Method for cooling a container produced by stretch blow moulding
Patent Information
- Application Number
- EP2023841234
- Authority / Receiving Office
- EP · EP
- Patent Type
- Applications
- Current Assignee / Owner
- Priority Date
- 2022-12-29
- Filing Date
- 2023-12-28
- Publication Date
- 2025-11-05
AI Technical Summary
The existing stretch-blow molding processes for manufacturing containers face challenges in achieving uniform material distribution and efficient cooling, particularly at the bottom of the container, leading to deformation and increased costs due to excessive pressurized air consumption.
A process involving a stretching rod with cylindrical orifices, an interior cavity, and an annular skirt to direct high-pressure air cooling towards the container's bottom, allowing for controlled depressurization and extended cooling duration without additional compressed air consumption.
This approach ensures effective cooling of the container, reduces deformation, and lowers manufacturing costs by optimizing the cooling process while maintaining efficient air usage.
Smart Images
Figure 1.1
Abstract
Description
[0001] DESCRIPTION
[0002] TITLE: Process for cooling a container manufactured by stretch-blow molding
[0003] Technical field
[0004] The present invention relates to the field of manufacturing containers by blow molding or stretch blow molding from preforms made of thermoplastic material, such as for example polyethylene terephthalate, hereinafter "PET" or recycled polyethylene terephthalate, hereinafter "rPET". It relates more particularly to a cooling method intended to be implemented in a stretch blow molding technique for forming containers.
[0005] State of the art
[0006] It is known to form containers from thermoplastic material by stretch blow molding preforms previously heated to a temperature sufficient to soften the walls.
[0007] For this purpose, a forming device is used which comprises a mold having a cavity shaped to the imprint of the container to be obtained. The preheated preform is received in the cavity. Then, its walls are subjected to a so-called "biaxial" stretching to fit the imprint of the mold. To do this, the preform is stretched axially by means of a stretching rod to cause the axial expansion of the preform. Simultaneously with this stretching operation, a pressurized fluid is injected into the preform so as to cause the radial expansion of the wall.
[0008] Such a forming process is well known. To ensure that the final container has a perfectly molded base, it is preferable that the drawing rod is adapted to ensure satisfactory container wall thickness. Poor material distribution is a recurring defect observed in containers produced by a molding and stretch / blow molding process. It is not necessarily a matter of ensuring that the container wall thickness is constant, as in some cases it may be desirable to thicken certain areas, particularly those intended to undergo significant stresses (particularly near the base). Rather, it is a matter of ensuring that the material thickness corresponds to the container specifications, as defined according to its shape and use. Furthermore, such variations in thickness, particularly in the base, can make it difficult, during the blowing phase, to evacuate the accumulated calories.The cooling provided by the heat transfer fluid circulating in the mold may then prove insufficient to properly cool the container material.
[0009] To meet these constraints, an additional internal cooling step can be very useful. This step consists of generating cooling of the bottom by the drawing rod, at the end of the blowing phase, over a very short time, at very localized locations on the bottom.
[0010] Processes have thus been developed to promote a distribution of material adapted to demanding specifications.
[0011] Furthermore, in the field of container manufacturing by molding and stretch / blow molding, recycled PET is increasingly being used for environmental reasons. This material further increases the problem of material distribution because it has different properties in terms of stretching capacity and heat absorption: controlling the cooling of the container thus formed is therefore even more crucial.
[0012] Furthermore, despite the precisions brought to the stretch blow molding processes, there are still problems of deformation of the base after demolding the bottle, in particular due to a lack of control of the cooling phase, a phenomenon of deformation increasing due to the constant acceleration of production rates.
[0013] In this regard, document JP2001088202 is known, which proposes a drawing and cooling rod, having orifices specifically provided for cooling the bottom of a preform. These orifices are located on the body of the rod, above the end piece formed at the end of said rod. The end piece is designed to be placed in contact with the bottom of the preform during drawing, then slightly set back during the cooling phase, to allow the gas to escape from the orifices and, by this effect, cool the bottom, at the end of the blowing phase. However, in this configuration, the cooling gas escapes in a poorly controlled manner, and is not directed precisely, in a localized manner towards the bottom of the container obtained. Furthermore, said cooling gas is provided by a source of pressurized air so that said cooling consumes a large quantity of air, which generates an additional cost in the manufacture of the containers.
