Abstract:
A device for blow-molding or stretch blow-molding of thermoplastic material performs, the mold including two half-molds and a mold base mutually mobile through actuating devices controlled by a fixed cam. A link rod device with three degrees of freedom in rotation is provided between one half-mold such that upon opening the two half-molds are spaced apart from each other without moving the base, then so that the base moves axially while the two half-molds continue to be mutually and completely spaced apart, and vice-versa.

Description:
FIELD OF THE INVENTION 
   The present invention relates to improvements made to the devices for blow-molding or stretch blow-molding of containers starting from preforms made of thermoplastic, said devices comprising a mold in three parts, namely two half-molds for the body of the container and a mold base for the base of the container, the lower parts of the two half-molds and the upper part of the mold base comprising means which can interlock, in the closed position of the mold, to provide the axial rigidity of the mold in the presence of the blow-molding pressure, the two half-molds being designed to be moved relative to one another, between an open position and a closed position, under the action of actuating means controlled by a fixed cam, this device comprising connection means between at least one half-mold and/or said means for actuating said half-molds, on the one hand, and the mold base, on the other hand, so that the movement of the mold base is controlled by the movement of at least one half-mold and/or said actuating means such that:
         during opening of the mold, said actuating means start to move said half-molds apart until said interlockable means are freed from one another, while said connection means remain inoperative and the mold base remains in its position, and then, while said actuating means continue to move the two half-molds apart, the connection means become operational and move the mold base so as to separate it axially from said half-molds;
 
and such that
   during closing of the mold, said actuating means start to bring the two half-molds together at the same time as said connection means control the axial movement of the mold base until it reaches its completely raised position, and then, with said connection means becoming inoperative, said actuating means finish bringing the two half-molds together, with engagement with the interlockable means mechanically and axially securing the two half-molds and the mold base.       

   DESCRIPTION OF THE PRIOR ART 
   For blow-molding or stretch blow-molding of containers such as bottles starting from heated preforms made of thermoplastic, such as PET, it is known practice to use molds consisting of two half-molds which can move relative to one another between an open position (loading/unloading of the mold) and a closed position (blow-molding or stretching/blow-molding). In particular, it is known practice to design the two half-molds in such a way that they can rotate relative to one another (hinged molds). Many embodiments of such molds, with their closing means and their means for locking them in the closed position, are known (see, for example, FR 2 646 802, FR 2 653 058, FR 2 659 265, FR 2 681 552, FR 2 733 176, FR 2 793 722, all in the name of the Applicant). 
   Constructing the mold as only two half-molds is possible when the container to be manufactured has a relatively simple shape and can be easily extracted from the mold. This is particularly the case when the base of the container does not have pronounced reliefs (semicircular base or flat base, for example). 
   The two half-molds are actuated mechanically during closing and opening with the aid of a roller, attached to the half-molds by transmission means, which engages with a cam arranged laterally and having the required profile. There is often a set of several molds mounted on a common rotating support (carousel) and the cam is mounted laterally as a fixed cam. 
   By contrast, when, as is found in the majority of cases, the base has a complex configuration (petaloid base or rounded base with an inwardly directed convexity, for example), it is not possible, without deformation and therefore without damage, for the container to be extracted from a mold in two parts. That is why use is made of molds in three parts to manufacture such containers having bases of complex shape, these molds comprising two half-molds which can be moved apart/brought together (rotatably articulated, in particular) for molding the body of the container, and a mold base which can be moved axially for molding the base of the container. 
   As is thus conventional, the actuation of the mold base is passed over to specific means which are equipped with their own roller engaging with a separate cam. 
   It should additionally be emphasized that, in order to mechanically reinforce the mold when it is subjected to the blow-molding pressure, a means of mechanically securing the two half-molds and the mold base when the mold is in the closed position has been provided. To this end, the lower part of the two half-molds and the upper part of the mold base are mutually overlapping and are equipped with interlockable means, such as, for example, peripheral groove/peripheral projection, for example in the form of an annular projection fitting into the groove. As a result, the axial movement of the mold base can only take place when the two half-molds are in a sufficiently parted position in which the interlocked means are released. It is therefore necessary for the movements of the half-molds and of the mold base to take place in a highly precise sequence. 
   These requirements lead to the necessity of a rigorous relative positioning of the two cams respectively controlling the movements of the half-molds and of the mold base, with the use of adjusting means for ensuring the required precision of this relative positioning. 
   Finally, the current design of the molding devices with a mold in three parts, employing two cams controlling the movements of the half-molds and of the mold base respectively, proves to be complex and space-consuming owing to the presence of the double actuating means, and costly to install and to maintain in order to ensure the correct mutual positioning of the two cams, on which the perfect synchronism of the movements of the three constituent parts of the mold is dependent. 
