Abstract:
An assembly for the compression molding of articles made of plastic material, composed of a main male plug and a complementary male plug which comprise a stem, actuated by an actuation element with a spindle guided in a tubular tang provided with a molding head cooperating with the main male plug; a first spring, arranged on the spindle acting between a collar of the spindle and the tubular tang; a second spring, arranged on the spindle acting on the collar or on the end of the tang that lies opposite the molding head, to determine an inactive molding step of the complementary male plug, a compression step, and a reduced compression step.

Description:
BACKGROUND OF THE INVENTION  
         [0001]    The present invention relates to an assembly for compression molding of articles made of plastics.  
           [0002]    An assembly of this kind is normally composed of a main male plug and a complementary male plug, which are coaxial and are actuated toward each other in order to mold a dose of plastic material deposited on the complementary male plug so as to form an article.  
           [0003]    When the step of deformation of the plastic material has ended, it is necessary to keep the main male plug and the complementary male plug pushed against each other, in order to allow the plastic material that has not yet hardened to maintain its shape until the process of stabilization of the plastic material has ended with the forming of a solid article.  
           [0004]    In known molding assemblies, in order to keep the shape of the article the main male plug and the complementary male plug are pushed against each other with the same compression force that determined the deformation of the plastic material. This force, by persisting over time, can cause damaging mechanical stresses on the main male plugs and complementary male plugs. However, currently no solutions have been devised that allow to reduce the compression force to a value that allows to maintain the shape of the article until it stabilizes.  
         SUMMARY OF THE INVENTION  
         [0005]    The technical aim of the present invention is now to obviate the above cited shortcomings of known molding assemblies by providing a solution that is technically simple and functionally valid.  
           [0006]    Within the scope of this technical aim, an object of the present invention is to provide a molding assembly that is suitable to be installed in carousel apparatuses for the compression molding of articles made of plastic material, which comprise a plurality of molding assemblies.  
           [0007]    This aim and this object are achieved with an assembly for the compression molding of articles made of plastic material, composed of a main male plug and a complementary male plug and characterized in that said complementary male plug is composed of: a stem, which is actuated by an actuation element and comprises a spindle that is guided in a tubular tang provided with a molding head that cooperates with said main male plug; a first spring, which is arranged on said spindle and acts between a collar of said spindle and said tubular tang; and a second spring, which is arranged on said spindle and is suitable to act, with a center bearing interposed, on said collar or on the end of said tubular tang that lies opposite said molding head, so as to determine: an inactive step of the complementary male plug, during which said first spring actuates said spindle into a stable position for resting against a shoulder of said tang, while said center bearing is spaced from said end of the tang and said second spring is locked between said stem and said collar; a compression step, during which both springs act on said tubular tang and said spindle does not rest against said shoulder, while said collar is spaced from said center bearing; and a reduced compression step, during which said first spring acts on said tubular tang and said second spring is locked between said stem and said collar, while said spindle does not rest against said shoulder and said center bearing is spaced from said end of said tang.  
           [0008]    Another object of the invention is to provide a carousel that comprises a plurality of molding assemblies having the characteristics defined in the appended claims. 
       
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0009]    Further details of the invention will become better apparent from the following description of a preferred embodiment thereof, illustrated by way of non-limitative example in the accompanying drawings, wherein:  
         [0010]    [0010]FIG. 1 is a sectional view of a carousel for molding articles, equipped with molding assemblies according to the invention;  
         [0011]    [0011]FIG. 2 is an enlarged-scale sectional view of a molding assembly;  
         [0012]    [0012]FIGS. 3, 4 and  5  are views of three successive operating conditions of the molding assembly.  
         [0013]    [0013]FIG. 1 illustrates a carousel for molding articles made of plastic material, disclosed in copending patent application by the same Applicant, entitled “Apparatus for molding and applying liners in caps”, claiming Italian priority N o  BO2001A000555, and to which reference is made here for better comprehension of the present invention. 
