Method for regulating a container production plant based on variations in the temperature of the internal wall of a preform

Abstract

Title: Method for regulating a container production installation based on the variation of the temperature of the internal wall of a preform. The present invention relates to a method for regulating the cyclic production of containers (2) by stretch blow molding from plastic preforms (4) in a machine comprising one or more stretch blow molding stations (44), said machine being positioned downstream of a thermal conditioning device (16) for said preforms (4), commonly called an oven, each of the stretch blow molding stations (44) being designed to produce one container (2) during a production cycle, each stretch blow molding station (44) comprising a mold (46) consisting of two half-molds (48, 50) delimiting a molding cavity, said preform (4) being blown into said mold (46), with at least one pre-blowing and / or blowing stage, said preform heating stages (4),pre-blowing and blowing are controlled by a control unit (84) based on various control parameters; said process is notable in that it comprises at least the following steps: Determining the temperature variation of the inner wall of the preform (4) and / or the temperature at the core of the wall of the preform (4), i.e., the temperature between the outer and inner walls of the preform (4), in the mold (46) of at least one blowing station (18); Modifying at least one of the control parameters as a function of said temperature variation of the inner wall of the preform (4) and / or the temperature at the core of the wall of the preform (4) and / or the average temperature of the preform (4) through its thickness. Figure for the abstract: Figure 1,

Description

Title of the invention: Method for regulating a container production installation based on the variation in temperature of the internal wall of a preform. Technical field

[0001] The present invention relates to a method for regulating the cyclic production of containers by stretch blow molding from plastic preforms in a machine comprising one or more stretch blow molding stations. More generally, the invention relates to the field of manufacturing containers obtained by transforming preforms, in particular by blow molding or stretch blow molding, the preforms being obtained notably by injection molding of thermoplastic material, for example polyethylene terephthalate (PET) and / or recycled polyethylene terephthalate (rPET). State of the art

[0002] It is well known that, for the manufacture of such containers, the preforms undergo prior thermal conditioning in a furnace in order to be brought to a temperature higher than the glass transition temperature of the constituent material.

[0003] The manufacture of containers such as bottles, flasks or any other type of hollow body is generally carried out in installations comprising such a preform heat conditioning oven associated with at least one preform-to-container transformation machine arranged downstream, such as a "blower" for example.

[0004] It will be recalled that a preform or blank in thermoplastic material comprises respectively a first part in its final shape which is made up of the neck and the collar, and a second part alone intended to be thermally conditioned in the oven which is made up of the body and the bottom.

[0005] The thermal conditioning of the second parts formed from the body and the bottom of the preforms is a particularly delicate operation because of the importance of the temperature of the material for the subsequent transformation operations, for example by blowing a gas under pressure (air) or by stretch-blowing or at least partly transformed by filling with a liquid under pressure.

[0006] On the one hand, the average temperature of the second part of the preforms must be above the glass transition temperature of the material (approximately 80°C for PET) in order to allow bi-orientation of the material during the transformation, while being below a crystallization temperature (approximately 140°C for PET) beyond which the material presents risks of crystallization which would render the preform unsuitable for any transformation.

[0007] Thus, a temperature that is too low of the preform can induce on the final container the appearance of a whitish pearlescence (pearl-like appearance) resulting from an overstretching of the preform causing at the molecular level a breakage of the long polymerized chains.

[0008] Conversely, an excessively high temperature of the preform can cause spherolitic crystallization of the constituent material, rendering the preform unsuitable for any transformation operation, particularly by blowing and / or filling.

[0009] On the other hand, the temperature distribution within the preform itself has an impact on the quality of the final container, and in particular on its transparency and on the distribution of the material in the body and the bottom of the container.

[0010] For the manufacture of containers from rPET, the distribution of the internal temperature and the control thereof is particularly important because a variation in the latter is likely to lead to a change in material distribution, a lightening of the bottoms, and ultimately an explosion of the bottle bottoms.

[0011] The temperature distribution in the body and bottom of the preform has several aspects, namely the distribution on the circumference of the preform (i.e. angularly around the main axis of the preform), then axially (i.e. parallel to said axis) and finally in the thickness of the wall of the body and bottom of the preform.

[0012] Thus, to ensure a temperature distribution over the entire circumference of the preform, the preforms are generally rotated on themselves, around their main axis, simultaneously with their movement in front of the heating means arranged on all or part of the heating path.

[0013] The rotation of the preforms in order to obtain a uniform circumferential distribution is however dependent on the applications, since for some applications a non-uniform circumferential distribution is also sometimes sought, in particular for containers of complex shape.

[0014] The rotation of the preforms is usually achieved using gripping means that hold the preforms in position, neck up or neck down, throughout the heating process. These gripping means are linked in movement to the transport device that performs the heating process in a loop. Such gripping means are described in particular in document WO00 / 48819.

