Liquid alloy casting flow monitoring method and system in metallurgical casting process

Abstract

The invention mainly relates to the technical field of metallurgy. In order to improve the precision and stability of a liquid alloy casting instantaneous flow monitoring result, the invention provides a liquid alloy casting flow monitoring method and system in the metallurgical casting process, and the core idea of the method is that a crucible and a casting mold are connected through a wire, so that a serial current loop is formed among liquid alloy in the casting process, the connected crucible and the casting mold; a constant-voltage power supply and an ampere meter are connected into the current loop; the ampere meter measures the real-time current intensity I of the current loop under the action of the constant-voltage power supply in real time; the instantaneous flow Q of the alloy is calculated based on the real-time current intensity of the current loop, the resistivity of the alloy, the length L of the alloy liquid flow between the pouring gate and the casting mold and the vertical distance h between the pouring gate and the casting mold, and the calculation result is higher in accuracy and stability.

Description

Technical Field

[0001] The present invention mainly relates to the field of metallurgical technology, and in particular, to a method and system for monitoring the pouring flow rate of liquid alloy during the metallurgical casting process. Background Art

[0002] The casting process is a key link in alloy smelting, and the instantaneous flow rate is a key process parameter during the casting process, which directly affects the solidification process of the alloy and indirectly affects the uniformity of the alloy composition and structure, especially for alloys with complex element compositions and difficult-to-control microstructures and precipitation phases. Generally, in alloy casting, to avoid blocking, it is necessary to consider the initial temperature of the liquid alloy and the temperature drop during the process. Theoretically, the higher the initial casting temperature, the better. However, in actual production, too high an initial temperature will reduce the solidification rate of the alloy billet, resulting in aggravated element segregation. If the material stays in certain temperature ranges for too long, it will lead to increased precipitation of harmful phases. Adjusting the instantaneous flow rate can also play a role in regulating the solidification rate of the billet. Therefore, in actual processes, the casting is often not at a constant speed, but needs to be adjusted accordingly according to the material properties, process conditions, and casting progress.

[0003] Monitoring the instantaneous flow rate of liquid alloy during the casting process has always been a technical problem. Except for some low-melting-point alloys (such as aluminum-based and magnesium-based alloys), the casting temperatures of most alloys are relatively high, and the test ends of conventional instantaneous flow rate monitoring devices often cannot withstand such high temperatures.

[0004] Currently, the commonly used method in metallurgical casting is to monitor the change of the alloy billet over time through a pressure sensor to estimate the actual instantaneous flow rate. This solution has some problems that need to be solved urgently: (1) Stability of test results: After the liquid alloy is injected into the mold, the test end of the sensor is subjected to impact loads. As the liquid surface swings, the sensor display results may fluctuate up and down, affecting the accuracy and stability of the test results.

[0005] (2) The test results may have hysteresis, affecting subsequent operation responses.

[0006] (3) The system tends to be complex, and the use and maintenance costs are relatively high. Summary of the Invention

[0007] The technical problem to be solved by the present invention is: to provide a method and system for monitoring the instantaneous flow rate of liquid alloy during the metallurgical casting process, aiming to improve the accuracy and stability of the monitoring results of the instantaneous flow rate of liquid alloy casting.

[0008] The technical solution adopted by the present invention to solve the above technical problems: On the one hand, the present invention provides a method for monitoring the instantaneous flow rate of liquid alloy during the metallurgical casting process, and the method includes: Connect the crucible and the liquid alloy in the mold using wires and electrodes respectively, and then connect to a constant voltage power supply to form a circuit. That is, consider the liquid alloy from the pouring gate to the bottom pad below the tundish during the casting process as a whole, which acts as a resistance R in the circuit; The test terminals of the non-contact ammeter are fixed at the pouring gate, allowing the liquid alloy to pass through the center of the test terminal coil. To prevent the splashing liquid alloy from damaging the test terminal coil, a ceramic sleeve is added to isolate their direct contact. The ammeter measures the real-time current intensity I of the current loop under the action of the constant voltage power supply in real time; Based on the real-time current intensity of the current loop, the resistivity of the alloy the length L of the alloy liquid flow from the pouring gate to the mold, and the vertical distance h from the crucible pouring gate to the liquid alloy surface, calculate the instantaneous flow rate Q of the alloy.

