METHOD OF MANUFACTURING A MOULDED PULP PRODUCT AND PULP MOULDING APPARATUS

Abstract

Method of manufacturing a moulded pump product. The method includes activating a vacuum source, injecting an amount of pulp into the internal mould chamber through the mould opening, thereby forming a pulp preform on the internal mould surface, injecting a dewatering and heating fluid through the mould opening at gradually increasing pressure until a maximum pressure, thereby performing a dewatering and drying step whereby the pulp preform on the internal mould surface is dewatered and dried, deactivating the injection of dewatering and heating fluid, deactivating the vacuum source, and extracting the moulded pulp product. An option further step includes initiating rotation of the mould about the central axis thereof and increasing rotational speed gradually, maintaining a maximum rotational speed of the mould at least during a substantial part of the dewatering and drying step, decreasing rotational speed gradually until standstill of the mould.

Claims

1. A method of manufacturing a moulded pulp product using a pulp moulding apparatus including a mould with an internal mould chamber generally having rotational symmetry about a central axis of the mould and having a closed end and an open end forming a mould opening, the internal mould chamber having an internal mould surface generally provided with a number of evacuation openings connected to a vacuum source, the method including the following steps of: activating the vacuum source, injecting an amount of pulp into the internal mould chamber through the mould opening, thereby forming a pulp preform on the internal mould surface, injecting a dewatering and heating fluid through the mould opening at gradually increasing pressure until a maximum pressure, thereby performing a dewatering and drying step whereby the pulp preform on the internal mould surface is dewatered and dried, deactivating the injection of dewatering and heating fluid, deactivating the vacuum source, extracting the moulded pulp product, initiating rotation of the mould about the central axis of the mould and increasing rotational speed gradually, maintaining a maximum rotational speed of the mould at least during a substantial part of the dewatering and drying step, decreasing rotational speed gradually until standstill of the mould.

2. A method of manufacturing a moulded pulp product according to claim 1, wherein the apparatus includes a rotary union having a rotatable fluid port connected to the mould opening, a stationary pulp port and a stationary dewatering and heating fluid port, wherein pulp is injected into the internal mould chamber through the stationary pulp port, and wherein the dewatering and heating fluid is injected into the internal mould chamber through the stationary dewatering and heating fluid port.

3. A method of manufacturing a moulded pulp product according to claim 1, wherein the mould is arranged inside a vacuum chamber connected to the vacuum source, and wherein the rotatable fluid port of the rotary union is connected to the mould opening through a tube extending through a wall of the vacuum chamber by a rotary shaft seal.

4. A method of manufacturing a moulded pulp product according to claim 1, wherein the relative injection pressure of the dewatering and heating fluid through the mould opening is increased gradually from approximately 0 to minimum 500 kPa, or from approximately 0 to minimum 700 kPa, or from approximately 0 to minimum 1 MPa.

5. A method of manufacturing a moulded pulp product according to claim 1, wherein the relative injection pressure of the dewatering and heating fluid through the mould opening is increased gradually with a pressure rate of dp/dt=1 to 20 kPa/s in the range p=0 to 200 kPa and with a pressure rate of dp/dt=1 to 50 kPa/s in the range p=200 to 400 kPa.

6. A method of manufacturing a moulded pulp product according to claim 1, wherein the rotational speed of the mould is increased gradually from 0 rpm to at least 5.0005000 rpm, or from 0 rpm to at least 7.0007000 rpm, or and from 0 rpm to about 10.00010000 rpm.

7. A method of manufacturing a moulded pulp product according to claim 1, wherein the rotational speed (r) of the mould is increased gradually with a rotation rate of dr/dt=10 to 1000 rpm/s until a maximum rotational speed.

8. A method of manufacturing a moulded pulp product according to claim 1, wherein simultaneous injection of dewatering and heating fluid and mould rotation is maintained for at least 10 seconds, or for at least 20 seconds, or for at least 40 seconds, or for about 1 minute.

9. A method of manufacturing a moulded pulp product according to claim 1, wherein fluid is evacuated to an outer surface of the mould through inner evacuation openings on the internal mould surface, and wherein each inner evacuation opening is connected to an outer evacuation opening on the outer surface of the mould by means of an evacuation channel having a gradually increasing cross-sectional area in the direction from the internal mould surface to the outer surface of the mould.

