Patent Application
20070189894
The present invention relates generally to turbine engines, and, more particularly to methods for welding turbine engine rotors.
At least some known turbine engine rotors include several rotor sections, wherein each rotor section may operate at a different temperature and/or at different operating conditions. For example, such rotors may include a high pressure rotor section, an intermediate pressure rotor section, and a low pressure rotor section. Because the different rotor sections are subjected to different operating temperatures and pressures, for example, within a rotor, at least some known rotor sections are fabricated with different materials. Known methods of coupling the different rotor sections include bolting and/or welding the sections together. Between the two coupling methods commonly employed, bolting the sections together is generally the least desirable because the flanges and bolts used generally result in the turbine rotor being longer than desired and increase the original weight of the rotor.
Known methods of welding rotor sections may subject the rotor to flaws if such welding processes require multiple passes, intermediate machining, and/or multiple heat treatments. In particular, multiple welding passes may increase risks of defects in the finished weld. For example, each pass may increase the risk for slag entrapment, lack of fusion, or porosity, which may serve as an initiation point for serious cracking.
To facilitate reducing risks associated with welding rotor sections together, at least one welding method uses a welding electrode to build up a layer on either side of the joint to be welded. However, this welding technique increases the width of the welding joint, which may increase the risk of slag entrapment and/or porosity. An alternative welding technique uses layered transition pieces fabricated from different composite materials. However, generally, such transition pieces have lower material strengths than other sections of the rotor. As a result, the rotor must be handled with special care to avoid damaging or weakening the transition pieces. Furthermore, the ends of such a rotor must be heat treated, which may subject the composite transition materials to excessive temperatures.
In one aspect, a method for welding two sections of a rotor together, wherein each rotor section includes a welding surface, is provided. The method includes positioning the welding surface of the first rotor section substantially flush against the welding surface of the second rotor section. The method also includes positioning the second section substantially flush against a flange circumscribing the first section such that a rabbeted joint is defined therebetween.
In another aspect, a rotor for a turbine engine is provided. The rotor includes a first rotor section including a welding surface and a flange. The rotor also includes a second rotor section including a welding surface. The first rotor welding surface is positioned substantially flush against the second rotor welding surface and the second rotor section is substantially flush against the flange such that a rabbeted joint is defined between the first rotor section and the second rotor section.
In a further aspect, a system for welding two sections of a rotor is provided. Both sections of the rotor include a welding surface. The first rotor section welding surface is positioned substantially flush against the second rotor section welding surface, and the second rotor section is substantially flush against a flange circumscribing the first rotor section such that a rabbeted joint is defined therebetween. The system includes a casing coupled to the rotor such that a chamber, defined by the casing, substantially circumscribes the joint. The chamber is vacuum pumped to create a vacuum therein or a partial vacuum. The system also includes an electron beam generator to weld the joint within the chamber.
Prior to beginning a welding operation, rotor sections 102 and 104 are positioned together to define joint 106. Specifically, second section surface 116 is positioned substantially flush against first section surface 114, and second section inner surface 122 is positioned substantially flush against rabbet upper surface 124 to define rabbeted joint 125. Rabbeted joint 125 facilitates coupling section 102 and section 104. The coupling of section 102 and section 104 also defines cavity 109. Alternatively, rotor 100 may include several joints 106 defined by multiple sections.
Casing 110 is coupled to rotor 100 such that casing 110 defines chamber 111 substantially circumscribing joint 106. The air is removed from the chamber 111 to create a vacuum surrounding joint 106. Because chamber 111 circumscribes a limited section of rotor 100, the need for large vacuum housings is eliminated.
After a vacuum is established within chamber 111, the welding process is performed. Specifically, in the exemplary embodiment, the welding is performed by electron beam generator 112. Electron beam generator 112 is coupled to casing 110, within chamber 111, such that it can be moved circumferentially around rotor 100. Electron beam generator 112 is aligned relative to joint 106 to enable an electron beam to be directed towards joint outer portion 107 with an intensity that enables it to penetrate to joint inner portion 108.
Electron beam generator 112 is rotated around the circumference of rotor 100 while directing the electron beam at joint outer portion 107. Alternatively the electron beam is kept stationary and the rotor is rotated to create a relative travel between the beam and the rotor circumference. During the rotation, the electron beam heats first section surface 114 and second section surface 116 to produce welded metal. Welded metal from surface 114 is fused with welded metal from surface 116 such that section 102 and section 104 are bonded into a unitary piece. Because electron beam generator 112 need only make one complete rotation around the circumference of joint 106 to bond surfaces 114 and 116, welding defects are facilitated to be reduced in comparison to welding techniques that require multiple passes. Specifically, because rabbeted joint 125 facilitates a tighter fit between sections 102 and 104, the electron beam is able to produce a more structurally sound weld with only one pass of electron beam generator 112. As a result, a structurally strong weld that is less susceptible to weld defects and distortion, is produced.
