Abstract:
An apparatus for attenuating the exchange of air in a freight container with the surrounding atmosphere comprises a flexible but substantially not resilient membrane which delimits in the container a first air volume from a second air volume in which cargo sensitive to humidity is stored. The first air volume is in communication with the surrounding atmosphere and capable of varying as a result of differences between atmospheric pressure and the pressure in the second air volume. Also disclosed is a freight container provided with the apparatus.

Description:
FIELD OF THE INVENTION  
       [0001]     The present invention relates to an apparatus for attenuating the exchange of air in containers that are not airtight, in particular freight containers, and to a freight container provided with such apparatus.  
       BACKGROUND OF THE INVENTION  
       [0002]     Cargo of various kinds is shipped in aluminium or steel freight containers usually being approximately 8×8×20 or 8×8×40 feet in size. Recently a freight container approximately 8×8×13 feet in size has been proposed as a new standard (WO 01/62631). A modular freight container of this sort is of generally rectangular parallelepipedal form and comprises a base, a pair of opposed side walls, at least one of which comprises a door, usually a double wing door, for loading and unloading freight, and a roof. The walls are usually made of corrugated plate. While freight containers are made to withstand severe weather conditions they are generally not airtight. To seal them completely is costly.  
         [0003]     Due to changes in temperature of the air inside of the freight container or in the atmosphere surrounding it, changes in atmospheric pressure, wind pressure, and the like, a difference in pressure between the air in the container and that surrounding it may be created, causing humid air to leak into the container from outside and affect cargo that is sensitive to humidity. As a precautionary measure drying devices, such as the one disclosed in WO 01/25707, are disposed in freight containers carrying sensitive cargo. The drying capacity of such devices is however limited. The problem of keeping the air in the container dry is enhanced by cargo of high specific weight. Due to its limited loading capacity only a minor portion of the freight container may be loaded with such cargo, for instance, humidity sensitive metal powders. For a given difference in air pressure the volume of humid air that enters the freight container increases in proportion with the empty space in the container. This aggravates the humidity problem.  
       OBJECTS OF THE INVENTION  
       [0004]     It is an object of the present invention to provide a means for attenuating the exchange of air between the air in a container of the aforementioned kind and the surrounding atmosphere.  
         [0005]     Further objects of the invention will become evident by the following summary of the invention, the description of preferred embodiments illustrated in a drawing, and the appended claims.  
       SUMMARY OF THE INVENTION  
       [0006]     According to the present invention is provided an apparatus for attenuating the exchange of air in a freight container with the surrounding atmosphere, comprising a flexible but substantially not resilient membrane which delimits within the container a first air volume from a second air volume in which cargo sensitive to humidity is stored, the first air volume being in communication with the surrounding atmosphere and capable of varying as a result of differences between atmospheric pressure and the pressure in the second air volume. It is preferred for the membrane to comprise a sealing means extending along its circumference. Preferably the membrane has the form of a thin-walled plastic bag or trough along the circumferential edge of which the sealing means is provided in form of an adhesive. The sealing means may, however, also be provided separately, for instance, in form of a clamping or lacing means or similar. By the sealing means the membrane is put in communication, directly or indirectly, with an opening in the container wall. Thereby communication between the first volume delimited by the membrane and the atmosphere surrounding the container is established. It is important that the membrane does not easily collapse by its own weight. Therefore it should be as light as possible. Particularly preferred are membranes of polymer material, such as polyethylene, polypropylene, and the like. Particularly preferred is pre-stretched polyethylene or polypropylene foil. Typically the membrane will have a thickness of 0.05 to 0.3 mm. In other words, the movement of the membrane should, as far as possible, only be caused by a difference in air pressure between the first and the second volume. It is preferred the first volume to be set at about half its maximum when mounting the membrane.  
