EP3227083A1

EP3227083A1 - Method for forming containers, with braking of a stretching pin during blowing

Info

Publication number: EP3227083A1
Application number: EP15810691.4A
Authority: EP
Inventors: Franck SANTAIS
Original assignee: Sidel Participations SAS
Current assignee: Sidel Participations SAS
Priority date: 2014-12-05
Filing date: 2015-12-01
Publication date: 2017-10-11
Also published as: FR3029447A1; FR3029447B1; CN107000299B; WO2016087761A1; CN107000299A

Abstract

A method for manufacturing a container (2) from a plastic preform (3) in a forming station (1) equipped with a mould (5), a device (11) for injecting fluid into the preform (3), and a pin (26) able to move between a raised position and a lowered position. The method comprises in succession: a phase of introducing the preform (3) into the mould (5); a pre-blowing phase involving the operations consisting in: injecting a fluid into the preform (3) at a preblowing pressure; moving the stretching pin (26) from its raised position into its lowered position; a blowing phase comprising an operation of injecting into the preform (3) a fluid at a blowing pressure, and an operation of mechanically braking the pin (26) in the lowered position.

Description

Container forming method with braking of a drawing rod during blowing

The invention relates to the manufacture of containers from plastic blanks (for example polyethylene terephthalate or PET) by stretch blow molding thereof.

Typically, a container comprises a body, a bottom closing the body at a lower end thereof, and a neck that opens at an upper end of the body to allow filling and emptying the container.

In order to manufacture the container, the blank (a blank preform or an intermediate container obtained from a preform which has undergone a preforming operation) is preheated and preheated to a temperature above the glass transition temperature of the material ( about 80 ° C in the case of PET), in a mold with a wall defining a cavity in the cavity of the container, and is injected into the blank, through the neck, a fluid under pressure, such as a gas (usually air), to press the material against the wall of the mold. The injection is generally carried out in two phases: a pre-blowing phase, which consists in injecting the fluid at a so-called pre-blowing pressure, generally between 5 and 10 bars, followed by a blowing phase, which consists in injecting the fluid at a so-called blowing pressure, greater than the pre-blowing pressure and generally between 20 and 40 bar.

During pre-blowing, the material softened by the heating forms a bubble that swells and develops both in an axial direction, parallel to the main axis of the mold, and in a radial direction perpendicular to the axis of the mold. The material is already in contact with the wall of the mold when the blowing is initiated, but the impression is not complete. Blowing allows the material to be tightly pressed against the wall and thus to complete the impression.

In order to avoid any misalignment of the container and to ensure a good distribution of the material, the axial stretching of the blank is forced by means of an axially displaceable rod in the mold. This rod comprises a distal end pushing the bottom of the blank until it comes to press against a mold bottom to the footprint of the bottom of the container. It has long been known to control the movement of the drawing rod by means of a pneumatic cylinder, cf. for example the French patent FR 2662631 (DYNAPLAST). The pneumatic supply of the cylinder is generally ensured by a simple connection to the compressed air network at 7 bar (100 psi), the speed of the rod being mechanically regulated by means of a cam.

It has recently been proposed to replace the pneumatic control by electromagnetic control, cf. French patent FR 2798093 or its US equivalent US 6,722,868, both in the name of SIDEL. This technology, which has the double advantage of saving air under pressure and limiting the use of wear parts (the magnetic control is made without contact), tends to gradually replace the pneumatic control, older and less efficient .

It is preferable that the rod is held against the bottom of the mold

(With the material of the container between them) during blowing, to prevent slippage of the material under the effect of the blowing pressure, especially when the bottom of the container (and thus the mold bottom) has complex reliefs. A slip would indeed lead to an inhomogeneous distribution of the material on the bottom, causing problems of mechanical strength and balance of the container.

But the pressure in the container generates on the distal end of the rod an axial resisting force which tends to move away from the mold base (that is to say to raise it). When the control is pneumatic, the cylinder must be dimensioned so as to exert on the rod a motor force greater than the resistant force. When the control is electromagnetic, maintaining the position of the rod consumes a large amount of current, may cause overheating of the control magnetic circuit.

