A key component of degradable magnesium alloy bridge plug prepared by semi-solid injection molding and a method thereof

Abstract

The application belongs to the technical field of oil and gas field downhole tool manufacturing and magnesium alloy net forming, and particularly relates to a key component of a degradable magnesium alloy bridge plug prepared by semi-solid injection molding and a method thereof, which comprises the following steps: preparing a semi-solid injection molding mold; preparing magnesium alloy semi-solid slurry by using degradable magnesium alloy, and quantitatively adding the magnesium alloy semi-solid slurry into a compression chamber on a fixed mold; preheating a movable mold and the fixed mold and clamping the molds; grading pushing the magnesium alloy semi-solid slurry in the compression chamber by using a push rod; discharging gas at a position where the magnesium alloy semi-solid slurry fills the end of a cavity through a gas discharge groove; immediately increasing pressure and keeping pressure after the cavity is filled with the semi-solid slurry, and then cooling until the slurry is completely solidified, opening the mold, taking out the key component of the degradable magnesium alloy bridge plug, and obtaining the key component; and the application can improve the one-time forming integrity, microstructure compactness and size consistency of a thin-wall corrugated structure.

Description

Technical Field

[0001] This invention belongs to the field of oil and gas field downhole tool manufacturing and magnesium alloy net forming technology, specifically relating to a key component of biodegradable magnesium alloy bridge plug prepared by semi-solid injection molding and its method. Background Technology

[0002] In the development of unconventional oil and gas resources, especially in horizontal well fracturing operations for shale gas and tight oil, biodegradable metal bridge plugs are crucial downhole tools for achieving segment isolation. Magnesium alloy bridge plugs, with their arc-shaped petal-like components, are key components responsible for anchoring and high-pressure sealing. Their outer surface typically features a multi-layered corrugated tooth structure, while the inner surface is usually a tapered bevel that mates with the bridge plug cone. During bridge plug setting, they must withstand significant radial expansion stress, axial engagement, and corrosive media in the high-temperature, high-salinity fluid environment of the downhole well. Therefore, the material must possess not only high specific strength and sufficient plasticity but also good microstructure, dimensional consistency, and controllable degradation capability.

[0003] Magnesium alloy bridge plugs typically feature an arc-shaped, petal-like profile, locally thick-walled connecting areas, and continuous thin-walled corrugated tooth areas, making them typical complex, irregularly shaped, thin-walled components. If conventional liquid die casting or general casting is used, the molten metal is prone to premature cooling in the continuous thin-walled corrugated tooth areas during the filling process, leading to defects such as cold shuts, undercasting, shrinkage porosity, gas entrapment, and gas bubbles. If subsequent machining is relied upon extensively to achieve the target shape, it results in low material utilization, interrupted metal flow lines, large dimensional dispersion, and localized stress concentration, making it difficult to simultaneously meet the forming quality and mechanical reliability required for downhole service. On the other hand, most existing semi-solid injection molding solutions achieve injection via screw delivery within the barrel. However, for components like magnesium alloy bridge plugs, which have both locally thick-walled connecting areas and continuous thin-walled corrugated tooth areas, if the specific filling path, gate location, and cavity end venting method are not specifically designed, problems such as unstable local filling, leading-edge flow splitting and breakage, end-gas retention, and initial cold material entrapment into the cavity will also occur. Summary of the Invention

[0004] The purpose of this invention is to provide a key component and method for preparing a biodegradable magnesium alloy bridge plug using semi-solid injection molding. This method enables the magnesium alloy semi-solid slurry to fill the mold stably from bottom to top along the axial direction of the cavity, reducing defects such as cold shuts, undercasting, air entrapment, shrinkage porosity, and inclusions. It also improves the one-time forming integrity, microstructure density, and dimensional consistency of thin-walled corrugated structures. At the same time, it reduces the amount of subsequent machining, improves material utilization and yield.

[0005] The technical solution of this invention is: a method for preparing a biodegradable magnesium alloy bridge plug key component using semi-solid injection molding, comprising the following steps:

[0006] S1. Prepare a semi-solid injection molding mold; the semi-solid injection molding mold includes a moving mold and a fixed mold. After the moving mold and the fixed mold are closed, a cavity matching the shape of the key component of the magnesium alloy bridge plug is formed. The key component of the magnesium alloy bridge plug is an arc-shaped petal component of the magnesium alloy bridge plug; the fixed mold is provided with a pressure chamber, a sprue and an ingate. The pressure chamber is connected to the cavity in sequence through the sprue and the ingate. The moving mold is provided with an venting groove and an overflow groove. The venting groove and the overflow groove are connected to each other and the venting groove is connected to the cavity.

[0007] S2. A semi-solid magnesium alloy slurry is prepared using a biodegradable magnesium alloy, and the semi-solid magnesium alloy slurry is quantitatively added to the pressure chamber of a fixed mold. The solid content of the semi-solid magnesium alloy slurry is 25% to 45%.

[0008] S3. Preheat the moving mold and the fixed mold and close the mold. Before filling, perform vacuum-assisted evacuation of the cavity.

[0009] S4. The magnesium alloy semi-solid slurry in the pressure chamber is pushed in stages by push rods, so that the magnesium alloy semi-solid slurry enters the cavity through the gating system and the ingate in sequence, and fills the cavity from bottom to top in the axial direction along the shape of the key component of the magnesium alloy bridge plug.

[0010] S5. At the end of the cavity, where the magnesium alloy semi-solid slurry is filled, the gas is discharged through the venting groove, and the first section of cold material or inclusions enters the overflow groove connected to the venting groove.

[0011] S6. After the cavity is filled with semi-solid slurry, it is immediately pressurized and held. After the pressure holding is completed, it is cooled until the slurry is completely solidified. The mold is opened and the part is removed to obtain the biodegradable magnesium alloy bridge plug key component.

[0012] Preferably, in step S1, both the moving mold and the fixed mold have parting surfaces. A first parting groove is provided on the parting surface of the moving mold, and a second parting groove is provided on the parting surface of the fixed mold. When the moving mold and the fixed mold are closed, the first parting groove and the second parting groove together form a cavity that matches the shape of the key component of the magnesium alloy bridge plug.

[0013] The first parting groove includes a non-smooth wall area, and an overflow groove is formed along the outer periphery of the non-smooth wall area. A corrugated thin-walled area is formed in the middle of the non-smooth wall area, and the internal area of ​​the cavity is divided into the lower area of ​​the corrugated thin-walled area, the area corresponding to the corrugated thin-walled area, and the upper area of ​​the corrugated thin-walled area according to the corrugated thin-walled area. An exhaust groove is formed on the moving mold, and the overflow groove is connected to the first parting groove through the exhaust groove. The top of the overflow groove forms a vacuum interface on the upper surface of the moving mold.

[0014] The second parting groove includes a thick-walled transition zone and a smooth-walled zone from bottom to top, with the thick-walled transition zone being inclined; a sprue is provided through the fixed mold, with one end of the sprue forming an ingate in the middle of the thick-walled transition zone, and the ingate being located below the corrugated tooth thin-walled zone; when filling the cavity with magnesium alloy semi-solid slurry, the magnesium alloy semi-solid slurry preferentially fills the area below the corrugated tooth thin-walled zone inside the cavity, and gradually expands towards the corrugated tooth thin-walled zone until it fills the entire cavity;

[0015] One side of the fixed mold is connected to a pressure chamber, which is connected to the sprue. One end of the pressure chamber is connected to a feeding port and a push rod. The feeding port is connected to the side wall of the pressure chamber. Magnesium alloy semi-solid slurry is filled into the pressure chamber through the feeding port. The push rod is placed inside the pressure chamber and pushes the magnesium alloy semi-solid slurry in the pressure chamber into the cavity through the sprue and the ingate.

[0016] Preferably, in step S2, the biodegradable magnesium alloy is a Mg-Al biodegradable magnesium alloy.

[0017] Preferably, the magnesium alloy semi-solid slurry is prepared by melting and refining the magnesium alloy under a protective atmosphere to remove slag and gas, and then cooling the molten magnesium alloy to a semi-solid range and holding it at that temperature to form a magnesium alloy semi-solid slurry with uniformly distributed primary solid particles; the holding range for preparing the magnesium alloy semi-solid slurry is controlled at 560-660°C, and the solid phase content is 25%-45%.

[0018] Preferably, in step S3, both the moving mold and the fixed mold in the semi-solid injection molding die are preheated with independent temperature control in different zones. The main body temperature of the moving mold and the fixed mold is set to 160-180°C, and the local temperature of the corrugated thin-walled area in the moving mold is controlled to 250-280°C. The local temperature of the lower part of the non-smooth wall area in the moving mold and the local temperature of the thick-walled transition area in the fixed mold are both controlled to 180-220°C. Before filling, the vacuum degree of the cavity is 30-70 mbar.

