Container moulding unit with system for detaching the bottom

Abstract

The present invention relates to a moulding unit (1) for manufacturing a container from a plastic preform (2), this moulding unit (1) having at least: a mould (3) comprising a wall (4) formed by two hinged half-moulds (3A, 3B) defining an internal cavity (5) distributed about a main axis of the mould (3) and defining at least partially an impression (6) for a side wall or body and having, at a lower end, a lower opening (7), a mould bottom (8) which fits into the lower opening (7) and has an upper surface defining an at least partial impression for the bottom of the container, the mould bottom (8) being pierced at its centre by an opening (9), an actuator (15) comprising a piston (16) and a rod (17) at the end of which is mounted an insert (10) capable of sliding through the opening (9) of the mould bottom (8), between an extended position, in which a free end of the insert (10) protrudes with respect to the mould bottom (8), and a retracted position, in which the free end of the insert (10) is situated in the vicinity of the mould bottom (8), and a saddle (14) on which the mould bottom (8) is mounted, the saddle (14) comprising at least a lower stage (14A) and an upper stage (14B) mounted on the lower stage (14A), the saddle (14) internally defining a recess (17) in which the piston (16) of the actuator (15) is mounted; the moulding unit being characterised in that the mould bottom (8) and / or the insert (10) comprise pneumatic means for detaching the wall from the bottom of the blown container, the pneumatic detachment means simultaneously providing cooling of the bottom of the blown container.

Description

Container molding unit with bottom detachment system

[0001] The present invention relates to the manufacture of containers, such as bottles, which are produced by stretch-blow molding from plastic preforms (mainly thermoplastic, for example PET or recycled PET known as rPET). State of the art

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

[0003] The manufacture of a container by blow molding generally comprises inserting a preform, also commonly called a blank, into a molding unit having a mold sidewall defining a counter-cavity of the wall portion of the container and a mold bottom defining a counter-cavity of the bottom of the container, said preform having been previously heated to a temperature above the glass transition temperature of the material, and injecting into the hot preform a fluid (such as air) under pressure. The blow molding can be (and generally is) completed by stretching the preform by means of a sliding rod called a stretching rod which is introduced into the preform.

[0004] Thus, blow molding while being stretched in the longitudinal direction by a coaxially provided stretching rod is well known.

[0005] Furthermore, as the amount of material required to manufacture each container is continually decreasing over the years for economic and environmental reasons, it is necessary to improve the structural rigidity of the container.

[0006] The improvement of the structural rigidity of the wall portion is achieved in a known manner by means of a series of annular grooves forming stiffeners whose function is to minimize the risk of ovalization of the container (i.e. the deformation of the section of the container from a circular shape to an oval shape).

[0007] Several techniques are also known to ensure the structural rigidity of the container bottom. One technique involves providing the container bottom with stiffening artifacts such as ribs, whose function is to minimize the risk of the bottom collapsing under bending stresses due to the hydrostatic pressure of the contents and, possibly, the weight of stacked containers on the same pallet.

[0008] Another technique is to provide additional stretching of the container bottom material to mechanically increase its crystallinity (and thus its mechanical rigidity). As indicated in published PCT application WO 99 / 52701, this is generally achieved by means of a movable mold bottom slidably mounted relative to the mold sidewall, so that the container material is first blown past the final shape in a retracted position of the mold base and then stamped to the final shape by moving the mold bottom to a raised position in which it completes, together with the mold sidewall, the counter-impression of the container. The molding unit comprises a cylindrical shell and at least a portion of the mold bottom has a cylindrical support slidably received in the cylindrical shell.

[0009] The mold bottom is typically moved by means of a linear actuator such as a hydraulic or pneumatic cylinder, comprising a cylindrical housing and a rod which is slidably mounted within the housing and to which the mold bottom cylinder liner is attached.

[0010] However, the outer surface of the embossed bottom of the container thus blown into the mold adheres to the inner lower surface of the mold bottom so that it is difficult to remove the container without the bottom of the container turning over, rendering the container unusable.

