A brake disc sand casting defect control method based on negative pressure exhaust

Abstract

The present application relates to the technical field of metal casting, in particular to a brake disc sand mold casting defect control method based on negative pressure exhaust, which first carries out structural pretreatment on the prepared ventilated brake disc sand core, then carries out adaptive floating butt joint and flexible sealing operation on the automatic casting production line, then carries out multi-section dynamic pressure compensation pouring, and finally carries out cascade purification and pipeline self-cleaning on the extracted mixed tail gas; meanwhile, instant flow sensor and high-frequency negative pressure sensor are installed in parallel on the negative pressure exhaust branch to carry out flow pressure dual-parameter closed-loop early warning. Through the use of high-temperature resistant metal bellows floating vacuum joint and hollow inflatable high-temperature resistant fluorine rubber sealing ring on the automatic molding line, multi-section dynamic pressure compensation logic, nanoscale aluminosilicate composite coating one-way air permeable liquid blocking film, three-stage cascade purification device and pulse backflushing program, vacuum short circuit air leakage and external cold air entrainment are eliminated, and mechanical sand sticking scrap rate is significantly reduced.

Description

Technical Field

[0001] This invention relates to the field of metal casting technology, specifically to a method for controlling defects in brake disc sand casting based on negative pressure exhaust. Background Technology

[0002] As a core safety component in automotive braking systems, brake discs typically incorporate internal ventilation holes for heat dissipation. During sand casting, the formation of these ventilation channels is highly dependent on the precise placement of the internal sand core and the smooth filling of the mold with molten metal. When the sand core comes into contact with the high-temperature molten metal, it undergoes a violent thermal decomposition reaction, instantly generating a large amount of volatile gases. If these gases cannot be expelled from the mold cavity in time, they can easily form fatal casting defects such as porosity, incomplete filling, and cold shuts in the brake disc body or near the heat dissipation channels.

[0003] To address the quality issues caused by gas retention, existing casting processes commonly employ negative pressure venting technology. This technology typically involves pre-setting venting channels inside the sand core and applying a continuous, constant negative pressure to the inside of the sand core during pouring using an external vacuum pump. Through this pressure difference, resin volatiles and other gases generated by the heated sand core are forcibly extracted, thereby reducing the back pressure inside the mold cavity and facilitating better filling of narrow heat dissipation fin areas by the molten metal.

[0004] Existing negative pressure exhaust systems have revealed serious engineering adaptability deficiencies in actual large-scale automated high-cycle production lines. The assembly tolerances between sand boxes and sand cores on automated molding lines are often on the order of millimeters. Traditional rigid pipe connections are prone to vacuum short circuits, allowing large amounts of external cold air to be drawn in, thus compromising exhaust efficiency. The globally constant high negative pressure creates a strong penetrating suction force on high-temperature liquid metal while extracting gas, causing molten iron to seep into the sand core pores, forming mechanically adhered waste that is difficult to clean. The mixture of extracted high-temperature resin tar vapor and silica sand dust rapidly condenses and agglomerates as it flows through the lower-temperature vacuum pipes and valves, causing frequent blockages and shutdowns of the exhaust system, significantly increasing equipment maintenance costs and reducing the overall production line uptime. Summary of the Invention

[0005] To address the shortcomings of existing technologies, this invention provides a method for controlling defects in brake disc sand casting based on negative pressure exhaust, which solves the problems of easy air leakage, mechanical sand adhesion, and frequent pipeline blockage in negative pressure exhaust systems under high-speed automated production lines.

