Method for manufacturing hollow bodies by blow moulding, and blow moulding station

Abstract

The invention relates to a method for manufacturing hollow bodies (12) of thermoplastic material by stretch blow moulding, the method comprising: - a step (E1) of receiving the hollow body (12) in the preform state in a moulding cavity (15) delimited by two half-moulds (14A, 14B), at least one of the half-moulds (14A) being able to be pushed towards the other half-mould (14B) by injection of forming fluid into a compensation chamber (32); - a step (E2) of increasing pressurization of the hollow body (12); - a depressurization step (E3) comprising at least one phase (E3-1, E3-1') for recovering the forming fluid into a storage tank (44A, 44B); characterized in that, prior to the pressurization step (E2), the compensation chamber (32) is placed under a priming pressure (Pc1) by injection of the forming fluid coming solely from the storage tank (44A, 44B).

Description

PROCESS FOR MANUFACTURING HOLLOW BODIES BY BLOW MOLDING AND BLOW MOLDING STATION TECHNICAL FIELD OF THE INVENTION

[0001] The invention relates to a method for manufacturing hollow bodies made of thermoplastic material in the state of final containers by stretch-blow molding comprising a succession of manufacturing cycles during each of which a new hollow body is manufactured, each manufacturing cycle comprising:- a step of receiving the hollow body in the preform state in a molding cavity delimited by at least two half-molds, at least one of the half-molds being capable of being pushed towards the other half-mold by injecting forming fluid into a compensation chamber;- a step of increasing pressurization of the hollow body up to a maximum blowing pressure by injecting a compressed forming fluid coming from at least one source of forming fluid at said maximum blowing pressure;- a depressurization step comprising at least one phase of recovering the forming fluid contained in the hollow body in a storage tank at a storage pressure lower than said maximum blowing pressure; TECHNICAL BACKGROUND OF THE INVENTION

[0002] It is known to produce containers from thermoplastic material, such as polyethylene terephthalate (PET), by a preform stretch-blow molding process.

[0003] Typically, a preform has an axisymmetric shape. The preform has a neck that already has its final shape, while a body of the preform is intended to be deformed during the forming process. The main axis of the preform passes through the center of the neck. The bottom of the preform generally has a hemispherical wall centered on the main axis of the preform.

[0004] To enable its deformation, the body of the preform is heated beyond a glass transition temperature, making the wall of the body malleable by significantly reducing its elastic limit. On the contrary, the neck is kept at a temperature below the glass transition temperature to prevent its deformation.

[0005] In order to produce containers having a wall of substantially constant thickness, it is known to carry out so-called biaxial stretching of the material constituting the wall of the preform to deform it plastically.

[0006] The forming process for this purpose involves injecting a compressed forming fluid at a maximum blowing pressure into the body of the preform so as to allow stretching of the material of the wall of the body of the preform to inflate the preform until it reaches its final shape.

[0007] Typically, this forming process is performed in a mold that has an imprint that conforms to the final container to be obtained. The wall of the preform body is pressed against the wall of the imprint under the pressure of the forming fluid to give the container its final shape.

[0008] When it begins to deform, the preform becomes an intermediate container before reaching its final container shape.

[0009] In the remainder of the description and in the claims, the term hollow body will be used to designate indifferently a preform, an intermediate container or a finished container.

[0010] As is known, each mold is made in at least two parts which can be joined to reconstitute the complete impression of the container to be produced.

[0011] Each mold is mounted in an associated blowing station. To enable the production of containers of different designs, each mold part is removably fixed in a mold holder associated with the blowing station. The mold holders are mounted so that they can move relative to each other between an open position, in which the two mold parts are separated, and a closed position, in which the two mold parts are joined. When changing container designs, the current molds simply need to be removed from the mold holders and replaced with new molds.

[0012] To allow the insertion of a new preform and the extraction of a finished container, the mold supports are controlled in their open position. During the blowing operation, it is imperative that the mold supports occupy a closed position in which the two mold parts are joined.

[0013] To avoid damaging the molds during closing, at least one of the two mold parts is mounted floating with limited play on its mold support. During blowing, a compressed fluid at the same pressure as the blowing fluid, for example 40 bars, is injected into a compensation chamber interposed between the mold support and the floating mold part to press the latter against the other mold part. This makes it possible to obtain containers with a barely visible parting line.

[0014] To ensure that the two mold parts are securely joined without causing the mold supports to open, the mold supports are usually locked in the closed position by a controlled locking device.

[0015] Furthermore, the invention relates in particular to a method where the pressure increase is carried out in stages by connecting the hollow body during manufacture, first to a first source of forming fluid at a pre-blowing pressure, then to a second source of forming fluid at the higher blowing pressure.

[0016] In addition, a portion of the pressurized forming fluid contained in the final container at the end of the blowing step may be recovered in at least one storage tank when the forming fluid is exhausted before extraction of the finished container from its mold. The forming fluid contained in this storage tank is advantageously used to supply the first source of forming fluid. Thus, a portion of the forming fluid is recycled, saving the energy required to pressurize it for the first blowing stages.

[0017] The invention aims to further improve the recycling measures of the pressurized forming fluid used for the operation of the forming unit. BRIEF SUMMARY OF THE INVENTION

[0018] The invention proposes a method for manufacturing hollow bodies made of thermoplastic material in the state of final containers by stretch-blow molding comprising a succession of manufacturing cycles during each of which a new hollow body is manufactured, each manufacturing cycle comprising:- a step of receiving the hollow body in the preform state in a molding cavity delimited by at least two half-molds, at least one of the half-molds being capable of being pushed towards the other half-mold by injecting forming fluid into a compensation chamber;- a step of increasing pressurization of the hollow body up to a maximum blowing pressure by injecting a compressed forming fluid coming from at least one source of forming fluid at said maximum blowing pressure;- a depressurization step comprising at least one phase of recovering the forming fluid contained in the hollow body in a storage tank at a storage pressure lower than said maximum blowing pressure; characterized in that during each cycle, prior to the pressurization step, the compensation chamber is first pressurized to an arming pressure lower than or equal to the storage pressure by injecting the forming fluid coming solely from the storage tank.;

[0019] According to another characteristic of the method carried out according to the teachings of the invention, the pressurization step comprises at least one phase of reuse of the forming fluid during which the forming fluid stored in said storage tank is injected into the hollow body at a pressure less than or equal to said storage pressure.

[0020] According to another characteristic of the method carried out according to the teachings of the invention, during the exhaust step, the compensation chamber is placed in communication with the interior of the hollow body so that the forming fluid contained in the compensation chamber is evacuated towards the storage tank during the recovery phase.

