Abstract:
A collapsible cargo container is disclosed wherein end walls are pivoted into the container when empty and locked against the roof, and then side walls buckle via hinges into a folded configuration. The folded configuration is achieved easily with a modified spreader without the need to otherwise disassemble or deconstruct the container, leaving no loose parts or tools. The cargo container preferably constructed with an improved light weight panel that facilitates loading of the container while improving strength and reducing weight.

Description:
CROSS-REFERENCES TO RELATED APPLICATIONS 
     This Application is a continuation-in-part of application Ser. No. 13/371,805 which is a continuation application that claims the benefit of National Stage Application No. 11/792,161, now U.S. Pat. No. 8,113,372, issued Feb. 14, 2012, which in turn claims the priority of PCT/US06/49366, filed on Dec. 27, 2006, which claims the priority from U.S. Provisional Application No. 60/831,273, filed on Jul. 17, 2006, now expired, and U.S. Provisional Application No. 60/756,342, filed on Jan. 5, 2006, now expired, the contents of which are fully incorporated herein by reference. 
    
    
     BACKGROUND 
     The shipping industry employs the use of large cargo containers to transport cargo to be shipped from one location to another. These containers can be easily and conveniently loaded and unloaded, and moved from one transport vehicle or vessel to another for transport across land and/or sea. These containers eliminate the historical requirement to manually transfer cargo from vessel to vessel and from vehicle to vehicle during its course of being transported from one place to another. 
     The cargo containers in use today have become standardized in dimension and structural, and are such that they can be easily, conveniently and securely stacked vertical in a side by side and end to end relationship to maximize the use of hold and deck space on ships and the like, on which such containers are placed. Trailers are standardized to carry the containers for delivery by trucks and the like. 
     The principal shortcoming found in the use of cargo containers of the character referred to above resides in the fact that day to day commerce can require that these containers be transported empty from a station or site of delivery of cargo to a next site or station for receipt or loading of cargo. Such transporting of empty containers is non-profitable since each such container occupies valuable and costly space on the ship that could otherwise accommodate a loaded or filled container. Further, the handling and shipping of both loaded and empty containers creates a multitude of other problems. One such problem resides in arranging light, empty containers and heavy, loaded containers aboard ships in such a manner that the ships are properly and safely trimmed. 
     When transporting a high percentage of empty containers, the voyage of such ships is uneconomical and must be made up somewhere along the way with increased costs of goods and shipping. Accordingly, large economic savings in shipping by containers could be realized if empty containers could be folded or collapsed so that they occupy a fraction of the space they occupy when in their expanded configuration. For example, if two containers when collapsed could occupy the space of one container in its normal configuration, the cost of shipping empty collapsed containers would be roughly reduced about one-half. 
     The prior art has proposed a number of nesting cargo container structures intended to effectively reduce the space required for their shipment when they are empty. While certain proposed nesting containers might well serve such an end, it is understood that they are seriously wanting in certain material respects. For example, a shortcoming found in space saving cargo containers proposed by the prior art includes the deconstruction of the container with the resultant burden of removable or separable parts which are subject to being misplaced, lost, damaged and/or stolen. Experience has taught that if parts of equipment such as cargo containers can be removed and lost or readily damaged, such parts will be removed, lost and/or damaged in the normal course of their use and that great difficulties and inconveniences will be experienced in maintaining such containers. 
     The construction of traditional cargo containers are made to comply with ISO standard 1496-1, which specifies dimensional and strength requirements but not construction methods. Cranes provided assistance for handling some loads and the advent of the fork lift truck led to the introduction of palletized loads which avoided handling of individual items when transferring between different types of transport at freight terminals. Palletized loads still offered limitations in relation to the speed of handling and especially in relation to their stacking capacity. This has led to development and widespread adoption of containers. 
