JPH0352753A - Complex casting method - Google Patents

Abstract

PURPOSE:To effectively utilize material strength being suitable to the necessary characteristics in each part of a casting product and to improve creep character istic, fatigue strength and toughness by combining merits of respective casting method by using two or more kinds of the casting methods. CONSTITUTION:In each part in the integrated machining member, while manufac turing each part with the casting methods for giving the characteristics matching to need at each part in these, the process for integrating by complexing these is executed. Therefore, in the case of exemplifying a turbine wheel for small size turbine, a blade part corresponding to a second member planted may be cast with unidirectional solidification in order to utilize this alloy characteristic. Further, a disk part corresponding to a first member may be cast as making fine crystal with rotary solidifying method in order to satisfy the characteristic to be needed. In this result, the blade part has metallurgical structure with the crystal grown in stress direction and improved in creep resistance and the disk part can have uniform characteristic to the whole direction.

Description

DETAILED DESCRIPTION OF THE INVENTION [Industrial Application Field] The present invention relates to a composite casting method in which parts having different required properties can be obtained as metal structures suitable for each part.

[Prior Art] Mechanical parts that have minute shapes and require high precision are usually manufactured by a lost wax precision casting method. For example, in the case of turbine wheels for small gas turbines, which have many blades protruding from the outer periphery of a circular disk that forms the center, the turbine alloy used itself is cut and processed. Since it is a very difficult material to cut, machining is expensive. Therefore, there are many examples in which the blade part and the desk part are integrated and manufactured by the lost wax method. According to the general lost wax precision casting method, a molten metal M is poured into a mold C which has been dewaxed from a wax mold as shown in FIG. 5, and a riser is applied. Thereafter, it was left to cool and a cast product P as shown in FIG. 6 was obtained. However, according to such a manufacturing method for a normal crystal product, the cast product P is obtained as having the same crystal structure as a whole.

[Problems to be Solved by the Invention] Therefore, for example, in a turbine wheel consisting of a disk portion and a blade portion, a mechanical member consisting of a first member such as a disk portion and a second member such as a blade portion attached thereto is conventionally As far as the method is concerned, the first part and the second part are cast from the same crystal structure as a whole; for example, in a turbine wheel, the desk part of the first part and the blade part of the second part have different parts. Even when a difference in properties is required, it is unavoidable to precipitate with an average crystal structure, and then to process it by local heat treatment etc. to satisfy the required function.

[Means for Solving the Problems] The present invention has been made in order to solve the problems of the conventional method described above and to allow the first member or the second member to maintain the characteristics required for each. That is, we propose a composite casting method that employs the most suitable casting means for the first and second members, and performs monolithic casting.

Therefore, the present invention provides: (a) Casting a second member attached to the first member by a predetermined casting method using a solidification method that can control the crystal precipitation state adapted to the function of the second member using a casting alloy. (b) creating a wax mold of the first member by placing the joint portion of the cast second member in a predetermined position on the first member; (c) placing the second member in a predetermined position on the first member; forming a mold in the implanted state, then dewaxing the solder; Casting is carried out in a state where the joint of the two members is surrounded by casting, whereby the second member is made into, for example, a unidirectionally solidified crystal, and the first member is made into an integrated cast product, for example, with a finely treated crystal. It is created with a purpose.

[Function of the invention] 4 In the method of the present invention, each part in an integrated mechanical member is created by a casting method that can impart characteristics that suit the needs of each part, and then composited. A step is taken to integrate them. Therefore, taking the example of a turbine wheel for a small gas turbine, the blade part corresponding to the second member to be implanted can be cast by unidirectional solidification to take advantage of its alloy properties, and the first member can be cast by unidirectional solidification. In order to satisfy the required properties, the desk part corresponding to the above can be cast into fine crystals using the rotational solidification method. As a result, the blade part, which is the second member, has a metal structure with crystals lengthened in the stress direction and has improved creep resistance, and the desk part, which is the first member, has a metal structure that has improved creep resistance. By making metal crystals finer, it is possible to give them properties that are uniform in all directions, making it possible to approach the properties obtained when solidification occurs in the centrifugal direction.

[Example] Hereinafter, specific examples of implementing the present invention will be described.

5 A turbine boiler for a small gas turbine was manufactured by the method of the present invention. In this case, the first member, the desk part, must have high toughness and excellent durability against low cycle fatigue since it rotates at high speed. Further, each blade, which is a second member protruding from the first member,
Since it is affected by a large centrifugal force due to high-speed rotation, it is necessary to avoid this state because it lacks tensile strength in the solidified state where it normally becomes a crystal.

(1) Creation of the blade The blade in this example includes a hollow portion in order to increase the cooling effect and reduce heat accumulation. This hollow part is created by a ceramic core. The ceramic core was formed using fine powder of alumina, zircon, spinel, etc. as an aggregate and an inorganic or organic binder. This ceramic core was set at a position where a predetermined hollow portion would be formed, a wax model was formed, a mold was made, and the wax was removed. Then, a blade was manufactured using a crystal control device so as to obtain unidirectionally solidified crystals. 6 That is, as shown in FIG. 1, the lower part of the mold C can be cooled by a water cooling plate 2, and the molten metal M is poured into it.

Then, in this state, the mold C is lowered into the heating atmosphere H by the high-frequency heating device 3. Mold C is high frequency heating device 3
Heat radiation h is performed from a portion past h, and the molten metal M in the mold C reaches the heat radiation h region and solidifies. The coagulation line is shown as l in FIG.