[0021] According to another characteristic of the method carried out according to the teachings of the invention, the pressurization step comprises at least:- a pre-blowing phase during which the hollow body in the preform state is placed at a first pre-blowing pressure lower than the maximum blowing pressure by connection to a source of forming fluid at said pre-blowing pressure; then- a final blowing phase during which the hollow body is placed at the maximum blowing pressure; the arming pressure of the compensation chamber being greater than or equal to the pre-blowing pressure.

[0022] According to another characteristic of the method carried out according to the teachings of the invention, during the pre-blowing phase, the hollow body is supplied with forming fluid coming from the storage tank, the pressure of the forming fluid being reduced by pressure reduction means prior to its injection into the hollow body.

[0023] According to another characteristic of the method carried out according to the teachings of the invention, the forming step comprises at least one intermediate blowing phase of the hollow body which is intercalated chronologically between the pre-blowing phase and the final blowing phase, the intermediate blowing phase consisting of increasing the internal pressure of the hollow body to an intermediate blowing pressure between the pre-blowing pressure and the storage pressure by injecting the forming fluid contained in the storage tank.

[0024] According to another characteristic of the method carried out according to the teachings of the invention, the pressure in the compensation chamber is maintained at the arming pressure throughout the duration of the pressurization step.

[0025] According to another characteristic of the method carried out according to the teachings of the invention, during the pressurization step, the compensation chamber is brought to said maximum blowing pressure by injecting forming fluid from said source of forming fluid at the maximum blowing pressure.

[0026] According to another characteristic of the method carried out according to the teachings of the invention, during the pressurization step, when the internal pressure of the hollow body is greater than or equal to the arming pressure, the compensation chamber is placed in communication with the interior of the hollow body.

[0027] The invention also proposes a blowing station for implementing the method according to the teachings of the invention, characterized in that it comprises:- a molding cavity delimited by two half-molds;- a blowing nozzle which is intended to be connected in a sealed manner with a hollow body in the preform state received in the molding cavity;- a source of forming fluid at a maximum blowing pressure which is connected to the blowing nozzle via a blowing valve controlled between an open state and a closed state;- at least one forming fluid storage tank which is connected to the blowing nozzle via a supply valve controlled between an open state and a closed state;- a compensation chamber delimited in part by one of the half-molds so that an increase in pressure in the compensation chamber pushes said half-mold towards the other half-mold;characterized in that it comprises a filling line which connects the storage tank to the compensation chamber, the filling line being connected to the storage tank upstream of the associated supply valve in a direction of flow of the forming fluid directed from the storage tank towards the blowing nozzle.;

[0028] According to another characteristic of the blowing station produced according to the teachings of the invention, the compensation chamber is connected in bypass with the blowing nozzle by means of a compensation pipe, a compensation valve making it possible to alternately connect the compensation chamber to the storage tank or to the blowing nozzle.

[0029] According to another characteristic of the blowing station produced according to the teachings of the invention, a filter is interposed in the compensation pipe.

[0030] According to another characteristic of the blowing station produced according to the teachings of the invention, the storage tank is connected to the blowing nozzle in parallel by a first associated pipe and by an associated recovery pipe, a filter being interposed in said recovery pipe.

[0031] According to another characteristic of the blowing station produced according to the teachings of the invention, it comprises a source of forming fluid at a pre-blowing pressure which is connected to the blowing nozzle and which is separate from the storage tank.

[0032] According to another characteristic of the blowing station produced according to the teachings of the invention, a regulator is inserted in the arming pipe. BRIEF DESCRIPTION OF THE FIGURES

[0033] Other characteristics and advantages of the invention will appear during the reading of the detailed description which follows for the understanding of which one will refer to the appended drawings briefly described below.

[0034] This is an axial sectional view which schematically represents a station for blowing a hollow body capable of implementing the method according to a first embodiment of the invention.

[0035] This is a top view showing a mold formed from two half-molds mounted in associated mold supports which are here in the closed position.

[0036] This is a view similar to that of in which the mold supports are in the open position.

[0037] This is a sectional view along a sectional plane orthogonal to the joint face of a compensated half-mold which represents a means of sliding guidance of the compensated half-mold relative to its mold support.

[0038] This is a front view of the compensated half-mold which represents its joint face in which an impression of a final container of large volume is made, the outline of a compensation chamber being represented in transparency by broken lines.

[0039] This is a view similar to that of the in which the compensated half-mold is provided with an impression of a final container of volume less than that of the.

[0040] This is a view similar to that of which schematically represents a station for blowing a hollow body capable of implementing the method according to a second embodiment of the invention.

[0041] This is a block diagram which represents the steps of the method carried out according to the first embodiment of the invention.

[0042] This is a block diagram which represents the steps of the method carried out according to the second embodiment of the invention. DETAILED DESCRIPTION OF THE FIGURES

[0043] In the remainder of the description, elements having an identical structure or similar functions will be designated by the same references.

[0044] In the remainder of the description, similar or identical elements will be designated by the same references.

[0045] As illustrated in Figures 1 and 7, a blow molding station 10 for stretch blow molding a hollow body 12, initially in the state of a thermoplastic preform, comprises a mold 14 forming a two-part molding cavity 15 which can move apart to release the hollow body 12 in the final container state. The hollow body 12 is preferably made of thermoplastic material, in particular polyethylene terephthalate (PET).

[0046] The blowing station 10 further comprises a blowing nozzle 16 which is intended to be connected in a sealed manner with the interior of the hollow body 12 received in the molding cavity 15. The blowing nozzle 16 is equipped with a stretching rod 18 movable vertically between a retracted position, shown in solid lines in Figures 1 and 7, and an extended position shown in broken lines in Figures 1 and 7.

[0047] As shown in more detail in Figures 2 and 3, the molding station 10 comprises two mold supports 20A, 20B which are mounted to move between a closed position, shown in, and an open position, shown in. In the example illustrated in the figures, the two mold supports 20A, 20B are mounted to pivot relative to each other about a vertical hinge axis A arranged along a transverse end edge of the mold supports 20A, 20B. Such an arrangement is generally called a wallet mold.

[0048] Although the invention is particularly advantageous with a wallet mold, it is also applicable to mold supports movable in translation relative to each other.

[0049] Each mold support 20A, 20B is delimited longitudinally by a vertical interior receiving face 22 facing the other mold support 20B, 20A when they occupy their closed position.

[0050] The blowing station 10 also comprises the mold 14 which has the molding cavity 15 having the shape of the container to be obtained by blowing. The molding cavity 15 opens vertically upwards through an orifice 24 intended to allow a neck of the hollow body 12 to pass through.

[0051] The mold 14 comprises at least two half-molds 14A, 14B. Each half-mold 14A, 14B has a transverse vertical interior joint face 26 in which the imprint of half of the molding cavity 15 is formed. When the two half-molds 14A, 14B occupy a joined position, as illustrated in FIGS. 1 and 2, the two half-molds 14A, 14B are pressed against each other by their respective joint face 26 so that their imprints reconstitute the molding cavity 15.

