Mold bottom with wide air vents for the forming of a container

Mold bottom for the manufacture by blow molding of a container that has a bottom that is equipped with a seat, with this mold bottom including a unit that has a molding face bearing the at least partial impression of the bottom of the container, with a pressure-release air vent being formed in the unit and emptying out, via an inner opening, on the molding face and, via an outer opening, into a pipe for exposure to air, with this mold bottom also including an insert that is provided with at least one projection housed in the air vent and that has a terminal face bearing the impression of at least one part of the seat of the container, with this insert being provided with an inner circuit for heat regulation of the projection and being mounted to move in relation to the unit.

BACKGROUND OF THE INVENTION

Field of the Invention

The invention relates to the forming of containers by blow molding or stretch blow molding of parisons made of plastic material, such as polyethylene terephthalate, with the term “parison” referring to a preform (ordinarily obtained by injection) or an intermediate container that has undergone a preliminary blow-molding operation starting from a preform.

Description of the Related Art

A container comprises a body, generally cylindrical in shape, a shoulder that forms a narrowing from an upper end of the body, an open neck that extends the shoulder for making possible the filling and the emptying of the container, and a bottom that closes the body at a lower end of the former.

The forming is generally carried out in a mold that delimits a cavity bearing the impression of the container. Such a mold commonly comprises a side wall bearing the impression of the body and the shoulder (this side wall being subdivided into two half-molds that are mutually articulated for making it possible to insert a parison into the mold), and a mold bottom bearing the impression of the bottom of the container, positioned in an opening made between the half-molds.

The preform, after having been heated to a temperature that is higher than the glass transition temperature of its material (a preform made of PET, whose glass transition temperature is approximately 80° C., is ordinarily heated to a temperature of higher than 100° C., typically on the order of 120° C.), is introduced hot into the mold. A pressurized fluid (such as air) is then injected therein to flatten the material, made soft by the heating, against the wall and the mold bottom and thus to impart to the preform the impression of the container.

Without heat regulation of the mold at a moderate temperature (on the order of 10° C. to 20° C.), the containers would emerge at a high temperature (higher than the glass transition temperature), would deform and could not be filled immediately, because they would not have sufficient mechanical strength to hold, without deforming, the pressure caused by the filling.

Allowing the containers to cool freely at the exit of the mold cannot be considered for two reasons. First, taking into account current production rates of the machines (on the order of 50,000 containers per hour per machine, representing more than 2,000 containers per hour and per mold), such cooling (that would take approximately one minute) would require the creation of a buffer stock of hundreds of containers, needlessly increasing the size and the complexity of the production line. Next, and primarily, the plastic material left free to cool would undergo an uncontrolled retraction and would thus lose the impression that is given to it by the mold.

This is why most of the molds are provided with a fluid cooling circuit that is designed to keep the wall and the bottom of the mold at a moderate temperature (on the order of 10° C. to 20° C.) in such a way as to set the material while keeping it under pressure to flatten it well against the wall and the bottom of the mold.

The blow molding furthermore requires evacuating the air that is trapped between the preform during forming and the mold. Evacuation is generally provided, on the one hand in the parting line between the two half-molds, and, on the other hand and primarily in the area of the mold bottom, since it is toward it that the air is pushed by the advance of the material front. For this purpose, the mold bottom is ordinarily pierced by one or more pressure-release air vents, more specifically in the zones reached at the end by the material. Thus, the international application WO 00/74925 (Krupp) illustrates a mold bottom that is designed with a petal-shaped bottom: this bottom is equipped with pressure-release air vents formed by perforations made in recessed reserved places of the bottom corresponding to feet of the container.

At the same time that they start to resolve the issue of the evacuation of air, such air vents raise a new issue, linked to their sizing. As a first approximation, it is necessary to maximize their size (i.e., their diameter or their width) since air is to be evacuated as easily as possible.

Then, however, the material will be introduced therein during the blow molding and will form projecting points of uncontrolled size on the surface of the container. As a second approach, it is therefore necessary to reduce the size of the air vents. It is all the more necessary since it was noted that when the air vents are too wide or when the time of cooling under pressure within the mold is brief (which is generally the case), the material is not correctly formed in the area of the air vents, because it undergoes there a retraction during the cooling of the container outside of the mold. Thermographies carried out by the applicant on the containers exiting from the mold actually show hot points located on the zones of the bottom that are located, in the mold, facing the air vents: In these non-thermoregulated zones of the bottom, the material of the container is not cooled.

