JP2013173152A - Method for manufacturing complicated-shape structure - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a method for manufacturing a complicated-shape structure which can reduce such a defect-occurring risk that a shrinkage cavity defect is generated in a cast product.SOLUTION: A method for manufacturing a complicated-shape structure including a rotationally-symmetrical shape part in which a space in which a rotation body rotates is formed inside a casing, and a rotationally-asymmetrical shape part continuously provided vertically below the rotationally-symmetrical shape part, includes: a first step of casting by pouring a predetermined amount of a molten metal from a downward in-gate 11 to a region located on a side lower than a boundary position in a height direction where a cavity C is partitioned into the rotationally-asymmetrical shape and the rotationally-symmetrical shape part; and a second step of casting by pouring a molten metal from an upward in-gate 21 to a region located on a side upper than the boundary position by interposing a predetermined time interval after completion of the first step.

Description

  The present invention relates to a method for manufacturing a complex structure having a large and complicated shape, such as a turbine casing of a steam turbine.

  Conventionally, a structure that becomes a casing of a rotating machine is generally manufactured by casting. In such a structure, for example, a turbine casing that constitutes a marine main engine, a rotationally symmetric shape portion that forms a space in which a rotating body rotates, and a non-rotating portion that is integrally formed with the rotationally symmetric shape portion and has an uneven portion. There is a complex-shaped structure (hereinafter, referred to as “complex-shaped structure”) including a symmetrically shaped portion. Note that a casing such as a turbine casing is generally integrated by casting each of two vertically divided casings and bolting the flange portion.

In the case of manufacturing the complex structure described above by casting, a liquid (hereinafter referred to as “molten metal”) obtained by heating and melting a metal material is poured into a mold space (hereinafter referred to as “cavity”), This is cooled and hardened to a desired shape. In this case, the molten metal is continuously poured to prevent discontinuity in the metal structure of the product.
Further, in the low pressure casting method, as disclosed in, for example, Patent Document 1 below, the mold member facing the portion where the molten metal should solidify quickly and the molten metal should be solidified with delay depending on the shape of the cavity. It has been proposed that a cooling medium is successively supplied with a time difference between the mold members facing the part and cast while the molten metal is directional solidified in a certain direction.

Japanese Patent Laid-Open No. 1-237065

  By the way, when casting a complex-shaped structure, particularly when casting a large-sized complex structure such as a turbine casing, if the drop of the molten metal poured into the cavity becomes large, air is introduced into the molten metal. There is a concern to involve. Such air entrainment is undesirable because it causes shrinkage defects in the cast product.

  That is, in normal casting, the molten metal poured from the lower part of the mold flows through the runner from the weir into the cavity at a relatively slow flow rate. However, in the case of a complex-shaped structure having an uneven portion, for example, in the recess, the molten metal that has flowed up the runner and then flowed into the cavity from the upper weir drops a large height difference in the cavity, and becomes a recess. Inflow may occur, and ambient air is likely to be involved when such molten metal falls. In addition, the risk of entraining air when the molten metal falls generally increases as the difference in height of the falling metal increases.

From such a background, when manufacturing a complex-shaped structure by casting, the risk of occurrence of defects that cause shrinkage defects in the cast product due to air entrainment from the viewpoint of improving product reliability and yield. Reduction is desired.
The present invention has been made to solve the above-described problems, and an object of the present invention is to provide a method for manufacturing a complex-shaped structure that can reduce the risk of occurrence of defects such as shrinkage defects in a cast product. It is in.

In order to solve the above problems, the present invention employs the following means.
The method for manufacturing a complex-shaped structure according to the present invention includes a rotationally symmetric shape portion that forms a space in which a rotating body rotates on the inner side of a casing, and a non-rotationally symmetric shape portion that is continuously provided vertically below the rotationally symmetric shape portion. A predetermined amount from the lower weir to a region below the boundary position in the height direction dividing the inside of the cavity into the non-rotationally symmetric shape portion and the rotation symmetric shape portion. A first step of pouring and casting the molten metal; and a second step of casting by pouring the molten metal from an upper weir into a region above the boundary position by providing a predetermined time difference after completion of the first step. It is characterized by being.

