surface of the resin sand mold cavity and dried to prevent the physical erosion of the cavity wall by the high temperature molten metal. The total mass ratio of non-metallic inclusions in the final casting matrix is ​​less than 0.005%, and the metallographic structure of the casting exhibits uniformity.

[0032] Example 2: In an industrial test platform simulating the production of a heavy-duty machine tool spindle box, the purification efficiency of high-viscosity gray cast iron melt in a non-ideal filling channel was verified. The test platform included a 3t rated capacity medium-frequency induction furnace and a flow-fed injection system with carrier gas pressure feedback regulation. The sampling frequency for acquiring the mass flow rate signal of the gray cast iron molten metal was set to 50Hz, and the temperature sensor's measurement accuracy was ±2℃. This was done to determine the instantaneous mass flow rate of the silicon-based slag remover powder in the mixed additives. The scaling factor needs to be adjusted. With temperature compensation coefficient Calibration is performed, and the scaling factor is adjusted. The value depends on the mass percentage concentration of the initial nonmetallic inclusions in the melt. The kinetic settling rate at 1450℃ was investigated. The effect of different slag amounts on the residual inclusion content after purification was tested under a constant temperature environment of 1450℃. The minimum slag-to-gold ratio of 0.0035, which resulted in a residual inclusion content below 0.005%, was selected as the minimum. The engineering value, and the temperature compensation coefficient The setting balances the increased collision frequency caused by the decrease in melt viscosity and the hysteresis of dissolution kinetics caused by heat loss. Based on the measured viscosity values ​​at different temperature gradients, The value was determined to be 0.12. Specifically, the control system extracted discrete calibration data of dynamic viscosity of multiple sets of gray cast iron molten metal within the engineering operation range of 1450℃ to 1480℃. The exponential decay function model of dynamic viscosity with temperature change was obtained by least squares mathematical fitting. The derivative of the model was used to extract the absolute value of the tangent slope of the decay function at the reference opening temperature of 1450℃. After dividing by the reference viscosity, the model was dimensionless. This result was directly used as the engineering constant value of 0.12 for the temperature compensation coefficient α, thereby constructing a deterministic dimension reduction mapping between the viscosity nonlinear response and the system compensation control.

[0033] The experimental design included three sample groups: an experimental group using the process of this invention, a first control group (removing ferrosilicon inoculant particles and retaining only silicon-based slag remover powder), and a second control group (removing silicon-based slag remover powder and retaining only ferrosilicon inoculant particles). During the in-flow injection process, a broadband thermal noise with a signal-to-noise ratio of 20 dB was actively superimposed on the experimental signal source, and a 5 Hz fluid pressure pulsation was introduced to simulate external interference in the actual casting environment. In the experimental group, the interfacial tension gradient flow intensity reached 0.85 in the local area 15 seconds after the addition of the mixed additive. Metallographic microscopy revealed that after the samples had settled, the average particle size of non-metallic inclusions in the experimental group increased from an initial 12.5 μm to a large slag agglomerate of 185.6 μm. The final non-metallic inclusion mass percentage in the formed casting was 0.0042%. In the first control group, due to the lack of latent heat of dissolution from the ferrosilicon inoculant particles, an effective local temperature gradient could not be established, and the interfacial tension gradient flow intensity was only [missing data]. In the first control group, micron-sized inclusions remained dispersed, and the proportion of non-metallic inclusions in the final casting was 0.0485%. In the second control group, due to the lack of silicon-based droplets as a collection carrier, the inclusions could not be directionally aggregated, and the final proportion was 0.0512%. This comparative data confirms the synergistic purification effect of thermocapillary convection generated by asymmetric particle size distribution.

