JP6350050B2 - Vacuum suction casting method - Google Patents

Description

  The present invention relates to a vacuum suction casting method, and more particularly to a vacuum suction casting method in which a plurality of molds are provided in multiple stages for casting.

  When performing precision casting or the like of a casting having a thin-walled portion, vacuum suction casting in which the inside of the mold is decompressed and the molten metal is sucked is often used. As described in Patent Documents 1 to 3, it is known that in vacuum suction casting, defects are generated in the casting due to poor hot water in the mold or entrainment of gas. Various techniques have been tried to suppress the occurrence of this type of defect and improve productivity.

  Specifically, in Patent Documents 1 and 2, a runner is connected to the molten metal introduction part, and a plurality of gate parts are branched radially from the runway, and the pressure is reduced from the holding furnace through the molten metal introduction part and the runway. It is described that when introducing the molten metal into the product cavity, the air permeability on the product cavity side is made larger than the air permeability in the vicinity of the runner and the gate portion. It is also described that the molten metal is introduced at a low speed from the holding furnace to the molten metal introduction part or the vicinity of the runner, and then introduced at a high speed from there to the product cavity. Patent Document 3 describes that the pressure reduction speed is controlled so that the actual pressure at the time of pressure reduction reaches the target pressure reduction value without excessive amount.

JP-A-9-239516 JP 9-239517 A Japanese Patent Laid-Open No. 3-5062

  As shown in FIG. 3, when performing vacuum suction casting by installing a plurality of molds 120 in multiple stages along the runner 110 provided in the chamber 130, the opening of the runner 110 that sucks the molten metal M is opened. In the mold 120 installed on the closed portion 111 side away from the portion 112, the occurrence of casting defects due to poor hot water and gas entrainment becomes particularly serious. Even if the methods disclosed in Patent Documents 1 to 3 are applied, the tendency itself that casting defects are more likely to occur in the mold 120 on the closing portion 111 side than on the mold 120 on the opening portion 112 side of the runner 110. Is difficult to resolve.

  The problem to be solved by the present invention is that in a mold disposed at a position away from an opening for sucking molten metal into the runner when performing vacuum suction casting by installing a plurality of molds along the runner in multiple stages. Another object of the present invention is to provide a vacuum suction casting method capable of suppressing the occurrence of casting defects.

  Thus, as a result of intensive studies by the present inventors, it has been found that the frequent occurrence of casting defects in the mold disposed at a position away from the runner opening is due to the growth and reflection of turbulent flow in the melt in the runway. Thus, the present invention has been completed from the viewpoint of suppressing the occurrence of casting defects due to the effects of such turbulent growth and reflection.

  That is, in order to solve the above problems, a vacuum suction casting apparatus according to the present invention includes a hollow tubular runner having a closed portion at one end in the axial direction and an opening at the other end, a length L, an inner diameter. A hollow cylindrical shape of D, which communicates with the hollow portion of the runner at the proximal end and protrudes from the runner, and a product cavity which is communicated with the hollow portion of the gate and provided at the distal end of the gate And a vacuum suction casting apparatus having a plurality of molds provided in a plurality of stages along the runner axis, and comprising at least one mold from the end of the runner on the closed portion side. The gate size ratio L / D in the upper stage portion is made larger than the gate dimension ratio L / D in the lower stage portion made of at least one mold located on the opening side of the upper stage portion, and the runner And decompress the mold from the opening of the runner And summarized in that for sucking the hot water.

  Here, when decompressing the runner and the mold, it is preferable to reduce the decompression speed in the initial stage and the final stage of the decompression compared to the intermediate period between the initial stage and the final stage.

  The gate dimension ratio L / D may be adjusted by varying the length L.

  In the vacuum suction casting method according to the present invention, the dimensional ratio L / D of the gate is large in the upper stage mold provided on the closed side of the runner. By increasing the dimensional ratio L / D, the gate exhibits a high rectifying action on the molten metal passing through the hollow portion. In the area on the closed part side of the runway, turbulent flow growth and reflection are likely to occur in the molten metal, which causes casting defects in the mold located on the closed part side, but the upper stage located on the closed part side. In the part, the molten metal introduced into the product cavity through the gate is subjected to a large rectifying action, so that it is possible to suppress the occurrence of casting defects in the mold located on the closed part side.