[0006] To achieve the above objectives, the present invention provides the following technical solution: a method for controlling defects in brake disc sand casting based on negative pressure exhaust, comprising the following steps: Step S1: Perform structural pretreatment on the prepared ventilated brake disc sand core. A honeycomb-shaped air-guiding blind channel is set in the non-stressed area inside the sand core. The end of the blind channel is gathered at the core head of the sand core and a high-temperature resistant ceramic air-guiding port is embedded. At the same time, a gradient coating operation is performed on the surface of the sand core to form a composite coating with one-way air permeability and liquid resistance characteristics. Step S2: Perform adaptive floating docking and flexible sealing operations on the automated casting production line. When the sand box equipped with the above-mentioned sand core is moved to the casting position, the floating vacuum connector at the end of the external negative pressure pipeline is driven to extend and spherically fit with the ceramic air inlet. Then, the instantaneous pressure difference generated by the pre-evacuation of the system causes the hollow inflatable sealing ring at the mating surface to expand, automatically compensating for the physical assembly tolerance between the sand mold and the core head. Step S3: Perform multi-stage dynamic pressure compensation casting. Based on the characteristics of molten metal filling and sand core heating and gas generation, the proportional servo valve is adjusted by a programmable logic controller to perform multi-stage dynamic pressure compensation pouring. The pouring process includes a forced venting stage and a micro negative pressure balancing stage. The system switches the vacuum level in the pipeline in real time based on the set filling time node or liquid level sensor signal to control the pressure state of the sand core surface and prevent high-temperature molten metal from penetrating into the sand core pores. Step S4: Perform cascade purification and pipeline self-cleaning on the extracted mixed exhaust gas. The mixed exhaust gas passes through three series modules: cyclone separation, condensation and liquefaction, and media filtration. Large particles of sand and liquefied high-temperature resin tar are removed, and fine aerosols are filtered out. After one casting cycle is completed and the main exhaust valve is closed, high-temperature and high-pressure gas is instantly introduced into the negative pressure pipeline to perform pulse backflushing and remove the uncured tar remaining on the pipe wall.

[0007] Preferably, the gradient coating operation in step S1 includes two independent coating processes, specifically: first, a highly permeable graphite base coating is uniformly applied to the surface of the sand core substrate, and then dried and cured to form a flow field conductive layer; then, a nano-scale aluminosilicate composite coating is applied to the outer surface of the base coating. The capillary repulsion generated by the nano-scale pores formed after the surface coating is cured prevents liquid metal from penetrating inward, while allowing the gas molecules that expand due to heat inside to overflow outward.

[0008] Preferably, the floating vacuum joint is internally equipped with a high-temperature resistant metal bellows, which can provide elastic displacement compensation in three-dimensional space. The hollow gas-filled sealing ring is made of high-temperature resistant fluororubber and is embedded in the end face groove of the floating joint.

[0009] Preferably, the multi-segment dynamic pressure compensation casting in step S3 specifically includes the following control logic: During the initial forced venting stage when the molten metal enters the mold cavity, the negative pressure setting value of the control pipeline is kept within the range of -0.04MPa to -0.06MPa to quickly extract the volatile gases that burst out when the sand core is heated. When the molten metal level is determined to rise to the height of the brake disc cooling fins, the system immediately enters the micro-negative pressure balance stage. At this time, the system commands the proportional servo valve to activate, rapidly reducing the negative pressure value of the pipeline to the range of -0.005MPa to -0.015MPa. This micro-negative pressure value is only equivalent to the residual gas generation pressure inside the current sand core, thereby establishing a zero-pressure difference balance state at the contact interface between the sand core and the molten metal.

[0010] Preferably, after the molten metal filling operation is completed, the system directly enters the pressure holding and solidification stage, maintaining the above-mentioned slight negative pressure state of -0.005MPa to -0.015MPa for 30 to 60 seconds until a dense solidified shell is formed on the outer surface of the brake disc casting. After this pressure holding time, the control system executes a step-by-step pressure relief program, smoothly restoring the pipeline pressure to the normal pressure environment at a rate of 0.002MPa per second.

[0011] Preferably, the specific path of the cascade purification process in step S4 is as follows: The exhaust gas containing impurities enters the cyclone separator tangentially for centrifugal dust removal. After preliminary dust removal, the gas is immediately introduced into the condenser chamber of the external water-cooled jacket. The gas temperature is rapidly and forcibly lowered to below the tar dew point. The condensed liquid tar is collected by gravity into the bottom drain tank. The remaining gas after cooling and oil removal finally passes through the composite sacrificial filter element composed of activated carbon and industrial non-woven fabric and enters the vacuum pump.