     Various sizes have now become standardized 20′ (6 m) long containers are the most common. The width has become standardized at 2438 mm. Containers can be loaded at the source and are easily transferred between different types of transport e.g. road, rail or ship. Forklift trucks can be used to load a container with palletized loads. Pallets are approximately 48″×40″ (1200-1000 mm) square. Ten pallet places can be accommodated in a standard container. Large ocean going vessels have been designed for handling the containers which can be stacked one on top of the other perhaps as many as seven high. Containers have the advantage of offering protection to the contents within. There is a constant flow of containers around the globe to meet the requirements for the supply of raw materials and products. To maximize container utilization it is desirable to be able to fill a container whenever it is moved from one location to another, but it has been calculated that 20% of containers are transported empty on re-positioning runs. 
     Typical “40-foot” container construction consists of 8 industry-standard corner fittings arranged in space at the corners of a generally 8′ wide by 8′6″ high by 40′ long rectangular box. Various tubes and channels formed from steel sheet are welded between the corner fittings. Steel sheets are welded between these tubes and channels, forming the roof, side walls and front wall. These sheets are typically corrugated to impart sufficient rigidity to the sheet to allow the walls to be made from a single sheet of steel. Door leaves are installed in place of a rear wall and allow cargo to be loaded and unloaded, while the floor is typically made from wood mounted atop a welded grid of steel channels.  FIG. 1  shows the construction of the side wall of a typical container. The corner fittings ( 1 ) are located at the corners of each wall. A portion of the wall has been removed to reveal the corrugation of the steel sheet ( 2 ), which is welded to front corner post ( 3 ), rear corner post ( 4 ), upper rail ( 5 ), and lower rail ( 6 ). This method of construction also generally applies to the opposite side wall, the front wall and also to the roof. The door leaves are typically constructed similarly, less corner fittings. 
     The result of this method of construction is that the interior and exterior faces of the walls are not flat and smooth. The heavy corrugations of the interior walls often make loading and unloading of cargo difficult as the forks and tires of the forklift get hung up on the corrugations while maneuvering. This is particularly troublesome where loads are balanced on pallets and the uneven surfaces can also cause spilling of the loads, sometimes requiring special lifting equipment to restack the pallets. There is a need in the art for a container that has more even surfaces that resist interference with forklift tires, forks, and the like. 
     Yet another shortcoming found in collapsible containers proposed by the prior art is the lack of structural features which enable or facilitate the folding down and setting up or opening of such containers in a simple and effective manner. 
     SUMMARY OF THE INVENTION 
     This document describes a new type of dry cargo container used for shipping freight over land and sea. Generally, the invention is a special configuration of container which allows it to collapse, saving space when not in use. Containers in current use are made to comply with ISO standard 1496-1 and are not collapsible. The new container is designed to comply with the external dimensional requirements of the ISO standard for containers of 20-foot length and above, but differs in other respects. Loaded containers are lifted from above using an apparatus called a spreader. The folding container described herein can be handled with standard spreaders, and can also be folded and unfolded using a special new spreader specifically designed for the purpose. 
     The cargo container described herein may take many different forms, but is characterized in that the ends of the container secure to the ceiling of the container, allowing the side walls collapse onto the floor to greatly reduce the height of the container while maintaining the same footprint. The preferred mechanisms by which the container folds and collapses is described in detail in the section below. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       For a better understanding of the present invention together with other and further objects, advantages and capabilities thereof, reference is made to the following disclosure and appended claims in connection with the above described drawings directed to an improved shipping container. 