10. A pulp moulding apparatus for manufacturing of moulded pulp products including a mould with an internal mould chamber generally having rotational symmetry about a central axis of the mould and having a closed end and an open end forming a mould opening, the internal mould chamber having an internal mould surface generally provided with a number of evacuation openings, a vacuum source connected to said evacuation openings, a pressurised pulp source arranged to inject pressurised pulp into the internal mould chamber through the mould opening, a dewatering and heating fluid source arranged to inject de-watering and heating fluid through the mould opening at gradually increasing pressure in order to perform dewatering and drying of a pulp preform on the internal mould surface, wherein the apparatus includes a rotary union having a rotatable fluid port connected to the mould opening, a stationary pulp port and a stationary dewatering and heating fluid port, in that the pressurised pulp source is connected to the stationary pulp port, in that the dewatering and heating fluid source is connected to the stationary dewatering and heating fluid port, in that a motor is arranged to rotate the mould about the central axis of the mould, and in that the pulp moulding apparatus is adapted to initiate rotation of the mould about the central axis of the mould and increase rotational speed gradually, maintain a maximum rotational speed of the mould at least during a substantial part of the dewatering and drying step, and decrease rotational speed gradually until standstill of the mould.

11. A pulp moulding apparatus according to claim 10, wherein the mould is arranged inside a vacuum chamber connected to the vacuum source, and wherein the rotatable fluid port of the rotary union is connected to the mould opening through a tube extending through a wall of the vacuum chamber by a rotary shaft seal.

12. A pulp moulding apparatus according to claim 10, wherein the mould has inner evacuation openings through which fluid may be evacuated to an outer surface of a mould wall, and wherein each inner evacuation opening is connected to an outer evacuation opening on the outer surface of the mould by means of an evacuation channel having a gradually increasing cross-sectional area in the direction from the internal mould surface to the outer surface of the mould.

Description

[0038] The invention will now be explained in more detail below by means of examples of embodiments with reference to the very schematic drawing, in which

[0039] FIG. 1 is a diagram of a pulp moulding apparatus according to the present invention;

[0040] FIG. 2 is a perspective view of a mould half of the moulding apparatus of FIG. 1;

[0041] FIG. 3 is a perspective view of a complete mould formed by two mould halves of which one is shown in FIG. 2;

[0042] FIG. 4 is a bottom view of the mould illustrated in FIG. 3;

[0043] FIG. 5 is a perspective view of a section illustrating, on a larger scale, the bottom of the mould half shown in FIG. 2;

[0044] FIG. 6 is a side view of the section of FIG. 5;

[0045] FIG. 7 is a perspective view of a section illustrating, on a larger scale, a middle part of the mould half shown in FIG. 2;

[0046] FIG. 8 is a side view of the section of FIG. 7, seen from outside the mould;

[0047] FIG. 9 is a cross-section taken along the line IX-IX of FIG. 8; and

[0048] FIG. 10 is a perspective view of a rotary mould clamp including a mould half as shown in FIG. 2.

[0049] FIG. 1 shows a pulp moulding apparatus 1 for manufacturing of moulded pulp products in the form of a bottle-shaped article suitable for beverage or the like. However, the moulded pulp products may have different shape and purpose and does not necessary have a bottleneck as the illustrated product. For instance, the method is also suitable for manufacturing of beakers.

[0050] The pulp moulding apparatus 1 includes a mould 2 with an internal mould chamber 3 generally having rotational symmetry about a central axis 4 of the mould 2 and having a closed end 5 and an open end 6 forming a mould opening 7 as seen in FIGS. 2 and 3. The internal mould chamber 3 has an internal mould surface 8 generally provided with a number of evacuation openings 9 through which fluid may be evacuated to an outer surface 19 of a mould wall 25 as described in further detail below. A vacuum source 10 is connected to said evacuation openings 9 in that the mould 2 is arranged in a vacuum chamber 15 and, a pressurised pulp source 22 is arranged to inject pressurised pulp into the internal mould chamber 3 through the mould opening 7, and a dewatering and heating fluid source 23 is arranged to inject dewatering and heating fluid in the form of hot air through the mould opening 7 at gradually increasing pressure in order to perform dewatering and drying of a pulp preform on the internal mould surface 8.