By using the crystal control device 10 that can solidify while maintaining the directionality in this way, a member 11 having a metal structure with a unidirectionally solidified crystal can be obtained (see FIG. 2). The ceramic core was removed from the blade while holding the core using a solvent such as sodium hydroxide, ammonium fluoride, or hydrogen fluoride. If the blade part as the second member is cast by the conventional method of pouring molten metal M into a mold C and taking out the cast product after cooling as shown in FIG. 7, the obtained member l1 is usually It has a crystalline metal structure. As shown in FIG. 8, the metal structure of this member is usually crystalline, and the crystals have no directionality.

(2) Preparation of the desk The blade obtained as described above was used in place of the wax model blade, and a wax model of the desk was made according to the conventional method for assembling an integral rotor.

Then, along with a large number of implanted blades, a mold material was coated by spraying or dipping to form a mold. After dewaxing, the disk is cast using a rotary solidification method, using a casting alloy that matches the properties required after the product is obtained, with the joints of each blade being individually cast.

In this casting method, as shown in FIG. 3, molten metal M is poured into a mold C in which a member 11 corresponding to the second member with a unidirectional solidification crystal structure is set at a required position. After pouring the metal, rotation R, vibration B, etc. are applied to the mold C to prevent solidification in a stationary state. By doing this, the crystal solidifies from each part in contact with the mold C while casting the joint part 1F of the member 11 corresponding to the second member, and the metal structure of the refined crystal is formed as shown in FIG. This is product 12.

This crystal refinement can be controlled by the degree of rotation and vibration applied to the mold C after pouring the molten metal M.

(3) Composite casting product As described above, for example, a turbine wheel obtained by the method of the present invention is an integral product in which the metal structure is composite, with the blade having a unidirectional crystal and the disk having a fine crystal structure.

In the composite casting method for turbine foils, turbine nozzles, etc. as shown in this example, when the first member is cast around the joint part of the second member, a reverse gradient is created in the joint part to prevent it from coming off in the centrifugal direction. However, since the first member is solidified while being rotated and/or vibrated during casting, the shape must be such that the molten metal can flow smoothly. Furthermore, in the joint portion between the first member and the second member,
It is possible to adopt both a means of not melting the joint portion of the second member into the first member and a means of melting the joint portion of the second member into the first member.

If it cannot be melted into the first member, the joint part of the second member may be plated with a high-melting point metal such as nickel, platinum, or chromium. It is preferable to remove the remaining scale and clean it by pickling, or to aluminize the joint, and to dissolve it with the molten metal for casting the first member. In this example, since the second member is cast in advance as a unidirectionally solidified crystal, the tensile strength at 650 to 750°C (kgf/mm") is higher than in the case of equiaxed crystal in conventional monolithic casting. has improved by about 6 to 7%, and the stress at break at the same temperature has increased by about 20%.Also, when the first member is refined by rotational solidification, it is difficult to obtain compared to 41
The tensile strength (kgf/mm'') at 0 to 430°C is improved by about 16%, and the low cycle fatigue strength under the same load is increased by 5 to 6 times.

[Effects] According to the method of the present invention, by using at least two types of casting methods and combining the advantages of each casting method, such as unidirectional solidification and rotational solidification, the following effects can be achieved. It worked.

(1) It becomes possible to effectively utilize the material strength that matches the required properties in each part of the cast product, and the creep characteristics, fatigue strength, and toughness of the cast product are improved.

(2) A cast product with high positioning accuracy between multiple members can be obtained.

(3) The second member can be reliably joined to the first member, whether by means of melting the joint portion of the second member into the first member or by means of not melting it into the first member.

(4) Combination casting of different alloys becomes possible.

(5) It becomes easy to cast an integrally cast product having a hollow structure.

(6) Combination casting of multiple members having overhang portions is possible.

Therefore, the turbine wheel for a small gas turbine as an example obtained by the method of the present invention has the above-mentioned characteristics, and can also be cast with a combination of various characteristics that meet each individual's needs. Therefore, it has great industrial applicability.

1 1-

[Brief explanation of drawings]

1 to 4 are diagrams showing an example of the implementation of the present invention. FIG. 1 is an explanatory diagram of a means for obtaining unidirectionally solidified crystals, and FIG. 2 is an illustration of the crystal state of a member obtained by the same means. Figure 3 is an explanatory diagram of the means for obtaining fine crystals, Figure 4 is a diagram showing the crystalline state of the product obtained by the same means, Figures 5 and 7 are
The figure is a cross-sectional view of casting by the conventional method, and Figures 6 and 8
The figures show the crystalline state of the cast products obtained by the conventional method shown in FIGS. 5 and 7, respectively. 1... 3... 10... 11... H... ■... Coagulation wire high frequency heating device Crystal control device parts Molten metal heating atmosphere 2... Water cooling plate 12... Product C. ...Mold h...Heat radiation l2 Fig. 1 Fig. 2 M Fig. 3 12 Fig. 4 Fig. 5 Fig. 7 Fig. 6 Fig. 8

Claims (1)

[Scope of Claims] (a) A second member attached to the first member is cast by a predetermined casting method using a solidification method that can control the state of crystal precipitation adapted to the function of the second member using a casting alloy. (b) creating a wax mold of the first member by placing the joint portion of the cast second member in a predetermined position on the first member; (c) implanting the second member in a predetermined position on the first member; (d) solidifying the first member with a casting alloy using a solidification method capable of controlling the state of crystallization to adapt the function of the first member to the second member; A composite casting method characterized by casting in a state where the joints of the parts are covered.