Abstract:
A mold clamping mechanism including a fixed platen and a movable platen is disclosed. The fixed platen includes upper and lower, left and right through-holes for allowing passage of tie-bars therethrough, and a cutout for separating the through-holes into mold-side holes and opposite-mold-side holes. The fixed platen is divided by the cutout into a mold-side part and an opposite-mold-side part. The mold-side part is provided with main leg part connected to the bed.

Description:
FIELD OF THE INVENTION 
       [0001]    The present invention relates to an improvement in a mold clamping mechanism that forms an injection molding apparatus. 
       BACKGROUND OF THE INVENTION 
       [0002]    Generally, an injection molding apparatus is comprised of a bed and a mold clamping mechanism placed on the bed. Mold clamping is performed by the mold clamping mechanism. A resin material is injected into a mold from an injection machine to thereby provide a molded article. Mold clamping mechanisms employing various devices are known (see, e.g., Japanese Utility Model Registration No. 2587035, hereinafter referred to as Patent Literature 1). 
         [0003]    The mold clamping mechanism disclosed in Patent Literature 1 will be described below with reference to  FIG. 10  hereof. 
         [0004]    As shown in  FIG. 10 , the mold clamping mechanism  100  wherein a fixed platen  102  and a pressure receiving platen  103  are secured to a bed  101 , tie-bars  104 ,  104  are disposed to extend between the two platens, a movable platen  105  is mounted to the tie-bars  104 ,  104 , and the movable platen  105  is moved by means of a mold clamping cylinder  106  provided to the pressure receiving platen  103 . 
         [0005]    The mold clamping mechanism disclosed in the registration is featured in the fixed platen  102  having a cutout  107 . In Patent Literature 1, the fixed platen  102  is described as receiving a reaction force and elastically deforming, as shown by a phantom line A, upon mold clamping. However, the present inventors have perceived a contradiction present in the description. 
         [0006]    Such a contradiction will be described with reference to  FIG. 11  hereof. The fixed platen  102  is firmly secured to the bed  101  by a leg part  108 . A vicinity of the leg part  108  has higher rigidity than other parts. As a result, a part shown by a phantom line B deforms only slightly while a part shown by a phantom line C and being remote from the let part  108  deforms largely. A maximum deformation point  109  resides at the center of the phantom line C and is deviated upward from the center of a nozzle  111  of an injection machine. As a result, attachment of the nozzle  111  of the injection machine to the mold becomes unstable whereby disadvantages such as an occurrence of resin leakage, failure in uniform transmission of a mold clamping force, mold deformation and production of defective products are experienced. 
         [0007]    For achieving appropriate or stable attachment of the nozzle  111 , uniform deformation as shown by a phantom line A is required. However, the leg part should not be omitted. 
         [0008]    Consequently, there is a demand for an improvement in the construction of the fixed platen such that while having the leg part connected to the bed, the fixed platen exhibits uniform deformation and does not impart adverse effects of the deformation to the mold and resulting products. 
       SUMMARY OF THE INVENTION 
       [0009]    It is an object of the present invention to provide a mold clamping mechanism with a fixed platen which, while having a leg part to be connected to a bed, deforms uniformly and wherein the deformation does not adversely affects an associated mold and resulting molded products. 
         [0010]    According to the present invention, there is provided a mold clamping mechanism which comprises: a bed; a fixed platen secured to the bed; a pressure receiving platen secured to the bed; upper and lower, left and right tie-bars extending between the fixed platen and the pressure receiving platen; and a movable platen mounted to the tie-bars, the movable platen and the fixed platen capable of being operated to effect clamping of a mold, wherein the fixed platen includes upper and lower, left and right through-holes for allowing passage of the tie-bars therethrough, and a cutout for separating the through-holes into mold-side holes and opposite-mold-side holes, the fixed platen is divided by the cutout into a mold-side part and an opposite-mold-side part, and the mold-side part is provided with main leg part connected to the bed. 