[0034] To verify the rationality of the parameter range, an out-of-range control group was further set up. When the mass ratio of ferrosilicon inoculant particles to silicon-based slag remover powder decreased to 2:1, the latent heat of dissolution was insufficient to compensate for the temperature drop loss of the large volume of molten metal, resulting in an increase in the viscosity of the molten metal before entering the casting ladle, a decrease in the interface slag removal efficiency, and ultimately a rise in the inclusion content to 0.0215%. When the mass ratio increased to 6:1, the excessive dissolution of silicon elements triggered local overheating, causing the graphite morphology to change from type A to type D. The tensile strength of the casting decreased from 305 MPa to 242 MPa, exhibiting a non-linear deterioration effect. The data trend indicates that the mass ratio range of 3:1 to 5:1 is... Balancing purification efficiency and metallographic quality, a gradient verification was conducted on molten metal with different initial purities. When the initial inclusion mass percentages were 0.08%, 0.15%, and 0.25%, the residual inclusion content after treatment was stably controlled within a narrow range of 0.0038% to 0.0055%, without linear escape as the initial contamination level increased. Scanning electron microscopy observation of the test samples revealed a tightly bound structure of micron-sized composite oxides and silicon-based melt within the slag clumps, confirming the physical disintegration effect of interfacial tension gradient flow on the boundary layer of high-viscosity fluids, thus improving the uniformity of the metallographic structure of the castings.

[0035] Example 3: When producing heavy-duty diesel engine cylinder block castings, the tapping temperature of gray cast iron molten metal fluctuates between 1460℃ and 1485℃. This temperature fluctuation alters the dynamic viscosity of the gray cast iron molten metal, causing deviations in the dispersion distribution of silicon-based slag remover powder droplets and the intensity of the interfacial tension gradient flow. The in-flow purification control system obtains the real-time temperature through an infrared temperature sensor installed at the inlet of the pouring channel. The reference mass of gray cast iron molten metal is obtained by using an electronic weighing module installed on the feeder. The sampling frequency for acquiring real-time temperature signals was set to 50Hz. A mean filtering algorithm was used to filter out environmental noise, and the real-time temperature was calculated. The difference from the reference temperature of 1450℃, and according to the formula Calculate the instantaneous mass flow rate of silicon-based slag remover powder. ;in, The instantaneous mass flow rate of the silicon-based slag remover powder. This is the proportionality coefficient. The reference mass for gray cast iron molten metal. This is the temperature compensation coefficient. The real-time temperature of the gray cast iron molten metal obtained at the furnace tapping point is 1450, the reference opening temperature is 1450, and the preset temperature adjustment range constant is 30. The proportionality coefficient is... The determination method is as follows: Samples with non-metallic inclusion mass percentages of 0.1%, 0.2%, and 0.3% were selected. The dosage of slag removal agent required to reduce the proportion of non-metallic inclusions to below 0.005% after purification was determined at 1450℃. Three sets of data were obtained, and their arithmetic mean was taken as the slag removal agent dosage. The value of is determined by the nonlinear loss of sensible heat caused by the injection of powdered auxiliary materials at room temperature into the molten metal. The control unit receives the instantaneous mass flow rate from the electronic weighing module in real time via a pre-set thermal balance decoupling calculation model. and real-time temperature The total sensible heat absorption flux required for the mixed additives to rise from the initial ambient temperature to the melting point is calculated, and the difference between the total sensible heat absorption flux and the latent heat release flux of phase change calculated based on the ratio of ferrosilicon inoculant is compared.

[0036] When the differential value indicates that the total sensible heat absorption flux exceeds the latent heat release flux of the phase change and the deviation exceeds the 15% preset tolerance band, a closed-loop heating command is generated and output to the material silo follow-up preheater to dynamically heat the sprayed mixed additive to the range of 300℃ to 350℃. Dynamic preheating removes the interference of sensible heat abrupt change in the initial stage of powder injection, ensuring the independent evolution of the temperature gradient field in the micro-region of the molten metal. The pulse width modulation module will control the instantaneous mass flow rate. The drive command is converted into a driving command output to the drive motor of the feeder, adjusting the speed to match the material feeding amount with the thermodynamic state of the gray cast iron molten metal. At the physical execution end of material injection, the feeding of the mixed additive is independently executed by coaxially arranged inner and outer double spiral micro feeders. The outer spiral structure is used to convey a fixed proportion of silicon-based slag remover powder at a constant reference flow rate, while the inner servo variable pitch spiral structure is controlled by real-time temperature drop feedback commands. By finely adjusting its instantaneous speed, it forms a differential speed compensation conveying with the outer spiral, thereby achieving continuous, dynamic, and precise physical replenishment of ferrosilicon inoculant particles with a mass ratio of 2% to 3% within the main mixing chamber of the carrier gas flow. The feeding amount of silicon-based slag remover powder is adjusted according to the change in melt viscosity. When the furnace outlet temperature fluctuates within ±15℃, the local temperature gradient generated around the ferrosilicon inoculant particles is maintained at... / m to / m, the shear force generated by the interfacial tension gradient flow peels away the high viscosity fluid boundary layer on the surface of non-metallic inclusions, driving the dispersed micron-sized composite oxide inclusions to migrate directionally towards the liquid droplets. After the gray cast iron molten metal is allowed to stand for 4 minutes, it is filled into the mold and smoothly poured into the cavity of the clay sand mold through a sprue equipped with a foam ceramic filter screen. The laminar flow filling state avoids secondary slag formation and air entrapment defects. The total mass ratio of non-metallic inclusions in the cylinder casting matrix is ​​in the range of 0.0035% to 0.0048%, and the gray cast iron structure exhibits metallographic homogeneity under fluctuating furnace conditions.

