Patent Publication Number: US-7586069-B2

Title: Inner box for cooker and method of integrating the same

Description:
BACKGROUND OF THE INVENTION 
     The present invention relates to an inner box for a cooker formed by bonding a plurality of sheets of plate members, particularly relates to an improvement in a bonding portion of a face plate. 
     Conventionally, a plate constitution of an inner box for a cooker is constituted by a front plate  51  having an opening portion, a rear plate  53 , an inner box main body  55  provided between the front plate  51  and the rear plate  53 , and a ceiling plate  57  covering from an upper face thereof as generally shown by  FIG. 9 . 
     In such an inner box main body  55 , as shown by a bonding portion for bonding the front plate  51  and a face plate  61  of the inner box main body  55  in  FIG.10(   a ), an end edge of the opening portion of the front plate  51  is formed with a fold-to-bend portion  59 , and a fold-to-bend portion  63  constituting a V-like shape relative to a face of the front plate  51  and skewedly projected to the face plate  61  of the inner box main body  55  is formed from the fold-to-bend portion  59 . Meanwhile, also at an end portion of the face plate  61  of the inner box main body  55 , similar to the front plate  51 , an end edge thereof is formed with a fold-to-bend portion  65  and a front end portion  65   a  thereof is arranged on an inner side of the fold-to-bend portion  63  to prepare for a calking step. 
     Further, as shown by  FIG. 10(   b ), in the calking step, in a state of supporting a lower side in the drawing of the front plate  51 , while inserting the front end portion  65   a  of the fold-to-bend portion of the face plate  61  into a space between the fold-to-bend portion  63  of the front plate  51  and the front plate  51 , a calking jig, not illustrated, is pressed from above the face plate  61  to the front plate  51  over an entire periphery of the bonding portion for bonding the face plate  61  and the front plate  51 . Thereby, the fold-to-bend portion  63  of the front plate  51  and the fold-to-bend portion  65  of the face plate  61  are brought into close contact with each other by being sandwiched by each other to thereby fix the front plate  51  and the face plate  61  of the inner box main body by end calking (refer to, for example, Japanese Utility Model Publication JP-UM-A-59-172904). 
     However, according to the above-described inner box for a cooker, four sheets of the face plates  61  to be bonded with the front plate  51  of the inner box main body  55  are simultaneously calked to bond to the front plate  51  and therefore, a pressure applied to the calking jig is considerable, further, also an equipment for the calking step becomes large-sized. Therefore, when the face plates  61  are successively bonded to the front plate  51  sheet by sheet instead of simultaneously calking to bond four sheets of the face plates  61  thereto, the calking step can be carried out simply and conveniently without applying the considerable pressure on the calking jig, however, a bonding structure having the above-described constitution poses the following problem. 
     That is, in pressing the face plate  61  of the inner box main body  55  by the calking jig, there is a play between the respective fold-to-bend portions  63 ,  65  in a pressing direction of the front plate  51  in calking, that is, both of the fold-to-bend portions  63 ,  65  are projected in height directions and therefore, a slide amount ΔH in the pressing direction of the face plate  61  is prolonged by pressing in calking. Therefore, when the calking step is carried out in a state of respectively dividing four sheets of the face plates  61  to be bonded with the front plate  51  of the inner box main body  55 , the above-described difference in height of ΔH is produced between the face plate after the calking step and the face plate before the calking step contiguous thereto. By the difference in height, warping is produced in the inner box main body  55  bonded with four sheets of the face plates and also the front plate  51  is bent. When the calking step is continued in a state in which the respective face plates and the front plate are respectively bent in this way, the inner box  55  is finished in a state of the inner box  55  being warped, bent are buckled. 
     Further, there is a case of carrying out a surface treatment of, for example, precoated metal (PCM) or the like on a surface of the front plate  51  and surfaces of the respective face plates  61  of the inner box  55  to meet a request of promoting a beautiful outlook in household electric appliances in recent times. In this case, since the precoated metal is provided with insulating performance, when the faces which are brought into close contact with each other by the calking step are constituted only by insulating faces, the respective face plates  61  are brought into an unconducted state and when a high frequency wave is irradiated into the inner box  55  for cooking, radio wave shielding of the inner box  55  becomes incomplete and leakage of radio wave is brought about. Therefore, shapes of the fold-to-bend portions  63 ,  65  are restricted in view of design since the respective face plates  61  need to be connected electrically. 
