Stress frame casting pouring system and casting method based on counter-pressure casting

Abstract

The invention discloses a stress frame casting pouring system and casting method based on differential pressure casting. The stress frame casting pouring system comprises a heat preservation furnace, and the heat preservation furnace is connected with a casting mold through a liquid lifting device; the casting mold comprises a pouring gate and a pouring gate, the pouring gate is communicated with a stress frame casting cavity, the stress frame casting cavity is communicated with a dead head, the pouring gate comprises a vertically-arranged first-stage sprue, a horizontally-arranged cross gate and a vertically-arranged second-stage sprue, the center of the cross gate is connected with the first-stage sprue, and the positions, close to the two ends, of the top of the cross gate are connected with the second-stage sprue. The secondary sprue is connected with a stress frame casting cavity; the casting system is adopted in the stress frame casting method. The method is particularly suitable for manufacturing the stress frame casting corresponding to the resin sand mold differential pressure casting process, the internal quality of the stress frame casting can reach the I-type casting standard, no defects such as air holes, shrinkage cavities and looseness exist in the casting, the surface quality is good, and the qualification rate of the casting is remarkably improved.

Description

Technical Field

[0001] The invention belongs to the technical field of sand casting, and in particular relates to a stress frame casting pouring system and a casting method based on differential pressure casting. Background Art

[0002] Due to the uneven wall thickness design during the casting process, a large amount of residual stress is generated in the casting during solidification shrinkage and heat treatment, and the uneven stress distribution will cause deformation, cracking or associated cracking trend of the casting, seriously affecting the yield and service life of the casting. For the stress evolution analysis of the resin sand mold differential pressure casting process of large-sized complex castings (profile dimensions exceeding 2500mm, wall thickness 15~90mm, wall thickness difference not less than 50mm), due to the complex structure and huge geometric dimensions of the castings, coupled with the limitations of existing testing equipment, the cycle of stress testing of castings at different manufacturing stages is long and the cost is high, and residual stress testing is extremely difficult or even impossible to detect.

[0003] As computer simulation technology matures in the casting field, "experience + computer CAD / CAE" technology has become the main way to realize the casting process and residual stress evolution analysis of castings. However, the simulation of the casting process of large-scale complex castings faces problems such as time-consuming meshing, huge computing workload, and low model accuracy.

[0004] In order to facilitate the stress detection of castings and save calculation time, the research object is simplified and designed as a typical stress frame structure. The stress and deformation during the casting process are relatively clear and can be used to simulate the influence of changes in the structural dimensions of castings (such as castings with different wall thickness difference structures) on their stress distribution, so as to facilitate the analysis of the causes of casting stress. In order to accurately detect and analyze the changes in stress distribution caused by changes in the structural dimensions of the stress frame and eliminate the interference of internal defects of the castings on stress distribution and evolution, higher requirements are put forward for the internal quality of the castings during the research process. However, the existing stress frame pouring system and its casting process are designed for metal mold gravity casting, which is not suitable for the casting of resin sand mold differential pressure casting stress frame. More importantly, how to achieve the internal quality of stress frame castings to meet Class I casting standards has always been a technical difficulty in this field. Summary of the invention

[0005] At least in order to solve the technical problems mentioned in the background technology, the present invention aims to provide a stress frame casting pouring system and a casting method based on differential pressure casting.

[0006] The present invention adopts the following technical solution.

[0007] A stress frame casting pouring system based on differential pressure casting comprises a heat preservation furnace, which is connected to a casting mold through a liquid rising device; the casting mold comprises a gate and a runner, the runner is connected to a stress frame casting cavity, the stress frame casting cavity is connected to a riser, the runner comprises a vertically arranged primary straight runner, a horizontally arranged cross runner, and a vertically arranged secondary straight runner, the center of the cross runner is connected to the primary straight runner, the top of the cross runner near both ends is connected to the secondary straight runner, and the secondary straight runner is connected to the stress frame casting cavity.

[0008] Furthermore, the secondary sprue is connected to the stress frame casting cavity through a transverse transition runner, and a horizontally arranged "Z"-shaped channel structure is formed by the secondary sprue, the riser, the stress frame casting cavity and the transverse transition runner.

