Abstract:
A strong lightweight airbag cushion for deployment in opposing relation to a vehicle occupant is provided. The cushion is formed from a body of wound yarn. The body includes an interior, a face portion for contact with the occupant and a rear portion including an inlet port for the introduction of an inflation medium. The body is formed by the continuous winding of yarn around a mandrel such that the yarn is spread across the face and is disposed preferentially across the back in the area surrounding the inlet port so as to provide added strength in that region.

Description:
RELATED APPLICATIONS  
       [0001]    This application is a Continuation-In-Part of U.S. patent application Ser. No. 09/996,010, filed Nov. 28, 2001, which was a Continuation of 09/167,060, filed Oct. 6, 1998. 
     
    
     
       FIELD OF THE INVENTION  
         [0002]    The present invention relates to inflatable protective cushions, and more specifically relates to a cushion formed by the highly efficient continuous winding of yarn. The cushion is particularly useful in the frontal or side protection of occupants in a transportation vehicle, such as an automotive vehicle, railroad, car, airplane or the like. A process for forming the cushion and an optimum shape for the cushion according to the present invention are also provided.  
         BACKGROUND  
         [0003]    Inflatable protective cushions used in passenger vehicles are a component of relatively complex passive restraint systems. The main elements of these systems are: an impact sensing system, an ignition system, a propellant material, an attachment device, a system enclosure, and an inflatable protective cushion. Upon sensing an impact, the propellant is ignited causing an explosive release of gases filling the cushion to a deployed state which can absorb the impact of the forward movement of a body and dissipate its energy by means of rapid venting of the gas. The entire sequence of events occurs within about 30 milliseconds. In the un-deployed state, the cushion is most commonly stored in or near the steering column, the dashboard, in a door panel, or in the back of a front seat placing the cushion in close proximity to the person or object it is to protect.  
           [0004]    Inflatable cushion systems commonly referred to as airbag systems have been used in the past to protect both the operator of the vehicle and passengers. Systems for the protection of the vehicle operator have typically been mounted in the steering column of the vehicle and have utilized cushion constructions directly deployable towards the driver. These driver-side cushions are typically of a relatively simple sewn configuration. Typically, traditional driver&#39;s side inflatable cushions have been formed by sewing together two circular pieces of coated fabric made of nylon or polyester yarn.  
           [0005]    Although such sewn products have generally performed quite adequately, they nonetheless have some inherent limitations. First, the sewn seam is generally applied or at least inspected manually. As will be appreciated, this is a relatively time consuming process which tends to increase manufacturing costs. Second, circular and elliptical cushions formed by sewing around the perimeter are prone to wrinkles which may result in high and low stress concentrations thereby reducing the maximum inflation pressure which can be maintained at the seam. Third, the introduction of a sewn seam necessarily gives rise to small openings for the sewing threads. These openings tend to act as an escape path for the inflation gases within the airbag which may lead to seam slippage or so called “combing” of the seam thereby giving rise to a potential mechanism for failure. Fourth, even after the two disk shaped components are sewn together, the area surrounding the gas introduction port (i.e. the mouth) must generally be reinforced with additional layers of fabric referred to as doublers so as to control the large forces applied in this area during an inflation event. As will be appreciated, the addition of these doublers gives rise to additional manual processing and the need for additional fabric. Finally, the use of substantially circular shapes results in substantial material waste during manufacturing due to the inherent inability of the manufacturer to cut disk patterns in close-packed spacing arrangement.  