     SUMMARY OF THE INVENTION 
     The invention has been carried out in order to resolve the above-described problem and it is an object there of to provide an inner box for a cooker capable of firmly carrying out a calking step for bonding by simple operation without requiring a large-sized equipment and capable of being integrated without a drawback of leakage of radio wave or the like at low cost and a method of integrating the same. 
     The above-described object is achieved by a constitution shown below. 
     (1) An inner box for a cooker which is an inner box for a cooker including a front plate having an opening portion and an inner box main body bonded to a peripheral edge of the opening portion for cooking at inside of the inner box main body, 
     wherein at least either one of the bonding portions of the front plate and the inner box main body is formed with a first fold-to-bend portion constituted by folding to bend an end portion thereof to invert to be brought into close contact therewith and a second fold-to-bend portion constituted by inverting a portion on a side of an end portion of the first fold-to-bend portion with a predetermined clearance therebetween, other of the bonding portions of the front plate and the inner box main body is formed with a flange portion inserted into the clearance between the first fold-to-bend portion and the second fold-to-bend portion, and the bonding portions are constituted by a structure in which the flange portion is inserted into the clearance to be calked to bond. 
     According to the inner box for a cooker, the flange portion on other side is arranged to the clearance between the first fold-to-bend portion and the second fold-to-bend portion on one side to be bonded and calked to bond therewith to thereby fix the front plate and the inner box main body to be sandwiched to fix by the bonding portions. Therefore, the face plates of the inner box main body are calked to bond with the front plate at positions at which the face plates of the inner box main body are brought into contact with the front plate and a positional shift is hardly produced between the face plates and the front plate between before calking and after calking. Further, the face plates and the front plate are dividedly calked to bond without being calked to the entire periphery of the bonding portion in one motion by large pressure and therefore, bonding is carried out by comparatively small pressure. Therefore, the integrating process can be simplified without needing a large amount of equipment investment. 
     (2) In the inner box for a cooker, the second fold-to-bend portion may be formed with a locking hole and the flange portion is formed with a locking projection inserted into the locking hole. 
     According to the inner box for a cooker, a shift in the bonding position is difficult to be brought about by the locking hole at the second fold-to-bend portion on one side to be bonded and the locking projection at the flange portion on other side. 
     (3) The locking projection may be a projection formed by punching. 
     According to the inner box for a cooker, a dowel can be formed by simple pressing without attaching a member separately. 
     (4) Further, insulating films maybe formed on a surface of the front plate on a side opposed to a side of being connected with the inner box main body and an outer side surface of the inner box main body. 
     According to the inner box for a cooker, even when an electrically insulating surface treatment is carried out on the surface of the front plate or the inner box main body, a conductive path is formed and a radio wave shielding effect can be achieved without being influenced by the electrically insulating surface treatment coating. Further, by bringing the locking projection into face contact with an inner peripheral face of the locking hole by calking to bond, conduction can firmly be ensured. 
     (5) According to the present invention, in a method of integrating the inner box for a cooker, end portions of face plates of the inner box main body connected to the front plate are bonded to the front plate individually for the respective face plates. 
     According to the method of integrating the inner box for a cooker, the inner box main body is not warped, further, the calking step can be carried out without requiring a large-sized equipment and fabricating cost can be restrained. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is a partially disassembled outlook perspective view of an inner box for a cooker according to a first embodiment of the invention. 
         FIG. 2  is a partially enlarged view of the inner box for a cooker shown in  FIG. 1  before a calking step. 
         FIG. 3  is a sectional view taken along a line A-A of  FIG. 2 . 
         FIG. 4  is a sectional view showing a behavior after the calking step of  FIG. 2 . 
         FIG. 5  is a partially disassembled outlook perspective view showing a state of a bonding portion after calking. 
         FIG. 6  is a disassembled view of an inner box for a cooker. 
         FIG. 7  is an explanatory view showing an example of bonding an inner box main body and a ceiling plate. 
         FIG. 8  is a sectional view of an example of constituting a locking projection formed at a flange portion by a drawn round hole projection. 
         FIG. 9  is a conceptual perspective view showing a plate constitution of an inner box for a cooker of a prior art. 