         FIG. 1  is a perspective view of a preferred embodiment of a shipping container of the present invention with portions of the container removed for clarity; 
         FIG. 2  is an enlarged, elevated perspective view of the juncture of the side wall, upper wall, and door juncture of the embodiment of  FIG. 1 ; 
         FIG. 3  is an elevated perspective view of the side wall with an outer panel removed to show a hinge assembly, and door assembly of  FIG. 1 ; 
         FIG. 4  is an elevated perspective view of the door assembly of  FIG. 1 ; 
         FIG. 5  is an enlarged, elevated perspective view of the down locks and connection of the door frame of  FIG. 1 ; 
         FIG. 6  is a cut-away side view of the ramp assembly as the door frame begins to swing upward toward the upper wall; 
         FIG. 7  is an enlarged, elevated perspective view of the door frame and lifting pins, lugs; 
         FIG. 8  is an elevated perspective view of the door frame and ramp assemblies as they are lifted toward the upper wall; 
         FIG. 9  is a side view, partially in cut-away, showing the door assembly and front wall being rotated toward the upper wall; 
         FIG. 10  is an elevated, perspective view of the lifting pins and lugs and alignment pins and brackets on the door and door frame assemblies; 
         FIG. 11  is lowered perspective view looking upward into the container showing the attachment of the door assembly and front wall against the upper wall using up locks; 
         FIG. 12  is an enlarged, perspective of the up locks of  FIG. 11 ; 
         FIG. 13  is a side view of the side wall collapsing about its hinge assemblies; 
         FIG. 14  is an enlarged, elevated perspective view of the alignment means of the support column; 
         FIG. 15  is an elevated, perspective view of the side wall assembly fully collapsed; 
         FIG. 16  is a perspective view of a modified spreader adapted for rotating the door frame and front wall against the upper wall and for collapsing the side walls of the container; 
         FIG. 17  is a perspective view of a preferred embodiment of the present invention showing an improved composite construction light weight panel; 
         FIG. 18  is an exploded view of the improved panel of  FIG. 17 ; 
         FIG. 19  is an enlarged, cut-away portion of the panel of  FIG. 17 ; 
         FIG. 20  is an elevated, perspective view of the panel in cut-away showing reinforcing bars in the channels; 
         FIG. 21  is an enlarged, elevated perspective view of the panel of  FIG. 17  showing vertical members disposed within the vertical channels of the panel; 
         FIG. 22  is an enlarged, elevated perspective view of a latching mechanism for retaining the container in a collapsed configuration, and protrusions for use with a lashing bar; 
         FIG. 23  is an elevated, perspective view of a stack of containers each incorporating the latching mechanism of  FIG. 22  and a lashing bar; 
         FIG. 24  an elevated, perspective view of an alternate floor arrangement including horizontal channels to accommodate rotation of the door; 
         FIG. 25  is an elevated perspective view of the door rotating with the alternate floor arrangement of  FIG. 24 ; 
         FIG. 26  is an enlarged, elevated perspective view of a twist lock for use with the collapsible container; and 
         FIG. 27  is an enlarged, elevated perspective view of a door frame locking mechanism. 
     
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
       FIG. 1  shows a first preferred embodiment of the shipping container  99  of the present invention in its fully expanded state. Portions of the right half of the container are omitted to better show the container&#39;s interior. The container is formed of a corrugated upper wall  100 , a substantially smooth floor  102 , a front wall  30 , first and second rear doors leaves  1 , and collapsible left and right walls  104 . The left-hand door leaf  1  is shown fully open, ready to load and unload cargo. The right hand door leaf is omitted for clarity but would operate similarly to the left hand door leaf. At each vertex of the adjoining walls are corner fittings  12  that cooperate with a spreader to lift and transfer the container  99 . Stacked containers  99  generally only contact each other at the corner fittings  12 , resulting in tremendous compressive loads carried between vertical pairs of corner fittings  12 . Loaded containers are lifted from above using a spreader  16  which locks into the upper corner fittings  12 . The weight of the container when carried by the spreader imparts a large tensile load between vertical pairs of corner fittings. 
