Apparatus and method for producing objects in continuous cycle from plastic material

Abstract

An apparatus (1) for producing objects in continuous cycle from plastic material comprises: a distributor unit (2); a forming station (4) for forming a plurality of objects by compression moulding; a metering unit (3) including an outlet valve system located in a respective outfeed branch (203) and switchable between an open configuration and a closed configuration and a plurality of partition elements (303), each positioned in a respective outfeed branch (203) upstream of the respective outlet valve and movable between an upper limit position (X1) and a lower limit position (X2) to vary the internal volume of the distributor unit (2); a control unit programmed to control the displacement of the partition elements (303) from the lower limit position (X2) to the upper limit position (X1) based on a value of pressure detected by a sensor system; a compensation unit (208), located upstream of the plurality of outfeed branches (203) and defining a compensation volume, variable between a maximum volume configuration and a minimum volume configuration depending on a cycle of charging and discharging the plurality of doses of plastic.

Description

[0001] DESCRIPTION

[0002] APPARATUS AND METHOD FOR PRODUCING OBJECTS IN CONTINUOUS CYCLE FROM PLASTIC MATERIAL

[0003] Technical field

[0004] This invention relates to an apparatus and a method for producing objects in continuous cycle from plastic material.

[0005] This disclosure addresses the sector of moulding objects from thermoplastic material. More specifically, the sector is that of moulding a plurality of objects simultaneously from plastic material. In an example embodiment, the objects are parisons intended for subsequent blow moulding to form containers.

[0006] Background art

[0007] Known in the prior art for this purpose are apparatuses in which a metering unit is configured to form a plurality of measured doses of plastic from a flow of molten plastic. An example of this type of apparatus is described in JP2017177455A, where rotary elements are configured to rotate as one to divide the flow of molten plastic into a plurality of identical doses. An apparatus of this kind, however, does not allow making the doses precisely or adjusting the quantity of plastic of one dose independently of the quantity of the other doses. In this regard, there are apparatuses known in the prior art which comprise a system for measuring and adjusting the quantity of material in order to adjust the quantity of plastic in each dose, as described, for example, in JPH06114867A; this document describes a plastic distributor comprising outlet ports, each provided with a weighing and injecting unit configured to measure and adjust the quantity of material forming the dose. The document does not, however, describe in sufficient depth the way in which the material is measured and adjusted to form the doses.

[0008] Patent document US5858420 describes a solution regarding an injection moulding system in which the continuous flow of plastic is divided and distributed and in which the injected plastic is measured by a volumetric system.

[0009] Patent document W02023180311 A1 describes an apparatus for the multiple metering of plastic; the apparatus described is not, however, very flexible in that it does not allow varying the quantity of plastic in each dose at will and also suffers from pressure-related problems which can lead to damage to the extruder.

[0010] Disclosure of the invention

[0011] This disclosure has for an aim to provide an apparatus and a method for producing objects in continuous cycle from thermoplastic material to overcome the above mentioned disadvantages of the prior art.

[0012] More specifically, the aim of this invention is to provide an apparatus and a method for producing objects in continuous cycle from plastic material and capable of dividing the material uniformly into a plurality of doses starting from a continuous flow of plastic.

[0013] Another aim of this invention is to propose an apparatus and a method for producing objects in continuous cycle from plastic material to allow adjusting the quantity of plastic of one dose independently of the other doses.

[0014] Yet another aim of this disclosure is to provide an apparatus and a method for producing objects in continuous cycle from plastic material where it is possible to obtain a plurality of doses whose volume is known with precision.

[0015] These aims are fully achieved by the apparatus and method of this disclosure for producing objects in continuous cycle from plastic material as characterized in the appended claims.

[0016] The apparatus comprises a distributor unit. The distributor unit is configured to distribute plastic in parts of the apparatus. The distributor unit includes an infeed duct. The infeed duct has an inlet. The inlet is configured to receive a continuous pressurized flow of molten plastic, for example, from an extruder unit, that is, from an extruder. The extruder unit (the extruder) may be configured to receive plastic in raw form and feed out a flow of molten plastic.

[0017] The distributor unit includes a plurality of outfeed branches. The plurality of outfeed branches, or each outfeed branch of the plurality of outfeed branches, has an outlet (thus defining a plurality of outlets). Each outfeed branch of the plurality of outfeed branches is in fluid communication with the infeed duct through a distribution zone. Preferably, the distribution zone is configured to put the inlet, that is, the infeed duct, in communication with each outfeed branch of the plurality of outfeed branches so as to allow the plastic to be fed towards and distributed, that is, divided between, the outfeed branches (and the outlets). In other words, the distribution zone is configured to divide the flow of plastic into a plurality of (separate) flows of plastic.

[0018] The distributor unit defines an internal volume between the inlet and the outlets, that is, between the plurality of outfeed branches.

[0019] The distribution zone may comprise a single distribution zone or it may comprise a plurality of distribution zones. For example, the plurality of distribution zones comprises a first distribution zone and a second distribution zone. The first distribution zone, located downstream of the infeed duct in the direction of feed of the plastic from the inlet to the outlets, may be configured to divide the flow of plastic into a plurality of (separate) flows of plastic, and the second distribution zone, located downstream of the first distribution zone, may be configured to receive the plurality of separate flows of plastic and to separate them further. In this example, the first and the second distribution zone constitute a first and a second branch for the incoming continuous flow of plastic towards the infeed duct.

[0020] The apparatus comprises a forming station. The forming station may be an injection moulding station, or an injection compression moulding station or, more preferably, a compression moulding station. The forming station is configured to form a plurality of plastic objects from a plurality of predetermined quantities of plastic, that is, of doses. The forming station includes a plurality of female elements, that is, a plurality of lower moulds, and a plurality of male elements, that is, a plurality of upper moulds. Preferably, the female elements of the plurality of female elements can be positioned at the plurality of outfeed branches of the distributor unit, that is to say, each female element can be positioned at a respective outfeed branch. Thus, each female element is configured to receive plastic from the outlet of the respective outfeed branch. Preferably, the female elements of the plurality of female elements define a corresponding plurality of seats, each seat being configured to receive a predetermined quantity of plastic, that is to say, a dose. The male elements of the plurality of male elements are configured to act in conjunction with the respective female elements of the plurality of female elements to delimit a corresponding plurality of forming cavities. The male elements of the plurality of male elements preferably act in conjunction with the respective female elements of the plurality of female elements to form a plurality of objects from plastic material by compression moulding. In an example, the objects are parisons intended for blow moulding to form containers.

[0021] The apparatus may form part of a line for the production of containers (for example, for liquids or other) in continuous cycle and the line for the production of containers may further comprise a station for the blow moulding of parisons to form containers.

[0022] The apparatus comprises a metering unit. The metering unit is configured to measure a predetermined quantity of plastic, that is to say, to form doses of predetermined quantities of plastic from the continuous flow. Preferably, the metering unit is configured to form a plurality of doses of plastic simultaneously.

[0023] The metering unit includes an outlet valve system. The outlet valve system is configured to interrupt, that is, to separate the plastic, for example, between a zone upstream of the outlet valve system and a zone downstream of the outlet valve system, relative to a feed direction of the plastic from the inlet to the outlets.

[0024] Preferably, the outlet valve system comprises a plurality of outlet valves. Each of the plurality of outlet valves can be positioned in a respective outfeed branch. The outlet valve system can be switched between an open configuration and a closed configuration.

[0025] For this purpose, the outlet valve system may comprise a plurality of valves, shutters or interrupters. For example, in the closed configuration of the outlet valve system, the outlet valve system is configured to interrupt a flow of plastic. For example, in the open configuration of the outlet valve system, the outlet valve system is configured to allow plastic to be discharged from the internal volume of the distributor unit. That way, in passing from the open configuration to the closed configuration of the outlet valves, the metering unit is configured to form a plurality of doses which are fed out from the corresponding plurality of outfeed branches of the distributor unit.