[0014] Also known is document US8574486B2 which describes a method for blow molding containers, in which a preform, after thermal conditioning inside a blow mold, is stretched by a stretching rod and transformed into a container under the effect of the blowing pressure, and in which pressurized gas is conducted into the container through the stretching rod to cool it. Said pressurized gas is introduced into the container by at least two flow paths, a first flow path extending through the stretching rod which has a plurality of orifices over a portion of its length, and a second flow path passing next to the stretching rod.
[0015] This type of process, although allowing cooling of the container by sweeping using the drawing rod, nevertheless has the disadvantage of being particularly consuming of pressurized air, which increases the manufacturing cost of the containers.
[0016] Disclosure of the invention
[0017] One of the aims of the invention is therefore to overcome these drawbacks by proposing a method for cooling a container manufactured by stretch-blow molding which is simple and inexpensive by limiting the consumption of pressurized air to cool the containers.
[0018] For this purpose, and in accordance with the invention, a method of manufacturing a container by stretch blow molding is proposed, comprising at least the following steps:
[0019] - placing a preheated preform in a blow mold having, in the closed position, a molding cavity forming the imprint of the container to be blown;
[0020] - closing of said blow mold;
[0021] - blowing said preform into the blowing mold via a blowing nozzle by introducing high-pressure air P into said preform and, substantially simultaneously, a step of stretching said preform by inserting a stretching rod inside said preform, bearing against the bottom of said preform so as to facilitate the axial elongation of the latter;
[0022] - cooling the interior of said container thus formed by projection of air via said drawing rod simultaneously or after degassing of the container, the cooling step being carried out via a drawing rod comprising an interior cavity made in its body and at least one orifice communicating with the interior cavity, the high-pressure air introduced into the preform during the blowing step being stored in the interior cavity of the drawing rod and then said high-pressure air escaping from the orifice of the drawing rod to cool the container until the pressure in the interior cavity of the drawing rod is substantially equal to the atmospheric pressure of the air in the container after degassing of the container;
[0023] - raising of said drawing rod;
[0024] - extraction of said blown container by opening said blow mold;
[0025] Said method being remarkable in that the orifices are cylindrical in shape, are at least five in number and have a diameter greater than or equal to 2 millimeters (mm).
[0026] Such a configuration of the drawing rod makes it possible to provide depressurization kinetics of said drawing which follows the depressurization kinetics of the container, providing more efficient cooling of the container.
[0027] According to an essential characteristic of the invention, in the extension of the body of the drawing rod, at its distal end, the drawing rod comprises a flat, an end piece projecting from this flat and an annular skirt in the extension of its body, the orifices, in communication with the interior cavity, being arranged and distributed on the flat, around said end piece so as to direct the cooling gas towards the bottom of the container, over the whole of its lower surface, and thus improve the cooling step.
[0028] Preferably, the cylindrically shaped orifices preferably have a diameter of less than 4 millimeters (mm).
[0029] According to a particularly advantageous embodiment, the high-pressure air P introduced into the preform during blowing is stored in a reservoir fluidly connected to the cavity of the drawing rod until the pressure in the cavity of the drawing rod and said reservoir is equal to the pressure of the high-pressure air P in the container. Said reservoir thus makes it possible to increase the cooling time and, ultimately, the efficiency of said cooling of the containers.
[0030] Furthermore, the cavity of the drawing rod and / or the reservoir are filled, during blowing, with high pressure air P through a plurality of orifices opening into the cavity of the drawing rod, said orifices being positioned over all or part of the height of the drawing rod and over all or part of the circumference of said drawing rod.
[0031] According to an alternative embodiment of the method according to the invention, the drawing rod begins to rise from the start of degassing of the container.
[0032] According to a second variant of the method according to the invention, the drawing rod begins to rise from the end of degassing of the container, that is to say when the pressure in the container is substantially equal to atmospheric pressure Pa.
[0033] According to another variant of the method according to the invention, the drawing rod begins to rise after a time delay ti from the start of degassing of the container.
[0034] Said time delay ti for the rise of the drawing rod is preferably between 0.01 and 1 second.
[0035] Preferably, the time delay ti for the rise of the drawing rod is greater than or equal to the duration of the degassing of the container.
