Method and apparatus for compression moulding plastic objects of concave shape

Abstract

A method for compression moulding plastic objects of concave shape, comprising the following steps: arranging a carousel (2), rotating around a central axis (Z), and a plurality of forming units (3), each positioned on the carousel (2) and including a male half-mould (31) and a female half-mould (32) supported by a female mould holder (33), wherein at least one of said male half-mould (31) and female half-mould (32) is movable with respect to the other along a moulding axis (S) between an open position and a closed position, to allow the forming unit (3) to move between an open configuration (CA), in which the half-moulds (31, 32) are spaced apart, and a closed configuration (CC), in which the half-moulds (31, 32) are coupled to delimit a forming cavity; arranging a transfer device (5); by means of the transfer device (5), feeding doses to the forming units (3) in a feeding station, wherein the transfer device (5) has a portion (51) operatively interposed between the male half-mould (31) and the female half-mould (32) of a corresponding forming unit (3), when it is positioned in the feeding station, in the open configuration (CA); for each forming unit (3), movement of the at least one movable half-mould (31, 32), from the open position to the closed position, so as to cause the crushing of a dose of plastic interposed therein; arranging, for each forming unit (3), a plurality of spacer elements (6) of different thicknesses, positionable between the female half-mould (32) and the respective female mould holder (33); on the occasion of a format change for the objects to be made, replacing the spacer elements (6), to vary a relative distance between the male half-mould (31) and the female half-mould (32), in the open configuration (CA) of the forming unit (3).

Description

[0001] DESCRIPTION

[0002] METHOD AND APPARATUS FOR COMPRESSION MOULDING PLASTIC OBJECTS OF CONCAVE SHAPE

[0003] Technical field

[0004] The present invention relates to a method and an apparatus for compression moulding plastic objects of concave shape. For example, the present invention relates to rotary machines for continuously producing plastic capsules, preferably caps or other capsules intended for closing containers for liquids.

[0005] Background art

[0006] Among the solutions known in this field, machines exist which are provided with a main carousel rotating around a vertical axis, on the periphery of which a plurality of moulds are arranged. The moulds are arranged to receive a dose and to form the dose by means of compression, generating the cap. Dose is intended as a portion of semi-solid plastic material, deformable by compression.

[0007] The moulds of the known machines comprise a lower half-mould and an upper half-mould, mutually movable. Usually, one half-mould is fixed and the other half-mould is movable.

[0008] Known solutions are described for example by documents WO2024 / 057281A1, EP4037884A1, US5807592, EP1585623, W00132390A1, W02007017418A2 and W02018051240A1 (in the name of the same Applicant).

[0009] These documents describe apparatuses for forming caps which have an upper male half-mould, fixed with respect to the carousel, and a lower female half-mould, movable to close against the male mould. The lower half-mould receives the dose in a low position, rises towards the upper half-mould, and, closing the forming cavity, forms the cap. The known apparatuses comprise a further carousel, also rotating around a verticalaxis, which has the task of feeding the doses into the mould and extracting the caps from the mould once they have been formed. The described solutions further include a control unit and a hydraulic circuit, connected to each other to manage the multiple electromechanical functions of the apparatus. The hydraulic circuit, inter alia, is in fluid communication with the actuator of the female half-mould, and makes different working pressures available to the actuator as a function of the rotation angle of the carousel.

[0010] In this context, there is a need to increase the productivity of the machines, that is, there is a need to increase the rotation speed of the machine (therefore, increase the moulding speed). The high rotation speed of the machine implies the need for a higher precision, and imposes substantial changes to multiple aspects of the machine, such as the sensors, the precision standards, the safety standards and the mechanical, electrical and hydraulic components.

[0011] At the same time, there is a need to optimise the energy consumption for the operation of such machines.

[0012] Typically, the hydraulic circuit, which is designated for the relative movement of the moulds, is fed with oil, which is pressurised inside the circuit by means of a system of motors and valves.