[0037] Example 4: In a production scenario using a new batch of silicon-based slag remover powder, the system corrects the proportional coefficient through a pre-process kinetic activity calibration. Three groups of 500 kg gray cast iron molten metal were selected as reference samples. A mixed additive with a mass ratio of 4:1 was added at a constant temperature of 1460℃. The evolution time of non-metallic inclusions from the dispersed state to the liquid droplet enrichment state was obtained using a high-speed imaging unit at the in-flow monitoring site. Evolution duration The calculations are as follows: The high-speed imaging unit acquires a continuous grayscale image sequence of the surface area of ​​the gray cast iron molten metal at a sampling rate of no less than 500 frames / second; the image processing module extracts isolated dark spot connected regions within a preset coordinate window frame by frame and calculates the average pixel area and equivalent contour roundness parameter of the connected regions; considering the strong blackbody radiation background interference of liquid metal at 1460℃, the front-end optical path of the high-speed imaging unit is specially equipped with a narrowband interference filter and polarizing lens group with a center wavelength of 450nm to physically suppress broadband long-wave thermal radiation background light, and utilizes the enriched slag agglomerates and high brightness The inherent physical differences in emissivity of the metal cleaning liquid surface in the short-wavelength band allow for the successful extraction of slag clumps converging on the melt surface from the bright background as isolated dark spots with high contrast morphology through hardware filtering. When the average pixel area of ​​the connected region exceeds the set slag clump aggregation calibration threshold for 10 consecutive sampling cycles, and the coefficient of variation of the equivalent contour roundness falls below 10% of the initial discrete state baseline value, the absolute timestamp of the current image frame generation time is recorded and locked as the enrichment state completion node. The time span from the initiation of the carrier gas injection to the enrichment state completion node is calculated and output as the evolution duration. By using dual morphological constraints of connected region area and contour roundness to eliminate artifact signals caused by liquid surface ripples and light spots, the physical evolution is converged to a definite time order, and the control unit is based on the evolution duration. Deviation from reference duration proportional correction factor The value is used to offset the fluctuations in interfacial tension gradient flow intensity caused by differences in surface activity between different production batches of silicon-based slag remover powder.

[0038] The control unit is based on the corrected proportional coefficient. Determine the drive pulse frequency of the screw feeder motor to achieve the instantaneous mass flow rate of the silicon-based slag remover powder. Matching the processing requirements of gray cast iron molten metal; when the system faces pouring channel conditions with specific heat capacity characteristics, the control system adjusts the temperature drop rate based on feedback from the outlet temperature measurement node. Corrected temperature compensation coefficient The temperature field distribution data of gray cast iron molten metal flowing through the flow channel was obtained by using an infrared sensor array. The heat transfer flux between the gray cast iron molten metal and the flow channel wall was calculated. The temperature difference gain term in the compensation formula was fine-tuned by using linear interpolation to balance the heat dissipation loss of the flow channel environment by the latent heat of phase change released by the ferrosilicon inoculant particles. After the system entered a stable state, the amount of mixed additives added changed with the real-time temperature of the gray cast iron molten metal. The average diameter of the slag agglomerates remained stable above 150 μm and maintained a continuous upward floating force. The proportion of non-metallic inclusions in the casting matrix remained below 0.005%.