[0015] It is also possible to control the axial temperature distribution, i.e., the heating profile parallel to the axis of the preform, by controlling, for example, the radiated power of the lamps (with infrared radiation) or diodes used as heating means in such ovens, using focusing means, as described in document FR 2 732 924, or by selectively adjusting the position of each lamp to vary the distance between each of the lamps and the corresponding portion of the second part of the preforms as described in document FR 2 872 734.

[0016] The temperature distribution in the thickness of the wall of the body and the bottom of the preform is, on the other hand, much more difficult to control even though this distribution, and more particularly the temperature at the core of the wall of the preform, i.e. the temperature between the inner wall and the outer wall, has an impact on the quality of the containers produced.

[0017] However, the regulation of prior art processes may lead to maintaining a stable external temperature reading while the temperature at the core of the preform wall varies, and this variation in the temperature at the core of the preform wall is likely to alter the quality of the containers produced from said preforms, more particularly when these containers are obtained from or contain recycled polyethylene terephthalate (rPET). Disclosure of the invention

[0018] One of the aims of the invention is therefore to remedy all or part of these drawbacks by proposing a method for regulating a cyclic production of containers by stretch-blowing of simple and inexpensive design allowing to avoid a change in material distribution, a lightening of the bottoms, and an explosion of the bottoms of the containers, more particularly for containers obtained in recycled polyethylene terephthalate (rPET).

[0019] To this end, and in accordance with the invention, a method is proposed for regulating the cyclic production of containers by stretch-blowing from plastic preforms in a machine comprising one or more stretch-blowing stations, said machine being positioned downstream of a thermal conditioning device for said preforms, commonly called an oven, each of the stretch-blowing stations being designed to produce one container during a production cycle and being equipped with a pre-blowing and / or blowing solenoid valve of a so-called blowing circuit fluidly connecting the preform to a pressurized fluid source providing at least a pre-blowing and / or blowing flow rate during a pre-blowing and / or blowing phase, each stretch-blowing station comprising a mold consisting of two half-molds delimiting a molding cavity, said preform being blown into said mold,with a pre-blowing and / or blowing stage, said preform heating, pre-blowing and blowing stages being controlled by a control unit based on various so-called control parameters such as the power of the oven heating elements, , the active time of the furnace heating elements, the ventilation power(s) used within the furnace, the blowing pressure in the mold and / or the pre-blowing pressure and / or the pre-blowing flow rate and / or the speed of the drawing rod and / or the ventilation flow rate in the furnace, for example, characterized in that it includes at least the following steps:

[0020] - Determination of the temperature variation of the internal wall of the preform and / or the temperature at the core of the preform wall, i.e. the temperature between the outer wall and the inner wall of the preform, in the mold of at least one blow molding station;

[0021] - Modification of at least one of the control parameters according to said variation in the temperature of the internal wall of the preform and / or the temperature at the core of the wall of the preform and / or the average temperature of the preform through its thickness.

[0022] The step of determining the variation in temperature of the inner wall of the preform and / or the temperature at the core of the preform wall comprises at least the following steps:

[0023] Measurement of the temperature of the external wall of the preform at the entrance of the oven between two production cycles;

[0024] Measurement of the temperature of the external wall of the preform at the exit of the oven between two production cycles;

[0025] Measurement of the temperature of the external wall of the intermediate parison in the mold, during the preform stretching phase, between two production cycles;

[0026] Determination of the variation of the internal temperature of the preform and / or the temperature at the core of the wall of the preform as a function of the temperatures of the external wall of the preform at the entrance of the oven, at the exit of the oven and in the mold.

[0027] Furthermore, preferably, the step of determining the variation of the internal temperature of the preform as a function of the temperatures of the external wall of the preform at the entrance to the oven, at the exit of the oven and in the mold is carried out by determining the variation of the external temperature of the intermediate parison, i.e. of the preform in the stretching phase, in the mold between two production cycles if the variation of the external temperature of the preform at the entrance to the oven between the two production cycles is zero or substantially zero and if the variation of the external temperature of the preform at the exit of the oven between the two production cycles is zero or substantially zero, the variation of the temperature of the internal wall of the preform being dependent on the regulation of the oven, i.e. dependent on the modification of at least one control parameter of said oven.

[0028] In addition, the temperature of the preform is measured at the level of the body of the preform, near the neck of said preform.

[0029] Preferably, the temperature of the preform is measured at the level of the body of the preform at a distance of between 1 mm and 60 mm from the neck of said preform and, preferably, at mid-height of the body of the preform.