[0013] Therefore, a need felt in the field is to use as little oil as possible for the movement of the moulds.

[0014] A further need felt in the field is for such machines to be capable of compression moulding objects of different formats. It is therefore important that a machine is capable of adapting in a practical and simple manner to the different formats to be moulded.

[0015] It is known to change the size of the extraction device depending on the size and format of the moulded object to be extracted. However, such a procedure is delicate, impractical and consequently not rapid, by an operator who needs to set a format change of the object to be moulded. Furthermore, such a procedure does not allow to optimise energyconsumption, since the stroke of the half-moulds necessarily remains calibrated on the format of the object to be moulded which is of greater size.

[0016] Disclosure of the invention

[0017] An object of the present invention is to provide a method and an apparatus for compression moulding plastic objects of concave shape which meet the aforementioned needs and simultaneously overcome the aforementioned drawbacks.

[0018] In particular, it is an object of the present invention to provide a method and an apparatus for compression moulding plastic objects of concave shape which are capable of minimising oil consumption.

[0019] In particular, it is an object of the present invention to provide a method and an apparatus for compression moulding plastic objects of concave shape which are capable of being versatile with respect to different object formats.

[0020] Said object is fully achieved by the method and by the apparatus for compression moulding plastic objects of concave shape which are the object of the present invention, which is characterized by what is contained in the claims below.

[0021] In particular, the method for compression moulding plastic objects of concave shape comprises a step of arranging a carousel.

[0022] The carousel is rotatable around a central axis according to a rotation direction.

[0023] Considering the central axis directed according to the vertical direction and a top view, the rotation direction is preferably clockwise.

[0024] The method comprises a step of arranging a plurality of forming units. Each forming unit is positioned on the carousel and includes a male halfmould and a female half-mould.

[0025] The female half-mould is supported by a female mould holder.At least one of said male half-mould and female half-mould is movable with respect to the other along a moulding axis between an open position and a closed position, to allow the forming unit to move between an open configuration and a closed configuration.

[0026] In the open configuration, the half-moulds are spaced apart from each other.

[0027] In the closed configuration, the half-moulds are coupled to delimit a forming cavity.

[0028] The method comprises a step of arranging a transfer device.

[0029] The method comprises a step, by means of the transfer device, of feeding doses to the forming units in a feeding station.

[0030] The doses are preferably doses of semi-solid plastic.

[0031] In the open configuration, the transfer device has a portion operatively interposed between the male half-mould and the female half-mould of a corresponding forming unit, when it is positioned in the feeding station. The method comprises a step of moving, for each forming unit, the at least one movable half-mould, from the open position to the closed position, so as to cause the crushing of a dose of plastic interposed therein.

[0032] The method comprises a step of arranging, for each forming unit, a plurality of spacer elements of different thicknesses, positionable between the female half-mould and the respective female mould holder.

[0033] The method comprises, on the occasion of a format change for the objects to be made, a step of replacing the spacer elements, to vary a relative distance between the male half-mould and the female half-mould, in the open configuration of the forming unit.

[0034] That is, when passing from the moulding of objects with a first format, to objects with a second format, there is a step of replacing the spacer elements between the female half-mould and the respective female mould holder.

[0035] Advantageously, spacer elements of different thicknesses allow to adapt to different formats of objects to be moulded and made.Advantageously, replacing the spacer elements allows to modify the distance between the half-moulds in the open configuration as a function of need, for example, based on the size of the object to be moulded.

[0036] Advantageously, the replacement of the spacer elements allows to adapt to different moulding configurations, in particular by acting on the forming units, guaranteeing versatility.

[0037] Advantageously, an operator can, for example, adapt the distance between the half-moulds at will by inserting spacer elements of different thicknesses.

[0038] In the replacement step, the spacer element can be selected, as a function of format information representative of a format of the objects to be made, so as to minimise the relative distance between the male half-mould and the female half-mould, in the open configuration of the forming unit.