[0009] Furthermore, the instantaneous flow rate of the alloy , where g is the acceleration due to gravity and U is the voltage value of the constant voltage power supply.

[0010] Furthermore, the constant voltage power supply is a constant voltage DC power supply or a constant voltage AC power supply.

[0011] Furthermore, if the mold is made of non-conductive material, a metal or alloy is provided at the bottom of the mold and connected in contact with the wire; if the mold is made of conductive material, the wire is directly connected to the mold.

[0012] Furthermore, if the crucible used for casting is made of non-conductive material, a graphite electrode or a heat-resistant metal electrode is inserted into the liquid alloy and connected to the wire, or the electrode material is processed into a sleeve and fixed at the water outlet of the liquid alloy and connected to the wire; if the crucible used for casting is made of conductive material, the wire is directly connected to the crucible wall.

[0013] Furthermore, the resistivity of the alloy is the resistivity of the alloy at the corresponding casting temperature.

[0014] On the other hand, the present invention also provides a monitoring system for the instantaneous flow rate of liquid alloy during the metallurgical casting process. The system includes: a constant voltage power supply, an ammeter, a contact circuit, and a control center. The contact circuit is used to connect the crucible and the mold, so that the liquid alloy during the casting process forms a series current loop between the connected crucible and the mold. The constant voltage power supply is used to provide voltage output for the current loop. The ammeter is used to detect the real-time current intensity I in the current loop under the action of the constant voltage power supply. The control center calculates the instantaneous flow rate Q of the alloy based on the real-time current intensity I, the resistivity of the alloy the length L of the alloy liquid flow from the pouring gate to the mold, and the distance h from the pouring gate to the liquid alloy surface.

[0015] Furthermore, the ammeter is a non-contact DC ammeter or a non-contact AC ammeter.

[0016] The beneficial effects of the present invention are as follows: A current loop is formed by conducting the liquid alloy in the crucible and the mold. A constant voltage power supply is connected to the current loop. By measuring the real-time current of the alloy, the instantaneous casting rate of the alloy can be calculated. The test result of the instantaneous alloy flow rate is not affected by the impact on the sensor when the liquid alloy is injected into the mold. The real-time performance, accuracy, and stability of the test results are high. And the test structure is simple, using mature equipment, safe and reliable, with low cost, and simple daily maintenance. Only the power supply and ammeter need to be calibrated regularly, and it can be linked with other equipment to realize the real-time measurement of the instantaneous alloy flow rate and achieve automatic casting. Description of the Drawings

[0017] Figure 1 It is a schematic structural diagram of the liquid alloy instantaneous flow rate monitoring system during the metallurgical casting process of the present invention; Figure 2 It is a schematic diagram showing the change in the cross-sectional area S of the liquid alloy flow under different instantaneous flow rates during the casting process; Figure 3 It is the test verification system in Embodiment 1; Figure 4 It is the test verification system in Embodiment 2; 1 crucible, 2 liquid alloy, 3 electrode, 4 wire, 5 non-contact ammeter, 6 ammeter test end, 7 tundish, 8 mold, 9 constant voltage power supply, 10 metal or alloy bottom pad. Detailed Embodiments

[0018] As Figure 1 shown, the wire 4 and the electrode 3 are respectively connected to the liquid alloy 2 in the crucible and the mold 8, and then a constant voltage power supply 9 is connected to form a circuit. That is, the liquid alloy 2 from the casting nozzle to the bottom pad below the tundish during the casting process is regarded as a whole and serves as a resistor R in the circuit; The ammeter test end 6 is fixed at the casting nozzle, and the liquid alloy 2 passes through the center of the coil of the ammeter test end 6. To prevent the splashing liquid alloy 2 from damaging the coil of the ammeter test end 6, a ceramic sleeve is added to isolate their direct contact. The non-contact ammeter 5 measures the current intensity I of the current loop under the action of the constant voltage power supply 9 in real time; Based on the real-time current intensity of the current loop, the resistivity of the alloy , the length L of the alloy liquid flow from the casting port to the mold 8, and the vertical distance h from the casting port of the crucible 1 to the liquid level of the liquid alloy 2, the instantaneous flow rate Q of the alloy is calculated.

[0019] First, according to the design of the casting system, the connection method of the external circuit is determined, that is, the type of power supply and the connection method of the electrode 3.