           [0006]    Various alternative sewn constructions have been proposed such as those disclosed in U.S. Pat. No. 5,482,317 to Nelsen et al; U.S. Pat. No. 5,520,416 to Bishop; U.S. Pat. No. 5,454,594 to Krickl; U.S. Pat. No. 5,423,273 to Hawthorn et al; U.S. Pat. No. 5,316,337 to Yamaji et al; U.S. Pat. No. 5,310,216 to Wehner et al; U.S. Pat. No. 5,090,729 to Watanabe; U.S. Pat. No. 5,087,071 to Wallner et al.; U.S. Pat. No. 4,944,529 to Buckhaus; and U.S. Pat. No. 3,792,873 to Buchner (all incorporated herein by reference). However, these constructions each rely on some seaming of precut fabric panels and thus exhibit some if not all of the limitations outlined above.  
           [0007]    The manufacture of airbag cushions by means of winding yarns and tape-like materials around a mandrel has been proposed in several publications including Japan Kokai Patent document 3-227751 in the name of Kanuma and Japan Kokai Patent document 3-276845 in the name of Ogami et al. (both incorporated herein by reference).  
           [0008]    While these referenced publications recognize many of the limitations inherent in traditional sewn airbags, and have broadly proposed the use of winding technology as a means to avoid those limitations, they nonetheless fail to provide a highly efficient practice for the proper distribution of yarn. Rather, the prior art in this area has relied generally upon the winding of broad, tape like structures or of a relatively large number of parallel yarns to achieve the substantially complete coverage of the cushion surface area. The prior art also fails to teach the ability to preferentially distribute yarns in the area surrounding the inlet opening so as to provide additional support in this area thereby substantially reducing or eliminating the need for the application of an additional reinforcement in this region.  
           [0009]    The airbag according to the present invention is formed from yarn which is substantially evenly distributed across the face of the cushion thereby avoiding the accumulation of yarn and the ultimate development of a nodule of undue thickness at the center of the cushion where impact with an occupant is likely to occur. In addition, the yarn is disposed in such a manner that a thickened ring of yarn is built up around the inflation opening thereby enhancing the strength of the cushion at the very location where reinforcement is generally required. The airbag according to the present invention thus provides a useful advancement over the present art.  
         SUMMARY OF THE INVENTION  
         [0010]    In view of the foregoing, it is a general object of at the present invention to provide an easily manufactured seamless airbag cushion.  
           [0011]    It is a more particular object of the invention to provide a seamless airbag cushion formed by the winding of yarn about a removable mandrel such that the yarn is substantially evenly distributed across the face of the cushion.  
           [0012]    It is a further object of the present invention to provide a seamless airbag cushion formed by the winding of yarn about a removable mandrel such that the yarn is disposed preferentially across the back of the cushion in the area surrounding the inlet port so as to form a localized region of enhanced thickness to provide additional strength in that region surrounding the inlet port.  
           [0013]    It is a further potential object of the present invention to provide a seamless airbag cushion formed by the winding of yarn about a removable rotating mandrel wherein the cushion includes a flexible permeability blocking layer of material holding the yarn in place.  
           [0014]    An additional object of the invention is to provide a low cost inflatable protective cushion of simple and structurally efficient design with a shape and construction that optimizes the cushion&#39;s ability to withstand inflation pressure and impact when deployed.  
           [0015]    It is a preferred feature of the present invention to provide a seamless airbag cushion formed by the winding of a yarn in a continuous fashion around a generally spheroidal rotating mandrel while systematically shifting the angle of placement of the yarn with respect to the axis of rotation of the mandrel about a point near the mouth of the bag structure being formed such that a localized region of enhanced thickness is formed around the mouth opening.  
           [0016]    It is yet a further potentially preferred feature of the present invention to provide a seamless airbag cushion formed by the winding of a yarn in a continuous fashion around a generally spheroidal rotating mandrel having a shape substantially similar to the desired shape of the finished cushion wherein the ratio of the depth of the cushion to its equatorial diameter is about 0.5 to 0.7.  
           [0017]    It is still a further potentially preferred feature of the present invention to provide a seamless airbag cushion formed by the winding of a yarn around a rotating mandrel having a release layer of film disposed about the rotating mandrel, such that when the airbag cushion is removed from the mandrel, it may be turned inside out so that the release layer of film is disposed about an outer surface of the airbag cushion. It is also a feature of the present invention to provide a method for manufacturing a seamless airbag cushion having the release layer of film disposed about an outer surface of the airbag cushion.  