  Here, when decompression of runners and molds is performed, in the initial and final stages of decompression, if the decompression rate is lower than the intermediate period between the initial and final stages, turbulent growth and reflection in the runway It can reduce itself. Thereby, generation | occurrence | production of a casting defect can be suppressed effectively.

  In addition, when adjusting the dimensional ratio L / D of the gate by changing the length L, the dimensional ratio is reduced without reducing the inner diameter D of the gate in the mold arranged on the side of the closed portion of the runner. L / D can be increased. If the inner diameter D of the gate is reduced, a hot water defect that causes a casting defect is likely to occur in the product cavity. However, by increasing the dimensional ratio L / D while maintaining the inner diameter D, the casting defect is effective. Can be suppressed.

(A) is a schematic diagram which shows an example of the vacuum suction casting apparatus used for the vacuum suction casting method concerning one Embodiment of this invention. (B) is an enlarged view for explaining the dimensions of the gate. It is a conceptual diagram which shows the change of pressure reduction speed. It is a schematic diagram which shows the conventional vacuum suction casting apparatus. It is a figure which shows the pressure reduction speed | velocity in an Example and a comparative example. It is a figure which shows the (a) gas defect incidence rate and (b) hot water around defect incidence rate which were obtained by actual measurement of an Example and a comparative example. It is a figure which shows the turbulent flow energy obtained by the simulation corresponding to an Example and a comparative example. It is a figure which shows the relationship between (a) gas defect occurrence rate and (b) hot-rolling failure occurrence rate obtained by actual measurement, the turbulent energy obtained by simulation, and the molten metal velocity for Comparative Example 1.

  Hereinafter, a vacuum suction casting method according to an embodiment of the present invention will be described with reference to the drawings.

[Outline of vacuum suction casting method]
A vacuum suction casting method according to an embodiment of the present invention is performed using a vacuum suction casting apparatus 1 as shown in FIG. The vacuum suction casting apparatus 1 includes a runner (sprue) 10, a plurality of molds 20, and a chamber 30.

  The runner 10 is formed of a metal member in a hollow cylindrical shape (for example, a cylindrical shape), and has a closing portion 11 at the distal end and an opening portion 12 at the proximal end. The runner 10 is arranged so that the closed portion 11 side is upward and the opening portion 12 side is downward. The plurality of molds 20 form a multi-stage tree T along the axis connecting the opening 12 and the closing part 11, and are provided so as to protrude outward from the outer wall of the runner 10. Each mold 20 has a hollow cylindrical (for example, cylindrical) gate 22 and a product cavity 21 integrally. The product cavity 21 is a cavity having the shape of a product manufactured by vacuum suction casting. The manufactured product may be any product including a part having a thin portion such as a turbine wheel. The hollow portion of the gate 22 of each mold 20 communicates with the hollow portion of the runner 10 at the gate proximal end portion 22a and communicates with the product cavity 21 at the distal end portion 22b. Thereby, the product cavity 21 of each casting_mold | template 20 is connected with the hollow part of the runner 10 through the gate 22. FIG. The mold 20 is made of a breathable material such as a sand material or a ceramic material. The entire runner 10 and the mold 20 thus connected are accommodated in an airtight chamber 30. The chamber 30 is provided with a decompression port 40 at the center position on the upper side of the closing portion 11, and a decompression pump (not shown) is connected to the tip of the decompression port 40.

  When performing vacuum suction casting, the atmosphere in the chamber 30 is appropriately replaced with an inert gas such as argon, and the opening 12 of the runner 10 is brought into contact with a metal (molten metal) M melted in an induction furnace or the like. When the inside of the chamber 30 is deaerated by the decompression pump, the runner 10 and the hollow portion of the mold 20 are decompressed through the wall surface of the mold 20 made of a breathable material. Thus, the molten metal M is sucked from the opening 12 of the runner 10 and reaches each product cavity 21 via the runner 10 and the gate 22. Then, the molten metal M is cooled and solidified in the product cavity 21 to cast the product. As the metal constituting the molten metal M, any castable alloy can be applied, and examples thereof include a nickel alloy, an iron alloy, a titanium alloy, and the like.

