Stretching and cooling rod for forming containers

Provided is a stretching rod for a molding unit for manufacturing a container from a preform and a method for manufacturing a container by stretch blow-molding. The stretching rod extends longitudinally, parallel to a main axis Y, and comprises a body of cylindrical or tubular form, a distal end in the extension of said body, at least one internal channel to allow the circulation of a cooling gas to said distal end, a flat situated at the distal end of the stretching rod, an end-fitting protruding from said flat and a plurality of orifices, said orifices being fluidically connected with said internal channel and being distributed around said end-fitting on said flat. The rod can include an annular skirt in the extension of said body, at said distal end, said skirt having a height less than the height of said end-fitting.

Technical field: The present invention relates to the field of the manufacturing of containers by blowing or stretch blow-molding from preforms made of thermoplastic material, such as, for example, polyethylene terephthalate, hereinafter “PET”. Its subject is more particularly a stretching and cooling rod intended to be implemented in a stretch-blow molding technique for forming containers. Another object is a method for manufacturing containers implementing the stretching and cooling rod according to the invention.

State of the art: It is known practice to form containers made of thermoplastic material by stretch blow-molding of preforms previously heated to a temperature that is sufficient to soften the walls thereof. To this end, a forming device is used which comprises a mold having a cavity shaped to the die of the container to be obtained. The previously heated preform is received in the cavity. Then, its walls are subjected to a so-called “biaxial” stretching so as to hug the die of the mold. For this, the preform is stretched axially by means of a stretching rod to provoke the axial expansion of the preform. Simultaneously with this stretching operation, a pressurized fluid is injected into the preform so as to provoke the radial expansion of the wall.

Such a forming method is well known. For the final container to have a bottom that is perfectly molded, it is preferable for the stretching rod to be adapted to guarantee a satisfactory thickness of the wall of the container. A bad distribution of the material is a recurrent defect found on the containers produced by a molding and stretch blow-molding method. What is required is not necessarily to be careful to ensure that the thickness of the wall of the container is constant, because in certain cases it may be desirable to thicken certain zones, in particular those intended to undergo significant strains (notably in proximity to the bottom). It is rather to ensure that the thickness of material corresponds to the specifications of the container, as defined according to its form and its use.

A material defect located at the center can, furthermore, generate zones that are hotter and sensitive to collapse. In order therefore to perfect the structure of the blown bottom, and to fix the material with respect to the die of the mold, an additional step of internal cooling can prove very useful. This step consists in generating a cooling of the bottom by the stretching rod, at the end of the blowing phase, over a very short time, at very localized points of the bottom.

Methods have thus been developed to promote a distribution of the material matched to demanding specifications.

Furthermore, in the field of the manufacturing of containers by molding and stretch blow-molding, use is increasingly being made of recycled PET, for environmental reasons. This material further increases the problem of distribution of the material because it exhibits different heat absorption properties: the control of the cooling of the container thus formed is therefore even more critical.

Moreover, despite the details provided for the stretch blow-molding methods, there are therefore still problems of deformation of the bottom after removal of the bottle from the mold, notably because of a lack of control of the cooling phase.

Technical background: The document JP2001088202 proposes a stretching and cooling rod, having orifices specifically provided for cooling the bottom of a preform.

These orifices are situated on the body of the rod, above the end-fitting formed at the end of said rod. The end-fitting is provided to be placed in contact with the bottom of the preform during the stretching, but slightly set back during the cooling phase, to allow the gas to escape from the orifices and, thereby, cool the bottom, at the end of the blowing phase. Nevertheless, in this configuration, the cooling gas escapes in an uncontrolled manner, and is not directed precisely, in a way localized toward the bottom of the container that is obtained.

Summary of the invention: The current solutions are not satisfactory and there is a need to further improve the cooling step in order to obtain containers of better quality.