According to such a method for manufacturing a complex-shaped structure of the present invention, the cavity is divided into a non-rotation symmetric shape portion and a rotation symmetric shape portion from the lower weir in a region below the boundary position in the height direction. A first step in which a predetermined amount of molten metal is poured and cast, and a second step in which a predetermined time difference is provided after the first step is finished and a molten metal is poured into the region above the boundary position from the upper weir and cast. Therefore, in the second step, the molten metal pouring waits for the molten metal surface poured into the non-rotationally symmetric shape portion in the cavity from the lower weir at a slow flow rate to rise to some extent as the time difference elapses. Done. For this reason, in the cavity, the height difference generated between the molten metal poured from the upper weir in the second step and the molten metal surface poured in the first step can be reduced. It is possible to reduce the risk that the molten metal dropping the difference entrains the air.
Furthermore, the molten metal cast in the first step and the second step can prevent a discontinuous surface from being formed in the metal structure by optimizing the time difference between the steps.

  In the above invention, the predetermined time difference is preferably calculated in advance based on the volume of the non-rotationally symmetric shape portion and the molten metal supply flow rate in the first step, whereby the molten metal poured in the second step is It becomes possible to set the height difference falling to the molten metal surface within a substantially desired range, and it is possible to reliably prevent the formation of a discontinuous surface in the metal structure.

  According to the present invention described above, by optimizing the time difference from the first step to the second step, the difference in height at which the molten metal falls can be minimized to prevent air entrainment, and the metal structure is not affected. Since it is also possible to prevent the formation of a continuous surface, the risk of occurrence of defects that cause shrinkage defects in a cast product due to air entrainment is reduced, and a remarkable effect is achieved in improving the reliability and yield of the product.

  In other words, the above-described manufacturing method of the present invention is intended to carry out two-step casting that is not normally performed at a predetermined time difference because of the problem that a discontinuous surface is formed in the metal structure of the product. For example, a product that is manufactured by casting a large complex shape structure in which a rotationally symmetric shape portion and a non-rotationally symmetric shape portion having an uneven portion are integrally formed, such as a turbine casing manufactured by dividing the upper and lower portions However, it is possible to reduce the risk of occurrence of defects such as shrinkage defects in the cast product, and to manufacture complex-shaped structures with high reliability and high yield.

BRIEF DESCRIPTION OF THE DRAWINGS It is a figure which shows one Embodiment of the manufacturing method of the complex shape structure which concerns on this invention, (a) is a figure which shows the runway structure example which flows a molten metal at a 1st process, (b) is a 2nd process at (a). It is a figure which adds and shows the runway which flows a molten metal in. It is a figure which shows the example of a general runner at the time of manufacturing a complicated-shaped structure by casting as a comparative example with this invention. It is a perspective view which shows a shape example about the lower casing of the turbine casing divided into upper and lower parts as an example of a complex-shaped structure. It is the perspective view seen from the lower surface side about the runner structural example shown in FIG. It is the perspective view seen from the upper surface side about the runner configuration example shown in FIG. It is a perspective view which shows the relationship between the shape of a complex-shaped structure, and a runner about embodiment shown in FIG.

Hereinafter, one embodiment is described based on Drawing 1-Drawing 6 about the manufacturing method of the complicated shape structure concerning the present invention. In the following, a turbine casing of a steam turbine applied to a marine main engine will be described as an example of a complex structure, but the present invention is not limited to this.
In a turbine casing of a steam turbine, an upper casing and a lower casing, which are manufactured by dividing the upper and lower casings, are integrally fastened with a plurality of bolts, for example, 9Cr-1Mo-Ni-V-Nb-N steel. It is a cast steel product for high temperature and high pressure in which Cr—Mo containing steel such as Cr—Mo—Ni—V and other containing steel is used as a raw material.

  FIG. 3 is a perspective view showing the external shape of the lower casing (complex shape structure) 1 of the turbine casing. The basic structure of the upper casing is substantially the same as that of the lower casing 1, and a rotationally symmetric shape portion that forms a space in which the rotating body rotates, and a non-rotationally symmetric shape that has an uneven portion integrally with the rotationally symmetric shape portion. And a structure having a complicated shape. Therefore, the same manufacturing method as that for the lower casing 1 described below can be applied to the upper casing.

  The illustrated lower casing 1 includes a rotationally symmetric shape portion 3 that forms a space 2 in which the turbine rotor (rotary body) rotates inside the casing 1, and various uneven portions 5 (for example, And a non-rotationally symmetric shape portion 6 having uneven portions 5a to 5c). In this case, the rotationally symmetric shape portion 3 is positioned above, and the non-rotationally symmetric shape portion 6 is provided continuously and integrally below the vertically downward portion thereof. Moreover, the code | symbol 4 in a figure is a penetration part which lets the rotating shaft (not shown) of a turbine rotor pass, and the code | symbol 7 is a flange part. In addition, about the bolt hole of the flange part 7, illustration is abbreviate | omitted.

