U.S. patent application number 10/520994 was filed with the patent office on 2006-06-15 for mdf press technology.
Invention is credited to Dieter Dohring, Josef Stutz.
Application Number | 20060127659 10/520994 |
Document ID | / |
Family ID | 7973064 |
Filed Date | 2006-06-15 |
United States Patent
Application |
20060127659 |
Kind Code |
A1 |
Stutz; Josef ; et
al. |
June 15, 2006 |
Mdf press technology
Abstract
The invention relates to a method for the production of a
construction element manufactured from wood fibers, matchwood
and/or sawdust, especially a board, comprising the following steps:
adhesive is applied to the wood fibers, matchwood and/or sawdust;
the wood fibers, matchwood and/or sawdust provided with adhesive
are pressed to form a construction element, especially a board.
Inventors: |
Stutz; Josef; (Nicosia,
CY) ; Dohring; Dieter; (Lampertswalde, DE) |
Correspondence
Address: |
PEARNE & GORDON LLP
1801 EAST 9TH STREET
SUITE 1200
CLEVELAND
OH
44114-3108
US
|
Family ID: |
7973064 |
Appl. No.: |
10/520994 |
Filed: |
December 24, 2002 |
PCT Filed: |
December 24, 2002 |
PCT NO: |
PCT/EP02/14751 |
371 Date: |
October 3, 2005 |
Current U.S.
Class: |
428/219 ;
264/122; 428/326 |
Current CPC
Class: |
B27N 1/02 20130101; Y10T
428/253 20150115 |
Class at
Publication: |
428/219 ;
264/122; 428/326 |
International
Class: |
D04H 1/00 20060101
D04H001/00 |
Foreign Application Data
Date |
Code |
Application Number |
Jul 10, 2002 |
DE |
202 10 718.3 |
Claims
1-37. (canceled)
38. A method of manufacturing a construction element made from wood
fibers, wood chips and/or sawdust comprising the steps of:
providing said wood fibers, wood chips and/or sawdust, applying an
adhesive to said wood fibers, wood chips and/or sawdust, and
pressing the wood fibers, wood chips and/or sawdust provided with
said adhesive to form said construction element.
39. The method of claim 38, wherein the step of providing said wood
fibers, wood chips and/or sawdust includes providing at least some
of said wood fibers, wood chips and/or sawdust as recycled wood
fibers, wood chips and/or sawdust from the manufacture of said
construction elements.
40. The method of claim 39, further including the step of grinding
said construction elements following said step of pressing, and
wherein said recycled wood fibers, wood chips and/or sawdust are
obtained from said grinding step.
41. The method of claim 38, wherein the step of pressing is done at
a temperature below 120.degree. C.
42. The method of claim 38, wherein the step of pressing is done at
a temperature below 95.degree. C.
43. The method of claim 38, wherein the step of pressing is done at
a temperature below 60.degree. C.
44. The method of claim 38, wherein said adhesive includes reactive
resins, that may be hardened by cross-linking, selected from the
group consisting of urea resins, melamine resins, acrylic resins,
epoxy resins, polyester resins and mixtures thereof, and the step
of pressing said wood fibers, wood chips and/or sawdust is free of
substantial hardening of said adhesive.
45. The method of claim 44, wherein said construction element
comprises from less than about 10% up to about 35% adhesive by
weight.
46. The method of claim 44, wherein said wood fibers, wood chips
and/or sawdust are broken down into solid and liquid components
within a gas-tight system, the liquid components being separated
from the solid components at a temperature in the range from about
less than 50.degree. C. up to about 90.degree. C., said liquid
components being added to said adhesive and applied to said solid
components to form said construction element.
47. The method of claim 46, wherein said adhesive is applied to
said wood fibers, wood chips and/or sawdust at a temperature less
than 100.degree. C.
48. The method of claim 47, further including the step of drying
said wood fibers, wood chips and/or sawdust in a drying device at a
drying temperature, and wherein the step of applying adhesive is
performed remote of said drying device at a temperature cooler then
said drying temperature.
49. The method of claim 48, wherein the step of applying adhesive
includes spraying an adhesive-gas mixture onto said wood fibers,
wood chips and/or sawdust.
50. The method of claim 49, wherein said adhesive is applied in an
amount such that the resulting construction element contains from
amount 45 kg/m.sup.3 to 55 kg/m.sup.3 of adhesive.
51. The method of claim 50, wherein the step of applying adhesive
includes placing said wood fibers, wood chips and/or sawdust onto a
belt weighing machine and maintaining a constant weight ratio of
said adhesive applied to said wood fibers, wood chips and/or
sawdust.
52. The method of claim 51, wherein said wood fibers, wood chips
and/or sawdust provided with said adhesive are mixed and/or stirred
in a cooled wall vessel.
53. The method of claim 52, wherein the step of applying said
adhesive includes initially forming a curtain or a mat of said wood
fibers, wood chips and/or sawdust and applying the adhesive to said
curtain or mat.
54. The method of claim 53, further including applying air at a
temperature of from about 40.degree. C. to about 70.degree.0 C.
together with said adhesive to said wood fibers, wood chips and/or
sawdust.
55. The method of claim 54, wherein the step of applying said
adhesive includes also applying a hardening agent to said wood
fibers, wood chips and/or sawdust.
56. The method of claim 55, wherein said adhesive applied to said
wood fibers, wood chips and/or sawdust has an outer surface that is
hardened by cross-linking.
57. The method of claim 56, further including laminating a
finishing component to said construction element at an elevated
temperature and completing the hardening by cross-linking of said
adhesive.
58. The method of claim 44, further including breaking down said
wood fibers, wood chips and/or sawdust into solid components and
liquid components, adding said liquid components to said adhesive,
and applying said adhesive and liquid components to said wood
fibers, wood chips and/or sawdust.
59. The method of claim 58, further including cooling said liquid
components by at least 30.degree. C. and then applying the liquid
components to said wood fibers, wood chips and/or sawdust.
60. The method of claim 58, wherein said liquid components include
lignin and hemicellulose, said liquid components comprising up to
about 20 percent by weight of said adhesive.
61. The method of claim 58, wherein synthetic material fibers
and/or glass fibers are added to said wood fibers, wood chips
and/or sawdust.
62. The method of claim 58, wherein said adhesive applied to said
wood fibers, wood chips and/or sawdust has an outer surface that is
hardened by cross-linking.
63. The method of claim 62, wherein said wood fibers, wood chips
and/or sawdust are charged with steam immediately before
pressing.
64. The method of claim 63, wherein said recycled wood fibers, wood
chips and/or sawdust are obtained from the manufacture of MDF
and/or HDF boards for flooring panels and molded parts.