[0012] Preferably, the triggering timing and parameter limitations of the pulse backflushing operation are as follows: before the next sand box to be poured enters the work station, the opening time of the backflushing solenoid valve is set to 0.3 to 0.8 seconds; the pressure of the high-temperature and high-pressure gas introduced into the pipeline is 0.5MPa to 0.7MPa, and the gas temperature is maintained between 120°C and 160°C.

[0013] Preferably, the method further includes a closed-loop early warning step based on both flow and pressure parameters, specifically: An instantaneous flow sensor and a high-frequency negative pressure sensor are installed in parallel on the negative pressure exhaust branch. The main control unit collects and compares the data returned by the dual sensors in real time. When the flow rate exceeds the upper limit of the calibration and the negative pressure drops to the lower limit of the calibration, the system immediately triggers an external air entrainment and leakage alarm. When the flow rate approaches zero and the negative pressure remains at an extreme high level for a long time, the system issues a pipeline or sand core blockage alarm and forcibly increases the number of pulse backflushing actions by a factor of two after the current pouring batch ends.

[0014] This invention provides a method for controlling defects in brake disc sand casting based on negative pressure exhaust. It has the following beneficial effects: 1. This invention introduces a floating vacuum joint with a high-temperature resistant metal bellows on an automated molding line, and embeds a hollow, gas-filled, high-temperature resistant fluororubber sealing ring on the mating end face. The instantaneous small pressure difference generated by the pre-evacuation of the system causes the sealing ring to automatically expand and fill the physical tolerance, which successfully overcomes the engineering barrier of gaps in the sand box fit of high-speed production lines, and achieves the elimination of vacuum short circuit leakage and external cold air entrainment.

[0015] 2. This invention implements a multi-stage dynamic pressure compensation logic based on the characteristics of molten metal filling and the gas generation of the sand core under heat. Combined with a one-way permeable liquid-blocking film composed of a nano-aluminosilicate composite coating on the surface, it uses high negative pressure to force exhaust in the early stage of filling and quickly switches to a micro-negative pressure state equal to the residual gas generation pressure inside the sand core when the liquid level rises to the heat dissipation fins. A zero-pressure difference equilibrium state is precisely constructed at the interface between the sand core and the molten metal, which completely cuts off the suction force of molten iron to penetrate into the pores of the sand core from a physical and mechanical perspective and significantly reduces the mechanical sand adhesion scrap rate.

[0016] 3. This invention utilizes a three-stage cascaded purification device, consisting of a cyclone separator, a condensate trap, and a sacrificial filter, connected in series in the exhaust gas pipeline. This device, combined with a pulse backflushing procedure that instantaneously introduces high-temperature, high-pressure gas into the pipeline after the casting cycle is complete, strips and collects solid-liquid mixed impurities using physical sedimentation and forced temperature reduction. The kinetic energy of the high-temperature gas flow then impacts the residual tar on the pipe wall, effectively preventing the tar-dust mixture from damaging the vacuum pump and significantly extending the maintenance frequency of the extraction system from daily cleaning to monthly routine maintenance. Attached Figure Description

[0017] Figure 1 This is a schematic diagram of the casting defect control process of the present invention. Detailed Implementation

[0018] 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. Example

[0019] like Figure 1 As shown in the figure, this invention provides a method for controlling defects in brake disc sand casting based on negative pressure exhaust, as detailed below: In step S1, the operator prepares a coated sand core or a cold-box resin sand core according to the specific specifications of the brake disc product. During the mold design stage, a three-dimensional honeycomb-shaped air-guiding channel is pre-reserved in the non-stressed area of ​​the sand core. This channel system concentrates and guides the gas generated in each internal area to the core head position at the end of the sand core. A highly thermally shock resistant alumina ceramic air vent is pre-embedded at the core head. In the coating process, a robotic arm holds the sand core and immerses it in a highly permeable graphite-based coating tank. After removal, it is dried at a specific temperature to ensure that the base coating forms a smooth gas guiding network between the sand particles. After the base coating is completely cured, a second spraying operation is performed to uniformly adhere the nano-aluminosilicate composite coating to the surface. This surface coating exhibits a significant microporous effect at high temperatures; liquid metal, constrained by surface tension, cannot penetrate the nanopores, while the thermally expanded gas molecules can flow freely into the channel system.

