METHOD FOR DIAGNOSING FORMING FLUID LEAKS IN A HOLLOW BODY FORMING STATION

Abstract

The invention relates to a method for diagnosing leaks of forming fluid in at least one forming station (10) for hollow bodies (12) during a succession of production cycles, each cycle comprising a first phase (P1) of pressurizing the hollow body (12) by connecting it to a source (22) of forming fluid compressed to a maximum blow-off pressure (Pfmax), followed by a second phase (P2) of passive pressurization during which the hollow body (12) is isolated from the source (22) of forming fluid, characterized in that the diagnostic method comprises a step (E1) of determining the evolution of the pressure of the forming fluid in the hollow body (12) by performing a series of several pressure measurements successively during the passive pressurization phase (P2). Figure for the abstract: Figure 1

Description

Title of the invention: METHOD FOR DIAGNOSING FORMING FLUID LEAKS IN A HOLLOW BODY FORMING STATION Technical field of the invention

[0001] The invention relates to a method for diagnosing leaks of forming fluid in at least one forming station of hollow bodies made of thermoplastic material during a succession of production cycles, each cycle comprising a first phase of pressurizing the hollow body by connecting it to a source of forming fluid compressed to a maximum blowing pressure via a blowing valve, followed by a second phase of passive pressure maintenance during which the hollow body is isolated from the source of forming fluid by closing the blowing valve, a phase of depressurizing the hollow body being triggered at the end of the passive pressure maintenance phase. Technical background

[0002] It is known to produce containers from thermoplastic material, such as polyethylene terephthalate (PET), by a stretch-blowing cycle of preforms.

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

[0004] To allow its deformation, the body of the preform is heated above a glass transition temperature, making the body wall malleable by significantly reducing its elastic limit. Conversely, the neck is maintained at a temperature below the glass transition temperature to prevent its deformation.

[0005] The actual forming of the preforms into final containers is carried out in a forming unit comprising at least one forming station. Generally, a forming unit comprises several forming stations to allow for the production of containers in large series. The forming unit includes, for example, a carousel around the periphery of which several forming stations are distributed.

[0006] Each forming cycle includes a phase of progressive preform pressurization during which a compressed forming fluid is injected at maximum blow-off pressure into the preform body so as to stretch the material constituting the wall of the preform body to "inflate" the preform until it reaches its final form.

[0007] In order to produce containers with a substantially constant wall thickness, it is known to perform a so-called "biaxial" stretching of the material constituting the wall of the preform to deform it plastically. The pressurization phase includes, for this purpose, a first pre-blowing sub-phase which is carried out prior to the injection of forming fluid at the maximum blowing pressure. During this pre-blowing sub-phase, a sliding stretching rod is inserted coaxially into the neck of the preform, pushing the bottom of the preform so as to stretch the body wall in an axial direction. To prevent the preform wall from contracting around the stretching rod during stretching, forming fluid is injected into the preform at a pre-blowing pressure lower than the maximum blowing pressure to initiate the outward expansion of the body, away from the stretching rod.

[0008] Generally, during its forming cycle, the preform is placed in a mold at the forming station. The mold has an cavity conforming to the final container to be obtained. The wall of the preform body is pressed against the wall of the cavity by the pressure of the forming fluid to give the container its final shape.

[0009] When it begins to deform, the preform becomes an "intermediate container" before reaching its final form as a "final container".

[0010] In the rest of the description and in the claims, the term "hollow body" will be used to refer indifferently to a preform, an intermediate container or a finished container.

[0011] During the mass production of containers, the forming stations implement numerous forming cycles at a very high frequency over long periods. For example, each forming station can implement several thousand cycles per hour during a day.

[0012] During the operating cycles of the forming station, certain wear parts, such as seals, undergo progressive deterioration. However, due to manufacturing and assembly tolerances for each forming station, the rate at which wear parts deteriorate can vary from one station to another. Therefore, fairly frequent maintenance operations are planned to allow for the replacement of wear parts before this affects the quality of the containers produced. Furthermore, despite the frequency of these maintenance operations, some wear parts may deteriorate too quickly, resulting in excessive consumption of pressurized forming fluid and / or the production of non-conforming final containers.

