Impeller manufacturing process

Details Impeller manufacturing process Impeller manufacturing process

1999-11-05

2001-08-21

Look, Edward K. (Department: 3745)

Fluid reaction surfaces (i.e., impellers)

Rotor having flow confining or deflecting web, shroud or...

Radially extending web or end plate

C416S22300B, C029S889200

Reexamination Certificate

active

06276899

ABSTRACT:

BACKGROUND OF THE INVENTION
This invention relates to impellers for centrifugal pumps, and more specifically to a process for manufacturing impellers.
A pump impeller is composed essentially of three parts: a hub portion, vanes, and a shroud portion. Traditionally, there have been several ways to manufacture impellers. In one method, molds for the vanes are placed on top of a hub. The molds are arranged as desired for the vanes, and filled with weld material. The material fills the mold, forms the vanes, and is attached to the hub. The shroud must then be attached to the vanes.
Several other manufacturing methods use pre-fabricated vanes, which are then welded in place between the hub and the shroud. In another method, a set of long vanes are attached to the hub, extending from the edge to the center. A set of shorter blades which do not extend all the way to the center of the hub are attached to the shroud. The complementary hub and shroud are then attached, with the vanes interleaved.
Other manufacturing methods deform the impeller pieces into their respective shapes, and then attach them to each other. The impeller parts may also be cast, and then assembled.
Another impeller manufacturing method creates two pre-formed parts—a hub, having the vanes attached to it, and a shroud. These pieces are placed in appropriate position relative to one another by means of a five-axis machine. Once in proper position, the pieces are then electron-beam welded together. Both the use of a five-axis machine, and the process of electron-beam welding are quite expensive and require long lead times for production. Further, this method of fabricating impellers allows the potential for crevice erosion, since electron beam welding does not make a complete joint from one side of each vane to the other. There is also the potential for poor mating between the hub-vanes portion of the impeller and the shroud portion of the impeller, since the respective surfaces of the shroud and vanes that are in contact with each other may not match up, and the intersection of the surfaces may leave gaps between them. In addition to allowing voids or gaps between the surfaces, when the shroud and the vanes are not specifically matched to one another, there is a likelihood of improper or imprecise alignment. In addition, the integrity of electron-beam welds between the shroud portion and the hub-vanes portion is unknown, in part due to the variation in surface contact. Finally, the cost of machining, assembling and welding the shroud and hub-vanes portions of the impeller, first utilizing a five-axis machine and then subsequently electron-beam welding the portions together is very high, both from a monetary and a time-management viewpoint.
Thus there exists the need for an economical process to manufacture high-strength, precision impellers, including hub, vane, and shroud components which fit together in a mating fashion, preventing large gaps between the components and ensuring proper alignment of the components.
SUMMARY OF THE INVENTION
The present invention is embodied in a method for manufacturing an impeller from three component portions—a hub, a core, and a shroud. A core, with first and second surfaces, is machined. A shroud, with a second surface that mates with the first surface of the core, is machined. For example, if there is a protrusion on the first surface of the core, there would be a matching recess on the second surface of the shroud, such that the surfaces would mate together. A hub, with a first surface which mates with the second surface of the core, is machined. Material is removed from the sides of the core, without disturbing the profile of its first and second surfaces, such that the remaining material of the core forms one or more vanes. The vanes formed from the core are placed on the first surface of the hub, such that the second surface of the vanes contacts the first surface of the hub, with the mating surfaces aligning the vanes and hub relative to one another. The second surface of the shroud is then placed on the first surface of the vanes, with the weight of the shroud acting to align the shroud with the vanes.
A feature of this method of manufacturing an impeller is that the components are mated to one another, and thus their contacting surfaces fit together tightly, without significant voids between them. This is important to strengthen the subsequent connection between the portions, by providing the contacting surfaces to be at a relatively fixed distance from one another, allowing for proper welding or other connection.
Another feature of this method is that the components may be individually machined, reducing the cost and time for such operation.
Another feature of this method is that the overall cost is reduced, as no casting or molding of the vanes is necessary. Economical machining is used, and there is no need for further deformation, or for expensive machinery to finish and align the components.
Another feature of this method is that because the components are mated with one another, when they are placed in the correct radial position the components self-align relative to one another. Thus the contacting surfaces are precisely aligned, and can be brazed rather than welded, providing a tight fit without gaps.
Another feature of this method is that the upper and lower surfaces of the vanes, which will mate with the shroud and hub respectively, are machined when the core is a single component, reducing the time and expense which would be required to individually machine the upper and lower surface of each vane, and increasing the precision of the mating surfaces.
Other features and advantages of the present invention will become apparent from the following description of the preferred embodiments, taken in conjunction with the accompanying drawings, which illustrate, by way of example, the principles of the invention.


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VanDine, et al, “A Manufacturing Implementation of Precision Shrouded Impellers”, Proceedings of 1997 ASME Fluids Engineering Division Summer Meeting FEDSM '97, Jun. 22-26, 1997, 1997, pp. 1-14.

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