DEVICE FOR MOVING MOULDS AND ASSOCIATED METHOD

Technical field

This invention relates to a device for moving moulds, in particular of the servo-hydraulic type.

Moreover, the invention relates to an assembly for making hollow bodies made of plastic materials comprising the above-mentioned movement device and a method for controlling the movement device.

In other words, the invention relates to a device for moving moulds for making hollow bodies made of plastic materials such as, for example, containers, and in particular, bottles or the like made of polyethylene, polypropylene or other materials, by means of a method for production by extrusion and blowing.

In particular, the extrusion and blowing method comprises making a continuous cylindrical pipe made of plastic material by extrusion and then positioning it in a forming station where the pipe is expanded by blowing inside a preformed mould to acquire the final shape of the body required. In particular, the forming operation is performed by closing a piece of pipe between a first half-mould and a second half-mould, which on the one hand give the shape of the final container and on the other hand seals the profile of the containers and cutting the waste material in excess at the edges.

Background art

Generally speaking, the making of the containers of the above-mentioned type comprises a specific method for moving moulds between a first configuration, wherein the first and the second half-moulds are spaced apart, and a second configuration, wherein the above-mentioned first halfmould and second half-mould are moved towards each other. The evolution from the first to the second configuration of the half-moulds usually occurs in different steps. In particular, there is a first step of moving the half-moulds towards each other followed by a subsequent step of clamping the half-moulds to seal the profiles of the bodies and cut the waste. The latter is achieved in some cases also by means of a so-called bumping effect obtained by means of a further pulse compression by means of a pulse increase in the closing speed. The clamping, and any bumping, is followed by a subsequent step of forming the hollow bodies by blowing. The operations for sealing and cutting the waste require that the two half-moulds be compressed with particular force relative to each other; thus requiring high forces to be applied in the closing step which may vary in the order of a few tons to a few tens of tons.

Traditionally, both the movements of the half-moulds during the above- mentioned steps and the high closing forces of the half-moulds are guaranteed by the use of movement systems based on cylinder-piston hydraulic movement devices. These movement systems generally require the use of hydraulic control units, hydraulic pumps with variable or fixed flow rates and directional solenoid valves designed to operate the hydraulic cylinder-piston movement devices for the various steps required. These movement systems are relatively complex and have several negative aspects. In particular, these systems have a very low efficiency (up to 80% of the energy used in the process is lost) and require the movement of large quantities of hydraulic operating fluid to guarantee the forces required. Consequently, these systems have a high energy cost required for the movement due to the high quantity of hydraulic fluid used. The impact is further aggravated by the potential losses which can occur whilst the system is operating; therefore, the need to provide a continuous cleaning of the working area must also be included.

In recent years, the use has changed from hydraulic systems to mechatronic systems, comprising movement devices based on electric motors combined with recirculating ball screw transmission systems and/or connecting rod and crank mechanism systems. The mechatronic actuation systems exceed the limits of the traditional hydraulic systems because they guarantee a lower energy cost, greater cleaning and lower maintenance costs. Compared with conventional hydraulic systems, however, the mechatronic systems lose flexibility of use since they often require the use of moulds with a tolerated thickness since the correct alignment of the connecting rod and crank type kinematic mechanisms must be guaranteed during the steps for clamping and cutting the waste. Similarly, given the fixed dimensions of the mechanical elements used in the movement of the moulds, the mechatronic movement systems are limited to using moulds characterised by a predetermined range of dimensions and geometries.

There are prior art hydraulic systems comprising simplified circuits powered by systems using double-acting cylinders which are a more efficient variant than the above-mentioned systems.

In particular, a first prior art example from patent document ES2611488T3 which comprises the use of a two-way piston wherein the movement of the piston is obtained by means of a simple circuit with a single forward and return channel powered by a pump-motor system exclusively by means of the alternative two-way movement of operating fluid between a first chamber, which when filling pushes the piston towards the outside of the cylinder, and a second chamber, which when filling pushes the piston towards the inside of the cylinder, both made inside the cylinder.