       FIG. 2  is a close-up view of the inside of the left door  1  where the door  1  is ajar. The door  1  is attached to a door aperture frame  2  via door hinges  3 . The door aperture frame  2  can be a weldment roughly forming a square defining the opening of the container  99  at the rear opening. The door hinges  3  are dog-legged shape which allows them to wrap around the side walls  104  when the door  1  is fully open, yet remain fully inboard of the side wall  104  when the door  1  is closed. Door leaf side pins  29  mounted on the door are disengaged from their corresponding holes  106  in the door aperture frame. The pins  29  when engaged with their respective holes increase the burst strength of the door leaves, and also to help to keep the lashing assembly  9  engaged with the door aperture frame  2 . Compression seals  49  along the periphery of the door seals out moisture and contaminants, as do mating seals  47 ,  48 . 
       FIG. 3  shows the left-hand door  1  in the fully closed position. In this position, the door  1  can be locked to the door aperture frame  2  by turning the door leaf locking lever  5  toward the stay  6 , causing the rod  7  to rotate and the door lock  8  to lock. Lashing assembly  9  is also operated by the lever  5 , and serves to tie the outboard edges of the door  1  to the door aperture frame  2  by causing a tab on the lashing assembly to rotate into a slot in the door aperture frame  2 . Several of these assemblies  9  may be required on each door leaf. The upper panel of the side wall  104  is not shown, revealing the rub strip  10  affixed along the vertical length of the door aperture frame. The purpose of the rub strip  10  is to reduce abrasion of the inboard faces of the side walls as the container is folded. Hinge pin  17  of the door aperture frame  2  is exposed via a hole  108  in the lateral edge  107  of the upper wall  100 . Hinge pin  17  is integrally formed with the door aperture frame  2 , and serves as a lifting pin. 
     The hinge  52  of side wall  104  includes a longitudinal axis that lies on, or slightly outboard of, the outer face of the side wall  104 , allowing the upper and lower portions of the side walls to rotate 180 degrees relative to each other. Compressive loads created when containers are stacked are primarily communicated through columns built into the fore and aft ends of the side walls  104 . These columns are vertical when the container is in the expanded, or unfolded state, and make contact with each other at compression faces  56  as observed with the upper side wall removed. Compression faces mate in pairs, with one face having an alignment groove  58  and the other face having as alignment tab  57  (see  FIG. 14 ), which cooperate to maintain the intended alignment. 
       FIGS. 4 and 5  show a ramp  13  (sectioned for clarity) at the opening to the rear entry. The ramp  13  is attached across the lower edge of the door aperture frame  2  via a continuous hinge  109 . The ramp acts as a temporary floor section that can be moved out of the way of the door aperture frame  2  as it is rotated into the roof. Down stops  14  which limit the travel of the door aperture frame are shown attached to the door sill  15 . The down stops  14  are slotted to receive pins  111  which are integral with the door aperture frame  2 . When engaged, these pins  111  help to support the floor by fastening the door sill  15 , via the down stops  14 , to the door aperture frame  2 , which is in turn fastened to the door  1  via the door locks  8 . 
       FIG. 5  shows one version of a down lock  18 , which keeps the door aperture frame  2  locked in place when the container  99  is fully unfolded. Portions of the floor assembly is not shown in  FIG. 5  for clarity. A spring  20  biases the down lock  18  toward the upward position. The spring  20 , as well as the inclined upper face  112  of the down lock  118 , allow the door aperture frame  2  to push the down lock  18  out of the way during the unfolding operation so that the door aperture frame  2  can move to its lower rest position shown in  FIG. 5 . The lock  18  springs up again once the door aperture frame  2  has passed, locking the door aperture frame into place. When the container  99  needs to be collapsed, a pin that is part of the spreader apparatus  16  pushes down on a rod within the vertical member of the door aperture frame ( 2 ), pushing the down lock  18  downward to allow the door aperture frame  2  to pass over the inclined upper face  112  in the opposite direction. A similar mechanism would be used for the front wall  30  at the opposite end of the container  99 . Other variations of the down lock  18 , such as a spring loaded pawl or a spring loaded bolt, will work well to secure the door aperture frame  2 . 
