INSTALLATION FOR MANUFACTURING HOLLOW BODIES BY STRETCH BLOW MOLDING

Abstract

The invention relates to an installation for manufacturing thermoplastic containers comprising: - a molding cavity (13) capable of receiving a hollow body (12); - a nozzle (14) connected to said hollow body (12); - a sliding stretching rod (16) in order to stretch the hollow body (12); - a pre-blowing pipe (20) which connects the nozzle (14) with a source (18) of pre-blowing fluid; - a pre-blowing valve (22) interposed in the pre-blowing pipe (20); - the pre-blowing pipe (20) comprising a limited flow section (24); characterized in that a bypass pipe (36) is arranged in parallel with the limited flow section (24), a bypass valve (38) being interposed in the bypass pipe (36). Figure for abstract: Figure 1

Description

Title of the invention: INSTALLATION FOR MANUFACTURING HOLLOW BODIES BY STRETCH BLOW MOLDING Technical field of the invention

[0001] The invention relates to an installation for manufacturing containers made of thermoplastic material, in particular PET, by stretch-blow molding of heated preforms, comprising: - at least one molding cavity capable of receiving a hollow body in the preform state; - at least one blowing nozzle capable of being connected in a sealed manner with said hollow body enclosed in the cavity; - at least one stretching rod which is controlled to slide in the cavity in order to stretch the hollow body during a pre-blowing phase; - at least one pre-blowing line which connects the blowing nozzle with a source of forming fluid at a pre-blowing pressure; - at least one controlled pre-blowing valve which is interposed in the pre-blowing line; - the pre-blowing line comprising at least one limited flow section which is interposed between the source of forming fluid at the pre-blowing pressure and the controlled pre-blowing valve, and which is capable of allowing the forming fluid to pass with a first limited flow. Technical background

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

[0003] In general, a preform has an axisymmetric shape. The preform has a neck which 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-shaped 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 it possible to make the wall of the body malleable by significantly reducing its elastic limit. On the contrary, the neck is maintained 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 in order to deform it plastically. The forming process comprises for this purpose a first pre-blowing phase during which a sliding stretching rod is introduced coaxially into the neck of the preform by pushing the bottom of the preform so as to stretch the wall of the body in an axial direction. To prevent the wall of the preform from contracting around the stretching rod during its stretching, forming fluid is injected at a first pre-blowing pressure into the preform to begin the expansion of the body outwards, away from the stretching rod.

[0006] At the end of this stretching step, a compressed forming fluid is injected at a blowing pressure, higher than the pre-blowing pressure, into the body of the preform so as to allow stretching of the material in a generally circumferential direction of the wall of the body of the preform to "inflate" the preform until it reaches its final shape.

[0007] In general, this forming process is carried out in a mold which has an imprint conforming to the final container to be obtained. The wall of the body of the preform is pressed against the wall of the imprint under the effect of 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 definitive shape of “final container”.

[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] 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 the pre-blowing pressure, then to a second source of forming fluid at the higher blowing pressure. This makes it possible to use cheaper sources of forming fluid at intermediate pressures rather than exclusively using a source of forming fluid at maximum pressure.

[0011] In addition, a portion of the pressurized forming fluid contained in the final container at the end of the blowing phase may be recovered in at least one storage tank during the exhaust of the forming fluid before extraction of the finished container from its mold.

[0012] However, existing installations allow more forming fluid to be recovered than they use. A significant portion of pressurized forming fluid is therefore not used and is released into the atmosphere as a waste. Summary of the invention

[0013] The invention proposes an installation for manufacturing containers made of thermoplastic material, in particular PET, by stretch-blow molding of heated preforms, comprising: - at least one molding cavity capable of receiving a hollow body in the preform state; - at least one blowing nozzle capable of being connected in a sealed manner with said hollow body enclosed in the cavity; - at least one stretching rod which is controlled to slide in the cavity in order to stretch the hollow body during a pre-blowing phase; - at least one pre-blowing line which connects the blowing nozzle with a source of forming fluid at a pre-blowing pressure; - at least one pre-blowing valve which is interposed in the pre-blowing line; - the pre-blowing line comprising at least one limited flow section which is interposed between the source of forming fluid at the pre-blowing pressure and the controlled pre-blowing valve, and which is capable of allowing the forming fluid to pass with a first limited flow; characterized in that a bypass line is arranged in parallel with the flow-limited section for connecting the forming fluid source at the pre-blowing pressure with the blow nozzle, the bypass line allowing the passage of forming fluid with a second additional flow rate, a controlled bypass valve being interposed in the bypass line.

