FIELD OF THE INVENTION This invention relates generally to mold stacks and in particular to mold stacks for molding preforms. More specifically, although not exclusively, this invention relates to mold stacks, molds and molding systems for molding preforms for subsequent blowing into containers, such as beakers, vials or cans, for example beverage containers or cans. BACKGROUND OF THE INVENTION

Molding is a process by virtue of which a molded article can be formed from molding material by using a molding system. Various molded articles can be formed by using the molding process, such as an injection molding process. One example of a molded article that can be formed, for example, from polyethylene terephthalate (PET) material is a preform that is capable of being subsequently blown into a container, such as a beverage container, bottle, can or the like.

As an illustration, injection molding of preforms involves heating PET material (or other suitable molding material for that matter) to a homogeneous molten state and injecting, under pressure, the so- melted material into a molding cavity defined, at least in part, by a female cavity piece and a male core piece mounted respectively on a cavity plate and a core plate of a mold. The cavity plate and the core plate are urged together and are held together by clamp force, the clamp force being sufficient to keep the cavity and the core pieces together against the pressure of the injected material. The molding cavity has a shape that substantially corresponds to a final cold-state shape of the molded article to be molded. The so-injected material is then cooled to a temperature sufficient to enable removal of the so-formed molded article from the molding cavity. When cooled, the molded article shrinks inside of the molding cavity and, as such, when the cavity and core plates are urged apart, the molded article tends to remain associated with the core piece. Accordingly, by urging the core plate away from the cavity plate, the molded article can be subsequently demolded by ejecting it off the core piece. Ejection structures are known to assist in removing the molded articles from the core halves. Examples of the ejection structures include stripper plates, stripper rings and neck rings, ejector pins, etc. When dealing with molding a preform that is capable of being subsequently blown into a beverage container, one consideration that needs to be addressed is forming a so-called "neck region". Typically and as an example, the neck region includes (i) threads (or other suitable structure) for accepting and retaining a closure assembly (ex. a bottle cap), and (ii) an anti-pilferage assembly to cooperate, for example, with the closure assembly to indicate whether the end product (i.e. the beverage container that has been filled with a beverage and shipped to a store) has been tampered with in any way. The neck region may comprise other additional elements used for various purposes, for example, to cooperate with parts of the molding system (ex. a support ledge, etc.). As is appreciated in the art, the neck region cannot be easily formed by using the cavity and core halves. Traditionally, split mold inserts (sometimes referred to by those skilled in the art as "neck ring") have been used to form the neck region.

A typical molding insert stack assembly that can be arranged (in use) within a molding machine includes a split mold insert pair that together with a mold cavity insert, a gate insert and a core insert defines a molding cavity. Molding material can be injected into the molding cavity from a source of molding material via a receptacle or port in the gate insert to form a molded article. In order to facilitate forming of the neck region of the molded article and subsequent removal of the molded article therefrom, the split mold insert pair comprises a pair of complementary split mold inserts that are mounted on adjacent slides of a slide pair. The slide pair is slidably mounted on a top surface of a stripper plate.

As commonly known, the stripper plate is configured to be movable relative to the cavity insert and the core insert, when the mold is arranged in an open configuration, whereby the slide pair, and the complementary split mold inserts mounted thereon, can be driven laterally, via a cam arrangement or any other suitable known means, for the release of the molded article from the molding cavity. One of the functions performed by the split mold insert pair is to assist in ejecting the molded article off the core insert by "sliding" the molded article off the core insert. U.S. Pat. No. 8,899,962 describes an alternative molding insert stack assembly that includes, in addition to the aforementioned elements, a stripper ring configured to define at least a portion of the top sealing surface of the neck region of the preform. The stripper plate is configured to actuate both the neck rings and the stripper ring, in unison, along an ejection path parallel to the longitudinal axis of the mold stack. The neck rings are driven laterally at least toward the end of the ejection path to release the molded article. The split line between the stripper ring and the neck rings extends radially from the periphery of a rim of the preform and the split line between the neck rings and the cavity extends radially from the periphery of a support ledge of the preform.

