Using method of riser tube for titanium alloy anti-gravity investment casting

Abstract

The invention provides a use method of a riser tube for titanium alloy anti-gravity investment casting, belongs to the technical field of titanium alloy casting, and solves the problems that the riser tube for titanium alloy anti-gravity investment casting needs to resist high temperature and also needs to avoid reaction with titanium melt. According to the using method of the riser tube, the influence degree of the wall thickness of the riser tube, the inner diameter of the riser tube and the preheating temperature of the riser tube on the melting time of the riser tube is analyzed through theoretical calculation, and then the riser tube parameter selection specification is obtained; selecting the wall thickness of the riser tube for casting, the inner diameter of the riser tube and the preheating temperature of the riser tube according to the riser tube parameter selection specification; and after the materials in the water-cooled copper crucible are completely melted, descending and casting are started, the preheated riser tube is inserted into the solution in the water-cooled copper crucible, and anti-gravity mold filling is carried out by adopting the linkage operation of casting mold descending and mold filling. And the cleanliness of the melt can be guaranteed, and the yield of titanium alloy anti-gravity casting is guaranteed.

Description

TECHNICAL FIELD

[0001] The application belongs to the technical field of titanium alloy casting, and particularly relates to a use method of a riser for titanium alloy counter-gravity investment casting. BACKGROUND

[0002] The principle of counter-gravity casting (mainly including low-pressure casting, differential pressure casting, pressure-adjusting casting and vacuum suction casting) is that the molten metal liquid overcomes gravity and fills the mold cavity along the liquid guide pipe (also known as the riser) under the action of external pressure. This mold filling process shows that counter-gravity casting usually adopts a bottom pouring system, that is, the metal liquid fills the cavity from bottom to top, which can avoid the "roller coaster" type flow convergence phenomenon of the metal liquid in the mold filling process, thereby reducing the casting defects such as gas entrapment, oxide film entrapment and slag inclusion. At the same time, the counter-gravity casting process has many advantages such as controllable mold filling speed, smooth mold filling, compact structure and high precision of the casting, which can overcome the casting defects such as insufficient pouring, lack of meat and cold shut in the production of complex thin-walled parts by traditional gravity casting and tilting casting. Therefore, with the development of lightweight, precision and batch production of large complex structures in the fields of aviation and aerospace, counter-gravity casting technology plays an irreplaceable role in the production of thin-walled complex structures.

[0003] The success of the counter-gravity casting process depends on whether the riser is reliable during the entire mold filling process. That is, the riser, as a channel connecting the melt in the crucible and the mold, can directly affect the stability of the melt filling and the final quality of the casting. Referring to the patent application No. CN202510726950.0, a counter-gravity investment casting device suitable for titanium alloy and a casting method thereof are disclosed. During the entire counter-gravity casting process, the lower end of the riser is inserted into the molten melt, and under the action of external gas pressure, the metal liquid is guided into the cavity. The riser bears the functions of transporting molten metal, preventing gas from penetrating through the pipe wall to cause gas entrapment in the casting and maintaining the required pressure of the pressure head. This process requires the riser to meet many stringent performance requirements, including excellent high-temperature strength, resistance to melt corrosion and even no reaction with the melt, good thermal shock resistance and excellent sealing performance.

[0004] At present, for low-melting-point lightweight aluminum-magnesium alloys, the riser material and use method have been 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, the domestic technology of riser material and use has also been broken through.