65. The method of claim 64, wherein said pressed construction
element is coated with at least paper provided with resins and
compressed in a press at temperatures above 150.degree. C. to
laminate said paper to said construction element and complete said
hardening by cross-linking said adhesive.
66. A construction element made entirely or predominantly from wood
fibers, wood chips and/or sawdust provided with adhesive and
compressed together, said construction element containing from
about 45 to about 55 kg/m.sup.3 of said adhesive.
67. The construction element of claim 66, wherein said adhesive
comprises non-hardened resins.
68. The construction element of claim 67, wherein said adhesive is
selected from the group consisting of urea resins, melamine resins,
acrylic resins, epoxy resins, polyester resins or mixtures of the
same.
69. The construction element of claim 68, wherein said construction
element is a board.
70. The construction element of claim 69, wherein said board
consists essentially of wood fibers secured together with said
adhesive.
71. The construction element of claim 68, wherein said construction
element contains more than 5 percent by weight of said sawdust.
72. The construction element of claim 68, wherein said construction
element has a density of at least 300 kg/m.sup.3.
73. The construction element of claim 68, wherein said construction
element has a density of less than 1500 kg/m.sup.3.
74. A construction element produced in accordance with the method
of claim 38.
75. A laminate panel having a plurality of layers including a
carrier board and one or more paper layers, said carrier board
being produced in accordance with the method of claim 38.
76. The laminate of claim 75, wherein said carrier board has a
density greater than 1500 kg/m.sup.3.
Description
[0001] The invention relates to a construction element manufactured
from wood particles such as fibres or chips. A method is specified
for the manufacture of construction elements. In particular, the
invention relates to boards made entirely or predominantly from
wood fibres.
[0002] A method for the manufacture of a wood-fibre board is
already known from the German specialist periodical HK 1/88, pp 74
to 75, "Manufacture of MDF-Boards". Boiled wood chips supplied to a
so-called refiner. In the refiner, the wood chips are processed by
means of grinding discs to form fibres, in fact, subject to the
additional supply of temperature and pressure. The fibres are
removed from the refiner by means of steam and transported via a
line known as a "blow line". In this context, the steam pressure is
approximately 10 bar. The temperature is approximately 150 to
160.degree. C. Adhesive is added in the "blow line". Phenol resins,
urea resins or mixed resins made from urea and melamine can be used
as the adhesive. After the addition of adhesive, the "blow line"
becomes wider. Turbulence is caused by this widening, and the
adhesive is mixed with the fibres. The proportion of adhesive to
fibres is approximately 22% by weight.
[0003] The "blow line" opens into the centre of a drying tube. The
drying tube has a diameter of, for example, 2.60 m. Air is blown
through the drying tube at a temperature of 160.degree. C., with a
maximum of 220 to 240.degree. C. In the drying tube, the moisture
is reduced from 100% to 8 to 11%. The resulting steam charged with
non-aqueous substances is separated from the fibres in subsequent
cyclones and released into the environment via chimneys.
[0004] The fibres provided with adhesive are supplied in the form
of layers to a moulding machine, where the fibres are pressed in
two phases. Initially, a preliminary pressing takes place. The
pre-pressed fibres are then compressed under high pressure with a
supply of heat to form a board. Specialists in this field have
determined that the boards split, if the temperature during
pressing to form a board falls below 150.degree. C., for example,
to 140.degree. C. During pressing, the temperatures are therefore
typically in the region of 180.degree. C.
[0005] Additional known details, which could be of interest for the
manufacture of wood-fibre boards are outlined below. An
adhesive-application device for the production of fibre boards is
known from the specification EP 0 744 259 A2. A method for
manufacturing boards from a timber material is known from the
specification U.S. Pat. No. 5,554,330. The document GB 791,554
discloses a method for mixing solid and liquid components. A device
for the continuous application of adhesive to wood chips is
disclosed in DE 41 15 047 C1. Continuous mixing of materials in the
form of chips and fibres with bonding agents is disclosed in DE-OS
1956 898. The specifications PCT/IB98/00607 and WO 98/37147
disclose the recovery of adhesive from timber components.
Preliminary steam-treatment methods are disclosed in DE-OS 44 41
017, U.S. Pat. No. 111,795 and in the Danish patent No.
0302/97.
[0006] The object of the present invention is to reduce
manufacturing costs.
[0007] The object of the invention is achieved by one of the
methods claimed. A board manufactured according to the method
comprises the features of the dependent claim.
[0008] According to general expert opinion, wood-fibre boards must
be pressed at temperatures above 150.degree. C., because it has
been established, that temperatures below 150.degree. C. lead to
defects in the surface. The boards split, if the temperature falls
below 150.degree. C., and cracks appear. If a temperature of
150.degree. C. is exceeded during pressing, splitting is avoided as
a result of an adequate hardening of the adhesives and/or resins
used.
[0009] The inventors have established that it is exclusively the
steam occurring at the high temperatures, which is responsible for
the splitting. No splitting occurs, if steam is not produced at
all, or, at least, if steam is produced only to a slight extent
because of sufficiently low temperatures.
[0010] Surprisingly, it was also found that splitting can be
avoided by selecting sufficiently low temperatures during pressing.
It is important that no steam or only a small amount of steam is
produced during pressing. Temperatures below 120.degree. C. have
already proved adequate. The temperature range between room
temperature and 95.degree. C. is preferred. By particular
preference, pressing is carried out at temperatures up to
60.degree. C. The rate of pressing is not influenced or hardly
influenced by the supply of heat. However, a delay can occur in
pressing, if, for example, the wood components are only brought up
to temperature in the press. In this case, a delay occurs because
heating requires time.
[0011] If the fibres with the resin are pressed at temperatures,
for example, of 200.degree. C., then the resins, which are
typically used, harden completely or almost completely. The resin
does not harden or hardens only to an insignificant extent, if it
is pressed together with the wood chips, wood fibres, sawdust or
mixtures thereof at temperatures below 120.degree. C. A person
skilled in the art was previously of the opinion that resin ought
to harden so that a surface, which is free from defects, can be
achieved in construction elements such as boards made from timber
materials.
[0012] The resins used are initially present in the form of
low-molecular weight components. Hardening means that the
low-molecular weight components cross-link with one another,
thereby forming a stable network.
[0013] The construction element manufactured according to the
method differs from the prior art, in particular, in that the
resins used are not hardened. The resin used can be detected in an
unchanged or almost unchanged state by chemical analysis of the
product. Accordingly, no chemical change and no chemical
cross-linking or practically no chemical cross-linking has taken
place.
