Abstract:
The invention concerns an apparatus for blowing and filling a container (22) from a preform (16), said apparatus comprising: —a mold (12) for enclosing a preform (16), —stretching means for stretching the preform (16) placed within said mold (12), —a pressurized liquid injection circuit (18) able to inject a liquid under pressure inside said preform (16) when said preform is placed inside said mold, —injection means which are adapted to inject a predetermined volume of liquid through said liquid injection circuit (18) into the preform and to stop injection of the liquid through said circuit into the preform when a blown and filled container (22) has been obtained, stopping the injection of the liquid through the liquid injection circuit into the preform creating an overpressure of the liquid within the liquid injection circuit, characterized in that the apparatus further comprises releasing means for releasing said overpressure of the liquid within the liquid injection circuit.

Description:
CROSS REFERENCE TO RELATED APPLICATIONS 
     The present application is a National Stage of International Application No. PCT/EP2013/053903, filed on Feb. 27, 2013, which claims priority to European Patent Application No. 12158583.0, filed Mar. 8, 2012, the entire contents of which are being incorporated herein by reference. 
     FIELD OF THE INVENTION 
     The invention relates to a method and an apparatus for blowing and filling containers from preforms. 
     BACKGROUND OF THE INVENTION 
     Plastic containers such as bottles of water are manufactured and filled according to different methods including blow moulding or stretch-blow moulding. 
     According to one of these known methods a plastic preform is first manufactured through a moulding process and then heated before being positioned inside a blowing mould. 
     The preform usually takes the form of a cylindrical tube closed at its bottom end and open at its opposite end. 
     Once the preform has been positioned within the mould only the open end of the preform is visible from above the mould. 
     The above-mentioned method makes use of a stretch rod which is downwardly engaged into the open end of the preform so as to abut against the closed bottom end thereof. The stretch rod is further actuated to be urged against the closed end, thereby resulting in stretching the preform. 
     After the stretching phase has been initiated a liquid is injected into the preform through its open end during a filling phase, as disclosed for instance in Applicant&#39;s patent EP 1 529 620 B1. This liquid injection causes expansion of the preform until coming into contact with the inner walls of the mould, thereby achieving the final shape of the bottle. 
     The Applicant has noticed that at the end of the filling phase when liquid injection is stopped, a back pressure occurs in the pressurized liquid injection circuit due to the nearly incompressibility of liquids. 
     This back pressure phenomenon causes mechanical stresses and possibly damages to different components which are used in connection with the liquid injection circuit. 
     More particularly, the above-described blowing and filling method makes use of a piston device for pushing the liquid throughout the liquid injection circuit for its injection into the preform. 
     Filling of the preform with liquid is performed and requires deceleration of the filling pace at the end of the filling phase. 
     However, control of deceleration proves to be very difficult with today hydraulic, pneumatic or electric technology. 
     In particular, due to inertia the piston device is always moving beyond the requested stopping point. 
     As the liquid is nearly incompressible, this results in a high pressure of liquid, thereby giving rise to the back pressure phenomenon within the liquid injection circuit. 
     The mechanical components which are in connection with the liquid circuit are thus submitted to mechanical stresses due to back pressure. 
     These stresses and their impact on the components repeat over time, which therefore leads to a reduced life time of these components. 
     Also, an inefficient control of liquid filling deceleration may lead to breakage of the container. 
     SUMMARY OF THE INVENTION 
     In this respect, the invention is a method as defined in claim  1 . 
     Thus, the overpressure is evacuated or discharged from the pressurized liquid injection circuit, which avoids repeated stresses on components that are in connection with this circuit and possible damages thereon over time. 
     Also, the invention makes it possible to fill the container at a high speed toward the end of the injection phase. 
     According to a possible feature, the method comprises opening a valve device that is connected to the pressurized liquid injection circuit so as to release said overpressure of liquid. 
     This is an easy and efficient way to evacuate or discharge the overpressure of liquid from the pressurized liquid injection circuit. 
     The discharge through the valve device may be operated automatically once a predetermined threshold of pressure has been reached or upon command. 