[0020] Power supply selection: The constant voltage power supply 9 is used as the main external power supply. For small-scale laboratory casting equipment, the flow rate of the liquid alloy 2 is small, and there may be a break in the flow in the middle and late stages. It is suitable to use a constant voltage AC power supply (AC). Its advantage is that the liquid alloy 2 drips in the form of droplets, and the non-contact ammeter 5 can also display the reading. The disadvantage is that the system is not sensitive to slight flow fluctuations during the casting process; for large-scale equipment in industrial production, a constant voltage DC power supply (DC) can be externally connected. Its advantage is that the current intensity is more sensitive to changes in the flow rate of the liquid alloy 2. The disadvantage is that once the liquid alloy 2 breaks off, the reading is not displayed.

[0021] Connection method at the crucible 1: ① If the material of the crucible 1 used for alloy casting is non-conductive (such as using oxide refractory materials to process the crucible for steel melting), graphite or heat-resistant metal is used as the electrode 3 (the electrode 3 is sheathed with a high-temperature resistant ceramic tube) and inserted into the molten liquid alloy 2 to be connected to the wire 4. The selection of the electrode 3 depends on the type of the liquid alloy 2 and technical requirements. The inserted electrode 3 is preferably in direct contact with the bottom of the crucible 1 to avoid the electrode 3 being separated from the liquid alloy 2 as the liquid level drops; ② The electrode 3 can also be processed into a sleeve and fixed at the water outlet of the liquid alloy 2 to be connected to the wire 4; ③ If the material of the crucible 1 is conductive (metal or graphite material), the electrode 3 can be directly connected to the wall of the crucible 1 and connected to the wire 4.

[0022] Connection method at the mold 8: ① If the material of the casting mold 8 is non-conductive, a metal or alloy bottom pad 10 can be processed and placed at the bottom of the mold 8 as the electrode 3 to be connected to the wire 4; ② If it is a conductive mold (metal or graphite material), the electrode 3 is directly connected to the mold 8 and connected to the wire 4.

[0023] Configure the non-contact ammeter 5: Configure the corresponding non-contact ammeter 5 according to the power supply type (DC power supply for DC ammeter; AC power supply for AC ammeter); the selection of the range and test accuracy of the non-contact ammeter 5 depends on the power supply parameter settings, and a non-contact ammeter 5 with high sensitivity is preferably selected. The types of the non-contact ammeter 5 include clamp type / fork type / flexible ammeter. The test end 6 of the ammeter is heat-treated (such as sheathing the test end with a heat insulation layer or inserting a ceramic tube in the center of the coil), and data can be transmitted over a long distance, and the data can be displayed and stored in real time.

[0024] Connect the two poles of the constant voltage power supply 9 to the crucible of the casting system and the liquid alloy 2 passing through the middle runner 7 in the mold 8 respectively to form a loop; fix the test end of the non-contact ammeter 5 at the path where the liquid alloy 2 passes.

[0025] Establish the functional relationship between the current intensity and the instantaneous flow rate: According to the relationship between current, resistance and voltage , when the external power supply voltage (U) is constant, an increase or decrease in the conductor resistance R will inevitably lead to a corresponding change in the current intensity I in the circuit. Conversely, the change in the conductor resistance can be inferred by monitoring the change in current.

[0026] The relationship between the resistance R and the cross-sectional area S of the conductor is . The resistivity ρ is only related to the electrical properties of the material itself. In the present invention, the liquid alloy between the crucible 1 and the mold 8 during casting is used as the conductor. When its composition is fixed, the resistivity can be regarded as a function ρ(T) with temperature T as the variable. When the temperature fluctuates only within a very small range, it is approximately considered that the resistivity ρ of the liquid alloy 2 is a constant value. L is the length of the alloy liquid flow between the casting port and the bottom of the mold 8, and L is defaulted to be a constant value (i.e., the value of Δl at the test end of the non-contact ammeter 5 is fixed). Then the resistance R is affected by the cross-sectional area S of the alloy liquid flow between the casting port and the mold 8, and is inversely proportional to the alloy liquid flow S between the casting port and the mold 8. Under the action of the constant voltage power supply 9, when the resistivity ρ and the length L of the liquid alloy in the mold 8 remain unchanged, a change in the cross-sectional area S of the alloy liquid flow between the casting port and the mold 8 will inevitably lead to a change in the current intensity I in the current loop. By monitoring the change in the current intensity I, the cross-sectional area S of the liquid flow of the liquid alloy 2 can be inferred. At the same time, as Figure 2 shown, the cross-sectional area S of the liquid flow of the liquid alloy 2 is only related to the instantaneous flow rate. Based on the above, the instantaneous flow rate Q of the alloy can be calculated based on the change in the current intensity I in the alloy.

