Container molding unit with adjusting gasket

Abstract

The invention relates to a moulding unit (1) for producing containers from preforms of plastic material, comprising at least: a mould (3) having a wall formed by two hinged mould halves (3A, 3B); an opening is formed in the center of the die bottom in a penetrating manner; an actuating cylinder having a piston and a rod, at the end of which an insert is mounted, the insert being adapted to slide through said opening of the mold base between a so-called extended position and a so-called retracted position; the invention relates to a moulding unit comprising a mould (3), half-moulds (3A, 3B) and a frame (14) on which the mould base is mounted, said frame (14) comprising at least a lower part (14A) and an upper part (14B) mounted on the lower part (14A), the upper end of the lower part (14A) of the frame (14) carrying a so-called wear ring (19) with a groove (20) into which a jaw (21) mounted on the half-moulds (3A, 3B) engages when the mould (3) is in the closed position, said moulding unit being notably characterized in that the mould base (14) has a lower part (14A) and an upper part (14B) mounted on the lower part (14A). According to the invention, the moulding unit comprises at least a gasket (23) which is removably interposed between the lower part (14A) and the upper part (14B) of the carrier (14) in such a way that the gasket (23) extends above the wear ring (19), said gasket (23) being provided with a through-hole which partially forms a receiving space (17) for mounting a piston (16) of the actuating cylinder (15), and the lower part (14A) of the carrier (14) being provided with a lower hole which is formed in such a way that the lower part (14A) of the carrier (14) extends above the wear ring (19). The lower bore forms a part of a receiving space (17) for receiving a piston (16) of the actuating cylinder (15).

Description

TECHNICAL FIELD

[0001] The present invention relates to the manufacturing of containers, such as bottles made of a preform of plastic material, mainly thermoplastic, such as PET or recycled PET, i.e. rPET, by stretch blow molding, and more particularly to a molding unit comprising at least one adjustment shim which allows avoiding adjustments of the machine, especially after changing the preform gauge. BACKGROUND

[0002] In the packaging field, it is known that a container comprises a wall portion, usually cylindrical, a neck portion open at the upper end of the wall portion, and a bottom portion closed at the lower end of the wall portion.

[0003] The manufacturing of a container by blow molding usually comprises the insertion of a preform, also commonly known as a blank, into a molding unit comprising a mold side wall which defines a counter-mold of the wall portion of the container and a mold bottom which defines a counter-mold of the bottom portion of the container; the preform is previously heated to a temperature higher than the glass transition temperature of the material and a pressurized fluid, such as air, is injected into the hot preform. The blow molding can (and usually is) be completed by stretching the preform by means of a slide rod, known as stretch rod, inserted into the preform.

[0004] Therefore, it is known that the blow molding is performed by stretching the preform in the longitudinal direction by means of a stretch rod provided coaxially. However, this method of manufacturing a container by stretch blow molding has the drawback of causing a shift of the axis of the preform and / or of the container during the blow molding, due to a phenomenon of oscillation of the preform in the transversal direction caused by the pressure of the air blown into the preform, which results in an uneven wall thickness of the obtained hollow container. Moreover, this method does not allow to achieve a speed of expansion of the pre-blowing or of the blow molding higher than the speed of the longitudinal stretching by adjusting the parameters, thus resulting in a shift of the center of the bottom of the preform, also known as injection point, with respect to the center of the bottom of the bottle.

[0005] In order to remedy this drawback, it has been envisaged to clamp the bottom of the preform between the stretch rod and a counter-rod extending from the mold bottom during the blow molding. This is particularly described in the patent documents US4547333 and JP10071641.