   To that should be added the problems caused, within rotating systems having multiple molds, by the rollers coming into contact with the fixed cams mounted laterally and by the rebound phenomena which ensue and which generate considerable vibration. Now, in a current three-part mold arrangement, there are at least two rollers which come into contact with two respective cams for each mold, which leads to a cumulation of the vibratory phenomena. 
   The search for increasingly higher operating speeds, leading to increasingly greater production rates, not only leads one to strive to achieve a structural simplification enabling inertia to be reduced but also to reduce as completely as possible the vibratory phenomena accompanying the rollers when they come into contact with the corresponding cam. 
   SUMMARY OF THE INVENTION 
   It is against this background that the invention proposes improving the molding device presented in the preamble, which, being arranged in accordance with the invention, is characterized in that the connection means comprise a connecting rod whose ends are provided with coupling means having three rotational degrees of freedom so as to connect it to the half-mold and/or to said means for actuating said molds and so as to connect it to the mold base, respectively, and in that the connection of the rod with the mold base is arranged so as, during opening of the mold, to pivot freely under the entraining action of the aforesaid half-mold and/or of said means for actuating said half-molds while the two half-molds are parting until a predetermined angular value is obtained, and then to bear against an abutment attached to the mold base when the half-molds are parting at said angular value and/or when said actuating means are in a position in which the half-molds are parting at said angular value, and finally to push the mold base away axially when the two half-molds complete their opening travel, and vice versa during closing of the mold. 
   Preferably, because it seems to be the simplest to implement, provision is made for said connection means to be interposed between one of the half-molds and the mold base. In particular, when each half-mold consists of a half-mold-carrier unit detachably supporting a metal block in which a half-cavity of the container body is machined, it is preferable for the connection means to be interposed between a mold-carrier unit and the mold base. Likewise, when the mold base comprises a block which is interchangeable to suit the shape of the container, which block is solidly attached to a supporting structure, it is then preferable for the connection means to be interposed between one of the half-molds (or one of the mold-carrier units) and the supporting structure. 
   By virtue of these provisions, it is possible to dispense with the independent means for actuating the mold base, which, on the one hand, simplifies the overall architecture of the machine and, on the other hand and above all, prevents the long and minute adjustments required for the correct mutual positioning of the two cams. Moreover, each mold now constitutes a complete functional unit which is mounted and installed as such and which is associated only with a single source of movement in the form of the single cam. 
   Finally, and this is not the least of the advantages, dispensing with the independent control of the mold base with its own cam makes it possible to considerably reduce the vibration-related problems mentioned above. It thus becomes possible to envisage operating such a device at substantially higher speeds than those used to date. 
   In a simple manner, the aforesaid coupling means having three rotational degrees of freedom are preferably spherical ball joint couplings or comprise, for one of them, a spherical ball joint coupling and, for the other, a universal coupling. 
   In a simple exemplary embodiment, the lower end of the rod is connected via said spherical ball joint coupling to a link rotatably articulated on a radial arm attached to the mold base, said abutment consisting of a portion of said arm. 
   Although it is possible to envisage various configurations, it is nevertheless advantageous to arrange for the link to be articulated on the radial arm by a pin perpendicular to the axis of the mold; provision can then be made in particular for the link to be made in the form of a solid shoe to which the respective coupling is connected. 
   Advantageously, elastic return means are coupled to the mold base to assist the axial movement of the mold base from its open position to its closed position. 
   By virtue of the provisions according to the invention, it is possible to set up a simple structure employing only a small number of component parts which do not include any frictional parts, which avoids wear and eliminates the appearance of play. The forces transmitted are relatively small and the relatively low masses of the moving parts lead to low inertia: such a mechanism is therefore capable of operating at high speeds, making it conceivable to raise the operating speeds of the molding installation. 
   Constructing the moving link in the form of a solid shoe leads to a mechanically strong structure capable of withstanding, without deformation, the thrust impacts marking the transition between the movement of the half-molds alone and the movement of the half-molds accompanied by the axial movement of the mold base. 
   Finally, although the hinge pin of the link, or of the shoe, is advantageously perpendicular to the axis of the mold, the position of this axis is in truth immaterial: it follows that the positioning of the radial arm does not have to be of very high precision, which simplifies the construction. 
   The provisions of the invention find a preferred, although not exclusive, application in the molding devices having a mold of the hinged type in which the two half-molds are mutually pivoting. 