[0039] That is, the format information indicates the format of the objects to be made and the spacer element can be chosen on the basis of such a format to minimise the relative distance between the male half-mould and the female half-mould.

[0040] Advantageously, minimising the relative distance as a function of the format of the object to be moulded allows to maintain an adequate space between the male half-mould and the female half-mould to accommodate the formed object, in the open configuration.

[0041] Advantageously, minimising the relative distance between the male halfmould and the female half-mould allows to minimise the stroke of the movable half-mould to pass from the open configuration to the closed configuration.

[0042] Advantageously, minimising the stroke allows to reduce the consumption of oil for the relative movement of the half-moulds.

[0043] Advantageously, reducing oil consumption allows to obtain energy optimisation and energy savings.

[0044] According to an aspect of the description, the method comprises a step of arranging a control unit designated for receiving format information,representative of a format of the objects to be made, wherein, in the replacement step, the spacer element is selected, by means of the control unit, as a function of format information representative of a format of the objects to be made, so as to minimise the relative distance between the male half-mould and the female half-mould, in the open configuration of the forming unit. This format information represents a format of the objects to be created. Advantageously, this aspect allows for the automated identification of the optimal spacer element.

[0045] Preferably, the transfer device includes a starwheel.

[0046] The starwheel is rotating around a transfer rotation axis parallel to the central axis.

[0047] Considering the central axis directed according to the vertical direction and a top view, if the rotation direction of the carousel is clockwise, the rotation of the starwheel is preferably counter-clockwise.

[0048] The starwheel includes an extraction disc and a feeding disc.

[0049] The extraction disc and the feeding disc are superimposed on each other along the transfer rotation axis.

[0050] When the forming unit is positioned in the feeding station, the extraction disc is proximal to the male half-mould and the feeding disc is proximal to the female half-mould.

[0051] Preferably, for each format of the objects to be made, the feeding disc is positioned at a fixed distance with respect to the male half-mould.

[0052] The extraction disc and the feeding disc can be concentric with each other.

[0053] The method can comprise a step of extracting a moulded object by means of the extraction disc.

[0054] The method can comprise, on the occasion of the format change, a step of adjusting the position of the transfer device.

[0055] The adjustment of the transfer device occurs by translation along an adjustment direction parallel to the transfer rotation axis.

[0056] Advantageously, adjusting the position of the transfer device allows tominimise the distance between the male half-mould and the female halfmould.

[0057] Advantageously, the transfer device is moved by translation and the distance between the male half-mould and the female half-mould is modified by means of the spacer element so that such a distance can be minimal, but at the same time the translation device can be interposed between the half-moulds.

[0058] Advantageously, the transfer device is only translated and no component of the transfer device itself is replaced. This guarantees greater simplicity and speed in the operations during the format change.

[0059] Preferably, the adjustment of the position of the transfer device along the adjustment direction is carried out as a function of the format information, to maintain a minimum distance between the transfer device and the female half-mould constant at a preset value, with the forming unit positioned in the feeding station, in the open configuration.

[0060] Advantageously, changing the distance between the half-moulds and adjusting the position of the transfer device as a function of the size of the object to be moulded allows the distance between the half-moulds to be best minimised, while ensuring that the transfer device can be interposed between the half-moulds.

[0061] Advantageously, maintaining the minimum distance between the transfer device and the female half-mould constant at a preset value allows to ensure that there are no contacts between the transfer device and the female half-mould, in particular in the operational moulding and / or movement steps thereof.

[0062] An operator, knowing the format of the objects to be moulded, during a format change, can translate the transfer device and / or change the distance between the half-moulds by means of the spacer elements as a function of tables, data, predetermined and known indications.

[0063] The plastic objects of concave shape can be closure capsules for containers for liquids.The present description also provides an apparatus for compression moulding plastic objects of concave shape.