[0020] The process moves to step S2, the automated production line flow. The sand box equipped with the coated sand core is precisely positioned at the casting station along the conveyor rollers. Upon receiving the positioning confirmation signal, the pneumatic actuator drives the floating vacuum connector, mounted on the side wall of the production line, to extend towards the sand box. The metal bellows inside the connector provides the entire contact surface with multi-degree-of-freedom flexible floating capability. When the connector end face contacts the ceramic air inlet, the bellows is compressed, eliminating hard impact stress and achieving spherical fit. The high-temperature resistant fluororubber sealing ring, embedded in the connector groove, has a hollow internal structure. The initial small negative pressure generated at the moment the vacuum pump starts is guided into the sealing ring cavity, forcing the rubber outer wall to elastically expand and tightly fit the uneven gap between the sand mold and the core head.

[0021] Step S3 constitutes the core thermodynamic control center of this method. During the initial time period 0 to t1, when the molten metal is poured into the mold cavity from the sprue, the high temperature causes the resin binder to decompose rapidly. The programmable logic controller (PLC) instructs the proportional servo valve to fully open, causing the pipeline negative pressure to rapidly rise and maintain within the high negative pressure range of -0.04 MPa to -0.06 MPa. This significantly reduces the back pressure inside the sand core, guiding the large amount of volatile gas generated by the transient burst to quickly escape along the blind channel. Based on calculations from the preset filling model or feedback from the liquid level sensor, the molten metal surface overflows the bottom of the heat sink fins, entering the time period t1 to t2. The PLC module immediately outputs an electrical signal to suppress the opening of the servo valve, precisely adjusting the pipeline pressure to the range of -0.005 MPa to -0.015 MPa. This micro-negative pressure setting is not arbitrary but is derived from the residual gas evolution rate of the sand core material at that moment. The slight negative pressure suction force cancels out the pressure of the sand core venting outwards, and the molten metal no longer experiences additional adsorption and pulling at this interface, thus eliminating mechanical sand adhesion. The time period from t2 to t3 after the pouring is the pressure holding and solidification period. The slight negative pressure continues for 30 to 60 seconds until the surface of the brake disc cools and transforms into a solid initial solidified shell. The PLC system then intervenes with a step-by-step depressurization procedure, adding a small amount of air to the pipeline at a gradual rate of approximately 0.002 MPa per second until the ambient pressure is fully restored, avoiding sand core shrinkage and cracking caused by sudden pressure loss.

[0022] The extracted exhaust gas undergoes rigorous physical purification and filtration in step S4. The mixed gas flow carrying a large amount of heat, solid dust, and gaseous resin tar rushes tangentially at high speed into the primary cyclone separator. Large particles of sand lose kinetic energy during centrifugal motion and slide down the cylinder wall to the bottom ash collection hopper. The coarsely filtered gas flow then enters the secondary condensation and liquefaction trap. This device is surrounded by a circulating cooling water jacket, which forcibly and rapidly lowers the internal gas flow temperature below the dew point limit of the tar substances. Gaseous tar condenses and gathers into droplets on the low-temperature pipe wall, and is discharged into a dedicated collection container at the bottom via a guide channel. The cooled and deoiled gas flow continues to pass through a third-stage sacrificial filter element made of layers of activated carbon and industrial non-woven fabric. Most of the fine water vapor and aerosols are intercepted here, reliably ensuring the cleanliness of the gas flow discharged into the vacuum pump. Once all processes on a single casting trolley are completed, the main exhaust valve is closed. The high-pressure air source system instantly activates the backflush solenoid valve, continuously injecting high-pressure hot air with a pressure between 0.5MPa and 0.7MPa and a temperature between 120℃ and 160℃ into the negative pressure pipeline for 0.3 to 0.8 seconds. The powerful hot air pulse carries enormous kinetic energy, instantly sweeping away and peeling off the tar residue that has not yet fully cross-linked and solidified on the pipe wall, and then blowing it into the ash collection hopper, ensuring the long-term smooth operation of the entire extraction system.