[0013] In addition, certain elements of the forming station must be adjusted according to the format of preforms processed by the forming unit; for example, the position of The blow nozzle relative to the mold. These settings are susceptible to unintentional movement during the numerous forming cycles implemented by the forming station. These unintended deviations can also lead to excessive consumption of pressurized forming fluid and / or the production of non-conforming final containers.

[0014] There is therefore a need to effectively diagnose the condition of the forming stations during the production of containers in order to avoid having to stop the forming unit too frequently to carry out maintenance operations. Summary of the invention

[0015] The invention proposes a method for diagnosing leaks of forming fluid in at least one forming station of hollow bodies made of thermoplastic material during a succession of production cycles, each cycle comprising a first phase of pressurizing the hollow body by connecting it to a source of forming fluid compressed to a maximum blowing pressure via a blowing valve, followed by a second phase of passive pressure maintenance during which the hollow body is isolated from the source of forming fluid by closing the blowing valve, a depressurization phase of the hollow body being triggered at the end of the passive pressure maintenance phase, characterized in that the diagnostic method comprises a step of determining the evolution of the pressure of the forming fluid in the hollow body by carrying out a series of several pressure measurements successively during the passive pressure maintenance phase.

[0016] According to another feature of the process carried out according to the teachings of the invention, the step of determining the evolution of the forming fluid pressure is followed by a step of calculating a criterion representative of the rate of pressure drop in the hollow body during the passive holding phase from the measurements taken during the first step of determining the evolution of the forming fluid pressure.

[0017] According to another feature of the process carried out according to the teachings of the invention, the second step of calculating a criterion representative of the rate of pressure drop consists of calculating the slope of a line defined by affine fitting of measurements of the forming fluid pressure as a function of time.

[0018] According to another feature of the method carried out according to the teachings of the invention, the slope of the line is obtained by a linear regression method, such as the least squares method.

[0019] According to another feature of the process carried out according to the teachings of the invention, the value of the slope associated with said forming station during the current cycle is recorded in a memory of an electronic control unit, the process comprising a third step of calculating an average of the slopes recorded during a determined period.

[0020] According to another feature of the process carried out according to the teachings of the invention, when the criterion calculated on a cycle is representative of a pressure drop below a first determined threshold, the hollow body formed during this cycle is ejected as scrap.

[0021] According to another feature of the process carried out according to the teachings of the invention, when the average calculated during the third step of calculating an average is less than a second determined threshold, a signal indicating a need for maintenance of the associated forming station is emitted by the electronic control unit.

[0022] According to another feature of the process carried out according to the teachings of the invention, the averages associated with said forming station are recorded in a memory of the electronic control unit, the process comprising a fourth additional prediction step in which a criterion representative of the slope of the averages as a function of time is calculated at each cycle, the electronic unit then calculating, as a function of the slope of the averages, a number of cycles remaining before the average becomes less than said second threshold.

[0023] According to another feature of the process carried out according to the teachings of the invention, the representative criterion of the pressure drop calculated during the second calculation step of a representative criterion of the pressure drop rate is applied to each forming station of a forming unit comprising a plurality of forming stations, being memorized at each cycle in correspondence with an identifier of the associated forming station to allow individual monitoring of each forming station.

[0024] According to another feature of the process carried out according to the teachings of the invention, the average calculated during the third step of calculating an average is recorded in a memory of the electronic control unit in correspondence with the associated forming station identifier.

[0025] According to another feature of the method carried out according to the teachings of the invention, in the first step, the first measurement of the series is carried out after a determined delay, for example of 40 ms, from the emission of a closing signal of the blow valve marking the end of the pressurization phase.

[0026] According to another feature of the process carried out according to the teachings of the invention, during the first step of determining the evolution of the forming fluid pressure, the series measurements are carried out with a frequency on the order of a thousandth of a second.

[0027] According to another feature of the method carried out according to the teachings of the invention, the duration of the passive holding phase is at least 40 milliseconds.

[0028] According to another feature of the process carried out according to the teachings of the invention, the first step of determining the evolution of the forming fluid pressure of the diagnostic process ends when a signal to open a valve allowing the start of depressurization of the hollow body is emitted by the electronic control unit.

[0029] According to another feature of the process carried out according to the teachings of the invention, the pressure measurements of the first step of determining the evolution of the forming fluid pressure are carried out by a pressure sensor which emits to the electronic control unit a signal representative of the forming fluid pressure in the hollow body.

