FR2828829A1 - Cooling procedure for blow-moulded hollow articles, uses cooling fluid injected into mould cavity - Google Patents

Abstract

The procedure, especially for cooling hollow articles (4) blow-moulded from parisons (6), consists of injecting a cooling fluid into the mould cavity on completion of moulding to reach at least one zone (17) of the article. The cooling fluid can be an atomized liquid or gas delivered through an injector (19) in a variable flow while the mould components (1, 2, 3) are in the moulding position and while the mould is being opened, with a view to extracting the moulded article. The injection can be synchronized with the commencement of mould separation, with the cooling fluid entering the gap between the lower mould component (3) and the cooled zone. The injector (19) has a nozzle and channels (20, 21) for pressurized liquid and atomizing gas.

Description

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 Method for cooling a hollow body at the end of its manufacture by hot molding and implementation device.

 The invention relates to improvements to the methods for cooling hollow bodies, after their manufacture by hot molding. It also relates to a molding device equipped with means for implementing the method.

 It applies very particularly, although not exclusively, to the cooling of hollow bodies, such as containers, bottles or the like, obtained by blowing, in a finishing mold, a blank whose constituent material is brought to a temperature above its softening temperature, also called the glass transition temperature of the material.

 A known drawback of hollow body molding methods lies in the fact that their constituent material must be sufficiently stabilized at the time of demolding. If, at the time of demolding, malleable zones remain, for example because they are still above the glass transition temperature of the material, and are therefore not thermally stabilized, this can have, in certain cases, more or less annoying consequences depending on the nature or destination of the hollow body.

 A first consequence which can arise in the event of demolding before stabilization is the appearance of deformations or spontaneous or caused deteriorations in the malleable zones. This can therefore result in appearance defects and / or an alteration in the characteristics of the hollow body making it unsuitable for the initial use for which it was intended.

 A second potential consequence is that of the impossibility of handling or using certain hollow bodies as long as their constituent material is not thermally stabilized, failing which they risk becoming deteriorated at the location of the areas which are still too malleable. This is for example the case of various containers or containers of thermoplastic material which it is not possible to fill before stabilization.

 To avoid the problems mentioned, while having acceptable production rates, it is known to force or accelerate the

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 thermal stabilization in molds by associating it with appropriate means.

 Thus, for example, it is known to arrange, in the mass of material constituting the walls of the molding cavities, cooling circuits constituted by conduits and / or by cavities formed in the walls and in which circulation is carried out. coolant, usually water. When the material of the hollow bodies comes into contact with the wall, it cools.

 However, the time required to cool distinct areas of their wall having notable differences in thickness is not the same. Due to the thermal inertia of the material of the object, the thicker areas cool more slowly.

 It follows that it is necessary to wait until the thicker zones have reached a sufficiently low temperature to consider demolding: the rate therefore depends on the time taken by the material in the thicker zones to cool, and to reach a temperature where may consider this material to be thermally stabilized.

 Furthermore, when the hollow bodies are obtained by blowing or stretching and then blowing of blanks made of thermoplastic material, as is the case for example with containers, bottles or the like, it has been observed, even if all the precautions are taken to unmold the hollow bodies after the material has reached a correct temperature, it sometimes appears cracks in areas of junction between thicker parts and thinner parts, sometimes going as far as ruptures in these areas .

 These cracks are due to the appearance of internal stresses during cooling between neighboring zones of different thickness, due to the temperature gradients which exist during cooling, in the thickness of the constituent material, between said zones because thicker areas take longer to cool.

These stresses develop and remain after cooling if the temperature gradients are present for a significant period allowing these internal stresses to freeze.

 In the case of containers, such as bottles made of thermoplastic material, such junction zones are located mainly around the center of their bottom. This results from the fact that in the center, the stretching of the

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 material is zero and increases to the walls where the most stretched areas are located.

 Thus, when the containers are obtained by stretching and then blowing pre-injected preforms, as is the case in the so-called injection-blowing processes, the cracks often delimit a substantially circular zone, centered on their bottom. This area is actually made of amorphous material, that is to say that was not stretched significantly during the blowing process.

