Fluid reaction surfaces (i.e. – impellers) – Specific working member mount – Blade held between separable surfaces
Reexamination Certificate
1999-09-03
2001-06-26
Look, Edward K. (Department: 3745)
Fluid reaction surfaces (i.e., impellers)
Specific working member mount
Blade held between separable surfaces
C416S232000, C416S239000, C416S21900R
Reexamination Certificate
active
06250886
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
This invention relates generally to axial flow fan and blade assemblies, and, more specifically, to large, industrial-type axial flow fans and improvements in the construction of blades therefor.
2. Background
It is generally preferable to use true tapered, twisted fan blades to achieve maximum air displacement efficiencies in large fan assemblies. It is also preferable to use lower cost fabricated light alloy fan blades in place of much more expensive molded fiberglass blades. But because of certain manufacturing complexities it has been practically impossible to reach suitable twist values in alloy fan blade airfoils without causing damage to the blade itself. One response to this limitation has been to add a tab to the trailing edge of an untwisted alloy fan blade in order to simulate the effects of a true twisted blade. Though this approach increases the effective displacement of air of an untwisted blade, a true twisted airfoil is still more efficient and desirable than the simulated effects of a modified trailing edge.
It is thus an object of this invention to provide an axial flow fan of the type described having blades fabricated from light alloy with a true twisted configuration to achieve maximum aerodynamic performance.
In connection with large, high performance fans it is also necessary to manage the stresses from aerodynamic loading generated in the airfoil skin. Heretofore fans of this type have utilized a relatively narrow cast, formed or fabricated transition piece from the fan hub to the airfoil section of the blade that limits the means of attachment to the airfoil skin and tends to concentrate stresses from the aerodynamic loading.
It is accordingly a further object of the invention to provide a axial fan having a transition from the fan hub to the airfoil section of the fan blade that not only allows for the use of a true twisted airfoil but also provides a mechanical joint between the airfoil skin and the transition piece which has a lower stress concentration pattern to better distribute aerodynamic loading forces.
SUMMARY OF THE INVENTION
These and other objects and advantages are achieved in the present invention wherein a true tapered, twisted airfoil section is constructed by cutting a flat piece of light alloy to a unique shape to obtain a flat pattern representative of a selected airfoil design, forming the airfoil section by making three simple bends in the pattern and joining the trailing edge with rivets or by other means. The required shape is obtained by “unfolding” a desired airfoil design into a representative pattern that is preferably laser cut from flat alloy stock.
The bending process does not result in any appreciable reduction of thickness in the formed airfoil skin, as is the case with conventional stretch forming processes, and requires simpler and less expensive tooling. The airfoil section is formed by making first and second bends of opposite directions to curve the long edges of a flat, generally flag-shaped quadrilateral airfoil skin, making a third bend at a dissecting line to form the leading edge, and then joining the long edges of the skin to form the trailing edge of the airfoil section.
In another aspect of the invention a transition piece is provided to connect the airfoil section to the fan hub. The transition piece has first and second airfoil bearing surfaces, substantially all of which are in contact with the interior surface of the airfoil section and which possess a twist complementary to the twist of the airfoil section. The transition is substantially flat and is preferably of a two piece design comprising juxtaposed first and second pieces joined along a peripheral flange. The airfoil bearing surface of each piece matches the curvature of the portion of the interior surface of the airfoil section it contacts.
In a further aspect of the invention, the transition piece allows for the use of a unique, generally U-shaped rivet pattern for the mechanical connection between the airfoil section and the transition which has significantly lower stress concentration patterns than previous parallel, perpendicular or zig-zag patterns of attachment.
In accordance with the preferred embodiment of the invention both the airfoil section and transition piece are constructed of aluminum so as to provide a lightweight, inexpensive fan blade. It is also preferred that the airfoil section be tapered from its root end to its tip so as to form, when constructed, a true tapered, twisted airfoil.
A better understanding of the present invention, its several aspects, and its objects and advantages will become apparent to those skilled in the art from the following detailed description, taken in conjunction with the attached drawings, wherein there is shown and described the preferred embodiment of the invention, simply by way of illustration of the best mode contemplated for carrying out the invention.
REFERENCES:
patent: Re. 34207 (1993-03-01), Nelson et al.
patent: D. 265502 (1982-07-01), Kearnes
patent: 1404298 (1922-01-01), Jacobs
patent: 1912979 (1933-06-01), Havill
patent: 2395193 (1946-02-01), Place
patent: 2511862 (1950-06-01), MArtin
patent: 2623599 (1952-12-01), Kearns, Jr.
patent: 2682925 (1954-07-01), Wosika
patent: 2814350 (1957-11-01), Nelson
patent: 2918977 (1959-12-01), Fedan et al.
patent: 3628888 (1971-12-01), Wooden
patent: 3799701 (1974-03-01), Rothman
patent: 3891349 (1975-06-01), Woollenweber, Jr.
patent: 4345877 (1982-08-01), Monroe
patent: 4618313 (1986-10-01), Mosiewicz
patent: 4636142 (1987-01-01), Baranski
patent: 4720244 (1988-01-01), Kluppel et al.
patent: 5035576 (1991-07-01), Byrnes et al.
patent: 5222297 (1993-06-01), Graff et al.
patent: 6022191 (2000-02-01), Moore et al.
patent: 1037057 (1958-08-01), None
patent: 2242218 (1973-09-01), None
patent: 1267976 (1963-05-01), None
patent: 60-30500 (1985-02-01), None
patent: 224357 (1924-11-01), None
Immell William F.
Scott Sean D.
Van Atta John W.
Chittom International, Inc.
Fellers Snider Blankenship Bailey & Tippens, P.C.
Look Edward K.
Nguyen Ninh
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