Turbine rotor

Abstract

To provide a turbine rotor which enables mass production with a low-cost apparatus and which capable of suppressing leaning of the rotor shaft after welding to improve the yield, while a turbine blade rotor 12 and the rotor shaft 14 are fit to each other with concave and convex portions 12a and 14a and are permitted to be rotated, laser beam L from a laser beam generating device 30 is applied to a joint face 16 along the circumferential direction to weld the welding portion. Then, laser beam L is polarized to temper a region X on the rotor shaft side containing the welding portion with laser beam L. In contrast to residual stress R.sub.1 having a local angular distribution generated during the welding, residual stress R.sub.2 is permitted to be generated over the entire circumference by tempering. Leaning of the rotor shaft 14 after cooling is thereby be suppressed.

Claims

1. A method for manufacturing a turbine rotor having a turbine blade made of a material containing heat-resistant metal and a rotor shaft made of a material containing carbon steel which are connected to each other by butt welding, comprising the steps of: welding a joint portion of the turbine blade and the rotor shaft at the joint portion by irradiation with a first beam for one revolution or two revolutions from a starting point of welding in a prescribed rotating direction; and after the welding, tempering a prescribed range of a rotor shaft side of the joint portion by irradiation with a second beam from the starting point of welding in the prescribed rotating direction, wherein when said welding is carried out for one revolution, said prescribed range of tempering is from the starting point to a point approximately 270° from the starting point; when said welding is carried out in two revolutions, said prescribed range of tempering is one revolution plus approximately 270° in a second revolution.

2. The manufacturing method for a turbine rotor according to claim 1, wherein the welding step includes welding by irradiation at the joint portion with the first beam for one revolution or two revolutions from the starting point of welding in the prescribed rotating direction, followed by welding by irradiation with the first beam while decreasing gradually an output of the first beam during approximately a half revolution.

3. The manufacturing method for a turbine rotor according to claim 1, comprising generating both the first beam used in the welding and the second beam used in the tempering from a laser beam generating device, in the welding step, collecting the laser beam generated from the laser beam generating device and applying the beam to the joint portion, and in the tempering step, distributing the laser beam generated from the laser beam generating device so as to apply to the joint portion over the prescribed range.

Description

BRIEF DESCRIPTION OF DRAWINGS

(1) FIG. 1A is a front view of a welding apparatus employing electron beam according to the present invention.

(2) FIG. 1B is a front view of a tempering apparatus employing laser beam according to the present invention.

(3) FIG. 2A is a chart for explaining a thermal treatment step according to the embodiment, FIG. 2B and FIG. 2C is each a cross-sectional view of a welding portion in the thermal treatment step.

(4) FIG. 3 is an explanatory chart showing a welding method and a tempering method according to the embodiment.

(5) FIG. 4 is an explanatory diagram illustrating laser beam applied in the embodiment.

(6) FIG. 5 is an explanatory diagram illustrating leaning of a rotor shaft of a conventional turbine rotor.

DETAILED DESCRIPTION

(7) Embodiments of the present invention will now be described in detail with reference to the accompanying drawings. It is intended, however, that unless particularly specified, dimensions, materials, shapes, relative positions and the like of components described in the embodiments shall be interpreted as illustrative only and not limitative of the scope of the present invention.

(8) An embodiment of the present invention will now be described with reference to FIG. 1A to FIG. 4. FIG. 1A is a view illustrating a welding apparatus for welding a turbine blade rotor 12 and a rotor shaft 14 constituting a turbine rotor 10. A motor 20 has an output shaft, which is connected to a chuck 22, and the lower end of the rotor shaft 14 is fixed to the chuck 22. The rotor shaft 14 is rotatable together with the chuck 22 by the motor 20. The rotor shaft 14 has a convex portion 14a having a diameter smaller than the rotor shaft 14, formed at the upper end of the rotor shaft 14. On the other hand, the turbine blade rotor 12 has a concave portion 12a to be fitted to the convex portion 14a, formed at the center of the lower face of the turbine blade rotor 12.