     According to a further possible feature, the valve device is located close to the place where liquid is injected into the preform. For example, the valve device is located close, or even attached to an injection head that is used for injecting the liquid into the preform. 
     According to another possible feature, the method comprises releasing said overpressure of liquid by discharging it through an expansion tank. 
     This is another easy and efficient way to evacuate or discharge the overpressure of liquid. This way of releasing the overpressure may be implemented automatically once a given level of pressure has been reached. 
     According to a possible feature, the stopping of the injection phase further comprises closing an injection valve device, said closing of the injection valve device enabling communication of liquid between the pressurized liquid injection circuit and at least one discharge channel through which the overpressure is released. 
     Thus, another way to release the overpressure may be automatically implemented with the closing of the injection valve device. No separate action has to be performed for releasing the overpressure. 
     The single closing of the injection valve device triggers the overpressure release. This therefore makes easy, reliable and efficient the implementation of the method. 
     According to a further possible feature, closing the injection valve device both prohibits the liquid that is in the pressurized liquid injection circuit from flowing through the injection valve device for being injected into the preform and enables liquid communication between the pressurized liquid injection circuit and the at least one discharge channel. 
     According to another possible feature, the starting of the injection phase comprises opening the injection valve device so as to enable flowing of the liquid that is pushed inside the pressurized liquid injection circuit through the open injection valve device for being injected into the preform. 
     According to a possible feature, the injection phase starts after the stretching phase has started. 
     According to another aspect, the invention is an apparatus in accordance with claim  8 . 
     This apparatus provides a simple solution to remedy at least one of the above-mentioned drawbacks. 
     In particular, the liquid overpressure releasing means are actuated or activated before that the blown and filled container is released or extracted from the mould. 
     According to another possible feature, the releasing means comprise at least one valve device that is connected to the pressurized liquid injection circuit and that is adapted to be opened so as to release said overpressure of liquid. 
     Arranging a mere valve device (or several ones) in connection with the pressurized liquid injection circuit enables easy and efficient release of the liquid overpressure. 
     According to a possible feature, said at least one valve device is designed so as to be automatically opened for a predetermined pressure of liquid. 
     According to a possible feature, said at least one valve device is a controlled valve. 
     According to a possible feature, the releasing means comprise an expansion tank that is connected to the pressurized liquid injection circuit. 
     According to another possible feature, the injection means comprise an injection valve device that includes at least one discharge channel and that is suitable for moving between an open and a closed position, the open position being such that it authorizes the liquid that is injected through the pressurized liquid injection circuit to flow through the open injection valve device for being injected into the preform, the at least one discharge channel being not in communication with the pressurized liquid injection circuit, the closed position being such that it does no longer authorise the liquid to flow though the closed injection valve device and it enables communication between the pressurized liquid injection circuit and the at least one discharge channel for the release of the overpressure therethrough. 
     Thus, the injection valve device performs two different functions when in closed position: preventing any further flow of liquid from passing through the valve device for being injected into the preform and simultaneously releasing or discharging the overpressure through the at least one discharge channel. 
     These releasing means are quite simple and efficient. 
     According to a possible feature, the injection valve device is suitable for moving along a longitudinal axis between the open and closed position and the pressurized liquid injection circuit is connected to the injection valve device transversally relative to said longitudinal axis. 
     Thus, the liquid inlet to the injection valve device is lateral. 
     According to a possible feature, the injection valve device is a piston device. 
     According to still another possible feature, the injection means comprise an injection head that is arranged above the mould and in sealing engagement therewith, the injection valve device being mounted within the injection head. 