[Dimension ratio L / D of gate]
In the vacuum suction casting apparatus 1, the length of the gate 22 of the mold 20 is L, the inner diameter (inner wall interval) is D (see FIG. 1B), and the dimensional ratio L / D constitutes each tree T. In the casting_mold | template 20, it is not the same, but it differs between upper stage T1 located in the upper direction (closed part 11 side), and lower stage T2 located in the downward direction (opening part 12 side). Specifically, the dimensional ratio L / D in the mold 20 located in the upper stage T1 is larger than the dimensional ratio L / D in the mold 20 located in the lower stage T2.

  In general, in vacuum suction casting, the occurrence of casting defects tends to be a problem. There are casting defects due to poor hot water and gas defects. Poor hot water is a phenomenon in which the molten metal M does not sufficiently reach a part of the product cavity 21 and causes a defect such as a lack of an end region such as an edge or corner of the product. On the other hand, the gas defect is a phenomenon in which a gas filled in the runner 10 and the mold 20 such as argon gas is drawn into the molten metal M at the time of decompression and solidifies as it is, thereby generating a cavity inside the product. Such casting defects reduce productivity in vacuum suction casting.

  As will be shown later in Examples, it has been clarified that the turbulent flow in the molten metal M causes the above casting defects by associating the result of the numerical simulation with the actual measurement result. Further, as schematically shown in FIG. 3, turbulent flow Fg grows in the process in which the molten metal M progresses upward from the opening 12 of the runner 10, and the turbulent flow is reflected at the closed portion 11, thereby In the conventional vacuum suction casting apparatus 100 in which the dimensional ratio L / D of the gates 22 is the same in all stages of the tree T due to the flow Fb, the casting 120 in the upper stage of the tree T is particularly cast. It became clear that defects were likely to occur.

  However, in the vacuum suction casting apparatus 1 according to the present embodiment, the dimensional ratio L / D of the gate 22 is made larger in the upper stage T1 of the tree T than in the lower stage T2, thereby passing through the gate 22 of the upper stage T1. A high rectifying action is given to the molten metal M. As a result, even if the components of the grown turbulent flow Fg and the backflow Fb existing in the vicinity of the upper stage T1 enter the gate 22 of the upper stage T1, they undergo rectification while passing through the gate 22 and then enter the product cavity 21. Inflow. Thereby, in the upper stage T1, which tends to generate defects due to the influence of turbulence compared to the lower stage T2, casting defects and gas defects due to poor hot water can be reduced.

  The value of the specific dimensional ratio L / D of the gate 22 in the upper stage T1 and the lower stage T2 may be appropriately selected according to the degree of the growing turbulent flow Fg and the backflow Fb, and as the degree increases, the lower stage T2 What is necessary is just to take large the dimensional ratio L / D of the upper stage T1 compared with. For example, the dimensional ratio L / D in the upper stage T1 is preferably about 1.2 to 3 times the dimensional ratio L / D in the lower stage T2. By setting it to 1.2 times or more, in the upper stage T1, a rectifying action can be effectively exhibited, and casting defects can be suppressed. Moreover, by setting it as 3 times or less, it can suppress that an excessive difference arises in casting conditions, such as the inflow speed of the molten metal M to the product cavity 21, between upper stage T1 and lower stage T2. Further, when the dimensional ratio L / D of the upper stage T1 is increased by increasing the length L, the material cost required for manufacturing the gate 22 is reduced by setting the dimensional ratio L / D to three times or less of the lower stage T2. Can be prevented from becoming expensive. More preferably, the dimensional ratio L / D in the upper stage T1 is not more than twice that of the lower stage T2.

  Further, in the example of FIG. 1, in the tree T having 10 stages, the upper stage T1 is 3 stages and the lower stage T2 is 7 stages, and the dimensional ratio L / D is made different between them, but the upper stage T1 and the lower stage T2 The ratio of the number of stages is not limited to this, and the number of stages of the upper stage T1 is appropriately set according to the height of the influence of the growing turbulent flow Fg and backflow Fb from the upper end of the runner 10. That's fine. Further, as described above, if the upper stage T1 and the lower stage T2 are divided into two parts and the two dimensional ratios L / D are applied, the overall configuration of the vacuum suction casting apparatus 1 can be simplified. If the gate dimension ratio L / D of at least one mold 20 from the end on the part 11 side is larger than the gate dimension ratio L / D of the mold 20 below (opening 12 side), the above The entire tree T may be divided into three or more stages and three or more dimension ratios L / D may be set. As an example of dividing the tree T in the most stages, the L / D may be changed for each stage.

