A vacuum consumable arc melting method

Abstract

The application provides a vacuum self-consumption arc smelting method and relates to the technical field of smelting. In the VAR smelting process, inert gas is filled into the annular gap between the cast ingot and the inner wall of the crystallizer, the pressure of the inert gas is periodically fluctuated between P0 and Pmax, and the fluctuation frequency f is 0.1 Hz-10 Hz. The inert gas is naturally dispersed into the annular gap, and the gas pressure in the gap is pulsed synchronously with the furnace cavity pressure. In the pressure rising stage of each pulsation cycle, the gas is pressed into the micro concave pits on the circumferential surface of the cast ingot, and the stagnant hot gas is forced to be replaced; in the pressure reducing stage, the hot gas expands rapidly and flows out, forming a convection heat exchange cycle, the gas in the gap is forced to change from laminar flow to turbulent flow state, the thermal boundary layer is actively destroyed, the heat exchange efficiency is effectively inhibited from decreasing, the heat exchange efficiency of the gap is improved, and therefore the chemical composition uniformity of the large-size cast ingot is improved.

Description

Technical Field

[0001] This invention relates to the field of smelting technology, and in particular to a vacuum self-consuming arc smelting method. Background Technology

[0002] Vacuum arc remelting (VAR) is a core process for preparing ingots of high-performance titanium alloys and nickel-based superalloys. During the remelting process, the ingot gradually shrinks as it solidifies, forming an annular air gap between itself and the crystallizer wall. The heat transfer efficiency of this gap directly affects the radial temperature gradient of the ingot, the morphology of the solidification front, and the final uniformity of the metallurgical structure.

[0003] In existing technologies, helium or argon is introduced into the aforementioned gaps to replace the vacuum, which has poorer thermal conductivity, thereby improving the gap heat transfer efficiency. However, existing gas filling schemes generally adopt a static pressure constant flow mode, that is, maintaining a static gas layer at a certain pressure with a constant flow rate. The static gas is in a laminar flow state within the gap, and the gas near the high-temperature surface of the ingot heats up rapidly, forming a thermal boundary layer. This leads to a shortening of the effective heat conduction path and a significant decrease in heat transfer efficiency as the ingot cools further. Summary of the Invention

[0004] This disclosure is not intended to identify key or essential features of the claimed technical solution, nor is it intended to limit the scope of the claimed technical solution.

[0005] Some embodiments of the present invention provide a vacuum self-consuming arc melting method to solve the technical problems mentioned in the background section above.

[0006] The vacuum self-consuming arc melting method provided by this invention involves filling an inert gas into the annular gap between the ingot and the inner wall of the crystallizer during the VAR melting process, and applying periodic pulsation control to the pressure of the inert gas, including the following steps: S1. When the VAR melting is not filled with inert gas, the real-time pressure P0 of the gap between the ingot and the inner wall of the crystallizer is detected, and P0 is used as the reference pressure for pulse control. S2. Through an electromagnetic pulsating valve installed in the VAR furnace inlet pipe, an inert gas with a periodic pressure fluctuation between P0 and Pmax is injected into the gap between the ingot and the inner wall of the crystallizer, where Pmax is the peak value of the pulsating pressure and the fluctuation frequency f is 0.1Hz to 10Hz.

[0007] Optionally, in step S2, the pulse inflation is paused once every 30 to 60 minutes for a pause time of 10 to 30 seconds, and the real-time pressure P0 of the gap is re-detected during the pause.

[0008] Optionally, the range of the peak pulsating pressure Pmax is 200 Pa to 2000 Pa.

[0009] Optionally, the ingot diameter is D, and the pulsation amplitude is ΔP; when D < 600 mm, f = 3 Hz ~ 10 Hz, ΔP = 200 Pa ~ 600 Pa; when 600 mm ≤ D ≤ 900 mm, f = 1 Hz ~ 5 Hz, ΔP = 500 Pa ~ 1500 Pa; when D > 900 mm, f = 0.1 Hz ~ 2 Hz, ΔP = 1000 Pa ~ 1800 Pa.

[0010] Optionally, when the peak pulsating pressure Pmax ≥ 2000 Pa, the gas intake is cut off by an electrically controlled shut-off valve installed in the VAR furnace intake pipeline.

