Abstract:
A method of producing containers, including a forming step in which thermoplastic performs are used to form containers including a body and a base; and, subsequently, a cooling step in which the formed containers are cooled by projecting a jet onto the containers in a localized manner on a target area including the base thereof, the jet consisting of a mixture of a gas and an atomized liquid which are both at a relative pressure of less than approximately 1 bar. The invention also relates to an installation for the production of containers, which is adapted for the aforementioned method.

Description:
FIELD OF THE INVENTION  
       [0001]     The invention is concerned with the production of containers.  
         [0002]     It relates more particularly to a method, and also to an installation, for the production of containers—particularly bottles—from thermoplastic preforms.  
       BACKGROUND OF THE INVENTION  
       [0003]     Such a method generally comprises a first step during which the preforms are heated as they file through a tunnel oven, followed by a second step, for the actual forming operation, during which the hot preforms are introduced into a blow molding or stretch blow molding device so as to be shaped into containers. The step of heating the preforms consists in bringing the thermo-plastic which constitutes them, or at the very least the temperature of the thermoplastic of their areas which are to be modified to obtain the containers, to a temperature exceeding the glass transition temperature, that is to say the softening temperature of said material. Thus, by way of example, when the containers to be produced are made of PET, in which case the transition temperature is around 80° C., the temperature to which the material is brought is around 120° C.-140° C.  
         [0004]     On leaving the forming unit (that is to say, in practice, on leaving the blow molding or stretch blow molding device), the containers thus formed will be directed either toward a storage unit to await subsequent filling or directly toward a filling unit.  
         [0005]     Whatever the case, when leaving the forming unit the containers may, at least locally in certain areas, remain at a temperature at which the thermoplastic has not recovered sufficient rigidity to allow the container to retain in the area in question the shape which it was given during the forming operation.  
         [0006]     This situation particularly affects the base of the containers, which is generally thicker than their body and, therefore, tends to cool more slowly than the body and to remain momentarily soft on leaving the forming unit.  
         [0007]     It consequently appears necessary, immediately after they have been formed, to cool the containers so as to fix the shape which they have been given. By way of example, PET containers, initially shaped at a temperature of greater than 80° C., must be returned to a temperature of less than 70° C. (preferably of around 60° C.).  
         [0008]     It is known from French patent application FR-2 732 002, or from its American equivalent U.S. Pat. No. 5,996,322, to cool the containers by blowing fresh air (that is to say at a temperature equal to or less than the ambient temperature).  
         [0009]     While this method is satisfactory for containers of simple shape, offering few obstacles to the flow of air or gas, its effectiveness nevertheless proves insufficient for containers having complex shapes, such as bottles with a petaloid base. In this instance, the heat transfer is not quick enough to prevent even minimal deformation of the base. This slow cooling progress negatively impacts the production rates.  
         [0010]     It has also been proposed to cool the containers by means of a nebulizer which sprays the containers with a mist composed of air loaded with water droplets.  
         [0011]     While such a solution does in fact make it possible to obtain quicker heat transfer than the simple air cooling described above, and therefore to carry out more effective cooling of the containers, it nevertheless has certain disadvantages.  
         [0012]     Firstly, the mist proves difficult to direct, which means that the whole of the containers, and not just the unstable areas, are sprayed. This results in an insufficient efficiency of the cooling unit, which is particularly manifested by excess water consumption.  
         [0013]     Secondly, the water which has not been vaporized on contact with the hot areas of the container tends to be deposited and to accumulate in areas from which it has to be drained.  
       SUMMARY OF THE INVENTION  
       [0014]     The invention is aimed particularly at overcoming the aforementioned disadvantages by providing a method and an installation for the production of containers whereby the containers can be cooled effectively in a simple and economic manner and whereby in fine the production rates can be increased.  