[0030] Furthermore, the temperature of the external wall of the preform is measured in the mold by means of a temperature sensor attached to said mold.

[0031] Said temperature of the external wall of the preform is preferably measured in the mold at the height of the body of the produced container and preferably at the level of the area of ​​the body suitable for receiving a label.

[0032] Preferably, the temperature of the outer wall of the preform is measured in the mold using a pyrometer attached to the mold and positioned flush with the inner wall of the mold.

[0033] If a variation in the temperature of the internal wall of the preform in the mold is determined, at least one of the ventilation flow control parameters in the oven is modified as a priority.

[0034] Furthermore, if a variation in the temperature of the internal wall of the preform in the mold is determined, at least one of the parameters for controlling the heating of the preforms in the oven is modified.

[0035] Furthermore, if a variation in the temperature of the internal wall of the preform in the mold is determined, the blow pressure control parameter in the mold and / or the pre-blow pressure control parameter and / or the pre-blow flow control parameter and / or the drawing rod speed control parameter is modified.

[0036] Another object of the invention relates to a machine for manufacturing containers by stretch blow molding from plastic preforms comprising at least one fluid source at a pre-blowing and / or blowing pressure, one or more stretch blow molding stations, each station comprising a mold having a cavity for receiving a preform, a solenoid valve of a so-called pre-blowing and / or blowing circuit suitable for connecting the interior of the preform, received in the cavity, with said fluid source according to at least a predetermined pre-blowing and / or blowing flow rate, a control device for opening and closing the solenoid valve, at least one sensor capable of measuring the pressure inside the preform or inside the blowing circuit or in the blowing block, said machine being positioned downstream of a thermal conditioning device for said preforms,and a memory unit in which various so-called control parameters are recorded, such as the oven heating temperature, the blowing pressure in the mold and / or the pre-blowing pressure and / or the pre-blowing flow rate and / or the speed of the drawing rod, for example, and a control unit including means for controlling the preform heating, pre-, blowing and blowing from said different piloting parameters, remarkable in that it includes means capable of implementing the process according to the invention.

[0037] Another object of the invention relates to a computer program product comprising a sequence of instructions which, when the program is executed by a computer, leads the latter to implement the steps of the process according to the invention.

[0038] A fourth object of the invention relates to a data processing device comprising means for implementing the steps of the process according to the invention.

[0039] A final object of the invention relates to a computer-readable recording medium comprising instructions which, when executed by a computer, lead the computer to carry out the steps of the process according to the invention. Brief description of the drawings

[0040] Other advantages and features will become clearer from the following description of several embodiments, given by way of non-limiting examples, of the method for regulating a cyclic production of stretch-blowing containers according to the invention, with reference to the accompanying drawings in which:

[0041] [Fig-1] is a schematic general view of a production installation of containers seen from above according to the invention;

[0042] [Fig.2] is a detail view of the medallion in [Fig.1] representing a preform;

[0043] [Fig.3] is a schematic cross-sectional view partially showing a unit of molding within the container production facility of [Fig.1];

[0044] [Fig.4] is a partial perspective view of a mold, inner wall side, of the molding unit within the container production facility of [Fig.1];

[0045] [Fig. 5] is a partial perspective view of a mold, outer wall side, of the molding unit within the container production facility of [Fig.1]. Method of embodying the invention

[0046] In the following description, elements having an identical structure or analogous functions will be designated by the same reference.

[0047] The longitudinal, vertical and transverse orientations will be adopted without limitation with reference to the trihedron (L, V, T) represented in the figures.

[0048] By convention, the longitudinal and transverse directions are fixed in relation to the molding devices so that the open or closed position occupied has no effect on said orientations.

[0049] The terms "front" and "rear" shall also be used, without limitation, with reference to longitudinal orientation, as well as "upper" and "lower" with reference to vertical orientation and finally "left" or "right" and "inside" or "outside" in reference to the transverse orientation.

[0050] A schematic representation is shown in [Fig.1], of a series production installation 1 of containers 2 made of thermoplastic material from preforms 4.

[0051] In the following description, the preforms 4 and the containers 2 move through the production installation along a production path from upstream to downstream. The preforms 4 are moved in a line along a production path T by conveying means which will be detailed later.

[0052] Without limitation, the containers here are bottles. The thermoplastic material is, for example, herein formed by polyethylene terephthalate, hereinafter referred to by its acronym "PET" and / or by recycled polyethylene terephthalate, known as "rPET"; however, the thermoplastic material may consist of any other thermoplastic material well known to those skilled in the art without departing from the scope of the invention.

[0053] Such a preform 4, with reference to [Fig. 2], has a principal axis "X" shown vertically in the figure. It has a cylindrical body 6 with a tubular wall 7 closed at one of its axial ends by a bottom 8, and which is open at its other end by a neck 10, also tubular. The neck 10 is delimited downwards by a collar 12 and upwards by an upper end edge called the drinking rim 14.

