U.S. patent application number 17/437222 was filed with the patent office on 2022-06-02 for method of manufacturing a moulded pulp product and pulp moulding apparatus.
The applicant listed for this patent is DANMARKS TEKNISKE UNIVERSITET. Invention is credited to Giuliano Bissacco, Prateek Saxena.
Application Number | 20220170211 17/437222 |
Document ID | / |
Family ID | 1000006195033 |
Filed Date | 2022-06-02 |
United States Patent
Application |
20220170211 |
Kind Code |
A1 |
Saxena; Prateek ; et
al. |
June 2, 2022 |
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.
Inventors: |
Saxena; Prateek; (Jaipur,
Rajasthan, IN) ; Bissacco; Giuliano; (Morarp,
SE) |
|
Applicant: |
Name |
City |
State |
Country |
Type |
DANMARKS TEKNISKE UNIVERSITET |
Kongens Lyngby |
|
DK |
|
|
Family ID: |
1000006195033 |
Appl. No.: |
17/437222 |
Filed: |
March 12, 2020 |
PCT Filed: |
March 12, 2020 |
PCT NO: |
PCT/EP2020/056715 |
371 Date: |
September 8, 2021 |
Current U.S.
Class: |
1/1 |
Current CPC
Class: |
D21J 3/10 20130101; D21J
1/06 20130101 |
International
Class: |
D21J 3/10 20060101
D21J003/10; D21J 1/06 20060101 D21J001/06 |
Foreign Application Data
Date |
Code |
Application Number |
Mar 14, 2019 |
IN |
201911010049 |
May 10, 2019 |
EP |
19173703.0 |
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
[0001] The present invention relates to a method of manufacturing a
moulded pulp product by means of 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: [0002] activating the
vacuum source, [0003] injecting an amount of pulp into the internal
mould chamber through the mould opening, thereby forming a pulp
preform on the internal mould surface, [0004] 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, [0005] deactivating the
injection of dewatering and heating fluid, [0006] deactivating the
vacuum source, [0007] extracting the moulded pulp product.
[0008] EP 1 104 822 A2 discloses a method of producing a pulp
moulded article comprising a papermaking step in which a pulp
slurry is fed to the papermaking net surface of a papermaking mould
having suction paths, and water contained in the pulp slurry is
sucked through the suction paths whereby the pulp is deposited on
the surface to form a wet preform, and a dewatering step in which
the wet preform is dewatered, wherein the temperature of the fed
pulp slurry is raised while the pulp is being deposited on the
surface. The dewatering step may be performed by injection of a
dewatering fluid into the cavity of the papermaking mould, and an
inflatable hollow pressing member may optionally be inserted into
and inflated inside the cavity while evacuating the cavity by
suction.
[0009] EP 1 288 369 A1 discloses a similar method of producing a
pulp moulded article wherein said undried moulded article formed on
the inner side of said papermaking screen is dewatered by feeding
pressurizing air into the cavity.
[0010] WO 2016/055073 A1 discloses a system for producing a moulded
article, in particular a bottle-shaped article, from pulp, said
system comprising a pressure device for applying a pressure to the
pulp, a first compressor, and a split mould having a central first
cavity, said first cavity having an opening for supplying said pulp
to said first cavity, one or more further cavities together
surrounding said first cavity, and a wall separating said first
cavity from said one or more further cavities, said wall having a
structure allowing for fluid to flow between said first cavity and
said one or more further cavities, said wall having a first surface
facing the interior of said first cavity and being for a layer of
said pulp deposited thereon. An expandable pressing tool in the
form of a balloon having a hollow inside may be inserted into the
first cavity and a heating device may be configured for heating
said expandable pressing tool. In an alternative embodiment, there
is no balloon, but instead the layer of deposited pulp is pressed
against the interior surface of the mould by use of superheated
steam.
[0011] GB191418339 discloses an apparatus for making bottles and
other receptacles from paper pulp of the type having a mould and a
distributing tube for the pulp inserted therein. The distributing
tube has openings varying in size proportionally to the size of
that portion of the mould opposite thereto. Centrifugal
packing-means are provided for packing the pulp in the mould in
that, when ejecting the fluid pulp through slots of the
distributing tube against the interior face of the rapidly rotating
mould, the pressure from a piston will force the pulp against said
mould and the centrifugal force due to rotation of said mould will
further tend to pack the pulp against the walls of the mould while
said rotation will also tend to distribute the pulp equally
circumferentially. Said mould being of net or otherwise perforated
the fluid in which the pulp is suspended will be forced outwardly
there through. However, this known apparatus is mostly suitable as
a manual method of making paper bottles having a rough uneven
surface and is not in any way suitable to meet today's demand for
packaging.