         [0007]     According to a first preferred aspect of the invention, in which the membrane is put into direct communication with an opening in the container wall, the sealing means comprises a rectangular frame capable of being mounted so as to make the membrane cover a door opening of the container; in such case a means for attaching the frame to the rebate of the door, such as an adhesive, is provided on the frame or on the rebate or both. Thereby the frame can be glued to the rebate of the container door after the container has been loaded with cargo, whereafter the door is closed. The first air volume in the container thus is formed between the membrane and the closed door; its communication with the atmosphere surrounding the container is by leaks between the door and the rebate and between the door wings if a door with wings is used. A membrane mounted in this manner utilises the leaks which normally occur at a container door and which most often are more prominent than the sum of other leaks in the container. A further advantage is provided in that the freight container door can be opened for visual inspection of the cargo without admitting humid air to the second volume in which the cargo is stored. Such inspection is common in case of interstate transport during which the cargo may be inspected by custom officers before being shipped to the final destination and unloaded. For this reason it is preferred for the membrane or a portion thereof to be made in a transparent material. It is also possible to put the volume defined by the membrane in direct communication with an opening in a wall of the freight container that is not a door opening and which will have to be provided separately, thereby defining said first volume. This is achieved by, for instance, gluing the free circumferential edge of a plastic bag to an inside portion of the container wall surrounding the opening. The free circumferential edge of the bag may also be mounted on a short tubular connection piece provided with a circular flange at its one end, the flange being fixed to the inside portion of the container wall surrounding the opening. In spite of the interposed connection piece the membrane still can be considered to be put in essentially direct communication with a through opening in a container wall.  
         [0008]     According to a second preferred aspect of the invention, the sealing means is put in indirect communication with a through opening in a freight container wall. The through opening is not a door opening and has to be provided separately, for instance, by drilling a hole in the container wall. In particular, the sealing means comprises an assembly for mounting the membrane to a container wall having a first through opening which is not a door opening in a manner to provide substantially unrestricted communication between the first volume and the surrounding atmosphere through the first through opening. The mounting assembly comprises an element for interposition between the first through opening and the assembly, the interposition element comprising a means for its fixation to the container wall in a manner so as to make it cover the first through opening, the fixation means comprising a first through bore for its fixation to the remainder of the mounting assembly and a second through bore for providing communication of atmospheric air to the first air volume.  
         [0009]     According to a variation of the second preferred aspect of the invention the mounting assembly comprises a means for its fixation to a second through bore in the container wall disposed adjacent to the first through bore. Also this second through bore has to be provided separately. It is preferred for the mounting assembly to comprise a mounting stud, a first tube extending from the mounting stud generally perpendicular to the stud axis, a second tube slidingly and sealingly disposed on the first tube or in the first tube, the second tube having, in respect of the stud, a an open proximal end and a closed distal end and comprising a neck extending from its closed end for air-tight fixation of membrane. It is also preferred for the mounting assembly to comprise a means for suspending the first or the second tube on a lashing eye fixed at the container wall. Such eyes are standard in most freight containers. The design of the mounting assembly allows it to adapt to variations in distance between the bore or bores in the container wall at which or near which the assembly is mounted, and the eye at which the second tube with the membrane is suspended about horizontally, albeit deviations from the horizontal level may be tolerated.  
         [0010]     Except for direct or indirect (by the interposed mounting element) mounting of the mounting assembly on the freight container wall the design of the mounting assembly of the second preferred aspect of the invention and the variation thereof is the same. The second tube is advantageously a corrugated tube which is slidingly and sealingly disposed on said first tube. In such case it is preferred for the suspension means to be capable of being fixed onto the second tube by clamping. While the membrane may have any form that is suitable for delimiting the first volume from the second volume, it will most often take the general form of a bag with a rectangular or circular bottom.  
         [0011]     According to a third preferred aspect of the invention the first volume is up to ten percent of the second volume, even more preferred up to six percent of the second volume, most preferred from up to four and up to ten percent of the second volume.  
         [0012]     According to a fourth preferred aspect of the invention the first volume is comprised by two or more apparatus according to the invention. Thus, for instance, a first volume of up to six percent of the second volume may be provided by two apparatus each having a first volume of up to three percent.  
         [0013]     According to a fifth preferred aspect of the invention the flow resistance of the communication between the atmosphere and the first volume is ten percent or less of the flow resistance of the combined leaks to the second volume. Thus, if the pressure of the air surrounding the container rises, a volume of air will enter the first volume, which is correspondingly larger than the volume of air entering the second volume. In an opposite situation, in which the pressure in the container exceeds the surrounding pressure, a correspondingly larger volume of air will leave the first volume. Drying devices disposed in the second volume where the cargo is stored thus will have to cope with considerably smaller amounts of humidity and hence will last longer and keep the average humidity in the second volume at a lower level.  