   
     BRIEF DESCRIPTION OF THE DRAWINGS 
     The invention will be better understood on reading the detailed description which follows of certain preferred embodiments given solely by way of nonlimiting examples. In this description, reference will be made to the attached drawings, in which: 
       FIG. 1  is a simplified schematic view, in axial section, of a mold in three parts toward which the invention is directed; 
       FIGS. 2A to 2C  are perspective views showing one of the half-molds of  FIG. 1  equipped according to the invention in three different operational positions respectively; 
       FIG. 3  is a perspective view illustrating a variant of the arrangements shown in  FIGS. 2A to 2C ; and 
       FIG. 4  is a perspective view illustrating a variant of the arrangements shown in  FIG. 3 . 
   

   DETAILED DESCRIPTION OF THE INVENTION 
   Referring first of all to  FIG. 1 , the invention aims to improve the devices for blow-molding or stretch blow-molding of containers starting from preforms made of thermoplastic, such as PET, which comprise a mold  1  in three parts, namely two half-molds  2  and a mold base  3 . 
   The two half-molds  2  each include an imprint  4  of half the body of the container to be manufactured (for example a bottle) and can be moved apart or brought together transversely. In the example illustrated, the two half-molds are designed with external lugs  6  so that they can be mounted on a common pin  5  and can be closed or opened by rotation about this pin (hinged mold). If the half-molds comprise respective mold-carrier units, the lugs  6  are formed on the latter. However, the improvements made by the invention, which will be explained later, may nevertheless be employed with molds of different design, for example with half-molds which can move by transverse translation. 
   Traditionally, the opening and closing of the half-molds  2  is controlled mechanically, by means consisting of articulated arms driven by a roller engaging with a fixed cam. Such means, not shown in  FIG. 1 , are described and illustrated, for example, in documents FR 2 653 058, FR 2 681 552 or FR 2 793 722. 
   The mold base  3 , the third part of the mold  1 , comprises the complex-shaped imprint  7  of the base of the container to be manufactured and can be moved axially along the axis  8  of the mold (axis of the container to be manufactured). 
   To provide a mechanical assembly of the mold base  7  with the two half-molds, in the closed position of the mold, which is capable of withstanding the forces generated by the high blow-molding pressure (for example 40×10 5  Pa), a secure connection is provided by interlockable means, such as groove/projection means. In the example illustrated in  FIG. 1 , the mold base  3  comprises a radial projection  9  extending over all or part of the lateral periphery of the mold base, in the upper part thereof covered by the lower parts of the half-molds  2 ; for their part, the half-molds  2  are each provided with a mating groove  10 . 
   In such a configuration, it is necessary, in order to open the mold, to start opening the half-molds  2  on their own, the mold base  3  remaining in place, until the grooves  10  have freed the projection  9 ; then, and only then, can the mold base  3  be moved axially while the half-molds  2  complete their respective movements. In order to close the mold, it is necessary, conversely, to return the mold base  3  axially while the half-molds  2  begin their movement toward one another, so that the mold base  3  is in place while the two half-molds  2  complete their movement toward one another and while the grooves  10  cover the projection  9 . 
   In order to eliminate the specific roller/fixed cam control used up until now for moving the mold base  3  and to avoid the difficulties brought about by the mutual positioning adjustments of the two cams controlling the half-molds  2  and the mold base  3 , respectively, so as to obtain perfect synchronization of the movements described above, connection means are provided between at least one half-mold and/or said means for actuating the half-molds  2 , on the one hand, and the mold base  3 , on the other hand, so that the above-described sequences of synchronized movements of the half-molds  2  and of the mold base  3  are retained both during the opening and closing of the mold. 
   According to the invention, provision is made for the connecting means to comprise a connecting rod  13  whose ends are provided with coupling means having three rotational degrees of freedom so as to connect it to the half-mold and/or to said means for actuating said half-molds and so as to connect it to the mold base, respectively, and the connection of the rod  13  with the mold base  3  is arranged so as, during opening of the mold, to pivot freely under the entraining action of the aforesaid half-mold and/or of said means for actuating said half-molds while the two half-molds are parting until a predetermined angular value α is obtained, and then to bear against an abutment attached to the mold base  3  when the half-molds  2  are parting at said angular value α and/or when said actuating means are in a position in which the half-molds are parting at said angular value α, and finally to push the mold base  3  away axially when the two half-molds  2  complete their opening travel, and vice versa during closing of the mold. 
   A simple embodiment consists in interposing said connection means between one of the half-molds and the mold base, and in arranging them in the following way, for example. 
     FIG. 2A  shows an external view of one of the half-molds  2  (there can be seen the lugs  11  on which are articulated the actuating arms (not shown) driven by the roller moved by the fixed cam discussed above). 