           [0018]    Additional objects and advantages of the invention will be set forth in part in the description which follows, and in part will be obvious from the description, or may be learned by practice of the invention. The objects and advantages of the invention will be realized and attained by means of the elements and combinations particularly pointed out in the written description and claims as well as the appended drawings.  
           [0019]    It is to be understood that both the foregoing general description and the following detailed description are exemplary and explanatory only and are not restrictive of the invention, as claimed. 
       
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0020]    The accompanying drawings which are incorporated in and constitute a part of this specification, serve to illustrate several preferred embodiments and practices according to the present invention and together with the description, serve to explain the principles of the invention wherein:  
         [0021]    [0021]FIG. 1A is a cutaway view of an inflatable cushion according to the present invention and inflation module housed within the steering column of a vehicle.  
         [0022]    [0022]FIG. 1B illustrates a cutaway view of an inflatable cushion according to the present invention in deployment between a passenger and the steering column.  
         [0023]    [0023]FIG. 2 illustrates the yarn winding operation for forming the airbag according to the present invention.  
         [0024]    FIGS.  3 - 5  are plan views of the airbag winding operation carried out according to the potentially preferred practice of the present invention.  
         [0025]    [0025]FIGS. 6A and 6B are, respectively, elevation views of the rear and front of an airbag cushion formed according to the potentially preferred practice of the present invention. 
     
    
     DESCRIPTION OF PREFERRED EMBODIMENTS  
       [0026]    Reference will now be made in detail to potentially preferred embodiments and practices. It is, however, to be understood that reference to any such embodiments and practices is in no way intended to limit the invention thereto. On the contrary, it is intended by the applicants to cover all alternatives, modifications and equivalents as may be included within the spirit and scope of the invention as defined by the appended claims.  
         [0027]    Airbags may be produced from a number of different materials using a multiplicity of techniques. However, commercially acceptable airbags have heretofore typically been formed, at least in part, from some type of woven textile material. By way of example only and not limitation, such textile materials are disclosed in U.S. Pat. No. 5,503,197 to Bower et al.; U.S. Pat. No. 5,477,890 to Krummheuer et al.; U.S. Pat. No. 5,277,230 to Sollars, Jr.; U.S. Pat. No. 5,259,645 to Hirabayashi, et al.; U.S. Pat. No. 5,110,666 to Menzel et al.; U.S. Pat. No. 5,093,163 to Krummheuer et al.; U.S. Pat. No. 5,073,418 to Thornton et al.; U.S. Pat. No. 4,921,735 to Bloch; and U.S. Pat. No. 3,814,141 to Iribe et al; (all incorporated herein by reference).  
         [0028]    A typical airbag deployment system  10  for use in opposing relation to the driver of a vehicle is illustrated in FIG. 1A. In general, similar equipment is used in passenger and side protection devices, although the geometry of the components therein may vary. The airbag deployment system  10  generally comprises an inflator  12 , an inflatable cushion  14  which includes a mouth portion surrounding the inflator  12  thereby permitting the cushion to be inflated by gas released from the inflator during a collision event. The cushion  14  and inflator  12  are typically housed beneath a frangible cover  16 , which breaks open along a notch  18  of reduced thickness during the deployment event. As illustrated in FIG. 1B, upon deployment the cushion  14  is in a position to receive a vehicle occupant  20 . As will be appreciated, the kinetic energy of the occupant  20  is dissipated by the collapse of the cushion  14  as gas is released either through inherent permeability of the material forming the cushion  14  and/or through internal pressure sensitive vents  22 . The cushion  14  may further include shape controlling tethers  24  which require the cushion to expand to a pre-determined desirable geometry upon inflation.  
