WO2000046011A1

WO2000046011A1 - Apparatus for stretch forming an article

Info

Publication number: WO2000046011A1
Application number: PCT/AU2000/000057
Authority: WO
Inventors: Graeme John Russell
Original assignee: Graeme John Russell
Priority date: 1999-02-02
Filing date: 2000-02-02
Publication date: 2000-08-10
Also published as: AUPP844999A0

Abstract

This invention relates to an apparatus for stretch forming a hollow article comprising: an upper moulding portion; and a lower tooling portion which is engageable with the upper moulding portion to locate a material to be stretched formed between the upper and lower portions, wherein the lower tooling portion comprises: a plurality of forming members, each forming member having a head portion adapted to engage the material to be stretch formed and a cam engaging portion; spacing means for maintaining the head portions of said forming members at a predetermined minimum distance from each other; mounting means for mounting the spacing means and the plurality of forming members wherein each of the plurality forming members is outwardly displacably connected relative to the mounting means; caming means for engaging the cam engaging portions of the plurality of forming members; and displacing means connected relative to the mounting means, the displacing means being actuable to displace the forming members upwardly into the upper moulding portion, whereby the cam engaging portions of the forming members engage the caming means as the displacing means is activated such that the head portions of the plurality of forming members are outwardly displaced relative to the mounting means to stretch the material upward into the moulding portion.

Description

APPARATUS FOR STRETCH FORMING AN ARTICLE

The present invention relates to an apparatus for stretch forming an article. In particular, the invention relates to an apparatus and method for stretch forming a hollow article from a sheet of thermoplastic material.

Processes and apparatuses for stretch forming or thermoforming hollow articles such as cups, cans, jars, tubes, pails and drums typically involve heating of a material to be formed into the article to a temperature at which the material can be readily formed to the desired shape. The material is generally then stretched in a longitudinal direction by a stretching rod having a multiplicity of expansion fingers which stretch the material in a circumferential direction. The deformation process is completed by the injection of compressed air to form the article. The mould into which the material is blown is then opened and the formed article is removed. Such devices typically involve a plunger type operation wherein the fingers pivot outwardly on downward movement of the plunger. Furthermore, these devices are generally limited in their application to the production of articles having their generally conical or frustroconical shape.

According to one aspect of the present invention there is provided an apparatus for stretch forming a hollow article comprising: an upper moulding portion; and a lower tooling portion which is engagable with the upper moulding portion to locate a material to be stretched formed between the upper and lower portions, wherein the lower tooling portion comprises: a plurality of forming members, each forming member having a head portion adapted to engage the material to be stretch formed and a cam engaging portion; spacing means for maintaining the head portions of said forming members at a predetermined minimum distance from each other; mounting means for mounting the spacing means and the plurality of forming members wherein each of the plurality forming members is outwardly displacably connected relative to the mounting means; earning means for engaging the cam engaging portions of the plurality of forming members; and displacing means connected relative to the mounting means, the displacing means being actuable to displace the forming members upwardly into the upper moulding portion, whereby the cam engaging portions of the forming members engage the earning means as the displacing means is activated such that the head portions of the plurality of forming members are outwardly displaced relative to the mounting means to stretch the material upward into the moulding portion.

The stretching of the material upward into the moulding portion using the plurality of forming members may be conducted in any number of steps and to any desired degree of stretching dependent upon the article being formed. In a preferred embodiment, the plurality of forming members travel from a first retracted position in which the head portions of the forming members are spaced at said predetermined minimum distance, to a second outwardly displaced position in which the plurality of forming members have stretched the material so that it engages an internal surface of the upper moulding portion.

Each of the plurality of forming members may be mechanically engaged in the first retracted position and the second outwardly displaced position, or may pivot freely relative to the mounting means. However, in a preferred embodiment the cam engaging portion of each of the plurality of forming members is resiliently outwardly biased such that when the plurality of forming members are in the first retracted position the respective head portions of the plurality of forming members are inwardly biased such that the forming members engage the spacing means and are spaced suitably for engagement with the material to be stretched.

The cam engaging portions may be outwardly biased by any suitable means. It is preferred that the cam engaging portions be resiliently outwardly biased by means of a spring loaded seat which is engaged by an inner surface of each of the cam engaging portions.

