Self-adaptive upward variable-speed drawing directional solidification device and method

Abstract

The invention belongs to the field of metal casting, and relates to a self-adaptive upward variable-speed drawing directional solidification device and method, and the device comprises a crystallizer, a cooler, a furnace chamber, a sealing cover, a heater, a crucible, an electric linear motion mechanism, a mold shell and a seed crystal; the sealing cover is detachably and hermetically connected to the top of the furnace chamber; the crucible is positioned in the furnace chamber; the heater penetrates through the outer wall of the furnace chamber and extends into the furnace chamber; the electric linear motion mechanism is arranged at the top of the sealing cover, the crystallizer vertically penetrates through the sealing cover and extends into the furnace chamber, the electric linear motion mechanism is connected with the top of the crystallizer, and the seed crystal is arranged at the bottom of the crystallizer; the mold shell is located under the seed crystal, cooling rings are wound around the top end outside the mold shell, the bottom end of the cooler is communicated with the two cooling rings, the cooler is parallel to the crystallizer and extends out of the furnace cavity from the top of the sealing cover, and the top end of the cooler is detachably connected with the electric linear motion mechanism. And the drawing speed of different stages can be controlled to control the bending degree of a solidification interface, and oblique crystals are controlled.

Description

Technical Field

[0001] The invention belongs to the field of metal casting and relates to an adaptive upward variable-speed drawing directional solidification device and method. Background Art

[0002] During the solidification process, crystals usually exhibit the growth characteristic of preferred orientation, which results in anisotropy of their physical properties in different directions. The specific mechanism of crystal growth mainly depends on the advancement process of the liquid-solid interface, which is largely affected by the temperature gradient at the front of the liquid-solid interface. At the same time, during the solidification process, due to the influence of the temperature gradient at that time, the solidification liquid surface will be bent, which further causes the growth of the tissue not to meet the expectations, resulting in defects such as inclined crystals, and finally affecting the service performance of single crystal blades. Summary of the Invention

[0003] The purpose of the invention is to overcome the above-mentioned shortcomings of the prior art and provide an adaptive upward variable-speed drawing directional solidification device and method, which can control the drawing speed in different stages to control the bending degree of the solidification interface and control the occurrence of inclined crystals.

[0004] To achieve the above purpose, the invention adopts the following technical solutions: An adaptive upward variable-speed drawing directional solidification device includes a crystallizer, a cooler, a furnace cavity, a sealing cover, a heater, a crucible, an electric linear motion mechanism, a mold shell and a seed crystal; The sealing cover is detachably and sealingly connected to the top of the furnace cavity; the crucible is located inside the furnace cavity, the opening of the crucible faces upward, and the inside of the crucible is used to hold the alloy liquid; the heater passes through the outer wall of the furnace cavity and extends into the furnace cavity; The electric linear motion mechanism is arranged on the top of the sealing cover, the crystallizer extends vertically through the sealing cover into the furnace cavity, the electric linear motion mechanism is connected to the top of the crystallizer, and the seed crystal is arranged at the bottom of the crystallizer; the mold shell is located directly below the seed crystal, and a cooling ring is wound around the outer top of the mold shell. The bottom end of the cooler is communicated with both cooling rings. The cooler is parallel to the crystallizer and extends out of the furnace cavity from the top of the sealing cover. The top end of the cooler is detachably connected to the electric linear motion mechanism.

[0005] Preferably, the crystallizer is of a circular rod structure, and an air duct and a chill are arranged on the crystallizer. The chill is located outside the crystallizer, and the air duct communicates from the top of the crystallizer to the bottom of the crystallizer.

[0006] Preferably, a plurality of bifurcations are arranged at the bottom of the air duct, and the plurality of bifurcations face the outer contour of the bottom of the crystallizer.

[0007] Preferably, the cross-section of the mold shell is U-shaped, a hollow tube is arranged in the middle of the mold shell, the hollow tube is located directly below the seed crystal, and the bottom of the hollow tube is communicated with the inside of the mold shell.

[0008] Preferably, the top of the hollow tube is a funnel-shaped structure.

[0009] Preferably, the electric linear motion mechanism includes a bearing, a screw slider, a screw, a second bevel gear, a first bevel gear, a servo motor and a connecting ring. There are two screws. The connecting ring is connected to the top of the crystallizer. The connecting ring is connected to the screw slider through a connecting rod. The screw slider is threadedly connected to the screw. The top of the screw is connected to the second bevel gear, the second bevel gear is meshed with the first bevel gear, and the first bevel gear is connected to the output shaft of the servo motor.

