Patent Application
20080170943
This invention relates to inlet guide vanes for compressors, and more specifically, to a composite vane constructed of multiple materials.
Current inlet guide vanes (or IGVs) are typically fabricated from GTD 450 precipitation-hardened stainless steel. Such vanes are subject to in-service distress in the form of wear and corrosion pitting-induced high cycle fatigue in the spindle area of the vane and corrosion pitting in the airfoil portion of the vane.
In one exemplary but non-limiting embodiment, there is provided an inlet guide vane (IGV) that is designed primarily on the basis of material compatibility, i.e., in accordance with a design philosophy that makes use of multiple materials strategically placed to take advantage of their most attractive attributes to solve specific challenges. For example, the majority of the cross-section of the airfoil portion of the vane, i.e., the inner core of the vane, may be composed primarily of fiberglass epoxy for its high static and fatigue strength and low cost. Carbon epoxy fabric is strategically placed in other areas of the airfoil portion requiring bi-directional stiffness, e.g., in areas close to the air passage surfaces for maximum flexural rigidity for frequency and displacement control, preferably comprising about 20% by volume of the airfoil portion of the blade. A relatively thin layer of fiberglass epoxy may be placed between the carbon epoxy fabric and the outer sheath.
The airfoil portion is covered by an outer metal sheath, preferably aluminum, for foreign object damage (FOD) and corrosion, erosion and moisture resistance. The sheath may be in the form of a discrete solid wrap bonded to the fiberglass epoxy, or in the form of an applied aluminum coating.
The vane airfoil is also formed with an integral, radially-inwardly projecting tab by which the airfoil is attached at its radially inner end to the spindle (or mounting) portion of the blade. The tab itself is also formed in a composite manner, with an extension of the epoxy fiberglass inner core sandwiched between extensions of the outer sheath.
Accordingly, in one aspect, the invention relates to a composite vane comprising an airfoil portion having an inner core composed primarily of fiberglass epoxy and an outer metal sheath surrounding the inner core.
In another aspect, the invention relates to a composite vane comprising an airfoil portion having an inner core composed primarily of fiberglass epoxy and an outer metal sheath surrounding the inner core, wherein the airfoil portion is further comprised of about 20% by volume of carbon/epoxy fabric located in selected areas of the airfoil portion outwardly of the inner core, and wherein additional fiberglass epoxy material is interposed between the carbon/epoxy fabric and the aluminum sheath.
The invention will now be described in detail in connection with the drawings identified below.
More specifically, the inner core 118 is comprised of an economical, continuous-reinforced fiberglass epoxy, having high tensile (and span-wise) strength and fatigue life. As is readily apparent from
Note that the continuous fiber reinforced carbon epoxy fabric 120 that surrounds the inner core 118 is placed in close proximity to the air passage surfaces 126, 128 (
A relatively thin layer of fiberglass epoxy material 122 encloses or surrounds the continuous reinforced carbon epoxy fabric 120, i.e., sandwiched between the fabric 120 and the metal sheath 124.
The outer aluminum sheath 124 may be on the order of 0.010 inch thick which provides protection against foreign object damage, erosion, corrosion, while enhancing moisture resistance. The sheath may be epoxy-bonded to the fiberglass epoxy layer 122, and co-cured with the fiberglass and carbon epoxy layers. Solution-hardened Series 3000 aluminum (for example, 3004 aluminum) is suitable for the solid sheath. The latter may also be strain-hardened up to 50 Ksi in UTS. This material has excellent corrosion resistance in aqueous media when the pH is between 4.0-8.5. The sheath may be folded from a flat sheet or preformed to airfoil shape in a die.
Alternatively, a cold-spray-deposited 7000 series aluminum coating may be applied over the outer fiberglass epoxy layer 122. Cold-spray aluminum is in nano-crystalline microstructure form, with increased surface hardness, superior corrosion resistance, and good fatigue and fracture toughness. The coating process can produce conventional (1-50 μm particles) and a layer with increased surface hardness and therefore wear resistance. Al—Zn—Mg—Cu—Zr or Al—Si—Fe—Ni are alloys of choice for the coating.
The aluminum sheath or coating 124 may be, in turn, coated with a phosphate-chromate sealer to enhance surface finish and extend the long term corrosion protection.
Referring now to
An alternative tab arrangement is shown in
The blade described herein is primarily intended for use as a compressor inlet guide vane, experiencing service temperatures up to about 250° F. The composite construction is suitable for other vanes, and including solid, rotating blades, with appropriate changes in material, depending on service temperatures.
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.