[0014] The board manufactured at sufficiently low temperatures can,
in particular, be used as a semi-finished product. In one
embodiment of the invention, this board is fed into a press in a
known manner together with decor paper, counteracting paper and
other components of a laminate flooring. Pressing is then carried
out at temperatures above 150.degree. C., preferably above
180.degree. C. The upper temperature limit is reached, when the
temperature causes damage to the product.
[0015] In this manner, not only are the papers connected to the
board, but the resins in the board are also hardened. Altogether,
considerable cost savings are achieved, because one heating stage
has been reduced or even completely eliminated.
[0016] A typical density of the board manufactured according to the
invention is around 650 kg/m.sup.3. The board should be pressed so
strongly, that the density does not fall below 300 kg/m.sup.3,
preferably 400 kg/m.sup.3, by particular preference 500 kg/m.sup.3,
in order to achieve a stable and therefore easily-handled board.
The density of the board is typically below 1000 kg/m.sup.3.
[0017] When the board is pressed to form the end product, for
example, a coated board for laminate flooring, it can be compressed
to a density above 1500 kg/m.sup.3, by particular preference to a
density above 2000 kg/m.sup.3. Accordingly, the density in one
exemplary embodiment is 2400 kg/m.sup.3.
[0018] The proportion of resin in the board is, for example, around
7.5% by weight, if the manufactured board is to be used as flooring
in the form of panels. In the case of door panels, the proportion
of resin is typically 2.5% by weight. To manufacture boards which
satisfy the EN438 standard, the proportion of resin should not
exceed 35% by weight. For economic reasons, the limit of
approximately 10% by weight resin should not be exceeded. A lower
limit at which the method still functions, is approximately 1% by
weight.
[0019] The resins used are reactive resins, that is to say resins
with components, which are chemically capable of forming a network.
Examples of reactive resins include: solid or liquid phenol resins,
amino resins, for example, urea resins, melamine resins, acrylic
resins, epoxy resins and/or polyester resins.
[0020] In one embodiment of the invention, wood chips made from
timber can first be separated into solid and liquid components. The
solid wood components are dried and provided with adhesive, that is
to say, reactive resins. The solid wood components provided with
adhesive are then pressed to form a moulded body, for example, a
board.
[0021] The liquid components comprise, in particular, lignin and
hemicellulose. At the temperatures predominating during drying,
these substances produce emissions, which cause odour pollution and
therefore also environmental pollution. By separating these liquid
components before drying, the corresponding emissions during and/or
following drying are reduced. Environmental pollution during the
manufacture of the boards is reduced correspondingly.
[0022] The liquid components are preferably disposed of and/or
further processed at temperatures, at which only minimal emissions
occur. If the temperatures of the liquid components are high, in
particular, if these temperatures are above 90.degree. C., then the
liquid components are held in a gas-tight system sealed from the
environment until the temperatures have fallen sufficiently.
[0023] In a further embodiment of the invention, the liquid
components, in particular lignin and hemicellulose, are used as an
adhesive, that is to say, according to the invention, these
components are mixed with the dried, solid wood components. The
solid wood components are preferably further processed to form
fibres or chips. The liquid components may, for example, be
separated from the solid wood components in a so-called agitator.
The components named above, are typically obtained in the following
proportions: 20 to 35% by weight hemicellulose, 45 to 50% by weight
cellulose and 20 to 35% by weight lignin. The cellulose is a solid
component of the wood.
[0024] In one embodiment, wood chips are first placed in a packing
screw. From the packing screw, the wood chips are conveyed in a
compressed condition to a boiling container where they are boiled
under high pressure. The boiling container is therefore designed
for high pressures. The pressure in the boiling container is, in
particular, at least 1.2 to 2.2 MPa (12 to 22 bar). According to
the prior art, wood chips are generally boiled at pressures of only
0.8 to 0.9 MPa. As a result of the steam-tempering treatment, the
solid wood components (cellulose) are separated from the lignin and
hemicellulose, which provide the liquid components. The cellulose
is present in solid form. The two other components lignin and
hemicellulose are liquids and can, in principle, be used as an
adhesive. The adhesive force in this case is achieved primarily by
the hemicellulose.
[0025] It is, in fact, already known from the specification WO
98/37147, that the lignin and hemicellulose contained in wood can
be separated from the solid components and subsequently used as an
adhesive for the manufacture of MDF boards. However, the
disadvantage with this method is the strong emissions, which
pollute the environment around a production site. According to the
invention, the problem of emissions is reduced, in that the liquid
components are separated from the solid components of the wood in a
gas-tight container. The liquid components are separated and
initially remain, for example, within a gas-tight system connected
to the container, in fact, at least while the temperatures of the
liquid are sufficiently high to cause strong emissions. After the
separation of the liquid components, these cool down to a
significant extent and are only removed from the gas-tight system
at relatively low temperatures, for example, for further
processing, especially by spraying via nozzles onto the fibres. The
liquid components are therefore significantly cooled, in
particular, by at least 30.degree. C., preferably by at least
50.degree. C., before they leave the gas-tight and therefore also
odour-tight, sealed system. In this relatively cool condition, the
development of odour is significantly reduced. Removal of the
liquid components from the gas-tight system is then
non-critical.
[0026] The liquid components can be used as an adhesive. This is
achieved in an environmentally-friendly manner in that the liquid
components of a wood are only removed from a gas-tight and
therefore odour-tight, sealed system at low temperatures,
especially at temperatures significantly below 100.degree. C.,
especially below 70.degree. C., by a particular preference below
50.degree. C., and applied to the fibres, for example, in this cool
condition.
[0027] Environmental pollution can thus be reduced in a
particularly economical manner.
[0028] The gas-tight system consists, for example, of the container
together with the connected lines. A further container, which can
be used, for example, for cooling, may also form part of the
gas-tight system.
[0029] With a treatment according to the prior art, the adhesive is
undesirably subjected to a temperature treatment in the drying
tube. From approximately 80.degree. C. the adhesive is, in fact,
disadvantageously stressed and/or activated. Activated adhesive can
no longer be used for the subsequent processing stage, in which the
glued, solid wood components are compressed to form the board.
[0030] With the prior art mentioned above, the active component of
the adhesive is reduced. Of the original 22% by weight normally
used, only 1 to 8% by weight is available for use, after the
fibre-adhesive mixture is removed from the drying tube. According
to the invention, the adhesive is applied to the solid wood
components in a relatively cool condition. This avoids any
unnecessary, premature and extensive activation of the
adhesive.
[0031] An adhesive based on formaldehyde-urea is currently used in
HDF boards, MDF boards and chip boards. Melamine is added to the
adhesive, if the boards are to be used for flooring. This prevents
swelling, which can occur as a result of moisture.