[0011] Optionally, multiple air inlets are provided between the electromagnetic pulsating valve and the gap, and the multiple air inlets are arranged in a ring evenly along the VAR furnace body, with adjacent air inlets at an angle of 90 to 120°.

[0012] Optionally, the length of the pipeline between the electromagnetic pulsating valve and the air inlet shall not exceed 500 mm.

[0013] Optionally, the pulsation waveform of the electromagnetic pulsation valve is a square wave; the duty cycle of the square wave is 40% to 60%.

[0014] Optionally, the inert gas is argon or helium with a purity ≥ 99.99%.

[0015] Optionally, the VAR furnace exhaust line is equipped with a filter.

[0016] The above embodiments of the present invention have the following beneficial effects: During the VAR melting process, inert gas is introduced into the annular gap between the ingot and the inner wall of the crystallizer. The pressure of the inert gas fluctuates periodically between P0 and Pmax, with a fluctuation frequency f of 0.1Hz to 10Hz. The inert gas naturally diffuses into the annular gap, and the gas pressure inside the gap pulsates synchronously with the furnace cavity pressure. During the pressurization phase of each pulsation cycle, the gas is forced into the microscopic pits on the circumferential surface of the ingot, forcibly displacing the stagnant hot gas; during the depressurization phase, the heated gas rapidly expands and flows out, forming a convective heat transfer cycle, forcibly changing the gas inside the gap from laminar flow to turbulent flow, actively disrupting the thermal boundary layer, effectively suppressing the decrease in heat transfer efficiency, and achieving dynamic enhancement of the gap heat transfer efficiency, thereby improving the metallurgical microstructure uniformity of large-size ingots. Attached Figure Description

[0017] To more clearly illustrate the specific embodiments of the present invention or the technical solutions in the prior art, the drawings used in the description of the specific embodiments or the prior art will be briefly introduced below. Obviously, the drawings described below are some embodiments of the present invention. For those skilled in the art, other drawings can be obtained from these drawings without creative effort.

[0018] Figure 1 This is a flowchart illustrating the overall process of the method of the present invention. Figure 2 This is a schematic diagram of the annular arrangement of the air inlet in the method of the present invention; Figure 3 This is a schematic diagram of the cooling system of the method of the present invention.

[0019] 1. Ingot; 2. Annular gap; 3. Crystallizer; 4. Air inlet. Detailed Implementation

[0020] The technical solution of the present invention will be clearly and completely described below with reference to the embodiments. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0021] In the description of this invention, it should be understood that the terms "center," "longitudinal," "lateral," "length," "width," "thickness," "upper," "lower," "front," "rear," "left," "right," "vertical," "horizontal," "top," "bottom," "inner," "outer," "clockwise," and "counterclockwise," etc., indicate the orientation or positional relationship based on the orientation or positional relationship shown in the accompanying drawings. They are used only for the convenience of describing this invention and simplifying the description, and do not indicate or imply that the device or element referred to must have a specific orientation, or be constructed and operated in a specific orientation. Therefore, they should not be construed as limiting this invention.

[0022] Furthermore, the terms "first" and "second" are used for descriptive purposes only and should not be construed as indicating or implying relative importance or implicitly specifying the number of indicated technical features. Thus, a feature defined as "first" or "second" may explicitly or implicitly include one or more of the stated features. In the description of this invention, "a plurality of" means two or more, unless otherwise explicitly specified. Furthermore, the terms "installed," "connected," and "linked" should be interpreted broadly; for example, they may refer to a fixed connection, a detachable connection, or an integral connection; they may refer to a mechanical connection or an electrical connection; they may refer to a direct connection or an indirect connection through an intermediate medium; and they may refer to the internal connection of two components. Those skilled in the art can understand the specific meaning of the above terms in this invention based on the specific circumstances.

[0023] This disclosure will now be described in detail with reference to the accompanying drawings and embodiments.