[0064] The apparatus comprises a carousel, rotating around a central axis according to a rotation direction.

[0065] The apparatus comprises a plurality of forming units.

[0066] Each forming unit is positioned on the carousel.

[0067] Each forming unit includes a male half-mould and a female half-mould supported by a female mould holder.

[0068] At least one of said male half-mould and female half-mould is movable with respect to the other along a moulding axis between an open position and a closed position, to allow the forming unit to move between an open configuration, in which the half-moulds are spaced, and a closed configuration, in which the half-moulds are coupled to delimit a forming cavity.

[0069] Each forming unit comprises an actuator.

[0070] The actuator is configured to move the at least one movable half-mould between the open position and the closed position, so as to cause the crushing of a dose of plastic interposed therein.

[0071] The actuator comprises a transfer device, configured to feed the doses to the forming units in a feeding station.

[0072] In the feeding station, the transfer device has a portion operatively interposed between the male half-mould and the female half-mould of a corresponding forming unit positioned in the feeding station, in the open configuration.

[0073] The apparatus comprises, for each forming unit, a plurality of spacer elements of different thicknesses.

[0074] Each spacer element is positionable between the female half-mould and the respective female mould holder.

[0075] The spacer elements of the plurality are interchangeable with each other, so as to vary a relative distance between the male half-mould and the female half-mould, in the open configuration of the forming unit.Advantageously, an operator can use the spacer, on the occasion of a format change of the object to be moulded, for example, and replace the spacer elements according to the desired thickness thereof, so as to position the female half-mould at the desired distance from the male halfmould.

[0076] Preferably, the transfer device includes a starwheel.

[0077] The starwheel is rotating around a transfer rotation axis parallel to the central axis.

[0078] The starwheel includes an extraction disc and a feeding disc superimposed on each other along the transfer rotation axis.

[0079] With the forming unit positioned in the feeding station, the extraction disc is proximal to the male half-mould and the feeding disc is proximal to the female half-mould.

[0080] The transfer device can be adjustable in position, by translation, along an adjustment direction parallel to the transfer rotation axis.

[0081] The apparatus can comprise a control unit.

[0082] The control unit is designated for receiving format information, representative of a format of the objects to be made.

[0083] The control unit is programmed to derive a setting value, representative of a desired position for the transfer device along the adjustment direction, as a function of the format information.

[0084] Advantageously, it is possible to know, by means of the control unit, in which position to translate the transfer device according to the format of the object to be moulded.

[0085] In other words, the control unit is programmed to derive an optimal vertical position for the transfer device.

[0086] The transfer device can be adjusted along the adjustment direction parallel to the transfer rotation axis, manually and / or automatically.

[0087] Preferably, the control unit is programmed to select, as a function of the format information, a spacer element of the plurality of spacer elements, so as to maintain a minimum distance between the transfer device and thefemale half-mould constant at a preset value, with the forming unit positioned in the feeding station, in the open configuration.

[0088] Advantageously, it is possible to know, by means of a control unit, which spacer element is to be positioned between the female half-mould and the female mould holder depending on the format of the object to be moulded in order to maintain a minimum distance between the transfer device and the female half-mould in the open configuration constant at a preset value. An operator can therefore know, by means of the control unit, which spacer element to interpose between the female half-mould and the female mould holder.

[0089] Preferably, the control unit is programmed to select, as a function of the format information, a spacer element of the plurality of spacer elements, so as to minimise the relative distance between the male half-mould and the female half-mould, in the open configuration of the forming unit.

[0090] Advantageously, it is possible to know, by means of a control unit, which spacer element is to be positioned between the female half-mould and the female mould holder depending on the format of the object to be moulded in order to minimise the relative distance between the male half-mould and the female half-mould, in the open configuration.