A goal is therefore to facilitate the holding of the drawing rod during blowing, so as to avoid over-dimensioning of the mechanical components of the control system (in the case of a pneumatic control) or to limit the power consumption (in the case of an electric control).

For this purpose, it is proposed, in the first place, a method of manufacturing a container from a plastic blank, in a forming station equipped with: a mold having a wall defining a cavity in the cavity of the container, extending along a main axis, and a mold bottom closing the cavity at a lower end of the wall;

an injection device comprising a pre-blowing circuit provided with a source of fluid at a pre-blowing pressure and a blowing circuit provided with a source of fluid at a blowing pressure higher than the pre-blowing pressure;

a drawing unit comprising a movable assembly including a shaft movable axially with respect to the wall, between a high position in which the shaft extends out of the cavity, and a low position in which a distal end of the shaft is located near the bottom of the mold;

this process comprising successively:

a phase of introduction of the blank into the mold, conducted in the upper position of the rod;

a pre-blast phase comprising the operations of:

injecting into the blank, by the pre-blowing circuit, a fluid at a pre-blowing pressure;

o Move the draw rod from its high position to its low position;

a blowing phase comprising an injection operation in the blank, by the blowing circuit, of a fluid at a blowing pressure greater than the pre-blowing pressure, and

- A mechanical braking operation of the rod in the low position.

This method may further comprise a depressurization phase of the container, subsequent to the blowing phase, the mechanical braking operation of the rod ending in this case simultaneously with the initiation of the depressurization phase.

The mechanical braking of the rod is preferably performed during at least part of the blowing phase.

Moreover, the mechanical braking operation of the rod in the low position can be initiated:

before the end of the pre-blowing phase,

- at the end of the pre-blast phase, or

after the initiation of the blowing phase. The mold bottom may be mounted movable relative to the wall between a retracted position in which the mold bottom is spaced from the cavity, and an extended position in which the mold base closes the cavity; in this case, the manufacturing method may comprise a boxing operation, which consists, from the retracted position of the mold base, to move it to its deployed position during at least part of the blowing phase. In this case, braking of the rod may be sufficient to prevent the spacing of the rod from the mold bottom, while allowing its rise under the push of the mold bottom.

It is proposed, secondly, a machine for manufacturing containers from plastic blanks, which comprises a forming station equipped with:

a mold having a wall defining a cavity in the cavity of the container, extending along a main axis, and a mold bottom closing the cavity at a lower end of the wall;

a control unit programmed to control the movement of the rod from its high position to its low position and reciprocally, and to control the successive injection, in a blank placed in the mold, of the fluid of the pre-blowing circuit and the circuit blowing;

in this machine:

the drawing unit comprises a mechanical brake controlled by the control unit, provided with an actuator and a shoe integral with the actuator, movable between a release position in which the shoe is removed from the crew mobile, and a position of braking in which the shoe is in contact with the moving equipment;

the control unit is programmed to control the displacement of the shoe towards its braking position during the injection into the blank of fluid of the blowing circuit.

Other objects and advantages of the invention will become apparent in the light of the description of an embodiment, given hereinafter with reference to the accompanying drawings, in which:

Figure 1 is a perspective view, in partial section, of a forming station equipped with a drawing unit, shown before the initiation of drawing and pre-blowing;

Figure 2 is a view similar to Figure 1, wherein the forming station is shown during the blowing phase, in the lower position of the rod, with inset a detail on an enlarged scale centered on the distal end of the rod;

FIG. 3 is a cross-sectional detail view of the forming station, according to the sectional plane III-III of FIG. 2, showing a mechanical brake of the moving element provided with a shoe which is here in a release position;

- Figure 4 is a detail view in section according to the inset IV of Figure 3, centered on one end of the shoe;

Figure 5 is a view similar to Figure 4, showing the shoe in a braking position in which the shoe is applied against a complementary portion of the moving element;

FIG. 6 is a diagram illustrating the positional variations of the drawing rod during a complete forming cycle; in this diagram are lettered the different phases of forming of the container and the feeding or cutting phases of the drawing unit.