[0010] Preferably, a connecting piece is provided at the top of the cooler, and one end of the connecting rod extends out of a screw slider and is detachably connected to the connecting piece.

[0011] An adaptive upward variable speed pulling directional solidification method includes the following processes: The crystallizer is inserted into the mold shell with the seed crystal, the raw metal is placed in the crucible, the heater is started, the raw metal is heated and melted to obtain the alloy liquid, and then the molten alloy liquid in the crucible is poured into the mold shell, and the mold shell is placed in the heating area of ​​the heater; when the alloy liquid is filled to 3-4 cm from the end of the seed crystal, the casting is stopped; according to the pulling speed corresponding to different areas of the casting, the electric linear motion mechanism is used to change the speed of the crystallizer and the cooler and pull them upward until the mold shell is completely out of the heating area of ​​the heater. After standing and cooling, the mold shell is disassembled to obtain the casting.

[0012] Preferably, the electric linear motion mechanism comprises a bearing, a screw slider, a screw, a second bevel gear, a first bevel gear, a servo motor and a connecting clamp ring, the number of screws is two, the connecting clamp ring is connected to the top of the crystallizer, the connecting clamp ring is connected to the screw slider through a connecting rod, the screw slider is threadedly connected to the screw, the top of the screw is connected to the second bevel gear, the second bevel gear is meshed with the first bevel gear, and the first bevel gear is connected to the output shaft of the servo motor; A connecting piece is arranged at the top of the cooler, and one end of the connecting rod extends out of a screw rod slider and is detachably connected to the connecting piece; The servo motor changes speed according to the pulling speed corresponding to different areas of the casting, and drives the screw to rotate through the second bevel gear meshing with the first bevel gear, so that the screw slider moves upward along the screw, and the connecting clamp and the connecting part move upward with the screw slider through the connecting rod, thereby driving the crystallizer and cooler to move upward. The cooler drives the mold shell to move upward synchronously with the crystallizer through the cooling ring.

[0013] Preferably, the calculation process of the pulling speed corresponding to different areas of the casting is: S1, establish a three-dimensional model of the casting; S2, dividing the three-dimensional model of the casting into regions along the axial direction, slicing both ends of each region, and calculating the cross-sectional area of ​​each slice; S3. Calculate the cross-sectional change factor of adjacent slices according to the cross-sectional area difference of adjacent slices; S4. Calculate the velocity change rate of adjacent slices based on the cross-sectional change factor of adjacent slices; S5. Set the initial drawing speed, and obtain the drawing speed corresponding to each area of the casting according to the initial drawing speed and the velocity change rate of adjacent slices.

[0014] Compared with the prior art, the present invention has the following beneficial effects: The present invention adopts an electric linear motion mechanism, which can drive the mold and the die shell to be drawn upward synchronously, and the electric linear motion mechanism can control and adjust the upward drawing speed in real time. While controlling the growth of crystals in a certain direction, it also controls the bending degree of its solidification interface, thereby controlling the growth direction of crystals, and thus preparing materials with precisely controllable physical properties in a specific direction. Description of the Drawings

[0015] Figure 1 It is a sectional view of the adaptive upward variable-speed drawing directional solidification device according to Embodiment 1 of the present invention; Figure 2 It is a schematic structural diagram of the electric linear motion mechanism according to Embodiment 1 of the present invention; Figure 3 It is a schematic diagram of the use process of the adaptive upward variable-speed drawing directional solidification device according to Embodiment 1 of the present invention; Figure 4 It is a schematic diagram of the convection caused by the upward growth of the single crystal process dendrite with adaptive variable-speed upward drawing according to Embodiment 1 of the present invention; Figure 5 It is a variable-speed broken line graph of the actual blade according to Embodiment 2 of the present invention; Figure 6 It is a schematic diagram of the change of defects caused by the change of different drawing speeds in the same interval according to Embodiment 2 of the present invention.

[0016] Among them, 1 - mold; 2 - cooler; 3 - furnace cavity; 4 - sealing cover; 5 - heater; 6 - ceramic ball; 7 - crucible; 8 - heat insulation pad; 9 - alloy liquid; 10 - electric linear motion mechanism; 11 - die shell; 12 - seed crystal; 13 - connecting piece; 14 - cooling ring; 101 - bearing; 102 - screw rod slider; 103 - screw rod; 104 - second bevel gear; 105 - first bevel gear; 106 - servo motor; 107 - connecting clamp ring. Detailed Embodiments

[0017] Next, the technical solutions in the embodiments of the present application will be clearly and completely described in conjunction with the drawings in the embodiments of the present application.