[0091] The control unit receives format information, representative of a format of the objects to be made, and, based on the format information, the control unit is programmed to:

[0092] - derive a setting value, representative of a desired position for the transfer device along the adjustment direction, as a function of the format information;

[0093] - select, as a function of the format information, a spacer element of the plurality of spacer elements, so as to maintain a minimum distance between the transfer device and the female half-mould constant at a preset value, with the forming unit positioned in the feeding station, in the open configuration;

[0094] - select, as a function of the format information, a spacer element of theplurality of spacer elements, so as to minimise the relative distance between the male half-mould and the female half-mould, in the open configuration of the forming unit.

[0095] Advantageously, the case where both the derivation of the setting value and the selection of the spacer element, based on the format information, are by means of the control unit, allows the identification of the optimal vertical position of the transfer device to be completely entrusted to the control unit, also taking into account the optimal spacer element and vice versa.

[0096] Preferably, the central axis is vertical and the female half-moulds are placed below the male half-moulds. The translation of the transfer device is along the vertical direction.

[0097] Preferably, for each forming unit, the female half-mould constitutes the movable half-mould.

[0098] Brief description of drawings

[0099] These and other features will become more apparent from the following description of one or more preferred embodiments, illustrated purely by way of non-limiting example in the accompanying drawings, wherein:

[0100] - Figure 1 illustrates a schematic representation, in a perspective view, of the apparatus according to the present description;

[0101] - Figure 2 illustrates a schematic representation, in a top view, of the apparatus according to the present description;

[0102] - Figures 3A and 3B illustrate a schematic representation, in a perspective view, of a detail of the apparatus according to the present description; - Figure 4 illustrates a schematic representation, in a sectional view, of a detail of the apparatus according to the present description;

[0103] - Figure 5 illustrates a schematic depiction in a sectional view of a solution of the prior art.

[0104] Detailed description of preferred embodiments of the inventionIn the drawings, an apparatus for compression moulding plastic objects of concave shape has been indicated by the reference number 1, in the present text also more simply indicated as apparatus 1.

[0105] The objects are preferably closing capsules for containers for liquids.

[0106] The apparatus 1 comprises a carousel 2.

[0107] The carousel 2 is rotatable around a central axis Z according to a rotation direction V.

[0108] The central axis Z is preferably vertical and the female half-moulds 32 are preferably placed below the male half-moulds 31.

[0109] The apparatus 1 comprises a plurality of forming units 3.

[0110] Each forming unit 3 is positioned on the carousel 2.

[0111] Each forming unit 3 includes a male half-mould 31 and a female halfmould 32.

[0112] As shown in Figure 4, the female half-mould 32 is supported by a female mould holder 33.

[0113] At least one of said male half-mould 31 and female half-mould 33 is movable with respect to the other along a moulding axis S between an open position and a closed position, to allow the forming unit 3 to move between an open configuration CA and a closed configuration CC.

[0114] In a preferred embodiment, for each forming unit 3, the female half-mould 32 constitutes the movable half-mould.

[0115] In the open configuration CA, the half-moulds 31, 32 are spaced apart from each other.

[0116] In the closed configuration CC, the half-moulds 31, 32 are coupled to delimit a forming cavity.

[0117] The apparatus 1 comprises, for each forming unit 3, a plurality of spacer elements 6 of different thicknesses, visible in Figure 4.

[0118] Each spacer element 6 is positionable between the female half-mould 32 and the respective female mould holder 33.

[0119] The spacer elements 6 of the plurality are interchangeable with each other, so as to vary a relative distance between the male half-mould 31and the female half-mould 32, in the open configuration CA of the forming unit 3.

[0120] Figure 3A shows the distance between the male half-mould 31 and the female half-mould 32 in the open configuration CA which defines the stroke of the at least one movable half-mould 31 , 32 to pass from the open position to the closed position. Consider the embodiment in which the female half-mould 32 is movable with respect to the male half-mould 31 : in Figure 3A the stroke of the female half-mould 32 to pass from the open position to the closed position in the absence of a spacer 6 is indicated with the reference Y and the stroke of the female half-mould 32 to pass from the open position to the closed position in the presence of a spacer 6 is indicated with the reference Y’.