[0024] Figure 1 This is a flowchart of the overall process of the method of the present invention, as follows: Figure 1 As shown, the vacuum self-consuming arc melting method provided in this application involves filling an inert gas into the annular gap between the ingot and the inner wall of the crystallizer during the VAR melting process, and applying periodic pulsation control to the pressure of the inert gas, including the following steps: S1. When VAR melting is not filled with inert gas, detect the real-time pressure P0 of the gap between the ingot and the inner wall of the crystallizer, and use P0 as the reference pressure for pulsation control. S2. An inert gas with a periodic pressure fluctuation between P0 and Pmax is injected into the gap between the ingot and the inner wall of the crystallizer through an electromagnetic pulsating valve installed in the gas inlet pipe of the VAR furnace. Pmax is the peak value of the pulsating pressure; the fluctuation frequency f is 0.1Hz to 10Hz.

[0025] In the VAR melting process, inert gas is introduced into the annular gap between the ingot and the inner wall of the crystallizer. The pressure of the inert gas fluctuates periodically between P0 and Pmax, with a fluctuation frequency f of 0.1Hz to 10Hz. The inert gas naturally diffuses into the annular gap, and the gas pressure within the gap pulsates synchronously with the furnace cavity pressure. During the pressurization phase of each pulsation cycle, the gas is forced into microscopic pits on the circumferential surface of the ingot, forcibly displacing the stagnant hot gas. During the depressurization phase, the heated gas rapidly expands and flows out, forming a convective heat transfer cycle. This forces the gas within the gap from laminar flow to turbulent flow, actively disrupting the thermal boundary layer, effectively suppressing the decline in heat transfer efficiency, and achieving dynamic enhancement of the gap's heat transfer efficiency, thereby improving the metallurgical microstructure uniformity of large-size ingots.

[0026] It should be noted that when VAR melting is not filled with inert gas, the gap is in a vacuum state of ≤0.5Pa, that is, the real-time pressure P0 of the gap between the ingot and the inner wall of the crystallizer is detected to be ≤0.5Pa.

[0027] In some embodiments, during step S2, the pulsed gas charging is paused every 30-60 minutes for a pause of 10-30 seconds. During this pause, the real-time gap pressure P0 is re-detected. During VAR melting, the ingot continuously contracts, and the gap width gradually expands from less than 0.1 mm at the initial arc initiation stage to several millimeters during normal melting, with the gap volume monotonically increasing over time. Under continuous gas charging, the steady-state pressure corresponding to the same gas flow rate decreases as the gap volume increases, causing the actual pulsation amplitude ΔP to deviate from the initial set value, and the heat exchange enhancement effect gradually diminishes as melting progresses. Pausing the pulsed gas charging for 10-30 seconds every 30-60 minutes stops the operation of the electromagnetic pulsation valve during this window, allowing the furnace pressure to naturally relax to the true equilibrium pressure corresponding to the current gap volume. This value is then used to update the reference pressure P0. After resuming gas charging, the pulsation amplitude ΔP is recalculated based on the updated P0, ensuring that Pmax always accurately reflects the actual gap state.

[0028] In some embodiments, the peak pulsating pressure Pmax ranges from 200 Pa to 2000 Pa. Below 200 Pa, the pressure gradient generated by the gas within the gap is too small, and the convection velocity of the gas molecules is insufficient to effectively disturb the thermal boundary layer. When the furnace pressure exceeds 2000 Pa, on the one hand, the pressure of the gas on the surface of the molten pool begins to cause measurable disturbance to the shape of the molten pool, affecting the depth of the molten pool and the morphology of the solidification front; on the other hand, high-pressure gas may rise into the molten pool region along the gap between the ingot and the inner wall of the crystallizer, introducing impurities or altering the local atmosphere.

[0029] In some embodiments, the ingot diameter is D, and the pulsation amplitude is ΔP. ​​When D < 600 mm, f = 3 Hz ~ 10 Hz, ΔP = 200 Pa ~ 600 Pa; when 600 mm ≤ D ≤ 900 mm, f = 1 Hz ~ 5 Hz, ΔP = 500 Pa ~ 1500 Pa; when D > 900 mm, f = 0.1 Hz ~ 2 Hz, ΔP = 1000 Pa ~ 1800 Pa. The gap width increases with the increase of the ingot diameter. The time required for gas to fill the gap is proportional to the gap volume. Large-diameter ingots have large gap volumes, requiring a longer time to complete one effective heat exchange cycle, therefore the frequency must be reduced. Small-diameter ingots have narrow gaps, resulting in a fast gas filling response. High-frequency pulsation can fully utilize each cycle, leading to higher heat exchange efficiency.