[0014] According to another characteristic of the installation produced according to the teachings of the invention, the additional flow rate is greater than the first limited flow rate.

[0015] According to another characteristic of the installation produced according to the teachings of the invention, the limited flow section of the pre-blowing pipe comprises at least one flow limiter to limit the flow rate of passage to said first limited flow rate.

[0016] According to another characteristic of the installation produced according to the teachings of the invention, the flow limiter is controlled to vary the first limited flow between a minimum flow and a maximum flow.

[0017] According to another characteristic of the installation produced according to the teachings of the invention, a downstream end of the bypass pipe is connected to the pre-blowing pipe upstream of the pre-blowing valve.

[0018] According to another characteristic of the installation produced according to the teachings of the invention, a downstream end of the bypass pipe is connected to the blowing nozzle downstream of the pre-blowing valve.

[0019] According to another characteristic of the installation produced according to the teachings of the invention, the source of pre-blowing fluid comprises a storage tank for forming fluid recovered by connection with the hollow body via a forming fluid recovery pipe.

[0020] According to another characteristic of the installation carried out according to the teachings of the invention, the storage tank comprises forming fluid stored at a first storage pressure greater than or equal to the pre-blowing pressure, the source of pre-blowing fluid comprising a pressure reducer which is arranged downstream of the forming fluid storage tank to bring the forming fluid to the pre-blowing pressure.

[0021] According to another characteristic of the installation produced according to the teachings of the invention, the installation comprises: - at least one source of forming fluid at a blowing pressure greater than the pre-blowing pressure, and - at least one blowing line which connects the source of forming fluid at the blowing pressure to the nozzle; - at least one blowing valve which is interposed in the blowing pipe.

[0022] The invention also proposes a method for implementing the installation produced according to the teachings of the invention, comprising a phase of pre-blowing the hollow body in the preform state at the first pre-blowing pressure comprising at least a first stretching step during which the pre-blowing valve is open, the bypass valve being closed, the hollow body being stretched by sliding of the stretching rod during this first step, characterized in that the first pre-blowing phase comprises a second step of opening the bypass valve which is triggered as a function of the stretching of the hollow body.

[0023] According to another characteristic of the method carried out according to the teachings of the invention, the second step of opening the bypass valve is triggered when the drawing of the hollow body is finished.

[0024] According to another characteristic of the method carried out according to the teachings of the invention, the second step of opening the bypass valve is triggered before the end of the drawing of the hollow body.

[0025] According to another characteristic of the method carried out according to the teachings of the invention, the bypass valve is closed after closing the pre-blowing valve.

[0026] According to another characteristic of the method carried out according to the teachings of the invention, it comprises at least one phase of blowing the hollow body at the blowing pressure by connection to the source of forming fluid compressed at the blowing pressure. Brief description of the figures

[0027] Other characteristics and advantages of the invention will appear during the reading of the detailed description which follows for the understanding of which reference will be made to the attached drawings.

[0028] [Fig.l] is an axial sectional view which schematically represents a station for blowing a hollow body capable of implementing the method according to the teachings of the invention.

[0029] [Fig. 2] is a diagram which represents the evolution of the forming fluid pressure in the hollow body as a function of time in the blowing station of [Fig. 1] during the implementation of the method carried out according to the teachings of the invention.

[0030] [Fig. 3] is a detailed view of the diagram of [Fig. 2] showing the distance of the stretching rod from the bottom of the cavity of the blowing station as it slides. Detailed description of the invention

[0031] In the remainder of the description, similar or identical elements will be designated by the same references.

[0032] As illustrated in [Fig.l], a blowing station 10 for stretch-blow molding a hollow body 12, initially in the state of a thermoplastic preform, comprises a mold forming a two-part molding cavity 13 which can move apart to release the hollow body 12 in the state of a final container. The blowing station 10 further comprises a blowing nozzle 14 equipped with a stretching rod 16 movable vertically between a retracted position, shown in solid lines in [Fig.l], and an extended position shown in broken lines in [Fig.l].

[0033] The blowing nozzle 14 is connected to at least one source 18 of forming fluid at a first pre-blowing pressure Pfl.