[0006] The documents US4547333 and JP10071641 describe a method for manufacturing a container from a preform of plastic material by stretch-blow moulding, the preform being heated beforehand, the base of the preform being held by a stretch rod inserted inside the preform and a counter-rod extending coaxially from the base of the mould to the stretch rod and bearing against the outside of the wall of the base of the preform, and the blow moulding being effected by retracting the counter-rod while the stretch rod is stretching the preform in the longitudinal direction. By stretching in the longitudinal direction and blow moulding while the lower part of the preform is clamped and fixed by the stretch rod and the counter-rod, it is possible to improve the distribution of the wall thickness of the container during shaping, while eliminating the transverse oscillations induced by the blow-moulding pressure, and the point of injection is always located at the centre of the axis, since it is held between the stretch rod and the counter-rod, which also makes it possible to avoid a non-uniform wall thickness of the container in the circumferential direction.

[0007] Furthermore, for economic and environmental reasons, the amount of material required to manufacture each container is decreasing year by year, and it is necessary to improve the structural rigidity of the container.

[0008] The improvement in the structural rigidity of the wall is achieved in a known manner by forming a series of annular grooves which function to minimise the risk of ovalisation of the container, i.e. deformation of the cross-section of the container from a circular shape to an oval shape.

[0009] Various techniques are also known for ensuring the structural rigidity of the base of the container. One technique consists in equipping the base of the container with a reinforcing member which acts to minimise the risk of collapse of the base under the action of the bending stresses resulting from the hydrostatic pressure of the contents and possibly the weight of the containers stacked on the same tray.

[0010] Another technique consists in pre-stretching the material of the base of the container to mechanically increase the crystallinity of the material (and thus its mechanical rigidity). As described in published PCT application WO 99 / 52701, this is generally achieved by means of a movable mould base mounted in a slidable manner with respect to the side walls of the mould, such that the container material is first blown into an over- shape in a retracted position of the base of the mould, then the container is moulded into the final shape by moving the base of the mould to a raised position in which the base of the mould forms a counter-mould with the side walls of the mould for the container. The moulding unit comprises a cylindrical housing, and at least one part of the base of the mould has a cylindrical support received in a sliding manner in the cylindrical housing.

[0011] The base of the mould is generally moved by means of a linear actuator (for example a hydraulic or pneumatic cylinder) comprising a cylindrical housing and a rod mounted in a sliding manner inside the housing, the bushing of the cylinder of the base of the mould being fixed to the rod.

[0012] The document US 2013 / 063461 describes a mould equipped with an actuation cylinder provided with a so-called counter-stretching rod which passes through the mould base and against which the bottom of the preform abuts during the stretching. For this purpose, the counter-stretching rod is mounted in sliding manner with respect to the mould base between an extended position (position of the rod at the beginning of the shaping) and a retracted position (position of the rod at the end of the shaping).

[0013] This architecture is certainly an improvement over the old one, but still has a major drawback: it is suitable only for a single size of preform. However, during production it can sometimes be necessary to change the preform model without changing the container model (and therefore without changing the mould). In particular, the length of the preform can vary. If the new preform is longer than the old one, the counter-stretching rod can risk piercing the bottom of the preform in the extended position because it is too long. Conversely, if the new preform is shorter than the old one, the counter-stretching rod can not be able to come into contact with the bottom of the preform in the extended position because it is too short, so that it cannot perform the function of keeping the preform on the axis of the mould.

[0014] To remedy this drawback, it has been envisaged to equip the mould with interchangeable counter-stretching rods, so that the mould can be adapted simply and quickly to preforms of different lengths, while ensuring that the preform is kept on the axis of the mould during shaping. This is the case, in particular, of the patent application WO 207 / 077209 filed by the Applicant.

[0015] The document WO 207 / 077209 describes a mould for manufacturing containers from preforms, comprising: a lateral wall; a mould base with a through hole in the centre; an actuation cylinder comprising a main body and a counter-stretching rod mounted in sliding manner with respect to the main body between an extended position (position in which the counter-stretching rod protrudes from the mould base) and a retracted position; and a seat on which the mould base is mounted, said seat comprising: a lower portion, an upper portion, and a spacer interposed in a removable manner between the upper portion and the lower portion, the spacer portion defining an accommodation cavity.

