NZ236527A - Composite pulp moulding die with flat rear face: outer mesh secured to inner mesh by fastenings passing through die body - Google Patents

Description

Patents Form # 5 NEW ZEALAND Patents Act 1953 COMPLETE SPECIFICATION' * AFTER PROVISIONAL NO : 236527 r DATED: 19 DECEMBER 1990 TITLE: "PULP MOULDING EQUIPMENT" * We, CARTER HOLT HARVEY PACKAGING LIMITED, a New Zealand company, of Auckland, New Zealand, and CARTER HOLT HARVEY PACKAGING (No. 2) LIMITED, a New Zealand company, of Auckland, New Zealand, jointly trading as PRINTPAC-UEB, having a trading address of 630 Great South Road, Greenlane South, Auckland, New Zealand, hereby declare the invention, for which we pray that a patent may be granted to us, and the method by which it is to be performed, to be particularly described in and by the following statement: The following page is number "la1 PF05.JWP FEE CODE -1050 la - 23G527 ABSTRACT A die for a wet pulp moulding machine to be mounted on the surface of a drum has a 5 first contoured metal mesh capable of receiving pulp on its outer surface, a main die body formed of a plastics material having a contoured outer surface corresponding to the shape of the metal wire mesh and having a substantially flat rear surface with drainage grooves therein. By forming the main die body from a block of plastics material it can be quickly and economically produced by a computer controlled routing 10 machine, and can be produced in a fraction of the time required to design and cast a metal die. The main die body having a plurality of passageways passing from the contoured outer surface through to the rear surface to enable suction to be applied through the main die body to the metal wire mesh. The main die body sits on a flat metal mesh and a substantially rigid perforate support frame is positioned adjacent said 15 flat metal mesh. The contoured metal wire mesh is tied to said substantially flat metal mesh by ties passing through the main die body. 4693CAP.D91/t0 23G52' FIELD This invention relates to pulp moulding equipment and has particular application to the 5 manufacture and use of dies in the production of moulded pulp articles.

BACKGROUND Moulded pulp articles such as fruit trays, egg cartons, and the like have traditionally 10 been formed by a free drying process, in which pulp is sucked onto a wire mesh having a shape complementary to that of the finished article, and dried. The contoured wire mesh is supported on a perforate metal die having an external contour matching that of the wire mesh. Traditionally such dies have been expensive and time consuming to manufacture, as they have been cast and machined from very hard alloys, eg bronze, 15 nickel bronze, or aluminium alloys. The manufacture of new dies from hard metal alloys typically takes five to six months from design of the finished article through to production of the finished metal die, and shaping of the wire mesh ready for installation in a pulp moulding machine.

OBJECT It is an object of this invention to provide an improved die and/or an improved method of manufacturing dies, or one which will provide a useful choice.

SUMMARY OF THE INVENTION In one aspect, the invention provides a die having a contoured outer surface corresponding to the shape of the desired article to be moulded on the die, and having a substantially flat rear surface, said die having a plurality of apertures therethrough 30 communicating between the contoured front surface and the rear surface.

Preferably the apertures communicating with the rear face have a larger cross section than the apertures communicating with the contoured front surface of the die. More preferably, the apertures are of circular cross section, and are stepped a predetermined 35 distance below the contoured front surface. This can most conveniently be achieved by drilling small diameter apertures through the material of the die, and then counter- 4693CAP.D91/to 23G527 drilling larger diameter apertures from the rear face, to create an internal step in each passageway as it passes from the small diameter at the surface of the die through to the larger diameter deeper in the die.

Preferably, the die is formed from a material that can be accurately and readily shaped. More preferably, the material is a non-metallic material which can be readily cut or shaped. The material may be chosen from the class of engineering plastics, composite wood-fibre materials, such as medium density fibreboard, and wood, or other non-70 metallic materials that can be readily machined by way of high speed routing machines, milling machines, laser cutters, carving machines or the like.

In another aspect, the invention provides a composite die for a pulp moulding machine including: (a) a first contoured metal mesh capable of receiving pulp on its outer surface, (b) a main die body having a contoured outer surface corresponding to the shape of the metal wire mesh, having a substantially flat rear surface upon 20 which surface drainage grooves have optionally been formed, and having a plurality of passageways passing from the contoured outer surface through to the rear surface to enable suction to be applied through the main die body to the metal wire mesh, (c) a substantially flat metal mesh adjacent the rear surface of the main die body, and (d) a substantially rigid perforate support frame adjacent said substantially flat metal mesh, and (e) means for tying said contoured metal wire mesh to said substantially flat metal mesh, and means for clamping the assembly together.