[0034] The source 18 of forming fluid at the pre-blowing pressure Pfl is connected to the blowing nozzle 14 via a pre-blowing pipe 20 in which a first pre-blowing valve 22 is interposed. The first pre-blowing valve 22 is controlled between a fully open state in which it supplies the blowing nozzle 14 with forming fluid at a maximum flow rate and a fully closed state in which the passage of the forming fluid is prohibited.

[0035] The pre-blowing pipe 20 comprises at least one limited flow section 24 capable of allowing the forming fluid to pass with a first determined flow rate "D1", called limited flow rate "D1". The limited flow section 24 is interposed between the source 18 of forming fluid at the pre-blowing pressure Pfl and the pre-blowing valve 22.

[0036] To limit the flow rate, the limited flow rate section 24 of the pre-blowing pipe 20 comprises, for example, at least one flow rate limiter 26. This is, for example, a flow rate limiter 26 controlled to vary the first limited flow rate "D1" between a minimum flow rate and a maximum flow rate.

[0037] The source 18 of forming fluid at the pre-blowing pressure Pfl here comprises a forming fluid storage tank 28. The storage tank 28 comprises forming fluid stored at a pressure "Ps" greater than or equal to the pre-blowing pressure Pfl. To enable the forming fluid to be delivered at the pre-blowing pressure Pfl, the source 18 of forming fluid at the pre-blowing pressure Pfl comprises a pressure reducer 30 which is arranged downstream of the forming fluid storage tank 28 to bring the forming fluid to the pre-blowing pressure Pfl. The pressure reducer 30 is arranged upstream of the flow-limited section 24.

[0038] The blowing nozzle 14 is also connected to the storage tank 28 via a recovery pipe 32 in which a recovery valve 34 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 to reduce the overall energy expenditure for producing a final container.

[0039] According to the teachings of the invention, a bypass pipe 36 is arranged in parallel with the limited flow section 24 to connect the source 18 of forming fluid at the pre-blowing pressure Pfl with the blowing nozzle 14.

[0040] The bypass pipe 36 has two ends. An upstream end is connected to the pre-blowing pipe 20 upstream of the limited flow section 24. A downstream end is here connected to the pre-blowing pipe 20 downstream of the pre-blowing valve 22.

[0041] The bypass line 36 is sized to allow the passage of the forming fluid at a second determined flow rate "D2". This second flow rate "D2" will subsequently be called "additional flow rate D2". A bypass valve 38 is interposed in the bypass line 36. The bypass valve 38 is controlled between a fully closed state and a fully open state.

[0042] Thus, even when the bypass valve 38 is open, the pre-blowing valve 22 must also be open to allow the blowing nozzle 14 to be supplied with forming fluid with the additional flow rate D2. The blowing nozzle 14 is thus supplied with the sum of the limited flow rate DI and the additional flow rate D2.

[0043] Preferably, the additional flow rate "D2" is greater than the first limited flow rate "D1".

[0044] In a variant of the invention not shown, the downstream end of the bypass pipe is connected to the nozzle 14 downstream of the pre-blowing valve 22. In this case, only the state of the bypass valve controls the supply of the nozzle with forming fluid at the additional flow rate D2, independently of the state of the pre-blowing valve 22.

[0045] The maximum flow rate at which the flow limiter 26 can be opened is here lower than the additional flow rate "D2".

[0046] The blowing nozzle 14 is also connected to a source 40 of forming fluid at a blowing pressure Pf2, for example approximately 40 bars. The source 40 of blowing forming fluid at the blowing pressure Pf2 is connected to the blowing nozzle 14 via a blowing pipe 42 in which a blowing valve 44 is interposed.

[0047] Generally, the blowing station 10 is arranged in a forming unit (not shown) comprising several identical blowing stations 10. In this case, the storage tank 28 may be common to several blowing stations 10.

[0048] The forming fluid is here formed by air.

[0049] The blowing pressure Pf2 is for example of the order of 40 bars. The pre-blowing pressure Pfl is lower than the blowing pressure Pf2. It is for example between 6 bars and 20 bars.

[0050] The blowing nozzle 14 is also connected to atmospheric pressure via an exhaust pipe 46 equipped with a silencer 48. An exhaust valve 50 is interposed in the exhaust pipe 46.

[0051] A pressure sensor (not shown) may be arranged in the blowing nozzle 14 so as to measure the instantaneous pressure prevailing in the hollow body 12.