[0039] Example 5: In a gray cast iron production environment with a flow-through purification device, before system startup, the vertical displacement between the nozzle outlet and the centerline of the molten gray cast iron is adjusted to 150mm, and the incident angle between the injection direction and the horizontal plane of the molten gray cast iron is set to 45°. By adjusting the carrier gas pressure within the range of 0.2MPa to 0.4MPa, the depth of the local depression caused by the impact of the mixed additives on the surface of the molten gray cast iron is monitored using a velocity sensor. The carrier gas pressure is selected when the depression depth is 0.35 times the flow depth of the molten gray cast iron. The gas pressure serves as the initial kinetic energy reference for system deployment, thereby anchoring the feeding parameters within the physical boundaries corresponding to the current channel geometry. The velocity sensor deployed here employs a dual-frequency Doppler radar detection architecture. While acquiring the axial downward scalar velocity of the mixed additives during the two-phase injection, it utilizes the Doppler frequency shift broadening effect of the echo reflected from the free liquid surface where the molten metal undergoes concave deformation. Through a time integration algorithm, it calculates the dynamic disturbance displacement along the gravitational direction generated by the continuous action of the gas-solid jet impulse on the free liquid surface, and extracts this displacement. The stable peak value of the displacement fluctuation sequence serves as an indirect characterization parameter of the local physical depression depth. A dual-frequency Doppler radar transmits two continuous microwave signals with a center frequency difference of 100 MHz to the free liquid surface. When the gas-solid jet impacts the molten iron surface to form a depression, the liquid surface generates low-frequency vertical oscillations during the balance between gravity and jet impulse. The center frequency shift of the echo signal directly reflects the transient velocity of the vertical motion of the liquid surface. The algorithm first performs a fast Fourier transform on the original echo to extract the Doppler frequency shift broadened power spectrum caused by the combined effects of liquid surface churning and jet scattering. Since there is a significant difference in frequency between the airflow scouring noise and the macroscopic oscillation of the liquid surface, the system filters out the high-frequency broadened components belonging to the jet itself through a bandpass filter, locking in the low-frequency principal component Doppler frequency shift representing the downward motion of the center of the free liquid surface. By integrating the vertical velocity scalar corresponding to this principal component Doppler frequency shift over time, the spatial geometric displacement of the free liquid surface from the initial equilibrium state to the maximum depression position can be obtained, thus accurately reconstructing the physical depression depth and eliminating the interference of velocity dispersion on spatial measurements.

[0040] When the system encounters a situation where the temperature measurement node experiences heat accumulation drift due to continuous pouring, the control unit corrects the real-time temperature by detecting the radiation energy of the flow channel wall during non-pouring intervals. The input reference is used to calculate the real-time temperature during the initial flow of molten gray cast iron. The rate of change over time is used to obtain the temperature drop slope index. If the temperature drop slope index deviates from the preset range, the control unit automatically adjusts the proportional coefficient. The compensation weight ensures that the intensity of the interfacial tension gradient flow generated locally meets the shear work requirement for peeling off the high viscosity fluid boundary layer on the surface of non-metallic inclusions under the dynamic fluctuation of the furnace exit environment, so that the proportion of non-metallic inclusions in the final casting matrix is ​​below 0.005%.

[0041] It will be apparent to those skilled in the art that the present invention is not limited to the details of the exemplary embodiments described above, and that the present invention can be implemented in other specific forms without departing from the spirit or essential characteristics of the present invention.

[0042] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention and are not intended to limit it. Although the present invention has been described in detail with reference to preferred embodiments, those skilled in the art should understand that modifications or equivalent substitutions can be made to the technical solutions of the present invention without departing from the spirit and scope of the technical solutions of the present invention.

