Abstract:
The invention provides an injection molding machine that prevents inclination of a stationary platen by a nozzle touch force. A groove is formed in a base along the axis of injection. Protrusions are provided on both lateral sides of the stationary platen. A bottom of the stationary platen is fixed on a bottom of the groove and bottoms of the protrusions are fixed on tops of ridged formed at opposite sides of the groove. A nozzle touch force applied by a nozzle provided on the front of a screw cylinder is applied against substantially the center portion of the stationary platen. A distance in the direction of height from the bottoms of the protrusions that fixedly mount the stationary platen on the base to the height position of the nozzle touch force is smaller than when the stationary platen is not fixedly mounted on the base using protrusions, and therefore the moment exerted by the nozzle touch force that attempts to incline the stationary platen is smaller than it would be otherwise, preventing the stationary platen from inclining.

Description:
BACKGROUND OF THE INVENTION 
   1. Field of the Invention 
   The present invention relates to an injection molding machine, and more particularly to an injection molding machine designed to prevent a stationary platen from inclining due to a nozzle touch force from an injection unit. 
   2. Description of the Related Art 
     FIGS. 6   a ,  6   b  and  7  are diagrams illustrating the conventional injection molding machine, and specifically a mold clamping mechanism thereof.  FIG. 6   a  shows a front view of the injection molding machine,  FIG. 6   b  shows a view from the right side as seen from the front in  FIG. 6   a , and  FIG. 7  shows a perspective view. 
   A conventional mold clamping mechanism of the injection molding machine comprises a stationary platen  20  fixedly mounted along its bottom edge on a base  1  of the injection molding machine, a rear platen  40  set on the base  1  by rear platen support members  9 , a plurality of (four) tie bars connecting the stationary platen  20  and the rear platen  40 , a movable platen  30  set on the base  1  by a movable platen support member  8 , and a drive mechanism, not shown, that moves the movable platen  30 . 
   A stationary-side mold, not shown, is mounted on the stationary platen  20 , a movable-side mold, not shown, is mounted on the movable platen  30 , and the movable platen  30  is moved toward the stationary platen  20  by the drive mechanism to close the mold and then clamp it. In addition, an injection unit is disposed on the side of the stationary platen  20  away from the movable platen  30 , the injection unit is advanced and a nozzle at the front of a screw cylinder  6  is pressed against a sprue bushing on the fixed-side mold, a nozzle touch force is applied, an injection screw is advanced and melted resin is injected into the clamped mold. It should be noted that, in  FIGS. 6   a ,  6   b  and  7 , reference numeral  7  indicates a nozzle touch drive shaft that advances the injection unit and touches the nozzle at the front of the screw cylinder  6  against the fixed mold. 
   The stationary platen  20  is fixedly mounted all along one edge (its bottom edge) on the base  1 , against a central portion of which the nozzle touch from the screw cylinder  6  is applied. If, as shown in  FIG. 6   a , a height (length) from the bottom edge of the stationary platen  20  (where the stationary platen  20  is continuously fixedly mounted on the base  1 ) to the point at which the nozzle touch force acts is L 1 , and the nozzle touch force from the screw cylinder  6  is F, then a moment L 1 ×F is applied to the stationary platen  20 , which tends to cause the stationary platen  2  to tilt toward the movable platen  30  and incline. Consequently, to prevent this inclination a variety of countermeasures have been proposed. 
   Known stationary platen inclination countermeasures include providing a rib on the lower part of the nozzle touch side of the stationary platen and connecting a support provided on the base with the rib to prevent the stationary platen from inclining (JP 2000-289069A); providing extensions that project toward the injection unit side from both ends of the bottom of the stationary platen and fixedly mounting the extensions on the base to prevent the stationary platen from inclining (JP 2003-25378A); and providing multiple (two) nozzle drive units arranged symmetrically around the central axis of the injection nozzle and composed of rod-shaped moving screws, tubular fixed shafts the base end parts of which are fixed to a stationary platen, and fixing nuts combined with the screws, with the screws rotated to advance the injection nozzle against the stationary platen as the nozzle touch force is balanced to prevent inclination of the stationary platen (JP 09-234765A). 
   SUMMARY OF THE INVENTION 
   The present invention provides an injection molding machine capable of preventing inclination of the stationary platen due to the effect of nozzle touch force using inclination prevention means that are different from the conventional stationary platen inclination prevention means described above. 
