Foam model vaporization control process in lost foam casting

Abstract

This invention relates to the field of casting molding technology and discloses a foam model gasification control process in lost foam casting. The process includes: collecting real-time pressure and ambient negative pressure along the suction path within the sand box; determining the sand layer permeability resistance coefficient based on the pressure difference and filling distance; determining the set pressure of the target suction path based on the model's characteristic length; controlling the output pulse of the target suction path to enhance negative pressure as the filling front approaches; and adjusting the opening of the gate valve in the casting pouring channel to reduce the rising speed of the molten metal when the permeability resistance coefficient exceeds a threshold. This invention achieves multi-loop spatial coordinated adjustment of the negative pressure amplitude and filling speed, ensuring that the negative pressure flow resistance field matches the gasification release distribution, eliminating localized air gap blockage, enabling directional and rapid gas discharge, maintaining the stability of the dry sand mold wall, and preventing air entrapment and box collapse in the casting.

Description

Technical Field

[0001] This invention belongs to the field of casting molding technology, and in particular relates to a foam model gasification control process in lost foam casting. Background Technology

[0002] Currently, in the lost foam casting process, the mainstream approach is to use a constant negative pressure of 0.02MPa to 0.05MPa set on the outside of the dry sand medium layer to draw out the gaseous substances generated when the foam comes into contact with the high-temperature molten metal. This static setting relies on a vacuum pump to continuously extract the gas inside the gas collection pipe at the bottom of the sand box, which reduces system complexity while providing a steady-state gas extraction path. It is a basic venting method for casting components with symmetrical structures and small volume. With the evolution of the manufacturing requirements for complex and irregularly shaped components, high temperature conduction causes the foam to undergo transient nonlinear pyrolysis phase transformation. The gasification rate changes drastically with the filling height. The unfilled dry sand layer undergoes local thermal expansion and particle rearrangement under the action of radiant heat and filling pressure. This causes the gas flow resistance of the dry sand layer to exhibit a nonlinear spatiotemporal evolution law. Traditional static negative pressure suction technology lacks the means to track the evolution of mass resistance in the venting path, which causes high-pressure gaseous products to accumulate at the filling interface and penetrate into the sand box in a disorderly manner, destroying the air permeability balance of the dry sand layer. This can easily lead to slag inclusions, wrinkles and loose structure on the casting surface, resulting in discontinuity in the internal structure of the metal matrix.

[0003] To address mold wall instability caused by gas accumulation, conventional improvement approaches tend to increase the power of the negative pressure pump station or add exhaust pipes. However, these crude adjustment methods cannot accommodate the nonlinear fluctuations in transient flow resistance. Excessive negative pressure can easily disrupt the internal mechanical balance of the sand mold, leading to localized mold wall collapse. The aforementioned improvements are limited to hardware modifications such as pipe distribution and pump station power; software aspects, such as control methods, also have shortcomings. For example, Chinese invention patent application CN105929864A discloses an automatic vacuum adjustment system and method for lost foam casting of large and complex castings, whose control logic is based on the vaporization release rate and the negative pressure deviation of the pipeline. The pre-defined condition of quasi-linear mapping for the difference deviates from the actual boundary conditions of complex casting conditions. Relying solely on the feedback of static air pressure deviation to adjust the valve opening cannot, on the one hand, detect the spatiotemporal abrupt changes in the mass transfer resistance of the dry sand layer itself, and there is a risk of response lag and air stagnation when facing irregularly shaped abrupt cross sections; on the other hand, the adjustment system is not linked to the casting flow field and lacks bidirectional interlocking linkage between negative pressure suction and the filling speed of molten metal. When the local vaporization release far exceeds the pipeline suction limit, the rising molten metal front can easily cover and engulf the high-pressure air gap because the filling speed cannot be actively controlled, which can lead to physical failures such as air entrapment, wrinkling, and mold wall collapse in the casting.

[0004] Therefore, the technical problem to be solved by this invention is how to dynamically identify the evolution of transient mass transfer resistance in the dry sand layer, correct the pressure gradient field of the target area through multi-loop spatial synergistic coupling, establish a two-way interlocking linkage control system for negative pressure suction and molten metal filling speed, and maintain the mechanical stability of the dry sand mold wall while directional and rapid gas removal. Summary of the Invention

[0005] This invention aims to solve the problem of imbalance in negative pressure field compensation and mechanical instability of mold wall caused by the dynamic evolution of mass transfer resistance in dry sand layer during the casting and filling process of complex components.

[0006] In this technical solution, a foam model vaporization control process in lost foam casting includes the following steps:

[0007] Step S1: Collect the real-time internal pressure at the airflow suction path of the sand box at different locations inside the sand box, and collect the basic environmental negative pressure in the external main pipe. Calculate the pressure difference between the real-time internal pressure and the basic environmental negative pressure. Obtain the vertical distance between the airflow suction path of the adjacent sand box and the current metal liquid filling front edge. Divide the pressure difference by the vertical distance to calculate the transient air permeability resistance coefficient of the sand layer, which characterizes the change of air permeability resistance of the dry sand layer.

[0008] Step S2: Determine the target sand box airflow suction path from multiple sand box airflow suction paths. Calculate the set pressure value of the target sand box airflow suction path based on the transient air permeability resistance coefficient of the sand layer and the preset model characteristic length. When the current metal liquid filling mold front is detected to be approaching the target sand box airflow suction path area, control the target sand box airflow suction path to output pulse-type enhanced negative pressure, and the amplitude of the pulse-type enhanced negative pressure corresponds to the set pressure value.

[0009] Step S3: Compare the transient permeability resistance coefficient of the sand layer with the preset flow resistance safety threshold. If the transient permeability resistance coefficient of the sand layer exceeds the flow resistance safety threshold, reduce the opening of the casting channel of the mold to reduce the rising speed of the molten metal and control the transient permeability resistance coefficient of the sand layer to be reduced to within the flow resistance safety threshold.

[0010] Preferably, step S1 includes the following sub-steps: step S11, subtracting the real-time internal pressure from the negative pressure of the base environment to determine the pressure difference; step S12, obtaining the height position of the airflow suction path of the sand box and the height position of the current metal liquid filling front edge, subtracting the height position from the height position to determine the vertical distance, and dividing the pressure difference by the vertical distance to calculate the transient air permeability resistance coefficient of the sand layer.