[0027] At the same time, the flow rate formula of the alloy during casting is: Q = SV, where Q is the flow rate, S is the cross-sectional area, and V is the instantaneous flow velocity of the alloy liquid.

[0028] According to Bernoulli's equation: , the ammeter test end 6 is located near the casting port of the crucible 1, V1 is the initial velocity at the alloy liquid surface in the crucible 1. Since the descending speed of the liquid alloy 2 is relatively slow, V1 is approximately 0, V2 is the instantaneous velocity of the alloy liquid passing through the meter test end 6, h1 is the height of the liquid alloy 2 surface in the crucible 1, h2 is the height of the casting port, and h = h1 - h2. Ignoring the influencing elements such as liquid viscosity and turbulence, it is approximately considered that the air pressure P1 on the alloy liquid surface in the crucible 1 is equal to the atmospheric pressure P2. To sum up, the simplified Bernoulli's equation is , h is the vertical distance from the liquid alloy 2 surface in the crucible 1 to the casting port, q is the density of the alloy liquid, g is the acceleration due to gravity, and V is the instantaneous velocity V2 of the alloy liquid passing through the meter test end 6. From this, the instantaneous liquid flow velocity can be obtained . Therefore, the instantaneous flow rate , since is a constant, it can be denoted as K. Then the instantaneous flow rate , so Q and I can be approximately considered to have a linear relationship. That is, on the basis of known g, L, ρ, U, and measured I and h, the instantaneous flow rate Q of the molten alloy can be obtained.

[0029] Example 1: Saturated brine was used to simulate the liquid alloy flow. Since saturated brine has a certain electrical conductivity, which is much lower than that of the alloy, once the brine flow rate can be monitored by the change in current intensity, the loss of the liquid alloy 2 can also be monitored. The specific test steps are as follows: 1) Prepare saturated brine: Ordinary table salt (NaCl) was used as the solute and dissolved in deionized water. During the salt dissolution process, sufficient stirring was carried out, and the solution was heated.

[0030] 2) Place the saturated brine in the test device as shown in Figure 3 . Use wire 4 to connect the metal crucible and the metal mold 8, so that a series current loop is formed among the liquid alloy 2, the crucible, and the mold 8 during the casting process. Connect the external constant voltage power supply 9 and connect a non-contact ammeter 5.

[0031] 3) Open the pipe valves respectively. The test device in this example has a total of six pouring ports, each pouring port is connected to a hose and is equipped with a valve. Since the electrical conductivity of saturated brine is relatively low, the sensitivity and test accuracy requirements for the non-contact ammeter 5 are relatively high. To ensure the smooth progress of the test, an additional design was used for assistance: ① The pouring port is connected to a hose. When the brine passes through the hose, its flow rate decreases under the action of friction; ② After the brine fills a single hose, it can be approximately considered that the cross-sectional area of the conductor in the pipe remains unchanged; by increasing or decreasing (switching) the number of hoses, the total cross-sectional area of the conductor can be adjusted.

[0032] 4) Record the reading on the non-contact ammeter 5: When different numbers of hoses are connected, the reading shown on the non-contact ammeter 5 changes significantly, and there is a linear relationship between the number of connected hoses and the current intensity.

[0033] The feasibility of the casting rate monitoring device involved in the present invention verified by Example 1, that is, after the flowing liquid conductor passes through an electric current, the change in the instantaneous flow rate during casting can be reflected by monitoring the change in the current magnitude.

[0034] Example 2: A low-melting-point Sn-Pb alloy was used as the medium to verify the feasibility of the scheme. In this example, the auxiliary hoses were removed, and the Sn-Pb alloy was directly poured into the lower container through the pouring port to fully simulate the actual casting process. The test device is as shown in Figure 4 . Still, multiple pouring ports were set, and the opening and closing of the pouring ports were controlled by bolts.