[0011] Furthermore, document US2020 / 262128A1 is also known, which describes a method for manufacturing a container provided with a base, in a mold which comprises a base with a base block provided with a raised molding face and a central opening, and an insert mounted in the central opening, this insert being provided with an end face at the imprint of a central zone of the base of the container, and being movable relative to the block between: a retracted position in which the end face extends in the extension of the molding face of the block, thus completing with it the imprint of the base of the container; an extended position in which the insert projects relative to the central opening.The method comprises an operation of boxing the central zone of the bottom of the container thus formed consisting, during or after the depressurization phase, of moving the insert towards its extended position so as to exert a thrust against said central zone of the bottom of the container and to increase the clearance of said central zone compared to the clearance it has at the end of the blowing. The insert may be provided with radial holes (possibly inclined) causing the conduit to open onto an external face of the insert, in the vicinity of the end face. The injection of fluid during boxing facilitates the detachment of the container bottom from the molding face (and therefore its deformation) while minimizing the risk of cracking.

[0012] Similarly, several other documents such as documents US10232545B2, US2017 / 0291346A1, US2009 / 130246A1 or JP2000102970A in particular describe molding units comprising inserts which allow the injection of fluid during boxing, facilitating the detachment of the container base from the molding face.

[0013] However, not all of these molding units are entirely satisfactory, as the outer surface of the embossed bottom of the container thus blown into the mold occasionally adheres to the lower inner surface of the mold bottom so that it is difficult to remove the container without the bottom of the container turning over. Disclosure of the invention

[0014] One of the aims of the invention is therefore to overcome these drawbacks by proposing a molding unit of simple and inexpensive design and allowing removal of the molded container without the bottom of the container turning over while cooling said bottom of the container and while also cooling a mechanical part without resorting to internal fluid circulation.

[0015] For this purpose and in accordance with the invention, a molding unit is proposed for manufacturing a container from a plastic preform, this molding unit comprising at least: a mold comprising a wall formed by two articulated half-molds defining an internal cavity distributed around a main axis of the mold and defining at least partially an imprint for a side wall or body and having, at a lower end, a lower opening, a mold base which fits into the lower opening and has an upper surface defining at least a partial imprint of the bottom of the container, the mold base being pierced in its center with an opening, a cylinder comprising a piston and a rod at the end of which is mounted an insert capable of sliding through said opening of the mold base,between a so-called deployed position in which a free end of the insert projects relative 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 saddle on which the mold base is mounted, said saddle comprising at least one lower stage and an upper stage mounted on the upper stage, said saddle internally defining a housing in which the piston of the jack is mounted; said molding unit is remarkable in that the mold base and the insert comprise pneumatic means for detaching the wall from the bottom of the blown container, said pneumatic detachment means simultaneously providing cooling of said bottom of the blown container, said insert comprising a central recess connected to a source of fluid under a determined pressure and, at its upper end, at least one orifice opening into said central recess and,on its side wall, near its upper end, a plurality of orifices opening into said central recess, and said mold base comprising a plurality of channels opening, at a first end, onto the upper face of the mold base, forming orifices, and opening, at the opposite end, into the central channel of the opening of the mold base in which the insert slides, said channels of the mold base opening into the central channel extending in line with the orifices of the insert when said insert is in its retracted position.,

[0016] Preferably, the axis of said orifices preferably forms an angle of between 30 and 80° with the longitudinal axis of the insert.

[0017] Incidentally, the central channel of the mold base comprises, at least above the channels opening into said central channel, a sealing gasket.

[0018] Furthermore, the axis of said channels of the mold base forms an angle of between 20 and 80° with the longitudinal axis of the insert.

[0019] Preferably, the orifices of the insert are angularly distributed around the side wall of said insert.

[0020] In addition, the channels of the mold bottom are also angularly distributed around the central axis of said mold bottom.

[0021] Advantageously, said molding unit comprises means for activating the circulation of the pressurized fluid in the mold base and / or in the insert in the container manufacturing cycle capable of controlling the start of said activation and the activation time so as to promote the detachment of the wall from the bottom of the blown container and / or to cool the insert and / or the mold base.