[0036] Furthermore, the volume of high-pressure air stored in the cavity of the drawing rod is between 10000 and 150000 mm 3 .
[0037] In addition, the volume of high-pressure air stored in the tank is between 1000 and 2000000 mm 3 .
[0038] Said drawing rod preferably comprises a plurality of orifices distributed along said drawing rod and angularly distributed around said drawing rod, equidistantly or not. Preferably, said drawing rod comprises at least one orifice positioned at the lower free end of said drawing rod in order to cool the bottom of the containers.
[0039] Incidentally, the introduction of high pressure air P into said preform and, ultimately, into the internal cavity of the drawing rod, is carried out at different increasing pressures PI, P2,...Pn.
[0040] Brief description of the drawings
[0041] Other advantages and characteristics will emerge more clearly from the following description of several variant embodiments, given as non-limiting examples, of the method of cooling a container manufactured by stretch-blow molding in accordance with the invention, with reference to the appended drawings in which:
[0042] [Fig. 1] is a schematic representation seen from above of a rotary type molding machine, illustrating in particular the molding units, with the exception of the blowing and stretching means, distributed around a carousel, said blowing units being, depending on their relative position with respect to the inlet or outlet of the machine, in the open position or in the closed position,
[0043] [Fig. 2] is a partial schematic representation in perspective of one of the molding units of the machine shown in Figure 1, illustrating in particular, outside the unit in the open position, an exploded view of a mold made in three parts, namely two half-molds and a mold base,
[0044] [Fig. 3] is a schematic representation along a vertical longitudinal median section of a molding unit of the machine, during a first stage of a blowing cycle of a container, showing in particular the insertion of the distal end of the rod into a preform enclosed within a mold,
[0045] [Fig. 4] is a schematic representation similar to Figure 3, during another subsequent step at the end of the blowing cycle, showing in particular the distal end of the rod introduced into the blown container and extending to the bottom of said blown container,
[0046] [Fig. 5] is a schematic representation similar to Figures 3 and 4, during another subsequent step after the blowing cycle, showing in particular the filling of the interior cavity of the drawing rod with pressurized air, corresponding to the blowing air,
[0047] [Fig. 6] is a schematic representation similar to Figures 3 to 5, during another subsequent step of starting degassing, [Fig. 7] is a schematic representation similar to Figures 3 to 6, during another subsequent step of starting cooling, showing in particular the distal end of the rod introduced into the blown container and extending to the bottom of said blown container,
[0048] [Fig. 8] is a schematic representation similar to Figures 3 to 7, during another subsequent cooling medium step, showing in particular the distal end of the rod introduced into the rising blown container,
[0049] [Fig. 9] is a schematic representation similar to figures 3 to 8, during a final stage corresponding to the end of cooling, showing in particular the distal end of the rod introduced into the blown container fully raised,
[0050] [Fig. 10] is a vertical longitudinal sectional view of a detail of the molding unit during the first blowing stage shown in Figure 3, showing more particularly the stretching rod extending inside the preform,
[0051] [Fig. 11] is a schematic perspective view of one embodiment of the distal end of the stretching rod,
[0052] [Fig. 12] is a longitudinal sectional view of the embodiment of the distal end of the stretching rod shown in Fig. 11,
[0053] [Fig. 13] is a schematic representation along a vertical longitudinal median section of an alternative embodiment of the molding unit of the machine, during a first stage of a blowing cycle of a container, showing in particular the insertion of the distal end of the rod into a preform enclosed within a mold,
[0054] [Fig. 14] is a schematic representation similar to Figure 13, during another subsequent step at the end of the blowing cycle, showing in particular the distal end of the rod introduced into the blown container and extending to the bottom of said blown container,
[0055] [Fig. 15] is a schematic representation similar to Figures 13 and 14, during another subsequent step after the blowing cycle, showing in particular the filling of the inner cavity of the drawing rod with pressurized air and a reservoir connected to the inner cavity of the drawing rod, the pressurized air corresponding to the blowing air,
[0056] [Fig. 16] is a schematic representation similar to Figures 13 to 15, during another subsequent stage of degassing start,
[0057] [Fig. 17] is a schematic representation similar to Figures 13 to 16, during another subsequent step of starting cooling, showing in particular the distal end of the rod introduced into the blown container and extending to the bottom of said blown container,
[0058] [Fig. 18] is a schematic representation similar to Figures 13 to 17, during another subsequent cooling medium step, showing in particular the distal end of the rod introduced into the rising blown container,
[0059] [Fig. 19] is a schematic representation similar to figures 13 to 18, during a final stage corresponding to the end of cooling, showing in particular the distal end of the rod introduced into the blown container fully raised.