FIG. 1 shows a station 1 for forming a container

2 by stretch blow molding from a plastic blank 3, in particular PET (polyethylene terephthalate). The blank 3 may be a raw injection preform (as in the example shown) or an intermediate container obtained by one or more preforming operations performed on a blank preform. In practice, the forming station 1 is mounted, with other similar forming stations, on a rotating carousel of a forming machine.

The forming station 1 is automatically controlled by a control unit 4 comprising at least one controller (for example of the API type - acronym for an industrial PLC) equipped with actuators.

Each forming station 1 comprises, in the first place, a mold 5 provided with a wall 6 defining a cavity 7 at the footprint of the container 2 to be formed, which extends along a main axis 8, and a bottom 9 mold having a surface 10 greater than the footprint of the bottom of the container 2 to form.

The mold 5 is for example of the wallet type and comprises two half-molds 5A, 5B hinged around a common hinge and which open to allow, successively, the evacuation of a container 2 formed and the introduction of a blank 3 previously heated in a thermal conditioning machine placed upstream of the forming machine.

Each forming station 1 comprises, secondly, an injection device 11 comprising a nozzle 12 defining an injection chamber 13. The nozzle 12 is mounted directly above the mold 5 while being axially movable relative thereto between a disengaged position in which the nozzle 12 is spaced from the mold to allow both the introduction of a blank 3 into the and evacuation of a container 2 formed, and a coupled position (illustrated in Figures 1 and 2) wherein the nozzle 12 is sealingly applied against the mold 5 around the blank 3 to ensure the setting in fluidic communication of the injection chamber 13 with the interior of the blank 3.

The injection device 11 furthermore comprises a pre-blowing fluidic circuit 14, which fluidly connects the injection chamber 13 to a source 15 of fluid at a so-called pre-blowing pressure, via a controlled pre-blast solenoid valve 16. by the control unit 4. In practice, the fluid is a gas, such as air. The pre-blowing pressure is for example between 5 and 10 bar. The injection device 11 further comprises a fluidic blowing circuit 17, which fluidly connects the injection chamber 13 to a source 18 of fluid at a so-called blowing pressure, greater than the pre-blowing pressure, via a solenoid valve 19 blowing controlled by the control unit 4. In practice, the fluid is air. The blowing pressure is for example between 20 and 40 bar. The injection device 11 comprises, finally, a degassing circuit 20 which fluidly connects the injection chamber 13 to the free air, via a solenoid valve 21 for venting controlled by the unit. 4 of control.

Each forming station 1 comprises, thirdly, a drawing unit 22 equipped with:

a frame 23 fixed on the carousel of the forming machine, and which extends substantially in line with the mold 5; in the illustrated example, the frame has a U-shaped horizontal section; a mobile crew 24 provided with a carriage 25 and a drawing rod 26, secured to the carriage 25 by a proximal end 27, and intended to hold the container 2 being shaped in the axis 8 of the mold 5 by a distal end 28 rounded opposite the proximal end 27;

an electric motor 29 coupled to the mobile crew 24 to ensure, under certain conditions, displacement. The electric motor 29 is connected to the control unit 4, which controls it by AC power via an electric circuit.

As can be seen in FIGS. 1 and 2, the rod 26 extends axially through the nozzle 12. A fluid seal of the primary source and the secondary source 18 is formed between the rod 26 and the nozzle 12 , for example by means of a dynamic seal carried by the nozzle 12 and in constant contact with the rod 26, regardless of the axial position thereof.

The motor 29 is for example a linear induction motor comprising:

a linear stator 31 integral with the frame 23, supplied with current via the circuit 30 to produce a magnetic field which moves linearly under the control of the control unit 4, a linear rotor 32 integral with the carriage 25, mounted facing the stator 31 and carrying a series of permanent magnets which move in synchronism with the magnetic field thereof. The carriage 25 (with the rod 26) is thus mounted to move in translation relative to the frame 23 (and therefore with respect to the mold 5) between:

a high position (Figure 1) in which the rod 26 is completely out of the mold 5, beyond even a blank 3 mounted in the mold 5;

a low position (FIG. 2) in which the rod 26 is received in the mold 5, its distal end being situated near the bottom 9 of the mold with the container 2 formed (or in the process of forming) sandwiched between the bottom 9 of the mold and the distal end 28 of the rod 26.