SUMMARY OF THE INVENTION

The present invention is directed, in particular but not exclusively, to a mold stack for molding a preform of the type for forming a container, such as a beaker, vial or beverage can, the container having a lid. The preform may have a base portion at a closed end, a neck finish at an open end and a body portion therebetween. The neck finish may include a radial flange that extends outwardly at or adjacent the open end of the neck finish and is configured for retaining the lid. In embodiments of the invention, the neck finish is free of features requiring split mold inserts. However, the invention may also be incorporated in mold stacks for molding other preforms, for example those described above. In addition, any of the foregoing features described in relation to known mold stacks, molds and molding systems may be incorporated within mold stacks, molds and molding systems according to the invention, insofar as they are consistent with the disclosure herein.

According to a first broad aspect of the present invention, there is provided a mold stack for molding a preform having a hollow body with a closed end, an open end and a radial flange at or adjacent the open end, the mold stack comprising a plurality of separable mold inserts with split lines described or defined at interfaces therebetween, the mold inserts, when in a molding configuration, describing or defining therebetween a molding cavity for molding the preform with a radial flange portion for molding the radial flange of the preform, the plurality of split lines comprising a first split line with a portion, e.g. a leadoff portion, extending about and/or directly from a periphery of the radial flange portion of the molding cavity in a different and/or non-radial and/or non-parallel direction relative thereto.

The preform may have a base portion at the closed end, a neck finish at or adjacent the open end and the body portion may extend therebetween. The neck finish may include the radial flange, which may extend outwardly at or adjacent the open end and/or be configured for retaining a lid. The plurality of mold inserts may include one or more of a cavity insert, a core insert and a stripper ring. The flange portion of the molding cavity may be described or defined at least in part between the stripper ring and the cavity insert. The first split line may comprise or be a cavity-stripper split line, which may be described or defined between the stripper ring and cavity insert.

According to another broad aspect of the present invention, there is provided a mold stack for molding a preform of the type for forming a container, such as a beaker, vial or beverage can, the container having a lid, the preform having a base portion at a closed end, a neck finish at or adjacent an open end and a body portion therebetween, the neck finish including a radial flange which extends outwardly at or adjacent the open end and which is configured for retaining the lid, the mold stack comprising: a plurality of mold inserts including a cavity insert, a core insert, and a stripper ring that are configured to cooperate when positioned in a molding configuration to define a molding cavity for molding the preform therein, and are displaceable relative one another, towards a stripping configuration, to effect removal of the preform, wherein the radial flange is molded in a flange portion of the molding cavity that is defined at least in part between the stripper ring and the cavity insert; and a plurality of split lines defined between the plurality of mold inserts to accommodate relative movement thereof, the split lines including a cavity- stripper split line defined between the stripper ring and the cavity insert; wherein the cavity- stripper split line extends from the flange portion of the molding cavity in a non-parallel direction relative thereto.

The radial flange may be disc-shaped, substantially planar and/or frusto-conical. The radial flange may be substantially flat-planar or substantially conic-planar, e.g. frusto-conical. The radial flange may comprise an axis or chord, which may be described or defined by or extend between a root or proximal or innermost end, e.g. cross- sectional end, of the radial flange and an outermost or free end thereof. The first split line portion may extend at an angle, e.g. a non-zero angle, such as a right or oblique angle, relative to the radial flange or relative to an axis or chord described or defined by or extending between its ends. The first split line portion may extend at an angle of at least 10 degrees, for example between 10 and 90 degrees or between 30 and 90 degrees, e.g. between 45 and 90 degrees, preferably between 60 and 90 degrees, more preferably between 80 and 90 degrees, for example between 80 and 85 degrees, relative to the radial flange or relative to an axis or chord described or defined by or extending between the ends of the flange or flange portion. The thickness of the radial flange may vary, for example along the axis or chord. The thickness of the radial flange may reduce from a root or proximal end of the radial flange or its cross-section to a free end thereof or vice versa. The first split line or a portion or leadoff portion thereof (hereinafter "leadoff portion", but any such reference to leadoff portion may be replaced simply with "portion") may be described or defined by opposed tapered surfaces of two of the mold inserts, e.g. the cavity insert and stripper ring. One of the mold inserts may comprise a tapered projection or male taper and another of the mold inserts may comprise a tapered recess or female taper, e.g. for receiving the tapered projection or male taper. The leadoff portion may be described or defined by the tapered projection or male taper and the tapered recess or female taper, e.g. opposed tapered surfaces thereof. The radial flange of the preform, or at least part thereof, or its thickness may be described or defined by a space between the tapered projection or male taper and the tapered recess or female taper, e.g. when the mold stack is in the molding configuration. One of the cavity insert and stripper ring may comprise the tapered projection (or male taper) and/or the other may comprise the tapered recess (or female taper). In some embodiments, the cavity insert comprises the tapered projection (or male taper) and the stripper ring comprises the tapered recess (or female taper). In other embodiments, the cavity insert comprises the tapered recess (or female taper) and the stripper ring comprises the tapered projection (or male taper).

