A vacuum levitation melting furnace based on high-frequency induction heating

Abstract

This invention discloses a vacuum levitation melting furnace based on high-frequency induction heating, relating to the field of vacuum levitation melting furnace control. The invention includes: evacuating the vacuum chamber and filling it with inert gas after system startup; heating the furnace charge after the vacuum level reaches the required standard; determining the charge position; adjusting the field strength parameters of the levitation system to prevent the charge from contacting the crucible wall when the charge position deviates; continuously acquiring the surface temperature signal of the molten pool through the observation window of the vacuum chamber using a dual-color infrared thermometer; changing the heating current through a power regulator when the temperature deviates from the required melting value; introducing cooling medium into the vacuum chamber wall and around the crucible while initiating vacuum evacuation during the vacuum preparation stage; continuously monitoring the return water temperature during the pouring process; and stopping cooling after both the furnace wall and crucible have cooled to room temperature. This achieves automated closed-loop control of the entire vacuum levitation melting process.

Description

Technical Field

[0001] This invention belongs to the field of vacuum levitation melting furnace control technology, and relates to a vacuum levitation melting furnace based on high-frequency induction heating. Background Technology

[0002] A vacuum suspension melting furnace is a melting device that uses electromagnetic induction eddy current heat to melt metal and relies on electromagnetic force to keep the metal charge in a suspended state in a water-cooled copper crucible. Under vacuum or protective atmosphere, the segmented water-cooled copper crucible is placed in an alternating electromagnetic field. The eddy current heat generated by the electromagnetic field melts the metal, and the electromagnetic force keeps the molten metal in a semi-suspended or fully suspended melting state in the crucible, thereby realizing metal melting.

[0003] Currently, existing technologies for vacuum suspension melting furnaces still have the following shortcomings: First, during the suspension heating process, the furnace charge is prone to positional displacement due to the combined effects of electromagnetic force, gravity, and changes in the melt state. Once the furnace charge contacts the crucible wall, it will reduce the induction heating efficiency and cause local overheating and damage to the crucible. At the same time, it will introduce contamination of the crucible material, affecting the purity of the casting. However, existing equipment cannot automatically adjust the suspension field strength parameters to push the furnace charge back to the center position when the furnace charge shifts.

[0004] In addition, the existing technology makes it difficult to monitor and automatically adjust the molten pool temperature, which makes the melting temperature susceptible to fluctuations in induction power, heat radiation, and changes in cooling conditions, causing it to deviate from the required range and resulting in alloy composition deviations or melting failure.

[0005] Furthermore, in the existing technology, the cooling system of the vacuum suspension melting furnace usually adopts the method of continuously introducing cooling medium to force cooling the vacuum chamber wall and crucible. When the cooling pipe is blocked, the cooling medium flow is insufficient, or the heat exchange efficiency decreases, it is difficult to detect the abnormality in time and make manual adjustments, which leads to the damage of the cooled components due to overheating, affecting the safety and reliability of the equipment in long-term operation. Summary of the Invention

[0006] In view of this, in order to solve the problems mentioned in the background art, the present invention provides a vacuum suspension melting furnace based on high-frequency induction heating.

[0007] The objective of this invention can be achieved through the following technical solution: a vacuum levitation melting furnace based on high-frequency induction heating, comprising the following modules: a vacuum preparation module, which evacuates the vacuum chamber and fills it with inert gas after the system is started, and controls the heating levitation module to work after the vacuum level reaches the standard;

[0008] The heating suspension module heats the furnace charge by applying electricity and determines the position of the furnace charge. If the position of the furnace charge shifts, the field strength parameters of the suspension system are adjusted to keep the furnace charge from contacting the crucible wall.

[0009] The temperature control module continuously monitors the temperature of the molten pool during the heating process, and changes the heating current through the power regulator when the temperature deviates from the required melting value.

[0010] The rotary casting module reduces the field strength parameter of the suspension system after the molten pool temperature stabilizes, causing the molten metal to flow out. At the same time, it collects the attitude data of the water-cooled copper crucible to control the crucible to tilt and rotate for casting. During the rotary casting process, the weight of the furnace body is monitored in real time to determine whether the casting is complete.

[0011] The cooling circulation module introduces cooling medium into the vacuum chamber wall and around the crucible while starting the vacuum preparation stage and continuously monitors the return water temperature during the pouring process. Cooling is stopped after the furnace wall and crucible have both cooled to room temperature.

[0012] Compared with the prior art, the beneficial effects of the present invention are as follows: (1) The present invention evacuates the vacuum chamber and fills it with inert gas after the system is started. After the vacuum level reaches the standard, the furnace charge is heated by electricity and the furnace charge position is judged. When the furnace charge position shifts, the field strength parameters of the suspension system are adjusted to keep the furnace charge from contacting the crucible wall. This avoids the reduction of induction heating efficiency, local overheating damage of the crucible and material contamination caused by the furnace charge contacting the crucible wall, and ensures the stability of the heating suspension stage and the purity of the casting.

[0013] (2) The present invention continuously collects the surface temperature signal of the molten pool through the observation window of the vacuum chamber by means of a dual-color infrared thermometer, and changes the heating current by means of a power regulator when the temperature deviates from the required value for smelting, so that the smelting temperature can be automatically maintained within the process requirements range when the induced power fluctuates and the cooling conditions change, thus avoiding the alloy composition from deviating from the target or smelting failure.

[0014] (3) This invention introduces cooling medium into the vacuum chamber wall and crucible while starting vacuuming during the vacuum preparation stage, and continuously monitors the return water temperature during the casting process. Cooling is stopped after the furnace wall and crucible have both dropped to room temperature. This realizes real-time monitoring and automatic adjustment of the cooling system throughout the melting process, avoids overheating damage to the cooled components due to insufficient cooling medium flow or reduced heat exchange efficiency, and improves the safety and reliability of the equipment during long-term operation. Attached Figure Description

[0015] To more clearly illustrate the technical solutions of the embodiments of the present invention, the accompanying drawings used in the description of the embodiments will be briefly introduced below. Obviously, the drawings described below are only some embodiments of the present invention. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0016] Figure 1 This is a schematic diagram showing the connections between the modules of the present invention;

[0017] Figure 2 This is a flowchart illustrating the process of determining the location of the furnace charge in this invention.