[0052] In a variant not shown, the mold can also have a base separate from the half-molds. Thus, each half-mold is suitable for forming the body of the container, while the base is suitable for forming the bottom of the container.

[0053] Referring again to the, each half-mold 14A, 14B also has a vertical exterior assembly face 28 opposite the joint face 26. The assembly face 28 here has a semi-cylindrical shape.

[0054] Each half-mold 14A, 14B is mounted in an associated mold support 20A, 20B by positioning its assembly face 28 against the associated receiving face 22 of the mold support 20A, 20B as shown in Figures 1 and 2.

[0055] One of the half-molds 14A, called compensated half-mold 14A, is mounted to slide orthogonally to the plane of the joint face 26 with a determined clearance E on its mold support 20A. The other half-mold 14B is here fixedly mounted on its mold support 20B, for example by screwing.

[0056] As shown in , the mounting and guiding of the compensated half-mold 14A on its mold support 20A is carried out by means of a rod 29 with an axis orthogonal to the plane of the joint face 26. The rod 29 comprises an inner end section which is removably fixed in a fixing orifice 31 of the assembly face 28 of the compensated half-mold 14A. The rod 29 is here fixed by screwing into the fixing orifice 31. The rod 29 also comprises an intermediate section which is received sliding axially in a passage orifice 33 which passes through the associated mold support 20A. For this purpose, the intermediate section is advantageously smooth. The rod 29 finally comprises an outer end head 35.

[0057] The length of the intermediate section of the rod 29 is determined so that, when the rod 29 is fixed to the compensated half-mold 14A, a longitudinal space E is reserved between the head 35 and a facing face of the mold support 20A to allow limited longitudinal movement of the half-mold 14A relative to the associated mold support 20A.

[0058] Preferably, an elastic member 37 in longitudinal compression is interposed between the head 35 and the outer face of the mold support 20A. The elastic member 37 makes it possible to constantly return the compensated half-mold 14A towards the receiving face 22 of the associated mold support 20A.

[0059] In the embodiment shown in the figures, each half-mold 14A, 14B is made in a single piece.

[0060] In an alternative embodiment of the invention, not shown, each half-mold is made from at least two parts which are fixed to one another. Each half-mold comprises, for example, a shell which carries the molding impression and a shell holder which is equipped with means for cooling the shell. In this case, the outer assembly face of each half-mold is formed by an outer vertical face of the shell holder.

[0061] In the closed position of the mold supports 20A, 20B, the half-molds 14A, 14B occupy their joined position, while in the open position, the joint faces 26 of the half-molds 14A, 14B are spaced apart from each other.

[0062] The transverse side opposite the hinge axis A of the mold supports 20A, 20B is provided with a mechanism 30 for locking in the closed position. This well-known locking mechanism 30 is not the subject of the invention and will not be described in more detail below.

[0063] During the forming of the hollow body 12, a pressurized forming fluid is injected through the orifice 24 of the molding cavity 15 into a hollow body 12 housed in the molding cavity 15 in order to deform and press the walls of the preform against the walls of the molding cavity 15, the mold supports 20A, 20B occupying their closed position. The forming fluid exerts pressure on the walls of the molding cavity 15 which tends to separate the half-molds 14A, 14B longitudinally from each other. To prevent a gap from forming between the two joint faces 26 during the forming of the hollow body 12 into a final container, it is known to equip the compensated half-mold 14A with a sealed compensation chamber 32.

[0064] The compensation chamber 32 is interposed longitudinally between the compensated half-mold 14A and its mold support 20A, as shown schematically in Figures 1 and 7. The compensation chamber 32 is thus delimited in part by said compensated half-mold 14A. The compensation chamber 32 is for example delimited by an annular seal 34 which is compressed between the receiving face 22 of the mold support 20A and the assembly face 28 of the compensated half-mold 14A. The annular seal 34 is for example received in a groove hollowed out in the assembly face 28 of the compensated half-mold 14A, as shown in Figures 1 and 7.

[0065] The compensated half-mold 14A is mounted to slide longitudinally on the mold support 20A between a retracted position in its mold support 20A in which the compensation chamber 32 has its minimum volume, not shown, and an extended position towards the other half-mold 14B, not shown, in which the compensation chamber 32 has its maximum volume.

[0066] As will be explained in more detail later, during operation of the blowing station 10, a pressurized fluid is introduced into the compensation chamber 32 to press the joint face 26 of the compensated half-mold 14A against the joint face 26 of the other half-mold 14B. Thus, an increase in pressure in the compensation chamber 32 pushes said compensated half-mold 14A towards the other half-mold 14B.

[0067] Furthermore, the blowing nozzle 16 is connected to at least one source 36 of forming fluid at a first pre-blowing pressure Pf1.

[0068] The source 36 of forming fluid at the pre-blowing pressure Pf1 is connected to the blowing nozzle 16 via a pre-blowing pipe 38 in which a first pre-blowing supply valve 40 is interposed. The first pre-blowing supply valve 40 is controlled between a fully open state in which it supplies the blowing nozzle 16 with forming fluid at a maximum flow rate and a fully closed state in which the passage of the forming fluid is prohibited.

[0069] The pre-blowing line 38 comprises at least one limited flow section 42 capable of allowing the forming fluid to pass with a first determined flow rate D1, called limited flow rate D1. The limited flow section 42 is interposed between the source 36 of forming fluid at the pre-blowing pressure Pf1 and the pre-blowing supply valve 40.

[0070] To limit the flow rate, the flow-limited section 42 of the pre-blowing line 38 comprises, for example, at least one flow limiter. This is, for example, a flow limiter controlled to vary the first limited flow rate D1 between a minimum flow rate and a maximum flow rate.

[0071] The blowing station 10 comprises at least one reservoir 44A, 44B for storing pressurized forming fluid which is connected to the blowing nozzle 16 via the associated supply valve 40, 78. The associated supply valve 40, 78 is controlled between an open state and a closed state.

[0072] Said storage tank 44A, 44B comprises forming fluid stored at a pressure Ps greater than or equal to the pre-blowing pressure Pf1.

[0073] The blowing nozzle 16 is also connected to said storage tank 44A, 44B via a recovery pipe 48, 80 in which a recovery valve 50, 82 is interposed. This makes it possible to reuse a portion of the pressurized forming fluid contained in the hollow body 12 at the end of its forming to participate in the forming of a subsequent hollow body 12 into a final container. This makes it possible in particular to reduce the overall energy expenditure for producing a final container.