The mold insert with the male taper may comprise a female taper surrounding the male taper thereof, for example with a shut off face described therebetween. Additionally or alternatively, the other mold insert with the female taper may comprise a male taper surrounding the female taper thereof, for example with a shut off face described therebetween. The shut off faces may be subjected, in use, to a compressive load when the mold stack is in the molding configuration. The leadoff portion of the first split line may be substantially frusto-conical. The leadoff portion of the first split line may extend outwardly from the periphery of the radial flange portion of the molding cavity at an angle from a longitudinal axis of the mold stack, for example an angle of less than 60 degrees or less than 45 degrees, e.g. less than 30 degrees or less than 20 degrees. The leadoff portion may extend at an angle of at least 1 degree, for example at least 2 degrees, e.g. at least 3, 4 or 5 degrees. The leadoff portion preferably extends at an angle of less than 20 degrees, for example between 1 and 15 degrees, e.g. between 5 and 10 degrees from the longitudinal axis of the mold stack. In embodiments, the leadoff portion of the first split line is substantially frusto-conical and extends outwardly from the periphery of the radial flange portion of the molding cavity at an angle of between 60 and 90 degrees relative to an axis or chord described between the ends of the flange portion and at an angle of between 5 and 10 degrees from the longitudinal axis of the mold stack.

The first split line or leadoff portion may comprise a venting gap, which may be described or defined by a clearance between opposed surfaces, e.g. the opposed tapered surfaces, when the mold stack is in the molding configuration. The venting gap may be sized and dimensioned to allow air to pass therethrough and/or to inhibit ingress of molten material injected, e.g. under normal molding conditions.

According to another broad aspect of the present invention, there is provided a mold stack for molding a preform having a hollow body with a closed end, an open end and a radial flange at or adjacent the open end, the mold stack comprising a plurality of separable mold inserts which together describe or define, when in a molding configuration, a molding cavity for molding the preform and including a radial flange portion for molding the radial flange of the preform, the mold stack comprising a vent, e.g. a venting gap, extending about and/or directly from a periphery of the radial flange portion of the molding cavity in a non-radial and/or non-parallel direction relative thereto. The mold stack may comprise an injection end, which may include an injection port through which molten material is introduced, in use, into the cavity and flows toward the flange portion. The leadoff portion of the first split line may extend directly from the periphery of the flange portion of the molding cavity toward the injection end of the mold stack, e.g. to inhibit molten material flowing, in use, from the body portion of the molding cavity into the flange portion from entering the vent. The plurality of mold inserts may comprise a gate insert, which may describe or define a base of the preform and/or the injection port.

The first split line may comprise one or more shut off portions, which may surround or circumscribe the venting gap. The shut off portions may comprise or be described or defined by opposing shut off faces of two of the mold inserts. In embodiments, the cavity insert and stripper ring comprise cooperating shut off faces, which may surround or circumscribe the venting gap or the tapered projection (or male taper) and the tapered recess (or female taper), for example as described above. The shut off faces may cooperate to prevent or at least inhibit the flow of molten material and, preferably, air therebetween as the molten material is injected, e.g. under normal molding conditions.

At least one of the shut off portions may include a venting channel, which may be in fluid communication with the venting gap. The venting channel may be sized and dimensioned to allow air to pass therethrough and/or to inhibit ingress of molten material injected, e.g. under normal molding conditions. At least one of the shut off faces may include a venting recess, for example describing or defining with an opposing shut off face or recess therein a venting channel in fluid communication with the venting gap, the venting channel being sized and dimensioned to allow air to pass therethrough but to inhibit ingress of molten material injected, e.g. under normal molding conditions.

The mold stack may comprise a venting port, which may connect the venting recess to atmosphere or to an exhaust circuit, for example via one or more passageways or drillings. The venting recess, venting port and the one or more passageways may be comprised or incorporated in one of the mold inserts, for example the stripper ring or the cavity.