[0030] According to another feature of the process carried out according to the teachings of the invention, the pressure sensor is arranged in a blow nozzle of the forming station which is intended to be connected in a hermetic manner to the hollow body during its forming. Brief description of the figures

[0031] Other features and advantages of the invention will become apparent during the reading of the detailed description which follows, for the understanding of which reference should be made to the attached drawings.

[0032] [Fig. 1] is an axial cross-sectional view that schematically represents a station of forming of a hollow body suitable for implementing the process according to the teachings of the invention.

[0033] [Fig.2] is a block diagram that represents the different phases of a cycle of forming of a hollow body in the finished container state from a hollow body in the preform state carried out by the forming station of [Fig.1], pressure being represented on the ordinates and time on the abscissas.

[0034] [Fig.3] is a diagram that represents the forming fluid pressure in a preform during the execution of the forming cycle of [Fig.2].

[0035] [Fig.4] is a block diagram that represents the different stages of a process of leak diagnosis carried out according to the teachings of the invention and applied to the forming station of [Fig.1] during several production cycles.

[0036] [Fig.5] is a larger-scale detail view of the diagram in [Fig.2] which re presents the curve during a phase of passive holding of the hollow body under pressure.

[0037] [Fig.6] is a schematic top view that represents a forming unit that is equipped with several forming stations identical to that of [Fig.1].

[0038] [Fig.7] is a diagram that represents the values ​​obtained by implementing the Diagnostic method at each of the forming stations of the forming unit in [Fig. 6], with the pressure drop represented on the ordinate and the identification number of each forming station represented on the abscissa. Detailed description of the invention

[0039] In the rest of the description, similar or identical elements will be designated by the same references.

[0040] Unless otherwise stated in the following description, each valve is controlled between a fully open state in which the forming fluid flows at maximum rate and a fully closed state in which the passage of the forming fluid is prohibited. Each valve is advantageously controlled automatically by an electronic control unit 50.

[0041] In the following description, the forming fluid is formed from a gas, in particular air. However, the invention is also applicable to a forming fluid formed from a liquid.

[0042] As illustrated in [Fig.1], a stretch-blow forming station 10 for molding a hollow body 12, initially in the state of a thermoplastic preform, includes a mold 14 forming a two-part molding cavity 16 that can be separated to release the hollow body 12 in the state of a final container.

[0043] The forming station 10 further comprises a blow nozzle 18 which is intended to be sealed between the inside of the hollow body 12 received in the molding cavity 16. The blow nozzle 18 is, for example, bell-shaped, covering the neck of the hollow body 12 and bearing against an upper face of the mold. A sealing gasket is advantageously interposed between the mold 14 and the blow nozzle 18 to ensure a sealed connection between the blow nozzle 18 and the hollow body 12.

[0044] The blow nozzle 18 is connected to a forming fluid source 22 at a maximum blow pressure Pfmax, for example approximately 40 bar. The blow forming fluid source 22 at the maximum blow pressure Pfmax is connected to the blow nozzle 18 via a blow line 24 in which a blow valve 26 is interposed.

[0045] The blowing nozzle 18 is also connected to atmospheric pressure Patm via an exhaust pipe 28. The exhaust pipe 28 is fitted with a silencer 30. An exhaust valve 32 is interposed in the exhaust pipe 28.

[0046] The hollow body 12 in the preform state comprises a neck 34 and a body 36 which is preheated before being introduced into the molding cavity 16. The neck 34 here protrudes outside the molding cavity 16 through an orifice 38 of the mold 14. During In stretch-blowing, the molding cavity 16 is closed around the body 36, the blow nozzle 18 coupling onto the neck 34.

[0047] In the example shown in [Fig.1], the blow nozzle 18 is here equipped with a vertically movable extension rod 40 between a retracted position, shown in solid lines in [Fig.1], and an extended position shown in dashed lines in [Fig.1].

[0048] By way of non-limiting example, the blow nozzle 18 is also connected to a source 42 of forming fluid at a pre-blow pressure Pfp.

[0049] The forming fluid source 42 at the pre-blowing pressure Pfp is connected to the blowing nozzle 18 via a pre-blowing line 44 in which a pre-blowing valve 46 is interposed.