[0074] A filter 51, 84 is advantageously interposed in the recovery pipe 48, 80 to prevent polluting particles from being reintroduced into a hollow body 12 during a subsequent blowing.

[0075] The blow nozzle 16 is also connected to a source 52 of forming fluid at a maximum blow pressure Pfmax, for example approximately 40 bars. The source 52 of blow forming fluid at the maximum blow pressure Pfmax is connected to the blow nozzle 16 via a blow pipe 54 in which a blow valve 56 is interposed.

[0076] Generally, the blowing station 10 is arranged in a forming unit (not shown) comprising several identical blowing stations 10. This is for example a forming unit having a rotating carousel at the periphery of which the blowing stations 10 are mounted. In this case, the storage tank 44A, 44B may be common to several blowing stations 10.

[0077] The forming fluid here is formed by air.

[0078] The maximum blowing pressure Pfmax is, for example, around 40 bars. The pre-blowing pressure Pf1 is lower than the maximum blowing pressure Pfmax. It is, for example, between 6 bars and 20 bars.

[0079] The blowing nozzle 16 is also connected to atmospheric pressure via an exhaust pipe 58. The exhaust pipe 58 is here equipped with a silencer 60. An exhaust valve 62 is interposed in the exhaust pipe 58.

[0080] The hollow body 12 in the preform state comprises a neck 64 and a body 66 which is preheated before being introduced into the molding cavity 15. During stretch-blow molding, the molding cavity 15 is closed around the body 66, the blow nozzle 16 is coupled to the neck 64.

[0081] According to the teachings of the invention, the storage tank 44A, 44B is connected to the compensation chamber 32 via a filling pipe 68. The filling pipe 68 is connected to the storage tank 44A, 44B upstream of the associated supply valve 40, 78 in a direction of flow of the forming fluid directed from the storage tank 44A, 44B towards the blowing nozzle 16.

[0082] A compensation valve 70 is interposed in the arming pipe 68 to allow the supply of the compensation chamber 32 with forming fluid from the storage tank 44A, 44B to be controlled.

[0083] The compensation chamber 32 is further connected in bypass with the blowing nozzle 16 via a compensation pipe 72.

[0084] The compensation line 72 is here connected to the blowing line 54 downstream of the blowing valve 56 in a direction of flow of the forming fluid directed from the source 52 of forming fluid at the maximum blowing pressure Pfmax towards the blowing nozzle 16.

[0085] A controlled valve makes it possible to connect the compensation chamber 32 with the blowing nozzle 16. The compensation valve 70 is here a three-way valve which is controlled between a first position in which it connects the compensation chamber 32 to the storage tank 44A, 44B, and a second position in which it connects the compensation chamber 32 to the blowing nozzle 16.

[0086] A filter 74 is interposed in the compensation pipe 72. As explained in more detail below, this makes it possible to avoid contaminating the hollow body 12 with particles, in particular particles of elastomeric material coming from the annular seal 34, when the forming fluid present in the compensation chamber 32 is discharged towards the blowing nozzle 16.

[0087] In a variant of the invention not shown, a pressure reducer, separate from the pressure reducer 46 of the source 36 of forming fluid at the pre-blowing pressure Pf1, is inserted in the arming pipe 68 upstream of the compensation valve 70. Such a pressure reducer makes it possible to constantly control the pressure in the compensation chamber 32 as a function of the force required to keep the two half-molds joined. The pressure reducer is for example controlled by the electronic control unit to make it possible to adapt the pressure in the compensation chamber 32 as a function of the ratio between the projected surface S1 of the impression on the joint face 26 and the projected surface of the compensation chamber 32 on the joint face 26.

[0088] A method of manufacturing hollow bodies 12 made of thermoplastic material in the state of final containers by stretch-blow molding using the blow molding station 10 described above is now described.

[0089] The manufacturing process involves a succession of manufacturing cycles during each of which a new hollow body 12 is manufactured.

[0090] Each manufacturing cycle comprises a first step E1 of receiving the hollow body 12 in the preform state in the molding cavity 15 delimited by the two half-molds 14A, 14B. The two mold supports 20A, 20B are closed.

[0091] This first reception step E1 is followed by a second step E2 of increasing pressurization of the hollow body 12 up to the maximum blowing pressure Pfmax by injecting a compressed forming fluid.

[0092] The E2 pressurization step generally includes at least one E2-1 pre-blowing phase followed by one E2-2 final blowing phase.

[0093] During the pre-blowing phase E2-1, the hollow body 12 in the preform state is brought to a first pre-blowing pressure Pf1 lower than the maximum blowing pressure Pfmax by connection to the source 36 of forming fluid at the pre-blowing pressure Pf1.

[0094] During the final blowing phase E2-2 during which the hollow body 12 is brought to the maximum blowing pressure Pfmax by connection with the source 52 of forming fluid at a maximum blowing pressure Pfmax.

[0095] Finally, this second pressurization step E2 is followed by a step E3 of depressurization of the hollow body 12 thus formed. This depressurization step E3 comprises at least one phase E3-1 of recovery of at least a portion of the forming fluid contained in the hollow body 12 during which the forming fluid is recovered in the storage tank 44A, 44B at a storage pressure lower than said final blowing pressure Pf max.

[0096] The pressurizing step E2 comprises at least one phase of reusing the forming fluid during which the forming fluid stored in said storage tank 44A, 44B is injected into the hollow body 12 at a pressure less than or equal to said storage pressure,

[0097] Prior to the pressurizing step E2, the compensated half-mold 14A is pushed toward the other half-mold 14B by injecting forming fluid into the compensation chamber 32. To do this, the compensation chamber 32 is first pressurized to an arming pressure Pc1 less than or equal to the storage pressure by injecting the forming fluid coming only from the storage tank 44A, 44B. This arming pressure Pc1 is sufficient to press the joint face 26 of the compensated half-mold 14A against the joint face 26 of the other half-mold 14B before the start of the pressurizing step E2.

[0098] The arming pressure Pc1 of the compensation chamber 32 is for example greater than or equal to the pre-blowing pressure Pf1, but less than the maximum blowing pressure Pfmax.

[0099] The arming pressure Pc1 is in particular sufficient to oppose the elastic return force of the elastic members 37.

[0100] During the depressurization step E3, the compensation chamber 32 is placed in communication with the interior of the hollow body 12 so that the forming fluid contained in the compensation chamber 32 is evacuated to the storage tank 44A, 44B during the recovery phase E3-1.

[0101] The invention thus makes it possible to use recycled forming fluid to bring the compensation chamber 32 to the arming pressure Pc1. This very advantageously makes it possible to save the energy required to pressurize the compensation chamber 32 to the arming pressure Pc1. This saving is all the more significant in the context of a large-scale production facility as is the case here.