The plurality of split lines may comprise a core- stripper split line, which may be described or defined between the stripper ring and the core insert. The core-stripper split line may comprise a venting gap, which may be in fluid communication with the one or more passageways, e.g. via a further venting port. The core may comprise a male taper and/or the stripper ring may comprise a female taper, which may together with the male taper describe or define the core-stripper split line or at least part thereof. At least one or each of the core and stripper ring may comprise a circumferential groove at an intermediate location of the split line. At least one of the circumferential grooves may comprise or be in fluid communication with the further venting port. The venting gap may be described or defined between portions of the core- stripper split line between one of the circumferential grooves and the molding surface. The core-stripper split line venting gap may be sized and dimensioned to allow air to pass therethrough but to inhibit ingress of molten material injected, e.g. under normal molding conditions. The mold stack may comprise an air blow port, e.g. for introducing pressurised air between the stripper ring and the core insert and/or to facilitate separation of the stripper ring from the core insert when the mold stack is moved from the molding configuration to a stripping configuration for effecting removal of the preform. The stripper ring may comprise the air blow port. The stripper ring may comprise one or more passageways connecting an air inlet port to the air blow port. The stripper ring may comprise a mounting flange for mounting the stripper ring to a stripper plate. The mounting flange may comprise a circumferential recess or groove, which may extend about the periphery thereof. The inlet port may be in or comprised or located in the mounting flange, for example a peripheral or outer surface thereof or the circumferential recess or groove. The mounting flange of the stripper ring may be configured to be received, in use, by a stripper plate such that the inlet port is fluidly connected, e.g. via the circumferential recess or groove, to a source of pressurised air.

The mold stack may comprise a core cooling tube. The core cooling tube may comprise an outer surface that approximates an inner surface of the core insert. The core cooling tube may comprise an inlet tube, e.g. with an engaging feature, with an inlet at one end of the core cooling tube and/or an outlet for receipt within a closed end of the core insert. The mold stack may comprise a core spigot, which may retain the core cooling tube within the core insert. A cooling channel may be described or defined within the core insert, for example extending between the inlet and an outlet defined between the inlet tube and the core spigot.

Another aspect of the invention provides a cavity insert for use in a mold stack as described above. The cavity insert may comprise any one or more features of the cavity insert of the mold stack described above.

Another aspect of the invention provides a core insert for use in a mold stack as described above. The core insert may comprise any one or more features of the core insert of the mold stack described above.

Another aspect of the invention provides a stripper ring for use in a mold stack as described above. The stripper ring may comprise any one or more features of the stripper ring of the mold stack described above.

Another aspect of the invention provides an injection mold comprising one or more, e.g. a plurality of, mold stacks according to any preceding claim. The injection mold may comprise a cavity plate, e.g. to which one or more cavity inserts and/or gate inserts are mounted, and/or a core plate, e.g. to which one or more core inserts and/or core cooling tubes and/or core spigots are mounted, and/or a stripper plate, e.g. to which one or more stripper rings are mounted. The stripper plate may be movably mounted to the core plate. The cavity plate may be separable, in use, from the core and/or stripper plates, for example to expose moulded preforms located on molding surfaces of the core inserts. The stripper plate may be movable away from the core plate, for example to apply an ejection force to the radial flange, e.g. thereby to remove the preforms from the core inserts. Another aspect of the invention provides a molding system comprising a mold stack as described above and/or an injection mold as described above.

Another aspect of the invention provides a computer program element comprising and/or describing and/or defining a three-dimensional design for use with a simulation means or a three-dimensional additive or subtractive manufacturing means or device, e.g. a three-dimensional printer or CNC machine, the three-dimensional design comprising an embodiment of one of the mold stack inserts described above.

For the avoidance of doubt, any of the features described herein apply equally to any aspect of the invention. Within the scope of this application it is expressly intended that the various aspects, embodiments, examples and alternatives set out in the preceding paragraphs, in the claims and/or in the following description and drawings, and in particular the individual features thereof, may be taken independently or in any combination. That is, all embodiments and/or features of any embodiment can be combined in any way and/or combination, unless such features are incompatible. For the avoidance of doubt, the terms "may", "and/or", "e.g.", "for example" and any similar term as used herein should be interpreted as non-limiting such that any feature so-described need not be present. Indeed, any combination of optional features is expressly envisaged without departing from the scope of the invention, whether or not these are expressly claimed. The applicant reserves the right to change any originally filed claim or file any new claim accordingly, including the right to amend any originally filed claim to depend from and/or incorporate any feature of any other claim although not originally claimed in that manner. Embodiments of the invention will now be described by way of example only with reference to the accompanying drawings in which:

FIG. 1 depicts a section view through a mold stack according to an embodiment of the invention;

FIG. 2 depicts a section view through a beverage can preform;

FIG. 3 depicts a perspective view of the core insert of the mold stack of FIG. 1; FIG. 4 depicts a perspective section view of the stripper ring of the mold stack of FIG. 1 showing the venting passageways;

FIG. 5 depicts a section view of the stripper ring of the mold stack of FIG. 1 showing the air blow passageways;

FIG. 6 is an enlarged view of the cavity portion of the mold stack section view of FIG. 1;

FIG. 7 is an enlarged view of the flange portion of the molding cavity section view of FIG. 6; and

FIG. 8 is an enlarged view of the neck finish of the beverage can preform of FIG. 2 with a lid being placed thereover.

With reference to FIGs. 1 and 2, there is depicted a non-limiting embodiment of a mold stack 1 for molding a preform 2 of the type for forming a beverage can (not shown). The mold stack 1 has a longitudinal axis L and includes a plurality of mold inserts 3, 4, 5, 6, which together define a cavity 7 for molding the preform 2 (shown in FIG. 2). The mold inserts include a core insert 3, a stripper ring 4, a cavity insert 5 and a gate insert 6. The mold stack 1 also includes a core cooling tube 8 received within the core insert 2 for introducing cooling water therein.

The mold stack 1 is configured to be incorporated in the mold 9, with simplified representations of the plates 91, 92, 93 being included schematically in FIG. 1 for illustrative purposes. The core insert

3, stripper ring 4 and cooling tube 8 form a first stack portion 11 associated, in use, with a first mold half 91, 92. The cavity insert 5 and gate insert 6 form a second stack portion 12 associated, in use, with a second mold half 93, although it is also envisaged that the cavity insert 5 and gate insert 6 could be formed as a single insert. Other arrangements are also envisaged without departing from the scope of the invention. The structure and operation of the foregoing is generally consistent with the prior art and hence a detailed description of known features has been omitted herein.

In this embodiment, the first stack portion 11 is separable from the second stack portion 12 along a first, cavity- stripper split line 13 defined between the cavity insert 5 and the stripper ring 4. The stripper ring 4 is also separable from the core insert 3 along a second, core-stripper ring split line 14 for ejecting the preform 2.

The preform 2 includes a hollow body 20 with a closed end 21, an open end 22 and a radial flange 23 extending outwardly from and about an outer surface 24 of the body 20 at the open end 22 to define a rim 25 of the preform. In this embodiment, the body 20 of the preform 2 tapers to form a conical hollow tubular form with a rounded, substantially part-ellipsoidal closed end 21. As will be appreciated by those skilled in the art, other designs of preform 2 are envisaged without departing from the scope of the present disclosure. Indeed, preforms having different shapes and configurations and/or incorporating more complex neck finishes, for example requiring split mold inserts, may benefit from the present disclosure.

The core insert 3, shown more clearly in FIG. 3, is hollow with a conical molding portion 30 at a closed end, a mounting flange 31 at an open end and a body 32 extending therebetween. The flange 31 extends radially outwardly from the open end and is substantially square in plan with mounting holes 31a for receiving fasteners (not shown) to secure the core insert 3 to a core plate 91. The core insert 3 has an internal surface 33 with a step 33a at the open end, a cylindrical portion within the body 32 and a tapering portion in the molding portion 30 that approximates the shape of the molding portion 30 so as to provide a wall thickness that is substantially constant.

The outer surface of the molding portion 30 defines a molding surface 30a for molding the internal surface of the preform 2. The outer surface of the body 32 includes a cylindrical portion 35 extending from the flange 31 to a stripper ring-facing male taper 36 leading to the molding portion 30. The stripper ring-facing male taper 36 includes a circumferential venting recess 37 spaced from the molding portion 30 and two longitudinal venting recesses 38 on opposite sides of the taper 36 and extending from the circumferential venting recess 37 toward the cylindrical portion 35. A leadoff portion 36a of the male taper 36 is defined between the molding surface 30a and the circumferential venting recess 37. The stripper ring 4, shown more clearly in FIGs. 4 and 5, is hollow and substantially cylindrical with an inner step 40 at a cavity-facing end of a main body 41. The stripper ring 4 also includes a radial mounting flange 42 extending from the main body 41 adjacent but spaced from its core-facing end. The step 40 includes a molding surface 40a with a radial ledge portion defining the rim 25 of the preform 2 and a circumferential portion defining an outer edge of the flange 23 of the preform 2. The step 40 also includes a cavity-facing female taper 43, which is substantially frusto-conical and is delineated from the molding surface 40a more clearly in FIG. 7.

