A method of using a riser for titanium alloy countergravity investment casting

Abstract

The application provides a use method of a liquid lifting pipe for titanium alloy counter-gravity investment casting, and belongs to the technical field of titanium alloy casting, and solves the problems that the liquid lifting pipe for titanium alloy counter-gravity investment casting needs to be resistant to high temperature and to avoid reaction with titanium melt. In the use method of the liquid lifting pipe, the influence degree of the wall thickness of the liquid lifting pipe, the inner diameter of the liquid lifting pipe and the preheating temperature of the liquid lifting pipe on the melting time of the liquid lifting pipe is analyzed through theoretical calculation, and then the liquid lifting pipe parameter selection specification is obtained; the wall thickness of the liquid lifting pipe, the inner diameter of the liquid lifting pipe and the preheating temperature of the liquid lifting pipe for casting are selected according to the liquid lifting pipe parameter selection specification; after the material in the water-cooled copper crucible is completely melted, the casting mold is started to be lowered, the preheated liquid lifting pipe is inserted into the solution in the water-cooled copper crucible, the counter-gravity filling is carried out by adopting the linkage operation of the casting mold lowering and the filling, and the cleanliness of the melt can be ensured, and the yield of titanium alloy counter-gravity casting can be ensured.

Description

Technical Field

[0001] This invention belongs to the field of titanium alloy casting technology, and in particular relates to a method for using a riser pipe in anti-gravity investment casting of titanium alloys. Background Technology

[0002] Anti-gravity casting (mainly including low-pressure casting, differential pressure casting, pressure regulating casting, and vacuum casting) operates on the principle that molten metal, under external pressure, overcomes gravity and fills the mold cavity against gravity along a liquid guide pipe (also known as a riser pipe). This filling process indicates that anti-gravity casting typically employs a bottom-pouring gating system, where the molten metal fills the cavity from bottom to top. This avoids the "roller coaster" flow phenomenon during filling, thus reducing casting defects such as air entrapment, oxide film entrapment, and slag inclusions. Furthermore, anti-gravity casting offers numerous advantages, including controllable filling speed, stable filling, dense microstructure, and extremely high casting precision. This allows it to overcome many casting defects encountered in traditional gravity casting and tilting casting methods when producing complex thin-walled parts, such as incomplete filling, missing material, and cold shuts. Therefore, as large and complex structural components in aerospace and other industries develop towards lightweight, precision, and mass production, anti-gravity casting technology is playing an increasingly irreplaceable role in the production of thin-walled complex structural components.

[0003] The success of anti-gravity casting hinges on the reliability of the riser pipe throughout the filling process. As the channel connecting the molten metal in the crucible to the mold, the riser pipe's performance directly impacts the stability of the molten metal filling and the final quality of the casting. See patent application CN202510726950.0 for a description of an anti-gravity investment casting apparatus and method for titanium alloys. In this process, the lower end of the riser pipe is inserted into the molten metal. Under external gas pressure, the molten metal is guided into the mold cavity. The riser pipe serves to transport the molten metal, prevent gas from seeping through the pipe wall and causing air entrapment in the casting, and maintain the pressure required by the pressure head. This process demands that the riser pipe meet numerous stringent performance requirements, including excellent high-temperature strength, resistance to melt erosion (even without reacting with the melt), good thermal shock resistance, and excellent sealing performance.

[0004] Currently, for low-melting-point lightweight aluminum-magnesium alloys, riser tube materials and application methods are mature and widely used in production. For high-melting-point alloys such as copper alloys, nickel-based high-temperature alloys, and cast iron and cast steel, China has also made breakthroughs in riser tube materials and manufacturing technologies.