[0011] Preferably, in step S2, during the process of controlling the output of pulse-enhanced negative pressure in the target sand box airflow suction path, the following self-healing adjustment steps for the airflow suction channel are also included: Step S301, monitoring the flow deviation between multiple branch pipes connecting the sand box airflow suction path; Step S302, calculating the real-time flow Reynolds number at the exhaust filter medium inside each branch pipe; Step S303, when the real-time flow Reynolds number is found to be lower than the preset flow attenuation threshold, determining that the corresponding branch pipe has a local blockage; Step S304, opening the reverse pulse flushing passage connected to the branch pipe with the local blockage, and introducing high-pressure reverse airflow to backwash the exhaust filter medium.

[0012] Preferably, the process of calculating the set pressure value in step S2 further includes the following dynamic correction steps: step S401, collecting the real-time pouring temperature inside the cavity; step S402, calculating the actual temperature fluctuation range of the real-time pouring temperature within the current filling cycle; step S403, compensating for the deviation of the set pressure value according to the actual temperature fluctuation range, and increasing the absolute value of the set pressure value proportionally when the real-time pouring temperature is higher than the preset process temperature calibration value.

[0013] Preferably, step S3 includes the following sub-steps: step S31, calculating the excess ratio coefficient when the transient air permeability resistance coefficient of the sand layer exceeds the flow resistance safety threshold; step S32, adjusting the gate valve opening of the casting pouring channel according to the excess ratio coefficient, controlling the reduction of the gate valve opening of the casting pouring channel to maintain a positive correlation with the excess ratio coefficient, so as to reduce the rising speed of the molten metal.

[0014] Preferably, the foam model includes a cross-sectional abrupt change region. When the current metal liquid filling front moves to the state before the cross-sectional abrupt change region, the corresponding model feature length is increased stepwise according to the contour size of the cross-sectional abrupt change region, so as to increase the set pressure value of the target sand box airflow suction path in advance.

[0015] Preferably, the basic environmental negative pressure inside the sand box is controlled within the pressure range of 0.02MPa to 0.05MPa, and when the target sand box airflow suction path outputs pulse-enhanced negative pressure, the duration of the pulse-enhanced negative pressure is maintained within the pulse time range of 10ms to 50ms.

[0016] Preferably, the height position of the current metal liquid filling front is determined by the on / off electrical signal status of the multi-point filling contact probes deployed on the surface of the foam model.

[0017] Preferably, before filling, the compactness of the dry sand layer in a dense state is calibrated in situ on a multidimensional high-frequency vibration compaction table under a preset amplitude and preset frequency compaction excitation state.

[0018] Compared with existing technologies, the foam model vaporization control process in lost foam casting of this invention has the following advantages:

[0019] 1. In the foam model gasification control, a spatially discrete negative pressure control loop is used in conjunction with liquid level detection of the fluid front position to change the flow resistance attenuation caused by the previous global uniform negative pressure suction. The control unit tracks the rising trajectory of the molten metal in real time and determines the current approaching area. The internal real pressure of the adjacent units that have not been activated is collected and compared with the basic ambient air pressure. Combined with the vertical spacing, the mass transfer resistance coefficient characterizing the evolution state of the flow resistance of the dry sand layer is calculated. Based on this, the set pressure of the target suction unit is dynamically corrected so that the negative pressure flow resistance field inside the sand box is closely matched with the temporal and spatial distribution of the transient release of foam degradation gasification products, ensuring that the gaseous products are discharged directionally along the preset path at the moment of generation.

[0020] 2. The system continuously identifies the flow characteristics of the medium during the operation of the target suction unit, compares the obtained mass transfer resistance coefficient with the critical shear flow resistance limit value of the dry sand medium in a compacted state, and determines that when the above resistance coefficient exceeds the preset flow resistance safety threshold, it directly controls the gate valve opening of the casting system to reduce the rising speed of the molten metal. This solves the contradiction of the decrease in permeability caused by excessive thermal expansion and particle rearrangement of dry sand under the combined action of high temperature radiation and filling pressure. It provides sufficient diffusion and mass transfer time for locally rapidly accumulating gaseous degradation products, maintains the mechanical stability of the dry sand mold wall under transient nonlinear high pressure air gap impact, and adaptively hedges the risk of dry sand collapse during the casting process.

[0021] 3. This method constructs a closed-loop self-healing regulation by monitoring the flow deviation of multiple branch pipelines and the feedback mechanism of pouring temperature deviation. It can identify local blockage of the filter medium caused by uneven air permeability of the coating layer or splashing of metal residues online. When an abnormal flow Reynolds number is detected at the filter medium, the reverse high-pressure air pulse path of the corresponding branch is automatically opened to clear the local accumulated foreign matter. At the same time, the pressure gradient control parameters are corrected according to the collected on-site pouring temperature fluctuation amplitude. The output energy level of the negative pressure field is flexibly adjusted from the mechanism level, avoiding the large-area shelling and air suction efficiency decline of the pipeline that are easy to occur in traditional molding exhaust systems. This ensures the long-term overflow steady state of the negative pressure pneumatic suction channel during the filling cycle. Attached Figure Description

[0022] Figure 1 This is a process flow diagram of controlling the negative pressure of foam model vaporization and the rising speed of molten metal in the lost foam casting process of this invention;

[0023] Figure 2 This is a structural diagram of the foam model vaporization control unit in the lost foam casting process of this invention. Detailed Implementation

[0024] The technical solutions of the embodiments of this application will be clearly described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of this application, not all embodiments. All other embodiments obtained by those skilled in the art based on the embodiments of this application are within the scope of protection of this application.

[0025] A process for controlling the vaporization of foam patterns in lost foam casting includes the following steps:

[0026] Step S1: Collect the real-time internal pressure at the airflow suction path of the sand box at different locations inside the sand box, and collect the basic environmental negative pressure in the external main pipe. Calculate the pressure difference between the real-time internal pressure and the basic environmental negative pressure. Obtain the vertical distance between the airflow suction path of the adjacent sand box and the current metal liquid filling front edge. Divide the pressure difference by the vertical distance to calculate the transient air permeability resistance coefficient of the sand layer, which characterizes the change of air permeability resistance of the dry sand layer.

[0027] Step S2: Determine the target sand box airflow suction path from multiple sand box airflow suction paths. Calculate the set pressure value of the target sand box airflow suction path based on the transient air permeability resistance coefficient of the sand layer and the preset model characteristic length. When the current metal liquid filling mold front is detected to be approaching the target sand box airflow suction path area, control the target sand box airflow suction path to output pulse-type enhanced negative pressure, and the amplitude of the pulse-type enhanced negative pressure corresponds to the set pressure value.