The linear guidance of the mobile crew 24 relative to the frame 23 is provided by means of one or more stirrups (33) secured to the carriage (25) and which cooperates (s) with one or more rail (s) 34 integral to the frame 23. This guidance is sufficiently precise to maintain a constant air gap 35 between the stator 31 and the rotor 32.

The forming station 1 comprises, fourthly, a mechanical brake 36 able to immobilize the moving crew 24 relative to the frame 23 - and thus to immobilize the rod 26 relative to the mold 5 and the bottom 9 of the mold.

According to an embodiment illustrated in FIG. 3, this brake 36 comprises a shoe 37 mounted to move between a braking position (FIG. 5) in which the shoe 37 is in plane contact with a track 38 integral with the mobile equipment (FIG. and more specifically the carriage 25) for generating, at the interface between the shoe 37 and the track 38, friction forces which oppose their mutual movement, and a release position (FIG. 4) in which the shoe 37 is removed from track 38.

The brake 36 comprises an actuator 39 configured to place the shoe 37 in one or other of its positions on command of the control unit 4. This actuator 39 may be electric but, according to a preferred embodiment illustrated in FIG. 3, the actuator 39 is fluidic (hydraulic or pneumatic). More specifically, in the example shown, the actuator 39 is in the form of a jack simple effect, which comprises a cylinder 40 and a rod 41 on which is mounted the shoe 37.

The rod 41 is integral with a piston 42 slidably mounted in the cylinder 40 between a braking position corresponding to the braking position of the shoe 37, and a release position (FIG. 3) corresponding to the release position of the shoe 37.

The cylinder 40 is fixed on the frame 23 (in particular by screwing), for example outside thereof. An opening 43 is then formed in the frame 23 to allow the passage of the rod 41.

The cylinder 40 is closed by a front wall 44 and a rear wall 45. The rod 41 passes through the wall 44 before sealing, and defines therewith a chamber 46 in which a fluid under pressure can be injected. The chamber 46 is in fluid communication, via a solenoid valve 48 controlled by the control unit 4, with a source 49 of fluid (for example air or oil) under pressure. In the illustrated example, the fluid is air, and the solenoid valve 48 is three-way: a first connected to the source 49, a second to the chamber 46 and the third to the open air.

Between the piston 42 and the rear wall 45 is interposed at least one return spring 47 operating here in compression - in the illustrated embodiment, the spring 47 is double return and includes two coaxial turns, which increases its stiffness as well as the compressive force that it exerts on the piston 42. In the absence of pressure in the chamber 46 (that is to say when the control unit 4 places, via the solenoid valve 48, the chamber 46 in the open air), the return spring 47 places the piston 42 (and therefore the shoe 37) in its braking position. Conversely, the injection of the fluid into the chamber 46, controlled by the control unit 4 via the solenoid valve 48, causes the passage of the piston 42 (and thus the shoe 37) towards its release position, against the return force exerted by the spring 47.

The braking track 38 may be in the form of an integrated insert to the mobile crew 24 being fixed on the carriage 25. According to an embodiment illustrated in FIGS. 3, 4 and 5, the track 38 has a T-shape, with a core 50 through which the track 38 is fixed on the carriage 25 and a plate 51 which extends transversely with respect to the core 50. The shoe 37 has an end face 52 which, in the braking position, abuts against the plate 51 to exert against it a frictional force.

As regards the materials, the shoe 37 may, in the manner of a disc brake lining, be made of a composite material comprising an organic matrix loaded with fibers, in particular glass or carbon, or in a ceramic. The track 38 may itself, in the manner of a brake disc, be made of steel, cast iron, carbon fiber composite, or in a ceramic.

The manufacture of a container 2 from a blank 3 (in particular a preform) first comprises a preliminary phase of introduction of the blank 3 into the mold, conducted in the first open position then closed the mold, and in the upper position of the rod 26 (FIG. 1).