The lower casing 1 described above is a cast part manufactured by a method for manufacturing a complex-shaped structure described below. That is, a manufacturing method is adopted in which molten material is poured into the cavity C (see FIG. 1) having the shape of the lower casing 1 in two stages of a first process and a second process.
FIG. 1 (a) shows a configuration example of a runner 10 through which molten metal flows in the first step. In addition, about the runner 20 used at a 2nd process, illustration to FIG. 1 (a) is abbreviate | omitted and it adds and shows in FIG.1 (b).

  This first step is performed on the region below the boundary line BL (see FIG. 3), which is the boundary position in the height direction, which is divided into the non-rotation symmetric shape portion 6 and the rotation symmetric shape portion 3, that is, the main In addition, a predetermined amount of molten metal is slowly poured into a region which becomes the non-rotationally symmetric shape portion 6 from a plurality of lower weirs 11 communicating with the runner 10 provided at the lower part of the cavity C and cast.

The main channel 10a of the runner 10 used in the first step is directed downward from the gate 12 that opens upward in the vicinity of the side end portion of the cavity C, for example, as in the configuration examples shown in FIGS. After the direction change of approximately 90 degrees below the lower surface of the cavity C, it passes through the vicinity of the lower central portion of the cavity C to the vicinity of the opposite side end portion. The gate 12 is opened at a position higher than the cavity C.
A plurality of (five in the illustrated configuration example) branch channels 10b are connected to the main channel 10a in a horizontal portion that passes near the lower center of the cavity C. A lower weir 11 that opens to the cavity C is provided on the outlet side of each branch channel 10b.

  In the second step, a predetermined time difference is provided after the end of the first step, and the vicinity of the center of the cavity C with respect to the region above the boundary position BL, that is, the region mainly serving as the rotationally symmetric shape portion 3. A predetermined amount of molten metal is added and slowly poured from a plurality of upper weirs 21 communicating with the runner 20 provided on the outer peripheral portion.

The runner 20 used in the second step is configured by a main flow path 20a and a branch flow path 20b having an upper weir 21 on the outlet side, as in the configuration examples shown in FIGS. 4 to 6, for example. This is the same as the runway 10 in the first step.
The illustrated main channel 20a is provided at a position higher than the main channel 10a, specifically, at a level near the boundary line BL so that the horizontal portion surrounds the three sides around the cavity C, and opens to a position higher than the cavity C. The molten metal is poured from three gates 22. That is, the main flow path 20a is directed downward from the three gates 22 opened upward in the vicinity of the side end portion of the cavity C, and is turned approximately 90 degrees at a level near the boundary line BL. It becomes a horizontal part provided to surround three sides along the outer peripheral part.

  In addition, eight branch channels 20b each having an upper weir 21 opened to the cavity C on the outlet side are connected to the horizontal portion of the main channel 20a. Note that the level at which the upper weir 21 opens is higher than the opening level of the lower weir 11 because it passes through the branch channel 20b having an upward channel from the main channel 20a.

Hereinafter, the procedure of the manufacturing method for casting a complex-shaped structure will be specifically described.
In the first first step, a predetermined amount of molten metal is poured from the gate 12 with the connecting channel 30 closed. As a result, the molten metal flows down to the horizontal portion through the vertical portion provided in the main channel 10a of the runner 10, and fills the main channel 10a and the branch channel 10b. When the molten metal is further poured from this state, since the gate 12 is at a position higher than the lower weir 11, the molten metal surface rises and slowly flows into the cavity C from each lower weir 11. In this case, the predetermined amount of the molten metal poured in the first step is a value at which the molten metal surface rises to the vicinity of the boundary line BL.
The boundary line BL can be cast in a predetermined manner even if there is a difference of ± 10% with respect to the determined value. In addition, as a molten metal to be cast in the first step and the second step to be described later, for example, a Cr-Mo-containing steel such as 9Cr-1Mo-Ni-V-Nb-N steel, which is a cast steel product for high temperature and high pressure, Cr-Mo -Ni-V and other steels can be applied, and the temperature of the molten metal is about 1550 ° C to 1600 ° C.