[0018] Embodiment 1: As shown Figure 1 in the figure, this embodiment provides an adaptive upward variable-speed drawing directional solidification device, which includes a mold 1, a cooler 2, a furnace chamber 3, a sealing cover 4, a heater 5, a ceramic ball 6, a crucible 7, a heat insulation pad 8, an electric linear motion mechanism 10, a mold shell 11 and a seed crystal 12.

[0019] The sealing cover 4 is placed on the top of the furnace chamber 3 and is detachably and sealingly connected to the top of the furnace chamber 3; the heat insulation pad 8 and the crucible 7 are located inside the furnace chamber 3, the heat insulation pad 8 is located on the inner bottom surface of the furnace chamber 3, the crucible 7 is placed on the heat insulation pad 8, the opening of the crucible 7 faces upward, the crucible 7 is used to hold the alloy liquid 9, and the heat insulation pad 8 is used to prevent the crucible 7 from directly contacting the furnace chamber 3; the heater 5 passes through the outer wall of the furnace chamber 3 and extends into the furnace chamber 3, and the heater 5 surrounds the crucible 7 or the mold shell 11 to realize the heating of the alloy liquid 9 in the crucible 7 and the mold shell 11. The ceramic ball 6 is located in the crucible 7 and covers the liquid surface of the alloy liquid 9 to play a heat preservation role, thereby indirectly increasing the temperature gradient near the solid-liquid interface.

[0020] The mold 1 extends vertically through the sealing cover 4 into the furnace chamber 3. The electric linear motion mechanism 10 is arranged on the top of the sealing cover 4, and the electric linear motion mechanism 10 is connected to the top of the mold 1 for moving the mold 1 up and down and adjusting the speed of the up and down movement of the mold 1.

[0021] The mold 1 is a circular rod structure, and an air passage, a chill and a seed crystal 12 are arranged on the mold 1. The chill is located at the outer position near the bottom of the mold 1, the seed crystal 12 is arranged at the bottom of the mold 1, the air passage communicates from the top of the mold 1 to the bottom of the mold 1, and a plurality of bifurcations are arranged at the bottom of the air passage, and the plurality of bifurcations face the outer contour of the bottom of the mold 1.

[0022] The material of the mold shell 11 is ceramic, the cross-section of the mold shell 11 is U-shaped, a hollow tube is arranged in the middle of the mold shell 11, the hollow tube is located directly below the seed crystal 12, the top of the hollow tube is set as a funnel-shaped structure, the bottom of the hollow tube communicates with the inside of the mold shell 11, and a cooling ring 14 is wound around the outer top of the mold shell 11, and the cooling ring 14 seals the outer top of the mold shell 11.

[0023] The bottom end of the cooler 2 is communicated with both cooling rings 14. The cooler 2 is parallel to the mold 1 and extends out of the furnace chamber 3 from the top of the sealing cover 4. A connecting piece 13 is arranged at the top end of the cooler 2, and the connecting piece 13 is detachably connected to the electric linear motion mechanism 10.

[0024] As shown Figure 2As shown in the figure, the electric linear motion mechanism 10 includes a bearing 101, a lead screw slider 102, a lead screw 103, a second bevel gear 104, a first bevel gear 105, a servo motor 106, and a connecting collar 107. The number of lead screws 103 is two. The connecting collar 107 is connected to the top of the mold 1. The connecting collar 107 and the lead screw slider 102 are connected by a connecting rod. One end of the connecting rod extends out of the lead screw slider 102 and is detachably connected to the connecting member 13. The lead screw slider 102 is threadedly connected to the lead screw 103. The top of the lead screw 103 is connected to the second bevel gear 104. The second bevel gear 104 meshes with the first bevel gear 105. The first bevel gear 105 is connected to the output shaft of the servo motor 106.

[0025] When the servo motor 106 rotates, it meshes with the second bevel gear 104 and the first bevel gear 105, driving the lead screw 103 to rotate, causing the lead screw slider 102 to move up and down along the lead screw 103. Both the connecting collar 107 and the connecting member 13 move up and down with the lead screw slider 102 through the connecting rod, thereby driving the mold 1 and the cooler 2 to move up and down. The cooler 2 drives the mold shell 11 to move up and down synchronously with the mold 1 through the cooling ring 14, ensuring that the alloy liquid of the seed crystal 12 solidifies downward directionally to form a single crystal.

[0026] Based on the above adaptive upward variable-speed drawing directional solidification device, this embodiment also provides an adaptive upward variable-speed drawing directional solidification method, as Figure 3 shown, which includes the following processes: As Figure 3 a- Figure 3 As shown in b, the mold 1 with the seed crystal 12 extends into the mold shell 11. The material of the seed crystal 12 is generally the same as that of the raw material metal, or a metal or ceramic with a higher melting point.