[0016] However, this type of mould has the drawback of requiring a process of adjustment of the settings of the machine in which it is installed, which can take several hours, causing serious production losses. SUMMARY

[0017] One of the aims of the present application is therefore to remedy these drawbacks by proposing a moulding unit which is simple and inexpensive to design, comprising at least one spacer which makes it possible to change the gauge of the preforms without adjusting the settings of the machine.

[0018] To this end, according to the application, a molding unit for manufacturing containers from preforms in plastic material is proposed, comprising at least: a mold having a wall formed by two hinged half-molds, said wall defining an internal cavity distributed around a main axis of the mold, the internal cavity at least partially defining a cavity for a side wall or a body, and said wall having a lower opening at a lower end; a mold base embedded in said lower opening and having an upper surface at least partially defining a cavity for a bottom of the container, the center of said mold base being pierced with an opening (9); an actuating cylinder having a piston and a rod, at the end of which is mounted an insert adapted to pass through said opening of the mold base, sliding between a so-called extended position, in which the free end of the insert projects with respect to the mold base, and a so-called retracted position, in which the free end of the insert is located in the vicinity of the mold base; and a seat frame on which the mold base is mounted, said seat frame comprising at least a lower portion and an upper portion mounted on the lower portion, the inside of said seat frame defining a housing cavity in which the piston of the actuating cylinder is mounted, the upper end of the lower portion of the seat frame bearing a so-called wear ring with a groove in which a jaw mounted on the half-mold is embedded when the mold is in the closed position; the molding unit being remarkable in that it comprises at least a spacer interposed in a removable manner between the lower portion and the upper portion of the seat frame, so that the spacer extends above the wear ring, the spacer being provided with a through hole which partially constitutes the housing cavity for mounting the piston of the actuating cylinder, and the lower portion of the seat frame being provided with a lower hole which constitutes a part of the housing cavity for accommodating the piston of the actuating cylinder.

[0019] Preferably, the spacer bears against the upper surface of the wear ring.

[0020] Furthermore, the upper end of the lower portion of the seat frame has an annular shoulder against which the wear ring bears.

[0021] The upper end of the wear ring projects from the upper end of the lower portion of the seat frame.

[0022] Furthermore, the spacer comprises a lower annular shoulder against which the upper end of the wear ring bears.

[0023] Furthermore, the jaw embedded in the groove of the wear ring is mounted in a removable manner at the lower end of the half-mold when the mold is in the closed position.

[0024] Preferably, the lower end of each half-mold has an internal semi-annular shoulder against which a so-called positioning spacer interposed in a removable manner between the semi-annular shoulder and the jaw bears.

[0025] Another object of the present application relates to a seat for the base of a molding unit for receiving containers made from a preform of plastic material, said molding unit comprising at least: a mold having a wall formed by two hinged half-molds, said wall defining an internal cavity distributed around a main axis of the mold, which at least partially defines a cavity for a side wall or a body, and having a lower opening at a lower end; a base which is inserted into said lower opening and has an upper surface which at least partially defines a cavity for the bottom of the container, said base having a central opening; an actuating cylinder having a piston and a rod, at the end of which is mounted an insert adapted to slide through said opening of the base between a so-called extended position, in which the free end of the insert protrudes with respect to the base, and a so-called retracted position, in which the free end of the insert is located in the vicinity of the base; and a seat on which the base is mounted, said seat comprising at least a lower portion and an upper portion mounted on the lower portion, the interior of said seat defining a housing cavity in which the piston of the actuating cylinder is mounted, the upper end of the lower portion of the seat carrying a so-called wear ring with a recess in which a jaw mounted on the half-molds is inserted when the mold is in the closed position, said seat being characterized in that it comprises at least a spacer which is interposed in a removable manner between the lower portion and the upper portion of the seat, so that the spacer extends above the wear ring, said spacer being provided with a through hole which partially constitutes the housing cavity for mounting the piston of the actuating cylinder, and the lower portion of the seat being provided with a lower hole which constitutes part of the housing cavity for accommodating the piston of the actuating cylinder.

[0026] Preferably, the spacer abuts against the upper surface of the wear ring.

[0027] Furthermore, the upper end of the lower portion of the seat has an annular shoulder against which the wear ring abuts.