     The pressurized liquid injection circuit is laterally connected to the injection head relative to the longitudinal axis of said injection head. It is to be noted that the injection valve device is axially movable along this longitudinal axis between the open and closed position. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       Embodiments of the present invention will now be described, by way of example only, with reference to the accompanying figures in which: 
         FIG. 1  is a schematic overall view of a system according to a first embodiment of the invention; 
         FIG. 2  is a schematic enlarged partial view of the injection head and mould of  FIG. 1 ; 
         FIG. 3  is a schematic view of an injection piston device; 
         FIG. 4  schematically illustrates a curve representing the variation in time of the volume of liquid injected into the preform; 
         FIG. 5  is a schematic overall view of a system according to a first variant embodiment of the invention; 
         FIG. 6  is a schematic overall view of a system according to a second variant embodiment of the invention; 
         FIG. 7A  is a schematic overall view of a system according to a second embodiment of the invention; 
         FIGS. 7B and 7C  are schematic enlarged partial views of the injection head of  FIG. 7A  system in an open and closed position of the injection nozzle; 
         FIG. 8  is a graph representing the typical weight of a container body as function of its volume. 
     
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
       FIG. 1  schematically represents an apparatus  10  for simultaneously blowing and filling containers, such as bottles, from preforms, according to an embodiment of the invention. 
     These preforms may be made of thermoplastic polymer. 
     Apparatus  10  comprises a mould  12  for enclosing a preform. 
     Mould  12  is for example a two-part mould of which the two parts  12   a ,  12   b  define an inner cavity  14  when assembled together. 
     As represented in  FIG. 1 , a preform  16  is inserted into cavity  14  at the beginning of a blowing and filling method according to the invention or just before. 
     The shape of the cavity corresponds to the shape of the achieved container and it will be wholly occupied by the formed container at the end of the blowing and filling method. 
     It is to be noted that mould  12  may alternatively be composed of more than two parts depending on the manufacturing process. 
     For instance, a third part (base mould) may be added at the bottom of the mould so as to constitute at least a part of the inner cavity bottom. 
     Apparatus  10  further comprises a pressurized liquid injection circuit  18  and injection means for injecting a liquid into preform  16 . 
     Injection means comprise an injection head  20  which comes into a sealing contact (for liquid tightness purpose) with mould  12  and preform  16 . 
       FIG. 2  is a schematic enlarged partial view of injection head  20  disposed above mould  12 . 
     Mould  12  encloses a blown and filled container  22  (here, for example, a bottle filled with water) that has been obtained from preform  16  through the blowing and filling method. 
     The injection head comprises an injection valve device  24  that includes an injection nozzle  28  mounted within an inner housing  26 . 
     Injection head  20  is substantially cylindrical in shape as partially illustrated in  FIG. 2  and inner housing  26  is also cylindrical in shape and both are coaxial. 
     Injection valve device  24 , and more particularly injection nozzle  28 , is moveable along a longitudinal axis A between an injection position (open position) allowing liquid to be injected into the preform and a rest position (closed position) in which the injection nozzle  28  rests against an inner surface  26   a  of the injection head in a sealing engagement so as to prevent any flow of liquid from the injection head into the preform. 
     Longitudinal axis A is here the vertical axis along which injection head  20  and mould  12  are substantially aligned. 
     Axis A is a symmetry axis to container  22 . 
     As represented in  FIG. 2 , injection nozzle  28  is in the closed position (lower position) which is occupied when the container has been blown and filled at the end of the manufacturing method. 
     In the open position injection nozzle  28  is in an upper position at a distance from the inner surface  26   a . This upper position is not represented in the drawing for the sake of clarity but it is located above a transverse channel  30  (represented in dotted lines) that is provided in a peripheral wall  32  of injection head  20 . 
     This feed channel is connected to pressurized liquid injection circuit  18 . 
     Moving the injection nozzle  28  away from inner surface  26   a  and above channel  30  makes it possible for the liquid that is in the circuit  18  to flow from channel  30  to the preform (in  FIG. 2  the preform is replaced with the formed container  22 ). 
       FIG. 3  schematically illustrates an example of injection valve device  24 . 
     Injection valve device  24  is an injection piston device that is operated thanks to a fluid, e.g. air. Other fluids may be used alternatively. 
     Fluid-operated piston device  24  comprises a piston  34  that is sliding longitudinally (along axis A) within a cylindrical housing  36  and a rod  35  provided with injection nozzle  28  at its end. 
     Fluid is supplied to piston device  24  by a fluid supply system (not represented in the drawing) which comprises controlling means (not represented) for controlling the supply of fluid to piston device  24 . 