         [0029]    In FIG. 2 a side view of the apparatus  30  for carrying out the yarn winding operation according to the present invention is illustrated. As shown, the apparatus  30  preferably includes a rotatable platform  32  for holding one or more packages  34  of yarn  36  for use in formation of the airbag according to the present invention. The yarn  36  is preferably wrapped around a spool  38  such that the yarn may be removed in a continuous fashion without the occurrence of tangling. While multiple packages  34  are illustrated, it is to be understood that the present invention does not require the delivery of more than one continuous yarn  36  in order to achieve effective bag formation. When the operation is carried out with a single continuous yarn, the use of multiple packages has the advantage of avoiding frequent package replacement since the packages are already in place.  
         [0030]    While the invention contemplates the use of a single yarn in the winding operation, it is likewise contemplated that two or more yarns  36  may be delivered and wrapped simultaneously in substantially side by side relation to one another during the winding operation. It is further contemplated that the yarns  36  and each of the packages  34  may be either of the same or of a different character. Thus, if an individual yarn  36  is to be wound according to the present invention the initial stages of the winding operation may be carried out using one type of yarn while the latter stages may be carried out using yarn of differing character. Likewise if two or more yarns  36  are to be wound simultaneously, it is contemplated that these yarns may be either of the same or differing character. As will be appreciated this ability to select combinations of yarns having different character may be of value in exploiting the benefits of various different yarn combinations within the structure to be formed.  
         [0031]    In the illustrated and potential preferred practice, the yarn  36  is delivered to a central eye  40  for subsequent transmission through a tubular guide path  42  for eventual delivery through a balanced hollow arm rotating winding apparatus  46 .  
         [0032]    The winding apparatus  46  is preferably a symmetrical structure having at least two yarn delivery arms  48 ,  50  extending outwardly from either end of an elongated support shaft the center of which preferably serves as the axis of rotation for the winding apparatus  46 . As shown, the winding apparatus may also include one or more additional arms  49  preferably disposed in balanced relation to the other arms. In one potentially preferred embodiment, the winding apparatus will have four hollow symmetrically disposed yarn delivery arms each of which deliver a separate yarn  36  from a separate package  34 .  
         [0033]    In the preferred embodiment, the winding apparatus  46  is preferably rotated about the axis of rotation  54  by means of a variable speed motor  56  controlled by a computer (not shown) or other control means as are known to those of skill in the art such that the rate of winding and number of revolutions may be preset and closely monitored during the winding operation.  
         [0034]    The yarn  36  which is delivered through the hollow winding apparatus to the end of at least one of the yarn delivery arms is initially secured in place against a collapsible mandrel  60  by either a small piece of adhesive tape by manually wrapping one or two loops around the mandrel such that frictional forces prevent the yarn from pulling away. Thereafter, the mandrel  60  rotated by means of its own independent variable speed motor  62  (FIG. 3) while simultaneously rotating the winding apparatus  46  such that the yarn  36  is continuously drawn from the winding apparatus around the mandrel. As will be appreciated, by controlling the rotation of both the mandrel  60  and the winding apparatus  46 , substantial control can be exerted over the final yarn distribution.  
         [0035]    The mandrel  60  is preferably covered at least in part by a thin releasable film of a material such as PVC, polypropylene, polyamide, polyurethane or the like to permit separation of the yarns  36  from the mandrel  60  following application of a permeability blocking coating layer as described below. In one embodiment, the releasable film is disposed across the surface of the mandrel  60  corresponding to the front of the cushion  14  against which the occupant  20  would be thrown, while the rear surface is wound without a release layer. This practice provides the dual advantage of minimizing the amount of release film utilized while at the same time providing an added barrier layer between the occupant and the inflation gases, which are generally hot and may carry particulates.  