[0018] Figure 3 This is a flowchart of the heating current regulation and control process for the smelting furnace of the present invention. Detailed Implementation

[0019] The technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. 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.

[0020] Please see Figure 1 As shown, this invention provides a vacuum levitation melting furnace based on high-frequency induction heating, comprising: a vacuum preparation module, a heating levitation module, a temperature control module, a rotary casting module, and a cooling circulation module. All modules are connected in the order described above.

[0021] The vacuum preparation module evacuates the vacuum chamber and fills it with inert gas after the system starts up. Once the vacuum level reaches the required standard, it controls the heating and levitation module to operate.

[0022] Considering that the oxygen and water vapor remaining in the furnace during high-temperature smelting will react with the metal charge to cause oxidation, resulting in the loss of alloying elements and metallurgical defects such as inclusions or porosity.

[0023] Furthermore, considering that alloy components with high vapor pressure are prone to volatilization loss and deviation from the target composition under complete vacuum conditions, and that the inductive coupling state is also affected by the vacuum level.

[0024] Based on this, the above-mentioned process of evacuating the vacuum chamber and filling it with inert gas after system startup includes: starting the mechanical pump to pre-evacuate the vacuum chamber, monitoring the pressure through the vacuum gauge, and switching to the high vacuum pump to continue evacuating to the background vacuum after the pressure drops to the transition pressure value.

[0025] The reason for adopting a staged pumping method of pre-pumping with a mechanical pump and then switching to a high vacuum pump is that the mechanical pump has the advantage of high pumping speed in the low vacuum range, while the high vacuum pump has the advantage of high compression ratio in the high vacuum range. The combination of the two can achieve efficient pumping across the entire pressure range. At the same time, the high vacuum pump can only be started at a lower pressure. The mechanical pump must first reduce the pressure in the vacuum chamber to below its allowable starting pressure to avoid overload damage to the high vacuum pump due to excessive gas load.

[0026] The process for determining the transition pressure value is as follows: A mechanical pump is started to continuously evacuate the vacuum chamber. During evacuation, the pressure reading of the vacuum gauge is read at fixed time intervals. When the change in pressure reading between two consecutive readings within three consecutive recording cycles is less than the minimum display scale value of the vacuum gauge within the corresponding range, this pressure value is recorded as the ultimate evacuation pressure of the mechanical pump. This ultimate evacuation pressure is used as the transition pressure value, and the system is switched to a high vacuum pump to continue evacuation. The fixed time interval is 2 seconds. When the system venting rate is high, the fixed time interval is increased; when the system venting rate is low, the fixed time interval is decreased.

[0027] Close the evacuation valve, alternately open the charging valve and the evacuation valve, and repeat the replacement operation of filling the vacuum chamber with inert gas and then evacuating it several times.

[0028] Simply evacuating and then filling with inert gas will not remove residual oxygen and water vapor molecules from the furnace walls and charge surfaces. A single evacuation and filling process is insufficient to completely remove these molecules. A cyclical replacement operation, involving filling with inert gas followed by evacuation, utilizes the inert gas as a carrier medium. This allows the residual active gas molecules adsorbed on the walls and charge surfaces to diffuse into the gas phase through a concentration gradient and be expelled from the vacuum chamber during the evacuation process. This reduces the active gas content inside the furnace to an even lower level before the final protective atmosphere is introduced.

[0029] In engineering practice, the number of replacement operations is preferably 2 to 4. The first replacement can remove most of the residual active gas. The removal effect of each subsequent replacement decreases with each replacement. After more than four replacements, the reduction of the concentration of residual active gas by a single replacement is limited. Continuing to increase the number of replacements will prolong the process preparation time.

[0030] After the final inert gas filling, the protective pressure value is maintained. The oxygen partial pressure and water pressure are detected by the residual gas analyzer. After confirming that both are below the allowable upper limit, a start signal is output to the heating suspension module.

[0031] After the final inert gas injection, a protective pressure value is maintained, ensuring that the furnace pressure is slightly higher than the ambient pressure. This pressure difference prevents external air from seeping in during subsequent heating processes due to minor leaks in the furnace or deformation of seals caused by heat, thus ensuring atmospheric safety throughout the smelting cycle. Simultaneously, before the heating suspension module is activated, the results of the residual gas analyzer are used as the final criterion for determining whether the smelting environment is up to standard. This avoids neglecting residual active gas exceeding the standard due to ignoring actual venting or minor leaks in pipelines by simply relying on the number of evacuations and replacements. In this way, the endpoint of atmosphere quality control is elevated from the completion of process operation to the level of meeting the test results.

[0032] The steps for determining the protection pressure value are as follows: During the final inert gas filling process, continuously monitor the pressure reading of the vacuum gauge. When the pressure reading rises to 0.5 kPa to 1 kPa higher than the external atmospheric pressure, stop filling. After closing the filling valve, observe the pressure reading. If it remains stable and does not drop within the set time, then the reading is determined as the protection pressure value.

[0033] The steps for determining the permissible upper limit are as follows: The background values ​​of oxygen partial pressure and water pressure measured by the residual gas analyzer after evacuating to the ultimate vacuum in a clean vacuum chamber are used as the permissible upper limit. The clean vacuum chamber is an empty vacuum chamber that has been ultrasonically cleaned with acetone for 15 minutes and then dried. The ultimate vacuum is defined as a pressure value lower than... The vacuum state of Pa.

[0034] The heating suspension module heats the furnace charge by applying electricity and determines the position of the furnace charge. If the position of the furnace charge shifts, the field strength parameters of the suspension system are adjusted to keep the furnace charge from contacting the crucible wall.

[0035] Because the furnace charge is affected by electromagnetic force, gravity and changes in the state of the melt during the suspension heating process, it may shift in position. Once it comes into contact with the crucible wall, it will reduce the induction heating efficiency, cause local overheating and damage to the crucible, and lead to material contamination.