 A first object of the invention is to obtain a method for cooling hollow bodies, after their manufacture by hot molding, while they are still in the molding cavity used for their manufacture, and a implementation device, which make it possible to promote the cooling of certain zones of these objects, in order to increase the rate of cooling compared to known methods, and which consequently make it possible to increase the overall rate of manufacture.

 A second object of the invention is that the cooling method and the implementation device are applicable to hollow decorps cooling which, produced by molding, have neighboring zones with notable differences in thickness, and which allow the thicker zones are cooled more quickly than with known methods and devices, in order to limit or reduce the risk of the appearance of cracks between two zones of different thickness.

 According to the invention, a method of cooling a hollow body, after its manufacture by hot molding in a molding cavity, while said hollow body is still in said cavity, of the kind consisting in forcing the cooling using a cooling fluid circulating in closed circuits formed in the walls of the cavity, is characterized in that, after molding, in order to favor the cooling of at least one area of the body hollow, cooling fluid is also injected inside the mold cavity, directly in contact with said area to be privileged to cool.

 Thus, at the location of said zone, unlike known methods, where the calories are evacuated via the constituent material of the mold, material which itself has a certain inertia

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 thermal, we obtain, thanks to the process of the invention, a better yield during cooling. As a result, thicker areas can be cooled more quickly than with known methods, which for their part can be used for neighboring, less thick areas, so that the temperature gradients disappear or, at least, are present for a shorter time, with the consequence that internal constraints do not have time to develop. In other words, we manage to create differentiated cooling zones, which is not possible with conventional methods, since in this case, the calories tend to be evacuated uniformly in the mass of constituent material. of the mold.

 In one implementation, the cooling fluid used is a liquid. In this case, it can be injected using injection means known per se, such as spraying or nebulizing means.

 In a variant, the fluid is a gas having a high cooling capacity, such as a gas expanded at the location of the zone to be privileged to cool.

 According to one characteristic, the molding cavity is made up of at least two elements which are movable relative to one another to allow the mold to be removed from the mold, and the fluid is injected inside the cavity, at the end molding, so as to come directly into contact with said zone to cool in a privileged manner while the elements are still in their molding position of said body.

 According to another characteristic, the molding cavity consists of at least two elements which are movable relative to each other to allow the mold to be removed from the mold, and the fluid is injected inside the cavity directly in contact of the said zone to be cooled in a privileged manner between the moment when the elements begin to be moved relative to one another at the end of the molding and that when they reach their position allowing the extraction of the hollow body.

 A device for implementing the method of the invention is characterized in that it comprises means for injecting fluid arranged so that the fluid is directed inside the cavity at least towards said zone to be cooled. in a privileged way.

 Other characteristics and advantages of the invention will appear on reading the description which follows, made with reference to the figures

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 annexed, which illustrate the principle of the invention applied to the cooling of the central zone of the bottom of a plastic container, manufactured using a manufacturing mold, consisting of at least two movable elements, one relative to the other to allow the container to be removed from the mold and on which: - Figure 1 is a sectional view of the mold while its constituent elements are still in their position for molding said body; - Figure 2 is a sectional view of the mold while its constituent elements are in an intermediate position between the molding position and their open position allowing the extraction of the hollow body.

 The mold illustrated in FIGS. 1 and 2 is a mold constituted, in a manner known per se, of three main elements 1, 2, 3, determining, when they are in the position of FIG. 1, a mold cavity 4 allowing to produce containers 5, here bottles having a petaloid bottom, from preforms, the initial outline 6 of which is shown in broken lines in FIG. 1.

 Two elements 1,2 determine the external shape of the shoulder and of the body of the bottles produced therein, and the third element 3d determines the external shape of the bottom, also called base, of the container.

 In Figure 1, the three elements are shown in a closed position of the mold, that is to say in a position where the manufacture of a container is possible.

 However, in a manner that is also known, in order to allow the preform to be put in place, then the container to be removed from the mold, the elements 1, 2, 3 are movable relative to one another. For these purposes, the elements 1, 2 determining the external shape of the shoulder and of the body of the bottles can deviate from one another and from the longitudinal axis 7 of the bottle (movement of spacing materialized by arrows 8, 9), and a relative movement between the element 3 and the container can be carried out in a direction parallel to the longitudinal axis 7, to allow demolding of the bottom of the container without interference with this element.