[0052] The hollow body 12 in the preform state comprises a neck 52 and a body 54 which is preheated before being introduced into the cavity 13. During stretch-blow molding, the cavity 13 is closed around the body 54, the blow nozzle 14 couples onto the neck 52 and the sensor can then measure the pressure in the body 54.

[0053] An electronic control unit 56 makes it possible to control all of the valves 22, 34, 38, 44, 50, for example according to a determined timing and / or as a function of the data communicated by the pressure sensor. The different forming fluid pressures inside the hollow body 12 are controlled by controlling the opening time of the valves 22, 34, 38, 44, 50.

[0054] The electronic control unit 56 also makes it possible to control the flow limiter 26 to control the limited flow rate "D1" of forming fluid, in particular as a function of the geometry of the hollow bodies 12 in the preform state. It is important to note that the limited flow rate "D1" is set at the start of production and remains invariable during the process of forming a container. The response time of such a device does not in fact make it possible to vary the flow rate "D1" in a controlled manner during the forming of a container.

[0055] During the implementation of the manufacturing method, the blowing station 10 successively manufactures several final containers during successive manufacturing cycles. During each manufacturing cycle, a new hollow body 12 in the final container state is manufactured from said hollow body 12 in the preform state.

[0056] When the blowing station 10 is in normal operation, the storage pressure Ps in the storage tank 28 is likely to vary, but it remains greater than or equal to the pre-blowing pressure Pfl.

[0057] Furthermore, the pre-blowing pressure Pfl and blowing pressure Pf2 setpoints are given to the electronic control unit 56 prior to the start of the process.

[0058] Each manufacturing cycle comprises successive phases of increasing pressure on the hollow body 12. The hollow body 12 is successively subjected to a first pre-blowing phase "S1", during which the hollow body 12 in the preform state is stretched axially completely and circumferentially partially, then a second blowing phase "S2", during which the wall of the hollow body 12 is stretched only circumferentially to press it against the mold cavity until it takes its complete shape.

[0059] As shown in more detail in [Fig. 3], the first pre-blowing phase S1 comprises at least a first step E1 of stretching the hollow body 12, between times t0 and t1. The hollow body 12 is then in the preform state. The stretching rod 16 descends into the body 54 to stretch it axially, as indicated by the curve C1, from a point 58 of contact of the stretching rod 16 with the bottom of the hollow body 12, until reaching a maximum stretching position indicated by the point 60 in which the bottom of the hollow body 12 is located close to the bottom of the cavity 13, as shown in broken lines in [Fig. 1].

[0060] Under the effect of this stretching, the body 54 tends to retract radially. To avoid this effect, in particular to prevent contact between the body 54 and the stretching rod 16, forming fluid at the pre-blowing pressure Pfl is injected into the body 54. The pressure in the body 54 increases under the effect of the injection of the forming fluid under pressure.

[0061] Furthermore, the partial circumferential stretching of the material under the effect of the injection of the forming fluid at the pre-blowing pressure at the same time as its axial stretching under the effect of the sliding of the stretching rod 16 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.

[0062] As represented by curve C2 of [Fig. 3], the pressurization is carried out by opening the pre-blowing valve 22, while all the other valves, including the bypass valve 38, are closed. The forming fluid is thus injected at the first pre-blowing pressure Pfl and with the flow rate "Dl" limited by the storage tank 28 via the flow limiter 26.

[0063] The limited flow rate "Dl" makes it possible not to stretch the body 54 radially too quickly, thus making it possible to obtain a better distribution of the material axially. volume of the body 54 gradually increasing under the effect of stretching, the forming fluid pressure inside the body 54 first increases to the pre-blowing pressure Pfl, as indicated by point 62 of [Fig.3], before decreasing to an end-of-stretching pressure "Pe", as indicated by point 64 of [Fig.3].

[0064] 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 54 more quickly to finalize the stretching of the walls in a circumferential direction.

[0065] If it is desired to still benefit from the pressure contained in the storage tank 28, it is necessary to leave the blowing nozzle 14 in communication with the storage tank 28. However, due to the presence of the flow limiter 26, the increase in pressure in the hollow body 12 will be slow, which will have the effect of reducing the productivity of the installation.

[0066] Furthermore, the reaction time of the flow limiter 26 is insufficient to allow a significantly higher filling to be obtained.