[0036] refer to Figure 2 As shown, the above determination of the furnace charge position includes: continuously taking images of the inside of the crucible, extracting the furnace charge outline and the crucible cavity outline from the images of the inside of the crucible respectively, and determining the geometric center point of the furnace charge outline as the furnace charge center point, and determining the geometric center point of the crucible cavity outline as the crucible center point.

[0037] The camera device used to capture images of the inside of the crucible is fixedly mounted outside the observation window of the vacuum chamber, with its optical axis perpendicular to the plane of the crucible opening. The frame rate of the camera device is no less than 25 frames per second. A ring light source is set around the camera device, with the illumination direction of the ring light source facing the inside of the crucible, so that a light and dark boundary is formed between the inner wall of the crucible and the furnace charge.

[0038] The outlines of the furnace charge and the inner cavity of the crucible were extracted from the internal image of the crucible. The following image processing steps were performed: the acquired color image was converted to a grayscale image, and median filtering was used to remove noise from the image. Gaussian filtering was first applied to the grayscale image to smooth the image and suppress noise. Then, the gradient magnitude and gradient direction of each pixel in the filtered image were calculated. Non-maximum suppression was then applied along the gradient direction to refine the edges. Finally, a double thresholding method was used to screen candidate edge points and connect them to form a complete edge contour. After edge extraction, contour tracking was performed on the obtained edge information. The closed contour with the largest area was selected as the inner cavity contour of the crucible, and the second largest closed contour was selected as the furnace charge contour. Gaussian filtering used a 5×5 kernel with a standard deviation of 1.0. The high threshold of the double thresholding method was set to the 70th percentile of the gradient magnitude histogram, and the low threshold was set to 50% of the high threshold.

[0039] The method for determining the geometric center point of the furnace charge outline is as follows: obtain the coordinates of all pixels within the area enclosed by the furnace charge outline, calculate the average value of the horizontal coordinate and the average value of the vertical coordinate of all pixels respectively, and take the coordinate point corresponding to the average value as the center point of the furnace charge.

[0040] The method for determining the geometric center point of the crucible's inner cavity profile is the same as the method for determining the geometric center point of the furnace charge profile.

[0041] When there is occlusion or uneven lighting between the furnace charge outline and the crucible cavity outline in the image, causing the outline to break, first dilate the broken outline image to expand the outline endpoints at the break point outward in their respective directions until the adjacent endpoints contact each other. Then, erode the expanded image to restore the expanded outline to close to the original width, thereby connecting the broken part into a continuous outline. After repair, the closed outline is extracted.

[0042] The accuracy of furnace charge position detection depends on the cleanliness of the vacuum chamber observation window, while the cooling circulation module cools the observation window to prevent metal vapor condensation, thereby indirectly ensuring the reliability of image detection.

[0043] The center point of the furnace charge is compared with the center point of the crucible, and the minimum radial distance between the furnace charge outline and the crucible inner cavity outline in the same radial direction is calculated. If the minimum radial distance is less than the preset safety threshold, it is determined that the furnace charge has shifted position.

[0044] When the charge is at the ideal suspension center position, the center point of the charge coincides with the center point of the crucible, and the distance between the charge outline and the crucible inner cavity outline in all radial directions is equal. When the charge deviates, the center point of the charge shifts relative to the center point of the crucible, the radial distance on the side of the deviation decreases, and the radial distance on the opposite side increases. Therefore, by detecting the minimum value of the distance in all radial directions, it can be determined whether the charge has approached the crucible wall.

[0045] The specific steps for calculating the minimum radial distance between the furnace charge outline and the crucible inner cavity outline in the same radial direction are as follows: extract all pixels on the furnace charge outline, calculate the distance from each pixel on the furnace charge outline to all pixels on the crucible inner cavity outline, take the minimum value as the corresponding radial distance, and after traversing all pixels on the furnace charge outline, take the minimum value as the minimum radial distance.

[0046] The steps for determining the preset safety threshold are as follows: Place the furnace charge in the center of the crucible cavity, start the suspension system, and gradually increase the current of the suspension coil until the furnace charge just leaves the bottom of the crucible and is suspended in the center position. Record the coil current value at this time as the initial suspension current. Keep the initial suspension current unchanged, and after the furnace charge is suspended and stabilized, continuously collect the position data of the center point of the furnace charge and record the maximum offset of the center point of the furnace charge as the preset safety threshold.

[0047] The above-mentioned adjustment of the field strength parameters of the suspension system to maintain the furnace charge from contacting the crucible wall includes: when the furnace charge shifts position, obtaining the offset direction of the center point of the furnace charge relative to the center point of the crucible.

[0048] When continuously capturing images of the inside of the crucible, an image coordinate system is established with the top left corner of the image as the origin, the horizontal axis pointing to the right as the positive direction, and the vertical axis pointing downwards as the positive direction. The center point of the crucible is used as the reference, and the offset direction is determined by comparing the difference between the horizontal and vertical coordinates of the center point of the furnace charge and the center point of the crucible: if the difference in the horizontal coordinate is positive, the offset is to the right, and if it is negative, the offset is to the left; if the difference in the vertical coordinate is positive, the offset is downwards, and if it is negative, the offset is upwards. The offset direction is obtained by combining the left-right direction of the horizontal coordinate and the up-down direction of the vertical coordinate.

[0049] The suspension system includes multiple independently controllable excitation coil segments evenly arranged along the circumference of the crucible. At least one coil segment corresponding to the side with the offset direction is taken as the coil segment to be strengthened, and at least one coil segment corresponding to the opposite direction is taken as the coil segment to be weakened.

[0050] Specifically, the offset direction of the center point of the furnace charge relative to the center point of the crucible is matched with the center orientation of each excitation coil segment. The coil segment with the smallest angle between the offset direction and the center orientation of the coil segment is taken as the coil segment pointed to by the offset direction. When the offset direction is between two adjacent coil segments, both adjacent coil segments are selected as the coil segment pointed to by the offset direction.

[0051] Furthermore, when the offset direction is between two adjacent coil segments, the two adjacent coil segments are selected as the coil segments to be strengthened, and the two adjacent coil segments on the other side opposite to the two adjacent coil segments are selected as the coil segments to be weakened.

[0052] The number of excitation coil segments is even, and they are arranged at equal angular intervals along the circumference of the crucible.

