Note: Descriptions are shown in the official language in which they were submitted.
CA 02416817 2002-12-06
1147-17
1
Mechanically Glued Board of Wood Material
The invention relates to a method of manufacture as well as associated
apparatus for a board made of fibres or wood chips, as well as a board
produced according to the method. The invention relates in particular to
MDF- or HDF- or chip-boards.
A typical known method of production far the manufacture of a board of
the kind stated in the introduction is performed as follows. Boiled wood
shavings for the production of the board made of fibres are first fed to a
so-called refiner. In the-refiner the wood shavings are reduced to fibres
and in fact under the application of heat and pressure with the aid of
milling discs. From the refiner the fibres are extracted using steam and
conducted through a pipe known as a '°Blue-Line". i:n this arrangement
the
steam pressure amounts to about 10 bar. The temperature lies a.t about
150 to 160°. Glue is added in to the "Blue-Iine" . Following the
addition of
the glue the "Blue-line" broadens out. Turbulence is caused by the
broadening. The glue mixes with the fibres. The pr oportion of the glue is
about 22 % by weight in relation to the fibres.
The "Blue-line" opens out into the middle of a drying tube. The drying
tube has a diameter of e.g. 2.60 m. Air is blown through the drying tube
at a temperature of 160°C, up 220 to 240°C maximum. The moisture
content is reduced in the drying tube from I00% to 8 to I1 %.
In particular in the drying tube the glue is e:~posed in a unwanted manner
to the effect of heat. From above about 80° glue is adversely affected
or
activated. Activated glue is no longer capable of use for the subsequent
treatment step, in which the glued fibres are pressed to form the board.
_ . 30
CA 02416817 2002-12-06
2
IO
The active part of the glue is reduced by the above-mentioned state of the
art. Of the original 22% by weight only around 1 to 8% by weight is still
capable of use in the stated state of the art, when the fibre-glue rr~ixture
leaves the drying tube.
In HDF-, MDF- boards and also in chipboards a glue based on a urea
formaldehyde resin x, currently used. 'Where boards are made for
flooring, melanin is added to the glue. This aims to prevent the swelling
which can arise as a result of damp.
The problem to solve is therefore that some of the glue is lost to the
actual process step as a result of the effect of heat. A drawback is also
that substantially more glue must be added to the fibres or the chi~as than
is necessary in order to press the fibres or the chips in a process ~rith the
I5 application of heat and thereby to obtain the desired result, namely to
produce MDF-boards. Currently an MDF board has around 60 kg of glue
per m3.
It is the aim of the invention to provide a board having a lower proportion
20 of glue in comparison with the state of the art.
The aim of the invention is met by a method having the features of the
main claim as well as by. equipment for carrying out the method and
having the features of the auxiliary claim. The result is a board having
25 the features of the further auxiliary claim. Preferred embodiments are
revealed by the subsidiary claims.
To solve the problerr~ of the invention the fibres or chips are in particular
first dried and then. glue gs mixed with the dried fibres or chips at
- 30 temperatures which lie substantially below the drying temperatures and in
fact in particular be:low I00°C. In this way one avoids the glove being
CA 02416817 2002-12-06
3
exposed in an unwanted manner to the relatively high temperatures ,which
arise during drying.
Furthermore the advantage is achieved that in the drier or drying tube
only water, but no chemicals are dried. Environmental advantagE;s are
obtained from this as the drying air is not disadvantageously loaded with
vapours, which in the state of the art originate from the glue.
The fibres or chips which are dried are preferably not coated with glue. -
Glue "disturbs" the drying process. Therefore in the drier, in comparison
with the state of the art, substantial quantities of energy are also saved,
which otherwise must be introduced for the drying. significant advantages
in cost are the conseqL~ence.
By the gluing proces:> according to the invention, in the field of MDF
boards the quantity of the glue required is reduced. A reduction to 45 to
55 kg per m3 of board is achieved. A typical value lies at 50 to 52 kg per
m3 of board.
