Closing unit for a double toggle molding apparatus and method
The present invention pertains, in general, to machines for the injection molding of plastic materials or for double-toggle die casting, and more specifically, to a closing unit for the die in said machines. 
     Machines for injection molding or for die casting usually comprise a base, four horizontal columns placed above the base according to the vertices of a quadrilateral and passing in a stationary die-holder plate, attached on the base and resting against blocks applied to one end of the columns, in a movable die-holder plate guided on the base and led along the horizontal columns towards and away from the attached die-holder plate, and in a closing or reaction plate positionable on the base and resting against reaction blocks applied to the other end of the columns. 
     In such machines thus structured, the shifts of locking/unlocking in closing the movable die-holder plate against the stationary die-holder plate are realized by means of a common, so-called double-toggle device, using those of the rods and hinged connecting rods which are extended and withdrawn when operated by at least one hydraulic cylinder. According to a known design, the toggles are normally withdrawn towards the axis of the machine, are connected to a movable crosshead plate, and this is led on a pair of additional guide columns placed in parallel between the horizontal columns of the machine. 
     However, it is evident that the presence of a crosshead plate and of additional columns for guiding it complicate the structure of the machine, obstruct a convenient access to the inside of the structure for maintenance or anything else, and having a negative influence on its production costs. 
     The present invention aims to eliminate these disadvantages and to provide a machine for injection molding or for die casting which has a very simple and open structure, is very easy to access and is very economical. 
     In fact, the principal purpose of the present invention is that of providing a machine in which the movable element, to which the toggles are connected, is guided on the machine&#39;s own horizontal columns, thus eliminating the additional guide columns present in the known toggle machines. 
     Another purpose of the invention is to provide a machine of the above-mentioned type in which the toggles at the opening of the machine are withdrawn towards the outside, the movable part to which they are connected may be guided on horizontal columns directly or through interposed elements, and control cylinders may be applied to the movable part or to the reaction plate of the machine. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     In any case, the exemplified embodiments of the invention will be made more evident by the description below with reference to the attached drawings in which: 
     FIG. 1 shows a machine in the closing position and in which the movable part is led directly on horizontal columns, and the hydraulic cylinders are on the edge of said part; 
     FIG. 2 shows a view similar to that in FIG. 1, but in the opening position; 
     FIG. 3 shows a cross section according to the arrows III--III in FIG. 1; 
     FIG. 4 shows a machine in the closing position as that in FIG. 1, but in which the movable part is led on the horizontal columns indirectly; 
     FIG. 5 shows a view of the machine in FIG. 4, but in the opening position; 
     FIG. 6 shows a machine as in FIG. 1 in the opening position, but with toggles placed between the movable part and the movable die-holder plate and control cylinders mounted on the reaction plate; 
     FIG. 7 shows a view of the machine in FIG. 6, but in the opening position; 
     FIG. 8 shows a cross section according to the arrows VIII-VIII in FIG. 6; 
     FIG. 9 shows a machine in the closing position as that in FIG. 6, but with the movable part led on the horizontal columns indirectly; and 
     FIG. 10 shows a view of the machine in FIG. 9, but in the opening position. 
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT 
     In the known manner, a machine for molding plastic materials or for die casting comprises a base 11 above which are horizontally extended four columns 12 displaced according to the vertices of a quadrilateral and passing in a stationary die-holder plate 13, in a movable die-holder plate 14 and in a closing or reaction plate 15, spaced apart in a parallel. The stationary die-holder plate 13 is attached on the base and rests against blocks 16 applied to the adjacent end of the columns 12. The movable die-holder plate 14 is shiftable on the base and along the columns 12 towards and away from the stationary plate for the closing/opening of the die. The closing plate 15 is positionable on the base and rests against reaction blocks 17 applied to the other end of the columns 12. 
     For the shifts of closing/opening of the movable die-holder plate 14 are provided toggle mechanisms 18 controlled by a pair of hydraulic cylinders 19 by means of a movable part 20 to which the toggles 18 are connected. 
     Very precisely and in accordance with the present invention, the movable part is essentially in the form of a control ring 20--FIGS. 1 and 6--placed and shiftable in parallel between the movable die-holder plate 14 and the closing plate 15 and crossed by the four horizontal columns 12 of the machine. 
     In the machine example shown in FIGS. 1, 2 and 3, the control ring 20 is guided and directly shiftable along the columns 12, and each toggle 18, on the one hand, is hinged, in 18a, to the movable die-holder plate 14, and on the other hand, is hinged, in 18b, to the closing or reaction plate 15, and in the intermediate part, is connected to the control ring 20 by means of a connecting rod 18c. The control hydraulic cylinders 19 are attached to two opposite sides of said ring 20, and their shafts 19a are connected to the movable die-holder plate 14. 
     The machine shown in FIGS. 4 and 15 is completely identical to that shown in FIGS. 1-3, with the only difference that the control ring 20 is not guided directly on the columns 12, but on sliding sleeves 21 fixed, and therefore movable, with the movable die-holder plate 14 and extending part of the length of the columns 12 towards the closing plate 15. 
     In both embodiments, the action of the hydraulic cylinders 19 determines a shift either in closing or in opening the movable die-holder plate, and likewise, the shifts are also limited by the control ring 20 for extending the toggle mechanisms 18 for locking in the closing position and withdrawing them in the opening position. In particular, in opening, the control ring recedes somewhat; the toggles 18, moved by the connecting rod 18c, withdraw, turning towards the outside of the machine from the side of the movable plate 14, between this and the closing plate; the movable plate 14 approaches the control ring 20--FIGS. 2 and 5. 
     In practice, the stroke of the control ring 20 along the columns 12 or their sliding sleeves 21 is somewhat brief with respect to that of the movable die-holder plate 14 by closing and opening, the control hydraulic cylinders being on the edge of said ring. 
     In the machine example shown in FIGS. 6, 7 and 8, the control ring 20 is guided directly along the columns 12 as in FIG. 1, but unlike this one, the control hydraulic cylinders 19 are attached to the closing or reaction plate with their shaft 19a connected to said ring, while the toggle mechanisms, in opening, withdraw, turning towards the outside of the machine from the side of said closing plate and in the circle comprised between the ring 20 and the movable die-holder plate. 
     The machine shown in FIGS. 9 and 10 is completely identical to that shown in FIGS. 6-8, with the only difference that the control ring 20 is guided on sliding sleeves 22 attached to the closing or reaction plate 15 and extending part of the length of the columns 12 towards the movable die-holder plate 14. 
     In this embodiment with the toggles in reversed position with respect to the executions in FIGS. 1-5 in the opening and closing phases, the control ring has a very extended stroke, the cylinders always remain attached to the closing plate, and the movable die-holder plate never strictly approaches said ring given the inter-position of the toggles.