[0027] Put the raw material metal into the crucible 7, start the heater 5, heat and melt the raw material metal to obtain the alloy liquid 9, and then pour the melted alloy liquid 9 in the crucible 7 into the mold shell 11. After the alloy liquid 9 enters the mold shell 11, it fills the side of the mold shell 11. The mold shell 11 is placed in the heating area of the heater 5. At this time, keep the temperature of the heater 5 to make the fluidity of the alloy liquid 9 better. When the alloy liquid 9 flows to the top of the side of the mold shell 11, it will be cooled by the cooling ring 14, restricting the height of the alloy liquid 9.

[0028] Observe the interface of the alloy liquid 9 in the mold shell 11. When the alloy liquid 9 fills to a position 3 - 4 cm from the end of the seed crystal 12, stop casting. According to the pre-calculated drawing speeds corresponding to different regions of the casting, as Figure 3As shown in c, the electric linear motion mechanism 10 is used to change the speed of the crystallizer 1 and the cooler 2 and pull them upward. The electric linear motion mechanism 10 pulls the crystallizer 1 and the cooler 2 upward together. The electric linear motion mechanism 10 is connected to the cooler 2 through the connecting piece 13. The cooler 2 is pulled upward synchronously with the crystallizer 1 together with the mold shell 11 through the cooling ring 14 until the mold shell 11 is completely separated from the heating area of ​​the heater 5. After standing and cooling, the mold shell 11 is disassembled to obtain a casting.

[0029] The calculation process of the pulling speed corresponding to different areas of the casting is: S1, establish a three-dimensional model of the casting; S2: Divide the three-dimensional model of the casting into regions along the axial direction (z direction), slice each region at both ends, and calculate the cross-sectional area of ​​each slice. .

[0030] S3, calculate the cross-sectional variation factor C of adjacent slices.

[0031] S4, based on the cross-sectional change factor C of adjacent slices, calculate the velocity change rate of adjacent slices .

[0032] S5, set the initial pulling speed, and change the speed according to the initial pulling speed and the speed of the adjacent slices , and obtain the pulling speed corresponding to each area of ​​the casting.

[0033] like Figure 4 As shown, in the adaptive variable speed upward pulling process of the single crystal of the present invention, dendrites grow upward. During the upward pulling process, convection occurs between the normal liquid phase area and the solid phase paste area below, and the nucleation direction of the grains is vertically upward to form dendrites.

[0034] The reason why the present embodiment performs adaptive variable speed pulling is that during the directional solidification process, due to the shape of the casting, if the casting is pulled upward at a certain speed, the shape of the casting will change, and the temperature gradient curve of the solid-liquid interface of the casting during solidification will bend. When the temperature gradient curve bends, the internal structure of the casting will tilt toward the grain boundary, thereby affecting the growth direction of the crystal, which will cause defects such as orthorhombic freckles. Therefore, the process of adaptive variable speed pulling sets different pulling speeds for sections of different shapes of the casting to ensure that the temperature gradient curve will not bend during cooling, thereby ensuring the growth orientation of the crystal to avoid the occurrence of defects.

[0035] The calculation principle of the pulling speed corresponding to different areas of the above casting is as follows: Taking the heating area of the heater 5 as the hot zone and the area above the heating area as the cold zone, assuming the imaginary plane between the hot zone and the cold zone is the hot-cold interface, the cross-sectional area of the casting passing through the hot-cold interface is , when the isotherm of the S / L interface of the casting remains at a constant horizontal position aligned with the hot-cold interface and remains unchanged throughout the directional solidification process, it is in an equilibrium state. At this time, the following conservation needs to be satisfied: (1) In the formula, represents the comprehensive cooling power of the casting at the isotherm of the S / L interface (i.e., the hot-cold interface), which is greatly affected by the geometry of the casting (i.e., ). The right term of formula (1) represents the latent heat released when the casting completely solidifies through the hot-cold interface per unit time, which is called latent heat and released energy. In formula (1), and respectively represent the crystallization density and crystallization latent heat of the alloy, while represents the critical withdrawal speed (critical pulling speed) required to keep the isotherm of the S / L interface stationary, aligned with the hot-cold interface.