[0005] However, this requirement is more stringent for titanium alloy counter-gravity investment casting. Firstly, because the melting point of titanium alloy is as high as 1600-1700℃, and the molten titanium liquid has extremely high chemical activity, it reacts with almost all refractory materials, so the application of the riser tube needs to solve the problems of high temperature resistance and reaction with titanium melt. Secondly, the lower end of the riser tube needs to be completely immersed in the high-temperature titanium liquid during mold filling, and the upper end is connected with the mold shell with relatively low temperature. The large temperature difference between the riser tube and the molten titanium liquid and the large axial temperature gradient will generate significant thermal stress inside the riser tube, which requires the application of the riser tube to have excellent thermal shock resistance to avoid cracking. Limited by the above problems, the research on titanium alloy counter-gravity casting process is almost blank, and a breakthrough is urgently needed. SUMMARY

[0006] Therefore, in order to solve the problem that the riser tube for titanium alloy counter-gravity investment casting needs to be resistant to high temperature and also avoid reaction with titanium melt, the application provides a use method of a riser tube for titanium alloy counter-gravity investment casting.

[0007] To achieve the above object, the application adopts the following technical scheme: The use method of the riser tube for titanium alloy counter-gravity investment casting, the riser tube is located above the water-cooled copper crucible and below the sprue inlet of the mold shell, and the riser tube is made of the same material as the smelting material in the water-cooled copper crucible; The use method of the riser tube for titanium alloy counter-gravity investment casting includes: Through theoretical calculation, the influence degree of the riser tube wall thickness, the riser tube inner diameter and the riser tube preheating temperature on the melting time of the riser tube is analyzed, and then the riser tube parameter selection specification is obtained; According to the riser tube parameter selection specification, the riser tube wall thickness, the riser tube inner diameter and the riser tube preheating temperature for casting are selected; After the material in the water-cooled copper crucible is completely melted, the mold is started to be lowered, the preheated riser tube is inserted into the solution in the water-cooled copper crucible, and the counter-gravity mold filling is carried out by using the mold lowering and mold filling linkage operation; The analysis of the influence degree of the riser tube wall thickness, the riser tube inner diameter and the riser tube preheating temperature on the melting time of the riser tube through theoretical calculation includes: The heat absorbed by the riser tube and the convective heat flow in the four stages of the first solid sensible heat, the phase change latent heat, the second solid sensible heat and the melting latent heat are calculated respectively; According to the smelting power, the melt mass and the mass of the riser tube inserted into the melt, the inductive heating power P of the riser tube inserted into the melt is calculated ind ; According to the four stages of the first solid sensible heat, phase change latent heat, the second solid sensible heat and melting latent heat, the riser absorbs heat and convective heat flow and the induction heating power P of the riser inserted into the melt ind , the total melting time of the riser inserted into the melt part is calculated ; A plurality of riser wall thicknesses, a plurality of riser inner diameters and a plurality of riser preheating temperatures are selected, the total melting time of the riser inserted into the melt part corresponding to any riser wall thickness, any riser inner diameter and any riser preheating temperature is calculated, and a time table of the melting of the riser caused by different influencing factors is obtained; According to the time table of the melting of the riser caused by different influencing factors, the influence degree of the riser wall thickness, the riser inner diameter and the riser preheating temperature on the melting time of the riser is analyzed.

[0008] As a preferred solution of the use method of the riser for titanium alloy countergravity investment casting, the length of the riser for titanium alloy countergravity investment casting is within 500 mm.

[0009] As a preferred solution of the use method of the riser for titanium alloy countergravity investment casting, the wall thickness of the countergravity investment casting casting is 1-3 mm.

[0010] As a preferred solution of the use method of the riser for titanium alloy countergravity investment casting, the mold lowering and filling linkage operation includes: taking the mold lowering into position signal as the automatic starting signal of filling, and immediately starting to pour inert gas into the down working tank for filling after the mold is lowered into position.

[0011] As a preferred solution of the use method of the riser for titanium alloy countergravity investment casting, the riser parameter selection specification includes: The riser wall thickness is preferentially controlled to adjust the melting time of the riser; The riser preheating temperature is selected in combination with the preheating temperature limit of the actual production equipment and the casting process design; The influence of the change of the riser inner diameter on the melting time of the riser is ignored, and the riser inner diameter is selected according to the requirements of the casting process design.

