Abstract:
An aircraft insulation product comprising a glass fiber blanket faced on at least one major face with an air permeable sheet. Insulating fibers coated with unbonded binder are directed to a web of the permeable sheet material supported on a moving collection chain, and the resulting fibrous layer and the web are sent to an oven where the binder is cured. The collection web thus becomes bonded to the blanket by the binder to become an integral part of the insulation product. A plurality of stacked blankets, the edges of which are covered by a film, may be used instead of a single faced blanket.

Description:
FIELD OF THE INVENTION 
     This invention relates to fibrous insulation material. More particularly, it relates to a fibrous insulation product, such as a fiber glass blanket, to which a facing sheet is adhered. 
     BACKGROUND OF THE INVENTION 
     Fibrous insulation products are available in various densities for use in a variety of different environments. One such product is a lightweight glass fiber blanket used to insulate structure which requires a high degree of insulation, such as aircraft hulls. In such an environment it is important that the weight be minimal so as not to add unnecessarily to the weight of the aircraft, and that the blanket be capable of providing an effective barrier to the high sound levels and cold temperatures encountered during flight. 
     Typical products now in use are comprised of fine glass fibers bonded together in blanket form and having a density of about 0.3 pound per cubic foot (pcf) to 1.5 pcf. Depending on the dimensions of the space required to be insulated, either a single blanket or several stacked blankets are wrapped and secured within a film, as by sewing or heat sealing, and the wrapping insulation is then attached to the aircraft fuselage by pins connected to the skin of the aircraft. In addition to holding the wrapped insulation in place, the pins prevent the insulation blankets from shifting with respect to each other. Due to the fragile nature of the insulation, a great many pins are required to satisfactorily hold the blankets in place. For example, it is not uncommon for as many as 10,000 pins to be used to install insulation in a large aircraft. This is not only a time consuming operation, but the cost of the pins themselves is expensive. Also, because the operation compresses the insulation blanket in the area surrounding the pins, some of the insulation performance value may be sacrificed. 
     While such products perform their insulating function satisfactorily, certain of their other characteristics could advantageously be improved. For example, although the low density, lightweight construction of the blankets makes them quite suitable as insulators, it also results in minimal physical properties, making the products susceptible to damage. In particular, the relatively low tensile strength of the product offers little resistance to stresses encountered during fabrication and installation. This is especially so in environments where the product is placed under tension by being wrapped about a structure. Handling of the individual layers and fabrication of the multi-layered product subject the material to additional stresses which tend to damage the weak fiber glass material. 
     In addition, the effectiveness of insulation wrapped in a film is likely to be reduced in service by condensation of water vapor trapped within the insulation. Because the commercial product usually requires an outer film to allow the insulating blanket to be handled and installed as desired, there would appear to be no easy solution to this problem. 
     It can be seen from the foregoing that it would be beneficial to improve the tensile strength of a blanket of fibrous insulating material without impairing its insulating ability and without adding significantly to its cost or weight. It would also be beneficial to be able to eliminate the condensation problem without adversely affecting the product. 
     BRIEF SUMMARY OF THE INVENTION 
     In accordance with the invention, a lightweight fibrous insulation blanket having a density in the range of 0.2 to 1.5 pcf and a thickness in the range of 3/8 inch to 2 inches, is comprised of fibers bonded together by cured thermosetting binder. A facing sheet which is permeable to air is bonded to a major face of the blanket by the cured thermosetting binder. Preferably, the fibers comprise glass fibers bonded together and to the facing sheet by phenolic binder, and the facing sheet is a porous woven or nonwoven organic or inorganic scrim. 
     The blanket may be employed in the form of a single layer or thickness, or may be encased with other blankets in stacked relationship within a heat sealable film. Preferably, the facing sheet is capable of being heat sealed to the film. 
     The facing improves the tensile strength of the insulation product and increases its stiffness. Further, the facing sheet is highly permeable so that it allows the free passage of air in and out of the blanket. This in turn allows the evaporation of any moisture from installed insulation, such as would be encountered in an aircraft installation, when the insulation is installed with the facing material facing the passenger side of the aircraft. 
     To adhere facing material to a face of lightweight, low density fibrous insulation would normally require a separate laminating operation, which would not only add to the manufacturing cost of the product but could also impair the structure of the insulating material if excessive pressure has to be applied in order to adhere the material to the insulation. Also, the adhesives employed in a separate laminating operation may add too much additional weight to the product and may further be of concern regarding fire resistance of the product. Instead of the facing being applied in a separate laminating operation, the porous nature of the facing permits it to be applied to the fibrous insulation by moving a sheet or web of air permeable facing material in a predetermined direction and at the same time directing fibers entrained in a moving stream of air against a major face of the moving permeable sheet. By creating a pressure differential between opposite major faces of the moving permeable sheet, the air passes through the sheet to the area of negative pressure while the fibers are collected on the sheet and built up to form a layer. The permeable sheet is permanently adhered to the fibrous layer as facing material to become an integral part of the product. By supporting the permeable sheet on the metal collection chain normally employed to collect the fibers, and passing the sheet and the layer of fibers through a curing oven, a thin, flexible sheet can be employed as the facing material and can be adhered to the fibrous layer without the necessity of a separate laminating step. 