[0019] Preferably, in step S4, the graded pushing includes primary pushing, secondary pushing, and tertiary pushing; primary pushing is a low-speed pushing at a pushing speed of 0.05~0.30m / s, used to smoothly move the magnesium alloy semi-solid slurry forward to fill the front end of the pressure chamber and enter the interior of the gating; secondary pushing is a medium-speed pushing at a pushing speed of 0.30~1.20m / s, used to allow the magnesium alloy semi-solid slurry inside the gating to enter the cavity through the ingate and fill the area below the corrugated tooth thin-walled area inside the cavity; tertiary pushing is a high-speed pushing at a pushing speed of 1.20~3.00m / s, used to complete the filling of the corrugated tooth thin-walled area and the end of the cavity; after the tertiary pushing is completed, the cavity is filled with magnesium alloy semi-solid slurry, resulting in a bridge plug mold assembly, and the bridge plug mold assembly is pressurized and held at a pressure of 60~80MPa for a holding time of 3~10s; after the pressurization and holding are completed, the bridge plug mold assembly is cooled for 8~20s.

[0020] Preferably, the switching positions between the first-level and second-level push, and between the second-level and third-level push, are determined by the stroke of the push rod and pressure sensors. Specifically, the magnesium alloy semi-solid slurry is injected into the pressure chamber through the feeding port. The push rod is pushed at the first-level push speed to allow the magnesium alloy semi-solid slurry to enter the gating system along the pressure chamber until the magnesium alloy semi-solid slurry reaches the ingate, at which point the push is switched to the second-level push. The push rod is pushed at the second-level push speed to allow the magnesium alloy semi-solid slurry at the ingate to enter the cavity until the magnesium alloy semi-solid slurry is about to contact the corrugated tooth thin-walled area, at which point the push is switched to the third-level push. The push rod is pushed at the third-level push speed to allow the magnesium alloy semi-solid slurry to fill the entire cavity from the corrugated tooth thin-walled area.

[0021] Preferably, in step S6, when opening the mold and removing the part, the fixed mold and the moving mold are first separated to open the semi-solid injection molding mold, and then the degradable magnesium alloy bridge plug key component is pushed out using the ejection mechanism; wherein, the ejection force of the ejection mechanism acts on the area corresponding to the thick-walled transition zone on the degradable magnesium alloy bridge plug key component, and the degradable magnesium alloy bridge plug key component is ejected in conjunction with the release agent, so as to reduce the deformation risk of the corrugated tooth structure formed by the degradable magnesium alloy bridge plug key component after molding.

[0022] This invention also provides a biodegradable magnesium alloy bridge plug key component prepared by semi-solid injection molding. The biodegradable magnesium alloy bridge plug key component is prepared by the above-mentioned method of preparing a biodegradable magnesium alloy bridge plug key component by semi-solid injection molding. The biodegradable magnesium alloy bridge plug key component has an arc-shaped petal-shaped body, an outer surface corrugated tooth structure, and an inner conical inclined surface that matches the bridge plug cone. The biodegradable magnesium alloy bridge plug key component is applied to shale gas extraction and oil field extraction.

[0023] The beneficial effects of this invention are as follows:

[0024] 1. The key components of the biodegradable magnesium alloy bridge plug are prepared and formed using magnesium alloy semi-solid slurry. The magnesium alloy semi-solid slurry exhibits a relatively stable flow state during the filling process, and the tendency of air entrapment, splashing and liquid segregation is significantly reduced, which can effectively improve the one-time forming quality of the corrugated tooth structure on the outer surface of the key components of the biodegradable magnesium alloy bridge plug.

[0025] 2. By arranging the ingate below the corrugated tooth thin-walled area, the magnesium alloy semi-solid slurry preferentially fills the area below the corrugated tooth thin-walled area in the cavity, and then extends from bottom to top along the cavity axial direction to the corrugated tooth thin-walled area and the end of the cavity. This helps to form a stable and continuous filling front, and reduces the risk of cold shut and undercasting in the corrugated tooth thin-walled area.

[0026] 3. By simultaneously setting venting grooves and overflow grooves at the end of the cavity, the gas at the end of the cavity and the first section of cold material of the magnesium alloy semi-solid slurry can be discharged and contained in a timely manner, reducing the local defects of the key components of the biodegradable magnesium alloy bridge plug caused by inclusions, shrinkage cavities and gas stagnation at the end of the cavity, and improving the compactness and dimensional consistency of the parts.

[0027] 4. The magnesium alloy semi-solid slurry is pushed into the mold cavity by a pusher-stage method, instead of a single-stage constant-speed push or direct injection by the screw in the barrel. This allows for switching between low-speed, medium-speed, and high-speed filling rhythms. The magnesium alloy semi-solid slurry can be segmented and matched to different flow requirements in the gating system, the area below the corrugated tooth thin-walled zone, and the area corresponding to the corrugated tooth thin-walled zone, thus achieving the dual goals of low air entrapment and high filling integrity.

[0028] 5. By using semi-solid injection molding dies to ensure near-net-shape forming of key components of magnesium alloy bridge plugs, the amount of material removed by traditional machining can be reduced, and excessive damage to the continuity of beneficial metal structure can be avoided. This helps to maintain the load-bearing stability of key components of biodegradable magnesium alloy bridge plugs during setting and service, while improving material utilization and reducing manufacturing costs. Attached Figure Description

[0029] To more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the drawings used in the description of the embodiments or the prior art will be briefly introduced below. Obviously, the drawings described below are only some embodiments of the present invention. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0030] Figure 1 This is a schematic diagram of the overall structure of the semi-solid injection molding die in this invention;

[0031] Figure 2 This is a cross-sectional view of the semi-solid injection molding die in this invention;

[0032] Figure 3 This is a schematic diagram of the cavity formed after the moving mold and the fixed mold are closed in this invention;

[0033] Figure 4 This is a cross-sectional view of the fixed mold in this invention;

[0034] Figure 5 This is a schematic diagram of the fixed mold structure in this invention;

[0035] Figure 6 This is a side view of the moving mold in this invention;

[0036] Figure 7 This is a distribution diagram of the lower region, middle region, and upper region of the non-smooth wall region of the moving mold in this invention.

[0037] In the diagram: 1. Fixed mold; 2. Moving mold; 3. Cavity; 3. Lower area of ​​the corrugated tooth thin-walled zone; 31. Area corresponding to the corrugated tooth thin-walled zone; 32. Upper area of ​​the corrugated tooth thin-walled zone; 33. Inner gate; 4. Runner; 5. Pressure chamber; 6. Vacuum interface; 7. Venting groove; 8. Overflow groove; 9. Feed port; 10. Ejector pin; 11. Parting surface; 12. Corrugated tooth thin-walled zone; 13. Thick-walled transition zone; 14. Non-smooth wall zone; 15. Smooth wall zone; 16. Detailed Implementation

[0038] 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.

[0039] In the description of this invention, it should be noted that the terms "center," "upper," "lower," "left," "right," "vertical," "horizontal," "inner," and "outer," etc., indicate the orientation or positional relationship based on the orientation or positional relationship shown in the accompanying drawings. They are used only for the convenience of describing the invention and for simplifying the description, and do not indicate or imply that the device or element referred to must have a specific orientation, or be constructed and operated in a specific orientation. Therefore, they should not be construed as limitations on the invention. The terms "first" and "second" are used for descriptive purposes only and should not be construed as indicating or implying relative importance. Furthermore, unless otherwise explicitly specified and limited, the terms "installed," "connected," and "linked" should be interpreted broadly. For example, they can refer to a fixed connection, a detachable connection, or an integral connection; they can refer to a mechanical connection or an electrical connection; they can refer to a direct connection or an indirect connection through an intermediate medium; and they can refer to the internal communication of two components. Those skilled in the art can understand the specific meaning of the above terms in this invention based on the specific circumstances.

[0040] In the following examples and comparative examples, unless otherwise specified, the key components of the prepared biodegradable magnesium alloy bridge plug are all arc-shaped petal-shaped components for biodegradable magnesium alloy bridge plugs, with a multi-layer corrugated tooth structure on the outer surface and a conical inclined surface on the inner surface that mates with the bridge plug cone.