In this embodiment, the cavity-facing female taper 43 tapers outwardly from the terminal peripheral edge of the molding surface 40a at an angle of between 5 and 10 degrees relative to a longitudinal axis L of the mold stack, which is between 80 and 85 degrees with respect to the radial flange portion 40a. Whilst it is envisaged (and may be preferable) that the cavity-facing female taper 43 may be parallel to the longitudinal axis L (and perpendicular to the flange portion 40a), a draft angle is beneficial for reasons that will be appreciated by those skilled in the art. The stripper ring 4 also includes a primary shut off surface 44 at its cavity-facing end and a secondary shut off surface 45 parallel to the primary shut off surface 44 and spaced therefrom. A cavity-facing male taper 46 extends between the primary and secondary shut off surfaces 44, 45. The cavity-facing male taper 46 is also substantially frusto-conical but tapers in the opposite direction to the cavity- facing female taper 43 and at a larger angle relative to the longitudinal axis L. A core-facing female taper 47 extends from the inner edge of the step 40 along the body 41 and tapers outwardly to form a substantially frusto-conical surface. The core-facing female taper 47 is substantially parallel to the cavity-facing male taper 46, thereby providing a conical cavity-facing end portion of the stripper ring 4 having a substantially constant thickness. The core-facing female taper 47 includes a circumferential venting recess 48 spaced from the step 40 and a pair of ports 48a on opposite sides of the stripper ring 4, which are formed by passageways 48b through the stripper ring 4. The passageways 48b extend at an oblique angle relative to the longitudinal axis L and vent to atmosphere. The primary shut off surface 44 includes a pair of venting recesses 44a in opposed portions thereof, each having a venting port 44b formed by passageways 44c that intersect the passageways 48b forming the ports 48a of the circumferential venting recess 48.

The flange 42 extends radially outwardly from an intermediate portion of the body 41, is circular in plan and includes a circumferential groove 42a about its periphery. In this embodiment, the stripper ring 4 includes a pair of air blow circuits 4a, 4b in opposed portions of the body 41 and offset circumferentially from the venting ports 48a by 90 degrees. Each air blow circuit 4a, 4b includes a radial passageway 42b, a longitudinal passageway 41a and an oblique passageway 41b. The radial passageway 42b extends from the base of the circumferential groove 42a of the flange 42 to the longitudinal passageway 41a. The longitudinal passageway 41a is a blind bore in the wall of the body 41, which extends from the core-facing end of the stripper ring 4 and terminates at the oblique passageway 41b. The oblique passageway 41b extends from the longitudinal passageway 41a at an oblique angle to a cylindrical internal surface 49 of the stripper ring 4. The stripper ring 4 receives the core insert 3 such that the cylindrical portion 35 of the body 32 of the core insert 3 faces the cylindrical internal surface 49 of the stripper ring 4 and such that the stripper ring-facing male taper 36 of the core insert 3 faces the core-facing female taper 47 of the stripper ring 4. The stripper ring-facing male taper 36 of the core insert 3 and the core-facing female taper 47 of the stripper ring 4 together define the core-stripper ring split line 14 for ejecting the preform 2. The leadoff portion 36a of the male taper 36 of the core insert 3 cooperates with the core-facing female taper 47 of the stripper ring 4 to define a leadoff portion of the core-stripper ring split line 14.