[0028] Furthermore, the upper end of the wear ring protrudes from the upper end of the lower portion of the seat.

[0029] The spacer has a lower annular shoulder against which the upper end of the wear ring abuts. BRIEF DESCRIPTION OF DRAWINGS

[0030] Further advantages and features of the molding unit according to the present application will be more clearly apparent from the following description of a number of variant embodiments given by way of non-limiting example, with reference to the attached drawings, in which:

[0031] Figure 1 perspective view of a molding unit according to the present application;

[0032] Figure 2 is a radial section view of a molding unit according to the present application, as shown in Figure 1

[0033] Figure 3 is an exploded perspective view of a seat of a molding unit according to the present application;

[0034] Figure 4 is a partial sectioned side view of a molding unit according to the present application, as shown in Figure 1

[0035] Figure 5 is a radial section view of a detail of a molding unit according to the present application;

[0036] Figure 6 is a partial radial section view of a lower end of a molding unit according to the present application;

[0037] Figures 7 to 19 are side views of different stages of replacement of a gasket of a seat of a molding unit according to the present application. DETAILED DESCRIPTION

[0038] In the following description of the molding unit according to the present application, identical numerical references designate identical elements. The different views are not necessarily drawn to scale.

[0039] Figure 1 and Figure 2 A molding unit 1 for manufacturing containers from a blank 2 of plastic material by blow molding (or stretch blow molding) is shown. In the illustrated example, the blank 2 is a preform, but can also be a transition container obtained from a preform subjected to one or more preliminary shaping operations. According to a preferred embodiment, the material used to make the blank is PET and / or rPET (recycled PET).

[0040] The molding unit 1 comprises first of all a mold 3. This mold 3 comprises a wall 4 formed by two hinged half-molds 3A, 3B, which define an internal cavity 5 distributed around a main axis of the mold 3, which forms the axis of symmetry of the mold 3 when the container to be shaped is a body of revolution.

[0041] The cavity 5 at least partially defines a molding cavity 6 for the side wall or body of the container. The wall 4 has an opening 7 which defines a passage for a mold base 8 provided with a central opening 9 and having an insert 10 mounted in a manner movable with respect to the mold base 8 between a retracted position, in which the insert 10 is spaced from the opening 9 (thus recessed extension with respect to the cavity 5), and an extended position, in which the insert 10 at least partially projects from the mold base 8 into the cavity 5.

[0042] ​​The mould base 8 has a shaped surface 9 which defines a cavity for the relevant portion of the container 2. An insert 10 projects from the mould base 8 in an extended position to complete the cavity of the container against which the material is applied during blowing. The "stroke" of the insert 10 is the distance separating the retracted position and the extended position. For greater clarity, in the configuration of the mould 3 shown, the stroke of the insert 10 is relatively large with respect to the height of the container. This configuration is in no way limiting; on the contrary, the stroke of the insert 10 can be very small with respect to the height of the container without thereby going beyond the scope of the present application.

[0043] As shown in Figure 2 the blank 2, and the container formed from it, rest on the upper surface of the mould 3 by means of the collar 11 of the blank 2 (or of the corresponding container), which delimits the neck 12 of the blank 2 (or of the corresponding container), which remains outside the mould 3. Below the collar 11, the blank 2 (and the container) has a main body 13 which extends integrally along an axial direction, and a base 14 which initially is hemispherical and then, once it has been shaped against the mould base 8, extends integrally from the lower end of the main body 13 along a radial direction.

[0044] To shape the container, the blank 2 is introduced into the mould 3 and a pressurised fluid (preferably a gas, for example air) is injected. The conventional shaping method comprises at least two phases, namely a pre-blowing phase, during which the blank 2 is injected with a fluid at a so-called pre-blowing pressure (which is generally less than or equal to 15 bars, for example in the range 7 to 12 bars), and a blowing phase, during which the blank 2 is injected with a fluid at a so-called blowing pressure (which is greater than or equal to 15 bars, for example in the range 30 to 40 bars).