Disadvantageously, that type of system is limited by the fact that it is possible to move the piston in a limited range of speeds and thrust powers, depending on the speed of filling and emptying of the two chambers and the thrust surfaces available in them on which the fluid can exert the thrust action. In particular, in the case of hydraulic systems for moving moulds used in forming processes, substantial variations in the thrust power in the final step are often required in order to effectively close the moulds opposing the resistance emitted by the materials inside the mould. A variant of the above-mentioned solution is known from patent document DE102013224386A1.

That document describes a system substantially similar to the system described in the previous document with the difference that the piston comprises a further third thrust chamber, which may be filled and actuated in assistance to the chamber dedicated to the translation towards the outside of the piston in such a way as to provide further thrust power, for example, in the final step.

Disadvantageously, in the system described the second chamber requires the use of a further circuit with separate power supply and a second pumpmotor system for its actuation, thus being a more complex and costly solution compared with the solution presented in the solution described above.

Aim of the invention

The technical purpose of the invention is to provide a device for moving moulds of the servo-hydraulic type, an assembly for making bodies comprising the above-mentioned movement device and a method for controlling the movement device which are able to overcome the drawbacks of the prior art.

The aim of the invention is to provide a device for moving moulds of the servo-hydraulic type, an assembly for making bodies comprising the above-mentioned movement device and a method for controlling the movement device which allow the limits of the prior art devices, of the hydraulic type, as well as mechatronic, to be overcome.

A further aim of the invention is to provide a device for moving moulds of the servo-hydraulic type, an assembly for making hollow bodies comprising the above-mentioned movement device and a method for controlling the movement device having a high efficiency and which allow energy not to be wasted.

Moreover, the aim of the invention is to provide a device for moving moulds of the servo-hydraulic type, an assembly for making hollow bodies comprising the above-mentioned movement device and a method for controlling the movement device which allow a minimum quantity of hydraulic operating fluid to be used, reducing the number of connections present inside the machine, thus reducing the possibility of losses of hydraulic operating fluid.

The technical purpose and aims specified are substantially achieved by a device for moving moulds of the servo-hydraulic type for making hollow bodies made of plastic materials configured for translating at least a first half-mould relative to a second half-mould.

The device comprises a hydraulic circuit comprising a two-way combined pump-motor system configured for controlling a flow of an operating fluid; a thrust chamber put in fluid communication with the hydraulic circuit and configured to contain when necessary the operating fluid; and at least one movement unit, connected with the hydraulic circuit.

The movement unit comprises a hollow cylinder extending about an axis of extension of the movement unit. The movement unit further comprises a movable rod, which is positioned inside the hollow cylinder and configured to slide along the cylinder, in both directions, in such a way as to translate the first half-mould relatively to the second half-mould. The movable rod further defines with the hollow cylinder an outer movement chamber containing a predetermined quantity of fluid.

The movement unit further comprises a fixed rod positioned inside the movable rod and defining a conduit for the passage of fluid towards an inner movement chamber formed inside the movable rod and containing in turn a predetermined quantity of operating fluid.

The movement unit is put into operation by the flow of hydraulic fluid controlled by the hydraulic circuit, between a first configuration, wherein the first and the second half-moulds are moved away from each other, and a second configuration, wherein the first and the second half-moulds are moved towards each other. During a movement from the first configuration to the second configuration, the hydraulic fluid is moved from the outer movement chamber to the inner movement chamber.

Further, the thrust chamber is configured to impart a thrust force to the movable rod using the operating fluid contained close to reaching the second configuration to perform a mutual clamping between the first half- mould and the second half-mould.

Moreover, the technical purpose indicated and the aims specified are substantially achieved by an assembly for making hollow bodies made of plastic material comprising at least a first half-mould, at least a second half-mould and a movement device configured for translating relative to each other the first half-mould and the second half-mould.

