Abstract:
An apparatus for compression molding plastic articles, comprising at least one molding unit composed of an upper punch and a lower mold provided with a cavity for molding the articles, the punch and mold being aligned with each other and movable between a spaced position and a closer positions, feeders for feeding doses of plastic material to be molded, comprising at least one removal element for removing, in succession, individual doses from an extruder and depositing a removed dose in the molding cavity of the mold when it is spaced from the respective punch, supporting elements for temporarily supporting said dose above the molding cavity, associated with the mold, and actuators for actuating the supporting elements so as to release a dose into the cavity before compression start.

Description:
BACKGROUND OF THE INVENTION 
   The present invention relates to an apparatus for pressure molding articles made of plastics, such as caps for closing a container and the like. 
   U.S. Pat. No. 5,807,592 by the same Assignee discloses apparatuses of the indicated type for the pressure-molding of caps for closing a container, such as screw caps. Such apparatuses comprise a carousel that rotates about a vertical axis and on which a plurality of pressure-molding units are mounted concentrically around the rotation axis of the carousel and at an identical mutual angular distance. Each one of said units comprises an upper punch, which cooperates with a lower mold that is aligned with said punch and has a molding cavity. 
   By virtue of the rotation of the carousel, the molding units trace a circular path, which comprises a first sector, in which the necessary doses of plastic material to be molded are deposited in the cavities of the molds, a second sector, in which the article is molded, a third sector, in which the molded article is cooled, and a fourth sector, in which the molded article is extracted and conveyed away. 
   In these known apparatuses, the plastic material to be molded is removed from an extruder by means of a rotating head provided with a plurality of removal elements, which trace a circular path that has a point of tangency with the extrusion nozzle and with the circular path traced by the molding units. The rotating head and the carousel are mutually in step, in order to allow the removal elements to remove in succession doses of plastic material from the extruder and deposit them in the cavities of the molds. 
   The conventional apparatuses suffer the drawback that in the time that elapses between the moment when the doses are deposited in the cavities and the moment when said doses are compressed, the portion of the dose that is introduced in the cavity, by making contact with the colder surface of the cavity, undergoes cooling and therefore a variation in the degree of plasticity of the plastic material that is located at said portion, which causes, during molding, aesthetic defects that can be observed on the outer surface of the molded article. These defects, which become apparent mostly in the form of regions whose surface differs in terms of opacity from the surrounding regions and which sometimes have a certain surface porosity, constitute an unacceptable qualitative depreciation of the molded article. 
   Another drawback is the fact that the doses usually are not deposited at the center of the cavities of the molds, and therefore during the compression step the distribution of the plastic material does not expand uniformly, since it does not start from the center, causing molding problems due to the asymmetry of the filling. 
   Other drawbacks due to the deposition of the doses in the molding cavities can be observed in apparatuses (see U.S. Pat. No. 5,885,408) for forming plastic caps, on the bottom of which a label for decorative purposes or bearing information is to be incorporated externally. In these apparatuses, the labels are deposited inside the molding cavity before the doses, so that said doses, when they make contact with the label, due to their high temperature, cause deformations of the labels, particularly creases, which are unlikely to be smoothed out during the compression step. 
   SUMMARY OF THE INVENTION 
   The aim of the present invention is therefore to provide an apparatus which, associated with each molding unit of compression molding apparatuses, allows to obviate the drawbacks cited above. 
   Within this aim, an object of the present invention is to provide an apparatus that is highly flexible in use in relation to the ability to work with plastic material of various kinds and consistencies. 
   This aim and this object are achieved with an apparatus whose characteristics are defined in the appended claims. 

   
     BRIEF DESCRIPTION OF THE DRAWINGS 
     Further features and advantages of the present invention will become better apparent from the following description on the basis of the accompanying drawings, wherein: 
       FIG. 1  is a schematic plan view of the apparatus according to a first embodiment; 
       FIG. 2  is a sectional view, taken along the radial line II—II of  FIG. 1 ; 
       FIG. 3  is a sectional plan view, taken along the line III—III of  FIG. 2 ; 
       FIG. 4  is a partially sectional view, taken along the tangential line IV—IV of  FIG. 2 ; 
       FIGS. 5 to 10  are views of the apparatus in six successive operating positions; 
       FIG. 11  is a view of a first variation, taken along a radial direction; 
       FIG. 12  is a partially sectional and tangential view taken along the line XII—XII of  FIG. 11 ; 
       FIG. 13  is a radial view, taken along the line XIII—XIII of  FIG. 12 ; 
       FIG. 14  is a plan view, taken along the line XIV—XIV of  FIG. 12 ; 
       FIGS. 15 to 17  are views of the apparatus according to the variation in three successive operating positions; 
       FIG. 18  is a tangential sectional view of a second variation which is similar to the variation of  FIG. 12 ; and finally 
       FIG. 19  is a sectional plan view of the variation of  FIG. 18 , taken along the line XIX—XIX. 