Various means of seeming the contoured metal wire mesh to the flat metal mesh may 35 be used, although it is preferred that the contoured wire mesh is secured to the substantially flat metal mesh by lacing or tying with fine wire which can be passed 4693CAP.D91/to 23G527 through the passageways in the main die body, and tied off on the rear surface of the substantially flat metal mesh so as to minimise any marks on the surface of the contoured metal wire mesh. This method is preferred as it minimises any cutting effect 5 of the wire through the die.

These and other aspects of this invention, which should be considered in all its novel aspects, will become apparent from the following description, which is given by way of example only, with reference to the accompanying drawings, in which: Figure 1 illustrates a schematic view of a moulding machine and transfer station.

Figure 2 illustrates a forming die positioned in a recess on the surface of an octagonal moulding machine - (but with details of the drum omitted).

Figure 3 illustrates an exploded view of a preferred composite forming die in accordance with this invention.

Figure 4 is an exploded cross section through the main die body of the preferred 20 composite forming die of this invention.

PREFERRED EMBODIMENT Wet pulp moulding machines typically involve the use of a plurality of forming dies 25 mounted on the surface of a drum which is partly immersed in a bath of paper pulp material, with its axis of rotation mounted above the surface of the bath, so that the forming dies on the exterior of the drum will be moved so as to dip into the bath, collect fibrous material on the surface thereof, and then re-emerge from the bath allowing partial drying of the fibrous material on the die. The pick-up and partial drying of the 30 fibrous material is achieved by means of suction, there being a vacuum passageway attached to the interior of the drum so as to draw a vacuum through the perforate or foraminous dies to pull the fibrous material onto the surface of the dies.

In most cases, it is preferable to use free drying or forced air drying to fully dry the pulp 35 articles. However, some applications call for die drying, in which an additional die is clamped over the surface of the article so that it is fully enclosed during the drying 4693CAP.D91/to 236527 process.

Figure 1 is a schematic view of a portion of a pulp moulding machine, and is based on a 5 flow diagram of an Emery moulding machine of the type illustrated in US patent 3,661,707 issued 9 May 1972 to Roy W Emery and John R Emery.

In this schematic view, details of the pulp tanks and pumps have been omitted. Typically the pulp is formed from waste papers or pulp bales to produce a liquid pulp 10 having approximately 4% solids with or without the addition of additives such as rosin, wax, aluminium sulphate, and colouring dyes, before the pulp is delivered to the pulp bath shown in Figure 1.

A moulding machine 10 is preferably in the form of a prismatic drum, in this case an 15 octagonal drum, mounted above a pulp bath 11. A suction pipe 12 passes from the central axis of the moulding machine 10 to a vacuum separator tank vacuum pumps (not shown). The pump 13 recirculates pulp around the pulp bath 11. The moulding machine has a plurality of dies on the surface, onto which the moulded pulp articles 15 are formed. These articles can be picked up by a transfer machine having a plurality of 20 transfer (or pick-off) dies. The transfer machine 16 gently carries the wet moulded pulp articles to a conveyor 17 which leads to a drying oven or the like. In the free drying process, moulded pulp articles are partly dried by suction applied to the pulp articles as they emerge from the bath, with final drying taking place in a curing tunnel.

Turning now to Figure 2, a portion of the octagonal drum of 10 is illustrated. This shows the exposed surface of a moulding die 20 and its clamping frame 21. The exposed surface of the moulding die is represented by a contoured metal mesh 22. This is preferably a fine stainless steel mesh pressed into a shape complementary to the shape of the pulp article to be moulded thereon. Although a variety of metal wire 30 meshes or indeed even non-wire meshes may be used, we prefer to use one or more stainless steel wire screens having a mesh size of between 40 and 70. We have found that stainless steel wire mesh screens last longer than screens formed of other materials.