Next, a pre-blast phase 100 of the blank 3 is provided, which comprises the operations of:

injecting into the blank 3 the fluid at the pre-blowing pressure; for this purpose, the control unit 4 controls the opening of the pre-blowing solenoid valve 16 to put in fluid communication the fluid source 15 at the pre-blowing pressure with the injection chamber 13 (and therefore with the blank 3);

moving the drawing rod 26 from its upper position to its lower position (FIG. 2) during a so-called downward phase of the rod; for this purpose, the control unit 4 controls the power supply of the motor 29.

The pre-blowing causes the swelling of the blank 3 to come into only partial contact with the wall 6 and the bottom 9 of the mold, the pre-blowing pressure not being sufficient to completely press the blank 3 against the wall 6. In other words, the impression is insufficient.

The resultant (white arrow in the detail medallion of FIG. 2) is marked R of the pressure-resistant forces (black arrows in the detail medallion of FIG. 2) which are exerted at the distal end 28 of the rod 26, and possibly on any shoulder (or staging) that it may have and which would extend in the blank 3 during forming. As can be seen in FIG. 6, if the pre-blowing phase 100 and the descending phase 110 of the rod 26 overlap, their respective beginnings and ends do not necessarily coincide. In particular, the descending phase 110 of the rod 26 is advantageously initiated before the pre-blowing phase 100, the latter being initiated when the distal end of the rod 26 reaches (in an estimated manner) the bottom of the blank 3 otherwise a misalignment of the blank 3 could occur. During the descent phase of the rod 26, the brake 36 remains in the release position.

There is then provided a phase 200 for blowing the blank 3, which comprises the operations of:

injecting into the blank 3 the fluid at the blowing pressure; for this purpose, the control unit 4 controls the closing of the pre-blowing solenoid valve 16 and the opening of the blowing solenoid valve 19 to put in fluidic communication the source

18 of fluid at the blowing pressure with the injection chamber 13 (and thus with the blank 3);

immobilizing the drawing rod 26 in its lower position (FIG. 2) during a phase 210 called blocking of the rod 26, to maintain, in the center of the bottom of the container 2, the material pinched between the rod 26 and the bottom 9 of the mold, to prevent slippage of the material under the effect of the blowing pressure.

The blowing plate intimately material of the blank 3 against the wall 6 of the mold 5 and against the bottom 9 mold, and thus takes the impression of the container 2.

The blow-off solenoid valve 19 is kept open for a predetermined duration (of a few tenths of seconds in practice) during which the material is subjected to cooling (or on the contrary annealing, depending on whether the wall 6 is cooled or cooled) in contact with the wall 6. heated) which tends to freeze and thus perpetuate the shape of the container 2.

When the rod 26 comes into contact with the bottom 9 of the mold (via the material of the container 2 which is pinched between them), the control unit 4 can detect or estimate, the latter, programmed to this effect, controls the stopping of the power supply of the motor 29 to prevent overheating thereof. This is why a mechanical braking operation is provided for the rod 26 in position low. This mechanical braking is performed, on command of the control unit 4 programmed for this purpose, by activation of the brake 36, that is to say by supplying fluid (from the source 49) of the chamber 46 of the actuator 39 via the solenoid valve 48, which causes the passage of the shoe 37 in the braking position. The friction force generated on the shoe 37 by contact with the braking track 38 compensates the resultant R and is sufficient to ensure the immobilization of the rod 26 during blowing.

The activation of the brake 36 initiates the blocking phase 210 of the rod 26. According to one embodiment, the initiation of the blocking phase 210 coincides with the initiation of the blowing phase 200. However, the initiation of the blocking phase 210 of the rod 26 and the initiation of the blowing phase 200 do not necessarily coincide, since the contact of the rod 26 with the bottom 9 of the mold may occur earlier or, as illustrated in Figure 6, later than the end of the pre-blast phase 100.

