The present invention relates generally to compressors and, more specifically, to techniques for welding compressor impellers.
A compressor is a machine which accelerates gas particles to, ultimately, increase the pressure of a compressible fluid, e.g., a gas, through the use of mechanical energy. Compressors are used in a number of different applications, including operating as an initial stage of a gas turbine engine. Among the various types of compressors are the so-called centrifugal compressors, in which mechanical energy operates on gas input to the compressor by way of centrifugal acceleration, e.g., by rotating a centrifugal impeller (sometimes also called a “rotor”) by which the compressible fluid is passing. More generally, centrifugal compressors can be said to be part of a class of machinery known as “turbo machines” or “turbo rotating machines”.
Centrifugal compressors can he fitted with a single impeller, i.e., single stag e configuration, or with a plurality of impellers in series, in which case they are frequently referred to as multistage compressors. Each of the stages of a centrifugal compressor typically includes an inlet conduit for gas to be compressed, an impeller which is capable of imparting kinetic energy to the input gas and a diffuser which converts the kinetic energy of the gas leaving the rotor into pressure energy.
An impeller generally includes a plurality of blades which are disposed radially relative to one another to form a plurality of passages which converge toward the center of the impeller and through which, in operation, the compressible gas flows, The blades are connected on one end to a hub and, on the other end, to a shroud. Such impellers are subjected to significant stresses during operation, attributable to, for example, the high speeds at which they are rotated and the high densities at which the compressible gases are provided to the centrifugal compressors. Thus, it is important to design such impellers to withstand such stresses and operate stably for long periods of time.
The manner in which the blades are connected to the huh and shroud are, therefore, quite important to the overall design of the impeller and a number of different connection techniques have been used previously. It is not unusual for the blades to be milled together with the hub as one piece, and then to be connected to the shroud, e.g., by welding. For example, as shown in
Automated, external connection techniques have also been proposed. For example, as shown in
Electron beam and laser beam welding techniques have also been used to connect impeller blades to the shroud. As shown in
Brazing techniques have also been used, either by themselves or in conjunction with beam welding techniques, to attach impellers to other surfaces. However these techniques also suffer from the lack of penetration, lack of fillet radii and incomplete welding issues described above. Moreover, the joint created using brazing techniques is not resulting in potentially reduced mechanical characteristics of the joint, especially in operating conditions which include corrosive gases that may attack the brazing material.
Accordingly, it would be desirable to design and provide techniques for electron beam/laser beam welding of impeller blades to other surfaces, e.g., shrouds, which overcome the aforementioned drawbacks of existing welding techniques.
Exemplary embodiments relate to systems and methods for enabling automated beam welding techniques to he used for joining an impeller blade to. e.g., a shroud. According to one exemplary embodiment, a connection area of the impeller blade has a “hammer”-shaped cross-sectional area which facilitates beam welding of the connection area to a slot in the surface or body to which the blade is to be connected.
According to an exemplary embodiment, a method for beam welding an impeller blade to a surface includes the steps of inserting an impeller blade connection area into a slot in the surface, performing a first beam welding pass on a first side of the impeller blade connection area to weld the first side of the impeller blade connection area to one side of the slot, and performing a second beam welding pass on a second side of the impeller blade connection area to weld the second side of the impeller blade connection area to another side of the slot.
According to another exemplary embodiment, an impeller includes a hub having a plurality of impeller blades milled therein, and a shroud having slots formed therein and connected to each of the plurality of impeller blades at impeller blade connection areas by beam welding of each of two sides Of the impeller blade connection areas to corresponding sides of one of the slots.
According to yet another exemplary embodiment, a turbo machine includes a rotor assembly including at least one impeller, a bearing connected to, and for rotatable supporting, the rotor assembly, and a stator, wherein the at least one impeller includes a huh having a plurality of impeller blades milled therein, and a shroud having slots formed therein and connected to each of the plurality of impeller blades at impeller blade connection areas by beam welding of each of two sides of the impeller blade connection areas to corresponding sides of one of the slots.
The accompanying drawings illustrate exemplary embodiments, wherein:
The following detailed description of the exemplary embodiments refers to the accompanying drawings. The same reference numbers in different drawings identify the same or similar elements. Also, the following detailed description does not limit the invention. Instead, the scope of the invention is defined by the appended claims.
To provide some context for the subsequent discussion relating to welding techniques and impeller blade connection area shapes according to these exemplary embodiments,
The multistage centrifugal compressor operates to take an input process gas from duct inlet 52, to accelerate the process gas particles through operation of the rotor assembly 48, and to subsequently deliver the process gas through various interstage ducts 54 at an output pressure which is higher than its input pressure. The process gas may, for example, be any one of carbon dioxide, hydrogen sulfide, butane, methane, ethane, propane, liquefied natural gas, or a combination thereof. Between the impellers 46 and the bearings 50, sealing systems (not shown) are provided to prevent the process gas from flowing to the bearings 50. The housing 42 is configured so as to cover both the bearings 50 and the sealing systems, so as to prevent the escape of gas from the centrifugal compressor 40.
A more detailed, but purely exemplary, illustration of an impeller 46 is provided in
Therein, the “hammer”-like shape of the connection area 70 of impeller blades 60 according to exemplary embodiments is seen. Unlike other impeller blade connection areas described above, it can be seen that the connection area 70 is wider (thicker) from its outer end 72 to its inner end 74 relative to the next adjacent portion of the impeller blade 60. Additionally, at the inner end 74, the connection area 70 joins the rest of the blade 60 via curved sections 76 and 78. These curved sections 76 and 78 are designed with a predetermined radius of curvature (fillet radius) of e.g., 3-4 mm, to provide the attached impeller blade with desired strength and bending characteristics. Thus, the width (thickness) of the connection area 70 can, for example, be equal to the thickness of the blade 60 plus twice the desired fillet radius.
According to an exemplary embodiment, to attach impeller blade 60 to the shroud 64 the welding technique shown in the flowchart of
Thus, according to an exemplary embodiment, a method for beam welding an impeller blade to a surface, e.g., a shroud of an impeller, can include the steps illustrated in the flowchart of
The above-described exemplary embodiments are intended to be illustrative in all respects, rather than restrictive, of the present invention. Thus the present invention is capable of many variations in detailed implementation that can be derived from the description contained herein by a person skilled in the art. All such variations and modifications are considered to be within the scope and spirit of the present invention as defined by the following claims. No element, act, or instruction used in the description of the present application should be construed as critical or essential to the invention unless explicitly described as such. Also, as used herein, the article “a” is intended to include one or more items.
Number | Date | Country | Kind |
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CO2009A000063 | Dec 2009 | IT | national |
This is a national stage application under 35 U.S.C. §371(c) of prior-filed, co-pending PCT patent application serial number EP10/069022, filed on Dec. 7, 2010, which claims priority to Italian Patent Application Serial No. CO2009A000063, filed on Dec. 11, 2009, the entire contents of which are incorporated herein by reference.
Filing Document | Filing Date | Country | Kind | 371c Date |
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PCT/EP2010/069022 | 12/7/2010 | WO | 00 | 10/5/2012 |