These hot points are located in the seat of the container (i.e., in the part of the container by which the former is designed to rest on a flat surface). Since any defect of shape of the seat is detrimental to the stability of the container (and therefore to its perceived quality), most of the manufacturers opted for a compromise approach: reducing the size of the air vents to avoid shape defects; increasing the blow-molding pressure to increase the flow rate of air evacuated via the air vents.

Then, however, the problem arises of meeting, without losing production speed, the new requirements of the market as regards the reduction in energy consumption, which call for reducing the blow-molding pressure.

SUMMARY OF THE INVENTION

This is an approach to all of these problems that this invention provides by first proposing a mold bottom that is designed for a mold for the manufacture, by blow molding or stretch blow molding of a parison made of plastic material, of a container that has a bottom that is provided with a peripheral seat, with this mold bottom comprising:A bottom unit that has a molding face in relief bearing the impression of at least a part of the bottom of the container, with a pressure-release air vent being formed in the unit and emptying out, via an inner opening, on the molding face and, via an outer opening, into a pipe for exposure to airAn insert provided with at least one projection housed in the air vent (or in each air vent) and that has a terminal face bearing the impression of at least one part of the seat of the container, with this insert being provided with an inner circuit for heat regulation of the (or each) projection, with this insert being mounted to move, in relation to the bottom unit, between:A retracted position in which the terminal face of the (or each) projection is separated from the inner opening and lets the former communicate with the pipe for exposure to air, andA deployed position in which the terminal face extends in the vicinity of the inner opening.

In the retracted position, the projection makes it possible for air to escape via the air vent. In the deployed position, it will impart its shape to the seat of the container while cooling the material (and therefore by setting it). It is therefore possible to increase the size of the air vents without running the risk of deforming the container.

Various additional characteristics can be provided, by themselves or in combination:In the deployed position, the terminal face of the (or of each) projection extends into the extension of the molding face;In the deployed position, the terminal face of the (or of each) projection extends in a setback manner, in relation to the inner opening, by a distance of between 0.5 mm and 5 mm;The terminal face is concave, or convex;The insert comprises a piston that is mounted in translation in a jacket that is integral with the bottom unit;The or each air vent comprises an inner portion, which extends to the opening, and an outer portion with a larger cross-section, which extends in the extension of the inner portion by being separated from the former by a shoulder;The mold bottom comprises a primary pipe for exposure to air, which empties into the air vent in the area of the shoulder;The mold bottom comprises a secondary pipe for exposure to air, which empties into the air vent in the area of the outer portion;The unit is provided with a number of air vents that are spaced from one another, and the insert comprises a peripheral series of projections that are spaced from one another;The molding face bears the impression of a petal-shaped bottom of the container and comprises alternating ribs bearing the impression of valleys of the petal-shaped bottom, which radiate from a central zone, and with recessed reserved places bearing the impression of feet of the petal-shaped bottom, which extend between the ribs, the air vents are made in the recessed reserved places, and the terminal face of each projection bears the impression of the feet of the container.

Secondly, a mold is proposed for the manufacture of a container from a parison made of plastic material, which comprises a side wall bearing the impression of the body of the container, and a mold bottom as presented above, which completes the impression of the container with the side wall.

Thirdly, a method for manufacturing a container is proposed, which method comprises the operations that consist in:Introducing into a mold as presented above a parison made of plastic material, heated in advance to a temperature that is higher than the glass transition temperature of the material;In the retracted position of the insert, injecting a pressurized gas into the parison;While maintaining the pressure in the parison, moving the insert toward its deployed position.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

FIG. 1shows a mold1for the forming of a container2by blow molding or stretch blow molding from a parison3made of plastic material (in particular PET).

The parison3can be an intermediate container that has undergone a first blow-molding operation starting from a preform. It can also be, as in the illustrated example, a crude injection preform. Also, hereinafter, the reference3will be used interchangeably to refer to any type of parison or preform.

The container2comprises an essentially cylindrical body4that extends along a main axis X, a shoulder5that extends, in narrowing, into the extension of the body4at an upper end of the former, a neck6that is open at an upper end of the shoulder5from which it is separated by a collar7, and a bottom8that closes the body4at a lower end of the former. The bottom8has a peripheral seat9by which the container2is intended to rest on a flat surface such as a table, and a raised central zone10(where an injection button11of the preform3is located), to which the seat9is connected by an arch.