[0026] The metering unit comprises a plurality of partition elements, or separating walls. The partition elements of the plurality may be movable between an upper position and a lower position, for example, to vary the internal volume of the distributor unit, that is to say, to vary the quantity of plastic containable inside the distributor unit.

[0027] Preferably, the metering unit includes, that is to say, it is operable in, an operative configuration or a plurality of operating configurations. For example, the metering unit comprises a charging configuration, in which the outlet valve system is in the closed configuration (to interrupt a flow of plastic leaving the distributor unit). For example, the metering unit comprises a discharging configuration, in which the outlet valve system is in the open configuration (to allow plastic to be discharged from the internal volume of the distributor unit).

[0028] The apparatus may comprise a control unit, configured to switch the metering unit from the charging configuration to the discharging configuration and vice versa.

[0029] In an embodiment, the metering unit comprises an additional valve system. The additional valve system is preferably configured to separate, that is, to interrupt, the flow of plastic, for example, from a zone upstream of the additional valve system to a zone downstream of the additional valve system. The additional valve system can be switched between an open configuration and a closed configuration. For this purpose, the additional valve system may comprise a plurality of valves, shutters or interrupters. For example, when the metering unit is in the charging configuration, the additional valve system is in the open configuration. When the metering unit is in the discharging configuration, the additional valve system is in the closed configuration. Preferably, the additional valve system is positioned upstream of the outlet valve system. That way, the outlet valve system is configured to separate, that is, to interrupt the plastic between a zone downstream of the additional valve system and a zone downstream of the outlet valve system.

[0030] The internal volume may comprise a working portion, included between the outlet valve system and the additional valve system. For example, the outlet valve system may be in the closed configuration and the additional valve system in the open configuration to allow plastic to be accumulated in the working portion of the internal volume. The outlet valve system may be in the open configuration and the additional valve system in the closed configuration to allow plastic to be discharged from the working portion of the internal volume.

[0031] In the example comprising the outlet valve system and the additional valve system, the partition elements of the plurality of partition elements are preferably disposed between the additional valve system and the outlet valve system. Preferably, each of the plurality of partition elements is movable between an upper limit position and a lower limit position to vary the working portion of the internal volume of the distributor unit. The working portion of the internal volume may be variable from a contracted configuration, where it has its minimum volume, to an expanded configuration, where it has its maximum volume. More specifically, the difference between the maximum volume and the minimum volume of the working portion is equal to the volume of one dose multiplied by the number of outfeed branches.

[0032] In this context, the metering unit may include a charging configuration, where the metering unit is configured to allow plastic to be accumulated, for example, in the working portion of the internal volume of the distributor unit. Preferably, in the charging configuration, the outlet valve system is in the closed configuration and the additional valve system is in the open configuration. That way, the plastic can be fed into the working portion of the internal volume. The metering unit may include a discharging configuration, where it is configured to allow plastic to be discharged, for example, from the working portion of the internal volume. In the discharging configuration, the metering unit may be configured to allow the doses of plastic, formed from the flow of plastic, to be discharged through the outlets. Thus, in the discharging configuration, the apparatus is configured to feed the doses to the plurality of seats of the plurality of female elements. Preferably, in the discharging configuration, the outlet valve system is in the open configuration and the additional valve system is in the closed configuration, so as to allow discharging the plastic from the working portion and feeding out the doses.

[0033] The control unit is preferably configured to switch the metering unit from the discharging configuration to the charging configuration with the plurality of partition elements disposed at the upper limit position. The control unit is preferably configured to switch the metering unit from the charging configuration to the discharging configuration with the plurality of partition elements disposed at the lower limit position.

[0034] In other words, the additional valve system is configured to separate a predetermined quantity of plastic from the continuous flow of plastic and to allow the predetermined quantity of plastic to advance into a zone between the additional valve system and the outlet valve system, that is, into the working portion; that way, the working portion is configured to be filled with the predetermined quantity of plastic and to expand its volume, while the partition elements are configured to move from the lower limit position to the upper limit position. The upper limit position of the partition elements is preferably a fixed position, that is to say, a position beyond which the partition element cannot move, meaning that the internal volume (or the working portion of the internal volume) cannot be expanded any further during a moulding operation.

[0035] In an example, the additional valve system comprises a main valve, located in the infeed duct. In an example, the additional valve system comprises a plurality of valves, each valve of the plurality being located in a respective outfeed branch of the plurality of outfeed branches.

[0036] It should be noted that in the example comprising the outlet valve system and the additional valve system, when the partition elements of the additional valve system are at the upper limit position, the outlet valve system is configured to separate an additional quantity of plastic from the predetermined quantity contained in the working portion; for this purpose, the outlet valve system is configured to switch to the open configuration and to allow the working portion to contract its volume to be emptied of the predetermined quantity of plastic it contains, while the partition elements are configured to move from the upper limit position to the lower limit position. Thus, the additional predetermined quantity of plastic separated by the outlet valve system is equivalent to the difference between a volume of the working portion with the partition elements at the upper limit position and a volume of the working portion with the partition elements at the lower limit position. More specifically, the additional predetermined quantity of plastic defines the volume of the plastic doses. Thus, the volume of each of the doses is known precisely.

[0037] In an embodiment, each partition element of the plurality of partition elements is positioned in a respective outfeed branch, upstream of the respective outlet valve. Each outfeed branch may include a first branch. In an example, each partition element is positioned in a respective first branch (upstream of the respective outlet valve).

[0038] For example, the partition elements are movable from the upper position to the lower position to vary the internal volume of the distributor unit. In the embodiment comprising the additional valve system and the plurality of partition elements, when the metering unit is in the charging configuration, the outlet valve system is in the closed configuration to interrupt a flow of plastic from the distributor unit and, for example, when the metering unit is in the discharging configuration, the outlet valve system is in the open configuration to allow plastic to be discharged from the internal volume of the distributor unit. In this context, moving the partition elements from the upper limit position to the lower limit position, with the metering unit in the discharging configuration, and from the lower limit position to the upper limit position, with the metering unit in the charging configuration, produces a plurality of doses of plastic fed to the plurality of seats. During the movement from the lower limit position to the upper limit position, the plastic advances from the inlet and accumulates inside the internal volume, with the outlet valve system in the closed configuration. During the movement from the upper limit position to the lower limit position, the plastic leaves the internal volume, with the outlet valve system in the open configuration. In the example comprising the outlet valve system and the plurality of partition elements, one dose, that is to say, one quantity of plastic forming a dose fed to a respective seat of the plurality, is defined by the quantity of plastic contained downstream of the respective outlet valve, with the outlet valve in the closed configuration and the respective partition element at the lower limit position.

[0039] Compared to the embodiment comprising the outlet valve system and the additional valve system, the apparatus comprising the outlet valve system has the advantage of being less complex, while maintaining the advantage of precision.

[0040] It is noted that the outlet valve system and the partition elements constitute distinct elements of the apparatus and that they also have two distinct functions: the outlet valve system has the function of dividing the continuous flow (or, when the additional valve system is also present, it has the function of further dividing the quantity of plastic contained in the working portion), while the partition elements have the function of feeding the dose from the internal volume (or, when the additional valve system is present, from the working portion of the internal volume), towards the outlet.

[0041] When present, the additional valve system is also a distinct element and has a different function than the partition elements; more specifically, the additional valve system has the function of dividing the continuous flow into doses.

[0042] The outfeed branch and / or the first branch of the outfeed branch can define a duct for the passage of plastic.