[0009] As a preferred solution, four sets of stress frame casting cavities, two secondary straight runners and one cross runner are provided, with the cross runner as the symmetry center, and the four sets of stress frame casting cavities are symmetrically arranged on both sides of the cross runner.

[0010] As one of the key points of the present invention, the lateral transition runner has two oblique sides, a straight side and an arc side, the arc side is connected to the secondary straight runner, the straight side is connected to the side wall of the stress frame casting cavity, and the arc length corresponding to the arc side is approximately equal to 1 / 3 of the circumference of the secondary straight runner.

[0011] Furthermore, a gas and slag storage chamber is provided at the top of the secondary sprue.

[0012] Furthermore, the primary sprue is located in the middle of the runner.

[0013] Furthermore, the runner height is 0.8 to 1.2 times the secondary runner diameter. A stress frame casting method using the above stress frame casting pouring system, comprising the following steps: Step 1, convey the refined melt to the holding furnace through the conveying device for standby use, the holding temperature is controlled to be (670~690)±5℃, the holding furnace and the pouring gate are connected to the liquid raising device, the electrode contacts are connected, the casting mold and the liquid raising device are built into the working cabin and sealed; Step 2, open the intercommunication valve between the working cabin and the holding furnace, introduce compressed air, and when the pressure in the working cabin and the holding furnace stabilizes to 250-450 kPa, close the intercommunication valve between the working cabin and the holding furnace, and then the upper tank of the working cabin begins to relieve pressure, so that the melt is gradually filled under the action of the pressure difference; In this step, the melt is raised at a pressure increase rate of 0.8-1.5 KPa / s, and the electrode contact is used to capture the liquid level information. When the melt flows to the riser, the filling is completed; Step 3: After the molding is completed, open the intercommunication valve between the working chamber and the holding furnace, discharge the compressed air directly, lift out the casting mold and the liquid riser, clean the casting equipment, and open the box and remove the sand 5 to 8 hours after the pouring is completed.

[0014] As the second key point of the present invention, in step 2: During the crust pressurization solidification stage, the pressure increase rate is controlled at 0.8~0.9KPa / s. After the pressure increases by 3~4KPa, the crust holding time is 10~20s, so that the melt forms a 2~4mm shell on the surface; During the crystallization pressurization and solidification stage, the pressure increase rate is controlled at 0.6~0.7KPa / s. After the pressure is further increased by 5~6KPa, the crystallization holding time is controlled at 500~800s.

[0015] Beneficial effects: The present invention is particularly suitable for the manufacture of stress frame castings corresponding to the resin sand mold differential pressure casting process, and can achieve the internal quality of the stress frame castings reaching the Class I casting standards, without defects such as pores, shrinkage holes and looseness inside the castings, and with good surface quality; the present invention adopts a mode of gas storage and slag storage + parallel synchronous filling and solidification, which can not only reduce or eliminate defects such as dispersed looseness, pores and slag inclusions in the castings, but also improve the manufacturing efficiency of stress frame castings, and is also beneficial to control variables during the subsequent use of the stress frame castings, facilitating further comparative tests; the present invention adopts a two-stage pressurized solidification method of crust pressurization + crystallization pressurization, which can not only effectively reduce the amount of mechanical sand adhesion and improve the surface quality of the stress frame castings, with the surface quality of the castings not less than Ra6.3μm, but also improve the shrinkage compensation effect of the aluminum melt in the pouring system on the castings, reduce or avoid the production of shrinkage holes, shrinkage porosity and other defects in the castings, improve the internal quality of the castings, and significantly improve the qualified rate of the castings. BRIEF DESCRIPTION OF THE DRAWINGS

[0016] Figure 1 It is a three-dimensional schematic diagram of the casting mold of the stress frame casting pouring system in Example 1; Figure 2 A schematic diagram of a top view of a casting mold of a stress frame casting gating system in Example 1; Figure 3 is a casting process curve diagram of the stress frame casting in Example 1; Figure 4 This is the simulation result of the stress frame casting casting process in Example 1.