         [0036]    In an alternate embodiment, the yarn may be wound onto the release layer of film disposed about the mandrel, and when the airbag cushion is removed from the mandrel, the airbag cushion may be turned inside out so that the release layer of film is then disposed about an outer surface of the wound yarn body. In this particular embodiment, a heat resistant adhesive such as silicone may be used to bond the yarn together with the release layer, in order to provide improved heat resistance. It has been found that such an arrangement provides a more robust airbag cushion. Such an arrangement also provides a smoother outer surface of the airbag cushion, as well as increased abrasion resistance and reduced coefficient of friction. This arrangement provides a surprisingly robust airbag cushion, particularly considering that one would expect the film to delaminate from the yarn and adhesive structure while positioned on an outer surface of the airbag cushion. However, no delamination has been observed.  
         [0037]    As best illustrated in FIGS.  3 - 5 , the mandrel  60  is preferably of a shape substantially corresponding to the final desired shape of the airbag cushion being formed. While any shape susceptible to rotation and yarn coverage may be utilized, it is contemplated that circular and ellipsoidal spheroids may be particularly preferred for driver&#39;s side airbag cushions.  
         [0038]    The mandrel  60  itself is necessarily of such a nature that it can be removed from the final airbag structure after formation is complete. Materials which may be particularly well suited to this purpose include sculpted foam rubber, collapsible segmented metal structures, and durable textile structures formed from material such as KEVLAR® or the like which may be held in an inflated state under modest gas pressures through connection to an air line during the processing sequence. As shown, the mandrel  60  is preferably connected to a hub  64  disposed along its axis of rotation. In the illustrated and potentially preferred practice, the placement and diameter of the hub  64  defines the size and location of the inlet port in the final airbag cushion.  
         [0039]    As will be appreciated by those in skill of the art, the region surrounding the inlet port serves as the location of connection between the inflatable cushion  14  and the inflator  12  (FIG. 1A) and must, therefore, withstand significant stress during a deployment event. These stresses can be overcome by providing enhanced thickness of the cushion in this localized region.  
         [0040]    It has been found that by orienting the mandrel  60  relative to the winding apparatus  46  such that the yarn placement plane  66  (as defined by the outlet of the yarn delivery arms) runs immediately adjacent to the hub  64 , that it is possible to obtain the desired increased thickness in the region immediately surrounding the mouth with gradually decreasing yarn concentration as the distance from the mouth is increased. This preferential yarn concentration is illustrated in FIG. 6A wherein the gas inlet  70  disposed within the rear portion of the cushion  14  is surrounded by a relatively thick collar of material which decreases in concentration as the distance from the center is increased. That is, the number of yarns per unit area decreases as the perimeter of the cushion is approached.  
         [0041]    Aside from the desire to enhance the strength of the cushion in the area surrounding the inlet port  70 , it is a further attribute of the cushion according to the present invention to avoid a preferential accumulation of yarns at the face of the inflatable cushion since such a build up gives rise to the formation of a generally undesirable hard nodule on the surface which is to be impacted by the vehicle occupant  20  during a collision event. It has been found that when the yarn  36  is wrapped around the rotating mandrel  60  while maintaining a fixed angle φ between the yarn placement plane  66  (FIG. 3) and the equatorial plane  72  of the mandrel, that each winding tends to cross over the prior windings within a relatively small localized location on the face of the inflatable cushion  14  which thereby causes the undesirable build-up of a thick nodule of yarn in this location on the face. Such a build-up of yarn is, of course, exactly what is desired in the region surrounding the inlet port  70  on the rear portion of the cushion  14 .  
         [0042]    It has been found that these seemingly conflicting goals of concentrating the yarn around the inlet port on the rear of the cushion while at the same time spreading the yarn substantially evenly across the face may be achieved by systematically shifting the angle of the yarn placement plane  66  with respect to the equatorial plane  72  of the rotating mandrel  60  about a pivot point selected such that the yarn placement plane  66  continues to fall substantially adjacent to the hub  64  on the rear portion of the rotating mandrel  60 . This systematic shifting of the yarn placement angle is best illustrated through reference to FIGS.  3 - 5  wherein in FIG. 3 the yarn placement plane  66  is at a first angle φ with respect to the equatorial plane  72  of the mandrel. In FIGS. 4 and 5 this angle is gradually increased until the two planes are nearly perpendicular.  