[0043] In an example, a distance between the lower limit position of at least one partition element (preferably, of each partition element) and a tangent to the duct (of the outfeed branch or of the first branch) is equal to zero. Hence, the partition element moves in the lower limit position so to be tangent to the duct. In another example, a distance between the lower limit position of at least one partition element (preferably, of each partition element) and a tangent to the duct (of the outfeed branch or of the first branch) is greater than zero.

[0044] Hence, the partition element moves in the lower limit position, stopping at a distance (predetermined) with respect to a tangent to the duct (of the outfeed branch or of the first branch). The fact that the partition element stops before being tangent to the duct

[0045] The fact that the partition element stops before being tangent to the duct prevents the presence of degraded plastic in the duct.

[0046] In an example, at least one of the plurality of partition elements may be movable between the lower limit position and the upper limit position by pressure applied by the plastic on the at least one partition element.

[0047] Alternatively, or in addition, the metering unit may comprise an actuator for at least one partition element of the plurality of partition elements or one actuator for each partition element of the plurality of partition elements. In an example, the metering unit may include a group of actuators, where each actuator of the group of actuators is connected to a respective partition element of the plurality of partition elements. The actuator may be configured to move the respective partition element between the upper limit position and the lower limit position, preferably continuously. The actuator has the advantage of precisely controlling the upper limit position and the lower limit position of a partition element, in particular during a moulding operation.

[0048] In an example, the control unit may be configured to drive one or more of the actuators of the group of actuators to move the corresponding partition elements from the upper limit position to the lower limit position, preferably with the metering unit in the discharging configuration. The control unit may be configured to drive one or more of the actuators of the group of actuators to move the corresponding partition elements from the lower limit position to the upper limit position, preferably with the metering unit in the charging configuration. That way, it is possible to make a plurality of doses of plastic which can be fed to the plurality of seats.

[0049] In an embodiment, the apparatus comprises a sensor system. The sensor system may include a pressure sensor to detect a pressure value. Preferably, the pressure sensor is located upstream of the outlet valve system.

[0050] Preferably, the control unit is configured to control the actuators of the group of actuators so as to displace the corresponding partition elements from the lower limit position to the upper limit position as a function of the pressure value detected by the sensor system. More preferably, the control unit controls the actuators to displace the partition elements from the lower limit position to the upper limit position as a function of the pressure value detected by the sensor system, for the entire upstroke from the lower limit position to the upper limit position.

[0051] In an embodiment, the apparatus comprises a compensation unit. The compensation unit may be located upstream of the plurality of outfeed branches. The compensation unit defines a compensation volume which is variable between a maximum volume configuration and a minimum volume configuration. Preferably, the compensation volume is variable depending on a cycle of charging and discharging the plurality of doses of plastic. The purpose of the compensation unit is to compensate the variations in the pressure applied by the plastic when the outlet valve system and / or the additional valve system (when present) is in the closed configuration.

[0052] In an embodiment, the control unit is programmed to control a speed of displacement of the partition elements from the lower limit position to the upper limit position. That way, the pressure detected by the sensor system is kept below a predetermined threshold pressure value. For example, the control unit may be programmed to compare the pressure value detected by the sensor system with a predetermined threshold pressure value. Responsive to the comparison (in particular, responsive to the detected pressure value being greater than or equal to the predetermined threshold pressure value), the control unit controls the displacement of the partition elements (in particular, the speed of displacement of the partition elements) from the lower limit position to the upper limit position. Thus, during the upstroke from the lower limit position to the upper limit position, the pressure detected by the sensor system is constant. It is noted that controlling the speed of upward displacement of the partition elements from the lower limit position to the upper limit position determines controlling the instant at which the partition elements reach the upper limit position. Preferably, the control unit is programmed to control the speed of displacement of the partition elements from the lower limit position to the upper limit position as a function of the detected pressure value and of the threshold pressure value, where the detected pressure value is detected in each charging and discharging cycle. Thus, the speed of displacement can be varied from one charging and discharging cycle to the next.

[0053] In particular, the upper limit position of each of the partition elements is adjustable based on the volume of the dose to be obtained. Preferably, the upper limit position is adjustable for each charging and discharging cycle. This allows the plastic to be metered flexibly and dynamically.

[0054] In an embodiment, the predetermined threshold pressure value is selected from a pressure range of between 10 and 25 bar, in particular between 15 and 20 bar.

[0055] In an example embodiment, the apparatus comprises an extruder, connected to the inlet of the infeed duct, to feed it with a continuous pressurized flow of molten plastic. In other words, the extruder unit (the extruder), in particular an outlet of the extruder unit may be located at the infeed duct of the metering unit. The extruder comprises a screw. The apparatus may comprise an actuator, connected to the screw to rotate the screw inside the extruder. The control unit may be programmed to control the actuator of the screw so as to vary a rotation speed of the screw inside the extruder. Preferably, the rotation speed of the screw is varied as a function of the charging and discharging cycle. In particular, the rotation speed of the screw is varied as a function of a control parameter detected with a periodicity linked to the charging and discharging cycle.

[0056] The compensation unit may comprise a compensating partition element. The compensating partition element may be configured to move between an upper limit position and a lower limit position to vary the compensation volume between the maximum volume configuration and the minimum volume configuration. In an embodiment, the control parameter (the parameter used as the basis for varying the rotation speed of the screw) represents (that is, is linked to) a position of the compensating partition element between the upper limit position and the lower limit position. In an example, the compensating partition element is configured to move from the lower limit position to the upper limit position as a function of the partition elements being located at the upper limit position. In other words, when the partition elements reach the upper limit position, the compensating partition element moves from the lower limit position to the upper limit position. Preferably, the compensating partition element is displaced by effect of the pressure of the plastic exerted on the compensating partition element. Thus, the displacement of the compensating partition element between the lower limit position and the upper limit position is not controlled, for example by the control unit (as it is for the partition elements of the plurality of partition elements). The purpose of displacing the compensating partition element from the lower limit position to the upper limit position responsive to the partition elements reaching the upper limit position is to compensate for the pressure increase caused by the fact that the partition elements are blocked at the upper limit position. It is noted that the upper limit position and the lower limit position of the compensating partition element may not necessarily be predetermined.

[0057] The compensating partition element may be operable in a free configuration, where it is free to move between an upper limit position and a lower limit position within the compensation volume. The compensating partition element may be operable in a blocked configuration, where the position of the compensating partition element is blocked at a position within the compensation volume.

[0058] The compensation unit may include an actuator, a pneumatic actuator, for example. The actuator may be configured to switch the compensating partition element from the free configuration to the blocked configuration and vice versa. In the blocked configuration, the compensating partition element may be pushed to the lower limit position by a retaining element and held at the lower limit position by the retaining element.

[0059] Thus, responsive to the partition elements reaching the upper limit position, the actuator may be configured to switch the compensating partition element from the blocked configuration to the free configuration so that the compensating partition element is displaced from the lower limit position to the upper limit position responsive to the pressure exerted by the plastic on the compensating partition element. The actuator may be configured to switch the compensating partition element from the free configuration to the blocked configuration so that the compensating partition element is displaced from the upper limit position to the lower limit position responsive to a pressure exerted by the retaining element on the compensating partition element. In particular, while being displaced from the upper limit position to the lower limit position, the compensating partition element is configured to push the plastic out of the compensation volume where it has accumulated.

[0060] In an embodiment, the control parameter represents a position of the partition elements. In addition or alternatively, the control parameter may represent a pressure value detected by the sensor system.

[0061] In the embodiment where the control parameter represents the position of the compensating partition element, the control parameter preferably represents the upper limit position of the compensating partition element. Thus, responsive to the compensating partition element reaching the upper limit position, the control unit varies the rotation speed of the extruder screw.