  In the example of FIG. 1, the inner diameter D of the gate 22 is the same in the upper stage T1 and the lower stage T2, but by increasing the length L of the gate 22 in the upper stage T1 from the lower stage T2, the dimension ratio L / D is increased at the upper stage T1. By reducing the inner diameter D of the gate 22, the dimensional ratio L / D can be increased. However, if the inner diameter D of the gate 22 is made too small, the flow rate of the molten metal M passing through the gate 22 decreases, It may cause defects due to defects. From the viewpoint of suppressing both the generation of defects due to the influence of the flow velocity and the generation of defects due to the influence of turbulence, by changing the length L of the gate 22 without changing the inner diameter D of the gate 22, It is preferable to increase the dimensional ratio L / D of the upper stage T1. If the gate 22 has a small diameter, the material cost required for the gate 22 can be reduced. Therefore, when the material cost of the mold 20 is high, the inner diameter D of the gate 22 is reduced. Thus, the dimensional ratio L / D may be increased.

[Decompression speed]
In addition to increasing the dimensional ratio L / D of the gate 22 in the upper stage T1, by controlling the pressure reduction speed when the chamber 30 is decompressed and the molten metal M is sucked in, the casting defects due to the influence of turbulence are further reduced. Generation can be reduced. Specifically, as shown in FIG. 2, the pressure reduction from the atmospheric pressure was started when the pressure was reduced from the state where the inert gas at the atmospheric pressure was filled in the runner 10 and the mold 20 until the predetermined target pressure was reached. In the initial period t1 which is a predetermined period immediately after and the final period t3 which is a predetermined period immediately before reaching the target pressure, the pressure reduction speed (pressure decreasing speed) may be made smaller than in the intermediate period t2 between them.

  The turbulent flow is likely to occur in the vicinity of the molten metal surface that is the front end surface of the molten metal M that enters the runner 10, but the turbulent flow is generated in the vicinity of the molten metal surface by reducing the pressure reduction rate at the initial t1. Can be suppressed. On the other hand, as the depressurization progresses, the molten metal M first flows into the lower mold 20 and then flows into the upper mold 20 in sequence, so that the depressurization of the mold 20 located in the upper stage T1 is reduced. The molten metal M flows into the end stage. Therefore, by reducing the decompression speed at the end t3, the turbulent flow that flows into the mold 20 of the upper stage T1 at the end t3 can be suppressed to be small.

  In this way, by reducing the pressure reduction speed of the initial t1 and the final t3 to be lower than that of the intermediate period t2, the inflow of turbulent flow into the mold 20 of the upper stage T1 is reduced, and the occurrence of casting defects due to turbulent flow is suppressed. Can do. In addition, by reducing the pressure reduction rate at the initial t1 and the final t3 in this way, it is possible to suppress the occurrence of turbulence and the growth itself in the runner 10, so that not only the upper stage T1 but also the template 20 of the entire tree T Is effective in reducing the occurrence of casting defects.

  The decompression speed at the end t3 and the initial t1 is preferably 10 to 80% of the decompression speed at the intermediate period t2. By making it 80% or less, it is possible to effectively suppress casting defects, and by making it 10% or more, it is possible to secure a realistic decompression speed and excessively take the time required for vacuum suction casting. Can be suppressed. Further, in order to increase the effect of reducing the turbulent flow, the decompression speeds at the initial t1 and the final period t3 are set to constant values smaller than the decompression speeds at the intermediate period t2, as shown in FIG. It is preferable that the decompression speed is gradually increased from 0 while finally reaching the decompression speed of the intermediate period t2, and at the final stage t3, the decompression speed is gradually decreased from the decompression speed of the intermediate period t2. The pressure reduction speed may be adjusted by adjusting the output of the pressure reduction pump or adjusting the conductance of the piping between the pressure reduction pump and the chamber 30.