[0017] Figure 5 This is a physical picture of the stress frame casting in Example 1; Figure 6 A schematic diagram of a casting mold top view of a gating system for a stress frame casting in Comparative Example 1; Figure 7 It is a partial schematic diagram of the top view of the casting mold of the stress frame casting gating system in comparative example 2; Figure 8 This is a partial schematic diagram of the top view of the casting mold of the stress frame casting pouring system in comparative example 3. DETAILED DESCRIPTION

[0018] The technical solution of the present invention is described clearly and completely below in conjunction with the accompanying drawings. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of the present invention. Example 1

[0019] Combination Figure 1 to Figure 2 As shown, a stress frame casting pouring system based on differential pressure casting includes a holding furnace, which is connected to a casting mold through a liquid rising device; the casting mold includes a gate 1 and a runner, the runner is connected to a stress frame casting cavity 2, the stress frame casting cavity 2 is connected to a riser 3, the runner includes a vertically arranged primary straight runner 11, a horizontally arranged cross runner 10, and a vertically arranged secondary straight runner 12, the center of the cross runner 10 is connected to the primary straight runner 11, the top of the cross runner 10 near both ends is connected to the secondary straight runner 12, and the secondary straight runner 12 is connected to the stress frame casting cavity 2. The secondary sprue 12 is connected to the stress frame casting cavity 2 through the transverse transition runner 13. The secondary sprue 12, the riser 3, the stress frame casting cavity 2 and the transverse transition runner 13 together constitute a "Z"-shaped channel structure. A gas and slag storage chamber 14 is arranged on the top of the secondary sprue 12. The primary sprue 11 is located in the middle of the transverse runner 10. The height of the transverse runner 10 is 0.8 to 1.2 times the diameter of the secondary sprue 12.

[0020] In this embodiment, a total of four sets of stress frame casting cavities 2, two secondary sprues 12 and one runner 10 are provided, and the four sets of stress frame casting cavities 2 are symmetrically arranged on both sides of the runner 10 with the runner 10 as the symmetry center. Each transverse transition runner 13 has two oblique edges 20, a straight edge 21 and an arc edge 22, the arc edge 22 is connected to the secondary sprue 12, the straight edge 21 is connected to the side wall of the stress frame casting cavity 2, and the arc length corresponding to the arc edge 22 is approximately equal to 1 / 3 of the circumference of the secondary sprue 12.

[0021] A stress frame casting method using the stress frame casting pouring system of the present embodiment is used to cast a certain type of ZL114A aluminum alloy stress frame casting (the casting is used to analyze the influence of the change of the wall thickness of the casting beam on the residual stress). It is required that the casting product has no internal defects such as shrinkage cavities and looseness after flaw detection. Its structure is as follows Figure 5 As shown, the main dimensions of the casting structure are 300×200×40mm.

[0022] According to the structural dimensions of the casting, the height of the riser 3 is designed to be 140 mm, the thickness of the connecting section between the gate 1 and the stress frame casting cavity 2 (i.e., the lateral transition runner 13) is designed to be 40 mm, the diameter of the secondary sprue 12 is designed to be 60 mm, and the height of the secondary sprue 12 is determined according to the height of a single sand box. The width of the cross runner 10 is designed to be 70 mm, and the height of the cross runner 10 is designed to be 60 mm; the diameter of the primary sprue 11 is determined according to the size of the riser pipe of the riser device, the height of the primary sprue 11 is designed to be 60 mm, and the hemispherical cross-sectional diameter of the gas and slag storage chamber 14 is designed to be 60 mm.

[0023] In order to verify the rationality of the pouring system of the stress frame casting in this embodiment, the pouring process of the casting is simulated by using Huazhu CAE software. The casting process curve of the ZL114A aluminum alloy stress frame casting is as follows: Figure 3 The simulation results are shown in Figure 4 As shown in the figure, it can be seen that the stress frame does not produce internal defects such as shrinkage holes and looseness, which preliminarily verifies the rationality of the casting system design.