 The spacing between the elements 1,2 can be obtained by any known means, for example by moving these two elements away from each other, or by causing a relative pivoting movement of one relative to the other.

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 Similarly, the relative movement between the element 3 and the container can be obtained using known means. Thus, it is for example possible to cause a longitudinal displacement of the container (in this case, the container manufacturing equipment includes means to allow this longitudinal displacement of the container) or even, preferably, as shown in the figures , a longitudinal displacement of the element 3, displacement illustrated by the arrow 10. In this case, the container manufacturing equipment comprises known means, not shown, to allow this longitudinal displacement of the element 3, such as, for example, cylinders or cam and roller guide devices or the like. In the example illustrated, in a known manner, this longitudinal displacement is only possible when the elements 1, 2 are spaced from one another, because to counteract the effects due to the blowing pressures necessary for the manufacture of bodies hollow, means for blocking the element 3 relative to the elements 1, 2 are provided to act when the device is in the position in FIG. 1, such as studs or an annular protuberance 11 formed at the periphery of the element 3 , "cooperating with complementary means produced in each of the elements 1,2, such as recesses receiving the studs or grooves 12,13 receiving the annular protuberance.

 Furthermore, again in known manner, the two elements 1, 2 determining the external shape of the shoulder and of the body of the bottles are provided with cooling means constituted in the example by conduits 14, 15 formed in the thickness of their constituent material and forming part of a cooling circuit (not shown), in which a circulation of cooling fluid is ensured.

 In known manner, the element 3 determining the external shape of the bottom of the container is provided, meanwhile, with cooling means such as conduits 16 in which a circulation of cooling fluid is ensured.

 According to the invention, in order to favor the cooling of at least one zone, here the central zone 17 of the bottom 18 of the container 5, thicker than other parts, the element 3 is further provided with means 19 allowing a direct injection of cooling fluid directly in contact with said area to be privileged to cool.

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 Tests have made it possible to demonstrate that simple means allowing direct injection of fluid onto each zone to be cooled in a privileged manner make it possible, in most cases, to overcome the problems known from the prior methods. However, these means should be arranged so that the material constituting the hollow body does not flow through them during this phase, under the effect of the molding pressure or due to the fluidity of the material during this phase.

 Indeed, if the material were to creep, it would result in the possibility of obtaining a non-conforming hollow body, since having a deformation due to creep; it would also result in the possibility of blockage of the means making them ineffective for cooling the hollow body considered; finally, the creep would still have the consequence of making demolding delicate, even impossible.

 It is therefore important that the means 19 are adapted and arranged to take into account the nature of the material used for producing the hollow body and its state of fluidity at the time of molding.

 Thus, in the illustrated embodiment, intended, it will be recalled, for cooling the bottom of a container, the means 19 are constituted by a liquid spray nozzle, known per se, comprising at least one inlet conduit 20 for pressurized liquid, as well as at least one gas inlet conduit 21, typically air, also under pressure, to cause spraying. The arrangement of the gas and liquid inlet conduits is such that it allows spraying towards the zone to be cooled in a privileged manner, here the bottom, but prevents any creep of the material constituting this zone inside the outlet of these conduits near said area.

 In addition, in certain cases, in order to optimize the cooling, it is preferable that the means 19 are adapted and arranged to deliver a jet whose parameters take account of the characteristics of the area. In particular, it may be desirable to take into account, in particular but not exclusively, the shape of the zone and / or its dimensions. In fact, for certain types of hollow body, it will be important to prevent the jet of cooling fluid from impacting the neighboring, less thick zones, which would have the consequence of not only accelerating the cooling of the zone to be cooled so privileged, but still that of neighboring areas, which could lead to

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 the appearance of temperature gradients and undesirable stresses detrimental to the good behavior of the hollow body. It may therefore prove important, for certain applications, that the shape and the section of the jet at its impact surface on the area to be cooled in a privileged manner are determined as a function of the shape and the section of said area.