[0032] The problem here is that some of the adhesive is lost for
the actual processing stage as a result of the temperature
treatment. It is therefore a disadvantage that considerably more
adhesive must be added to the fibres or the chips, than is
necessary in order to press the fibres or the chips in a press with
a supply of heat and in order to achieve the desired outcome, such
as, an MDF board. At present, an MDF board can contain
approximately 60 kg of adhesive per m.sup.3. This quantity can be
considerably reduced, if the adhesive is applied in a relatively
cool condition.
[0033] In one embodiment of the invention, the liquid components,
hemicellulose and lignin, obtained in the manner described above,
are applied as an adhesive to the solid wood components in a cooled
or cool condition. In the cooled or cool condition, these
components can advantageously be mixed with another adhesive. In
this case, the other adhesive is not obtained from the liquid
components of the wood. The proportion of hemicellulose and lignin
in the adhesive mixture prepared in this manner is preferably no
more than 20% by weight. Furthermore, the mixture especially
contains an adhesive based on formaldehyde-urea. Moreover, the
adhesives specified in the prior art can be used.
[0034] If an adhesive mixture, which contains more than 20% by
weight hemicellulose and lignin, is used, then the pressing time
(with a supplementary use of currently available, conventional
synthetic adhesives), during which the glued fibres are pressed to
form a board, is relatively long. It is therefore more economical,
to mix the hemicellulose and lignin with another adhesive or
adhesive mixture. On the one hand, conventional adhesive can be
saved, and on the other hand, the method is not relatively
prolonged, thereby becoming less economical, because of the long
pressing times. The economically meaningful upper limit for the
proportion of hemicellulose and lignin is dependent upon the
reactivity of the adhesive, with which the hemicellulose and lignin
components are mixed. The named upper limit of 20% by weight
therefore merely represents a guide value or respectively a value
based on current experience.
[0035] In one embodiment of the invention, the solid wood
components are first dried, and adhesive is then mixed with the dry
components at temperatures, which are considerably lower than the
drying temperatures, in particular below 100.degree. C. This avoids
exposing the adhesive to undesirable, relatively hot temperatures,
which occur during drying. With the prior art, the adhesive also
contributes to emissions. Since the adhesive is now no longer
exposed to hot drying temperatures, but is applied to the solid
wood components at relatively cool temperatures, emissions
originating from the adhesive are also avoided. In the drier and/or
drying tube, only water but not chemicals are dried. Corresponding
environmental advantages result from this, because the dry air is
not disadvantageously charged with vapours originating from the
adhesive, as in the prior art. The manufacture of the boards is
therefore more environmentally friendly. This embodiment has the
additional advantage that proportions of the adhesive are not
disadvantageously activated during the drying process and therefore
unavailable for the actual gluing of the wood components to form
the board.
[0036] The solid wood components, which are present particularly in
the form of fibres or chips, and which are dried, are also
advantageously not charged with liquid components of the wood
material and, in the embodiment named above, also not charged with
adhesive. The corresponding liquid phases are therefore also not
dried in the drier. By comparison with the prior art, considerable
energy savings are achieved. The saving of energy not only leads to
considerable cost advantages, but also protects natural resources
and therefore the environment.
[0037] Because the adhesive is only applied to the wood components
after drying, the quantity of adhesive required for the manufacture
of the boards is reduced. A reduction to 45 to 55 kg/m.sup.3 board
can be achieved. A typical value is around 50 to 52 kg/m.sup.3 of
board.
[0038] One essential parameter in order to achieve a suitable
gluing of fibres or chips is the "correct" ratio of the solid wood
components to the adhesive. In one embodiment of the method
according to the invention therefore, the solid wood components are
supplied to a belt weighing machine before the application of the
adhesive. On the belt weighing machine, the solid wood components
are not only transported by means of a circulating conveyor belt,
they are also weighed. As a result, information is obtained
regarding the quantity of adhesive to be added to the solid
components of the wood in the following stage.
[0039] The solid wood components are transferred to the subsequent
device by means of the belt weighing machine. In one embodiment,
possible fluctuations in the weight of the solid wood components
supplied are measured, registered and stored during transport.
These data are prepared and can be used as parameters for adjusting
the quantity of adhesive, which is subsequently applied to the
solid wood components.
[0040] In one embodiment of the invention, the rate of transport on
the belt weighing machine is controlled in such a manner that a
uniform quantity of solid wood components is supplied to the
downstream adhesive-application device (in which the solid wood
components are provided with adhesive). By changing the rate of the
feeder, a constant quantity of material can be supplied to the
downstream devices. The weight of the solid wood components, which
may be present in the form of fibres or chips, can be registered in
extremely small steps. This allows a uniform supply of the solid
wood components with an accuracy, for example, of .+-.1%.
[0041] It is not easy to provide the solid wood components with
adhesive in a uniform manner, especially if the solid wood
components are present in the form of fibres. Fibres have a
tendency to clump together in the form of a wad. It is then
difficult to distribute the adhesive uniformly on the fibres. In
one embodiment of the invention, the application of the adhesive is
carried out in a mixer, in which the adhesive and the solid wood
components are mixed with one another.
[0042] In one embodiment of the invention, the mixer provides means
for cooling its housing. For this purpose, in one particularly
simple embodiment, an at least partially double-walled housing, for
example, a double-walled tube, which forms a part of the housing of
the mixer, is provided. A cooled liquid, for example, cooled water,
is supplied through the double-walled housing, in order to cool the
mixer or respectively its walls. As a result of the cooling, a
layer of condensation water is formed on the walls. The cooling is
designed accordingly. As a result of the layer of condensation
water, solid wood components provided with adhesive do not adhere
to the walls and clog the mixer.
[0043] After drying, the solid wood components are spread,
according to one embodiment of the invention, in a flat manner,
forming a type of curtain or mat. This is especially appropriate if
the solid wood components are present in the form of fibres,
because a mat and/or a curtain can readily be formed from fibres.
Adhesive is then added, in particular, sprayed onto the curtain. By
preference, an air-adhesive mixture is sprayed, in order to
guarantee the most uniform possible distribution of the adhesive.
As a result of the formation of a curtain, the adhesive is
distributed uniformly on the solid wood components. This is
particularly appropriate if the solid wood components are present
as fibres.
[0044] In one embodiment, a curtain or mat formed from solid wood
components is fed into the mixer. An air-adhesive mixture is then
blown through nozzles onto the curtain or mat. The adhesive is
therefore supplied to the curtain or mat via the nozzles. Following
this, the curtain or mat is transported through the mixer
preferably in a contactless manner. Contactless transport
advantageously prevents the adhesion of the solid wood components
to the walls. Problems of contamination and the associated costs
are therefore reduced.