         FIGS.10(   a ) and  10 ( b ) illustrate views showing a calking step of the conventional art,  FIG. 10(   a ) is an explanatory view showing a state before being calked to bond and  FIG. 10(   b ) is an explanatory view showing a state after being calked to bond. 
     
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     A detailed explanation will be given of an embodiment of an inner box for a cooker according to the invention and a method of integrating the same in reference to the drawings as follows. 
       FIG. 1  is a partially disassembled outlook perspective view of an inner box for a cooker according to a first embodiment of the invention,  FIG. 2  is a partially enlarged view of the inner box for a cooker shown in  FIG. 1  before a calking step, and  FIG. 3  is a sectional view taken along a line A-A of  FIG. 2 . 
     As shown by  FIG. 1 , an inner box  100  for a cooker according to the first embodiment of the invention is constituted by including an inner box main body  23  comprising a front plate  13  having an opening portion  11 , a bottom plate  15 , a ceiling plate  17 , a rear plate  19 , and a side plate  21 , and when the inner box  100  is formed as a heating chamber of a high frequency cooker as an example of a cooker, the inner box  100  becomes a box member for heating an object to be heated contained at inside of the inner box by irradiating a high frequency wave into the inner box. 
     The front plate  13  is opposed to an opening/closing door, not illustrated, for closing the opening portion  11  (an inserting port of the object to be heated) and is formed with the opening portion  11  at a central portion thereof. A peripheral edge portion of the opening portion  11  is formed with a first fold-to-bend portion  25  constituted by folding to bend to invert an end portion thereof to be brought into close contact with the front plate  13 , and a second fold-to-bend portion  27  constituted by inverting a portion of an end portion side of the first fold-to-bend portion  25  with a predetermined clearance therebetween. Thereby, the first fold-to-bend portion  25  and the second fold-to-bend portion  27  are formed substantially in U-shape. A bonding portion  28  of the faceplate  13  is calked to bond with four sheets of the face plates (the bottom plate  15 , the ceiling plate  17 , and the respective side plates  21 ) of the inner box main body  23 . 
       FIG. 2  shows a conceptual partially enlarged disassembled view of before calking the bonding portion bonded with the inner box main body at the peripheral edge portion of the front plate  13 . 
     An inverted portion  25   a  of the first fold-to-bend portion  25  is brought into close contact with the front plate  13  to promote a rigidity by an increase in a modulus of section. The second fold-to-bend portion  27  is inclined relative to the front plate  13  to open a clearance  29  in a state before calking. Further, the second fold-to-bend portion  27  is formed with a plurality of locking holes  31  in shapes of long holes which act as dowel holes at predetermined intervals along a direction of a peripheral edge of the bonding portion  28 . 
     Meanwhile, a bonding portion of the face plate on a side of the inner box main body  23  is formed with a flange portion  33  inserted into the clearance  29  between the first fold-to-bend portion  25  and the second fold-to-bend portion  27  of the front plate  13 . Further, the flange portion  33  is provided with a plurality of locking projections  35  which act as dowels in correspondence with the locking holes  31  on a side of the front plate  13 . According to the locking projection  35 , the projection can simply be formed by punching by pressing or the like from a rear face (lower side in the drawing) of the flange portion  33 . 
       FIG. 3  shows a section taken along a line A-A of  FIG. 2  when the front plate and the inner box main body are integrated. According to the face plate of the inner box main body  23 , a position of the face plate of the inner box main body  23  in a B direction relative to the front plate  13  is restricted by inserting the flange portion  33  of the bonding portion  28  into the clearance  29  between the first fold-to-bend portion  25  and the second fold-to-bend portion  27  to press in the B direction of the drawing. Further, by pressing a calking jig  37  in a direction of bonding the both under the state, the second fold-to-bend portion  27  of the front plate  13  is pressed to the side of the front plate  13  by fitting to insert the locking projections  35  of the flange portion  33  into the locking holes  31 . As shown by  FIG. 4 , by the calking step, according to the front plate  13  and the face plate of the inner box main body, the first fold-to-bend portion  25 , the flange portion  33 , and the second fold-to-bend portion  27  are brought in to close contact with each other and bonded together substantially in parallel with each other. The locking projections  35  of the flange portion  33  are spread in the locking holes  31  by a pressure and inner peripheral faces of the locking holes  31  and the locking projections  35  are brought into face contact with each other to prevent from being drawn out. Further, by forming the locking hole  31  in the shape of the long hole, a dimensional error in sheet metal drawing is permitted. 