 Thus, using the example of implementation illustrated by the figures, when the area to be privilegedly cooled is in the form of a circular patch centered on the bottom 18 of a container 5, the aforementioned spray nozzle constituting the means 19 for cooling said zone, would in this case preferably be arranged to deliver a jet having a circular section, that is to say a section corresponding to that of the zone to be cooled in a preferred manner.

 The operation of the device according to the invention is as follows: in known manner, during blow molding, in the case of a container, cooling fluid circulates continuously in the conduits 14, 15, 16 formed in the elements 1,2, 3 constituting the mold, so as to allow the material constituting these elements to be kept at an appropriate temperature, sufficiently low, so that, when the material constituting the hollow body comes into contact with the walls of the mold cavity, its cooling begins without delay.

 As regards the zone to be cooled in a privileged manner, the cooling fluid is injected into the means 19 after the molding is completed: it is indeed necessary to prevent the injection of the fluid from creating an obstacle to the molding, and therefore wait the end of the molding to start this injection.

 In a first implementation variant, the fluid is injected while the elements are in the molding position, that is to say in the position illustrated in FIG. 1. However, this solution is not fully satisfactory, since the surface material of the zone to be privilegedly cooled is then in contact with the outlet of the injection conduits and therefore prevents good diffusion of the cooling fluid over the zone. This solution can therefore be envisaged, especially when the surface of the zone is very small and / or when the injected fluid has a very high cooling capacity.

 This is why the variant of FIG. 2 is preferred: it consists in starting to inject the cooling fluid, using the means 19,

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 during the mold opening phase, after molding and after the mold element, here element 3, on which said means 19 are arranged, has started to be moved apart relative to the part of the hollow body which it was used to mold. Thus, the fluid is injected into the gap 22 which is created between the said mold element and the considered part of the hollow body containing the area to be cooled in a preferred manner. In this case, the area to be privilegedly cooled is no longer maintained by the element in question of the mold. However, it does not have time to deform since the injection of fluid begins quickly after the end of the molding, so that the material of the zone to be privilegedly cooled begins to freeze immediately.

 In a preferred implementation, the injection of cooling fluid begins in synchronism with the moment when the element of the mold, here element 3, on which said means 19 are arranged, begins to be moved apart relative to the part of the hollow body which it served to mold and which contains the zone to be cooled in a privileged way. More precisely, when, as illustrated in FIG. 2, the zone to be privilegedly cooled is in the form of a circular patch centered on the bottom 18 of the container, the fluid is injected in synchronism with the beginning of the longitudinal movement of the element 3, that is to say immediately after the elements 1, 2 have been sufficiently spaced from one another allowing the locking means 11, 12, 13 of the element 3 relative to the elements 1, 2 of to liberate oneself.

 It emerges from the above that, if one or more zones to be privilegedly cooled also existed on the body of the container 5, that is to say in its part determined by the elements 1, 2, then one and / or the other of these elements would be provided with means allowing a direct injection of cooling fluid directly in contact with each of said areas of the body to be privileged to be cooled. In this case, again, the cooling of each of these zones would be carried out either when the mold is in the closed position (position illustrated in FIG. 1), or, preferably, in synchronism with the start of the spacing phase. elements 1 and 2 relative to each other, that is to say, in this case, even before the longitudinal disengagement movement of element 3 relative to the bottom of the container has been

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 initiated, therefore in an intermediate phase between those illustrated in the figures.

 Of course, the invention is not limited to the means described in the present description, but embraces all the variants or equivalents thereof within the reach of the skilled person.

 In particular, a person skilled in the art will have no particular difficulty in adapting the teaching of the present description for the manufacture of other types of hollow body, using other types of molds, the essential being to have, at the appropriate locations of the molds, means allowing direct injection of cooling fluid directly in contact with each of said zones to be privileged to be cooled.

 In addition, instead of using means into which a sprayed liquid is injected, it is conceivable to use means making it possible to inject a gas having a high refrigerating capacity, or means allowing gas expansion, such as injectors calibrated or porous injectors, taking care, of course in all cases, that the means used do not allow the material of the hollow body to flow through.

