Patent Application
20060231531
This invention relates to electron beam or laser welding and, specifically, to a steam turbine rotor weld prep joint configured to facilitate a single pass full penetration fusion weld of axially-aligned rotor forgings using a focused high energy beam.
Certain turbine rotors are comprised of a one piece “monoblock” forging. More recently, to facilitate manufacture, shipment and assembly, discrete rotor components or forgings have been welded together to duplicate the original single forging. Welded rotors have not been completely satisfactory, however, due to difficulty in alignment and preparation of end faces for welding.
This invention provides a unique weld prep joint for rotor forgings having two geometry aspects that are particularly beneficial. First, the weld prep joint is configured to provide a rabbet interference fit for consistent concentric assembly of axially-aligned rotor forging components prior to welding. Secondly, the radial surfaces to be welded are offset from the rabbet surfaces such that the rabbet surfaces act as a backing, thus preventing burn-through and material drop-through from forming on the rotor bore surfaces, thus eliminating internal rotor surface rework.
In the exemplary embodiment, the rotor components are machined to provide mating axial rabbet surfaces on each of the two components creating a concentric interference fit between the axially-aligned forging components, thereby eliminating rotor vibration. The arrangement also allows relative axial movement of the two components prior to the welding operation.
More specifically, one of the rotor forging components is provided with a first axial rabbet surface and a radial weld surface. The other rotor forging component is machined to include an underlying axial lip with a second axial rabbet surface mated to the axial rabbet surface of the first component, and a second radial weld surface adapted for engagement with the first radial weld surface of the first rotor forging. The laser or electron beam welding process produces a radially extending weld area along the first and second radial weld surfaces, and also extending radially into the lip portion of the second rotor forging component. By extending the weld area radially inwardly of the mated rabbet surfaces (i.e., into a low stress area), the potential for stress cracking at the rabbet surface joint is minimized.
Accordingly, in one aspect, the present invention relates to a weld prep joint for welding a pair of axially aligned first and second machine rotor forgings comprising a first weld joint configuration in an end of the first rotor forging including a first radial weld surface and a first axial rabbet surface; a second weld joint configuration on an end of the second rotor forging including a second radial weld surface adapted to engage the first radial weld surface, a second axial rabbet surface adapted to engage the first axial rabbet surface, and a third radial non-weld surface extending radially inwardly of the second rabbet surface and axially offset from the second radial weld surface.
In another aspect, the invention relates to a welded rotor assembly comprising a pair of axially aligned rotor forgings joined by a circumferentially extending weld area, the weld area defined by a pair of axially aligned weld prep joints including a first weld joint configuration in an end of the first rotor forging having a first radial weld surface and a first axial rabbet surface, and a second weld joint configuration on an end of the second rotor forging including a second radial weld surface engaged with the first radial weld surface; a second axial rabbet surface engaged with the first axial rabbet surface; and a third radial non-weld surface extending radially inwardly of the second rabbet surface and axially offset from the second radial weld surface.
In still another aspect, the invention relates to a method of welding a pair of axially-aligned rotor forgings comprising (a) preparing weld prep joints on opposed ends of the rotor forgings, one of the joints including a first radial weld surface and a first axial rabbet surface, the other of the joints including a second radial weld surface and a second axial rabbet surface; (b) joining the rotor forgings axially by a concentric interference fit between the first and second axial rabbet surfaces with the first and second radial weld surfaces engaged; and (c) utilizing a laser or electron beam welding machine, welding the rotor forgings together, creating a weld area at least along the first and second radial weld surfaces.
The invention will now be described in detail in connection with the drawings identified below.
Referring to
The rotor forging component 16 is machined to include a second radial weld surface 30 adapted to engage first weld surface 24, and an annular axial lip 32 radially inward of the first rabbet surface 28. The lip 32 is formed to include a second annular, axially extending rabbet surface 34 adapted to engage rabbet surface 28, and a forward face surface 33 of 2 or more inches in radial height forming an axial termination surface of the lip. Surfaces 30 and 33 are thus axially offset by a distance equally the length of the lip 32.
More specifically, the mating rabbet surfaces 28, 34 are machined so as to obtain a concentric interference fit between the axially-aligned forging components 14, 16. At the same time, the radial facing weld surface 26, 30 abut each other at a location where the lip 32 joins with the remainder of the forging component, i.e., the weld location at the interface of radial weld surfaces 24, 30 is axially offset from the mating rabbet surfaces 28, 34 so that there is no need for a full penetration weld that would otherwise require rework to clean up burn-through and/or drop-through material from the welding process. An annular groove 36 at the juncture of the rabbet surface 34 and radial weld surface 30 provides a receptor for molten metal during the welding process and is believed to assist in controlling the weld area termination point within the lip 32.
With the forging components located as shown in
While the invention has been described in connection with what is presently considered to be the most practical and preferred embodiment, it is to be understood that the invention is not to be limited to the disclosed embodiment, but on the contrary, is intended to cover various modifications and equivalent arrangements included within the spirit and scope of the appended claims.
