METHOD OF PRODUCING MOULDED PULP ARTICLES WITH A HIGH CONTENT OF DRY MATTER

Abstract: Method of manufacturing articles from an aqueous fibre suspension, by deposition of fibres on a suction mould (2), comprising the steps of: applying suction to the suction mould, supplying a fibre suspension to the mould by immersing the suction mould in a vat (5) containing the fibre suspension, raising the suction mould from the fibre suspension, flowing ambient air by said suction through an article formed by a layer of fibre material deposed on the suction mould, characterised by the steps of: providing a substantially hermetically sealed space over the article or articles on the suction mould, supplying a de-watering fluid to the sealed space, and flowing substantially exclusively the de-watering fluid through the article or articles.

Description: METHOD OF PRODUCING MOULDED PULP ARTICLES WITH A HIGH CONTENT OF DRY MATTER TECHNICAL FIELD The present invention relates to a method of producing moulded pulp articles with a high content of dry matter when leaving the suction wheel according to the preamble of claim 1 and to an apparatus for carrying out the method according to the preamble of claims 12 and 29. In this connection the term "pulp" is to be understood as applying to a fibre containing pulp mass, that may also contain or constitute of waste paper. BACKGROUND ART Document US-3,654,076 discloses a method of continuous mass production of articles from pulp material using a moulding machine with a rotatable mould carrier, on the periphery of which suction moulds are placed side by side. The moulded pulp articles are formed by immersing the suction moulds into a vat of suspended pulp material while suction is applied in order to form a body of pulp in the shape of the desired article by fibre deposition. The suction mould is then withdrawn from the vat of suspended pulp material, and the suction is generally continued to compact the deposited fibres while exhausting residual liquid therefrom. The moist moulded articles are removed from the suction mould, partly by blowing air through the suction mould, and partly by aspirating the articles onto a corresponding transfer rotor. From the transfer rotor, the articles are placed onto supporting and conveying means adapted to convey the articles to a drying oven for a drying process. The moulded articles have, when leaving the suction mould, a relatively low dry matter content, which is typically about 25 weight %. A dry matter content of about at least 90 weight % has to be achieved by drying the articles in a drying oven. The low initial dry content of the articles when leaving the suction mould results in a high amount of energy used for drying the articles in the oven. Moreover, the articles with their low dry content are difficult to handle due to their low form stability, i.e. they need to be handled carefully. US4,448,640 discloses a method of continuous mass production of articles from pulp material using a moulding machine with a rotatable mould carrier according to the above described principles which is provided with a stationary hood that roughly encapsulates a part of the rotatable mould carrier. This arrangement allows to flow a mixture of hot air or humid hot air and ambient air through the articles on the suction moulds. DISCLOSURE OF THE INVENTION On the above background it is the object of the present invention to provide a method of the kind referred to initially, with which it is possible to produce articles with a high dry matter content when leaving the suction mould. The advantages of a high dry content are a better form stability resulting in easier handling of the articles in following production steps, such as e.g. after-pressing and a reduction in the energy needed to dry the articles. This object is achieved with the method as defined in claim 1. By delivering a de-watering fluid to an substantially hermetically sealed space over the article, it is possible to flow de-watering fluid through the article which is not mixed with ambient air and thus achieve a substantially improved de-watering effect leading to a higher dry matter content of the moulded pulp articles. The present invention also relates to an apparatus to carry out the above-mentioned method as defined in claims 12 and 29. By providing a hood over the suction moulds or the mould carrier in combination with gaskets sealing between the moulds and the hood or hoods, a space over the article can be efficiently sealed from the ambient air. By delivering a de-watering fluid to the encapsulated space over the mould surface, only the de-watering fluid is flowed by suction through the moulded pulp articles on the mould without ambient air being mixed into the de- watering fluid. It is a further object of the invention to provide a method of the kind referred to initially in which steam is used as a de-watering fluid. BRIEF DESCRIPTION OF THE DRAWINGS In the following detailed portion of the description the invention will be explained in more detail with reference to the drawings, in which Figure 1 diagrammatically shows an embodiment of a pulp moulding machine, a conveyor system and a drying oven, Figure 2 shows a detailed view of the rotating mould carrier and the hood, and Figure 3 shows a view of the rotatable mould carrier and the hood lateral to the view