A method and apparatus for designing a self-expanding and feeding riser neck for ductile iron castings.

Abstract

This invention discloses a method and apparatus for designing a self-expanding and feeding riser neck for ductile iron castings, belonging to the field of cast iron casting technology. The design method includes: S1. For a module of M... 铸件 S1. For castings, pre-designed risers are used to feed the castings; S2. The overall shrinkage and expansion of the castings are obtained in real time by measuring the changes in the liquid level at the risers, thereby determining the equilibrium time point τ of shrinkage and expansion. 平衡点 S3. Monitor the temperature of the riser neck and the casting to obtain a temperature-time curve, based on the eutectic solidification temperature T of the cast iron. e Find the riser neck solidification time τ on the curve. 颈凝固 S4. Determine the appropriate riser neck module M 合适冒口颈 S5. According to M 合适冒口颈 The device for designing riser necks includes a floating component, a displacement sensor, a temperature sensor, and a data logger. Compared with existing technologies, the design method and device of this invention can accurately design riser necks, reduce casting shrinkage defects, and improve casting yield.

Description

Technical Field

[0001] This invention relates to the field of cast iron casting technology, specifically providing a method and apparatus for designing a riser neck for self-expansion feeding of ductile iron castings. Background Technology

[0002] Ductile iron, with its excellent comprehensive mechanical properties, plays a vital role in the manufacture of key components such as wind turbine gearbox housings, rail transit brake discs, and nuclear power valves. However, ductile iron has a pasty solidification characteristic, making it highly susceptible to defects such as shrinkage porosity and porosity due to insufficient feeding during the casting process. Statistics show that the scrap rate of ductile iron parts due to improper riser design can reach as high as 35%.

[0003] Typically, castings undergo three stages of solidification: liquid shrinkage, solidification shrinkage, and solidification shrinkage. If liquid shrinkage is not compensated, shrinkage cavities will form in the casting. If solidification shrinkage is not compensated, shrinkage porosity will occur. To address shrinkage cavities and porosity defects, risers are usually added to the casting to compensate for the shrinkage. For most metal castings, such as cast steel, a sequential solidification riser design is commonly used for feeding, meaning the casting solidifies first, then the riser neck, and finally the riser itself. Therefore, large-capacity risers can be used to ensure sufficient liquid replenishment, thus guaranteeing effective feeding.

[0004] However, during the casting process, ductile iron castings undergo eutectic solidification and graphite precipitation. When graphite precipitates, the casting expands, meaning it doesn't continuously contract throughout the solidification process. As the temperature drops to the eutectic solidification temperature, graphite gradually precipitates. When the expansion caused by graphitization exceeds the contraction caused by austenite precipitation, the casting expands as a whole. This expansion offsets the initial liquid shrinkage and some solidification shrinkage. Therefore, fully utilizing this expansion can improve the feeding efficiency of ductile iron. For this reason, ductile iron typically uses practical risers for feeding. The riser neck must solidify and "lock" the casting at the start of expansion to prevent graphitization from forcing molten metal to overflow back into the riser through the neck, thus failing to achieve self-feeding. Therefore, the key to riser design for ductile iron is the design of the riser neck, ensuring it solidifies at the shrinkage-expansion equilibrium point and preventing molten metal from overflowing back into the riser. The time it takes for the riser neck to solidify and "get stuck" is proportional to the riser neck modulus. Therefore, to ensure that the riser neck "gets stuck" when the casting expands, it is necessary to design a suitable riser neck modulus.

[0005] Currently, the main methods for designing this type of riser neck are empirical methods and simulation calculation methods. For example, a commonly used empirical method is to design the riser neck modulus as 0.67 times the casting modulus. However, this empirical method is usually not accurate enough and cannot be universally applied to castings of different sizes and complex structures, resulting in the riser neck failing to solidify in time during casting expansion and "jamming." Simulation calculation methods generally use commercial simulation software to calculate the casting expansion time to determine the riser neck modulus. However, the models and parameters used in simulation calculations often differ from reality, leading to insufficient accuracy in the calculation results. This method has a low accuracy in determining the riser neck modulus. Summary of the Invention

[0006] This invention addresses the shortcomings of the prior art by providing a self-expanding and shrinkage-compensating riser neck design method for ductile iron castings. This method enables precise design of the riser neck, reduces casting shrinkage defects, and improves the casting yield.

