GB2456502A

GB2456502A - A permeable shaping tool, a method of shaping and of handling an article

Info

Publication number: GB2456502A
Application number: GB0722660A
Authority: GB
Inventors: Ian David Halliday; Philip Kilburn
Original assignee: 3T RPD Ltd
Current assignee: 3T RPD Ltd
Priority date: 2007-11-17
Filing date: 2007-11-17
Publication date: 2009-07-22
Also published as: GB0722660D0

Abstract

A permeable shaped tool, for use in methods of forming and handling articles by pulp moulding, is used as a mould and water is extracted from a pulp slurry through the mould leaving a shaped article formed against the contours of the tool. The tool has a surface member (40) against which the pulp article is moulded, and a plurality of perforations (48) through the surface member and leading into a space (70) between the surface member and an underlying supporting inner member (20). A plurality of spacer legs (50) support the surface member over the inner member. Evacuation channels (28) in the inner member complete a route enabling fluid under suction to pass from the pulp slurry into the surface member from its outer surface (42), through the perforations (48) and the space (70) and out through the channels (28), while pulp from the slurry is retained and built up on the outer surface (42). The article may be removed from the tool, with a handling tool, for drying. In the case of a two part tool, both portions of the tool may be formed by a additive layer manufacturing process.

Description

2456502

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A PERMEABLE SHAPED TOOL, AND METHODS OF FORMING AND HANDLING AN

ARTICLE

This invention relates to a permeable shaped tool, to a forming tool utilising the tool structure, to an article handling tool utilising 5 the tool structure, to a method of forming an article using the tool, and to a method of handling an article using the tool. Tools embodying the structure are particularly useful in the field of pulp moulding.

In pulp moulding, a fibre article is formed by extracting water from 10 a pulp slurry through the mesh of a pulp mould, leaving fibres to build up against the mesh until the desired article is formed. These articles can have quite elaborate three-dimensional shapes, typically up to 200mm high. The pulp is typically cellulose fibres in water, and can be derived from recycled paper and like materials, 15 to give a lightweight product often used for protecting fragile goods in transit.

In a typical pulp moulding process the pulp mould comprises a stainless steel wire mesh overlying an apertured shaped support to which it is secured. This forms a permeable mould tool, which is 20 submerged into an aqueous cellulose pulp slurry, and a vacuum is then drawn on the permeable tool. Water from the slurry is drawn through the mesh, but the fibres in the slurry do not pass through. Accordingly, a fibre mat builds up on the mesh in a shape determined by the shape of the tool. The thickness of the mat depends on the 25 duration of the process. When a desired thickness is reached, which may be up to about 5mm, but perhaps more commonly around l-2mm, the tool is raised from the bath and the vacuum is continued to remove as much water from the mat as possible

The process can continue with a number of further steps. A permeable 30 de-mould tool, of complementary shape to the mould tool, may be passed over the moulding to compress the external surface of the formed article to improve the finish and the form of the outer surface. The vacuum on the mould tool can be released and a vacuum

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drawn in the de-mould tool instead, transferring the article from the mould tool to the de-mould tool. The de-mould tool moves the article to a conveyor, releases the vacuum, and the article moves away to a drying stage. Meanwhile the mould tool is rinsed and a 5 positive pressure may be applied to clean the mesh of residual fibres.

The above described process is suitable for open articles, such as bowls, which can be made with a single part mould. For forming articles with interior surfaces, such as bottle shapes, a multi-part

10 mould is used. The use of a de-mould tool can be omitted, and the formed article can be ejected from the mould tool simply by opening the mould and switching from negative air pressure to positive air pressure after removing excess water from the article. The ejected article will again move on to a final drying stage.

15 The pulp mould needs to be corrosion resistant, strong enough to withstand the applied pressure differential under vacuum, and of the correct form to produce the desired article. Desirably, it should also be capable of convenient manufacture, avoiding unnecessary delays between mould design and production.

2 0 This invention is concerned to provide a novel tool structure which can be produced in permeable shaped embodiments, including forming and handling tools suitable for this and other purposes.

