Abstract:
A heat-sealing apparatus includes a packing bag stretcher adapted to stretch open the mouth of the loaded packing bag, and a vacuum pump adapted to draw air out of the loaded packing bag before sealing the loaded packing bag.

Description:
BACKGROUND OF THE INVENTION  
         [0001]    The present invention relates to a heat-sealing apparatus and, more particularly, to such a heat-sealing apparatus, which draws air out of the packing bag when sealing it.  
           [0002]    In order to keep food fresh, a polymeric packing bag may be used to seal food, and a vacuum pump may be used to draw air out of the packing bag when sealing it. Because the top and bottom side edges of the mouth of a polymeric packing bag are normally closely attached to each other, it takes much time to open the mouth and to keep the mouth open when drawing air out of the packing bag. U.S. Pat. No. Re,34,929 discloses a packing bag  1  for use with a vacuum pump  12 . The packing bag  1  has intersected ribs  11  on the inner surface around the mouth. Because of the presence of the intersected ribs  11 , the mouth of the packing bag  1  can easily be opened. However, the manufacturing cost of this particularly designed packing bag  1  is high.  
         SUMMARY OF THE INVENTION  
         [0003]    It is the main object of the present invention present invention to provide a heat-sealing apparatus, which draws air out of the packing bag when sealing it. According to one aspect of the present invention, the bottom shell of the heat sealing apparatus has a top center recess, and a packing bag stretcher supported on a compression spring in the top center recess and adapted to stretch open the mouth of the loaded packing bag for enabling a vacuum pump to draw air out of the loaded packing bag when sealing it. According to another aspect of the present invention, the packing bag stretcher comprises a bearing plate supported on the compression spring, a press plate suspending above the bearing plate for pressing the bottom side edge of the mouth of the loaded packing bag on the bearing plate, two L-shaped clamping plates disposed at two sides of the bearing plate and adapted to clamp the mouth of the loaded packing bag on the press plate, and two torsional springs respectively connected between two sides of the gearing plate and the two L-shaped clamping plates. According to still another aspect of the present invention, the bearing plate has a transversely extended air hole connected to the vacuum pump in the bottom shell by a suction tube for enabling the vacuum pump to draw air out of the loaded packing bag. 
       
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0004]    [0004]FIG. 1 illustrates the application of a polymeric packing bag according to the prior art.  
         [0005]    [0005]FIG. 2 is a perspective view of a heat-sealing apparatus according to the present invention (the top shell excluded).  
         [0006]    [0006]FIG. 3 is an exploded view of the heat-sealing apparatus according to the present invention.  
         [0007]    [0007]FIG. 4 illustrates a polymeric packing bag loaded in the packing bag stretcher according to the present invention. 
     
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT  
       [0008]    Referring to FIGS. 2 and 3, a heat-sealing apparatus in accordance with the present invention comprises a body  100  formed of a top shell  2  and a bottom shell  3 . The top shell  2  is hinged to the bottom shell  3 . An electric heating element  31  is provided in the bottom shell  3  near its front side. The bottom shell  3  has a top center recess  32 , and a through hole  33  in the top center recess  32 . A packing bag stretcher  4  is installed in the bottom shell  3 . The packing bag stretcher  4  comprises a bearing plate  41 , the bearing plate  41  having a vertical bottom rod  44  inserted into the through hole  33  in the top center recess  32  of the bottom shell  3 , a compression spring  45  sleeved onto the vertical bottom rod  44  of the bearing plate  41  and supported between the top center recess  32  and the bearing plate  41 , two L-shaped clamping plates  42  disposed at two sides of the bearing plate  41 , two torsional springs  43  respectively connected between two sides of the bearing plate  41  and the L-shaped clamping plates  42  to hold the L-shaped clamping plates  42  in the non-clamping position, and a press plate  46  suspending above the bearing plate  41 . The press plate  46  has a transversely extended air hole  461 . A vacuum pump (not shown) is installed in the bottom shell  3 , having a suction tube  47  connected to the air hole  461  of the press plate  46 . Further, the size of the bearing plate  41  is slightly smaller than the top center recess  32  of the bottom shell  3 . When assembled, the L-shaped clamping plates  42  are respectively aimed at two opposite vertical sidewalls of the top center recess  32  of the bottom shell  3 .  
         [0009]    Referring to FIGS. from  4  through  6 , when sealing a polymeric packing bag  5 , the bottom side edge of the mouth of the packing bag  5  is attached to the bottom side of the press plate  46  and the top side edge of the mouth of the packing bag  5  is attached to the top side of the press plate  46 , and then the top shell  2  is pressed on the bottom shell  3  to force the press plate  46  downwards against the packing bag stretcher  4 . When pressing the press plate  46  on the packing bag stretcher  4 , the bearing plate  41  is lowered to compress the compression spring  45 , and the L-shaped clamping plates  42  are forced by the two opposite vertical sidewalls of the top center recess  32  of the bottom shell  3  to turn inwards toward each other and to clamp the mouth of the packing bag  5  on the press plate  46 , and at the same time, the vacuum pump in the bottom shell  3  is started to draw air out of the packing bag rapidly. When lowering the top shell  3  to the lower limit position, the top shell  3  gives a pressure to the packing bag  5  against the electric heating element  31 , and therefore the packing bag  5  is sealed when a vacuum is produced in the packing bag  5 .  
         [0010]    A prototype of heat-sealing apparatus has been constructed with the features of FIGS.  2 ˜ 6 . The heat-sealing apparatus functions smoothly to provide all of the features discussed earlier.  
         [0011]    Although a particular embodiment of the invention has been described in detail for purposes of illustration, various modifications and enhancements may be made without departing from the spirit and scope of the invention. Accordingly, the invention is not to be limited except as by the appended claims.