Claims

1. A slag removal and purification process in gray cast iron production, characterized in that, Includes the following steps: Step S1: Obtain gray cast iron molten metal with a furnace exit temperature of 1450℃ to 1480℃, and control the flow of gray cast iron molten metal through the pouring channel. Step S2: Using carrier gas, a mixed additive is simultaneously injected into the gray cast iron molten metal flow in the pouring channel. The mixed additive is composed of ferrosilicon inoculant particles and silicon-based slag remover powder mixed in a mass ratio of 3:1 to 5:1, wherein the particle size of the ferrosilicon inoculant particles is 1.5 mm to 3.0 mm, and the particle size of the silicon-based slag remover powder is 0.1 mm to 0.3 mm. Step S3: The highly dispersed liquid droplets formed by the melting of silicon-based slag remover powder in gray cast iron molten metal capture micron-sized inclusions, and the latent heat of phase change released by the silicon-iron inoculant particles during the dissolution process are used to establish a local temperature gradient in the micro-region of molten metal around the silicon-iron inoculant particles. Step S4: The local temperature gradient is used to induce the interfacial tension gradient flow in the micro-region of the molten metal. The interfacial tension gradient flow shears and peels off the high viscosity fluid boundary layer on the surface of the micron-sized inclusions, and pumps the dispersed micron-sized inclusions into highly dispersed liquid droplets to aggregate into slag agglomerates. Step S5: Pour the gray cast iron molten metal into the casting ladle and let it stand. Utilize the density difference between the slag clump and the gray cast iron molten metal to complete the floating and slag removal.

2. The slag removal and purification process in gray cast iron production according to claim 1, characterized in that, In step S2, the amount of mixed additives added is adjusted according to the tapping temperature of gray cast iron molten metal. When the tapping temperature drops by 5°C, the mass ratio of ferrosilicon inoculant particles in the mixed additives is increased by 2% to 3%. The increased latent heat of phase change dissolution released by the ferrosilicon inoculant particles is used to compensate for the heat loss in the micro-region of the molten metal, so as to maintain the adsorption intensity of the interfacial tension gradient flow.

3. The slag removal and purification process in gray cast iron production according to claim 1, characterized in that, Step S2 includes the following sub-steps: Step S21, coating the surface of the silicon-based slag remover powder with a flux film of 5μm to 10μm thickness; Step S22, placing the coated silicon-based slag remover powder and ferrosilicon inoculant particles in a sealed mixing chamber, and performing high-frequency vibration mixing under a nitrogen purging pressure of 0.2MPa to 0.4MPa.

4. The slag removal and purification process in gray cast iron production according to claim 1, characterized in that, The ferrosilicon inoculant granules contain, by mass percentage, 72% to 78% silicon, 1.5% to 2.5% barium, 1.0% to 2.0% calcium, less than 1.5% aluminum, with the remainder being iron and unavoidable impurities.

5. The slag removal and purification process in gray cast iron production according to claim 1, characterized in that, The components of the silicon-based slag remover powder, by mass percentage, include: 60% to 70% silicon dioxide, 10% to 15% aluminum oxide, 3% to 5% sodium oxide, 2% to 4% magnesium oxide, 1% to 3% sodium hexafluoroaluminate, with the balance being unavoidable impurities, and the dynamic viscosity of the silicon-based slag remover powder at 1450°C is less than 0.5 Pa·s.

6. The slag removal and purification process in gray cast iron production according to claim 1, characterized in that, In step S1, by adjusting the valve opening at the outlet of the pouring channel, the Reynolds number of the gray cast iron molten metal is limited to below 2000, so that the gray cast iron molten metal enters the pouring ladle involved in step S5 in a laminar flow state.

7. The slag removal and purification process in gray cast iron production according to claim 1, characterized in that, In step S5, a negative pressure environment with a vacuum degree of 0.05MPa to 0.08MPa is established above the liquid surface of the casting ladle, and an argon gas flow of 2L / min to 5L / min is introduced into the bottom of the gray cast iron molten metal to assist in the enrichment of slag clumps by using the drag force generated by the rising argon bubbles.

8. The slag removal and purification process in gray cast iron production according to claim 3, characterized in that, The flux film in step S21 has a melting point of 1100℃ to 1200℃ and is composed of calcium fluoride, borax and sodium carbonate in a mass ratio of 2:1:

1.

9. The slag removal and purification process in gray cast iron production according to claim 1, characterized in that, After completing the slag removal in step S5, the gray cast iron molten metal is controlled to be filled into the cavity of the sand mold at a flow rate of 0.5 m / s to 1.2 m / s, and the total mass ratio of non-metallic inclusions in the gray cast iron casting matrix after filling is less than 0.005%.

Images