Abstract:
A rotary machine for producing recipients made of a thermoplastic material by drawing and blowing performs by a molding device which is provided with an openable mold and a movable drawing rod, a device for supporting and driving the drawing rod, which is embodied in such a way that it is mechanical and includes a power take-off device for generating, on the basis of a monodirectional rotary rotation, two rotary motions of given angular amplitudes of a rocker in two predetermined angular places of a merry-go-round path and a device for converting the two rotary movements of the rocker into two opposite linear alternately descending and ascending displacements of a drive unit connected to the drawing rod.

Description:
FIELD OF THE INVENTION 
   The invention relates to the field of machines for producing containers made of thermoplastic by stretching and blow molding a preform which is produced beforehand by injection molding. These machines are used in particular to produce containers, such as bottles, from polyethylene terephthalate (PET). 
   In such a machine, substantially tubular preforms are used, which are closed at one of their axial ends and of which the other axial end is open and already has the final shape of the neck of the final container. 
   Each preform is heated in a thermal conditioning oven to heat the body of the preform to a temperature above the glass transition temperature of the thermoplastic. The preform thus conditioned is transferred to a blowing mold in which a cavity in the shape of the container to be obtained is bounded. The preform is arranged in the mold so that its open end extends outside the mold. Thus, a blow molding device can be conveyed to the neck of the preform in order to inject pressurized air into the preform. Simultaneously, a stretch rod is introduced axially into the preform so as to bear against the closed end at the bottom of the preform. The stretch rod thereby serves to efficiently control the axial deformation of the preform during the blow molding of the container. 
   The invention can be implemented more particularly in a stretch-blow molding machine of rotary type comprising several molding devices mounted on the periphery of a turntable which is continuously rotated about its axis. Each molding device comprises in particular an openable mold, a blow molding device and a stretching device. 
   DESCRIPTION OF THE PRIOR ART 
   According to a known design, the movement of the stretch rod is controlled by a pneumatic cylinder which supplies the power necessary for the movement of the rod, but the stretching rate is controlled by a roller and cam device which serves to perfectly synchronize the axial position of the stretch rod according to the angular position of the blow molding station concerned about the axis of rotation of the turntable. 
   These systems, widely developed today, provide full satisfaction in terms of the operation of the blow molding process. 
   However, the known systems have a high total power consumption. In fact, one of the main factors in the power consumption of the machines concerned consists of the pressurized air which is commonly employed for miscellaneous functions. These include the pneumatic control of the cylinders actuating the stretch rod of each blow molding station, which must be supplied with pressurized air both for lowering and for raising the rod. 
   Solutions have certainly already been proposed to try to reduce the consumption of pressurized air necessitated by the actuation of the stretch rod, for example, by actuating the pneumatic cylinder only for the lowering of the stretch rod and by causing the rod to rise under the action of the blowing pressure prevailing in the container at the end of the blow molding process (document FR-2 814 392). 
   The pure and simple elimination of the pneumatic control of the stretch rod has also been considered, and its replacement by a magnetic control system (document FR-2 798 093). 
   However, these attempts have not proved advantageous, and in most present day machines, the stretch rod continues to be actuated pneumatically, both for lowering and for raising. 
   SUMMARY OF THE INVENTION 
   It is therefore an object of the invention to propose an improved but simple solution which leads to a total eradication of the pneumatic control of the stretch rods and which consequently leads to a smaller pneumatic installation within the machine. 
   For these purposes, the invention proposes a machine for producing containers made of a thermoplastic by stretching and blow molding preforms, this machine comprising a continuously rotating turntable supporting at least one molding device comprising an openable mold and a stretch rod which can be sequentially moved, by support and driving means, along the axis of the mold to stretch the preform during the container production operation, which machine, being designed according to the invention, is characterized in that the means for supporting and driving the stretch rod are mechanical means which comprise:
         power takeoff means functionally associated with said turntable and able to generate, based on the continuous unidirectional rotation of the turntable, two rotary movements of given angular amplitudes of a rocker occurring at two respective predetermined angular locations of the circular route of the turntable, and   movement conversion means able to convert said two rotary movements of given angular amplitudes of the rocker into two alternately descending and ascending opposite linear movements of a drive member along a route substantially parallel to the axis of the mold, said drive member being connected to the stretch rod.       