Moreover, the technical purpose indicated and the aims specified are substantially achieved by a method for controlling a movement device inside an assembly for making hollow bodies made of plastic material comprising various steps. The various steps consist in a step of achieving a controlled flow of an operating fluid inside the hydraulic circuit by means of said combined pump-motor system; a step of movement of a predetermined quantity of operating fluid from the inner movement chamber to the outer movement chamber by means of the combined pump-motor system for moving in a controlled manner the movable rod included in the movement unit in such a way as to move alongside relatively the first half-mould and the second half-mould; a step of saturating the operating fluid of the thrust chamber; a step of putting in communication the operating fluid of the thrust chamber with said combined pump-motor system; a step of clamping said first half-mould with said second half-mould for sealing the profile of the bodies and cutting the waste, increasing the pressure of the operating fluid in the thrust chamber and in the inner movement chamber by means of said combined pump-motor system; and lastly, a step of inversion of the flow so as to move said movement unit from said second configuration to said first configuration in such a way as to move away said first half-mould and second half-mould. Preferably, the method for controlling the device may comprise a so-called bumping effect, obtained by a pulse increase in the closing speed before conclusion of the step of clamping the first half-mould respectively to the second half-mould in order to increase the effectiveness during the activities for sealing the profile of the hollow bodies and cutting waste. The particular features of the device allow a combination of positive aspects of mechatronic systems to be used together with a greater flexibility of the hydraulic systems, in order to favour the use of moulds with thicknesses not tolerated or also with different dimensions but by using a limited quantity of hydraulic fluid.

Brief description of the drawings

Further features and advantages of the invention are more apparent in the non-limiting description which follows of one or more embodiments of a device for moving moulds of the servo-hydraulic type, an assembly for making hollow bodies comprising the above-mentioned movement device and a method for controlling the movement device.

The description is set out below with reference to the accompanying drawings which are provided solely for purposes of illustration without restricting the scope of the invention and in which:

- Figure 1 is an overall view of an assembly for making bodies made of plastic material to which is associated a device for moving moulds made according to the invention, in which the mould is shown in the open position;

- Figure 2 is an overall view of the assembly of Figure 1 , in which the mould is shown in the closed position;

- Figure 3 schematically shows a hydraulic circuit forming part of the movement device made according to the invention;

- Figure 4 is a schematic view of a movement unit made according to the invention. Detailed description of preferred embodiments of the invention

With reference to the accompanying drawings, the numeral 1 denotes in its entirety an assembly for making hollow bodies made of plastic material, for example containers such as bottles or the like (not illustrated) comprising a device for moving moulds 2. The term hollow bodies made of plastic material may mean hollow bodies made, for example, of polyethylene, polypropylene or other plastic materials.

The assembly 1 comprises two half-moulds 3 and 4, fixed relative to two respective support plates 5 and 6. In particular, the half-moulds 3 and 4 are fixed, respectively, to a first portion of the plates 5 and 6, whilst a second portion of the plates 5 and 6 is used to receive a movement system based on a guide unit 7. Preferably, but not exclusively, the guide unit 7 is in an assembly comprising a plurality of sliding cylinders and at least one opposing system 8, opposing the force exerted on the halfmoulds 3 and 4 by the device for moving moulds 2.

The guide unit 7 and the device for moving moulds 2 are anchored to each other by means of a structural frame 9, in such a way that the two halfmoulds 3 and 4 maintain a corresponding mutual alignment during all the operational steps, from a first configuration, in which the first half-mould 3 and the second half-mould 4 are spaced apart, to a second configuration, in which the first half-mould 3 and the second half-mould 4 are moved towards each other, respectively shown in Figure 1 and in Figure 2.

Further, according to the embodiment of Figures 1 and 2 (non-limiting for the purposes of the invention), the movement device 2 is connected exclusively to the plate 5 by suitable connecting means 11 , allowing a direct translating action on the half-mould 4, whilst the plate 6 is moved indirectly by the movement device by means of suitable central synchronising means (not illustrated), which are configured in such a way as to translate in a synchronised fashion relative to each other said first half-mould 3 and said second half-mould 4 maintaining a constant mutual orientation. This feature together with the above-mentioned arrangement of the structural frame 9 allows the assembly 1 to use in a flexible fashion moulds of different dimensions and geometries, without the need for the moulds used to have tolerated thickness.

The device 2 is in a movement system of the hydraulic cylinder-piston type, fixed inside the frame 9, having a mobile rod 12 which is able to slide axially in two directions.