     These and other features and aspects of the invention, as well as their benefits, will be made more clear in the following detailed description of the preferred embodiments. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     FIG. 1 is a schematic representation of the method employed to produce the faced insulation blanket of the present invention; 
     FIG. 2 is an enlarged transverse sectional view taken on line 2--2 of FIG. 1; 
     FIG. 3 is a partial pictorial view of the insulating product of the invention; 
     FIG. 4 is a transverse sectional view of an insulation product comprised of a plurality of blankets in stacked relationship adhered to a film; 
     FIG. 5 is a transverse sectional view of another embodiment of the invention; 
     FIG. 6 is a transverse view similar to that of FIG. 4, but showing stacked blankets comprised of double-faced blankets; 
     FIG. 7 is a transverse sectional view of another embodiment of a product comprised of double-faced blankets; 
     FIG. 8 is a partial schematic representation of a modified portion of the apparatus of FIG. 1, showing the introduction of a top web to the insulation product; and 
     FIG. 9 is a partial pictorial view of the faced blanket of the invention encased in an outer film and attached to the skin of an aircraft fuselage. 
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     Referring to FIG. 1, which illustrates the preferred method of manufacturing the faced blanket of the invention, a source 10 supplies glass fibers 12, which are sprayed with binder by nozzles 14 as the fiberstravel toward a moving screen 16. The source may be of any desired type, such as a rotary spinner, into which molten glass is introduced and which upon rapidly rotating causes the molten glass to exit through small holes in the side walls, resulting in the formation of fibers. A so-called &#34;pot and marble&#34; operation could also be used, wherein marbles or pellets of glass are melted in a pot, with the molten glass being drawn from the pot through bushings in the form of fibers. 
     Whether one of these processes or a different process entirely is the source of the fibers, a fiber glass blanket is normally produced by directing a stream of air-entrained fibers against the moving screen 16. The moving screen, which is known in the art as a collection chain, is typically an open-weave endless metallic conveyor trained about rollers 18, 20 and 22. Suction is created within the path of the collection chain by any suitable means, as by the suction boxes 24 mounted directly beneaththe collection chain in the upward and downward runs between the roller 20 and the rollers 18 and 22. The vacuum or negative pressure in the collection chamber in which the collection chain runs causes the air stream carrying the fibers to pass through the collection chain. Because the openings in the chain are small enough to filter out most of the fibers contacting it, the fibers so filtered are deposited on the chain and are able to support the fibers which are deposited on them. In so doing, a fiber glass layer of predetermined weight or thickness is built up. It will be understood that the rate of fiber production, the type of fibers produced and the speed of the collection chain are all correlated to provide control over the thickness of the layer. 
     The manufacturing process typically includes an endless conveyor 26 trainedabout a roller 28 located near the collection chain 16. The fibrous web is transferred from the collection chain to the conveyor 26 and may be further contacted on its upper surface by an upper conveyor 30 arranged sothat the space between conveyors 30 and 26 just prior to entering oven 32 corresponds to the desired final thickness of the blanket. The blanket mayalso be compressed by conveyors or rollers inside the oven, not shown, to the final desired thickness. The heat in the oven cures the binder on the fibers, and the cured binder holds the fibers in place. The finished product may be trimmed or slit into smaller widths by one or more slitters34 and may be cut to length by knife 36, after which the cut lengths can bepackaged or attached to other lengths to form a thick laminated blanket. 
     In accordance with the preferred method of producing the product of the invention, a web of permeable material 38 is drawn from a roll 40 by rollers 42 and 44 and is directed to the upward run of the collection chain 16. The pressure differential existing on opposite sides of the collection chain causes the web 38 to contact and be supported by the collection chain. Because the material 38 is highly permeable, the air stream carrying the fibers is able to pass through the web, depositing thefibers directly onto the web. The web thus in effect functions as the outersurface of the collection chain, moving in unison with it. 
     As shown in FIGS. 1 and 2, the fibers have built up on the outer surface ofthe web 38 to form a layer or blanket 46 while the web is supported by the collection chain 16. When the fibrous layer is stripped from the collection chain in transferring to the conveyor 26, the web of permeable material is stripped off along with it, so that the fibrous layer 46 and the web 38 are fed as a unit to the oven 32. There, the curing of the binder results not only in the fibers being bonded to one another, but in the fibers being bonded to the web 38 as well. 