[0102] Furthermore, the fact of placing the compensation chamber 32 at an arming pressure Pc1 lower than the maximum blowing pressure Pfmax initially makes it possible very advantageously to reduce the wear of the joint faces 26 of the molds by preventing them from colliding too violently during pressurization.

[0103] In addition, during the third depressurization step E3, the compressed forming fluid contained in the compensation chamber 32 can be reused. This reuse is notably implemented when the compensation chamber 32 is put at a pressure Pc2 higher than that of the storage tank 44A, 44B as will be explained later.

[0104] This reuse is also likely to be implemented when the blowing station 10 comprises several storage tanks 44A, 44B as will be explained in a second embodiment of the invention, and in particular when one of the storage tanks has a storage pressure lower than that of the storage tank which supplies the compensation chamber 32.

[0105] According to a first embodiment of the invention shown in , the source 36 of forming fluid at the pre-blowing pressure Pf1 here comprises a first forming fluid storage tank 44A. The first forming fluid storage tank 44A is connected to the blowing nozzle 16 via the first pre-blowing supply valve 40 which is controlled between an open state and a closed state.

[0106] The first storage tank 44A comprises forming fluid stored at a pressure PsA greater than or equal to the pre-blowing pressure Pf1 and less than the maximum blowing pressure Pfmax. To enable the forming fluid to be delivered at the pre-blowing pressure Pf1, the source 36 of forming fluid at the pre-blowing pressure Pf1 comprises pressure reducing means which are arranged downstream of the first forming fluid storage tank 44A to bring the forming fluid to the pre-blowing pressure Pf1. This is a pressure reducer 46. The pressure reducer 46 is arranged upstream of the limited flow section 42.

[0107] The blowing nozzle 16 is also connected to the first storage tank 44A via a first recovery pipe 48 in which a first recovery valve 50 is interposed. This makes it possible to reuse a portion of the pressurized forming fluid to participate in the forming of a subsequent hollow body 12 into a final container. This makes it possible in particular to reduce the overall energy expenditure necessary for pressurizing the forming fluid to produce a final container.

[0108] A filter 51 is advantageously interposed in the first recovery pipe 48 to prevent polluting particles from being reintroduced into a hollow body 12 during a subsequent blowing.

[0109] The first storage tank 44A is connected to the compensation chamber 32 via the arming line 68 as previously described.

[0110] In the example shown in 1, the arming line 68 is connected to the pre-blowing line 38 upstream of the limited flow section 42 in a direction of flow of the forming fluid directed from the first storage tank 44A towards the blowing nozzle 16. This makes it possible to fill the compensation chamber 32 more quickly as will be explained later.

[0111] In the example shown in , the arming line 68 is connected to the pre-blowing line 38 downstream of the regulator 46 in a direction of flow of the forming fluid directed from the first storage tank 44A towards the blowing nozzle 16. This makes it possible to fill the compensation chamber 32 with a controlled pressure.

[0112] In a variant of the invention not shown, the arming line is connected to the storage tank upstream of the regulator in order to benefit from higher pressure.

[0113] An electronic control unit (not shown) makes it possible to automatically control each valve 40, 50, 56, 62, 70. The electronic control unit makes it possible in particular to control all of the valves 40, 50, 56, 62, 70, for example according to a determined timing and / or as a function of the data communicated by a pressure sensor inside the blowing nozzle 16. The different forming fluid pressures inside the hollow body 12 are controlled by controlling the opening time of the valves 40, 50, 56, 62, 70.

[0114] The electronic control unit also allows the flow limiter of the limited flow section 42 to be controlled to control the limited flow D1 of forming fluid, in particular depending on the geometry of the hollow bodies 12 in the preform state. It is important to note that the limited flow D1 is set at the start of production and remains invariable during the container forming process.

[0115] The method of implementing the blowing station 10 according to this first embodiment is now described with reference to the.

[0116] At the end of the reception step E1, when the mold supports 20A, 20B are closed, the compensation valve 70 is controlled in its first position so as to put the first storage tank 44A into communication with the compensation chamber 32. The pressure in the compensation chamber 32 increases to a setting pressure Pc1 which is equal to the pressure delivered by the source 36 of forming fluid at the pre-blowing pressure Pf1. The increase in pressure in the compensation chamber 32 is almost instantaneous because the setting pipe 68 is connected to the pre-blowing pipe 38 upstream of the limited flow section 42.

[0117] The arming pressure Pc1 in the compensation chamber 32 here becomes equal to the pre-blowing pressure Pf1 because the arming line 68 is connected to the pre-blowing line 38 downstream of the regulator 46.

[0118] Alternatively, when the arming line 68 is connected to the first storage tank 44A upstream of the regulator 46, the arming pressure Pc1 is equal to the storage pressure PsA.

[0119] Then the second pressurization step E2 starts with the first pre-blowing phase E2-1. This first pre-blowing phase E2-1 is accompanied by a stretching operation of the hollow body 12. The hollow body 12 is then in the preform state. The stretching rod 18 descends into the body 66 to stretch it axially until it reaches a maximum stretching position in which the bottom of the hollow body 12 is located close to the bottom of the molding cavity 15, as shown in broken lines in the figure.

[0120] During stretching, forming fluid at the pre-blowing pressure Pf1 is injected into the body 66. The pressure in the body 66 increases under the effect of the injection of the forming fluid under pressure. The injection of the forming fluid at the pre-blowing pressure at the same time as the axial stretching under the effect of the sliding of the stretching rod 18 makes it possible to correctly distribute the material in the wall of the hollow body 12. This distribution makes it possible to obtain a substantially constant thickness in the wall of the finished container.

[0121] Pressurization is carried out by opening the pre-blowing supply valve 40. The forming fluid is thus injected at the first pre-blowing pressure Pf1 and with the flow rate D1 limited by the first storage tank 44A via the flow limiter of the flow-limited section 42. Thus, the hollow body 12 is supplied with forming fluid from the first storage tank 44A, the pressure of the forming fluid being reduced by the pressure reducer 46 prior to its injection into the hollow body 12.

[0122] The limited flow rate D1 makes it possible not to stretch the body 66 radially too quickly, thus allowing for better distribution of the material axially.

[0123] After the end of the stretching, the material constituting the walls of the hollow body 12 is correctly distributed. It is therefore possible to increase the pressure in the body 66 more quickly to finalize the stretching of the walls.

[0124] At the end of pre-blowing phase E2-1, pre-blowing valve 40 is closed.

[0125] Then the final blowing phase E2-2 is triggered. During this final blowing phase E2-2, the body 66 continues to expand until it is pressed against the wall of the molding cavity 15.