         [0014]     According to a sixth preferred aspect of the invention the mounting assembly comprises a mounting stud and a tube element extending from the mounting stud perpendicularly or obliquely to the stud axis and being in fluid communication with the stud, the tube element comprising, at its free end, means for sealing fixation of the membrane; wherein it is preferred for the membrane to have the form of a bag and for the fixation means to comprise screw and/or hook means.  
         [0015]     Also disclosed is a freight container provided with the apparatus of the invention.  
         [0016]     The invention will not be explained in detail by reference to a number of preferred embodiments illustrated in a drawing. 
     
    
     SHORT DESCRIPTION OF THE DRAWING  
       [0017]      FIG. 1  is a perspective view of a freight container, with portions of its end and side walls and its roof removed, provided with two pressure equalisers according to the invention, each consisting of a mounting assembly and a collapsible bag, mounted on the left container wall;  
         [0018]      FIG. 2  is an enlarged partial view of one of the pressure equalisers in  FIG. 1 , in the same view;  
         [0019]      FIG. 3  is a still more enlarged partial view of the mounting assembly of the pressure equaliser of  FIG. 2 , with the container wall omitted, in the same view;  
         [0020]      FIG. 4  is an axial section (C-C;  FIG. 7 ) corresponding to  FIG. 3  but with a portion of the collapsible bag also shown;  
         [0021]      FIG. 4   a  is an enlarged partial view of  FIG. 4 , illustrating the connection between the mounting assembly and the collapsible bag;  
         [0022]      FIG. 5  is a section (B-B;  FIG. 3 ) through the suspension device of the mounting assembly;  
         [0023]      FIG. 6  is a top view (in the same direction as the view in  FIG. 3 ) of the arrangement of through bores in a lock disk covering a larger through bore in the container wall;  
         [0024]      FIG. 7  is an axial section (A-A;  FIG. 4 ) of the proximal end portion of the mounting assembly of  FIG. 3 , in a mounted state;  
         [0025]      FIG. 8  is a partial view of a the proximal end portion of the mounting assembly of a second embodiment of the pressure equaliser of the invention, in a mounted state and in a view corresponding to that in  FIG. 7 ;  
         [0026]      FIG. 8   a  is a section through a lock for sealing through bores in the container wall that had been provided to allow the mounting of the embodiment of  FIG. 8 ;  
         [0027]      FIG. 9  is a perspective view of a third embodiment of the pressure equaliser of the invention;  
         [0028]      FIG. 10  is a partial perspective view of a freight container, with the door wings removed;  
         [0029]      FIG. 11  is a perspective view of the embodiment of  FIG. 10  mounted in the rebate of the doorframe of the container of  FIG. 10 ;  
         [0030]      FIG. 12  is a perpendicular section through the frame of the embodiment of  FIG. 9 ;  
         [0031]      FIG. 13  is an axial section of a fourth embodiment of the pressure equaliser of the invention, in a mounted state;  
         [0032]      FIG. 14  is an axial section of a variation of the fourth embodiment of the pressure equaliser of the invention, in a mounted state. 
     
    
     DESCRIPTION OF PREFERRED EMBODIMENTS  
       [0033]     The large freight container of  FIG. 1  is 8×8×20 feet in size. It is of rectangular parallelepipedal form and comprises a base  2 , an first end wall  5  provided with a double wing door (not shown), right  1  (seen from the first end) and left  3  side walls (corrugation not shown on left section  3 ′), a second end wall  4 , and a roof  6 . The container walls are made of corrugated steel plate. The freight container is loaded with boxes  11 ,  12  on pallets. On the inner face of its left side wall  3  first  7 ,  9  and second  8 ,  10  pressure equalisers according to the invention are mounted, each comprising a mounting assembly  9 ,  10  and a collapsible bag  7 ,  8 . The left pressure equaliser  7 ,  9  will now be described in more detail by reference to  FIGS. 2-7 .  