In particular, the movable rod 12 comprises a first head stretch 13 configured to slide axially, in both directions, from the inside to the outside of the device 1 and vice versa, and which is able to apply a thrust force on the plate 5 through the connecting means 11. A second bottom stretch of the movable rod 12, or base 14 of the movable rod 12 is, on the other hand, positioned in a slidable fashion permanently inside the movement device 2.

In particular, with reference to Figure 3, the movement device 2 comprises a movement unit 15 powered by a hydraulic operating fluid positioned adjacent to a thrust chamber 16, configured to contain when necessary the hydraulic operating fluid and placed in fluid communication with the movement unit 15. The thrust chamber 16 is placed in fluid communication with a hydraulic circuit 17 comprising a combined two-way pump-motor system 18, configured for controlling the flows of hydraulic operating fluid inside the circuit 16.

The specific use of the combined pump-motor system 18 allows the movement device 2 to control all the steps of the configuration of moving the first half-mould 3 towards the second half-mould 4, that is to say, mutual movement towards each other, clamping and, if necessary, also bumping.

The combined pump-motor system 18 comprises a two-way pump.

In particular, the two-way pump is a variable-speed four-quadrant pump.

The combined pump-motor system 18 further comprises an axial electric motor of the brushless type. This coupling allows a precise variation of the hydraulic flow by controlling the pump thanks to the brushless axial electric motor, allowing the circuit 17 to be much simpler than traditional hydraulic systems. The combined pump-motor system 18 directly controls the flow of hydraulic operating fluid entering and leaving the movement unit 15, without the aid of a hydraulic unit and not even a valve for directional control of the flow. In particular, the combined pump-motor system 18 is able to precisely control the extent and the speed of the translation of the mobile rod 12, applying an adjustable pressure on the hydraulic operating fluid present in the circuit and consequently precisely calibrating the speed and the mechanical force transmitted by the mobile rod 12 in the various steps of moving towards and clamping (and if necessary bumping) of the halfmoulds 3 and 4. Moreover, the combined pump-motor system 18 allows the movement of the flow of hydraulic operating fluid in both directions along the circuit 17 simply by inverting the direction of the flow of hydraulic operating fluid by reversing the direction of rotation of the pump, thus being able to control both the configuration for moving towards and away of the half-mould 3 relative to the half-mould 4, without the aid of directional valves.

The combined pump-motor system 18 according to the above-mentioned arrangement allows the circuit 17 to be defined as a closed circuit, which controls a limited and predetermined quantity of operating fluid, consequently limiting the losses of operating fluid. Compared with conventional hydraulic systems, the use of the combined pump-motor system 18 allows a greater efficiency to be obtained, as it is able to save up to 70% of the energy in terms of the energy used for moving the flow of the operating fluid during the various steps.

The movement unit 15 receives internally the movable rod 12, comprising the first head stretch 13, configured to slide axially, in both directions, from the inside to the outside of the movement unit 15, and the second bottom stretch 14, positioned in a slidable fashion permanently inside the movement unit 15.

The movement unit 15 further comprises an outer movement chamber 19 and an inner movement chamber 20, receiving a predetermined quantity of operating fluid and it is able to exchange between them the operating fluid, such that this exchange causes the axial translation of the movable rod 12 in such a way as to achieve the placing alongside of the first half-mould 3 the second half-mould 4.

In particular, the outer movement chamber 19 and the inner movement chamber 20 are connected by means of the hydraulic circuit 16, where a first stretch 21 is connected and in communication with the outer movement chamber 19 and a second stretch 22 is connected and in communication with the inner movement chamber 20. The combined pump-motor 17 system activates the axial translation of the movable rod 12 towards the outside of the movement unit 15, moving a predetermined quantity of operating fluid from the outer movement chamber 19 to the inner movement chamber 20, in particular, sucking it from the outer movement chamber 19 by means of the first stretch 21 and releasing it by means of the second stretch 22 in the inner movement chamber 20.

