WO2012016951A1

WO2012016951A1 - Forming machine equipped with a moulding unit having compensating means controlled by at least one automatically actuated valve

Info

Publication number: WO2012016951A1
Application number: PCT/EP2011/063222
Authority: WO
Inventors: Alexandre Toutoux
Original assignee: Sidel Participations
Priority date: 2010-08-03
Filing date: 2011-08-01
Publication date: 2012-02-09
Also published as: FR2963580A1; FR2963580B1

Abstract

The invention relates to a machine (14) for forming thermoplastic containers, comprising at least one moulding unit (16), each moulding unit (16) comprising: - a mould (20) made of at least two half-moulds (20A, 20B), each of which is supported on a carrier (28A, 28B); - at least two fluid-pressure compensating devices (40A, 40B) which are interposed between at least one carrier (28A) and the associated half-mould (20A), and which push the half-moulds (20A) from a pushed-back position into an advanced position in the direction of the other half-mould (20B); - each compensating device (40A, 40B) being connected to a pressurized-fluid source (45) with the interposition of an activation valve (48B), each activation valve (48B) being able to be controlled selectively between an open position and a closed position; characterized in that the activation valves (48B) are automatically actuated valves.

Description

"Forming machine equipped with a molding unit comprising compensation means controlled by at least one automatically actuated valve"

The invention relates to a machine for forming containers made of thermoplastic material.

The invention relates more particularly to a machine for forming containers made of thermoplastic material comprising at least one molding unit, each molding unit comprising:

a mold made of at least two half-molds delimiting a molding cavity when their two joint faces are transversely clamped against each other;

two supports each of which carries a half-mold, the two supports being movable between an open position in which the two half-molds are spaced apart from one another to allow the extraction of a finished container, and a position closed in which the two half-molds are supported against each other by their front face seal;

at least two fluid pressure compensation devices which are interposed between at least one support and the associated half-mold, and which push the half-mold from a retracted position to an advanced position in the direction of the other half-mold ;

each compensation device being connected to a source of pressurized fluid via pipes;

at least one activation valve which is interposed between the source of fluid under pressure and the second associated compensation device, the activation valve being capable of being selectively controlled between an open position in which the second compensation device is activated, and a closed position in which the second compensation device is deactivated. The forming of a final container is generally made from a preform which is heated to a so-called glass transition temperature. The preheated preform is arranged in the cavity of the mold, then at least one forming fluid is injected under pressure inside the preform to cause expansion of the preform until it is pressed against the walls. of the cavity to form the final container.

The pressure of the forming fluid injected into the cavity produces on each half-mold a spreading force which tends to separate the two half-molds from one another. This spreading force is transmitted to the support of the mold.

The spreading force is applied substantially to the center of gravity of the surface of the half cavity reserved in each mold. Thus, the point of application of the spreading force on the support of a mold depends on the size of the impression, that is to say of its shape and its dimensions.

In this type of machine, it is also provided compensation means which are interposed transversely between at least one half-mold and the associated support for pushing said half-mold transversely towards the other half-mold.

These compensation means make it possible to prevent the two half-molds from being able to deviate from one another during the injection of the press-forming fluid.

They also make it possible to press the faces facing the two half-molds against each other in order to reduce the thickness of the joint plane of the two half-molds. It has indeed been found that the presence of a thick bead of seal on the final container was capable of appreciably modifying the volume of the final container. In addition, this type of container with a marked joint plane has an unsightly appearance that is generally rejected by manufacturers. In known manner, in these forming machines, the molds carried by the supports are interchangeable. Thus, it is possible to make containers of various shapes using the same forming machine. The molds are changed by operators by the implementation of a mold changing process.

It is common that the same forming machine is brought to produce containers of different heights. However, the point of application of the spreading force on the support of the mold depends on the format of the cavity. Thus, the spreading force is not applied to the same height on the support of a mold that produces large format containers as on the support of a mold that produces small format containers.

But a back pressure that is not adapted to the size of the mold cavity may cause unwanted movements of the mold or the support. These undesirable movements can cause premature matting of some parts, or even a blockage of the molds on the supports, thus making the mold changing operation difficult.