[0012] As a preferred solution of the use method of the riser for titanium alloy countergravity investment casting, the heat absorbed by the riser in the first solid sensible heat stage is calculated by the formula: ; wherein m is the mass of the riser inserted into the melt part, kg; is the specific heat capacity of the smelting material in the water-cooled copper crucible, J / kg•℃; T0 is the preheating temperature of the riser, ℃; T β is the phase change temperature, ℃; The heat absorbed by the riser in the second solid sensible heat stage is calculated by the formula: , the liquid up-tube absorbs heat in the phase change latent heat stage; wherein, J; is the solid phase change latent heat value, kJ / kg; The liquid up-tube absorbs heat in the second solid sensible heat stage by the formula: , wherein, is the melting temperature, ℃; The liquid up-tube absorbs heat in the melting latent heat stage by the formula: , wherein, is the melting latent heat value, kJ / kg.

[0013] As a preferred solution of the use method of the liquid up-tube for titanium alloy counter-gravity investment casting, the convective heat flow of the liquid up-tube in the first solid sensible heat stage is calculated by the formula: , wherein, h is the convective heat transfer coefficient, ; A is the sum of the inner surface area and the outer surface area of the lower end of the liquid up-tube inserted into the melt, m 2 ; ; is the melt temperature, ℃; The convective heat flow of the liquid up-tube in the phase change latent heat stage is calculated by the formula: , wherein, ; The convective heat flow of the liquid up-tube in the second solid sensible heat stage is calculated by the formula: , wherein, ; The convective heat flow of the liquid up-tube in the melting latent heat stage is calculated by the formula: , wherein, .

[0014] As a preferred solution of the use method of the liquid up-tube for titanium alloy counter-gravity investment casting, the total melting time of the liquid up-tube inserted into the melt is calculated according to the heat absorption and the convective heat flow of the liquid up-tube in the four stages of the first solid sensible heat, the phase change latent heat, the second solid sensible heat and the melting latent heat, and the induction heating power P ind of the liquid up-tube inserted into the melt. The total melting time of the liquid up-tube inserted into the melt is calculated by the formula: , wherein, ; ; ; ; .

[0015] Compared with the prior art, the liquid up-tube for titanium alloy counter-gravity investment casting and the use method thereof provided by the present application have the following beneficial effects: (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.

[0016] (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.

[0017] (3) It specifically points out the application scenarios of titanium alloy riser pipes for anti-gravity casting of titanium alloys, including the length of riser pipes, operation linkage and appropriate casting wall thickness, which ensures the yield of titanium alloy anti-gravity casting. Attached Figure Description

[0018] 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: 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; Figure 2 A photograph of the riser tube taken after the filling process is completed; Figure 3 These are photos of the sandbox taken after the molding process is completed; Figure 4 This is a photo of the mold shell filled during the removal of the sandbox. Detailed Implementation

[0019] 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.

[0020] 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.

[0021] 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.

[0022] The selection of the riser pipe with the same material as the smelting material in the water-cooled copper crucible is based on the fact that the titanium alloy needs to go through multiple processes such as solid sensible heat, phase change latent heat and melting latent heat before melting, and the riser pipe made of titanium alloy needs to be heated constantly until the riser pipe is finally melted. Therefore, the anti-gravity filling of the titanium alloy can be completed during the time before the riser pipe is completely melted. Therefore, the time from the insertion of the riser pipe to the melting of the riser pipe needs to be determined, and the filling operation needs to be completed before the riser pipe is melted, otherwise the filling operation will fail if the filling operation is not completed after the riser pipe is melted.

[0023] The riser pipe with the same material as the smelting material in the water-cooled copper crucible is processed, and the flange plate is threadedly connected with the riser pipe, then welding and root cleaning are performed to ensure the sealing property, and then the riser pipe can be assembled into the anti-gravity investment casting device. The structure of the riser pipe for the anti-gravity investment casting of the titanium alloy and the installation position and connection relationship in the anti-gravity investment casting device are the same as those in the anti-gravity investment casting device and the casting method suitable for the titanium alloy disclosed in the patent application with the patent number CN202510726950.0, and thus will not be described herein.