[0005] However, the requirements are even more stringent for anti-gravity investment casting of titanium alloys. Firstly, because titanium alloys have a melting point as high as 1600-1700℃, and molten titanium has extremely high chemical reactivity, reacting with almost all refractory materials, the riser tubes used must overcome the challenges of high-temperature resistance and reaction with the molten titanium. Secondly, during mold filling, the lower end of the riser tube needs to be completely immersed in the high-temperature molten titanium, while the upper end connects to the relatively cooler mold shell. The significant temperature difference between the riser tube and the molten titanium, as well as the large axial temperature gradient, will generate significant thermal stress inside the riser tube. This necessitates that the riser tube possess extremely excellent thermal shock resistance to prevent cracking. Due to these challenges, research on anti-gravity casting technology for titanium alloys is currently almost nonexistent, and a breakthrough is urgently needed. Summary of the Invention

[0006] In view of this, in order to solve the problem that the riser pipe used in anti-gravity investment casting of titanium alloys needs to be resistant to high temperature and also avoid reaction with the titanium melt, this invention proposes a method for using a riser pipe in anti-gravity investment casting of titanium alloys.

[0007] To achieve the above objectives, the present invention adopts the following technical solution:

[0008] A method for using a riser pipe in anti-gravity investment casting of titanium alloys, wherein the riser pipe is located above a water-cooled copper crucible and below the gating inlet of the mold shell, and the riser pipe is made of the same material as the molten material in the water-cooled copper crucible.

[0009] The method of using the riser pipe for anti-gravity investment casting of titanium alloys includes:

[0010] Through theoretical calculations, the influence of riser wall thickness, riser inner diameter, and riser preheating temperature on riser melting time is analyzed, and thus riser parameter selection specifications are obtained.

[0011] According to the selection specifications for riser parameters, the wall thickness, inner diameter, and preheating temperature of the riser used for casting are selected.

[0012] After the material in the water-cooled copper crucible has completely melted, the mold begins to descend. The preheated riser tube is inserted into the melt in the water-cooled copper crucible. The mold descent and filling are linked to perform anti-gravity filling.

[0013] The theoretical calculations analyzed the influence of riser wall thickness, riser inner diameter, and riser preheating temperature on the melting time of the riser, including:

[0014] Calculate the heat absorbed by the riser tube and the convective heat flow in the four stages: the first solid sensible heat, the latent heat of phase change, the second solid sensible heat, and the latent heat of fusion.

[0015] Calculate the induction heating power P of the riser tube inserted into the melt based on the melting power, melt mass, and mass of the riser tube inserted into the melt. ind ;

[0016] Based on the heat absorbed by the riser tube and the convective heat flux in the four stages of the first solid sensible heat, the latent heat of phase change, the second solid sensible heat, and the latent heat of fusion, as well as the induction heating power P of the riser tube inserted into the melt, ind Calculate the total melting time of the riser tube inserted into the molten section. ;

[0017] By selecting multiple riser wall thicknesses, multiple riser inner diameters, and multiple riser preheating temperatures, the total melting time of the riser tube inserted into the melt is calculated for any riser wall thickness, any riser inner diameter, and any riser preheating temperature, thus obtaining the timetable of riser tube melting caused by different influencing factors.

[0018] Based on the timeline of riser tube melting caused by different influencing factors, the influence of riser tube wall thickness, riser tube inner diameter, and riser tube preheating temperature on the melting time of the riser tube is analyzed.

[0019] As a preferred embodiment of the above-mentioned method of using the riser tube for anti-gravity investment casting of titanium alloys, the length of the riser tube for anti-gravity investment casting of titanium alloys is within 500 mm.

[0020] As a preferred embodiment of the above-mentioned method of using the riser tube for anti-gravity investment casting of titanium alloys, the wall thickness of the casting produced by anti-gravity investment casting is 1~3 mm.

[0021] As a preferred embodiment of the above-mentioned method of using the riser pipe for anti-gravity investment casting of titanium alloys, the mold descent and filling linkage operation includes: using the mold descent signal as the automatic filling start signal, and immediately starting to inject inert gas into the lower working tank for filling after the mold descent is in place.

[0022] As a preferred embodiment of the above-mentioned method of using the riser pipe for anti-gravity investment casting of titanium alloys, the parameter selection specifications for the riser pipe include:

[0023] Prioritize controlling the riser tube wall thickness to adjust the riser tube melting time;

[0024] Based on the casting process design and the actual preheating temperature limit of the production equipment, the preheating temperature of the riser pipe is selected.

[0025] The effect of changes in the inner diameter of the riser tube on the melting time of the riser tube is negligible. The inner diameter of the riser tube is selected according to the casting process design requirements.