[0041] like Figures 1 to 6 As shown, a method for preparing a biodegradable magnesium alloy bridge plug key component using semi-solid injection molding includes the following steps:

[0042] S1. Prepare a semi-solid injection molding mold; the semi-solid injection molding mold includes a moving mold 2 and a fixed mold 1. After the moving mold 2 and the fixed mold 1 are closed, a cavity 3 is formed that matches the shape of the key component of the magnesium alloy bridge plug. The key component of the magnesium alloy bridge plug is an arc-shaped petal component of the magnesium alloy bridge plug. The fixed mold 1 is provided with a pressure chamber 6, a sprue 5 and an ingate 4. The pressure chamber 6 is connected to the cavity 3 in sequence through the sprue 5 and the ingate 4. The moving mold 2 is provided with an venting groove 8 and an overflow groove 9. The venting groove 8 and the overflow groove 9 are connected to each other, and the venting groove 8 is connected to the cavity 3.

[0043] In this embodiment, both the moving mold 2 and the fixed mold 1 have parting surfaces 12. A first parting groove is provided on the parting surface 12 of the moving mold 2, and a second parting groove is provided on the parting surface 12 of the fixed mold 1. When the moving mold 2 and the fixed mold 1 are closed, the first parting groove and the second parting groove together form a cavity 3 that matches the shape of the key component of the magnesium alloy bridge plug. The first parting groove includes a non-smooth wall area 15, and an overflow groove 9 is provided along the outer periphery of the non-smooth wall area 15. A corrugated tooth thin-walled area 13 is provided in the middle of the non-smooth wall area 15, and the internal area of ​​the cavity 3 is divided into a lower area 31 of the corrugated tooth thin-walled area, an area 32 corresponding to the corrugated tooth thin-walled area, and a lower area 31 of the corrugated tooth thin-walled area. The upper region 33 of the corrugated tooth thin-walled area; the top of the moving mold 2 is provided with an exhaust groove 8, and the overflow groove 9 is connected to the first parting groove through the exhaust groove 8. The top of the exhaust groove 8 forms a vacuum interface 7 on the upper surface of the moving mold 2; the second parting groove includes a thick-walled transition area 14 and a smooth wall area 16 from bottom to top. The thick-walled transition area 14 is inclined; the fixed mold 1 is provided with a runner 5, and one end of the runner 5 forms an inner gate 4 in the middle of the thick-walled transition area 14; a pressure chamber 6 is connected to one side of the fixed mold 1. The pressure chamber 6 is connected to the runner 5. One end of the pressure chamber 6 is connected to a feeding port 10 and a push rod 11. The feeding port 10 is connected to the side wall of the pressure chamber 6, and the push rod 11 is placed inside the pressure chamber 6.

[0044] S2. A semi-solid magnesium alloy slurry is prepared using a biodegradable magnesium alloy, and the semi-solid magnesium alloy slurry is quantitatively added to the pressure chamber 6 on the fixed mold 1. The solid phase of the semi-solid magnesium alloy slurry is 25% to 45%.

[0045] The biodegradable magnesium alloy is a Mg-Al biodegradable magnesium alloy. By mass percentage, the Mg-Al biodegradable magnesium alloy comprises Al 5.5%–7.0%, Cu 1.5%–2.5%, Zn 0.5%–1.2%, Mn 0.2%–0.5%, Fe 0.005%–0.02%, Ni 0.001%–0.01%, with the balance being Mg and unavoidable impurities. The chemical composition of the Mg-Al biodegradable magnesium alloy is shown in Table 1.

[0046]

[0047] Specifically, in this embodiment, the biodegradable magnesium alloy, by mass percentage, comprises Al 6.0%, Cu 2.0%, Zn 0.8%, Mn 0.3%, Fe 0.01%, Ni 0.005%, with the balance being Mg and unavoidable impurities. Cu, Mg, and Al form a Cu-enriched second phase, which creates a micro-galvanic corrosion between the Cu-enriched second phase and the magnesium matrix. This promotes the dissolution of the magnesium matrix in a chlorine-containing downhole fluid environment, thereby increasing the degradation rate of the key components of the biodegradable magnesium alloy bridge plug. Al is used to ensure the strength, fluidity, and semi-solid forming performance of the magnesium alloy semi-solid slurry. Zn is used for solid solution strengthening and to regulate the distribution of the Cu-enriched second phase. Mn is used to reduce the interference of impurity elements on the localized corrosion behavior of the key components of the biodegradable magnesium alloy bridge plug, improving the consistency of the key components during the degradation process.

[0048] Specifically, the magnesium alloy semi-solid slurry is prepared as follows: the magnesium alloy is melted and refined to remove slag and gas under a protective atmosphere, and then the molten magnesium alloy is cooled to the semi-solid range and held at that temperature to form a magnesium alloy semi-solid slurry with uniformly distributed primary solid particles; the slurry preparation temperature is controlled at 560-660℃ and the solid content is 25%-45%.

[0049] S3. Preheat the moving mold 2 and the fixed mold 1 and close the mold. Before filling, vacuum-assisted evacuation is performed on the cavity 3.

[0050] In this embodiment, both the moving mold 2 and the fixed mold 1 in the semi-solid injection molding die adopt independent temperature control preheating in zones. Independent temperature control preheating divides the complete moving mold 2 or fixed mold 1 into multiple independent temperature control preheating zones in space. Each temperature control preheating zone has its own independent heating element, temperature sensor, and temperature control circuit to achieve differentiated temperature control without interference. Specifically, in this embodiment, the multiple independent temperature control preheating zones are the lower region, middle region, and upper region of the non-smooth wall region 15 in the moving mold 2, and the thick-walled transition region 14 and smooth wall region 16 in the fixed mold 1. It should be noted that... Figure 7In the diagram, L represents the lower region of the non-smooth wall region 15, M represents the middle region of the non-smooth wall region 15, and N represents the upper region of the non-smooth wall region 15. The main body temperature of the moving mold 2 and the fixed mold 1 is set to 160-180℃. The local temperature of the middle region of the non-smooth wall region 15 in the moving mold 2 is controlled at 250-280℃. Since the middle of the non-smooth wall region 15 is provided with a corrugated thin-walled region 13, the local temperature of the corrugated thin-walled region 13 is controlled at 250-280℃. The local temperature of the lower region of the non-smooth wall region 15 and the thick-walled transition region 14 is controlled at 180-220℃. Before filling, the vacuum degree of the cavity 3 is 30-70mbar.

[0051] S4. The magnesium alloy semi-solid slurry in the pressure chamber 6 is pushed in stages by push rod 11, so that the magnesium alloy semi-solid slurry enters the cavity 3 through the gating 5 and the inner gate 4 in sequence, and fills the cavity 3 in the axial direction from bottom to top along the shape of the key component of the magnesium alloy bridge plug, that is, the cavity 3 is filled in the manner from bottom to top.

[0052] In this invention, the graded pushing means that the push rod 11 does not push the slurry in the pressure chamber 6 forward at a single constant speed, but controls the stability of the magnesium alloy semi-solid slurry and the filling state of different areas in the cavity 3 by switching different pushing speeds in three stages according to the different flow stages of the magnesium alloy semi-solid slurry.

[0053] The graded pushing process includes first-level pushing, second-level pushing, and third-level pushing: First-level pushing is a low-speed pushing at a pushing speed of 0.05~0.30m / s, used to smoothly move the magnesium alloy semi-solid slurry to fill the front end of the pressure chamber 6 and enter the interior of the gating 5; Second-level pushing is a medium-speed pushing at a pushing speed of 0.30~1.20m / s, used to allow the magnesium alloy semi-solid slurry inside the gating 5 to pass through the ingate 4 and fill the lower region 31 of the corrugated tooth thin-walled area in the cavity 3; Third-level pushing is a high-speed pushing at a pushing speed of 1.20~3.00m / s, used to complete the filling of the corrugated tooth thin-walled area 13 and the end of the cavity 3. It should be noted that the cavity 3 is filled from bottom to top, and the end of the cavity 3 is the upper region 33 of the corrugated tooth thin-walled area in the cavity 3.

[0054] The first-stage low-speed push is to avoid significant turbulence and splashing of the magnesium alloy semi-solid slurry at the front end of the pressure chamber 6 and in the gating 5, reducing the risk of air entrapment. The front end of the pressure chamber 6 is the end that connects the pressure chamber 6 and the gating 5. The second-stage medium-speed push ensures that the magnesium alloy semi-solid slurry inside the gating 5 remains continuous and stable when entering the ingate 4 and the thick-walled transition zone 14, without significant front-end breakage. The third-stage high-speed push is used to overcome the flow resistance of the corrugated tooth thin-walled zone 13, quickly filling the complex corrugated structure in the corrugated tooth thin-walled zone 13 while the magnesium alloy semi-solid slurry still has sufficient flow capacity. Through this graded push method, the spatial sequence inside the cavity 3 from bottom to top can be correlated with the process rhythm of the magnesium alloy semi-solid slurry moving forward smoothly at low speed, being introduced into the area below the corrugated tooth thin-walled zone 13 in the cavity 3 at medium speed, and finally completing the filling and molding of the corrugated tooth thin-walled zone 13 at high speed, thereby achieving more stable filling of the internal space of the cavity 3.