[0024] The application provides a use method of a riser pipe for anti-gravity investment casting of a titanium alloy, which comprises the following steps: The melting time of the riser pipe is theoretically calculated. Through theoretical calculation, the influence degree of the wall thickness of the riser pipe, the inner diameter of the riser pipe and the preheating temperature of the riser pipe on the melting time of the riser pipe is obtained, and then the riser pipe parameter selection specification is obtained.

[0025] The use state of the riser pipe is that after the titanium alloy material in the water-cooled copper crucible is completely melted, the smelting power is kept, and then the preheated riser pipe is inserted to perform the anti-gravity filling. Therefore, the calculation of the melting time of the riser pipe is a complex transient engineering thermodynamics problem, which can be decomposed and calculated step by step through the engineering estimation method to obtain a reasonable approximate result for reference.

[0026] Specifically, the heat absorption and the convective heat flow of the riser pipe in the first solid sensible heat, the phase change latent heat, the second solid sensible heat and the melting latent heat are calculated respectively; the inductive heating power P ind of the riser pipe inserted into the melt is calculated according to the smelting power, the mass of the melt and the mass of the riser pipe inserted into the melt; and the total melting time T ind of the riser pipe inserted into the melt is calculated according to the heat absorption and the convective heat flow of the riser pipe in the first solid sensible heat, the phase change latent heat, the second solid sensible heat and the melting latent heat and the inductive heating power P ; selecting multiple riser wall thicknesses, multiple riser inner diameters, and multiple riser preheating temperatures, coupling calculation of total melting time of the riser inserted into the melt corresponding to any riser wall thickness, any riser inner diameter, and any riser preheating temperature to obtain a riser melting time table caused by different influencing factors; and obtaining the influence degree of the riser wall thickness, the riser inner diameter, and the riser preheating temperature on the melting time of the riser according to the riser melting time table caused by different influencing factors.

[0027] In the embodiment, ZTC4 titanium alloy is taken as an example, about 25 kg of material is put into the water-cooled copper crucible, and actual smelting parameters are obtained. Table 1 is a table of smelting parameters in the actual smelting process. When the riser is inserted into the melt, the length of the riser inserted into the melt is about 18 cm, and the frequency of the medium-frequency induction heating of the water-cooled copper crucible at this time is 5.85 kHz. Due to strong electromagnetic stirring, convection heating is the main heat source for the riser heating, and the convection heat transfer coefficient h of the core range is 1100-1600 W / ( m 2 ·k) calculated by electromagnetic force and characteristic flow velocity. A classic value 1300 W / ( m 2 ·k) is taken. In addition to convection conduction heating, the riser is also subjected to certain induction heating. At this time, the induction heating power P ind of the riser inserted into the melt can be estimated according to the product of the unit mass power and the mass of the riser inserted into the melt, wherein the unit mass power is the ratio of the smelting power 500 kW and the melt mass 25 kg, that is, the unit mass power is 20 kW / kg.

[0028] Table 1 is a table of smelting parameters in the actual smelting process.

[0029] Skin depth , wherein f is the induction heating frequency, the resistivity , the vacuum permeability . The calculated skin depth is about 8.6 mm. The skin depth refers to the thickness of the layer in which the current is mainly concentrated on the surface of the conductor in an alternating current or alternating electromagnetic field, which decreases with the increase of the frequency, and reflects the uniformity of the object being heated. For titanium alloy counter-gravity casting, the wall thickness of the riser generally does not exceed the skin depth, so it can be assumed that the induction heating is relatively uniform within the pipe wall.

[0030] The heat demand calculation of the riser being melted is performed, that is, the riser is heated from the preheating temperature T0 to absorb the melting latent heat T s , and T s =1605℃. The total heat absorbed by the solidus 1605℃ includes sensible heat and latent heat, and the latent heat includes β phase transition latent heat and melting latent heat. The heat absorbed by the riser is calculated in stages: First solid-state sensible heat stage (T0→T) β ): 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℃.