     The control of the fluid supply enables appropriate upward and downward movements of injection nozzle  28  along axis A so as to occupy either open or closed position. 
     Reverting to  FIG. 1 , apparatus  10  also comprises stretching means  38  for stretching preform  16  when enclosed within mould  12 . 
     Stretching means comprise a stretch rod  38  which is in a sliding connection with the injection nozzle  28 . 
     In  FIG. 2 , the stretch rod is not represented for the sake of clarity. For example, stretch rod  38  may be in alignment with axis A and traverse injection nozzle  28  in a fluid-tight manner. 
     The stretch rod  38  of  FIG. 1  embodiment is actuated upon command to be inserted downwardly into preform  16  so as to stretch the latter while a filling liquid is injected thereinto with a view to causing expansion of said preform within the mould. 
     Actuating means for actuating rod  38  have not been represented for the sake of clarity. 
     Apparatus  10  comprises a valve device  40  that enables flowing of liquid through circuit  18  when opened and prevents liquid from flowing through the valve device and downstream thereof when closed. 
     Valve device  40  is actuated upon command. 
     Liquid to be injected into the preform, e.g. water, is supplied from a source of liquid S which feeds said liquid to a pump device  42  of apparatus  10 . 
     Pump device  42  is located upstream of valve device  40 . 
     Such a pump device is suitable for delivering a constant pressure, e.g. between 3 and 7 bars. 
     Pump device  42  is suitable for providing a predetermined volume of liquid and pushing or injecting it through liquid injection circuit  18 . Pump device  42  is part of the injection means of apparatus  10  and acts as liquid pushing means. 
     As further represented in  FIG. 1 , a flow valve  44  is mounted in parallel of pump device  42  as a safety valve. 
     This valve acts as a discharge valve in order to protect the pump device, for instance when the liquid pressure is building up or if there is no container being manufactured. 
     Apparatus  10  comprises a duct  46  that is connected to pump device  42  at one end and to injection head  20  at the opposite end. Valve device  40  is mounted onto duct  46 . It is to be noted that duct  46  is part of liquid injection circuit  18 . 
     In a variant embodiment illustrated in dotted lines in  FIG. 1 , liquid pushing means  52  may be used as an alternative to pump device  42 . 
     Pushing means  52  are here represented by a piston device that is able to displace a predetermined volume of liquid through liquid injection circuit  18  and, more particularly, duct  46 . 
     It is to be noted that any other means that are capable of displacing a volume of liquid may be alternatively used. 
     Apparatus  10  also comprises a valve device  60  that is connected to liquid injection circuit  18  and here, more particularly, to duct  46 . 
     As represented in  FIG. 1 , valve device  60  is located close to injection head  20 . In particular, it is located as close as possible to injection head  20  in order to reduce as much as possible the dead volume. 
     In the course of performance of the blowing and filling method according to an embodiment of the invention, the stretch rod  38  is actuated during a stretching phase whereas valve device  40  is in a closed position, thereby preventing liquid from being injected into preform  16 . 
     Stretch rod  38  is downwardly engaged into the open end of the preform  16  so as to come into contact with the closed bottom end thereof. The stretch rod is then further actuated to push the closed end downwardly and stretch the preform accordingly in a controlled manner. 
     After a predetermined period of time has elapsed after the start of the stretching phase, the injection phase starts for injecting the liquid into the preform both for forming the container and filling it. 
     The injection phase starts with the opening of valve device  40  and operation of pump device  42  (or, alternatively, piston device  52 ). Actuation of valve device  40  may be controlled through a processor or a computer or manually. 
     Also injection nozzle  28  is actuated to be raised in its upper position (open position). 
     Pump device  42  (or piston device  52 ) is operated in a controlled manner so that liquid is pushed or injected through liquid injection circuit  18  and injection head  20  to preform  16  (for being injected thereinto) in accordance with a predetermined injection or filling curve. 
       FIG. 4  represents the variation over the time of the volume of liquid that is injected or displaced by pump device  42  during the injection phase. 