An important quantit~~ for obtaining the appropriate gluing of fibres or
chips is the "correct" ratio of fibres or chips to glue. According to the
invention, therefore, i:n one embodiment of the method the dried fibres or
chips are fed to a weighing conveyor. On the weighing conveyor the
fibres or chips on the one hand are transported by means of a moving
conveyor belt and on the other hand they are weighed. In this way
information is obtained on what quantity of glue needs to be added to the
fibres in the subsequent step.
The fibres or chips which are supplied are carried by the ~w~:ighing
conveyor to the next device. Possible variations in weight of these. fibres
which are so fed are detected during transport, registered and stored in
CA 02416817 2002-12-06
4
one embodiment. This data is processed and serves as setting magnitudes
for the subsequent gluing step. In one embodiment this regulation also
takes into account the travelling time of the material which passes
between the point of measurement and the moment of reaching the
subsequent equipment, such as for example drawing-in rollers. I:n this
way it is ensured that the alteration in the drawing-in speed also follows
the actual variation in weight.
By alteration of the drawing-in speed a constant quantity of material is
supplied to the subsequent devices. The determination of the weight of the
fibres or the chips can take place in fine steps and makes possible a
uniform feed of the fibres or the chips with an accuracy of, for example,
~ 1%.
i5 , it is not easy to provide fibres with sufficient glue, as fibres are
inclined
to bunch together Like cotton wool. It is then difficult to distribute the
glue uniformly on tree fibres. Therefore, in one embodiment of the
invention the gluing takes place in a mixer, in which the glue and fibres
are mixed together. The use of the mixer offers comparable advantages in
the case of chips.
In one embodiment of the invention the mixer has means for cooling its
housing. For this purpose, in one particularly simple embodiment, a
housing which is at least partially double-walled is provided, for example
a double-walled tube which is part of the housing of the mixer. A cooled
fluid, for example cooled water, is conducted through the double-wailed
housing in order to cool the mixer, or rather its walls. A Layer of
condensed water is intended to arise on the walls inside as a result of the
cooling. The cooling is designed accordingly. The Layer of condensed
-- 30 water has the result that glued as well as unglued chips do not
i°ernain
adhering to the walls and block the mixer.
CA 02416817 2002-12-06
In one embodiment of the invention, after the drying of the fibres they are
spread out flat and so a kind of curtain is formed of the fibres. Glue is
subsequently added and in particular sprayed onto the curtain. Preferably
an air-glue mixture is sprayed in order to achieve as a uniform as possible
5 distribution of the glue. By the formation of a curtain the result is
achieved that the glue is distributed uniformly. on the fibres in comparison
with the case in which the fibres are present in lumps.
In a further embodiment of the invention the fibres are introduced into the
mixer in the form of a curtain or a mat. The curtain or mat has an air-
glue mixture blown onto ~it through nozzles. 7,he glue is therefore fed to
the curtain through the nozzles. The curtain is subsequently preferably
conducted through the mixer without contact. Adhesion of fibres to the
walls is advantageously avoided by the contactless feed. Contamination
problems and the costs associated with them are thereby reduced.
The glue is blown into the dried fibres together with air, in particular at a
temperature of 40 to '70°C, preferably at a temperature of 55 to
6()°C. In
this way the result is achieved that the glue reaches a dry external skin. It
is therefore activated to a minimum extent. Hereby the result is better
achieved that the subsequent glue-fibre mixture does not remain adhering
to the conveying devices and equipment, for example to the interiors of the
mixer.
In one embodiment of the invention the glue is prepared so that it cures
after a predetermined time. Thus the glue can be set suitably by the
application of heat. furthermore a hardener can be included or added;
curing after e.g. 60 seconds. The preparation of the glue is carried. out in
particular in the mixer, or a hardener together with the glue is added to
the dried fibres immediately before the mixer.