[0024] The specific steps of the stress frame casting method of the stress frame casting pouring system in this embodiment include: Step 1, convey the refined ZL114A melt to the holding furnace through the conveying device for standby use, the holding temperature is controlled to (670~690)±5℃, the holding furnace and the gate 1 are connected to the liquid lifting device, the electrode contacts are connected, the casting mold and the liquid lifting device are built into the working cabin and sealed (cover the upper tank body of the working cabin to ensure that the upper tank of the working cabin and the lower tank of the holding furnace are a closed space, the structure and use method of the conveying device, the liquid lifting device and the working cabin are all conventional technologies, which will not be described in detail in this example); Step 2, open the intercommunication valve between the working cabin and the holding furnace, introduce compressed air, and when the pressure in the working cabin and the holding furnace stabilizes to 300kpa, close the intercommunication valve between the working cabin and the holding furnace, and then the upper tank of the working cabin begins to relieve pressure, so that the melt is gradually filled under the action of the pressure difference; In this step, the melt is raised at a pressure increase rate of 0.8-1.5 KPa / s, and the electrode contact is used to capture the liquid level information. When the melt flows to the riser 3, the filling is completed; specifically: During the crust pressurization solidification stage, the pressure increase rate is controlled to be 0.9 KPa / s. After the pressure increases by 4 KPa, the crust holding time is 15 seconds, so that the melt forms a 2-3 mm shell on the surface. During the crystallization pressurization solidification stage, the pressure increase rate is controlled at 0.7 KPa / s. After the pressure is increased by another 6 KPa, the crystallization pressure holding time is controlled at 600 s to ensure that the casting is fully solidified under pressure. Step 3: After the molding is completed, open the intercommunication valve between the working cabin and the holding furnace, discharge the compressed air directly, lift out the casting mold and the liquid riser, clean the casting equipment, open the box and shake out the sand 5 to 8 hours after the pouring is completed, and clean the sand mold to obtain the stress frame casting. Figure 5 shown.

[0025] X-ray flaw detection equipment was used to detect the internal quality of the four castings in Example 1. The results showed that there were no internal defects such as shrinkage cavities, looseness and cracks, and the internal quality of the stress frame castings reached the Class I casting standard.

[0026] Comparative Example 1: A stress frame casting method, the stress frame casting gating system used is referred to in Example 1 and combined with Figure 6 As shown, the difference between it and Example 1 is that the transverse transition runner 13 is rectangular, the transverse transition runner 13 is opposite to a single cavity of the stress frame casting cavity 2, and the cross-sectional area of ​​the transverse transition runner 13 is equal to the cross-sectional area of ​​a single cavity of the stress frame casting cavity 2.

[0027] Comparative Example 2: A stress frame casting method, the stress frame casting gating system used is referred to in Example 1 and combined with Figure 7 As shown, the difference between it and embodiment 1 is that the riser 3 is located in the middle of the stress frame casting cavity 2.

[0028] Comparative Example 3: A stress frame casting method, the stress frame casting gating system used is referred to in Example 1 and combined with Figure 8 As shown, the difference from Example 1 is that the transverse transition runner 13 is rectangular, each section of the transverse transition runner 13 is opposite to the three chambers of the stress frame casting cavity 2, and the cross-sectional area of ​​the transverse transition runner 13 is equal to the cross-sectional area of ​​the stress frame casting cavity 2.

[0029] X-ray flaw detection equipment was used to detect the internal quality of the twelve castings in the comparative example. The results showed that two of the four castings in comparative example 1 had loose defects, and all four castings had cracks, four of the four castings in comparative example 2 had crack defects, and one of the four castings in comparative example 3 had a loose defect, and the other had a crack defect.

[0030] The scheme in Example 1 is particularly suitable for the manufacture of stress frame castings corresponding to the resin sand mold differential pressure casting process, and can achieve the internal quality of the stress frame casting to meet the Class I casting standard, without defects such as pores, shrinkage holes and looseness inside the casting, and the surface quality is good; the scheme adopts a gas and slag storage + parallel synchronous filling and solidification mode, and adopts a two-stage pressurized solidification method of crust pressurization + crystallization pressurization, which can not only reduce or eliminate defects such as dispersed looseness, pores and slag inclusions in the casting, but also achieve the improvement of the manufacturing efficiency of the stress frame casting, and is also beneficial to the control of variables in the subsequent use of the stress frame casting, so as to facilitate further comparative tests; the scheme can not only effectively reduce the amount of mechanical sand adhesion and improve the surface quality of the stress frame casting, the surface quality of the casting is not less than Ra6.3μm, but also can improve the shrinkage compensation effect of the aluminum melt in the pouring system on the casting, reduce or avoid the production of shrinkage holes, shrinkage and other defects in the casting, improve the internal quality of the casting, and significantly improve the qualified rate of the casting.