[0026] As a preferred embodiment of the above-mentioned method of using the riser pipe for anti-gravity investment casting of titanium alloys, the formula is: Calculate the heat absorbed by the riser tube during the first solid-state sensible heating stage; where m is the mass of the lower end of the riser tube inserted into the melt, in kg; T0 is the specific heat capacity of the material being smelted in the water-cooled copper crucible, J / kg•℃; T0 is the preheating temperature of the riser pipe, ℃; T0 is the temperature of the material being smelted in the water-cooled copper crucible. β The phase transition temperature is given in °C.

[0027] Through the formula: Calculate the heat absorbed by the riser tube during the latent heat stage of phase change; where J; The latent heat of phase transition in solid state is expressed in kJ / kg.

[0028] Through the formula: Calculate the heat absorbed by the riser tube during the second solid-state sensible heating stage; among which, The melting temperature is ℃;

[0029] Through the formula: Calculate the heat absorbed by the riser tube during the latent heat of melting stage; among which, The value represents the latent heat of fusion, in kJ / kg.

[0030] As a preferred embodiment of the above-mentioned method of using the riser pipe for anti-gravity investment casting of titanium alloys, the formula is: Calculate the convective heat flux of the riser tube in the first solid-state sensible heat stage; where h is the convective heat transfer coefficient. A is the sum of the inner and outer surface areas of the portion of the riser tube inserted into the melt, m 2 ; ; The melt temperature is ℃;

[0031] Through the formula: Calculate the convective heat flux of the riser tube during the latent heat stage of phase change; among which, ;

[0032] Through the formula: Calculate the convective heat flux of the riser tube during the second solid-state sensible heating stage; where, ;

[0033] Through the formula: Calculate the convective heat flux of the riser tube during the latent heat of melting stage; where, .

[0034] As a preferred embodiment of the above-mentioned method of using the riser tube for anti-gravity investment casting of titanium alloys, the riser tube absorbs heat and convective heat flow in four stages: first solid sensible heat, latent heat of phase change, second solid sensible heat, and latent heat of fusion, as well as the induction heating power P of the riser tube inserted into the melt. ind Calculate the total melting time of the riser tube inserted into the molten section. include:

[0035] Through the formula: Calculate the total melting time of the riser tube inserted into the molten section; where, ; ; ; .

[0036] Compared with the prior art, the beneficial effects of the riser pipe for anti-gravity investment casting of titanium alloys and its usage method provided by the present invention are as follows:

[0037] (1) Selecting a riser pipe made of the same material as the titanium melt smelted in a water-cooled copper crucible ensures that the melt is clean and does not cause any contamination.

[0038] (2) The theoretical calculations have explained the weight of the factors affecting the melting time of the riser tube in anti-gravity casting of titanium alloys, and proposed the selection specifications for riser tube parameters, which has clear guiding significance for casting process design.

[0039] (3) It specifically points out the application scenarios of titanium alloy riser pipes for anti-gravity casting of titanium alloys, including riser pipe length, operation linkage and appropriate casting wall thickness, which ensures the yield of titanium alloy anti-gravity casting. Attached Figure Description

[0040] The accompanying drawings, which form part of this invention, are used to provide a further understanding of the invention. The illustrative embodiments of the invention and their descriptions are used to explain the invention and do not constitute an undue limitation of the invention. In the drawings:

[0041] Figure 1 This is a schematic diagram of the riser pipe for anti-gravity investment casting of titanium alloys provided in a specific embodiment of the present invention;

[0042] Figure 2 A photograph of the riser tube taken after the filling process is completed;

[0043] Figure 3 Photos of the sandbox taken after the molding process is completed;

[0044] Figure 4 This is a photo of the mold shell filled during the removal of the sandbox. Detailed Implementation

[0045] The technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. It should be noted that, unless otherwise specified, the embodiments and features in the embodiments of the present invention can be combined with each other, and the described embodiments are only some embodiments of the present invention, not all embodiments.

[0046] like Figure 1 This is a schematic diagram of the riser tube used in anti-gravity investment casting of titanium alloys. The riser tube is located above the water-cooled copper crucible and below the gating inlet of the mold shell. The riser tube is made of the same material as the material being smelted inside the water-cooled copper crucible.