[0028] Step S3: Compare the transient permeability resistance coefficient of the sand layer with the preset flow resistance safety threshold. If the transient permeability resistance coefficient of the sand layer exceeds the flow resistance safety threshold, reduce the opening of the casting channel of the mold to reduce the rising speed of the molten metal and control the transient permeability resistance coefficient of the sand layer to be reduced to within the flow resistance safety threshold.

[0029] Preferably, step S1 includes the following sub-steps: step S11, subtracting the real-time internal pressure from the negative pressure of the base environment to determine the pressure difference; step S12, obtaining the height position of the airflow suction path of the sand box and the height position of the current metal liquid filling front edge, subtracting the height position from the height position to determine the vertical distance, and dividing the pressure difference by the vertical distance to calculate the transient air permeability resistance coefficient of the sand layer.

[0030] Preferably, in step S2, during the process of controlling the output of pulse-enhanced negative pressure in the target sand box airflow suction path, the following self-healing adjustment steps for the airflow suction channel are also included: Step S301, monitoring the flow deviation between multiple branch pipes connecting the sand box airflow suction path; Step S302, calculating the real-time flow Reynolds number at the exhaust filter medium inside each branch pipe; Step S303, when the real-time flow Reynolds number is found to be lower than the preset flow attenuation threshold, determining that the corresponding branch pipe has a local blockage; Step S304, opening the reverse pulse flushing passage connected to the branch pipe with the local blockage, and introducing high-pressure reverse airflow to backwash the exhaust filter medium.

[0031] Preferably, the process of calculating the set pressure value in step S2 further includes the following dynamic correction steps: step S401, collecting the real-time pouring temperature inside the cavity; step S402, calculating the actual temperature fluctuation range of the real-time pouring temperature within the current filling cycle; step S403, compensating for the deviation of the set pressure value according to the actual temperature fluctuation range, and increasing the absolute value of the set pressure value proportionally when the real-time pouring temperature is higher than the preset process temperature calibration value.

[0032] Preferably, step S3 includes the following sub-steps: step S31, calculating the excess ratio coefficient when the transient air permeability resistance coefficient of the sand layer exceeds the flow resistance safety threshold; step S32, adjusting the gate valve opening of the casting pouring channel according to the excess ratio coefficient, controlling the reduction of the gate valve opening of the casting pouring channel to maintain a positive correlation with the excess ratio coefficient, so as to reduce the rising speed of the molten metal.

[0033] Preferably, the foam model includes a cross-sectional abrupt change region. When the current metal liquid filling front moves to the state before the cross-sectional abrupt change region, the corresponding model feature length is increased stepwise according to the contour size of the cross-sectional abrupt change region, so as to increase the set pressure value of the target sand box airflow suction path in advance.

[0034] Preferably, the basic environmental negative pressure inside the sand box is controlled within the pressure range of 0.02MPa to 0.05MPa, and when the target sand box airflow suction path outputs pulse-enhanced negative pressure, the duration of the pulse-enhanced negative pressure is maintained within the pulse time range of 10ms to 50ms.

[0035] Preferably, the height position of the current metal liquid filling front is determined by the on / off electrical signal status of the multi-point filling contact probes deployed on the surface of the foam model.

[0036] Preferably, before filling, the compactness of the dry sand layer in a dense state is calibrated in situ on a multidimensional high-frequency vibration compaction table under a preset amplitude and preset frequency compaction excitation state.

[0037] Example 1: When the system faces the situation of pouring complex and large irregularly shaped castings into the mold cavity of lost foam casting in an intelligent casting island, the foam model undergoes transient nonlinear degradation and vaporization under the thermal radiation of high-temperature molten metal. The unfilled dry sand layer undergoes local thermal expansion and particle rearrangement under the action of radiant heat and filling pressure, resulting in a nonlinear spatiotemporal evolution law of gas flow resistance in the dry sand layer. Traditional constant negative pressure suction lacks the means to track the evolution of mass resistance evolution in the exhaust path, causing gaseous products generated in the cross-sectional abrupt region to accumulate at the filling interface and randomly penetrate into the sand box, disrupting the air permeability balance of the dry sand layer, causing slag inclusions, wrinkles, and loose structure on the casting surface, and causing the dry sand mold wall to become unstable and collapse when the local air pressure drops suddenly. During the pouring process of lost foam casting, the control unit determines the height position of the current molten metal filling front by responding to the on / off electrical signal status of multi-point filling contact probes arranged on the surface of the foam model. The control unit collects the real-time internal pressure at the sand box airflow suction path at different positions inside the sand box. And collect the basic environmental negative pressure inside the external main pipe. Real-time internal pressure negative pressure of the basic environment The pressure difference is determined by subtracting the values ​​of the two heights. Simultaneously, the height of the sand box airflow suction path and the height of the current molten metal filling front are obtained. The difference between these heights is then used to determine the vertical distance between the adjacent sand box airflow suction path and the current molten metal filling front. Then divide the pressure difference by the vertical distance. This coefficient, in its physical form, belongs to the flow resistance status register of the data storage within the control unit. Its bound and attached objectively measurable input parameters are the pressure difference and vertical distance, acquired in real-time by the pressure sensor and contact probe. The control unit executes a discrete division operation, dividing the pressure difference by the vertical distance, and outputs a dynamic gas-phase flow mass transfer resistance gradient value in megapascals per meter (MPa / m). This gradient serves as the determination state for the subsequent stage control system to correct the negative pressure amplitude of the target suction unit, thus clarifying the physical dimension of its pressure gradient. This gradient is used to drive the calculation of the corresponding transient permeability resistance coefficient of the sand layer, characterizing the change in permeability resistance of the dry sand layer. Its linear calculation formula is expressed as ,in, is the transient air permeability resistance coefficient of the sand layer, where the subscript st indicates transient; This represents the real-time internal pressure at the airflow suction path of the sand box, where the subscript adj indicates real-time. The base environmental negative pressure within the external main pipe, where the subscript env indicates the environment; The vertical distance between the airflow suction path of the adjacent sand box and the current metal liquid filling front edge, where the subscript 'v' indicates vertical. To ensure that the target setpoint calculated under gauge pressure conforms to the characteristics of negative pressure enhancement technology, the system calculates the set pressure value. When introducing a dimensionless direction correction factor with a value greater than zero. The corresponding mathematical formula is Among them, the pressure value is set. The target negative pressure gauge value required for the suction path is set to a negative value. The control unit adjusts the pressure according to the set pressure value. The converted control current signal directly controls the regulating valve, setting the pressure value. With real-time internal pressure The differential input regulator outputs a corresponding voltage duty cycle signal to the regulating valve solenoid coil, changing the magnitude of the current flowing through the coil and controlling the valve core to generate displacement, thereby adjusting the suction negative pressure of the sand box airflow suction path to the corresponding set amplitude.