CA 02416817 2002-12-06
6
The advantage is achieved that on the.subsequent pressing of the fibres to
form a board the glue immediately rapidly sets. In this way short press
times can be achieved . In the respective individual case the inst~~nt of
curing is deliberately set by the expert in the art in order to achieve
particularly short press times. This represents a further important
economic advantage over the state of the art, in which these short press
times could not be achieved because of the curing times of the glue which
were needed.
As the glue is exposed to substantially lower temperatures than hitherto,
it is possible to introduce more reactive glues i:n comparison with the state
of the art. Furthermore it is possible to reduce the proportion of
chemicals such as for example formaldehyde. This results in further
environmental advantages .
In one embodiment of the invention the glue is stirred up using heated air
and this air-glue mixture is fed to the dried fibres or chips. The hot air,
which is for example fed to the mixer through a container together with
the glue and the dried fibres, activates the surfaces of the resulting
droplets of glue. In this way adhesion of fibres or chips to subsequent
devices, for example to the walls of the mixer, is appropriately
countered. Otherwise the mixer would need to be cleaned after a very
short time, for example. The production would then have to be halted,
which is a disadvantage. Furthermore unwanted cleaning costs are
correspondingly reduced. These significant economic drawbacks are to be
weighed against drawbacks that the glue is activated a little and they have
to be compared with one another: 13y performing a few experiments the
expert in the art can determine to what extent the surface of the glue can
be activated, in order to arrive at optimum economic results . The
- 30 proportion of activated glue will always be small in comparison with the
state of the art. ,
CA 02416817 2002-12-06
In one embodiment of the invention, after the addition of the glue to the
dried fibres or chips the free surface of the glue is somewhat further
activated by a device suitable for the purpose, in order thereby to
simplify the further treatment steps. After the addition of the glue to the
dried fibres or chips, in particular after leaving the mixer, the fibres or
chips coated with glue are accordingly preferably passed into a rising
tube, which is in particular 10 to 30 m, preferably about 20 m, long. The
diameter of the rising tube is in particular around 1 to 4 metres.
The rising tube is preferably likewise cooled and in its turn then for
example has double walls, in order to allow the passage of a cooling fluid
between the two walls of a double wall. The aim is again the formation of
a layer of condensed water on the inner walls of the rising tube so that the
glue-coated fibres or chips do not remain adhering to the walls.
The glue-coated fibres or chips can be conducted through the rising tube
in a particularly simple contactless manner by a stream of air or gas.
It has been found that ~;he fibres or chips should be conducted through the
rising tube at a speed of at least 25 m/sec, preferably of at least 35 metres
per second. If the s~aeed is lower, fibres or chips remain adhering
significantly to the rising tube despite the above-mentioned measure:.. The
rising tube is thereby unnecessarily rapidly contaminated. When lower
speeds have been provided, the rising tube had to be cleaned already after
8 hours. By setting of an appropriate speed the cycle cari be extended to 7
to 8 days. Therefore the rising tube needs to be cleaned only once a
week
The maximum speed with which the glue-coated fibres or chips are blown
through .- the rising tube depends on the capacity of the following
components and devices. In this connection care must be taken that the
r
CA 02416817 2002-12-06
8
following components or devices must be in a position to handy: the
incoming quantity of fibres or chips. In practice at the present tinge an
upper limit of 40 metres per second could be achieved without difficulty.
Beyond 50 metres per second the following components used up to now
were overloaded. It will be evident that the upper speed Limit can be
increased as soon as following components of higher performance are
available. Basically it is true that higher transport speeds in the oiling
tube are an advantage, as then problems of contamination and resulting
halting of production are correspondingly reduced.
By the provision of the rising tube the result is achieved that the surface
of the glue is somewhat further activated in order to be able to perform
suitably the succeeding processing steps. The length of the rising tube is
therefore matched by the expert in the art to the desired degree of
I5 activation of the glue. In designing the layout the expert will take into
account the transport speed in the rising tube.