[0050] The maximum blowing pressure Pfmax is, for example, on the order of 40 bar. The pre-blowing pressure Pfp is lower than the maximum blowing pressure Pfmax. For example, it is between 6 bar and 20 bar.

[0051] The forming station 10 is intended to form a finished container from a hollow body 12 in the preform state of thermoplastic material during a container production cycle.

[0052] As shown in Figures 2 and 3, each container production cycle includes a first "PI" pressurization phase of the hollow body 12, during which the body 36 of the hollow body 12 is deformed by progressively increasing the pressure inside the hollow body 12. To achieve this, during at least one final sub-phase "Pl-3" of this "PI" pressurization phase, the interior of the hollow body 12 is connected to the source 22 of forming fluid compressed to the maximum blow pressure Pfmax by opening the blow valve 26. At the end of this "PI" pressurization phase, the hollow body 12 is filled with forming fluid at the maximum blow pressure Pfmax.

[0053] In the example shown in the figures, the first pressurization phase "PI" initially comprises a first pre-blowing sub-phase "Pl-1" during which the hollow body 12 is stretched by the stretching rod 40. Simultaneously with this stretching, the blowing nozzle 18 is connected to the forming fluid source 42 at the pre-blowing pressure Pfp by opening the pre-blowing valve 46. This increases the pressure in the hollow body 12 to the pre-blowing pressure Pfp.

[0054] Then, the pre-blowing valve 46 is closed and the blowing valve 26 is opened to cause a further pressure rise of the forming fluid inside the hollow body 12 up to the maximum blowing pressure Pfmax during a second sub-phase "P 1-2" of blowing.

[0055] At the end of this second sub-phase "Pl-2" of blowing, the last sub-phase "Pl-3", called sub-phase "Pl-3" of active pressure maintenance, is triggered. During In this last sub-phase "P 1-3", the blow valve 26 remains open to maintain the forming fluid in the hollow body 12 at the maximum blow pressure Pfmax for a sufficient time to allow the hollow body 12 to retain the shape of the mold cavity 16 impression at the end of this "PI" pressurization phase.

[0056] It has been observed that, during this "Pl-3" active pressure holding sub-phase, as shown in [Fig.3], the pressure of the forming fluid inside the hollow body 12 oscillates around its maximum blowing pressure value Pfmax by resonance effects.

[0057] The first pressurization phase "PI" is followed by a second phase "P2" of passive pressure holding during which the hollow body 12, then in its finished container state, is isolated from the forming fluid source 22 at the maximum blowing pressure Pfmax by closing the blowing valve 26. During this second phase "P2" of passive pressure holding, all valves communicating with the blowing nozzle 18 are closed so as to completely enclose the pressurized forming fluid in the hollow body 12 and in the blowing nozzle 18.

[0058] A third phase "P3" of depressurization of the body 12 is triggered at the end of the second phase "P2" of passive holding under pressure in order to bring the inside of the hollow body 12 back to atmospheric pressure Patm to allow its extraction from the mold 14. During this third phase "P3" of depressurization, the pressurized forming fluid is evacuated, in particular to the atmosphere by opening the exhaust valve 32.

[0059] It is virtually impossible to maintain the forming fluid under pressure in a perfectly sealed manner within the blow nozzle 18 and the hollow body 12 during the second phase "P2" of passive pressure maintenance. The forming fluid can, for example, leak at the joint face between the two mold parts 14, or through the sealing means of the connection between the blow nozzle 18 and the hollow body 12, or even through a malfunctioning valve or a perforated pipe. Thus, during this phase, a more or less rapid drop in the forming fluid pressure is observed due to leaks of forming fluid from the forming station 10.

[0060] It is necessary to quickly identify excessive leaks of forming fluid at the level of the blow nozzle 18 and the hollow body 12 to avoid overconsumption of forming fluid under pressure.

[0061] To solve this problem, the invention proposes a method for diagnosing leaks of forming fluid in a forming station 10. An example of the implementation of the method is shown in Figures 4 and 5.

[0062] This process is advantageously implemented while the forming station 10 is currently producing containers. This means that container production does not have to be interrupted to carry out this diagnostic process.

[0063] The process includes a step "El" of determining the evolution of the pressure of the forming fluid in the hollow body 12 by carrying out a series of several pressure measurements successively during the phase "P2" of passive holding under pressure.