The axial translation of the movable rod 12 is given by a combined effect of lowering the pressure of the operating fluid inside the outer movement chamber 19, and increasing the pressure of the operating fluid inside the inner movement chamber 20. The axial translation of the rod 12 outside the movement unit 15 is in turn accompanied further by a contraction in volume of the outer movement chamber 19 and an expansion in volume of the inner movement chamber 20.

Since no particularly high forces are required during the step of moving, respectively, the first half-mould 3 towards the second half-mould 4, the variation of the pressure of the fluid inside the outer movement chamber 19 and the inner movement chamber 20 as mentioned above is sufficient to translate the movable rod 12 outside the movement unit 15 and, consequently, perform the relative moving towards each other of the first half-mould 3 and the second half-mould 4.

On the other hand, the clamping step requires a high compressive force to be applied between the first half-mould 3 and the second half-mould 4 so that the forming and the cutting of waste of the hollow bodies are correctly executed. For this operation it is necessary to also use a further thrust action by the fluid contained inside the thrust chamber 16. In particular, the combined pump-motor system 18 causes a sudden and constant increase in the pressure of the operating fluid contained in the thrust chamber 16 to transmit, in a combined fashion with the fluid contained in the inner movement chamber 20, a compression action, respectively, between the half-mould 3 and the half-mould 4.

However, before executing the clamping step, the thrust chamber 16 must be saturated with operating fluid. According to non-limiting embodiment, the hydraulic circuit 16 comprises a tank 23 for storing the hydraulic operating fluid and a one-way filling valve 24 configured for supplying the thrust chamber 16. In particular, during the step for moving towards each other, the movement of the fluid from the outer chamber 19 to the inner chamber 20 causes the axial translation of the movable rod 12 outside the movement unit 14. Since the thrust chamber 16 is positioned adjacent to the movable rod 12 and is in fluid communication with it, the translation of the movable rod 12 is accompanied by a lowering of the pressure of the fluid present inside the thrust chamber 16. Further, the translation of the movable rod is accompanied by an expansion in volume of the thrust chamber 16.

Due to the lowering of the pressure formed inside the thrust chamber 16, the thrust chamber 16 sucks the operating liquid contained in the storage tank 23, by means of the one-way filling valve 24. In particular, the oneway filling valve 24 allows the passage of the operating fluid to be sucked inside the thrust chamber 16 only when caused by the negative pressure inside the chamber 16.

Advantageously, this arrangement allows the use of a reduced volume of operating fluid inside the hydraulic circuit 17. Moreover, the storage tank 23 may be made with reduced dimensions specifically only for the requirements of the thrust chamber 16.

The mutual clamping between the first half-mould 3 and second half-mould 4 (followed, if necessary, by bumping) occurs at the end of the step for moving towards each other when the movement means 15 is close to reaching the second configuration of the half-moulds 3 and 4. The thrust chamber 16 and the inner movement chamber 20 are close to full expansion and saturation in volume of operating fluid.

In order to perform the clamping between the first half-mould 3 and the second half-mould 4, the movement device 2 activates a dedicated auxiliary channel 25 of the circuit 17 by means of a solenoid valve 26 where the combined pump-motor system 18 is further connected also to the thrust chamber 16.

The combined pump-motor system 18 may now apply the maximum thrust force by increasing the pressure on the operating fluid contained simultaneously both in the thrust chamber 16 and in the inner operating chamber 20, by means of the corresponding second stretch 22 and the dedicated auxiliary channel 25 of the circuit 17. This increase in pressure is adjusted in such a way as to exert a sudden and continuous compression of the half-mould 3 against the half-mould 4.

When necessary, at the end of the clamping step the device for moving moulds 2 may further comprise a bumping step. The bumping substantially requires the same movements described for the clamping step with the difference that the combined pump-motor system 18 performs a pulse type compression of the half-mould 3 against the half-mould 4.

At the end of the above-mentioned steps, the combined pump-motor system 18 reverses the flow of the operating fluid inside the circuit 16, in such a way as to move the first half-mould 3 away from the second halfmould 4. The operating fluid initially present in the inner movement chamber 20 is sucked and transferred to the outer movement chamber 19. The operating fluid causes the expansion of the outer chamber 19 and the contraction of the inner chamber 20, causing the movable rod 12 to withdraw inside the movement unit 15. Similarly, the axial translation of the movable rod 12 towards the inside of the movement unit 15 causes in turn a compression on the thrust chamber 16.