[0060] Method of carrying out the invention
[0061] In the remainder of the description of the container according to the invention, the same numerical references designate the same elements. The different views are not necessarily drawn to scale. Furthermore, the present invention is more particularly intended to be implemented in an installation for manufacturing PET bottle containers; however, it is quite obvious that the invention can be adapted for the manufacture of any type of container without departing from the scope of the invention.
[0062] With reference to Figure 1, said container manufacturing installation usually comprises a molding machine 1 comprising at least molding units 2 distributed circularly, in the form of a carousel 3. Each molding unit 2, with reference to Figures 1 and 2, comprises at least one mold 4 and blowing means integrating a drawing rod 5, said mold 4 comprising at least two half-molds 4a, 4b which each comprise an internal molding face and which are respectively mounted on supports 6 movable around an axis X, between at least one open position and a closed position of the molding unit 2, in which said internal faces of said at least two joined half-molds 4a, 4b together delimit a molding cavity 7 of the container.
[0063] In practice, the blow molds 4 are distributed circularly, in the form of a carousel 3 as visible in Figure 1, and surmounted by respective blowing installations. In practice, still, and as visible in Figure 2, the body of the blowing installation extends substantially vertically above the mold and substantially coaxially with the molding cavity 7 of the blow mold 4. Figure 2 schematically represents a perspective view of one of the molding units 2 of the machine according to the embodiment example of Figure 1, illustrating in particular, outside the unit in the open position, an exploded view of a mold 4 made in three parts, namely two half-molds 4a, 4b and a mold base 8.
[0064] All these elements being well known to those skilled in the art, they will not be described in more detail for a better understanding of the invention.
[0065] With reference to Figure 3, which is a schematic representation along a vertical longitudinal median section of a molding unit 2 of the machine, during a first step of a cycle for blowing a container from a preform 9 made of PET and / or recycled PET, showing in particular the insertion of the distal end of the rod 5 into a preform 9 enclosed within a mold 4 and intended to be stretched and blown in one of the blowing molds 4 of an installation briefly described above, so as to form a container 2, such as a bottle, said stretching rod 5 is in the high position and being inserted into the preform 9.
[0066] Said rod 5 is designed to be mounted in the body of the blowing installation also mentioned above. Said stretching rod 5 extends longitudinally, parallel to the main axis Y. The stretching rod 5 according to the invention is a hollow stretching rod, which then ensures a dual function, a stretching function on the one hand and another function of cooling the container on the other hand as will be detailed a little later. To do this, it has a first so-called proximal end (not shown) capable of being secured to a displacement device internal to the manufacturing installation.
[0067] Said preform 9, shown in more detail in Figure 10, conventionally comprises a body 10 of elongated, tubular shape, with a longitudinal axis of revolution, limited by a wall 11 secured in the upper part to a threaded neck 12, the neck 12 being separated from the body 10 by a radial flange 13 projecting towards the outside of the preform, and in the lower part by a substantially hemispherical bottom 14. Thus, said preform 9 illustrated in Figure 10 has a symmetry of revolution around its longitudinal axis which is substantially coaxial with the axis Y of the rod 5 when the preform 9 is placed in the molding unit 2. It will be noted that, in the remainder of the description, any direction parallel to the axis of revolution Y of the rod 5 will be called "vertical" and any direction perpendicular to the axis of revolution Y of the rod 5 will be called "transverse".
[0068] With reference to Figures 10 to 12, the stretching rod 5 comprises a cylindrical or tubular body 15. In embodiments, not shown in the figures, the body 15 of the stretching rod 5 may have a shoulder, that is to say have two longitudinal sections having two different diameters. This is particularly advantageous for blowing small diameter preforms.
[0069] Said body 15 also comprises a central interior cavity 16 extending axially and communicating with a plurality of orifices 17 through which a cooling gas, in particular air, is injected inside the manufactured container in order to cool it. The orifices 17 are therefore in fluid communication with the interior cavity 16. In the extension of the body 15, at its distal end, the drawing rod 5 comprises a flat 18. An end piece 19 projects from this flat 18. Said drawing rod 5 further comprises an annular skirt 20 in the extension of its body 15.
