CN1153500A - Semi-rigid, lightweight fiberglass/polyimide foam sandwich insulation plies - Google Patents

Abstract

A semi-rigid, lightweight insulating layer sheet (20) consisting of a porous framework (12) sandwiched between layers of glass fibers (10). The polyimide carcass (12) prevents the dielectric plies, particularly in the dome and upper sidewall regions of the aircraft, from collapsing, thus maintaining a predetermined gap from the aircraft fuselage surface, thereby reducing moisture accumulation and corrosion of the primary structure. This configuration provides similar acoustic performance and weight savings as the prior art.

Description

Semi-rigid, lightweight fiberglass/polyimide foam sandwich insulation plies

This invention relates to insulating interlayer plies, and more particularly to fiberglass insulating plies for use in aircraft interiors and other aerospace equipment.

Prior patent literature includes U.S. Patent No. 4,964,936 to Ferro, which discloses an insulating material that differs from the insulating plies of the present invention in that its polyimide-filled honeycomb core has open cells, whereas the present invention Inventing the insulating ply is a laminate of solid sheets of polyimide sandwiched between layers of fiberglass.

US Patent No. 5,169,700 to Meier et al. discloses a single or multiple plies of fibrous material, specifically fiberglass, each single ply bonded to a layer of breathable facestock. The plies of multi-layer material are edge-stitched or encased in a heat-sealable film. Insulation plies range in density from 0.2 to 1.5 pounds per cubic foot, and unlike the above, the present invention employs a multi-ply stack-up format in which a stiffer polyimide foam core is sandwiched between fiberglass plies . The present invention uses the aforementioned combination of materials with different impedances and densities, and provides superior noise propagation attenuation characteristics compared to the single-density material insulation layer within the range used in the above-mentioned Meier et al. invention.

Various problems are associated with insulating plies for aircraft interiors. Typical problems encountered are as follows:

(a) Using existing manufacturing methods, Mylar is overlaid on fiberglass plies and stitched to maintain shape. Extensive stitching and/or joining stitches are required to keep the insulating batt from sinking into the bag material or fabric.

(b) The batting insulation needs to be stitched to the fabric and the stitched area needs to be patched. Because the ply absorbs moisture through the pins, it must be patched to prevent moisture ingress through capillary action.

(c) All peripheral and internal cutouts require intricate stitching which must be sealed to prevent moisture absorption and accumulation, adding to cost and weight.

(d) Inhalation of moisture will cause the weight of the insulation to increase, and the accumulated moisture will cause a decrease in acoustic and thermal performance.

(e) The maintenance cost of the existing insulator removal and reinstallation work is high for airline customers.

(f) Since the insulation plies are usually the heaviest item of payload since they cover the entire surface area of the fuselage, a small reduction in unit weight can result in a substantial reduction in overall weight and an increase in aircraft performance.

The invention disclosed herein presents a design to solve some of the problems commonly associated with insulating ply glass fibers used in aircraft interiors and other aerospace equipment. The insulation scheme presented below consists of layers of a resilient cellular material (semi-rigid framework with porous cavities), such as polyimide foam or other foam with similar properties, sandwiched between layers of fiberglass. In a preferred combination of materials, the impedance of the material varies continuously as sound waves pass through the plies, which improves noise performance and reduces weight. This new sandwich insulator is 10 to 15 percent lighter than an all-fiberglass ply configuration and has similar noise and thermal performance. Also, it has a good combination of transverse stiffness and longitudinal flexibility. This improved combination of stiffness and flexibility allows for easier and stronger installation of the insulation plies. Increased stiffness helps reduce corrosion of the fuselage surface by preventing the insulating ply from contacting the fuselage surface. Also, this composite fiberglass foam insulation resists moisture ingestion and accumulation better than existing all-fiberglass plies.

This fiberglass polyimide foam composite ply can be used to replace existing equal thickness full fiberglass insulation plies in aircraft. The material will not slump and will retain substantially its original manufactured shape and density for the life of the aircraft. In the existing practice, the fiberglass insulation between the aircraft frame will collapse in the circumferential direction. Slumping creates gaps at ply junctions and causes non-uniform density and thickness distributions, reducing noise and thermal performance inside the aircraft. In many cases, this deterioration of the internal environment occurs unconsciously.

Contrary to the inconvenient handling of existing fiberglass plies, the insulation system introduced by the present invention facilitates the removal and reinstallation of insulation plies as required for corrosion inspection or other testing.

1 is a fragmentary perspective view of a part of an insulating ply according to a first embodiment of the invention;

Figure 2 is a vertical cross-sectional view of a second embodiment of an insulating ply according to the invention;

Figure 3 is a vertical cross-sectional view of a third embodiment of an insulating ply according to the invention;

Figure 4A is a perspective view showing the collapse of a prior art fiberglass insulation ply relative to an aircraft stringer and frame;

4B is a perspective view illustrating the slump reduction of fiberglass and polyimide foam sandwich insulation plies of the present invention relative to aircraft stringers and frames;

FIG. 5A is a schematic diagram showing collapse between prior art fiberglass insulation plies and aircraft frame and ply-to-ply junctions;

Figure 5B is a schematic diagram showing the reduction in slump of fiberglass and polyimide insulation plies of the present invention;

Fig. 6 is under the pressurized condition of engine room, the contrast graph line of the noise propagation attenuation of glass fiber and polyimide foam insulating layer sheet of the present invention and prior art glass fiber insulating layer sheet;

Fig. 7 is a comparison graph of noise attenuation similar to Fig. 6 under the condition that the cabin is not pressurized.

