Abstract:
A latch apparatus for a blast-resistant container, comprising a chain hook on an edge of the container, a hook seat on a sliding door, a base, a connecting piece, a latch and a nut. The latch has a curved surface next to the hook seat and a front plate with a wedge-shaped cross-section. When the latch is turned into a locked state, the curved surface and front plate thereof push a hook on the chain hook tightly into the hook seat, so that in the locked state the chain hook will not loosen and will expose only a short lever arm, providing improved protection from a blast.

Description:
FIELD OF THE INVENTION  
       [0001]     The present invention relates to a latch apparatus for a blast-resistant container, particularly to a latch apparatus for a blast-resistant container having a latch with a curved surface and a wedge plate which during a locking process push a chain hook tightly into a seat, so that in a locked state the chain hook will not loosen and will expose only a short lever arm, providing improved protection from a blast.  
       DESCRIPTION OF RELATED ART  
       [0002]     As shown in  FIG. 7 , Chinese patent no. CN ZL02230761.3 discloses a strengthened door structure having four sides each being furnished with a hook A and a hook seat C on a sliding door plate B. During a closing movement of the sliding door towards a closing edge (right side in the Fig.), the hook seat C to the right on the sliding door plate B engages with a chain hook D. For convenience of engaging chain hook D and hook seat C, the chain hook D is given a generous angular range. To prevent the chain hook D from disengaging from the hook seat C, which would impair resistance against a blast, at least one latch secures the chain hook D in the engaged position thereof.  
         [0003]     As shown in  FIG. 8 , the engagement structure cited above further has a clamp E attached to the sliding door plate B for preventing the chain hook D from disengaging from the hook seat C. However, this arrangement does not provide for a sufficiently precise movement of the chain hook, and a test of resistance against blasts requires a large amount of time for position checking.  
         [0004]     Referring now to  FIG. 9 , Taiwan patent no. 171592 discloses a latch apparatus comprising a handle F mounted on a sliding door plate B, a latch G, and a supporting spring H, which after releasing the handle F drives automatic closing of the latch apparatus.  
         [0005]     As shown in  FIG. 10 , Taiwan patent no. 197769 discloses a latch apparatus similar to the latch apparatus shown in  FIG. 9 , comprising a handle I and a latch J, but having a wave-shaped plate spring K substituted for the supporting spring for positioning the handle I.  
         [0006]     To summarize, The latch apparatuses shown in  FIGS. 8-10  provide only for blocking in a horizontal direction, preventing the chain hook D from disengaging from the hook seat C, but not for positioning of the chain hook D relative to the hook seat C. Usage and looks of these latch apparatuses are in need of improvement.  
         [0007]     Above conventional latch apparatuses all do not allow to fix the relative positions of the chain hook D and the hook seat C, with a gap left in between. As shown in  FIGS. 11A and 11B . When an explosion occurs in the container. The shock wave will indure extremely high membrane stress on the container structure instantly. If lever arms L 1 &gt;L 2  formed by the chain hook D and the hook seat C. Since the lever arms are relatively large, high bending stress and subsequent damage result, and resistance against blasts is lost.  
       SUMMARY OF THE INVENTION  
       [0008]     It is the object of the present invention to provide a latch apparatus for a blast-resistant container having a latch with a curved surface and a wedge plate which during a locking process push a chain hook tightly into a seat, so that in a locked state the chain hook will not loosen and will expose only a short lever arm, providing improved protection from a blast.  
         [0009]     The present invention can be more fully understood by reference to the following description and accompanying drawings.  
     
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS  
       [0010]     The latch apparatus for a blast-resistant container of the present invention comprises: a door plate  10  with a front side and a rear side; a base  20 ; a connecting piece  30 ; a latch  40 ; a nut  50 ; and a chain hook  60  fastened to an edge of a container. The base  20  and the connecting piece  30  together pass through the doorplate  10 . The latch  40  is mounted on the connecting piece  30 , performing a turning movement thereon. Further details will be explained below.  
         [0011]     A hook seat  11  is fastend on the doorplate  10 . The doorplate  10  has a through hole  12  surrounded by holes  13 .  
         [0012]     The base  20  comprises an axis  21  and a base plate  22  attached thereto. The base plate  22  is placed on the rear side of the door plate  10 , with the axis  21  reaching through the through hole  12 , having a far end with a thread  24  on the front side of the door plate  10 . Positioning holes  23  on the base plate  22  surround the axis  21 .  
         [0013]     The connecting piece  30  comprises a tubelet  31  with a front end and a rear plate  33  attached to the tubelet  31  opposite to the front end thereof. The connecting piece  30  is put over the base  20 , with the tubelet  31  surrounding the axis  21  and the rear plate  33  being set on the front side of the door plate  10 . A step  32  is cut into the tubelet  31  near the front end thereof. The rear plate  33  has a rear side from which several pins  34  extend rearward.  
         [0014]     The latch  40  at a central hole  41  thereof is set on the rear end of the tubelet  31  of the connecting piece  30 . A handle  42  is integrated into the latch  40 . Opposite to the handle  42  the latch has an engaging section with a curved surface  43 . A wedge plate  44  with a wedge-shaped cross section is attached to the latch  40 . The central hole  41  is surrounded by a circular depression  41   a.    
         [0015]     The nut  50  is screwed on the thread  24  of the axis  21  of the base  20 .  