[0047] Because titanium alloys are highly reactive in the molten state and can react with almost all existing refractory materials, the riser tube is made of the same material as the molten material in the water-cooled copper crucible. In other words, the riser tube is made of titanium alloy. This fundamentally avoids contamination of the titanium alloy melt in the water-cooled copper crucible, ensuring the cleanliness of the melt and thus guaranteeing the high metallurgical quality of the casting.

[0048] The rationale for choosing a riser tube made of the same material as the material being smelted in the water-cooled copper crucible is that titanium alloys undergo multiple processes before melting, including sensible heat in the solid state, latent heat of phase transformation, and latent heat of fusion. This requires continuous heating of the titanium alloy riser tube until it melts completely. Therefore, the anti-gravity filling of the titanium alloy can be completed during the time before the riser tube completely melts. Thus, the time from insertion of the riser tube to its melting must be clearly defined. The filling operation must be completed before the riser tube melts; otherwise, if the filling is not completed after the riser tube melts, the filling process will be considered a failure.

[0049] A riser pipe made of the same material as the material being smelted in the water-cooled copper crucible is machined. After the flange is threadedly connected to the riser pipe, welding and root cleaning are performed to ensure a tight seal. It can then be assembled into the anti-gravity investment casting apparatus. The structure of this riser pipe for anti-gravity investment casting of titanium alloys, as well as its installation position and connection relationship in the anti-gravity investment casting apparatus, are identical to those disclosed in patent application CN202510726950.0, which discloses an anti-gravity investment casting apparatus and casting method for titanium alloys. Therefore, further details are omitted here.

[0050] This invention provides a method for using a riser pipe in anti-gravity investment casting of titanium alloys, comprising:

[0051] The melting time of the riser tube is theoretically calculated. Through theoretical calculation, the influence of riser tube wall thickness, riser tube inner diameter, and riser tube preheating temperature on the melting time of the riser tube is obtained, and thus the parameter selection specifications for the riser tube are derived.

[0052] The riser tube is used after the titanium alloy material in the water-cooled copper crucible has completely melted, while maintaining the melting power. At this point, the preheated riser tube is inserted for anti-gravity filling. Therefore, calculating the melting time of the riser tube is a complex transient engineering thermodynamics problem. It can be solved by decomposing the problem into steps using engineering estimation methods to obtain a reasonable approximate result for experimental reference.

[0053] Specifically, the heat absorbed and convective heat flux of the riser tube in the four stages of the first solid-state sensible heat, the latent heat of phase change, the second solid-state sensible heat, and the latent heat of fusion are calculated respectively; based on the melting power, the mass of the melt, and the mass of the riser tube inserted into the melt, the induction heating power P of the riser tube inserted into the melt is calculated. ind Based on the heat absorbed by the riser tube and the convective heat flux in the four stages of the first solid-state sensible heat, the latent heat of phase change, the second solid-state sensible heat, and the latent heat of fusion, as well as the induction heating power P of the riser tube inserted into the melt. ind Calculate the total melting time of the riser tube inserted into the molten section. Multiple riser wall thicknesses, multiple riser inner diameters, and multiple riser preheating temperatures are selected, and the total melting time of the riser section inserted into the melt is calculated for any riser wall thickness, any riser inner diameter, and any riser preheating temperature. This yields a timetable of riser melting caused by different influencing factors. Based on the timetable of riser melting caused by different influencing factors, the degree of influence of riser wall thickness, riser inner diameter, and riser preheating temperature on the melting time of the riser is obtained.

[0054] In this embodiment, ZTC4 titanium alloy is used as an example. Approximately 25 kg of material is placed in a water-cooled copper crucible to obtain actual smelting parameters. Table 1 shows the smelting parameters for the actual smelting process. After the riser tube is inserted into the melt, the length of the part of the riser tube inserted into the melt is approximately 18 cm. The medium-frequency induction heating frequency of the water-cooled copper crucible is 5.85 kHz at this time. Due to the strong electromagnetic stirring, convection heating is the main heat source for the riser tube heating. Its convective heat transfer coefficient h is calculated to be 1100-1600 W / (m³) based on electromagnetic force and characteristic flow velocity. 2 ·k), taking the classic value of 1300 W / (m 2 ·k). In addition to convection heating, the riser tube is also subjected to induction heating. At this time, the induction heating power P of the riser tube inserted into the melt is... ind It can be estimated based on the product of the unit mass power and the mass of the riser tube inserted into the melt. The unit mass power is the ratio of the smelting power of 500 kW to the melt mass of 25 kg, that is, the unit mass power is 20 kW / kg.