[0062] In the embodiment where the control parameter represents a position of the partition elements the control parameter preferably represents the upper limit position of the partition elements.

[0063] In an example embodiment, the sensor system comprises a plurality of pressure sensors, each sensor of the plurality being positioned in a respective outfeed branch at a corresponding partition element of the plurality of partition elements. Thus, the control unit may be programmed to control the actuators so as to displace the partition elements from the lower limit position to the upper limit position as a function of the pressure values detected by the pressure sensors. In particular, each sensor of the plurality of pressure sensors may be located at a respective partition element of the plurality of partition elements. In an example, the sensor system comprises a compensating pressure sensor, located at the compensating partition element (that is, at the compensation volume). In an example, the sensor system comprises a distribution pressure sensor, located in the distribution zone, and / or a plurality of distribution pressure sensors, each located in a respective outfeed branch.

[0064] In the case where the additional valve system is present, the pressure sensor is preferably located downstream of the additional valve system.

[0065] In an embodiment, the control unit is configured to close the additional valve system responsive to the partition elements being positioned at the upper limit position and to move the partition elements from the upper limit position to a further upper limit position, the further upper limit position being higher up than the upper limit position. Thus, responsive to the partition elements reaching the upper limit position, the control unit is configured to close the additional valve system and to drive the actuators of the partition elements so as to move the partition elements from the upper limit position to a further upper limit position (where the upper limit position is between the further upper limit position and the lower limit position). The purpose of displacing the partition elements from the upper limit position to the further upper limit position is to create decompression.

[0066] In the embodiment where the apparatus comprises the additional valve system and the extruder, the control unit may be configured to drive the actuator of the screw to vary the rotation speed of the screw inside the extruder as a function of a control parameter detected with a periodicity linked to the charging and discharging cycle. In this case, the rotation speed may be varied to make it higher than a steady-state speed. In other words, the rotation speed of the screw can be varied between a minimum speed and a maximum speed relative to a steady-state speed. The minimum speed and / or the maximum speed can be set on the basis of a control parameter detected with a periodicity linked to the charging and discharging cycle. Thus, the rotation speed of the screw may be varied in each charging and discharging cycle.

[0067] In particular, the control parameter may represent the position of the compensating partition element; more particularly, the upper limit position of the compensating partition element. For example, the control unit may control the speed of the screw based on whether the control parameter is greater than and / or less than a threshold value. For example, in the case where the upper limit position of the compensating partition element is greater than a (predetermined) threshold value, the control unit may be programmed to control the rotation speed of the screw so as to slow it down to a minimum speed relative to a steady-state speed. For example, in the case where the upper limit position of the compensating partition element is less than a (predetermined) threshold value, the control unit may be programmed to control the rotation speed of the screw so as to accelerate it to a maximum speed relative to a steady-state speed. Thus, such speed variations relative to the steady-state speed can be carried out in each charging and discharging cycle.

[0068] In an example embodiment (preferably in the embodiment comprising the extruder, without the additional valve system), the rotation speed of the screw may be configured to vary between a maximum value and a minimum value. In particular, the maximum value may be equal to a steady-state speed. The minimum value may be zero.

[0069] For example, the control unit is configured to stop the screw at every charging and discharging cycle. Preferably, the speed varies within each cycle. In this case, the control unit may be programmed to control the speed of the screw and to set the speed of the screw to a minimum value, with the partition elements at the upper limit position (in other words, when the partition elements reach the upper limit position). The control unit may be programmed to control the speed of the screw and to set the speed of the screw to a maximum value (for example, equal to the steady-state speed) with the compensating partition element at the upper limit position (in other words, when the compensating partition element reaches the upper limit position).

[0070] The steady-state rotation speed of the screw may be set on the basis of a production speed of a container production line.

[0071] In an example, the compensation unit is located between the extruder and the distribution zone. The compensation unit may comprise an actuator connected to the compensating partition element. The control unit may be programmed to drive the actuator so as to vary the position of the compensating partition element in a controlled manner. Alternatively, the compensation unit comprises a retaining element, configured to hold the compensating partition element at the lower limit position and leave it free to move by the effect of a pressure of the plastic present in the duct in which the partition element is inserted.

[0072] In an embodiment, the compensation unit is located in an extruder. The control unit may be configured to vary a position of the screw inside the extruder so as to vary the compensation volume of the compensation unit. In this case, it is noted that the compensation unit is actuated by an actuator connected to the screw, to vary the position of the screw inside the extruder.

[0073] In particular, the extruder may have a direction of extension (that is, it has a cylindrical duct); the screw is movable inside the extruder along the direction of extension.

[0074] This disclosure also relates to a method for producing objects in continuous cycle from plastic material. Preferably, the method is carried out by an apparatus made according to one or more aspects of this disclosure. Thus, the steps of the method described below are understood as being executable on an apparatus according to this disclosure.

[0075] In particular, the method comprises a step of providing a distributor unit, including a plurality of outfeed branches having respective outlets, an infeed duct having an inlet and in communication with the outfeed branches through a distribution zone. The distributor unit defines an internal volume between the inlet and the outlets. The method comprises a step of receiving a flow of molten plastic at the inlet of the infeed duct. The method comprises a step of distributing the flow of plastic through the distribution zone to the plurality of outfeed branches.

[0076] The method comprises a step of providing a metering unit. The metering unit includes an outlet valve system having a plurality of outlet valves, each outlet valve being positioned in a respective outfeed branch. The metering unit includes a plurality of partition elements, each partition element of the plurality of partition elements being positioned in a respective outfeed branch, upstream of the respective outlet valve. Each partition element of the plurality of partition elements is movable between an upper limit position and a lower limit position to vary the internal volume of the distributor unit.

[0077] The metering unit comprises a group of actuators, each actuator of the group of actuators being connected to a respective partition element of the plurality of partition elements to move it between the upper limit position and the lower limit position.

[0078] The method comprises a step of detecting a pressure value via a pressure sensor of a sensor system located upstream of the outlet valve system. The method comprises a step, via a control unit, of closing the outlet valve system to interrupt the flow of plastic feeding out from the distributor unit. The method comprises a step, via a control unit, of controlling one or more actuators of the group of actuators to move the corresponding partition elements from the lower limit position to the upper limit position, preferably as a function of the pressure value detected by the sensor system.

[0079] The method comprises a step, via a control unit, of detecting the opening of the outlet valve system to allow plastic to be discharged from the internal volume of the distributor unit. The method comprises a step of controlling one or more actuators of the group of actuators to move the corresponding partition elements from the upper limit position to the lower limit position so as to make a plurality of doses of plastic.

[0080] The method comprises a step of varying a compensation volume of a compensation unit between a maximum volume configuration and a minimum volume configuration depending on a cycle of charging and discharging the plurality of doses of plastic.

[0081] The method comprises a step of feeding the doses to a plurality of seats of a plurality of female elements, positioned at the plurality of outfeed branches.

[0082] The method comprises a step of compressing the doses between a plurality of female elements and a corresponding plurality of male elements to form a plurality of objects of plastic material.

[0083] In an embodiment, the method comprises a step, via the control unit, of controlling the speed of displacement of the partition elements from the lower limit position to the upper limit position so as to keep the pressure detected by the sensor system below a predetermined threshold pressure value.

[0084] For example, the method may comprise a step, via the control unit, of comparing the pressure value detected by the sensor system with a predetermined threshold pressure value. Responsive to detecting a pressure value that is greater than or equal to the predetermined threshold pressure value, the method may comprise a step, via the control unit, of controlling the speed of displacement of the partition elements from the lower limit position to the upper limit position.

[0085] In an embodiment, the method comprises a step, via an extruder connected to the infeed duct, of feeding the continuous flow of pressurized molten plastic to the infeed duct.