         [0034]     Firstly reference is made in particular to  FIGS. 3, 4  (section C-C in  FIG. 7 ), and  4   a . The mounting assembly  9 , comprises a stud  14  the axis D-D ( FIG. 7 ) of which is disposed perpendicular to the container wall  3 . From the mounted stud  14  extends horizontally a tube  19  disposed about in parallel with the container wall  3 . Its free end  26  facing away from stud  14  is open. Co-axially (axis A-A) and slidingly disposed on the tube  19  is a corrugated hose  15  against which it is sealed by a rubber ring  24  held in the first corrugation at its open end proximal stud  14 . At its other, distal end the hose  15  is closed by a wall  25 . Over a portion of the hose  15  extending from its closed end  25  in the direction of its open end the hose  15  is joined to a neck  16  of hollow truncated prismatic form which carries a bag mounting flange  20  at its base. Where the hose  15  and the neck  16  are joined a portion of the wall of the hose  15  is removed which provides for communication of the interior of the neck/flange portion  16 ,  20  with the lumen of hose  15  and from there with that of the tube  19 . At its open end the collapsible bag  7  is mounted on the flange  20  and held there by a resilient U-profile ring  21 .  
         [0035]     The stud  14  and a portion of the tube  19  extending from it shown in section A-A ( FIG. 4 ) in  FIG. 7 . The bore of stud  14  communicates with the lumen of the tube  19  by opening  32 . The stud  14  is mounted on a flat portion  34  of the left container wall  3  via a mounting disk  35  fixed by snap means  37  to a through bore in the flat container wall portion  34 . The mounting disk  35  is provided with an array of through bores, a central bore  36  and eight peripheral bores  38  disposed in a rectangular pattern around the central bore  36  ( FIG. 6 ). The central bore  36  is penetrated by the treaded end portion  29  of a locking screw  27 , the head  28  of which is sealingly abutting a conical face  31  of the stud  14 . The open end of the stud  14  seals against the mounting disk  35  by means of a polyurethane foam ring  33  mounted in a circular grove disposed at the free end face of stud  14 . At its head face the locking screw  27  carries a grip  30  for turning it by hand. In  FIG. 6  broken circles  39 ,  40 ,  41  indicate the inner and outer contours of sealing ring  33  and the contour of the bore in the container wall portion  34 .  
         [0036]      FIG. 2  illustrates the suspension of the mounting assembly  9  of the invention and the collapsible bag  7 . A substantially flat suspension plate  18  is clamped onto the corrugated hose  15  by a finger  52  thereof so as to circularly enclose the corrugated hose perpendicularly to its axis A-A for an angle of more than 180°. Opposite to the finger  52  the clamping plate  18  is provided with a hook  50  by which it is hung up on a lashing eye  13  of a kind normally provided on the inside wall faces of large freight containers. A support portion  51  disposed beneath the hook  50  abuts the container wall  3  in a mounted position and provides for correct distance of the mounting assembly  9  from the container wall  3 . The sliding relationship of tube  19  and corrugated hose  15  allows the mounting assembly  9  to adapt to varying distances between lashing eyes, such as eye  13 , and through bores in the container wall which determine the mounting position of the stud  14 .  
         [0037]      FIGS. 8 and 8   a  relate to a second embodiment of the mounting assembly of the invention which differs from the first embodiment by the omission of a mounting disk and the provision of the trough bore pattern of  FIG. 6  directly in flat container wall portion  42 , the central bore being identified in the drawing by reference number  46  and peripheral bores by number  48 . In this embodiment the stud  44 , which corresponds to the stud  14  of the first embodiment, abuts directly the flat wall portion  42  via its sealing ring  45 . The stud  44  is fixed at the container wall by a deformable screw  43  secured in the central bore  46 .  
         [0038]     To protect the contents of the container when a pressure equaliser according the aforementioned embodiments of the invention is not mounted the bore(s) in the container wall can be covered by a lock disk in  FIG. 8   a . A lock disk  47  designed to cover the array of bores  46 , 48  provided in the freight container wall for mounting the second embodiment is shown fixed in bores  48  by snap fingers  49 . A corresponding lock disk for use with the first embodiment would have the form of the mounting disk  35  but lack the bores  36 ,  38  thereof. A person skilled in the art will realise that the bores can be arranged in many other useful patterns.  