According to the invention, a permeable shaped tool for engaging the surface of an article comprises a surface member having an exposed

2 5 support surface for co-operating with a complementary shaped surface of an article, an inner rigid member provided with a plurality of evacuation channels, a plurality of spacer legs within the tool extending between the surface member and the inner member and supporting the surface member over the inner member with space

3 0 between them, and a plurality of perforations through the surface member extending from the support surface to said space between the said members, wherein said perforations, space and evacuation channels together form a route adapted to enable a fluid under

suction to pass into and through the surface member, around the spacer legs, and away through the evacuation channels of the inner member.

The tool may be used as a former or mould against which an article can be built up and formed The tool engages the surface of the article as it is formed. Accordingly, in a particular aspect of the invention a forming tool for forming articles from a liquid-solid slurry or the like by extracting liquid through a support surface while retaining solids thereon to form an article comprises such a tool. The tool is used with an evacuation pump connected to the evacuation channels.

In another aspect of the invention, a handling tool for handling articles while holding them by suction against a shaped support surface comprises such a tool and a suction pump connected to the evacuation channels.

In a further aspect of the invention, a method of forming an article from a liquid-solid slurry comprises extracting liquid from the slurry through a plurality of perforations in a support surface of a surface member of a tool while retaining and supporting solids thereon to form the article, passing the extracted liquid through the surface member into a space between the surface member and a rigid inner member from which the surface member is spaced by a plurality of spacer legs, and evacuating the liquid from the space through a plurality of evacuation channels of the inner member.

In this aspect, the invention may comprise the further steps of removing the formed article from the support surface, optionally with a handling tool also in accordance with the invention, and drying the formed article.

In a further aspect, a method of handling an article comprises engaging a shaped surface of the article with a complementary shaped support surface of a surface member of a tool having an inner rigid member provided with a plurality of evacuation channels, a plurality

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of spacer legs within the tool extending between the surface member and the inner member and supporting the surface member over the inner member with space between them, and a plurality of perforations through the surface member extending from the support 5 surface to said space between the said members, and applying suction to the evacuation channels of the inner member to retain the article against the support surface of the tool.

It is envisaged that the inner member may provide the principal structural strength for the tool. It suitably comprises a wall 10 defining the basic shape of the forming tool and of the article to be formed thereon, the wall being of sufficient thickness, according to the material of which it is made, to provide a secure support for the surface member which is supported above it by the spacer legs. However, additionally or alternatively, it is also envisaged that 15 the structural strength may largely derive from the three-dimensional composite structure provided by the surface member, the support legs and the inner member in combination.

The term 'inner' is used in reference to the exposed support surface of the tool. The surface member exhibits the exposed support surface 20 which co-operates with the article, and the inner member is located inwardly of the tool, away from the exposed surface. The exposed surface may be convex or may be concave, or may be both; egg boxes or trays are examples of pulp-formed articles such as may be made by this invention which exhibit both convex and concave formed surfaces 25 in the same article.

While it is possible, in principle, to provide evacuation channels in the form of surface grooves on the inner member, it is preferred to direct the evacuation channels, or at least a majority of them, through the inner member by the most direct route away from the 3 0 surface member. Since a principal use of the forming tool is to form articles which have significant variations in shape through three dimensions, the support surface is frequently distinctly curved, and may be convex or concave or both according to the requirements of the article to be formed. These curved configurations may imply

areas with short radii of curvature. If the surface member is considered to be a first sheet of material, and the inner member a second sheet of material, and the surface member has perforations extending directly through from one side to the other, and the inner member has evacuation channels extending directly through from one side to the other, it can be seen that in regions of sharp curvature the openings to these perforations and channels need to be relatively widely spaced on the outside of the curve if the openings on the inside of the curve are not to coincide. Coincidence of openings would, of course, imply a reduced sheet thickness and an irregular inner surface to the sheet. In order to achieve close spacing of the perforations on the support surface of the surface member in convex regions of the surface, it is therefore necessary to have as thin a surface member as possible. However, the thinner the surface member, and the greater the number of perforations for efficient liquid extraction from the slurry, the weaker is the surface member and the more support is required.