       FIG. 6  shows the door aperture frame  2  after the down locks  18  have been released, being pushed into the roof assembly as the container  99  is being folded. The ramp  13  is designed as a wedge so that it lifts itself out of the recess in the floor  113 .  FIG. 7  shows door aperture frame  2  in the same position, but from a different angle, revealing the lifting lug  25  and lifting pin  26 . The lifting pin  26  is integral with the door aperture frame  2 , and along with door aperture frame hinge pin  17 , forms a path for tensile lifting loads between vertical pairs of corner fittings at the back end of the container. 
       FIG. 8  shows door aperture frame  2  pushed further toward the roof under influence of the spreader. The ramp  13  is displaced from its recess in the floor, and begins to drag across the floor&#39;s upper surface as it is pushed by the door aperture frame. The side wall support pins  27  have disengaged from the side wall support brackets  28 . The pins  111  can also be seen disengaged from down locks  14 . In this view it can be seen that the door leaves  1  remain locked to the door aperture frame via door locks  8  and lashing assembly  9  as the container is folded. Conventional flat rubber seals  47  attached to the edges of the door leaves help to seal out water by covering the gaps between the leaves and the door aperture frame  2 . A similar seal is attached to the right-hand door leaf to seal the vertical gap between the leaves on the container centerline. L-shaped rubber seals  48  of various lengths seal the gap between the outer perimeter of the door aperture frame  2  and the other components of the container. This type of seal is also used across the top edge of the front wall, and may be used on the sides of the front wall as well. 
       FIG. 9  illustrates how the front wall  30  folds into the roof in a similar manner to the door aperture frame  2 . The door leaves are removed to more clearly show the door aperture frame  2 . The front wall in most cases will not open for loading and unloading cargo, and does not contain door leaves. The front wall hinges on hinge pins  35  are similar to those on the door aperture frame  2 , and are locked in position when the container is completely unfolded via down locks similar to those used to lock the door aperture frame in place. Ramp  13  has now pivoted clockwise into contact with the door aperture frame  2 , which acts as a stop for the ramp  13 . Door aperture frame up lock  36  serves to retain the door aperture frame  2  against the upper wall  100  when the container is folded. A similar up lock  37  serves to retain the front wall frame  30  against the upper wall when the container is folded. Various up stops  38  keep the door aperture frame  2 , ramp  13  and front wall  30  from bouncing against the upper wall  100  when the container is folded. 
       FIG. 10  shows the vertical transverse flange  31  on the front sill  32 , which acts as a down stop for the front wall  30 . Lifting pins  34  integral with the front wall  30  engage lifting holes  33  in the flange  31  of front sill  32 . These pins  34 , along with the front wall hinge pins  35 , form the path for tensile lifting loads between vertical pairs of corner fittings at the front end of the container. This view also shows the side wall support pins  27  disengaged from the side wall support brackets  28 . Also shown is a seal  49  that serves to help seal out water primarily by resting above flange  31  and serving as a sort of overhanging roof. 
       FIG. 11  is a perspective view looking up at the upper surface of the container with the door frame and front wall rotated into the locked position against the upper wall  100 . The door aperture frame  2  carrying the door leaves  1  is locked against the upper wall  100  by the up lock  36  and the front wall  30  is locked by up lock  37 . 
       FIG. 12  is a close-up sectional view of up lock  36 . A spring  39  biases the up lock in the inboard direction as shown. The spring, as well as the inclined inboard face  117  of the up lock  36 , allow the door aperture frame  2  to push the up lock  36  out of the way during the folding operation, so that the door aperture frame can move to its upper rest position. The lock  36  springs inboard again once the door aperture frame has passed, locking the door aperture frame  2  into place. When the container needs to be unfolded, a pin on the spreader apparatus passes through hole  40  and pushes on lever  41  of the up lock  36 , causing the up lock to move outboard and allowing the door aperture frame  2  to pass in the opposite direction. A similar arrangement is used for the front wall. 