   According to one aspect of the present invention, an injection molding machine comprises: a base; a mold clamping mechanism arranged on the base and including a stationary platen, a rear platen, tie bars connecting the stationary platen and the rear platen, and a movable platen arranged movable close to and apart from the stationary platen along the tie bars, so that a mold is clamped between the stationary platen and the movable platen; and an injection cylinder having a nozzle at an end thereof and arranged movable along an injection axis so that the nozzle is brought into contact with and pressed against a sprue of the mold clamped by the mold clamping mechanism in performing an injection operation, wherein the base has a groove along the injection axis to form ridges at opposite sides of the groove, and the stationary platen has a pair of protrusions on lateral sides thereof, a lower portion of the stationary platen under the protrusions is inserted into the groove, and bottom surfaces of the protrusions are fixed on top surfaces of the ridges. 
   A bottom surface of the stationary platen may be fixed on a bottom surface of the groove. Further, side surfaces of the stationary platen may be fixed on side surfaces of the groove. 
   According to another aspect of the present invention, an injection molding machine comprises: a base; a mold clamping mechanism arranged on the base and including a stationary platen, a rear platen, tie bars connecting the stationary platen and the rear platen, and a movable platen arranged movable close to and apart from the stationary platen along the tie bars, so that a mold is clamped between the stationary platen and the movable platen; and an injection cylinder having a nozzle at an end thereof and arranged movable along an injection axis so that the nozzle is brought into contact with and pressed against a sprue of the mold clamped by the mold clamping mechanism for performing an injection operation, wherein the base has a groove along the injection axis to form ridges on opposite sides of the groove, and a lower portion of the stationary platen is inserted into the groove, and side surfaces of the lower portion of the stationary platen are fixed to side surfaces of the groove. In this case also, a bottom surface of the stationary platen may be fixed on a bottom surface of the groove. 
   In the above structure of the injection molding machine, a bottom surface of the rear platen and a bottom surface of the movable platen may be in contact with a bottom surface of the groove directly or through support members. 
   Side surfaces of the rear platen and side surfaces of the movable platen may be in contact with side surfaces of the groove. 
   The rear platen may have a pair of protrusions on lateral sides thereof, and bottom surfaces of the protrusions may be in contact with top surfaces of the ridges directly or through support members. 
   The movable platen may have a pair of protrusions on lateral sides thereof, and bottom surfaces of the protrusions of the movable platen may be in contact with top surfaces of the ridges directly or through support members. 
   A depth of the groove may be substantially equal to or less than a distance between a bottom of the mold clamping mechanism and ones of the tie bars closest to the base. 
   A depth of the groove may be substantially equal to a distance between a bottom of the mold clamping mechanism and a position where the nozzle of the injection cylinder is brought into contact with the sprue of the mold. 
   With an injection molding machine having the structure described above, the moment exerted by the nozzle touch force that attempts to incline the stationary platen is smaller than it would be otherwise, preventing the stationary platen from inclining. In addition, the lower portions of the movable platen and the rear platen are inserted into the groove and movable in contact with the sides of the groove so as to keep the stationary platen, the movable platen and the rear platen parallel to each other. 

   
     BRIEF DESCRIPTION OF THE DRAWINGS 
       FIGS. 1   a  and  1   b  are diagrams showing front and side views illustrating the general structure of a first embodiment of the present invention; 
       FIG. 2  is a diagram showing a perspective view of a mold clamping mechanism of the first embodiment; 
       FIGS. 3   a  and  3   b  are diagrams showing front and side views illustrating the general structure of a second embodiment of the present invention; 
       FIG. 4  is a diagram showing a perspective view of a mold clamping mechanism of the second embodiment; 
       FIG. 5  is a diagram showing a perspective view of the first embodiment of the present invention with a cover provided on the mold clamping mechanism; 
       FIGS. 6   a  and  6   b  are diagrams showing front and side views illustrating the general structure of the mold clamping mechanism of the conventional injection molding machine; and 
       FIG. 7  is a diagram showing a perspective view of the mold clamping mechanism of the conventional injection molding machine. 
   

   DETAILED DESCRIPTION 
   A detailed description will now be given of embodiments of the present invention, with reference to the accompanying drawings. 