The invention aims to resolve this problem and, to this end, proposes a stretching rod which ensures a stretching of the preform along its axis, by avoiding the undesirable contacts between the outside of the rod and the inside of the body of the preform, while improving the distribution of the cooling gas, notably on the bottom of the container that is obtained. The trajectory of the cooling gas is controlled and mastered through the use of a stretching rod in accordance with the invention.

To this end, the invention relates to a stretching rod for a molding unit for manufacturing a container from a preform, said stretching rod extending longitudinally, parallel to a main axis Y, comprisinga body of cylindrical or tubular form;a distal end in the extension of said body;at least one internal channel to allow the circulation of a cooling gas to said distal end;a flat situated at the distal end of the stretching rod;an end-fitting protruding from said flat, anda plurality of orifices, said orifices being fluidically connected with said internal channel and being distributed around said end-fitting on said flat.

Said stretching rod is characterized in that it comprises an annular skirt in the extension of said body, at said distal end, said skirt having a height less than the height of said end-fitting.

Advantageously, the edges of the skirt and/or the end of the end-fitting protruding from the stretching rod are rounded.

According to embodiments, the outer body and the skirt comprise a single piece.

Advantageously, the end-fitting of the stretching rod is of conical form.

In embodiments, the flat extends orthogonally to the main axis Y.

In embodiments, the orifices are oriented outward in the direction of the main axis Y, and by an angle of between 1 and 50 degrees, preferentially by an angle of 30 degrees.

Advantageously, the annular skirt of the stretching rod has a crenelated form.

In embodiments, the annular skirt of the stretching rod has a crenelated form with rounded and convex peak edges and concave trough edges.

Advantageously, the flat of the stretching rod has a recess in the form of an internal rosette.

The invention relates also to a method for manufacturing a container by stretch blow-molding implementing the stretching rod according to the invention, comprising at least the following steps ofplacing a previously heated preform in a blowing mold having, in closure position, a molding cavity forming the die of the container to be blown;closing said blowing mold;blowing said preform in the blowing mold via a blowing nozzle and, substantially simultaneously, a step of stretching said preform by inserting the stretching rod inside said preform by bearing against the bottom of said preform so as to facilitate the axial elongation of said preform;cooling the inside of said container that is thus formed by injection of air via said stretching rod, provided with said plurality of orifices provided for this purpose,retracting said stretching rod;extracting said blown container by opening said blowing mold.

Detailed description of the invention: Hereinafter in the description, elements that have an identical structure or similar functions will be designated by a same reference.

The invention is designed to be implemented in an installation for manufacturing containers2. Such an installation comprises, normally, a molding machine as represented inFIG.1, comprising at least molding units18, each molding unit18comprising at least blowing means incorporating a stretching rod1, said mold14comprising at least two half-molds140which each have an inner molding face and which are respectively mounted on supports142that are movable about an axis Y, between at least one open position and one closed position of the molding unit18, in which said inner faces of said at least two joined half-molds140together delimit a molding cavity15for the container2.

In practice, the blowing molds14are distributed circularly, in the form of a carousel170, as can be seen inFIG.1, and topped by respective blowing installations. In practice, always, and as can be seen inFIG.2, the body of the blowing installation extends substantially vertically above the mold and substantially coaxially to the molding cavity15of the blowing mold14.

FIG.2schematically represents a perspective view of one of the molding units18of the machine according to the exemplary embodiment ofFIG.1, illustrating in particular, outside of the unit in open position, an exploded view of a mold14produced in three parts, namely two half-molds140and a mold bottom141.

All these elements are well known to the person skilled in the art and are not described in detail for a better understanding of the invention.

Reference is made toFIG.3, showing a first embodiment of a rod1according to the invention, in a partial longitudinal cross-sectional view, which is implemented with a preform3made of PET or of recycled PET, intended to be stretched and blown in one of the blowing molds14of an installation described briefly above, so as to form a container2, such as a bottle.