[0054] The neck 10 generally presents its final shape while the body 6 of the preform is intended to undergo a relatively large deformation to form the final container 2 during a forming step after a prior heat conditioning step.

[0055] As shown in [Fig.1], the container manufacturing installation 1 comprises at least one heat conditioning unit 16 and one forming unit 18.

[0056] The heat conditioning unit 16, also called an oven, heats a series of preforms to a reference temperature. The reference temperature is chosen so that the body of each preform exiting the heat conditioning unit 16 is in a malleable state, allowing the heated preform body 6 to be deformed in order to form the container 2 in the forming unit 18. The reference temperature is between the glass transition temperature and the crystallization temperature of the plastic material of the preform. In the case of PET, the reference temperature is, for example, close to 110°C. The value of the reference temperature may vary depending on the product with which the container will be filled or the container filling technique.Thus, the reference temperature differs for hot filling, for a carbonated product, or for preforms obtained in rPET, for example.

[0057] According to the embodiment shown in [Fig.1], the heat conditioning unit 16 is a scroll oven, in which the preforms 4 are transported to be exposed to a plurality of radiant heating sources 22.

[0058] For this purpose, the thermal conditioning unit 16 includes a means for conveying preforms circulating along a frame 23 through the thermal conditioning unit along a heating path extending between an inlet 25 and an outlet 27 of the thermal conditioning unit defining a trajectory T.

[0059] Said conveying means comprises a plurality of conveying devices 26 capable of receiving a preform by fitting its neck.

[0060] The furnace also includes a heating cavity which includes two lateral walls 36 facing each other and at least one of these walls being the one which supports several radiation sources 22, arranged one above the other and one next to the other opposite the preforms.

[0061] In other words, the heat conditioning unit 16 comprises a plurality of radiation sources 22 distributed along the path of the trajectory T and at a height substantially corresponding to the height of the preforms, such that the entire height of the body of each preform is exposed to the radiation sources along the preform's path in the heat conditioning unit. By rotating the preforms 4 around their principal axis X, the conveying devices 26 allow the entire body 6 of the preforms to be uniformly exposed to the radiation sources 22. In this particular embodiment, the radiation sources 22 are distributed on only one side of this path, and a reflective wall 38 is arranged on the other side of the heating path, directly opposite the radiation sources 22, to reflect the heat back towards the preforms 4.

[0062] In another embodiment not shown, the radiation sources 22 can be distributed on either side of the heating path without going out of the scope of the invention.

[0063] It should also be noted that the radiation sources 22 are arranged, where applicable, so as not to expose the neck 10 to the heat emitted by the radiation sources. Indeed, as previously stated, only the body 6 of the preform 4 is heated to produce the container. Consequently, the neck 10 must not be deformed during forming and must not be heated. To prevent heating of the neck 10, the furnace may include a ventilation device, not shown in the figures, positioned at the necks 10 to remove the heat that could be absorbed by said necks 10.

[0064] Each radiation source 22 is formed by an incandescent lamp emitting infrared radiation.

[0065] In another embodiment, each radiation source 22 is a laser diode emitting infrared radiation.

[0066] In other words, each radiation source 22 is a laser (for example laser diodes) emitting in the infrared and arranged by juxtaposition and / or superposition to form one or more matrices.

[0067] In another embodiment, each radiation source 22 is a microwave generator.

[0068] It is quite obvious that the radiation sources 22 may consist of any radiation source well known to the Man skilled in the art, or a combination of these radiation sources without going out of the scope of the invention.

[0069] Then, once the preform 4 has been heat-conditioned in the heat conditioning unit 16, it is transferred to the forming unit 18 to be formed there.

[0070] The unit for forming containers 18 from preforms 4 consists of a forming wheel 42 rotating a plurality of stretch-blow stations 44 from an inlet to an outlet, at which a succession of containers are formed from the preforms and then extracted, as shown in [Fig. 1]. The axis of rotation of the forming wheel is, for example, substantially parallel to the principal axis X of the preforms when they are transported by the forming wheel.

[0071] Each stretch-blowing station 44 includes a mold 46 having walls forming a molding cavity having the shape of the container to be formed and arranged to receive a preform so that the body of the preform extends into the molding cavity.

[0072] As shown in [Fig. 3], each blow-drawing station 44 further comprises:

[0073] -the mold 46 comprising two half-molds 48, 50 articulated around a hinge and a base 52;

[0074] -a housing 54 defining a nozzle 56 which, during the manufacture of the container 2, cooperates with the neck 10 of the preform 4.