   The invention is based on the simple but hitherto unexploited fact that the rotating turntable represents a source of movement from which it is possible, by purely mechanical means, to derive the movements necessary to actuate the stretch rods. This addition of auxiliary movements obviously has repercussions on the rotary drive of the turntable, and it is accordingly necessary to provide motor drive means dimensioned commensurately. However, the additional electric power required for the proper drive of the turntable remains minor compared to the cost of the pneumatic installation for driving all the stretch rods (in particular, the air compressor becomes less powerful, hence smaller and less costly). 
   In a preferred embodiment due to its structural simplicity, the power takeoff means comprise:
         fixed cam means extending at least in a circular arc, and advantageously circular, and coaxial with the turntable, having at least two bosses at the respective predetermined locations for controlling the movements of the stretch rod, and   a rocker with at least one idler roller supported in a freely rotating manner about a vertical axis by the turntable and driven thereby along the cam means, the rocker being able to be rotated over a predetermined angular range when the idler roller passes each boss of the cam means.       

   In this case, a practical example of implementation consists in that:
         the cam means comprise two superimposed fixed cams, these cams comprising, for said each predetermined location, two respective bosses arranged angularly offset to one another, and   the rocker comprises two pairs of two idler rollers, vertically offset to one another for respectively cooperating with said two cams, this rocker comprising two arms in the form of a cross integral with each other and supporting said rollers at their respective ends, the axis of rotation of the rocker coinciding with the intersection of said two arms,
 
whereby, at each of the abovementioned predetermined locations, the rocker, by passing over the two successive bosses of the cam means, rotates by 180°.
       

   In a concrete exemplary embodiment, said cams comprise respective cam surfaces which are cylinders of revolution and coaxial with the axis of the turntable and the rocker is moved within the cylindrical space bounded by the cams. 
   Also in a simple manner, the movement conversion means can then be arranged to comprise:
         a caliper formed from two arms hinged freely by one of their respective ends, these two arms being arranged in a substantially vertical plane,   the first of these arms having its other end hinged freely at a fixed point of the turntable and   the second of these arms having its other end hinged on a slide mounted on a guide parallel to the mold axis, said slide supporting said stretch rod,
           and a drive rod having a first of its ends made integral, via a rotary hinge with three degrees of freedom, with a rotary arm integral with the axis of the rocker and having its other end connected via a rotary hinge with three degrees of freedom to said first arm of said caliper.   
               

   According to the desired purpose, the arrangements according to the invention make it possible to completely eliminate the pneumatic actuation of the stretch rods, which is replaced by a totally mechanical drive actuated by the rotation of the turntable. 

   
     BRIEF DESCRIPTION OF THE DRAWINGS 
     The invention will be better understood from a reading of the detailed description that follows of certain embodiments provided exclusively as nonlimiting examples. In this description, reference is made to the drawings appended hereto in which: 
       FIG. 1  is a partial perspective schematic view of a machine for molding containers by stretch-blow molding, which is arranged according to the invention; 
       FIGS. 2A ,  2 B and  2 C are at larger scale only showing the supporting and drive means of the stretch rod respectively in a side view, a perspective view and, for part of said means, in a plan view, said means being shown in a first functional position (stretch rod in high position outside the mold); 
       FIGS. 3A and 3B  are views of the supporting and drive means of the stretch rod respectively in a side view and a front view, said means being shown in a second functional position (stretch rod in intermediate position, partially embedded in the mold); and 
       FIGS. 4A and 4B  are views of the supporting and drive means of the stretch rod respectively in a side view and a perspective view, said means being shown in a third functional position (stretch rod in the low position, completely embedded in the mold, causing the complete stretching of a preform). 
   