InFIG.3, the stretching rod1is in high position and being inserted into the preform3. The rod1is designed to be mounted in the body of the blowing installation described also above. Said stretching rod1extends longitudinally, parallel to the main axis Y. The stretching rod1according to the invention is a hollow stretching rod, which then has a dual function, a stretching function on the one hand and another function of cooling of the container on the other hand. For this, it has a first, so-called proximal end (not represented), that can be secured to a displacement device internal to the manufacturing installation.

As can be seen inFIG.6, the preform3comprises, in a classic manner, a body of elongate and tubular form, of axis Y, limited by a wall31integral in the upper part with a threaded neck32and in the lower part with a substantially hemispherical bottom30. Between the neck32and the body of the preform, a radial collar33protrudes outward from the preform3.

Generally, the preform3illustrated inFIG.6has a symmetry of revolution about its axis Y.

When the preform is placed in the blowing installation, the axis Y of the rod1substantially coincides with the axis of revolution of the preform3. Hereinbelow, Y will be used without distinction to designate the axis of the rod1or that of the preform3.

Hereinbelow, “vertical” will be used to qualify any direction parallel to the axis of revolution of the rod and “transverse” will be used to qualify any direction at right angles to the axis of revolution of the rod.

As represented inFIG.3, or also inFIG.4, the stretching rod1comprises a cylindrical or tubular body4. In embodiments, the body4of the stretching rod1can have a shoulder, that is to say have two longitudinal sections with two different diameters. That is particularly advantageous for the blowing of preforms of small diameter.

The body4also comprises a central internal channel6extending axially and connecting with a plurality of orifices9through which a cooling gas10, in particular air, is injected into the manufactured container2in order to cool it. The orifices9are therefore fluidically connected with the internal channel6. In the extension of the body4, at the distal end5, the stretching rod1comprises a flat7. An end-fitting8protrudes from this flat7.

As represented inFIG.7, the stretching rod1further comprises an annular skirt11in the extension of its body4.

FIG.4schematically represents another step of a blowing cycle, in which the stretching rod1is in low position and therefore placed at the bottom of the preform3during the blowing step. During this step, the preform3becomes a container2.

FIG.5schematically represents an embodiment of another step of a blowing cycle, in which the stretching rod1, still in low position, performs the cooling step, called sweep phase, of the container2thus formed by injection of the cooling gas10. The cooling gas10then passes through the internal channel6of the stretching rod1to be diffused locally and precisely on the bottom of the container2. The injection of the cooling gas is represented in the form of arrows inFIG.5.

In embodiments, and as represented inFIG.7, the diameter of the annular skirt11is equal to the diameter of the body4of the stretching rod1. In this advantageous configuration, the cooling gas10is directed in a very localized manner.

In embodiments, the outer body4and the annular skirt11are obtained in a single piece. In other words, they form one and the same piece.

According to other embodiments, the outer body4and the annular skirt11are two separate pieces.

The structural modifications of the stretching rod1offer the advantage of directing the cooling gas10toward the bottom of the container2, over all of its bottom surface, and thus improving the cooling step.

An embodiment can be seen inFIG.7in which the orifices9, connected with the internal channel6, are arranged and distributed on the flat7, around said end-fitting8. The orifices9allow the cooling gas10to be injected onto the bottom of the blown container. The orifices9are disposed on the flat7, and over all of its circumference, therefore allowing the injection of the cooling gas10from the internal channel6to the interior of the blown container2.

The orifices9are for example of cylindrical form and preferably have a diameter of between 0.3 and 3 millimeters (mm). They can also be of another form, for example of oblong form.

According to a preferred embodiment, the injection surface is between 3 and 6 millimeters square (mm2) and does not exceed 20 millimeters square (mm2). The injection surface corresponds to the sum of the diameters of the orifices9. It represents the quantity of cooling gas10that can be injected by virtue of the configuration of the rod1, comprising orifices9serving as restriction orifices. Thus, by virtue of the invention, it is possible to obtain an internal cooling of the formed container1while minimizing the consumption of cooling gas10. The stretching rod1in fact has a very small dead volume and a design optimized for the internal cooling of a blown container2.