[0051] Furthermore, the apparatus 1 includes a rotary union 11 having a rotatable fluid port 12 connected to the mould opening 7, a stationary pulp port 13 and a stationary dewatering and heating fluid port 14. The pressurised pulp source 22 is connected to the stationary pulp port 13, the dewatering and heating fluid source 23 is connected to the stationary dewatering and heating fluid port 14, and a motor 24 is arranged to rotate the mould 2 about the central axis 4 of the mould 2. The vacuum chamber 15 is connected to the vacuum source 10, and the rotatable fluid port 12 of the rotary union 11 is connected to the mould opening 7 through a tube 16 extending through a wall 17 of the vacuum chamber 15 by means of a rotary shaft seal 18. The pulp moulding apparatus 1 is adapted to initiate rotation of the mould 2 about the central axis 4 of the mould 2 and increase rotational speed gradually, maintain a maximum rotational speed of the mould 2 at least during a substantial part of the dewatering and drying step, and decrease rotational speed gradually until standstill of the mould 2. In order to rotate the mould 2, the motor 24 is via a belt 27 rotatably coupled to a main rotating shaft 47 including the tube 16.

[0052] As further seen in FIG. 1, the apparatus 1 includes a control panel 33 adapted to control by means of a first frequency drive 31 the speed of a pump forming the pressurised pulp source 22. The pump receives pulp from a pulp tank 29 provided with a stirrer and the pulp is pumped to the mould 2 via a pressure vessel 30 or expansion vessel in order to maintain a suitable pressure during pumping. The raw materials in this case are wood fibres. With an existing manufacturing process, wood obtained from trees is chipped and converted to paper fibres. They can easily be obtained from any commercial pulp supplier. Once the fibres are obtained, the next step is to make a slurry. The paper fibres, which are primarily made-up of cellulose, are mixed with water to form a viscous and thick slurry. The water content in the slurry is important, because it is the water molecule which facilitates the binding of cellulosic material with the help of hydrogen bonding. The pulp suspension is stirred continuously in the tank 29 to avoid settling down of fibres and to have a uniform distribution of the fibres inside the suspension. The control panel 33 is further adapted to control by means of a second frequency drive 32 the speed of the motor 24 for rotation of the mould. Furthermore, the control panel 33 is adapted to control the dewatering and heating fluid source 23 which has the form of an air compressor, a heater 26 for the dewatering and heating fluid, the vacuum source 10 in the form of a vacuum pump connected to the vacuum chamber 15 via a waste tank 28, and flow controllers 35, 36, 37. A data logger 34 is provided for data collection and is connected to pressure sensors 38-42. As the skilled person will understand, the flow controllers 35, 36, 37 in cooperation with the pressure sensors 38-42 form respective pressure regulators adapted to regulate the pressure of the dewatering and drying fluid, the vacuum provided and the pressure of the pulp supplied.

[0053] As seen in FIGS. 2 and 3, the mould 2 has a wall 25 forming the internal mould chamber 3 with the mould opening 7 through which pulp may be injected. The internal mould surface 8 of the internal mould chamber 3 is generally provided with a number of inner evacuation openings 9 through which fluid may be evacuated to the outer surface 19 of the mould wall 25. As illustrated in FIG. 9, each inner evacuation opening 9 is connected to an outer evacuation opening 20 on the outer surface 19 of the mould 2 by means of an evacuation channel 21 having a gradually increasing cross-sectional area in the direction from the internal mould surface 8 to the outer surface 19 of the mould 2.

[0054] The mould wall 25 has a considerable wall thickness of at least 2 millimetres, preferably at least 4 millimetres, more preferred at least 5 millimetres, and most preferred at least 6 millimetres. Thereby, a strong mould 2 may be obtained without increasing the risk that an evacuation opening gets clogged. In fact, the risk of clogging is reduced considerably, because a pulp particle being able to enter an inner evacuation opening 9 may also pass through the corresponding evacuation channel 21 which has a gradually increasing cross-sectional area and out through the corresponding outer evacuation opening 20. Moreover, if any pulp would nevertheless be trapped in an evacuation channel 21, it is easy to blow it out by means of compressed air from the inside of the mould chamber 3. Therefore, the mould 2 is more or less self-cleaning and in any event much easier to clean than known solutions. Because of the strength of such a mould 2, it is possible to both form and dry the produced pulp product in one single mould as opposed to known methods as described above. Thereby, a substantial increase in production speed may be possible.