   DETAILED DESCRIPTION OF THE INVENTION 
   By first referring to  FIG. 1 , a machine for producing thermoplastic containers by stretch-blow molding of preforms, of the type considered by the invention, comprises a turntable  1  (shown schematically by its central drum  2 ) rotating continuously and unidirectionally at constant speed (arrow R) about its axis  3 . 
   The central drum  2  supports at least one molding device  4  (in practice a plurality of molding devices are distributed on the periphery of the drum). Each molding device  4  comprises an openable mold  5  (for example, as shown, a “billfold” or “jackknife” mold formed from two pivoting half-molds, optionally with a vertically moving bottom), said mold  5  being supported on the drum via a cradle  6 . 
   To make the drawing more legible, the high pressure pneumatic blowing means—which can expand a heated thermoplastic preform into a molded container—which are not directly involved, from the technical standpoint, in the design of the means of the invention, are not shown in  FIG. 1 . 
   Mechanical stretching means  7  comprise a stretch rod  8  which is movable axially and vertically (double arrow V) and sequentially, to lower it into the mold  5  in order to mechanically stretch the hot preform axially in synchronism with the blow molding and to extract it from the mold once the container is molded. 
   The stretching means  7  further comprise supporting and drive means  9  of the stretch rod  8  according to the required movement and sequence, said means  9 , according to the invention, being purely mechanical means as will now be explained. 
   Said supporting and drive means  9  of the stretch rod  8  comprise:
         power takeoff means  10  which are functionally associated with the turntable  2  and which are able to generate, based on the continuous unidirectional rotation R of the turntable  2 , two rotary movements of given angular amplitudes of a rocker  11 , these movements occurring at two predetermined respective angular locations of the circular route of the turntable, and   movement conversion means  12  able to convert the two abovementioned rotary movements of given angular amplitudes of the rocker  11  into two, respectively descending and ascending, opposed linear movements of a drive member  13  along a route substantially parallel to the axis of the mold  5 , said drive member  13  being connected to the stretch rod  8 .       