  Hereinafter, the present invention will be described more specifically with reference to examples.

[Test method]
(1) Casting test (Example 1)
Using a vacuum suction casting apparatus similar to that shown in FIG. 1, vacuum suction casting was performed. The gate dimension ratio L / D was 0.8 for the upper stage (upper three stages) and 0.5 for the lower stage (lower seven stages). Then, as shown by a broken line in FIG. 4, vacuum suction casting was performed while decompressing at a constant speed. As a molten alloy, 74.17% Ni-0.12% C-12.5% Cr-4.2% Mo-2% Nb-6.1% Al-0.8% Ti-0 by weight%. A nickel alloy having a composition of 1% Zr-0.01% B was used.

(Example 2)
Using the same vacuum suction casting apparatus as used in Example 1 above, as shown by the solid line in FIG. 4, the vacuum pressure casting in the initial stage and the final stage is made smaller than the vacuum speed in the intermediate period, and vacuum suction casting is performed. went.

(Comparative Example 1)
As shown in FIG. 3, using a vacuum suction casting apparatus in which the dimensional ratio L / D of the gates in all stages of the tree is 0.5, the vacuum suction is performed while reducing the pressure at a constant speed as shown by the broken line in FIG. Casting was performed.

(2) Casting simulation A casting simulation using a thermal fluid analysis similar to that disclosed in JP-A-2005-246439 was performed to evaluate the state of turbulent flow during vacuum suction casting. A finite volume method was used for the calculation, and a two-equation model k-ε model was used as the turbulent flow model. A casting apparatus corresponding to each of Examples 1 and 2 and Comparative Example 1 and a simulation corresponding to the decompression conditions were performed. In addition to estimating the spatial distribution of turbulent flow and its change over time, the turbulent energy and molten metal flow velocity (velocity of the molten metal flowing into the mold) in the mold at each stage of the tree were calculated.

[Results and discussion]
(1) Correlation between turbulent energy and casting defects In the simulation according to Comparative Example 1, as the pressure decreases and the molten metal progresses upward from the opening, It was observed that the melt flowed in order toward the mold. Then, turbulent flow grows from the bottom to the top of the runner, and the turbulent flow is reflected at the upper end (blocking portion) of the runner to generate backflow. These turbulent components are transferred to the upper mold. Inflow was observed. Therefore, when the turbulent energy flowing into the mold is calculated for each stage of the tree, as shown in FIG. 6, the turbulent energy flowing into the mold is large particularly in the three-stage mold from the upper side (closed portion side) of the tree. It was confirmed that

  On the other hand, in the casting test of Comparative Example 1, the castings obtained with the molds at each stage of the tree were visually observed, and as a ratio of the volume of defects to the total volume of the castings, the occurrence rate of gas defects and the occurrence of poor hot water occurred. When the rate was calculated, as shown in FIG. 5, it was found that both gas defects and poor hot water were increased in the upper three stages of the tree. Comparing the results of the simulation and the actual measurement, it is possible to read the tendency that gas defects and poor hot water are likely to occur in the upper three stages where the turbulent energy of the molten metal flowing into the mold is large.

In order to confirm this tendency, FIG. 7 shows the turbulent flow at each stage estimated by simulation as a function of the occurrence rate of (a) gas defects and (b) hot water defects at each stage obtained by actual measurement. A plot of energy (■) and melt flow rate (x) is shown. As can be seen, there is a strong first-order positive correlation between the turbulent energy, the gas defect occurrence rate, and the hot water defect occurrence rate, as shown by the solid line in the figure. That is, it turns out that the turbulent flow in the molten metal is a cause of gas defects and poor hot water.