[0055] As seen in FIG. 2, over at least the main part of the internal mould surface 8, the inner evacuation openings 9 are distributed, preferably substantially evenly, with at least 500.000 holes pr. square metre, preferably at least 800.000 holes pr. square metre, and most preferred at least 900.000 holes pr. square metre.

[0056] The inner evacuation openings 9 have a smallest cross-sectional dimension of less than 600 micrometres, preferably less than 400 micrometres, more preferred less than 300 micrometres and most preferred less than 250 micrometres. Thereby, depending of the general size of the pulp fibres used for the moulding process, it may be avoided that the evacuation openings of the internal mould surface 8 replicate on the surface of the moulded pulp product. Thereby a smooth finish of the surface of the final product may be ensured. The pulp may be formed by fibres generally having a length of approximately 1 to 2 millimetres and generally having a cross-sectional dimension of approximately 20 to 40 micrometres. For instance, if the pulp fibres generally have a length of approximately 1.2 to 1.9 millimetres and generally have a cross-sectional dimension of approximately 25 to 35 micrometres, and the inner evacuation openings 9 have a circular cross-section with a diameter of less than 250 micrometres, and preferably about 200 micrometres, then a very smooth finish of the moulded product without any visible replications of the evacuation openings may be obtained.

[0057] The inner evacuation openings 9 have a smallest cross-sectional dimension of more than 50 micrometres, preferably more than 70 micrometres, more preferred more than 80 micrometres and most preferred more than 90 micrometres. In this way, an efficient draining of the wet pulp preform may be ensured.

[0058] Each evacuation channel 21 is conical with a draft angle D of at least 1 degree, preferably at least 1.5 degrees and most preferred about 2 degrees. Thereby, the risk of clogging is even better reduced.

[0059] The total volume of all evacuation channels 21 is at least 40 per cent, preferably at least 45 per cent, more preferred at least 50 per cent and most preferred at least 55 per cent of the total volume of the material of the mould 2. In this way, an efficient draining of the wet pulp preform may be ensured.

[0060] Referring in particular to FIGS. 8 and 9, it is seen that each evacuation channel 21 has a circular cross-section from the internal mould surface 8 to the outer surface 19 of the mould 2, and all evacuation channels 21 are arranged so that the respective outer evacuation openings 20 are separated from each other by having a minimum material thickness between each other at the outer surface 19 of the mould 2. Thereby, a strong mould may be obtained which is useful for forming as well as drying of a pulp preform.

[0061] In the illustrated embodiment, the mould 2 is a split-mould composed of two moulds halves 43, 44, as illustrated in FIGS. 2, 3 and 10. The illustrated mould 2 which is intended for production of paper bottles is further designed in a CAD system in sections which are, however, integrated in the final mould 2. The sections of each mould half 43, 44 are as follows: neck section 51, shoulder section 52, middle section 53, and bottom section 54. The illustrated mould halves 43, 44 each has four middle sections 53.

[0062] Comparing FIGS. 7 and 8, illustrating a middle section 53 seen in perspective from the inside and from the outside, respectively, it is seen in FIG. 8 that the outer evacuation openings 20 are arranged closely packed in a so-called round straight configuration. However, in FIG. 7, it is seen that the inner evacuation openings 9 of the internal mould surface 8 are arranged closer to each other in the peripheral direction of the internal mould surface 8 than in the longitudinal direction of the internal mould surface 8. This is an advantageous arrangement of the evacuation channels 21, because the internal mould surface 8 forms a circle about the central axis 4 of mould 2. In this way, the tapering channels may be arranged very close to each other. The same principle has been applied when designing the bottom section 54 as illustrated in FIGS. 5 and 6. Here, the outer evacuation openings 20, in the upper part of the bottom section 54, are arranged closely packed in a so-called round straight configuration. In this upper part of the bottom section 54, the inner evacuation openings 9 of the internal mould surface 8 are arranged closer to each other in the longitudinal direction of the internal mould surface 8 than in the peripheral direction of the internal mould surface 8. This is advantageous, because in this case, the internal mould surface 8 has a smaller radius of curvature about a horizontal axis than about a vertical axis. As seen in FIG. 4, in the centre of the bottom section 54, the outer evacuation openings 20 are arranged closely packed in straight configuration, whereas the inner evacuation openings 9 are arranged directly over outer evacuation openings 20 so that a central axis of the evacuation channels are arranged at right angles to the mould wall 25. This arrangement is advantageous, because the centre of the bottom section 54 has a flat configuration. However, according to the present invention, the illustrated configuration of the inner and outer evacuation openings 9, 20 and the evacuation channels 21 may be varied in many different ways.