[0038] The control unit determines the target sand box airflow suction path from multiple sand box airflow suction paths, based on the transient air permeability resistance coefficient of the sand layer. With the preset model feature length Calculate the set pressure value of the airflow suction path of the target sand box. Its specific calculation formula is expressed as follows ,in, This sets the pressure value for the airflow suction path of the target sand box, where the subscript tar indicates the target. This represents the base environment negative pressure within the external main pipe, where the subscript env indicates the environment. This represents the transient air permeability resistance coefficient of the sand layer, where the subscript 'st' indicates transient. The preset model feature length is given, where the subscript 'c' represents the feature. The plus sign operation in the above formula is based on the scalar incremental control logic of the absolute value of negative pressure set inside the control unit. In order to ensure that the final calculated target set value conforms to the technical characteristics of negative pressure enhancement under gauge pressure, the control unit performs the calculation at the hardware driver layer, with the basic environmental negative pressure... With resistance compensation term All participate in the internal difference calculation in the form of absolute value scalars, and their essential control logic corresponds to ,in, A preset directional correction coefficient greater than zero is used to ensure that the set pressure value calculated and output to the regulating valve is accurate even under extreme conditions of high-intensity vaporization. The gauge pressure is always maintained at a negative value. Through the calculation of the absolute value scalar mentioned above, the negative pressure field is prevented from turning into positive pressure jet due to excessive resistance, so as to maintain the advanced pulse suction energy level of the exhaust path. When the current metal liquid filling mold front is detected to be approaching the target sand box airflow suction path area, the control unit controls the target sand box airflow suction path to output pulse-enhanced negative pressure, so that the amplitude of the pulse-enhanced negative pressure corresponds to the set pressure value. This allows for feedback coordination between positional parameters and flow resistance calculations along the exhaust path when the foam model encounters a region of abrupt cross-sectional changes leading to an increased gasification rate. At the instant of gasification, a pressure gradient is constructed between the air gap front and the exhaust path, causing transient pyrolysis gaseous products to exit along a predetermined path. This balances the evolutionary relationship between high-pressure gas accumulation and mold wall mechanical instability, thus determining the size of the abrupt cross-sectional change region and the model's characteristic length. In terms of the mapping relationship, on the physical entity level, the initial value of the model feature length is pre-stored as a geometric constant in the static parameter register of the control unit, and the specific value is set to 0.50m to characterize the thickness of the standard uniform cross-section foam model. In order to completely eliminate and replace the following in the action steps, the system pre-stores the geometric mutation feature length mapping matrix, and the control unit reads the pre-imported three-dimensional model file of the foam model to calculate the rate of change of the continuous filling cross-sectional area. When the rate of change of the cross-sectional area of ​​the continuously filled mold satisfies At this time, the control unit directly skips any matrix black box and drives the hardware multiplier to multiply the value in the constant register from the initial 0.50m by 1.15, and the closed-loop output is a deterministic parameter state whose absolute value is steppedly increased to 0.575m. This state directly participates in the real-time control calculation of the set pressure. When the condition is met... When the model feature length is... The initial value is increased by 40%, and the change in geometric boundary is converted into a feedforward constraint condition for the set pressure value.

[0039] To prevent the dry sand layer from experiencing reduced air permeability due to excessive thermal expansion and particle rearrangement, the control unit adjusts the transient air permeability resistance coefficient of the sand layer. With the preset flow resistance safety threshold In comparison, among them, The flow resistance safety threshold, where the subscript... This represents the safety threshold, specifically the transient air permeability resistance coefficient of the sand layer. Exceeding the flow resistance safety threshold Under these conditions, the control unit reduces the opening of the mold pouring channel to decrease the rising velocity of the molten metal, providing sufficient mass transfer and diffusion time for local gaseous degradation products inside the cavity, and controlling the transient permeability resistance coefficient of the sand layer. Reduce to the flow resistance safety threshold Within this framework, an interlocked feedback network is constructed, encompassing the spatial coordinates of the fluid front, the mass transfer resistance of the sand layer, and the filling speed of the molten metal. This enables the suction circuit and the casting channel to form a dynamically balanced system that depends on each other. When the negative pressure amplitude and filling speed are under the coordinated control of the multi-circuit space, the gasification products are discharged directionally along a preset path at the moment of generation. The fluctuation range of the air gap pressure is within the preset process threshold. The dry sand mold wall maintains mechanical stability during the high-temperature filling process. The causes of failure due to localized air entrapment, wrinkling, and carbon precipitation are eliminated. The intelligent casting island maintains the set system stability when facing the nonlinear evolution of the gasification flow resistance of the irregular foam model.