[0055] Table 1. Smelting parameters for the actual smelting process

[0056]

[0057] Skin depth ,in f For induction heating frequency, resistivity Vacuum permeability The calculated skin depth is approximately 8.6 mm. Skin depth refers to the thickness of a layer on the surface of a conductor where the current is concentrated in an alternating current or electromagnetic field. It decreases with increasing frequency and reflects the uniformity of heating of the object. For anti-gravity casting of titanium alloys, the wall thickness of the riser tube generally does not exceed the skin depth, so it can be assumed that induction heating is relatively uniform within the tube wall.

[0058] Calculate the heat requirement for the riser tube to melt, i.e., the heat required for the riser tube to absorb the latent heat of fusion T from the preheating temperature T0. s T s =1605℃. The total heat to be absorbed at the solidus of 1605℃ includes sensible heat and latent heat. Latent heat includes the latent heat of β-phase change and the latent heat of fusion. The heat absorbed by the riser pipe is calculated in stages:

[0059] First solid-state sensible heat stage (T0→T) β ):

[0060] Through the formula: Calculate the heat absorbed by the riser tube during the first solid-state sensible heating stage; where m is the mass of the lower end of the riser tube inserted into the melt, in kg; T0 is the specific heat capacity of the material being smelted in the water-cooled copper crucible, J / kg•℃; T0 is the preheating temperature of the riser pipe, ℃; T0 is the temperature of the material being smelted in the water-cooled copper crucible. β T represents the phase transition temperature, in °C. β =995℃.

[0061] Phase transition latent heat stage (T β ):

[0062] Through the formula: Calculate the heat absorbed by the riser tube during the latent heat stage of phase change; where J; The latent heat of phase transition in solid state is expressed in kJ / kg. =80 kJ / kg.

[0063] Second solid-state sensible heat stage (T) β →T s ):

[0064] Through the formula: Calculate the heat absorbed by the riser tube during the second solid-state sensible heating stage; among which, , where is the melting temperature, in °C.

[0065] Latent heat stage of melting (T) s ):

[0066] Through the formula: Calculate the heat absorbed by the riser tube during the latent heat of melting stage; among which, The latent heat of fusion is expressed in kJ / kg. =330 kJ / kg.

[0067] The total heat required for the riser tube to melt is: Q total =Q1+Q2+Q3+Q4.

[0068] Heat transfer in riser tubes includes convective heat transfer and induction heating, and its total heat flux... In the formula, A is the sum of the inner and outer surface areas of the portion of the riser tube inserted into the melt, and m 2 h is the convective heat transfer coefficient, W / (m²). 2 •k). T m This is the melt temperature, which remains essentially constant at this point. t Let T be the temperature of the riser tube at time t. Due to the temperature difference (T... m -T t The heat flux is calculated using the phased average temperature difference method as it changes over time. The heating time is simplified by using the lumped system method in stages (the actual Biot number is greater than 0.1, which has a certain error, but it can be used for engineering estimation; the actual time may be about 10% longer).

[0069] First solid-state sensible heat stage ( ):

[0070] Through the formula: Calculate the convective heat flux of the riser tube in the first solid-state sensible heating stage. Where h is the convective heat transfer coefficient, h = 1300 W / (m²). 2 •k); A is the sum of the inner and outer surface areas of the portion of the riser tube inserted into the melt, m 2 ; is the melt temperature, in °C.

[0071] Through the formula: Calculate the time t1 of the first solid-state sensible heat stage.

[0072] Phase transition latent heat stage ( (ΔT2 temperature difference is constant)

[0073] Through the formula: Calculate the convective heat flux of the riser tube during the latent heat stage of phase change.

[0074] Through the formula: Calculate the time t2 of the latent heat stage of phase transition.