[0022] Other advantages and characteristics will emerge more clearly from the following description of several variant embodiments, given as non-limiting examples, of the molding unit according to the invention, with reference to the appended drawings in which:

[0023] is a perspective view of the molding unit according to the invention,

[0024] is a radial sectional view of the molding unit according to the invention shown in the,

[0025] is a radial sectional and perspective view of the saddle of the molding unit according to the invention,

[0026] is a radial sectional view of the saddle of the molding unit according to the invention,

[0027] is a perspective view from above of the mold base and the insert of the molding unit according to the invention,

[0028] is a radial sectional view of the saddle of the molding unit according to the invention, with the insert in the retracted position,

[0029] is a radial sectional view of the saddle of the molding unit according to the invention, with the insert in the deployed position.

[0030] Method of carrying out the invention

[0031] In the following description of the molding unit according to the invention, the same numerical references designate the same elements. The different views are not necessarily drawn to scale.

[0032] Figures 1 and 2 show a molding unit 1 for manufacturing a container by blow molding (or stretch blow molding) from a blank 2 made of plastic material. In the example illustrated, the blank 2 is a preform, but it could be an intermediate container obtained from a preform having undergone one or more preliminary forming operations. According to a preferred embodiment, the material from which the blank is made is PET and / or rPET (recycled PET).

[0033] Said molding unit 1 comprises, firstly, a mold 3. This mold 3 comprises a wall 4 formed by two articulated half-molds 3A, 3B, defining an internal cavity 5 distributed around a main axis of the mold 3 which, when the containers to be formed are symmetrical in revolution, forms an axis of symmetry of the mold 3.

[0034] The cavity 5 at least partially defines an imprint 6 for a side wall or body of the container. The wall 4 has an opening 7 defining a passage for a mold base 8 provided with a central opening 9 and comprising an insert 10 mounted to move relative to the mold base 8 between a retracted position in which the insert 10 is spaced from the opening 9 (and therefore extends back relative to the cavity 5), and a deployed position in which the insert 10 at least partially projects from the mold base 8 into the cavity 5.

[0035] Said mold base 8 has a molding surface 9 defining an imprint for the relevant part of the container 2. In the deployed position, the insert 10 projects from the mold base 8, thus completing the imprint of the container, against which the material is applied during blowing. The distance separating the retracted position from the deployed position is called the "stroke" of the insert 10. For the sake of clarity, the mold 3 has been shown in a configuration where the stroke of the insert 10 is relatively large compared to the height of the container. This configuration is in no way limiting; on the contrary, the stroke of the insert 10 may be small compared to the height of the container without departing from the scope of the invention.

[0036] Furthermore, said mold base 8 can be mounted to move relative to the wall 4 between a retracted position in which the mold base 8 is spaced from the opening 7 (and therefore extends back relative to the cavity 5), and a deployed position in which the mold base 8 projects at least partly into the cavity 5.

[0037] As illustrated in the, the blank 2, then the container formed from it, rest on an upper face of the mold 3 by means of a collar 11 of the blank 2 (respectively of the container), which delimits a neck 12 of the blank 2 (respectively of the container), held outside the mold 3. Under the collar 11, the blank 2 (then the container) has a body 13, which extends generally in the axial direction, and a bottom, which is initially hemispherical, then, once formed against the mold bottom 8, extends generally in the radial direction from a lower end of the body 13.

[0038] To form the container, the blank 2 is introduced into the mold 3, and a fluid (preferably a gas, for example air) is injected under pressure. Conventionally, the forming can comprise at least two phases, namely: a pre-blowing phase, during which a fluid is injected into the blank 2 at a so-called pre-blowing pressure (the pre-blowing pressure usually being less than or equal to 15 bars, and for example of the order of 7 to 12 bars), and a blowing phase during which a fluid is injected into the blank 2 at a so-called blowing pressure (the blowing pressure being greater than or equal to 15 bars, and for example of the order of 30 to 40 bars).