     A curve referred to as (a) represents the desired theoretical curve of liquid injection over the time. This curve comprises a first portion in which the volume of liquid increases and a second flat portion in which the volume has reached a maximum value and is kept constant. 
     This liquid injection causes together with the movement of the stretch rod expansion of the preform  16  until coming into contact with the inner walls of the mould. The final stage of the container is thus achieved ( FIG. 2 ). 
     At the beginning of the injection phase valve device  60  is in a closed position. 
     As represented in  FIG. 4 , the volume of liquid that is being displaced through liquid injection circuit  18  is greater than the volume required for filling the container. This additional volume of liquid is referred to as (b) on the curve. 
     By appropriately controlling the timing of the injection phase the injection nozzle  28  is actuated to be lowered for closing the liquid injection valve and pump device  42  (or piston device  52 ) is commanded to stop pushing or injecting liquid through circuit  18 . 
     The additional volume of liquid pushed or injected into circuit  18  and, therefore duct  46 , results in an increase in pressure (pressure in excess) within circuit  18  due to closing of injection nozzle  28 . 
     In order to avoid a back pressure phenomenon within circuit  18  valve device  60  is commanded, by a processor or a computer or manually, to be open at an appropriate time relative to the  FIG. 4  time-based volume curve (e.g. after a given period of time or time delay has elapsed). In particular, valve device  60  is opened when the required amount of liquid (volume) has been injected into the preform/container. Alternatively, valve device  60  is actuated to be opened depending on the position of piston device  52 . 
     Thus, the volume of liquid in excess within duct  46  is discharged through valve device  60  so as to release the overpressure of liquid. The discharged liquid may then be recovered and recycled in this process. 
     Valve device  60  acts, therefore, as releasing means that enable release of a liquid overpressure (at the end of the injection phase) outside the liquid injection circuit. 
     By displacing a greater of volume of liquid during the injection phase and discharging this extra amount of liquid through valve device  60  (discharge valve) it is therefore made possible to attain the flat portion of the curve (a) in  FIG. 4 . It is also possible to complete the filling of the container at a high speed or filling rate. 
       FIG. 5  illustrates an apparatus  100  for blowing and filling a container in accordance with a first variant embodiment of the invention. 
     Apparatus  100  differs from apparatus  10  of  FIG. 1  by a controlled valve  102  which replaces valve device  60 . All the other elements of apparatus  100  are identical to those of apparatus  10  and bear the same references. 
     Controlled valve  102  performs the same function as valve device  60 , i.e. it releases the liquid overpressure outside the pressurized liquid injection circuit. 
     Controlled valve  102 , therefore, behaves as a discharge valve. 
     Controlled valve  102  releases the overpressure of liquid automatically once the predetermined volume of liquid has been injected into the preform/container and a predetermined liquid pressure level has been reached within the liquid injection circuit. 
     Controlled valve  102  may have been pre-set accordingly through appropriate settings beforehand so as to open depending on the amount of liquid pressure within the circuit. 
     Alternatively, controlled valve  102  may be actuated based on a pressure switch. 
       FIG. 6  illustrates a second variant embodiment of an apparatus  110  according to the invention. 
     Apparatus  110  differs from apparatus  10  by an expansion tank  112  which replaces valve device  60 . All the other elements of system  110  are identical to those of apparatus  10  and bear the same references. 
     Expansion tank  112  performs the same function as valve device  60 , i.e. it releases the liquid overpressure outside the liquid injection circuit and, therefore, discharges the latter from this pressure in excess as soon as the pressure within the liquid injection circuit  18  has reached a predetermined value or level (threshold). 
       FIG. 7A  illustrates a second embodiment of an apparatus  120  for blowing and filling a container according to the invention. 
     Apparatus  120  is almost identical to  FIG. 1  apparatus  10  except that discharge valve device  60  has been removed and injection head  20  (partially represented in  FIG. 2 ) has been modified as illustrated in  FIGS. 7B and 7C . 
     Apparatus  120  comprises a modified injection head  122  with a new injection valve device arrangement  124 . 
     The enclosure or casing in which injection valve device  124  is installed is the same as that described with reference to  FIG. 2 . The illustration of the arrangement between injection head  122  and mould  12  has been voluntarily simplified for the sake of clarity. Only mould  12  and its internal cavity  14  have been represented. 