     FIGS. 1   a ,  1   b  and  2  are diagrams illustrating the general structure of an injection molding machine of a first embodiment of the present invention, focusing on a mold clamping mechanism thereof.  FIG. 1   a  shows a front view,  FIG. 1   b  is a side view as seen from the right in  FIG. 1   a , and  FIG. 2  is a perspective view thereof. Elements in  FIGS. 1   a ,  1   b  and  2  that are the same as those of the conventional injection molding machine shown in  FIGS. 6   a ,  6   b  and  7  are given the same reference numerals and a description thereof omitted. 
   The difference between the first embodiment of the present invention and the conventional injection molding machine is that a recess or groove  10  is provided on the base  1  to form ridges at opposite sides of the groove and the mold clamping mechanism is placed on the groove  10  and the ridges. 
   As shown in  FIGS. 1   b  and  2 , the groove  10  is formed in the base  1  along an axis of injection. Protrusions  2   a  are provided on both lateral sides of the stationary platen  2 . The stationary platen  2  is fixedly mounted on the bottom of the groove  10  of the stationary platen  2  and the bottoms of the pair of protrusions  2   a  are fixedly mounted on the tops of the ridges  10   a.    
   Protrusions  4   a  are also provided on both lateral sides of a rear platen  4  coupled to the stationary platen  2  by multiple (four) tie bars  5 , with the bottoms of the pair of protrusions  4   a  set on the tops of the ridges  10   a  by rear platen support members  9 , and further, the bottom of the rear platen  4  is set on the bottom of the groove  10 . In other words, the bottoms of the rear platen  4  and the protrusions  4   a  are set on the bottom of the base  1  and on the tops of the ridges  10   a , respectively, and in this first embodiment the bottoms of the protrusions  4   a  rest on support members  9  set on the base  1 . However, the bottom of the rear platen  4  also may rest on support members  9  and set on the bottom of the groove  10 , and either or both the bottom of the rear platen  4  and the bottoms of the protrusions  4   a  may rest on support members  9  that rest on the base  1 . Alternatively, the bottom of the rear platen  4  and the bottoms of the protrusions  4   a  may be set directly on the base  1  without providing support members  9 . 
   In addition, protrusions  3   a  may also be provided on both lateral sides of a movable platen  3  disposed between the stationary platen  2  and the rear platen  4 , and the movable platen  3  set on the bottom of the groove  10  and the bottoms of the pair of protrusions  3   a  set on the tops of the ridges  10   a  through movable-platen support members  8 . It should be noted that in the case of the movable platen  3  as well, either or both the bottom of the movable platen  3  and the bottoms of the protrusions  3   a  may be placed indirectly on the base  1  by support members or both the movable platen  3  and the protrusions  3   a  may be placed directly on the base  1  without providing support members. It should be noted that, in  FIGS. 1   a ,  1   b  and  2 , the stationary platen  2 , the movable platen  3 , the rear platen  4  and the tie bars  5  of the mold clamping mechanism are shown but the drive mechanism that moves the movable platen  3  is omitted. 
   In the first embodiment, although the rear platen  4  and the movable platen  3 , like the stationary platen  2 , are also provided with protrusions  4   a  and  3   a , respectively, it is not necessary that these protrusions  4   a ,  3   a  be provided. Thus, alternatively, the bottoms of the rear platen  4  and the movable platen  3  may be set directly on the bottom of the groove  10  or indirectly through support members, without providing protrusions  4   a ,  3   a . Furthermore, where protrusions  4   a ,  3   a  are provided and the rear platen  4  and the movable platen  3  are supported on the base  1  by the protrusions  4   a ,  3   a , it is not necessary to support the bottoms of the rear platen  4  and the movable platen  3  with the bottom of the groove  10 . 
   In the first embodiment shown in  FIGS. 1   a ,  1   b  and  2 , the depth of the groove  10  is such as to accommodate the lower tie bars  5  (that is, the tie bars on the base  1  side), so that the tie bars  5  do not interfere with removal of the finished product from the mold. It should be noted that although the depth of the groove of the groove  10  is approximately the same as the height of the lower tie bars  5 , alternatively the groove  10  may be of any depth that does not interfere with the removal of the finished product from the mold. 
   In  FIGS. 1   a ,  1   b  and  2 , reference numeral  6  indicates a screw cylinder of an injection unit and  7  indicates a nozzle touch drive shaft for moving the injection unit when pressing a nozzle provided on the front of the screw cylinder  6  against a sprue bushing on a mold mounted on the stationary platen  2  so as to seat the nozzle against the sprue bushing (nozzle touch). 