[0040] Example 2: In the experimental verification of the foam model vaporization control process in lost foam casting, the test platform was configured around the sand box of a multi-loop suction structure. The pressure sensor used to detect pressure changes inside the sand box has a measurement range of -100 kPa to 100 kPa, a physical resolution of 10 Pa, and a signal sampling rate of 1000 Hz. The contact probe assembly used to determine the height of the leading edge of the molten metal filling mold has a spatial resolution of 0.5 mm, and the sampling period of the control unit is... As a process parameter, its value is limited by the transient vaporization rate during the high-temperature degradation of the foam model and the bandwidth throughput of the control bus, thus requiring a shorter sampling cycle. This will increase the computational load on the processor in the control unit and prolong the sampling period. This would result in missed detection of transient air gap pressure peaks. In order to fully capture the drastic transient pressure fluctuations at the vaporization interface while reducing the processor's computational load, the control unit adjusts the sampling period based on the maximum rising speed of the molten metal's rising edge. When the ascent speed is within the process range of 50 mm / s to 80 mm / s, the control unit controls the sampling period. The sampling period tends towards a lower limit of 2 ms. In this experiment, the sampling period is... Set to 5 ms, to test the anti-interference performance in an industrial electromagnetic environment, the experiment superimposed a 50 Hz power frequency harmonic interference and a 5 kPa random high-frequency noise onto the raw voltage signal output by the pressure sensor. The unprocessed raw pressure data exhibited random spike fluctuations with a maximum amplitude of 12.4 kPa. The signal disturbance in the raw data caused the valve in the suction path to oscillate at high frequencies. In the test group using the method claimed in this invention, the acquired pressure signal was passed through a low-pass digital filter module with a time constant of 15 ms, suppressing the noise ripple amplitude to within 0.3 kPa, thereby obtaining the real-time internal pressure. As input parameters for subsequent calculations, to address the measurement and control interference caused by the high-temperature multiphase flow composed of the pyrolysis gas and liquid phases within the branch pipeline on the flow state, the system employs a multiphase flow parameter conversion method. Differential pressure sensors with a measurement range of 0 to 50 kPa, a measurement accuracy of 0.05%, and a sampling frequency of 2000 Hz are symmetrically installed at both ends of the exhaust filter medium in the branch pipeline. These sensors collect the flow resistance pressure difference data before and after the exhaust filter medium and input it into the control unit. The data is then imported into a built-in first-order low-pass digital filter to filter out random high-frequency pressure noise generated by multiphase flow droplet collisions, extracting the mass transfer pressure difference through the filter flow. This data is collected over five consecutive sampling cycles. When the ratio of the flow rate difference to the reference pressure difference exceeds a preset attenuation factor threshold, the control unit sends a control command to the corresponding branch pipeline to open a high-pressure reverse airflow to backwash the exhaust filter medium. In actual operation, this flow rate attenuation threshold is physically attributed to the comparison configuration register of the internal data storage of the control unit. The objective characteristic input parameter bound to it is the transient flow rate difference to the filter collected by the high-frequency differential pressure sensor and the initial reference pressure difference under clean equipment conditions. The control unit reads the above input parameters through discrete timing control flow in five consecutive sampling cycles. The system performs a discrete division operation, dividing the current pressure difference by the initial reference pressure difference. When the calculated real-time dimensionless ratio reaches a fixed 2.5 times, it represents the physical state where the effective porosity of the porous medium decreases from the initial 38% to 25% due to crusting. In physical engineering terms, this corresponds to the following: the flow attenuation threshold is defined as the lower limit of the critical dimensionless Reynolds number. Its derivation is based on the modified expression of Darcy's law in the multiphase flow gas dynamics of porous media. Considering that the multiphase flow condition of high-temperature pyrolysis gas phase and condensate phase mixing will generate transient droplet collision noise, the system connects in parallel to the branch pipeline. High-frequency differential pressure sensors before and after the air filter medium continuously collect the mass pressure difference of the filter flow, and use a first-order low-pass digital filter to eliminate random pressure fluctuation noise. When the exhaust filter medium is partially blocked due to coating crusting or metal splash residue, the effective porosity of the fluid through the porous medium declines, causing the measured actual flow Reynolds number to fall below the dimensionless lower limit. By setting the above-mentioned preset attenuation multiple threshold to a fixed 2.5 times, the control unit can accurately eliminate random noise interference in the complex environment of severe fluctuations in multiphase flow and identify the state of flow cross-section reduction caused by the decline in filtration efficiency online.

[0041] This experiment sets up three problem intensity gradients composed of different foam model wall thicknesses, and establishes: a control group using constant negative pressure suction; a partially missing control group one with selective removal of spatial multi-loop suction control; and a partially missing control group two with selective local segmentation of the interlocking linkage between the mold pouring channel opening and the molten metal rising speed; and a model characteristic length... Control group 1 and control group 2, whose set values ​​deviate from the value window, have a negative base environment pressure within the external main pipe. Under the baseline condition of -30.0 kPa: the wall thickness of the low-strength gradient foam model is 20 mm; the test group using the method claimed in this invention has an initial peak vaporization pressure of 4.32 kPa, when the contact probe assembly measures the vertical distance between the adjacent sand box airflow suction path and the current molten metal filling front. The real-time internal pressure was collected when the diameter was shortened to 0.20 m. The transient permeability resistance coefficient of the sand layer was -25.71 kPa, and the control unit obtained it through a linear calculation formula. The initial vaporization pressure peak was 21.45 kPa / m, and the wall thickness of the medium-strength gradient foam model was 50 mm. In the test group using the method claimed in this invention, the initial vaporization pressure peak increased to 11.64 kPa at a vertical distance of [missing information]. The real-time internal pressure was measured at a distance of 0.20 m. The transient permeability resistance coefficient of the sand layer calculated by the control unit is -18.36 kPa. Increased to 58.20 kPa / m, at the model characteristic length The calculated set pressure value was obtained under the condition of 0.50 m. The pressure was -0.90 kPa, and the wall thickness of the high-strength gradient foam model was 100 mm. In the test group using the method claimed in this invention, intensified local vaporization led to a peak initial vaporization pressure of 27.38 kPa at a vertical distance. The real-time internal pressure was measured at a distance of 0.20 m. The corresponding transient permeability resistance coefficient of the sand layer is -3.22 kPa. Reaching 133.90 kPa / m, at the model feature length The calculated set pressure value under the condition of 1.00 m. The pressure was 103.90 kPa. Under high-intensity gradient conditions, the local pressure of the control group subjected to constant negative pressure suction reached 34.56 kPa. The real-time internal pressure of the aberrant change zone in the partially missing control group under medium-intensity gradient conditions was also observed. The pressure was elevated to 18.87 kPa, and the transient permeability resistance coefficient of the sand layer measured under high intensity gradient was partially missing in control group 2. The pressure was 133.90 kPa / m, but the opening of the casting channel remained at 100%, and The set pressure value corresponding to the medium intensity gradient, with a setting of 0.02 m. The calculated result is -28.84 kPa, exceeding the range of control group two in terms of model feature length. The set pressure value corresponding to the medium intensity gradient at a set depth of 1.50 m. The calculated result is 57.30 kPa. The experimental data shows that under low intensity gradients, the test group using the method claimed in this invention applies a suction pressure of -27.86 kPa to the target sand box airflow suction path. This is due to the transient air permeability resistance coefficient of the sand layer. The flow resistance safety threshold does not exceed 60.00 kPa / m. The opening of the casting pouring channel is maintained at 100%, and the measured surface roughness of the casting is... for The surface roughness of the casting is 0.2 μm and no inclusions or loose microstructure defects were found. Under medium strength gradient: when a suction pressure of -0.90 kPa is applied and the opening of the casting mold gating channel is maintained at 100%, the measured surface roughness of the casting is... With a thickness of 4.6 μm and a defect rate of 0%, under high strength gradients: due to the transient air permeability resistance coefficient of the sand layer... It reached 133.90 kPa / m and exceeded the flow resistance safety threshold. The control loop was used to adjust the opening of the casting pouring channel from 100% to 42.5%, limiting the rising velocity of the molten metal from 45.28 mm / s to 18.35 mm / s to increase the venting mass transfer time. Under high-intensity vaporization impact, the measured surface roughness of the casting was... It is stable at 5.7 μm and the deformation of the cavity mold wall is only 0.4 mm.

