JUUL NIELS (DK)
RASMUSSEN TORBEN (DK)
BERTELSEN SVEND (DK)
JUUL NIELS (DK)
RASMUSSEN TORBEN (DK)
| DE3837467A1 | 1990-05-17 | |||
| DK167254B1 | 1993-09-27 |
| 1. | Suction mould for producing papiermache objects by suction moulding a dispersion of pulp onto a shaping surface, said mould being permeable to air and liquid and placed above a suction and pressure chamber and com¬ prising a sieve of mutually connected aluminium particles provided at the shaping surface, c h a r a c t e r ¬ i z e d in that the aluminium particles are constituted by irregular, angular granules mutually connected by a hardened organic binder. |
| 2. | Suction mould according to claim 1, c h a r a c ¬ t e r i z e d in that the particle sizes of the aluminium particles lie in the interval from approx. 0.2 to approx. 0.7 mm. |
| 3. | Suction mould according to claim 1 or 2, c h a r¬ a c t e r i z e d in that the organic binder is a cold setting polyurethane binder. |
| 4. | Suction mould according to any or any one of the preceding claims, c h a r a c t e r i z e d in that the suction mould as a whole consists of mutually con nected aluminium particles. |
| 5. | Suction mould according to claim 4, c h a r a c ¬ t e r i z e d in that the internal part of the suction mould consists of particles in the form of chips produced by machining aluminium, said aluminium chips being mutu¬ ally connected by the same organic binder as the aluminium particles at the shaping surface. |
| 6. | Suction mould according to any one or any of the claims 15, c h a r a c t e r i z e d in that the shaping surface is covered by filter cloth. |
| 7. | Method for making a suction mould according to any one or any of the claims 15, and comprising a sieve of mutually connected aluminium particles provided at the shaping surface and placed above a suction and pressure chamber, by using an auxiliary mould with a shaping sur¬ face complementary to the shaping surface of the suction mould, c h a r a c t e r i z e d by the following steps ad: a) aluminium particles in the form of irregular angular granules are mixed with a coldsetting organic binder, b) the mixture formed in step a) is applied in a paste like condition to the complementary shaping surface of the auxiliary mould, possibly after prior application of a release agent, c) the mixture is allowed to or made to set, and d) the sieve shell formed in the previous steps is removed from the auxiliary mould and secured to a base above a suction and pressure chamber in the latter, possibly after having been planished on the underside. |
| 8. | Method according to claim 7, c h a r a c t e r i z e d in that as binder there is used a polyurethane binder added in an amount constituting between 5 and 8 per cent by weight of the amount of aluminium particles used. |
| 9. | Method according to claim 8, c h a r a c t e r ¬ i z e d in that prior to being mixed with the polyure¬ thane binder, the aluminium particles are moistened with approx. 2 per cent by weight of water. |
| 10. | Method according to any one or any of the claims 7 9, c h a r a c t e r i z e d in that the central part of the suction mould is filled with the same mixture or a similar mixture. |
| 11. | Method according to claim 10, c h a r a c t e r ¬ i z e d in that the central part of the suction mould is filled by using a mixture of particles in the form of chips produced by machining aluminium and 24 per cent by weight of polyurethane binder. |
| 12. | Method according to any one or any of the claims 7 11, c h a r a c t e r i z e d in that parts of the suction mould is subjected to machining. |
| 13. | Method according to any one or any of the claims 7 12, c h a r a c t e r i z e d in that the shaping sur¬ face of the suction mould is covered with a filter cloth. |
TECHNICAL FIELD
The present invention relates to a suction mould of the kind set forth in the preamble of claim 1. The pressure chamber referred to is used for removing the suction- moulded pulp object from the mould surface by blowing it off.
BACKGROUND ART
German published specification No. 3,837,467 describes a suction mould having at the shaping surface a sieve con¬ sisting of small balls or spheres of metal, such as alu¬ minium, that are sintered together. The moulding tools made of metal used for mould-pressing of this sieve prior to the sintering of the aluminium balls or for the sin- tering step itself are extremely costly to manufacture, especially if the shaping surface of the suction mould has any but a simple shape. Likewise, the sintering pro¬ cess itself requires specialized and costly measures for exact control and monitoring of the sintering temperature and process, which has to be carried out in a reducing atmosphere. Although this manufacturing method may be well suited for making a greater number of identical suction moulds, the latter again being well suited for making a very large number of identical papier-mache objects, it is for economic reasons completely unsuitable for making a single suction mould to be used for producing a small series of identical papier-mache objects.
Admittedly, DK Patent Specification No. 167,254 describes a suction mould produced at low cost, its shape-giving part consisting of a gravel-like particulate stone mate¬ rial, the particles of which are bonded together, e.g. by means of a hardening binder, so as to form a structure with an external contour of stable shape with air passages extending to the outside of the mould. Such a mould may be manufactured at low cost, but in practice it has proved less than satisfactory, as in operation, the air passages referred to are increasingly clogged by pulp material, so that in a normal process of production only a very limited number of papier-mache objects can be manufactured using the same mould. For this reason, suction moulds of this kind are more suited for making a small number of prototypes of papier-mache objects than for any but small-scale production. The clogging referred to is prob¬ ably due to the special tendency of the pulp material to adhere to the rough surface of the crushed particles of stone material. Further, these suction moulds cannot be machined with cutting tools, e.g. for drilling screw holes for securing purposes or for making the underside of the mould plane.