[0064] The series comprises at least 2 measures, preferably more than 3 measures. Advantageously, the series comprises about one hundred measures.

[0065] The pressure measurements are here carried out by a pressure sensor 48 which emits a signal representative of the forming fluid pressure to an electronic control unit 50.

[0066] The pressure sensor 48 is arranged in a location that allows it to measure a pressure representative of the pressure inside the hollow body 12 at any time during the forming cycle, and in particular during the second phase "P2" of passive holding. The pressure sensor 48 is here arranged in the blow nozzle 18 of the forming station 10.

[0067] The leak diagnosis is therefore applied to the hollow body 12, to the blow nozzle 18 and to all volumes which communicate with the nozzle 18 during the second phase “P2” of passive holding.

[0068] During the first step "El" of determining the evolution of the forming fluid pressure, the first measurement of the series is carried out after a determined delay "dl", for example of 40 ms, from the emission of a closing signal of the blowing valve 26 by the electronic control unit 50 at the end of the pressurization phase "PI".

[0069] This delay "dl" is sufficient to allow the blow-off valve 26 to close completely, taking into account its response time.

[0070] In addition, this delay "dl" is preferably sufficient for the pressure oscillations due to resonance effects to be attenuated or even completely eliminated.

[0071] The duration of the passive holding phase "P2" is at least 40 milliseconds. Preferably, the duration of the passive holding phase "P2" is longer, for example on the order of a second, in particular about 2 seconds. This duration allows measurements to be collected over a sufficient period to obtain a relevant indication of the evolution of the forming fluid pressure in the hollow body 12.

[0072] During this first step "El" of determining the evolution of the forming fluid pressure, the series measurements are taken at a frequency as high as permitted by the pressure sensor 48 to obtain an accurate measurement. For example, the frequency is on the order of a thousandth of a second. This makes it possible to obtain a large number of measurements allowing the evolution of the Forming fluid pressure in the hollow body 12. For example, measurements are taken every 0.4 milliseconds.

[0073] The first step "El" of the process of determining the evolution of the forming fluid pressure ends at the end of the "P2" passive holding phase, when a signal to open a valve allowing the start of depressurization of the hollow body 12 is emitted by the electronic control unit 50 to trigger the third "P3" depressurization phase.

[0074] The step "El" of determining the evolution of the forming fluid pressure is followed by a step "E2" of calculating a criterion representative of the pressure drop rate in the hollow body 12 during the phase "P2" of passive holding from the measurements taken during the first step "El" of determining the evolution of the forming fluid pressure.

[0075] The second step "E2" of calculating a criterion representative of the pressure drop rate consists here of calculating a slope "|3i" of a straight line 52 defined by affine fitting of the series of measurements taken during the first step "E1" of determining the evolution of the forming fluid pressure as a function of time. This second step "E2" of calculating a criterion representative of the pressure drop rate is performed automatically by the electronic control unit 50.

[0076] The affine fit can be obtained by linear regression, in particular by the least squares method, or by other methods based for example on a segmentation of values ​​to use the smoothing phenomena (for example the Mayer method or the median-median method).

[0077] In one embodiment example, the slope "|3i" of the line 52 is obtained by a linear regression method, in particular by the least squares method.

[0078] According to this method, each measure "n;" has coordinates:

[0079] - "y;" corresponding to the measured pressure;

[0080] - "Xj" corresponding to the time at which the measurement was carried out.

[0081] The number "n" represents the number of measurements taken during the series.

[0082] The slope "|3i" of the line 52 obtained by linear regression from all the The measurements of the series will be given by the following formula: [Math 1]

[0083] _ 1 -nLxy

[0084] Since the pressure cannot increase during this "P2" phase of passive pressure maintenance, the slope "|3i" is necessarily negative or zero. The rate at which the pressure drops is proportional to the slope "|3i" thus calculated. This means that if the slope "|3i" falls below a first determined threshold "SI", it means that the hollow body 12 is probably punctured, causing a very rapid leakage of the forming fluid and therefore a rapid pressure drop. When the electronic unit 50 of The command detects that the slope "|3i" thus calculated is less than the first threshold "SI" determined, it automatically commands the ejection to the scrap of the hollow body 12 formed during this cycle because it is considered to be pierced.