[0042] Control group vs. partially missing control group 1: Due to the lack of directional suction of gaseous products, gas accumulates at the cavity interface, resulting in a localized plastic displacement of 12.85 mm on the dry sand mold wall and causing a 40.0% probability of mold collapse. The surface roughness of the remaining casting is... The surface roughness decreased to 85.3 μm and was accompanied by wrinkling defects, indicating that gas accumulation caused deformation of the mold wall's mechanical structure. Control group two was partially missing: due to the lack of a deceleration interlock for the rising speed of the molten metal, the rising fluid front directly covered the unvented air gap, leading to air entrapment inside the casting and a measured internal carbon precipitation defect rate of 25.3%. The diameter changed to 42.1 μm, indicating a coupling constraint between negative pressure suction and filling speed. This exceeds the range of control group one: due to the characteristic length of the model. The value was too small, resulting in insufficient suction pressure gradient to overcome the flow resistance of the dry sand layer, causing large-area wrinkling on the cavity surface and a measured defect rate of 18.5%, exceeding the range. Control group two: Because... Setting the value too high causes the suction pressure to exceed the shear strength limit of the dry sand medium. Data shows that when the model's characteristic length... Beyond the boundary point of 1.20 m, shear suction causes localized fluidization collapse of the dry sand layer, which then seeps into the molten metal. The range of values ​​from 0.10 m to 1.00 m and the corresponding control strategy can balance cavity venting efficiency and sand mold structure mechanical stability.

[0043] Example 3: When the system faces the high-temperature pouring condition of a dry sand cavity with a spatially heterogeneous multi-suction branch structure implementing an irregularly shaped foam model in an intelligent casting island, the filling front is thermally decomposed to produce gaseous products. These gaseous products undergo transient mass transfer and diffusion to the surrounding dry sand medium, causing nonlinear dynamic transitions in the porosity and flow resistance characteristics within the dry sand layer. If the control unit sets the judgment conditions based solely on fixed values, or if the actuators such as electric regulating valves experience a lag in mechanical transmission when facing changes in flow resistance, fluctuations in the air gap pressure inside the cavity will occur. This will lead to local mechanical deformation of the dry sand mold wall into the cavity. To determine a control criterion that can accurately characterize the shear strength limit of the dry sand mold wall, the control unit acquires the flow resistance safety threshold before the cavity pouring begins. The experimental data were obtained in a mass transfer testing laboratory. The dry sand material used in the test was natural silica sand with a mesh size of 20 to 40 mesh. The sample was placed in a container with a cross-sectional area of ​​0.05. The standard cylindrical sample tube was filled with a sample and 0.05 μL was applied. The compaction stress was used to simulate the initial compaction state of dry sand inside the sand box, and the gas flow rate was controlled at 0.01. The step size is from 0.01 The regularity was increased to 0.10. By passing through a layer of natural silica sand, differential pressure transmitters deployed on both sides of the dry sand layer were used to collect the pressure difference before and after the dry sand layer in real time under each flow gradient. This difference was divided by the flow velocity gradient and the sample height of the natural silica sand layer. The resistance slope was calculated through linear fitting, and axial shear stress was increased until the sample slipped and failed. Data showed that when the pressure difference caused by gas flow resistance exceeded 24.0... And the corresponding resistance slope is greater than 120.0. At this time, the steric pinning between dry sand particles peels off, leading to instability and failure of the porous media's mechanical structure. Therefore, 50.0% of the critical differential pressure value is selected as the safety boundary, and the flow resistance safety threshold is set accordingly. The value was determined to be 60.0. Specifically, this flow resistance safety threshold The numerical selection and the positive correlation step rule of a 5.0% relative decrease in valve opening for every 10.0 kPa / m increase were both based on physical boundary limit tests of multiple sets of dry sand particle size distributions and foam model densities. When the mesh size of the natural silica sand varied between 20 and 40 mesh, and the internal porosity of the dry sand layer dropped drastically from the initial 38% to 25% due to high-temperature radiative thermal expansion, the experimentally measured lower limit of the critical resistance slope for slippage and fluidization instability between dry sand particles was consistently 120.0 kPa / m. This was achieved by introducing a 50%... With a safety physical margin, the globally applicable safety threshold can be locked at 60.0 kPa / m; the aforementioned 5.0% reduction rule in the opening step is determined by establishing a momentum conservation equation between the throttling area of ​​the casting channel and the upward flow velocity of the molten metal. This ensures that the reduction in gas generation rate caused by the reduced upward flow velocity of the melt matches the reduction in venting capacity caused by excessive flow resistance on an order of magnitude, achieving engineering self-consistency of the control rule. In the real-time casting control process of the intelligent casting island, the control unit receives physical input signals collected by pressure sensors and contact probe components, in a 5 Sampling period Continuously read the real-time internal pressure of the target sand box airflow suction path in the time domain. And read the basic environmental negative pressure in the external main pipe. The transient air permeability resistance coefficient of the sand layer was calculated according to the aforementioned formula. The numerical value, the internal flow control operator path of the control unit executes the following ordered discretization rule flow: the processor will take the transient air permeability resistance coefficient of the sand layer at the current sampling time. Numerical values ​​and flow resistance safety thresholds Amplitude comparison is performed; the sliding window register records the comparison results, and the transient permeability resistance coefficient of the sand layer is recorded within three consecutive sampling periods. All are greater than the flow resistance safety threshold. When the cavity venting system is determined to be in a potential gas pressure buildup risk state, the state machine is triggered to jump and output a deceleration control command; the processor reads the current value of the gate valve opening of the current casting channel. Based on the transient air permeability resistance coefficient of the sand layer Deviation from the safe threshold of flow resistance The positive deviation amplitude is calculated based on the resistance exceeding 10.0. The valve opening is reduced in increments of 5.0, and the reduction in the opening of the casting channel is calculated using this step rule. The processor calculates the target gate valve opening control value. and set the target gate valve opening control value The data is written into the valve controller's drive bus interface to adjust the throttling area of ​​the casting channel. This is because the mechanical transmission mechanism of the electrically controlled valve experiences a 120.0-degree delay between receiving the control command and reaching its designated position. The response hysteresis delay, this execution deviation, will cause instantaneous pressure fluctuations inside the cavity when the leading edge approaches, and the control unit will calculate the target gate valve opening control value. The current opening degree is reduced by using the first derivative of the pressure change from the previous sampling period. Incremental fine-tuning is performed to advance the valve adjustment action before the arrival of the pressure peak, thereby controlling the transient air permeability resistance coefficient of the sand layer. Converging to the flow resistance safety threshold Within this framework, to achieve precise spatiotemporal coupling between the gate valve's speed regulation action (with a mechanical hysteresis of hundreds of milliseconds) and the transient vaporization pulse event (with a hysteresis of tens of milliseconds) at the physical level, the control unit constructs an interlocked control closed loop based on feedforward prediction and the fluid inertial buffering of porous media. Since the upward flow field of the molten metal and the thermal cracking and vaporization of the foam model exhibit continuously progressive fluid dynamic characteristics in the overall time series, the first derivative of the pressure change in the previous sampling period can accurately extrapolate and predict the nonlinear evolution trend of gas resistance within the next 150.0 ms. Simultaneously, the dry sand layer inside the sand box, as a typical porous medium, possesses a natural mass transfer damping and volume buffering effect on the disordered infiltration of high-pressure gaseous products, causing a certain physical time delay in the process of localized pressure buildup evolving from surface accumulation to overall wall instability. The control unit utilizes this fluid inertial buffering time window of the dry sand layer to predict the large-diameter electric regulating gate valve 120.0 ms in advance using a feedforward prediction operator. The valve issues a pre-action command, throttling the gate valve opening to align with the peak value of the transient gas pressure at the cross-sectional abrupt change region as the filling front moves. This establishes a deterministic physical causal interlock between the overall filling flow field velocity and the surface pulse negative pressure field. To mitigate the action lag of the large-diameter electric regulating gate valve in response to the 10ms to 50ms transient pulse negative pressure within the 120.0ms mechanical response hysteresis period, a pulse response bypass is set in parallel along the sand box airflow suction path. A high-speed electromagnetic pilot valve with a built-in opening and closing action time of no more than 2.0ms is used. When the control unit measures that the metal liquid filling front is approaching and the duration is within the 10ms to 50ms time range, the large-diameter electric regulating gate valve maintains its current opening. The control unit sends a pulse current signal to the control port of the high-speed electromagnetic pilot valve, driving the valve core to complete the opening and closing switch within 2.0ms. Gas is suctioned using the pulse response bypass to match the spatiotemporal distribution of transient vaporization release.