In the latter case, and as illustrated in FIG. 6, the initiation of the blowing phase 200 (that is to say the opening control of the blowing solenoid valve 19) then precedes the initiation of the phase 210 blocking the rod 26 in the low position. Given the response time of the solenoid valves (and in particular the solenoid valve 19 for blowing), and the time (a few hundredths of a second) necessary to establish the blowing pressure in the blank 3, the delay of the beginning of the Blocking phase 210 of the rod 26 with respect to the beginning of the blowing phase 200 is only apparent. The stroke of the shoe 37 being small, its passage from its release position to its braking position is extremely short (of the order of a hundredth of a second), so that in practice, the effective immobilization of the rod 26 in low position is achieved before the pressure in the blank 3 has reached the blowing pressure. In other words, the resultant R of the forces never reaches a value sufficient to lift the rod 26 from its low position.

Alternatively, the initiation of the pre-blowing phase 200 may be subsequent to the initiation of the blocking phase 210 of the rod 26, when it reaches the bottom 9 of the mold before the end of the pre-blowing phase 100. It will be observed that in the absence of mechanical braking of the rod 26 during blowing, it would be necessary to maintain a full power supply of the stator 31 during blowing, which would cause rapid overheating of the stator 31, the rotor 32 remaining blocked in position by the stop of the rod 26 against the bottom 9 of the mold

It is however possible, during the blocking phase 210, to maintain a partial power supply of the stator 31 to add to the mechanical force exerted by the brake 36 on the rod 26 an electromagnetic component (without, however, resulting in overheating stator 31).

The blocking phase 210 of the rod 26 extends during at least part of the blowing phase 200. In the example illustrated in FIG. 6, the blocking phase 210 ends at the same time as the blowing phase 200, the control unit 4 controlling simultaneously (taking into account the response times) the tilting of the brake 36 towards its release position and the closure of the solenoid valve 19 blowing.

Alternatively, the blocking phase 210 may terminate before the end of the blowing phase 200. In this case, the control unit 4 controls in advance the tilting of the brake 36 towards its release position and the power supply of the stator 31 to raise the rod 26. As the resultant R helps to raise the rod, However, it is not necessary to fully power the stator 31, which saves the electrical energy consumed by the drawing unit 22.

The immobilization of the rod 26 can be maintained as long as the pressure in the blank 3 (and then the container 2) is equal to the blowing pressure.

According to a particular embodiment, the bottom 9 of the mold is movably mounted relative to the wall between a retracted position in which the bottom 9 of the mold is spaced from the cavity 7, and an extended position in which the mold bottom 9 closes the cavity 7, to allow, during at least part of the blowing phase, a boxing operation consisting, from the retracted position of the mold base 9, to move it to its deployed position to give the bottom material 9 additional stretching to increase its mechanical strength. In this case, the braking of the rod 26 is dosed so as to be sufficient to prevent the spacing of the rod 26 of the bottom 9 mold, while allowing the rise of the rod 26 under the thrust of the mold base 9 during boxing.

The blowing phase 200 is followed by a depressurization phase 300, which comprises the operations of:

o vent container 2; for this purpose, the control unit 4 controls the closure of the solenoid valve 19 for blowing and the opening of the solenoid valve 21 for venting;

o if necessary, perform a scan of the container 2 by injection (simultaneous with the venting) fluid in the container 2 by the rod 26, provided for this purpose with holes opening laterally (that is to say perpendicular to the main axis 8). In this case, the injection device 11 comprises a scanning circuit including a source of fluid at a purge pressure equal to or less than the blowing pressure and greater than the pre-blowing pressure, and a solenoid valve controlled by the unit 4. control device for bringing the source of sweeping fluid into communication with the rod 26 (and thus the container 2);

moving the drawing rod 26 from its low position to its upper position during a phase 310 of raising the rod 26 to allow the evacuation of the container 2 of the mold 5 after opening thereof.

If venting is provided alone, it is called degassing and the pressure in the vessel 2 quickly reaches atmospheric pressure by balancing pressures. In this case, as illustrated in FIG. 6, the rise of the rod 26 can be initiated at the same time as the degassing. If a sweep is planned, it is carried out for a predetermined duration (of a few hundredths of a second) before being interrupted. In this case, the rise of the rod 26 is delayed to allow scanning, and then initiated at the interruption thereof. The venting is then maintained to achieve a final degassing of the container 2.

To evacuate the container 2, the control unit 4 controls the rise of the nozzle 12 and the opening of the mold 5, as well as the closing of the solenoid valve 21 venting. The container 2 is evacuated and the cycle can start again.