[0055] Specifically, the switching positions between the first-level and second-level push, and between the second-level and third-level push, are determined by the stroke of the push rod 11 and the pressure sensor. The magnesium alloy semi-solid slurry is injected into the pressure chamber 6 through the feed port 10. The push rod 11 is pushed at the first-level push speed to allow the magnesium alloy semi-solid slurry to enter the gating system 5 along the pressure chamber 6 until it reaches the ingate 4, at which point the push is switched to the second-level push. The push rod 11 is pushed at the second-level push speed to allow the magnesium alloy semi-solid slurry at the ingate 4 to enter the cavity 3 until it is about to contact the corrugated tooth thin-walled area 13 inside the cavity 3, at which point the push is switched to the third-level push. The push rod 11 is pushed at the third-level push speed to allow the magnesium alloy semi-solid slurry to fill the entire cavity 3 from the corrugated tooth thin-walled area 13.

[0056] The switching of graded push is determined by the stroke of push rod 11, the effective cross-sectional area of ​​pressure chamber 6, the volume of each region inside cavity 3, and the signal from the pressure sensor; the effective cross-sectional area of ​​pressure chamber 6 is A, the displacement of push rod 11 is S, the effective filling coefficient of magnesium alloy semi-solid slurry is η, the equivalent volume of the pre-gating channel 5 entering the inner gate 4 is V0, and the equivalent volume of the region below the corrugated tooth thin-walled region 13 in cavity 3 is V1. Therefore, the effective pushing volume V of push rod 11 pushing the magnesium alloy semi-solid slurry into the gating channel 5 is:

[0057] V=η·A·S

[0058] The switching stroke between the first-level push and the second-level push, that is, during the process of pusher 11 pushing the magnesium alloy semi-solid slurry inside the gating channel 5 to the ingate 4, the first-level push stroke S1 of pusher 11 is:

[0059] S1=V0 / (η·A)

[0060] The switching stroke between the secondary and tertiary push stages, i.e., during the process of push rod 11 filling the area corresponding to the corrugated tooth thin-walled region 13 in cavity 3 with magnesium alloy semi-solid slurry inside the gating 5 through the ingate 4, the secondary push stroke S2 ​​of push rod 11 is as follows:

[0061] S2=(V0+V1) / (η·A)

[0062] The effective filling coefficient η of the magnesium alloy semi-solid slurry is used to correct the difference between the displacement volume of the pusher and the actual effective filling volume. η is a correction coefficient that comprehensively considers the gap between the pressure chamber 6 and the pusher 11, the retention volume of the ingate 4 and the runner 5, the compaction of the magnesium alloy semi-solid slurry, the cold material in the first stage, local flow loss, and the actual filling efficiency. The effective filling coefficient η is preferably 0.88 to 0.93. Specifically, in this embodiment, η is taken as 0.90. η can be determined and corrected by flow simulation or by the correspondence between the stroke of the pusher 11 and the actual filling volume. It should be noted that the volume of the pressure chamber 6 is larger than the internal volume of the cavity 3 to ensure the complete filling of the magnesium alloy semi-solid slurry inside the cavity 3.

[0063] S5. At the end of the cavity 3, where the semi-solid slurry of degraded magnesium alloy is filled, the gas is discharged through the venting groove 8, and the first section of cold material or inclusions enters the overflow groove 9 connected to the venting groove 8.

[0064] S6. After the cavity is filled with semi-solid slurry, it is immediately pressurized and held. After the pressure holding is completed, it is cooled until the slurry is completely solidified. The mold is opened and the part is removed to obtain the biodegradable magnesium alloy bridge plug key component. The biodegradable magnesium alloy bridge plug key component is a biodegradable magnesium alloy bridge plug arc-shaped petal component.

[0065] After the three-stage pushing is completed, the cavity 3 is filled with magnesium alloy semi-solid slurry, which is the state of completed filling. Therefore, after the three-stage pushing is completed, the bridge plug mold assembly is obtained, and the bridge plug mold assembly is pressurized and held at a pressure of 60-80 MPa for 3-10 seconds. After the pressurization and holding are completed, the bridge plug mold assembly is cooled for 8-20 seconds.

[0066] In the process of mold opening and part removal, the fixed mold 1 and the moving mold 2 are first separated to open the semi-solid injection molding mold. Then, the key component of the biodegradable magnesium alloy bridge plug is pushed out using the ejection mechanism. The ejection mechanism is a device that facilitates part removal and can safely and undamagedly eject the molded key component of the biodegradable magnesium alloy bridge plug from the cavity 3. The ejection mechanism is a commonly used device by those skilled in the art and is not specifically described in this application. The ejection force of the ejection mechanism acts on the area corresponding to the thick-walled transition zone 14 on the key component of the biodegradable magnesium alloy bridge plug, and is used in conjunction with the release agent to eject the key component of the biodegradable magnesium alloy bridge plug, so as to reduce the deformation risk of the corrugated tooth structure formed by the key component of the biodegradable magnesium alloy bridge plug after molding.

[0067] In this embodiment, biodegradable magnesium alloy is first melted, refined, and degassed under a protective atmosphere to prepare a semi-solid magnesium alloy slurry with a solid content of 25%–45%. The semi-solid magnesium alloy slurry is then quantitatively added to the pressure chamber 6 through the feeding port 10. A pusher rod 11 is used to push the semi-solid magnesium alloy slurry in the pressure chamber 6 in three stages. First, the pusher rod 11 is pushed at a first-stage pushing speed to push the semi-solid magnesium alloy slurry inside the pressure chamber 6 into the gating system 5, allowing it to fill the gating system 5 at a low speed. Then, the pusher rod 11 is pushed at a second-stage pushing speed, allowing the semi-solid magnesium alloy slurry in the gating system 5 to pass through the ingate 4 at a medium speed and stably enter the corrugated tooth thin mold cavity 3. In the lower region 31 of the wall area, since the ingate 4 is located below the corrugated tooth thin-walled region 13, the ingate 4 avoids the corrugated tooth thin-walled region 13, ensuring that the magnesium alloy semi-solid slurry preferentially fills the lower part of the corrugated tooth thin-walled region 13 inside the cavity 3 and gradually expands towards the corrugated tooth thin-walled region 13; finally, the push rod 11 is pushed at a three-stage pushing speed, so that the magnesium alloy semi-solid slurry completes the filling of the corrugated tooth thin-walled region 13 inside the cavity 3 and the end of the cavity 3 at a high speed; after the filling of the cavity 3 is completed, the bridge plug mold assembly is obtained. The bridge plug mold assembly is pressurized and held. After the magnesium alloy semi-solid slurry inside the cavity solidifies, the mold is opened and ejected to obtain the biodegradable magnesium alloy bridge plug key component.

[0068] On the other hand, the present invention also provides a biodegradable magnesium alloy bridge plug key component prepared by semi-solid injection molding. The biodegradable magnesium alloy bridge plug key component is prepared by the above-mentioned method of preparing a biodegradable magnesium alloy bridge plug key component by semi-solid injection molding. The biodegradable magnesium alloy bridge plug key component has an arc-shaped petal-shaped body, an outer surface corrugated tooth structure, and an inner conical inclined surface that matches the bridge plug cone. The biodegradable magnesium alloy bridge plug key component is applied to shale gas extraction and oil field extraction.

[0069] The cavity 3, which is composed of the first parting groove and the second parting groove, is used to prepare the arc-shaped petal-shaped body of the biodegradable magnesium alloy bridge plug key component. The corrugated tooth structure on the outer surface of the biodegradable magnesium alloy bridge plug key component is formed by the corrugated tooth thin-walled region 13, and the inner conical inclined surface of the biodegradable magnesium alloy bridge plug key component is formed by the thick-walled transition region 14.

[0070] Example 1

[0071] This embodiment is an experiment conducted entirely according to a method for preparing a biodegradable magnesium alloy bridge plug key component using semi-solid injection molding. The biodegradable bridge plug key component is prepared using Mg-Al based biodegradable magnesium alloy. A semi-solid injection molding scheme of external slurry preparation, quantitative feeding, and three-stage graded pushing by pusher 11 is adopted to obtain a biodegradable magnesium alloy bridge plug key component prepared by semi-solid injection molding.