[0075] -an elongation rod 58 mounted to slide in the nozzle 56, as well as relative to the mold 46 along a principal axis A (generally of revolution) of the latter, between a high position allowing the introduction of the preform 4 into the mold and a low position where, at the end of the drawing of the preform 4, the rod 58 reaches the bottom of the mold 52 by pressing the bottom 8 of the preform against it,

[0076] The stretch-blowing station 44 further comprises several fluidic circuits opening into the nozzle 56 via the housing 54, namely:

[0077] - a 60 pre-blowing air circuit at medium pressure (between 3 and 16 bars), this circuit 60 comprising a pre-supply air source 62 and a duct 64 (which can be formed at least partially in the housing 54) connecting this source 62 to the nozzle 56 with the interposition of a first solenoid valve 66, called the pre-blowing solenoid valve,

[0078] - a high-pressure (between 30 and 40 bar) blowing air circuit 68, comprising a blowing air source 70 and a duct 72 (which may be at least partially formed in the housing 54) connecting this source 70 to the nozzle 56 with the interposition of a second solenoid valve 74, called the blowing solenoid valve,

[0079] - a degassing circuit 76 comprising a vent 78 for release to the atmosphere and a conduit 80 connecting the nozzle 56 to this mouth 78 with interposition of a third solenoid valve 82, called degassing solenoid valve.

[0080] The solenoid valves 66, 74, 82 are electrically connected to a control unit 84 which controls their opening and closing (taking due account of their response times).

[0081] It should be noted that the blowing station may include other solenoid valves and other air sources to allow in particular air recovery during degassing or air sweeping during the stretching phase, well known to those skilled in the art without going outside the scope of the invention.

[0082] This control unit 84 includes in particular a computer 86 (or processor), a database 88 and a console (or graphical interface) for interaction with an operator.

[0083] The manufacture of a container 2 from a preform 4 is carried out as follows.

[0084] The preform 4 is first introduced into the oven where it is heated in the conditions described above. Upon exiting the oven, the preform 4 is gripped by a clamp on a transfer wheel and inserted into a previously opened mold. In this position, the elongation rod 58 is in its raised position.

[0085] As the carousel rotates, the mold closes on the preform 4 and begins a forming cycle.

[0086] The forming cycle is repeated for each stretch-blow station 44. It includes at least one step of injecting a fluid under pressure into the preform 4, followed by a depressurization step.

[0087] More specifically, a forming cycle comprises:

[0088] - a first phase, called pre-blowing, consisting of injecting into the preform a fluid under a pre-blowing pressure, by connecting the nozzle 56 with the air source 62 at the pre-blowing pressure to radially stretch the body of the preform. For this purpose, the control unit 84 commands, via its actuator, the opening of the pre-blowing solenoid valve 66, at a pre-blowing start time, with a pre-blowing flow rate, a pre-blowing duration, and a pre-blowing pressure, i.e. a part of the blowing parameters;

[0089] - substantially simultaneously with this first phase, a stretching phase during in which a free end of the elongation rod 58 is inserted coaxially into the body of the preform through its neck 10 to the bottom of the mold to axially stretch the body of the preform, at a starting instant of stretching and / or with a stretching speed to arrive at a low position, i.e. another part of the blowing parameters.

[0090] At the end of the pre-blowing, the container 2 is not completely formed but the material has reached the walls of the mold without intimately conforming to its contours;

[0091] - a second phase, called blowing, consisting of injecting into the container 2 no In the final stage, a fluid under blowing pressure is connected to the nozzle 56 by the air source 70 at blowing pressure to press the preform wall against the mold 46. For this purpose, the control unit 84, via their respective actuators, controls the opening of the blowing solenoid valve 74 and the closing of the pre-blowing solenoid valve 66. At the end of the second phase, the container 2 is completely formed, the material intimately conforming to the contours of the mold wall 46;

[0092] - a third phase, called depressurization, which optionally includes, a so-called recovery step consisting of depressurizing the container 2 by connecting the nozzle 56 with a recovery tank (not shown) and / or a degassing step consisting of completely depressurizing the container 2, in this case by connecting the nozzle 56 with the open air; for this purpose, the control unit 84 commands, via its actuator, the closing of the recovery solenoid valve 82 and the opening of a solenoid valve (not shown) for venting to the open air.

[0093] As shown in [Fig.1], the container manufacturing installation 1 comprises a heat conditioning unit 16, a forming unit 18, and a control unit 84 for these, including in particular a computer 86, a database 88, a console for interaction with the operator (not shown) and at least two temperature measuring devices 90 for the preforms 4, a first temperature measuring device 90 positioned at the inlet 25 of the heat conditioning unit 16 and a second temperature measuring device 90 positioned at the outlet of the heat conditioning unit 16, and a temperature measuring device 92 for the external wall temperature of the intermediate parison in the mold, during the preform stretching phase, between two production cycles.