During the welding process, rabbet 118 prevents materials, including welded metal and/or slag, from falling into cavity 109 such that fusing between the welded metal of surface 114 and the welded metal of surface 116 is facilitated to be optimized. As such, the bond provided between section 102 and section 104 is structurally sound, and brittleness and cracking within the weld is facilitated to be reduced. Moreover, by preventing welded metal from falling into cavity 109, a more complete bond can be obtained between sections 102 and 104, resulting in fewer defects.
In the exemplary embodiment, electron beam generator 112 is operable through a range of powers indicative of the intensity of the electron beam. Because joint outer portion 107 has a greater circumference than joint inner portion 108, the inner portion will be welded 360 degrees before the outer portion is completed as shown in
After completion of the weld a stress relieving heat treat process is applied locally to the area near the joint. This is needed because of two reasons. The first reason is that any weld process will leave some residual stresses at the joint. The second reason is that most materials will undergo metallurgical transformation in the heat affected zone of the weld which may change their mechanical properties. The selection of temperature for this heat treatment is based on the materials being welded. After the heat treat process the materials properties at the joint are mostly restored close to the original base material properties.
The material used in fabricating shim 130 is selected based on the materials used in fabricating first section 102 and second section 104. For example, if CrMoV steel were being welded to NiCrMoV steel, a shim fabricated of an intermediate composition of the two steel alloys could be used. Moreover, and for example, if steel materials are being coupled to nickel-based alloys, an alloy such as alloy 625 or alloy 617 could be used. In each embodiment, the shim material of the appropriate thickness is selected to facilitate preventing potentially harmful phases from forming in the weld, while maintaining the properties of the weld metal. In the exemplary embodiment, a similar process to the above-described welding process and heat treat process is utilized when shim 130 is inserted between section 102 and section 104.
Prior to beginning welding operations, rotor sections 102 and 104 and shim 130 are positioned together to define joint 106. Specifically, shim first surface 132 is positioned substantially flush against first section surface 114 and shim second surface 134 is positioned substantially flush against second section surface 116. Furthermore, shim inner surface 136 is positioned substantially flush against rabbet upper surface 124. Shim width 138 is sized such that second section inner surface 122 is positioned substantially flush against rabbet upper surface 124. The coupling of sections 102 and 104 with shim 130 also defines cavity 109. Alternatively, rotor 100 may include several joints 106 defined by multiple sections and multiple shims.
Casing 110 is coupled to rotor 100 such that chamber 111 substantially circumscribes joint 106. The air is removed from the chamber 111 to create a vacuum surrounding joint 106. Because chamber 111 circumscribes a limited section of rotor 100, the need for large vacuum housings is eliminated. After a vacuum is established within chamber 111, the welding process is performed with electron beam generator 112 coupled to casing 110, within chamber 111.
During the rotation of electron beam generator 112 around rotor 100, the electron beam heats surface 114 and surface 116 to produce welded metal. Furthermore, shim 130 is melted by the electron beam. Melted shim 130 fuses with the rotor metal on either side to bond section 102 and section 104 into a unitary piece. In the exemplary embodiment electron beam generator 112 completes one rotation around the circumference of joint 106. Moreover, the intensity of electron beam generator 112 is reduced as the rotation nears completion.
After completion of the weld a stress relieving heat treat process is applied locally to the area near the joint. This is needed relieve residual stresses at the joint and to restore the material properties of the metal. The selection of temperature for this heat treatment is based on the materials being welded. After the heat treat process the material properties at the joint are mostly restored close to the original base material properties.
The above-described methods and systems facilitate a turbine rotor being efficiently welded with a weld joint that is subject to less brittleness and/or cracking within the joint. Specifically, the rabbeted joint facilitates coupling the rotor sections together, such that they can be welded using only a single pass of an electron beam generator. As such, two sections of the rotor are welded using a technique which facilitates reducing defects, such as slag entrapment or porosity, within the weld. Furthermore, the methods and system described herein can be used to weld two rotor sections fabricated from different materials. The shim described herein enables at least two rotor sections being properly bonded together despite each having different material properties. Moreover, the shim does not effect the need for only one pass of the electron beam generator. As a result, rotor sections can be welded together with a structurally sound joint that is cost effective and reliable.
As used herein, an element or step recited in the singular and proceeded with the word “a” or “an” should be understood as not excluding plural said elements or steps, unless such exclusion is explicitly recited. Furthermore, references to “one embodiment” of the present invention are not intended to be interpreted as excluding the existence of additional embodiments that also incorporate the recited features.
Although the methods and systems described herein are described in the context of welding a turbine rotor, it is understood that the welding methods and systems described herein are not limited to turbine rotors. Likewise, the welding system components illustrated are not limited to the specific embodiments described herein, but rather, components of the welding system can be utilized independently and separately from other components described herein.
While the invention has been described in terms of various specific embodiments, those skilled in the art will recognize that the invention can be practiced with modification within the spirit and scope of the claims.