of Figure 2. Figure 4 diagrammatically shows a second embodiment of the invention, Figure 5 diagrammatically shows a third embodiment of the invention, Figure 6 diagrammatically shows a fourth embodiment of the invention, Figure 7 diagrammatically shows a fifth embodiment of the invention, and Figure 8 diagrammatically shows a sixth embodiment of the invention. DESCRIPTION OF THE PREFERRED EMBODIMENT Figure 1 shows diagrammatically a suction moulding station for moulding articles from pulp material. The station comprises a rotatable mould carrier 1 , on the outside of which are placed several liquid-permeable suction moulds 2 adapted to be connected with a source of sub-atmospheric and to a source of super-atmospheric pressure. The mould carrier 1 is with a part of its circumferential surface immersed in a pulp vat 5 containing a fibre pulp suspension. This pulp may be made from a fibre-containing raw material, including waste paper or cardboard. During the immersion in the pulp mass, a layer of fibre material is deposited by suction on the mould surfaces of the suction mould 2. Subsequently, when the moulds 2 are withdrawn from the fibre suspension in the pulp vat 5, the suction is continued to compact the deposited fibres while exhausting residual liquid therefrom. After withdrawing the mould from the pulp vat 5, the mould will follow the rotary trajectory of the rotatable mould carrier 1 and thereby pass under a hood 3 which in sealing interaction with gaskets 4 placed on the rotatable mould carrier 1 seals off the mould surface from the ambient air. A de-watering fluid is introduced in the sealed-off space between the hood 3 and the suction mould 2, whilst the source of sub- atmospheric pressure is connected to the mould 2. The de-watering fluid is thus flowed through the freshly moulded article on the mould surface. The article is thereby de-watered, and dry matter content of the article is increased. After withdrawing the mould 2 from the pulp vat 5 and before supplying the de-watering fluid, water is sprayed on the articles in order to remove residual pulp. The articles are typically 3D-moulded pulp packaging such as fruit- and egg trays. These articles have a relatively thin wall of fibre material. The hood 3 may cover a substantial section of the rotatable mould carrier 1 in order to provide enough time for the de-watering fluid to flow through the moulded articles. After passing under the hood 3, the moulds 2 are rotated further to engage a transfer rotor 6 which is placed with its axis parallel to the axis of the rotatable mould carrier 1 and facing the latter's periphery. From the suction mould 2 on the rotatable mould carrier 1 the fibre layer having been deposited by suction is blown off by supplying air under pressure to the latter coming from the source of super- atmospheric pressure. At the same time, the moist article is being aspirated on to transfer moulds 14 on the transfer rotor 6. From the transfer rotor 6 the moist article is blown off and laid on to a conveying track 7, on which the article is conveyed through a drying oven 8. From the drying oven 8, the substantially or completely dried article is placed on a conveying surface (not shown), from which it is conveyed up to and passes a number of after-treatment stations (not shown) for completing its processing. Figure 2 shows a detailed view on the side of the hood 3 covering a sector of the rotatable mould carrier 1. The coverage of the hood 3 starts just above the point where the moulds leave the pulp vat and extends over the approximately a quarter of the circumference of the rotatable mould carrier 1 and ends before the transfer rotor 6. The hood 3 comprises a curved wall extending over the width of the rotatable mould carrier. The curved wall of the hood 3 follows an arc with its center of rotation falling together with the axis of the rotatable mould carrier 1 (Figure 3). At least two side walls 3a, 3b extend substantially perpendicularly from the curved wall along the sides of the rotatable mould carrier 1 towards the axis of the latter. The side walls of the hood are provided with gaskets 4a, preferably in the form of a labyrinth sealing, that sealingly interact with the side walls of the rotatable mould carrier, or vice versa. The curved wall of the hood is in sealing contact with gaskets 4 placed on the rotatable mould carrier 1 before and after each suction mould or group of suction moulds. The gaskets 4 extend in a direction substantially parallel to the axis of the rotatable mould carrier. The rotatable mould carrier 1 is thus divided by gaskets 4 into groups of single or groups of several moulds 2. When passing under the hood 3, an encapsulated space is formed over each of the moulds 2 or group of moulds between two gaskets 4. A source of de-watering fluid 9 is connected to the hood 3 by a conduit 10 leading the de-watering fluid under the curved surface of the hood. The de-watering fluid is supplied at a pressure higher than that of the sub-atmospheric source of pressure. A valve 11 is placed in the conduit 10 delivering the de-watering fluid to the hood, so that the delivery of the de- watering fluid can be controlled. The delivery conduit 10 may be split into several conduits each comprising a valve 11 , so that a controlled delivery to different parts of the hood 3 is possible in