According to an embodiment that is illustrated in the figures (and more particularly inFIGS. 9 and 11), the bottom8of the container2is petal-shaped and comprises alternating spaced feet12that end by ends that jointly form (although in a discrete manner in the mathematical meaning of the term) the seat9, and valleys13with an essentially circular radial cross-section that radiate from the central zone10to the body4.

The preform3comprises a body14with an essentially tubular shape, designed to form the body4and the shoulder5of the container2, a neck6which is that of the container2and remains unchanged during the forming, and a hemispherical bottom15that is designed to form the bottom8of the container2.

The mold1comprises a side wall16that defines a cavity17bearing the impression of the body4and the shoulder5of the container2. The side wall16extends along a main axis that, when the container2is formed, is merged with the main axis X of the former. Below, the expression “main axis” interchangeably refers to the axis of the container or that of the side wall16.

According to a conventional embodiment, the side wall16is subdivided into two half-molds that can move in relation to one another (for example by being articulated around a hinge that is parallel to the main axis X), between an open position in which the two half-molds are separated angularly from one another to make possible the introduction of the preform3and the evacuation of the container2, and a closed position in which the two half-molds are flattened against one another to define together the cavity17, as described in, for example, the French patent application FR 2 856 333 or the corresponding international application WO 05/002820 (Sidel).

The side wall16defines an upper opening18, by which the preform3is suspended by its collar7, and an opposite lower opening19. Since the line ofFIG. 1is merged with a parting line between the two half-molds, only one of them is shown there.

The mold1is also equipped with a mold bottom20that comprises, firstly, a bottom unit21(for example made of steel or in an aluminum alloy) having a molding face22in relief bearing the impression of at least one part of the bottom8of the container2, and which completes the impression of the former with the side wall16.

The bottom unit21is attached to a support23that is itself mounted (for example by means of a screw24) on a stand25that can move in translation in relation to the side wall16between a loading/unloading position in which the unit21is separated from the cavity17to make possible the evacuation of the container2that is formed and the installation of a new preform3, and a forming position (illustrated inFIGS. 1, 2 and 4), in which the molding face22seals the cavity17to complete with the former the impression of the container2that is to be formed.

The mold bottom20is equipped with at least one pressure-release air vent26that is formed in the mold unit21and that empties, via an inner opening27, onto the molding face22and, via an outer or peripheral opening28, into at least one pipe29,30for exposure to air. The air vent26(or each air vent26) is formed by a scalloping made in the unit21in a direction that is essentially parallel to the main axis X, in a seating zone corresponding to the seat9of the container2and formed by recessed reserved places31.

According to an embodiment that is illustrated in the figures, where the container2has a petal-shaped bottom8, the molding face22, bearing the impression of the former, comprises alternating ribs32(bearing the impression of the valleys13), which radiate from a central zone33(bearing the impression of the central zone10of the bottom8), and recessed reserved places31(each forming the above-mentioned seating zone) bearing the impression of the feet12(here, five in number), which extend between the ribs32. In this case, the bottom unit21comprises a series of air vents26(here, five in number) that are spaced (here, distributed over a circular sector), made in the recessed reserved places31. More specifically, as in the illustrated example, an air vent26is made in the bottom of each recessed reserved place31.

Secondly, the mold bottom20comprises an insert34that is provided with at least one projection35that is housed in the air vent26(when there is only one of them) or in each air vent26(when there are several of them, as in the illustrated example) and that has a terminal face36bearing the impression of at least a part of the seat9of the container2.

According to an embodiment that is illustrated in the figures, in which the container2has a petal-shaped bottom8, the insert34comprises a number of spaced air vents26(here, distributed in a circular sector). In this case, the terminal face36of each projection35has an impression of the end of a foot12. The terminal faces36of the projections35then form the impression of the entire seat9of the container2, consisting of all of the ends of the feet12. In this case, the terminal face36is concave.

The insert34is provided with an internal circuit37for heat regulation of the (or of each) projection35, in such a way that the former is kept at a moderate temperature (between 5° C. and 30° C., and preferably between 10° C. and 20° C.).