         [0011]    In the invention as arranged above, the fixed platen has the mold-side part and the opposite-mold-side part separated by the cutout. The mold-side part is secured to the bed by means of the main leg part. During mold clamping, the upper and lower, right and left tie-bars are pulled, whereby the opposite-mold-side part deforms uniformly. However, since the mold-side part is separated from the opposite-mold-side part by the cutout, deformation becomes small with the result that the associated force is transmitted uniformly to the mold so that the deformation of the mold and the generation of mal-molding are suppressed. 
         [0012]    Preferably, the mold-side hole has a diameter larger than that of the opposite-mold-side hole. Even when the mold-side part deformed largely, it may not contact the tie-bars. 
         [0013]    Desirably, the opposite-mold-side part is provided with a sub-leg part connected to the bed, the sub-leg part being provided within the left and right through-holes. The sub-leg part is disposed at a position freed from the deformation. This enables fixing of the opposite-mold-side part as well to the bed. 
         [0014]    It is preferred that the sub-leg part have an extension extending toward the injecting machine beyond the opposite-mold-side surface of the opposite-mold-side part. As a result, downfall of the fixed platen can be suppressed. 
         [0015]    Preferably, the mechanism further comprises a connection part connecting the mold-side part and the opposite-mold-side part. The connection part may be comprised of a center part surrounding a sprue; an upward protrusion protruding upward from the center part; a leftward protrusion protruding leftward from the center part; a rightward protrusion protruding rightward from the center part; and a downward protrusion protruding downward from the center part. With is arrangement, it becomes possible to reduce the weight of the fixed platen while maintaining the required rigidity at the connection part. 
         [0016]    Desirably, the downward protrusion comprises at least two strap-shaped protruding parts spaced from each other in a left-and-right direction. 
         [0017]    It is preferred that the upward protrusion be T-shaped and have an orthogonal part extending along an upper side of the mold-side part, that the leftward protrusion be T-shaped and have an orthogonal part extending along a left side of the mold-side part, and that the rightward protrusion be T-shaped and have an orthogonal part extending along a right side of the mold-side part. 
         [0018]    The opposite-mold-side part may be connected to the left and right main leg parts through the left and right connection parts. 
     
    
     
       BRIEF DESCRIPTION OF THE ACCOMPANYING DRAWINGS 
         [0019]      FIG. 1  is a view illustrating in front elevation an injection molding apparatus employing a mold clamping mechanism according to the present invention; 
           [0020]      FIG. 2  is a view of the injection molding apparatus as seen in the direction of arrow  2  of  FIG. 1 ; 
           [0021]      FIG. 3  is a view of a fixed platen as seen in the direction of arrow  4  of  FIG. 2 ; 
           [0022]      FIG. 4  is a cross-sectional view taken along line  4 - 4  of  FIG. 2 ; 
           [0023]      FIG. 5  is a view illustrating the state of distortion of the fixed platen; 
           [0024]      FIG. 6  is a view illustrating an example alteration of the fixed platen; 
           [0025]      FIG. 7  is a cross-sectional view taken along line  7 - 7  of  FIG. 6 ; 
           [0026]      FIG. 8  is a cross-sectional view taken along line  8 - 8  of  FIG. 7 ; 
           [0027]      FIG. 9  is a cross-sectional view taken along line  9 - 9  of  FIG. 7   
           [0028]      FIG. 10  is a view illustrating in front elevation a conventional mold clamping mechanism; and 
           [0029]      FIG. 11  is a view illustrating a problem in the mold clamping mechanism. 
       
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
       [0030]    Preferred embodiments of the present invention will now be described with reference to the accompanying drawings. 
         [0031]    As shown in  FIG. 1 , an injection molding apparatus  10  is comprised of a bed  11 , an injection machine disposed on the bed  11 , and a mold clamping mechanism  30 . 