[0063] The mould 2 is produced by designing a 3D model of the mould 2 in a CAD system, and the mould 2 is produced by means of a metal 3D printing technique, such as additive manufacturing (AM), preferably Powder bed fusion (PBF). However, the mould could also be produced in plastic material using a 3D printing technique. The CAD model of the part in the form of the mould is given as an input to the manufacturing system. A base on which the intended part is to be produced, is kept inside the machine. The metal powder is then added. With a piston system, the base is slowly lowered down, layer by layer in the vertical direction. Each time when the base is lowered, a scraper distributes a fresh layer of powder. The laser beam scans the layer, following a path determined by the intended geometry of the part. The path on which laser moves is consolidated due to power melting and the rest of the powder is left loose. The loose powder is known as powder cake and can be reused again in the next production cycle. Once the process is finished, the part with support structure is taken out and the structure is dismantled. The parts and tools produced by this method are very fast compared to the conventional manufacturing methods. The method is capable of producing micro-features even below 300 microns, which is very challenging to produce by any other means in shorter time durations. The method is very economical to be commercialized for production of moulds for paper bottles and the like. The mould 2 is preferably fabricated using aluminium powder.

[0064] As seen in FIGS. 2 and 3, each mould half 43, 44 is provided with mounting flanges 50 for mounting the mould in the mould setup 49. The mould setup 49 is illustrated in FIG. 10. The mounting flanges 50 of the mould halves 43, 44 are mounted between two rotating frame parts 45, 46 so that the mould halves 43, 44 are pressed against each other and form the complete mould 2. The two rotating frame parts 45, 46 are arranged on a pivoting shaft 48 so that they may be pivoted between a closed position in which the mould halves 43, 44 are fixed in place and an open position in which the mould halves 43, 44 may be mounted or exchanged. The two rotating frame parts 45, 46 are further arranged on the vertical, main rotating shaft 47 for rotation of the mould 2 during the dewatering and drying step.

[0065] The method according to the invention of manufacturing a moulded pulp product by means of the pulp moulding apparatus 1 includes the following steps: activating the vacuum source 10, injecting an amount of pulp into the internal mould chamber 3 through the mould opening 7, thereby forming a pulp preform on the internal mould surface 8, injecting a dewatering and heating fluid through the mould opening 7 at gradually increasing pressure until a maximum pressure, thereby performing a dewatering and drying step whereby the pulp preform on the internal mould surface 8 is dewatered and dried, deactivating the injection of dewatering and heating fluid, deactivating the vacuum source 10, extracting the moulded pulp product. These steps are not necessarily performed exactly in the mentioned sequence and additional steps may be performed. When the injection of pulp into the internal mould chamber 3 is finished, excess pulp may optionally be pumped out of the mould 2 by means of the pump of the pressurised pulp source 22. However, in the illustrated setup, the mould opening 7 points downwards, and excess pulp may therefore simply leave back to the pressure vessel 30 as a result of gravity. In order to efficiently dewater and dry the pulp preform during the dewatering and drying step, rotation of the mould 2 about the central axis 4 of the mould is initiated and rotational speed is increased gradually, a maximum rotational speed of the mould 2 is maintained at least during a substantial part of the dewatering and drying step, and the rotational speed is decreased gradually until standstill of the mould 2. Rotation of the mould 2 may possibly be initiated before the dewatering and drying step. The pulp is injected into the internal mould chamber 3 through the stationary pulp port 13, and the dewatering and heating fluid is injected into the internal mould chamber 3 through the stationary dewatering and heating fluid port 14.