[0094] The first measuring device 90 for the temperature of the preforms 4 is positioned at the inlet 25 in a measuring zone of the heat conditioning unit 16, thus allowing the temperature of the preforms 4 entering the heat conditioning unit 16 to be measured. The second measuring device 90 of the The temperature of the preforms 4 is positioned at the outlet 27 in a measurement zone of the thermal conditioning unit 16, thus allowing the temperature of the preforms 4 exiting the thermal conditioning unit 16 to be measured.

[0095] As will be detailed later, the temperature measurements of the preforms at the inlet 25 and outlet 27 of the thermal conditioning unit 16 make it possible to determine the variation of the internal temperature of the preform and / or the temperature at the core of the wall of the preform as a function of the temperatures of the external wall of the preform at the inlet of the oven, at the outlet of the oven and in the mold.

[0096] Each preform temperature measurement device 90 may consist of any type of temperature measurement device, preferably non-contact, well known to those skilled in the art such as, for example, an infrared temperature sensor.

[0097] Furthermore, with reference to Figures 3 to 5, the temperature of the external wall of the preform is measured in the mold 46 by means of a temperature sensor 92 attached to said mold 46. More particularly, at least one of the half-molds 48, 50 has a through hole 94, more particularly visible in Figures 4 and 5, in which a pyrometer 92 is positioned flush with the internal wall of said half-mold 48, 50.

[0098] It is quite obvious that said pyrometer 92 can be substituted by any other type of equivalent temperature measuring device 92 well known to a person skilled in the art, such as a thermal micro-camera for example, without departing from the scope of the invention.

[0099] Furthermore, it will be observed that only one mold 46 of the forming unit 18 is equipped with such a measuring device 92; however, it goes without saying that each mold 46 of the forming unit 18 can be equipped with a measuring device without going out of the scope of the invention even if this is not necessary for the implementation of the process according to the invention.

[0100] In this regard, the process according to the invention is a process for regulating the cyclic production of containers 2 by stretch blow molding from plastic preforms 4 in a machine comprising one or more stretch blow molding stations, said machine being positioned downstream of a thermal conditioning device 16 for said preforms 4, each of the stretch blow molding stations being designed to produce one container 2 during a production cycle and being equipped with a pre-blow and / or blow solenoid valve of a so-called blow circuit fluidly connecting the preform to a pressurized fluid source providing a pre-blow and / or blow flow during a pre-blow and / or blow phase, each stretch blow molding station comprising a mold 46 consisting of two half-molds 48, 50 delimiting a molding cavity, said preform 4 being blown into said mold 46, with a pre-blowing step, said preform heating steps 4, pre-blowing and blowing being controlled by a control unit 84 from various so-called control parameters such as the power of the heating elements of the oven 16, the blowing pressure in the mold 46 and / or the pre-blowing pressure and / or the pre-blowing flow rate and / or the speed of the drawing rod and / or the ventilation flow rate in the oven 16 for example.

[0101] Said method according to the invention advantageously includes at least the following steps of determining the variation of the temperature of the inner wall of the preform 4 and / or of the temperature at the core of the wall of the preform 4, i.e. the temperature between the outer wall and the inner wall of the preform 4, in the mold 46 of at least one blowing station, and of modifying at least one of the control parameters as a function of said variation of the temperature of the inner wall of the preform 4 and / or of the temperature at the core of the wall of the preform 4.

[0102] Said step of determining the variation in temperature of the inner wall of the preform 4 and / or of the temperature at the core of the wall of the preform 4 comprises at least the following steps of measuring the temperature of the outer wall of the preform at the inlet of the furnace 16, i.e.at the inlet of the thermal conditioning unit 16, between two production cycles, by means of the first temperature measuring device 90; of the temperature of the external wall of the preform 4 at the outlet of the oven 16 between two production cycles by means of the second temperature measuring device 90; of the temperature of the external wall of the intermediate parison in the mold 46, during the preform drawing phase, between two production cycles, by means of the temperature measuring device 92 equipping said mold 46; and of the determination of the variation of the internal temperature of the preform 4 and / or of the temperature at the core of the wall of the preform 4 as a function of the temperatures of the external wall of the preform at the inlet of the oven 16, at the outlet of the oven 16 and in the mold 46. .

[0103] It will be noted that the measurement of the temperature of the external wall of the preform 4 at the exit of the oven 16 can be carried out continuously at each production cycle or discontinuously, the measurement of the temperature of the external wall of the preform 4 at the exit of the oven 16 being then synchronized with the measurement of the temperature of the external wall of the intermediate parison in the mold 46.