By providing this support by means of spacer legs, to create a space under the surface member through which liquid can flow to larger and substantially more widely separated evacuation channels, the inner member can be constructed with a relatively thick wall and the channels spaced sufficiently far apart that they do not coincide at any degree of curvature, concave or convex, while providing the necessary structural strength and inner efficiency.

With this kind of structure, spacer legs which coincide with the perforations of the surface member or the evacuation channels of the inner member will be ineffective to provide support, and will have at least a partial blocking effect on the respective perforation or channel. Since the evacuation channels are often substantially larger than the perforations, and for the sake of forming the article evenly and regularly over its whole extent, it is preferred to avoid obstructing the perforations of the surface member by arranging for the spacer legs to be integral with the surface member. They may extend from the surface member between perforations. In alternative structures the spacer legs may be

formed integrally with the inner member and extend towards the surface member, or may be formed integrally with both the surface member and the inner member, or may be provided by an intermediate network of interconnected spacer legs extending and retained between the surface member and the inner member, but integrating the spacer legs with the surface member is preferred.

It is possible to design an arrangement of the spacer legs so that they will not obstruct any perforation or evacuation channel even partially, but integrating the legs with the surface member can avoid risk of obstructing the perforations, and provided that the widths of the ends of the spacer legs are small in relation to the widths of the evacuation channel openings, it is in practice not a problem simply to distribute the spacer legs uniformly and not complicate the design and manufacturing processes by arranging for the spacer legs to be absent from these regions. Preferably, the spacer legs are distributed as uniformly as the tool shape permits.

The inner member provides strength for the tool to withstand pressures arising from the applied vacuum during the forming process, and during normal use. The thickness of the inner member is chosen in accordance with the foregoing considerations of curvature and separation of the evacuation channels, the strength required, and the manufacturing cost and material cost. As many evacuation channels as possible, consistent with support and strength, are desired. Greater channel widths require greater separation and therefore more uneven drainage through fewer channels, place more demands on the liquid drainage route through the space between the surface member and the inner member, and increase the unsupported area of the surface member, although allowing freer flow of liquid through the channels.

As has been implied in the foregoing description, for convenience a two-part tool is often preferred. In a two-part tool, the surface member may be manufactured separately from the inner member, and the spacer legs may be manufactured integrally with the surface member. Effectively, the two parts of the tool thus formed are a mesh

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portion which provides the perforated support surface, and a base portion (the inner portion) which supports the mesh portion and facilitates drainage. Since the base portion is usually strong and durable in comparison with the mesh portion which is anticipated to 5 be more delicate, any damage that arises in the mesh portion through wear or other hazards of use can be remedied in a two-part tool by replacing the mesh portion only, reserving the base portion for reuse. Furthermore, small variations in the shape to be formed can be accommodated by changing one mesh portion for another, while keeping 10 the base portion unchanged.

There can however be occasions when a one-part, monolithic tool is preferred, for example in forming small, intricately shaped articles. On the other hand there may also be times when a structure with more than two separate parts is preferred, in order 15 to meet particular requirements. Thus the inner member may itself be positioned over a further supporting member with further drainage channels.

It is a particular advantage of the invention that both portions of the tool can be made by an additive layer manufacturing process. In 20 such a process, a complex three-dimensional shape can be built up, layer by layer, in a bed of powder from which the part is to be made, by selectively fusing or sintering successive layers of powder. A thin layer of powder is spread on a base, and this is followed by a pass of local heating means to fuse or sinter selected 25 areas of the powder surface. This is followed by a further thin layer of powder and a further heating pass. Suitable local heating means include lasers and other highly directional local heating devices, and area heaters with masking means to localise the heat reaching the powder. In this way the article is built up layer by 3 0 layer in an ever deepening bed of loose unfused powder. When the structure of the article is completely formed, it can be taken from the bed of unfused powder and cleaned of loose powder.

Using such a process, the components of the tool can be built up out of structural thermoplastics, especially polyamides, for example

Nylon 12, and carbon filled polyamide. Other suitable plastics include polypropylene. Suitable metallic powder materials include aluminium, cobalt chrome, stainless steel, titanium and bronze in particular. Glass, and many other materials and combinations of materials, eg glass-filled nylon and aluminium-filled nylon, may also be used.