[0045] Together with air, the adhesive is blown into the dried
solid wood components, especially at a temperature from 40 to
70.degree. C., preferably at a temperature from 55 to 60.degree. C.
This means that the adhesive reaches a dry exterior skin.
Accordingly, it is activated only to a minimal extent. As a result,
the subsequent mixture of solid wood components and adhesive does
not adhere to transport equipment and devices, for example, in the
interior of the mixer.
[0046] Because the adhesive is exposed to considerably lower
temperatures than hitherto, it is possible to use more reactive
adhesives by comparison with the prior art. Moreover, it is
possible to reduce the proportion of chemicals such as
formaldehyde. This leads to further environmental advantages.
[0047] In one embodiment of the invention, the adhesive is brought
into turbulence with heated air, and this air-adhesive mixture is
supplied to the dried, solid wood components, for example, fibres
or chips. The heated air, which is supplied to the mixer, for
example, together with the adhesive and the dried, solid wood
components, via a cabin or cell, to a certain extent activates the
surfaces of the adhesive droplets formed in this manner. As a
result, an adhesion of the solid wood components to downstream
devices, for example, to the walls of the mixer, is appropriately
prevented. Otherwise, the mixer would have to be cleaned, for
example, after very short intervals, thereby disadvantageously
interrupting production. Undesirable cleaning costs would also be
incurred. Regarding the disadvantage, that the adhesive is slightly
activated, the considerable economic disadvantages referred to
above must be evaluated and weighed against one another. With a few
experiments, a person skilled in the art can determine the extent,
to which the surface of the adhesive should be activated in order
to achieve an optimum economic result. The proportion of activated
adhesive will always be small by comparison with the prior art.
[0048] In one embodiment of the invention, in order to facilitate
subsequent processing stages, the free surface of the adhesive is
somewhat further activated after the adhesive has been added to the
dried solid wood components such as fibres or chips by means of a
device suitable for this purpose. After the adhesive has been added
to the dried, solid wood components, that is, to the fibres or
chips, especially after leaving the mixer, the solid wood
components provided with the adhesive are preferably conveyed into
an ascending pipe, which is, in particular, 10 to 30 m long, by
preference, approximately 20 m long. The diameter of the ascending
pipe is, in particular, from 1 to 4 m.
[0049] The ascending pipe is preferably also cooled and is, for
example, also double walled in order to allow a flow of cooling
liquid between the two walls. Once again, the aim is to form a
layer of condensation water on the interior walls of the ascending
pipe, so that the glued solid wood components do not adhere to the
walls.
[0050] The glued, solid wood components can be conveyed through the
ascending pipe in a particularly simple, contactless manner, by
means of an air or gas flow.
[0051] It has been shown that the solid wood components, especially
if these are present in the form of fibres, should be conveyed
through the ascending pipe at a rate of at least 25 m per second,
preferably at least 35 m per second. At a slower rate, the fibres
or chips would adhere more intensively to the ascending pipe in
spite of the measures mentioned above. As a result, the ascending
pipe would be contaminated unnecessarily quickly. With slower
rates, the ascending pipe had to be cleaned after 8 hours. By
adjusting an appropriate rate, the cleaning cycles were extended to
7 to 8 days. Accordingly, the ascending pipe need only be cleaned
once a week.
[0052] The maximum rate, at which the solid wood components
provided with adhesive are blown through the ascending pipe,
depends upon the performance of the equipment and/or devices
downstream. In this context, it must be taken into consideration
that the downstream equipment and/or devices must be capable of
processing the incoming quantity of solid wood components. In
practice, at present, an upper limit of 40 m per second can be
realised without difficulty. From 50 m per second, currently used
downstream equipment was overloaded. The upper speed limit can be
increased, as soon as downstream equipment of higher performance is
available. In principle, faster transport rates in the ascending
pipe are advantageous, because problems of contamination and the
associated interruption of production are reduced accordingly.
[0053] Providing an ascending pipe means that the adhesive is
further activated to some extent on the surface, in order to allow
the implementation of downstream processing stages in an
appropriate manner. The length of the ascending pipe should
therefore be adapted by the person skilled in the art to the
desired degree of adhesive activation. The person skilled in the
art will take the rate of transport through the ascending pipe into
account within the design process.
[0054] Following the addition of adhesive to the dried, solid wood
components, in particular, following the partial activation of the
adhesive in the ascending pipe, the solid wood components, which
are provided with adhesive, are transported into a cyclone. Here,
the surface of the adhesive has been activated adequately as a
result of the measures named above, so that it does not adhere in
the cyclone. In the cyclone, the solid wood components are
separated and transported to the next processing stage by a
transport means such as a conveyor belt. The solid wood components
are separated from the air in the cyclone. In one embodiment, the
transport means conveys the solid wood components into a screening
device. In the screening device, the solid wood components are
screened for coarse components. Any coarse components are
automatically removed. Coarse components include, for example,
lumps of adhesive.
[0055] From the screening device, the solid wood components are
transported by a belt to the press, where they are compressed to
form a board. The press preferably consists of circulating
compression belts pressed against one another, which are tempered
appropriately. This allows continuous pressing. The temperature
should be adjusted for the relevant adhesive by a person skilled in
the art. According to one embodiment, the quantity of energy and
the resulting temperatures for the two compression belts are
selected to be different, in order to prevent a distortion of the
board manufactured. However, according to the invention, a
tempering of the press can also be completely omitted.
[0056] In one embodiment of the invention, the nozzles through
which the adhesive is supplied to the solid wood components are
preferably designed to be conical. The adhesive then emerges from
the tip of the cone in the form of droplets, thereby advantageously
promoting and improving a uniform distribution of the adhesive.
[0057] To avoid cleaning work and an associated interruption of
production, attention should be paid to the fact that the adhesive
emerging, for example, from nozzles, does not come into contact
with downstream tools, such as tools disposed in the mixer. The
adhesive is therefore preferably directed, in particular, sprayed,
towards the solid wood components in order to achieve the most
uniform possible distribution. Moreover, it is particularly
important to ensure an adequate distance between the nozzles and
the tools downstream in the mixer. In practice, it has been shown
that the distance between the tools in the mixer and the nozzles
should be at least 1 m, preferably at least 2 m, if the adhesive is
sprayed in a horizontal direction. The solid wood components are
then introduced vertically at the start of the mixer and further
transported within the mixer in a horizontal direction. The actual
distance values named relate, of course, only to an individual
exemplary case. They are not generally applicable, because these
values are ultimately dependent upon the rate, at which the
adhesive emerges from the nozzles.