[0007] The technical solution adopted by this invention to solve its technical problem is: a method for designing a riser neck for self-expansion feeding of ductile iron parts, characterized by including:

[0008] S1. For a modulus of M 铸件 For castings, pre-designed feeding risers are used to feed the castings, and the pre-designed riser module M 冒口 and the pre-designed riser neck module M 预冒口颈 All are not less than M 铸件 ;

[0009] S2. During the casting process, the overall shrinkage and expansion of the casting are obtained in real time by observing the changes in the riser liquid level, thereby determining the equilibrium time point τ between shrinkage and expansion. 平衡点 ;

[0010] S3. During the casting process, the temperature of the riser neck and the casting is monitored in real time to obtain a temperature-time curve, which is derived from the eutectic solidification temperature T of the cast iron. e Find the riser neck solidification time τ on the curve. 颈凝固 ;

[0011] S4. Determine the appropriate riser neck module M using the following formula. 合适冒口颈 :

[0012] ;

[0013] S5. According to M 合适冒口颈 =V 冒口颈 / S 冒口颈 The principle is to design the riser neck so that its volume is V 冒口颈 With heat dissipation surface area S 冒口颈 The ratio is equal to M 合适冒口颈 (V) 冒口颈 S is the riser neck volume. 冒口颈(This refers to the heat dissipation area of ​​the riser neck).

[0014] The riser neck obtained using the above design method is the optimal riser neck for mass production of this casting. It ensures liquid feeding in the early stages of casting. When the casting expands due to the precipitation of graphite during eutectic solidification, the riser neck can solidify and "lock" in time, preventing the feeding molten metal from flowing back into the riser under the action of expansion force. This establishes expansion force inside the casting, achieving self-feeding and improving feeding efficiency. This design method overcomes the limitations of traditional riser design methods and can design riser necks in shapes not limited to columnar, plate, or truncated cone, making it particularly suitable for complex cast iron parts.

[0015] Preferably, in step S1, M 冒口 =(1.1~1.5)M 铸件 Pre-designed riser neck module M 预冒口颈 =(1~1.2)M 铸件 .

[0016] Preferably, step S2 includes:

[0017] S21. Place a floating component on the surface of the molten iron in the riser. During the casting process, use a displacement sensor to test the vertical displacement of the floating component and record the displacement data.

[0018] S22. Plot the displacement as a curve over time, and differentiate the curve once to obtain the differential curve. The first inflection point of the differential curve is the equilibrium time point τ between the shrinkage and expansion of the casting. 平衡点 .

[0019] As the target for receiving displacement sensor signals, the floating plate can be made of any refractory material that is not easily corroded by molten iron at high temperatures, including graphite, silicate, alumina, corundum and other refractory materials, and its shape is not limited.

[0020] Preferably, the floating component includes a lower floating plate, and further, the bottom surface of the lower floating plate is an arc surface.

[0021] Preferably, the floating component further includes a guide rod and an upper floating plate. The lower end of the guide rod is fixedly connected to the top surface of the lower floating plate, and the top end of the guide rod is fixedly connected to the bottom surface of the upper floating plate. The top surface of the upper floating plate is a horizontal plane.

[0022] Preferably, the displacement sensor is a laser displacement sensor with an accuracy of 200 micrometers, acquiring data every 0.1 to 2 seconds. The laser displacement sensor can be fixed on a bracket to facilitate adjustment of its relative position to the riser. A high-temperature protective sleeve can be installed on the laser displacement sensor to reduce the impact of the riser's high temperature.

[0023] Preferably, step S3 uses a temperature sensor to test the temperature change of the riser neck and casting over time. The temperature sensor is a high-temperature testing thermocouple, including but not limited to K, C, and S type thermocouples.

[0024] A further technical objective of the present invention is to provide a device for riser neck design.

[0025] The device for riser neck design is characterized by including a floating element, a displacement sensor, a temperature sensor, and a data logger. The floating element is the target object that receives the signal from the displacement sensor and can float on the surface of the molten iron in the riser, moving up and down with the liquid surface. The displacement sensor is used to test the vertical displacement of the floating element and transmit the data to the data logger. The temperature sensor is used to test the temperature change of the riser neck and the casting over time and transmit the data to the data logger.

