Patent Publication Number: US-2004045847-A1

Title: Air cargo containers

Description:
[0001] The present invention is concerned with improving containers used to contain cargo in an aircraft hold.  
       [0002] Commonly cargo to be conveyed by aircraft is first loaded into containers at the airport and the filled container is then loaded into the aircraft hold. At its destination the filled container is removed and the cargo returned to its owners. For the purposes of this application cargo should be understood to include passenger luggage, mail or other cargo.  
       [0003] Aircraft cargo containers must meet extensive national and international performance standards (e.g. the Civil Aviation Authority standard) which determine performance in sustaining vertical, lateral, and impact loads, shear loads and fire resistance as well as the practical requirements including security (e.g. against smuggling), minimal weight, durability under repeated handling, considerable changes in pressure, temperature and humidity, maximising use of the aircraft hold capacity, ease of loading and unloading, cleanliness (e.g., to prevent the unwanted import of foreign bioforms into the local environment) cost and appearance.  
       [0004] Conventionally aircraft cargo containers are made from sheet aluminium panels and sometimes polycarbonate panels riveted together. Commonly each container has a base panel, upstanding opposing front and back end walls and side panels which support an overlying roof panel. Doors are usually provided in one or both side walls. Most commonly one end wall has an upper vertical portion and a lower inclined portion so that the shape of this wall conforms more closely to the interior walls of an aircraft cargo hold and so the cargo hold space may be utilised with most efficiency.  
       [0005] It is desirable to be able to pack air cargo containers closely together. Any deformation of a container is liable to cause problems in loading or unloading the containers from the hold and possibly in subsequent transport. However, aluminium sheet is characteristically vulnerable to deformation, both elastic and plastic under load. The use of reinforcement by heavier gauge aluminium sheet or intrusive reinforcing sections is prejudiced by the consequent additional mass, reduced payload space and cost. Reinforcing members or corrugations cause other problems in manufacture, handling and use.  
       [0006] An object of the present invention is to provide a means of alleviating the aforementioned problems experienced with prior art aircraft cargo containers.  
       [0007] Accordingly the present invention provides a load spreader for installation in the floor of an aircraft cargo container, said load spreader comprising a skin of moulded plastics material forming a shell and a foam filling the shell.  
       [0008] The load spreader is shaped and sized in order to closely fit the floor space comprising the base panel of a conventional aluminium container with the exposed foam face of the load spreader facing the floor and the tough skin of the shell facing up. Preferably the shell has a flat upper surface and depending side walls. The load spreader has the effect of stiffening the floor and spreading the load uniformly over the floor panel thereby substantially reducing deformation of the floor. A consequence of reducing the floor deformation is a corresponding reduction in the deformation of the rest of the container.  
       [0009] For purposes of security and cleanliness the skin of the load spreader may be formed to extend over the lower surface of the load spreader so producing a substantially impervious hard shell which completely envelopes the foam core filling the shell. A load spreader with exposed foam can be abused by smugglers digging out the foam and inserting contraband. Another problem is that the uneven surface of the foam attracts and retains fouling and provides a refuge for bioforms such as insects. Because the lower surface is subject to little or no load perpendicular to the surface and is support d by engagement with the preexisting floor of the cargo container it is pref rable to make the membrane of the shell covering this surface substantially thinner than the upper load bearing membrane. It may also be desirable to apply anti-tamper patterns to the shell to further enhance security. Such patterns are well known in the field of packaging.  
       [0010] Preferably the load spreader is formed by rotational moulding although other moulding techniques may be used.  
       [0011] Preferably a frame is provided in the shell underlying and possibly engaging the inner surface of the shell. In this case the foam fills the space remaining within the shell and acts to retain the frame. The frame is introduced to the shell during the moulding process and may consist of pultrusions forming a preferably rectangular grid. In a preferred form of the invention longitudinally extending pultrusions have an “I” beam section while the laterally extending pultrusions have a cylindrical tubular section. Conveniently the laterally extending sections are retained in correspondingly shaped closely fitting holes formed in the web of the “I” section. The flanges of one end of the “I” section bear against the inner upper surface of the skin while the flange at the opposite end of the “I” section are substantially flush with the lower surface of the foam.  
       [0012] In some embodiments of the invention where there is a demand for a very large load spreader it is most convenient to form the load spreader from several elongate sections each comprising an enveloping shell and having parallel elongate sides. The opposing elongate sides of each section are preferably moulded one with a tongue section and the other with a groove adapted to receive the tongue of an adjacent section. This permits a plurality of such sections to be secured together preferably by glue.  
       [0013] The present invention also comprises an air cargo container having a load spreader reinforcing a floor panel.  