The clamping frame 21 preferably has removable rails or escutcheons 23 bolted to the 35 periphery of the clamping frame, to enable the periphery of the moulded article to be varied by varying the number, position and shape of the rails 23. For example, in the 4693CAP.D91/tO 2Qnro»*) O ^ ( case of a moulded fruit tray, it is desirable to include finger apertures at each end, and stacking release portions on either side of the tray. These portions of the moulded article can be formed by the protrusions 24 and 25 shown on the rails. The substantially 5 rigid support frame 29 underlies the clamping frame 21.

Turning now to the exploded view of the preferred composite forming die shown in Figure 3, it will be apparent that the die is formed of a series of layers. It is held in place by the clamping frame 21 and the optional rails 23. In this drawing, there is 10 illustrated an outer contoured metal mesh screen 22, a main foraminous die portion 27, a substantially flat metal mesh 28, and a substantially rigid plate, or reinforcing metal member 29. Moulded article 15 is shown below the transfer die 14, which includes a cast backing plate 14a perforated by a plurality of holes 14b. All of these portions of the die are provided with apertures 36 therethrough to enable a suction to be drawn on 15 the surface of the die constituted by the outer contoured metal mesh screen. The composite die sits within a die box on the outer surface of the moulding machine 10. This die box has a perforate floor, or similar, so that the vacuum applied to the interior of the drum of the moulding machine will be applied to the apertures and passageways 36 through the die body, in order to suck the pulp onto the surface of the contoured 20 metal wire mesh screen when it is immersed in the pulp bath.

Preferably the contoured metal wire mesh screen is held against the contoured outer surface of the main die portion over substantially the entire surface thereof by appropriate fixing means. The fixing means may take the form of rivets, soldered 25 wires, wire tying, lacing or the like. Nevertheless, we prefer to use a fine stainless steel wire to tie the outer mesh to the inner mesh by passing a small loop or u-shaped portion of wire 37 through the outer mesh, and through pairs of passageways in the main die body, so that two free ends of the wire pass through portions of the rear metal mesh and are then gripped and tied off in a wire tying machine. Preferably the wire is a stainless 30 steel wire of diameter to suit the openings in the shaped wire mesh.

The main die body 27 is best seen in Figure 4 which is a sectional view and is "exploded" for clarity. It has a contoured outer surface 34 corresponding to the shape of the outer wire mesh 22 and hence to the shape of the moulded pulp article. It has a 35 substantially flat rear surface 35. There are a plurality of passageways 36 passing through the main die body, and these passageways are preferably stepped so that the 4 6 93CAP•D91/to 23G527 upper portion of the passageway 36a adjacent the contoured surface is of a narrower diameter than the lower portion of the passageway communicating with the rear surface 35 of the die body. Preferably the upper narrow portion of the passageway 36a extends 5 for a predetermined depth below the upper contoured surface 34 of the die so that a line drawn through the stepped interface between the passageways 36a and 36b will follow the contour of the outer surface of the die in order to provide a substantially uniform pressure drop across the entire surface of the die.

The substantially flat rear face of the die 35 may have a series of shallow grooves or indentations 38 to prevent blocking of the passageways by the reinforcing frame and/or metal mesh which are sandwiched against the rear face of the die. In this drawing the sectioned reinforcing frame is shown as a series of cross bars, with apertures passing therethrough. Alternatively the reinforcing member may consist of a flat metal plate 15 having apertures therein corresponding to the apertures 36 passing through the main die body, and thus may be of the same diameter as the lower passageways 36b, or slightly larger diameter, so as not to interfere with the vacuum drawn on the main die body and hence on the contoured outer metal mesh.

Preferably the main die body is formed from a softer material than that previously used for forming dies in pulp moulding machines. Hitherto, these dies have been manufactured from a cast rigid hard-wearing metal or metal alloy. We are aware that such dies have typically been made from bronze, nickel-bronze aluminium alloys requiring approximately five to six months from design to casting and final machining 25 before they can be assembled in a moulding machine. Alternately such dies can be cast, and if requiring an intricate contoured front and rear surface, they can be formed by a lost wax, or lost expanded polystyrene foam moulding process (the EPS process).