[0045] Furthermore, the moulding unit 1 also comprises a stretch rod, not shown in the figures, which is adapted to extend coaxially with the longitudinal axis of the blank 2 into the interior of the blank 2 and is movable along said longitudinal axis so as to stretch the blank 2 during the pre-blowing phase in a manner known per se.

[0046] Secondly, the moulding unit 1 comprises a push system, also known as a seat 14. The term "push" is used herein to refer to the operation of compacting the material of the container during shaping. The seat 14 first of all comprises an actuating cylinder 15 for controlling the position of the insert 10 of the mould base 8, which is fixed to the upper end of said seat 14.

[0047] The actuating cylinder 15 comprises a piston 16 which extends into a housing cavity 17 made in the seat 14, and a stem 18 which carries, at its upper end, the insert 10. The piston 16 and the stem 18 are fixedly movable with respect to the body of the actuating cylinder constituted by the housing cavity 17 made in the seat, between a retracted position, corresponding to the retracted position of the insert 10 of the die bottom 8, and an extended position, corresponding to the extended position of the insert 10 of the die bottom 8.

[0048] Furthermore, with reference to Figure 2 and Figure 3 , the seat 14 comprises at least a lower portion 14A and an upper portion 14B mounted on the lower portion, the seat 14 internally defining a housing cavity 17 in which the piston 16 of the actuating cylinder 15 is mounted. In the present specific embodiment, the seat 14 also comprises a cooling circuit, not shown in the figures, which comprises at least two ducts, an input duct and a discharge duct, in which a cooling fluid circulates.

[0049] As shown in Figures 3 to 6 , the upper end of the lower portion 14A of the seat 14 is provided with a so-called wear ring 19 in the form of a ring, the periphery of which is provided with an annular groove 20 in which the jaws 21 mounted on the half-moulds 3A, 3B are engaged when the mould 3 is in the closed position. Each jaw 21 is in the form of an approximately semi-annular ring and is mounted in a removable manner at the lower end of the half-moulds 3A, 3B by means of screws 22.

[0050] Furthermore, the seat 14 comprises a gasket 23 which is removably interposed between the lower portion 14A and the upper portion 14B of the seat 14, so that the gasket 23 extends above the wear ring 19. The gasket 23 is in the form of a ring and rests on the upper surface of the wear ring 19. In particular, the gasket 23 is fixed to the wear ring 19 by means of screws, not shown in the figures, and the upper portion 14B of the seat is fixed to the gasket 23 by means of other screws.

[0051] Furthermore, the gasket 23 is provided with a through hole 24 which partially constitutes the housing cavity 17 in which the piston 16 of the actuating cylinder 15 is mounted. Furthermore, the lower portion 14A of the seat 14 is provided with a lower hole which constitutes part of the housing cavity 17 for housing the piston 16 of the actuating cylinder 15.

[0052] In the present embodiment, the upper end of the lower part 14A of the seat 14 is provided, at its periphery, with an annular shoulder 25 against which the wear ring 19 rests, and the upper end of which protrudes from the upper end of the lower part 14A of the seat 14. Furthermore, the gasket 23 has, at its periphery, a lower annular shoulder 26 against which the upper end of the wear ring 19 rests, the depth of which is substantially equal to the height by which the wear ring 19 protrudes with respect to the upper end of the lower part 14A of the seat 14.

[0053] Furthermore, the jaws 21, which are embedded in the recess 20 of the wear ring 19, are mounted in a removable manner at the lower end of the half-moulds 3A, 3B when the mould 3 is in the closed position.

[0054] In this regard, the lower end of each half-mould 3A, 3B is provided with an internal semi-annular shoulder 27 against which a so-called positioning pad 28, which is interposed in a removable manner between the semi-annular shoulder 27 and the jaws 21, rests. The pad 28 is in the form of a semi-annular ring and is held between the jaws 21 and the semi-annular shoulder 27 by means of screws 22.

[0055] The different steps for changing the gasket 23 of the seat 14 when changing the gauge of the preform will now be described with reference to Figures 7 to 19 , the figures.