  On the other hand, there is no clear correlation between the gas defect occurrence rate, the hot water defect occurrence rate, and the molten metal flow rate. Conventionally, in vacuum suction casting, it has been said that gas defects are more likely to occur as the molten metal flow rate is larger, and hot water defects are more likely to occur as the molten metal flow rate is smaller, while turbulent energy also affects the occurrence of casting defects. The cause of casting defects has not been clearly confirmed. However, with this verification, the occurrence of gas defects and poor hot water can be evaluated using the turbulent energy as an index rather than the molten metal flow velocity. Both gas defects and poor hot water are likely to occur as the turbulent energy increases. It became clear that

(2) Comparison of Casting Defects in Examples and Comparative Examples FIG. 5 shows (a) gas defect occurrence rate and (b) hot water defect occurrence rate actually measured in casting tests according to Examples 1, 2 and Comparative Example 1. For each level of the tree. When attention is paid to the gas defect occurrence rate in FIG. 5A, in the first comparative example in which the gate size ratio L / D of all the stages constituting the tree is the same, the gas defect occurrence rate of the upper three stages is lower than the lower seven stages. In Example 1 in which the dimensional ratio L / D of the upper three steps is larger than that of the lower seven steps, the gas defect occurrence rate in the upper three steps is greatly reduced. It is almost the same as the gas defect occurrence rate in the lower seven stages.

  Furthermore, in Example 2, the gas defect occurrence rate is further reduced by reducing the pressure reduction rate at the initial stage and the end stage instead of a constant value. Here, the gas defect occurrence rate is reduced not only in the upper three stages but also in all stages.

  A tendency similar to that in the case of the gas defect occurrence rate is also observed in the hot water defect occurrence rate in FIG. In Example 2, the hot water run-out defect occurrence rate is reduced to a level that can be approximated to 0% in all stages.

  FIG. 6 shows the turbulent energy estimated in the simulations corresponding to Examples 1 and 2 and Comparative Example 1 for each stage of the tree. The occurrence of gas defects in FIGS. 5 (a) and 5 (b) is shown. The behavior is similar to the rate and the rate of occurrence of poor hot water. This also indicates that the main cause of gas defects and poor hot water is turbulent flow in the melt.

(3) Summary From the above casting test and casting simulation, in the vacuum suction casting, the gate size ratio L / D of the upper stage of the tree is made larger than the dimension ratio L / D of the lower stage gate, and further the pressure reduction It has been clarified that the occurrence of casting defects due to gas defects and poor hot water can be reduced by making the initial and final decompression speeds lower than in the intermediate period. In addition, it has been clarified that there is a close relationship between the turbulent energy and the incidence of gas defects and poor hot water. The detailed conditions concerning the vacuum suction casting, such as the shape (for example, the specific dimension ratio L / D value, the number of stages of the upper stage T1 and the lower stage T2) and the pressure reduction conditions (for example, the shape of the specific pressure reduction curve) It is possible to optimize so as to suppress casting defects.

  While the embodiments and examples of the present invention have been described above, the present invention is not particularly limited to these embodiments and examples, and various modifications can be made. For example, even when the pressure reduction rate of only one of the initial stage and the final stage is made smaller than that of the intermediate period, it is possible to obtain the effect of suppressing casting defects according to each contribution.

DESCRIPTION OF SYMBOLS 1 Vacuum suction casting apparatus 10 Runway 11 Closure part 12 Opening part 20 Mold 21 Product cavity 22 Gate 30 Chamber D Gate width L Gate length Fb Back flow Fg Grown turbulent flow M Molten metal T1 Upper stage T2 Lower stage

Claims (3)

A hollow tubular runner having a closed portion at one end in the axial direction and an opening at the other end,
A hollow cylinder having a length L and an inner diameter D, which is communicated with the hollow portion of the runner at the proximal end and protruding from the runner, and communicated with the hollow portion of the gate and connected to the distal end of the gate Using a reduced-pressure suction casting apparatus comprising a plurality of molds provided in a plurality of stages along the runner axis,
The gate size ratio L / D in the upper stage portion made of at least one mold from the end of the runner closed side is set to the lower stage section made of at least one mold located on the opening side of the upper stage portion. Greater than the dimensional ratio L / D of the gate at
A vacuum suction casting method, wherein the molten metal and the mold are decompressed and the molten metal is sucked from the opening of the molten metal.   2. The vacuum suction casting method according to claim 1, wherein when the runner and the mold are depressurized, the depressurization speed is made lower in the initial and final depressurization than in the intermediate period between the initial and final periods. .   The vacuum suction casting method according to claim 1 or 2, wherein the dimensional ratio L / D of the gate is adjusted by making the length L different.

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