DISCLOSURE OF THE INVENTION
On the background of the above, it is the object of the present invention to provide a suction mould of the kind referred to initially, that may be manufactured at low cost without using expensive moulding tools, and which may be used without problems in a normal manufacturing process to manufacture a practically unlimited number of papier-mache objects, and this object is achieved with a suction mould of said kind, which according to the present invention is characterized by the features set forth in
the characterizing clause of claim 1.
Since the materials used for making the suction mould according to the invention are relatively cheap, and since the suction mould may be manufactured in a simple and low-cost manner to be explained below, it meets the primary condition for a suction mould to be used for making a small series of identical papier-mache objects. The voids existing between the angular aluminium par- tides, or rather between the layers of binder surrounding and interconnecting them, communicate with each other, thus forming air passages extending right through the mould. By suitably choosing the average particle size and the particle-size distribution for the aluminium particles it is possible to avoid the air passages between the particles being clogged by pulp material during use of the suction mould.
For this reason, the aluminium particles preferably have sizes in the interval set forth in claim 2, the smallest average particle size being used for suction moulds or parts of such that are to have an especially smooth sur¬ face.
Aluminium particles suitable for use in making suction moulds according to the present invention are marketed in Denmark by the firm of Vilh. Schertiger & Co. A/S under the trade name "aluminiumgranulat nr. 2".
In principle, any known cold-setting one-component or two-component binder may be used as an organic binder, but for the present purpose, the binders set forth in claim 3 have proved highly suitable; in Denmark, these binders are marketed by the firm of BOSTIK A/S under the
type designations "Bostik durobond 800" and "Bostik traelim ("wood cement") 810 polyuretan".
The suction mould according to the present invention may solely consist of the sieve provided at the shaping sur¬ face in the form of a hollow shell, the cavity of which then constituting a part of the suction and pressure chamber, but to make the suction mould more mechanically stable, it is preferred that it is constructed as set forth in claim 4, thus constituting a "compact" body placed above a suction or pressure chamber provided in a base.
In this case, the embodiment set forth in claim 5 is preferred, partly reducing the cost of making suction moulds according to the present invention by re-cycling rejected aluminium chips, partly providing a greater air permeability in the internal parts of the suction mould due to the larger particle size of these chips.
In the suction mould according to the present invention, the shaping surface may, as set forth in claim 6, be covered by a filter cloth; the latter may e.g. consist of metal wire mesh, plastic filament mesh or woven or non-woven textile material. Further, such a filter cloth counteracts the penetration of pulp-fibre material in the through-going passages of the suction mould.
The present invention also relates to a method of manu- facturing a suction mould according to the invention, such as set forth in the preamble of claim 7, and accord¬ ing to the invention, this method is characterized by the process steps set forth in the characterizing clause of claim 7.
By proceeding in this manner, it is possible in the sim¬ plest case to use an auxiliary mould in the form of a mould of plastic or elastomeric material having been cast or moulded against a pattern corresponding to the suction- mould desired, said pattern e.g. being made of polyethy¬ lene, or - especially if the suction mould desired has a complicated shape - the auxiliary mould may be made by machining a suitable block of polyethylene.
The mixing of aluminium particles with a binder may be carried out in a suitable mixer of any type, in which the binder is evenly distributed over the surfaces of the particles.
The paste-like mixture is preferably applied to the shaping surface of the auxiliary mould in layers and in such a manner that the first layer is applied in sweeping strokes along the shaping surface, causing plane surfaces of the angular particles to abut against the shaping sur¬ faces, thus giving the suction mould produced a smoother surface.
In this case, the shaping surface of the auxiliary mould may have been treated with a release agent, especially one having surface properties acting in a "repellent" manner towards the mixture being applied.
After hardening or setting and removing of the sieve shell having been formed from the auxiliary mould, it may be necessary to planish the underside of the shell, such as by grinding, before the shell is secured to a base above a suction or pressure chamber in the latter.
As mentioned above, it is preferred, such as also set forth in claim 8, to use a polyurethane binder added in a quantity between 5 and 8 per cent by weight of the quantity of aluminium particles being used, particles with a small average particle size requiring a greater amount of binder than particles with a large average particle size. Adding binder to this extent has proved to give the hardened mixture sufficient strength without substantially reducing the air permeability of the sieve shell.
The mixture of aluminium particles and urethane binder may have an undesired tendency to create a foam, and this may be counteracted by proceeding as set forth in claim 9. The moisture referred to has also proved to accelerate the setting of the binder.
A preferred embodiment of the method of the present in¬ vention is set forth in claim 10, and this embodiment is preferably combined with the embodiment set forth in claim 11. In this case it is possible, due to the greater particle size of the chips referred to, to add smaller amounts of binder than when using the aluminium particles, and yet achieve the same strength in the hardened mix- ture.
By proceeding as set forth in claim 12 it is possible, partly to provide through-going screw holes for securing the suction mould to the base, partly to carry out ma- chining operations on parts of the shaping surface, that are difficult or impossible to shape using the auxiliary mould.
Finally, the method according to the invention may be
carried out as set forth in claim 13, such as described above in connection with the description of the suction mould according to the invention.