[0039] Furthermore, the molding unit 1 also comprises a stretching rod, not shown in the figures, capable of extending inside the blank 2, coaxially with the longitudinal axis of said blank 2, and of being moved along said longitudinal axis, in order to stretch said blank 2 during the pre-blowing step, in particular in a manner well known per se.

[0040] The molding unit 1 comprises, secondly, a boxing system called a saddle 14. The term "boxing" is used here to designate an operation of pushing back the material of the container during forming. This saddle 14 comprises, firstly, a jack 15 for controlling the position of the insert 10 of the mold base 8 which is secured to the upper end of said saddle 14.

[0041] Said jack 15 comprises a piston 16 extending in a housing 17 made in the saddle 14 and a rod 18 carrying at its upper end said insert 10. The piston 16 and the rod 18 are integrally movable relative to the jack body formed by the housing 17 made in the saddle between a retracted position, corresponding to the retracted position of the insert 10 of the mold base 8, and a deployed position, corresponding to the deployed position of said insert 10 of the mold base 8.

[0042] With reference to Figures 2 to 5, the insert 10 extends through the mold bottom 8 in the opening 9 coaxially with the drawing rod, said insert 10 being able to be moved from a so-called retracted position in which the upper end of the insert 10 extends inside the opening 9 which forms in the saddle 14 a vertical central channel 19, to a so-called active position in which said insert 10 projects from said mold bottom 8.

[0043] According to an essential characteristic, with reference to Figures 3 and 4, said insert 10 comprises pneumatic means for detaching the wall from the bottom of the blown container. More precisely, said insert 10 comprises a central recess 20 connected to a source of fluid (not shown in the figures) under a determined pressure and, at its upper end, at least one orifice 21 opening into said central recess 20. In this particular embodiment, said insert 10 comprises on its side wall, near its upper end, a plurality of orifices 21 opening into said central recess 20. The axis of said orifices 21 forms with the longitudinal axis of said insert 10 an angle of between 30 and 80°, and preferably an angle of between 30 and 50°.

[0044] Furthermore, advantageously, said mold base 8 also comprises a plurality of channels 22 opening onto the upper face of the mold base 8, forming orifices 23, said channels 22 being fluidically connected to a source of pressurized fluid. More specifically, said mold base 8 comprises a plurality of channels 22 opening, at a first end, onto the upper face of the mold base 8, forming orifices 23, and opening, at the opposite end, into the central channel 19 of said mold base 8, through which the insert 10 extends. The axis of said channels 22 forms with the longitudinal axis of the insert 10 an angle of between 20 and 80°. Said channels 22 of the mold base 8 open into the central recess 19 and extend in line with the orifices 21 of the insert 10 when said insert 10 is in its retracted position.Thus, when the insert 10 is in its retracted position, the orifices 21 of the insert 10 extend in line with the channels 22 of the mold base 8 in order to supply them with pressurized fluid and detach the bottom of the container from the mold base 8.

[0045] In this particular embodiment, the central channel 19 of the mold base 8 does not have a seal so that the air also escapes at the opening 9 of the mold base 8, between the insert 10 and the edge of the opening 9 of said mold base 8.

[0046] According to an alternative embodiment, the central channel 19 of the mold base 8 may comprise, at least above the channels 22 opening into said central channel 19, a sealing joint.

[0047] Furthermore, and preferably, the orifices of the insert 10 23 are angularly distributed around the side wall of said insert 10 and the channels 22 of the mold base 8 are angularly distributed around the central axis of said mold base 8.

[0048] It will be observed that, advantageously, depending on the moment of activation of the circulation of the pressurized fluid in the insert 10 and / or the mold base 8 in the cycle, and the activation time, said activation means being included in a control unit not shown in the figures, the invention makes it possible to promote the detachment of the wall from the bottom of the blown container and / or to cool the mold base 8 devoid, due to its integration and its mobility, of any internal cooling source, such as fluid circulation.

[0049] According to an alternative embodiment, with reference to figures 6 and 7, the insert 10 extends, in the same manner as previously, through the mold base 8 in the opening 9 coaxially with the drawing rod, said insert 10 being able to be moved from a so-called retracted position in which the upper end of the insert 10 extends inside the opening 9 which forms a vertical channel 19 in the saddle 14, to a so-called active position in which said insert 10 projects from said mold base 8.