[0086] The method may comprise a step, via the control unit, of controlling an actuator of a screw of the extruder, in particular so as to vary a rotation speed of the screw of the extruder, preferably as a function of a control parameter detected with a periodicity linked to the charging and discharging cycle. Brief description of drawings

[0087] These and other features will become more apparent from the following description of a preferred embodiment, illustrated by way of non-limiting example in the accompanying drawings, in which:

[0088] - Figure 1 shows a part of a container production line comprising the apparatus according to one or more aspects of this disclosure;

[0089] - Figure 2 shows an apparatus according to one or more aspects of this disclosure;

[0090] - Figures 3A-3E show an apparatus according to one or more aspects of this disclosure;

[0091] - Figure 4 shows a partition element of an apparatus according to one or more aspects of this disclosure;

[0092] - Figures 5A-5H show an operating sequence of part of an apparatus according to one or more aspects of this disclosure;

[0093] - Figures 6A and 6B show the trend of parts of an apparatus according to one or more aspects of this disclosure, in a sequence of charging and discharging cycles.

[0094] Detailed description of preferred embodiments of the invention

[0095] With reference to the accompanying drawings, the numeral 1 denotes an apparatus for producing objects in continuous cycle from plastic material.

[0096] The apparatus 1 comprises a distributor unit 2, configured to distribute a flow of molten plastic. The distributor unit 2 includes an infeed duct 201 , having an inlet 202, configured to receive a flow of plastic, preferably from an extruder 101. For this purpose, the apparatus 1 may comprise an extruder 101 , connected to the infeed duct 201 (that is, to the inlet 202), to feed the flow of plastic to the infeed duct 201 . Preferably, the extruder 101 supplies the pressurized flow of plastic. The extruder 101 has a direction of extension and comprises a screw which is configured to rotate inside the extruder 101. The extruder 101 comprises an actuator connected to the screw to control it.

[0097] The distributor unit 2 includes a plurality of outfeed branches 203, each in fluid communication with the infeed duct 201 through a distribution zone 204, to receive the flow of plastic from the infeed duct 201 . The distribution zone 204 receives the flow of molten plastic from the infeed duct 201 and distributes it to each outfeed branch 203, dividing it among the plurality of outfeed branches 203. Each outfeed branch 203 includes an outlet 205, configured to supply the plastic leaving the distributor unit 2. The distributor unit 2 defines an internal volume between the inlet 202 and the outlets 205.

[0098] In an example, each outfeed branch 203 includes a first branch 203A, configured to receive the plastic from the distribution zone 204, and a second branch 203B including the outlet 205. The first branch 203A and the second branch 203B are in communication with each other. In an example, they are disposed perpendicularly to each other.

[0099] In an example, the distribution zone 204 comprises a first distribution zone 204A, located downstream of the infeed duct 201 , and a second distribution zone 204B, located downstream of the first distribution zone 204A; the first distribution zone 204A divides the flow of plastic from the infeed duct 201 into a plurality of flows of plastic, while the second distribution zone 204B further divides each flow of plastic into a further plurality which is subsequently received by the outfeed branches 203.

[0100] The apparatus 1 comprises a metering unit 3, located inside the distributor unit 2 and configured to form, from the continuous flow of plastic fed into the infeed duct 201 , the doses fed out from the outlets 205. The metering unit 3 comprises an outlet valve system 302 which can be switched between a closed configuration and an open configuration. For example, the outlet valve system 302 comprises a plurality of pushers 302A and each pusher 302A is located in a respective outfeed branch 203. More specifically, each pusher 302A is inserted in the second branch 203B and is movable reciprocally between a retracted position of non-interference with a flow of plastic in the second branch 203B, and a plurality of advanced positions where it closes the respective second branch 203B. At the plurality of advanced positions, the pusher 302A is configured to push the respective dose through the outlet 205, by moving in an extraction direction between the advanced positions so as to keep the respective valve closed. Thus, at the retracted position and at the advanced position (in particular, at the plurality of advanced positions), the pusher 302A defines an open configuration and a closed configuration, respectively.

[0101] The metering unit 3 comprises a plurality of partition elements 303, each movable between an upper limit position X1 and a lower limit position X2. That way, it varies the internal volume of the distributor unit 2. Each partition element is positioned in a respective outfeed branch 203, upstream of the respective outlet valve (or pusher 302A).

[0102] The apparatus 1 comprises a compensation unit 208, located in the infeed duct 201 , upstream of the distribution zone 204 (when the extruder 101 is present, the compensation unit 208 is located downstream of the extruder 101 ). The compensation unit 208 defines a compensation volume. The compensation unit 208 comprises a compensating partition element 206, movable between an upper limit position X1 and a lower limit position X2, so as to vary the compensation volume between a maximum volume configuration and a minimum volume configuration depending on a cycle of charging and discharging the plurality of doses of plastic.

[0103] In an embodiment, the compensation unit 208 comprises a retaining element for holding the compensating partition element at the lower limit position X2 or for leaving it free to move by the effect of a pressure of the plastic present in the infeed duct 201 in which the partition element is inserted. The retaining element may release the compensating partition element 206 so as to expand the compensation volume. The retaining element can block the compensating partition element 206 so as to push the plastic out of the compensation volume and hold the compensating partition element 206 at the lower limit position X2. The metering unit 3 includes a charging work configuration, in which the pushers 302A are in the closed configuration to interrupt the flow of plastic feeding out from the distributor unit 2. In the charging configuration, the partition elements 303 are disposed at the upper limit position X1 and the internal volume adopts an expanded configuration, that is, a maximum volume configuration, because the partition elements 303 are disposed at the upper limit position X1. The metering unit 3 includes a discharging work configuration, in which the pushers 302A are in the open configuration to interrupt the flow of plastic leaving the distributor unit 2. In the discharging configuration, the partition elements 303 are disposed at the lower limit position X2 and the internal volume adopts a contracted configuration, that is, a minimum volume configuration, because the partition elements 303 are disposed at the lower limit position X2. In passing from the charging to the discharging configuration, the partition elements 303 move from the upper limit position X1 to the lower limit position X2, thus pushing the plastic out of the outlets 205, with the pushers 302A at the retracted position. The pushers 302A move to the advanced position so as to push the plastic out of the distributor unit 2.

[0104] In particular, each partition element 303 of the plurality of partition elements 303 is located in a respective first branch 203A.

[0105] The first branch 203A defines a duct of the passage of plastics. The partition elements 303 are configured for moving from the upper limit position X1 to the lower limit position X2 so to stop at a distance D with respect to a tangent to a duct of the first branch 203A. In an example, the distance D is equal to zero (the partition element 303 moves in the lower limit position X2 so to be tangent to the duct). In another example, the distance D is higher than zero (the partition element 303 moves in the lower limit position X2 so to stop at a predetermined distance, higher than zero, with respect to a tangent to the duct).

[0106] The apparatus 1 comprises a control unit 5, configured to switch the metering unit 3 from the charging configuration to the discharging configuration, with the partition elements 303 positioned at the lower limit position X2, and from the discharging configuration to the charging configuration, with the partition elements 303 positioned at the upper limit position X1 .