[0058] If an air-adhesive mixture is sprayed towards the solid wood
components, an air stream, by means of which the solid wood
components can be blown and therefore transported, initially with
the minimum possible contact, through the downstream devices such
as a mixer or an ascending pipe, is advantageously provided at the
same time. Another gas may in principle also be used instead of
air.
[0059] Stirring devices, which achieve a mixing of the solid wood
components with the adhesive are used, in particular, as the tools
within the mixer.
[0060] To achieve good results, the solid wood components are
brought in front of the nozzles in the form of a curtain.
Accordingly, in addition to the advantages already named, this
prevents the adhesive from being sprayed into the mixer and
contaminating the tools disposed there. Otherwise, the solid wood
components would adhere to the tools, and the mixer would become
clogged in a very short time and would have to be cleaned in short
intervals.
[0061] In one embodiment, the tools in the mixer are attached to a
centrally mounted axis and consist of rods projecting in a
star-shape, each of which merges into a flat region similar to the
blade of a paddle. Altogether, each star is formed, for example, by
four tools. Two tools respectively enclose an angle of 90.degree..
The blades of the paddles are positioned diagonally relative to the
air stream, which flows through the mixer. As a result, a
turbulence is created in the air, thereby providing a good mixing
of the solid wood components with the adhesive. Several "stars"
formed by the tools are attached to the axis at regular intervals.
The solid wood components are then transported through the mixer
parallel to the axis. In general, the tools are specially designed
to cause turbulence in the air near the solid wood components.
Propeller-like tools or tools acting as propellers are therefore
preferred.
[0062] A curtain is preferably formed from the solid wood
components as follows.
[0063] A transport means, such as a conveyor belt and/or a belt
weighing machine, is provided with at least one roller, preferably
more than one, roller at the end. The solid wood components are
passed through the roller(s). In particular, the rollers are
pressed against one another. A gap remaining between two rollers,
or between one roller and an adjacent surface, is, in principle,
unproblematic. A kind of curtain or mat is formed from the solid
wood components as they pass through the rollers. The form of a
curtain is therefore created by the rollers.
[0064] In this context, a conveyor belt is used by preference,
because this guarantees a uniform supply of solid wood components,
which are especially provided entirely or predominantly in the form
of fibres, to the rollers. In one embodiment, a belt weighing
machine is used to control the rate of supply to the rollers,
thereby supplying a particularly constant quantity of solid wood
components to the rollers. According to the prior art, worm screws
are routinely used for the transport of solid wood components in
the manufacture of boards. However, the solid wood components leave
the worm screws in a relatively uneven manner. This would form a
correspondingly uneven curtain from the solid wood components. A
curtain of uniform thickness and width is advantageous in order to
achieve a uniform distribution of adhesive. This also means that
the curtain reliably separates sprayed adhesive from downstream
tools.
[0065] In particular, rollers compressed together or with a gap
between them for the production of the curtain, prevent the solid
wood components, especially if these are present entirely or
predominantly in the form of fibres, from being transported in a
wad-like or clump-like manner. This would impair the desired
uniform application of adhesive.
[0066] In one embodiment, in order process a sufficiently large
quantity of solid wood components to form a curtain and to achieve
a particularly uniform curtain, more than two rollers, through
which the solid wood components are guided to form a curtain, are
provided. The rollers are preferably arranged above one another
offset in such a manner that an acute angle is enclosed between the
rollers and a transport medium, for example, a conveyor belt and/or
belt weighing machine. Accordingly, sufficient material can be
supplied to the transport medium, for example, the belt weighing
machine, in order to process a sufficiently large quantity of solid
wood components in a uniform manner.
[0067] It has already been shown in practice, that a total of four
rollers is particularly advantageous in order to create a curtain
from the solid wood components, to which adhesive is subsequently
applied by mechanical means.
[0068] The opening, through which the curtain consisting of the
solid wood components is guided into or in front of the mixer,
preferably corresponds to the maximum width of the mixer housing,
for example, the diameter of the named tube, which at the same time
forms the walls of the mixer. This ensures that the entire width of
the mixer is covered by the curtain. Otherwise, adhesive could be
sprayed into the interior of the mixer through the remaining
openings at the sides of the curtain, and the problems of
contamination mentioned above would occur.
[0069] If the entire width of the mixer was not covered, adhesive
would not only be sprayed into the mixer, but any solid wood
components disposed at the edge would be drawn along more strongly
and could form clumps. This would impair the quality of the
material and could lead to corresponding production problems. The
material would have to be re-processed in a disadvantageous and
cost-intensive manner.
[0070] In practice, the lateral walls of the mixer are preferably
cooled to 7 to 15.degree. C., especially to 10 to 12.degree. C.
This means that a layer of condensation water is deposited on the
walls. Adhesion to the walls is avoided by the layer of
condensation water.
[0071] The temperatures named above are also suitable for the
formation of a layer of condensation water on the interior walls
inside the ascending pipe.
[0072] Since a gaseous medium such as air is provided, inter alia,
for the transport of the fibres with the adhesive through the
mixer, the nozzles for supplying adhesive, in one embodiment of the
invention, are disposed at a distance from the housing of the
mixer. The nozzles in this case are disposed in front of an opening
of the mixer housing. A gap or an annular gap, through which air is
drawn and can therefore be supplied in an appropriate manner, then
remains between the nozzles and the opening. Moreover, with this
embodiment, air, which is introduced via the gap or annular gap,
can be pre-heated in order to achieve a desired temperature in the
mixer, especially to promote a desired activation of the adhesive
at the surface.
[0073] In one embodiment, tools in the interior of the mixer are
attached to an axle. The nozzles for supplying the adhesive in this
case are arranged in a ring around the axle, in order to supply
adhesive to the fibres in a uniform manner. The fibres or
respectively the curtain consisting of fibres are/is then
preferably transported perpendicular to the axle between the
nozzles and the tools. In dependence upon the diameter of the
mixer, the nozzles are arranged in a ring of one or more rows. With
a correspondingly large diameter, the entire opening of the mixer
is sprayed with adhesive by arranging a second row of nozzles in a
ring shape around the axle.
[0074] In one embodiment of the invention, glass fibres or
synthetic-material fibres are added in addition to the fibres
consisting of solid wood components. These fibres are added
especially in the mixer or immediately in front of the mixer. As a
result, particularly good, board-like, moulded parts can be
manufactured, for example, as an interior lining in a motor
vehicle. Moulded boards of this kind can be used in the automobile
industry, for example, as a hat shelf. In this context, it is
sufficient if the layer system is subjected only to preliminary
pressing. A final pressing need not be carried out.