[0085] The forming station 10 is intended for use in the mass production of containers. Therefore, the forming station 10 undergoes numerous successive production cycles. It is thus advantageous to be able to implement the diagnostic procedure at each cycle in order to obtain a robust diagnosis of forming fluid leaks in said forming station 10. This makes it possible, in particular, to rule out specific cases in which the pressure drop is due to a perforated hollow body 12.

[0086] To this end, the slope "|3i" associated with said forming station 10 during the current cycle is recorded in a memory of the electronic control unit 50. The diagnostic process includes a third step "E3" of calculating an average "|3av i" recorded over a determined period.

[0087] The determined periods are successive and do not overlap. Thus, at the end of a time period, the electronic control unit 50 calculates the average "|3av" of the slopes "|3i" recorded during said time period. Then, a new period begins.

[0088] The period determined here is a period of time, for example 24 hours.

[0089] Alternatively, the determined period is a number of container production cycles.

[0090] When the average "|3av" calculated during the third step "E3" of calculating an average "|3av" is less than a second predetermined threshold "S2", which is, for example, greater than the first predetermined threshold "SI", a signal indicating a need for maintenance of the associated forming station is emitted by the electronic control unit 50. This means that the forming station 10 is leaking forming fluid regardless of the condition of the hollow body 12 and that intervention is therefore necessary to replace wear parts or make adjustments.

[0091] Optionally, the diagnostic process may also include a fourth additional prediction step "E4" aimed at estimating the number of cycles remaining to perform maintenance operations before the average "|3av" falls below the second predetermined threshold "S2". During this fourth additional prediction step "E4", the averages "|3av" associated with said forming station 10 are recorded in a memory of the electronic control unit 50, and a criterion representing the slope "|32" of the average "|3av" as a function of time is calculated for each cycle. The electronic unit 50 then calculates a number of cycles remaining as a function of the slope "|32" of the average "|3av" before the average "|3av" falls below said second threshold "S2".

[0092] For this additional fourth prediction step “E4”, the criterion represents The slope "p2" of the average "Pav" is calculated on a collection of averages "Pav" calculated over several successive defined periods. For example, when a defined period is set to 24 hours, the slope "p2" of the average "Pav" is calculated on a collection of averages "Pav" calculated over several days.

[0093] The additional fourth prediction step "E4" here consists of calculating the slope "P2" of a line defined by affine fitting of the means "Pav" as a function of time. This additional fourth prediction step "E4" is performed automatically by the electronic control unit 50.

[0094] As in step "E2" of calculating a criterion representative of the pressure drop rate, the affine fit can be obtained by linear regression, in particular by the least squares method, or by other methods based for example on a segmentation of values ​​to use the smoothing phenomena (for example the Mayer method or the median-median method).

[0095] In one embodiment, the slope "p2" of the line is obtained by a linear regression method, such as the least squares method.

[0096] According to this method, each average "pav" has coordinates:

[0097] - "pi" corresponding to the calculated average;

[0098] - "qi" corresponding to the determined period at which the average "pav" was calculated.

[0099] The number "m" represents the number of determined periods taken into account to calculate the slope "p2".

[0100] The slope "p2" of the line obtained by linear regression from all the measurements of the series will be given by the following formula: [Math 2] _ Ep£^^ 2 (Ep;P»Ez4

[0101] The method of the invention thus makes it possible to detect very efficiently a hollow pierced body 12, to detect the moment when it is necessary to carry out a maintenance operation on a particular forming station and even to anticipate this moment.

[0102] For example, it is possible to calculate the remaining time before maintenance of a forming station 10 using the following equation: [Math 3] 52-^| T ctnps avanfma^tenanee ~

[0103] in which: - "|3i" is the slope calculated during step "El" of determining the evolution of the forming fluid pressure for the current cycle, as previously defined; - "p2" is the slope of the line calculated during the fourth step "E4" supplement prediction comment for the last determined period completed; - "S2" is the second threshold determined.

[0104] This operation is automatically implemented by the electronic control unit 50, for example at iteration of the process or at each beginning of a new determined period.

[0105] During the implementation of the process, the first step "E1" of determining the evolution of the forming fluid pressure and the second step "E2" of calculating a criterion representative of the pressure drop rate are carried out at each production cycle performed by the associated forming station 10. The third step "E3" of calculating an average "|3av" is carried out only at the end of each predetermined period, for example, once a day. The additional fourth step "E4" of prediction is carried out at the end of several successive predetermined periods, for example, once a week.