[0126] During this final blowing phase E2-2, the pressure in the hollow body 12 increases from the pre-blowing pressure Pf1 to the maximum blowing pressure Pfmax. The maximum blowing pressure Pfmax is thus greater than the pre-blowing pressure Pf1. Pressurization is carried out by opening the blowing valve 56. The hollow body 12 is thus supplied with forming fluid by the forming fluid source 52 at the maximum blowing pressure Pfmax.

[0127] The final blowing phase E2-2 ends by maintaining the hollow body 12 in the final container state at said maximum blowing pressure Pfmax for a determined holding time. Maintaining the maximum blowing pressure Pfmax allows the hollow body 12 to match all the shape details imposed by the molding cavity 15 to be shaped into the final container.

[0128] During the final blowing phase E2-2, when the walls of the hollow body 12 are pressed against the molding cavity 15, the pressure of the forming fluid contained in the hollow body 12 exerts a separation force on the two half-molds 14A, 14B. This separation force is more particularly equal to the surface S1 of the orthogonal projection of the impression on the plane of the joint face 26 multiplied by the pressure of the forming fluid. This surface is subsequently called the projected surface S1 of the impression, as illustrated in Figures 5 and 6.

[0129] To prevent the two half-molds 14A, 14B from being separated from each other, it is necessary for the pressure in the compensation chamber 32 to generate a force greater than this separation force. The compensation force generated by the pressure in the compensation chamber 32 is equal to the surface S2 of the orthogonal projection of the contour of the compensation chamber 32 delimited by the annular seal 34 on the joint face 26 of the compensated half-mold 14A multiplied by the pressure in the compensation chamber 32. This surface will subsequently be called the projected surface S2 of the compensation chamber 32 as illustrated in Figures 5 and 6.

[0130] The projected area S2 of the compensation chamber 32 is generally greater than or equal to the projected area S1 of the impression. Therefore, by ensuring that the pressure in the compensation chamber 32 is at least equal to the pressure in the hollow body 12 at all times, it is guaranteed that the compensation force will always be greater than or equal to the separation pressure.

[0131] Preferably, the projected surface area S2 of the compensation chamber 32 is greater than the projected surface area S1 of the impression. Therefore, even if the pressure in the compensation chamber 32 is slightly lower than the pressure in the hollow body 12, it is possible to obtain a compensation force greater than or equal to the sum of the separation force and the elastic restoring force of the elastic members 37.

[0132] At the start of the final blowing phase E2-2, or prior to the start of the final blowing phase E2-2, the compensation chamber 32 is put into communication with the blowing nozzle 16 by controlling the compensation valve 70 in its second position. Thus, when the internal pressure of the hollow body 12 becomes greater than or equal to the arming pressure Pc1, the compensation chamber is put into communication with the interior of the hollow body 12.

[0133] Thus, during the final blowing phase E2-2, the compensation chamber 32 is placed at a pressure Pc2 equal to said maximum blowing pressure Pfmax by placing it in communication with said source 52 of forming fluid at the maximum blowing pressure Pfmax.

[0134] The compensation force is thus always greater than or equal to the sum of the separation force and the elastic restoring force of the elastic members 37.

[0135] In an alternative embodiment of the method, the pressure in the compensation chamber 32 is maintained at the arming pressure Pc1 throughout the duration of the step E2 of pressurizing the hollow body 12, including during the final blowing phase E2-2. This is particularly possible when the projected surface S1 of the cavity is much smaller than the projected surface S2 of the compensation chamber 32. This is for example the case when the molds 14 have a cavity of very small dimensions compared to their size. In this case, the compensation valve 70 remains in its first position until the end of the pressurizing step E2.

[0136] For example, molds 14 may have an imprint to produce large capacity containers, for example 2L, as illustrated in. Molds 14 of the same size may have a smaller imprint to produce small capacity containers, for example 0.5L, as illustrated in. As a result, the separation force produced during the production of small containers is much lower than that produced during the production of large containers. Since the dimensions of the compensation chamber 32 remain the same for the production of these two types of containers, it is possible to compensate for the separation force produced during the production of small containers with a pressure much lower than the pressure required to compensate for the separation force produced during the production of large containers.

[0137] Each cycle then includes a step E3 of depressurizing the forming fluid until the hollow body 12 in the final container state is at atmospheric pressure.

[0138] Although the hollow body 12 is in the final container state, the mold cannot be opened directly to recover the hollow body 12 because the air is still at the maximum blowing pressure Pfmax. The pressure in the hollow body 12 must be lowered before opening the mold.

[0139] Thus, the pressurization step E2 is followed by the depressurization step E3 comprising a first phase E3-1 of recovery of the forming fluid. During this recovery phase E3-1, the pressure in the hollow body 12 decreases from the maximum blowing pressure Pfmax to a recovery pressure Pr. The recovery pressure Pr is thus lower than the maximum blowing pressure Pfmax. The forming fluid is released by opening the first recovery valve 50, the pre-blowing supply valve 40 and the blowing valve 56 being of course closed. The forming fluid is thus discharged to the first storage tank 44A.

[0140] The first recovery pressure Pr is greater than or equal to the storage pressure Ps.

[0141] During this first recovery phase E3-1, the compensation valve 70 remains in its second position, or is controlled in its second position if it occupied its first position. Thus, the forming fluid contained in the compensation chamber 32 is evacuated with the forming fluid contained in the hollow body 12 towards the first storage tank 44A.

[0142] To prevent particles present in the compensation chamber 32 from polluting the hollow body 12, the forming fluid first passes through the filter 74 before reaching the blowing nozzle 16.

[0143] Finally, during an exhaust phase E3-2 of the depressurization step E3, the remainder of the pressurized forming fluid still present in the hollow body 12 and in the compensation chamber 32 is discharged to the atmosphere via the exhaust pipe 58. During this exhaust phase E3-2, the exhaust valve 62 is open while all the other valves are closed and the compensation valve 70 still occupies its second position.

[0144] According to a second embodiment of the invention shown in , the blowing station 10 comprises a source 36 of forming fluid at the pre-blowing pressure Pf1 and a second storage tank 44B which is separate from the source 36 of forming fluid at the pre-blowing pressure Pf1.

[0145] By way of non-limiting example, the source 36 of forming fluid at the pre-blowing pressure Pf1 can be produced, as in the first embodiment. Thus, the blowing station 10 here comprises the first storage tank 44A associated with the source 36 of forming fluid at the pre-blowing pressure Pf1, and the second storage tank 44B which is separate from the first storage tank 44A.

[0146] In this embodiment, the blowing nozzle 16 is connected to the source 36 of forming fluid at the pre-blowing pressure Pf1 and to the source 52 of forming fluid at the maximum blowing pressure Pfmax in a manner identical to that described in the first embodiment. Only the differences with this first embodiment will be described in detail subsequently.