         [0032]    The injection machine  20  includes a heating cylinder  23  having at its top end a nozzle  21  and a built-in screw, a hopper  24  for supplying a resin material into the heating cylinder  23 , a nut  25  connected to a proximal part of the screw  22 , a threaded shaft  26  threadedly engaged with the nut  25 , and a turning member  27  for turning the threaded shaft  26 , and is configured to inject the resin material out from the nozzle  21 . 
         [0033]    The mold clamping mechanism  30  includes a fixed or stationary platen  40  fixed to the bed  11 , a pressure receiving platen  60  disposed on the bed  11 , tie-bars  32 ,  32  extending between a pressure receiving platen  60  and a fixed or stationary platen  40 , a movable platen  33  movably mounted to the tie-bars  32 ,  32 , a toggle link  34  extending, for moving the movable platen  33 , between the movable platen  33  and the pressure receiving platen  60 , and a toggle driver  35  for driving the toggle link  34 . 
         [0034]    A fixed die  36  is mounted to the fixed platen  40  while a movable die  37  is mounted to the movable platen  33 . A mold  38 , formed by the fixed die  36  and the movable die  37 , is closed and opened by the mold clamping mechanism  30 . 
         [0035]    Of the fixed platen  40 , a part which is proximate to the mold  38  is hereinafter called “mold-side” (first side) while another part which is remote from the mold  38  is hereinafter called “opposite-mold-side” (second side). 
         [0036]    As shown in  FIG. 2 , the fixed platen  40  is in the form of a generally rectangle and has a sprue  41  at a center thereof and a through-hole at each of four corners thereof, namely, a left upper through-hole  42 , a right upper through-hole  43 , a left lower through-hole  44  and a right lower through-hole  45 . 
         [0037]    As shown in  FIG. 3 , the fixed platen  40  includes a mold-side part  47 , an opposite-mold-side part  48  and a constricted connection part  49 . The mold-side part  47  has left and right main leg parts  51 L,  51 R formed integrally. The opposite-mold-side part  48  includes a sub-leg part  52  provided centrally thereof. The sub-leg part  52  has an extension  54  extending beyond an opposite-mold-side surface  53  of the opposite-mold-side part  48  toward the injection machine  20 . 
         [0038]    As shown in  FIG. 4 , the left lower through-hole  44  is separated by a circumferential-groove-shaped cutout  55  into a mold-side hole  56  and an opposite-mold-side hole  57 . The right upper through-hole  43  is also separated by the cutout  55  into the mold-side hole  56  and the opposite-mold-side hole  57 . The left upper through-hole  42  and the right lower through-hole  45  shown in  FIG. 2  are also constructed similarly. The connection part  49  has an octagonal cross-section surrounded by the cutout  55 , as shown by a dashed line. 
         [0039]    The opposite-mold-side hole  57  is set to have a size corresponding to an outside diameter of the tie-bar  32  shown by a phantom line in  FIG. 4 . In contrast, the mold-side hole  56  is set to have a size larger than the outside diameter of the tie-bar  32  so as to leave a gap of t (10-20 mm) with respect to the tie-bar  32 . Consequently, even when the tie-bar  32  is inclined, the tie-bar  32  will not contact a mold-side part  47 . The main leg part  51 L is provided to the mold-side part  47 . 
         [0040]    An operation of the thus-configured fixed platen  40  will now be described. 
         [0041]    As shown in  FIG. 5 , when mold clamping is carried out, the tie-bars  32 ,  32  are pulled and stretched with the result that the injection-side part  48  deforms generally vertically uniformly such that the position of a maximum deformation point P 2  coincides with a generally center  41   a  of the sprue  41 . This enables a satisfactory nozzle attachment. 
         [0042]    On the other hand, because the influence of the deformation of the opposite-mold-side part  48  is relaxed by the cutout  55 , the degree of deformation of the mold-side part  47  becomes small, as shown by phantom line D compared to phantom line E. In particular, the vicinity of the main leg part  51 L, having high rigidity, hardly ever deforms. As a result, deformation of the mold is suppressed and generation of defects in molded products can be prevented. 