[0121] The apparatus 1 comprises an actuator 4, configured to move the at least one movable half-mould 31 , 32 between the open position and the closed position, so as to cause the crushing of a dose of plastic interposed therein.

[0122] The apparatus 1 comprises a transfer device 5, configured to feed the doses to the forming units 3 in a feeding station.

[0123] In the feeding station, the transfer device 5 has a portion 51 operatively interposed between the male half-mould 31 and the female half-mould 32 of a corresponding forming unit 3 positioned in the feeding station, in the open configuration CA.

[0124] In Figure 5 a representation of a known solution should be noted which, unlike the present solution, has a spacer element 6’ in a transfer device 5’. In an embodiment, the transfer device 5 includes a starwheel 52.

[0125] The starwheel 52 is rotating around a transfer rotation axis B.

[0126] The transfer rotation axis is parallel to the central axis Z.

[0127] The starwheel 52 includes an extraction disc 53 and a feeding disc 54. The extraction disc 53 and the feeding disc 54 are superimposed on each other along the transfer rotation axis B.

[0128] As can be seen in Figures 1 and 2, with the forming unit 3 positioned inthe feeding station, the extraction disc 53 is proximal to the male halfmould 31 and the feeding disc 54 is proximal to the female half-mould 32. Preferably, the transfer device 5 is adjustable in position, by translation along an adjustment direction D parallel to the transfer rotation axis B. Preferably, the apparatus 1 comprises a control unit U, designed to receive format information, representative of a format of the objects to be made.

[0129] The control unit U is programmed to derive a setting value, representative of a desired position for the transfer device 5 along the adjustment direction D, as a function of the format information.

[0130] In an embodiment, the control unit U is programmed to select, as a function of the format information, a spacer element 6 of the plurality of spacer elements 6, so as to maintain a minimum distance L between the transfer device 5 and the female half-mould 32 constant at a preset value, with the forming unit 3 positioned in the feeding station, in the open configuration CA.

[0131] In an embodiment, the control unit U is programmed to select, as a function of the format information, a spacer element 6 of the plurality of spacer elements 6, so as to minimise the relative distance between the male half-mould 31 and the female half-mould 32, in the open configuration CA of the forming unit 3.

[0132] A method for compression moulding plastic objects of concave shape is defined.

[0133] The method comprises a step of arranging a carousel 2, rotating around a central axis Z according to a rotation direction V, and a plurality of forming units 3.

[0134] Each forming unit 3 is positioned on the carousel 2 and includes a male half-mould 31 and a female half-mould 32, supported by a female mould holder 33, wherein at least one of said male half-mould 31 and female half-mould 32 is movable with respect to the other along a moulding axis S between an open position and a closed position, to allow the forming unit 3to move between an open configuration CA, in which the half-moulds 31 , 32 are spaced apart, and a closed configuration CC, in which the halfmoulds 31 , 32 are coupled to delimit a forming cavity.

[0135] The method comprises, for each forming unit 3, a step of moving the at least one movable half-mould 31 , 32, from the open position to the closed position, so as to cause the crushing of a dose of plastic interposed therein.

[0136] The method comprises a step of arranging a transfer device 5.

[0137] The method comprises a step, by means of the transfer device 5, of feeding doses to the forming units 3 in a feeding station, wherein the transfer device 5 has a portion 51 operatively interposed between the male half-mould 31 and the female half-mould 32 of a corresponding forming unit 3, when it is positioned in the feeding station, in the open configuration CA.

[0138] Preferably, the transfer device 5 includes a starwheel 52, rotating around a transfer rotation axis B parallel to the central axis Z.