To allow the counterpressure exerted by the compensation means to be adjusted to each cavity format, it is known to arrange a plurality of compensation means distributed over the height of the support.

Thus, when a large-format mold is arranged in the support, all the compensation means are activated simultaneously, whereas when a small-format mold is arranged in the support, only the compensation means which are arranged in the support are activated. same level as the cavity.

The selective activation operation of the compensation means is performed manually during the mold changing process. This has the effect of considerably slowing down the mold changing process. In addition, these manual activation operations are subject to error. To avoid these problems, the invention proposes a machine of the type described above, characterized in that a fluid discharge pipe directly connects the second compensation device with the source controlled in parallel with respect to the valve, the control conduit. evacuation being equipped with means preventing the flow of fluid from the source to the second compensation device.

According to other features of the invention:

the source is controlled via a control valve which is capable of occupying a first supply position in which the lines are fed with pressurized fluid, and an evacuation position in which the lines are connected. to the atmosphere;

the activation valve is a valve with automatic operation by receiving a control signal;

the forming machine comprises means for entering data relating to the format of the molds fitted to each molding unit, means for controlling the transmission of a control signal to each activation valve as a function of the data entered;

the forming machine comprises an electronic control unit which is arranged at a distance from the molding unit and which comprises the data acquisition means relating to the format of the mold in use, a memory in which is pre-recorded an array of association between the different data that can be entered and a selection of the activation valves to be actuated, means for transmitting the control signal to said activation valves;

the forming machine comprises a plurality of molding units, the electronic control unit being common to all the molding units;

the electronic control unit is able to simultaneously control other operating parameters. each molding unit according to the data entered;

the support which is equipped with the compensation means is also provided with means for automatically entering data relating to the format of the mold, the data relating to the format of the mold being carried by the half-mold associated with said support, the data being coded under a form readable by the data entry means;

each molding unit is provided with associated means of data entry;

the data are stored in a transponder which is carried by the half-mold, the input means being formed by a radio transceiver which is carried by the support associated with the half-mold.

Other characteristics and advantages of the invention will appear during the reading of the detailed description which follows for the understanding of which reference will be made to the appended drawings, among which:

- Figure 1 is a top view schematically showing a container manufacturing facility which comprises a forming machine made according to the teachings of the invention and having a plurality of molding units, and a control panel;

Figure 2 is a perspective view showing a portion of a molding unit of Figure 1;

FIG. 3 is an exploded perspective view showing a support, a mold carrier and a half-mold of the molding unit of FIG. 2;

- Figure 4 is a side view in longitudinal section which schematically shows the molding unit of Figure 2 in the closed position; FIG. 5 is a front view which represents the front face of the left support of FIG. 4, the support being provided with two superposed compensation chambers,

- Figure 6 is a view similar to that of Figure 5 which shows a variant in the arrangement of the compensation chambers;

FIG. 7 is a diagram showing in more detail the activation valve of the second chamber and the control valve of the controlled source of pressurized fluid.

In the remainder of the description, longitudinal, transverse and vertical orientations indicated by the "L, V, T" trihedron of FIG. 3 will be adopted without limitation.

In the remainder of the description, elements having similar, similar or identical functions will be designated by the same reference numbers.

FIG. 1 shows a plant 10 for manufacturing containers, in particular bottles, made of thermoplastic material from preforms or blanks (not shown).

The installation 10 includes in particular an oven 12 and a forming machine 14. The preforms are conveyed automatically in the oven 12 to be preheated to a sufficient temperature to allow their subsequent deformation in the forming machine 14.

The forming machine 14 comprises at least one molding unit 16 which carries out the forming operation which conforms the preform to the final container.

The forming machine 14 shown in FIG. 1 is intended to produce containers at the high speed chain. The duration of a forming cycle for each molding unit 16 is of the order of a few seconds. To further increase the production capacity of the containers, the forming machine 14 comprises a plurality of molding units 16 which are carried by a carousel 18. The carousel 18 is rotatably mounted about a vertical axis "A".