[0030] In some embodiments, when the peak pulsating pressure Pmax ≥ 2000 Pa, the intake gas is cut off by an electrically controlled shut-off valve installed in the intake pipeline of the VAR furnace.

[0031] Figure 2This diagram illustrates the annular arrangement of the air inlets. Multiple air inlets are positioned between the electromagnetic pulse valve and the gap, forming a uniform ring around the VAR furnace body. Adjacent air inlets are at 90–120° angles. This annular distribution ensures consistent heat transfer enhancement across the circumference, simultaneously improving the roundness and microstructure uniformity of the ingot cross-section. Furthermore, the parallel operation of the multiple air inlets allows for basic circumferential coverage even if a single inlet is blocked or experiences a pipeline failure. This prevents the loss of the entire pulse cooling function due to a single-point failure, providing a degree of redundancy and fault tolerance.

[0032] In some embodiments, the pipe length between the electromagnetic pulsation valve and the air inlet does not exceed 500mm. After the air inlets are evenly distributed, the pipe length of each air inlet is basically equal, ensuring that the pressure waveform of each air inlet arrives synchronously and avoiding different pulsation phases at different points in the circumference due to different pipe lengths.

[0033] In some embodiments, the pulsation waveform of the electromagnetic pulsation valve is a square wave; the duty cycle of the square wave is 40% to 60%. The duty cycle is the ratio of the high-level (inflation phase) time of the square wave to the complete cycle time. A duty cycle of 40% to 60% means that the inflation time and the deflation time in each pulsation cycle are close to 1:1, which is a nearly symmetrical square wave.

[0034] During the gas filling stage: gas is rapidly injected into the gap, and the pressure inside the gap quickly rises to Pmax. Gas molecules are forced into the microscopic contact area between the surface of the ingot and the inner wall of the crystallizer. The thermal boundary layer is destroyed by the gas dynamic pressure, and the thermal resistance of the ingot to the crystallizer is reduced.

[0035] During the gas shut-off phase: the solenoid valve closes, the gas in the gap relaxes outward, the pressure drops back to around P0, the gas flow rate in the gap decreases, and the gas carrying heat escapes with the pressure gradient, completing the heat dissipation of one heat exchange cycle.

[0036] When the duty cycle is below 40%, the inflation time is too short, resulting in insufficient gas injection in each cycle, a decrease in the effective heat exchange time, and a weakening of the overall heat exchange enhancement effect. When the duty cycle is above 60%, the gas stop time is too short, and the hot gas injected in the previous cycle has not been fully discharged. When the new gas is injected in the next cycle, a large amount of hot gas remains in the gap. The mixing of old and new gas leads to a decrease in the effective temperature difference and a decline in heat exchange efficiency. At the same time, maintaining high pressure for a long time also increases the risk of overpressure.

[0037] Because the rising and falling edges of a square wave are approximately perpendicular, the gas reaches Pmax at the fastest speed during the inflation phase, and the thermal boundary layer disturbance intensity reaches its peak in the shortest time. During the depressurization phase, the pressure drops rapidly, resulting in high heat dissipation efficiency. Compared to the gradual inflation and deflation of a sine wave, a square wave completes more effective heat exchange cycles per unit time under the same frequency and amplitude conditions.

[0038] In some embodiments, the inert gas is argon or helium with a purity of ≥99.99% to avoid impurities contaminating the molten pool.

[0039] In some embodiments, the VAR furnace outlet pipeline is equipped with a filter, which not only prevents volatile impurities entrained in the inert gas from polluting the environment, but also enables the inert gas to be reused.

[0040] After the ingot feeding period ends, continue to maintain auxiliary cooling of the solidified area at the top of the ingot with low-frequency small-amplitude pulsations of f=0.5Hz~1Hz and Pmax-P0=200Pa~400Pa until the ingot exit temperature drops below 300℃, in order to refine the solidified structure at the head of the ingot and reduce the shrinkage cavity depth.