     
    
     DESCRIPTION OF THE PREFERRED EMBODIMENTS  
       [0014]    The carousel is generally designated by the reference numeral  1  and is part of an apparatus for molding and applying liners made of plastic material in caps. The plastic material, by means of a dosage machine that is not shown, is deposited in doses on shuttles which, by way of transfer elements, are conveyed into the illustrated molding carousel  1 , where the doses are compressed on the shuttles so as to form disk-like liners that are designated by the reference letter G in FIG. 2. The liners are then conveyed onto another carousel, where they are removed from the shuttles and inserted in the caps.  
         [0015]    As shown by FIG. 2, the shuttles are designated by the reference numeral  2  and are shaped like disks provided with an external slot  3 .  
         [0016]    The molding carousel  1  comprises a cylindrical box  4 , which is rigidly coupled to the footing  5  and in which a vertical shaft  6  is supported rotatably; said shaft has an axis A and is turned by transmission elements, not shown in the drawings. The top end  7  of the shaft  6  is supported, by means of a bearing  8 , by a structure  9  that rises from the footing  5 . A drum  10  is keyed on the vertical shaft  6  and has an upper annular portion  11  and a lower annular portion  12 , between which there remains an annular recess  13 . The upper annular portion  11  has a plurality of cylindrical through seats  14 , whose axis B is parallel to the rotation axis A. The seats  14  are concentric to the axis A and angularly equidistant.  
         [0017]    In the upper annular portion  11  there are multiple upper channels  15  and lower channels  16 , which run radially and connect the respective cylindrical seats  14  to a source of cooling fluid. A further plurality of cylindrical seats  17  is formed coaxially to the seats  14 , in the lower annular portion  12 .  
         [0018]    The lower portion  12  has an annular cavity that divides it into two superimposed collars  18  and  19 , both of which are crossed by the seats  17 . In the upper collar  18  there is a respective additional cylindrical seat  20  (see also FIG. 2) that is radially internal with respect to each cylindrical seat  17  and is parallel to said seat.  
         [0019]    In the lower collar  19  there are multiple vertical slits  21 , which are arranged radially and whose central planes contain the axes of the corresponding cylindrical seats  17  and  20 . An annular axial cam  22  rests under the drum  10  on the footing  5 , is concentric to the axis A, and comprises two vertically elongated concentric profiles. The cam  22  and the lower collar  19  are protected by a cylindrical jacket  23 , which has an upper edge  24  that skims the outer edge of the collar  19 .  
         [0020]    Each one of the upper cylindrical seats  14  is closed in an upward region by an L-shaped body  25  and accommodates a main male plug, generally designated by the reference numeral  26 , which together with a respective complementary male plug  27  accommodated in the seats  17  forms one of the assemblies for molding the liners G. The main male plug  26  of each molding assembly is composed of a sleeve  28 , which is permanently inserted in the seat  14  and is closed in an upward region by a cylindrical head  29  that is slidingly and hermetically engaged in said sleeve and is provided with a diametrical hole  30  which is connected, through holes  31  of the sleeve  28 , to a respective channel  15  of the portion  11  of the drum  10 . The head  29  has a step for resting against a shoulder  32  of the sleeve  28  and a screw  33  is screwed into its top end; a screw  33   a  having an axis B (see FIG. 1) and screwed through the L-shaped body  25  acts on said screw  33 . The upper end portion of the sleeve  28  has an outer step  33   b , on which there rests a ring made of rubber-like material  33   c , compressed between two metallic center bearings  33   d  and  33   e  and retained by an elastic ring  33   f . The ring  33   c  rests against a shoulder  33   g  of the seat  14 . In this manner, by acting on the screw  33   a  it is possible to preload the ring  33   c  against the shoulder  33   g  and therefore the main male plug  26 . The head  29  has a tubular extension to which a cannula  34  is connected; said cannula forms a channel  35  that is connected to the diametrical hole  30 . The cannula  34  lies inside a tubular stem  36 , forming with it an interspace  37 , which is connected, by means of holes  38  of the tubular stem and of the sleeve, to a respective radial channel  16 . At the lower end, the tubular stem  36  is closed by a molding element that is constituted by a sort of cup  39 , which connects the interspace  37  to the channel  35 . The cup  39 , whose bottom constitutes the actual male plug, is accommodated in a bush  40 , whose inside diameter is greater than the outside diameter of the cup, so that an annular gap or interspace  41  is formed between them. The bush  40  is rigidly coupled to a ring  42 , which can slide on the stem  36  and in which there is a passage  43  that connects the gap  41  to a hose  44  for delivering compressed air. Each hose  44  is connected to a respective valve  44   a , which is actuated cyclically as the carousel turns by an abutment  44   b  that is fixed to the structure  9 . The valve  44   a  cyclically connects the hose  44  to a duct  44   c  for feeding compressed air. The ring  42 , by means of a spring  45  that is interposed between said ring and the sleeve  28 , is actuated so as to rest against a shoulder  46  of the tubular stem  36 . Conveniently, the length of the bush  40  is such that in the position in which it rests against the shoulder  46  its lower edge protrudes below the cup  39 . Furthermore, the diameter of the bush  40  is smaller than the outside diameter of the shuttle  2 .  