The additive layer manufacturing process is of course computer controlled, and the shapes to be formed by the selective heating can be more efficiently defined and calculated if regular polygons are substituted for circles, because the data processing requirement is often less. Accordingly, when computer processor power is a factor to be taken into account, it may be preferred that the spacer legs be polygonal in cross section, and likewise that the perforations in the surface member be polygonal in cross section. Given the large number of spacer legs and of perforations, the computational demands on the control software and hardware are eased if the cross sectional shapes are squares or regular hexagons or octagons.

The process is capable of wide variations. Any suitable material can be used. Powder size is generally about 70 micrometres, in the broader range from 20 to 3 0 micrometres up to 90 micrometres. Typically, the surface member may be made about 2mm thick, and the spacer legs about 1mm wide. The perforations likewise may be about 1mm wide, their fineness depending on how reliably the process can form small apertures.

The numerical ratio between the number of spacer legs and the number of perforations may be about 1:2 to 1:4, although variations are possible according to specific design requirements. Ratios up to 1:1 and down to 1:10 may well be utilised.

In the case of the evacuation channels extending directly into the inner member, the width of the channel openings on to the space below the surface member may be substantially greater than the width of the tips of any spacer legs. If the channel opening width is greater than twice the width of the tips of the nearest legs, a leg

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extending from the surface member towards the channel will not obstruct the channel unacceptably. However, in general, the channel opening widths are not subject to maxima or minima. The channel opening widths on to the space between the surface and inner members 5 may be as small as the widths of the perforations in the surface member.

The invention is illustrated in the accompanying drawings, which show different aspects, by way of non-limiting example. In the drawings:

10 Figure 1 is an isometric view of an assembled forming tool in accordance with the invention for the manufacture of a bowl shaped article;

Figure 2 is an isometric view of one quarter or quadrant of an inner member suitable for use in a tool similar to that shown in Figure 1;

15 Figure 3 is an elevational view showing the interior and the sectioned edge of the quadrant of Figure 2;

Figure 4 is a view corresponding to Figure 2 of a mesh portion, that is to say a surface member with integral spacer legs, that can be used in combination with the inner member of Figure 2;

2 0 Figure 5 is an elevation showing an interior view of the quadrant of Figure 4;

Figure 6 is an enlarged view of the circled portion of Figure 5, showing details of the perforations and spacer legs on the inner surface of the surface member;

2 5 Figure 7 shows the parts of Figure 2 and Figure 4 assembled together, as in a complete forming tool;

Figure 8 is an elevation showing an edge section and interior view of the tool of Figure 7and

Figure 9 is an isometric view showing, in a section through its diameter, the tool of Figure 1 together with a corresponding formed pulp article.

Figure 1 shows a forming tool 10 in accordance with the invention for use as a pulp mould, in this case for forming a bowl shaped article. The mould comprises a perforated surface member with a support surface 12 which defines the shape of the interior of the eventual article. The support surface is integral with a solid circular surrounding ring 14 which overlies a corresponding ring 16 forming the rim of an inner member, not otherwise visible in Figure 1, which lies below the surface member.

The structure of an inner member 20 is shown in Figures 2 and 3. It has a curved wall portion 22 approximating the shape of the article to be formed, surrounded by a rim 24 which, in use, allows the inner member to be combined with a surface member, as in Figure 1, and to be fixed together into a pulp moulding machine, (not shown in the drawings) . The wall portion 22 has substantial thickness, to give strength to the forming tool, and is pierced by a plurality of evacuation channels 28 extending directly through the wall by the shortest route. That is to say, the axis of each evacuation channel is normal to the curved surfaces of the wall in the region where the evacuation channel is formed. However, while the axes of the channels are shown here as perpendicular to the outer surface of the inner member, they may be set at other angles. For example, an inner member may be provided with strengthening ribs on the inside of wall portion 22, and in such a case evacuation channels may be evenly spaced on the outside of the wall portion, but may be set at oblique angles in the vicinity of such ribs to avoid the ribs on the inside of the wall portion. Because of the varying positive and negative curvature over the whole area of the wall portion 22 the channels are set at different angles to one another.