[0075] Second solid-state sensible heat stage ( ):

[0076] Through the formula: Calculate the convective heat flux of the riser tube in the second solid-state sensible heat stage.

[0077] Through the formula: Calculate the time t3 of the second solid-state sensible heat stage.

[0078] Latent heat of fusion stage ( ):

[0079] Through the formula: Calculate the convective heat flux of the riser tube during the latent heat stage of melting.

[0080] Through the formula: Calculate the time t4 of the latent heat stage of melting.

[0081] The total melting time of the riser tube inserted into the molten part is .

[0082] In actual experiments, the temperature of the TC4 titanium alloy melt at a melting power of 500 kW needs to be obtained. The thermocouple temperature measurement is 1710℃, and the infrared temperature measurement is 1713℃. In this embodiment, a constant melt temperature of 1710℃ is selected.

[0083] The melting time of the riser tube is directly related to its preheating temperature, wall thickness, and inner diameter. Therefore, it is necessary to calculate and obtain the influence of riser tube wall thickness, inner diameter, and preheating temperature on the melting time, and then obtain the riser tube parameter selection specifications to directly guide the selection of experimental parameters.

[0084] For anti-gravity casting of titanium alloys, due to the use of a water-cooled copper crucible induction solidification melting process, the superheat of the titanium melt is relatively low. Therefore, the preheating temperature of the riser tube needs to be as high as possible to reduce heat loss of the titanium melt in the riser tube. Thus, in this embodiment, the melting time of the riser tube corresponding to three characteristic preheating temperatures (600℃, 800℃, and 1000℃) is calculated. Furthermore, the inner diameter of the riser tube should not be too small or too large. If the inner diameter is too small, the high-viscosity titanium melt will encounter greater resistance during filling, making successful filling difficult. If the inner diameter is too large, a large amount of titanium melt will be consumed within the riser tube, and combined with the solidification in the water-cooled copper crucible, the actual amount of titanium melt available for casting will be significantly reduced. Therefore, in this embodiment, the melting time of the riser tube corresponding to three characteristic inner diameter values ​​(30 mm, 40 mm, and 50 mm) is calculated. Finally, the wall thickness of the riser tube must consider machinability, melting time, and practical operability. Therefore, in this embodiment, the melting time of the riser tube corresponding to the three characteristic values ​​of riser tube wall thickness (2 mm, 3 mm and 5 mm) is calculated.

[0085] The total melting time of the riser tube inserted into the molten body was calculated by coupling the calculations for any riser tube wall thickness, any riser tube inner diameter, and any riser tube preheating temperature. This yielded a timetable of riser tube melting caused by different influencing factors. Table 2 shows the melting timetable for riser tubes caused by different influencing factors. According to the timetable, the fastest melting condition is a wall thickness of 2 mm and an initial preheating temperature of 1000℃, with a melting time of approximately 9.5 s; the slowest melting condition is a wall thickness of 5 mm and an initial temperature of 600℃, with a melting time of approximately 19.7 s. The influence of the riser tube preheating temperature on the melting time is within 1.5 s, which is relatively small. The change in the riser tube inner diameter has a negligible impact on the melting time (the difference in melting time caused by different riser tube inner diameters is <0.1 seconds), because as the inner diameter increases, the mass and surface area of ​​the riser tube increase proportionally, and the heat transfer rate changes synchronously with the heat demand.

[0086] Table 2. Timeline of Melting of Lifting Tubes Due to Different Influencing Factors

[0087]

[0088] Based on the above calculations and analyses, the following specifications for selecting riser pipe parameters are obtained: In process design, priority should be given to controlling the riser pipe wall thickness to adjust the riser pipe melting time; the riser pipe preheating temperature should be selected in combination with the casting process design and the actual production equipment preheating temperature limit; the influence of riser pipe inner diameter variation on riser pipe melting time is negligible, and the riser pipe inner diameter should be selected according to the casting process design requirements.

[0089] Based on the above-mentioned selection specifications for riser parameters, the wall thickness, inner diameter, and preheating temperature of the riser used for casting are selected.