       FIG. 13  shows how the side walls  104  are hinged, allowing the container  99  to fold. Upper side wall hinge  51 , mid side wall hinge  52 , and lower side wall hinge  53  are positioned at respective junctures of the side wall  104 . These hinges may be continuous “piano-type” hinges as shown in the drawings, or may be a series of shorter hinges. The hinges may be replaceable and may fasten with bolts. With the container resting on a supportive surface, the spreader apparatus begins to lower toward the ground. The door aperture frame  2  can be seen folded and locked into the roof by up lock  36 . The hinges along the side walls are designed with flanges  42  that help to prevent water from entering the container by keeping the hinges covered. 
       FIG. 14  shows the container partially folded, revealing lower side wall hinge  53  of  FIG. 13 , including integral water sealing flange  42 . This flange contacts surface  54  when the container is in the unfolded state, serving to cover the hinge and help keep water out of the container. This arrangement, with the flange  42  pointing down on the outboard side of the hinge, on the upper mating component, is typical of the side wall hinges  51  and  53  as seen in  FIG. 13 . Compression face  56 , the exposed end of a compression column inside side wall  104 , can be seen, as well as alignment features  57  and  58 . It can be seen that the side wall hinge stops short of reaching the end of the wall, so as not to be involved with the compressive load path when the container is in the unfolded state. This is typical for all the side wall hinges, and at both front and rear ends of the container. 
       FIG. 15  shows the container  99  fully collapsed. The side walls  104  can be seen resting on the floor.  FIG. 16  is a cut-away side view showing a catch  43  that holds ramp  13  down firmly when the container is unfolded. The catch is biased by a spring  45  against a stop  46 , which is integral with the floor. The catch engages with pin  44 , which is integral with the ramp. The shape of the catch and the presence of the spring allow the catch to move out of the way, so as not to interfere with the movement of the ramp as it find its way into the recess in the floor. Engagement of pin  44  does not require that the pin  44  move laterally or diagonally into engagement with the catch  43 . It can just as easily engage vertically, should the ramp not drop into place as expected. 
       FIG. 16  shows the specially-designed spreader apparatus  59  engaged with the container via the upper corner fittings, which are not visible. An arm  60  on the spreader is seen as it pushes the door aperture frame  2  (carrying the door leaves) and the front wall  30  against the upper wall. The specially-designed spreader also serves to unlock the door aperture frame  2  and front wall  30  from their extreme positions. 
     The construction of the container provides for a tensile load path at the rear end of the container when a loaded container is lifted by the spreader apparatus. Load is carried from the upper corner fitting  12 , through the side rail of the roof, out to the hole in the side wall that receives the door aperture frame hinge pin, through the pin  17 , down the door aperture frame  2 , through the lifting pin of the door aperture frame, to the lifting lug  25 , which is welded the top of the lower corner fitting  12 . The side wall hinges are isolated from load. 
     There is also a compressive load path at the rear end of the container when other containers are stacked on top. Load is carried from the upper corner fitting  12 , through the side rail of the roof, through the vertical compression columns built into the ends of the side walls, and through the side rail of the floor, that is welded to the lower corner fitting  12 . The side wall hinges are isolated from load. Because the side walls carry the bulk of the vertical compressive loads, and because the side wall hinges promote buckling of the load path, it is critical to maintain the side walls in proper alignment with the load path. The side wall support pins  27  and side wall support brackets  28  accomplish this by tying the side walls  104  into the vertical member of the door aperture frame  2 . The vertical member of the door aperture frame should remain straight (viewed from the rear), since it is not exposed to compressive loads, and since it is tied into the door leaves  1  via lashing assembly  9 . The holes in side wall support brackets  28  that receive the side wall support pins  27  may be slotted vertically to help to insure that compressive loads are not introduced into the door aperture frame. 
     There is also a tensile load path at front end of the container. Load is carried from the upper corner fitting  12 , through the side rail of the roof, out to the hole in side wall that receives the front wall hinge pin, through the pin  35 , down the front wall  30 , through the lifting pin  34  of the front wall, and through the flange  31  of front sill  32  that is welded to the top of the lower corner fitting  12 . The side wall hinges are isolated from the tensile load. 