   

   DESCRIPTION OF THE PREFERRED EMBODIMENTS 
   With reference to  FIGS. 1 to 5 , the apparatus comprises a carousel, generally designated by the reference numeral  1 , which is rotationally actuated in the direction X about a vertical axis. The carousel comprises a supporting element  2 , termed drum hereinafter, on which a plurality of molding units are mounted (see  FIG. 5 ); each molding unit comprises an upper punch  3 , which is substantially stationary with respect to the drum  2 , and a lower mold  4 , which can move along an axis B for alignment with the punch  3 . 
   The molding units are distributed at an identical radial and angular distance around the axis A, and therefore their axes B trace a circular path C (see  FIG. 1 ). 
   Each mold  4  has a cavity  5  (see  FIG. 4 ), which is open upward and in which a dose D of plastic material is molded; said dose is introduced therein in the pasty state and is fed by a rotating head  6 , which can rotate in the direction Y about an axis E that is parallel to the axis A. 
   The mold  4  is mounted at the top of a vertical stem  4   a , which is guided in a seat of the drum  2  and is actuated by a hydraulic jack (not shown), which can be connected, by way of suitable valve systems, to a source of pressurized fluid. When the pressurized fluid pushes the stem  4   a  upward, the mold  4 , in an appropriate region of the path C of the carousel, compresses the dose D of plastic material against the punch  3 , performing, along a subsequent arc of the path C, the molding of the article, which in the described case is a cap-type closure F. 
   Said rotating head  6  is shown only schematically in the accompanying drawings, since it is not relevant to the inventive concept of the present invention. In any case, it can be understood more clearly from the aforesaid U.S. Pat. No. 5,807,592. 
   As shown in  FIGS. 1 and 5 , the rotating head  6  is composed of a shaft  7 , which rotates about the axis E and to the top of which a flange  8  is rigidly coupled; a plate  9  is fixed on top of the flange  8 , and a disk  10  is also fixed thereto above the plate and is provided with recesses  11  that give the disk a star-like appearance. 
   A plurality of elements  12  for removing the doses of plastic material are fixed to the downward face of the flange  8  and are distributed around the axis E at an equal circumferential distance that is equal to the one by which the molds  4  are spaced around the axis A. Each removal element  12  comprises a sort of cup, which has a concave portion orientated in the rotation direction Y. The lower edge of the cups  12  is co-planar to the outlet of a nozzle  13  of an extruder  14 , whose opening is directed upward so that during the rotation of the head  6  each cup  12  can remove from the nozzle a dose D of plastic material that corresponds to the dose that exits from the nozzle in the time that elapses between the passage of two successive cups in front of said nozzle. 
   The cups  12  trace a path G that is tangent to the path C traced by the molds  4 , and the angular velocities of the carousel  1  and of the rotating head  6  are linked so that at the point of tangency of the paths C and G each cup  12  is substantially aligned with a respective mold  4 . The transfer of the dose D from the cups  12  into the cavities  5  of the molds can be performed as described in the aforesaid U.S. Pat. No. 5,807,592 by virtue of the action of a jet of compressed air that is directed downward, possibly combined with a mechanical action obtained by providing, in each cup, an expulsion piston that can move vertically and is actuated by compressed air by way of valve means. 
   The recesses  11  of the star  10  are shaped so as to receive and retain on the upper face of the plate  9  the molded caps F, which after the cooling step are diverted in succession so as to leave the carousel. The caps F that engage the recesses  11  are conveyed between two guides  15  and  16 , which are arranged at the level of the plate  9 , so as to form a channel  17  for removing the caps. 
   As explained initially, with carousels for compression molding of the type described above, the dose D of plastic material, after being removed by the cups  12  and introduced in the cavities  5 , remains in contact with the internal surface of the cavity for some time before the compression step begins. During this time, the portion of the dose D that is in contact with the internal surface of the cavity  5  undergoes a cooling that alters its consistency, so that during the molding step the plastic material flows unevenly, causing defects that are visible in particular on the outer surface of the bottom of the cap. 
