Metal/polymer laminate ducting and method of making same

“METAL / POLYMER LAMINATED Duct AND METHOD FOR THE MANUFACTURING”

Background of the Invention

The present invention relates generally to turbine engine duct structures and methods for their manufacture.

Related Technique

Gas turbine engines, especially those for aircraft propulsion applications, use ducts to extract air flow from one part of the engine, for example to provide a cooling air source, which air flow needs to be returned to another part of the engine.

One such structure that requires transport ducts is known as the air oil cooler (to cool the engine lubricating oil). This device requires an inlet duct, which directs the cooling air, from a turbine front (inlet) from a vent stream through the air oil cooler. On the downstream side of the chiller heat exchange structure, a discharge duct directs “used” cooling air back into the vent stream.

Ducts serving the oil-air cooler (and other such engine duct structures) typically need to be able to meet a variety of design parameters: 1) ducts must withstand temperatures ranging in the range from -54 ° C (-65 ° F) to ) to approximately 371 ° C (700 ° F); 2) the ducts must withstand relatively low pressure, for example, from approximately 55 to 124 kPa (8-18 psig); 3) the ducts must be fireproof and / or flame resistant; 4) the ducts must be vibration resistant;

5) the ducts must be non flammable; and 6) the ducts must be as light as possible.

Such internal motor duct structures have typically been formed as all-metal structures, often made from one or more high performance materials such as corrosion resistant stainless steel (Cres) or titanium.

For example, Peyton et al., US 3,911,961 discloses the production of high-temperature aircraft-resistant multilayer ducts, including outer insulating sleeves formed from a resin-impregnated sheet and fabric press and an inner metal duct. , separated by a space with air. Fischer et al., US 4,934,412 discloses a tubular cooling line for a turbine engine, which has an inner layer of charge-resistant fiber-reinforced thermosetting resin surrounded by a heat-insulating layer of reinforced resin. Fiber

Norek, US 7,047,615 B2 discloses a method for producing turbine engine transport duct bodies without longitudinal welds by hydroforming two duct bodies abutted with inflating bellows attached to the open ends of the duct body. This allows the manufacture of duct bodies with detailed characteristics and high pressure without using compression cylinders. Multilayer transit duct bodies may also be assembled with layers of different materials, for example having a heat resistant layer within a high strength outer layer. They can also be mounted using cold contraction and thermal expansion. Additionally, anti-friction and anti-vibration coatings can be applied between layers for performance enhancement.

It would be desirable to provide a duct structure, for example for gas turbine engines, which is lightweight, durable and resistant to heat, fire and vibration.

These and other desirable features of the invention will become apparent in view of the present specification, including the claims and drawings.

Summary of the Invention

The present invention comprises in part a laminated duct structure for conducting air from a first location to a second location in a gas turbine engine. The duct structure comprises a metallic inner layer; and a polymeric outer layer, joined to an outer surface of the metallic inner layer. Such a polymeric outer layer may be of polyimide resin impregnated fiberglass fabric.

The inner metal layer may be made from one of the following materials: corrosion resistant steel; titanium. As mentioned, a preferred polymeric outer layer may comprise polyimide resin impregnated fiberglass fabric.

The present invention also comprises in part a method for producing a laminated duct structure for conducting air from a first position to a second position in a gas turbine engine.

The method for producing a laminated duct structure comprises the steps of: forming the first and second portions of the inner metal layer each having an inner surface and an outer surface;

forming the frangible first and second support members for positioning within the first and second portions of the inner metal layer;

positioning the first and second support members to structurally support the inner surface of each of the first and second portions of the metallic inner layer, respectively;

align the first and second portions of the inner metal layer together;

permanently joining the first and second portions of the inner metal layer together;

forming a polymeric outer layer on the outer surfaces of the first and second portions of the metallic inner layer;

cure the polymeric outer layer; and removing the brittle first and second support members.

A preferred polymeric layer may comprise polyimide resin impregnated fiberglass fabric.

The step of forming first and second members of the metallic inner layer may further comprise the step of forming the first and second members of the metallic inner layer from one of the following materials: corrosion resistant steel, titanium.

The step of forming the first and second support members brittle may further comprise the step of forming the first and second support members brittle from a mortar material.

The step of permanently joining the first and second members of the metallic inner layer may comprise the step of welding the first and second members of the metallic inner layer together.

The step of forming a polymeric outer layer on the outer surfaces of the first and second portions of the metallic inner layer may further comprise the step of forming the polymeric polyimide outer layer, preferably polyimide resin impregnated fiberglass fabric.

The curing step of the polymeric outer layer may comprise the step of placing the assembled inner and outer layers in an oven, heating it until the polymeric outer layer has been cured.