We prefer to use much softer materials that can be machined readily rather than being 30 cast. We prefer to use engineering plastics materials, or composite particulate material, such as medium density fibreboard, or fibrous or grainy materials such as wood. For the working dies, in most cases we prefer to use an engineering plastics material, and examples of such materials include: nylon, high molecular weight polyethylene (HMPE), ultra-high molecular weight polyethylene (UHMWPE), 35 polytetrafluoroethylene (PTFE), PETE, polycarbonate, etc. 4693CAP.D91/to 230527 Of these materials, we prefer to use medium density fibreboard (MDF) for prototyping of our dies, and to use HMWPE for the finished dies. Both of these materials can be readily machined by routing machines, at high speed, so that the outer contoured 5 surface of the dies can be formed using a numerically controlled routing machine. We prefer to design our dies on a CAD/CAM computer and to convert the output from our CAD programme to numerical code for a computer controlled routing and drilling machine. This enables the dies to be quickly and easily produced and reproduced - i.e. cloned. The material can be clamped so that the outer surface is exposed to the routing 10 machines, and the outer surface can be contoured by controlling the routing machines to cut away the material to the desired planar contours. Conveniently, a number of such dies can be machined simultaneously by using multi-head drilling/routing machine. The computer controlled routing/drilling machine can then be used to drill the series of small diameter apertures 36a through the block of material, typically such apertures 15 being of 3mm diameter and of 10mm rectangular spacing to form a rectangular matrix of holes through the entire block of material. The material can then be turned over, and the larger diameter apertures 36b, preferably of 5mm diameter drilled on the same centres, but to differing depths to correspond to the internal contour of the interface plane which will correspond to the outer contoured surface.

Flexure or "panting" of the main die body can be minimised by tightly clamping it against the rear mesh and the metal reinforcing member which should be rigid enough to resist downwards movement of the rear face of the main die body as suction is applied to the die body. This suction is typically halted at the point of drum rotation 25 where the moulded pulp article is to be moved to the transfer die, as the suction is released and sometimes additional air is blown in behind the wet moulded pulp article to cause it to jump across the gap to the transfer die.

Finally, it will be appreciated that various alterations or modifications may be made to 30 the foregoing without departing from the spirit or scope of this invention as exemplified by the following claims. 4693CAP.D91/to 536527

Claims (9)

1. WHAT WE CLAIM IS: 5 1. A composite die for a pulp moulding machine having an outer contoured mesh capable of receiving pulp on its outer surface, and supported on a main die body having a contoured outer surface corresponding to the shape of the outer mesh, wherein: the main die body has a a substantially flat rear surface and having a plurality of 10 passageways passing from the contoured outer surface through to the rear surface to enable suction to be applied through the main die body to the outer mesh, a substantially flat mesh is positioned adjacent the rear surface of the main die body, a substantially rigid perforate support frame is positioned adjacent said 15 substantially flat mesh, and said outer mesh is secured to the inner mesh by securing means passing through said apertures in the main die body.
2. 2. A composite die for a pulp moulding machine as claimed in claim 1, wherein both 20 of said meshes are of metal, at least said outer contoured mesh being of wire.
3. 3. A composite die for a pulp moulding machine as claimed in claim 2, wherein the contoured metal wire mesh is secured to the substantially flat metal mesh by lacing or tying with fine wire(s) which pass through the passageways in the main 25 die body, and are tied off on the rear surface of the substantially flat metal mesh.
4. 4. A composite die as claimed in any one of claims 1-3, wherein the die is formed from a material selected from the class of engineering plastics, composite wood-fibre materials, wood, or other machinable non-metallic materials. 30
5. 5. A composite die as claimed in claim 4, wherein the main die body is machined from a solid block of material by routing, milling, laser cutting, or carving.
6. 6. A composite die as claimed in any one of claims 1-5, wherein the apertures 35 communicating with the rear face have a larger cross section than the apertures : ^ communicating with the contoured front surface of the die. « .5 ftPU 1994 4693CAP.D91/to ft « , m f r 20 25 ■ 10- 236527
7. 7. A composite die as claimed in claim 6, wherein the apertures are of circular cross section, and are stepped a predetermined distance below the contoured front surface. 5
8. 8. A die as claimed in claim 4 or claim 5, wherein the apertures are formed by drilling small diameter apertures through the material of the main die body, and then counter-drilling larger diameter apertures from the rear face, to create an internal step in each passageway as it passes from the small diameter at the outer surface of 10 the main die body through to the larger diameter deeper in the main die body.
9. 9. A composite die substantially as herein described with reference to any one of the accompanying drawings. 15 JAMES W PIPER & CO Attorneys for PRINTPAC-UEB 30 ft. r 35 .y*" V . % *~G APR 1994 *7 4693CAP,D91/tO