         [0039]     A third embodiment of the invention is shown in  FIGS. 9-12 . For mounting this embodiment makes use of the door opening of a freight container  60  where leaks are most prone to occur. The pressure equaliser of the third embodiment consists of thin polymer foil  62  in the rough form of a trough, which extends from the inner contour of a rectangular frame  63 . The frame  63  is of a size to make the polymer foil trough  62  fit exactly into the freight container door frame, that is, the inner contour of the frame  63  is substantially superposable to the inner contour of the door opening, and to allow it to be fastened to the rebate  61  of the door. A detailed sectional view of the frame  63  perpendicular to its inner and outer contours is shown in  FIG. 12 . At its peripheral edge the polymer foil trough  62  is clamped between a U-formed sheet of cardboard to which it has been fixed by warming to a melting temperature of the polymer. A flange  66  of the cardboard sheet extends to protect the foil trough  62  against abrasive wear by the doorframe. The face of the cardboard frame  63  facing the rebate  61  is provided with an adhesive  64  which is protected by a ribbon  65  of non-sticking material. Prior to mounting the ribbon  65  is removed.  
         [0040]     A fourth embodiment of the invention is shown in  FIG. 13 . The mounting assembly comprises a stud  114  the axis of which is disposed perpendicular to the container wall  134 . From the mounted stud  114  extends downwards and away from the container wall  134  a funnel-shaped piece  119  ending in a neck  120 . The neck  120  serves for mounting a collapsible plastic bag  107  the wall thickness of which is greatly exaggerated in the Figure. The bag  107  is secured on the neck  120  by a hose clamp  140 . The bore of the stud  114  is in communication with the lumen of the funnel-shaped piece  119 . The stud  114  is mounted on a flat portion of the container wall  134  via a mounting disk  135  fixed by snap means  137  to a through bore in the wall  134 . The mounting disk  135  is provided with an array of through bores, a central bore and eight peripheral bores  138  disposed in a rectangular pattern around the central bore similar to the bore array in  FIG. 6 . The central bore of the array is penetrated by the treaded end portion  139  of a locking screw  127 , the head  128  of which is sealingly abutting a conical face  131  of the stud  114 . The open end of the stud  114  seals against the mounting disk  135  by means of a polyurethane foam ring  133  mounted in a circular grove disposed at the free end face of stud  114 . At its head face the locking screw  127  carries a grip  130  for turning it by hand. In a variation of the mounting assembly of  FIG. 13  the mounting disk  135  can be dispensed with and the screw  127  mounted in the central bore of a bore array corresponding to that in  FIG. 6  or in any other suitable array. In this variation the bore array is arranged directly in the container wall similar to that shown in  FIG. 8 .  
         [0041]     A variation of the fourth embodiment is shown in  FIG. 14 . The mounting assembly comprises a stud  214  the axis of which is disposed perpendicular to the container wall  234 . From the mounted stud  214  extends downwards and away from the container wall  234  a funnel-shaped piece  219  ending in a neck  220 . The neck  220  serves for mounting a collapsible plastic bag  207  the wall thickness of which is greatly exaggerated in  FIG. 14 . The bag  207  is secured on the neck  220  by a hose clamp  240 . The bore of the stud  214  is in communication with the lumen of the funnel-shaped piece  219 . The stud  214  is mounted on a flat portion of the container wall  234  via a mounting disk  235  fixed by snap means  237  to a through bore in the wall  234 . The mounting disk  235  is provided with an array of through bores, a central bore and eight peripheral bores  238  disposed in a rectangular pattern around the central bore  239  similar to the bore array in  FIG. 6 . The central bore  239  of the array is penetrated by the end portion  228  of an L-shaped locking hook from the shaft  227  of which it extends perpendicularly. A threaded portion  229  extending from the free end of the shaft  227  passes through an end wall  231  of the stud  214 . In a mounted state the end wall  231  is disposed about parallel with the container wall  234 ; a wing nut  232  threaded on the threaded portion  229  of the shaft  227  is tightened against the end wall  231  to press the stud  214  against the mounting disk  235 . The open end of the stud  214  seals against the mounting disk  235  by means of a polyurethane foam ring  233  mounted in a circular grove disposed at the free end face of stud  214 . Alternatively the mounting disk  235  can be dispensed with and the hook  227 ,  228  mounted in the central bore or any other bore of a bore array corresponding to that in  FIG. 6  or in any other suitable bore array. In this case the bore array is arranged in the container wall in a manner similar to that shown in  FIG. 8 .