         [0043]    Note that the sub-leg part  52  shown in  FIG. 2  may be omitted. However, when there is a concern over downfall of the fixed platen  40 , the sub-leg part  52  may be provided so that the phantom line E can be maintained. Namely, as shown in  FIG. 5 , the opposite-mold-side part  48  receives on large magnitude a tension of the tie-bars  32 ,  32 . The deformation shown by the phantom line E includes the components of the tension of the tie-bars  32 ,  32 . 
         [0044]    If the sub-leg part  52  is provided to the vicinity of the left lower through-hole  44  or the vicinity of the right lower through-hole  45 , as shown in  FIG. 2 , there will appear in  FIG. 5  a large discrepancy between the deformation by the upper tie-bar  32  and the deformation by the lower tie-bar  32 . This is because the lower one exhibits smaller deformation. As a result, the phantom line D may not be obtained. 
         [0045]    To this end, in the present invention, the sub-leg part  52  is provided to an intermediate position between the left lower through-hole  44  and the right lower through-hole  45 , which is remotest from the left lower through-hole  44  and the right lower through-hole  45 , as shown in  FIG. 2 , whereby the phantom line E can be obtained. Provision of the extension  54 , as shown in  FIG. 3 , causes the sub-leg part  52  to protrude largely whereby the fixed platen  40  freed from downfall is provided. 
         [0046]    Next, description will be made as to a modification of the fixed platen with reference to  FIGS. 6 through 9 . 
         [0047]    As shown in  FIG. 6 , the fixed platen  40 B takes the form of a generally rectangle and has a left upper through-hole  42 , a right upper through-hole  43 , a left lower through-hole  44  and a right lower through-hole  45  at four corners thereof. 
         [0048]    Turning now to  FIG. 7 , the left lower through-hole  44  is separated, by the cutout  55  in the form of a circumferential groove, into the mold-side hole  56  and the opposite-mold-side hole  57 . Similarly, the right upper through-hole  43  is separated into the mold-side hole  56  and the opposite-mold-side hole  57  by the cutout  55 . The left upper through-hole  42  and the right lower through-hole  45  shown in  FIG. 7  are also configured similarly. The connection part  49  is surrounded by the cutout  55  into a cross shape as shown by a dashed line. 
         [0049]    As shown in  FIG. 7 , the opposite-mold-side hole  57  is set to have a size corresponding to an outside diameter of the tie-bar  32 , as shown by a phantom line. On the other hand, the mold-side hole  56  is set to be larger than the outside diameter of the tie-bar  32  so as to leave a gap of t (10-20 mm) relative to the tie-bar  32 . Consequently, when the tie-bar  32  is inclined unexpectedly, it will not contact the mold-side part  47 . The main leg part  51 L is provided to the mold-side part  47 . 
         [0050]    Discussion will be made next as to the details of the construction of the connection part  49  with reference to  FIG. 8  which is a cross-sectional view taken along line  8 - 8  of  FIG. 7 . 
         [0051]    As shown in  FIG. 8 , the connection part  49  includes a center part  62  of octagonal shape surrounding the sprue  41 , an upward protrusion  63  protruding upward from the center part  62 , a rightward protrusion  65  protruding rightward from the center part  62 , and a downward protrusion  66  protruding downward from the center part  62 . With this arrangement, it is possible to provide the cutout  55  which is large enough for the through-hole  42  in the vicinity of the latter. Other through-holes  43 - 45  are also provided with such large-enough cutouts  55  in their vicinities. 
         [0052]    Consequently, as described with reference to  FIG. 5 , owing to the cutout  55 , deformation of the mold-side part  47  is minimized because the influence of the deformation of the opposite-mold-side part  48  is minimized or relaxed, whereby production of defective molded products can be kept to a minimum. 