When a predetermined amount of molten metal is poured from the total amount spout 12 in this way, a predetermined time difference is provided and the process proceeds to the second step. This time difference takes into account the time required for the molten metal that has been poured into the total amount to reach the molten metal surface that is assumed in advance, and can be determined based on experience values and the like. However, in order to determine a more accurate time difference, for example, it is calculated in advance based on the volume of the non-rotationally symmetric portion 6 and the molten metal supply flow rate in the first step, or the optimum value is changed by appropriately changing the conditions in the trial production stage. It may be determined. In addition, even if this time difference has a difference of ± 10% with respect to the determined value, predetermined casting is possible.
Thus, when the optimum value of the time difference for shifting from the first step to the second step is determined, the difference in height at which the molten metal poured in the second step falls on the molten metal surface is reduced and set within a substantially desired range. It becomes possible to do. In addition, the optimization of the time difference is also effective in preventing the formation of discontinuous surfaces in the metal structure in the product after casting because the temperature change of the molten metal surface is minimized.

Here, the reduction in the height difference at which the molten metal poured in the second step falls from the upper weir 21 onto the molten metal surface will be described in comparison with the configuration example of the runner that performs the general one-stage casting shown in FIG. To do. In FIG. 2, the same reference numerals are given to the same parts as those in the above-described embodiment, and detailed description thereof is omitted.
The runner 40 shown in FIG. 2 includes a main channel 40a and a plurality of branch channels 40b branched from the main channel 40a. Each branch passage 40b is provided with a weir 41 having an outlet side opened to the cavity C. In addition, since the main flow path 40a and the branch flow path 40b in FIG. 2 overlap in the front-rear direction, not all are illustrated.

A plurality of gates 42 are provided in the main channel 40 a of the runner 40. The molten metal poured from the gate 42 flows down through the vertical part of the main channel 40a and flows into the horizontal part of the main channel 40a. Thereafter, the molten metal filling the main flow path 40a slowly flows into the cavity C from the weir 41 through the branch flow path 40b having the upward flow path.
At this time, a large height difference is formed between the weir 41 and the lowermost surface of the cavity C, for example, in the vicinity of the regions S1 to S4 surrounded by broken lines in the figure, since the weir 41 is at a high position. That is, the molten metal flowing into the cavity C from the weir 41 falls as shown by the arrow f, and therefore the molten metal flow becomes turbulent as the flow rate increases, resulting in air entrainment. Easy situation.

On the other hand, when divided into the above-described two stages, for example, in the region Sa shown in FIG. 1B, the height difference from the upper weir 21 is H in a state where the liquid level of the molten metal has risen near L. The amount of decrease in the height difference H is significant when compared with the flow of the arrow f described above. Therefore, the flow of the molten metal flowing down the height difference H becomes slow without increasing the flow velocity, and there is almost no turbulence generated in the flow.
For this reason, it is possible to reduce the risk that the molten metal falling in the height difference H entrains air, and it is possible to reduce the risk of occurrence of defects that cause shrinkage defects in the cast product due to the entrainment of air.

Thus, according to the above-described embodiment, by optimizing the time difference from the first step to the second step, it is possible to minimize the height difference H at which the molten metal falls and prevent air entrainment. Because it can also prevent the formation of discontinuous surfaces in the metal structure, it can reduce the risk of defects that cause shrinkage defects in cast products due to air entrainment, and improve product reliability and yield Can do.
In addition, this invention is not limited to embodiment mentioned above, In the range which does not deviate from the summary, it can change suitably.

1 Lower casing (complex shape structure)
3 Rotationally symmetric shape part 6 Non-rotationally symmetric shape part 10, 20, 40 Runway 10a, 20a, 40a Main flow path 10b, 20b, 40b Branch flow path 11 Lower weir 12, 22, 42 Pouring gate 21 Upper weir 41 Weir C Cavity BL border

Claims (2)

In a method for manufacturing a complex-shaped structure having a rotationally symmetric shape portion that forms a space in which a rotating body rotates inside a casing and a non-rotationally symmetric shape portion that is continuously provided vertically below the rotationally symmetric shape portion,
A first step of pouring a predetermined amount of molten metal from a lower weir into a region below a boundary position in the height direction dividing the cavity into the non-rotationally symmetric shape portion and the rotation symmetric shape portion;
A second step in which a predetermined time difference is provided after the end of the first step, and the molten metal is poured from an upper weir into a region above the boundary position and cast;
The manufacturing method of the complex-shaped structure characterized by comprising. The method of manufacturing a complex-shaped structure according to claim 1, wherein the predetermined time difference is calculated in advance based on a volume of the non-rotationally symmetric shape portion and a molten metal supply flow rate in the first step.

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