[0056] After opening the mould 3, i.e. after opening the half-moulds 3A, 3B and releasing the jaws 21 from the recess 20 of the wear ring 19, the seat 14 is pre-dismounted, as shown in Figure 7 .

[0057] The screws 29 which fasten the upper part 14B to the gasket 23 are unscrewed ( Figure 8 ), and the upper part 14B, which contains the piston 16 of the actuating cylinder 15, is separated from the lower part 14A of the seat 14 ( Figure 9 ), then the screws 30 which fasten the gasket 23 to the wear ring are removed ( Figure 10 ), and the so-called upper toric joints 31 of the cooling circuit of the seat 14 are removed ( Figure 11 ), and finally the gasket 23 is removed ( Figure 12 ).

[0058] The so-called second lower toric joints 32 of the cooling circuit, which correspond to the lower face of the gasket 23, are also removed ( Figure 13 ), and are replaced with new lower toric joints 32 before installing a new gasket 23 of a height adapted to the dimensions of the new preform ( Figure 14 and Figure 15 ), then before fastening the new gasket 23 to the upper face of the wear ring 19 by means of the screws 30 ( Figure 16 and Figure 17), a new upper O-ring 31 is placed on the upper surface of the gasket 23 (Fig. 4). Figure 15 and Figure 16 ).

[0059] Finally, with reference to Figs. 3 and 4, the upper portion 14B of the seat 14 is fixed to the gasket 23 by means of screws 29. Figure 18 Figure 19 It is clear, moreover, that, simultaneously with the installation of the new positioning blocks 28 at the lower ends of the half-moulds 3A, 3B, new O-rings 31 are placed on the upper surface of the gaskets 23, so that the jaws 21 can be correctly inserted in the grooves 20 of the wear rings 19.

[0060] It is clear, moreover, that, simultaneously with the installation of the new positioning blocks 28 at the lower ends of the half-moulds 3A, 3B, new O-rings 31 are placed on the upper surface of the gaskets 23, so that the jaws 21 can be correctly inserted in the grooves 20 of the wear rings 19.

[0061] It is clear, moreover, that, simultaneously with the installation of the new positioning blocks 28 at the lower ends of the half-moulds 3A, 3B, new O-rings 31 are placed on the upper surface of the gaskets 23, so that the jaws 21 can be correctly inserted in the grooves 20 of the wear rings 19.

[0062] Finally, it is clear that the examples described above are merely illustrative and in no way limit the field of application of the present application.​

Claims

1. A molding unit (1) for manufacturing containers from a preform (2) of plastic material, said molding unit (1) comprising at least: Mould (3) having a wall (4) formed by two hinged half-moulds (3A, 3B) which define an internal cavity (5) distributed around a main axis of the mould (3), which at least partially defines a cavity (6) for a side wall or body, and which has a lower opening (7) at a lower end; a mould base (8) which is inserted in the lower opening (7) and has an upper surface which at least partially defines a cavity for the bottom of the container, the centre of the mould base (8) being pierced by an opening (9); an actuating cylinder (15) having a piston (16) and a rod (17), at the end of which is mounted an insert (10) which is adapted to slide through the opening (9) of the mould base (8) between a so-called extended position, in which the free end of the insert (10) projects with respect to the mould base (8), and a so-called retracted position, in which the free end of the insert (10) is located close to the mould base (8); and a seat (14) on which the mould base (8) is mounted, the seat (14) comprising at least a lower portion (14A) and an upper portion (14B) mounted on the lower portion (14A), the inside of the seat (14) defining a housing cavity (17) in which the piston (16) of the actuating cylinder (15) is mounted, the upper end of the lower portion (14A) of the seat (14) carrying a so-called wear ring (19) with a recess (20) in which a jaw (21) mounted on the half-moulds (3A, 3B) is inserted when the mould (3) is in the closed position, characterized in that the moulding unit comprises at least a spacer (23) which is interposed in a removable manner between the lower portion (14A) and the upper portion (14B) of the seat (14) so that the spacer (23) extends above the wear ring (19), the spacer (23) being provided with a through hole which partially constitutes the housing cavity (17) for mounting the piston (16) of the actuating cylinder (15), and the lower portion (14A) of the seat (14) being provided with a lower hole which constitutes part of the housing cavity (17) for accommodating the piston (16) of the actuating cylinder (15).

