AU2006202239A1 - Moulding method - Google Patents

Description

Regulation 3.2

AUSTRALIA

Patents Act 1990 COMPLETE SPECIFICATION FOR A STANDARD PATENT

(ORIGINAL)

Name of Applicant: Actual Inventor(s): Address for Service: Invention Title: LOUIS LANCE MAGYAR and ILONA MAGYAR LOUIS LANCE MAGYAR ILONA MAGYAR SANDERCOCK COWIE SUITE 8C, 50-54 ROBINSON STREET DANDENONG VIC 3175 MOULDING METHOD Details of Associated Provisional Application(s): No(s): Australian Provisional Application No. 2005902702 Filed: 2 6 t h May, 2005 The following statement is a full description of this invention, including the best method of performing it known to us: 1 Fc2GO6-05-26Z:\Filinl\agyar. rile.wpd. I la- TITLE: MOULDING METHOD FIELD OF THE INVENTION This invention concerns a method of moulding thin-walled articles.

2006-05-26,Z \Specifiutionsxnagyar uapwpd. I -2- BACKGROUND OF THE INVENTION The invention will be described with reference to food trays for supermarket use but persons skilled in the art will appreciate that the method is applicable to other thin-walled mouldings. Vacuum or superatmospheric moulding of food trays for supermarket use is common. Those trays which hold food which must be film wrapped require edge treatment to ensure that the tray rim does not split the film. One method of modifying the rim is to follow the initial moulding step which produces a rim flange with a second moulding step which softens the flange and bends part of the flange at right angles into a downwardly depending perimeter. This profile reduces the incidence of film splitting.

But this process occupies two stages and this downwardly depending perimeter profile is not the best which can be achieved.

SUMMARY OF THE INVENTION The method aspect of the invention provides a method of moulding a thin-walled article from a sheet blank by a pressure differential operation comprising applying a differential to one face of the blank to cause contact with a first mould surface and applying a differential to the opposite face of the partially shaped blank to cause contact with a second mould surface and optionally severing the moulded article from waste.

The application of the first differential may be preceded by sealing the blank between a blank supporting surface and the die defining the first mould surface.

Sealing the blank as described above may be preceded by feeding the blank between the 2006-05-26.Z:\Specifications\magyar cap wld.2

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die and the blank support surface.

If the blank is a ribbon of sheet plastic, the feed motion may be by indexing. The application of the second differential is to the remainder of the blank surrounding the die while the seal is maintained. This allows the remainder of the blank to contact the second N die surface without disturbing the shape imposed by the first die surface. The second die IDsurface may belong to a floating die which establishes a sealing and non-sealing position Swith the first die.

A second die may surround the blank supporting surface. The article may be severed from the waste by a floating die which closes on the knife.

A second die may have a bevelled periphery and the knife too may have a bevelled periphery of steeper angle so as to subject the wall of the article to shear.

The floating die may reciprocate toward and away from the knife. The knife may be static and the bevel may move toward and away from the knife. Accordingly the bevel may float because even though the knife contacts the bevel in the floating die at a slightly different place during each operation, the shearing and severing will occur with the same result, that is the minimisation of whiskers of plastic extending from the severed edge.

The pressure differentials may be imposed on the faces of the blank simultaneously.

When the differentials are applied one after the other, a precursor is first formed and then modified.

2006-OS-26Z:\Specification\mgyar.cap pd,3 -4- BRIEF DESCRIPTION OF THE DRAWINGS Figure 1 is a diagrammatic side view of the forming apparatus in the forming mode.

Figure 2 is a diagrammatic side view of the forming apparatus in the eject mode.

Figure 3 is an enlarged section through the forming apparatus of Figure 1 when the knife is about to sever the tray from the ribbon.

Figures 4-6 show the forming stages.

Figure 7 shows the tray produced by the method when film wrapped.

Figure 8 shows the shape of the prior art tray.

DETAILED DESCRIPTION WITH RESPECT TO THE DRAWINGS Referring now to Figures 1 and 2 of the drawings, press 2 has a static aluminium plate 4 and a rise and fall plate 6. Plate 6 rides on press guide pillars 8. Bottom tool plate is fixed to the rise and fall press plate 6 and top tool plate 12 is fixed to static plate 4.

Pedestal 14 supports bottom former 16. Air passage 18 passes through both former and pedestal and connects to a valve and compressed air supply (not shown). Air and coolant conduit 20 passes through the plates 4 and 12 to atmosphere. Hollow top former assembly 22 is suspended from the top plate 12 by springs 24 and conduit 20. Top knife 26 is rectangular in plan and projects from top plate 12 and cooperates with bottom knife 2006-05-26.Z \SpecificationsVmagyar cap wpd.4 assembly 28 to sever articles from film 30 which is fed between the top and bottom formers by an indexing mechanism (not shown).

Top and bottom sheet heaters set at 320 0 C and 315'C respectively (not shown) prepare the polystyrene sheet for forming.

Bottom knife assembly 28 is also rectangular in plan and is seated on floating die plate 32 which slides on four posts 34 which depend from top plate 12. Stops 36 arrest the floating die plate at the position shown in Figure 2. The severed tray 38 (13 x 6.5 inches) is shown in the EJECT position in Figure 2.

The top and bottom formers are seen in greater detail in Figure 3. Ribbon 30 is 0.6mm thick polystyrene 200mm wide and is pneumatically formed into corrugated meat trays (13 x 62 inches) for supermarket use.