[0053] An even number of excitation coil segments ensures that each coil segment has another coil segment arranged 180° opposite it in the circumferential direction. This creates a corrective torque with opposite forces and lines of action on the same diameter during adjustment. The corrective torque points towards the center of the crucible, avoiding additional torque or lateral disturbances caused by force line deviation.

[0054] The method of setting the equal angular interval is to divide the 360° circumference by the total number of excitation coil segments, and use the quotient as the included angle between two adjacent coil segments, thereby arranging them sequentially along the circumference of the outer wall of the crucible.

[0055] The drive channel of the coil segment to be strengthened is given an instruction to increase the current, and the drive channel of the coil segment to be weakened is given an instruction to decrease the current. The electromagnetic force generated by the levitation coil is proportional to the square of the coil current. Increasing the current of the offset coil can increase the magnetic field gradient on that side, generating a magnetic pressure gradient force pointing towards the center of the crucible, pushing the furnace charge away from the wall. At the same time, weakening the current of the coil on the opposite side can eliminate the back drag force on the furnace charge on that side, preventing it from hindering the return of the furnace charge to the center.

[0056] The relative position between the center point of the furnace charge and the center point of the crucible is continuously acquired. When the deviation between the two is less than the overlap threshold, each drive channel maintains the current value unchanged to keep the furnace charge stably suspended in a non-contact state.

[0057] When the deviation between the center point of the furnace charge and the center point of the crucible is less than the overlap threshold, it indicates that the furnace charge is already within the allowable area near the center of the crucible. Continuing to adjust the current may cause over-adjustment, which would disrupt the current stable suspension state. At this time, keeping the current value of each drive channel unchanged, and utilizing the principle that electromagnetic force and gravity have reached a dynamic balance in the current state, the furnace charge is kept stably suspended in a non-contact state. This avoids unnecessary adjustment actions and prevents system oscillations caused by repeated adjustments.

[0058] The steps for determining the overlap threshold are as follows: First, during the system debugging phase, place the furnace charge at the center of the crucible, start the levitation system, and adjust the current of each coil until the furnace charge is stably suspended at the center. Continuously collect data on the position of the center point of the furnace charge and record the maximum deviation value of the center point of the furnace charge relative to the center point of the crucible within a set time period, preferably 60 seconds. Use this maximum deviation value as the initial overlap threshold. Then, keeping the current of each coil constant, artificially apply a momentary disturbance to the furnace charge, such as briefly increasing the current of a certain coil and then restoring it. After the furnace charge stabilizes again, collect the position data again and record the maximum deviation value of the center point of the furnace charge relative to the center point of the crucible. Finally, take the larger of the maximum deviation value measured in the first step and the measured maximum deviation value, multiply it by a safety factor of 1.2 to 1.5, and use this as the overlap threshold.

[0059] The temperature control module continuously monitors the temperature of the molten pool during the heating process, and changes the heating current through the power regulator when the temperature deviates from the required melting value.

[0060] Since the temperature of the induction-heated molten pool is determined by the thermal balance between the input Joule heat and the dissipation heat, changes in the charge state will disrupt the thermal balance and cause temperature drift. Furthermore, the vapor pressure and surface tension of the melt both change with temperature, affecting the alloy composition and suspension stability.

[0061] refer to Figure 3 As shown, when the temperature deviates from the required melting value, changing the heating current through the power regulator includes: fixing a dual-color infrared thermometer outside the observation window of the vacuum chamber, so that the detection light path passes through the observation window and continuously collects the surface temperature signal of the molten pool.

[0062] The dual-color infrared thermometer utilizes the principle of dual-wavelength ratio measurement, making the temperature measurement results independent of changes in optical path transmittance and target emissivity. Thus, even under conditions where the observation window of the vacuum chamber is contaminated by metal vapor, changes in the surface state of the melt, and unstable field of view caused by liquid surface sloshing, it can still obtain continuous and accurate temperature signals, ensuring the reliability of the input data of the temperature control module.

[0063] Calculate the temperature deviation between the temperature signal at the current sampling time and the target melting temperature, compare the current temperature deviation with the temperature deviation at the previous sampling time, and obtain the actual direction of temperature change.

[0064] The target melting temperature is determined as follows: based on the grade of the metal material to be melted, the recommended melting temperature range is found in the material handbook, and the median value of the recommended melting temperature range is taken as the target melting temperature.

[0065] When the temperature deviation exceeds the allowable range and the actual temperature change direction is away from the target melting temperature, a signal to change the heating current is output to the power regulator, and the adjustment direction is opposite to the actual temperature change direction.

[0066] This indicates that the molten pool temperature is in an out-of-control divergence state. If there is no timely intervention, the temperature will continue to deviate from the target value until it exceeds the limit allowed by the process, resulting in alloy composition failure or crucible damage. At this time, the power regulator outputs an adjustment signal in the opposite direction to the actual temperature change, that is, when the temperature rises, the heating current is reduced, and when the temperature falls, the heating current is increased, so that the input heat changes in the direction of compensation deviation, forcing the molten pool temperature to return to near the target value.

[0067] When the actual temperature change is approaching the target melting temperature, even if the current temperature deviation still exceeds the allowable range, it indicates that the system is automatically returning to the target value. At this time, maintaining the current heating current without intervention can avoid oscillations caused by over-adjustment.

[0068] When the actual temperature change direction is approaching the target melting temperature, a signal is output to the power regulator to maintain the current heating current.

[0069] When the actual temperature change direction is towards the target melting temperature, it indicates that the thermal effect generated by the current heating current has caused the molten pool temperature to return to the target value, and the system is naturally approaching thermal equilibrium. If the heating current is changed at this point, excessive adjustment will occur due to the thermal inertia and response delay of the heating system, causing the temperature to deviate from the target value in the opposite direction. Therefore, maintaining the current heating current unchanged can avoid temperature oscillations caused by over-adjustment, allowing the molten pool temperature to continuously and stably approach the target value under the existing heat input conditions.