The stretching rod1therefore has a plurality of orifices9disposed on the flat7. The protruding end-fitting8can be of any form. In particular, said end-fitting8can be of conical form, of rounded conical form, of ovoid form, of hemispherical form, etc.

According to a preferred embodiment, as represented inFIG.7, the flat7is at right angles to the body4of the stretching rod1. That allows a better distribution and a better control of the cooling gas10which then escapes from the orifices9uniformly.FIG.8schematically represents a longitudinal median cross-sectional view of an exemplary embodiment of the distal end of the stretching rod1, showing in particular an annular skirt11having rounded edges and an end-fitting8of cylindrical form. In this embodiment, the edges12of the annular skirt11are rounded. This is particularly advantageous because it makes it possible to avoid any risk of tearing if said edges12were to touch the wall of the preform3, for example during the stretching phase. This variant of rounded edges12of the skirt11can also be applied to other embodiments of the invention.

In this exemplary embodiment, the annular skirt11has the same diameter as the diameter of the body4of the stretching rod1. On the flat7, five orifices9are disposed around the protruding end-fitting8.

Furthermore, as can be seen inFIG.8, the annular skirt11has a height110less than the height80of the end-fitting8such that said end-fitting8protrudes from the annular skirt11. In other words, the distal end of the stretching rod1is formed by the end-fitting8and the annular skirt11is an extension of the outer body4with respect to the flat7. That makes it possible to direct the cooling gas10in a controlled manner when it leaves the internal channel6through the orifices9.

In a preferred embodiment, the height110of the annular skirt11is less than the height80of the end-fitting8by a value of between 0.5 and 4 millimeters (mm), even more preferentially by a value of 1 mm.

In embodiments, the height110of the annular skirt11varies over all of its circumference. For example, the annular skirt11can have toothed or embellished edges, and therefore have peaks and troughs, as can be seen inFIG.13. Nevertheless, in this case, the height110remains less than the height80of the end-fitting8.

FIG.8schematically represents a longitudinal median cross-sectional view of the first embodiment ofFIG.7. The internal channel6is divided into different sections to emerge on the orifices9.

The cooling step is an additional step in a method for manufacturing containers made of PET or of recycled PET (“rPET”). The flow of the cooling gas10is represented schematically inFIG.5by arrows. This cooling step notably makes it possible to reduce the internal temperature of the container that is obtained, and its aim is to limit the transfer of heat from the inside to the outside after the container2that is obtained has been taken from the mold. That also makes it possible to limit the collapsing at the bottom, this collapsing generally having a negative stress impact, which increases the risk of rejects. Indeed, a bottom that has too high a temperature will tend to sag in the step of extraction from the mold.

The container2that is obtained can then potentially have leaks or other defects. The presence of the annular skirt11according to the invention has the advantage of considerably improving the cooling step by amplifying the action of the injected cooling gas10, the gas being directed in a localized manner at the point where its presence is necessary. That then makes it possible to considerably improve the step of cooling of the container2that is obtained, and therefore achieve an optimal cooling, even when, for production rate reasons, the duration of the cooling step has to be very short.

In embodiments, as represented inFIG.9, the orifices9are oriented slantwise, outward in the direction of the main axis Y, toward the bottom of the blank over a deviation of 1 to 50 degrees.

In a preferred embodiment, the orifices9are oriented outward in the direction of the main axis Y, by a deviation of 30 degrees.

The orientation of the orifices allows the cooling gas10to be distributed uniformly toward the bottom of the preform3and therefore toward the bottom of the container2that is thus formed, that is to say over all of its surface. Furthermore, that makes it possible to further improve the cooling of the bottom, at the point where the latter has the highest temperatures, and therefore at the point where stress zones, promoted by its sagging, can develop.