[0031] Phase transition latent heat stage (T β ): 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.

[0032] Second solid-state sensible heat stage (T) β →T s ): 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.

[0033] Latent heat stage of melting (T) s ): 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.

[0034] The total heat required for the riser tube to melt is: Q total =Q1+Q2+Q3+Q4.

[0035] 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 tThe 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).

[0036] First solid-state sensible heat stage ( ): 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.

[0037] Through the formula: Calculate the time t1 of the first solid-state sensible heat stage.

[0038] Phase transition latent heat stage ( (ΔT2 temperature difference is constant) Through the formula: Calculate the convective heat flux of the riser tube during the latent heat stage of phase change.

[0039] Through the formula: Calculate the time t2 of the latent heat stage of phase transition.

[0040] Second solid-state sensible heat stage ( ): Through the formula: Calculate the convective heat flux of the riser tube in the second solid-state sensible heat stage. Through the formula: Calculate the time t3 of the second solid-state sensible heat stage.

[0041] Latent heat of fusion stage ( ): Through the formula: Calculate the convective heat flux of the riser tube during the latent heat stage of melting.

[0042] Through the formula: Calculate the time t4 of the latent heat stage of melting.

[0043] The total melting time of the riser tube inserted into the molten part is .

[0044] 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.

[0045] The melting time of the riser is directly related to the preheating temperature, wall thickness and inner diameter of the riser. Therefore, it is necessary to calculate and obtain the influence degree of the riser wall thickness, riser inner diameter and riser preheating temperature on the melting time of the riser, and then obtain the riser parameter selection specification to directly guide the selection of test parameters.

[0046] For the titanium alloy counter-gravity casting, since the water-cooled copper crucible induction condensate smelting process is adopted, the titanium melt superheat is low, and therefore the riser preheating temperature needs to be as high as possible to reduce the heat loss of the titanium melt in the riser. Therefore, in the embodiment, the riser melting time corresponding to three riser preheating characteristic temperatures (600℃, 800℃ and 1000℃) is calculated. In addition, the riser inner diameter cannot be too small or too large, because when the riser inner diameter is too small, the high-viscosity titanium melt will be subjected to greater resistance of the riser during mold filling, and it is difficult to successfully fill the mold; when the riser inner diameter is too large, a large amount of titanium melt will be consumed in the riser, and the actual available titanium liquid in the water-cooled copper crucible will be greatly reduced. Therefore, in the embodiment, the riser melting time corresponding to three riser inner diameter characteristic values (30 mm, 40 mm and 50 mm) is calculated. Finally, the riser wall thickness needs to consider the machinability, melting time and actual operability. Therefore, in the embodiment, the riser melting time corresponding to three riser wall thickness characteristic values (2 mm, 3 mm and 5 mm) is calculated.

[0047] The total melting time of the riser inserted into the melt corresponding to any riser wall thickness, any riser inner diameter and any riser preheating temperature is coupled to obtain a riser melting time table caused by different influencing factors. Table 2 is a riser melting time table caused by different influencing factors. According to the riser melting time table caused by different influencing factors, it can be seen that the fastest melting condition of the riser is a wall thickness of 2 mm and an initial preheating temperature of 1000℃, and the melting time is about 9.5 s; the slowest melting condition is a wall thickness of 5 mm and an initial temperature of 600℃, and the melting time is about 19.7 s. The influence of the riser preheating temperature on the melting time is less than 1.5 s, which is relatively small. The influence of the riser inner diameter on the melting time of the riser is very small (the difference in the melting time of the riser caused by different riser inner diameters is less than 0.1 s), because when the inner diameter increases, the mass and surface area of the riser increase by the same ratio, and the heat transfer rate and heat demand change synchronously.