[0044] In specific casting applications, when the flow front reaches the point where the cross-section of the irregularly shaped casting widens, the degradation mass transfer area of ​​the foam model increases, leading to an increase in the gas phase release rate. The real-time internal pressure measured by the pressure sensor during each sampling period. The transient permeability resistance coefficient of the sand layer was calculated by substituting the physical characteristic parameters into the data as the pressure changed from -18.36 kPa to -1.15 kPa. The coefficient jumped from 58.20 kPa / m to 144.25 kPa / m. The sliding window register detected that the coefficient remained in an over-limit state of 144.25 kPa / m, 144.30 kPa / m and 144.18 kPa / m for three consecutive sampling periods, which met the trigger condition for starting discrete gradient adjustment.

[0045] The processor calculates the reduction in opening based on the magnitude of the resistance deviation. The target opening degree is 42.5%. Through time delay error correction combined with the first derivative of the current pressure change, incremental fine-tuning is performed. Finally, the controller outputs a hardware drive signal corresponding to the 57.5% opening target to the control port of the electric regulating valve. This causes the pouring gate valve to complete the opening position change within 120.0 ms, increasing the flow damping in the casting pouring channel and reducing the rising velocity of the molten metal from 45.28 mm / s to 18.35 mm / s. The speed of mm / s provides the gas-fluid mass transfer time for the dry sand layer in a localized gas accumulation state, thereby stabilizing the nonlinear causal relationship between the filling rise speed and the mechanical balance of the mold wall. By decomposing the overall control action into a time-domain discrete stepper operator and incrementally compensating for the mechanical time delay hysteresis of the valve actuator, the diffusion behavior of the degradation gas is suppressed at the physical source. The negative pressure gradient field of the multi-suction loop and the rising flow field of the molten metal achieve a dynamic causal closed loop. The maximum pressure amplitude of the gas accumulation inside the mold cavity is stably maintained below the critical load of mechanical instability and failure of the natural silica sand layer. The internal gas entrapment defects after the casting cools and solidifies are eliminated, and the surface quality and surface grain structure of the finished irregular metal casting meet the manufacturing specifications.

[0046] Example 4: Based on the aforementioned casting island structure, this example controls the lost foam filling and gasification process through real-time feedback and dynamic adjustment. The system discretely arranges negative pressure suction paths along the vertical direction of the model inside the sand box. Each suction path corresponds to a negative pressure execution unit. A main suction pipeline is provided outside the sand box, connected to a negative pressure source and maintaining a negative pressure environment. The control unit monitors the real-time height coordinates of the leading edge of the molten metal filling mold via a liquid level sensor. Simultaneously acquire the installation height coordinates of the target negative pressure actuator. The control unit collects the instantaneous negative pressure inside the target negative pressure actuator in real time. Transient mass transfer resistance coefficient of sand layer The calculation process is as follows: The control unit reads the vertical distance between the current filling front and the target negative pressure actuator. The control unit calculates the instantaneous negative pressure. negative pressure of the basic environment The pressure difference value, divided by the vertical distance. ,get Its linear calculation formula is: The control unit is based on the calculation With the preset model feature length Dynamically adjust the set pressure of the target negative pressure actuator. Set pressure The calculation formula is: ,in, A constant characterizing the geometric complexity of a local section of the model is derived from the three-dimensional structural features of the model and is set before filling.