[0041] In existing technologies, for large-diameter ingots exceeding 600mm, the gap width gradually expands from less than 0.1mm during the arc initiation phase to several millimeters during the feeding phase. This leads to inconsistent cooling rates at different axial positions of the ingot, inducing quality problems such as component segregation or shrinkage cavity enlargement. In this application, based on the real-time gap pressure feedback from the pressure sensor, when the gap pressure fluctuation amplitude Δp < 0.3 × (Pmax - P0), the controller automatically increases the pulsation amplitude to compensate for the heat transfer attenuation caused by the gap expansion due to ingot shrinkage.

[0042] Figure 3 The diagram shows the pulsed cooling system of the present invention, which consists of a pulsed gas supply unit, a furnace cavity gas inlet distribution unit, a pressure sensing and feedback unit, a safety protection unit, and a gas purification and recovery unit.

[0043] Before the melting begins, the pressure sensing and feedback unit detects the real-time pressure of the gap between the ingot and the inner wall of the crystallizer in the furnace cavity. The pressure at this time without gas filling is recorded as the reference pressure P0, and the P0 value is transmitted to the control module of the pulsating gas supply unit.

[0044] After the smelting process officially begins, the electromagnetic pulsating valve in the pulsating gas supply unit opens according to a square wave signal, outputting the inert gas from the gas storage tank in a pulsating manner. The pressure fluctuates periodically between P0 and Pmax, with a fluctuation frequency f of 0.1Hz to 10Hz and a square wave duty cycle of 40% to 60%. The pulsating gas flow enters the furnace cavity through multiple inlets in the furnace cavity gas distribution unit. Each inlet is evenly arranged in a ring around the furnace body, with an angle of 90° to 120° between adjacent inlets to ensure that the inert gas is evenly dispersed into the circumferential gaps of the ingot.

[0045] During the smelting process, the pressure sensing and feedback unit continuously monitors the furnace cavity pressure and feeds the signal back to the pulsed gas supply unit in real time to perform closed-loop regulation of the pulsed parameters. Every 30 to 60 minutes, the system pauses the pulsed gas supply for 10 to 30 seconds. During this period, the gap pressure is re-detected and the reference pressure P0 is updated to compensate for the change in gap volume caused by the cold shrinkage of the ingot.

[0046] When the furnace chamber pressure reaches Pmax≥2000Pa, the safety protection unit receives a safety protection signal, and the electrically controlled shut-off valve immediately activates to cut off the gas inlet pipeline and prevent overpressure in the furnace chamber. The gas discharged from the VAR furnace chamber outlet enters the gas purification and recovery unit, and is discharged or recovered after being filtered by the outlet pipeline filter to avoid environmental pollution from volatile impurities carried in the inert gas.

[0047] Example 1: The pulsed cooling method was applied to the VAR melting of TC4 titanium alloy with a diameter of Φ640mm.

[0048] S1. Establishment of gap reference pressure: Load the furnace and evacuate it until the furnace pressure Pfurnace≦5Pa, and the initial gap reference pressure P0=Pfurnace.

[0049] S2. Pulsed gas flow application: High-purity argon gas (99.99% purity) is selected, and the pulse waveform is selected as a square wave (ingot diameter range of 600-900mm). The initial setting of f is 2Hz, Pmax=1800Pa, and the pulse amplitude is 1800Pa. The gas is supplied to the entire furnace cavity through four axially distributed gas inlets installed on the side wall of the furnace body. After the gas is dispersed in the furnace cavity, it naturally enters the annular gap between the ingot and the crystallizer wall. The gas outlet of the furnace cavity is regulated by a mass flow controller and a gas outlet valve. The recovered gas is filtered, dried, and recycled.

[0050] S3. During the melting and feeding period, the frequency is reduced to 1Hz, and Pmax decreases to 600Pa; low-frequency pulsating assisted cooling continues until the ingot is unloaded. Compared with the same specification static pressure gas-filling scheme, the uniformity of the ingot grain size is improved, and the shrinkage cavity depth is reduced. Example 2

[0051] The pulsed cooling method was applied to the VAR melting of 800mm TA15 titanium alloy.