[0070] In this particular embodiment, the diameter of the annular skirt 20 is equal to the diameter of the body 15 of the drawing rod 1. In this advantageous configuration, the cooling gas is directed in a very localized manner. It is obvious that the outer body 15 and the annular skirt 20 can be obtained in one piece or in two parts without departing from the scope of the invention.
[0071] Said drawing rod 5 has the advantage of directing the cooling gas towards the bottom of the container, over its entire lower surface, and thus of improving the cooling step.
[0072] In this particular embodiment, the orifices 17, in communication with the interior cavity 16, are arranged and distributed on the flat 18, around said end piece 19. The orifices 17 allow the cooling gas to be projected onto the bottom of the blown container. The orifices 17 are arranged on the flat 18, and over its entire circumference, thus allowing the projection of the cooling gas from the interior cavity 16 to the interior of the blown container. The orifices 17 are for example of cylindrical shape and preferably have a diameter of between 1 and 4 millimeters (mm). They may also be of another shape, for example of oblong shape.
[0073] Furthermore, according to a preferred embodiment, the projection surface is between 3 and 6 square millimeters (mm 2) and does not exceed 20 square millimeters (mm2). The projection surface corresponds to the sum of the surfaces of the orifices 17. It represents the quantity of cooling gas that can be projected thanks to the configuration of the rod 5, comprising orifices 17 acting as restriction orifices. The projecting tip 19 can be of any shape. In particular, said tip
[0074] 19 may be conical in shape, rounded conical in shape, ovoid in shape, hemispherical in shape, etc. In addition, the flat 18 is preferably perpendicular to the body 15 of the drawing rod 5. Incidentally, the edges of the annular skirt 20 are rounded. This is particularly advantageous because it avoids any risk of tearing when said edges of the annular skirt 20 come into contact with the wall of the preform 9, for example during the drawing phase. The annular skirt 20 has, for example, the same diameter as the diameter of the body 15 of the drawing rod 5. In addition, the annular skirt
[0075] 20 has a height less than the height of the tip 19 so that said tip 19 projects from the annular skirt 20. In other words, the distal end of the drawing rod 5 is formed by the tip 19 and the annular skirt 20 is an extension of the outer body 15 relative to the flat 18. This makes it possible to direct the cooling gas in a controlled manner when it leaves the inner cavity 16 through the orifices 17. For example, the height of the annular skirt 20 is less than the height of the tip 19 by a value between 0.5 and 4 millimeters (mm), even more preferably by a value of 1mm.
[0076] According to a preferred embodiment, the drawing rod 5 comprises at least five orifices 17 whose diameter is at least equal to 2 mm. Such a configuration of the drawing rod 5 makes it possible to provide depressurization kinetics of said drawing rod 5 which follows the depressurization kinetics of the container, thus providing more efficient cooling of said container.
[0077] Preferably, said drawing rod 5 comprises a plurality of orifices 17 distributed along said drawing rod 5 and angularly distributed around said drawing rod 5, said orifices 17 being in communication with the interior cavity 16 of said drawing rod 5, to cool the entire body of the container and at least one orifice 17 positioned at the lower free end of said drawing rod 5 in order to cool the bottom of the containers.
[0078] The cooling step is an additional step in a manufacturing process for PET and recycled PET ("rPET") containers. This cooling step notably reduces the internal temperature of the resulting container, and aims to limit the transfer of heat from the internal to the external after the resulting container has been removed from the mold. This also limits the collapse of the base, which generally has a negative impact on stress, which increases the risk of rejects. Indeed, a base with too high a temperature will tend to collapse during the mold removal step. The resulting container may then potentially exhibit "stress" or other defects. "Stress" refers to signs of stress such as cracks, for example.It will be observed that the presence of the annular skirt 20 of the drawing rod 5 has the advantage of considerably improving the cooling step by amplifying the action of the cooling gas, the gas being directed in a localized manner where its presence is necessary. This then makes it possible to considerably improve the cooling step of the bottom of the container obtained, and therefore to achieve optimal cooling, even when, for reasons of throughput, the duration of the cooling step must be very short.