   Preferred embodiments of the abovementioned drive means will now be described with more particular reference to  FIG. 1  and also to  FIGS. 2A to 2C  which show these means in an isolated and clear manner respectively in a perspective view ( FIG. 2A ), a side view ( FIG. 2B ), and a partial plan view ( FIG. 2C ). 
   Firstly, as regards more particularly the power takeoff means  10 , they can be constituted as follows. 
   Cam means  14  extending at least in an arc of circle are supported fixedly on the frame (not shown) of the machine and coaxially with the turntable. Preferably, the cam means  14  are circular as shown in the figures, this embodiment currently appearing to be the simplest to implement. These cam means  14  comprise at least two bosses,  15  and  16 , angularly spaced from one another and located at respective predetermined locations for controlling the vertical movements, in one direction and in the other, of the stretch rod  8 . 
   The abovementioned rocker  11  is a rocker with idler roller that is supported in a freely rotating manner about a vertical axis  17 , by the turntable (for example, via a bracket or support column  20  which is integral with the drum  2  and which also supports all the abovementioned movement conversion means  12 ). The rocker  11  is thus driven along the cam means  14 , the rocker  11  being able to be rotated over a predetermined angular range when the idler roller passes each boss  15 ,  16  of the cam means  14 . 
   The angular distance between the abovementioned two predetermined locations of the turntable route, in other words, between the two bosses  15 ,  16 , is determined according to the speed of rotation of the turntable and the precise sequence according to which the stretching phase is to be conducted, so that—one complete turn of the turntable corresponding to one complete cycle of the stretch-blow molding process including the loading of the preform and the unloading of the molded container—the passage of the rocker  11  first on the first boss  15 , and then on the second boss  16  coincides, in the turntable rotation cycle, with the times when, in the container production cycle, the stretch rod  8  must first be lowered into the mold (stretching, in correspondence with the boss  15 ), and then raised outside the mold (end of blow molding, in correspondence with the boss  16 ), the blow molding process taking place in correspondence with the movement of the rocker  11  in the interval between the bosses  15  and  16 . 
   It is advisable for the rotation undergone by the rocker  11  during its passage on each boss  15 ,  16  to extend over an extended angular range, particularly for example over about a half-turn. 
   For this purpose, in a preferred exemplary embodiment, the following arrangement can be provided. 
   The cam means  14  comprise two fixed circular and superimposed cams  14 A,  14 B, the numeral  14 A denoting, for example, the lower cam and the numeral  14 B denoting the upper cam. For their part, the two bosses  15 ,  16  also consist in duplicate form, that is, the boss  15  comprises a first boss  15 A formed on the lower cam  14 A followed (in the movement direction of the rocker  11 ) by a second boss  15 B formed on the upper cam  14 B; the boss  16 , similarly comprises a first boss  16 A on the cam  14 A and a second boss  16 B on the cam  14 B. The angular distance between the two successive bosses  15 A,  15 B and the two successive bosses  16 A and  16 B is relatively small and just necessary to cause a double rotation of the rocker  11  which is arranged as follows. 
   The rocker  11  is equipped with two pairs of idler rollers respectively  18 A and  18 B which are vertically offset to each other in order to be located opposite the two cams  14 A,  14 B, respectively. More precisely, the rocker  11  comprises two arms  19 A,  19 B, integral with one another, arranged in a cross, offset to each other vertically, and supporting the pairs of rollers  18 A and  18 B respectively. The rocker  11  thus formed is idly supported, by its axis  17  coinciding with the intersection of the arms  19 A,  19 B, on a plate  21  integral with the column  20 . 
   Hence the rocker is in the form of a freely pivoting carriage, which bears on the two cams  14 A,  14 B via two respective rollers  18 A,  18 B. Every time a roller  18 A or  18 B is positioned in front of a boss  15 A,  16 A or respectively  15 B,  16 B, the rocker rotates about its axis so that the roller opposite the same arm bears against the respective cam, the corresponding rotation of the rocker being a quarter of a turn. Thanks to the use of two successive bosses  15 A,  15 B, respectively  16 A,  16 B, the rocker  11  is caused to rotate, on each occasion, by a half-turn, as desired. 
   Although the design of the cam means  14  and hence also that of the rocker  11 , can give rise to various embodiments, it is nevertheless advantageous for the two cams  14 A,  14 B to be made in the form of annular rings of which the inner face (that is in general the face forming a cylinder of revolution notwithstanding the presence of the abovementioned bosses) represents the rolling surface of the corresponding rollers of the rocker  11 . Accordingly, the rocker  11  moves within the cylindrical space surrounded by the cams. The overall system thus has a minimum size. Furthermore, the centrifugal force applied to the moving rocker helps to maintain it in contact with the rolling surfaces of the cams  14 A,  14 B. 
