Abstract:
A blow molding system for a thermoplastic blank which is supported in a mold. The system includes a fixed tubular body connected to a high-pressure fluid source and, at the lower end thereof, supporting moveable equipment consisting of a tuyere, the tuyere being defined laterally by a terminal sleeve of the moveable equipment and the bottom thereof being the front wall of the body, wherein the lateral inner wall of the sleeve is configured in such a way that the pressure of a fluid inside the tuyere does not result in a reaction force component on the lateral wall, which is directed opposite to the wall of the mold.

Description:
FIELD OF THE INVENTION 
       [0001]    The present invention relates to improvements made to blow-molding systems able to supply a blow-molding fluid at high pressure into a thermoplastic parison which is supported, in a blow-molding mold, by its neck emerging from a wall of the mold, said system comprising a stationary tubular body which is in communication with a source of high-pressure fluid and which, at its lower end, coaxially and slidably supports a movable equipment comprising a blowing nozzle able, in the blowing position, to be placed in sealed communication with the neck of the parison, the nozzle being laterally defined by a terminal part, in the form of a sleeve, of the movable equipment, the tubular body having a transverse face which lies a fixed distance from said wall of the mold. 
       BACKGROUND OF THE INVENTION 
       [0002]    Various blow-molding systems of the type in question are known, particularly systems equipped with various types of nozzles either designed to be brought into physical contact with the neck of the parison that is to be blow-molded (nozzles butting in a sealed fashion against the mouth of the neck of the parison, conical nozzles engaged in sealed fashion inside the neck of the parison, nozzles fitted tightly over the neck of the parison), or designed such that they are oversized relative to the neck of the parison so as to be brought to bear frontally and in a sealed manner against the wall of the mold supporting the parison while surrounding said neck from a distance (bell-shaped nozzles: see, for example, document FR 2 764 544). 
         [0003]    The force with which the nozzle, whatever its type, is held bearing in a sealed fashion against the neck of the parison or against the wall of the mold has to be high enough to oppose the reaction thrust, in the opposite direction, due to the high pressure (typically of the order of 40×10 5  Pa) of the blow-molding fluid which is exerted on the walls of the nozzle. This bearing force has also to be high enough to seal the cooperation between the nozzle and the neck of the parison by slight elastic deformation of the thermo-plastic material and, in the case of the bell-shaped nozzle, for the seal provided transversely across the nozzle to be compressed enough that it is not driven radially off its seating under the effect of the high blowing pressure. 
         [0004]    In practice, the movable equipment incorporating the nozzle is moved and kept bearing in a sealed fashion against the neck of the parison or the wall of the mold using a pneumatic actuator operated by a fluid under high pressure at least equal to the pressure of the blow-molding fluid, and the fluid delivered to the pneumatic actuator is the blow-molding fluid itself. Now, from a financial standpoint, producing fluid at high pressure, typically at pressures of 40×10 5  Pa, represents a very significant item of expenditure in the operation of the entire thermoplastic receptacle (particularly bottle) production line: specifically, the higher the consumption of high-pressure fluid, the more highly specified the compressor needs to be, and therefore the more expensive it is, and furthermore, the higher its electrical power consumption. 
         [0005]    Users are nowadays looking for manufacturing systems of improved profitability with higher production rates and lower operating costs. In this context, reducing the amount of high-pressure fluid used by the receptacle manufacturing line and, more particularly, by the blow-molding system, would seem to be desirable. 
       SUMMARY OF THE INVENTION 
       [0006]    It is therefore an object of the invention to meet this expectation and propose a blow-molding system as mentioned hereinabove which consumes appreciably less high-pressure fluid than the current systems. 
         [0007]    To these ends, a blow-molding system as mentioned in the preamble is characterized, being in accordance with the invention, in that
       the end wall of the nozzle is formed by said transverse wall of the tubular body, and the lateral interior wall of the sleeve is shaped in such a way that fluid pressure inside the nozzle does not generate, on said lateral wall, a reaction force component directed away from said wall of the mold.       
 
         [0009]    Because of the design proposed according to the invention, all the reaction components resulting from the pressure of the blow-molding fluid during the phase of blow-molding the receptacle and which are exerted on the movable equipment are radial and therefore cancel one another out because of the symmetry of revolution of the lateral internal wall of the nozzle and, if there is an axial component, this component is directed toward the wall of the mold and plays a part in holding the nozzle in place. Thanks to this design, the means for moving the movable equipment and for keeping the nozzle in the blow-molding position need to develop a force that is considerably lower than is required in current systems, and therefore can be produced in a scaled-down and simplified form. 