2. The molding unit of claim 1, wherein, The spacer (23) abuts against the upper surface of the wear ring (19).

3. The molding unit according to claim 1 or 2, characterized in that The upper end of the lower portion (14A) of the seat (14) has an annular shoulder (25) on which the wear ring (19) abuts.

4. The molding unit according to any one of claims 1 to 3, characterized in that, The upper end of the wear ring (19) projects from the upper end of the lower portion (14A) of the seat (14).

5. The molding unit of claim 4, wherein, The spacer (23) has a lower annular shoulder (26) so that the upper end of the wear ring (19) abuts against the lower annular shoulder (26). The spacer (23) has a lower annular shoulder (26) so that the upper end of the wear ring (19) abuts against the lower annular shoulder (26).

6. The molding unit of any of claims 1 to 5, wherein, The jaws (21) embedded in the grooves (20) of the wear ring (19) are mounted in a removable manner at the lower end of the half-moulds (3A, 3B) when the latter are in the closed position.

7. The molding unit of claim 6, wherein, The lower end of each half-mould (3A, 3B) has an internal half-annular shoulder (27) on which abut the so-called positioning spacers (28) interposed in a removable manner between the half-annular shoulder (27) and the jaws (21).

8. A seat (14) for receiving a mould base (8) of a moulding unit (1) for manufacturing containers from a preform (2) of plastic material, said moulding unit (1) comprising at least: Mould (3) having a wall (4) formed by two hinged half-moulds (3A, 3B) defining an internal cavity (5) distributed around a main axis of the mould (3), which at least partially defines a cavity (6) for a side wall or a body, and having a lower opening (7) at the lower end; a mould base (8) embedded in the lower opening (7) and having an upper surface at least partially defining a cavity of the bottom of the container, the centre of the mould base (8) being pierced by an opening (9); an actuating cylinder (15) having a piston (16) and a rod (17) on the end of which is mounted an insert (10) adapted to slide through the opening (9) of the mould base (8) between a so-called extended position, in which the free end of the insert (10) projects with respect to the mould base (8), and a so-called retracted position, in which the free end of the insert (10) is located in the vicinity of the mould base (8); and a seat (14) on which the mould base (8) is mounted, the seat (14) comprising at least a lower portion (14A) and an upper portion (14B) mounted on the lower portion (14A), the inside of the seat (14) defining a housing cavity (17) in which the piston (16) of the actuating cylinder (15) is mounted, the upper end of the lower portion (14A) of the seat (14) carrying a so-called wear ring (19) with grooves (20) in which are embedded the jaws (21) mounted on the half-moulds (3A, 3B) when the latter are in the closed position, characterized in that the seat comprises at least a spacer (23) interposed in a removable manner between the lower portion (14A) and the upper portion (14B) of the seat (14) so that the spacer (23) extends above the wear ring (19), the spacer (23) being provided with a through hole which partially constitutes the housing cavity (17) for mounting the piston (16) of the actuating cylinder (15), and the lower portion (14A) of the seat (14) being provided with a lower hole which constitutes a part of the housing cavity (17) for accommodating the piston (16) of the actuating cylinder (15).

9. The seat frame of claim 8, wherein The spacer (23) abuts against the upper surface of the wear ring (19).

10. A seat pan according to claim 8 or 9, characterised in that The upper end of the lower portion (14A) of the seat (14) has an annular shoulder (25) against which the wear ring (19) abuts.

11. A seat pan according to any one of claims 8 to 10, wherein The upper end of the wear ring (19) protrudes from the upper end of the lower portion (14A) of the seat (14).

12. The seat frame of claim 11, wherein The spacer (23) has a lower annular shoulder (26) against which the upper end of the wear ring (19) abuts.

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