[0070] The rotary casting module reduces the field strength parameter of the suspension system after the molten pool temperature stabilizes, causing the molten metal to flow out. At the same time, it collects the attitude data of the water-cooled copper crucible to control the crucible to tilt and rotate for casting. During the rotary casting process, the weight of the furnace body is monitored in real time to determine whether the casting is complete.

[0071] The above-mentioned reduction of the field strength parameters of the suspension system to allow the molten metal to flow out, while simultaneously collecting the attitude data of the water-cooled copper crucible to control the crucible's tilting and rotation for pouring, includes: after receiving the temperature stabilization signal output by the temperature control module, collecting an image inside the crucible to identify the relative distance between the bottom of the molten metal and the pouring gate, which is recorded as the suspension gap.

[0072] The method for determining the temperature stability signal is as follows: continuously collect the molten pool temperature signal, and when the absolute value of the temperature value collected in three consecutive sampling cycles is less than ±5℃ relative to the target molten temperature, the temperature control module outputs a temperature stability signal.

[0073] The suspension gap is the vertical distance between the lowest point of the molten metal and the upper edge of the bottom gate of the crucible. The specific identification method is as follows: extract the bottom contour of the molten metal from the image inside the crucible and obtain the coordinates of the lowest point of the bottom contour of the molten metal; extract the upper edge contour of the bottom gate of the crucible cavity and obtain the coordinates of the center point of the upper edge of the gate; calculate the distance between the two in the same vertical direction as the suspension gap.

[0074] Method for extracting the bottom contour of molten metal: The boundary line between the liquid surface and the inner wall of the crucible is extracted by edge detection, and the arc segment in the bottom area of ​​the crucible is taken as the bottom contour of the molten metal.

[0075] When the suspension gap is greater than the reference distance, the suspension coil current is reduced at a first rate. When the suspension gap is less than the reference distance, the suspension coil current is reduced at a second rate lower than the first rate. When the suspension gap is equal to the reference distance, the current suspension coil current is maintained, and the auxiliary heating coil around the gate is turned on for preheating.

[0076] The reference distance is 0.5 to 1.5 times the diameter of the bottom gate of the crucible. This setting is based on the fact that when the suspension gap is greater than the reference distance, it indicates that the bottom of the molten metal is far from the gate, and the current of the suspension coil needs to be reduced at a fast rate to make the molten metal fall quickly; when the suspension gap is less than the reference distance, it indicates that the molten metal is close to the gate, and the current needs to be reduced at a slow rate to avoid the molten metal impacting the gate and causing splashing or unstable flow.

[0077] The first rate is greater than the second rate, wherein the value of the first rate is 1% / second to 5% / second of the rated current of the suspension coil, and the value of the second rate is 0.1% / second to 1% / second of the rated current of the suspension coil. The rated current of the suspension coil is a fixed value when the equipment leaves the factory.

[0078] The auxiliary heating coil is an induction coil arranged around the gate. Its function is to preheat the gate area before the molten metal flows out, so that the gate temperature is raised to close to the liquidus temperature of the molten metal, so as to prevent the molten metal from solidifying and blocking the gate when it comes into contact with the cold wall.

[0079] While reducing the current of the suspension coil, the motion controller drives the crucible tilt angle to gradually increase and acquires the tilt angle and rotation angle of the crucible in real time. When the molten metal begins to flow out of the gate, the tilt angle is stopped and the crucible is driven to rotate around the axis, so that the molten metal is injected into the mold through the gate.

[0080] The specific implementation method for gradually increasing the crucible tilt angle is as follows: The motion controller drives the crucible to accelerate its rotation around the tilt axis from a stationary state with a constant acceleration, so that the tilt angle gradually increases according to the square of time. When the tilt angle increases until a trigger signal is received that the molten metal begins to flow out, the motion controller drives the crucible to decelerate with a constant deceleration until the angular velocity is zero, and stops tilting.

[0081] The real-time monitoring of the furnace weight during the above-mentioned rotary casting process to determine whether the casting is complete includes: obtaining the total weight of the furnace body during the tilting and rotating casting process of the crucible, subtracting the weight of the empty furnace body from the total weight of the furnace body to obtain the weight of the remaining molten metal, and calculating the change in the weight of the remaining molten metal in adjacent sampling periods.

[0082] The specific implementation method for obtaining the total weight of the furnace body is as follows: a weighing sensor is installed on the furnace body support structure, and the weighing sensor continuously outputs a weight signal.

[0083] When the change is less than the minimum resolvable change of the weighing sensor multiple times in a row, it is determined that the molten metal has been poured. The crucible tilting and rotation is stopped, the auxiliary heating coil is turned off, and the current of the suspension coil is restored to the current value before the start of pouring. The restored electromagnetic force is used to constrain the residual molten metal droplets on the inner wall of the crucible to prevent them from dripping to the bottom of the vacuum chamber.

[0084] When the change in the weight of the remaining molten metal within an adjacent sampling period is lower than the physical resolution of the weighing sensor itself, the change in the sensor output signal can no longer be distinguished from the system noise. At this point, the weight reading obtained by the sensor no longer reflects the actual weight reduction, and continuing to wait will not yield a recognizable weight change signal. Therefore, the phenomenon of multiple consecutive times being lower than this resolution limit is determined as the pouring end point. This avoids the indefinite extension of the pouring time due to waiting for a signal change lower than the sensor's resolution capability. Here, multiple times is taken as 5 times.

[0085] The minimum resolvable change of a load cell is its resolution value at full scale. The resolution specification can be directly read from the load cell's product technical specifications.

[0086] The cooling circulation module introduces cooling medium into the vacuum chamber wall and around the crucible while starting the vacuum preparation stage and continuously monitors the return water temperature during the pouring process. Cooling is stopped after the furnace wall and crucible have both cooled to room temperature.

[0087] Given that the vacuum chamber wall and crucible will be subjected to a large amount of thermal radiation during the subsequent heating process, a cooling medium needs to be introduced in advance to establish a thermal equilibrium state before the heating is started. At the same time, the return water temperature can reflect the thermal load state of the cooled components, so the return water temperature needs to be continuously monitored during the casting process to obtain information on the changes in the cooling effect.