In the example shown in Figure 1, the carousel 18 here comprises twelve molding units 16. This figure is given as a non-limiting example. The molding units 16 are all identical. The description of a molding unit 16 which will follow will therefore be applicable to all other molding units 16.

As shown in FIG. 2, the molding unit 16 comprises a mold 20 which is made of at least two half-molds 20A, 20B delimiting a cavity 22 for molding when their two faces 24 of longitudinal vertical seams face one another. screws are tightened transversely against each other.

The mold 20 here has a cylindrical shape cut axially in two parts to form each half-mold 20A, 20B. Each half-mold 20A, 20B has a half-cavity of the cavity 22 of molding which is hollowed in a face 24 of joint.

Each half-mold 20A, 20B further comprises a rear face 26, visible in Figure 3, which is opposite to the face 24 of the joint, and which has generally the shape of a half-cylinder of revolution substantially coaxial with the vertical main axis of the molding cavity 22.

Each molding unit 16 comprises at least two supports 28A, 28B on each of which an associated half-mold 20A, 20B can be mounted. Thus, each support 28A, 28B carries a half-mold 20A, 20B associated.

The mold 20 currently mounted on the molding unit 16 will be referred to hereafter as "mold 20 in use".

The two supports 28A, 28B are movable between an open position, as shown in Figure 2, wherein the two half-molds 20A, 20B are spaced transversely from each other to allow the extraction of a finished container and a closed position, as illustrated in FIG. 4, in which the two half-molds 20A, 20B bear one against the other by their face 24 before joining.

In the example described here, the molding unit 16 is of the type known as a portfolio. The two supports 28A, 28B are connected in rotation by a hinge 30 of vertical axis. Each half-mold 20A, 20B may be removably attached to a support 28A, 28B associated.

According to a variant not shown of the invention, the two supports are mounted movable transversely relative to each other in a transverse direction.

The removable fastening means are not the subject of the present invention. They will not be described later. Examples of such fastening means are described in detail in WO-A-2008/000938 and EP-B-0.821.641.

The first support 28A is subsequently described with reference to FIG. 3. This description will also be applicable to the other support 28B.

The support 28A is formed by a casing which externally envelops the associated half-mold 20A. The support comprises in particular a front face 32 which faces the rear face 26 of the half-mold 20A.

The molding unit 16 is also provided with means (not shown) for regulating the temperature of the cavity 22.

In the embodiment shown in the figures, the temperature regulation means are formed by heat transfer fluid lines which are formed in the thickness of a mold carrier 34. Said mold carrier 34 is interposed between the half mold 20A and the front face 32 of the associated support 28A. The mold carrier 34 is permanently supported by the support 28A.

The half-mold 20A is intended to be received in a housing 36 of the associated mold holder 34 to occupy a mounted position. The housing 36 has a shape complementary to that of the rear face 26 of the half-mold 20A so that the rear face 26 of the half-mold 20A and the bottom of the housing 36 of the mold carrier 34 are in contact, pressed against each other, to allow heat transfer and a better distribution of efforts.

According to a variant not shown of the invention, the temperature control means are made directly in the mold, and the mold is directly mounted on the support without interposition of a mold carrier.

The molding unit 16 is also equipped with means (not shown) for injecting at least one fluid under pressure into the preform arranged in the mold 20.

These are blowing or stretch-blow molding means well known to those skilled in the art. For more information on this subject, refer for example to document FR-A-2.764.544.

The cavity 22 of the mold 20 is open towards the top when the mold 20 is joined. A preform (not shown), generally of thermoplastic material, previously heated is introduced into this cavity 22. A pressurized fluid is then injected into this preform to give it a desired shape corresponding to that of the cavity 22.

The invention is also applicable to molding units equipped with pressurized fluid filling forming means, with or without a prior blowing step.

As shown in FIG. 4, during the forming operation, the pressure of the forming fluid is likely to exert a strong "F1" spacing force pushing the supports 28A, 28B towards their open position. To avoid this problem, the supports 28A, 28B are equipped with locking means 38 in the closed position which are visible in FIG.