[0104] Furthermore, preferably, the step of determining the variation in the internal temperature of the preform 4 as a function of the temperatures of the external wall of the preform 4 at the inlet of the oven 16, at the outlet of the oven 16 and in the mold 46 is carried out by calculating the variation in the external temperature of the intermediate parison, i.e. of the preform in the drawing phase, in the mold 46 between two production cycles if the variation in the external temperature of the preform 4 at the inlet of the oven 16 between the two production cycles is zero or substantially zero and if the variation of the external temperature of the preform 4 at the exit of the oven 16 between the two production cycles is zero or substantially zero, the variation of the temperature of the internal wall of the preform 4 being dependent on the regulation of the oven, i.e. dependent on the modification of at least one control parameter of said oven.

[0105] In addition, the temperature of the preform 4 is measured at the level of the body of the preform, near the neck of said preform 4, whether at the entrance of the oven 16 and / or at the exit of the oven 16 and / or in the mold 46.

[0106] Preferably, the temperature of the preform is measured at the level of the body of the preform 4 at a distance between 1 mm and 60 mm from the neck of said preform and, preferably, at mid-height of the body of the preform 4, whether at the entrance of the oven 16 and / or at the exit of the oven 16 and / or in the mold 46.

[0107] Furthermore, the temperature of the outer wall of the preform 4 is measured in the mold 46 by means of a temperature sensor 92 attached to said mold 46 and positioned flush with the inner wall of said mold 46 as described in more detail with reference to Figures 3 to 5.

[0108] Preferably, the temperature of the outer wall of the preform 4 is measured in the mold 46 by means of a pyrometer 92 attached to said mold 46 and positioned flush with the inner wall of said mold 46.

[0109] If a variation in the temperature of the internal wall of the preform 4 in the mold is determined, at least one of the parameters for controlling the ventilation flow in the oven 16 is modified as a priority.

[0110] Furthermore, if a variation in the temperature of the internal wall of the preform 4 in the mold 46 is determined, at least one of the parameters for controlling the heating temperature of the preforms in the oven 16 is modified.

[0111] Furthermore, if a variation in the temperature of the internal wall of the preform 4 in the mold 46 is determined, the blow pressure control parameter in the mold 46 and / or the pre-blow pressure control parameter and / or the pre-blow flow control parameter and / or the drawing rod speed control parameter is modified.

[0112] It is understood that the process is implemented by means of a computer program product comprising a sequence of instructions which, when the program is executed by a computer, leads the latter to implement the steps of the process according to the invention, said computer program being stored in a memory unit of the control unit 84 for example.

[0113] Finally, it is quite clear that the examples just given are only particular illustrations and in no way limiting as to the fields of application of the invention.

Claims

1. Demands Method for regulating the cyclic production of containers (2) by stretch blow molding from plastic preforms (4) in a machine comprising one or more stretch blow molding stations (44), said machine being positioned downstream of a thermal conditioning device (16) for said preforms (4), commonly called an oven, each of the stretch blow molding stations (44) being designed to produce one container (2) during a production cycle and being equipped with a pre-blow and / or blow solenoid valve (66) (74) of a blow circuit (60, 68) fluidly connecting the preform (4) to a pressurized fluid source (62, 70) providing a pre-blow and / or blow flow during a pre-blow and / or blow phase, each stretch blow molding station (44) comprising a mold (46) consisting of two half-molds (48,50) delimiting a molding cavity, said preform (4) being blown into said mold (46),with at least one pre-blowing and / or blowing step, said preform heating (4), pre-blowing and blowing steps being controlled by a control unit (84) based on various so-called control parameters such as the power of the furnace heating elements, the active time of the furnace heating elements, the ventilation power(s) used within the furnace (16), the blowing pressure in the mold (46) and / or the pre-blowing pressure and / or the pre-blowing flow rate and / or the speed of the drawing rod (58) and / or the flow rate of the ventilation(s) in the furnace (16), for example, characterized in that it comprises at least the following steps of:, - Determination of the variation in temperature of the inner wall of the preform (4) and / or of the temperature at the core of the wall of the preform (4), i.e. the temperature between the outer wall and the inner wall of the preform (4), in the mold (46) of at least one blowing station (18); - Modification of at least one of the control parameters as a function of said variation of the temperature of the internal wall of the preform (4) and / or of the temperature at the core of the wall of the preform (4) and / or of the average temperature of the preform (4) in the thickness.