         [0021]    The complementary male plug  27  comprises a stem  47  crossed by a radial pivot  48 , which supports two free rollers  49  that engage, by rolling thereon, the pair of profiles of the cam  22  that is fixed to the footing  5 . A pin  50  is driven through the stem  47  and rotatably supports an additional upper pair of rollers  51  and  52 . Both rollers are arranged at the end of the pin that is external to the stem  47  relative to the axis B. The roller  51  engages the vertical slit  21  of the collar  19 , while the roller  52  can engage a sector that is fixed inside the cylindrical case  23 . The stem  47  contains a threaded bush  53 , into which the threaded end of a cylindrical spindle  54  is screwed; said spindle is mounted so that it can slide in a tubular tang  55 , to the top of which a screw  56  is screwed whose head has a larger diameter than the sliding hole of the spindle, so as to be able to abut against a shoulder  57  of the tubular tang  55 . A recess  58  is formed in said tubular tang and accommodates a ring  59 , which is monolithic with the spindle  54 , and a spring  60 , which acts between the tang  55  and the ring  59 , with a spacer ring  61  interposed, so as to actuate the head of the screw  56  into abutment against the shoulder  57 . An additional spring  62  is accommodated in a recess  63  of the stem  47  that surrounds the bush  53  so as to act, with a center bearing  64  interposed, against the lower edge of the tang  55  and act as a resting element for the ring  59 . The spring  62  rests on the bottom of the recess  63  with a spacer ring  64   a . The rings  61  and  64   a  allow to adjust the preloading of the springs  60  and  62 . A seat is provided at the top end of the tubular tang  55 , and a shuttle holder insert  65  is screwed therein; said insert has a central pivot  66 , which is suitable to engage in the central hole of the shuttle  2  so as to constitute, together with said shuttle, a molding head. An interspace  67  remains between the insert  65  and the head of the screw  56  and allows the spindle  54  to perform a short stroke with respect to the tang  55  in contrast with the return action applied by the spring  60 . When the head of the screw  56  rests on the shoulder  57 , an interspace  67   a  that is not as high as the interspace  67  is formed between the center bearing  64  and the lower edge of the tubular tang  55 .  
         [0022]    A bush  68  is fixed in each one of the cylindrical seats  20 , and a rod  69  can slide therein; the pin  50  is inserted in a downward region in said rod. The rod  69  has an upper portion that has a reduced diameter and forms inside the bush  68  an abutment  69   a , which protrudes out of the bush  68 . A block  70  is fixed slidingly on said portion, and two superimposed forks  71  and  72  protrude from said block; the prongs of said forks form two semicircular curves: the upper one is suitable to receive the bush  40  and the lower one is suitable to receive the slot  3  of the shuttle  2 . The numeral  73  designates a spring that is interposed between the block  70  and a nut  73   a  that is screwed onto the end of the rod  69 . The purpose of the spring  73  is to actuate the block  70  downward in order to keep it rested against the abutment  69   a  when the rod  69  is actuated upward by the cam  22  together with the stem  47 . A washer  73   b  is arranged on the rod  69 , and a spring  74  rests therein in abutment against the lower edge of the bush  68  that guides the rod  69 .  