   The nozzle touch drive shaft  7  is driven to advance the injection unit, the nozzle mounted on the front of the screw cylinder  6  is contacted against the mold mounted on the stationary platen  2  and a nozzle touch force F is applied. In addition, the mold clamping mechanism is driven and the movable platen  3  advances along the tie bars  5 , the molds mounted on the stationary platen  2  and the movable platen  3  are clamped together, the injection unit is driven, an injection screw is advanced, and metered and kneaded melted resin is injected into the mold. Thereafter the resin is pressurized, cooled, the movable platen  3  withdrawn, the mold opened and the finished product removed from the interior of the mold. This injection molding process is no different from the conventional injection molding process. 
   In this first embodiment of the present invention, even though the nozzle touch force F is applied against substantially the center of the stationary platen  2 , since the stationary platen  2  is fixedly mounted on the base  1  by the protrusions  2   a , if the height distance from the bottoms of the protrusions fixedly mounted on the base  1  to the position at which the nozzle touch force is exerted as shown in  FIG. 1   a , then the moment exerted in the stationary platen  2  is L 2 ×F. 
   Compared to the conventional injection molding machine shown in  FIGS. 6   a ,  6   b  and  7 , the position at which the stationary platen  2  is fixedly mounted on the base  1  in the first embodiment is moved toward the nozzle touch force effect side by a distance equal to the depth of the groove  10 , such that L 2 &lt;L 1 . Accordingly, the moment exerted on the stationary platen  2  in the conventional injection molding machine that was L 1 ×F becomes L 2 ×F, in other words decreases (since L 2 ×F&lt;L 1 ×F), and therefore tilt or inclination of the stationary platen  2  can be prevented. 
     FIGS. 3   a ,  3   b  and  4  are diagrams illustrating the general structure of an injection molding machine according to a second embodiment of the present invention.  FIG. 3   a  shows a front view,  FIG. 3   b  is a side view as seen from the right in  FIG. 3   a , and  FIG. 4  is a perspective view thereof. Elements in  FIGS. 1   a ,  1   b  and  2  that are the same as those of the conventional injection molding machine shown in  FIGS. 6   a ,  6   b  and  7  are given the same reference numerals. 
   The only difference between the second embodiment of the present invention and the first embodiment shown in  FIGS. 1   a ,  1   b  and  2  is that the depth of the groove  10  is increased. 
   In this second embodiment, a groove  10 ′ is formed deep in the base  1 . As shown in  FIG. 3   b , the surface of attachment between the bottoms of a pair of protrusions  2   a ′ provided on both lateral sides of a stationary platen  2 ′ and the tops of ridges  10   a ′ is arranged at the same height as the position at which the nozzle provided at the front of the screw cylinder  6  contacts the mold mounted on the stationary platen  2 ′. The remainder of the structure of the second embodiment is identical to that of the first embodiment. 
   The bottom of the stationary platen  2 ′ is fixedly mounted on the bottom of the groove  10 ′ and the bottoms of the protrusions  2   a ′ provided on both lateral sides of the stationary platen  2 ′ are fixedly mounted on the tops of the ridges  10   a ′. Moreover, the bottom of a rear platen  4 ′ also is set on the bottom of the groove  10 ′, and the bottoms of a pair of protrusions  4   a ′ are set on the tops of the ridges  10   a ′ through support members  9 . 
   In addition, a movable platen  3 ′ also is set on the bottom of the groove  10 ′ and the bottoms of a pair of protrusions  3   a ′ are set on the tops of the ridges  10   a ′ through support members  8 . 
   It should be noted that, as with the first embodiment, in this second embodiment as well the bottoms of the rear platen  4 ′ and the movable platen  3 ′ may be set directly or through support members on the groove  10 ′. In addition, the pairs of protrusions  4   a ′,  3   a ′ of the rear platen  4 ′ and the movable platen  3 ′, respectively, may be set directly or through support members on the tops of the ridges  10   a ′. It should be noted that, in the second embodiment as well, the bottoms of the rear platen  4 ′ and the movable platen  3 ′ may simply be set directly or through support members on the bottom of the groove  10 ′ without providing protrusions  4   a ′,  3   a ′ on the rear platen  4 ′ and the movable platen  3   a ′. Moreover, if the rear platen  4 ′ and the movable platen  3 ′ are supported on the base  1  by protrusions  4   a ′,  3   a ′, it is not necessary to support the rear platen  4 ′ and the movable platen  3 ′ with the bottom of the groove  10 ′. 