[0139] The starwheel 52 includes an extraction disc 53 and a feeding disc 54 superimposed on each other along the transfer rotation axis B, wherein, with the forming unit 3 positioned in the feeding station, the extraction disc 53 is proximal to the male half-mould 31 and the feeding disc 54 is proximal to the female half-mould 32.

[0140] The method comprises a step of arranging, for each forming unit 3, a plurality of spacer elements 6 of different thicknesses, positionable between the female half-mould 32 and the respective female mould holder 33.

[0141] The method comprises, on the occasion of a format change for the objects to be made, a step of replacing the spacer elements 6, to vary a relative distance between the male half-mould 31 and the female half-mould 32, in the open configuration CA of the forming unit 3.

[0142] In an embodiment, in the replacement step, the spacer element 6 is selected, as a function of format information representative of a format ofthe objects to be made, so as to minimise the relative distance between the male half-mould 31 and the female half-mould 32, in the open configuration of the forming unit 3.

[0143] Preferably, the method comprises, on the occasion of the format change, a step of adjusting the position of the transfer device 5, by translation along an adjustment direction D parallel to the transfer rotation axis B. In an embodiment, the adjustment of the position of the transfer device 5 along the adjustment direction D is carried out as a function of the format information, to maintain a minimum distance L between the transfer device 5 and the female half-mould 32 constant at a preset value, with the forming unit 3 positioned in the feeding station, in the open configuration CA.

Claims

CLAIMS1. A method for compression moulding plastic objects of concave shape, comprising the following steps:- arranging a carousel (2), rotating around a central axis (Z) according to a rotation direction (V), and a plurality of forming units (3), each of which is positioned on the carousel (2) and includes a male half-mould (31) and a female half-mould (32), supported by a female mould holder (33), wherein at least one of said male half-mould (31) and female half-mould (32) is movable with respect to the other along a moulding axis (S) between an open position and a closed position, to allow the forming unit (3) to move between an open configuration (CA), in which the half-moulds (31, 32) are spaced apart, and a closed configuration (CC), in which the half-moulds (31 , 32) are coupled to delimit a forming cavity;- arranging a transfer device (5);- by means of the transfer device (5), feeding doses to the forming units (3) in a feeding station, wherein the transfer device (5) has a portion (51) operatively interposed between the male half-mould (31) and the female half-mould (32) of a corresponding forming unit (3), when it is positioned in the feeding station, in the open configuration (CA);- for each forming unit (3), moving the at least one movable half-mould (31, 32), from the open position to the closed position, so as to cause the crushing of a dose of plastic interposed therein,characterised in that it further comprises the following steps:- arranging, for each forming unit (3), a plurality of spacer elements (6) of different thicknesses, positionable between the female half-mould (32) and the respective female mould holder (33);- on the occasion of a format change for the objects to be made, replacing the spacer elements (6), to vary a relative distance between the male halfmould (31) and the female half-mould (32), in the open configuration (CA) of the forming unit (3).

2. The method according to claim 1, wherein, in the replacement step, the spacer element (6) is selected, as a function of format information representative of a format of the objects to be made, so as to minimise the relative distance between the male half-mould (31) and the female halfmould (32), in the open configuration of the forming unit (3).

3. The method according to claim 2, wherein the transfer device (5) includes a starwheel (52), rotating around a transfer rotation axis (B) parallel to the central axis (Z), the starwheel (52) including an extraction disc (53) and a feeding disc (54) superimposed on each other along the transfer rotation axis (B), wherein, with the forming unit (3) positioned in the feeding station, the extraction disc (53) is proximal to the male halfmould (31) and the feeding disc (54) is proximal to the female half-mould (32).

4. The method according to claim 3, comprising, on the occasion of the format change, a step of adjusting the position of the transfer device (5), by translation along an adjustment direction (D) parallel to the transfer rotation axis (B).

5. Method according to claim 4, wherein the adjustment of the position of the transfer device (5) along the adjustment direction (D) is carried out as a function of the format information, to maintain a minimum distance between the transfer device (5) and the female half-mould (32) constant at a preset value, with the forming unit (3) positioned in the feeding station, in the open configuration (CA).