[0023] The system safety monitoring mechanism operates independently in step S5. The microprocessor concurrently reads the sampling parameters of the instantaneous flow sensor and the high-frequency negative pressure sensor at a millisecond frequency. The logic unit continuously compares the slope of the changes in the two sets of data. If the flow reading exceeds the set high threshold and the negative pressure reading drops sharply, the system immediately triggers an audible and visual alarm signal for seal failure. If the flow index continues to be low and approaches zero, and the negative pressure reading remains locked in the extremely high negative pressure range for a long period, the system determines that there is a serious blockage in the exhaust blind channel or external pipeline. The control center then archives the anomaly record and, during the interval after the completion of this round of pouring, forcibly increases the execution frequency of the hot air pulse backflushing action to more than three times the standard setting in order to clear the blockage and restore the flow field connectivity.

[0024] Although embodiments of the invention have been shown and described, it will be understood by those skilled in the art that various changes, modifications, substitutions and alterations can be made to these embodiments without departing from the principles and spirit of the invention, the scope of which is defined by the appended claims and their equivalents.

Claims

1. A method for controlling defects in brake disc sand casting based on negative pressure exhaust, characterized in that, Includes the following steps: Step S1: Perform structural pretreatment on the prepared ventilated brake disc sand core. A honeycomb-shaped air-guiding blind channel is set in the non-stressed area inside the sand core. The end of the blind channel is gathered at the core head of the sand core and a high-temperature resistant ceramic air-guiding port is embedded. At the same time, a gradient coating operation is performed on the surface of the sand core to form a composite coating with one-way air permeability and liquid resistance characteristics. Step S2: Perform adaptive floating docking and flexible sealing operations on the automated casting production line. When the sand box equipped with the above-mentioned sand core is moved to the casting position, the floating vacuum connector at the end of the external negative pressure pipeline is driven to extend and spherically fit with the ceramic air inlet. Then, the instantaneous pressure difference generated by the pre-evacuation of the system causes the hollow inflatable sealing ring at the mating surface to expand, automatically compensating for the physical assembly tolerance between the sand mold and the core head. Step S3: Perform multi-stage dynamic pressure compensation casting. Based on the characteristics of molten metal filling and sand core heating and gas generation, the proportional servo valve is adjusted by a programmable logic controller to perform multi-stage dynamic pressure compensation pouring. The pouring process includes a forced venting stage and a micro negative pressure balancing stage. The system switches the vacuum level in the pipeline in real time based on the set filling time node or liquid level sensor signal to control the pressure state of the sand core surface and prevent high-temperature molten metal from penetrating into the sand core pores. Step S4: Perform cascade purification and pipeline self-cleaning on the extracted mixed exhaust gas. The mixed exhaust gas passes through three series modules: cyclone separation, condensation and liquefaction, and media filtration. Large particles of sand and liquefied high-temperature resin tar are removed, and fine aerosols are filtered out. After one casting cycle is completed and the main exhaust valve is closed, high-temperature and high-pressure gas is instantly introduced into the negative pressure pipeline to perform pulse backflushing and remove the uncured tar remaining on the pipe wall.