(9) These concave and convex portions 12a and 14a are fitted to each other, and the turbine blade rotor 12 and the rotor shaft 14 are thereby positioned, and they are rotatable together. The turbine blade rotor 12 is made of a heat-resistant material such as inconel, and the rotor shaft 14 is made of carbon steel. Accordingly, the rotor shaft 14 has a larger thermal conductivity and a larger heat capacity than the turbine blade rotor 12.

(10) The turbine blade rotor 12 is rotatably supported by the chuck 24 at the center of the upper end, and the turbine blade rotor 12 is synchronously rotatable with the rotor shaft 14 by means of the chuck 22. The concave and convex portions 12a and 14a are in contact with each other to form a joint face 16. An electron beam generating device 30 disposed near the positioned turbine blade rotor 10 emits electron beam L toward the joint face 16. A vacuum valve 300 is provided to maintain the environment within the vacuum chamber 301 as a vacuum.

(11) In the above structure, while the concave portion 12a of the turbine blade rotor 12 and the convex portion 14a of the rotor shaft 14 are fitted to each other, the motor 20 is rotated to rotate the turbine blade rotor 12 and the rotor shaft 14. The electron beam L is collected to the center side by a collecting lens 34 and then applied toward the joint face 16. The peripheral portion of the joint face 16 is thereby heated and melted, whereby the joint face 16 is welded.

(12) FIG. 2A is a chart for explaining a thermal treatment step according to the embodiment employing the electron beam generating device 30. Firstly, the temperature is raised from room temperature to 450° C.-550° C. to perform a preheating step A over the entire circumference.

(13) Next, from the electron beam generating device 30, electron beam L is applied to the joint face 16 to perform a welding step B where the temperature is raised to 1,500° C.-1,700° C. for one revolution (360°) over the entire circumference, and then the output is gradually decreased during about half revolution (180°) to complete the welding.

(14) FIG. 1B is a view of a tempering apparatus to temper the welded joint face. The laser generating device 30′ has a collecting lens 34 provided within a duct 32, and laser beam L is collected by the collecting lens 34 and then is applied to the joint face 16. The duct 32 has a branched duct 36, to which a shield gas S such as argon or helium, is supplied. The shield gas S is supplied to around the laser beam L applied toward the joint face 16 as a shield gas to prevent oxidation of a molten metal.

(15) By means of this apparatus, a tempering step C is performed. In the tempering step C, as illustrated in FIG. 1B, the region X on the rotor shaft side, including the welding portion, near the welding portion is heated at a temperature of 400° C.-750° C. with a high-frequency heat source or laser beam L and then is cooled. In a case of employing laser beam in this tempering step C, sweeping with laser beam L is performed to temper the region X for one revolution for (360°) or two revolutions (720°). In this case, it is preferred that the laser beam L is not applied to a range of 0° to 90° of an angular region of completion of the welding. The laser beam L can be polarized by permitting the laser beam L to be reflected by a reflecting mirror (not shown) provided within the laser beam generating device 30′.

(16) FIG. 3 is a chart showing a case where welding for the joint face 16 is performed for one revolution, and then tempering for the region X at the rotor shaft side including the welding portion is performed for a degree of [one revolution 360°)-90°]. In this case, in the welding step B, irradiation is started from the starting point of 0°, and the peripheral portion of the joint face 16 is irradiated until the irradiation position completes one revolution around the joint face 16 and comes back to the position of 0°. Then, in the tempering step C, the laser beam L is polarized to the region X on the rotor shaft side containing the welding portion. The irradiation with the laser beam L is started from the position of 0° C. and is continued to the position of 270°.