accordance with suction moulds 2 passing under the hood. The inlet openings in the hood 3 for entry of the de-watering fluid are preferably concentrated towards the side of the hood 3 where the suction moulds 2 come in. The pressure of the de-watering fluid delivered to the hood can be varied and is in a range of 0.1 to 12 bars; preferably 0.5 to 2 bars. When a suction mould 2 or a group of suction moulds is under the hood 3 and forms the sealed chamber, the valve 11 is opened and the de-watering fluid enters the encapsulated space over the mould or moulds, whereupon it is sucked through the moulded pulp article on the mould 2, thereby de-watering the latter. After passing the hood 3, the moulds 2 are further rotated to the position where the articles are blown off from the suction moulds 2 and aspirated on to the transfer rotor 6. After a part of a revolution of the transfer rotor the articles are blown off therefrom onto a conveyor 7 which transports the articles to a drying oven for a drying procedure. In the drying oven, the articles reach their final dry matter weight content of at least 90 weight per cent. The dry weight content of the articles when they are blown off from the suction mould depends on the kind of de-watering agent that is used. The de-watering fluid can be delivered in the form of a vapour. According to a preferred embodiment of the present invention, the de-watering agent is steam. Steam with a temperature of up to 300°C has a better drying effect than hot air. This effect is, however, minimised when ambient air is mixed in together with the steam. The steam has preferably a temperature in the range between 100 and 150° C. Other de-watering fluids such as heated and/or compressed air, or other gases suitable for dehydration are used in an other embodiment of the invention. The valves in the conduit leading the de-watering fluid to the hood are preferably of an electromagnetic type so as to allow control from a logic control unit. The logic control unit may be integral with a logic control unit steering the complete production process. The logic control unit can be programmed to choose the amount of de- watering fluid, as well as its pressure and the time of delivery. In particular such choice may be made automatically under consideration of other process parameters such as the production speed. The use of valves can be avoided if a constant flow is wanted. Before supplying the de-watering agent, water may be sprayed on the articles as they leave the pulp vat in order to remove any residual pulp on places where pulp deposition is not desired. By adjusting the size of the sector of the rotatable mould carrier which is enclosed by the hood, the time available for the de-watering fluid to pass through the articles can be adjusted according to circumstances. In a mass production moulding machine the speed of rotation of the rotatable mould carrier is relatively high. Typically there are only a few seconds available for passing the de-watering fluid through the freshly moulded article. Therefore, the present invention offers a great advantage in improving this part of the moulding procedure. If necessary, the opening and closing of the electric valves 11 is controlled by a PLC 12. The PLC may also be used for controlling other process parameters. The second embodiment of the invention as shown in Figure 4, comprises a number of movable hoods 23 coupled to a movable hood carrier 21 which rotates synchronously with the rotatable mould carrier 1. The movable hoods 23 engage with the suction moulds 2 on the rotatable mould carrier 1 in order to form a hermetically sealed space over the articles on the suction moulds 2. The movable hoods 23 are provided with gaskets (not shown) that come into sealing abutment with the suction mould 2 or the rotatable mould carrier 1 in order to provide for a hermetic sealing. The advantage of this embodiment is that there is stationary sealing abutment between the hood 23 and the suction mould 2. The third embodiment of the invention as shown in Figure 5 is in principle substantially equal to the embodiment according to Figure 4, but instead of a rotatable hood carrier, a conveyor belt 25 is used to move the movable hoods 23, by coupling them to the conveyor belt 25. The conveyor belt 25 runs along a curved path forming an arc of a circle with its centre at the axis of the rotatable mould carrier 1. The fourth embodiment of the invention as shown in Figure 6 comprises a stationary hood in the form of a curved plate 28 extending along an arc of a circle with its centre at the axis of the rotatable mould carrier 1. Each of the suction moulds 2 is surrounded by radially extending sealing plates 30, 33. The plates 30 which extent parallel with the direction of the rotational movement of the rotatable mould carrier 1 have a circumferential rim which co-operates with the curve plate 28 to form a hermetical seal, for example by using a labyrinth typed seal. The sealing plates 33 which extend transversely to the rotational movement of the rotatable mould carrier 1 come into sealing abutment with the curved plate 28. The fifth embodiment of the invention as shown in Figure 7, comprises a curved moving belt 35 instead of a curved plate 28. Thus, the sealing plates 30 with the curved rim can come into stationary contact with the belt 35 forming