     The compressive load path at the front end of the container is described as follows. Load is carried from the upper corner fitting  12 , through the side rail of the roof, through the vertical compression columns built into the ends of the side walls, and through the side rail of the floor, which is welded to the lower corner fitting  12 . The side wall hinges are isolated from the compressive load. The side wall support pins  27  and side wall support brackets  28  tie the side walls  104  into the front wall  30  to stabilize the side walls. The front wall  30  should remain straight since it is not exposed to compressive loads. The holes in side wall support brackets  28  that receive the side wall support pins  27  may be slotted vertically to help to insure that compressive loads are not introduced into the front wall. 
       FIG. 17  illustrates a preferred embodiment of the present invention with a modified panel for the side walls  104  and end wall  30 . The side wall  104  includes upper and lower sections that fold along the hinge as previously described.  FIG. 18  illustrates an exploded view of the panel of the proposed construction. Although the following description of the new panel preferably uses steel for all of the various parts, and fusion of the various parts by welding, other materials such as aluminum and composites (fiberglass), and other methods of fusion such as riveting and bonding may be substituted in any combination. 
     The outer skin  207  which serves as the exterior face of the wall structure is a pressing formed from steel sheet. The various pressed recesses  211  result in the formation of inclined faces which serve as structural stiffening ribs  210 . The inner skin  208  which serves as the interior face of the wall structure is a plain steel sheet without contour. Outer skin  207  and inner skin  208  are welded to perimeter frame  209  along their outer edges. Perimeter frame  209  is a weldment of various steel tubes or channels. Outer skin  207  and inner skin  208  contact, and are welded to each other in the areas of the pressed recesses  211 . 
       FIG. 19  is a cut-away view of the panel, showing how the fusion of outer skin  207  and inner skin  208  result in the formation of structural box members  212  which impart great strength to the wall assembly and eliminate the necessity of incorporating separate internal framework or core structure. The outer skin  207  in the areas of the pressed recesses  211  can be removed to create weight reducing holes that serve to reduce container weight, facilitate weld inspection, and allow adhesive to escape in the case of fusion via bonding. 
     The pressed recesses  211  can take other forms such as round dimples, squares, stripes, etc. in repeating geometric patterns of various arrangements, instead of triangular recesses as described, eliminating the need for the incorporation of a separate core material or separate ribs to tie the skins together. The outer skin meets, and is fused to, the flat and smooth inner skin via welding in each case. 
       FIG. 20  shows a variation of the improved panel of the invention used in the construction of a front wall. The panel is sectioned on its centerline to reveal the contours of the inner skin  208  and outer skin  207 . In this case, both face skins incorporate pressed recesses  211  which meet and are fused together, again, eliminating the need for the incorporation of a separate core material or separate ribs. This version is appropriately used where walls are especially thick or where smooth faces are not deemed necessary. The panels are also reinforced with strengthening members  232  within the channel portions that serve to make the panel more rigid. 
       FIG. 21  illustrates vertical members  214  between the outer skin panels  207  and inner skin panels  208 . Outer skin panels  207  are shown butted against each other, but may overlap as an option. Inner panels  208  are shown butted against each other, but also may overlap as an option. 
       FIG. 22  illustrates a locking mechanism for locking the container in the collapsed configuration. When the container is collapsed, the side wall is compressed between the upper panel and the lower panel as shown. The bottom panel  601  has a spring loaded latch  603  that is biased to engage the upper panel in the collapsed configuration, where a hook portion  605  inserts into a recess  607  to lock the upper panel and lower panel together as shown. A spring (not shown) in a housing  609  ensures that the latch rotates against the upper panel and into the recess  607  when the container is collapsed and the lower panel is brought in proximity with the upper panel. The latch at the hook portion  605  includes an inclined surface  611 , wherein a downward force on the inclined surface  611  provides a separating force to disengage the latch  603 , overcoming the spring&#39;s bias, to allow the container to expand. The spreader can be equipped with a bar or other structure that moves downward along the upper panel&#39;s side surface until it contacts the inclined surface  611 , rotating the latch  603  away from the upper panel. With the latch disengaged, the spreader can then lift the upper panel to expand the container as described previously. The locking mechanism can be placed at each corner of the container, and ensures that the container, once collapsed, will remain in a tight, stowed configuration until it is ready to be filled. 