[0107] The apparatus 1 comprises a forming station 4 for compression moulding. The forming station 4 includes a plurality of female elements 401 , positionable at the plurality of outfeed branches 203 of the distributor unit 2, to receive the plurality of doses being fed out from the outlets 205. The plurality of female elements 401 defines a corresponding plurality of seats

[0108] 402 configured to receive a corresponding plurality of doses of plastic being fed out. In particular, in the discharging configuration, the outlet valve system 302 is in the open configuration to feed the doses to the plurality of seats 402 of the plurality of female elements 401. The forming station 4 includes a plurality of male elements 403, configured to act in conjunction with the plurality of female elements 401 to delimit a corresponding plurality of forming cavities to form a plurality of objects simultaneously from plastic material by compression. For this purpose, each female element 401 is movable along a longitudinal axis of displacement between a spaced-apart position of non-interference with the respective male element 403, and a close-together position where it closes a forming cavity, acting in conjunction with the respective male element

[0109] 403 to compress a dose. In an example, the control unit 5 is programmed to move each female element 401 along the longitudinal axis of displacement. In an example embodiment, the objects of plastic material are parisons intended for subsequent blow moulding to form containers.

[0110] For this purpose, the apparatus 1 may form part of a line 100 for the production of containers (for example, for liquids or other) in continuous cycle and the production line 100 may comprise a parison blow moulding station 102 for forming containers, and an extruder unit 101 .

[0111] The metering unit 3 comprises one or more actuators 304, connected to the partition elements 303 to move them between the upper limit position X1 and the lower limit position X2. When the pushers 302A are at the closed position, the actuators 304 move the partition elements 303 from the lower limit position X2 to the upper limit position X1 ; when the pushers 302A are at the open position, the actuators 304 move the partition elements 303 from the lower limit position X2 to the upper limit position X1 . In particular, the apparatus 1 comprises a sensor system. The sensor system comprises a pressure sensor, located at the partition elements 303 to detect a pressure value. The sensor system comprises a plurality of pressure sensors, each located in a respective outfeed branch 203 at a corresponding partition element. The sensor system may comprises a compensating pressure sensor, located at the compensating partition element 206 (that is, at the compensation volume or compensation unit 208). In an example, the sensor system comprises a distribution pressure sensor, located in the distribution zone 204, and / or a plurality of distribution pressure sensors, each located in a respective outfeed branch 203, upstream of the partition elements 303 (and upstream of the additional valve system 301 , when present).

[0112] The control unit 5 is configured to control the actuators 304 to displace the corresponding partition elements 303 from the lower limit position X2 to the upper limit position X1 as a function of the pressure value detected by the sensor system, for the entire upstroke from the lower limit position X2 to the upper limit position X1. More particularly, the control unit 5 is programmed to compare the pressure value detected by the sensor system with a predetermined threshold pressure value. Responsive to the detected pressure value being greater than or equal to the predetermined threshold pressure value, the control unit 5 controls the displacement of the partition elements 303 and the speed of displacement of the partition elements 303 from the lower limit position X2 to the upper limit position X1 . The control unit 5 is programmed to control the actuator of the screw of the extruder 101 so as to vary a rotation speed of the screw as a function of the charging and discharging cycle. In particular, the rotation speed of the screw is varied as a function of a control parameter which is detected with a periodicity linked to the charging and discharging cycle.

[0113] In an embodiment, the metering unit 3 comprises an additional valve system 301 , located upstream of the outlet valve system 302 relative to the feed direction of the plastic from the inlet 202 to the outlets 205. The additional valve system 301 can be switched between an open configuration and a closed configuration. The internal volume comprises a working portion, included between the outlet valve system 302 and the additional valve system 301. The partition elements 303 are disposed between the additional valve system 301 and the outlet valve system 302 so that their movement between the upper limit position X1 and the lower limit position X2 varies the working portion of the internal volume. In particular, in the charging configuration, the additional valve system 301 is in the open configuration and the outlet valve system 302 is in the closed configuration to allow plastic to accumulate in the working portion of the internal volume. In the discharging configuration, the additional valve system 301 is in the closed configuration and the outlet valve system 302 is in the open configuration, to allow plastic to be discharged from the working portion of the internal volume. In particular, the additional valve system 301 includes a main valve 301 A, located in the infeed duct 201 of the distributor unit 2, downstream of the compensation unit 208. Thus, the working portion of the internal volume is located between the infeed duct 201 and the plurality of outfeed branches 203. In this case, the volume of each dose is equal to the difference between the working portion in the expanded configuration and the working portion in the contracted configuration, divided by the number of outfeed branches 203. The control unit 5 is configured to switch the main valve 301 A between an open configuration, to allow the plastic to flow into the working portion, and a closed configuration, to prevent the plastic from flowing into the working portion. In an example, the additional valve system 301 comprises a plurality of main valves 301 A located in a respective outfeed branch 203, upstream of the partition element. Thus, the working portion of the internal volume is located inside the plurality of outfeed branches 203. The control unit 5 is configured to switch the plurality of main valves 301 A between an open configuration, to allow the plastic to flow into the working portion, and a closed configuration, to prevent the plastic from flowing into the working portion.

[0114] In this case, the volume of one dose is equal to the difference between the working portion in the expanded configuration and the working portion in the contracted configuration of a single outfeed branch 203.

[0115] Thus, there are (at least) three possible embodiments. In a first embodiment, the apparatus 1 comprises the outlet valve system 302. In a second embodiment, the apparatus 1 comprises the outlet valve system 302 and the main valve 301 A. In a third embodiment, the apparatus 1 comprises the outlet valve system 302 and the plurality of main valves 301 A.

[0116] Thus, the control unit 5 can vary a rotation speed of the screw as a function of a control parameter detected with a periodicity linked to the charging and discharging cycle.

[0117] In an embodiment, the rotation speed of the screw is configured to vary between a maximum value, coinciding with a steady-state rotation speed, and a minimum value, substantially equal to zero. Thus the control unit 5 can set the speed of the screw to the minimum value with the partition elements 303 at the upper limit position X1 and to the maximum value (that is, steady-state) with the compensating partition element 206 at the upper limit position X1. In the embodiment that comprises the additional valve system 301 , the rotation speed of the screw is configured to vary between a maximum value and a minimum value relative to a steady-state value; in particular, the control unit 5 can set the speed of the screw to a value greater than the steady-state value responsive to the upper limit position X1 of the compensating partition element 206 exceeding a predetermined threshold value, and can set the speed of the screw to a value less than the steady-state value responsive to the upper limit position X1 of the compensating partition element 206 going below a predetermined threshold value. It is noted that these speed variations are smaller in extent than the steady-state speed and thus do not constitute substantial speed variations as in the case of the embodiment without the additional valve system 301 , where the extruder 101 is substantially stopped.

[0118] In an operating sequence of the apparatus 1 , at the start of the charging and discharging cycle, the speed of the screw of the extruder 101 is set to a steady-state value (hence to a maximum value). When the control unit 5 reads a detected pressure value that is greater than a predetermined threshold value, it sets the speed of the upstroke from the lower limit position X2 to the upper limit position X1 , to allow the plastic to flow into the internal volume. In the case where the additional valve system 301 is present, the valves 301 are in the open configuration to allow the plastic to flow into the working portion. After reaching the upper limit position X1 (determined by the control unit 5, based on a certain volume which the dose is required to have), the control unit 5 blocks the partition elements 303 at the upper limit position X1 . At this point, the pressure increases on account of the partition elements 303 stopping. In the case where the additional valve system 301 is present, the control unit 5 closes the additional valve system 301 . After reaching the upper limit position X1 , the control unit 5 can stop the rotation speed of the screw of the extruder 101 (in the embodiment comprising the additional valve system 301 , the control unit 5 adjusts the rotation speed of the screw relative to the steadystate speed, increasing or decreasing it based on the upper limit position X1 reached by the compensating partition element 206, hence the rotation speed is preferably not stopped); the control unit 5 releases the retaining element of the compensation unit 208 so that the compensating partition element 206 is free to be displaced from the lower limit position X2 to the upper limit position X1 . That way, the compensation unit 206 compensates for the increase in the pressure of the distributor unit 2. In the meantime, the control unit 5 commands the outlet valves 302 to open; in particular, the pushers 301 A reach a retracted position so as to put the outfeed branch 203 in communication with the outlet 205.. Once the outlet 205 is open, the plastic leaving the distributor unit 2 flows towards the outlet 205 and the pressure is further decreased. The control unit 5 brings the partition elements 303 back from the upper limit position X1 to the lower limit position X2, so as to discharge the plastic that has accumulated inside the internal volume towards the outlet 205. The pushers advance from the retracted position to an advanced position where they once again close the outlet 205 and at the same time push the plastic out through the outlet 205. When the compensating partition element 206 reaches the upper limit position X1 , the control unit 5 can set the rotation speed of the screw of the extruder 101 to the steady-state speed (preferably, when the apparatus 1 comprises the additional valve system 301 , the rotation speed remains substantially equal to the steady-state speed, or set to a smaller or larger value). The retaining element of the compensation unit 208 pushes the compensating partition element 206 from the upper limit position X1 to the lower limit position X2 so as to make the plastic inside the internal volume flow towards the outfeed branches 203. As the plastic flows towards the outfeed branches, the control unit 5 once again commands the partition elements 303 to move upwards towards the upper limit position X1 , thus proceeding to the next plastic charging and discharging cycle.