Such locking means 38 are known and will therefore not be described in more detail. These locking means 38 have the particular function of preventing any opening unexpectedly when blowing for which the pressures can reach 30 to 40 bar according to the applications.

For further details on the structure and operation of such locking means 38, one can for example refer to the document FR 2.646.802.

In order to compensate for the tendency of the half-molds 20A, 20B to move apart under the action of the press-forming fluid and to press them effectively against each other, the molding unit 16 according to the invention comprises fluid pressure compensation means which are interposed transversely between the support 28A and the associated half-mold 20A to push the half-mold 20A considered in the direction of the other half-mold 20B by the exercise of a counterpressure force "F2".

Of course, the half-mold 20A is then slidably mounted in the transverse direction relative to the associated support 28A between a retracted position and an advanced position. In practice, it is expected that the maximum transverse travel of the half-mold 20A relative to the support 28A is of the order of one millimeter. This clearance in transversely sliding advantageously makes it possible to avoid wear by matting of the faces 24 of the seal of the mold 20 during the closing of the supports 28A, 28B.

In the example shown in Figure 4, the half-mold 20A is fixedly mounted on the associated mold holder 34, and it is said mold holder 34 which is slidably mounted transversely on the support 28A. Such an assembly is well known to those skilled in the art and will not be detailed here.

In the proposed embodiment, there is provided compensation means only between the first support 28A and the half-mold 20A associated. The second half-mold 20B is rigidly attached to the second support 28B. In addition, the installation 10 is intended to produce containers of different shapes. For this purpose, the molds 20 are caused to be changed, sometimes several times a day, by the implementation of a mold changing process 20 in which the molds 20 in use are replaced by the second replacement molds 20 having a cavity 22 of different shape.

In this regard, the compensation means may be adapted to the format of the cavity 22 of the various molds 20 may be mounted on the molding units 16.

Thus, each compensation means comprises at least two fluid pressure compensation devices which are interposed between the support 28A and the associated half-mold 20A, and which push the half-mold 20A from a retracted position to an advanced position in the direction of the other half-mold 20B.

Each compensation device is here formed by a chamber 40A, 40B which is provided at the interface between the rear face of the mold carrier 34 associated with the half-mold 20A and the front face 32 of the associated support 28A.

As shown in Figure 5, each chamber 40A, 40B is more particularly defined by an annular seal 42 which is housed in a groove of the rear face of the mold carrier 34 and in a groove coincidental support 28A. The seal 42 is elastically compressed permanently between the mold carrier 34 and the support 28A regardless of the transverse position of the mold carrier 34 relative to the support 28A so as to ensure a permanent seal of the associated chamber 40A, 40B.

As shown in Figure 5, the molding unit 16 is here equipped with two chambers 40A, 40B which are arranged vertically one above the other.

According to a variant shown in FIG. 6, the second chamber 40B is arranged inside the first chamber 40A. The second chamber 40B is thus separated from the first chamber 40A by a joint 42 joint.

Each chamber 40A, 40B has an associated orifice 44 for supplying pressurized fluid. As shown in FIG. 4, the supply port 44 of the first chamber 40A is connected to a controlled source of fluid under pressure through a first conduit 46A to increase the pressure in said first chamber 40A. to push the mold carrier 34 forward.

Similarly, the supply port 44 of the second chamber 40B is connected to said controlled fluid source 45 via a second conduit 46B to increase the pressure in said second chamber 40B to urge the carrier mold 34 forward. The second conduit 46B is more particularly connected to the first conduit 46A downstream of the controlled source 45, as is shown in detail in FIG. 7.

The source 45 is thus common to the two chambers 40A,

40B.

The source 45 is here controlled according to the fluid pressure injected into the preform. As shown in FIG. 7, the source 45 is controlled by a control valve 47 which is capable of occupying a first supply position in which the first duct 46A is supplied with fluid under pressure by the source 45, and a second discharge position in which the first pipe 46A is directly connected to the atmosphere 49. The control valve 47 is common to the two pipes 46A, 46B, in other words, the control valve 47 makes it possible to control the simultaneous supply of the two lines 46A, 46B in pressurized fluid.