The plurality of forming members may take any suitable form provided that they each have a head portion adapted to engage the material to be stretch formed into the article, and a cam engaging portion. Preferably, the plurality of the forming members comprises a plurality of elongate fingers. The plurality of elongate fingers are pivotally connected relative to the mounting means in an arrangement which will depend on the shape of the article to be manufactured. Accordingly the plurality of elongate fingers may be pivotally connected relative to the mounting means in a circular, square, rectangular or multi-sided arrangement. In a preferred embodiment the cam engaging portion of each of the plurality of forming members is preferably an outwardly displaced arm located across the pivotal connection to the mounting means such that as the earning means engages and urges inwards the cam engaging portions, the head portions are urged outwards.

The earning means with which the cam engaging portions of the plurality of forming members engage may also take any suitable form provided that the earning means acts on each of the plurality of forming members when the displacing means is activated to outwardly displace the forming members such that the material is stretched upwardly and outwardly into the moulding portion. In a preferred embodiment the earning means comprises earning surfaces extending longitudinally on a inner surface of the lower tooling portion wherein the earning surfaces provide a substantially frustroconical surface for engagement with the cam engaging portions of the plurality of forming members.

The displacing means may include any suitable means capable of displacing the forming members upwardly into the upper moulding portion. Preferably, the displacing means is a push rod which acts as a piston, forcing the plurality of forming members upward into the moulding portion. Furthermore, it is preferable that the push rod be resiliently biased so that downward movement of the plurality of forming members towards the first retracted position is opposed. The push rod may preferably be resiliently biased with a spring.

The mounting means for mounting the spacing means and the plurality of forming members may take any suitable form, and may be connected relative to the displacing means by suitable means. For example, the mounting means may be formed integrally with either or both of the spacing means and the displacing means. Preferably, the mounting means is disposed on a shaft extending axially from the displacing means. Furthermore, in a preferred embodiment the mounting means is a mounting block and each of the plurality of forming members are internally pivoted about a plurality of respective locating pins within the mounting block.

The spacing means may be of any form which is suitable for spacing the plurality of forming members.

Preferably the lower tooling portion additionally comprises a head portion limiting means whereby said limiting means locates the head portions of the plurality of forming members in desired first position. The limiting means may be integral with the mounting means or, in the preferred embodiment, may be a disc upon which the plurality of forming members rest in the first position. Preferably the disc limiting means is displaceable relative to the plurality of forming members such that the degree of stretching of the material as the plurality of forming members are upwardly and outwardly displaced is controlled and the thick mass of stretched material between the plurality of forming members is advantageously controlled to a high degree.

The lower tooling portion is engagable with the upper moulding portion to locate the material to be stretched formed between the upper moulding portion and the lower tooling portion. Engagement of the upper and lower portions may take any suitable form. For example, the upper moulding portion may simply be seated on the lower tooling portion, or may physically engage the lower tooling portion. In a preferred embodiment, the lower tooling portion is engagable with the upper moulding portion to provide an air tight seal. Most preferably, the lower tooling portion is engagable with the upper moulding portion about a sealing member.

In use, the upper moulding portion engages the lower tooling portion with a layer of material to be stretched formed disposed there between. It is preferable that the stretch forming apparatus also include a flange release located adjacent the seal to facilitate ejection of excess material from the seal when the upper moulding portion and lower tooling portion are engaged. If excess material is ejected from the seal, it is also preferred that the apparatus be provided with means for receiving the ejected material. In this regard, the apparatus is preferably provided with a cooling fin adapted to receive the excess material ejected from the seal. The cooling fin is preferably located on the exterior surface of the lower tooling portion.

In order to ensure complete moulding of the material into the upper moulding portion, the apparatus is preferably provided with at least one inlet port for introducing pressurized gas into the moulding portion beneath the material to be stretch formed. Most preferably, the at least one inlet port is located in the lower tooling portion of the apparatus. In a most preferred embodiment, the at least one inlet port comprises a plurality of inlet ports spaced circumferentially around the base of the lower tooling portion.

In some instances, it may be advantageous to provide means for facilitating removal of the moulding article from the upper moulding portion. This may be particularly the case if the article being formed comprises a neck portion. Therefore, in a preferred embodiment at least a portion of the upper moulding portion of the apparatus is retractable to facilitate removal of the formed article from the upper moulding portion. In a particularly preferred embodiment the upper moulding portion comprises an ejection system for facilitating ejection of the formed article from the upper moulding portion. The ejection system preferably comprises an ejector and a vacuum means, the vacuum means being adapted to prevent premature ejection of the formed article from the mould by securing the formed article in the mould upon activation of the ejector.