Claims

1. A stress frame casting pouring system based on differential pressure casting, comprising a holding furnace, the holding furnace being connected to a casting mold via a liquid lifting device; The casting mold comprises a gate (1) and a runner, the runner is connected to the stress frame casting cavity (2), and the stress frame casting cavity (2) is connected to the riser (3), and is characterized in that: The runner comprises a first-level sprue (11) arranged vertically, a horizontal runner (10) arranged horizontally, and a second-level sprue (12) arranged vertically. The center of the horizontal runner (10) is connected to the first-level sprue (11), and the top of the horizontal runner (10) near both ends is connected to the second-level sprue (12). The second-level sprue (12) is connected to the stress frame casting cavity (2).

2. The stress frame casting pouring system according to claim 1, characterized in that: The secondary sprue (12) is connected to the stress frame casting cavity (2) via a transverse transition sprue (13), and a "Z"-shaped channel structure is formed by the secondary sprue (12), the riser (3), the stress frame casting cavity (2) and the transverse transition sprue (13).

3. The stress frame casting pouring system according to claim 2, characterized in that: A total of four sets of stress frame casting cavities (2), two secondary straight runners (12) and a cross runner (10) are provided, with the cross runner (10) being the symmetry center, and the four sets of stress frame casting cavities (2) being symmetrically arranged on both sides of the cross runner (10).

4. The stress frame casting pouring system according to any one of claims 2-3, characterized in that: The lateral transition runner (13) has two oblique edges (20), a straight edge (21) and an arc edge (22), the arc edge (22) is connected to the secondary straight runner (12), the straight edge (21) is connected to the side wall of the stress frame casting cavity (2), and the arc length corresponding to the arc edge (22) is approximately equal to 1 / 3 of the circumference of the secondary straight runner (12).

5. The stress frame casting pouring system according to claim 4, characterized in that: A gas and slag storage chamber (14) is provided on the top of the secondary sprue (12).

6. The stress frame casting pouring system according to claim 5, characterized in that: The primary sprue (11) is located in the middle of the runner (10).

7. The stress frame casting pouring system according to claim 6, characterized in that: The height of the horizontal runner (10) is 0.8 to 1.2 times the diameter of the secondary straight runner (12).

8. A stress frame casting method using the stress frame casting pouring system according to any one of claims 1 to 7, characterized in that the steps include: Step 1, conveying the refined melt to a holding furnace through a conveying device for standby use, controlling the holding temperature to (670-690) ±5°C, connecting the holding furnace and the pouring gate (1) to a liquid raising device, connecting electrode contacts, placing the casting mold and the liquid raising device in a working chamber and sealing them; Step 2, open the intercommunication valve between the working cabin and the holding furnace, introduce compressed air, and when the pressure in the working cabin and the holding furnace stabilizes to 250-450 kPa, close the intercommunication valve between the working cabin and the holding furnace, and then the upper tank of the working cabin begins to relieve pressure, so that the melt is gradually filled under the action of the pressure difference; In this step, the melt is raised at a pressure increase rate of 0.8-1.5 KPa / s, and the electrode contact is used to capture the liquid level information. When the melt flows to the riser (3), the filling is completed; Step 3: After the molding is completed, open the intercommunication valve between the working chamber and the holding furnace, discharge the compressed air directly, lift out the casting mold and the liquid riser, clean the casting equipment, and open the box and remove the sand 5 to 8 hours after the pouring is completed.

9. The stress frame casting method according to claim 8, characterized in that: In step 2: During the crust pressurization solidification stage, the pressure increase rate is controlled at 0.8~0.9KPa / s. After the pressure increases by 3~4KPa, the crust holding time is 10~20s, so that the melt forms a 2~4mm shell on the surface; During the crystallization pressurization and solidification stage, the pressure increase rate is controlled at 0.6~0.7KPa / s. After the pressure is further increased by 5~6KPa, the crystallization holding time is controlled at 500~800s.

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