The fluid under pressure is here formed by compressed air. At least one pipe 46A, 46B of pressurized fluid is equipped with an activation valve 48B which is capable of activating the second chamber 40B.

In the example shown in the figures, the first chamber 40A is intended to be permanently activated. It therefore does not include an activation valve.

According to a not shown variant of the invention, an activation valve may also be interposed between the upper chamber and the source of fluid under pressure to control the activation of the upper chamber.

When a compensation chamber 40A, 40B is activated, it can be supplied with fluid under pressure by the source 45. When the second compensation chamber 40B is deactivated, the pressurized fluid emitted by the source 45 is blocked by the associated activation valve 48B.

The activation valve 48B is thus capable of being actuated independently between a closed position in which the associated second chamber 40B is not capable of being supplied with fluid under pressure by the source 45, and an open position in which the second chamber 40B associated is likely to be supplied with fluid under pressure by the source 45. In other words, in the open position of the activation valve 48B, the second associated compensation chamber 40B is activated, while in closed position of the activation valve 48B, the associated second compensation chamber 40B is deactivated.

Thus, the activation of the second compensation chamber 40B can be selectively controlled according to the format of the cavity 22 molding.

When the mold 20 in use is of large size, as illustrated in FIG. 4, the two compensation chambers 40A, 40B are activated so that the counterpressure is distributed over the entire height of the cavity 22. When the mold is small, as shown in broken lines by the reference 41 of FIG. 4, only the first compensation chamber 40A is activated, the second compensation chamber 40B being deactivated. The counterpressure is thus exerted in a balanced manner with respect to the spreading force.

At the end of its forming, the container must be ejected from the mold 12. To do this, it is necessary to open the mold 12. When opening the mold 12, it is preferable to evacuate the fluid under pressure contained in rooms 40A, 40B. To do this, the control valve 47 is controlled in its evacuation position. Thus, the pressurized fluid is discharged via the lines 46A, 46B towards the atmosphere 49.

When the second compensation chamber 40B is deactivated, it is not intended to contain any pressurized fluid. However, it happens that the seal between the two chambers 40A, 40B is not ensured correctly by the seal 42, in particular in the configuration shown in FIG. 6. The second chamber 40B is thus capable of filling with fluid under pressure through joint 42 joint. The second chamber 40B is deactivated, the pressurized fluid from the leak can not be discharged to the atmosphere 49 because the valve 48B blocks its passage.

To solve this problem, a fluid discharge pipe 50 directly connects the second compensation chamber 40B with the control valve 47 of the controlled source 45. The discharge pipe 50 is thus connected in parallel with the valve 48B. In the example shown in FIG. 7, the upstream end of the evacuation pipe 50 is connected to the pipe 46B between the activation valve 48B and the second chamber 40B, while the downstream end of the pipe 50 discharge is connected to the line 46B between the branch with the first line 46A and the valve 48B. The exhaust pipe 50 is equipped with a means preventing fluid flow from the source 45 to the second compensation chamber 40B. Such means is here formed by a non-return valve 52 which is interposed in the discharge pipe 50. Thus, the activation of the second chamber 40B remains controlled only by the activation valve 48B.

With this arrangement, even when the activation valve 48B is in its closed position, the second chamber 40B is connectable to the atmosphere 49 via the control valve 47.

Such an arrangement thus makes it possible to avoid the accidental rise in pressure of the second chamber 40B in the event of leakage of the joint gasket 42.

In addition, the fact that the second chamber 40B is not connected directly to the atmosphere 49 via the activation valve 48B makes it possible to avoid a leakage of fluid under pressure towards the atmosphere 49 when the valve 47 The control is in the feeding position via the joint gasket 42.

The activation valve 48B is an automatically operated valve, such as a solenoid valve, a hydraulic valve or a pneumatic valve.

The activation valve 48B can be remotely actuated by a control signal sent by an electronic control unit 52 which is arranged at a distance from the molding unit 16. The electronic control unit 52 is here arranged in a desk 54 which is arranged outside the carousel 18, as shown diagrammatically in FIG.