   In the second embodiment, the position at which the protrusions  2   a ′ of the stationary platen  2 ′ are fixedly mounted on the base  1  is at the same height as the position at which the nozzle touch force F is applied to the stationary platen  2 ′ from the nozzle of the screw cylinder  6 , and thus the height distance L 3  between the two is 0. Therefore, the moment exerted on the stationary platen  2  by the nozzle touch force F is L 3 ×F=0×F=0, thereby eliminating any tilt or inclination of the stationary platen  2 ′ due to the nozzle touch force F. However, in this second embodiment, the sides of the base  1  extend to the height of the center of the stationary platen  2 ′, which hinders removal of the finished product from the mold. Accordingly, this second embodiment is suitable for types of injection molding machines in which the finished product is removed from above. 
   It should be noted that in the first and second embodiments described above the bottom of the stationary platen  2 ,  2 ′ is fixedly mounted on the bottom of the groove  10 ,  10 ′. Alternatively, however, provided that the joints are of sufficient strength, only the bottoms of the protrusions  2   a ,  2   a ′ may be fixedly mounted on the tops of the ridges  10   a ,  10   a ′, without fixedly mounting the bottom of the stationary platen  2 ,  2 ′ at the bottom of the groove  10 ,  10 ′. 
   In addition, together with fixedly mounting only the bottoms of the protrusions  2   a ,  2   a ′ on the tops of the ridges  10   a ,  10   a ′, the lateral sides of the stationary platen  2 ,  2 ′ inserted into the groove  10 ,  10 ′ below the protrusions  2   a ,  2   a ′ may be fixedly mounted to the sides of the groove  10 ,  10 ′. For greater strength, the bottoms of the protrusions  2   a ,  2   a ′ and the bottom and lateral sides of the stationary platen  2 ,  2 ′ may be fixedly mounted on the tops of the ridges  10   a ,  10   a ′, the bottom and the sides of the groove  10 ,  10 ′, respectively. 
   In addition, the sides of the stationary platen  2 ,  2 ′ inserted in the groove  10 ,  10 ′ may be fixedly mounted on the sides of the groove  10 ,  10 ′ without providing protrusions  2   a ,  2   a ′ on the stationary platen  2 ,  2 ′. Further, fixedly mounting the bottom of the stationary platen  2 ,  2 ′ mounted on the bottom of the groove  10 ,  10 ′ so as to further strengthen the attachment of the stationary platen  2 ,  2 ′ to the groove  10 ,  10 ′ enables the same effects as with the first and second embodiments described above to be achieved. 
   Thus, as described above, the first and second embodiments reduce or eliminate the moment acting on the stationary platen by the nozzle touch force, thereby reducing or eliminating inclination of the stationary platen. These embodiments also further enable forward inclination of the movable platen to be improved, for the following reason. When the mold is mounted on the movable platen, the weight of the mold tends to tilt the movable platen forward. However with the first and second embodiments described above, the height at which the movable platen  3 ,  3 ′ is supported on the base  1  by the protrusions  3   a ,  3   a ′ approaches (or is the same as) the height of the center of the movable platen, which has the effect of reducing the influence of the weight of the mold on the movable platen  3 ,  3 ′, enabling the present invention to provide an inexpensive, accurate mold clamping mechanism. 
   In addition, the lower parts of the rear platen  4 ,  4 ′ and the movable platen  3 ,  3 ′, which move attached to the groove  10 ,  10 ′ by protrusions  4   a ,  4   a ′ and  3   a ,  3   a ′, respectively, and slide along the sides of the groove  10 ,  10 ′ as they moving. Thus, the movement of the rear platen  4 ,  4 ′ and the movable platen  3 ,  3 ′ are guided by the sides of the groove  10 ,  10 ′ so as to keep the stationary platen, the movable platen and the rear platen parallel to each other. 
   In addition, although not shown, a portion of the drive mechanism that moves the movable platen  3 ,  3 ′ also can be disposed within the groove  10 ,  10 ′, allowing a mold clamping mechanism safety cover like that indicated by the dashed-and-dotted line shown in  FIG. 5  to be made more compact. It should be noted that  FIG. 5  shows an example of a cover  11  is provided on the first embodiment of the present invention. In  FIG. 5 , reference numeral  11   a  indicates a port for the removal of the finished product.