The invention embodied by the embodiment of Figs. 1, 2 and 3 has been proved in laboratory tests to be acoustically effective for transport aircraft, aerospace and industrial applications. Existing aircraft insulation plies are formed by stacking multiple layers of glass fiber flocs of standard thickness (i.e. 3/8 ", 1/2 " or 1 "). The present invention described below applies various materials and densities The combination is used to optimize the noise transmission attenuation in its enclosed space. The insulating ply of the present invention combines fiber material (glass fiber or other materials with similar characteristics) and polyimide foam with a multi-layer stacked structure. For example, prior art The center layer of three or five one inch thick all fiberglass plies is replaced by one inch thick (equal thickness) polyimide foam 12 as shown in FIG. 1 .

The embodiment of the insulating ply 20 shown in FIG. 1 has a polyimide core 12 sandwiched between outer layers of fiberglass 10 and has a typical thickness of about 3 inches. Referring to the second embodiment of the insulating ply 30 shown in FIG. 2, it can be seen that the polyimide core 12 is sandwiched between multiple layers of glass fibers 10, resulting in a total thickness of the insulating ply 30 of about 5 inches, each layer is about an inch thick.

In Fig. 3, the total thickness of insulating ply 40 is 5 inches, and its core layer 10 is the glass fiber sandwiched between a pair of polyimide layers 12, and these two layers of polyimide 12 are sandwiched in a pair Between the outer layers 10 of fiberglass.

In the exemplary embodiments of the invention described above, different polyimide and fiberglass layers, densities, and thicknesses were used to optimize performance characteristics based on the particular application.

The advantages of using the lightweight configuration of the present invention in improving the slump, moisture absorption, installation and cost issues of the insulating plies of the present invention will be described below:

1. Polyimide foam increases the rigidity of the board, makes it easy to install and can reduce the connection points, clips, nails, bolts, pins, patches, etc. for reinforcement materials and flocs. This reduces installation costs and material weight.

2. The polyimide foam increases the lateral hardness of the insulation layer, so that the insulation layer remains between the frames without causing protrusion. In other words, especially in the dome, upper and lower deck sidewall areas, hemispherical airtight bulkhead, airtight bulkhead and floor of the aircraft, this foam helps to prevent the collapse of the insulation layer.

3. It only needs fewer pins to connect the insulation board cover to control the material collapse caused by fatigue, gravity, vibration, pressure, etc.

4. Due to the combination of longitudinal flexibility and transverse rigidity of the foam, the glass fiber foam sandwich configuration layer can be made to match the curve of the fuselage without distorting the insulating floc.

5. This new sandwich configuration helps to maintain a constant gap between the ply and the fuselage surface, thereby reducing the corrosion of the main structure by humidity.

6. Polyimide foam is used. Compared with the full glass fiber insulator of the same thickness, this composite insulator has better weight (light), rigidity, strength, flexibility, processability and flame retardant and Water resistance.

7. As shown in the figure (Figures 6 and 7, under the test conditions with and without pressurization, respectively), the three-inch thick fiberglass polyimide foam sandwich ply configuration is lighter than the same thickness of the full glass fiber insulation 12.5%, and have the same or better acoustic performance.

8. Replacing the glass fiber layer with polyimide foam of equal thickness will not change the processing and production procedures of the existing layers. Moreover, it is not necessary to change the configuration of the aircraft sidewall system (i.e., the spacing between the outer molding lines of the frame and the inner molding lines of the tabs) for this new type of insulation ply, which means that this type of sandwich panel can be installed on existing aircraft. superior.

FIG. 4A shows the inward collapse of a prior art all fiberglass insulation ply 40 (at the upper sidewall, dome, hemispherical airtight frame and sealing frame), causing a gap 41. FIG. Such fiberglass panels 40 would also sag outwards (lower bulkhead), which could bring the plies into contact with the aircraft surface. Typical contact points 44 of aircraft structures such as stringers 42 and frames 43 are shown. For comparison, Figure 4B shows a polyimide foam and fiberglass interlayer insulation ply 50 of the present invention used in an aircraft to reduce slump conditions.

FIG. 5A shows another example of fiberglass panel 40 slump, where the fibers collapse to the lower portion of the insulation ply, resulting in a reduction in insulation efficiency. In contrast to Figure 5A, Figure 5B shows the application of the polyimide and fiberglass sandwich insulating ply 50 of the present invention to minimize slump.

Claims (4)

1. An aircraft insulation layer assembly, comprising: Insulation plies connected between aircraft structural frames; The insulating ply has a semi-rigid porous framework to support the outer layer of fiberglass to maintain a predetermined distance between the outer layer of fiberglass and the inner surface of the aircraft, thereby preventing the insulating ply from contacting the inner surface of the aircraft . 2. An aircraft insulation layer assembly, comprising: A sandwich structure having multiple layers of material comprising a core layer having a density of about ^0.3 Ib/ft and outer layers of said layers having a density of about ^0.42 Ib/ft. 3. The aircraft insulation ply assembly of claim 2, wherein said core layer is a polyimide foam layer having a thickness of about one inch. 4. An aircraft insulation ply assembly, comprising: multiple fiberglass layers; A core structure between the plurality of fiberglass layers, the core structure having a density less than the density of the plurality of fiberglass layers.

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