[0012] WO 2018/033209 A1 discloses a method for manufacturing a
moulded article from pulp in the form of a detergent packaging
which is not rotation symmetric. Pulp is distributed in the mould
by rotation about one or more axes and the pulp may be kept in
place on the mould by means of vacuum. The mould may be heated by
means of a heating element which can comprise at least one duct
through which a heating medium such as a heating fluid, in
particular a heating liquid can flow so that the mould and, thus,
the pulp contained in the mould can be heated by said heating
medium. However, the method of distributing the pulp material by
rotation of a mould about several axes seems not fast enough and
not suitable for mass production of paper bottles of the like.
[0013] WO 2016/132328 A1 discloses a moulding process and a
moulding apparatus for the moulding of articles by using paper
and/or wood and, more precisely, pulp of paper and/or wood,
recycled and milled paper and/or paper powder. The moulding process
comprises the phases of loading milled paper or pulp of paper
and/or wood into the mould, adding water or water vapour by means
of an injection device to the milled paper or to the pulp of paper
and/or wood into the mould, rotating the mould on itself with
respect to at least two axes so as to have the milled paper or the
pulp of paper and/or wood arranged on the mould walls. Due to the
centrifugal force, the mixture of paper and/or wood is arranged on
the walls of the mould ontaking the same shape of the mould. A
lattice is arranged around an injection device to act as a drainage
filter so as to drain the excess water in the shell and ensure the
release of the water vapour from the shell itself when the milled
paper or the pulp of paper and/or wood is heated for its
solidification. However, the method of distributing the pulp
material by rotation of a mould about several axes seems not fast
enough and not suitable for mass production of paper bottles of the
like.
[0014] DE 102004059268 A1 describes the production of rotationally
symmetric seamless hollow bodies of paper or fibrous material,
comprising introduction of a fiber suspension into a porous mold in
a centrifuge drum and spinning the drum.
[0015] In the known methods of manufacturing moulded pulp products,
however, production speed and accuracy of the final pulp products
may be a challenge. In order to obtain efficient drying of the pulp
preform and to still obtain a final product having a smooth
surface, most known methods in reality make use of a first
dewatering mould having an internal mould surface formed by a net
allowing water to drain and a second drying mould made of porous
material allowing vapour to escape and incorporating heating
channels.
[0016] The reason for the above known setup is as follows. The
first dewatering mould having an internal mould surface formed by a
net allows substantially draining of the wet preform which would
not be possible using a porous mould. However, this first
dewatering mould does not allow for a substantial internal pressure
to be applied on the wet preform, because the net would deform, and
this first dewatering mould cannot be heated itself by heating
channels or the like. Furthermore, the net of the first dewatering
mould tends to leave a visible pattern on the moulded product if
excess pressure is applied to the preform. On the other hand, the
second drying mould made of porous material allows incorporation of
heating channels and allows for a substantial internal pressure to
be applied on the wet preform. The second drying mould even leaves
the final moulded product with a surface of desired texture, such
as a smooth surface. As a further known measure, an inflatable
balloon may be used in the first or both moulds in order to apply a
pressure on the wet preform. As it will be understood, the use of a
first dewatering mould and a second drying mould involves moving
the wet preform from the first mould to the second mould, thereby
increasing production time considerably. Additionally inflating and
deflating a balloon in one or both moulds adds even further to
production time.
[0017] According to the known solutions, as mentioned above, the
second drying mould is typically made of porous material which
allows vapour to escape through the wall of the mould. The
micro-structure of the porous material gives rise to
inter-connected channels inside the mould. These channels can be
utilized as evacuation pathways for flushing out water-steam during
the pulp moulding process. However, the pulp fibres may be very
small and tend to enter the tool material. This results in clogging
of the tool. With a limited fraction of area available for
water-steam transport, a water evacuation capability from the tool
is hard to achieve. Cleaning of the tool is in reality not possible
due to the labyrinth of closed pathways in the porous material.
Clogging over long durations of time reduce the fatigue life of
tool, due to development of internal cracks in the tool.