2. A method according to claim 1 characterized in that the step of determining the variation in temperature of the inner wall of the preform (4) and / or the temperature at the core of the wall of the preform (4) comprises at least the following steps: - Measurement of the temperature of the outer wall of the preform (4) at the inlet of the oven (16) between two production cycles; - Measurement of the temperature of the outer wall of the preform (4) at the outlet of the oven (16) between two production cycles; - Measurement of the temperature of the outer wall of the intermediate parison in the mold (46), during the drawing phase of the preform (4), between two production cycles;- Determination of the variation of the internal temperature of the preform (4) and / or the temperature at the core of the wall of the preform (4) as a function of the temperatures of the external wall of the preform (4) at the inlet (25) of the oven (16), at the outlet (27) of the oven (16) and in the mold (46).;

3. A method according to claim 2 characterized in that the step of determining the variation of the internal temperature of the preform (4) as a function of the temperatures of the external wall of the preform (4) at the inlet (25) of the oven (16), at the outlet (27) of the oven (16), and in the mold (46) is carried out by determining the variation of the external temperature of the intermediate parison, i.e., of the preform (4) in the drawing phase, in the mold (46) between two production cycles, if the variation of the external temperature of the preform (4) at the inlet (25) of the oven (16) between the two production cycles is zero or substantially zero and if the variation of the external temperature of the preform (4) at the outlet (27) of the oven (16) between the two production cycles is zero or substantially zero, the variation of the temperature of the internal wall of the preform (4) being dependent on the regulation of the oven (16), i.e.dependent on the modification of at least one control parameter of said oven.

4. A method according to any one of claims 2 or 3 characterized in that the temperature of the preform (4) is measured at the body (6) of the preform (4), near the neck (10) of said preform (4).

5. A method according to claim 4 characterized in that the temperature of the preform (4) is measured at the body (6) of the preform (4) at a distance between 1 mm and 60 mm from the neck (10) of said preform (4) and, preferably, at mid-height of the body (6) of the preform (4).

6. A method according to any one of claims 2 to 5 characterized in that the temperature of the outer wall of the preform (4) is measured in the mold (46) by means of a temperature sensor (92) attached to said mold (46).

7. The method according to claim 6 characterized in that the temperature of the outer wall of the preform (4) is measured in the mold (46) at the height of the body of the container (2) produced and, preferably, at the level of the area of ​​the body suitable for receiving a label.

8. A method according to any one of claims 6 or 7 characterized in that the temperature of the outer wall of the preform (4) is measured in the mold (46) by means of a pyrometer (92) attached to said mold (46) and positioned flush with the inner wall of said mold (46).

9. A method according to any one of claims 1 to 8 characterized in that, if a variation in the temperature of the internal wall of the preform (4) in the mold (46) is determined, at least one of the parameters for controlling the ventilation flow rate in the oven (16) is modified as a priority.

10. A method according to any one of claims 1 to 9 characterized in that, if a variation in the temperature of the internal wall of the preform (4) in the mold (46) is determined, at least one of the parameters for controlling the heating temperature of the preforms (4) in the oven (16) is modified.

11. A method according to any one of claims 1 to 10 characterized in that, if a variation in the temperature of the internal wall of the preform (4) in the mold (46) is determined, the blow pressure control parameter in the mold (46) and / or the pre-blow pressure control parameter and / or the pre-blow flow control parameter and / or the drawing rod speed control parameter (58) is modified.

12. Machine for manufacturing containers (2) by stretch blow molding from plastic preforms (4) comprising at a source (62,70) of fluid at a pre-blowing and / or blowing pressure, one or more stretch-blowing stations (44), each stretch-blowing station (44) comprising a mold (46) having a cavity for receiving a preform (4), a solenoid valve (66,74) of a so-called pre-blowing and / or blowing circuit suitable for connecting the interior of the preform (4), received in the cavity with said source (62,70) of fluid according to at least a predetermined pre-blowing and / or blowing flow rate, a control device for opening and closing the solenoid valve, at least one sensor capable of measuring the pressure inside the preform (4) or inside the blowing circuit or in the blowing block, said machine being positioned downstream of a thermal conditioning device (16) for said preforms (4),and a memory unit in which are recorded various so-called control parameters such as the heating temperature of the oven (16), the blowing pressure in the mold (46) and / or the pre-blowing pressure and / or the pre-blowing flow rate and / or the speed of the drawing rod (58) for example, and a control unit (84) comprising means for controlling the heating steps of the preforms (4), pre-blowing and blowing from said various control parameters, characterized in that it comprises means capable of implementing the process according to any one of claims 1 to 11.

13. Product computer program comprising a sequence of instructions which, when the program is executed by a computer, causes the computer to carry out the steps of the process according to any one of claims 1 to 11.

14. Data processing device comprising means for carrying out the steps of the process according to any one of claims 1 to 11.

15. A computer-readable recording medium comprising instructions which, when executed by a computer, cause the computer to carry out the steps of the process according to any one of claims 1 to 11.