         [0010]    In practice, it is advantageous to maintain, as in the earlier systems, pneumatic operation of the movable equipment, by contriving for respective portions of the tubular body and of the movable equipment which face each other to be arranged as an at least single-acting pneumatic actuator for moving the movable equipment along the tubular body in the direction of the mold and holding the nozzle in said sealed communication with the neck of the parison. A result of this is that the nozzle can be kept pressed in a sealed fashion against the neck of the receptacle or against the wall of the mold using a pressure that is appreciably lower than the high pressure of the blow-molding fluid; as for the moving of the movable equipment by the pneumatic actuator, a low pressure driving fluid is sufficient here too. Thus, the movable equipment including the nozzle can be operated (apart from the actual blowing itself) using a relatively low-pressure driving fluid; typically, it will be possible to use compressed air at 7×10 5  Pa which is commonly available in all industrial facilities. 
         [0011]    The design of a blow-molding system according to the invention leads to a substantial saving in high-pressure fluid which can now be reserved simply for the blow-molding phase. A result of this is that it is possible, in order to produce the high-pressure fluid, to use a compressor of an appreciably lower capacity, which is therefore less expensive to purchase and requires less electrical power to run; furthermore, it is less bulky and its smaller size, together with other modifications made to the remainder of the manufacturing system, lead to designs of manufacturing systems which occupy less floorspace. 
         [0012]    Although various structural arrangements are conceivable, in a simple and therefore advantageous embodiment, the movable equipment is external to the tubular pipe. It is then advantageous for the pneumatic actuator to comprise a stationary piston formed by a widening of the tubular body and a movable chamber formed by a widening of the movable equipment housing the piston in a sealed fashion. 
         [0013]    As a preference, the movable equipment is moved pneumatically not only as it is lowered with the nozzle kept bearing in a sealed manner against the neck of the parison or against the wall of the mold, but also as it is raised once the receptacle has been blown: for these reasons, the pneumatic actuator is a double-acting actuator. 
         [0014]    The provisions according to the invention can be applied irrespective of the type of nozzle used; in particular, they can be applied in cases where the nozzle is designed to collaborate positively and in a sealed fashion with the neck of the parison that is to be blow-molded, particularly being engaged in said neck; as a preference, they can be applied in cases where the nozzle is designed in the form of a bell-shaped nozzle having a widened terminal part able to press in a sealed fashion via its transverse face against the wall of the mold while at the same time fitting over the neck of the parison without being in contact therewith. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0015]    The invention will be better understood from reading the detailed description which follows of certain embodiments which are given solely by way of nonlimiting examples. In this description, reference is made to the attached drawings in which: 
           [0016]      FIG. 1  is a sectioned schematic view of part of a blow-molding system arranged according to a preferred embodiment of the invention and shown in a non-functional position; 
           [0017]      FIG. 2  is a sectioned schematic view of the blow-molding system of  FIG. 1 , shown in a functional position; and 
           [0018]      FIGS. 3 and 4  are sectioned schematic views of two embodiment variants of a blow-molding system according to the invention, both shown in a functional position. 
       
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
       [0019]      FIG. 1 , to which reference is made first of all, depicts part of a blow-molding system in which only those elements necessary for understanding the invention are depicted. 
         [0020]    The blow-molding system comprises a stationary body  1  supported by a support structure (not depicted) over a mold  2 , it too supported in a stationary manner by the same support structure. In practice, this support structure may form part of a revolving structure or carousel combining numerous molds distributed about the circumference and surmounted by respective blow-molding systems. In practice also, the body  1  of the blow-molding system extends more or less vertically above the mold and more or less coaxially with respect to the molding cavity  3  of the mold. 
         [0021]    So as to present a more concrete example, a parison  4  (in this instance a preform) has been shown in position in the mold  2  awaiting blowing. The parison  4  is positioned in such a way that it is supported, via its flange  5 , on the wall  6  (top wall) of the mold into which the molding cavity  3  opens so that only the neck  7  emerges from the mold whereas only the body  8  of the parison  4  is engaged in the molding cavity  3 . 
         [0022]    The body  1  is arranged in the form of a tubular body through the entire height of which there passes a bore  9  into which there opens, for example toward its upper end, a radial duct  10  that can be coupled to a source of fluid at high pressure (typically of the order of 40×10 5  Pa). In general (in the case of a stretch-blow-molding molding process), the bore  9  has a diameter large enough to accommodate a stretching rod  11  passing through it from top to bottom, the stretching rod being supported moved by means which have not been depicted in order to stretch the parison  4  axially at a point in the stretch-blow-molding process, generally at the beginning thereof. 
         [0023]    The upper and lower ends of the bore  9  are shaped to guide the stretching rod in a sealed manner in its axial movement. 