In a preferred embodiment, the skirt11has rounded edges and the orifices9of the rod are oriented slantwise.

In embodiments, the annular skirt11of the stretching rod1have straight and beveled edges. This embodiment is illustrated inFIG.9.

In an embodiment illustrated inFIG.10, the annular skirt11has a crenelated form with rounded and convex peak edges and concave trough edges.

In embodiments in which the annular skirt11has peaks and troughs, the orifices9can be aligned with a trough or with a peak. According to a preferred embodiment, the orifices9are aligned with a peak, in order to concentrate the cooling gas on the bottom of the container2.

In another variant, as illustrated inFIG.11, the annular skirt11has a diameter that converges from the body4of the rod1toward the protruding end-fitting8. In other words, its diameter decreases toward the free end portion and the annular skirt11therefore has a narrowed form. The annular skirt11has a section which decreases from the flat7, to its distal free end.

According to another variant, not represented, the diameter of the annular skirt11is greater than the diameter of the body4of the stretching rod1. The annular skirt11then has a flared form. The expression “flared form” will be understood to mean a form whose section increases. Thus, a free end portion of annular skirt11of flared form means that the end portion of said skirt has a section which enlarges from the flat7to its free end.

FIG.12shows another view of the rod1according to the invention, with a skirt11having an annular edge inscribed in a same plane, as well as the end-fitting8and the flat7in dotted lines.

FIGS.13to15show variant embodiments of the annular skirt11, having troughs and peaks.

FIG.13shows a skirt11with straight crenelated edges, with peaks and troughs, with a skirt height110still less than the height of the end-fitting8.

FIG.14shows an exemplary embodiment in which the skirt11has rounded crenelated edges.

FIG.15shows an embodiment in which the skirt11has edges that are smooth and of constant height, but in which the flat7has a recess in the form of an inner rosette. The inner rosette is centered in the recess of the flat7with respect to the end-fitting8and extends over the recess of said flat7to the edges of the skirt11.

Advantageously, it can be hollowed out in the flat7. According to other embodiments, the inner rosette has edges. In this way, the skirt11and the edges of the inner rosette form a double wall.

According to embodiments, the edges of the inner rosette have a height less than or equal to the height110of the skirt11. According to a variant, the edges of the inner rosette have a height less than the height80of the end-fitting8. This embodiment advantageously makes it possible to channel the cooling gas10and further improve its direction toward the bottom of the container2.

Advantageously, each orifice9is situated at a vertex of a branch of the inner rosette.

The invention relates also to a method for manufacturing a container2by stretch blow-molding implementing the stretching rod1previously described.

The manufacturing method according to the invention comprises at least the following steps of:placing a previously heated preform3in a blowing mold14having, in closure position, a molding cavity15forming the die of the container2to be blown;closing said blowing mold14;blowing said preform3in the blowing mold14via a blowing nozzle16and, substantially simultaneously, a step of stretching said preform3by inserting the stretching rod1into said preform3to bear against the bottom30of said preform3so as to facilitate the axial elongation of said preform3;cooling the inside of said container2that is thus formed by the injection of a cooling gas10, usually air, via said stretching rod1, provided with a plurality of orifices9provided for that purpose;retracting said stretching rod1;gripping the blown container3by external handling means;opening said blowing mold14.

FIG.1represents a top view which schematically represents an exemplary embodiment of a molding machine of rotary type and which illustrates the molding units18(without the blowing and stretching means) distributed circumferentially over the carousel170and which, depending on their relative position with respect to the input or the output of the machine, are in open position or in closed position. The manufacturing of a container2is performed by blowing a hot preform3in a mold14of a molding unit18of the installation by means of at least one pressurized fluid, generally air.

In the exemplary embodiment, the manufacturing of the containers2is performed by stretch blow-molding. The blowing means advantageously incorporate at least one stretching rod1.

The stretching rod1is driven axially, along the axis Y, in displacement by associated driving means (not represented).