[0119] When the additional valve system 301 is present, the control unit 5 does not completely stop the rotation speed of the screw but makes adjustments to the speed relative to the steady-state speed.

[0120] For exemplary purposes only, Figures 6A and 6B show the trend of parts of an apparatus 1 in a sequence of charging and discharging cycles. The line labelled a indicates the rotation speed of the screw of the extruder 101 ; the line labelled b indicates the position of one of the plurality of partition elements 303; the line labelled c indicates the position of the compensating partition element of the compensation unit 208; the line labelled d indicates the position of the valve 302 (that is, of the pusher 302A); the lines labelled p1, p2 and p3 indicate the pressure values detected respectively at one of the plurality of partition elements 303, at one of the plurality of outfeed branches 203 upstream of the partition element 303 and at the compensating partition element 206; the lines labelled e1 and e2 indicate a valve 301 of the additional valve system 301 respectively in an open state and in a closed state.

[0121] Figure 6A shows the trend of parts of the apparatus 1 . When the extruder screw rotates at steady-state speed (line a), the partition element 303 moves from the lower limit position X2 to the upper limit position X1 to accumulate plastic (line b). When the partition element 303 reaches the upper limit position X1 , determined by the volume of the dose to be obtained, the control unit 5 stops the rotation of the screw; at this stage, the internal pressure increases (lines p1, p2 and p3} because the partition element 303 is blocked at the upper limit position X1 . The compensating partition element 206 moves upwards towards the upper limit position X1 to compensate for the pressure increase, accumulating the excess plastic. At the same time, the outlet valve 302 (the pusher 302A) moves upwards and opens the outfeed branch 203 so that the plastic can flow out of the outfeed branch 203 towards the outlet 205 and the partition element 303 moves down to push the accumulated plastic towards the outlet 205. The outlet valves 302 close (that is to say, the pusher 302A moves down), pushing the plastic out completely.

[0122] Figure 6B shows the trend of parts of the apparatus 1 in the embodiment comprising the additional valve system 301. When the valve 301 switches to the closed state (line e2), the compensating partition element 206 of the compensation unit 208 is displaced towards the upper limit position X1 (line c), thus accumulating inside it the plastic produced by the screw of the extruder 101. When the valve 301 switches to the open state (line e1), the plastic enters the working portion of the internal volume; The compensating partition element 206 of the compensation unit 208 is displaced towards the lower limit position X2 (line c) to discharge the plastic previously accumulated which, together with that produced by the extruder 101 , enters the working portion of the internal volume. When the plastic enters the working portion of the internal volume, the partition element 303 moves from the lower limit position X2 to the upper limit position X1 to accumulate plastic (line b). At this stage, the control unit 5 adjust the upstroke speed of the partition element 303 as a function of the pressure detected at the partition element 303 (line p1). The partition element 303 stops at the upper limit position X1 , that is, at the height where the dose having the required volume is produced. When the partition element 303 stops, the valve 301 switches to the closed state and the partition element 303 moves upwards from the upper limit position X1 to a further upper limit position so as to depressurize the working portion. The outlet valve 302 opens (line d) to put the outfeed branch 203 in communication with the outlet 205 and to push the plastic out through the outlet 205, while the partition element 303 moves from the upper limit position X1 (or from the further upper limit position) to the lower limit position X2, to discharge the plastic from the working portion. At this point, the valves 302 move down, closing the outfeed branch 203 and pushing the plastic out completely through the outlet 205. The screw of the extruder 101 (not shown in Figure 6B) is configured to rotate at a steadystate speed and (if necessary) to vary its rotation speed relative to the steady-state speed based on whether the upper limit position X1 is less than or greater than a predetermined threshold value.

Claims

CLAIMS1. An apparatus (1 ) for producing objects in continuous cycle from plastic material, comprising:- a distributor unit (2), including an infeed duct (201 ), having an inlet (202) configured to receive a continuous pressurized flow of molten plastic, and a plurality of outfeed branches (203), each outfeed branch (203) having an outlet (205) and being in fluid communication with the infeed duct (201 ) through a distribution zone (204), the distributor unit (2) defining an internal volume between the inlet (202) and the outlets (205);- a forming station (4) for forming a plurality of objects by compression moulding, including a plurality of female elements (401 ), positionable at the plurality of outfeed branches (203) of the distributor unit (2) and defining a corresponding plurality of seats (402), a plurality of male elements (403), acting in conjunction with the plurality of female elements (401 ) to delimit a corresponding plurality of forming cavities to form a plurality of objects from plastic material by compression;- a metering unit (3), including an outlet valve system having a plurality of outlet valves (302), each outlet valve being positioned in a respective outfeed branch (203), wherein the outlet valve system is switchable between an open configuration and a closed configuration; a plurality of partition elements (303), each partition element (303) of the plurality of partition elements (303) being positioned in a respective outfeed branch, upstream of the respective outlet valve, and each partition element (303) of the plurality of partition elements (303) being movable between an upper limit position (X1 ) and a lower limit position (X2) to vary the internal volume of the distributor unit (2); a group of actuators (304), each actuator of the group of actuators being connected to a respective partition element (303) of the plurality ofpartition elements (303) to move it between the upper limit position (X1) and the lower limit position (X2), wherein the metering unit (3) includes the following operating configurations: a charging configuration, wherein the outlet valve system (302) is in the closed configuration to interrupt a flow of plastic feeding out from the distributor unit (2); a discharging configuration, wherein the outlet valve system (302) is in the open configuration to allow plastic to be discharged from the internal volume of the distributor unit (2);- a sensor system, including a pressure sensor located upstream of the outlet valve system (302) to detect a pressure value;- a control unit (5), configured for switching the metering unit (3) from the charging configuration to the discharging configuration and vice versa, and for driving the actuators (304) of the group of actuators to move the corresponding partition element (303) from the upper limit position (X1 ) to the lower limit position (X2), with the metering unit (3) in the discharging configuration, and from the lower limit position (X2) to the upper limit position (X1 ) as a function of the pressure value detected by the sensor system, with the metering unit (3) in the charging configuration, so as to make a plurality of doses of plastic, the doses being fed to the plurality of seats (402);- a compensation unit (208), located upstream of the plurality of outfeed branches (203) and defining a compensation volume, variable between a maximum volume configuration and a minimum volume configuration depending on a cycle of charging and discharging the plurality of doses of plastic.

2. The apparatus (1 ) according to claim 1 , wherein the control unit (5) is programmed to control a speed of displacement of the partition elements (303) from the lower limit position (X2) to the upper limit position (X1 ) so asto keep the pressure detected by the sensor system below a predetermined threshold pressure value.