       FIG. 5  shows a state of the bonding portion after calking by a perspective view. When the inner box  10  is used in a high frequency cooker, by constituting a pitch P in the peripheral edge direction of the locking projections  35  and the locking holes  31  to be equal to or smaller than ¼ of a wave length of a high frequency wave, the leakage of radio wave to outside of the box can be prevented. 
     Further, when the inner box  10  is used for a high frequency cooker, in order to achieve a radio wave shielding effect at inside and outside of the box, the respective face plates need to conduct and for that purpose, the bonding portions between the respective face plates need to electrically conduct. However, one surface of each of the front plate  13  and the face plates of the inner box main body  23  is formed with a surface treatment coating having an electrically insulating property of a precoated metal or the like, according to the above-described integrating method of integrating the flange portion  33  into the clearance  29  between the first fold-to-bend portion  25  and the second fold-to-bend portion  27 , both of the front plate  13  and the face plates of the inner box main body  23  are brought into contact with each other on sides of insulating faces thereof to bring about an unconducted state. Hence, the both can be brought into a conducted state by providing the locking holes  31  and the locking projections  35  inserted there into as shown by  FIG. 4 . 
     That is, the inner peripheral face of the locking hole  31  shown in  FIG. 4  is not formed with a surface treatment coating (insulating film)  41  to constitute a conducted face. Further, a surface on a side of projecting the locking projection  35  is a face on a side opposed to a side of forming the surface treatment coating  41  and is a matrix metal face having a conductivity. Therefore, by bringing the locking projection  35  having the conducted face into contact with the inner peripheral face of the locking hole  31  constituting the conducted face, the front plate  13  and the face plate of the inner box main body  23  are electrically connected and an excellent radio wave shielding effect is achieved. 
     Further, with regard to the locking hole  31  and the locking projection  35 , when it is not necessary to electrically connect the face plates to be bonded and a problem of a positional shift, a bonding strength or the like is not severe at all, there may be constructed a constitution dispensing with the locking hole  31  and the locking projection  35 . In this case, a simple bonding structure can be constituted. 
     Next, an explanation will be given of a method of integrating the above-described inner box for a cooker. 
       FIG. 6  shows a disassembled view of the inner box for a cooker and  FIG. 7  shows an example for bonding the inner box main body and the ceiling plate. 
     The inner box main body  23  is formed by constituting a frame member having a section in a rectangular shape by the side plates  21 ,  21  and the bottom plate  15  by pressing one sheet plate and bonding the ceiling plate  17  to a side of an opening of the frame member (an upper face in the drawing) by calking to bond or welding by spot welding, or by engaging a locking claw  43  and a locking hole  45  as shown in  FIG. 7 . The inner box main body  23  bonded with the four faces is made to overlap the peripheral edge portion of the opening portion  11  of the front plate  13  to bring respective end portions of the four faces into a meshed state as shown by  FIG. 3 . That is, there is constituted a state of inserting the flange portions  33  of the respective face plates of the inner box main body  23  into the clearances  29 . Further, sides thereof are successively calked to bond by the calking jig side by side. 
     According to such an integrating method, even when the sides are successively calked to bond side by side, the sides are not shifted relative to contiguous ones of the face plates in the height direction as mentioned above and therefore, the sides can be bonded without producing warping by the height shift. Further, the pressure required for the calking step is made to be smaller than that in the case of simultaneously calking to bond the four sides to the front plate  13  after bonding four sheets of the face plates of the inner box main body  23 . Therefore, the calking step can be carried out by a small-sized pressing apparatus, large-sized formation of the calking apparatus is restrained and an integrating step can be carried out at low cost. Further, with regard to the method of integrating the inner box main body  23 , other than the above-described method, a section in a shape of a square cylinder may be constituted by pertinently bonding the face plate to the frame member having three sides of square, further, the invention is not limited to the section having tree sides but the section in the shape of the square may finally be formed by pertinently combining single sheets of the face plates or two sheets or more of the face plates. That is, the inner box main body  23  may be integrated by a most pertinent method from various integrating methods in consideration of a purpose of use, a material, a fabrication efficiency or the like of the inner box, and even a method other than the integrating method exemplified in the embodiment can be provided to the invention without hindrance. 