   It should be observed that in this embodiment and as shown better in  FIG. 2C , the pivot axis  17  of the rocker  11  moves along a circular route parallel to the rolling surfaces (to the exclusion of the bosses) of the cams  14 A,  14 B. When a roller bearing on a cam (for example, in  FIG. 2C , the roller  18 A bearing on the cam  14 A) reaches a boss (for example  16 A), the pivoting of the rocker  11  takes place with maintenance of the other roller bearing against the other cam (for example the roller  18 B bearing against the cam  14 B). However, the length of the half-arm  19 B supporting said roller  18 B is greater than the radial distance between the axis  17  and the surface of the cam  14 B. To allow the unrestricted pivoting movement of the rocker, a recess  22  is therefore provided in each cam  14 A,  14 B, located opposite the boss provided on the other cam. 
   As regards the movement conversion means  12 , various embodiments are feasible for converting the discontinuous unidirectional rotary movement of given angular amplitude (particularly over 180°) generated by the rocker  11  into a vertical linear reciprocating movement of the stretch rod  8 . Structurally simple means capable of reliably withstanding the high production rates of the type of machines concerned can advantageously be formed as follows. 
   A caliper  25  is formed by two arms  23 ,  24  freely hinged in rotation with one another and arranged in a substantially vertical plane. The first arm  23  has its other end freely hinged in rotation on a fixed part of the turntable, for example on a bracket  26  integral with the abovementioned column  20 . The second arm  24  has its other end hinged on the abovementioned drive member  13  formed as a slide moving freely on a vertical guide  27  (that is, parallel to the axis of the mold  5 ); the slide  13  supports the upper end of the stretch rod  8 . 
   In the exemplary embodiment shown more clearly in  FIG. 1 , the bracket or column  20  is arranged with a back  28  in the shape of a vertical plate that, at the top, supports the abovementioned plate  21  and which is, at the bottom, integral with an underframe  29  for fixing it to the drum  2  of the turntable. The assembly of the column  20  accordingly has the general shape of a reclining U within which a stiffener plate  30  is attached, at the top of which the abovementioned bracket  26  is fixed. Under the bracket  26 , the frontal edge of the stiffener plate  30  is arranged to constitute or to support the vertical guide  27  of the slide  13 . 
   The arrangement of the column  20  just described serves to combine the advantage of a very good stiffness of the column—which, on the one hand, guarantees proper support of the rocker  11  on the cam means  14  and, on the other, the indeformability of the guide  27  necessary for the stretch rod  8  to travel correctly along the axis of the mold—with the advantage of an integration of certain components in the structure of the column  20 , thereby providing a gain of space and of weight. 
   To convey the pivoting movement of the rocker  11 , located internally in the cam means  14 , to the caliper  25  and to the stretch rod  8  located outside said cam means  14 , a gear transmission is provided, with a first gearwheel  13  coinciding with the axis  17  of the rocker  11  and hence integral therewith in rotation and gearing with a second gearwheel  32  supported in free rotation by the plate  21 . The axis of the second gearwheel  32  rigidly supports a radial arm  33 . This arm  33  is therefore actuated with a pivoting movement, controlled by the rocker  11 , over an angular range determined by the gearing down ratio of the two gearwheels  31 ,  32 . In the example more particularly shown in FIGS.  1  and  2 A- 2 C, in which the rocker  11  pivots by a half-turn on the passage of each pair of bosses  15 A,  15 B and  16 A,  16 B, the gearing down ratio of the gearwheels  31 ,  32  is determined so that the end of the arm  33  makes a half-turn synchronized with the rocker  11  when the latter makes a half-turn. 
   A drive rod  34  is further inserted between the end of the arm  33  and an intermediate part of the arm  23  of the caliper  25 , with which it is integral via links  35  with three degrees of rotational freedom (for example, ball joints and/or universal joints). 
   The arm  33  coincides with the axis of the second gearwheel  32  so as to extend approximately into the plane defined by the caliper  25  when the rocker  11  moves outside the bosses  15 ,  16  of the cam means  14 . In this case, the rod  34  also extends into this plane. 
   The functioning of the mechanism just described clearly appears in the appended drawings. 
   In  FIGS. 2A to 2C , the angular positioning of the rocker  11  along the cam means  14  is such that the arm  33  extends toward the axis  3  of rotation of the turntable. In this position, the end of the arm  33  has driven the rod  34 , which, in its turn, has caused the raising of the arm  23  of the caliper  25  by rotation on the plate  26 . The caliper  25  is thus in a closed conformation, with the slide  13  conveyed to the top of the guide  27 . The stretch rod  8  is then in the raised position, outside the mold  5 . 
   In  FIGS. 3A and 3B , the rocker  11  is crossing a boss  15  or  16  and, more particularly, it is presumed to be at mid-pivot between the bosses  15 A,  15 B or respectively  16 A,  16 B. The arm  33  is then pivoted by 90° ( FIG. 3B ), the rod  34  is diagonally inclined and the slide  13  is at mid-distance of the guide  27 . The stretch rod is half engaged in the mold  5 . 
   In  FIGS. 4A and 4B , the rocker  11  has passed the previous boss  15  or  16  and has therefore completed its pivoting. The arm  23  is now rotated opposite the axis of the turntable so that the rod  34  pushes the arm  23  of the caliper  25  downward. The caliper  25  is thus opened to the maximum, the slide  13  being located at the bottom of the guide  27 . The stretch rod  8  is then embedded to the maximum in the mold. This is the situation also shown in  FIG. 1 .