Following the addition of glue to the dried fibres or chips, in particular
following the partial activation of the glue in the rising tube the i;ibres,
coated with glue, pass to a cyclone. Here the surface of the glue hays now
been sufficiently activated on the basis of the measures mentioned above,
so that it no longer remains adhering in the cyclone. In the cyclone the
fibres or chips are precipitated out and fed to the next treatment step by
transport means such as a coriveyor belt. The fibres or chips are separated
from the air in the cyclone. The transport means in one embodiment
conduct the fibres or chips to an inspection station: In the inspection
station the fibres are checked for coarse particles. The coarse particles
are automatically sorted out. Coarse particles are for example lumps of
glue. '
CA 02416817 2002-12-06
From the inspection station the fibres or chips are transported further by
means of a conveyor belt to the press and here pressed together to form
the board. The press preferably comprises moving pressing bands,
suitably tempered, which are pressed together. Thus the pressing can take
place continuously. The temperature is matched by the expert to thw glue
currently being used:. The quantity of energy and the resulting
temperatures for the two pressing bands are accordingly chosen
differently in one embodiment, in order thereby to avoid distortion of the
board which is produced. The temperature difference amounts straight
away to 20° at pressing temperatures lying around 200°C.
The nozzles through which the glue is fed to the fibres in one embodiment
of the invention are preferably of conical shape. The glue emerges
through the tips of t:he cones in droplets, so that thereby a uniform
distribution of the glue is advantageously obtained, and thE:refore
improved.
It is of advantage to avoid cleaning operations and a consequent repeated
halting of production, if the glue for example emerging from the ziozzles
does not contact subsequent tools, thus for example the tools present in
the mixer. The glue is accordingly preferably directed straight towards
the fibres or chips for example, therefore for example sprayed.
Furthermore particular attention should then be paid to a sufficient
spacing between nozzles and following tools i.n a mixer. In practic:~ it has
been found that the space between tools in the mixer and the nozzles
should amount to at Least 1 metre, preferably at least 2 metres, when the
glue is sprayed in. horizontally. The fibres are then introduced
perpendicularly at the start of the mixer and transported further in it in a
horizontal direction. The stated firm spacing values naturally relate only
- 30 to one concrete individual example. They are not generally true as it
also
depends on the speed with which the glue emerges from the nozzle;>.
CA 02416817 2002-12-06
If a glue-air mixture is sprayed towards the fibres, preferably at the same
time an air stream is available by which the fibres are in addition blown
through following devices such as a mixer or a rising tube and thereby
transported initially as far as possible without contact. Basically, inatead
5 of air a gas could also be used.
In particular stirring devices are used as tools in a mixer, by which
mixing of the fibres 'vith the glue is achieved.
10 In order to obtain good results, the fibres pass in front of the nozzles in
the form of a curtain. Thereby, in addition to the advantages already
mentioned, one avoids the glue being sprayed into the mixer and tools
there being contaminated. Otherwise the fibres would stick to the tools
and the mixer would be brought to a halt in a very short time and would
have to be cleaned at frequent intervals.
In one embodiment the tools in the mixer are attached to a centrally
mounted spindle and comprise rods extending away in a star pattern, each
merging into a flat portion Like the blade of an oar. Overall a star pattern
is made up for example of four tools. Each adjacent pair of tools make
an included angle of 90°. In relation to the air stream which passes
through the mixer, the oar blades are set at an inclination. This results in
turbulence of the air and thereby a thorough mixing of the fibres or chips
with the glue. A nurr~ber of "stars" formed by tools are attached to the
spindle at uniform svpacings. The fibres or chips are then tranL;ported
through the mixer parallel to the spindle. Quite generally the tools are
therefore arranged in particular so that the air is made turbulent as well
as the fibres or chips. Therefore tools acting as propellers or propeller-
like tools are to be preferred.
3p
A curtain is preferably formed from the fibres as follows.
r
CA 02416817 2002-12-06
1I
The transport medium, for example a conveyor belt or a weighing
conveyor is provided at the end with at least one, and preferably several,
rollers. The fibres are fed through the roller or rollers. The rollers are in
particular pressed against one another. If a gap remains between two
rollers or between the roller and a bounding surface, this basically causes
no harm. In this way tkze result is achieved that a kind of curtain or mat is
formed from the fibres by the rollers. Therefore the curtain shape is
produced by the rollers.