[0075] The automobile industry does not require moulded parts in a
quantity comparable with the normal, economical production of
fibres on a large industrial scale. It is therefore more economical
to manufacture moulded parts, especially for use in the automobile
industry, together with MDF boards (for the manufacture of panels),
in order to utilise the quantities of fibre on a large industrial
scale. The wood-fibre boards provided for the manufacture of panels
have an upper side and a lower side, which run parallel to one
another and are flat. These boards are a few millimetres thick.
They do not generally contain synthetic-material fibres or glass
fibres, because no special forms, differing from a flat surface
have to be realised.
[0076] In manufacturing moulded parts, sharp edges, for example, as
specified in the German specialist periodical HK 3/88, page 278,
are problematic. Sharp edges are susceptible to damage. Problems of
this kind can be avoided or significantly reduced by reinforcement
with glass fibres or synthetic-material fibres.
[0077] Moulded parts of the type named are also used in the
furniture industry. Moulded parts of this kind are required, for
example, for doors, which are shaped in a special manner for design
reasons.
[0078] By contrast with boards consisting of fibres, for example,
MDF boards or HDF boards, which are used as the carrier board for
flooring panels, moulded parts, need only be subjected to
preliminary pressing.
[0079] Preliminary pressing is carried out at considerably lower
pressures than the final pressing stage. The preliminary-pressing
pressure may be only one third of the pressure used in the final
pressing stage. The final pressing stage can be carried out at
pressures from 75 to 80 kg/cm.sup.2.
[0080] The proportion of glass fibres and/or synthetic-material
fibres in a moulded part is up to 25% by weight, preferably up to
15% by weight, in order to achieve cost favourable results. At
least 1% by weight, by particular preference, at least 5% by weight
of glass fibres should be used.
[0081] Even regardless of the other named measures and features
according to the invention, separating the wood fibres, which are
used for the manufacture of MDF boards or HDF boards for panels,
especially flooring panels, from the wood fibres for the
manufacture of moulded parts, is particularly economical by
comparison with the prior art.
[0082] In a further embodiment of the invention, solid wood
components provided with adhesive are arranged in a layer--for
example, on a conveyor belt--and charged with hot steam, for
example, by steam shock. Following this, the layer is compressed in
a press--for example, between two circulating belts pressed against
one another--to form a board. The invention is particularly
appropriate for the manufacture of fibre boards.
[0083] In one embodiment, the two main exterior surfaces of the
layer are treated with steam from the outside. This can be carried
out at the same time as a preliminary pressing or compacting of the
layer. For example, the layer of solid wood components are
transported between two rigid plates by means of a steam-permeable
conveyor belt. One plate is disposed below the conveyor belt while
the other plate is disposed above the conveyor belt. The distance
between the two plates can be reduced in the direction of
transport, thereby compressing the layer. The layer is charged with
steam via nozzles disposed in the plates. The moisture in the
surface region of the layer is then increased, especially by at
least 2% by weight, for example, up to 4% by weight, and therefore,
for example, from 7% by weight up to 9 to 11% by weight. The
temperature of the steam is typically 100 to 130.degree. C.
[0084] As a result of the steam treatment, the thermal conductivity
is increased towards the middle of the layer. Overall, this
improves the pressing performance and therefore reduces the
pressing time.
[0085] In one embodiment, the layer or the already-compacted layer
made from solid wood components provided with adhesive can be split
to form, so to speak, two layers one disposed above the other. For
this purpose, the layer is transported, for example, on a conveyor
belt. A strip or rail is arranged above the conveyor belt and
transverse to the conveyor belt, in such a manner that it splits
the layer disposed on the conveyor belt. A steam treatment device,
which is disposed in this manner between the two layers, is
connected to the strip or the rail. The adjacent sides of the two
layers resulting from the splitting, or at least one of these, is
steam treated as described above, in order to allow a more rapid
pressing time. Following this steam treatment, the upper layer is
disposed on the lower layer. The steam treated layers are
transported into the press and compressed here to form a board.
[0086] The steam treatment means that a direct or indirect rapid
heating of the fibres provided with adhesive takes place directly
before and/or during pressing.
[0087] When manufacturing panels for flooring, it is important that
the panels provide hard outer layers and a soft inner layer. As a
result, footfall noise, for example, can advantageously be reduced.
If the surface is steam treated in a targeted manner, and the
interior region remains relatively dry, then the surfaces are
compressed in a targeted manner. The cause for this is, inter alia,
that moist material can be compressed better than dry material. In
this manner, the surface regions are therefore compressed in a
targeted manner. The preliminary steam treatment, also allows a
control of the temperature course. Accordingly, harder outer layers
by comparison with the middle layer can be achieved in an improved
manner.
[0088] Furthermore, additives, which contribute to the hardening,
can be added to the steam. In this manner, the desired hard
surfaces can be improved, if the surfaces are steam treated before
pressing.
[0089] If harder covering layers are present, these may be
relatively thin. Overall, material can therefore be saved with the
same board thickness, because the soft middle layer is manufactured
from comparatively less material.
[0090] The invention will now be described in greater detail with
reference to the following diagrams.
[0091] FIG. 1 shows a section through a belt weighing machine 1
with a mixer 2 located downstream. As indicated by the arrow 3,
dried fibres, which have been manufactured from wood chips, are
supplied to the belt weighing machine 1 via an opening of the
housing 4. A bevel 5 guides the incoming fibres towards the belt of
the belt weighing machine.
[0092] The belt weighing machine registers and controls the
quantity of material, which is transported towards the three
rollers 6. The three rollers 6 are arranged above one another and
offset in such a manner that they enclose an acute angle alpha with
the belt weighing machine 1. The fibres disposed on the belt
weighing machine are conveyed into this acute angle. They pass the
rotating rollers 6. Accordingly, a curtain is formed from the
fibres, which is transported perpendicularly downwards along the
arrow 7 subject to the force of gravity. In this manner, the
curtain enters the mixer 2 between a plurality of nozzles 8 and
tools 9.
[0093] The mixer consists of a tubular housing. The housing is
formed by a double wall 10 and 11. An axle 12, to which the tools 9
are attached, is arranged centrally in the interior of the housing.
A tool 9 encloses a right angle with the axle 12. In each case,
four paddle-like tools 9 are combined in a star shape. Several of
these combined tools are attached at uniform intervals to the axle
12. The front region, into which the curtain consisting of fibres
is introduced, is free from tools. This ensures a sufficiently
large distance between the tools 9 and the nozzles 8. This distance
is required so that the adhesive sprayed from the nozzles 8 does
not strike the tools directly during operation.