[0048] Table 2 Riser melting time table caused by different influencing factors

[0049] Through the above calculation and analysis, the obtained selection specification of the riser parameters includes: in the process design, the riser wall thickness is preferentially controlled to adjust the riser melting time; the riser preheating temperature is selected in combination with the casting process design and the actual production equipment preheating temperature limit; the influence of the riser inner diameter change on the riser melting time is ignored, and the riser inner diameter is selected according to the casting process design requirements.

[0050] According to the above riser parameter selection specification, the riser wall thickness, the riser inner diameter and the riser preheating temperature for casting are selected.

[0051] When the material in the water-cooled copper crucible is completely melted, the mold starts to descend, the preheated riser is inserted into the melt in the water-cooled copper crucible, and the mold descending and filling operation are combined to perform the counter-gravity filling.

[0052] Since the titanium alloy riser faces the melting problem, the filling time is short, and therefore the application scenario of the riser needs to be explained: the patent application with the patent number CN202510726950.0 has given a method for counter-gravity casting of titanium alloy, that is, after the titanium alloy material in the water-cooled copper crucible is completely melted, the mold starts to descend, the riser is inserted into the melt, and after the mold is in place, the inert gas is injected into the working tank to complete the filling. Here, the mold descending and filling operation are combined, that is, the mold in-place signal is used as the automatic filling start signal, which can further increase the effective filling time. In addition, the riser length needs to be strictly required. The problems caused by the excessive length of the riser mainly include: first, the titanium melt with low superheat degree will suffer serious heat loss when passing through the long riser channel, which may result in filling failure; second, the long riser length will cause the riser time of the titanium melt to be too long, increasing the risk of riser melting. In combination with the filling speed of counter-gravity casting of titanium alloy, the length of the titanium alloy riser is required to be within 500 mm. Finally, when the riser made of the same material as the titanium melt in the water-cooled copper crucible is applied, the castings require to be thin-walled castings, the wall thickness of the castings is 1-3 mm, and the size should not be too large. The size should not be too large in order to complete the rapid filling. The requirement of thin-walled castings is to ensure that the castings (melt with low superheat degree) are rapidly solidified before the riser is melted, and there is a short holding time to make the casting quality excellent, thereby effectively solving the difficulty in casting of titanium alloy thin-walled parts.

[0053] According to the riser parameter selection specification and the application scenario description, a titanium alloy ultra-thin-walled cabin part (with a wall thickness of 1 mm, reaching the casting limit) is selected for test verification. The titanium alloy riser preheating temperature is 800℃, the riser inner diameter is 50 mm, and the riser wall thickness is 5 mm. The filling is successfully completed within the melting time calculated in the above theory, and the part slightly melts after the riser is pulled out and inserted into the melt, Figure 2 is a photo of the riser pulled out after the filling is completed; Figure 3These are 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.

[0054] 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 of using a riser for counter-gravity investment casting of titanium alloys, the riser being located above a water-cooled copper crucible and below a sprue inlet of a mold shell, the method comprising: The liquid lifting pipe is made of the same material as the material in the water-cooled copper crucible; The method for using the liquid lifting pipe for titanium alloy counter-gravity investment casting comprises the following steps: The influence 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 parameter selection specification of the liquid lifting pipe is obtained; According to the parameter selection specification of the liquid lifting pipe, 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 used for casting are selected; After the material in the water-cooled copper crucible is completely melted, the casting mold is started to descend, the preheated liquid lifting pipe is inserted into the melt in the water-cooled copper crucible, and the counter-gravity filling is performed through the linkage operation of the mold descending and filling; The analysis of the influence 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 through theoretical calculation comprises the following steps: The heat absorbed by the liquid lifting pipe and the convective heat flow in the four stages of the first solid sensible heat, the phase change latent heat, the second solid sensible heat and the melting latent heat are calculated respectively; The induction heating power P of the riser inserted into the melt is calculated from the smelting power, the mass of the melt and the mass of the riser inserted into the melt ind ; According to the four stages of the heat absorbed by the riser and the convective heat flow and the induction heating power P of the riser inserted into the melt, solid sensible heat, phase change latent heat, second solid sensible heat and melting latent heat ind , the total melting time of the riser inserted into the melt portion is calculated ; A plurality of liquid lifting pipe wall thicknesses, a plurality of liquid lifting pipe inner diameters and a plurality of liquid lifting pipe preheating temperatures are selected, and the total melting time of the inserted melt part of the liquid lifting pipe corresponding to any liquid lifting pipe wall thickness, any liquid lifting pipe inner diameter and any liquid lifting pipe preheating temperature is calculated, so as to obtain a time table of the melting of the liquid lifting pipe caused by different influencing factors. The length of the liquid lifting pipe for titanium alloy counter-gravity investment casting is within 500 mm.