Claims

A method of manufacturing a container (2) from a plastic blank (3) in a forming station (1) equipped with:

a mold (5) having a wall (6) defining a cavity (7) at the cavity of the container (2), extending along a main axis (8), and a bottom (9) mold closing the cavity (7) at a lower end of the wall (6);

- An injection device (11) comprising a pre-blowing circuit (14) provided with a source (15) of fluid at a pre-blowing pressure and a blowing circuit (17) provided with a source (18). fluid at a blowing pressure higher than the pre-blowing pressure;

- a drawing unit (22) comprising a movable assembly (24) including a rod (26) movable axially with respect to the wall (6), between a high position in which the rod (26) extends out of the cavity (7), and a low position in which an end (28) distal from the rod (26) is located in the vicinity of the bottom (9) of the mold;

this process comprising successively:

a step of introducing the blank (3) into the mold (5), conducted in the upper position of the rod (26);

a pre-blast phase (100) comprising the steps of:

o injecting into the blank (3), by the pre-blowing circuit (14), a fluid at a pre-blowing pressure;

moving the drawing rod (26) from its upper position to its lower position;

a blowing phase (200) comprising an injection operation in the blank (3), by the blowing circuit (17), of a fluid at a blowing pressure greater than the prespuffing pressure;

this method being characterized in that it comprises a mechanical braking operation of the rod (26) in the low position.

2. Method according to claim 1, characterized in that the mechanical braking operation of the rod (26) is performed during at least a portion of the blowing phase (200).

3. Method according to claim 1 or claim 2, characterized in that the mechanical braking operation of the rod (26) is initiated before the end of the phase (100) pre-blowing.

4. Method according to claim 1 or claim 2, characterized in that the mechanical braking operation of the rod (26) is initiated at the end of the phase (100) pre-blowing.

5. Method according to claim 1 or claim 2, characterized in that the mechanical braking operation of the rod (26) is initiated after the initiation of the blowing phase (200).

6. Method according to one of the preceding claims, characterized in that it comprises a depressurization phase of the container (2), consecutive to the blowing phase, and in that the mechanical braking operation of the rod (26). ) ends simultaneously with the initiation of the depressurization phase.

7. Method according to one of the preceding claims, characterized in that, the bottom (9) of mold being movably mounted relative to the wall (6) between a retracted position in which the mold base is spaced from the cavity ( 7) and an extended position in which the bottom (9) of the mold closes the cavity, the method comprises an operation of moving the bottom (9) of the mold from its retracted position to its deployed position during at least part of the phase ( 200) of blowing.

8. Machine for manufacturing containers (2) from plastic blanks (3), which comprises a forming station (1) equipped with: a mold (5) provided with a wall (6) defining a cavity (7) at the cavity of the container (2), extending along a main axis (8), and a bottom (9) of the mold closing the cavity (7) at a lower end of the wall (6). );

an injection device (11) comprising a pre-blowing circuit (14) provided with a source (15) of fluid at a pre-blowing pressure and a blowing circuit (17) provided with a source (18) of fluid at a blowing pressure higher than the pre-blowing pressure; a drawing unit (22) comprising a movable assembly (24) including a rod (26) axially displaceable with respect to the wall (6), between a high position in which the rod (26) extends out of the cavity (7), and a low position in which an end (28) distal from the rod (26) is located near the bottom (9) of the mold;

a control unit (4) programmed to control the displacement of the rod (26) from its upper position to its lower position and vice versa, and to control the successive injection, in a blank (3) placed in the mold ( 5), fluid of the pre-blowing circuit and the blowing circuit;

characterized in that

the stretching unit (22) comprises a mechanical brake (36) controlled by the control unit (4), provided with an actuator (39) and a shoe (37) integral with the actuator (39). ), movable between a release position in which the shoe (37) is spaced apart from the moving crew (24), and a braking position in which the shoe (37) is in contact with the moving crew (24);

the control unit (4) is programmed to control the displacement of the shoe (37) towards its braking position during the injection into the blank (3) of fluid of the blowing circuit (17).