[0094] The diameter of the housing of the mixer corresponds to the
width of the opening, through which the curtain consisting of
fibres is introduced into the mixer. The width of the curtain is
adapted to the width of the opening. The nozzles 8 are arranged in
an upper region in a semicircle around the axle 12. As a result, on
the one hand, the curtain is uniformly provided with adhesive and,
on the other hand, the adhesive emerging from the nozzles 8 does
not strike parts of the mixer directly. A gap is provided between
the nozzles 8 and the housing 10, 11, thereby forming a type of
annular gap. Air is drawn in through this annular gap. Means for
heating the air drawn in are not shown in the diagram. Accordingly,
an air-adhesive mixture is formed. The curtain (in other words, a
mat formed predominantly or entirely of fibres) provided with
adhesive is transported by the air stream through the mixer 2
parallel to the axis 12. The axle and also the tools 9 rotate
during transport. At this stage, the adhesive is further mixed with
the fibres. A cooled liquid is passed between the two walls 10 and
11 of the double wall to cause the formation of layer of
condensation water on the interior walls in the interior of the
mixer.
[0095] FIG. 2 shows a front elevation of the mixer parallel to the
axle 12. For reasons of simplicity, only two tools 9 are shown. In
particular, FIG. 2 shows a single-row, semicircular arrangement of
nozzles in the upper region.
[0096] FIG. 3 shows an overview of an embodiment of the method.
[0097] Deciduous or coniferous timber in the form of trunk,
branches and/or wood from saw mills and industrial timber is used
as the starting material. The wood is first cut into wood chips of
approximately 20.times.5 mm in a shredding device 31. These wood
chips can also come directly from the plantation or from saw mills.
The chips can be screened in order to separate excessively small or
excessively large particles. When the chips have been sorted to the
correct size, they can be washed to remove adhering foreign matter,
(especially, sand and earth). This protects and prevents damage to
cutting equipment and other tools in downstream manufacturing and
processing stages.
[0098] Sawdust, which is provided in a silo 32, can advantageously
be re-used.
[0099] The wood components are conveyed by means of conveyor belts
from the shredding device 31 and from the silo 32 to a
funnel-shaped preliminary-steam-treatment container.
[0100] The supply is typically in the proportion of approximately
6:4 (60% by weight wood chips; 40% by weight sawdust). In this
manner, sawdust is also re-used. This allows a further reduction of
costs, because supplies of raw material are saved. The proportion
of wood chips should predominate, because fibres and, at a later
stage, fibre mats can be formed from these wood chips, thereby
providing mechanical stability. A lower limit for the proportion of
sawdust does not therefore need to be observed.
[0101] In the preliminary steam treatment container 33, the wood
components are mixed, subjected to preliminary steam treatment and
heated to 60 to 70.degree. C. The wood components are then supplied
to a boiler 34, for example, by means of a packing screw. In the
boiler 34, the wood components are boiled for approximately 2 to 3
minutes at a pressure of 11 to 16 bar and a temperature from 140 to
180.degree. C. Pressure and temperature are selected in such a
manner that a separation into liquid and solid wood components
takes place.
[0102] The liquid components are separated from the solid
components and fed into a line 35, which is connected to the boiler
34 in a gas-tight manner.
[0103] The solid wood components are supplied to a fibre refining
machine 36 (refiner or defibrator). The fibre refining machine 36
typically comprises a stator and a rotor, which are driven by a
motor. Here, the solid wood components are broken down into
fibres.
[0104] The fibres, which in one embodiment are mixed with sawdust,
are fed pneumatically to a drying tube 37. Reference is made to
fibres in the following paragraphs regardless of the above. In the
drying tube 37, the fibres are dried at 160 to 220.degree. C. The
drying takes place relatively quickly and in a cost favourable
manner, because the liquid wood components have already been
removed.
[0105] From the drying tube, the fibres are transported into
cyclones 38, where the steam is separated. The fibres are removed
from the bottom. The temperature of the fibres is then typically
50.degree. C. Adhesive is then applied mechanically at
comparatively cool temperatures to the fibres in
adhesive-application devices 39. The subsequently glued fibres
typically have a temperature of 35 to 40.degree. C.
[0106] The glued fibres are then transported into one or more
screening devices 40. In one embodiment, the screening devices 40
comprise heating devices to heat the fibres to 55 to 60.degree. C.
Increasing the temperature is advantageous if the boards are to be
pressed, for example, at temperatures of 80.degree. C. The pressing
stage can therefore be accelerated, because the desired temperature
need not be reached exclusively by means of the heated press.
Shorter pressing times lead to increased production capacity or
smaller procurement costs for the presses with circulating belts,
because these belts can then be shorter. The space requirement for
presses of this kind is smaller, which also helps to reduce
costs.
[0107] The pre-glued fibres are then supplied to one or more
separating devices 41. From the separating devices 41, the
pre-glued fibres are transported to a spreading station 42. The
spreading station 42 places the pre-glued fibres on a conveyor
belt. The conveyor belt transports the fibres to a preliminary
press 44. Here, the fibres are subjected to preliminary pressing
being compressed in this manner. The preliminary press comprises
circulating belts, between which the fibres are passed and
therefore compressed. Following this, the fibres pass through a
moulding tract 45, which comprises various devices, which ensure
that the fibres are present in the desired form. In one embodiment,
the moulding tract leads towards a steam treatment device 46. Here,
the fibres are treated with steam from above and/or below. The
fibres can be split parallel to the conveyor belt so that they can
be steam-treated in the "interior".
[0108] Finally, the fibres are transported to the main press 47,
which consists of two circulating steel belts pressed one against
the other. Pressing takes place here, for example, at 80.degree.
C.
[0109] The boards are then sawn by means of a sawing device 48 and
transported to a holding device 49. In the holding device, the
boards are held in such a manner that they do not touch. The boards
are cooled in this manner.
[0110] The separated liquid components, which are supplied to the
line 35, are cooled within the gas-tight sealed system. When these
liquid components have been sufficiently cooled, they are either
disposed of or supplied to the adhesive-application device 39.
[0111] Following this, the boards are further processed, for
example, to form panels. The boards may then, for example, be
coated with papers and the layer system supplied to a press. In the
press, the layer system is compressed at temperatures above
150.degree. C., for example at temperatures between 180.degree. C.
and 230.degree. C. The resins used then harden. The board is
further sawn and provided with connecting elements by milling. The
panels can be used as a covering for walls or floors. If they are
used as a floor covering, the panels are provided on the upper,
decorated side with an abrasion-resistant, transparent layer.
* * * * *