[0088] Therefore, the above-mentioned process of introducing cooling medium into the vacuum chamber wall and around the crucible while starting vacuuming during the vacuum preparation stage, and continuously monitoring the return water temperature during the pouring process includes: starting the cooling medium pump when the vacuum preparation module starts vacuuming, first opening the first branch valve to allow the cooling medium to flow into the vacuum chamber wall cooling channel, and then opening the second branch valve to allow the cooling medium to flow into the cooling channel around the crucible after the rate of change of the return water temperature in the vacuum chamber wall cooling channel is less than the rate of change threshold within a preset time.

[0089] It should be added that before the vacuum preparation module starts evacuating, nitrogen gas at 0.2 MPa should be introduced into the cooling channel and pressurized for 3 minutes. If the pressure does not drop, the seal is considered qualified. After the seal is qualified, the cooling medium pump should be started when the vacuum preparation module starts evacuating.

[0090] The cooling channels for the vacuum chamber wall and the cooling channels around the crucible have different heat capacities and thermal response characteristics. Simultaneously opening both branches leads to uneven distribution of the cooling medium flow, making it difficult to guarantee the cooling effect of the vacuum chamber wall and the stability of the crucible's levitation electric field. Therefore, opening the first branch first allows the vacuum chamber wall cooling channel to establish a cooling cycle. Once the temperature stabilizes, the second branch is then opened to cool the area around the crucible. This avoids flow competition and thermal shock when both channels are activated simultaneously.

[0091] The first branch valve is a flow regulating valve installed at the inlet of the vacuum chamber wall cooling channel, used to control the flow rate of the cooling medium flowing into the vacuum chamber wall cooling channel; the second branch valve is a flow regulating valve installed at the inlet of the cooling channel around the crucible, used to control the flow rate of the cooling medium flowing into the cooling channel around the crucible.

[0092] Method for obtaining the return water temperature change rate: When detecting the return water temperature, rotate the pouring module to continuously collect the return water temperature value at a preset sampling period, calculate the difference between the return water temperature at the current sampling time and the return water temperature at the previous sampling time, and then divide by the sampling period to obtain the return water temperature change rate.

[0093] The preset time is set as follows: during the commissioning phase, with only the vacuum chamber wall cooling channel open, the average time required from the start of the cooling medium introduction until the return water temperature change rate drops to a constant value is recorded as the preset time.

[0094] Method for determining the rate of change threshold: Divide the measurement accuracy of the temperature sensor by the sampling period, and use the resulting value as the rate of change threshold.

[0095] During the process of simultaneously introducing cooling medium into two channels, the return water temperature at the outlet of each channel is collected. When the return water temperature of a certain channel is higher than the upper limit of the cooling temperature range, the opening of the branch valve is increased; when the return water temperature of a certain channel is lower than the lower limit of the cooling temperature range, the opening of the branch valve is decreased.

[0096] When the return water temperature is higher than the upper limit, it indicates that the current cooling medium flow rate is insufficient to remove the heat from the cooled components. The valve opening needs to be increased to increase the flow rate and improve the cooling effect. When the return water temperature is lower than the lower limit, it indicates that the current flow rate is too high, resulting in overcooling. The valve opening needs to be reduced to decrease the flow rate and allow the return water temperature to rise to a reasonable level, thereby maintaining the match between the cooling effect and the flow rate.

[0097] The upper and lower limits of the cooling temperature range are fixed temperature values ​​set at the factory and stored in the cooling circulation module. The upper limit is determined based on the highest allowable return water temperature of the cooling system under the equipment's design operating conditions, while the lower limit is determined based on the combination of the ambient temperature of the equipment's installation location and the type of cooling medium. Specifically, when the ambient temperature is higher than 25℃, the lower limit is the ambient temperature plus 5℃; when the ambient temperature is lower than or equal to 25℃, the lower limit is 30℃. The ambient temperature is collected by a temperature sensor located on the outer wall of the vacuum chamber, 1.5m above the ground, and protected from direct sunlight.

[0098] During the pouring process, if the return water temperature in any channel exceeds the upper limit of the cooling temperature range, the opening of the corresponding branch valve is increased until the return water temperature falls back below the upper limit of the cooling temperature range, and then the valve is restored to the current opening value.

[0099] When the return water temperature exceeds the upper limit of the cooling temperature range during the pouring process, it indicates that the thermal balance between the heat generated by the cooled component and the heat carried by the cooling medium has been broken, and the heat generation rate is higher than the heat carrying rate. Heat continues to accumulate within the cooled component, and if not intervened in time, the component temperature will continue to rise. In this case, increasing the opening of the corresponding branch valve to increase the cooling medium flow rate increases the total amount of cooling medium flowing through the cooled component per unit time, thereby improving heat exchange efficiency, allowing the heat carried to match the heat generated, and suppressing further temperature increases. This judgment uses the upper limit as an objective dividing point; when the return water temperature reaches or exceeds the upper limit, it indicates that the thermal balance can no longer be maintained, and adjusting the valve opening is a direct and effective means of restoring thermal balance.

[0100] When the rate of change of the return water temperature in both channels approaches zero over several consecutive monitoring cycles, the current opening degree of the two valves is locked.

[0101] The specific method for determining when the rate of change approaches zero is as follows: when the rate of change of the return water temperature in both channels is less than half the resolution of the temperature sensor in multiple consecutive monitoring cycles, it is determined to be approaching zero.

[0102] The specific number of continuous monitoring cycles is 3 to 5, thereby eliminating misjudgments caused by single or accidental measurement fluctuations.

[0103] The above-mentioned process of stopping cooling after the furnace wall and crucible have both cooled to room temperature includes: turning off the heating power supply after pouring is completed, switching the levitation power supply to standby mode, and keeping the cooling medium flowing continuously.

[0104] It should be noted that the power output of the heating power supply should be disconnected first, and then the floating power supply should be switched to standby mode to prevent the floating power supply from triggering overcurrent protection or causing damage to the power module due to sudden load changes when the heating power is not turned off.

[0105] The reason for keeping the cooling medium circulating is that after casting, the crucible and vacuum chamber walls still retain a lot of residual heat. If cooling is not continued, the residual heat will cause the temperature of the crucible and vacuum chamber walls to continue to rise, which may damage the equipment or prolong the cooling time.