   The connection means  12  interposed between the half-mold  2  and the mold base  3  comprise a connecting rod  13  provided at its two ends with spherical ball joints in order to respectively constitute a coupling  14  with the half-mold  2  and a coupling  15  with the mold base  3 . 
   Preferably, the two couplings  14 ,  15  are ball joint couplings. If appropriate, one of the ball joints may be replaced by a universal joint; alternatively, one or both of these couplings may be replaced by any device providing the three degrees of freedom required to perform the abovementioned sequences. 
   The coupling  14  is situated on the outer wall of the half-mold  2 , at a point on this wall which is relatively distant from the axis of rotation of the pin  5 , so as to benefit from sufficient amplitude of movement. 
   The coupling  15  is advantageously provided not on the mold base itself but on the end of a radially extending arm  16  attached to the mold base  3 , so that the rod  13  extends approximately parallel to the contact face  17  (parting line) of the half-mold  2 . 
   In order for the movements indicated above to be broken down sequentially, the coupling  15  is attached to a moving part or link  18  which, in the example illustrated in  FIG. 2A , is produced in the form of a solid shoe housing the spherical socket accommodating the spherical ball attached to the rod  13 . The shoe  18  is rotatably articulated on the end of the arm  16  by a pin  19  which, in the example illustrated, is substantially perpendicular to the axis  8  of the mold (or to its pivot pin  5 ). 
   Furthermore, elastic return means (spring  20 ) are associated with the mold base  3  in order to return the latter to the closed position. In  FIG. 2A , the spring  20  is interposed between a frame part  21  of the molding device and a slide  22  attached to the mold base  3  and cooperating with a fixed guide  23  in order to guide the mold base  3  in its axial movement. 
     FIG. 2A  shows the half-mold  2  and the mold base  3  in the closed position (position illustrated also in  FIG. 1 ). 
   When starting to open the half-molds  2  by pivoting them about their pin  5 , one of these half-molds causes, by way of the rod  13 , the shoe  18  to rotate about its pin  19 , as illustrated in  FIG. 2B . However, the articulated connection between the shoe  18  and the arm  16  is designed in such a way (for example, as illustrated, the pin  19  is raised with respect to the arm and the shoe  18  possesses a lower face having a cant  24 ) that the shoe  18  can rotate freely. 
   Consequently, during this phase of movement of the half-molds  2 , the mold base  3  is not subjected to any entraining force and it remains in its closed position, retained by the spring  20 . 
   When the two half-molds  2  have passed through a predetermined angular range α ( FIG. 2B ), it is ensured that the grooves  10  have released the projection  9 . At that moment, the face  24  of the shoe  18  comes into contact with a bearing surface  25 , forming an abutment, of the arm  16 , as illustrated in  FIG. 2B . 
   From this moment, the shoe  18  continues to be pushed away by the rod  13 , but can no longer swivel with respect to the arm  16 . The assembly formed by the rod and the shoe thus constitutes a strut bearing on the arm  16  and exerting thereon a downwardly directed force component. The mold base  3  is thus entrained axially in the direction of opening, as illustrated in  FIG. 2C . 
   In the opposite direction, in order to close the mold, the half-mold  2  entrains, by way of the rod  13 , the mold base  3  which arrives in its raised position when the half-mold  2  still has an angular range α to pass through. At that moment, the shoe  18  leaves its bearing point on the abutment  25  of the arm  16  and, with the mold base  3  then being detached kinematically from the half-mold  2 , the latter completes its closing travel alone, with its groove  10  coming to cover the projection  9  on the mold base. During the first phase of the movement, the return force that the spring  20  exerts on the mold base  3  in order to tend to lift the latter toward its raised position for closing the mold keeps the abutment  25  of the arm  16  in contact with the shoe  18 , with the result that the mold base  3  accompanies the movement of the half-mold  2 . 
   Of course, numerous variants are conceivable. It should be emphasized in particular that the position of the pin  19  defining the axis of rotation of the shoe  18  is immaterial, which offers the advantage that the positioning of the arm  16 , during the manufacturing operation, does not have to be of high precision. By way of example,  FIG. 3  (in which the mold  1  is shown in its entirety, in perspective, at a different angle of view) illustrates the coupling  15  mounted at the end of an elongate link  26 , itself connected at its other end to the arm  16  attached to the mold base  3  so that this link is able to rotate by means of a pin  27  approximately parallel to the axis  8  of the mold. Similarly,  FIG. 4  illustrates another embodiment modeled on that of  FIG. 3  and in which the connecting rod  13 , constituting the aforesaid connection means, is interposed between the link  26  and an arm  28  (only partly visible) rotatably connected to the lugs  11  (the coupling  14  with the arm  28  being hidden).