[0036] In the actual directional solidification process, the isotherm of the S / L interface can move above or below the hot-cold interface and enter the cold zone or the hot zone according to the selected withdrawal speed (pulling speed) V. In this case, the actual comprehensive cooling power consists of and lateral radiation heat dissipation. When the isotherm of the S / L interface is in the cold zone, the part of the casting between the hot-cold interface and the isotherm of the S / L interface encounters additional lateral radiation cooling because it is hotter than the inner wall of the furnace chamber 3, increasing > ). On the contrary, when the isotherm of the S / L interface is in the hot zone, the casting section between the hot-cold interface and the isotherm of the S / L interface is subjected to additional lateral radiation heating from the heater 5, resulting in decreasing ( < ). The additional lateral radiation power due to the shift of the isotherm position of the S / L interface relative to the equilibrium situation is defined as . The value of (2) The relationship between the power and V can be expressed as: (3) Based on radiative heat transfer, the power P r can be expressed as: (4) where represents the effective area of lateral radiative heat transfer. Its value is equal to the perimeter of the isotherm of the S / L interface at the z-direction position multiplied by the height difference between the isotherm of the S / L interface and the cold / hot zone interface where . represents the effective temperature of the radiative surface ; represents the corresponding inner wall temperature of the furnace chamber 3 (cold zone or hot zone). The symbol is a coefficient to be determined, adjusted according to the process to reflect the actual situation, and equal to 1 under ideal conditions. The symbol represents the emissivity of the radiative surface, is the Stefan-Boltzmann constant, taking 5.67×10 -8 W / (m 2 K 4 ).

[0037] Assume that at a certain solidification moment, the center of the cross-section of the cold / hot zone interface of the casting is 0, then the downward power can be considered as the sum of each infinitesimal downward powder . The shape of the infinitesimal can be regarded as a sector with 0 and as the vertex and radius. Therefore can be expressed as Equation 5 and Equation 6. The area of the infinitesimal sector in the direction is approximately equal to the area of a triangle, that is , is the lateral displacement distance.

[0038] (5) (6) Similarly, the additional radiative power can also be considered as the sum of each infinitesimal lateral radiative power along the radius direction. The shape of the infinitesimal should be a rectangle, i.e., the arc length of the sector) and as the two side lengths. The area of the rectangular infinitesimal in the direction can be calculated as . Therefore, can be expressed as: (7) (8) Among them, is the height of the radiation surface, and its specific height is the height at which the actual solid-liquid interface deviates from the hot-cold division interface.

[0039] In and 's definitions, is positive when aligned with the retraction direction (i.e., the negative z-axis direction), is positive when extending radially along radius. Therefore, for any radius direction, the slope can be approximated as - / . The S / L interface isotherm should be perpendicular to this slope, so: (9) (10) In equations (9) and (10), C represents the cross-sectional change factor related to the z position, including the effects of radiative heat transfer and casting geometry. Reducing the slope of the isotherm to zero requires to be zero. is roughly linearly dependent on , and is related to C at different z positions. Then, can be analytically expressed as: (11) From equation (11), it can be seen that the slope of any radial S / L interface isotherm has a linear relationship with the withdrawal speed V, and the influencing factors are only related to the casting cross-sectional shape factor α (α = ) and the critical withdrawal speed . Equation (11) establishes a linear relationship between the inclination angle θ of the S / L interface isotherm (k = tan(θ)) and the pulling speed V . To ensure that the S / L interface isotherm is flat and eliminate the formation of misoriented grains, the slope k needs to approach zero as much as possible. From equation (11), it can be seen that the pulling speed V should be set to . Therefore, the derivation of the pulling speed is based on the power balance of latent heat release and heat transfer during solidification, and the basic assumption is that the heat transfer capacity of the system is fully matched. In this case, the solidification speed R will be affected by the pulling-out speed V, and the pulling speed V will in turn affect the power balance through heat transfer. This form conversion from "force" to "speed" will make it easier to apply to the case of complex shapes.