         [0043]    In the illustrated and potentially preferred practice of the present invention, shifting of the yarn placement plane is effected by pivoting the winding apparatus  46  about a pivot  80  (FIG. 2) through use of an extensible and retractable power cylinder  82  acting on the support for the winding apparatus. In the illustrated and potentially preferred practice, the pivot  80  is placed such that its center is aligned just outside the outer perimeter of the hub  64  which serves to define the inlet port  70 . As a power cylinder  82  is retracted from its fully extended position in FIG. 3 through an intermediate position in FIG. 4 to a fully retracted position in FIG. 5, the yarn placement on the front of the mandrel  60  is substantially changed. However, due to the selection of the pivot point location, the yarn placement on the rear of the mandrel is not significantly altered. Thus, the seemingly contradictory need to concentrate yarn around the inlet port while simultaneously spreading yarn across the face can be met. Moreover, since the power cylinder  82  may be cycled by the computer or other control means independently from the rotation of the mandrel and the winding apparatus, the pivoting action provides the operator with yet another degree of freedom with which to control the manufacturing process.  
         [0044]    While it is contemplated that a wide variety of combinations of operating parameters may be utilized to produce inflatable restraint cushions according to the present invention, by way of example only, and not limitation, it is believed that in the preferred practice the mandrel  60  should be rotated at a rate of about 0.05 to about 30.0 revolutions per minute, the winding apparatus should be operated at a rate of about 50 to about 600 revolutions per minute, the angle between the yarn placement plane  66  and the equatorial plane  72  should be cycled between about 46° and about 90° with about 1 to about 20 full cycles of extension and retraction of the power cylinder  82  per minute.  
         [0045]    While it is likewise contemplated that any number of different types of yarns  36  may be utilized, it is believed spun or filament polymeric yarns formed from fiber materials such as polyester, nylon 6, nylon 6.6, nylon 4.6, KEVLAR® and SPECTRA® characterized by yarn linear densities in the range of about 40 to 1200 denier (preferably about 70 to 200 denier) and filament linear densities in the range of about 2 to 6 denier per filament (preferably 3 to 5 denier per filament) may be preferred. The average yarn concentration as measured by dividing the total mass of yarn utilized in a given bag by the surface area for that bag including regions of both low and high yarn concentration is preferably in the range of about 50 to 300 grams per m 2 .  
         [0046]    As will be appreciated, in some instances, the concentration of yarn itself may not be sufficient to block air flow. In addition, the release film which is carried with the cushion is preferably of a very light weight character and may not provide complete porosity blocking performance. Moreover such release films may be completely absent if the mandrel is of such a nature that a release layer is unnecessary. By way of example only, it is contemplated that a mandrel formed of a textile material coated with Teflon, silicone or other adhesion resistant material may make the use of a release layer unnecessary. Accordingly, in one potentially preferred practice it is desirable to apply a porosity blocking coating of material across the wound yarn structure so as to hold the yarn in place and to provide containment for the gaseous inflation media generated during an expansion event. While any number of coating materials may be utilized, it is required that such material be flexible in nature such that it can span the voids between the yarns without failing under pressure. It is believed that thermoplastic or thermosetting compositions of polyurethane, polyamide, polypropylene, PVC, acrylics and mixtures of these materials may be useful. These materials may be applied by spray coating, knife coating, dip coating or other commercial processes as may be known to those of skill in the art. By way of example only, it is believed that the weight concentration of the elastomer in the final bag may be in the range of about 40 to 900 grams per m 2 .  