[0035] 1) Put the alloy into a metal box simulating a crucible, and place the metal box on a controllable electric hot plate and heat it to 250 °C to completely melt the alloy.

[0036] 2) Connect the external power supply, then pull out the plug to allow the liquid alloy 2 to flow into the lower metal container; 3) Record the reading on the non-contact ammeter 5.

[0037] 4) Change the number of open pouring ports and record the change in the reading.

[0038] Test results: ① The non-contact ammeter 5 detected a change in current, confirming that the above solution can detect the instantaneous flow rate change of the Sn-Pb alloy; ② When the liquid metal drips, there is a current interruption (the surface tension of the Sn-Pb alloy is relatively large). Because of the external AC power supply, the non-contact ammeter 5 still shows a reading. ③ When the charged metal droplets contact the metal container, arc light appears, which should be avoided as much as possible during practical operation, that is, try to avoid current interruption during the pouring process.

Claims

1. A method for monitoring the pouring flow rate of liquid alloy during the metallurgical casting process, characterized in that, The method includes: Select a constant voltage power supply, an ammeter, and a non-contact ammeter. Based on the contact circuit, a closed circuit loop is formed between the molten alloy from the casting port to the mold and the constant voltage power supply. The test end of the non-contact ammeter is set at the casting port, and the molten alloy passes through the center of the coil of the test end of the ammeter during the casting process. The ammeter measures the real-time current intensity I of the current loop under the action of the constant voltage power supply in real time. Based on the real-time current intensity of the current loop, the resistivity of the alloy , the length L of the alloy liquid flow from the casting gate to the mold, and the vertical distance h from the liquid alloy surface in the ladle to the casting gate, calculate the instantaneous casting flow rate Q of the alloy.

2. The method for monitoring the pouring flow rate of liquid alloy in the metallurgical casting process according to claim 1, characterized in that, Instantaneous casting flow rate of the alloy , where g is the acceleration due to gravity and U is the voltage value of the constant voltage power supply.

3. A method for monitoring the pouring flow rate of liquid alloy during the metallurgical casting process according to claim 1, characterized in that, The resistivity of the alloy is the resistivity of the alloy at the corresponding casting temperature.

4. A method for monitoring the pouring flow rate of liquid alloy during the metallurgical casting process according to claim 1, characterized in that, The constant voltage power supply is a constant voltage DC power supply or a constant voltage AC power supply, and the non-contact ammeter is a non-contact DC ammeter or a non-contact AC ammeter.

5. A method for monitoring the pouring flow rate of liquid alloy during the metallurgical casting process according to any one of claims 1-4, characterized in that, If both the ladle and the mold are made of conductive materials, the contact circuit includes a wire; if the ladle and / or the mold is made of non-conductive materials, the contact circuit includes a wire and an electrode.

6. The method for monitoring the pouring flow rate of liquid alloy during the metallurgical casting process according to claim 5, wherein, If the mold is made of non-conductive materials, the electrode is a metal or alloy bottom pad set at the bottom of the mold, and the positive and negative poles of the constant voltage power supply are connected through a wire.

7. A method for monitoring the pouring flow rate of liquid alloy during the metallurgical casting process according to claim 5, characterized in that, If the ladle is made of non-conductive material, the electrode is graphite or heat-resistant metal. The electrode is processed into a sleeve and fixed at the water outlet of the molten alloy, and the positive and negative poles of the constant voltage power supply are connected through a wire.

8. A liquid alloy casting flow monitoring system for a metallurgical casting process, which is used to implement a liquid alloy casting flow monitoring method for a metallurgical casting process as described in any one of claims 1-7, characterized in that, The system includes: a constant voltage power supply, an ammeter, a contact circuit, and a control center. The contact circuit is used to connect the crucible and the mold, so as to form a series current loop between the liquid alloy during the casting process and the constant voltage power supply. The constant voltage power supply is used to provide voltage output for the current loop. The ammeter is used to detect the real-time current intensity I in the current loop under the action of the constant voltage power supply. The control center calculates the instantaneous casting flow rate Q of the alloy based on the real-time current intensity I, the resistivity of the alloy , the length L of the alloy liquid flow from the casting gate to the mold, and the vertical distance h from the liquid alloy surface to the casting gate.

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