[0040] As the reference equilibrium speed, It needs to be obtained by specifying the cross-sectional projection shape, so it should be a function of Z . However, since varies with the shape of the casting (i.e., the cross-sectional area of the casting), therefore, directly determining the distribution of V through the constants α and by formula (11) may lead to inaccuracies. However, if the variable speed strategy is recalculated considering the cross-sectional changes at each position , then the corresponding needs to be recalculated separately for each position , which makes this algorithm too cumbersome to use in engineering. To solve the contradiction between accuracy and simplicity, this algorithm needs to correct the influence of complex shapes once based on a pair of constant shape factors (α, ), rather than directly solving the variable speed strategy through formula (11). Because the recorded at each time node (measured or simulated) is itself the result of the interaction of various physical fields at the corresponding position. That is, it implicitly contains the heat transfer information (including heat conduction, convection, and radiation) caused by the original complex shape of the casting. If the solidification process strictly follows formula (9), the appropriate drawing speed should satisfy ΔZ = 0 (k = 0) at each position. It should be emphasized that to achieve the condition of k = 0 through ΔZ = 0, the conservation of formula (2) must be satisfied. However, in a more general case, even if ΔZ = 0 is satisfied at the beginning of solidification, the isotherm position of the S / L interface cannot remain unchanged during the directional solidification process, and it will also move vertically at a speed of V m (the subscript m represents movement). Therefore, the actual formula (2) cannot be achieved. Therefore, the existence of V m can cause the observed ΔZ≠0 even when k = 0. That is, when formula (2) is not satisfied, there is: (12) At the observation position Z V m not equal to 0, the observed ΔZ consists of three parts: (1) the part affected by the isothermal slope k, denoted as ΔZ k ; (2) the cumulative displacement error ΔZ error , where t is the time from the start of solidification (t = 0) to the observation time (t = t record , t record is the observation moment) calculated as ∫V m dt, and d is the integral symbol; (3) ΔZ initial is the height difference between the initial solidification interface and the plane Z = 0 (when the two are on the same horizontal plane, ΔZ initial= 0). In this case, keeping the isothermal line slope of the S / L interface at zero (k = 0) is equivalent to ensuring that only the component affected by the slope is zero (ΔZ k = 0), when considering errors, ΔZ should be corrected to ΔZ k .

[0041] Therefore, if the furnace allows early intervention control, V m can be corrected in real time to make ΔZ error close to 0. If the initial solidification interface is taken as the Z = 0 plane, ΔZ initial can also be set to 0. In this case, the observed ΔZ can be considered approximately equivalent to ΔZ k (ΔZ≈ΔZ k ). In this case, an optimal withdrawal speed strategy that is still effective even without strict protection can be generated, and the information provided in ΔZ can be fully utilized. First, through Equation (11), multiple sets of constant withdrawal speed processes can be carried out as a reference to calculate a unique reference . Then, the withdrawal speed is compensated to obtain the adaptive control distribution V i (i = 1,2,3......n) as follows: (13) where V c (ΔZ ki ) represents the compensation function of the withdrawal speed. When ΔZ ki (taking ΔZ k at the i position, i = 1,2,3... ...n) is positive, a positive withdrawal speed should be compensated to increase V i (V i > ), otherwise, a negative withdrawal speed is adjusted to decrease V i (V i < ). Referring to Equation (9), assuming that the compensated withdrawal speed has an approximately linear relationship with ΔZ i , then the maximum value ΔZ i is selected from all ΔZ ki values (all being ΔZ max ) to determine the coefficient Cc. The absolute value of the reciprocal of this coefficient |1 / Cc| represents the most conservative linear compensation factor, aiming to minimize the modification of Vi to prevent unreasonable withdrawal speeds. For example, a set of ΔZ baseline is measured at a constant speed V i of 8 mm / min (ΔZ error = 0, ΔZ initial = 0), V baseline is the pulling speed of the traditional process, and the measurement of a certain casting was 2 mm / min, and the observed ΔZ max was 12 mm. In this case, the velocity difference (V baseline - ) was 8 - 2 = 6 mm / min, and the maximum ΔZ i was 12 mm. That is to say, for every 1 mm compensation of ΔZ (correct to 0), a speed of 0.5 mm / min (6 / 12) is required. Therefore, formula (13) can be changed to formula (14): (14) where V baseline represents the reference withdrawal rate used in the process of deriving ΔZ. The function of formula (14) is to make ΔZ i constantly approach 0 from the beginning of the directional solidification process, the faster the better. This operation is used to correct the cumulative ΔZ error outlined in formula (12) at each stage of the extraction process, ensuring that after compensation, ΔZ error is approximately equal to 0. Therefore, the condition of k = 0 is essentially equivalent to ΔZ initial being 0 when the observed ΔZ = 0. Therefore, when using formula (14) to calculate the exit distribution, it will not be negatively affected by ΔZ error , thus making the result have satisfactory accuracy. The formation of misaligned grains in directional solidification is the collective result of the isothermal line slopes of the S / L interface at each cross-sectional position along the axial direction of the casting at different time points during the directional solidification process. Therefore, the average deviation angle θ mg of the misaligned grains (θ mg-i at each position, i = 1, 2, 3......n) should be related to the average isothermal k i value of the entire directional solidification process and correspond to the empirical ratio C m of the casting material. It can be expressed as formula (15) and formula (16): (15) (16) where the average deviation slope k mg of the misaligned grains can be obtained through metallographic inspection. -1 / k mg represents that the growth direction is perpendicular to the growth plane. Through the above derivation and discussion, the functional relationship between the deviation angle of the misaligned grains and the withdrawal speed is established. Through formula (14), the optimal adaptive variable withdrawal speed strategy can be obtained under specified conditions.