In this embodiment and as illustrated in FIG. 1, the clearance between the cylindrical surfaces 35, 49 is selected so as to enable the stripper ring 4 to translate relative to the core insert 3 along the longitudinal axis L. When in the molding configuration, the stripper ring-facing male taper 36 of the core insert 3 engages the core-facing female taper 47 of the stripper ring 4 to centralise the core insert 3 within the stripper ring 4. The leadoff portion 36a of the male taper 36, however, is recessed slightly to provide a venting gap between it and the core-facing female taper 47 of the stripper ring 4. Thus, a venting passage is provided in which air is able to escape through the venting gap at the leadoff portion 36a of the male taper 36 to the circumferential and longitudinal venting recesses 37, 38 of the core insert 3 and out to atmosphere via the circumferential venting recess 48, venting ports 48a and venting passageways 48b of the stripper ring 4. The stripper ring 4 is mounted to a stripper plate 92 by captivating the flange 42 within a pocket such that movement of the stripper plate 92 toward or away from the core plate 91 causes the stripper ring 4 to move relative to the core insert 3 along the core-stripper ring split line 14 in order to eject the preform 2 from the core insert 3. The pocket also includes an outlet operatively connected to a source of pressurised air that is aligned with the circumferential groove 42a to selectively supply pressurised air to the air blow circuits 4a, 4b, thereby to assist with the separation of the stripper ring 4 from the core insert 3. The cavity insert 5, shown more clearly in FIGs. 6 and 7, includes a hollow and substantially cylindrical body 50 with an internal molding surface 50a including a body portion for molding the outer surface of the body 20 and a radial ledge portion defining the underside of the radial flange 23 of the preform 2. The cavity insert 5 also includes a stripper ring-facing male taper 53 extending from the radial ledge portion of the molding surface 50a and a primary shut off surface 54 surrounding the stripper ring-facing male taper 53. A secondary shut off surface 55 is included at the stripper ring- facing end of the cavity insert 5 with a stripper ring-facing female taper 56 extending therebetween.

Thus, the stripper ring-facing female taper 56 defines a recess in the cavity insert 5, whose base defines the primary shut off surface 54. The stripper ring-facing male taper 53 provides a projection within the recess, with an inner circumferential surface thereof providing a terminal part of the body portion of the molding surface 50a and a peak thereof providing the radial ledge portion of the molding surface 50a.

The cavity insert also includes cooling channels 57 on the outer surface of the body 50 a mounting flange 58 for mounting the cavity insert 5 to a cavity plate 93. The cooling channels 57 are stepped in this embodiment to more closely approximate the tapered portion of the body molding surface 51. The mounting flange 58 surrounds the stripper ring-facing female taper 56 and includes the secondary shut off surface 55. The gate insert 6, also shown in FIG. 6, is substantially cylindrical in shape with a rounded, part- ellipsoid molding surface 60a at a cavity-facing end thereof for molding the closed end 21 of the preform 2. The gate insert 6 is also mounted within the cavity plate 93 such that the molding surface 60a of the gate insert 6 aligned with the molding surface 50a of the cavity insert 5 with the gate insert 6 sealingly engaged with the cavity insert 5. The gate insert 6 also includes a nozzle interface pocket 61 on the opposite side thereof to the molding surface 60a with an injection port 62 joining the interface pocket 61 and the molding surface 60a. The interface pocket 61 cooperates, in use, with a nozzle (not shown) of a melt distribution apparatus (not shown), such as a hot runner, for introducing melt into the molding cavity 7.

In the molding configuration, shown in FIGs. 1, 6 and 7, the cavity-facing female taper 43 and the cavity-facing male taper 46 of the stripper ring 4 are aligned, respectively, with the stripper ring-facing male taper 53 and the stripper ring-facing female taper 56 of the cavity insert 5. When a clamping force is applied, the primary and secondary shut off surfaces 44, 45 of the stripper ring 4 engage, respectively, the primary and secondary shut off surfaces 54, 55 of the cavity insert 5. The cooperating tapers 43, 53 and 46, 56 and shut off surfaces 44, 54 and 45, 55 of the stripper ring 4 and cavity insert 5 together define the cavity-stripper split line 13. In addition, the cavity-facing female taper 43 and the stripper ring-facing male taper 53 together define a leadoff portion 13a of the cavity- stripper split line 13.

In this embodiment, the leadoff portion 13a includes a venting gap defined by the clearance between the cavity-facing female taper 43 and the stripper ring-facing male taper 53. Thus, a venting passage is provided in which air is able to escape through the venting gap of the leadoff portion 13a through the venting recesses 44a in the primary shut off surface 44 of the stripper ring 4 and out to atmosphere via the venting ports 44b and venting passageways 44c, 48b of the stripper ring 4.