[0026] Preferably, the floating component consists of a lower floating plate, a guide rod, and an upper floating plate. The lower floating plate and the upper floating plate are fixedly connected to the lower end and the upper end of the guide rod, respectively. The bottom surface of the lower floating plate is an arc surface, and the top surface of the upper floating plate is a horizontal surface.

[0027] Compared with the prior art, the riser neck design method and device for self-expansion feeding of ductile iron parts of the present invention has the following outstanding advantages:

[0028] (I) During the solidification process of ductile iron, it undergoes multiple stages: liquid shrinkage, solidification shrinkage, solidification expansion, and solid shrinkage. Utilizing the expansion force during the solidification expansion stage to self-compensate the casting is a conventional method to improve the feeding efficiency of ductile iron, that is, to ensure that the riser neck solidifies and "locks in" at the beginning of the casting expansion. However, current conventional methods struggle to accurately design the riser neck and its modulus to ensure timely solidification and "locking in" during casting expansion. In particular, complex castings have different wall thicknesses and structures in different parts, resulting in asynchronous solidification. Thin-walled areas typically solidify before thick-walled areas, meaning that while thin-walled areas are undergoing solidification expansion, thick-walled areas may be shrinking. Whether the casting as a whole shrinks or expands depends on the sum of the shrinkage and expansion values ​​of each part. The most effective time for the riser neck to solidify and "lock in" is at the point of equilibrium between shrinkage and expansion. The design method of this invention can accurately find the point of equilibrium between shrinkage and expansion, overcoming the shortcomings of existing technologies that obtain the equilibrium point through calculation, which suffers from poor accuracy.

[0029] (ii) Beforehand, risers and riser necks with moduli greater than that of the casting are used to conduct feeding tests on the casting, meaning that the risers and riser necks solidify later than the casting. Therefore, during the casting process, if the casting shrinks as a whole, the liquid level in the riser will drop to feed the casting; if the casting expands, the liquid level in the riser will rise. Therefore, by measuring the change in the riser liquid level, the shrinkage-expansion equilibrium point of the casting can be accurately obtained, that is, the time point at which the riser neck should be "locked" in time can be found. Then, based on this time point and the solidification curve of the riser neck, the optimal riser neck modulus, volume, and surface area can be easily calculated. Then, the determined final riser neck replaces the pre-selected riser neck, so that it can make full use of the expansion and self-feeding of ductile iron to feed the casting, obtain the most efficient feeding effect, reduce casting shrinkage defects, improve casting yield, and save molten iron consumption.

[0030] (iii) Laser displacement sensors cannot directly measure the surface of molten iron at high temperatures (above 1380℃), and the surface of the liquid inside the riser is not flat, making direct measurement difficult. This invention converts the height change of the liquid surface inside the riser into the vertical displacement of the floating component. By using a laser displacement sensor to indirectly measure the upper plane of the floating device, the height change value of the liquid surface inside the riser can be obtained, significantly improving accuracy and ensuring data accuracy. Attached Figure Description

[0031] Figure 1 This is a schematic diagram of the device for riser neck design according to the present invention;

[0032] Figure 2 yes Figure 1 Schematic diagram of the floating component structure in the device;

[0033] Figure 3 yes Figure 2 3D view of floating components;

[0034] Figure 4 These are the riser surface displacement-time and temperature-time curves obtained in Example 1;

[0035] Figure 5 These are the riser liquid level displacement-time and temperature-time curves obtained in Example 2.

[0036] The markings in the attached diagram represent:

[0037] 1. Bracket, 2. Laser displacement sensor, 3. Floating component, 31. Lower floating plate, 32. Guide rod, 33. Upper floating plate, 4. Casting, 5. Thermocouple, 6. Sand mold, 7. Sprue, 8. Temperature recorder, 9. Displacement recorder. Detailed Implementation

[0038] The present invention will be further described below with reference to specific embodiments, but this is not intended to limit the present invention.

[0039] Example 1:

[0040] As attached Figure 1 , 2 As shown in Figures 1 and 3, the device used for riser neck design in this embodiment mainly consists of a support 1, a laser displacement sensor 2, a floating component 3, a thermocouple 5, a temperature recorder 8, and a displacement recorder 9.