     Adjacent the locking mechanism is a pair of protrusions  615 ,  620  that cooperate with a lashing bar to secure four or more containers in the collapsed state to each other. The protrusion  620  on the bottom panel is preferably a lug having a slot in which the bottom portion of the lashing bar  650 , while the protrusion  615  may just include a lip  617 . Once the lashing bar  650  is placed over the protrusions, as shown in  FIG. 23 , the lip  617  and the groove  622  keep the bar in place. With lashing bars  650  placed on each corner of a stack of four containers, the stack can be lifted by the spreader like an ordinary container and placed on a ship, cargo hold, or other storage location. The lashing bar  650  is preferably a heavy duty metal having sufficient strength to carry the four empty containers without warping or deforming. Although four containers are shown as bound by the lashing bar  650 , other number of containers can be retained depending on the needs of the user. 
       FIG. 24  illustrates another embodiment of the present invention wherein the ramp of the earlier embodiment is replaced with a floor section  660  having a plurality of horizontal channels  662  extending from the opening of the container rearward. That channels  662  replace the ramp, and allow the door to swing upward with adequate clearance for the fixtures on the bottom of the door to move past the floor section because the channels  662  are aligned with the fixtures. The spacing the channels  662  can be selected to eliminate any issues with a fork lift wheel base, so that the fork lift will not become trapped in the channels.  FIG. 25  illustrates the door moving upward with the fixtures passing through the channels  662 , allowing the door to rotate all the way to the container ceiling. The channels  662  may be rectangular as shown, or ramped up so that they are deeper at the front of the container and shallower as the channels extend rearward, thereby accommodating the arc of the door as it rotates about its axis of rotation. 
       FIG. 26  illustrates a twist lock  700  that can be positioned at the corner fittings  12 , where the twist lock  700  can be used for alignment and retention. The twist lock  700  comprises a base  710  and a swiveling member  712  that extends upward from the corner fitting  12 . The containers (or spreader) are configured with an opening sized to receiver the swiveling member  712  in a first position, but not a second position. Thus, by placing the second container over the first container, and then rotating the swiveling member  712  from the first position to the position, the two containers will be coupled together by the twist lock  700 . Four containers can be aligned and coupled for transport using the twist locks  700  at each corner, and a spreader can also be configured to use the twist locks  700  for alignment purposes. 
       FIG. 27  illustrates a door locking mechanism for retainer the front and rear doors in their respective frames after expansion of the container. The door  1  includes at a bottom surface a pair of pins  725  horizontally aligned below the bottom surface and extending from a block  730 . the frame of the door includes a retention member configured to receive the pins  725  in a U-shaped recess  735  when the door is positioned in the frame. A trapezoidal reciprocating member  740  has an inclined surface proximal to the door as it approaches the frame, causing the reciprocating member to be pushed downward out of the path of the block  730 . Once the block  730  clears the trapezoidal reciprocating member  740 , the reciprocating member  740  moves upward via a spring (not shown) to lock the door  1  in the frame. Various methods can be used to withdraw the trapezoidal reciprocating member  740  when it is time to collapse the container, most likely the spreader will engage the trapezoidal member  740  prior to the door  1  being rotated inward. 
     The foregoing are illustrative of the concepts embodied by the present invention, although other embodiments would be known to one of ordinary skill in the art and the invention should be deemed to include such embodiments. Accordingly, the invention should not be limited by the preceding descriptions, but rather only by the words in the appended claims presented below.