[0106] During the cooling process, the return water temperature of both channels is continuously monitored. When the return water temperature of both channels shows a monotonically decreasing trend and the temperature difference between adjacent sampling cycles gradually decreases, the sampling interval monitoring is extended while maintaining regular sampling.

[0107] The specific method for determining a monotonically decreasing trend is as follows: if the return water temperature value at each sampling time is less than the return water temperature value at the previous sampling time within three consecutive sampling periods, that is, the temperature sequence shows a strict decreasing trend, it is determined to be monotonically decreasing.

[0108] The specific method for determining that the temperature difference is gradually decreasing is as follows: calculate the temperature difference between two adjacent samples within each sampling period. When the temperature difference is less than the difference of the previous sampling period for 3 to 5 consecutive sampling periods, it is determined that the temperature difference is gradually decreasing.

[0109] The purpose of extending the sampling interval is to reduce the data acquisition density when the temperature approaches a stable state, avoid introducing too much measurement noise that interferes with the stability determination due to excessive sampling, and reduce the data processing burden of the system.

[0110] When the return water temperature remains stable below the ambient temperature threshold within the extended sampling interval and shows no upward trend, it is determined that the furnace wall and crucible have both dropped to ambient temperature. The cooling medium pump is then turned off, and the first branch valve and the second branch valve are disconnected.

[0111] The criteria for determining whether the temperature is stable below the normal temperature threshold are as follows: If the return water temperature is collected multiple times consecutively within an extended sampling interval, and each collected temperature value is lower than normal temperature, and the difference between two adjacent collected temperature values ​​is less than ±1℃, then the temperature is considered stable below the normal temperature threshold. Normal temperature is 25℃ ± 5℃.

[0112] The specific method for determining no upward trend is as follows: within the extended sampling interval, the continuously collected temperature values ​​are arranged in chronological order. If the temperature value at the later sampling time is not greater than the temperature value at the previous sampling time, it is determined that there is no upward trend.

[0113] The execution sequence for shutting down the cooling medium pump and cutting off the valves is as follows: The cooling circulation module first outputs a stop signal to the cooling medium pump. After the cooling medium pump has completely stopped running, it outputs a shut-off signal to the first branch valve and the second branch valve to cut off the flow of cooling medium in both channels.

[0114] When the return water temperature stabilizes below the ambient temperature threshold and shows no upward trend, it indicates that the cooled component no longer releases heat into the cooling medium, and the temperature of the cooled component has become consistent with the ambient temperature. At this time, stopping the cooling can avoid the cooling medium pump running dry and wasting energy or condensation at low temperature.

[0115] The above embodiments can be implemented, in whole or in part, by software, hardware, firmware, or any other combination thereof. When implemented using software, the above embodiments can be implemented, in whole or in part, in the form of a computer program product.

[0116] Those skilled in the art will recognize that the modules and algorithm steps of the various examples described in conjunction with the embodiments disclosed herein can be implemented in electronic hardware, or a combination of computer software and electronic hardware. Whether these functions are implemented in hardware or software depends on the specific application and design constraints of the technical solution. Those skilled in the art can use different methods to implement the described functions for each specific application, but such implementation should not be considered beyond the scope of this application.

[0117] In addition, the functional modules in the various embodiments of this application can be integrated into one processing module, or each module can exist physically separately, or two or more modules can be integrated into one module.

[0118] The above description is merely a specific embodiment of this application, but the scope of protection of this application is not limited thereto. Any variations or substitutions that can be easily conceived by those skilled in the art within the scope of the technology disclosed in this application should be included within the scope of protection of this application. Therefore, the scope of protection of this application should be determined by the scope of the claims.

[0119] Finally, the above description is only a preferred embodiment of the present invention and is not intended to limit the present invention. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the present invention should be included within the protection scope of the present invention.

Claims

1. A vacuum levitation melting furnace based on high-frequency induction heating, characterized in that: Includes the following modules: The vacuum preparation module evacuates the vacuum chamber and fills it with inert gas after the system starts up. Once the vacuum level reaches the standard, it controls the heating and levitation module to work. The heating suspension module heats the furnace charge by applying electricity and determines the position of the furnace charge. If the position of the furnace charge shifts, the field strength parameters of the suspension system are adjusted to keep the furnace charge from contacting the crucible wall. The temperature control module continuously monitors the temperature of the molten pool during the heating process, and changes the heating current through the power regulator when the temperature deviates from the required melting value. The rotary casting module reduces the field strength parameter of the suspension system after the molten pool temperature stabilizes, causing the molten metal to flow out. At the same time, it collects the attitude data of the water-cooled copper crucible to control the crucible to tilt and rotate for casting. During the rotary casting process, the weight of the furnace body is monitored in real time to determine whether the casting is complete. The cooling circulation module introduces cooling medium into the vacuum chamber wall and around the crucible while starting the vacuum preparation stage and continuously monitors the return water temperature during the pouring process. Cooling is stopped after the furnace wall and crucible have both cooled to room temperature.

2. The vacuum levitation melting furnace based on high-frequency induction heating according to claim 1, characterized in that: The process of evacuating the vacuum chamber and filling it with inert gas after system startup includes: Start the mechanical pump to pre-pump the vacuum chamber, monitor the pressure through the vacuum gauge, and when the pressure drops to the transition pressure value, switch to the high vacuum pump to continue pumping to the background vacuum. Close the evacuation valve, alternately open the charging valve and the evacuation valve, and repeat the replacement operation of filling the vacuum chamber with inert gas and then evacuating it several times. After the final inert gas filling, the protective pressure value is maintained. The oxygen partial pressure and water pressure are detected by the residual gas analyzer. After confirming that both are below the allowable upper limit, a start signal is output to the heating suspension module.

3. A vacuum levitation melting furnace based on high-frequency induction heating according to claim 1, characterized in that: The determination of the furnace charge location includes: Continuously capture images of the inside of the crucible, extract the outline of the furnace charge and the outline of the crucible cavity from the images, and determine the geometric center point of the furnace charge outline as the furnace charge center point, and determine the geometric center point of the crucible cavity outline as the crucible center point. The center point of the furnace charge is compared with the center point of the crucible, and the minimum radial distance between the furnace charge outline and the crucible inner cavity outline in the same radial direction is calculated. If the minimum radial distance is less than the preset safety threshold, it is determined that the furnace charge has shifted position.

