GB2246737A - Pulp moulding tool - Google Patents

Abstract

A pulp moulding tool comprising a former having a moulding surface shaped to the required mould product configuration, and a cover adapted to conform closely to the surface and to retain slurry fibres drawn towards the surface during a moulding operation, whereby the cover is of a stretchable material brought into contact with the surface during a pulp moulding operation, the cover being of a material permeable to slurry liquid.

Description

PULP MOULDING TOOL This invention relates to a pulp moulding tool and in particular to a moulding tool for forming pulp (fibre) mouldings from a (wet) fibre slurry.

BACKGROUND OF THE INVENTION Pulp moulding are typically used for positioning items during transit, particularly fragile or damagable items as during despatch from a supplier to a customer. The items can be despatched individually and require protection against "external" impacts, but alternatively a number of articles (such as filled bottles) will be packaged in one carton as a multiple pack, and in addition therefore need to he kept apart to prevent multiple "internal" impacts and perhaps fracture. Often separate compartments will be required for accompanying ancillary items such as screws, operating manuals, and the like.

Pulp mouldings are suitably formed from a fibrous wood material, usefully as a dry moulding made from reconstituted wet paper fibres, from a slurry. The pulp moulding tool comprises a former having a shaped moulding surface with spaced conduits therethrough, and a covering for the moulding surface and closely conforming thereto and having openings permitting the passage of the slurry liquid e.g. water, but sized to retain the fibres.

If differential pressure is applied whilst the moulding surface is immersed in the slurry, slurry can be drawn to the tool, whereupon the water passes first through the covering and then through the conduits, with the slurry fibres being retained on the covering. If the "exhaust" conduits are correctly positioned, the fibres form a wet mat of substantially constant thickness upon the covering, which can be removed and then allowed to dry. A suitable slurry stock may be 90% water and 10% fibre, by volume.

It is a disadvantage of the currently-available pulp moulding tools that both the former and its associated (conforming) covering need to be precision made. Usually therefore these are only set up for long production runs, and are thus not suitable for customers requiring a relatively small number of mouldings, and on a just-in-time basis. Furthermore, whilst drying-out the mouldings may tend to distort unacceptably, unless in the tool design the mould maunufacturer includes additional strengthening ribs and angles i.e. extra design features of relatively complicated format not specifically required to locate items in transit but needed to ensure a consistent dry mould product; with current tools, both the mould and covering need these extra design features inbuilt. Furthermore, it is not easy to replace such a covering which has been removed to allow the conduits to be cleaned.

Whilst it is difficult to fabricate the former to the required configuration, it is even more difficult to fabricate the mould surface covering for the former; this is conventionally of metal mesh, of limited flexibility and needing to be cut to shape; often the covering will be fabricated from several smaller sections of the metal mesh e.g. of copper, brass, phospher bronze, and the join lines are likely to show in the dry moulding.

It will be understood that the covering needs closely to conform with the complicated but necessary rib and angle formations on the former, not only because the dried mould will conform to the shape of the covering rather than of the former, but also because the water exhaust conduits through the former are designed for uni form throughput for consistent dry mould thickness and so the covering passageways should not close off any of these conduits.

SUMMARY OF THE INVENTION We now propose an improved pulp moulding tool for making mouldings from a fibre slurry which includes a former having a moulding surface, and a moulding surface cover of a permeable and stretchable material.

Because the material is permeable it will permit the passage of slurry liquid, but the pore size will be selected to prevent the passage therethrough of slurry fibres. In the present invention, the pore size will permit and prevent as above mentioned in the stretched condition, and preferably but not necessarily also in the unstretched condition i.e. in the unstrtched condition the material may not permit a sufficiently fast throughput of slurry liquid e.g. water, with or without soluble additives, for commercial operation.

Preferably the stretchable material will be resilient, so that it can be re-used, with the same or with a different former.

Usefully the cover is of a woven material, with openings therethrough providing water flow passageways of a size determined by the spacing of the warp and/or weft threads; and then conveniently the threads are of elastic filaments which need not themselves be water-permeable. The size of the openings can be increased if and when desired by extra stretching of the material. The warp and weft threads or filaments can be of different materials. We do not however exclude the use of a water permeable stretchable sheet material, such as a non-woven fabric.

When the tool is not in use, the cover is spaced from the former; it is in conforming relationship with the former only when the differential pressure is active to effect slurry flow.

DETAILED DESCRIPTION OF THE INVENTION The invention will be further described by way of example with reference to the accompanying schematic drawings, in which: Fig.1 is a cross-section of a known pulp moulding tool; Fig.2 is of the too ] of Fig.1, but shown in perspective; Fig.3 is of the modified pulp moulding tool according to the present invention; Fig.4 is of the tool of Fig.3, shown in perspective; and Fig.5 is of the tool of Fig.3, but with vacuum applied.

The known pulp moulding tool is a cast metal former 10 secured to a base plate 12, to define a hollow chamber 14 having respective internally-disposed surfaces 10a,12a: in an alternative known embodiment the former 10 is machined from a metal block. Exhaust conduits 16 are drilled through the former 10 at selected spacings, from the outer surface 10b to the inner surface 10a. Base plate 12 includes a vacuum pipe 18, and when the pipe 18 is connected to a vacuum pump, air is removed from chamber 14, so that slurry water can be drawn through exhaust conduits 16, into chamber 14 and out through pipe 18.

Secured in conforming relation with the outer surface 10b of former 10 is a mould surface covering of wire mesh 20, in this embodiment of copper, but in alternative embodiments of brass or of phospher bronze. The openings in wire mesh 20 are intended to allow the passage of slurry water but not of the slurry fibres.