     According to the inner box for a cooker explained as described above, in bonding plate members in right angle as in bonding the face plate of the inner box main body  23  to the front plate  13 , whereas at least either one of the bonding portions of the front plate  13  and the inner box main body  23  is formed with the first fold-to-bend portion constituted by folding to bend the end portion to invert to be brought into close contact therewith and the second fold-to-bend portion constituted by inverting the portion on the side of the end portion of the first fold-to-bend portion with the predetermined clearance therebetween, other of the bonding portions of the front plate  13  and the inner box main body  23  is formed with the flange portion inserted into the clearance between first fold-to-bend portion and the second fold-to-bend portion and the bonding portions of the front plate  13  and the inner box main body  23  are constituted by the structure in which the flange portion is inserted into the clearance to be calked to bond, thereby, the calking step can be carried out without requiring a large-sized equipment and fabricating cost can be restrained. 
     That is, there is provided the calking step of bringing the second fold-to-bend portion  27  into press contact with the first fold-to-bend portion  25  via the flange portion  33  in a state in which the flange portion  33  is brought into contact with the first fold-to-bend portion  25  which has already been formed to fold to bend and therefore, calking is carried out at a position at which the face plate of the inner box main body  23  is brought into contact with the front plate  13  and there is hardly a positional shift between the face plate and the front plate  13  between before calking and after calking. That is, no influence is effected to the contiguous face plate. Further, calking is not carried out in one motion to the entire periphery of the bonding portion by the large pressure but calking is carried out separately and therefore, bonding is carried out by comparatively small pressure. Therefore, an integrating process can be simplified without needing a large amount of equipment investment. 
     Further, the second fold-to-bend portion  27  is formed with the locking hole  31 , the flange portion  33  is formed with the locking projection  35  to be inserted into the locking hole  31  and therefore, even when an unconductive surface treatment is carried out on the surface of the front plate  13  or the inner box main body  23 , a conductive path is formed by the locking hole  31  of the front plate  13  and the locking projection  35  of the flange portion  33 , the radio wave shielding effect can be achieved without being influenced by the insulating surface treatment coating. Further, by bringing the locking projection  35  into face contact with the inner peripheral face of the locking hole  31  by calking, conduction can firmly be ensured. Further, by both of the locking hole  31  and the locking projection  35 , the shift in the bonding position is difficult to be brought about. 
     Next, an explanation will be given of a second embodiment of an inner box for a cooker according to the invention.  FIG. 8  is a sectional view of an example for constituting a locking projection formed at a flange portion by a drawn round hole projection. According to the embodiment, a drawn round hole projection  47  having an opening hole is formed at an end portion of a face plate of a inner box main body by drawing and the drawn round hole projection  47  is inserted into the locking hole  31  of the front plate  13  to be calked to bond. In this way, the shape of the locking projection may be constituted by a shape brought into contact with the inner peripheral face of the locking hole  31  to lock to thereby achieve operation and effect similar to above-described. 
     Further, the inner box for a cooker according to the invention is not limited to the above-described embodiments but can pertinently be modified or improved. For example, similar operation and effect are achieved even when the front plate  13  is formed with the flange portion and the respective face plates of the inner box main body are formed with the first fold-to-bend portions and the second fold-to-bend portions to combine. 
     According to the inner box for a cooker of the invention, whereas at least one of the bonding portions of the front plate and the inner box main body is formed with the first fold-to-bend portion constituted by folding to bend the end portion to invert to be brought into close contact therewith and the second fold-to-bend portion constituted by inverting the portion of the side of the end portion of the first fold-to-bend portion with the predetermined clearance therebetween, other of the bonding portions of the front plate and the inner box main body is formed with the flange portion inserted into the clearance between the first fold-to-bend portion and the second fold-to-bend portion and the bonding portions of the front plate and the inner box main body are constituted by the structure of inserting the flange portion into the clearance to be calked to bond, thereby, the positional shift of the face plate is not brought about between before and after the calking step and the calking step can simply be carried out. 
     Further, according to the method of integrating the inner box for a cooker, by bonding four sheets of the face plates to be connected with the front plate to the front plate individually for the respective face plates, the calking step can be carried out by a comparatively small pressure without requiring a large-sized equipment and the fabricating cost can be restrained.