     As shown in FIG. 3, the resulting product 48 is a compressed layer 46 of bonded fibers and a sheet 38 of permeable material bonded to a major face of the layer. Although the faced blanket can be used in this condition, itis more likely to be installed in multiple layers as previously discussed. Such an arrangement is illustrated in FIG. 4, wherein three faced blankets46 are aligned in stacked face-to-face relationship within a wrapper or sleeve of film 50. The ends of the film terminate at the edge portions of the outer facing sheet 38 as indicated at 52, where they are attached to the faced blanket 48 as by stitching, not shown, or by heat seal, which isthe preferred manner of attachment. 
     If desired, both faces of the blanket may be provided with a facing sheet. This design is illustrated in FIG. 5, where both major faces of the blanket 46 are provided with similar porous facing sheets 38 and 54, whichprovides additional strength and stiffness to the product and also enables the user to install either side of the product facing the passenger side. A double-faced blanket may be used in a multiple layered arrangement, suchas shown in FIG. 6, where the film 56 is shown as being attached to both ofthe facing sheets 38 and 54 at the overlapped portions 58 and 60, as by stitching or heat sealing. 
     Another form of product comprised of double-faced blankets is illustrated in FIG. 7, wherein the facing sheets 54 and 38 extend out beyond the fiberglass material and are attached to each other, as by heat sealing or stitching, to form a bonded flange 62 comprised of the overlapping sheets.The resulting pillow-shaped product is simpler to fabricate than the product of FIG. 6. It will be understood that such an arrangement is not limited to two layers as illustrated. 
     As shown in FIG. 8, to provide a second facing sheet on the insulation blanket a web of facing material 54 is introduced from a roll 64 to the upper face of the insulation layer 46 just prior to the layer passing beneath the conveyor 30, so that the facing material 54 is in place when the insulation layer enters the oven 32. The curing of the binder in the insulation layer will then bond the facing material to the upper face of the layer. 
     A typical installation of the product in an aircraft is shown in FIG. 9, wherein a number of faced blankets have been encased in a film 50 which isheat sealed to the edge portions of the facing sheet 38, leaving the major portion of the sheet exposed. The film-encased insulation is attached to the aircraft structure 66 by means of pins 68 which penetrate the blanketsand are secured to the structure by any suitable means, such as by welding,clamps or bolts. 
     Although the facing material has to be sufficiently permeable so as not to impede the flow of air through the collection chain during the manufacturing process or through the facing sheet of the installed faced insulating blanket product, it should also be capable of adding to the tensile strength of the final product and should have sufficient strength to remain intact during the fiber collection process. A sheet capable of functioning in the manner described should be porous, strong, tear resistant and lightweight, for example, less than 1.5 ounces per square yard. Generally, it can be any porous woven or nonwoven scrim or reinforcement media, composed of organic or inorganic fibers with a flame retardant system meeting the flammability requirements of 49 CFR part 25 (FAR 25.853) or BMS 8-142. The air permeability of the facing sheet shouldbe such that at least 1000 cubic feet of air can pass through, as measured in accordance with the Frazer Air Permeability Test (ASTM D 737-1982). In addition, the facing sheet material should be heat sealable to itself and to the film which may be used to encase the insulation prior to installation. An example of such a material is polyester scrim available from Snow Filtration Company and sold under the name Reemay. 
     The film material may comprise any of the conventional films currently usedin the installation of insulation blankets in aircraft. One example is a film comprised of Orcon, available from Orcon Corporation. The film employed should also be of a heat sealable nature. 
     The faced blanket should possess certain minimum properties in order to meet the requirements of performance and the rigors of installation. The tensile strength of a single-faced blanket should be at least three times that of the insulation blanket alone and the impact resistance of the product, as measured by the Mullen Burst test, should be at least 12 psi. 
     Although the invention has been described mainly in connection with a facing sheet applied to fiber glass insulation comprised of fine glass fibers, it will be understood that the concept is applicable to other fibers as well. Also, while the type of facing sheet may vary in accordance with the desired end product, it will also be understood that sheets comprised of a variety of different materials and different physical configurations can be used. In order to prevent fire damage to the final installation, it is preferred that the material be fire resistant. 
     The invention results in a number of advantages over currently available products. In addition to the improved installation performance and the ability to allow condensed moisture to escape through the porous facing sheet, the method of collecting the insulating fibers on the porous facingsheet itself may result in reducing the amount of fibers and binder that are normally lost due to passing through the open weave of the collection chain. 
     It should now be clear that the invention provides a simple but unique solution to the problems enumerated above in connection with lightweight fibrous insulation products, and particularly in connection with low density blankets comprised of fine fibers. The resulting product is physically superior to previously produced insulation products and lends itself to superior assembly and installation procedures. 
     It should now be apparent that the invention need not necessarily be limited to all the specific details described in connection with the preferred embodiment, but that changes to specific features of the preferred embodiment which do not alter the overall basic function and concept of the invention may be made without departing from the spirit andscope of the invention defined in the claims.