         [0047]    As previously indicated, aside from a fundamental formation technique, the present invention further contemplates a potentially preferred shape for the inflatable cushion  14  so as to optimize the strength characteristics of the load bearing yarns  36  within the structure. Hence, this optimized shape characteristic would be used in the design of the mandrel  60  for use in the winding procedure described above.  
         [0048]    It is believed that the maximum strength of a composite material such as the wound airbag structure of the present invention is obtained when the strains in the individual components are matched. Thus, the optimum shape for maximum strength in the airbag of the present invention is obtained when there is uniform tension in the yarns. It has been discovered that the shape which results in uniform tension in the yarns is a geometric curve which can be characterized parametrically in cylindrical coordinates for one quadrant by the equations.  
         z   a     =       ∫   0   Θ                (     sin        (       π   2     -   u     )       )       (     1   2     )       2             u                   r   a     =       sin        (       π   2     -   Θ     )         1   2               0   ≤   Θ   ≤     π   2                           
 
         [0049]    Where r is the radial coordinate and z is the axial coordinate.  
         [0050]    The radius at the equator is given by the equation:  
       a   =       [     V     2      π          ∫   0     π   2              sin        (       x   2     -   Θ     )                (     sin        (       π   2     -   Θ     )       )       (     1   2     )       2             Θ             ]       1   3                             
 
         [0051]    or approximately  
       a   =     .714   ·     V     1   3                               
 
         [0052]    Where V is the desired volume of the bag at low inflation pressure.  
         [0053]    The height to equatorial diameter ( 2   a ) ratio is:  
           2   ·   h       2   ·   a       =       ∫   0     π   2                  (     sin        (       π   2     -   u     )       )       (     1   2     )       2             u                               
 
         [0054]    or approximately:  
           2   ·   h       2   ·   a       =   .599                         
 
         [0055]    It is believed that the benefit of this shape in providing uniform yarn tension is achievable in substantial respect so long as the radial coordinate of the shape is within about plus or minus ten percent of its ideal value in relation to the other coordinates.  
         [0056]    The following working example is presented to provide a more complete understanding of the invention. The specific techniques, conditions, materials, and reported data should be understood to be exemplary only and should in no way be construed as in way limiting the scope of the invention which is intended to be defined and limited only by the full lawful scope of allowed claims and equivalents thereto.  
       EXAMPLE  
       [0057]    An inflatable round spheroidal rotating mandrel formed of KEVLAR® reinforced nylon film having an equatorial diameter of 22 inches and a central depth of 11.75 inches was wrapped with a 1 mil thick film of PT9611 Polyurethane and inflated to a pressure of 1 psi and rotated at a rate of 0.322 revolutions per minute while a 112 denier multifilament yarn of polyester having a denier per filament rating of 3.4 was delivered by a winding arm at a rate of 240 revolutions per minute for a period of 15.5 minutes. During the winding operation, the angle between the plane of yarn placement and the equator of the mandrel was cycled from about 64.3 degrees to about 83.5 degrees and back every 0.134 minutes. The total mass of yarn delivered around the mandrel was 2.36 ounces over an area of 0.6836 square meters. An air line was used to maintain the mandrel in an inflated state during the winding operation. While still under inflation, the mandrel and yarns wrapped thereabout were coated with an aqueous base polyurethane composition. The dried add on weight of the coating composition was 63.4 grams for the entire structure. After drying, the sample was tested to failure by rapidly exposing it to air heated to 1000° F. A pressure of 19.4 psi was attained before the sample burst.  
         [0058]    While specific preferred embodiments and materials have been illustrated, described and identified, it is to be understood that the invention is in no way limited thereto since modifications may be made and other embodiments of the invention will occur to those of skill in the art to which this invention pertains. Thus, it is intended to cover any such modifications and other embodiments ads incorporated the features of this invention within the full lawful scope of the allowed claims as follows.