       [0014] Further according to the present invention there is provided a method of producing a load spreader comprising the steps of:  
       [0015] introducing a plastics material into a mould from which a skin is rotomoulded to form an enclosing skin,  
       [0016] introducing a plastics foam to fill the enclosure  
       [0017] opening the mould and removing the moulding.  
       [0018] The method may also include the step of splitting the moulding along a plane to form two load spreaders each having a single skin shell formed of a part of the skin enclosure.  
       [0019] In forming a load spreader having an enveloping skin it is very preferable to insert a frame into the mould before forming the enveloping shell. The frame is preferably formed from a plurality of parallel spaced longitudinal members and a plurality of parallel spaced lateral members. It is preferable that the longitudinal members extend vertically between the inside of the upper surface of the shell and either the lower surface of the foam and or the inside of the lower surface of the shell to provide support for the upper load bearing surface in use. The laterally extending frame members are preferably formed with a section to slot through closely fitting holes formed through the longitudinal members.  
       [0020] The method may include the steps of introducing a pair of frames supported in back to back relation into a hollow mould before forming the skin enclosure and  
       [0021] introducing the plastics material into the hollow mould from which the skin is rotomoulded to enclose the pair of frames. In this case the foam fills the enclosure formed by the skin and secures the frames in place in relation to the skin. In one preferred version of the invention the frames are supported to be moved to engage a respective opposite side of the enclosing skin. In this case the step of splitting splits the moulding along a plane separating the two frames to form two load spreaders.  
       [0022] The pair of frames is preferably supported by means of a jig within the mould. Preferably the jig is provided with yieldable members such as elastic bands or breakable fastenings to hold each frame on the jig. During the rotational moulding step of forming the skin each frame is held centrally in the mould. Once the skin has formed the jig is actuated to press each frame against a corresponding side of the interior of the skin enclosure while the foam is introduced and set.  
       [0023] Upon opening the mould the moulding can be split into two load spreaders simply by cutting down the middle between the two frames. However, it is preferable that at least the skin which will form the shells of each load spreader is separated while in the mould, for example by the provision of a separating member in the mould. This avoids the problems presented by the cutting process step.  
       [0024] The method permits the introduction of other components and features into the load spreader, for example, anchor points such as bolt holes or identifying devices such as transponders. Such surface components as anchor points can be provided by retaining them on the inside surface of the mould during the formation of the skin. Components such as tracking and identifying transponders may be supported on the frame or jig to be moulded into the foam or retrofitted afterwards.  
       [0025] Greater multiples of the load spreader may be produced by use of a single mould which produces additional back to back pairs of the load spreaders in side by side relation.  
       [0026] According to a further aspect of the invention there is provided a floor for a cargo container comprising:  
       [0027] a hollow completely enveloping shell of moulded plastics material, and a foam core filling and supporting the shell,  
       [0028] said shell having edges adapted to engage and support upstanding walls of a floorless conventional air cargo container.  
       [0029] Preferably the floor is planar and provided with said edges by adaptive edge members which can be fastened permanently to the peripheral edges of the floor. The floor can thus be made of a standard size and adapted by selection of suitable edge members to support any conventional aircraft cargo container.  
       [0030] The shell is preferably formed with an internal supportive frame consisting of a plurality of longitudinally extending members and a plurality of laterally extending members. The laterally extending members may be slotted through close fitting holes formed in the longitudinal members to form a rigid frame with the longitudinal members spaced parallel to each other and perpendicular to the lateral members. Preferably the ends of some of the frame members project through the edges of the shell to engage in corresponding slots formed in the edge members.  
       [0031] Preferably the edge members and the edge of the shell have a complementary profile which provides for good mechanical engagement of the edge member and the edge of the shell and particularly is adapted to permit the edge member to be securely fastened to the edge by glue or perhaps welding.  
       [0032] The invention also comprises an aircraft cargo container comprising a floor constructed in accordance with the preceding four paragraphs and having opposing side walls and opposing end walls, each said wall upstanding from an adaptive edge member secured to the edges of the shell of the floor.  
       [0033] Preferably the side walls and end walls are formed from aluminium panels.  
       [0034] Further the invention comprises a method of constructing a floor for an air cargo container comprising the steps of:  
       [0035] moulding a shell of plastics material in a mould,  
       [0036] filling the enveloping shell with a foam,  
       [0037] forming the edges of the shell to engage the lower edges of the upstanding walls of a conventional, floorless air cargo container.  
       [0038] Preferably the method includes the step of inserting a supportive frame into the mould before moulding the shell around it.  
       [0039] Preferably the edges are moulded separately from the shell to be attached in a subsequent step so that a common shell can be adapted by selecting and attaching suitable edge members to a range of different conventional air cargo containers. Accordingly an aspect of the invention may also include the step of attaching a set of edge members to the edges of a shell to form a floor and attaching the floor to the lower edges of the upstanding walls of an air cargo container. 