4. A vacuum levitation melting furnace based on high-frequency induction heating according to claim 1, characterized in that: The method of adjusting the field strength parameters of the suspension system to prevent the furnace charge from contacting the crucible wall includes: When the furnace charge shifts position, obtain the offset direction of the furnace charge center point relative to the crucible center point; The suspension system includes multiple independently controllable excitation coil segments evenly arranged along the circumference of the crucible. At least one coil segment corresponding to the side with the offset direction is taken as the coil segment to be strengthened, and at least one coil segment corresponding to the opposite direction is taken as the coil segment to be weakened. The current output to the drive channel of the coil segment to be strengthened is increased, and the current output to the drive channel of the coil segment to be weakened is decreased. The relative position between the center point of the furnace charge and the center point of the crucible is continuously acquired. When the deviation between the two is less than the overlap threshold, each drive channel maintains the current value unchanged to keep the furnace charge stably suspended in a non-contact state.

5. A vacuum levitation melting furnace based on high-frequency induction heating according to claim 1, characterized in that: The method of changing the heating current via a power regulator when the temperature deviates from the required melting value includes: The dual-color infrared thermometer is fixed outside the observation window of the vacuum chamber, so that the detection light path passes through the observation window and is aimed at the surface of the molten pool to continuously collect the surface temperature signal of the molten pool. Calculate the temperature deviation between the temperature signal at the current sampling time and the target melting temperature, compare the current temperature deviation with the temperature deviation at the previous sampling time, and obtain the actual direction of temperature change. When the temperature deviation exceeds the allowable range and the actual temperature change direction is away from the target melting temperature, a signal to change the heating current is output to the power regulator, and the adjustment direction is opposite to the actual temperature change direction. When the actual temperature change direction is approaching the target melting temperature, a signal is output to the power regulator to maintain the current heating current.

6. A vacuum levitation melting furnace based on high-frequency induction heating according to claim 1, characterized in that: The process of reducing the field strength parameters of the levitation system to allow the molten metal to flow out, while simultaneously collecting attitude data of the water-cooled copper crucible to control its tilting and rotation during pouring, includes: After receiving the temperature stabilization signal output by the temperature control module, the image inside the crucible is collected to identify the relative distance between the bottom of the molten metal and the pouring gate, which is recorded as the suspension gap. When the suspension gap is greater than the reference distance, the suspension coil current is reduced at a first rate. When the suspension gap is less than the reference distance, the suspension coil current is reduced at a second rate lower than the first rate. When the suspension gap is equal to the reference distance, the current suspension coil current is maintained, and the auxiliary heating coil around the gate is turned on for preheating. While reducing the current of the suspension coil, the motion controller drives the crucible tilt angle to gradually increase and acquires the tilt angle and rotation angle of the crucible in real time. When the molten metal begins to flow out of the gate, the tilt angle is stopped and the crucible is driven to rotate around the axis, so that the molten metal is injected into the mold through the gate.

7. A vacuum levitation melting furnace based on high-frequency induction heating according to claim 1, characterized in that: The real-time monitoring of the furnace weight during the rotary casting process to determine whether casting is complete includes: The total weight of the furnace body is obtained during the tilting and rotating pouring process of the crucible. The weight of the empty furnace body is subtracted from the total weight of the furnace body to obtain the weight of the remaining molten metal. The change in the weight of the remaining molten metal is calculated in adjacent sampling periods. When the change is less than the minimum resolvable change of the weighing sensor multiple times in a row, it is determined that the molten metal has been poured. The crucible tilting and rotation are stopped, the auxiliary heating coil is turned off, and the current of the suspension coil is restored to the current value before the start of pouring.

8. A vacuum levitation melting furnace based on high-frequency induction heating according to claim 1, characterized in that: The step of introducing cooling medium into the vacuum chamber walls and around the crucible while initiating vacuuming during the vacuum preparation stage, and continuously monitoring the return water temperature during the pouring process includes: When the vacuum preparation module starts vacuuming, the cooling medium pump is started. First, the first branch valve is opened to allow the cooling medium to flow into the cooling channel of the vacuum chamber wall. After the change rate of the return water temperature in the vacuum chamber wall cooling channel is less than the change rate threshold within a preset time, the second branch valve is opened to allow the cooling medium to flow into the cooling channel around the crucible. During the process of simultaneously introducing cooling medium into two channels, the return water temperature at the outlet of each channel is collected. When the return water temperature of a certain channel is higher than the upper limit of the cooling temperature range, the opening of the branch valve is increased; when the return water temperature of a certain channel is lower than the lower limit of the cooling temperature range, the opening of the branch valve is decreased. During the pouring process, if the return water temperature in any channel exceeds the upper limit of the cooling temperature range, the opening of the corresponding branch valve is increased until the return water temperature falls back below the upper limit of the cooling temperature range, and then the valve is restored to the current opening value. When the rate of change of the return water temperature in both channels approaches zero over several consecutive monitoring cycles, the current opening degree of the two valves is locked.

9. A vacuum levitation melting furnace based on high-frequency induction heating according to claim 8, characterized in that: The step of stopping cooling after both the furnace wall and the crucible have cooled to room temperature includes: After pouring is complete, turn off the heating power supply and switch the suspension power supply to standby mode to keep the cooling medium flowing. During the cooling process, the return water temperature of the two channels is continuously monitored. When the return water temperature of both channels decreases monotonically and the temperature difference between adjacent sampling cycles gradually decreases, the sampling interval is extended while maintaining regular sampling. When the return water temperature remains stable below the ambient temperature threshold within the extended sampling interval and shows no upward trend, it is determined that the furnace wall and crucible have both dropped to ambient temperature. The cooling medium pump is then turned off, and the first branch valve and the second branch valve are disconnected.

10. A vacuum levitation melting furnace based on high-frequency induction heating according to claim 4, characterized in that: The number of excitation coil segments is even, and they are arranged at equal angular intervals along the circumference of the crucible.

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