a sealing abutment. The belt 35 may be provided with sealing plates 36 which extent transversely to the direction of movement of the belt 35 and spaced such that each of the suction moulds 2 is surrounded by sealing plates. This embodiment may instead comprise (not shown in Figure 7) stationary sealing plates 33 arranged on the rotatable mould carrier 1 in order to surround the suction moulds with sealing plates. Thus, all sealing is by stationary abutment. The belt 35 runs synchronously with the rotatable mould carrier 1 allowing stationary abutment between the sealing plates 33 and the belt 35. The sixth embodiment according to the invention as shown in Figure 8 comprises a foldable hood 26 associated with a suction mould 2 and arranged on the rotatable mould carrier 1. After the suction mould 2 has undergone a submergement into the pulp vat 5, the foldable hood is drawn over the suction mould 2 to seal it hermetically from the ambient air. The de-watering fluid is provided through a conduit (not shown) which is integrated in the rotatable mould carrier 1. When the de-watering fluid has passed the article, the foldable hood 26 is collapsed in order to uncover the suction mould 2 so that it is ready to be submerged in the pulp vat 5 again. The foldable hood co-operates with the radially extending sealing plates with a curved rim 30. According to another embodiment (not shown), the mould carrier is a step-operating carrier that moves the mould carrier downwards to submerge the suction mould or moulds on the mould carrier in the pulp vat and moves upwards to retract the mould or moulds from the pulp vat. In this embodiment, the hood extends over one side of the mould carrier to define the sealed-off space. Various modifications are possible within the scope of the invention as defined in the claims such as blowing the de-watering fluid through the article by applying an over- pressure in the sealed-off space over the article. LIST OF PARTS 1 rotatable mould carrier 2 suction mould 3 hood 4 gasket 4a gasket 5 pulp vat 6 transfer rotor 7 conveyor 8 drying oven 9 source of de-watering fluid 10 conduit 11 valve 12 PLC 13 source of sub-atmosphere pressure 14 transfer mould 21 rotatable hood carrier 23 movable hood 25 conveyor belt 26 foldable hood 28 curved plate 30 sealing plate with curved rim 33 sealing plate 35 belt 36 sealing plates

Claims: CLAIMS: 1. Method of manufacturing articles from an aqueous fibre suspension, by deposition of fibres on a suction mould (2), comprising the steps of: - applying suction to the suction mould (2), - supplying a fibre suspension to the mould (2) by immersing the suction mould in a vat (5) containing the fibre suspension, - raising the suction mould (2) from the fibre suspension, - flowing ambient air by said suction through an article formed by a layer of fibre material deposed on the suction mould (2), characterised by the steps of - providing a substantially hermetically sealed space over the article or articles on the suction mould (2) - supplying a de-watering fluid to the sealed space and - flowing substantially exclusively the de-watering fluid through the article or articles. 2. Method according to claim 1 , characterised in that the suction mould (2) is placed on a rotatable mould carrier (1). 3. Method according to claim 1 or 2, characterised in that the de-watering fluid is flowed by suction through the article when it is placed on the suction mould (2), and/or by applying over-pressure to the space over the article. 4. Method according to any of claims 1 - 3 characterised by providing a movable hood (23) over each suction mould (2) which moves together with such single suction mould (2) over a certain distance of the rotational movement of the suction mould (2) in order to define the sealed space over the article or articles 5. Method according to claim 4, characterised in that the movable hoods (23) are coupled to a rotatable hood carrier (21 ) moving synchronously with the rotatable mould carrier (1 ), or to a conveyor chain or belt (25). 6. Method according to any of claims 1 - 3, characterised by the step of providing a stationary hood (3) placed over a sector of the rotatable mould carrier to thereby seal-off one or more suction moulds (2) from the ambient air and thus define the encapsulated space over the article or articles. 7. Method according to any of claims 1 - 6, characterised in that the de-watering fluid is steam, saturated steam or overheated steam. 8. Method according to claim 7, characterised in that the temperature of the steam is up to 300 °C, preferably in the range of between 100 and 150°C. 9. Method according to any of claims 1 - 8, characterised in that pressure of the de-watering fluid is supplied with an overpressure in the range of 0.1 to 12 bar, preferably 0.5 to 2 bar. 10. Method according to any of claims 1 - 9, characterised in that the de-watering fluid is heated and/or compressed air. 11. Method according to any of claims 1 - 10, characterised in that the de-watering fluid is applied for a period of 0.1 to 10 seconds, preferably 0.1 to 1.0 seconds. 