2. The method of using a riser for counter-gravity investment casting of titanium alloys of claim 1, wherein: The wall thickness of the counter-gravity investment casting is 1-3 mm.

3. The method of using a riser for titanium alloy counter-gravity investment casting of claim 1, wherein: The linkage operation of the mold descending and filling comprises the following steps: the mold descending in place signal is used as the automatic starting signal of the filling, and the inert gas is injected into the down working tank to fill immediately after the mold is descended in place.

4. The method of using a riser for counter-gravity investment casting of titanium alloys of claim 1, wherein: The parameter selection specification of the liquid lifting pipe comprises the following steps:

5. The method of using a riser for counter-gravity investment casting of titanium alloys of claim 1, wherein: The liquid lifting pipe wall thickness is preferentially controlled to adjust the melting time of the liquid lifting pipe; The liquid lifting pipe preheating temperature is selected in combination with the preheating temperature limit of the actual production equipment and the casting process design; The influence of the change of the inner diameter of the liquid lifting pipe on the melting time of the liquid lifting pipe is ignored, and the inner diameter of the liquid lifting pipe is selected according to the requirements of the casting process design.

6. The method for using the liquid lifting pipe for titanium alloy counter-gravity investment casting according to claim 1, wherein 7. The method for using the liquid lifting pipe for titanium alloy counter-gravity investment casting according to claim 6, wherein The heat absorbed by the riser in the first solid sensible heat stage is calculated by the formula: , wherein m is the mass of the riser lower end inserted into the melt portion, kg; is the specific heat capacity of the smelting material in the water-cooled copper crucible, J / kg•℃; T0 is the preheating temperature of the riser, ℃; T β is the phase change temperature, ℃; The heat absorbed by the liquid rising pipe in the phase change latent heat stage is calculated by the formula: ; wherein, J; is the solid phase change latent heat value, kJ / kg. The heat absorbed by the riser in the second solid sensible heat phase is calculated by the formula: wherein is the melting temperature, °C. The heat absorbed by the riser during the latent heat of fusion phase is calculated by the equation: wherein is the latent heat of fusion value, kJ / kg.

8. The method for using the liquid lifting pipe for titanium alloy counter-gravity investment casting according to claim 7, wherein The convective heat flow of the riser in the first solid sensible heat phase is calculated by the formula: , wherein h is the convective heat transfer coefficient, ; A is the sum of the inner surface area and the outer surface area of the riser lower end inserted into the melt portion, m 2 ; ; is the melt temperature, ℃; The convective heat flow of the riser in the phase change latent heat stage is calculated by the formula: ; wherein, ; The convective heat flow of the riser during the second solid sensible heat phase is calculated by the equation: where ; The convective heat flow of the riser during the latent heat of fusion phase is calculated by the equation: where . ​ According to the four stages of the heat absorbed by the riser and the convective heat flow and the induction heating power P of the riser inserted into the melt, solid sensible heat, phase change latent heat, second solid sensible heat and melting latent heat ind , the total melting time of the riser inserted into the melt portion is calculated It comprises: The total melt time of the riser inserted into the melt section is calculated by the equation: , wherein ; ; ; .

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