6. The method according to any one of the preceding claims, wherein the objects are closing capsules for containers for liquids.

7. The method according to any one of the preceding claims, comprising a step of arranging a control unit (U) designated for receiving format information, representative of a format of the objects to be made, wherein, in the replacement step, the spacer element (6) is selected, by means of the control unit (U), as a function of format information representative of a format of the objects to be made, so as to minimise the relative distancebetween the male half-mould (31) and the female half-mould (32), in the open configuration of the forming unit (3).

8. An apparatus for compression moulding plastic objects of concave shape, comprising:- a carousel (2), rotating around a central axis (Z) according to a rotation direction (V);- a plurality of forming units (3), each forming unit (3) being positioned on the carousel (2) and including:a male half-mould (31) and a female half-mould (32) supported by a female mould holder (33), wherein at least one of said male half-mould (31) and female half-mould (32) is movable with respect to the other along a moulding axis (S) between an open position and a closed position, to allow the forming unit (3) to move between an open configuration (CA), in which the half-moulds (31, 32) are spaced apart, and a closed configuration (CC), in which the half-moulds (31, 32) are coupled to delimit a forming cavity;an actuator (4), configured to move the at least one movable halfmould (31 , 32) between the open position and the closed position, so as to cause the crushing of a dose of plastic interposed therein;- a transfer device (5), configured to feed the doses to the forming units (3) in a feeding station, wherein, in the feeding station, the transfer device (5) has a portion (51) operatively interposed between the male half-mould (31) and the female half-mould (32) of a corresponding forming unit (3) positioned in the feeding station, in the open configuration (CA), characterised in that it comprises, for each forming unit (3), a plurality of spacer elements (6) of different thicknesses, each of which is positionable between the female half-mould (32) and the respective female mould holder (33), the spacer elements (6) of the plurality being interchangeable with each other, to vary a relative distance between the male half-mould (31) and the female half-mould (32), in the open configuration (CA) of the forming unit (3).

9. The apparatus according to claim 8, wherein the transfer device (5) includes a starwheel (52), rotating around a transfer rotation axis (B) parallel to the central axis (Z), the starwheel (52) including an extraction disc (53) and a feeding disc (54) superimposed on each other along the transfer rotation axis (B), wherein, with the forming unit (3) positioned in the feeding station, the extraction disc (53) is proximal to the male halfmould (31) and the feeding disc (54) is proximal to the female half-mould (32).

10. The apparatus according to claim 9, wherein the transfer device (5) is adjustable in position, by translation along an adjustment direction (D) parallel to the transfer rotation axis (B).

11. The apparatus according to claim 10, comprising a control unit (U), adapted to receive format information, representative of a format of the objects to be made, and programmed to derive a setting value, representative of a desired position for the transfer device (5) along the adjustment direction (D), as a function of the format information.

12. The apparatus according to claim 11, wherein the control unit (U) is programmed to select, as a function of the format information, a spacer element (6) of the plurality of spacer elements (6), so as to maintain a minimum distance between the transfer device (5) and the female halfmould (32) constant at a preset value, with the forming unit (3) positioned in the feeding station, in the open configuration (CA).

13. The apparatus according to any one of claims from 8 to 12, wherein the control unit (U) is designed to receive a format information, representative of a format of the objects to be made, and is programmed to select, as a function of the format information, a spacer element (6) of the plurality of spacer elements (6), so as to minimise the relative distance between the male half-mould (31) and the female half-mould (32), in the open configuration (CA) of the forming unit (3).

14. The apparatus according to any one of claims from 8 to 13, wherein the central axis (Z) is vertical and the female half-moulds (32) are placedbelow the male half-moulds (31).

15. The apparatus according to claim 14, wherein, for each forming unit (3), the female half-mould (32) constitutes the movable half-mould.

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