12. Apparatus for carrying out the method according to claim 1 comprising - a rotatable mould carrier (1 ) provided with at least one suction mould (2) on the periphery of the rotatable mould carrier (1 ), - a vat (5) containing an aqueous fibre suspension in which the rotatable mould carrier (1 ) is partially submerged, - a source of sub-atmospheric pressure (13) connectable to the at least one suction mould (2), characterised by comprising - means (3) for covering one or more moulds (2) in a sector of the rotatable mould carrier (1 ) to thereby define an encapsulated space over the mould or moulds (2) that is substantially hermetically sealed from the ambient air, and further comprising a means (9, 10, 11 ) for providing a de-watering fluid to the encapsulated space. 13. Apparatus according to claim 12, characterised by at least two transverse gaskets (4) extending radially with respect to the rotatable mould carrier (1 ) and spaced circumferentially with one or more suction moulds (2) between them. 14. Apparatus according to claim 12 or 13, characterised by comprising a stationary hood (3) having an arc-shaped wall with which the gaskets (4) come in sealing contact to define a sealed-off space to which the de-watering fluid can be supplied. 15. Apparatus according to claim 14, characterised in that two side walls (3a, 3b) extend substantially perpendicularly from the curved wall of the hood (3) towards the rotatable mould carrier (1 ). 16. Apparatus according to claim 15, characterised by comprising gaskets (4a,4b), preferably of the labyrinth type, provided on each side wall (3a, 3b) of the hood (3) and co-operating with a peripheral element of the rotatable mould carrier (1 ). 17. Apparatus according to claim 12 or 13 characterised by comprising a movable hood (23) over each suction mould (2)) which moves together with such single suction mould (2) over a certain sector of the rotational movement of the suction mould (2) in order to define the sealed space over the article or articles 18. Apparatus according to claim 17, characterised in that the movable hood (23) is coupled to a rotatable hood carrier (21 ) moving synchronously with the rotatable mould carrier (1 ). 19. Apparatus according to claim 17, characterised in that the movable hoods (23) are coupled to a conveyor chain or belt (25) moving synchronously with the rotatable mould chamber (1 ). 20. Apparatus according to claims 12 or 13, characterised by comprising a stationary hood (3) placed over a sector of the rotatable mould carrier to thereby seal-off one or more suction moulds (2) from the ambient air and thus define the encapsulated space over the article or articles, whereby gaskets (4,4a) are preferably provided between the stationary or movable hood (3,23,26) and the rotatable mould carrier (1 ). 21. Apparatus according to any of claims 12 - 20, characterised in that the de- watering fluid is supplied to at least one de-watering inlet opening in the stationary or movable hood (3,23,26). 22. Apparatus according to claim 21 , characterised in that several de-watering inlet openings are distributed over the stationary or movable hood (3,23,26). 23. Apparatus according to claim 22, characterised in that the de-watering inlet openings are concentrated at the end of the stationary or movable hood (3,23,26) where the suction moulds (2) enter. 24. Apparatus according to any of claims 14 - 16 characterised in that the stationary hood (3) is formed by a curved plate (28) extending along an arc of a circle with its centre at the axis of the rotatable mould carrier (1 ). 25. Apparatus according to any of claims 16 - 23 characterised in that the movable hood is formed by a belt (35) moving along a curved trajectory extending along an arc of a circle with its centre at the axis of the rotatable mould carrier (1 ) wherein the belt possibly is provided with transversally extending sealing plates (36) which seal before and after a suction mould (1). 26. Apparatus according to any of claims 12 - 25, characterised in that the rotatable mould carrier (1 ) is equipped with a number of sealing plates having a circular rim (30) co-operating with the curved plate (28) or the belt (35) to create a sealed-off space. 27. Apparatus according to claims 12 - 26, characterised in that the suction moulds (1 ) are surrounded by radially extending gaskets or sealing plates (30,33) that co-operate with the curved plate (28) or the belt (35) to define a sealed-off space. 28. Apparatus according to any of claims 12 - 27, characterised by comprising one or more electrically controlled valves (11 ) regulating the delivery of the de-watering fluid. 29. Apparatus for carrying out the method according to claim 1 , comprising - a step operating up-down mould carrier provided with at least one suction mould - a vat containing an aqueous fibre suspension in which the up-down mould carrier is periodically submerged, - a source of sub-atmospheric pressure connectable to the at least one suction mould, characterised by comprising - means for covering the up-down mould carrier to thereby define an encapsulated space over mould or moulds (2) that is sealed from the ambient air, and further comprising a means (9, 10, 11 ) for providing a de-watering fluid to the sealed-off area. 30. Apparatus according to claim 29, characterised in that the up-down mould carrier (1 ) comprises gaskets for engaging the hood (3) in sealing abutment.

Inventors: JUUL NIELS, JUUL, NIELS
Applicants: HARTMANN AS BRDR, JUUL NIELS, BROEDRENE HARTMANN A/S, JUUL, NIELS
Application year: 2000
Main classification: D21J7
IPC codes: D21J7