         [0023]    The operation of the described carousel is as follows.  
         [0024]    The shuttles  2 , already provided with a dose of plastic material preformed in the dosage machine, are transferred by an appropriate transfer element onto the molding carousel  1 , where they are accommodated in the recesses formed between the prongs of the lower forks  72  that engage in the slot  3  of said shuttles.  
         [0025]    The shuttles  2  are then locked by the subsequent upward stroke of the complementary male plugs  27 , which are actuated by the cam  22  that causes the engagement of the pins  66  in the holes of the shuttles  2  so that they cannot escape from the seats between the prongs  72  of the block  70 .  
         [0026]    As the upward stroke of the complementary male plugs continues, the shuttles  2  make contact with the lower edge of the bushes  40  and therefore actual molding begins, compressing the doses of plastic material previously deposited on the shuttles  2  against the bottoms of the cups  39  so as to form circular liners G.  
         [0027]    The molding performed by each assembly composed of a main male plug  24  and a complementary male plug  27  occurs according to the following sequence.  
         [0028]    In the initial position (shown in FIGS. 2 and 3), i.e., when the resistance to compression offered by the dose is not yet significant, the screw  56  abuts against the abutment  57  and the spring  62  is locked, in the preloaded condition, between the bottom of the recess  63  and the collar  59  of the spindle  54 . The interspace  67   a  between the center bearing  64  and the edge of the tang  55 , owing to the preloading of the spring  60 , remains unchanged.  
         [0029]    As the resistance offered by the plastic material increases as the stem  47  and the spindle  54  rigidly coupled thereto rise, the spindle  54  moves with respect to the tang  55 , so that the center bearing  64  stops against the lower edge of the tang  55 , allowing the collar  59  to move away from it.  
         [0030]    At this point one has the situation of FIG. 4, in which the maximum compression thrust applied by the cam  22  is transmitted to the tang  55  and therefore to the shuttles  2  by means of the two springs  60  and  62 , which are arranged in parallel.  
         [0031]    The doses of plastic material are sized so as to widen due to compression until they occupy the entire chamber comprised between the shuttle  2  and the bottom of the cup  39  and is surrounded peripherally by the bush  40 . Once the liners G have been molded, the cam  22  allows the spindles  54  to descend, so as to allow the collar  59  to abut against the center bearing  64  and therefore, by descending further, to entrain it under the edge of the tang  55 , so as to render ineffective the lower spring  62 , which is locked once again between the collar  59  and the stem  47  (see FIG. 5). When the center bearing  64  descends below the edge of the tang  55 , the compression with which the complementary male plug  27  acts on the liner, which is molded by then, is applied only by the upper spring  60  and is maintained by it by way of the cam  22  for a rotation angle of the carousel  1  that is sufficient to ensure that the shape of the liners is maintained until it has stabilized.  
         [0032]    Once the molding step has ended with the spacing of the complementary male plug  27  from the main male plug  26 , the shuttles that support the already-formed liners G are then transferred onto an insertion carousel, where the liners G are separated from the shuttles  2  along a first arc of rotation and the liners are inserted in caps along a subsequent arc.  
         [0033]    It is evident that the assemblies according to the invention perfectly achieve the intended aim and objects. In particular, it is possible to reduce the compression force after molding the liners to a value that maintains the shape of the liners until it has stabilized yet reduces the mechanical stresses on the main male plugs and complementary male plugs.  
         [0034]    The invention can of course be applied also in carousels that do not have shuttles and in which the molding heads are integrated in the inserts  65  so that the plastic material is compressed between the cup-like element  39  and the upper face of the insert  65 .  
         [0035]    The disclosures in Italian Patent Application No. BO2001A000557 from which this application claims priority are incorporated herein by reference.