[0052] The furnace pressure Pfurnace ≤ 5 Pa, and the gap reference pressure P0 = Pfurnace; f = 3 Hz, Pmax = 2000 Pa; gas is supplied to the entire furnace cavity through four axially distributed air inlets on the side wall of the furnace body; during the feeding period, the frequency is gradually reduced to 1 Hz, and Pmax decreases to 300 Pa; low-frequency pulsating assisted cooling continues until the ingot is unloaded. Compared with the static pressure gas-filling scheme of the same specifications, the uniformity of grain size in the same ingot structure is improved, and the shrinkage cavity depth is reduced. Example 3

[0053] The pulsed cooling method was applied to the VAR melting of 1020mm TA1 ultra-large ingots.

[0054] The furnace pressure Pfurnace ≤ 5 Pa, and the gap reference pressure P0 = Pfurnace; f = 1.5 Hz, Pmax = 1800 Pa; gas is supplied to the entire furnace cavity through six axially distributed gas inlets on the side wall of the furnace body; the feeding period is gradually reduced, and finally maintained at f = 0.8 Hz and Pmax reduced to 200 Pa until tapping. Compared with the static pressure gas supply scheme of the same specifications, the uniformity of grain size in the same ingot structure is improved, and the shrinkage cavity depth is reduced.

[0055] 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 the foregoing embodiments, those skilled in the art should understand that modifications can still be made to the technical solutions described in the foregoing embodiments, or equivalent substitutions can be made to some or all of the technical features therein. Such modifications or substitutions do not cause the essence of the corresponding technical solutions to deviate from the scope of the technical solutions of the embodiments of the present invention.

Claims

1. A vacuum self-consuming arc melting method, characterized in that, In the VAR melting process, an inert gas is introduced into the annular gap between the ingot and the inner wall of the crystallizer, and the pressure of the inert gas is periodically pulsated and controlled, including the following steps: S1. When the VAR melting is not filled with inert gas, the real-time pressure P0 of the gap between the ingot and the inner wall of the crystallizer is detected, and P0 is used as the reference pressure for pulse control. S2. Through an electromagnetic pulsating valve installed in the VAR furnace inlet pipe, an inert gas with a periodic pressure fluctuation between P0 and Pmax is injected into the gap between the ingot and the inner wall of the crystallizer, where Pmax is the peak value of the pulsating pressure and the fluctuation frequency f is 0.1Hz to 10Hz.

2. The vacuum self-consuming arc melting method according to claim 1, characterized in that, In step S2, the pulsating inflation is paused once every 30 to 60 minutes for a pause time of 10 to 30 seconds. During the pause, the real-time pressure P0 of the gap is re-detected.

3. The vacuum self-consuming arc melting method according to claim 1, characterized in that, The range of the peak pulsating pressure Pmax is 200 Pa to 2000 Pa.

4. The vacuum consumable arc melting method according to claim 3, characterized in that, The ingot diameter is D, and the pulsation amplitude is ΔP. ​​When D < 600 mm, f = 3 Hz ~ 10 Hz, ΔP = 200 Pa ~ 600 Pa; when 600 mm ≤ D ≤ 900 mm, f = 1 Hz ~ 5 Hz, ΔP = 500 Pa ~ 1500 Pa; when D > 900 mm, f = 0.1 Hz ~ 2 Hz, ΔP = 1000 Pa ~ 1800 Pa.

5. The vacuum self-consuming arc melting method according to claim 3, characterized in that, When the peak pulsating pressure Pmax ≥ 2000 Pa, the gas intake is cut off by an electrically controlled shut-off valve installed in the VAR furnace intake pipeline.

6. The vacuum self-consuming arc melting method according to claim 1, characterized in that, Multiple air inlets are provided between the electromagnetic pulsating valve and the gap. The multiple air inlets are arranged in a ring and uniformly along the VAR furnace body, with adjacent air inlets at an angle of 90 to 120°.

7. The vacuum consumable arc melting method according to claim 6, characterized in that, The length of the pipeline between the electromagnetic pulsating valve and the air inlet shall not exceed 500 mm.

8. The vacuum self-consuming arc melting method according to claim 1, characterized in that, The pulsating waveform of the electromagnetic pulsating valve is a square wave; the duty cycle of the square wave is 40% to 60%.

9. The vacuum self-consuming arc melting method according to any one of claims 1 to 8, characterized in that, The inert gas is argon or helium with a purity of ≥99.99%.

10. The vacuum consumable arc melting method according to any one of claims 1 to 8, characterized in that, The VAR furnace exhaust line is equipped with a filter.

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