     
    
    
     [0040] A load spreader and a floor for an air cargo container and a method of manufacturing a load spreader and a floor for an air cargo container, embodying the present invention, will now be described, by way of example, with reference to the accompanying drawings in which:  
     [0041]FIG. 1 is a perspective view of a conventional cargo container  
     [0042]FIG. 2 is a perspective view of part of a frame  
     [0043]FIG. 3 is a diagrammatic section of a mould  
     [0044]FIG. 4 is a perspective view of a load spreader  
     [0045]FIG. 5 is a section through the load spreader of FIG. 4,  
     [0046]FIGS. 6 a - 6   e  are sectional views, some enlarged, illustrating the internal detail of a second embodiment of the load spreader having a completely enveloping shell,  
     [0047]FIGS. 7 a ,  7   b  and  7   c  illustrate a load spreader of large size formed in sections, in side elevation, plan and part section,  
     [0048]FIGS. 8 a - g  illustrate the invention embodied in a floor for an air cargo container having adaptive edges, 
    
    
     [0049] A conventional aircraft cargo container  1  shown in FIG. 1 is formed mainly from sheet aluminium panels riveted together. The container  1  has a base panel  2 , upstanding front wall  3 , opposing a back end wall  4  and side panels  5  which support an overlying roof panel  6 . A door  7  is provided in one or both side walls  5  and each door is ordinarily provided with a closure (not shown). The back end wall  4  has an upper vertical portion  4   a  and a lower inclined portion  4   b  so that the shape of this wall conforms closely to the interior wall of an aircraft cargo hold.  
     [0050]FIG. 2 illustrates the construction of a frame used in the formation of the rotomoulded load spreader. The frame consists of seven longitudinal members provided by “I” beam sectioned pultrusions  8  each approximately 1.4 meters long and lying in parallel with the each web  8   a  disposed vertically and the flanges  8   b  horizontal. The “I” beams are connected by five lateral members provided by cylindrical tubular pultrusions  9  which lie perpendicular to and intrude through correspondingly sized holes formed in the webs  8   a . The pultrusions may be formed from any suitable material, however examples of suitable material include glass reinforced plastics using polyester resin, mowdar, carbon fibre or phenolic resin. Although pultrusions of “I” beam section and cylindrical tubes are preferred other sections may be used such as tubular and or rounded “I” beam, a rounded channel section, rectangular section or solid cylindrical or oval sections. The “I” beam profile may be rounded over the top to facilitate easier material flow while it is in the mould.  
     [0051]FIG. 3 is a section through a mould  10  for use in simultaneously rotational moulding two load spreaders. The mould is made in two mirror image parts  10   a  and  10   b  two frames F 1  and F 2  are mounted on a jig  11  which supports each frame, one to each side of the jig  11  and mould. The frames are retained by yieldable members (not shown) such as elastic bands so that the flanges of the “I” beams or other parts of the frames bear against cams  12 . The frames are supported so that they are separated by a gap from the wall of the mould. The mould is closed and a suitable skin forming material, for example, polyethylene, is introduced to the mould. Any plastics material suitable for rotational moulding which is capable of forming a tough, impact and fire resistant shell may be used and may be reinforced with glass fibre or other fibre reinforcement and fire retardant additives may be introduced. The conditions in the mould are then changed to allow the plastics material to mould the skin and set as the mould is rotated, for example by heating or the introduction of a catalyst. The plastics material thus fuses over the entire interior surface of the mould forming a continuous shell  13  of the desired thickness. Once the rotational moulding plastics material has fused, the rotation is stopped. The jig  11  is actuated by rotation of the cams  12 , which cause the frames to move towards the walls of the mould until the flanges are pressed against the interior surface of the shell  13 . In this condition a foam  14  is introduced to fill the cavity within the shell  13 . The inventor also contemplates the use of a one-shot foam system in which the foam is put into the mould at the start of the process, rather than a second step in the process. The foam is preferably a polyethylene resin material with a foaming agent to form a polyethylene foam although other suitable foams may be used. Once the foam is set the mould is opened and the two halves of the moulding formed by the process are split down the middle to produce the load spreader shown in FIGS. 4 and 5. The step of splitting may be achieved by cutting or sawing. However, it is possible to produce the moulding as two seperable load spreaders by the provision of one or more dividers within the mould.  
     [0052] In use the load spreader is laid on the floor  2  of the container with the shell  13  facing up to provide impact resistance. The frame provides great stiffness and is retained by the foam  14 . To improve the bonding between the frame and the foam, the pultrusions are preferably finished with a peel-ply, etching or other roughened surface.  