 Furthermore, whatever the variant envisaged, the flow rate of cooling fluid can be variable, in order to compensate for the initial temperature gradients at the end of the molding.

Claims (19)

claims 1. Method for cooling a hollow body, after its manufacture by hot molding in a molding cavity (1,2, 3), while said hollow body is still in said cavity, of the type consisting to force cooling with the aid of a cooling fluid circulating in circuits arranged in the walls of the cavity, characterized in that, after molding, in order to favor the cooling of at least one zone ( 17) of the hollow body, the cooling fluid is also injected inside the molding cavity, directly in contact with said area (17) to be privileged to cool.  2. A cooling method according to claim 1, characterized in that the cooling fluid is selectively injected into the area to be cooled in a preferred manner 3. A cooling method according to one of claims 1 or 2, characterized in that the cooling fluid is a liquid.  4. A cooling method according to claim 3, characterized in that the liquid is sprayed (20,21).  5. A cooling method according to claim 1, characterized in that the cooling fluid is a gas.  6. A cooling method according to claim 5, characterized in that the cooling is obtained by expansion of the gas through means (19) of injection, at the location of the zone to be cooled in a preferred manner.  7. Method according to one of claims 1 to 6, characterized in that the fluid flow is variable.  8. Method according to one of claims 1 to 7, characterized in that it consists in injecting the fluid while the elements (1,2, 3) constituting the molding cavity are in the molding position of the hollow body ( figure 1).  9. Method according to one of claims 1 to 7, characterized in that it consists in injecting the fluid during the opening phase of the molding cavity, with a view to the extraction of the hollow body. <Desc / Clms Page number 12>  10. Method according to claim 9, characterized in that it consists in starting to inject the fluid into a gap (22) which appears between a mold element (3) and a part (18) of the hollow body containing an area ( 17) to cool in a privileged manner that said element has been used to mold, after this element, with which are associated means (19) of privileged cooling of said zone, has started to be moved away from the part of the hollow body comprising said zone to cool in a privileged way (figure 2).  11. Method according to claim 10, characterized in that it consists in starting to inject the fluid in synchronism with the moment when the element (3) of the mold, with which the cooling means (19) are associated, begins to be separated relative to the part (18) of the hollow body which it was used to mold and which contains the zone (17) to be privileged to cool 12. Manufacturing device, by hot molding of hollow bodies, comprising at least two elements (1,2, 3) movable with respect to each other to determine, when they are in a first so-called closed position , a hollow body molding cavity (5), and to allow, when in a second so-called open position, the withdrawal of the hollow body, each element determining the external shape of a respective part of the hollow body, characterized in that the hollow body having at least one zone (17) to be privileged to cool, the respective element (3) serving for molding the part of the hollow body in which said zone is located is provided with means (19) injection of a cooling fluid inside the molding cavity, directly in contact with said zone.  13. Device according to claim 12, characterized in that the injection means (19) consist of at least one liquid spray nozzle.  14. Device according to claim 13, characterized in that the nozzle comprises a pipe (20) for supplying pressurized liquid and a pipe (21) for supplying pressurized gas to cause the spraying of the liquid.  15. Device according to claim 12, characterized in that the injection means (19) consist of at least one cooling gas injector. <Desc / Clms Page number 13>  16. Device according to one of claims 12 to 15, characterized in that the means (19) for injecting cooling fluid into an area are arranged to deliver a selective jet of fluid over this area.  17. Device according to claim 16, characterized in that the means (19) for injecting fluid into a zone are arranged to deliver a jet having a section corresponding to that of said zone.  18. Device according to one of claims 12 to 17, for the manufacture of containers by blowing preforms (6) previously brought to a softening temperature of their constituent material, characterized in that the molding cavity comprises at least one element (3) determining the external shape of the bottom (18) of the containers, and in that the said element is provided with means (19) for injecting a cooling fluid, directly in contact with the bottom (18) of the container.  19. Device according to claim 18, characterized in that the means (19) are arranged to direct the cooling fluid towards the central zone (17), slightly drawn from the bottom (18) of the container.