[0079] With reference to Figures 3 to 9, the method of manufacturing a container by stretch blow molding with a particularly advantageous cooling step according to the invention of a container from the previously described stretch rod will be described below.
[0080] With reference to Figure 3, a heated preform 9 being previously placed in a blow mold 4 having, in the closed position, a molding cavity 7 forming the imprint of the container to be blown, the blow mold 4 being closed, the stretching rod 5 is positioned in the preform 5 such that the latter extends coaxially with the preform 5.
[0081] Then, with reference to Figure 4, said preform 9 in the blowing mold 4 is blown via a blowing nozzle 21 by introducing high-pressure air P into said preform 9 and, substantially simultaneously, a step of stretching said preform 9 by vertical downward movement of said stretching rod 5 in said preform 9 while bearing against the bottom 14 of said preform 9 so as to facilitate the axial elongation of the latter.
[0082] With reference to Figure 5, the gas introduced into said preform 9, and ultimately the container formed by said blowing, enters the inner cavity 16 of the drawing rod 5 through the orifice(s) 17, until the pressure inside said inner cavity 16 of the drawing rod is substantially equal to the pressure P of the air initially introduced into the preform 9 to form the container. Thus, high-pressure air P introduced into the preform during the blowing step is stored in the inner cavity 16 of the drawing rod 5.
[0083] Once the container has been blown, with reference to Figure 6, the high-pressure gas P contained in the container is degassed through the blowing nozzle 21 and then, with reference to Figure 7, the high-pressure air P stored in the inner cavity 16 of the drawing rod 5 escapes from the orifice(s) 17 of the drawing rod 5 to cool the container until the pressure in the inner cavity 16 of the drawing rod 5 is equal to the atmospheric pressure Pa of the air in the container after the degassing of said container.
[0084] During this cooling step, that is to say the escape of the air initially stored in the interior cavity 16 of the drawing rod 5, the latter is gradually raised, with reference to FIG. 7, until said drawing rod 5 reaches its high position, the high position of the drawing rod corresponding to the end of the container cooling step.
[0085] In a final step, not shown in the figures, said container thus formed and cooled is extracted in a conventional manner by opening said blow mold 4.
[0086] It is understood that, according to the method according to the invention, the step of cooling the blown container is carried out without having to consume additional compressed air dedicated solely to cooling, which makes it possible to reduce the consumption of compressed air, although a little more compressed air is consumed during the blowing step, and ultimately to reduce the manufacturing costs of the containers. In this particular example of embodiment, the drawing rod 5 begins to rise from the start of the degassing of the container; however, according to an alternative embodiment of the method according to the invention, the drawing rod 5 may begin to rise from the end of the degassing of the container, that is to say after the pressure in the container is substantially equal to atmospheric pressure Pa.It will be observed that, in this last variant of execution of the process, the air contained in the interior cavity is entirely projected onto the bottom of the container so that the cooling of said bottom of the container is optimal.
[0087] According to another variant of the method according to the invention, the drawing rod 5 begins to rise after a time delay ti from the start of degassing of the container. In this case, said time delay ti for the rise of the drawing rod is preferably between 0.01 and 1 second.
[0088] Furthermore, the volume of high-pressure air stored in the inner cavity 16 of the drawing rod 5 is between 10000 and 150000 mm 3 to ensure sufficient cooling of the container.
[0089] According to a particularly advantageous variant embodiment, shown in Figures 13 to 19, the high-pressure air P introduced into the preform 9 during blowing is stored in a reservoir 22 fluidly connected to the inner cavity 16 of the drawing rod 5 until the pressure in the cavity of the drawing rod and said reservoir is equal to the pressure of the high-pressure air P in the container. Said reservoir 22 thus makes it possible to increase the cooling time and, ultimately, the effectiveness of said cooling of the containers.
[0090] Thus, with reference to figure 13, a heated preform 9 being previously placed in a blow mold 4 having, in the closed position, a molding cavity 7 forming the imprint of the container to be blown, the blow mold 4 being closed, the stretching rod 5 is positioned in the preform 5 such that the latter extends coaxially with the preform 5.