[0066] Preferably, the relative injection pressure of the dewatering and heating fluid through the mould opening 7 is increased gradually from approximately 0 to minimum 500 kPa, preferably from approximately 0 to minimum 700 kPa and most preferred from approximately 0 to minimum 1 MPa. Preferably, the relative injection pressure p of the dewatering and heating fluid through the mould opening 7 is increased gradually with a pressure rate of dp/dt=1 to 20 kPa/s in the range p=0 to 200 kPa and with a pressure rate of dp/dt=1 to 50 kPa/s in the range p=200 to 400 kPa.

[0067] Preferably, the rotational speed r of the mould 2 is increased gradually from 0 rpm to at least 5.000 rpm, preferably from 0 rpm to at least 7.000 rpm, and most preferred from 0 rpm to about 10.000 rpm. Preferably, the rotational speed r of the mould 2 is increased gradually with a rotation rate of dr/dt=10 to 1000 rpm/s until a maximum rotational speed.

[0068] Preferably, simultaneous injection of dewatering and heating fluid and mould rotation is maintained for at least 10 second, preferably at least 20 seconds, even more preferred at least 40 seconds and most preferred for about 1 minute.

[0069] Purely as an example, suitable process parameters may be as follows: [0070] Pulp is preheated to about 70° C. in the heater 26. [0071] Before first moulding operation, mould may be preheated to about 150° C., for instance by means of blowing preheated dewatering and drying fluid in the form of hot air through the mould. [0072] Suction pressure is about −30 kPa (relative pressure). [0073] Pulp is pumped to the mould 2 at a pressure of about 200 to 300 kPa (relative pressure). [0074] Pulp injection time about 10 seconds. [0075] Temperature of dewatering and drying fluid in the form of hot air is about 150-250° C. [0076] Pressure of dewatering and drying fluid in the form of hot air: from about 0 kPa and gradually increased to about 1 MPa (relative pressure). [0077] Pressure rate of dewatering and drying fluid in the form of hot air: dp/dt=1 to 20 kPa/s in the range p=0 to 200 kPa and with a pressure rate of dp/dt=1 to 50 kPa/s in the range p=200 to 400 kPa. [0078] Rotational speed range of mould 2: about 0-10.000 rpm starting from 0 rpm. [0079] Time of dewatering and drying step with rotation of mould 2: about 0-60 seconds.

[0080] LIST OF REFERENCE NUMBERS

[0081] D draft angle

[0082] 1 pulp moulding apparatus

[0083] 2 mould

[0084] 3 internal mould chamber

[0085] 4 central axis of mould

[0086] 5 closed end of mould

[0087] 6 open end of mould

[0088] 7 mould opening

[0089] 8 internal mould surface

[0090] 9 inner evacuation openings of internal mould surface

[0091] 10 vacuum source

[0092] 11 rotary union

[0093] 12 rotatable fluid port of rotary union

[0094] 13 stationary pulp port of rotary union

[0095] 14 stationary dewatering and heating fluid port of rotary union

[0096] 15 vacuum chamber

[0097] 16 tube

[0098] 17 wall of vacuum chamber

[0099] 18 rotary shaft seal

[0100] 19 outer surface of mould

[0101] 20 outer evacuation opening

[0102] 21 evacuation channel

[0103] 22 pressurised pulp source

[0104] 23 dewatering and heating fluid source

[0105] 24 motor

[0106] 25 mould wall

[0107] 26 heater

[0108] 27 belt

[0109] 28 waste tank

[0110] 29 pulp tank and stirrer

[0111] 30 pressure vessel

[0112] 31 frequency drive for pulp source

[0113] 32 frequency drive for motor

[0114] 33 control panel

[0115] 34 data logger

[0116] 35, 36, 37 flow controllers

[0117] 38-42 pressure sensors

[0118] 43, 44 moulds halves

[0119] 45, 46 rotating frame parts

[0120] 47 main rotating shaft

[0121] 48 pivoting shaft

[0122] 49 mould setup

[0123] 50 mould flanges

[0124] 51 neck section of mould half

[0125] 52 shoulder section of mould half

[0126] 53 middle section of mould half

[0127] 54 bottom section of mould half