According to this embodiment, the one-way valve 26 is constituted in such a way that it can be opened by means of a suitable opening system with an elastic element, such as, for example, a spring, to allow the operating fluid to be moved again into the storage tank 23. In particular, the opening of the one-way valve can be activated by a suitable actuator 27 and allow the operating fluid contained by the thrust chamber 16, under pressure due to withdrawal of the movable rod 12 towards the inside of the movement unit 15, to return into the storage tank 23.

The set of the above-mentioned movements allow the movable rod 12 to be repositioned at the initial state, allowing the movement device 2 to translate the moulds 3 and 4 from the second configuration where the halfmoulds 3 and the half-mould 4 are relatively close to the first configuration where they are relatively spaced apart.

With reference to Figure 4, the information provided is described in more detail below, describing in more detail the internal formation of the movement unit 15.

The movement unit 15 is interposed inside a suitable supporting structure 28, where said structure is designed to provide, on the one hand, a structural reinforcement for the movement unit 14 and, on the other hand, to anchor the movement unit 14 to the frame 9.

The movement unit 14 comprises a hollow cylinder 29 extending about an axis of extension “AA”. The cylinder 29 is positioned in a fixed manner inside the movement unit 14 and in particular, delimited and anchored at its ends by the supporting structure 28.

The cylinder 29 receives the movable rod 12 internally, which is also located around the axis of extension “AA” and is capable of translating inside the cylinder 29 along the axis “AA” and along the inner surfaces of the cylinder 29. In particular, the cylinder 29 partly receives the top stretch 13 and entirely the bottom stretch or base 14.

The movable rod 12 is substantially cylindrical in shape, extending around the axis “AA” where the diameter of the top stretch 13 is less than the diameter of the bottom stretch 14.

Whilst the base can slide along the inner surfaces of the cylinder 29, a recess with an annular cross-section is formed along the head stretch between the outer surface of the movable rod 12, and in particular along the head stretch 13, and the inner wall of the cylinder 29.

The recess constitutes the outer movement chamber 19.

Further, the outer movement chamber 19 is delimited laterally at a first end by a first step 30, formed when the base 14 and the head stretch 13 of the movable rod 12 meet, and at a second end by a second step 31 formed by a step-like extension on the inner surface of the cylinder 29. The relative arrangement of the first step 30 and of the second step 31 not only delimits the stroke of the movable rod 12, but also the variation of the lateral extension of the outer movement chamber 19. In particular, the axial translation of the movable rod 12 towards the outside of the movement unit 15 corresponds to a movement of the first step 30 towards, respectively, the second step 31. Consequently, the movable rod 12 reaches its end of stroke when between translation of the first step 30 it is physically stopped by contact with the second step 31. Simultaneously, this movement towards each other causes the gradual reduction of the volume of the outer movement chamber 19.

The movable rod 12 has an inner cavity 32 which is also positioned about the axis of extension “AA”. The cavity 32 has an opening facing the rear surface of the base 14 and is configured to receive internally a fixed rod 33, which, unlike the movable rod 12, keeps in a fixed fashion its arrangement inside the cylinder 29. In particular, the movable rod 12 is positioned externally around and receiving the fixed rod 33, in a superposed configuration and, preferably, concentric relative to the axis “AA”. The inner surface of the cavity 32 is compatible in shape with the fixed rod 33, allowing the movable rod 12 to slide axially, in both directions, along the body of the fixed rod 33.

The fixed rod 33 has an inner through cavity defining an inner conduit 34. The inner conduit 34 extends along the entire body of the fixed rod 31 and on one side has a first end 35 communicating with the inner cavity 32 of the movable rod 12 and on the other side a second end 36 communicating with the circuit 18, and in particular with the second stretch 22, putting in fluid communication the inner operating chamber 20 with the outer operating chamber 19.