Brief Description of the Drawings

Figure 1 is a perspective view of an air oil cooler for a gas turbine engine showing possible intake and discharge duct structures.

Figure 2 is a schematic flow chart illustrating the steps in the process of forming the metal "halves" or "skins" of the duct according to a preferred embodiment of the invention.

Figure 3 is a schematic flowchart illustrating the process of assembling the metal "halves" or "skins" of the duct according to a preferred embodiment of the invention, and the subsequent formation of the polymeric outer layer thereon.

Detailed Description of the Invention

Although such an invention is susceptible of embodiments in many different forms, a specific embodiment is represented in the drawings and details herein, with the understanding that the present disclosure is to be considered an exemplification of the principles of the invention and is not intended to limit the scope of the invention. invention to the illustrated embodiment.

The present invention in part comprises a novel laminated duct structure suitable for use in gas turbine engines, such as turbine engines for use in aircraft. A further aspect of the present invention comprises a method for producing the laminated duct structure.

An oil-air chiller 10 for a gas turbine engine is shown in Figure 1. Chiller 10 includes heat exchanger 12, together with inlet duct 14 and discharge duct 16, which respectively lead to one side and to each other the airflow in the engine, in front of the combustion region (s) of the engine. The configurations of heat exchanger 12, and inlet and discharge ducts 14 and 16, respectively, are shown by way of example only, and, being functions of the engine architecture as a whole, will vary by engine. Accordingly, the specific shape and configuration of inlet duct 14, and discharge duct are not part of the present invention except as described and claimed herein.

Referring to Figure 2, according to a preferred embodiment of the invention, a duct is formed by first creating a three-dimensional ("3D") image 20 of the duct using computer aided design techniques ("CAD"). The 3D image is used to in turn determine the inner molding line or inner surface contour (“IML”) and outer molding line or outer surface contour (“OML”) (collectively, numeral reference 30) of the upper and lower portions (alternatively known as “skins” or “halves”, though not literally) of the duct, which is then used to create the patterns of the stamping dies (for example, 40) for each upper and lower portion of the duct. Although in the schematic illustrations of Figures 2 and 3, the portions of the metal inner layer of the duct are shown to be highly regular and symmetrical, in practice the metal duct components may be highly asymmetrical (as generally reflected in Figure 1). Typically, for each metal portion of the duct structure, usually only two parts will be required to be formed separately and then joined together.

As mentioned herein, the metallic inner layer of the duct is preferably quite thin, for example preferably of the order of 0.15 mm (0.006 ”) thick, such that the clearance between the outer surface of the die 50 and the inner surface of the molds will be of a similar dimension, although that dimension is representative, and the invention is not to be construed as limited thereto.

The molds 40 are used not only for stamping the actual metal portions of the duct, but also as molds for the supporting blocks 60, the use of which will be described in detail below. Preferably, the support blocks 60 are made of any suitable brittle material such as mortar material.

As mentioned above, the metal portion of the duct will be quite thin (e.g., preferably on the order of 0.15 mm (0.006 ”) thick, and preferably formed from corrosion resistant steel (Cres) or titanium (Ti), although other metals which have similar performance characteristics for the application may also be used. After the two metal portions (or "hides"), for example, hides 70, have been individually stamped, they are joined together with two opposite positioned welds, generally extending longitudinally 80 (e.g., "pencil" welds), after the two corresponding support blocks 60 have been placed into the respective metal skins.

Support blocks 60 serve to provide support and rigidity to the metal duct during the process steps described below. A layer 90 of polymeric material, preferably polyimide resin impregnated fiberglass fabric or in a single thickness measure or multiple thickness measurements, wherein each thickness measure is approximately 0.25 mm (0.010 ”) thick. applied to the outside of the heat-cured metal duct, in an appropriate atmosphere, at a sufficient temperature and for a sufficient time appropriate to the material, to ensure that the polyamide is firmly bonded to the outer surfaces of the metal skins.

Preferably, the uncured polyimide resin fiberglass fabric is cut to a desirable contour to fit over the inner metal layer. Multiple layers or thickness measurements of this fabric can be used to add strength or pressure bearing capabilities. As part of the curing process, the entire metal / polyimide assembly is wrapped with retractable tape, retractable wrap, or vacuum bag to press the metal / polyimide layers together and join them together.

Once the curing process has been completed, the mortar support blocks 60 are broken from the end portion 100, and the interior of the metal layer is cleaned of debris and mold released material (if any).

The description and drawings presented so far are merely illustrative for explaining the invention, and are not to be construed as limiting it, and those of ordinary skill in the art will be able to make modifications and variations to the present invention without departing from the scope of the invention. .