         [0015]     To this end, the invention provides, according to a first aspect, a method for the production of containers, which comprises: 
        a forming step, starting from thermoplastic preforms, to form containers comprising a body and a base, followed by     a cooling step to cool the formed containers, in which method, in the cooling step, the formed containers are sprayed in a localized manner over a target area comprising the base of the containers with a jet composed of a mixture of a gas and of an atomized liquid, both at a relative pressure of less than approximately 1 bar.        
 
         [0018]     According to another feature, the spraying is carried out over a target area of the containers.  
         [0019]     The inventors have observed a high degree of cooling efficiency, particularly on account of the fineness of the particles which, on contact with the containers, tend to evaporate completely, this change of phase being accompanied by considerable heat transfer.  
         [0020]     According to a second aspect, the invention provides an installation for the production of containers, which comprises: 
        a forming unit for shaping the containers by forming from thermoplastic preforms, and     a cooling unit for cooling the formed containers, which comprises: 
            a pressurized-gas supply circuit,     a pressurized-liquid supply circuit, and     an atomizing nozzle to which said circuits are connected, this nozzle being designed to spray the formed containers with a jet composed of a mixture of gas and of atomized liquid.   
               
 
     
    
     BRIEF DESCRIPTIONS OF THE DRAWINGS  
       [0026]     Other objects and advantages of the invention will become apparent in the light of the description given below with reference to the appended drawings, in which:  
         [0027]      FIG. 1  is a schematic top plan view showing an installation according to the invention;  
         [0028]      FIG. 2  is a top plan view illustrating a detail of the installation of  FIG. 1 , corresponding to the inset II;  
         [0029]      FIG. 3  is an elevation view in partial section, illustrating the cooling unit of the installation of  FIG. 1 ;  
         [0030]      FIG. 4  is a side elevation view in partial section illustrating the cooling unit of  FIG. 3 , as seen from a perpendicular angle of view;  
         [0031]      FIG. 5  is a top plan view illustrating a mask of a cooling unit as represented in  FIGS. 3 and 4 ;  
         [0032]      FIG. 6  is a schematic diagram of the cooling unit of  FIG. 3 . 
     
    
     DETAILED DESCRIPTION OF THE INVENTION  
       [0033]      FIG. 1  shows an installation  1  for the production of containers  2  such as bottles, starting from thermoplastic preforms.  
         [0034]     The installation  1  comprises a forming unit  3  to form the containers  2 , a filling unit  4  to fill the containers  2 , a conveyor  5  for conveying the formed containers  2  from the outlet  6  of the forming unit  3  toward the filling unit  4 , and a cooling unit  7  placed at the outlet  6  of the forming unit  3  along the path of the containers  2  formed by the conveyor  5 .  
         [0035]     The containers  2  are made for example of polyethylene terephthalate (PET), polyethylene naphthalate (PEN), or any other suitable thermoplastic. Once formed, each container  2  has a body  8  (which may be cylindrical), a neck  9  and, at the opposite end to the neck  9 , a base  10 .  
         [0036]     The installation  1  additionally comprises a supply unit  11  which delivers the preforms to the forming unit  3 . The supply unit  11  comprises, for example, a hopper  12  in which the preforms, prefabricated by injection molding, are loosely piled, this hopper  12  being connected to the inlet  13  of the forming unit  3  via a sorter  14  which isolates and positions the preforms (which are cold, that is to say at ambient temperature) on a slide  15 .  
         [0037]     The preforms are subsequently mounted on a transfer chain  16  and then heated as they file through a tunnel oven  17  before being introduced hot into a blow molding or stretch blow molding device of the carousel type  18  having multiple molds (not shown).  
         [0038]     The containers  2  are then transferred, by means of a transfer wheel  19  provided with indentations  20  (visible in  FIG. 2 ), from the molds of the blow molding device toward the conveyor  5  at the outlet  6  of the forming unit  3 , where the containers  2  are cooled prior to being conveyed toward the filling unit  4 .  
         [0039]     The transfer wheel  19  is rotated by means of a transmission belt  21  connected to the carousel  18  in such a way as to synchronize the rotational speed of the wheel  19  with the tangential speed of the carousel  18 .  