[0047] The real-time directional guidance execution process is as follows: When the liquid level sensor determines that the leading edge of the metal liquid filling type is approaching the effective suction range of the target negative pressure actuator, the control unit drives the negative pressure actuator to output a pulse-type enhanced negative pressure. The amplitude of this pulse-type enhanced negative pressure is set to... This operation establishes a pressure gradient between the vaporization front and the exhaust branch, driving the gaseous products to exit along a preset path. Furthermore, the control unit is equipped with a flow resistance safety threshold. During the filling process, the control unit continuously compares... and The numerical value, when determining At the same time, the control unit outputs control commands to adjust the opening of the gate valve of the casting system to reduce the filling speed of the molten metal, so that the generation rate of gaseous products matches the gas discharge capacity of the negative pressure suction system. This scheme establishes... and The functional relationship between the negative pressure field distribution and the filling dynamics is realized in real time. Compared with the constant negative pressure process, this embodiment can suppress local air gap pressure fluctuations and avoid air entrapment and box collapse during the molten metal filling process.

[0048] The embodiments of this application have been described above with reference to the accompanying drawings. Unless otherwise specified, the embodiments and features in the embodiments of this application can be combined with each other. This application is not limited to the specific embodiments described above. The specific embodiments described above are merely illustrative and not restrictive. Those skilled in the art can make many other forms under the guidance of this application without departing from the spirit of this application and the scope of protection of this invention, and all of these forms are within the protection scope of this application.

Claims

1. A process for controlling the vaporization of foam models in lost foam casting, characterized in that, Includes the following steps: Step S1: Collect the real-time internal pressure at the airflow suction path of the sand box at different locations inside the sand box, and collect the basic environmental negative pressure in the external main pipe. Calculate the pressure difference between the real-time internal pressure and the basic environmental negative pressure. Obtain the vertical distance between the airflow suction path of the adjacent sand box and the current metal liquid filling front edge. Divide the pressure difference by the vertical distance to calculate the transient air permeability resistance coefficient of the sand layer, which characterizes the change of air permeability resistance of the dry sand layer. Step S2: Determine the target sand box airflow suction path from multiple sand box airflow suction paths. Calculate the set pressure value of the target sand box airflow suction path based on the transient air permeability resistance coefficient of the sand layer and the preset model characteristic length. When the current metal liquid filling mold front is detected to be approaching the target sand box airflow suction path area, control the target sand box airflow suction path to output pulse-type enhanced negative pressure, and the amplitude of the pulse-type enhanced negative pressure corresponds to the set pressure value. Step S3: Compare the transient permeability resistance coefficient of the sand layer with the preset flow resistance safety threshold. If the transient permeability resistance coefficient of the sand layer exceeds the flow resistance safety threshold, reduce the opening of the casting channel of the mold to reduce the rising speed of the molten metal and control the transient permeability resistance coefficient of the sand layer to be reduced to within the flow resistance safety threshold.

2. The foam model gasification control process in lost foam casting according to claim 1, characterized in that, Step S1 includes the following sub-steps: Step S11, subtract the real-time internal pressure from the negative pressure of the base environment to determine the pressure difference; Step S12, obtain the height position of the airflow suction path of the sand box and the height position of the current metal liquid filling front edge, subtract the height position from the height position to determine the vertical distance, and divide the pressure difference by the vertical distance to calculate the transient air permeability resistance coefficient of the sand layer.

3. The foam model gasification control process in lost foam casting according to claim 1, characterized in that, In step S2, during the process of controlling the output of pulse-enhanced negative pressure in the target sand box airflow suction path, the following self-healing adjustment steps for the airflow suction channel are also included: Step S301, monitoring the flow deviation between multiple branch pipes connected to the sand box airflow suction path; Step S302, calculating the real-time flow Reynolds number at the exhaust filter medium inside each branch pipe; Step S303, when the real-time flow Reynolds number is found to be lower than the preset flow attenuation threshold, determining that the corresponding branch pipe has a local blockage; Step S304, opening the reverse pulse flushing passage connected to the branch pipe with the local blockage, and introducing high-pressure reverse airflow to backwash the exhaust filter medium.

4. The foam model vaporization control process in lost foam casting according to claim 1, characterized in that, In step S2, the process of calculating the set pressure value also includes the following dynamic correction steps: Step S401, collecting the real-time pouring temperature inside the cavity; Step S402, calculating the actual temperature fluctuation range of the real-time pouring temperature within the current filling cycle; Step S403, compensating for the deviation of the set pressure value according to the actual temperature fluctuation range, and increasing the absolute value of the set pressure value proportionally when the real-time pouring temperature is higher than the preset process temperature calibration value.

5. The foam model vaporization control process in lost foam casting according to claim 1, characterized in that, Step S3 includes the following sub-steps: Step S31, calculate the excess ratio coefficient when the transient air permeability resistance coefficient of the sand layer exceeds the flow resistance safety threshold; Step S32, adjust the gate valve opening of the casting channel according to the excess ratio coefficient, and control the reduction of the gate valve opening of the casting channel to maintain a positive correlation with the excess ratio coefficient, so as to reduce the rising speed of the molten metal.

6. The foam model gasification control process in lost foam casting according to claim 1, characterized in that, The foam model includes a cross-sectional abrupt change region. When the current metal liquid filling front moves to the state before the cross-sectional abrupt change region, the corresponding model feature length is increased stepwise according to the contour size of the cross-sectional abrupt change region, so as to increase the set pressure value of the target sand box airflow suction path in advance.

7. The foam model vaporization control process in lost foam casting according to claim 1, characterized in that, The basic environmental negative pressure inside the sand box is controlled within the pressure range of 0.02MPa to 0.05MPa, and when the target sand box airflow suction path outputs pulse-enhanced negative pressure, the duration of the pulse-enhanced negative pressure is maintained within the pulse time range of 10ms to 50ms.

8. The foam model vaporization control process in lost foam casting according to claim 1, characterized in that, The current height of the molten metal filling front is determined by the on / off electrical signal status of the multi-point filling contact probes deployed on the surface of the foam model.

9. The foam model vaporization control process in lost foam casting according to claim 1, characterized in that, Before filling, the compactness of the dry sand layer in a dense state is calibrated in situ on a multi-dimensional high-frequency vibration compaction table under a preset amplitude and preset frequency compaction excitation state.

Images