[0090] Once the material in the water-cooled copper crucible has completely melted, the mold begins to descend. The preheated riser tube is then inserted into the melt inside the water-cooled copper crucible. The mold descent and filling are linked to perform anti-gravity filling.

[0091] Because titanium alloy riser tubes face the problem of melting, the allowed filling time is relatively short. Therefore, it is necessary to explain the application scenario of this riser tube. Patent application CN202510726950.0 already describes a method for anti-gravity casting of titanium alloys. This method involves lowering the mold after the titanium alloy material has melted in a water-cooled copper crucible, inserting the riser tube into the melt, and then injecting inert gas into the lower working vessel after the mold is in place to complete the filling. Here, the mold lowering and filling are linked, with the mold arrival signal serving as the automatic filling start signal, which can further increase the effective filling time. In addition, the length of the riser tube must be strictly controlled. Excessive riser tube length causes several problems: first, the titanium melt with low superheat will experience significant heat loss when passing through a long riser tube channel, potentially leading to filling failure; second, an excessively long riser tube results in a prolonged rising time for the titanium melt, increasing the risk of the riser tube melting. Considering the filling speed of anti-gravity casting of titanium alloys, the length of the riser tube for titanium alloys should be within 500 mm. Finally, when using a riser tube made of the same material as the titanium melt in a water-cooled copper crucible, the casting must be a thin-walled casting with a wall thickness of 1-3 mm and a size that is not too large. The size should not be too large in order to achieve rapid filling. The requirement for a thin-walled casting is to ensure that the casting (with low superheat of the melt) solidifies rapidly before the riser tube melts, and to have a short holding time, so that the casting quality reaches its best, thereby effectively solving the current dilemma of casting thin-walled titanium alloy parts.

[0092] Based on the specifications for selecting riser tube parameters and the application scenario, a titanium alloy ultra-thin-walled chamber component (wall thickness of 1 mm, reaching the casting limit) was selected for experimental verification. The titanium alloy riser tube was preheated to 800℃, with an inner diameter of 50 mm and a wall thickness of 5 mm. Successful filling occurred within the theoretically calculated melting time. After the riser tube was removed, the portion inserted into the molten metal showed slight melting. Figure 2 A photograph of the riser tube taken after the filling process is completed; Figure 3 Photos of the sandbox taken after the molding process is completed; Figure 4 The image shows the mold shell filled during the sandbox removal process. This demonstrates that although the above calculation case is presented as an example, it still has universality, and the application of theoretical calculation results has certain guiding significance for engineering practice.

[0093] Obviously, the above-disclosed embodiments of the present invention are merely illustrative of the invention. The embodiments do not exhaustively describe all details, nor do they limit the invention to the specific implementations described. Many modifications and variations can be made based on the content of this specification. This specification selects and specifically describes these embodiments to better explain the principles and practical applications of the invention, thereby enabling those skilled in the art to better understand and utilize the invention. It is neither necessary nor possible to exhaustively describe all embodiments herein.

Claims

1. A method for using a riser pipe in anti-gravity investment casting of titanium alloys, wherein the riser pipe is located above a water-cooled copper crucible and below the gating inlet of the mold shell, characterized in that... The riser tube is made of the same material as the material being smelted in the water-cooled copper crucible; The method of using the riser pipe for anti-gravity investment casting of titanium alloys includes: Through theoretical calculations, the influence of riser wall thickness, riser inner diameter, and riser preheating temperature on the melting time of the riser is analyzed, and thus the riser parameter selection specifications are obtained. According to the selection specifications for riser parameters, the wall thickness, inner diameter, and preheating temperature of the riser used for casting are selected. After the material in the water-cooled copper crucible has completely melted, the mold begins to descend. The preheated riser tube is inserted into the melt in the water-cooled copper crucible. The mold descent and filling are linked to perform anti-gravity filling. The theoretical calculations analyzed the influence of riser wall thickness, riser inner diameter, and riser preheating temperature on the melting time of the riser, including: Calculate the heat absorbed by the riser tube and the convective heat flow in the four stages: the first solid sensible heat, the latent heat of phase change, the second solid sensible heat, and the latent heat of fusion. Calculate the induction heating power P of the riser tube inserted into the melt based on the melting power, melt mass, and mass of the riser tube inserted into the melt. ind ; Based on the heat absorbed by the riser tube and the convective heat flux in the four stages of the first solid sensible heat, the latent heat of phase change, the second solid sensible heat, and the latent heat of fusion, as well as the induction heating power P of the riser tube inserted into the melt, ind Calculate the total melting time of the riser tube inserted into the molten section. ; By selecting multiple riser wall thicknesses, multiple riser inner diameters, and multiple riser preheating temperatures, the total melting time of the riser tube inserted into the melt is calculated for any riser wall thickness, any riser inner diameter, and any riser preheating temperature, thus obtaining the timetable of riser tube melting caused by different influencing factors. Based on the timeline of riser tube melting caused by different influencing factors, the influence of riser tube wall thickness, riser tube inner diameter, and riser tube preheating temperature on the melting time of the riser tube is analyzed.