         [0040]     In the filling unit  4 , the containers  2  are arranged on a filling device  22  of the rotary drum type, from which, once filled, they are withdrawn and presented to a capping device  23 . The containers  2  are then discharged toward a labeling unit (not shown) and then toward a packaging unit (not shown).  
         [0041]     As is represented in  FIG. 3 , the conveyor comprises two rails  24  facing one another, from which the containers  2  are suspended by their neck  9  and on which they slide while pushing one another under the driving force of the transfer wheel  19 .  
         [0042]     The rails  24  are supported by cylindrical legs  25  which are themselves carried by a frame  26  which forms the bearing structure of the conveyor  5 .  
         [0043]     To make it possible to convey containers having necks  9  of different diameters, the rails  24  are mounted so that they can slide transversely on their supports, their distance apart being adjustable by means of hand wheels  27 .  
         [0044]     As is visible in  FIG. 2 , the conveyor  5  comprises, at the outlet  6  of the forming unit  3 , a bottom plate  28  arranged below and facing the bottom  10  of the containers  2 . Since the containers  2  are suspended from the rails  24 , they do not rest on the bottom plate  28 , the vertical positioning of which plate (that is to say its distance from the rails  24 ) being adjustable, depending on the size of the containers  2 , so that the gap separating the bottom plate  28  from the base  10  of the containers  2  is as small as possible.  
         [0045]     We will see in the following how this adjustment is performed.  
         [0046]     The cooling unit  7  for its part comprises a pressurized-gas supply circuit  29 , the gas typically being air, and a pressurized-liquid supply circuit  30 , the liquid typically being water, both circuits being connected to a nozzle  31  arranged below the bottom plate  28  and at a certain distance therefrom, as is represented in  FIGS. 3 and 4 .  
         [0047]     Thus, when it is supplied with air and water, the nozzle  31  generates a jet  32 , composed of a mixture of air and of water in suspension, directed, outside the containers  2 , toward their base  10 , which here constitutes a target area which it is desired to cool from the outside, immediately after forming the containers  2 .  
         [0048]     The nozzle  31  has an orifice  33  directed toward an opening  34  made in the bottom plate  28  at the outlet  6  of the forming unit  3 , the bases  10  of the containers  2  filing past perpendicularly to this opening.  
         [0049]     To prevent sprays of liquid from reaching surrounding sensitive parts of the installation  1 , the nozzle  31  is placed in a casing  35  which confines the jet  32  and allows condensed water to be recovered.  
         [0050]     The casing  35  has a lateral wall  36  which is terminated by an upper end  37  by means of which the casing  35  is fastened to the bottom plate  28 , the wall  36 , of square cross section in the example shown, bordering the opening  34 .  
         [0051]     The casing  35  comprises, on the opposite side to its upper end  37 , a receptacle  38  for recovering the condensed water which flows along the lateral wall  36 . As is shown in  FIG. 4 , the receptacle  38  has an orifice  39  to which can be connected a pipe (not shown) for draining the water to outside the installation  1 .  
         [0052]     As is additionally visible in  FIG. 4 , the recovery receptacle  38 , which closes the casing  35  at the bottom, is detachable to allow access to the nozzle  31 . In practice, the receptacle  38  is mounted on the lateral wall  36  by means of wing nuts  40  which allow the receptacle  38  to be fitted and removed rapidly without the use of a tool.  
         [0053]     In view of the installation  1  being adapted to the production of containers  2  of various sizes, means  41  are provided for adjusting the distance separating the nozzle  31  from the bases  10  of the containers  2 , that is to say, in practice, for adjusting the distance separating the nozzle  31  from the bottom plate  28 .  
         [0054]     As illustrated in  FIGS. 3 and 4 , these means  41  take the form of at least one attached spacer which is mounted on the upper end  37  of the casing  35 , being interposed between this casing and the bottom plate  28 , which is thereby raised, this spacer having a lateral wall  42  which thus extends the lateral wall  36  of the casing  35 .  