The insert34is mounted to move, in relation to the bottom unit21, between:A retracted position (FIGS. 1, 2, 3, 4) in which the terminal face36of the (or of each) projection35is separated from the inner opening27of the air vent26and lets the former communicate freely with the (or each) pipe29,30for exposure to air, andA deployed position (FIGS. 7, 8, 9, 11) in which the terminal face36extends in the vicinity of the inner opening27.

According to a first embodiment, illustrated inFIGS. 7, 8 and 9, the terminal face36of the (or of each) projection35extends, in the deployed position of the insert34, into the extension of the molding face22. In this case, the material at the end of the blow molding adopts a continuous curvature at the bottom of the seat9(i.e., at the bottom of the feet12in the petal-shaped case that is illustrated), and a bottom8is obtained that has a clearance (defined as the distance between the central button11and the seat9) denoted H1, cf.FIG. 10.

According to a second embodiment that is illustrated inFIG. 11, the terminal face36of the (or of each) projection35extends, in the deployed position of the insert34, in an offset manner in relation to the inner opening27, by a distance that is advantageously between 0.5 mm and 5 mm. In this case, the material adopts, at the end of the blow molding, a variation of curvature in the area of the inner opening27and forms an extrusion that extends to the terminal face36of the projection35and constitutes, at the bottom of each foot12, a bump that increases the clearance of the bottom8to a value H2(cf.FIG. 11) that is higher than H1. This increased clearance H2makes it possible for the bottom8to deform according to a greater amplitude under the pressure of the contents of the container2, without it being necessary to modify the geometry of the feet12and valleys13, which ensure the performances of the bottom8in terms of mechanical strength. It will be noted that if the set-back distance of the terminal face36in relation to the inner opening27is too large, the material runs the risk of not reaching the terminal face36of the projection(s)35and therefore of forming a bump of uncontrolled shape that can make the seat9wobbly (primarily in the case where the former is formed by several feet12as in the petal-shaped bottom8that is illustrated).

According to a third embodiment that is illustrated inFIGS. 13 and 14, the terminal face36of the (or of each) projection35is bent (or convex) and forms, in the deployed position of the insert, a bump at the end of the foot12, toward the inside of the container2. In this way, when the container2is formed, each foot12is provided, at its end, with a hollow12′ projecting toward the inside of the container2. The container2thus formed has, empty, a clearance H3that is smaller than the clearance H1of the first embodiment described above. Since the container2is transferred after forming toward a filling unit (not shown) by being suspended by its collar7, the absence of a stable seat for the container2does not pose a problem. The filling of the container2with carbonated contents puts it under pressure and causes the return of hollows12′ that form the seat9, with the container2consequently able to rest, thanks to the former, on a flat surface (typically a conveyor or, subsequently, a table). The advantage of this embodiment is to make possible, with an equivalent seat diameter, a reduction in the blow-molding pressure or, with equivalent blow-molding pressure, increasing the seat diameter. In the two cases, it is possible to increase the clearance of the bottom8, denoted H4inFIG. 14.

It is preferable that the terminal face36be solid, i.e., have no perforations. However, it can be considered to provide in the terminal face36one or more air vents of small width (or diameter) that contribute to facilitating the evacuation of air without, however, running the risk of forming hot points on the container2.

According to an embodiment that is illustrated in the figures, the insert34comprises a base that is shaped like a piston38. This piston38has an upper face39from which the projections35emerge axially.

The piston38is mounted in translation in a jacket40that is integral with the mold unit21. More specifically, in the illustrated example, the jacket40is formed in the support23; this jacket40extends in an annular manner around a central shaft41and is delimited axially by an upper wall42that belongs to the support23and by a lower opposite wall43that belongs to the stand25. The upper wall42is pierced by openings44that partly define the air vents26and in which are housed the projections35when the piston38, also in annular form, is mounted in the jacket40.

In the jacket40, the piston38delimits an upper chamber45, from the side of the upper wall42, and a lower chamber46, from the side of the lower wall43. A fluid intake pipe47is formed in the stand25and empties, via the lower wall43, into the lower chamber46, to inject into the former a pressurized fluid (such as air or oil) that pushes back the piston38toward the upper wall42, and therefore the insert34toward its deployed position. In the illustrated example, the jack that is constituted by the piston38and the jacket40is of the single-action type, and the mold bottom20comprises one (or multiple) return spring(s)48inserted between the upper wall42and the piston38, and which permanently stress the former toward the inside wall43, and therefore the insert34toward its retracted position. In the illustrated example, five return springs48are provided, cf.FIG. 5.