If the moulding tool is lowered into a water-fibre slurry, with vacuum applied through pipe 18, water can exit through pipe 18 whilst the fibres build up to a required mould thickness on mesh 20. When the moulding tool is withdrawn from the slurry, the moulding 22 can be removed and dried, and the tool re-used to form another wet mould.

Fig.2 is of the moulding tool of Fig.l with the former covered in wire mesh. Though the illustrated tool is of a basic shape, with therefore a relatively simple surface profile for the former, the mesh covering nevertheless needs to be fabricated from numerous small sections joined together, to follow each intricacy and contour of the tool, including stiffening parts so that the resulting dry mould is of acceptable profile.

In the embodiment of Fig.3 constructed according to t.'-#e invention, the cover 30 for the moulding face 110b of former 110 is of a woven elasticated material held across the former 110 by hold-down plate 34 and screws 36. In an alternative embodiment, the former 110 has a retaining laterally-extending side edge or platform, with screw holes near its outer periphery, so that a (wider) hold-down plate can be retained, but without the screws reeding to pass though the material; in a further alternative embodiment, a different hold-down means is used, such as quick-release clamps acting between the hold-down plate and ribs on external side walls of the former. The hold-down plate can be in two parts with the peripheral edge of the cover 30 sandwiched therebetween.

One advantage of our arrangement is that the openings in the cover material can if desired readily be made much smaller than is possible with a covering of wire or plastics mesh. Another advantage is that the tension in the material can be chosen within wide limits so that the cover 30 will not only conform to the former 110, as seen in Fig.5, but so that the size of the openings in the material and thus the water flow rate therethrough and the fibre retention proportion can be pre-selected. The tension can be adjusted between moulding cycles, as well as at the start of a production run.If a cover for one mould becomes damaged during use, it can quickly be replaced by another, perhaps from a tool not currently in use, so that the tool downtime is kept low; equally, when worn, the cover can be replaced without need to wait for the skilled craftsman to fabricate another, nor indeed with the former being out of service for the extended period necessary whilst the conforming mesh of Fig is prepared and fitted. The cover will conform to the moulding surface even if fitted at an incorrect angle relative thereto.

Particularly if the cover 30 is selected to have an increased number of openings as compared to the existing wire mesh coverings, we expect that it will also be advantageous to use a former with a greater number of more closely spaced exhaust conduits extending between the outer surface 110b of the former, to its inner surface 110a defining in part the exhaust chamber 114. Thus we propose a former 110 of an investment cast plastics material, conveniently a resin moulded former, to provide a series of sprues 112 in the casting when the (lower melting point) wax is melted out. This arrangement has the advantage that the moulding face 110b is better supported, since it does not have a chamber 14 therebehind but only a series of cavities of discrete width; it can thus be more durable. Having a better supported moulding face 110b, the former can be made from easier-worked materials.The lower volume of water in the sprues as compared to cavity 14 can be more quickly and perhaps more easily removed directly from the former, with a reduced volume of residual water to settle and perhaps back-flow when the vacuum pump is switched off.

An advantage of our arrangement is that the smaller openings possible with a stretch material, perhaps no "openings" with a sheet material, can allow a much smoother surface finish to the moulding.

The slurry can include a proportion of fibres of materials other than those derived from wood e.g. cellulose or cotton, and perhaps of glass, for special effects and/or applications.

A particular advantage is is the reduced cost in manufacture of a precision tool; usually several prototypes have to be made before former 10 is correct, and for each a separate wire mesh 20 has to be cut and assembled to shape. The tool designer for our pulp moulding tool is less likely to be inhibited by consideration of the practicalities of mesh assembly; cost and lead time should be reduced. The tool performance can be expected to improve, as compared to the tool of Fig.l, because the cover is drawn against the former when differential pressure is applied; output will be increased, if tool downtime is reduced.

Claims (10)

1. A pulp moulding tool for making mouldings from a fibre slurry which includes a former having a moulding surface, and a moulding surface cover of a permeable and stretchable material.

2. A pulp moulding tool for making mouldings from a fibre slurry which includes a former and a cover, the former having a moulding surface shaped to the desired mould product configuration, the surface being interrupted by conduits, the cover being adapted to conform closely to the moulding surface and to retain fibres drawn towards the former during a moulding operation, the cover being of a stretchable material permeable during a moulding operation to slurry liquid, the cover normally being spaced from the moulding surface but engageable during a moulding operation with the moulding surface, the conduits providing removal routes for slurry liquid which has passed through the material.

3. A pulp moulding tool according to claim 2 in which the material is a woven material, with warp and weft threads defining passageways for slurry liquid whereby to make the cover permeable.

4. A pulp moulding tool according to claim 3 in which the threads are of an elastic, and not themselves permeable.

5. A pulp moulding tool according to claim 3 in which the warp and weft threads are of different composition.

6. A pulp moulding tool according to claim 2 in which the former is bounded by edges to which the cover is secured.

7. A pulp moulding tool according to claim 2 in which the former is bounded by edges to which the material is clamped, whereby the cover is not punctured during securement to the former.

8. A pulp moulding tool according to claim 2 in which the former has a hollow interior and a part for mounting a pressure reducing means coupled to the hollow interior, the pressure reducing means both encouraging the flow of slurry liquid through the cover and the said conduits, and also acting to remove slurry liquid from the hollow interior.

9. A pulp moulding tool according to claim 2 in which the former is an investment casting.

10. A pulp moulding tool constructed and arranged substantially as described with reference to Figs.3-5 of the accompanying drawings.