[0072] A semi-solid injection molding mold specifically designed for key components of magnesium alloy bridge plugs is selected. After the fixed mold 1 and moving mold 2 of the semi-solid injection molding mold are closed, an arc-shaped petal-shaped cavity 3 is formed, which is consistent with the structure of the key component of magnesium alloy bridge plugs. An inner gate 4 is provided in the fixed mold 1. The inner gate 4 is located in the middle of the thick-walled transition zone 14 and is located below the corrugated tooth thin-walled zone 13. The inner gate 4 avoids the area corresponding to the corrugated tooth thin-walled zone 13 inside the cavity 3. An venting groove 8 is provided at the final filling point of the cavity 3, and an overflow groove 9 is provided along the outer periphery of the cavity 3. Both the venting groove 8 and the overflow groove 9 are opened at the parting surface 12 of the moving mold 2.

[0073] Specifically, magnesium alloy ingots are cut into easily meltable blocks and placed in a crucible furnace with a protective atmosphere for melting. The protective atmosphere is a mixture of nitrogen and carbon dioxide. The magnesium alloy is heated to 660°C and held for 15 minutes to fully melt it and obtain a magnesium alloy melt. Subsequently, slag removal and degassing are performed to remove oxide inclusions and gases from the magnesium alloy melt. After slag removal and degassing, the surface of the magnesium alloy melt is kept covered by the protective atmosphere to reduce secondary oxidation.

[0074] The magnesium alloy melt after slag and degassing is cooled to 585℃ and held for 4 minutes to allow it to enter the semi-solid zone. The solid phase ratio of the magnesium alloy semi-solid slurry is controlled at 35%. During this stage, the primary solid particles are uniformly distributed in the liquid phase by temperature control and holding in the crucible to obtain a magnesium alloy semi-solid slurry suitable for injection.

[0075] The semi-solid injection molding mold is preheated using a zoned independent temperature control preheating method. The complete moving mold 2 or fixed mold 1 is spatially divided into multiple independent temperature control preheating zones. The main body temperature of the fixed mold 1 and moving mold 2 in the semi-solid injection molding mold is set to 160~180℃. The corrugated tooth thin-walled area 13 in the moving mold 2 has its local temperature controlled at 250~280℃ through an independent heating circuit. The thick-walled transition area 14 and the inner gate 4 in the fixed mold 1 have their temperature controlled at 200℃ through an independent temperature control circuit. After the temperature of each temperature control preheating zone stabilizes, it is kept at that temperature for 20 minutes to ensure the reproducibility of the internal temperature of the cavity 3 and to prevent the magnesium alloy semi-solid slurry from losing temperature too early before entering the cavity 3.

[0076] The preheated semi-solid injection mold is closed and locked, and the cavity 3 is evacuated through the vacuum interface 7 and the venting groove 8 to control the absolute pressure in the cavity 3 to 45 mbar; the vacuum is maintained until the first stage push of the ejector 11 begins, in order to reduce the residual air content in the cavity 3 and the runner 5.

[0077] The magnesium alloy semi-solid slurry is transferred to the preheated 250°C pressure chamber 6 using a measuring spoon, with the amount added being 70%–85% of the effective volume of the pressure chamber 6. The pusher 11 is aligned with the rear end of the pressure chamber 6, and the magnesium alloy semi-solid slurry is pushed forward in a staged pushing procedure. The pushing speed of the first stage is set to 0.15 m / s to ensure smooth forward movement of the magnesium alloy semi-solid slurry and avoid surface rolling due to excessively high initial speed. The pushing speed of the second stage is set to 0.70 m / s. When the push rod 11 reaches the marked position near the ingate 4 at the leading edge of the magnesium alloy semi-solid slurry, it switches to the second-stage push, so that the magnesium alloy semi-solid slurry continuously passes through the ingate 4 and preferentially fills the area 31 below the corrugated tooth thin-walled area inside the cavity 3; the push speed of the third-stage push is set to 2.10m / s. When the push rod 11 reaches the marked position corresponding to the equivalent cavity volume of the area below the corrugated tooth thin-walled area 13, it switches to the third-stage push, so as to quickly fill the entire corrugated tooth thin-walled area 13 and the end of the cavity 3 at high speed.

[0078] In the three-stage pushing process, the magnesium alloy semi-solid slurry is pushed to the end of the cavity 3, where it is fully filled. Gas is discharged through the venting groove 8, and the first section of cold material or inclusions of the magnesium alloy semi-solid slurry enters the overflow groove 9 through the venting groove 8. After the three-stage pushing process, the bridge plug mold assembly is obtained. The bridge plug mold assembly is immediately pressurized with a pressure of 60 MPa and a holding time of 6 seconds. After the holding time, cooling continues for 12 seconds to completely solidify the magnesium alloy semi-solid slurry in the cavity 3. Since this embodiment uses a bottom-up stable filling method to fill the cavity 3, and the venting groove 8 and overflow groove 9 can promptly discharge the end gas and the first section of cold material of the magnesium alloy semi-solid slurry inside the cavity 3, the edge contour of the biodegradable magnesium alloy bridge plug key component is complete, and the tooth top and tooth root transition areas of the biodegradable magnesium alloy bridge plug key component are clearly formed.

[0079] After cooling, the mold is opened, and the ejection force of the ejection mechanism is applied to the area corresponding to the thick-walled transition zone 14 in the key component of the magnesium alloy bridge plug. Before ejection, release agent is sprayed on the corresponding part of the key component of the biodegradable magnesium alloy bridge plug. After the part is removed, the excess material at the ingate 4 and the solidified material at the overflow groove 9 are cut off, and the edges of the prepared key component of the biodegradable magnesium alloy bridge plug are slightly trimmed.

[0080] The preparation conditions, molding phenomena, and performance trends of the biodegradable magnesium alloy bridge plug prepared according to Example 1 are shown in Table 2:

[0081]

[0082] Comparative Example 1

[0083] This comparative example uses the same semi-solid injection molding mold structure as Example 1. The position of the ingate 4 inside the cavity 3 is the same. The arrangement of the venting groove 8 and the overflow groove 9 and the graded pushing method of the push rod are the same as in Example 1. However, the magnesium alloy semi-solid slurry is replaced with a completely liquid magnesium alloy melt for forming, in order to examine the differences between semi-solid injection molding and liquid die casting in the forming of key components of biodegradable magnesium alloy bridge plugs.

[0084] Comparative Example 1 uses a semi-solid injection molding die specifically designed for key components of magnesium alloy bridge plugs. This semi-solid injection molding die is identical to that used in Example 1. Magnesium alloy ingots are cut into easily meltable blocks and placed in a crucible furnace with a protective atmosphere for melting. The protective atmosphere is a mixture of nitrogen and carbon dioxide. The magnesium alloy is heated to 660°C and held for 15 minutes to fully melt it, resulting in a magnesium alloy melt. Subsequently, slag removal and degassing are performed to remove oxide inclusions and gases from the magnesium alloy melt. After slag removal and degassing, the surface of the magnesium alloy melt is kept under a protective atmosphere to reduce secondary oxidation. The slag- and degassed magnesium alloy melt is heated to 650–660°C under a protective atmosphere and held for 4–8 minutes to keep it completely liquid before being added to pressure chamber 6.

[0085] The semi-solid injection molding mold is preheated using a zoned independent temperature control preheating method. The complete moving mold 2 or fixed mold 1 is spatially divided into multiple independent temperature control preheating zones. The main body temperature of the fixed mold 1 and moving mold 2 in the semi-solid injection molding mold is set to 170℃, the temperature of the corrugated tooth thin-walled area 13 in the moving mold 2 is set to 265℃, the temperature of the thick-walled transition area 14 and the inner gate 4 in the fixed mold 1 is set to 200℃, and the temperature of the pressure chamber 6 is set to 250℃. After the temperature of each temperature control preheating zone stabilizes, it is kept at that temperature for 20 minutes to ensure the reproducibility of the internal temperature of the cavity 3 and to prevent the magnesium alloy melt from losing temperature too early before entering the cavity 3.

[0086] The preheated semi-solid injection mold is closed and locked, and the cavity 3 is evacuated through the vacuum interface 7 and the venting groove 8 to control the absolute pressure of the cavity 3 to 45mbar; the vacuum is maintained until the first stage push of the ejector 11 begins, in order to reduce the residual air content in the cavity 3 and the gating system 5.

[0087] The fully molten magnesium alloy was transferred to the pressure chamber 6, which was preheated to 250°C, using a measuring spoon. The pusher 11 was aligned with the rear end of the pressure chamber 6, and the fully molten magnesium alloy was pushed forward according to the same graded pushing procedure as in Example 1, thereby completing the filling of the cavity 3. After filling, the pressure was immediately increased to 60 MPa and held for 6 seconds. After holding the pressure, the cooling continued for 12 seconds to solidify the molten magnesium alloy in the cavity 3. Compared with Example 1, the fully molten magnesium alloy was prone to splashing and air entrapment in the pressure chamber 6, the gating system 5, and the corrugated tooth thin-walled area 13. During solidification, the tendency for shrinkage porosity, air bubbles, and segregation was higher. The root of the key component of the biodegradable magnesium alloy bridge plug and the area corresponding to the end of the cavity 3 were more prone to local defects.