[0067] The first pre-blowing phase SI therefore comprises a second step E2 of opening the bypass valve 38 in order to allow the forming fluid to enter the hollow body 12 with the additional flow rate "D2" to increase the pressure in the hollow body 12 very quickly. This step E2 takes place between times t1 and t2 of FIGS. 2 and 3. The control of the bypass valve 38 in fact has a response time adapted in comparison with the duration of the process. This therefore makes it possible to obtain a very rapid increase in pressure from the end of stretching pressure until reaching the pre-blowing pressure Pfl. This is indicated by the slope of curve C2 of [Fig. 3] which increases suddenly.

[0068] The second step "E2" is triggered depending on the position of the stretching rod 16. Preferably, the second step "E2" is triggered when the stretching of the preform by the stretching rod 16 is finished.

[0069] In a variant of the invention not shown, the second step "E2" is triggered a little before the end of the step "El" of stretching the preform 12.

[0070] The pre-blowing pressure Pfl is generally a pressure determined as a function of the geometry of the hollow body 12 in the preform state, either by calculations or by laboratory tests. The pre-blowing pressure Pfl setpoint may optionally be adjusted manually by an operator. The pressure "Ps" in the storage tank 28 is preferably at least 0.5 bar higher than the pre-blowing pressure Pfl to ensure a good flow rate of forming fluid during the second step.

[0071] At the end of step "E2", the pre-blowing valve 22 is closed. To further reduce the duration of the pre-blowing phase S1, the bypass valve 38 is preferably closed after the closing of the pre-blowing valve 22. Thus, the time of The reaction for closing the bypass valve 38 is partly carried out in masked time during the closing of the pre-blowing valve 22. This is all the more important since the second step "E2" only lasts a few milliseconds, for example of the order of 10 ms.

[0072] Then comes a blowing phase S2 which makes it possible to transform the hollow body 12 into the final container. During this blowing phase S2, the body 54 continues to expand until it is pressed against the wall of the cavity 13.

[0073] During this blowing phase S2, indicated between times t2 and t3 of [Fig. 2], the pressure in the hollow body 12 increases from the pre-blowing pressure Pfl to a blowing pressure Pf2. The blowing pressure Pf2 is thus greater than the pre-blowing pressure Pfl. Pressurization is carried out by opening the blowing valve 44, while all the other valves are closed. The hollow body 12 is thus supplied with forming fluid by the forming fluid source 40 at the blowing pressure Pf2.

[0074] At the end of this blowing phase S2, the hollow body 12 in the final container state is maintained at said blowing pressure Pf2 between times t3 and t4 during a holding phase S3. Maintaining the final blowing pressure Pf2 allows the hollow body 12 to match all the shape details imposed by the cavity 13 to be shaped into the final container.

[0075] Each cycle then comprises successive phases of exhausting the forming fluid until the hollow body 12 in the final container state is at atmospheric pressure.

[0076] 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 in it is still at 40 bars. The pressure in the hollow body 12 must be lowered before opening the mold.

[0077] Thus, the holding phase S3 is followed by a phase S4 of recovery of the forming fluid between times t4 and t5. During this recovery phase S4, the pressure in the hollow body 12 decreases from the blowing pressure Pf2 to a recovery pressure Pr. The recovery pressure Pr is thus lower than the blowing pressure Pf2. The forming fluid is released by opening the recovery valve 34, while all the other valves are closed. The forming fluid is thus discharged to the storage tank 28.

[0078] The first recovery pressure Pr is controlled at an equilibrium value with the storage pressure Ps.

[0079] The equilibrium value of the first recovery pressure Pr is equal to the first storage pressure Ps increased by a constant K determined, according to the following equation: Pr = Ps + K

[0080] The determined constant K is preferably strictly greater than 0 bar and is preferably less than or equal to 1 bar. The constant K is for example equal to 0.5 bar.

[0081] Finally, during a final exhaust phase S5, the remainder of the pressurized forming fluid still present in the hollow body 12 is discharged to the atmosphere via the exhaust pipe 46. During this exhaust phase S5, the exhaust valve 50 is open while all the other valves are closed.

[0082] In a variant of the invention not shown, the blowing phase can be carried out in several stages involving additional recovery tanks to improve the overall efficiency of the process.

[0083] The invention thus makes it possible to use a greater quantity of forming fluid recovered from the storage tank which supplies the forming fluid source at the pre-blowing pressure. This is achieved without extending the duration of the manufacturing process and with well-controlled repeatability.