   In order to obviate this drawback, a device is associated with each mold  4  and supports with minimal contact and temporarily the dose D to be introduced in the corresponding cavity, so as to allow the punch to approach it before the actual molding step is started. 
   As shown by  FIGS. 2 to 4 , said device is composed of two pairs of levers  18 ,  19  and  20 , 21 , which are pivoted on diametrically opposite sides of the mold  4  by means of threaded pivots  22 ,  23  and  24 ,  25 , which are screwed into the base of the mold so as to allow the oscillation of the levers on parallel planes that are substantially radial with respect to the rotation axis A of the carousel. 
   The levers  18 – 21  extend upward so that their tops protrude above the edge of the cavity  5 . The tops of the levers  18 ,  19  are connected to the tops of the respective levers  20 ,  21  by means of two mutually parallel rods  26 ,  27  that are diametrical above the cavity  5 . The levers  18  and  20  are articulately connected to the levers  19  and  21 , respectively, by means of pins  28  and  29 . In order to allow the play that is necessary for the levers  18 – 21  to be able to oscillate about the pivots  22 – 25 , the pins  28  and  29  are driven through arms that protrude from the lower ends of the levers  18  and  20  and engage in elongated slots  30  (see  FIG. 2 ) of arms that are coupled in a mirror-symmetrical fashion to the lower ends of the levers  19  and  21 . 
   The levers  18 – 21  of each pair are actuated toward each other by virtue of traction springs  31  (see  FIG. 2 ) which, along an angular portion of the path of the carousel  1 , retain them in a position in which the rods, above their respective cavities, are adjacent at a mutual distance that allows to momentarily support a dose D of plastic material deposited between them by a cup  12 , as will become better apparent hereinafter. 
   The movement of the pairs of levers  18 – 21  associated with each mold  4  is controlled by a cam  32  that is fixed to the drum  2 . 
   Each cam  32  has a profile that is composed of a ramp  33 , which continues upward with a straight portion  34  that is parallel to the axis A. A cam follower cooperates with each cam  32  and is constituted by a roller  35  that is supported rotatably by two arms  36  and  37  that protrude at right angles from the respective levers  18  and  20  toward the axis A. 
   The operation of the described apparatus is described hereinafter by following what happens in a molding unit during the 360° rotation of the carousel  1 . 
   By virtue of the rotation of the head  6 , the cups  12  remove in succession doses of plastic material from the outlet of the nozzle  13 . The consistency of the plastic material at the outlet of the nozzle  13  is such as to allow the dose to adhere to the wall of the cups  12 . 
   When a cup  12  of a molding unit, after removing a dose D from the nozzle  13  of the extruder  14 , is located at the point of tangency between its path G and the path C of the molds  4 , the dose D is propelled downward and collected on the rods  26  and  27 , which in this step in which the mold  4  has not yet started its lifting stroke are close one another (see  FIG. 5 ). 
   In the angular position a, the lifting of the mold  4  begins. However, the rods  26  and  27  still remain mutually adjacent until, after reaching the angular position β, the mold  4  has reached the level at which the roller  35  abuts against the ramp  33  of the cam  32 , causing the divarication of the rods (see  FIG. 6 ) and making the dose D fall into the cavity  5 . As shown in  FIG. 6 , the rods  26 ,  27  open in the cavity  5  when the mold  4  is close to the punch  3 . The compression of the dose D is completed (see  FIGS. 7 and 8 ) by virtue of the subsequent rotation of the molding unit to the angular position γ. 
   As shown in  FIG. 8 , throughout the step for molding and stabilizing the cap (which continues until the corresponding molding unit has reached the angular position δ), the rods  26 ,  27  remain spaced due to the engagement of the roller  32  on the straight portion  34  of the cam  32 . 
   Once the angular position δ has been reached, the descent of the mold  4  begins; when the roller  35  has descended below the ramp  33 , said descent allows the rods  26  and  27 , due to the action of the springs  31 , to move adjacent one another again above the cavity  5 , and be ready to receive a new dose D. 
   As shown in  FIG. 9 , the molded cap F remains attached to the punch and, after being deposited on the plate  9  of the head  6 , is collected by the recesses  11  of the star conveyor  10  (see  FIG. 10 ) and conveyed along the channel  17  toward the removal means. 