[0018] None of the known methods has succeeded in both obtaining a
commercially profitable production rate and a suitable final
product having a desired smooth surface quality. There is therefore
a need for an improved method of manufacturing a moulded pulp
product.
[0019] The object of the present invention is to provide a
simplified method of manufacturing a moulded pulp product whereby
production speed may be increased.
[0020] In view of this object, the method is characterised by
[0021] initiating rotation of the mould about the central axis of
the mould and increasing rotational speed gradually, [0022]
maintaining a maximum rotational speed of the mould at least during
a substantial part of the dewatering and drying step, [0023]
decreasing rotational speed gradually until standstill of the
mould.
[0024] Thereby, by gradually initiating rotation of the mould and
maintaining a maximum rotational speed of the mould at least during
a substantial part of the dewatering and drying step, a synergistic
effect between rotation of the mould and gradual injection of
dewatering and heating fluid into the mould is obtained in the
following way. The synergistic effect facilitates the evacuation of
the water absorbed by the pulp fibres which is defined as bound
water. When heating the bound water by means of the dewatering and
heating fluid, the water is desorbed and acts as free water which
is defined as the water that is not absorbed by the pulp fibres.
When the free water is subjected to the centrifugal force, the
evacuation of the water from the mould is accelerated, because the
free water is now free to move away from the pulp. This synergism
between rotation and heating, when subjected to vacuum, results in
much faster drying of the pulp than according to the prior art
methods and will also mean a reduction in energy costs.
[0025] In a structurally particularly advantageous embodiment, 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, pulp is injected into
the internal mould chamber through the stationary pulp port, and
the dewatering and heating fluid is injected into the internal
mould chamber through the stationary dewatering and heating fluid
port.
[0026] In an embodiment, the mould is arranged inside a vacuum
chamber connected to the vacuum source, and 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 means of a
rotary shaft seal.
[0027] In an embodiment, the relative injection pressure of the
dewatering and heating fluid through the mould opening 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. By increasing the relative
injection pressure of the dewatering and heating fluid gradually,
it is avoided that the wet pulp preform is negatively affected by
the injection. Otherwise, the already formed pulp preform could
deform during the injection.
[0028] In an embodiment, the relative injection pressure (p) 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. By increasing the relative injection
pressure of the dewatering and heating fluid gradually, it is
avoided that the wet pulp preform is negatively affected by the
injection.
[0029] In an embodiment, the rotational speed of the mould 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. By increasing the rotational speed of the mould
gradually, it is avoided that the wet pulp preform is negatively
affected by the rotation. Otherwise, the already formed pulp
preform could deform during the rotation.
[0030] In an embodiment, 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. By increasing the rotational
speed of the mould gradually, it is avoided that the wet pulp
preform is negatively affected by the rotation.
[0031] In an embodiment, simultaneous injection of dewatering and
heating fluid and mould rotation is maintained for at least 10
seconds, preferably at least 20 seconds, more preferred at least 40
seconds and most preferred for about 1 minute.
[0032] In an embodiment, fluid is evacuated to an outer surface of
the mould through inner evacuation openings on the internal mould
surface, and 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. Thereby, a mould with a considerable wall
thickness and resulting strength 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 the inner evacuation opening may also pass through
the evacuation channel which has a gradually increasing
cross-sectional area. Moreover, if any pulp would nevertheless be
trapped in an evacuation channel, it may quite simply be blown out
by means of compressed air from the inside of the mould chamber.
Therefore, the mould 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, 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.
[0033] The present invention further relates to a 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
dewatering 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.
[0034] The moulding apparatus is characterised in that 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, and in that a motor
is arranged to rotate the mould about the central axis of the
mould. Thereby, the above mentioned features may be obtained.
[0035] In an embodiment, the mould is arranged inside a vacuum
chamber connected to the vacuum source, and 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 means of a
rotary shaft seal. Thereby, the above mentioned features may be
obtained.
[0036] In an embodiment, 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. Thereby, the above
mentioned features may be obtained.
[0037] In an embodiment, the mould has inner evacuation openings
through which fluid may be evacuated to an outer surface of a mould
wall, and 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. Thereby, the above mentioned features may be
obtained.
[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.degree. C. in the
heater 26. [0071] Before first moulding operation, mould may be
preheated to about 150.degree. 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.degree. 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
* * * * *