         [0024]    This being the case, the body  1  is, in its entirety, in the form of a stationary tubular pipe which has an annular transverse face  12  (through which the stretching rod  11  passes) and which, because the body  1  and the mold  2  are supported by the same support structure, is a fixed distance D from the wall  6  facing it of the mold  2 . 
         [0025]    The body  1  coaxially and with sliding supports movable equipment  13  comprising a blowing nozzle  14 . 
         [0026]    Although the movable equipment can be moved and the nozzle held in the blowing position in any way (using mechanical, electromagnetic, pneumatic, means), it is preferable for this to be done pneumatically. To these ends, respective portions facing one another belonging to the body  1  and to the movable equipment  13  are arranged as an at least single-acting pneumatic actuator  21  for moving the movable equipment  13  along the body  1  toward the mold and for keeping the nozzle in sealed communication with the neck  7  of the parison  4 . 
         [0027]    In the simple and preferred embodiment illustrated in  FIG. 1 , the movable equipment  13  surrounds the body  1  and the pneumatic actuator  21  comprises a stationary piston  15  formed by a part of increased diameter, or a widening, of the body  1  and a movable chamber  16  formed by a part of increased diameter of the movable equipment  13  which in sealed fashion houses the piston  15 . A duct  17  opens laterally into the upper part of the body  1  and, running parallel to the axial bore  9 , opens radially from the lateral wall of the body  1  into the chamber  16  level with the upper face of the piston  15 , so as to drive the movable equipment  13  downward. 
         [0028]    The pneumatic actuator  21  formed by the piston  15  and the chamber  16  is preferably a double-acting actuator so that the movable equipment  13  can be raised back up, after blowing, also pneumatically. To these ends, a second duct  18  is provided in the body  1  with an arrangement similar to that of the duct  17 , except that it opens at the bottom into the chamber  16  in the lateral face of the body level with the upper face of the piston  15 . 
         [0029]    According to the invention, the nozzle  14  is defined, laterally, by a sleeve-shaped terminal part  19  of the movable equipment  13  and its end wall is formed solely of the aforesaid transverse face of the body  1 . Furthermore, the lateral interior wall  20  of the sleeve is shaped in such a way that fluid pressure within the nozzle does not give rise, on this lateral interior wall  20 , to any reaction force component directed away from the wall  6  of the mold  2  (that is to say upward in  FIG. 1 ). 
         [0030]    In other words, the only surface subjected, when a fluid pressure is present, to an upwardly-directed force is the transverse face  12  of the body  1  which, because of the structure of the system, is stationary with respect to the wall  6  of the mold  2 , whereas all the surfaces of the sleeve  19  are subjected to no upwardly-directed force component. Hence, when the blow-molding fluid is introduced, the nozzle does not tend to be pushed up from its functional position and remains pressed against the wall  6  of the mold  2 , and remains so irrespective of the pressure of the fluid let in. 
         [0031]    One important consequence of this is that the nozzle is held in the functional position during blow-molding by applying a relatively low retaining force to the movable equipment. In practice, what this means is that the pneumatic actuator  21  can be supplied with a relatively low pressure fluid (typically a fluid at the industrial pressure of 7×10 5  Pa commonly available in workshops), instead of the very high pressure (typically 40×10 5  Pa) of the blow-molding fluid hitherto used for this purpose. 
         [0032]    In the exemplary embodiment illustrated more specifically in  FIG. 1 , the lateral interior wall  20  of the sleeve  19  is typically a cylinder of revolution, with a diameter significantly greater than the exterior diameter of the neck  7  of the parison, which means that the transverse face  22  (which is fitted with an annular seal  23 ) of the sleeve bears in sealed contact with the wall  6  of the mold when the nozzle is brought into the functional position, the lateral interior wall  20  being distant from the neck  7  (bell-nozzle). 
         [0033]    For guidance, it will be noted that the sleeve  19  preferably consists of an assembly of several parts so that a thin and elastic diaphragm  28 , pierced for the passage of the stretching rod  11  and of the blow-molding fluid is held inside the nozzle. The purpose of this diaphragm is to bear elastically against the mouth  24  of the neck  7  so as to keep the parison  4  in the correct position in which it is more or less coaxially aligned with the stretching rod  11  and prevent it from lifting when the high-pressure blow-molding fluid is introduced. 
         [0034]    It may be emphasized that the arrangement just described is structurally very simple and that the movable equipment  13  may be of small height (the sleeve  19  following on immediately from the part defining the chamber  16  of the pneumatic actuator  21 ): the movable equipment  13  therefore has low inertia, something which is advantageous from the viewpoint of a system that operates at high throughput rates. 
         [0035]    It will also be noted that the body  1 , which is the part which has the greatest vertical development, is a stationary part which can be secured to the support structure in any appropriate way able to give it perfect stability. The movable equipment  13  that it slideably supports is therefore assured of precise guidance, in spite of the functional clearances necessary for it to move, and this guidance, combined with the relatively short travel, means that the nozzle can be positioned accurately in the functional blowing position. 