[0088] After cooling, the mold is opened, and the ejection force of the ejection mechanism is applied to the area corresponding to the thick-walled transition zone 14 in the biodegradable magnesium alloy bridge plug key component. Before ejection, release agent is sprayed on the corresponding part of the biodegradable magnesium alloy bridge plug key component. After taking out the part, the excess material at the ingate 4 and the solidified material at the overflow groove 9 are removed, and the edges of the prepared biodegradable magnesium alloy bridge plug key component are slightly trimmed.

[0089] Comparative Example 2

[0090] This comparative example uses the same method as Example 1 for preparing the magnesium alloy semi-solid slurry, the vacuum conditions and holding pressure of the semi-solid injection molding mold, and the graded pushing of the magnesium alloy semi-solid slurry by the ejector 11. However, the ingate 4 is changed to be located in the upper or middle part of the fixed mold 1, so that the magnesium alloy semi-solid slurry is poured from the upper region 33 of the corrugated tooth thin-walled region in the cavity 3 or the region 32 corresponding to the corrugated tooth thin-walled region. This is to examine the necessity of pouring into the lower thick-walled transition region 14, that is, to determine the necessity of filling the magnesium alloy semi-solid slurry from the lower region 31 of the corrugated tooth thin-walled region in the cavity 3.

[0091] A semi-solid injection molding mold specifically for key components of magnesium alloy bridge plugs is selected. The semi-solid injection molding mold consists of a fixed mold 1 and a moving mold 2. After the mold is closed, an arc-shaped petal-shaped cavity 3 is formed that is consistent with the structure of the key component of magnesium alloy bridge plugs. Unlike Example 1, in this comparative example, the ingate 4 is changed to be located in the upper or middle part of the smooth wall area 16 in the fixed mold 1, so that the slurry no longer enters the cavity 3 from the thick wall transition area 14. The venting groove 8 is still set at the last filling point of the cavity 3, and an overflow groove 9 is set along the outer periphery of the cavity 3.

[0092] Specifically, magnesium alloy ingots are cut into easily meltable blocks and placed in a crucible furnace with a protective atmosphere for melting. The protective atmosphere is a mixture of nitrogen and carbon dioxide. The magnesium alloy is heated to 660°C and held for 15 minutes to fully melt it and obtain a magnesium alloy melt. Subsequently, slag removal and degassing are performed to remove oxide inclusions and gases from the magnesium alloy melt. After slag removal and degassing, the surface of the magnesium alloy melt is kept covered by the protective atmosphere to reduce secondary oxidation.

[0093] The magnesium alloy melt after slag and degassing is cooled to 585℃ and held for 4 minutes to allow it to enter the semi-solid zone. The solid phase ratio of the magnesium alloy semi-solid slurry is controlled at 35%. During this stage, the primary solid particles are uniformly distributed in the liquid phase by temperature control and holding in the crucible to obtain a magnesium alloy semi-solid slurry suitable for injection.

[0094] A zoned independent temperature control preheating method is adopted, which divides the complete moving mold 2 or fixed mold 1 into multiple independent temperature control preheating zones in space; the main body temperature of the fixed mold 1 and moving mold 2 in the semi-solid injection molding mold is set to 170℃, the temperature of the corrugated tooth thin-walled area 13 in the moving mold 2 is set to 265℃, the temperature of the thick-walled transition area 14 and the inner gate 4 in the fixed mold 1 is set to 200℃, and the temperature of the pressure chamber 6 is set to 250℃; after the temperature of each temperature control preheating zone stabilizes, it is kept at the temperature for 20 minutes to ensure the reproducibility of the internal temperature of the cavity 3 and to avoid premature temperature loss of the magnesium alloy semi-solid slurry before entering the cavity 3.

[0095] The preheated semi-solid injection mold is closed and locked, and the cavity 3 is evacuated through the vacuum interface 7 to control the absolute pressure in the cavity 3 to 45mbar; the vacuum is maintained until the first stage push of the push rod 11 begins, in order to reduce the residual air content in the cavity 3 and the runner 5.

[0096] By changing the position of the ingate 4, the magnesium alloy semi-solid slurry enters the cavity 3 from the upper region 33 of the corrugated tooth thin-walled region or the region 32 corresponding to the corrugated tooth thin-walled region, and no longer fills the cavity 3 from bottom to top along the axial direction of the cavity 3; the push rod 11 still operates according to the graded pushing in Example 1, but due to the change in the inlet position, the slurry front edge is prone to diversion, collision and local rollback when filling in the corrugated tooth thin-walled region 13, and the sequential filling relationship between the region below the corrugated tooth thin-walled region 13 and the corrugated tooth thin-walled region 13 is disrupted.

[0097] Magnesium alloy semi-solid slurry is transferred to pressure chamber 6, which is preheated to 250°C, using a metering spoon. The amount added is 70% to 85% of the effective volume of pressure chamber 6. The pusher 11 is aligned with the rear end of pressure chamber 6, and the magnesium alloy semi-solid slurry in pressure chamber 6 is pushed forward using the same graded pushing procedure as in Example 1, thereby completing the filling of cavity 3. Immediately after the graded pushing is completed, pressurization is performed. The pressurization pressure is set to 60 MPa, and the holding time is 6 seconds. After the holding time is completed, cooling is continued for 12 seconds to solidify the magnesium alloy semi-solid slurry in cavity 3. Compared with Example 1, the magnesium alloy semi-solid slurry is poured from the area 33 above the corrugated tooth thin-walled area in cavity 3 or the area 32 corresponding to the corrugated tooth thin-walled area, making the end venting path and cold material discharge path of cavity 3 unstable. The biodegradable magnesium alloy bridge plug key components prepared are more prone to cold shuts, undercasting, insufficient tooth root filling, or dimensional fluctuations in the area corresponding to the corrugated tooth thin-walled area 13.

[0098] After cooling, the mold is opened, and the ejection force of the ejection mechanism is applied to the area corresponding to the thick-walled transition zone 14 in the biodegradable magnesium alloy bridge plug key component. Before ejection, release agent is sprayed on the corresponding part of the biodegradable magnesium alloy bridge plug key component. After taking out the part, the excess material at the ingate 4 and the solidified material at the overflow groove 9 are removed, and the edges of the prepared biodegradable magnesium alloy bridge plug key component are slightly trimmed.

[0099] Comparative Example 3

[0100] This comparative example uses the same magnesium alloy semi-solid slurry state, the position of the inner gate in the semi-solid injection molding mold, the vacuum conditions, and the graded pushing procedure of the ejector 11 as in Example 1. However, the overflow groove 9 is removed, and the venting groove 8 is only retained at the last full position of the cavity 3 to examine the necessity of the venting groove 8 and the overflow groove 9 being set together.

[0101] A semi-solid injection molding mold specifically designed for key components of magnesium alloy bridge plugs is selected. After the fixed mold 1 and moving mold 2 of the semi-solid injection molding mold are closed, an arc-shaped petal-shaped cavity 3 is formed, which is consistent with the structure of the key component of magnesium alloy bridge plugs. An inner gate 4 is provided in the fixed mold 1. The inner gate 4 is located in the middle of the thick-walled transition zone 14 and is located below the corrugated tooth thin-walled zone 13. The inner gate 4 avoids the area corresponding to the corrugated tooth thin-walled zone 13 inside the cavity 3. An venting groove 8 is provided at the final filling point of the cavity 3, and the overflow groove 9 on the outer periphery of the cavity 3 is eliminated.

[0102] Specifically, the magnesium alloy ingot is cut into easily meltable blocks and placed in a crucible furnace with a protective atmosphere for melting. The protective atmosphere is a mixture of nitrogen and carbon dioxide. The magnesium alloy is heated to 660°C and held for 15 minutes to fully melt it. Then, slag removal and degassing are performed to remove oxide inclusions and gases from the melt. After slag removal and degassing, the surface of the magnesium alloy melt is kept covered by the protective atmosphere to reduce secondary oxidation.

[0103] The magnesium alloy melt after slag and degassing is cooled to 585℃ and held for 4 minutes to allow it to enter the semi-solid zone. The solid phase ratio of the magnesium alloy semi-solid slurry is controlled to be about 35%. During this stage, the primary solid particles are evenly distributed in the liquid phase by temperature control and holding in the crucible to obtain a magnesium alloy semi-solid slurry suitable for injection.