(17) In FIG. 4, difference in the light collection degree of the laser beam L depending on the irradiation objects. Laser beam L.sub.1 indicates a light collection degree in the welding step B. In the welding step B, the light collection degree is increased by collecting the laser beam at a point on the joint face 16 by the collecting lens 34. A high power density can thereby be obtained, which results in instant melting, whereby a rapid welding may become possible, and the welding time may be shortened. (Accordingly, laser beam may be used for welding in place of electron beam.)

(18) In the present invention, laser beam L.sub.2 is used in the tempering step C. In this case, as illustrated in FIG. 1B and FIG. 4, the collecting range of the laser beam L.sub.2 is distributed corresponding to the range of the region X on the rotor shaft side containing the welding portion. It is thereby possible to reduce the power density to a degree at which the heating temperature required in the tempering step C may be obtained. Further, by expanding the collecting range, the entire region of the region X on the rotor shaft side containing the welding portion with irradiation for one revolution. The laser beam L.sub.1 or the laser beam L.sub.2, or electron beam or laser beam is applied toward the joint face 16 or the region X on the rotor shaft side containing the welding portion in such a way.

(19) In FIG. 2B, a states of a residual stress generated in the welding portion 40 at the point D in the FIG. 2A, after carrying out the welding step B. As shown in FIG. 3, when irradiation of the laser beam L is performed for one revolution from 0° as the starting point, a residual stress R.sub.1 is generated in the angular region of completion of the welding at 270° or later. This is considered because, since the angular region of completion of the welding is exposed to welding heat for the longest period of time, the largest tensile force is applied due to the thermal expansion of a portion of the rotor shaft near the welding portion, and this tensile force becomes a local residual stress in the angular region of completion of the welding.

(20) Accordingly, in this embodiment, in the tempering step C, the laser beam L.sub.2 is applied to a region from the starting point of 0° to 270° without laser beam application to the region of completion. The rotor shaft 14 is thereby expanded in the region other than the angular region of completion, and a residual stress is generated in the welding portion 40. Therefore it is possible to generate a residual stress R.sub.2 evenly over the entire circumference of the welding portion 40, as seen in FIG. 2C.

(21) Accordingly, as the residual stress R.sub.2 is balanced along the circumferential direction of the welding portion 40, such a balanced state of the residual stress may be maintained even after cooling. Thus, leaning of the rotor shaft 14 will not occur, and leaning will not occur even in a case of heating in operation. According to this embodiment, when the turbine rotor 10 is employed in a turbocharger for a car, the shaft center leaning Δσ measured at a circumference of the turbine blade rotor can be suppressed to at most 0.2 mm in operation of the turbocharger for a car. By suppressing the shaft center leaning Δσ to at most 0.2 mm, it is possible to suppress actual noise or shaft vibration within an allowable range.

(22) Further, by using at least the laser beam generating device 30′, a high power density may be obtained, whereby rapid welding may become possible, which is suitable for mass production. Further, the heat input is small and the heat effect on the surrounding part is small, and the position of beam irradiation may be precisely controlled. Further, since the environment surrounding the welding portion is not required to be maintained as a vacuum as in the case of electron beam, the cost may be reduced. Further, in the tempering step C, as the collecting range of the laser beam L is permitted to correspond to the region X on the rotor shaft side containing the welding portion, the tempering step C can be completed only with one revolution or two revolutions of the turbine rotor 10, whereby the tempering step C may be shortened.

(23) This embodiment is an example where a laser beam generating device is used as the heating device for tempering, but a high-frequency heating device may also be used in place of the laser beam generating device. A high-frequency heating device enables downsizing and weight saving of a device and capable of high-efficiency power generation, which enables power saving and cost reduction. Further, as it is capable of rapid high-temperature heating, it is suitable for mass production, and the heating temperature may be precisely controlled without contact by a high-frequency electromagnetic field.

INDUSTRIAL APPLICABILITY

(24) According to the present invention, the shaft center leaning of the rotor shaft after welding can be suppressed, whereby it is possible to improve the yield and to produce a turbine rotor enabling mass production, at low cost.