The inner movement chamber 20 is defined by the portion left free by the fixed rod 33 inside the cavity 32, in particular having laterally a first end configured to be put in fluid communication with the first end 35 of the conduit 33 and a second end facing an inner surface of the inner cavity 32 of the movable rod 12.

During the step for moving towards each other, the fluid moved progressively inside the inner movement chamber 20 increases the thrust force on the inner surfaces of the inner movement chamber 20, coinciding with the inner surfaces of the cavity 32 inside the rod 12. After reaching a predetermined pressure level, the thrust causes the axial translation of the movable rod 12 towards the outside of the cylinder 29 and, therefore, outside the movement unit 15.

Simultaneously with the translation of the movable rod 12, the inner operating chamber 20 also expands laterally along the direction of translation of the movable rod 12, being delimited by the inner surface of the cavity 32 inside the movable rod 12 and the fixed rod 33.

The thrust chamber 16 is positioned adjacent to the movable rod 12 and received inside the supporting means 28. In particular, the thrust chamber comprises an annular thrust section positioned adjacent to the bottom end of the movable rod 12, and, in particular, the annular section is positioned around the fixed rod 33 and facing the rear of the base 14.

During the step for moving towards each other, in addition to the expansion of the inner operating chamber, the translation of the rod along the axis of extension “AA” also causes the expansion in volume of the thrust chamber 16. As the thrust chamber 16 is positioned adjacent to the base 14, the base delimits a relative lateral end. The translation of the base therefore causes an expansion of the volume of the chamber.

Further, this expansion of the volume of the thrust chamber 16 causes the above-mentioned internal negative pressure and the consequent sucking of operating fluid from the storage tank 23 by means of the one-way valve 24.

At the end of the step for moving towards each other, the movable rod is almost completely translated outside the movement means 14.

The thrust chamber 16 and the inner movement chamber 20 are close to being totally expanded and reach a saturation equilibrium in the volume of operating fluid, whilst the outer movement chamber 19 is close to being completely contracted.

When the clamping steps are started, following the activation of the dedicated auxiliary channel 25 by means of the solenoid valve 20, the combined pump-motor system 18 is in fluid communication both with the thrust chamber 15 and the inner movement chamber 20. By means of the dedicated auxiliary channel 25, the combined pump-motor system 18 is enabled to exert the maximum thrust pressure on the movable rod 12 both by exerting pressure force on the rear surface of the base 14 and by exerting pressure force inside the movable rod 12 by means of the inner movement chamber 20, and consequently, moving the movable rod 12 completely to the end of its stroke.

In the reverse cycle, which comprises the moving away of the half-moulds 3 and 4 from the second configuration to the first configuration, the combined pump-motor system reverses the suction direction of the fluid, in particular moving the fluid contained in the inner movement chamber 20 inside the outer movement chamber 19. This movement is accompanied by the translation of the movable rod 12 towards the inside of the cylinder 15 due to the simultaneous contraction of the inner movement chamber 20 in negative pressure and the expansion of the outer movement chamber in expansion due to the increase of the pressure of the fluid flowing inside it.

Similarly, the hydraulic operating fluid from the thrust chamber 16 is returned to the storage tank 23. In particular, the translation of the movable rod 12 towards the inside of the cylinder 15 causes a compression on the thrust chamber 16. Once the actuator 27 is activated and the one-way valve 24 is open, the pressurised fluid inside the thrust chamber 16 flows inside the tank 23 and the thrust chamber 16 is able to contract.

Further, according to this embodiment, in order to optimise the flow of fluid inside the circuit 16, the storage tank 23 is suitably positioned adjacent to the movement unit 15 and anchored to the supporting unit 28 in such a way as to minimise the distance of movement of the fluid between the thrust chamber 16 and the storage tank 23.

The description of the assembly 1 provided for making bodies made of plastic material and comprising at least a first half-mould 3, at least a second half-mould 4, and at least one movement device 14 coincides with one or more of the passages of the above description.

The description of the method for controlling a movement device 14 included in the assembly 1 provided for making bodies made of plastic materials coincides with one or more of the passages of the above description.