         [0055]     This results in joint modularity of the cooling unit  7  and of the conveyor  5  depending on the size of the containers  2 .  
         [0056]     As is illustrated in  FIG. 4 , the nozzle  31  is designed to generate a jet  32  of conical shape. In order to optimally locate the jet  32  on the base  10  of the containers  2  outside these containers and as far as possible prevent water spraying beyond the bottom plate  28 , the cooling unit  7  comprises a mask  43  which, mounted at the upper end  37  of the casing  35  across the opening  34 , delimits a window  44  of adjustable width.  
         [0057]     The mask  43  comprises two shutters  45 ,  46  arranged in a plane perpendicular to the axis of the nozzle  31  (that is to say to the general direction of the jet  32 ), these shutters having internal edges  47 ,  48  jointly delimiting the window  44 . As is shown in  FIG. 5 , at least one of the shutters  45 ,  46  is slideably mounted to allow adjustment of the size (more precisely of the width) of the window  44  and thus regulate the cross section of the jet  32  at the outlet of the casing  35  depending particularly on the diameter of the base  10  of the containers  2 .  
         [0058]     The nozzle  31  is an atomizing nozzle: it is designed to atomize the water into fine droplets, that is to say of a diameter of less than 200 μm, whereas the conventional nebulizing nozzles generate large water droplets, that is to say of a diameter of greater than 400 μm.  
         [0059]     The inventors have in fact observed that on contact with the hot plastic, that is to say at a temperature of greater than or equal to approximately 80° C., the atomized particles pass virtually immediately to the gaseous state. The transfer of heat accompanying this change of state from liquid to gas is what causes the cooling of the exposed parts of the containers  2  (in this instance the base  10 ).  
         [0060]     Since the transfer of heat accompanying the change of state from liquid to gas is greater than that accompanying the simple heating of the water (as is the case during cooling by means of nebulization), cooling by means of spraying an atomized jet proves to be more efficient that nebulization.  
         [0061]     There additionally result arrangements which precede the following advantages.  
         [0062]     First, the water consumption is considerably reduced (the volume of a droplet having a diameter of 200 μm in fact represents one eighth of the volume of a droplet having a diameter of 400 μm).  
         [0063]     Secondly, a significant reduction in soiling on the body  8  of the containers  2  is observed. Specifically, whereas large droplets which are deposited on the bodies  8  run down and leave behind traces which must then be removed, fine droplets do not have the opportunity to become deposited on the bodies  8 , either because they have been vaporized on contact with the hot base  10  or because they have been stopped by the mask. The cleanliness of the containers is thus improved.  
         [0064]     Thirdly, the vaporization of the fine droplets prevents contamination of the installation  1 , that is to say water being sprayed onto the surrounding parts of the installation  1 , which could in particular have harmful consequences in terms of electrical safety. Encasing the nozzle  31  also contributes to reducing this contamination.  
         [0065]     A description will now be given of the arrangement and the equipment of the pressurized-air and pressurized-water supply circuits  29 ,  30  with reference to  FIGS. 3 and 6 .  
         [0066]     The air supply circuit  29  comprises an air feed line  49  connected to a general pressurized-air circuit (not shown; in industry, the relative air pressure in the general circuit is generally equal to 7 bar).  
         [0067]     It should be noted that “relative” air pressure means the pressure difference between the measured air pressure and the atmospheric pressure.  
         [0068]     The air feed line  49  is connected to a first solenoid valve  50  operated by a controller (not shown), the circuit  29  being closed when the installation  1  is at a standstill and being opened when it is operating.  
         [0069]     Along the air supply circuit  29  is then placed, between the solenoid valve  50  and the nozzle  31 , a pressure regulator  51  (in this instance a relief valve) designed so that the relative air pressure at its outlet is less than approximately 1 bar, preferably equal to approximately 0.7 bar. A manometer  52  (needle-type or digital) is attached to the regulator  51 .  