The stretching rod1is therefore mounted to slide axially so as to be introduced into the preform3through the opening delimited radially by its neck32, an annular space being left free between the neck32and the rod1to allow passage of the blowing fluid. The stretching rod1is mounted to be axially movable between at least one first, high position and one second, low position.

In the first position, the rod1extends out of the mold14and, in the second position, called low position, the rod1is displaced downward to axially stretch the preform3inside the mold14, during the blowing.

FIGS.3to5illustrate some of the steps in manufacturing a container2and the different positions of the stretching rod1during these steps.

A first step, as can be seen inFIG.3, therefore relates to the introduction of a preform3into a blowing mold14. The preform3has been previously heated to a temperature greater than the glass transition temperature of the material (which is approximately 80° C. in the case of PET).

Once the preform3is in position and the mold14is closed, as can be seen inFIG.4, the stretching rod1is inserted into the preform3, to come into the low position, that is to say that it is positioned on the bottom of the preform3.

In a preferred embodiment, the low position of the stretching rod1corresponds to a position in which the end-fitting8touches the bottom of the preform3.

In other embodiments, the low position of the stretching rod1corresponds to a position in which the end-fitting8is slightly set back from the bottom of the preform3. Substantially simultaneously with the insertion of the stretching rod1into the preform3, the blowing step, or the stretch blow-molding step, takes place during which a fluid (for example air) is injected into the preform3, first at a median, so-called pre-blowing pressure of between 5 bar and 15 bar, while displacing the stretching rod1from its high position to its deployed low position.

The blowing step ends with a momentary increase in pressure to a high pressure, greater than the pre-blowing pressure, to make sure that the material is well pressed against the cavity15of the blowing mold14and thus impart on it the die of the container2, as represented inFIG.4. The blowing pressure is greater than or equal to bar, and for example approximately 35 to 40 bar.

The stretching rod is maintained in the deployed position to avoid any unwanted slippage of material on the bottom of the mold as long as the pressure in the container has not reached the blowing pressure.

There follows a cooling step performed by the injection of a cooling gas10toward the bottom of the container2that is thus formed. The stretching rod1is then in low position, as can be seen inFIG.5.

According to embodiments, the cooling step, also called sweeping step, consists in accelerating the cooling of the container2from the inside. In an embodiment illustrated inFIG.5, the stretching rod1, in low position, performs the cooling step. The output of the gas10is represented by arrows.

In embodiments, the stretching rod1is displaced axially inside the molding cavity15during said cooling step to axially perform a sweep of the molding cavity15, for example from the top to the bottom and vice versa, along a determined travel. In variants, the stretching rod1is driven selectively in rotation to perform a circular sweep of each molding cavity15of the molds14cooled by means of said at least one cooling gas10.

The stretching rod1is for example driven continually on itself to perform a sweep over 360 degrees or, in a variant, sequentially.

The driving of the stretching rod1in rotation is performed advantageously in combination with the axial displacement of said rod, the assembly being controlled by selectively controlling the driving means.

Finally, at the end of the cooling step, the mold14is opened and the formed container2is discharged from it, which loops the cycle. A new cycle can then begin with the introduction of a new preform3.

The implementation of a stretching rod1according to the invention allows a better control of the cooling step. Through this improved control, it is possible to increase the blowing rates, while limiting the diffusion of heat from the inside to the outside. Moreover, an improved cooling of the bottom of the container2makes it possible to limit the risks of sagging.

Furthermore, the use of such a stretching rod1offers greater flexibility in the use of a preform, notably those whose form would not be perfectly suited to a bottle. It has finally been found that the use of the stretching rod1according to the invention makes it possible to accelerate the cooling of the bottom30of the preform3, while reducing the number of containers2of unsatisfactory quality. This is directly linked to the design of the stretching rod1, which now comprises an annular skirt11, making it possible to direct the cooling gas10in a precise and controlled manner toward the bottom of the container2that is thus formed.