Thus, to place the insert34in its deployed position, a pressurized fluid (such as air or oil) is injected into the lower chamber46, via the intake pipe47(and by means of, for example, a branched hose on the stand by means of a connector49—partially shown inFIG. 7), which fluid pushes back the piston38toward the upper wall42(and therefore the insert34toward its deployed position) against the return spring(s)48. In contrast, to place the insert34in the retracted position, the lower chamber46is exposed to open air, which balances the pressures in the two chambers45,46and makes it possible for the spring(s)48to push the piston back toward the lower wall43(and therefore the insert34toward the retracted position).

The travel of the insert34between its retracted position and its deployed position is between 5 mm and 15 mm, and advantageously approximately 10 mm.

The sealing between the two chambers45,46is advantageously carried out by means of annular segments50housed in grooves made in a peripheral manner in the piston38.

As a variant, the movement of the insert34can be controlled by mechanical and non-pneumatic (or hydraulic) means, for example by a cam. For this purpose, a lower end of the insert can carry a cam follower (such as a roller), which works with a cam groove, with the permanent contact of the cam follower with the cam groove being ensured by, for example, a return spring. The cam groove has an upper section that moves the cam follower toward the top (and therefore the insert34toward its deployed position) and a lower section that makes it possible for the cam follower to come down (and therefore the insert34to return toward its retracted position).

In the illustrated example, where the container2has a petal-shaped bottom8, each air vent26has in cross-section a profile of an essentially oval shape, of which the angular extension (measured in a transverse plane from the main axis X) is denoted A, the radial extension (also called small width) is denoted B, and the perimeter extension (also called large width, and measured perpendicularly to the radius passing through the geometric center of the inner opening27) is denoted C.

Furthermore, the diameter of the pitch circle that passes through the points of the terminal faces36of the projections35corresponding to the ends of the feet12(also called seat circle) is denoted D1, and the outer diameter of the molding face22, corresponding to the overall diameter of the bottom8of the container2, is denoted D2.

The air vents26, indicated inFIG. 6by a gray pattern, can be sized in the following manner:The angular amplitude A of each air vent26is between 10° and 45°; in the case (illustrated) of a petal-shaped bottom8, this angular amplitude A is advantageously between 17° and 35°, and, for example, approximately 35°:
10°≤A≤45°Advantageously, for a petal-shaped bottom:
17°≤A≤35°And, for example,
A≅35°The small width B of each air vent26is between 20% and 60% of the radius of the pitch circle, and advantageously, for a petal-shaped bottom8as illustrated, approximately 40% of the radius of the pitch circle:

B≅0.4·D⁢⁢12The large width C of each air vent26is between the small width B and twice the small width, and advantageously, for a petal-shaped bottom8as illustrated, approximately 1.45 times the small width:
B≤C≤2·BAnd advantageously, for a petal-shaped bottom8:
C≅1.45·BThe individual surface, denoted Su, of each air vent26on a transverse plane, is between 1% and 4% of the projected surface of the bottom8(i.e., the surface of the disk of diameter D2), and advantageously, in the case of a petal-shaped bottom8, approximately 3% of the former:

Su≅0.03⁣·π⁡(D⁢⁢222)The cumulative surface, denoted S, of the projection of the air vents26(the number of which is denoted N) on a transverse plane, is proportional to the individual surface Su of each one, in a ratio that is equal to the number N of air vents:

S=N·SuOr⁢:0.01·N·π⁡(D⁢⁢222)≤S≤0.04·N·π⁢⁢(D⁢⁢222)In practice, the cumulative surface S is between 10% and 30% of the projected surface of the bottom8(i.e., the surface of the disk with diameter D2), and advantageously, in the case of a petal-shaped bottom8, approximately 15% of the former:

Each projection35has, in cross-section (i.e., in a plane that is perpendicular to the main axis X), a profile that is complementary to that of the air vent26in which the projection35is housed, by taking into account an operational play necessary to its sliding.

In the deployed position of the insert34, this play is approximately 0.25 mm in the area of the inner opening27.