[0091] Then, with reference to Figure 14, said preform 9 in the blowing mold 4 is blown via a blowing nozzle 21 by introducing high-pressure air P into said preform 9 and, substantially simultaneously, a step of stretching said preform 9 by vertical downward movement of said stretching rod 5 in said preform 9 while bearing against the bottom 14 of said preform 9 so as to facilitate the axial elongation of the latter.
[0092] With reference to Figure 15, the gas introduced into said preform 9, and ultimately the container formed by said blowing, enters the inner cavity 16 of the drawing rod 5 through the orifice(s) 17, as well as into the reservoir 22, until the pressure inside said inner cavity 16 of the drawing rod and the reservoir is substantially equal to the pressure P of the air initially introduced into the preform 9 to form the container. Thus, high-pressure air P introduced into the preform during the blowing step is stored in the inner cavity 16 of the drawing rod 5 and in the reservoir 22.
[0093] Once the container has been blown, with reference to Figure 16, the high-pressure gas P contained in the container is degassed through the blowing nozzle 21 and then, with reference to Figure 17, the high-pressure air P stored in the inner cavity 16 of the drawing rod 5 and in the reservoir escapes from the orifice(s) 17 of the drawing rod 5 to cool the container until the pressure in the inner cavity 16 of the drawing rod 5 and in the reservoir 22 is equal to the atmospheric pressure Pa of the air in the container after the degassing of said container.
[0094] During this cooling step, that is to say the escape of the air initially stored in the interior cavity 16 of the drawing rod 5 and in the reservoir 22, the latter is gradually raised, with reference to figure 18, until said drawing rod 5 reaches its high position, the high position of the drawing rod corresponding to the end of the cooling step of the container, with reference to figure 19.
[0095] In a final step, not shown in the figures, said container thus formed and cooled is extracted in a conventional manner by opening said blow mold 4.
[0096] In the same way as previously, the drawing rod 5 preferably begins to rise from the start of degassing of the container; however, according to an alternative embodiment of the method according to the invention, the drawing rod 5 may begin to rise from the end of degassing of the container, that is to say after the pressure in the container is substantially equal to atmospheric pressure Pa. According to another alternative embodiment of the method according to the invention, the drawing rod 5 begins to rise after a time delay ti from the start of degassing of the container. In this case, said time delay ti for the rise of the drawing rod is preferably between 0.01 and 1 second. The time delay ti for the rise of the drawing rod is preferably greater than or equal to the duration of degassing of the container, which corresponds to a rise of the rod after the end of degassing of the container.
[0097] It will be observed that the volume of high pressure air stored in the tank 22 is preferably between 1000 and 2000000 mm 3 , the volume of high-pressure air stored in the inner cavity 16 of the drawing rod 5 being between 10,000 and 150,000 mm 3 in the same way as before.
[0098] Furthermore, preferably the inner cavity 16 of the drawing rod 5 and / or the reservoir 22 are filled, during blowing, with high pressure air P through a plurality of orifices 17 opening into the inner cavity 16 of the drawing rod 5, said orifices 17 being positioned over all or part of the height of the drawing rod 5 and over all or part of the circumference of said drawing rod 5.
[0099] In order for the cooling to be as homogeneous as possible, said drawing rod 5 preferably comprises a plurality of orifices 17 distributed along said drawing rod 5 and angularly distributed around said drawing rod 5. In addition, said drawing rod 5 comprises at least one orifice 17 positioned at the lower free end of said drawing rod 5 in order to cool the bottom of the containers.
[0100] Finally, and incidentally, the introduction of high-pressure air P into said preform and, ultimately, into the internal cavity 16 of the drawing rod 5 and / or into the reservoir 22, is carried out at different increasing pressures PI, P2,...Pn. Said increasing pressures PI, P2,...Pn correspond to the different blowing pressures well known in the methods of the prior art including air recovery in particular.
[0101] It goes without saying that the person skilled in the art will size the section of the orifice(s) 17 of the rod, the volume of the internal cavity 16 and of the reservoir 22, as a function of the degassing speed (said degassing speed depending on the volume of the blown container, the blowing pressure and the diameter of the neck in particular) in order to optimize the cooling of the bottom of the container.
[0102] Finally, it is clear that the examples just given are only specific illustrations and are in no way limiting as to the fields of application of the invention.