3. The apparatus (1 ) according to claim 2, wherein the predetermined threshold pressure value is selected from a pressure range of between 10 and 25 bar.

4. The apparatus (1 ) according to any one of the preceding claims, comprising an extruder (101 ), connected to the inlet (202) of the infeed duct (201 ) to feed it with a continuous flow of pressurized molten plastic and comprising a screw, wherein the apparatus (1 ) comprises an actuator, connected to the screw to rotate it inside the extruder (101 ), and the control unit (5) is configured to drive the screw actuator to vary the rotation speed of the screw inside the extruder (101 ) as a function of a control parameter detected with a periodicity linked to the charging and discharging cycle.

5. The apparatus (1 ) according to claim 4, wherein at least one of the following conditions is true: i) the compensation unit (208) comprises a compensating partition element (206) configured to move between an upper limit position (X1 ) and a lower limit position (X2) to vary the compensation volume between the maximum volume configuration and the minimum volume configuration and the control parameter represents a position of the compensating partition element (206); ii) the control parameter represents a position of the partition elements (303); iii) the control parameter represents a pressure value detected by the sensor system.

6. The apparatus (1 ) according to claim 5, wherein at least one of the following conditions is true: i) the control parameter represents the upper limit position (X1 ) of the compensating partition element (206); ii) the control parameter represents the upper limit position (X1 ) of the partition elements (303).

7. The apparatus (1 ) according to any one of claims 4 to 6, wherein the control unit (5) is configured to stop the screw at every charging and discharging cycle.

8. The apparatus (1 ) according to any one of the preceding claims, wherein the sensor system comprises a plurality of pressure sensors, each sensor of the plurality being positioned in a respective outfeed branch (203) at a corresponding partition element (303) of the plurality of partition elements.

9. The apparatus (1 ) according to any one of the preceding claims, wherein the metering unit includes an additional valve system (301 ), positioned upstream of the outlet valve system (302) relative to a feed direction of the plastic from the inlet (202) to the outlets (205), wherein the outlet valve system (302) and the second, additional valve system (301 ) is each switchable between an open configuration and a closed configuration, the internal volume comprising a working portion, included between the outlet valve system (302) and the additional valve system (301 ), wherein the plurality of elements (303) are disposed between the additional valve system (301 ) and the outlet valve system (302), so as to vary the working portion of the internal volume of the distributor unit, wherein, in the charging configuration the additional valve system (301 ) is in the open configuration to allow plastic to accumulate in the working portion of the internal volume, and in the discharging configuration, the additional valve system (301 ) is in the closed configuration to allow plastic to be discharged from the working portion of the internal volume.

10. The apparatus (1 ) according to claim 9, wherein the control unit (5) is configured to close the additional valve system (301 ) responsive to the partition elements (303) being positioned at the upper limit position (X1 ) and to move the partition elements (303) from the upper limit position (X1 ) to a further upper limit position, the further upper limit position being further up than the upper limit position (X1 ).

11. The apparatus (1 ) according to claim 9 or 10, comprising an extruder (101 ), connected to the inlet (202) of the infeed duct (201 ) to feed it with acontinuous flow of pressurized molten plastic and comprising a screw, wherein the apparatus (1 ) comprises an actuator, connected to the screw to rotate it inside the extruder (101 ), and the control unit (5) is configured to drive the screw actuator to vary the rotation speed of the screw inside the extruder (101 ) between a minimum speed, lower than a steady-state speed, and a maximum speed, higher than the steady-state speed, as a function of a control parameter detected with a periodicity linked to the charging and discharging cycle.

12. The apparatus (1 ) according to any one of the preceding claims, wherein the compensation unit (208) is located between the extruder (101 ) and the distribution zone (204) and comprises a compensating partition element (206) configured to move between an upper limit position (X1 ) and a lower limit position (X2) to vary the compensation volume between the maximum volume configuration and the minimum volume configuration, wherein at least one of the following conditions is true: i) the compensation unit (208) comprises an actuator connected to the compensating partition element (206) and the control unit (5) is programmed to drive the actuator to vary the position of the compensating partition element (206) in a controlled manner; ii) the compensation unit (208) comprises a retaining element, configured to hold the compensating partition element (206) at the lower limit position (X1) and leave it free to move by the effect of a pressure of the plastic present in the duct in which the partition element is inserted.

13. The apparatus (1 ) according to any one of the preceding claims, comprising an extruder (101 ), connected to the inlet (202) of the infeed duct (201 ) to feed it with a continuous flow of pressurized molten plastic and including a screw, the extruder (101 ) having a direction of extension and the screw being movable inside the extruder (101 ) along the direction of extension, wherein the apparatus (1 ) comprises an actuator connected to the screw, and the control unit (5) is configured to drive the screw actuator to vary a position of the screw inside the extruder (101 ) so as to vary thecompensation volume of the compensation unit (208).

14. A method for producing objects in continuous cycle from plastic material, comprising the following steps:- providing a distributor unit (2), including a plurality of outfeed branches (203) having respective outlets (205), an infeed duct (201 ) having an inlet (202) and in communication with the outfeed branches (203) through a distribution zone (204), the distributor unit (2) defining an internal volume between the inlet (202) and the outlets (205);- receiving a flow of molten plastic at the inlet (202) of the infeed duct (201 );- distributing the flow of plastic through the distribution zone (204) to the plurality of outfeed branches (203);- providing a metering unit (3), including an outlet valve system having a plurality of outlet valves (302), each outlet valve being positioned in a respective outfeed branch (203), a plurality of partition elements (303), each of the plurality of partition elements being positioned in a respective outfeed branch, upstream of the respective outlet valve (302), and each partition element of the plurality of partition elements (303) being movable between an upper limit position (X1 ) and a lower limit position (X2) to vary the internal volume of the distributor unit (2), a group of actuators (304), each actuator of the group of actuators being connected to a respective partition element of the plurality of partition elements (303) to move it between the upper limit position (X1 ) and the lower limit position (X2),- detecting a pressure value via a pressure sensor of a sensor system located upstream of the outlet valve system (302);- via a control unit (5), closing the outlet valve system (302), to interrupt the flow of plastic feeding out from the distributor unit (2), and controlling one or more actuators (304) of the group of actuators to move the corresponding partition elements (303) from the lower limit position (X2) to the upper limitposition (X1) as a function of the pressure value detected by the sensor system, opening the outlet valve system (302) to allow plastic to be discharged from the internal volume of the distributor unit (2) and controlling one or more actuators (304) of the group of actuators to move the corresponding partition elements from the upper limit position to the lower limit position so as to make a plurality of doses of plastic,- varying a compensation volume of a compensation unit (208) between a maximum volume configuration and a minimum volume configuration depending on a cycle of charging and discharging the plurality of doses of plastic;- feeding the doses to a plurality of seats (402) of a plurality of female elements (401 ), positioned at the plurality of outfeed branches (203),- compressing the doses between the plurality of female elements (401 ) and a corresponding plurality of male elements (403) to form a plurality of objects of plastic material.

15. The method according to claim 14, comprising, via the control unit (5), a step of controlling the speed of displacement of the partition elements (303) from the lower limit position (X2) to the upper limit position (X1 ) so as to keep the pressure detected by the sensor system below a predetermined threshold pressure value.

16. The method according to claim 14 or 15, comprising the following steps: -via an extruder (101 ) connected to the infeed duct (201 ), feeding the continuous flow of pressurized molten plastic to the infeed duct (201 );- via the control unit (5), controlling an actuator of a screw of the extruder (101 ), so as to vary a rotation speed of the screw of the extruder (101 ) as a function of a control parameter detected with a periodicity linked to the charging and discharging cycle.

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