         [0016]     The chain hook  60  is fastened to the container and is, as well as the hook seat  11 , made using conventional art, which does not need to be explained further.  
         [0017]     The present invention is assembled by first having the axis  21  of the base  20  pass through the through hole  12  of the door plate  10 , so that the base plate  22  leans close to the door plate  10  at the rear side thereof. Then the tubelet  31  of the connecting piece  30  is put on the far end of the axis  21 , with the pins  34  passing through the holes  13  in the door plate  10  and the positioning holes  23  of the base  20 , preventing the connecting piece  30  from turning around the axis  21 . After that, the latch  40  is at the central hole  41  thereof set on the tubelet  31  of the connecting piece  30 , allowing the latch  40  to turn around the tubelet  31 . Finally, the nut  50  is put on the far end of the axis  21  and screwed tight on the thread  24  thereof, preventing the latch  40  from separating from the connecting piece  30 .  
         [0018]     As shown in  FIGS. 2A and 2B , in an open state, the latch  40  is placed to the left of the chain hook  60 , with the curved surface  43  thereof leaning against a hook  61  of the chain hook  60 . In this state, the hook  61  is not engaged with a groove  14  of the hook seat  11 . Therefore, the doorplate  10  can be freely opened or closed using the handle  42 .  
         [0019]     Referring to  FIGS. 2C and 2D , in a locked state, the handle  42  has been moved down, as indicated by the arrow, resulting in the curved surface  43  pushing the hook  61  of the chain hook  60  into the groove  14  of the hook seat  11 . At the same time, the wedge plate  44 , due to the shape thereof, pushes the hook  61  close to the hook seat  11 , minimizing a resulting lever arm composed of the hook  61  and the hook seat  11  (see  FIGS. 11A and 11B , L 2 &lt;L 1  ). Thus resistance against a blast is improved.  
         [0020]     In the embodiment shown, the latch  40  undergoes a turning angle of 90 degrees between the open and locked states. By altering the dimensions of the curved surface  43  and the wedge plate  44 , the turning angle is variable.  FIGS. 3A and 3B  show a latch with a turning angle of 180 degrees.  
         [0021]     Referring to  FIG. 4 , in a second embodiment of the present invention, a helical spring  70  is inserted into said circular depression  41   a  of said latch  40 . After the chain hook  60  having entered the groove  14  of the hook seat  11 , the spring  70  stably holds the latch  40 .  
         [0022]     Referring to  FIG. 5 , in a third embodiment of the present invention, the latch  40  has a positioning device  401  for positioning of the latch  40  in several steps. The positioning device  401  comprises several depressions  35  on a peripheral outer surface of the tubelet  31  of the connecting device  30 , a tunnel  45  on the curved surface  43 , which is connected with the central hole  41 , a steel ball  46 , a spring  47 , and a threaded worm  48 . The steel ball  46  and the spring  47  are inserted into the tunnel  45  and held there by the threaded worm  48 . The steel ball  46  is pressed against the peripheral surface of the tubelet  31 . Turning of the latch  40  causes the steel ball  46  to wander around the tubelet  31 , stably remaining in the depressions  35  thereof at certain angular positions of the latch  40 , thus providing angular positioning of the latch  40 .  
         [0023]     Referring to  FIG. 6 , in a fourth embodiment of the present invention, the handle  42  has a handle grip  49  that perpendicularly extends away. In the open state, the handle grip  49  is oriented perpendicular to an opening direction of the doorplate  10 , allowing to open the doorplate  10  by pushing the handle grip  49 .  
         [0024]     The main characteristic of the present invention, as compared to conventional art, lies in that upon closing the door, the latch at the curved surface and wedge plate thereof quickly and precisely pushes the hook into the hook seat, keeping the hook in a tight position, thus achieving maximum resistant against various kinds of blasts.  
         [0025]     While the invention has been described with reference to preferred embodiments thereof, it is to be understood that modifications or variations may be easily made without departing from the spirit of this invention which is defined by the appended claims.  
       BRIEF DESCRIPTION OF THE DRAWINGS  
       [0026]      FIG. 1  is a perspective view of the latch apparatus of the present invention when disassembled.  
         [0027]      FIGS. 2A-2E  are schematic views of the latch apparatus of the present invention with the hook seat and the chain hook disengaged or engaged.  
         [0028]      FIGS. 3A and 3B  are perspective views of the latch of the present invention designed for a turning angle of 180 degrees.  
         [0029]      FIG. 4  is a perspective view of the latch apparatus of the present invention in the second embodiment when disassembled.  
         [0030]      FIG. 5  is a perspective view of the latch apparatus of the present invention in the third embodiment when disassembled.  
         [0031]      FIG. 6  is a perspective view of the latch of the present invention in the fourth embodiment.  
         [0032]      FIG. 7  (prior art) is a side view of a conventional blast-resistant container structure.  
         [0033]      FIG. 8  (prior art) is a perspective view of a chain hook engaged with a hook seat of a conventional latch apparatus.  
         [0034]      FIG. 9  (prior art) is a side view of another conventional latch apparatus.  
         [0035]      FIG. 10  (prior art) is a side view of a further conventional latch apparatus.  
         [0036]      FIG. 11  (prior art) is a schematic illustration of lever arms resulting from the hook seat engaging with the hook of a conventional latch apparatus.