Claims
CLAIMS
1. A method of manufacturing a container by stretch blow molding, comprising at least the following steps: - placing a pre-heated preform (9) in a blow mold (4) having, in the closed position, a molding cavity (7) forming the imprint of the container to be blown; - closing said blow mold (4); - blowing said preform (9) into the blowing mold (4) via a blowing nozzle (21) by introducing high-pressure air P into said preform (9) and, substantially simultaneously, a step of stretching said preform (9) by inserting a stretching rod (5) inside said preform (9) while bearing against the bottom (14) of said preform (9) so as to facilitate the axial elongation of the latter; - cooling the interior of said container thus formed by projection of air via said drawing rod (5) simultaneously or after degassing of the container, the cooling step being carried out via a drawing rod (5) comprising an interior cavity (16) made in its body (15) and at least one orifice (17) communicating with the interior cavity (16), the high pressure air P introduced into the preform (9) during the blowing step being stored in the interior cavity (16) of the drawing rod (5) then said high pressure air P escaping from the orifice (17) of the drawing rod (5) to cool the container until the pressure in the interior cavity (16) of the drawing rod (5) is substantially equal to atmospheric pressure Pa of the air in the container after degassing of the container - raising of said drawing rod (5); - extraction of said blown container by opening said blowing mold (4); characterized in that the orifices (17) are cylindrical in shape, are at least five in number and have a diameter greater than or equal to 2 millimeters (mm).
2. Method according to claim 1 characterized in that, in the extension of the body (15) of the drawing rod (5), at its distal end, the drawing rod (5) comprises a flat (18), an end piece (19) projecting from this flat (18) and an annular skirt (20) in the extension of its body (15), the orifices (17), in communication with the internal cavity (16), being arranged and distributed on the flat (18), around said end piece (19) so as to direct the gas from cooling towards the bottom of the container, over its entire lower surface, and thus improve the cooling step.
3. Method according to any one of claims 1 or 2 characterized in that the orifices (17) of cylindrical shape preferably have a diameter of less than 4 millimeters (mm).
4. Method according to any one of claims 1 to 3 characterized in that the high pressure air P introduced into the preform (9) during blowing is stored in a reservoir (22) fluidly connected to the interior cavity (16) of the stretching rod (5) until the pressure in the interior cavity (16) of the stretching rod (5) and said reservoir (22) is substantially equal to the pressure of the high pressure air P in the container.
5. Method according to any one of claims 1 to 4 characterized in that the internal cavity (16) of the drawing rod (5) and / or the reservoir (22) are filled, during blowing, with air under high pressure P through a plurality of orifices (17) opening into the internal cavity (16) of the drawing rod (5), said orifices (17) being positioned over all or part of the height of the drawing rod (5) and over all or part of the circumference of said drawing rod (5).
6. Method according to any one of claims 1 to 5 characterized in that the drawing rod (5) begins to rise from the end of degassing of the container, that is to say when the pressure in the container is substantially equal to atmospheric pressure Pa.
7. Method according to any one of claims 1 to 5 characterized in that the drawing rod (5) begins to rise from the start of degassing of the container.
8. Method according to any one of claims 1 to 5, characterized in that the drawing rod (5) begins to rise after a time delay ti from the start of degassing of the container.
9. Method according to claim 8 characterized in that the time delay ti for the rise of the drawing rod (5) is between 0.01 and 1 second.
10. Method according to any one of claims 8 or 9 characterized in that the time delay ti for the rise of the drawing rod (5) is greater than or equal to the duration of the degassing of the container.
11. Method according to any one of claims 1 to 10 characterized in that the volume of high pressure air stored in the internal cavity (16) of the drawing rod (5) is between 10000 and 150000 mm 3 .
12. Method according to any one of claims 4 to 11 characterized in that the volume of high pressure air stored in the tank (22) is between 1000 and 2000000 mm 3 .
13. Method according to any one of claims 1 to 12 characterized in that said drawing rod (5) comprises a plurality of orifices (17) distributed along said drawing rod (5) and angularly distributed around said drawing rod (5).
14. Method according to any one of claims 1 to 13 characterized in that said drawing rod (5) comprises at least one orifice (17) positioned at the lower free end of said drawing rod (5).
15. Method according to any one of claims 1 to 14 characterized in that the introduction of air under high pressure P into said preform (9) and, ultimately, into the internal cavity (16) of the drawing rod (5), is carried out at different increasing pressures PI, P2,...Pn.