[0042] Example 2: In this example, the adaptive upward variable speed drawing directional solidification device and the adaptive upward variable speed drawing directional solidification method of Example 1 are used to prepare blades.

[0043] The raw material metal is DZ409 nickel-based directional high-temperature alloy. First, install the crystallizer 1 with the airway processed, install the seed crystal 12 made of DZ409 to the bottom of the crystallizer 1, and then install the U-shaped mold shell 11. The inner diameter of the hollow tube of the mold shell 11 is 12 mm, and the overall average cross-section of the mold shell 11 is 40 mm. Then, the procast simulation model is used to obtain the speed compensation value corresponding to different pulling distances, so as to obtain the polyline of distance and speed as shown in the figure: Figure 5 As shown, this broken line is then introduced into the control program of the servo motor 106. Then, the DZ409 nickel-based directional high-temperature alloy block to be used is placed in a crucible 7 made of D100, and the equipment is installed according to the adaptive upward variable speed pulling directional solidification device of the present invention. Then, the heater 5 is started to melt the alloy, and the surface of the alloy liquid 9 is covered with ceramic balls 6 with a size of 20 mm, and then the sealing device 4 is used to seal, and the furnace chamber 3 is converted to an Ar gas atmosphere to keep the alloy liquid 9 overheated by 50°C above the melting point.

[0044] The alloy liquid 9 melted in the crucible 7 is poured into the mold shell 11 . After entering the mold shell 11 , the alloy liquid 9 fills the side of the mold shell 11 .

[0045] The electric linear motion mechanism 10 starts to pull the crystallizer 1 upward at a set speed. At this time, the crystallizer 1 and the mold shell 11 move upward together. Driven by the electric linear motion mechanism 10, different pulling speeds are adopted for different sections.

[0046] like Figure 6 a. Figure 6 b and Figure 6 As shown in Figure c, when the pulling speeds are 3 mm / min, 4 mm / min, and 5 mm / min, the microscopic defects observed in the cross section of the casting have defect volume fractions of 0.082%, 0.074%, and 0.062%, respectively. Figure 6 As shown in d, the quality of the castings formed is different when different pulling speeds are used in the same section. It can be seen that the quality of the castings obtained in one area is different when different pulling speeds are used, so different pulling speeds should be selected for different cross-sectional sections.

[0047] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present application, rather than to limit it. Although the present application has been described in detail with reference to the aforementioned embodiments, those skilled in the art should understand that they can still modify the technical solutions described in the aforementioned embodiments, or replace some or all of the technical features therein with equivalents. However, these modifications or replacements do not cause the essence of the corresponding technical solutions to deviate from the scope of the technical solutions of the embodiments of the present application.

Claims

1. An adaptive upward variable-speed drawing directional solidification device, characterized in that, It includes a mold (1), a cooler (2), a furnace cavity (3), a sealing cover (4), a heater (5), a crucible (7), an electric linear motion mechanism (10), a mold shell (11) and a seed crystal (12); The sealing cover (4) is detachably and sealingly connected to the top of the furnace cavity (3); the crucible (7) is located inside the furnace cavity (3), the opening of the crucible (7) faces upward, and the inside of the crucible (7) is used to hold the alloy liquid (9); the heater (5) passes through the outer wall of the furnace cavity (3) and extends into the furnace cavity (3); The electric linear motion mechanism (10) is arranged on the top of the sealing cover (4), the mold (1) extends into the furnace cavity (3) vertically through the sealing cover (4), the electric linear motion mechanism (10) is connected to the top of the mold (1), and the seed crystal (12) is arranged at the bottom of the mold (1); the mold shell (11) is located directly below the seed crystal (12), a cooling ring (14) is wound around the outer top of the mold shell (11), the bottom end of the cooler (2) is communicated with both cooling rings (14), the cooler (2) is parallel to the mold (1), extends out of the furnace cavity (3) from the top of the sealing cover (4), and the top end of the cooler (2) is detachably connected to the electric linear motion mechanism (10).

2. The adaptive upward variable-speed drawing directional solidification device according to claim 1, wherein The mold (1) is of a circular rod structure, and an air channel and chill blocks are arranged on the mold (1), the chill blocks are located outside the mold (1), and the air channel communicates from the top of the mold (1) to the bottom of the mold (1).

