The present invention relates to an apparatus for pressure
molding articles made of plastics, such as caps for closing a container and the
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 patent
) 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.
Disclosure 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.
According to the invention there is provided a method whose
characteristics are defined in the appended claims.
Brief description o the Drawings
Further features and advantages of the present invention
will become better apparent from the following description on the basis of the accompanying
Ways of carrying out the Invention
- Figure 1 is a schematic plan view of the apparatus according to a first embodiment;
- Figure 2 is a sectional view, taken along the radial line II-II of Figure 1;
- Figure 3 is a sectional plan view, taken along the line III-III of Figure 2;
- Figure 4 is a partial sectional view, taken along the tangential line IV-IV
of Figure 2;
- Figures 5 to 10 are views of the apparatus in six successive operating positions;
- Figure 11 is a view of a first variation, taken along a radial direction;
- Figure 12 is a partially sectional and tangential view taken along the line
XII-XII of Figure 11;
- Figure 13 is a radial view, taken along the line XIII-XIII of Figure 12;
- Figure 14 is a plan view, taken along the line XIV-XIV of Figure 12;
- Figures 15 to 17 are views of the apparatus according to the variation in three
successive operating positions;
- Figure 18 is a tangential sectional view of a second variation which is similar
to the variation of Figure 12; and finally
- Figure 19 is a sectional plan view of the variation of Figure 18, taken along
the line XIX-XIX.
With reference to figures 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 Figure 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 Figure 1).
Each mold 4 has a cavity 5 (see Figure 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 4a,
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 4a 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
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
As shown in Figures 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 patent
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 Figures 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
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
Figure 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 Figure 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
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 3. 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 Figure 5).
In the angular position &agr;, the lifting of the mold
4 begins. However, the rods 26 and 27 still remain mutually adjacent until, after
reaching the angular position &bgr;, 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 Figure 6) and making the dose D fall into the cavity 5.
As shown in Figure 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 Figures 7 and 8) by virtue of the subsequent rotation of the molding unit to
the angular position y.
As shown in Figure 8, throughout the step for molding and
stabilizing the cap (which continues until the corresponding molding unit has reached
the angular position &dgr;), 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 &dgr; 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
As shown in Figure 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 Figure 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 a
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 force 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.
Figures 11 to 14 illustrate a solution which, as shown
more clearly in Figures 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
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 Figures 15 to 17), which is constituted by a bulge that protrudes from an
element 42a 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 Figure 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
Figures 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 Figure 15), the roller 40, by surmounting the cam 42, causes the rods
45 and 46 to perform a rapid movement to open (see Figures 15 and 16) and close
(see Figure 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
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 variant of the apparatus is shown in Figures 18
and 19. Said solution is a constructive simplification with respect to the solution
of Figures 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 variants provide for the thermal conditioning of
the rods by means of resistor-type plugs, by induction or by means of a jet of air.