This electronic control unit 52 is advantageously capable of simultaneously controlling several operating parameters of each unit 16 of and molding 12 according to the format of the cavity 22 of the molds 20 installed in the molding units 16.

The forming machine 14 is here designed so that all the molding units 16 are simultaneously provided with molds 20 having the same cavity format 22. In this respect, the electronic control unit 52 is common to all the molding units 16. . Thus, it is capable of simultaneously controlling all the activation valves 48B of each molding unit 16.

The console 54 comprises means (not shown) for entering data relating to the format of the cavity 22 of the mold 20 in use. The input means may be formed by a keyboard, an optical reader such as a bar code reader, an electromagnetic signal reader or any other suitable input means.

The data entered can be transmitted to the electronic control unit 52. The electronic control unit 52 comprises a memory (not shown) in which the various control parameters are recorded according to the mold model and in particular according to the format of the final container to be obtained.

The electronic control unit 52 also comprises means (not shown) for transmitting a control signal towards the various control members of the installation 10.

In a nonlimiting and non-exhaustive manner, the parameters to be controlled relate to the temperature and distribution of preform heating, the duration of the various steps of the forming process, etc.

In the memory of the electronic control unit 52 is also pre-recorded an association table between:

the different cavity formats (22) that can be seized; and a selection of activation valves 48B to be activated.

This table is made according to the format, including the height, the cavity 22 of each mold 20 may be installed in the molding units 16.

The electronic control unit 52 also comprises means for transmitting the appropriate control signal to the actuating means of said activation valves 48B. Thus, in a single operation of capturing data relating to the format of the mold, an operator is able to set all the control parameters of the installation 10, including the selection of the activation valves 48B to be activated.

Thus, the operator responsible for replacing the molds 20 no longer has time to actuate successively the twelve activation valves 48B. All these activation valves 48B are actuated automatically and simultaneously by the electronic control unit 52. This both saves time and avoids errors that may occur during manual adjustment.

According to a second non-illustrated embodiment of the invention, each molding unit 16 is provided with associated data acquisition means and associated means for controlling the transmission of a control signal to the activation valves 48B in accordance with the invention. data entered.

In this second embodiment, only the differences with the first embodiment will be detailed. The reference numbers are given by analogy to the figures illustrating the first embodiment.

In this case, the data acquisition means are advantageously carried by the support 28A which is equipped with compensation chambers 40A, 40B.

The data relating to the format of the cavity 22 are for example coded in the form of a bar code, or any other code adapted visual, which is carried by the rear face 26 of the half-mold 20A. The input means are then formed by a suitable optical reader which is carried by the support 28A.

According to a not shown variant of the second embodiment of the invention, the data relating to the format of the cavity 22 of the mold 20 are recorded in a transponder of "RFID" type, sometimes called RFID tag or radio-tag, which is implanted. in the half-mold 20A. The input means are then formed by a radio wave transceiver which is arranged in the support 28A near the transponder when the half-mold 20A is mounted.

The transceiver is associated with an electronic control unit which is capable of transmitting an appropriate control signal to the activation valves 48B associated with said support 26A.

Thus, when a new mold 20 is put into operation, the transceiver remotely reads the data recorded in the transponder. Then, based on these data, the electronic control unit activates or deactivates the appropriate compensation chambers by actuating the corresponding activation valves.

In these first two variants of the second embodiment, the data acquisition means are contactless reading means.

According to a third variant, not shown, of the second embodiment of the invention, the data relating to the format of the mold 20 are formed by a structural element which is carried by the half-mold 20A.

The data acquisition means are formed by a push-button switch which is carried by the associated support 28A. The switch is capable of controlling the actuation of the activation valve 48B in the open position. The switch is arranged vis-à-vis the structural element of the half-mold 20A. The switch is resiliently biased to a forward position in which the lower activation valve 48B is in the closed position.

Thus, for the large format molds 20, the structural element is formed by a finger that is likely to push the switch when the half-mold 20A is mounted in its support 28A. This thus makes it possible to actuate the activation valve 48B in the open position.

For the small format molds, the structural member is shaped so as not to push the switch so that only the first chamber 40A is activated.