[0147] Thus, the second forming fluid storage tank 44B is connected to the blowing nozzle 16 by an intermediate blowing pipe 76. An intermediate blowing supply valve 78 is interposed in this intermediate blowing pipe 76. The intermediate blowing supply valve 78 is controlled between an open state and a closed state.

[0148] The second storage tank 44B comprises forming fluid stored at a pressure PsB between the pre-blowing pressure Pf1 and the maximum blowing pressure Pfmax.

[0149] The blowing nozzle 16 is also connected to the second storage tank 44B via a second recovery pipe 80 in which a second recovery valve 82 is interposed. This makes it possible to reuse a larger portion of the pressurized forming fluid to participate in the forming of a subsequent hollow body 12 into a final container. This makes it possible in particular to further reduce the overall energy expenditure for producing a final container.

[0150] A filter 84 is advantageously interposed in the second recovery pipe 80 to prevent polluting particles from being reintroduced into a hollow body 12 during a subsequent blowing.

[0151] In this second embodiment, instead of being connected to the pre-blowing line 38, the arming line 68 is connected to the second storage tank 44B. Thus, the arming line 68 connects the second storage tank 44B with the compensation chamber 32 via the compensation valve 70 when it occupies its first position.

[0152] The method of implementing the blowing station 10 according to this second embodiment is very similar to that of the first embodiment. Subsequently, only the differences will therefore be described with reference to the.

[0153] The reception step E1 is here identical to that of the first embodiment.

[0154] Unlike the method according to the first embodiment, at the end of the reception step E1, when the mold supports 20A, 20B are closed, the compensation valve 70 is controlled in its first position so as to put the second storage tank 44B into communication with the compensation chamber 32. The pressure in the compensation chamber 32 increases up to the storage pressure PsB of the second storage tank 44B. This pressure PsB is here higher than the storage pressure PsA in the first storage tank 44A.

[0155] The arming line 68 being connected to the intermediate blowing line 76 upstream of the intermediate blowing supply valve 78, the increase in pressure in the compensation chamber 32 is almost instantaneous.

[0156] The arming pressure Pc1 in the compensation chamber 32 here becomes higher than the storage pressure PsA of the first storage tank 44A.

[0157] The arming pressure Pc1 is for example equal to the storage pressure PsB because the arming line 68 is connected directly to the second storage tank 44B.

[0158] In a variant of the invention not shown, a pressure reducer is inserted in the arming line 68 between the intermediate blowing line 76 and the compensation valve 70. This makes it possible to constantly control the pressure in the compensation chamber 32 independently of pressure variations in the second storage tank 44B.

[0159] The pressurization step E2 here comprises a phase E2-1' of intermediate blowing of the hollow body 12 which is chronologically inserted between the pre-blowing phase E2-1 and the final blowing phase E2-2.

[0160] The intermediate blowing phase E2-1' consists of increasing the internal pressure of the hollow body 12 from the pre-blowing pressure Pf1 to an intermediate blowing pressure Pf2 between the pre-blowing pressure Pf1 and the storage pressure PsB by injecting the forming fluid contained in the second storage tank 44B into the hollow body 12.

[0161] The final blowing phase E2-2 is here identical to that of the first embodiment.

[0162] However, during the blowing phase E2-2, the source 52 of forming fluid at the maximum blowing pressure Pfmax is only used to increase the pressure in the hollow body 12 from the intermediate blowing pressure Pf2 to the maximum blowing pressure Pfmax. This therefore makes it possible to reduce the quantity of forming fluid at the maximum blowing pressure Pfmax used in each cycle.

[0163] As in the first embodiment, at the start of the final blowing phase E2-2, or prior to the start of the final blowing phase E2-2, the compensation chamber 32 is placed in communication with the blowing nozzle 16 by controlling the compensation valve 70 in its second position. Thus, when the internal pressure of the hollow body 12 becomes greater than or equal to the arming pressure Pc1, the compensation chamber is placed in communication with the interior of the hollow body 12.

[0164] Thus, during the final blowing phase E2-2, the compensation chamber 32 is brought to said maximum blowing pressure Pfmax by being placed in communication with said source 52 of forming fluid at the maximum blowing pressure Pfmax.

[0165] The compensation force is thus always greater than or equal to the sum of the separation force and the elastic restoring force of the elastic members 37.

[0166] In an alternative embodiment of the method, the pressure in the compensation chamber 32 is maintained at the arming pressure Pc1 throughout the duration of the step E2 of pressurizing the hollow body 12, including during the final blowing phase E2-2. This is particularly possible when the projected surface S1 of the cavity is much smaller than the projected surface S2 of the compensation chamber 32. This is for example the case when the molds 14 have a cavity of very small dimensions compared to their size. In this case, the compensation valve 70 remains in its first position until the end of the pressurizing step E2.

[0167] In this second embodiment, the depressurization step E3 comprises a first phase E3-1' of recovery of the forming fluid and a second recovery phase E3-1.

[0168] During the first recovery phase E3-1', the forming fluid is first discharged to the second storage tank 44B. The pressure in the hollow body 12 decreases from the maximum blowing pressure Pfmax to a first recovery pressure PrB. The first recovery pressure PrB is thus lower than the maximum blowing pressure Pfmax. The forming fluid is released by opening the second recovery valve 82. The forming fluid is thus discharged to the second storage tank 44B.

[0169] The first recovery pressure PrB is greater than or equal to the storage pressure PsB of the second storage tank 44B.

[0170] During this first recovery phase E3-1', the compensation valve 70 remains in its second position, or is controlled in its second position if it occupied its first position. Thus, the forming fluid contained in the compensation chamber 32 is evacuated with the forming fluid contained in the hollow body 12 towards the second storage tank 44B.

[0171] This first phase E3-1' of recovery of the forming fluid is followed by a second phase E3-1 of recovery of the remaining compressed forming fluid to the first storage tank 44A. During this second recovery phase E3-1, the pressure in the hollow body 12 decreases from the first recovery pressure PrB to a second recovery pressure PrA. The second recovery pressure PrA is thus lower than the second recovery pressure PrB. The forming fluid is released by opening the first recovery valve 50. The forming fluid is thus discharged to the first storage tank 44A.

[0172] The second recovery pressure PrA is greater than or equal to the storage pressure PsA of the first storage tank 44A.

[0173] During this second recovery phase E3-1, the compensation valve 70 remains in its second position. Thus, the forming fluid contained in the compensation chamber 32 is discharged with the forming fluid contained in the hollow body 12 to the first storage tank 44A.

[0174] During these two recovery phases E3-1' and E3-1, to prevent particles present in the compensation chamber 32 from polluting the hollow body 12, the forming fluid first passes through the filter 74 before reaching the blowing nozzle 16.

[0175] This second recovery phase E3-1 is followed by an exhaust phase E3-2 identical to that described previously.