The illustrated evacuation channels are circular in cross section, but they may be of other shapes, such as regular or irregular polygonal. They are also tapered. This enables the channels to be

more easily cleaned of powder when the tool is first manufactured, and more easily cleaned of pulp when the tool is rinsed after use. It can be seen from the exposed section of wall portion 22 that the different inclinations of the evacuation channels are represented by differently tapering conformations. While the degree of taper may vary among the channels across the tool, the taper of each channel is conveniently in the same direction, so that a flow of air or liquid through the member from one side to the other can consistently be in the direction in which the channels widen, to facilitate cleaning. The taper could be in the opposite direction to that illustrated if the tool is proposed to be cleaned by positive air pressure alone applied to the inside of the tool.

The inner member 20 forms the base portion of a pulp mould and supports a surface member 40 illustrated in Figures 4 to 6. These Figures illustrate the perforated support surface 42, having regions of both positive and negative curvature, surrounded by an outer rim 46. The support surface is the exterior surface of a thin wall 44 which is perforated with a very large number of closely spaced perforations 48. Integrally formed on the interior surface of the wall are a plurality of spacer legs 50.

Legs 50 and perforations 48 are most clearly shown in enlarged detail in Figure 6. They are all hexagonal in cross section. The perforations are a plurality of distinct through passages in the wall 44 and are typically from 0.5mm up to 2mm wide at the surface 42. The integral legs extend from the wall between adjacent perforations. In this case, legs and perforations are both about 1mm in width and in the case of the legs about 2mm long. The perforations in this embodiment are greater in total number and smaller in individual area than the evacuation channels. These channels are at least 2mm wide and typically substantially wider, as illustrated in the drawings, although channel sizes down to 0.5mm can be used if they are present in sufficient numbers to provide the required evacuation rates.

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Figures 7 and 8 illustrate the assembly of a forming tool from the base portion constituted by inner member 20 and the mesh portion constituted by the surface member 40. Rim 46 of the latter is supported directly over rim 24 of the former, and the plurality of 5 spacer legs 50 reach exactly as far as the surface of the inner member, supporting the surface member in the event that external pressure is applied on to the support surface 42. When no pressure is applied, support is purely nominal, in that the spacer legs extend exactly across a space 70 formed between the surface member 10 and the inner member. It can be seen that the relative widths of the spacer legs 50 and the evacuation channels 28 are such that a single spacer leg cannot significantly obstruct the entrance to a evacuation channel. In this embodiment, leg tip width is less than half any channel inlet opening width. Each of the perforations 48 in 15 the support surface 42 communicates with space 70 between the surface member 4 0 and the inner member 20 to form a liquid drainage route through the surface member, around the spacer legs, and away through the evacuation channels to the interior of the forming tool.

The use of such a forming tool is illustrated in Figure 9, where the 20 tool of Figure 1 is shown in diametrical cross section, allowing the inner ends of evacuation channels 28 to be seen. A corresponding section of a bowl shaped article 90 that can be formed on the tool from a paper pulp slurry, by the method previously detailed herein, is shown. For this purpose, the tool is positioned in a suitable 25 mounting (not shown) on which it can be dipped into a pulp slurry, and is used under suction in accordance with conventional practice in the art. An evacuation pump (not shown) is connected to the evacuation channels to draw slurry towards the forming surface, which retains the pulp and builds up the article 90 while the water 30 passes through the perforations 48, into space 70, around spacer legs 50, and away through the evacuation channels 28 of the inner member 20.

As described, the forming tool has a convex support surface 12 to form an inner surface of a bowl shaped article 90. It will be 3 5 understood that the structure of the tool can be inverted, so that

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it presents a concave exposed forming surface against which a convex outer surface of an article can be formed. In such a case, the inner member of the tool may partially enclose the surface member while it underlies the surface member.

5 The inverted structure described above is also suitable for a handling tool for the article 90. Such a tool may be used as a de-mould and handling tool, first to compress the wet formed article, and then to take it from the forming tool by releasing the suction on the forming tool and initiating suction on the de-mould and 10 handling tool instead. The article may then be transferred by the handling tool to a drying stage, where the article is released from the tool by relaxing the suction. For these purposes, a suction pump is connected to the evacuation channels, and the article is held to the support surface, which is of a shape that is complementary to 15 the shape of the article, by air pressure.