         [0053]    In  FIG. 8 , the downward protrusion  66  is formed of two strap-shaped protruding parts  67 L,  67 R spaced a distance W from each other in a left-and-right direction. Leaving the distance W between the two protruding parts contributes to weight reduction of the platen while enabling maintenance of desired connection rigidity. Alternatively, the downward protrusion  66  may formed of three or more strap-shaped protruding parts. 
         [0054]    The upward protrusion  63  is T-shaped and has at its top end an orthogonal part  63   a  extending along an upper side of the mold-side part  47  while the leftward protrusion  64  is T-shaped and has at its top end an orthogonal part  64   a  extending along a left side of the mold-side part  47 . Similarly, the rightward protrusion  65  may be T-shaped and has at its top end an orthogonal part  65   a  extending along a right side of the mold-side part  47 . With this arrangement, it becomes possible to reduce the weight of the fixed platen  60 B while maintaining the required connection rigidity. The left and right protrusions  64 ,  65  are also constructed similarly. 
         [0055]    Reference is now made to  FIG. 9 , which is a cross-sectional view taken along line  9 - 9  of  FIG. 7 , illustrating the opposite-mold-side part  48  in vertical cross section. Connection parts  68 L,  68 R locally connecting the opposite-mold-side part  48  to main leg parts  51 L,  51 R. Namely, the opposite-mold-side part  48  is preferably connected to the left main leg part  51 L via the left connection part  68 L and to the right main leg part  51 R via the right connection part  68 R. 
         [0056]    Next, the connection part  68 L will be described. 
         [0057]    The connection part  68 L is represented by X-form diagonal lines. It is recommendable to provide the connection part  68 L but it may be omitted, if desired. In case the connection part  68 L is not provided, that portion of the opposite-mold-side part  48  which is proximate to the left lower through-hole  44  deforms easily in a Figure-sheet-front-back direction when an external force is applied in the Figure-sheet-front-back direction to the portion around the left lower through-hole  44 . As a result, the same function (only the opposite-mold-side part  48  deforms) as discussed in relation to  FIG. 5  is achieved easily. 
         [0058]    In contrast, if the connection part  68 L is provided, depending on the form of the connection part  86 L, that portion of the opposite-mold-side part  48  which is proximate to the left lower through-hole  44  becomes hard to warp. 
         [0059]    As a solution, provided between the lower side of the opposite-mold-side part  48  and the mail leg part  41 L is a U-shaped groove  69 L having a required depth and opening leftward. Distance L 2  which is from the center of the left lower through-hole  44  to the bottom of the U-shaped groove  69 L may be set to be larger than a distance L 1  which is from the center of the left lower through-hole  44  to the left side of the opposite-mold-side part  48 . 
         [0060]    Distance L 1  is desirably set to be 0.7-1.0 time the hole diameter d of the left lower through-hole  44 , whilst the distance L 2  may be set to be larger than the distance L 1 , namely, 0.9-1.2 times the hole diameter d of the left lower through-hole  44 . 
         [0061]    Owing to the presence of the distance L 2 , the part in the vicinity of the left lower through-hole  44  easily deforms in the Figure-sheet-front-back direction. The opposite-mold-side part  48  is connected to the mold-side part  47  ( FIG. 7 ) via the connection part  49  extending toward the back side of the Figure sheet. Since the opposite-mold-side part  48  is additionally connected to the left and right main leg parts  51 L,  51 R through the left and right connection parts  68 L,  68 R, there is no concern over the opposite-mold-side part  48  being displaced downward. 
         [0062]    Stated otherwise, provision of the left and right connection parts  68 L,  68 R enables omission of the sub-leg part  52  shown in  FIG. 2 . 
         [0063]    Obviously, various minor changes and modifications of the present invention are possible in light of the above teaching. It is therefore to be understood that within the scope of the appended claims the invention may be practiced otherwise than as specifically described.