[0041] The floating component 3 is made of refractory materials such as graphite, silicate, alumina, or corundum, and can float on the surface of molten iron at the riser. In this embodiment, the floating component 3 consists of a lower floating plate 31, a guide rod 32, and an upper floating plate 33. The lower floating plate 31 and the upper floating plate 33 are fixedly connected to the lower and upper ends of the guide rod 32, respectively. The bottom surface of the lower floating plate 31 is an arc surface to facilitate the stable floating of the floating component 3 on the liquid surface. The top surface of the upper floating plate 33 is a horizontal surface.

[0042] The laser displacement sensor 2 is fixed on the cantilever of the bracket 1 to test the vertical displacement of the floating component 3 and transmit the data to the displacement recorder 9.

[0043] Two thermocouples 5 can be placed in the riser neck and the casting respectively to test the temperature change of the riser neck and the casting over time, and transmit the data to the temperature recorder 8.

[0044] Example 2:

[0045] The experiment used a QT400-18 ductile iron box casting with a casting modulus of 3.5. A riser with a modulus of 3.9 and a riser neck modulus of 3.8 was pre-selected based on the casting modulus for feeding. The riser diameter was 120 mm, and the riser neck dimension was 60 mm. An S-type thermocouple 5 was installed in the riser neck and the casting, and the temperature sensor was calibrated to ensure normal operation. An aluminum silicate floating component 3 was placed inside the riser, and a laser displacement sensor 2 with an accuracy of 200 micrometers was installed and calibrated to ensure the measurement was within its range, collecting data every 0.5 seconds.

[0046] Molten iron is melted to 1390℃ and then poured into the sand mold 6 of the box casting through the gating system 7. The activated laser displacement sensor 2 is then moved above the riser of the mold, aligning the laser with the upper floating plate 33. Throughout the casting process, a recorder is used to record the laser sensor displacement data and the temperature sensor temperature. Measurements are stopped when the casting reaches its solidification temperature.

[0047] The measured displacement change data are differentiated and plotted as a displacement versus time curve. Figure 4 Find the time τ corresponding to the equilibrium point of shrinkage and expansion of the casting on the displacement-time curve. 平衡点(740s). Plot the temperature (T) versus time (τ) curve using the temperature sensor data. Based on the cast iron composition, find the eutectic solidification temperature T of the cast iron. e (1160℃), find T on the T-τ curve. e The corresponding time τ 颈凝固 (2050s) is the time it takes for the riser neck to solidify.

[0048] The appropriate riser neck modulus M is determined by the following formula. 合适冒口颈 :

[0049] ,

[0050] M is derived 合适冒口颈 =2.3 is the optimal riser neck modulus that can ensure the self-expansion feeding of the casting, according to M 合适冒口颈 =V 冒口颈 / S 冒口颈 A suitable riser neck was designed, resulting in a riser diameter of 120mm, a riser height of 140mm, and a riser neck size of 36mm. The newly designed riser and riser neck were then used to feed the box casting. Batch production verification showed a product qualification rate of 98%, with no castings scrapped due to shrinkage porosity.

[0051] Example 3:

[0052] The experiment used a QT500-7 ductile iron support casting with a casting modulus of 2. A riser was pre-selected for feeding based on the casting modulus, with a riser modulus of 2.6, a riser neck modulus of 2.4, a riser diameter of 100 mm, and a riser neck dimension of 50 mm. A type C thermocouple 5 was installed in the riser neck and the casting, and the temperature sensor was calibrated to ensure normal operation. An aluminum silicate-graphite composite floating component 3 was placed inside the riser, and a laser displacement sensor 2 with an accuracy of 200 micrometers was installed and calibrated to ensure the measurement was within its range, collecting data every 0.5 seconds.

[0053] Molten iron is melted to 1400℃ and then poured into the support casting sand mold 6 through the gating system 7. The activated laser displacement sensor 2 is then moved above the mold riser, aligning the laser with the upper floating plate 33. Throughout the casting process, a recorder is used to record the laser sensor displacement data and the temperature sensor temperature. Measurements are stopped when the casting reaches its solidification temperature.

[0054] The measured displacement change data are differentiated and plotted as a displacement versus time curve. Figure 5 Find the time τ corresponding to the equilibrium point of shrinkage and expansion of the casting on the displacement-time curve. 平衡点 (480s). Plot the temperature (T) versus time (τ) curve using the temperature sensor data. Based on the cast iron composition, find the eutectic solidification temperature T of the cast iron.e (1150℃), find T on the T-τ curve. e The corresponding time τ 颈凝固 (1680s) is the time it takes for the riser neck to solidify.