2. The method of using the riser pipe for anti-gravity investment casting of titanium alloys according to claim 1, characterized in that: The length of the riser pipe used for anti-gravity investment casting of titanium alloys is within 500 mm.

3. The method of using the riser pipe for anti-gravity investment casting of titanium alloys according to claim 1, characterized in that: The wall thickness of castings produced by anti-gravity investment casting is 1~3 mm.

4. The method of using the riser pipe for anti-gravity investment casting of titanium alloys according to claim 1, characterized in that: The mold descent and filling linkage operation includes: using the mold descent signal as the automatic filling start signal, and immediately starting to inject inert gas into the lower working tank for filling after the mold descent is in place.

5. The method of using the riser pipe for anti-gravity investment casting of titanium alloys according to claim 1, characterized in that: The selection criteria for the riser tube parameters include: Prioritize controlling the riser tube wall thickness to adjust the riser tube melting time; Based on the casting process design and the actual preheating temperature limit of the production equipment, the preheating temperature of the riser pipe is selected. The effect of changes in the inner diameter of the riser tube on the melting time of the riser tube is negligible. The inner diameter of the riser tube is selected according to the casting process design requirements.

6. The method of using the riser pipe for anti-gravity investment casting of titanium alloys according to claim 1, characterized in that: Through the formula: Calculate the heat absorbed by the riser tube during the first solid-state sensible heating stage; where m is the mass of the lower end of the riser tube inserted into the melt, in kg; T0 is the specific heat capacity of the material being smelted in the water-cooled copper crucible, J / kg•℃; T0 is the preheating temperature of the riser pipe, ℃; T0 is the temperature of the material being smelted in the water-cooled copper crucible. β The phase transition temperature is given in °C. Through the formula: Calculate the heat absorbed by the riser tube during the latent heat stage of phase change; where J; The latent heat of phase transition in solid state is expressed in kJ / kg. Through the formula: Calculate the heat absorbed by the riser tube during the second solid-state sensible heating stage; among which, The melting temperature is ℃; Through the formula: Calculate the heat absorbed by the riser tube during the latent heat of melting stage; among which, The value represents the latent heat of fusion, in kJ / kg.

7. The method of using the riser pipe for anti-gravity investment casting of titanium alloys according to claim 6, characterized in that: Through the formula: Calculate the convective heat flux of the riser tube in the first solid-state sensible heat stage; where h is the convective heat transfer coefficient. A is the sum of the inner and outer surface areas of the portion of the riser tube inserted into the melt, m 2 ; ; The melt temperature is ℃; Through the formula: Calculate the convective heat flux of the riser tube during the latent heat stage of phase change; among which, ; Through the formula: Calculate the convective heat flux of the riser tube during the second solid-state sensible heating stage; where, ; Through the formula: Calculate the convective heat flux of the riser tube during the latent heat of fusion stage; where, .

8. The method of using the riser pipe for anti-gravity investment casting of titanium alloys according to claim 7, characterized in that: Based on the heat absorbed by the riser tube and the convective heat flux in the four stages of the first solid sensible heat, the latent heat of phase change, the second solid sensible heat, and the latent heat of fusion, as well as the induction heating power P of the riser tube inserted into the melt, ind Calculate the total melting time of the riser tube inserted into the molten section. include: Through the formula: Calculate the total melting time of the riser tube inserted into the molten section; where, ; ; ; .

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