     [0053] As shown in FIGS. 4 and 5 the load spreader can usefully be formed with an overhanging portion  15  along all edges where it is necessary to accommodate the framework of the aluminium container.  
     [0054] Referring now to the second embodiment illustrated in FIGS. 6 a - 6   e , this embodiment has a fully enveloping shell  13   a  instead of the overlying shell  13  of the first embodiment. Because an underlying membrane  13   b  of the shell which engages the pre-existing floor of the cargo container is supported by the pre-existing floor and otherwise has little load on it the underlying membrane  13   b  can advantageously be made substantially thinner than an overlying membrane  13   c . Because the load spreader of this embodiment has a fully enveloping shell  13   a  the process of the previous embodiment cannot be used to produce the load spreaders in a back to back manner from a single mould. Instead, a mould of more conventional design is constructed to produce one load spreader from each chamber within the mould because such moulds are substantially conventional no detailed illustration of the process is given here.  
     [0055]FIG. 6 b  shows a detailed enlarged section from A in FIG. 6 a , of a lateral frame member-provided by an arcuately I beam sectioned tubular pultrusion  9  received through a longitudinal frame member provided by I section pultrusion  8 . FIG. 6 c  shows a view on I-I from FIG. 6 b  illustrating the holes  8   c  cut by water jets in the webs  8   a  to receive the lateral frame members  9 . FIGS. 6 d  and  6   e  illustrate different surface finishes which may be applied to the upper shell membrane  13   c . Notably the small spaced projections  13   d  shown on the upper membrane surface  13   c  in FIG. 6 d . The upper membrane surface shown in FIG. 6 e  is smooth.  
     [0056]FIG. 7 a  to show a third embodiment of the load spreader for the constructions of exceptionally large load spreaders. In this case production from a single moulding is not possible and the load spreader must be formed from multiple spreader sections  16 , in the example the load spreader is formed from four spreader sections  16 . The moulding and interior detail of each spreader section  16  is substantially the same as that for the second embodiment described above. However, as shown in the enlarged section of FIG. 7 c  the one long edge of each spreader section  16  is formed with a tongue  17  protruding from it. The opposite edge is formed with a groove  18  rebated into it of a size to closely accommodate the tongue of an adjacent edge of a spreader section  16 . To assemble the load spreader each section is laid sequentially onto the floor of the air cargo container with the tongue of one section slotted into the groove of an adjacent section.  
     [0057]FIGS. 8 a - 8   e  illustrate a floor for an air cargo container embodying the invention. The floor consists primarily of a floor shell  13   d  moulded in much the same way as the load spreaders of the previous embodiments to include a reinforcing frame formed from longitudinal and laterally extending members  8  and  9  and a foam core  14 . The shell  13   d  differs from the load spreader of the second embodiment mainly in that the edges  19  are formed with a profile such that, for use, adaptive edge members  20  having a complementary profile  21  can be attached to it by means of adhesive. Pins may also be used to attach the adaptive edge members. A further difference is apparent in that the pultrusions  8  and  9  and shell  13  are so arranged in the mould during production that the pultrusions project from the edges of the shell  13  as is exemplified at  9   c . The adaptive edge members  20  are formed with holes corresponding in shape and location through the complementary profile surface  21  to receive the projecting ends of the pultrusions  8  and  9 . Thus the adaptive edge members  20  can be very securely attached to the edges of the shell to form a floor for a cargo container.  
     [0058] The adaptive edge members  20  vary in the detail of their design apart from the uniformity of the complementary surface  21  because they are intended to be secured to the lower edge of the walls of a conventional air cargo container, especially an aluminium air cargo container. To this end they may be provided with features such as a groove  22 , or a riser  23 . As shown in FIG. 8 f , the adaptive edge members may be joined at the corners by a corner member  24 . which is profiled to slot into the tubular profiles of the edge members  20 .  
     [0059] The integers in the drawing are named as follows:  
                                   Integer   Name                  1   aircraft cargo container       2   base panel       3   front wall       4   back end wall        4a   upper vertical portion of the back end wall        4b   lower inclined portion of the back end wall       5   side panels       6   roof panel       7   door       8   I beam sectioned pultrusion        8a   web of 8        8b   flange of 8        8c   holes for lateral pultrusions       9   cylindrical tubular pultrusions        9c   projecting pultrusion end received in adaptive edge member       10    mould       10a   mould parts       10b   frames F1, F2       11    jig       12    cams       13    shell       13a   enveloping shell       13b   lower shell membrane       13c   upper shell membrane       13d   floor shell       14    foam       15    overhanging portion       16    spreader section       17    tongue       18    groove       19    floor shell edges       20    adaptive edge members       21    edge member profile surface       22    groove in edge member       23    riser       24    comer member