         [0070]     The water circuit  30  for its part comprises a water feed line  53  connected to the general water supply circuit (not shown), in this instance via a manually operated tap  54 .  
         [0071]     Between the tap  54  and the nozzle  31 , the water encounters, along the circuit: 
        a first scale-inhibiting filter  55 , of the electromagnetic type, intended to perform a first softening of the water by retaining the particles having a diameter of greater than 7 μm;     a second solenoid valve  56  operated by the afore-mentioned controller, the circuit  30  being closed when the installation  1  is at a standstill and being opened in contrast when this installation is operating;     a second scale-inhibiting filter  57  intended to perform a second softening of the water by retaining the particles having a diameter of greater than 5 μm;     a pressure regulator  58  to which a manometer  59  is attached, and     a flow limiter  60 .        
 
         [0077]     The pressure regulator  58  and the flow limiter  59  are respectively regulated so that the relative water pressure is less than 1 bar (preferably equal to approximately 0.7 bar) and the water throughput is less than 3 l/h.  
         [0078]     In fact, the inventors have observed that, with these values, combined with a relative air pressure of less than 1 bar, the cooling unit has a maximum efficiency.  
         [0079]     In addition, in order to purge the nozzle  31  on the water infeed side so as to prevent it from scaling up, particularly if the installation  1  is at a standstill for a prolonged period, the air supply circuit  29  is connected to the water supply circuit  30  by means of a bypass circuit  61  connected, on the one hand, to the air supply circuit  29  upstream of the first solenoid valve  50  and, on the other hand, to the water supply circuit  30  between the flow limiter  60  and the nozzle  31 .  
         [0080]     The bypass circuit  61  comprises, in succession, a third solenoid valve  62  operated by the controller when purging is judged necessary, and a nonreturn valve  63  intended to prevent water from rising into the air supply circuit  29 .  
         [0081]     The operation of the installation  1  is as follows.  
         [0082]     The preforms are first introduced into the forming unit  3  by the supply unit  11 . Within the forming unit  3 , the containers  2  are formed from the preforms. The hot containers  2  are then transferred by the wheel  19 , at the outlet  6  of the forming unit  3 , toward the conveyor  5 .  
         [0083]     The containers  2  then pass across the opening  34 , their base  10  being impinged by the jet  32  coming from the nozzle  31  and consequently cooled by the heat transfer accompanying the changeover from the liquid state of the atomized water particles to the gaseous state.  
         [0084]     The invention cannot be limited to the foregoing description, with variants being conceivable.  
         [0085]     Thus, although the nozzle  31  is supplied continuously, it is conceivable to program the controller in such a way as to generate the jet  32  intermittently as soon as a container  2  is presented across the window  44 , in order to save water and prevent liquid being sprayed through the gap separating two successive containers  2 .  
         [0086]     Furthermore, although the cooling unit  7  is a fixed unit in the foregoing, it is conceivable to mount it on a sliding carriage accompanying the containers  2  over some of their journey along the conveyor  5  in order to cool the bases  10  further still.  
         [0087]     It is also conceivable to place the nozzle  31  in line with the transfer wheel  19  or, more precisely, in line with the path followed by the indentations  20 , in order for the containers  2  to be cooled while they are being transferred toward the conveyor  5 , even before they leave the forming unit  3 . Such an arrangement does not call for any specific modification of the actual structure of the cooling unit  7 .  
         [0088]     Moreover, although in the foregoing the area to be cooled (“target area”) comprises the base  10  of the containers  2 , it is conceivable to select another target area depending on the shape of the containers. For example, this may concern areas on the body  8  which are provided with stiffeners, where the profile and/or the thickness of the wall vary locally.  
         [0089]     In addition, it is of course possible to replace the air with any other inert gas (for example nitrogen), and the water with any other liquid, preferably a noncorrosive and nonpolluting liquid.  
         [0090]     As for the mask  43 , although embodied by means of sliding shutters  45 ,  46 , it is conceivable to replace these shutters  45 ,  46  with a contractile diaphragm.