The present invention is concerned with improving containers used to contain cargo in an aircraft hold.
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.
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.
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.
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.
An object of the present invention is to provide a means of alleviating the aforementioned problems experienced with prior art aircraft cargo containers.
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.
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.
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.
Preferably the load spreader is formed by rotational moulding although other moulding techniques may be used.
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.
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.
The present invention also comprises an air cargo container having a load spreader reinforcing a floor panel.
Further according to the present invention there is provided a method of producing a load spreader comprising the steps of:
introducing a plastics material into a mould from which a skin is rotomoulded to form an enclosing skin,
introducing a plastics foam to fill the enclosure
opening the mould and removing the moulding.
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.
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.
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
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.
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.
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.
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.
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.
According to a further aspect of the invention there is provided a floor for a cargo container comprising:
a hollow completely enveloping shell of moulded plastics material, and a foam core filling and supporting the shell,
said shell having edges adapted to engage and support upstanding walls of a floorless conventional air cargo container.
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.
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.
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.
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.
Preferably the side walls and end walls are formed from aluminium panels.
Further the invention comprises a method of constructing a floor for an air cargo container comprising the steps of:
moulding a shell of plastics material in a mould,
filling the enveloping shell with a foam,
forming the edges of the shell to engage the lower edges of the upstanding walls of a conventional, floorless air cargo container.
Preferably the method includes the step of inserting a supportive frame into the mould before moulding the shell around it.
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.