[0106] This process is very precise because it is based on a series of measurements carried out at each cycle, which makes it possible to calculate a very reliable and robust criterion which makes it possible to smooth out measurement errors due, for example, to transient fluctuations in the pressure of the forming fluid in the hollow body 12 or to measurement noise from the pressure sensor.

[0107] Generally, the forming station 10 is arranged in a forming unit 54 comprising several identical forming stations 10. The forming unit 54 comprises, for example, a carousel 56 around the periphery of which several forming stations 10 are evenly distributed. The forming unit 54 comprises, for example, twenty forming stations 10. Such a forming unit 54 is particularly used in a container production plant for very large series, for example at a rate of 60,000 containers per hour.

[0108] All forming stations 10 are identical to the forming station 10 described previously. Without limitation, each pressurized forming fluid source 22, 42 is common to all forming stations 10 of the forming unit; however, each forming station 10 has associated valves so that it can be controlled individually.

[0109] As shown in [Fig. 6], the diagnostic procedure is advantageously implemented individually for each of the forming stations. To enable the electronic control unit 50 to associate the values ​​calculated during a diagnostic procedure with the corresponding forming station 10, each forming station 10 is advantageously identified by a unique identifier.

[0110] Thus, the representative criterion of the pressure drop calculated during the second step "E2" of calculating a representative criterion of the pressure drop speed is stored at each cycle in correspondence with the associated forming station identifier 10 to allow individual monitoring of each forming station 10.

[0111] Similarly, the average "|3av" calculated during the third step "E3" of calculating an average "|3av" is recorded in a memory of the electronic control unit 50 corresponding to the identifier of the associated forming station 10.

[0112] As shown in [Fig.7], each forming station 10 is identified by a number. For each forming station 10, we have the average "|3av", the extreme values ​​"|3imax" and "|3imin" of the collection and possibly the values ​​"|3iout" of slopes which are considered too far from the average "|3av" and are therefore not taken into account for the calculation thereof.

[0113] It is thus possible to know at any time the individual sealing characteristics of each forming station 10. This allows intervention at the best time to minimize the number of maintenance operations.

[0114] This saves pressurized forming fluid and, consequently, energy.

[0115] This advantage is all the more important when combined with the advantages obtained by recycling part of the pressure forming fluid.

[0116] In the example shown in [Fig. 1], the forming fluid source at the pre-blowing pressure Pfp comprises a pressurized forming fluid storage tank 58 which is connected to the blow nozzle 18 via the associated pre-blowing valve 46. This storage tank 58 contains forming fluid stored at a pressure Ps greater than or equal to the pre-blowing pressure Pfp. To enable the delivery of the forming fluid at the pre-blowing pressure Pfp, the pre-blowing source further comprises a pressure regulator 60 which reduces the pressure of the forming fluid from its storage pressure Ps to its pre-blowing pressure Pfp.

[0117] The blow nozzle 18 is also connected to said storage tank 58 via a recovery line 62 in which a recovery valve 64 is interposed. This allows a portion of the pressurized forming fluid contained in the hollow body 12 at the end of its forming to be reused in the forming of a subsequent hollow body 12 into the final container. This notably reduces the overall energy expenditure for producing a final container.

[0118] A filter 66 is advantageously interposed in the recovery conduit 62 to prevent polluting particles from being reintroduced into a hollow body 12 during a subsequent blowing.

[0119] Thus, the third depressurization phase "P3" previously described includes here a first sub-phase "P3-1" of evacuation of the pressurized forming fluid from the hollow body 12 to the storage tank 58 by opening the recovery valve 64.

[0120] When the pressure in the hollow body 12 has dropped to a slightly When the pressure exceeds the storage pressure Ps, a second sub-phase "P3-2" is triggered. The recovery valve 64 is then closed and the exhaust valve 32 is opened to allow the remaining forming fluid to escape into the atmosphere until the pressure inside the hollow body 12 is substantially equal to atmospheric pressure Patm.