According to another embodiment of the present invention there is provided a method for stretch forming a hollow article using the apparatus described above comprising the steps of: disposing a sheet of material to be stretch formed between said upper moulding portion and said lower tooling portion; bringing the upper moulding portion and the lower tooling portion into sealing engagement so as to engage the sheet material between the upper moulding portion and the lower tooling portion; longitudinally and laterally stretching the sheet material by displacing said plurality of forming members upward into the mould; further stretching the resultant longitudinally and laterally stretched material by blowing a gas into the mould under pressure to form the article; and removing the article from the mould.

The apparatus and/or method according the invention may be used to stretch form thermoplastic materials which may include, for example, sheets consisting of a mono layer of material of copolymer, homopolymer or nucleated polymers such as polypropylene, low density polyethylene (LDPE), high density polyethylene (HDPE), polyethyleneterephthalate (PET), polyethylene nitrate (PEN), polycarbonate or poly vinyl chloride.

The processing of such thermoplastic material is preferably achieved by inserting sheets of 5 the material into the apparatus at a temperature above its crystallinity point.

The materials may also include multilayers structures incorporating inner and outer layers consisting of one or more of the above mentioned polymers, an adhesive layer, an oxygen barrier layer comprises, for example, ethylene vinyl alcohol (EVOH), and one or two layers 10 of in-house regrind with or without a master batch and/or a stabilizer.

Advantageously the present invention allows the use of more molten polymeric material than otherwise possible. While the apparatus and method of the present invention have been described whereby the tooling portion is mounted beneath the moulding portion, is some 15 instances it may be desirable to employ alternative orientations.

Preferred embodiments of the invention will now be described with reference to the drawing in which:

Figure 1 illustrates an apparatus for stretch forming a whole article; 20 Figure 2 illustrates an apparatus for stretch forming a hollow article having a neck portion; and

Figure 3 illustrates a machinery layout diagram.

Referring to Figure 1, the stretch forming apparatus 10 comprises an upper moulding portion 25 12 and a lower portion tooling portion 14. The upper moulding portion 12 and the lower tooling portion 14 engage a sheet of thermoplastic material 16 which is disclosed between the upper portion 12 and the lower portion 14. In this regard, the upper portion is provide with a flange ring 18 which is seated on the material 16 which is in turn seated on a seating 20 of the lower portion 14 thus, a flange 22 of the material 16 is formed between the flange ring 30 18 and the seating 20. The lower portion 14 is also provided with a forming ring 24 which extends circumferentially around the upper end of the lower portion 14. Advantageously, the forming ring 24 provides an air tight seal when the upper portion 12 is located on the lower portion 14.

As the upper portion 12 engages the material 16 disclosed between the upper portion 12 and the lower portion 14, excess material 26 is squeezed out into a flange relief 28. The excess 5 material then flows onto cooling fins 30 where it is cooled and solidified. It will be recognised that the thickness of the flange 22 may be varied depending on the spacing of the stops (not shown) which limit the movement of the upper portion 12 relative to the lower portion 14 when they are brought into engagement with the material 16 disposed between the upper portion 12 and the lower portion 14. 10

The lower portion 14 comprises a plurality of elongate forming members 32, each of which has a head portion 34 and a cam engaging portion 36. The forming members 32 are pivotally mounted inside a mounting block 35 at pivot points 38.

15 The cam engaging portions 36 of the forming members 32 are outwardly displaced by a spring loaded reseating cam 40 which engages the inner side of the cam engaging portions 36 of the forming members 32. Thus, the head portions 34 of the forming members 32 are forced to pivot toward each other about pivot points 38 due to the outward displacing force of the spring loaded reseating cam 40. Inward movement of the head portions 34 of the forming

20 members 32 is set at a minimum predetermined distance by a limiting disc 42 which is disposed centrally between the forming members 32. In a preferred embodiment, the spacing member 42 is circular and the forming members 32 are pivotally and circumferentially disposed on the mounting block 35 around the limiting disc 42.

25 The lower tooling portion 14 is also provided with an internal earning surface 44 with which the cam engaging portions 36 of the forming members 32 engage on upward movement of the forming members 32. In this regard, the mounting block 35 is located on a push rod 46 which is n return located on a pushup plate 48 which is adapted to mechanically push the push rod 46 is an upward direction. As the push rod 46 is forced upward by the pushup plate

30 48, the cam engaging portions 36 of the forming members 32 engage the earning surface 44 located on the wall 50 of the lower portion 14. As the push rod is forced further upward the cam engaging portions 36 are forced inward against the spring loaded reseating cam 40 such that the forming members 32 pivot about pivot points 38. In doing so, the forming members 32 disengage the limiting disc 42, and the head portions 34 are upwardly and outwardly displaced into the upper moulding portion 12.