3. The adaptive upward variable-speed drawing directional solidification device according to claim 2, wherein A number of bifurcations are arranged at the bottom of the air channel, and the number of bifurcations faces the outer contour of the bottom of the mold (1).

4. The adaptive upward variable-speed drawing directional solidification device according to claim 1, wherein, The cross section of the mold shell (11) is U-shaped, a hollow tube is arranged in the middle of the mold shell (11), the hollow tube is located directly below the seed crystal (12), and the bottom of the hollow tube is communicated with the inside of the mold shell (11).

5. The adaptive upward variable-speed drawing directional solidification device according to claim 4, characterized in that, The top of the hollow tube is of a funnel-shaped structure.

6. The adaptive upward variable-speed drawing directional solidification device according to claim 1, wherein, The electric linear motion mechanism (10) includes a bearing (101), a lead screw slider (102), a lead screw (103), a second bevel gear (104), a first bevel gear (105), a servo motor (106) and a connecting collar (107). The number of lead screws (103) is two. The connecting collar (107) is connected to the top of the mold (1), the connecting collar (107) is connected to the lead screw slider (102) through a connecting rod, the lead screw slider (102) is threadedly connected to the lead screw (103), the top of the lead screw (103) is connected to the second bevel gear (104), the second bevel gear (104) meshes with the first bevel gear (105), and the first bevel gear (105) is connected to the output shaft of the servo motor (106).

7. The adaptive upward variable-speed drawing directional solidification device according to claim 6, wherein A connecting piece (13) is arranged at the top end of the cooler (2), and one end of the connecting rod extends out of the lead screw slider (102) and is detachably connected to the connecting piece (13).

8. An adaptive upward variable-speed drawing directional solidification method based on the adaptive upward variable-speed drawing directional solidification device according to any one of claims 1-7, characterized in that, It includes the following processes: The mold (1) extends into the mold shell (11) with the seed crystal (12). The raw metal is placed in the crucible (7), and the heater (5) is started to heat and melt the raw metal to obtain the alloy liquid (9). Then, the molten alloy liquid (9) in the crucible (7) is poured into the mold shell (11), and the mold shell (11) is placed in the heating area of the heater (5). When the alloy liquid (9) fills to a position 3 - 4 cm from the end of the seed crystal (12), the casting is stopped. According to the drawing speed corresponding to different regions of the casting, the electric linear motion mechanism (10) is used to draw the mold (1) and the cooler (2) upward at a variable speed until the mold shell (11) completely disengages from the heating area of the heater (5). After standing and cooling, the mold shell (11) is disassembled to obtain the casting.

9. The adaptive upward variable-speed drawing directional solidification method according to claim 8, wherein The electric linear motion mechanism (10) includes a bearing (101), a lead screw slider (102), a lead screw (103), a second bevel gear (104), a first bevel gear (105), a servo motor (106), and a connecting collar (107). The number of lead screws (103) is two. The connecting collar (107) is connected to the top of the mold (1). The connecting collar (107) is connected to the lead screw slider (102) through a connecting rod. The lead screw slider (102) is threadedly connected to the lead screw (103). The top of the lead screw (103) is connected to the second bevel gear (104). The second bevel gear (104) meshes with the first bevel gear (105). The first bevel gear (105) is connected to the output shaft of the servo motor (106). A connecting piece (13) is provided at the top end of the cooler (2). One end of the connecting rod extends out of the lead screw slider (102) and is detachably connected to the connecting piece (13). The servo motor (106) rotates at a variable speed according to the drawing speed corresponding to different regions of the casting. Through the meshing of the second bevel gear (104) and the first bevel gear (105), the lead screw (103) is driven to rotate, causing the lead screw slider (102) to move upward along the lead screw (103). The connecting collar (107) and the connecting piece (13) both move upward along with the lead screw slider (102) through the connecting rod, thereby driving the mold (1) and the cooler (2) to move upward. The cooler (2) drives the mold shell (11) to move upward synchronously with the mold (1) through the cooling ring (14).

10. The adaptive upward variable-speed drawing directional solidification method according to claim 8, wherein The calculation process of the drawing speed corresponding to different regions of the casting is as follows: S1. Establish a three-dimensional model of the casting. S2. Divide the three-dimensional model of the casting into regions along the axial direction, slice both ends of each region, and calculate the cross-sectional area of each slice. S3. Calculate the cross-sectional change factor of adjacent slices according to the difference in cross-sectional areas of adjacent slices. S4. Calculate the speed change rate of adjacent slices based on the cross-sectional change factor of adjacent slices. S5. Set the initial drawing speed. According to the initial drawing speed and the speed change rate of adjacent slices, obtain the drawing speed corresponding to each region of the casting.

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