Claims

Demands

1. A method for diagnosing leaks of forming fluid in at least one forming station (10) of hollow bodies (12) made of thermoplastic material during a succession of production cycles, each cycle comprising a first phase (PI) of pressurizing the hollow body (12) by connecting it to a source (22) of forming fluid compressed to a maximum blow pressure (Pfmax) via a blow valve (26), followed by a second phase (P2) of passive pressurization during which the hollow body (12) is isolated from the source (22) of forming fluid by closing the blow valve (26), a phase (P3) of depressurizing the hollow body (12) being triggered at the end of the passive pressurization phase (P2),characterized in that the diagnostic process comprises a step (E1) of determining the evolution of the forming fluid pressure in the hollow body (12) by carrying out a series of several pressure measurements successively during the phase (P2) of passive holding under pressure.

2. A method according to the preceding claim, characterized in that the step (El) of determining the evolution of the forming fluid pressure is followed by a step (E2) of calculating a criterion representative of the rate of pressure drop in the hollow body (12) during the phase (P2) of passive holding from the measurements taken during the first step (El) of determining the evolution of the forming fluid pressure.

3. Method according to the preceding claim, characterized in that the second step (E2) of calculating a criterion representative of the pressure drop rate consists of calculating the slope (Pi) of a straight line (52) defined by affine fitting of measurements of the forming fluid pressure as a function of time.

4. A method according to the preceding claim, characterized in that the slope (Pi) of the line (52) is obtained by a linear regression method, such as the least squares method.

5. A method according to any one of claims 2 to 4, characterized in that the value of the slope (Pi) associated with said forming station during the current cycle is recorded in a memory of an electronic control unit (50), the method comprising a third step (E3) of calculating an average (Pav) of the slopes (Pi) recorded during a determined period.

6. A method according to any one of claims 2 to 5, characterized in that, when the criterion calculated on a cycle is representative of a pressure drop below a first determined threshold (SI), the hollow body (12) formed during this cycle is ejected as scrap.

7. Method according to claim 5, characterized in that, when the mean (|3av) calculated during the third step (E3) of calculating a mean (|3av) is less than a second determined threshold (S2), a signal indicating a need for maintenance of the associated forming station (10) is emitted by the electronic control unit (50).

8. A method according to the preceding claim, characterized in that the averages (|3av) associated with said forming station (10) are recorded in a memory of the electronic control unit (50), the method comprising an additional fourth prediction step (E4) in which a criterion representative of the slope (|32) of the averages (|3av) as a function of time is calculated at each cycle, the electronic unit (50) then calculating, as a function of the slope (|32) of the averages (|3av), a number of cycles remaining before the average (|3av) becomes less than said second threshold (S2).

9. A method according to any one of claims 2 to 8, characterized in that it is applied to each forming station (10) of a forming unit (54) comprising a plurality of forming stations (10), the representative criterion of the pressure drop calculated during the second step (E2) of calculating a representative criterion of the pressure drop rate being stored at each cycle in correspondence with an identifier of the associated forming station (10) to allow individual monitoring of each forming station (10).

10. A method according to the preceding claim, taken in combination with claim 5, characterized in that the average (|3av) calculated during the third step (E3) of calculating an average (|3av) is recorded in a memory of the electronic control unit (50) corresponding to the associated forming station identifier (10).

11. A method according to any one of the preceding claims, characterized in that, during the first step (El), the first measurement of the series is carried out after a determined delay (dl), for example of 40 ms, from the emission of a closing signal of the blowing valve (26) marking the end of the pressurization phase (PI).

12. A method according to any one of the preceding claims, characterized in that, during the first step (E1) of determining the evolution of the forming fluid pressure, the series measurements are carried out with a frequency on the order of a thousandth of a second.

13. A method according to any one of the preceding claims, characterized in that the duration of the passive holding phase (P2) is at least 40 milliseconds.

14. A method according to any one of the preceding claims, characterized in that the first step (El) of determining the evolution of the forming fluid pressure of the diagnostic process ends when a signal to open a valve (32, 64) allowing the start of depressurization of the hollow body (12) is emitted by the electronic control unit (50).

15. A method according to any one of the preceding claims, characterized in that the pressure measurements of the first step (El) of determining the evolution of the forming fluid pressure are carried out by a pressure sensor (48) which emits to the electronic control unit (50) a signal representative of the forming fluid pressure in the hollow body (12).

16. Method according to the preceding claim, characterized in that the pressure sensor (48) is arranged in a blow nozzle (18) of the forming station (10) which is intended to be connected in a hermetic manner to the hollow body (12) during its forming.

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