[0104] A zoned independent temperature control preheating method is adopted, which divides the complete moving mold 2 or fixed mold 1 into multiple independent temperature control preheating zones in space; the main body temperature of the fixed mold 1 and moving mold 2 in the semi-solid injection molding mold is set to 170℃, the temperature of the corrugated tooth thin-walled area 13 in the moving mold 2 is set to 265℃, the temperature of the thick-walled transition area 14 and the inner gate 4 in the fixed mold 1 is set to 200℃, and the temperature of the pressure chamber 6 is set to 250℃; after the temperature of each temperature control preheating zone stabilizes, it is kept at the temperature for 20 minutes to ensure that the cavity temperature field is repeatable and to avoid premature temperature loss of the magnesium alloy semi-solid slurry before entering the cavity 3.

[0105] The preheated semi-solid injection mold is closed and locked, and the cavity 3 is evacuated through the vacuum interface 7 to control the absolute pressure in the cavity 3 to 45mbar; the vacuum is maintained until the first stage push of the push rod 11 begins, in order to reduce the residual air content in the cavity 3 and the runner 5.

[0106] Subsequently, the magnesium alloy semi-solid slurry was transferred to the pressure chamber 6, which was preheated to 250°C, using a measuring spoon. The amount added was 70% to 85% of the effective volume of the pressure chamber 6. The pusher 11 was aligned with the rear end of the pressure chamber 6, and the magnesium alloy semi-solid slurry in the pressure chamber 6 was pushed forward according to the same graded pushing procedure as in Example 1, thereby completing the filling of the cavity 3. Immediately after the graded pushing was completed, the pressure was increased to 60 MPa and the holding time was 6 seconds. After the holding time was completed, the slurry was cooled for another 12 seconds to solidify the magnesium alloy semi-solid slurry in the cavity 3. Since the overflow groove 9 was eliminated, although some gas could be discharged through the venting groove 8 at the end of the cavity 3, the first section of cold material, oxide inclusions and a small amount of heat loss slurry of the magnesium alloy semi-solid slurry lacked a space to accommodate them. They were prone to stagnation at the end of the prepared biodegradable magnesium alloy bridge plug key component or near the venting groove 8, resulting in an increase in local inclusions, shrinkage porosity or edge defects.

[0107] After cooling, the mold is opened, and the ejection force of the ejection mechanism is applied to the area corresponding to the thick-walled transition zone 14 in the biodegradable magnesium alloy bridge plug key component. Before ejection, release agent is sprayed on the corresponding part of the biodegradable magnesium alloy bridge plug key component. After taking out the part, the excess material at the ingate 4 is cut off, and the edge of the prepared biodegradable magnesium alloy bridge plug key component is slightly trimmed.

[0108] Comparative Example 4

[0109] This comparative example uses the same method for preparing magnesium alloy semi-solid slurry, structure of semi-solid injection molding mold, position of inner gate 4 on fixed mold 1, and setting of venting groove 8 and overflow groove 9 as in Example 1. However, the step-by-step pushing procedure of push rod 11 is cancelled and replaced with single-stage constant speed pushing to examine the effect of step-by-step pushing on the forming stability of key components of biodegradable magnesium alloy bridge plug.

[0110] Comparative Example 4 uses a semi-solid injection molding die specifically designed for key components of magnesium alloy bridge plugs. This semi-solid injection molding die is identical to that used in Example 1. Magnesium alloy ingots are cut into easily meltable blocks and placed in a crucible furnace with a protective atmosphere for melting. The protective atmosphere is a mixture of nitrogen and carbon dioxide. The magnesium alloy is heated to 660°C and held for 15 minutes to ensure complete melting. Subsequently, slag removal and degassing are performed to remove oxide inclusions and gases from the melt. After slag removal and degassing, the surface of the melt is kept covered by the protective atmosphere to reduce secondary oxidation. The magnesium alloy melt after slag removal and degassing is cooled to 585°C and held for 4 minutes to allow the magnesium alloy melt to enter the semi-solid region. The solid phase ratio of the magnesium alloy semi-solid slurry is controlled to be approximately 35%. During this stage, temperature control and holding within the crucible are used to ensure uniform distribution of primary solid particles in the liquid phase, resulting in a magnesium alloy semi-solid slurry suitable for injection.

[0111] A zoned independent temperature control preheating method is adopted, which divides the complete moving mold 2 or fixed mold 1 into multiple independent temperature control preheating zones in space; the main body temperature of the fixed mold 1 and moving mold 2 in the semi-solid injection molding mold is set to 230℃, the temperature of the corrugated tooth thin-walled area 13 in the moving mold 2 is set to 265℃, and the temperature of the thick-walled transition area 14 and the inner gate 4 in the fixed mold 1 is set to 205℃; after the temperature of each temperature control preheating zone stabilizes, it is kept at the temperature for 20 minutes to ensure the reproducibility of the internal temperature of the cavity 3 and to avoid premature temperature loss of the magnesium alloy semi-solid slurry before entering the cavity 3.

[0112] The preheated semi-solid injection mold is closed and locked, and the cavity 3 is evacuated through the vacuum interface 7 to control the vacuum level inside the cavity 3 at 45 mbar; the vacuum is maintained until the first stage push of the push rod 11 begins, in order to reduce the residual air content in the cavity 3 and the runner 5.

[0113] Subsequently, the magnesium alloy semi-solid slurry was transferred to the pressure chamber 6, which was preheated to 250°C, using a metering spoon. The amount added was 70% to 85% of the effective volume of the pressure chamber. After the magnesium alloy semi-solid slurry was added to the pressure chamber 6, the pusher 11 pushed the slurry forward at a constant speed of 1.80 m / s throughout. Immediately after the single-stage push of the pusher 11, the pressure was increased to 60 MPa and the holding time was 6 s. After the holding time was completed, the slurry was cooled for another 12 s to solidify the magnesium alloy semi-solid slurry in the cavity 3. Compared with Example 1, the single-stage constant speed push could not simultaneously meet the low air entrapment requirements of the pressure chamber 6 and the area below the corrugated tooth thin-walled area 13 in the cavity 3, as well as the rapid filling requirements of the corrugated tooth thin-walled area 13. If the constant speed was too high, front-end rollover and air entrapment were likely to occur at the beginning stage of filling the cavity 3. If the constant speed was too low, the corrugated tooth thin-walled area 13 was likely to be underfilled or cold shut.

[0114] After cooling, the mold is opened, and the ejection force of the ejection mechanism is applied to the area corresponding to the thick-walled transition zone 14 in the biodegradable magnesium alloy bridge plug key component. Before ejection, release agent is sprayed on the corresponding part of the biodegradable magnesium alloy bridge plug key component. After taking out the part, the excess material at the ingate 4 and the solidified material at the overflow groove 9 are removed, and the edges of the prepared biodegradable magnesium alloy bridge plug key component are slightly trimmed.

[0115] In summary, as can be seen from Examples 1, 1, 2, 3, and 4, for complex irregularly shaped parts such as biodegradable magnesium alloy bridge plug key components, which have thick walls at the bottom and thin walls at the top, the combination of using magnesium alloy semi-solid slurry, pouring from the area 31 below the thin-walled corrugated tooth region, using venting grooves 8 and overflow grooves 9 at the end of the cavity 3 to treat the gas inside the cavity 3 and the first section of cold material or inclusions in the magnesium alloy semi-solid slurry, and using push rods 11 to push the magnesium alloy semi-solid slurry in stages, is more conducive to forming a stable bottom-up sequential filling path in terms of process mechanism. To further illustrate the effect of the present invention compared to the single-condition change scheme, the biodegradable magnesium alloy bridge plug key components obtained in Comparative Examples 1 to 4 can be compared and evaluated with the biodegradable magnesium alloy bridge plug key components prepared in Example 1 in terms of appearance integrity, corrugated tooth filling integrity, sectional pore defects, end cold material inclusions, dimensional consistency, and simulated setting and bearing stability. The comparison and evaluation results are shown in Table 3.

[0116]

[0117] Therefore, this invention does not rely solely on single parameter optimization, but rather reduces the probability of defects such as cold shuts, undercasting, air entrapment, shrinkage porosity, and inclusions during the preparation of key components of biodegradable magnesium alloy bridge plugs by synergistic matching between material state, injection position, structure of venting groove and overflow groove at the end of the cavity, and pusher pushing speed. This improves the one-time forming integrity, microstructure density, and service reliability of key components of biodegradable magnesium alloy bridge plugs.

[0118] Finally, it should be noted that the above description is only a preferred embodiment of the present invention and is not intended to limit the present invention. Although the present invention has been described in detail with reference to the foregoing embodiments, those skilled in the art can still modify the technical solutions described in the foregoing embodiments or make equivalent substitutions for some of the technical features. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the present invention should be included within the protection scope of the present invention.