The core cooling tube 8, shown more clearly in FIGs. 1 and 6, includes substantially cylindrical body 80 with a tapered end 81 to approximate the internal surfaces of the core insert 3. The body 80 includes a central longitudinal bore 82 with an outlet 83 at the apex of the tapered end 81 for directing cooling fluid to the closed end of the core insert 3 and an inlet tube 84 at the opposite end. The inlet tube 84 is secured in the bore 82 and includes a radial flange 85 at its free end. The body 80 also includes castellations 86 at the end that receives the inlet tube 83. The core cooling tube 8 is retained within the core insert 3 by a core spigot 87 received within the step 33a of the core insert 3 when the core insert 3 is mounted to the core plate 91. The castellations 86 of the body 80 cooperate with a facing surface of the core spigot 87 to define radial channels 88 that feed into an annular outlet channel 89 defined between the outer surface of the inlet tube 84 and a bore in the core spigot 87. The radial flange 85 of the inlet tube 84 and the core spigot 87 are adapted to connect, respectively, to an inlet and an outlet with a cooling circuit (not shown) in the core plate 91. As illustrated in FIG. 1, the gap between the outer surface 80 of the core cooling tube 8 and the internal surface 33 of the core insert 3 creates a restriction along the molding portion 30 to provide effective cooling.

In use, molten material is injected from the nozzle (not shown) into the cavity 7 through the injection port 62. The molten material flows into the cavity 7 from the injection port 62 toward the flange portion 40a of the cavity 7. Air contained within the cavity 7 is forced through the venting passage 36a, 47, 37, 38, 48, 48a, 48b between the core 3 and the stripper ring 4 and through the venting passage 13a, 44a, 44b, 44c, 48b between the stripper ring 4 and the cavity 5.

When the cavity 7 is filled with molten material, static injection pressure is maintained for a period as cooling fluid is circulated about and through the mold stack to solidify the molten material. The static injection pressure is then released and the flow of material through the nozzles (not shown) is closed. When the material has solidified sufficiently, the first mold half 91, 92 is separated from the second mold half 93 to expose the preform 2. As the material solidifies, the preform 2 tends to shrink onto the molding portion 30 of the core insert 3, thereby facilitating its removal from the cavity insert 5. Ejection of the preform 2 from the core insert 3 is then effected by moving the stripper plate 92 relative to the core plate 91, which causes the molding surface 40a of the stripper ring 4 to urge the rim 25 along the longitudinal axis L away from the core insert 3.

As is generally known, in certain circumstances molten material injected into the cavity 7 may be forced into the leading portion 36a, 47, 13a of the venting passages, thereby causing flash. One cause of flash is insufficient clamp force for a given injection pressure, wherein the pressure at which the molten material is injected into the cavity causes the first mold half 91, 92 to separate slightly from the second mold half 93. Other causes will also be understood by those skilled in the art, for example volatile molding conditions on startup, component wear and so on. The applicant has determined that by configuring the cavity- stripper split line 13 with a leadoff portion 13a extending in a non-parallel direction relative to the radial flange portion 40a of the cavity 7, venting can be improved, the risk of mold flashing can be reduced and the impact of mold flashing can also be mitigated. More specifically and as illustrated in FIG. 8, the open end 22 of the preform 2 is configured to cooperate with a lid 28 for sealingly closing a can (not shown) formed by the preform 2. The lid 28 has a peripheral curl 29, which is placed, in use, over the flange 23 and crimped in a manner known in the art to sealingly close the can (not shown). In the event of flash occurring in a traditional mold stack design, where the split line would extend in a radial direction from the flange portion of the cavity, such flash would interfere with the peripheral curl 29 of the lid as it descends over the flange 23. In the present invention, however, if the flange 23 is formed with a flash portion 23a, the peripheral curl 29 of the lid 28 is able to descend over the flange 23 uninhibited. The peripheral curl 29 would then either clear the flash portion 23a altogether or the flash portion 23a would not interfere with the crimping operation due to its inevitably slender thickness. Another advantage of the present invention is that the sharp changes in flow direction through the body portion of the cavity 7, then through the flange portion 40a of the cavity 7 and finally through the leadoff portion 13a of the cavity- stripper split line 13 has been found to provide a reduced likelihood of flash. Yet another advantage of the present invention is that longitudinal movement between the cavity-facing female taper 43 and the stripper ring-facing male taper 53 would cause minimal separation of the facing surfaces, since they are nearly parallel to the direction of movement. Thus, the thickness of the venting gap at the leadoff portion 13a of the cavity- stripper split line 13 remains substantially constant, even in the aforementioned case of slight separation between the first mold half 91, 92 and the second mold half 93. It will be appreciated by those skilled in the art that several variations to the aforementioned embodiments are envisaged without departing from the scope of the invention. It will also be appreciated by those skilled in the art that any number of combinations of the aforementioned features and/or those shown in the appended drawings provide clear advantages over the prior art and are therefore within the scope of the invention described herein.