[0055] The appropriate riser neck modulus M is determined by the following formula. 合适冒口颈 :

[0056] ,

[0057] M is derived 合适冒口颈 =1.3, which is the optimal riser neck modulus to ensure self-expansion feeding of the casting. According to M... 合适冒口颈 =V 冒口颈 / S 冒口颈 A suitable riser neck was designed, resulting in a riser diameter of 100mm, a riser height of 120mm, and a riser neck size of 27mm. The newly designed riser and riser neck were then used to feed the support casting. Batch production verification showed a product qualification rate of 98.5%, with no casting scrap due to shrinkage porosity.

Claims

1. A method for designing a self-expanding and feeding riser neck for ductile iron castings, characterized in that, include: S1. For a modulus of M 铸件 For castings, pre-designed feeding risers are used to feed the castings, and the pre-designed riser module M 冒口 and the pre-designed riser neck module M 预冒口颈 All are not less than M 铸件 ; S2. During the casting process, the overall shrinkage and expansion of the casting are obtained in real time by observing the changes in the riser liquid level, thereby determining the equilibrium time point τ between shrinkage and expansion. 平衡点 ; S3. Real-time monitoring of the riser neck and casting temperature to obtain temperature-time curves, based on the eutectic solidification temperature T of cast iron. e Find the riser neck solidification time τ on the curve. 颈凝固 ; S4. Determine the appropriate riser neck module M using the following formula. 合适冒口颈 : ； S5. According to M 合适冒口颈 =V 冒口颈 / S 冒口颈 The principle is to design the riser neck so that its volume is V 冒口颈 With heat dissipation surface area S 冒口颈 The ratio is equal to M 合适冒口颈 .

2. The riser neck design method for self-expansion feeding of ductile iron parts according to claim 1, characterized in that, In step S1, M 冒口 =(1.1~1.5)M 铸件 Pre-designed riser neck module M 预冒口颈 =(1~1.2)M 铸件 .

3. The riser neck design method for self-expansion feeding of ductile iron parts according to claim 1, characterized in that, Step S2 includes: S21. Place a floating component on the surface of the molten iron in the riser. During the casting process, use a displacement sensor to test the vertical displacement of the floating component and record the displacement data. S22. Plot the displacement as a curve over time, and differentiate the curve once to obtain the differential curve. The first inflection point of the differential curve is the equilibrium time point τ between the shrinkage and expansion of the casting. 平衡点 .

4. The riser neck design method for self-expansion feeding of ductile iron parts according to claim 3, characterized in that, The floating component includes a lower floating plate, the bottom surface of which is an arc surface.

5. The riser neck design method for self-expansion feeding of ductile iron parts according to claim 4, characterized in that, The floating component also includes a guide rod and an upper floating plate. The lower end of the guide rod is fixedly connected to the top surface of the lower floating plate, and the top end of the guide rod is fixedly connected to the bottom surface of the upper floating plate. The top surface of the upper floating plate is a horizontal plane.

6. The riser neck design method for self-expansion feeding of ductile iron parts according to claim 3, characterized in that, The displacement sensor is a laser displacement sensor.

7. The riser neck design method for self-expansion feeding of ductile iron parts according to claim 1, characterized in that, Step S3 uses a temperature sensor to test the temperature change of the riser neck and casting over time. The temperature sensor is a high-temperature thermocouple.

8. A device for riser neck design, characterized in that... Includes floating components, displacement sensors, temperature sensors, and data loggers. The floating component is the target object that receives the signal from the displacement sensor and can float on the surface of the molten iron at the riser and move up and down with the liquid surface. The displacement sensor is used to test the vertical displacement of the floating component and transmit the data to the data logger. The temperature sensor is used to test the temperature change of the riser neck and casting over time and transmits the data to the data logger.

9. The device for riser neck design according to claim 8, characterized in that, The floating component consists of a lower floating plate, a guide rod, and an upper floating plate. The lower floating plate and the upper floating plate are fixedly connected to the lower end and the upper end of the guide rod, respectively. The bottom surface of the lower floating plate is an arc surface, and the top surface of the upper floating plate is a horizontal surface. The displacement sensor is a laser displacement sensor.

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