Claims

Claims

1. Installation for manufacturing containers made of thermoplastic material, in particular PET, by stretch-blow molding of heated preforms, comprising: - at least one molding cavity (13) capable of receiving a hollow body (12) in the preform state; - at least one blowing nozzle (14) capable of being connected in a sealed manner with said hollow body (12) enclosed in the cavity (13); - at least one stretching rod (16) which is slidably controlled in the cavity (13) in order to stretch the hollow body (12) during a pre-blowing phase (SI); - at least one pre-blowing pipe (20) which connects the blowing nozzle (14) with a source (18) of forming fluid at a pre-blowing pressure (Pfl); - at least one pre-blowing valve (22) which is interposed in the pre-blowing pipe (20);- the pre-blowing pipe (20) comprising at least one limited flow section (24) which is interposed between the source (18) of forming fluid at the pre-blowing pressure (Pfl) and the controlled pre-blowing valve (22), and which is capable of allowing the forming fluid to pass with a first limited flow rate (Dl); characterized in that a bypass pipe (36) is arranged in parallel with the limited flow section (24) to connect the source (18) of forming fluid at the pre-blowing pressure (Pfl) with the blowing nozzle (14), the bypass pipe (36) allowing the passage of forming fluid with a second additional flow rate (D2), a controlled bypass valve (38) being interposed in the bypass pipe (36).;

2. Installation according to the preceding claim, characterized in that the additional flow rate (D2) is greater than the first limited flow rate (D1).

3. Installation according to the preceding claim, characterized in that the limited flow section (24) of the pre-blowing pipe (20) comprises at least one flow limiter (26) for limiting the flow rate of passage to said first limited flow rate (D1).

4. Installation according to the preceding claim, characterized in that the flow limiter (26) is controlled to vary the first limited flow rate (Dl) between a minimum flow rate and a maximum flow rate.

5. Installation according to any one of the preceding claims, characterized in that a downstream end of the bypass pipe (36) is connected to the pre-blowing pipe (20) upstream of the pre-blowing valve (22).

6. Installation according to any one of claims 1 to 3, characterized in that a downstream end of the bypass pipe (36) is connected to the blowing nozzle (14) downstream of the pre-blowing valve (22).

7. Installation according to any one of the preceding claims, characterized in that the source (18) of pre-blowing fluid comprises a reservoir (28) for storing forming fluid recovered by connection with the hollow body (12) via a forming fluid recovery pipe (32).

8. Installation according to the preceding claim, characterized in that the storage tank (28) comprises forming fluid stored at a first storage pressure (Ps) greater than or equal to the pre-blowing pressure (Pfl), the source (18) of pre-blowing fluid comprising a pressure reducer (30) which is arranged downstream of the forming fluid storage tank (28) to bring the forming fluid to the pre-blowing pressure.

9. Installation according to any one of the preceding claims, characterized in that the installation comprises: - at least one source (40) of forming fluid at a blowing pressure (Pf2) higher than the pre-blowing pressure (Pfl), and - at least one blowing pipe (42) which connects the source (40) of forming fluid at the blowing pressure (Pf2) to the nozzle (14); - at least one blowing valve (44) which is interposed in the blowing pipe (42).

10. Method for implementing the installation produced according to any one of the preceding claims, comprising a phase (SI) of pre-blowing the hollow body (12) in the preform state at the first pre-blowing pressure (Pfl) comprising at least a first stretching step (El) during which the pre-blowing valve (22) is open, the bypass valve (36) being closed, the hollow body (12) being stretched by sliding of the stretching rod (16) during this first step (El); characterized in that the first pre-blowing phase (SI) comprises a second step (E2) of opening the bypass valve (38) which is triggered as a function of the stretching of the hollow body (12).

11. Method according to the preceding claim, characterized in that the second step (E2) of opening the bypass valve (38) is triggered when the stretching of the hollow body (12) is finished.

12. Method according to claim 10, characterized in that the second step (E2) of opening the bypass valve (38) is triggered before the end of the stretching of the hollow body (12).

13. Method according to any one of claims 10 to 12, characterized in that the bypass valve (38) is closed after closing the pre-blowing valve (22).

14. Method according to any one of claims 10 to 13, characterized in that it comprises at least one phase (S2) of blowing the hollow body at the blowing pressure (Pf2) by connection to the source (40) of forming fluid compressed at the blowing pressure (Pf2).

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