Thus, whatever the variant under which the second embodiment is made, the data are read automatically by the gripping means when the half-mold 20A is mounted in its support 28A by an operator. As in the first embodiment, the operator does not need to manually adjust each activation valve 48B of each molding unit 16.

According to a not shown variant of the invention which is applicable to the two embodiments, each molding unit comprises at least three compensation chambers which are superimposed. In this case, each of the two lower compensation chambers comprises an associated activation valve. Both valves can be operated independently of each other to allow selective activation of the compensation chambers.

Claims

A thermoplastic container forming machine (14) having at least one molding unit (16), each molding unit (16) comprising:

a mold (20) made of at least two half-molds

(20A, 20B) delimiting a mold cavity (22) when their two seal faces (24) are transversely clamped against each other;

two supports (28A, 28B) each carrying a half-mold (20A, 20B), the two supports (28A, 28B) being movable between an open position in which the two half-molds (20A, 20B) are spaced apart, and a closed position in which the two half-molds (20A, 20B) bear against each other by their face (24) before joint;

at least two fluid pressure compensation devices (40A, 40B) which are interposed between at least one support (28A) and the associated half-mold (20A), and which push the half-mold (20A) from a position moved back to an advanced position towards the other half-mold (20B);

- each compensation device (40A, 40B) being connected to a source (45) controlled common fluid under pressure via pipes (46A, 46B) associated;

at least one activation valve (48B) which is interposed between the source (45) of fluid under pressure and the associated second compensation device (40B), the activation valve (48B) being capable of being selectively controlled between an open position in which the associated compensation device (40B) is activated, and a closed position in which the second compensation device (40B) is deactivated;

characterized in that a fluid discharge line (50) directly connects the second compensation device (40B) with the source (45) controlled in parallel relative to the valve (48B), the evacuation pipe (50) being equipped with means (52) preventing the flow of fluid from the source to the second compensation device (40B).

characterized in that it comprises data acquisition means relating to the format of the molds (20) fitted to each molding unit (16), means for controlling the transmission of a control signal to each valve (48B) of activation according to the data entered.

2. Machine (14) according to the preceding claim, characterized in that the source (45) is controlled via a valve (47) of control which is likely to occupy a first feed position in which the conduits (46A, 46B) are supplied with pressurized fluid, and a discharge position in which the lines (46A, 46B) are connected to the atmosphere (49);

3. Machine (14) according to any one of the preceding claims, characterized in that the valve (48B) activation is a valve with automatic operation by receiving a control signal;

4. Machine (14) according to the preceding claim, characterized in that it comprises data acquisition means relating to the format of the molds (20) fitted to each molding unit (16), means for controlling the emission of a control signal to each activation valve (48B) according to the data entered.

5. Machine (14) according to the preceding claim, characterized in that it comprises an electronic control unit (52) which is arranged at a distance from the molding unit (16) and which comprises the relative data acquisition means. in the format of the mold (20) in use, a memory in which is pre-recorded an association table between the various data that can be entered and a selection of the activation valves (48B) to be actuated, means for transmitting the control signal to said activation valves (48A, 48B).

6. Machine (14) according to the preceding claim, characterized in that it comprises a plurality of molding units (16) and in that the electronic control unit (52) is common to all units (16). molding.

7. Machine (14) according to any one of claims 5 or 6, characterized in that the electronic control unit (16) is capable of simultaneously controlling other operating parameters of each molding unit (16). function of the data entered.

8. Machine (14) according to claim 4, characterized in that the support (28A) which is equipped with the compensation means is also provided with automatic data acquisition means relating to the format of the mold (20), and in that the data relating to the format of the mold (20) is carried by the half-mold (20A) associated with said support (28A), the data being coded in a form readable by the data-entry means.

9. Machine (14) according to the preceding claim, characterized in that each molding unit (16) is provided with associated means of data entry.

10. Machine (14) according to any one of claims 8 or 9, characterized in that the data are stored in a transponder which is carried by the half-mold (20A), and in that the input means are formed by a radio transceiver which is carried by the support (28A) associated with the half-mold (20A).