[0176] This second embodiment advantageously makes it possible to recover even more forming fluid, even when the pressure in the compensation chamber 32 remains equal to the arming pressure Pc1 throughout the pressurization step E2. The arming pressure Pc1 is in fact greater than the storage pressure PsA of the first storage tank 44A, which makes it possible to recover a portion of this forming fluid from the depressurization step E3.

[0177] In a variant of this second embodiment (not shown), the arming line is also connected to the pre-blowing line 38. Thus, the compensation chamber can be supplied alternately by the first storage tank, by the second storage tank or by the source of forming fluid at the maximum blowing pressure. In this case, the compensation valve is, for example, a four-way valve.

Claims

Method for manufacturing hollow bodies (12) made of thermoplastic material in the state of final containers by stretch-blow molding comprising a succession of manufacturing cycles during each of which a new hollow body (12) is manufactured, each manufacturing cycle comprising: - a step (E1) of receiving the hollow body (12) in the preform state in a molding cavity (15) delimited by at least two half-molds (14A, 14B), at least one of the half-molds (14A) being capable of being pushed towards the other half-mold (14B) by injecting forming fluid into a compensation chamber (32); - a step (E2) of increasing the pressure of the hollow body (12) up to a maximum blowing pressure (Pfmax) by injecting a compressed forming fluid coming from at least one source (52) of forming fluid at said maximum blowing pressure;- a depressurization step (E3) comprising at least one phase (E3-1, E3-1') of recovering the forming fluid contained in the hollow body (12) in a storage tank (44A, 44B) at a storage pressure (PsA, PsB) lower than said maximum blowing pressure (Pfmax); characterized in that during each cycle, prior to the pressurization step (E2), the compensation chamber (32) is first pressurized to an arming pressure (Pc1) lower than or equal to the storage pressure (PsA, PsB) by injecting the forming fluid coming only from the storage tank (44A, 44B).; Method according to the preceding claim, characterized in that the pressurizing step (E2) comprises at least one phase (E2-1, E2-1') of reusing the forming fluid during which the forming fluid stored in said storage tank (44A, 44B) is injected into the hollow body (12) at a pressure less than or equal to said storage pressure (PsA, PsB). Method according to any one of the preceding claims, characterized in that during the exhaust step (E3), the compensation chamber (32) is placed in communication with the interior of the hollow body (12) so that the forming fluid contained in the compensation chamber (32) is evacuated towards the storage tank (44A, 44B) during the recovery phase (E3-1, E3-1'). Method according to any one of the preceding claims, characterized in that the pressurizing step (E2) comprises at least: - a pre-blowing phase (E2-1) during which the hollow body (12) in the preform state is placed at a first pre-blowing pressure (Pf1) lower than the maximum blowing pressure (Pfmax) by connection to a source (36) of forming fluid at said pre-blowing pressure (Pf1); then - a final blowing phase (E2-2) during which the hollow body (12) is placed at the maximum blowing pressure (Pfmax); the arming pressure (Pc1) of the compensation chamber (32) being greater than or equal to the pre-blowing pressure (Pf1). Method according to the preceding claim, characterized in that during the pre-blowing phase (Pf1), the hollow body (12) is supplied with forming fluid coming from the storage tank (44A, 44B), the pressure of the forming fluid being reduced by pressure reduction means (46) prior to its injection into the hollow body (12). Method according to claim 4, characterized in that the pressurizing step (E2) comprises at least one intermediate blowing phase (E2-1') of the hollow body (12) which is intercalated chronologically between the pre-blowing phase (E2-1) and the final blowing phase (E2-2), the intermediate blowing phase (E2-1') consisting of increasing the internal pressure of the hollow body (12) from the pre-blowing pressure (Pf1) to an intermediate blowing pressure (Pf2) between the pre-blowing pressure (Pf1) and the storage pressure (PsB) by injecting the forming fluid contained in the second storage tank (44B) into the hollow body (12). Method according to any one of the preceding claims, characterized in that the pressure in the compensation chamber (32) is maintained at the arming pressure (Pc1) throughout the duration of the pressurization step (E2). Method according to any one of claims 1 to 6, characterized in that during the pressurization step (E2), the compensation chamber (32) is brought to said maximum blowing pressure (Pfmax) by injecting forming fluid from said source (52) of forming fluid at the maximum blowing pressure (Pfmax). Method according to the preceding claim, characterized in that during the pressurization step (E2), when the internal pressure of the hollow body (12) is greater than or equal to the arming pressure (Pc1), the compensation chamber (32) is placed in communication with the interior of the hollow body (12). Blowing station (10) for implementing the method according to any one of the preceding claims, characterized in that it comprises:- a molding cavity (15) delimited by two half-molds (14A, 14B);- a blowing nozzle (16) which is intended to be connected in a sealed manner with a hollow body (12) in the preform state received in the molding cavity (15);- a source (52) of forming fluid at a maximum blowing pressure (Pfmax) which is connected to the blowing nozzle (16) via a blowing valve (56) controlled between an open state and a closed state;- at least one forming fluid storage tank (44A, 44B) which is connected to the blowing nozzle (16) via a supply valve (40, 78) controlled between an open state and a closed state;- a compensation chamber (32) delimited in part by one of the half-molds (14A, 14B) so that an increase in pressure in the compensation chamber (32) pushes said half-mold (14A) towards the other half-mold (14B); characterized in that it comprises a filling pipe (68) which connects the storage tank (44A, 44B) to the compensation chamber (32), the filling pipe (68) being connected to the storage tank (44A, 44B) upstream of the associated supply valve (40, 78) in a direction of flow of the forming fluid directed from the storage tank (44A, 44B) towards the blowing nozzle (16).; Blowing station (10) according to the preceding claim, characterized in that the compensation chamber (32) is connected in bypass with the blowing nozzle (16) via a compensation pipe (72), a compensation valve (70) making it possible to alternately connect the compensation chamber (32) to the storage tank (44A, 44B) or to the blowing nozzle (16). Blowing station (10) according to the preceding claim, characterized in that a filter (74) is interposed in the compensation pipe (72). Blowing station (10) according to any one of claims 10 to 12, characterized in that the storage tank (44A, 44B) is connected to the blowing nozzle (16) in parallel by a first associated pipe (38, 76) and by an associated recovery pipe (48, 80), a filter (51, 84) being interposed in said recovery pipe (48, 80). Blowing station (10) according to any one of claims 10 to 13, characterized in that it comprises a source (36) of forming fluid at a pre-blowing pressure (Pf1) which is connected to the blowing nozzle (16) and which is separate from the storage tank (44B). Blowing station (10) according to any one of claims 10 to 14, characterized in that a pressure reducer is inserted in the arming pipe (68).

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