   The described apparatus therefore achieves the intended aim and object. In fact, according to a fundamental aspect of the invention, the time that elapses between the deposition of the dose D in the cavity  5  and the beginning of the deformation of the plastic material is practically reduced to zero. In this manner, the dose D remains in localized contact with the inner surface of the cavity  5  for a time that is insufficient to cause significant changes in the consistency of the plastic material. Therefore, the temperature of the plastic material of the deposited dose remains substantially constant in every point, so as to ensure uniform plastic deformation during compression. 
   The fact that the deposition of the dose and the beginning of the compression are substantially simultaneous also offers the advantage that in the case of caps provided with an incorporated label, the time for which the doses remain on the labels, which are introduced beforehand in the molding cavities, is insufficient to cause deformations of the label. Therefore, the labels remain always perfectly flat and are smoothed out once compression is complete. 
   One highly advantageous aspect of the invention is the fact that the speed of the mold  4  is usually such as to cause the separation of the dose D from the rods  26  and  27 . In particular, the dose D is propelled against the punch with such an impact forces that it adheres to said punch. Therefore, the region of the dose that makes contact with the punch and may form defects, actually, during the compression step, remain inside the cap, so that any defects, once molding has been completed, also remain inside the cap, and do not endanger the aesthetics of the product because they are not visible externally. 
   The described apparatus is susceptible of numerous modifications and variations, all of which are within the scope of the same inventive concept. 
     FIGS. 11 to 14  illustrate a solution which, as shown more clearly in  FIGS. 15 to 17 , orientates the rods  26  and  27  radially with respect to the rotation axis A of the carousel. 
   Differently from the previously described solution, the levers  20  and  21  support two respective free rollers  38  and  39 , which are mounted in a cantilevered fashion approximately halfway along their length, while the pin  28 , which articulates to each other the levers  18  and  19 , supports a roller  40  that protrudes outward. 
   The levers  18 – 21  are actuated by an internal cam  41 , which is coupled to the cylindrical part of the rotating drum  2 , and by an external cam  42  (see  FIGS. 15 to 17 ), which is constituted by a bulge that protrudes from an element  42   a  that is stationary with respect to the carousel  1 . 
   The internal cam  41  comprises two slots  43  and  44 , and a respective roller  38  and  39  engages in each of said slots and acts as a cam follower. 
   Each one of the slots  43  and  44  comprises two parallel and vertical portions, which are connected by an inclined intermediate portion. The upper portions of the slots are further apart than the lower portions. In this manner, when the molds are lifted, the rollers  38  and  39 , by following the slots  43  and  44 , cause the divarication of the levers  18 – 21  and the spacing of the rods  26  and  27 . 
   The cam  42  is arranged at the point of tangency between the paths C and G, and during the rotation of the carousel  1  raises in succession the rollers  40 , causing a rapid mutual spacing and approach of the rods  26  and  27 . 
   Conveniently, the rods are provided centrally with curved portions  45  and  46  (see  FIG. 14 ), which form a seat that is adapted to receive a dose D of plastic material deposited therein by a cup  12 . 
   The activation of the levers  18 – 21  by the cam  42  precedes the activation performed by the cam  41 . The operating sequence can be deduced from  FIGS. 15 to 17 . In particular, after a dose D has been removed by a cup  12  and deposited on the curved portions  45  and  46  of the rods  26  and  27  of a respective mold  4  (see  FIG. 15 ), the roller  40 , by surmounting the cam  42 , causes the rods  45  and  46  to perform a rapid movement to open (see  FIGS. 15 and 16 ) and close (see  FIG. 17 ), which allows the dose not to fall into the cavity  5  of the mold  4  and instead continue to be retained in the seat formed by the curved portions  45  and  46 . The opening and closing movement of the rods  26  and  27  can be synchronized with the stroke of the mold  4 , so as to catch the dose D released into the cavity  5 . 
   The steps for molding the cap F follow one another in the manner described in the preceding example, taking into account the fact that the opening and closing movement of the rods, due to their radial arrangement, occurs in a tangential direction. 
   Another variation of the apparatus is shown in  FIGS. 18 and 19 . Said solution is a constructive simplification with respect to the solution of  FIGS. 11 to 14  owing to the absence of the external levers  18  and  19 , so that the rods  26  and  27  are fixed in a cantilevered fashion only to the internal levers  20  and  21 , forming a sort of fork. 
   Further variations provide for the thermal conditioning of the rods by means of resistor-type plugs, by induction or by means of a jet of air. 
   The disclosures in Italian Patent Application No. BO2002A000226 from which this application claims priority are incorporated herein by reference.