Apparatus for pressure molding articles made of plastics, such as caps for closing a container and the like

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.

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.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

With reference toFIGS. 1 to 5, the apparatus comprises a carousel, generally designated by the reference numeral1, which is rotationally actuated in the direction X about a vertical axis. The carousel comprises a supporting element2, termed drum hereinafter, on which a plurality of molding units are mounted (seeFIG. 5); each molding unit comprises an upper punch3, which is substantially stationary with respect to the drum2, and a lower mold4, which can move along an axis B for alignment with the punch3.

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 (seeFIG. 1).

Each mold4has a cavity5(seeFIG. 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 head6, which can rotate in the direction Y about an axis E that is parallel to the axis A.

The mold4is mounted at the top of a vertical stem4a, which is guided in a seat of the drum2and 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 stem4aupward, the mold4, in an appropriate region of the path C of the carousel, compresses the dose D of plastic material against the punch3, 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 head6is 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 inFIGS. 1 and 5, the rotating head6is composed of a shaft7, which rotates about the axis E and to the top of which a flange8is rigidly coupled; a plate9is fixed on top of the flange8, and a disk10is also fixed thereto above the plate and is provided with recesses11that give the disk a star-like appearance.

A plurality of elements12for removing the doses of plastic material are fixed to the downward face of the flange8and are distributed around the axis E at an equal circumferential distance that is equal to the one by which the molds4are spaced around the axis A. Each removal element12comprises a sort of cup, which has a concave portion orientated in the rotation direction Y. The lower edge of the cups12is co-planar to the outlet of a nozzle13of an extruder14, whose opening is directed upward so that during the rotation of the head6each cup12can 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 cups12trace a path G that is tangent to the path C traced by the molds4, and the angular velocities of the carousel1and of the rotating head6are linked so that at the point of tangency of the paths C and G each cup12is substantially aligned with a respective mold4. The transfer of the dose D from the cups12into the cavities5of 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 recesses11of the star10are shaped so as to receive and retain on the upper face of the plate9the molded caps F, which after the cooling step are diverted in succession so as to leave the carousel. The caps F that engage the recesses11are conveyed between two guides15and16, which are arranged at the level of the plate9, so as to form a channel17for 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 cups12and introduced in the cavities5, 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 cavity5undergoes 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 mold4and 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 byFIGS. 2 to 4, said device is composed of two pairs of levers18,19and20,21, which are pivoted on diametrically opposite sides of the mold4by means of threaded pivots22,23and24,25, 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 levers18–21extend upward so that their tops protrude above the edge of the cavity5. The tops of the levers18,19are connected to the tops of the respective levers20,21by means of two mutually parallel rods26,27that are diametrical above the cavity5. The levers18and20are articulately connected to the levers19and21, respectively, by means of pins28and29. In order to allow the play that is necessary for the levers18–21to be able to oscillate about the pivots22–25, the pins28and29are driven through arms that protrude from the lower ends of the levers18and20and engage in elongated slots30(seeFIG. 2) of arms that are coupled in a mirror-symmetrical fashion to the lower ends of the levers19and21.

The levers18–21of each pair are actuated toward each other by virtue of traction springs31(seeFIG. 2) which, along an angular portion of the path of the carousel1, 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 cup12, as will become better apparent hereinafter.

The movement of the pairs of levers18–21associated with each mold4is controlled by a cam32that is fixed to the drum2.

Each cam32has a profile that is composed of a ramp33, which continues upward with a straight portion34that is parallel to the axis A. A cam follower cooperates with each cam32and is constituted by a roller35that is supported rotatably by two arms36and37that protrude at right angles from the respective levers18and20toward 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 carousel1.

By virtue of the rotation of the head6, the cups12remove in succession doses of plastic material from the outlet of the nozzle13. The consistency of the plastic material at the outlet of the nozzle13is such as to allow the dose to adhere to the wall of the cups12.

When a cup12of a molding unit, after removing a dose D from the nozzle13of the extruder14, is located at the point of tangency between its path G and the path C of the molds4, the dose D is propelled downward and collected on the rods26and27, which in this step in which the mold4has not yet started its lifting stroke are close one another (seeFIG. 5).

In the angular position a, the lifting of the mold4begins. However, the rods26and27still remain mutually adjacent until, after reaching the angular position β, the mold4has reached the level at which the roller35abuts against the ramp33of the cam32, causing the divarication of the rods (seeFIG. 6) and making the dose D fall into the cavity5. As shown inFIG. 6, the rods26,27open in the cavity5when the mold4is close to the punch3. The compression of the dose D is completed (seeFIGS. 7 and 8) by virtue of the subsequent rotation of the molding unit to the angular position γ.

As shown inFIG. 8, throughout the step for molding and stabilizing the cap (which continues until the corresponding molding unit has reached the angular position δ), the rods26,27remain spaced due to the engagement of the roller32on the straight portion34of the cam32.

Once the angular position δ has been reached, the descent of the mold4begins; when the roller35has descended below the ramp33, said descent allows the rods26and27, due to the action of the springs31, to move adjacent one another again above the cavity5, and be ready to receive a new dose D.

As shown inFIG. 9, the molded cap F remains attached to the punch and, after being deposited on the plate9of the head6, is collected by the recesses11of the star conveyor10(seeFIG. 10) and conveyed along the channel17toward 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 cavity5and 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 cavity5for 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 mold4is usually such as to cause the separation of the dose D from the rods26and27. 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 14illustrate a solution which, as shown more clearly inFIGS. 15 to 17, orientates the rods26and27radially with respect to the rotation axis A of the carousel.

Differently from the previously described solution, the levers20and21support two respective free rollers38and39, which are mounted in a cantilevered fashion approximately halfway along their length, while the pin28, which articulates to each other the levers18and19, supports a roller40that protrudes outward.

The levers18–21are actuated by an internal cam41, which is coupled to the cylindrical part of the rotating drum2, and by an external cam42(seeFIGS. 15 to 17), which is constituted by a bulge that protrudes from an element42athat is stationary with respect to the carousel1.

The internal cam41comprises two slots43and44, and a respective roller38and39engages in each of said slots and acts as a cam follower.

Each one of the slots43and44comprises 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 rollers38and39, by following the slots43and44, cause the divarication of the levers18–21and the spacing of the rods26and27.

The cam42is arranged at the point of tangency between the paths C and G, and during the rotation of the carousel1raises in succession the rollers40, causing a rapid mutual spacing and approach of the rods26and27.

Conveniently, the rods are provided centrally with curved portions45and46(seeFIG. 14), which form a seat that is adapted to receive a dose D of plastic material deposited therein by a cup12.

The activation of the levers18–21by the cam42precedes the activation performed by the cam41. The operating sequence can be deduced fromFIGS. 15 to 17. In particular, after a dose D has been removed by a cup12and deposited on the curved portions45and46of the rods26and27of a respective mold4(seeFIG. 15), the roller40, by surmounting the cam42, causes the rods45and46to perform a rapid movement to open (seeFIGS. 15 and 16) and close (seeFIG. 17), which allows the dose not to fall into the cavity5of the mold4and instead continue to be retained in the seat formed by the curved portions45and46. The opening and closing movement of the rods26and27can be synchronized with the stroke of the mold4, so as to catch the dose D released into the cavity5.

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 inFIGS. 18 and 19. Said solution is a constructive simplification with respect to the solution ofFIGS. 11 to 14owing to the absence of the external levers18and19, so that the rods26and27are fixed in a cantilevered fashion only to the internal levers20and21, 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.