Claims

1. A method for preparing a biodegradable magnesium alloy bridge plug key component using semi-solid injection molding, characterized in that, Includes the following steps: S1. Prepare a semi-solid injection molding mold; the semi-solid injection molding mold includes a moving mold and a fixed mold. After the moving mold and the fixed mold are closed, a cavity matching the shape of the key component of the magnesium alloy bridge plug is formed. The key component of the magnesium alloy bridge plug is an arc-shaped petal component of the magnesium alloy bridge plug; the fixed mold is provided with a pressure chamber, a sprue and an ingate. The pressure chamber is connected to the cavity in sequence through the sprue and the ingate. The moving mold is provided with an venting groove and an overflow groove. The venting groove and the overflow groove are connected to each other and the venting groove is connected to the cavity. S2. A semi-solid magnesium alloy slurry is prepared using a biodegradable magnesium alloy, and the semi-solid magnesium alloy slurry is quantitatively added to the pressure chamber of a fixed mold. The solid content of the semi-solid magnesium alloy slurry is 25% to 45%. S3. Preheat the moving mold and the fixed mold and close the mold. Before filling, perform vacuum-assisted evacuation of the cavity. S4. The magnesium alloy semi-solid slurry in the pressure chamber is pushed in stages by push rods, so that the magnesium alloy semi-solid slurry enters the cavity through the gating system and the ingate in sequence, and fills the cavity from bottom to top in the axial direction along the shape of the key component of the magnesium alloy bridge plug. S5. At the end of the cavity, where the magnesium alloy semi-solid slurry is filled, the gas is discharged through the venting groove, and the first section of cold material or inclusions enters the overflow groove connected to the venting groove. S6. After the cavity is filled with semi-solid slurry, it is immediately pressurized and held. After the pressure holding is completed, it is cooled until the slurry is completely solidified. The mold is opened and the part is removed to obtain the biodegradable magnesium alloy bridge plug key component.

2. The method for preparing a biodegradable magnesium alloy bridge plug key component by semi-solid injection molding according to claim 1, characterized in that, In step S1, both the moving mold and the fixed mold have parting surfaces. A first parting groove is provided on the parting surface of the moving mold, and a second parting groove is provided on the parting surface of the fixed mold. When the moving mold and the fixed mold are closed, the first parting groove and the second parting groove together form a cavity that matches the shape of the key component of the magnesium alloy bridge plug. The first parting groove includes a non-smooth wall area, and an overflow groove is formed along the outer periphery of the non-smooth wall area. A corrugated thin-walled area is formed in the middle of the non-smooth wall area, and the internal area of ​​the cavity is divided into the lower area of ​​the corrugated thin-walled area, the area corresponding to the corrugated thin-walled area, and the upper area of ​​the corrugated thin-walled area according to the corrugated thin-walled area. An exhaust groove is formed on the moving mold, and the overflow groove is connected to the first parting groove through the exhaust groove. The top of the overflow groove forms a vacuum interface on the upper surface of the moving mold. The second parting groove includes a thick-walled transition zone and a smooth-walled zone from bottom to top, with the thick-walled transition zone being inclined; a sprue is provided through the fixed mold, with one end of the sprue forming an ingate in the middle of the thick-walled transition zone, and the ingate being located below the corrugated tooth thin-walled zone; when filling the cavity with magnesium alloy semi-solid slurry, the magnesium alloy semi-solid slurry preferentially fills the area below the corrugated tooth thin-walled zone inside the cavity, and gradually expands towards the corrugated tooth thin-walled zone until it fills the entire cavity; One side of the fixed mold is connected to a pressure chamber, which is connected to the gating system. One end of the pressure chamber is connected to a feeding port and a push rod. The feeding port is connected to the side wall of the pressure chamber. Magnesium alloy semi-solid slurry is filled into the pressure chamber through the feeding port. The push rod is placed inside the pressure chamber. Pushing the push rod pushes the magnesium alloy semi-solid slurry in the pressure chamber through the gating system and the ingate into the cavity.

3. The method for preparing a biodegradable magnesium alloy bridge plug key component by semi-solid injection molding according to claim 1, characterized in that, In step S2, the biodegradable magnesium alloy is a Mg-Al biodegradable magnesium alloy.

4. The method for preparing a biodegradable magnesium alloy bridge plug key component by semi-solid injection molding according to claim 3, characterized in that, The magnesium alloy semi-solid slurry is prepared by melting and refining the magnesium alloy under a protective atmosphere to remove slag and gas, and then cooling the molten magnesium alloy to the semi-solid range and holding it at that temperature to form a magnesium alloy semi-solid slurry with uniformly distributed primary solid particles. The holding temperature range for preparing the magnesium alloy semi-solid slurry is controlled at 560-660℃, and the solid phase content is 25%-45%.

5. The method for preparing a biodegradable magnesium alloy bridge plug key component by semi-solid injection molding according to claim 1, characterized in that, In step S3, both the moving mold and the fixed mold in the semi-solid injection molding mold adopt zoned independent temperature control preheating. The main body temperature of the moving mold and the fixed mold is set to 160-180℃, and the local temperature of the corrugated thin-walled area in the moving mold is controlled to 250-280℃. The local temperature of the lower part of the non-smooth wall area in the moving mold and the local temperature of the thick-walled transition area in the fixed mold are both controlled to 180-220℃. Before filling, the vacuum degree of the cavity is 30-70mbar.

6. The method for preparing a biodegradable magnesium alloy bridge plug key component by semi-solid injection molding according to claim 1, characterized in that, In step S4, the graded pushing includes primary pushing, secondary pushing, and tertiary pushing. Primary pushing is a low-speed pushing at a pushing speed of 0.05~0.30m / s, used to smoothly move the magnesium alloy semi-solid slurry forward to fill the front end of the pressure chamber and enter the interior of the runner. Secondary pushing is a medium-speed pushing at a pushing speed of 0.30~1.20m / s, used to allow the magnesium alloy semi-solid slurry inside the runner to enter the cavity through the ingate and fill the area below the corrugated tooth thin-walled area inside the cavity. Tertiary pushing is a high-speed pushing at a pushing speed of 1.20~3.00m / s, used to complete the filling of the corrugated tooth thin-walled area and the end of the cavity. After the tertiary pushing is completed, the cavity is filled with magnesium alloy semi-solid slurry, resulting in a bridge plug mold assembly. The bridge plug mold assembly is then pressurized and held at a pressure of 60~80MPa for 3~10s. After the pressurization and holding are completed, the bridge plug mold assembly is cooled for 8~20s.

7. The method for preparing a biodegradable magnesium alloy bridge plug key component by semi-solid injection molding according to claim 6, characterized in that, The switching positions between primary and secondary push, and between secondary and tertiary push, are determined by the stroke of the push rod and pressure sensors. Specifically, the magnesium alloy semi-solid slurry is injected into the pressure chamber through the feed port. The push rod is propelled at the primary push speed to allow the magnesium alloy semi-solid slurry to enter the gating system along the pressure chamber until it reaches the ingate, at which point it switches to secondary push. The push rod is then propelled at the secondary push speed to allow the magnesium alloy semi-solid slurry at the ingate to enter the cavity until it is about to contact the corrugated tooth thin-walled area, at which point it switches to tertiary push. The push rod is then propelled at the tertiary push speed to allow the magnesium alloy semi-solid slurry to fill the entire cavity, starting from the corrugated tooth thin-walled area.

8. The method for preparing a biodegradable magnesium alloy bridge plug key component by semi-solid injection molding according to claim 1, characterized in that, In step S6, during mold opening and part removal, the fixed mold and the moving mold are first separated to open the semi-solid injection molding mold. Then, the degradable magnesium alloy bridge plug key component is ejected using the ejection mechanism. The ejection force of the ejection mechanism acts on the area corresponding to the thick-walled transition zone of the degradable magnesium alloy bridge plug key component, and is combined with a mold release agent to eject the degradable magnesium alloy bridge plug key component, thereby reducing the deformation risk of the corrugated tooth structure formed by the degradable magnesium alloy bridge plug key component after molding.

9. A key component of a biodegradable magnesium alloy bridge plug prepared by semi-solid injection molding, characterized in that, The biodegradable magnesium alloy bridge plug key component is prepared by any one of claims 1 to 8 using a semi-solid injection molding method. The biodegradable magnesium alloy bridge plug key component has an arc-shaped petal-shaped body, an outer surface corrugated tooth structure, and an inner conical inclined surface that matches the bridge plug cone. The biodegradable magnesium alloy bridge plug key component is applied to shale gas extraction and oil field extraction.

Images