Hollow top former assembly 22 consists of aluminium die 40 from which central shaft 42 extends upwardly into cylindrical passage 20. Shaft 42 is a slide fit in passage Die 40 defines tapered cavity 44. Die 40 has cooling passages 46 which are fed with coolant through passage 48 in shaft 42. Springs 24 allow a small upward displacement of the die in response to final motion added to ram movement applied to the press plate 6. Air escape passage 50 allows air above the admitted film to escape when forming begins. The feed surface for the film is the top face of floating die 32. Floating die 32 has a rectangular aperture 52 surrounded by lower knife 28. The lower knife has a continuous bevel 54. A continuous undercut 56 meets the bevel 54 at a continuous edge 58.

2006-OS.26.Z \Specificzons'rnagya -6- Static knife 60 has a shearing bevel 62 and depends from top plate 12. Bevel 62 closes on continuous edge 58 when the knife enters space 64 between die 40 and floating die 32.

Continuous rubber ring seal 66 surrounds the knife and the top and bottom formers and nips a portion of the film when plate 6 closes against plate 4 to begin the forming.

Referring now to Figures 4-6, in operation the heated ribbon is indexed across the feed surface to lie between the separated top and bottom formers (Figure 2) covering the aperture 52. Plate 6 rises and the seal 66 closes on the film. Former 16 closes against die trapping the film 30. Springs 24 ensure sealing contact of die 40 with the film.

Air at 1 Spsi is admitted to cavity 52 for about 1.5 seconds (see Figure The tray forms expelling air through passage 20 to atmosphere. Air at 8psi is admitted through a side duct 68 to the space between die 40 and the knife 60 reaching space 24 where it presses the film against undercut 56 and continuous edge 58 for a further five second period. The tray cools and shrinks.

A small upward movement is imparted to the pedestal which lifts the floating die slightly pressing the bevel against the static knife whereupon the tray is severed from the surrounding film. The formers separate and the 8psi air injection escapes from below the film to atmosphere via the small gap between the former 16 and the floating die and from above the film to atmosphere.

The film indexes and is ready for the next cycle which lasts 4.5-5 seconds. In a commercial variant, the film is 700mm wide and the press plates support three side by side sets of formers.

2006-0-26.Z:\Spccificarmtion agya cap wpd.6 -7- We have found the advantages of the above embodiment to be: 1. The tray rim formed in this two stage process causes the clear film which is subsequently applied over the meat to be tensioned over nose 62 instead of a sharp edge.

2. Complex profiles are possible because two dies are available for shaping.

It is to be understood that the word "comprising" as used throughout the specification is to be interpreted in its inclusive form, ie. use of the word "comprising" does not exclude the addition of other elements.

It is to be understood that various modifications of and/or additions to the invention can be made without departing from the basic nature of the invention. These modifications and/or additions are therefore considered to fall within the scope of the invention.

2006-OS.26.ZASpecifica lion\magyar cap wpd.7

Claims (8)

1. A method of moulding a thin-walled article from a sheet blank by a pressure differential operation comprising applying a differential to one face of the blank to cause contact with a first mould surface and applying a differential to the opposite face of the partially shaped blank to cause contact with a second mould surface and optionally severing the moulded article from waste.

2. A method as claimed in Claim 1, including preceding application of the first differential by sealing the blank between a blank supporting surface and a die defining the first mould surface.

3. A method as claimed in Claim 1 or 2, including reciprocating the second mould surface between sealing and non-sealing positions with the die.

4. A method as claimed in Claim 2 or 3, including indexing the blank between the blank supporting surface and the first die.

A method as claimed in any one of Claims 1-4, including applying the second differential to the remainder of the blank surrounding the first die while the seal is maintained.

6. A method as claimed in Claims 1-5, wherein the pressure differentials are imposed simultaneously to the opposite faces of the blank.

2006-O5-26,Z SpcciicationsVnagyarcapwpd I-9- \O O

7. A method as claimed in any one of the preceding claims, including severing the moulded article from waste by a knife which closes on the second die.

8. A method as claimed in Claim 7, wherein the second die has a bevelled periphery and the knife too has a bevelled periphery of steeper angle so as to subject the C article to shear. S9. A method as claimed in Claim 8, including reciprocating the bevel of the second die toward and away from the static knife and allowing the second die to be guided during shearing by the bevel on the second die. A method substantially as herein described with reference to Figures 1-3. 11. Articles when made by a method as claimed in any one of the preceding claims. 12. Food trays for shops when made by a method as claimed in any one of Claims 1- 13. A method as claimed in any one of the preceding claims, wherein the article is a tray and the second mould surface surrounds the first mould surface and modifies the edge of the tray. 14. A die assembly comprising a first die which is capable of sealing to a mouldable sheet of plastic from which an article is to be moulded and a second die capable 2006-O3-26.Z \Specificationsmagyar.cap wpd.9 N O O of modifying the shape of at least part of the article made by the first die. A die assembly as claimed in Claim 14, including a die bed against which the first (N die closes to form the article. (N CN 16. A die assembly as claimed in Claim 14 or 15, including means to reciprocate at s least one of the dies to allow a plastic sheet to index through the assembly. 17. A die assembly as claimed in Claim 15 or 16, wherein the second die has a continuous edge surrounding the first die and an inclined surface against which a knife closes to shear the sheet. 18. A die assembly as claimed in Claim 17, wherein the second die is mounted for exerting a floating action whereby the inclined surface strikes the static knife. 19. A die assembly substantially as herein described with reference to the drawings. Dated this 26 th day of May, 2006. SANDERCOCK COWIE PATENT ATTORNEYS FOR LOUIS LANCE MAGYAR and ILONA MAGYAR 2006-05-26.Z \SPecifictionVinagya cap wpd.IO