Advantageously, prior to displacement of the forming members 32 into the upper moulding portion 12, the material 16 in contact with the head portions 34 of the forming members 32 cools slightly. As a result, sliding of the head portions 34 on the material 16 during upward displacement of the forming members 32 is minimized. As such, the minimum distance between the heads 34 of the forming members 32, as set by the spacing member 42 determines the final thickness of the base of the article being formed.

During the stretch forming operation the forming fingers 32 travel from a first retracted position (as shown in Figures 1 and 2), to a second extended position (not shown) wherein the head portions 34 of the forming members 32 urge the material 16 against the outer circumferential corners 52 of the roof of the upper portion 12 to form a preform. Thus, the material 16 is stretched by the forming members 32 substantially into the shape of the upper moulding portion 12 when the forming members 32 are in the second extended position.

When the forming members 32 are fully extended, and the material 16 engages the upper corners 52 of the upper moulding portion 12, a blast of pressurized gas, such as air, is introduced to the lower portion 14 via inlets 54. The blast of high pressure gas is advantageously applied to ensure that the material 16 is completely formed into the shape defined by the internal surfaces of the upper moulding portion 12. Also, during the initial stretching of the material 16 by the forming members 32 into the upper moulding portion 12, low pressure air may be introduced to the lower tooling portion 14 via the inlets 54. This advantageously enables variation of the distribution of the material 16 in the final article, and may also assist in the speed of production of the article. In this regard, by varying the air pressure introduced via the inlets 54 during the initial stretching process, the wall thickness of the final article may be made even, or alternatively the wall thickness of the final article may be made thicker in an upper or lower portion thereof. The introduction of low pressure air via the inlets 54 may also be used to reduce marking of the inside of the article by the forming members 32 during the initial stretching of the material 16. After the high pressure blast to finally form the desired article, the push rod 46 is withdrawn so that the forming members 32 are retracted from the upper moulding portion 12. As the forming members 32 are lowered, the cam engaging portions 36 travel downward along the earning surface 44, once again due to the outward force of the spring loaded reseating cam 40. The forming members 32 continue to travel downward until they are relocated in the first retracted position. Advantageously, the downward movement of the forming members 32 is biased by a spring 56 which engages the spring loaded reseating cam 40. As such, when the forming members 32 are in the first retracted position, they are both outwardly biased by the spring loaded reseating cam 40 and are upwardly biased by the spring 56.

To ensure smooth movement of the push rod 46, the bearings 58 are provided along the travel path of the push rod 46.

To facilitate ejection of air held in the upper moulding portion 12 prior to stretching of the material 16 by the forming members 32, the base plate 60 of the upper moulding portion 12 is provided with vents 62. The vents may also be connected to a vacuum which ensures that the formed article is held within the upper moulding portion 12 on retraction of the forming members 32 as desired. Furthermore, on release of such a vacuum, high pressure air may be blown through the vents 62 to facilitate ejection of the formed article from the upper moulding portion 12.

Referring the Figure 2, the apparatus 10 may also be used in the stretch forming of articles having a neck portion, such as bottles or jars. In this case, the upper moulding portion 12 is provided with a necking moulding portion 70 which may be provided with a thread mould 72. The diameter of the necking moulding portion 70 is, as typically the case, smaller than the main body of the upper moulding portion 12. As a result, it is not possible to simply retract the forming members 32 from the upper moulding portion 12 and subsequently eject the formed article from the upper moulding portion 12 without the assistance of a more complex ejection system.

In Figure 2, for convenience the ejection system 74 is shown in forming mode 76 and ejecting mode 78. The ejection system 74 comprises a moving ejector 80 which on movement of the ejection system the forming mode 76 to the ejecting mode 78 moves downward to pool the necking moulding portion 70 sideward, removing the necking moulding portion 70 from the neck 82 of the article being formed. This leaves the side portion of the mould corresponding to the ejection system 74 open to facilitate ejection of the formed article.

Referring the Figure 3, when the apparatus is used on a commercial scale, a continuous run of upper moulding portions A and corresponding continuous run of lower tooling portions B are disposed adjacent each other. As will be seen from the drawing, the material to be stretch formed 16 is introduced between the series of upper portions A and lower portions B on a conveyor belt 90. A skeleton 92 is ejected from the tooling during the processing and removed. After tooling, the final articles 94 are ejected from respective upper moulding portions and suitably collected or packaged.