     More particularly, the injection nozzle  126  of injection valve device  124  forms a body at the upper part  126   a  of which a discharge channel  128  is provided. 
     The lower part  126   b  of the body remains the same as that of injection nozzle  28  in  FIG. 2 . This lower part has a liquid-tight function which is carried out when injection nozzle  126  is in a lower closed position ( FIG. 7C ) and bears against the inner surface  26   a.  In the upper open position of the injection nozzle ( FIG. 7B ) lower part  126   b  does not serve this purpose. 
     As represented in  FIG. 7B , discharge channel  128  has two opposite ends, a first end  128   a  that opens onto a lateral or side face  126   c  of the injection nozzle body and a second end  128   b  that opens onto a top face  126   d  of the body. 
     Discharge channel  128  forms a bend between its two opposite ends. The bend illustrated in  FIG. 7B  is at right angle. However, a bend with a smoother curvature may be alternatively used. It is to be noted that the channel may instead have a rectilinear inclined shape from side face  126   a  to top face  126   d.    
     In  FIG. 7B  discharge channel  128  is facing the inner wall of inner housing  26 . 
     It is to be noted that several discharge channels may be used instead of a single one in order to augment the flow rate. As represented in  FIG. 7B , injection nozzle  126  has been raised in the upper open position so as to authorize the liquid that is pushed by pump device  42  through pressurized liquid injection circuit  18  and channel  30  to flow through the open valve as indicated by the arrow F. The liquid that is authorized to pass is injected into the preform placed within cavity  14  in the course of operation of the injection phase. 
     When the injection phase terminates, injection nozzle  126  is commanded to be lowered in the lower closed position of  FIG. 7C  and lower part  126   b  comes into a sealing engagement with inner surface  26   a.    
     Also pump device  42  is commanded to stop pushing or injecting a volume of liquid into the liquid injection circuit  18 . 
     Thus, the injection nozzle  126  occupies the axial position represented in  FIG. 7C , thereby obstructing any further flow of liquid to be injected into the container that has been formed. 
     In this axial position the discharge channel  128  is facing feed channel  30  which is connected to duct  46 . Thus, a communication is established between channel  30  and discharge channel  128  so as to enable circulation of liquid through the latter. This discharge of liquid enables release of the liquid overpressure that is present within liquid injection circuit  18 . 
     Liquid discharge is evacuated from top of the injection nozzle with a view to being recovered and possibly recycled. 
     Liquid discharge stops naturally when the pressure within the container is at the atmospheric pressure if the discharge channel or circuit is vented to the atmospheric pressure. 
     The location of discharge channel  128  is adjusted along the height or axial extension of the injection nozzle body (axis A) so as to provide efficient release of the liquid overpressure. 
     In a variant embodiment, discharge channel  128  may be disposed in a lower position, i.e. its lateral opening end  128   a  may be lowered, which lengthens the channel. Its curvature may be the same as that illustrated in  FIG. 7C  or different. 
     By way of example, the diameter of this channel is 6 mm. 
     More generally, the diameter may lie between 4 mm and 8 mm. 
     The apparatus according to the invention is particularly suitable for manufacturing lightweight thermoplastic polymer containers. 
     Lightweight preforms may be defined with respect to the graph of  FIG. 8 . 
     This graph illustrates the typical weight of a preform or container body expressed in grams (g) as a function of the volume of the latter expressed in centilitres (cl.). 
     The lightweight preforms or containers are located below the curve C. 
     In the present embodiment, the container which is being blown and filled is a bottle filled with still water. 
     However, other containers may be envisaged as well as other liquids. 
     Other graphs may be easily obtained by the person skilled in the art for defining lightweight containers intended to be filled with other liquids. 
     It should be understood that various changes and modifications to the presently preferred embodiments described herein will be apparent to those skilled in the art. Such changes and modifications can be made without departing from the spirit and scope of the present invention and without diminishing its attendant advantages. It is therefore intended that such changes and modifications be covered by the appended claims.