2. The method for controlling defects in brake disc sand casting based on negative pressure exhaust according to claim 1, characterized in that, The gradient coating operation in step S1 includes two independent coating processes: first, a highly permeable graphite base coating is uniformly applied to the surface of the sand core substrate, and then dried and cured to form a flow field conductive layer; then, a nano-scale aluminosilicate composite coating is applied to the outer surface of the base coating. The capillary repulsion generated by the nano-scale pores formed after the surface coating is cured prevents liquid metal from penetrating inward, while allowing the gas molecules that expand due to heat inside to escape outward.

3. The method for controlling defects in brake disc sand casting based on negative pressure exhaust according to claim 1, characterized in that, The floating vacuum joint is internally equipped with a high-temperature resistant metal bellows, which can provide elastic displacement compensation in three-dimensional space. The hollow gas-filled sealing ring is made of high-temperature resistant fluororubber and is embedded in the end face groove of the floating joint.

4. The method for controlling defects in brake disc sand casting based on negative pressure exhaust according to claim 1, characterized in that, The multi-segment dynamic pressure compensation casting in step S3 specifically includes the following control logic: During the initial forced venting stage when the molten metal enters the mold cavity, the negative pressure setting value of the control pipeline is kept within the range of -0.04MPa to -0.06MPa to quickly extract the volatile gases that burst out when the sand core is heated. When the molten metal level is determined to rise to the height of the brake disc cooling fins, the system immediately enters the micro-negative pressure balance stage. At this time, the system commands the proportional servo valve to activate, rapidly reducing the negative pressure value of the pipeline to the range of -0.005MPa to -0.015MPa. This micro-negative pressure value is only equivalent to the residual gas generation pressure inside the current sand core, thereby establishing a zero-pressure difference balance state at the contact interface between the sand core and the molten metal.

5. The method for controlling defects in brake disc sand casting based on negative pressure exhaust according to claim 1, characterized in that, After the molten metal filling operation is completed, the system directly enters the pressure holding and solidification stage, maintaining a slight negative pressure state of -0.005MPa to -0.015MPa for 30 to 60 seconds until a dense solidified shell is formed on the outer surface of the brake disc casting. After this pressure holding time, the control system executes a step-by-step pressure relief program, smoothly restoring the pipeline pressure to the normal pressure environment at a rate of 0.002MPa per second.

6. The method for controlling defects in brake disc sand casting based on negative pressure exhaust according to claim 1, characterized in that, The specific path of the cascaded purification process in step S4 is as follows: The exhaust gas containing impurities enters the cyclone separator tangentially for centrifugal dust removal. After preliminary dust removal, the gas is immediately introduced into the condenser chamber of the external water-cooled jacket. The gas temperature is rapidly and forcibly lowered to below the tar dew point. The condensed liquid tar is collected by gravity into the bottom drain tank. The remaining gas after cooling and oil removal finally passes through the composite sacrificial filter element composed of activated carbon and industrial non-woven fabric and enters the vacuum pump.

7. The method for controlling defects in brake disc sand casting based on negative pressure exhaust according to claim 1, characterized in that, The triggering timing and parameter limitations of the pulse backflushing operation are as follows: before the next sand box to be poured enters the work station, the opening time of the backflushing solenoid valve is set to 0.3 to 0.8 seconds; the pressure of the high-temperature and high-pressure gas introduced into the pipeline is 0.5MPa to 0.7MPa, and the gas temperature is maintained between 120℃ and 160℃.

8. A method for controlling defects in brake disc sand casting based on negative pressure exhaust according to any one of claims 1-7, characterized in that, The method also includes a closed-loop early warning step based on both flow and pressure parameters, specifically: An instantaneous flow sensor and a high-frequency negative pressure sensor are installed in parallel on the negative pressure exhaust branch. The main control unit collects and compares the data returned by the dual sensors in real time. When the flow rate exceeds the upper limit of the calibration and the negative pressure drops to the lower limit of the calibration, the system immediately triggers an external air entrainment and leakage alarm. When the flow rate approaches zero and the negative pressure remains at an extreme high level for a long time, the system issues a pipeline or sand core blockage alarm and forcibly increases the number of pulse backflushing actions by a factor of two after the current pouring batch ends.

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