So as to facilitate the evacuation of the air during the blow molding of the container2, the or each air vent26comprises an inner portion26A, which extends axially up to the inner opening27, and an outer portion26B with a larger section, which extends axially into the extension of the inner portion26A by being separated from the former by a shoulder51. The height of the inner portion26A of the air vent26is less than the travel of the insert34in such a way that in the retracted position of the former, the terminal face36of the projection35is located in the outer portion26B, set back in relation to the shoulder51. The result is an increase in the section of passage for the air around the projection35, and therefore an increase in the evacuation flow rate of the air. The play between the projection and the outer portion26B of the air vent26is advantageously greater than or equal to 0.5 mm, and, for example, on the order of 0.7 mm.

According to an embodiment that is illustrated inFIGS. 2 and 3, the mold bottom20comprises a primary pipe29for exposure to air, which empties into the air vent26in the area of the shoulder51. When the insert34is in its retracted position, the inner opening27communicates directly with the primary pipe29. The former, made radially in the bottom unit21, furthermore empties into the open air on an outer face of the unit21.

The mold bottom20also advantageously comprises a secondary pipe30for exposure to air that empties into the air vent26in the area of the outer portion26B. When the insert34is in its retracted position, the secondary pipe30empties opposite the projection35, but the relatively significant play between the projection35and the outer portion26B makes it possible for the air to circulate easily from the inner opening27to the secondary pipe30. It will be noted that the secondary pipe30, furthermore, produces the exposure to air (and therefore the holding at atmospheric pressure) of the upper chamber45.

The heat regulation circuit37of the insert is, for example, of the fluid type and in this case comprises channels52formed in a closed circuit in each projection35, in which a refrigerating fluid (such as water) circulates. In the example that is illustrated inFIG. 4, these channels52are fed by a collector53that is connected to an outer circuit via pipes54that are perforated in the stand25, visible in the lower part ofFIG. 6.

To form the container2from the preform (or more generally from a parison)3, the procedure is as follows.

With the insert34being in the retracted position, the preform3(illustrated in dotted lines inFIG. 1) that is first heated to a temperature that is higher than the glass transition temperature of the material is introduced into the mold1.

A pressurized gas (such as air) is then injected into the preform3while stretching it, preferably by means of an elongation rod. The pressure is increased during injection, from a pre-blow-molding pressure of approximately 7 bars to a blow-molding pressure on the order of 17 bars. The material flattens against the side wall16and against the molding face22of the mold bottom20. The air between the material during deployment and the bottom20is evacuated via the air vents26by being free to escape via the pipes29,30for exposure to air in communication with the inner opening27.

The insert34is always in its retracted position when the blow molding begins at 17 bars.

Under these conditions, the material faithfully takes the impression of the molding face22, with the evacuation of the air continuing via the air vents26.

Under the blow-molding pressure, the material first penetrates into each air vent26to form a bump55there (in solid lines inFIGS. 3 and 4, with the material in its final position being shown in dotted lines). It is noted, however, that this penetration is limited by the internal stress of the material, whose stretching imparts to it a partially crystalline structure and therefore a certain mechanical rigidity.

While maintaining the blow-molding pressure, the insert34is moved toward its deployed position. Each projection35then pushes back the bump55to give it the impression of the terminal face36, either in the extension of the molding face22(the case ofFIGS. 8 and 9), or slightly set back in relation to the former (the case ofFIG. 11).

The material of the bottom8of the container2that is thus formed is quickly cooled not only in the zones in contact with the molding face22of the unit21(by means of a cooling circuit56that is visible in particular inFIGS. 1, 2 and 7), but also in the zones (here corresponding to the feet12of the container2) that are in contact with the terminal faces36of the projections35, since the former are held at a moderate temperature by the heat regulation circuit37.

In this way, the material that supplies the zones where the air vents26are positioned sets and does not undergo any subsequent uncontrolled deformation. It is consequently possible to make the air vents26wide by providing them with a significant scope in relation to the projected surface of the bottom20, as is evident from the examples that are provided above for the angular amplitude A, the widths B and C, and the surface S.

The result is a better blowability of the container2(“blowability” of a container is defined as its capacity to be formed by blow molding) thanks to the increased flow of air through air vents26, which are released when the insert34is in the retracted position, with the openings27,28being in free communication with the pipes29,30for exposure to air.

This likewise makes it possible to reduce the blow-molding pressure on the order of 2 to 3 bars, enhancing energy savings. Thus, a container that requires a blow-molding pressure of 20 bars to be formed in a mold that is equipped with standard air vents only requires a blow-molding pressure on the order of 17 to 18 bars, or a savings of 10 to 15%, to be formed in the mold1that was just described (with equal impression).