Throughout this specification and the claims which follow, unless the context requires otherwise, the word "comprise", or variations such as "comprises" or "comprising", will be understood to imply the inclusion of a stated integer or group of integers but not the exclusion of any other integer or group of integers.

Those skilled in the art will appreciate that the invention described herein is susceptible to variations and modifications other than those specifically described. It is to be understood that the invention includes all such variations and modifications. The invention also includes all of the steps, features, compositions and compounds referred to or indicated in this specification, individually or collectively, and any and all combinations of any two or more of said steps or features.

Claims

THE CLAIMS DEFINING THE INVENTION ARE AS FOLLOWS: 1. An apparatus for stretch forming a hollow article comprising: an upper moulding portion; and a lower tooling portion which is engagable with the upper moulding portion to locate a material to be stretched formed between the upper and lower portions, wherein the lower tooling portion comprises: a plurality of forming members, each forming member having a head portion adapted to engage the material to be stretch formed and a cam engaging portion; spacing means for maintaining the head portions of said forming members at a predetermined minimum distance from each other; mounting means for mounting the spacing means and the plurality of forming members wherein each of the plurality forming members is outwardly displacably connected relative to the mounting means; earning means for engaging the cam engaging portions of the plurality of forming members; and displacing means connected relative to the mounting means, the displacing means being actuable to displace the forming members upwardly into the upper moulding portion, whereby the cam engaging portions of the forming members engage the earning means as the displacing means is activated such that the head portions of the plurality of forming members are outwardly displaced relative to the mounting means to stretch the material upward into the moulding portion.

2. An apparatus according to claim 1 wherein the plurality of forming members travel from a first retracted position in which the head portions of the forming members are spaced at said predetermined minimum distance, to a second outwardly displaced position in which the plurality of forming members have stretched the material so that it engages an internal surface of the upper moulding portion.

3. An apparatus according to either claim 1 or claim 2 wherein the cam engaging portion of each of the plurality of forming members is resiliently outwardly biased such that when the plurality of forming members are in the first retracted position the respective head portions of the plurality of forming members are inwardly biased such that the forming members engage the spacing means and are spaced suitably for engagement with the material to be stretched.

4. Is an apparatus according to any one of claims 1 to 3 wherein the plurality of elongate fingers are pivotally connected relative to the mounting means in a circular arrangement.

5. An apparatus according to claim 4 wherein the cam engaging portion of each of the plurality of forming members is preferably an outwardly displaced arm located across the pivotal connection to the mounting means such that as the earning means engages and urges inwards the cam engaging portions, the head portions are urged outwards.

6. An apparatus according to any one of claims 1 to 5 wherein the earning means comprises earning surfaces extending longitudinally on a inner surface of the lower tooling portion wherein the earning surfaces provide a substantially frustroconical surface for engagement with the cam engaging portions of the plurality of forming members.

7. An apparatus according to any one of claims 1 to 6 wherein the displacing means is a push rod which acts as a piston, forcing the plurality of forming members upward into the moulding portion.

8. An apparatus according to any one of claims 1 to 7 wherein the push rod be resiliently biased so that downward movement of the plurality of forming members towards the first retracted position is opposed.

9. An apparatus according to any one of claims 1 to 8 wherein the mounting means is disposed on a shaft extending axially from the displacing means.

10. An apparatus according to any one of claims 1 to 9 wherein the mounting means is a mounting block and each of the plurality of forming members are internally pivoted about a plurality of respective locating pins within the mounting block.

11. An apparatus according to any one of claims 1 to 10 wherein the lower tooling portion additionally comprises a head portion limiting means whereby said limiting means locates the head portions of the plurality of forming members in desired first position.

12. An apparatus according to any one of claims 1 to 11 wherein the lower tooling portion is engagable with the upper moulding portion to provide an air tight seal.

13. An apparatus according to any one of claims 1 to 12 wherein the stretch forming apparatus also include a flange release located adjacent the seal to facilitate ejection of excess material from the seal when the upper moulding portion and lower tooling portion are engaged.

14. A method for stretch forming a hollow article in an apparatus as claimed in claim 1 comprising the steps of: disposing a sheet of material to be stretch formed between said upper moulding portion and said lower tooling portion; bringing the upper moulding portion and the lower tooling portion into sealing engagement so as to engage the sheet material between the upper moulding portion and the lower tooling portion; longitudinally and laterally stretching the sheet material by displacing said plurality of forming members upward into the mould; further stretching the resultant longitudinally and laterally stretched material by blowing a gas into the mould under pressure to form the article; and removing the article from the mould.