         [0036]      FIG. 1  illustrates the blow-molding system in a non-functional position, with the movable equipment  13  in the raised position in which the transverse face  22  of the sleeve  19  and the seal  23  are located above the level of the mouth  24  of the neck of the parison  4 . The movable equipment  13  is brought into and held in this position by injecting low-pressure fluid into the duct  17  (arrow  25 ). 
         [0037]      FIG. 2  illustrates the blow-molding system in the functional position, with the movable equipment  13  in the lowered position in which the seal  23  is clamped between the transverse face  22  of the sleeve  19  and the wall  6  of the mold  2 , thus providing sealing. The movable equipment  13  is brought into and kept in this position by injecting low-pressure fluid into the duct  18  (arrow  26 ). The high-pressure blow-molding fluid can then be introduced (arrow  27 ) into the bore  9  and the nozzle. 
         [0038]    The arrangements according to the invention have just been described more specifically in the context of a blow-molding system equipped with a bell-shaped nozzle, this type of system being in widespread use because of its attractive advantages. However, the arrangements according to the invention are not exclusive to the use of a bell-shaped nozzle and may also be associated with other types of nozzle (nozzles engaged inside the neck of the parison, nozzles butting against the mouth of the neck of the parison). 
         [0039]    By way of example,  FIG. 3  illustrates a blow-molding system arranged in accordance with the invention and which again adopts the same structure as the system of  FIG. 1 , except for the shaping of the nozzle. In  FIG. 3 , the nozzle  14 ′ is designed to be engaged inside the neck  7  of the parison  4  and to these ends its terminal part is shaped in the form of a downwardly-projecting annular skirt  29 , the external face of which is frustoconical and able to be forcibly inserted against the interior edge of the mouth  24  of the neck  7  of the parison  4 . The skirt  29  is borne by an end wall  30 , running transversely. The remainder of the movable equipment  13 ′ may be identical to that in  FIG. 1 . 
         [0040]    In such an embodiment, the pressure of the blow-molding fluid is applied to the internal face of the end wall  30  so that the corresponding force combines with the force developed by the pneumatic actuator  21  to keep the nozzle pressed against the mouth  24 . 
         [0041]    In an embodiment variant, the end wall  30 , instead of being transverse, could be frustoconical with its conicity facing downward, with similar results. 
         [0042]    An arrangement more or less analogous with that of  FIG. 3  could be adopted in the case of a nozzle able to be butted against the mouth  24 . 
         [0043]    In the above description, the arrangements according to the invention call for movable equipment  13  arranged externally to the stationary body  1 , because that is the arrangement that is the simplest and easiest to produce with parts of relatively simple shapes that are inexpensive to machine. Furthermore, this arrangement allows the chamber delimited by the nozzle, when the latter is in a functional position, to have the smallest possible volume compatible with the dimensions of the neck of the parison, thus playing a part in saving on blow-molding fluid: indeed it should be noted that it is blow-molding air which is conveyed into the volume of the nozzle and which adds to the volume needed to form the receptacle. Thus, if the volume of the chamber delimited by the nozzle is of the order of 30 cm 3 , blow-molding at a pressure of 40×10 5  Pa entails compressing 12 liters of additional air simply to fill the nozzle. 
         [0044]    However, this technical solution is not the only conceivable one and, should it prove necessary to do so, although this would be less advantageous in terms of air consumption, it would be possible to use movable equipment internal to the stationary body, as illustrated in  FIG. 4 , in conjunction with a nozzle of the bell-shaped nozzle type. It should be noted that the nozzle could be of the type  14 ′ shown in  FIG. 3 . 
         [0045]    The stationary body  1 ′ is arranged at its lower end in a widened form with a wall  31  which acts internally as a guide for the movable equipment  13 ″ that it houses. The wall  31  is itself locally widened (at  32 ) to define an annular chamber  16 ′ at the ends of which there open two ducts  17 ′,  18 ′ hollowed from the wall  31 . The movable equipment  13 ″ is in the overall form of a tubular member that is a cylinder of revolution comprising an external annular projection forming a piston  33  housed in sealed fashion in the chamber  16 ′ defined by the wall  32 . At its lower part, the aforesaid tubular member is arranged as illustrated in  FIG. 1  to form the nozzle  14  analogous with the one described above. It will be noted that, in this embodiment also, the pressure of the blow-molding fluid generates, on the upper annular transverse wall  34  of the movable equipment  13 ′, a downwardly directed force, which plays a part in keeping the nozzle pressed in sealed fashion against the wall  6  of the mold.