[0050] Furthermore, in the same way as previously, said insert 10 comprises pneumatic means for detaching the wall from the bottom of the blown container. More precisely, said insert 10 comprises a central recess 20 connected to a source of fluid (not shown in the figures) under a determined pressure and, at its upper end, at least one orifice 21 opening into said central recess 20. In this particular embodiment, said insert 10 comprises on its side wall, near its upper end, a plurality of orifices 21 opening into said central recess 20. The axis of said orifices 21 forms with the longitudinal axis of said insert 10 an angle of between 30 and 80°, and preferably an angle of between 30 and 50°.

[0051] Thus, this variant embodiment differs from that previously described by the fact that the mold base 8 does not have channels 22 opening into the central channel 19.

[0052] Finally, it is clear that the examples just given are only specific illustrations and are in no way limiting as to the fields of application of the invention.

Claims

Molding unit (1) for manufacturing a container from a plastic preform (2), this molding unit (1) comprising at least: a mold (3) comprising a wall (4) formed by two articulated half-molds (3A, 3B) defining an internal cavity (5) distributed around a main axis of the mold (3) and defining at least partially an imprint (6) for a side wall or body and having, at a lower end, a lower opening (7), a mold base (8) which fits into the lower opening (7) and has an upper surface defining at least a partial imprint of the bottom of the container, the mold base (8) being pierced in its center with an opening (9), a jack (15) comprising a piston (16) and a rod (17) at the end of which is mounted an insert (10) capable of sliding through said opening (9) of the mold base (8),between a so-called deployed position in which a free end of the insert (10) projects relative to the mold bottom (8) and a so-called retracted position in which the free end of the insert (10) is located in the vicinity of the mold bottom (10), and a saddle (14) on which the mold bottom (8) is mounted, said saddle (14) comprising at least one lower stage (14A) and an upper stage (14B) mounted on the upper stage (14A), said saddle (14) internally defining a housing (17) in which the piston (16) of the jack (15) is mounted, characterized in that the mold bottom (8) and the insert (10) comprise pneumatic means for detaching the wall from the bottom of the blown container, said pneumatic detachment means simultaneously providing cooling of said bottom of the blown container, said insert (10) comprising a central recess (20) connected to a source of fluid under a determined pressure and, at its upper end,at least one orifice (21) opening into said central recess (20) and, on its side wall, near its upper end, a plurality of orifices (21) opening into said central recess (20), and said mold base (8) comprising a plurality of channels (22) opening, at a first end, on the upper face of the mold base (8) forming orifices (23), and opening, at the opposite end, into the central channel (19) of the opening (9) of the mold base (8) in which the insert (10) slides, said channels (22) of the mold base (8) opening into the central channel (19) extending in line with the orifices (21) of the insert (10) when said insert (10) is in its retracted position., Molding unit (1) according to claim 1 characterized in that the axis of said orifices (21) forms with the longitudinal axis of the insert (10) an angle of between 30 and 80°. Molding unit (1) according to any one of claims 1 or 2, characterized in that the central channel (19) of the mold base (8) comprises, at least above the channels (22) opening into said central channel (19), a seal. Molding unit (1) according to any one of claims 1 to 3, characterized in that the axis of said channels (22) of the mold base (8) forms with the longitudinal axis of the insert (8) an angle of between 20 and 80°. Molding unit (1) according to any one of claims 1 to 4, characterized in that the orifices (21) of the insert (10) are angularly distributed around the side wall of said insert (10). Molding unit (1) according to any one of claims 1 to 5, characterized in that the channels (27) of the insert (8) are angularly distributed around the central axis of said insert (8). Molding unit (1) according to any one of claims 1 to 6, characterized in that it comprises means for activating the circulation of the pressurized fluid in the mold base (8) and / or in the insert (10) in the manufacturing cycle of the containers capable of controlling the start of said activation and the activation time so as to promote the detachment of the wall from the bottom of the blown container and / or to cool the insert (10) and / or the mold base (8).

Images