Both the base portion and the mesh portion of the forming tools illustrated in the accompanying drawings are suitably made of a heat fusible thermoplastic such as Nylon 12 by the additive layer manufacturing method noted above.

20 While specific examples of the invention have been described and illustrated, it will be understood by those skilled in the art that the invention may be practiced with variations and modifications in the details given. In particular, the internal structures between the perforated support surface and the internal outlets of the 25 evacuation channels may be substantially varied, and further layers to the drainage route may be provided if required. For example, an intermediate thin apertured inner member may be supported on spacer legs over a lower inner member with still larger evacuation channels. A multi-layered structure can have benefits in relation to 30 strength and weight. In addition, the uses to which the forming tool may be put are essentially unlimited. Use as a pulp mould is a preferred application of the invention, but other applications will be apparent to those skilled in the different arts.

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Claims

1. A permeable shaped tool for engaging the surface of an article, comprising a surface member having an exposed support surface for co-operating with a complementary shaped surface of an

5 article, an inner rigid member provided with a plurality of evacuation channels, a plurality of spacer legs within the tool extending between the surface member and the inner member and supporting the surface member over the inner member with space between them, and a plurality of perforations through the surface 10 member extending from the support surface to said space between the said members, wherein said perforations, space and evacuation channels together form a route adapted to enable a fluid under suction to pass into and through the surface member, around the spacer legs, and away through the evacuation channels of the inner 15 member.

2. A tool according to claim 1 wherein the spacer legs are integral with the surface member.

3. A tool according to claim 2 wherein the spacer legs extend from the surface member between adjacent perforations.

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4. A tool according to any one of the preceding claims wherein the evacuation channels extend through the inner member.

5. A tool according to any one of the preceding claims wherein the perforations comprise a plurality of distinct through passages in the surface member.

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6. A tool according to claim 5 wherein the passages are circular or regular polygonal.

7. A tool according to claim 5 or claim 6 wherein the passage width at the surface is up to 2mm.

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8. A tool according to any one of claims 5 to 7 wherein the passage width at the surface is at least 0.5mm.

9. A tool according to any one of the preceding claims wherein the evacuation channels are circular or regular polygonal.

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10. A tool according to any one of the preceding claims wherein the evacuation channels are at least 0.5mm wide.

11. A tool according to any one of the preceding claims wherein the perforations are greater in number and smaller in area than the evacuation channels.

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12 . A tool according to any one of the preceding claims wherein the spacer legs are circular or regular polygonal.

13. A tool according to any one of the preceding claims wherein the support surface is convex or concave.

14 . A forming tool for forming articles from a liquid-solid slurry 15 or the like by extracting liquid through a support surface while retaining solids thereon to form an article, which comprises a tool according to any one of the preceding claims and an evacuation pump connected to the evacuation channels.

15. A handling tool for handling articles while holding them by 20 suction against a shaped support surface, which comprises a tool according to any one of claims 1 to 13 and a suction pump connected to the evacuation channels.

16. A method of forming an article from a liquid-solid slurry, comprising extracting liquid from the slurry through a plurality of

25 perforations in a support surface of a surface member of a tool while retaining and supporting solids thereon to form the article, passing the extracted liquid through the surface member into a space between the surface member and a rigid inner member from which the surface member is spaced by a plurality of spacer legs, and

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evacuating the liquid from the space through a plurality of evacuation channels of the inner member.

17 . A method according to claim 16 comprising the further steps of removing the formed article from the support surface and drying the 5 formed article.

18. A method according to claim 16 comprising the further step of removing the formed article from the support surface with a handling tool according to claim 15.

19. A method of handling an article, comprising engaging a shaped 10 surface of the article with a complementary shaped support surface of a surface member of a tool having an inner rigid member provided with a plurality of evacuation channels, a plurality of spacer legs within the tool extending between the surface member and the inner member and supporting the surface member over the inner member with 15 space between them, and a plurality of perforations through the surface member extending from the support surface to said space between the said members, and applying suction to the evacuation channels of the inner member to retain the article against the support surface of the tool.