In this arrangement preferably a conveyor belt is used as this achieves a
z
uniform feeding of fibres to the rollers. If a 'weighing conveyor is used,
then in one embodiment the speed of feeding to the rollers is controlled so
that a particularly uniform quantity of fibres is fed to the rollers.
According to the state of the art usually screw conveyors are used for
feeding fibres in the manufacture MDF boards. However fibres generally
leave screw conveyors relatively non-uniformly: A correspondingly non-
uniform curtain formed from the fibres would be the result. A contain of
uniforms thickness a.nd width is of advantage in order to achieve a
uniform distribution of the glue. Furthermore the result is achieved that
the curtain effectively separates the sprayed-in glue from the tools which
follow.
In particular, by using the (pressed together) rollers for producing the
curtain one avoids the fibres being fed in a wad-like or lumpy form. This
would prevent the desired uniform gluing.
In order to be able to process a sufficiently Large quantity of fibres to
form a curtain as well as in order to achieve a particularly uniform
curtain, in one embodiment more than two r~~llers are employed, through
which the fibres are guided to produce a curtain. The rollers are
preferably arranged over one another, offset in such a way that an acute
CA 02416817 2002-12-06
12
angle is included between the rollers and a transport medium, for example
a conveyor belt or a weighing conveyor. In this way sufficient material
can be fed to the transport medium, l.c. for example delivered to the
weighing conveyor, in order to be able to handle uniformly a sufficiently
Large quantity of fibres.
r 10
In practice it has so far been found that four rollers in total are
particularly advantageous in order to produce from the fibres a curtain
which is subsequently mechanically glued.
In one embodiment the opening, through which the curtain made of fibres
is introduced into or ahead of the mixer, preferably corresponds to the
maximum width of the mixer housing, therefore for example the diameter
of the said tube, which simultaneously forms the walls of the mixer. In
this way it is ensured that the whole width in the mixer is covered by the
curtain. Otherwise glue could be sprayed through the remaining gaps at
the sides, past the curtain and into the interior of the mixer, and the
above-mentioned contamination problems would arise.
If the whole width of the mixer were not covered, not only would glue be
sprayed into the mixer, but also heavy peripheral fibres would be carried'
along and form lumps. 'This would adversely affect the quality of the
material. Corresponding production problems and post-treatment of the
material would have to be performed, at substantial cost.
In practice the side walls of the mixer are preferably cooled to 7 to
15°C,
in particular to 10 to 12°C. In this way the result is achieved that a
coating of condensed water is deposited on the walls. Adhesion is
prevented by the layer of condensed water.
CA 02416817 2002-12-06
13
The cited temperatures are also suitable for the formation of a layer of
condensed water on the inside walls within the rising tube.
In a further embodiment of the invention initially wood chips or wood
shavings are broken down into the solid wood component cellulose and
the liquid components lignin and liquid hemicellulose. Lignin and
hemicellulose are separated from the solid components and used as glue,
thus according to the invention mixed with the dried wood fibres or wood
chips. The solid wood components are further processed to form fibres or
14 chips. The liquid components could for example be separated from the
solid components in a so-called agitator. The above-mentioned
components which are obtained lie typically at 20 to 35% by weight
hemicellulose, 45 to 50% by weight cellulose and 20 to 35% by weight
lignin.
In one embodiment wood shavings are first introduced into a plug screw.
From the plug screw the wood shavings pass in a compressed state into a
boiler and here they are boiled at high pressure. The boiler is designed to
handle high pressures. The pressure in the boiler amounts in particular to
at least 12 to 22 bar. According to the state of the ant wood shavings are as
a
rule boiled at pressures of only 8 to 9 bar. As a result of the heated
steam treaiment the solid wood components (cellulose) are separated from
the lignin and hemicellulose, which represent the liquid parts. The
cellulose is present in solid form. The two other components lignin and
hemicellulose are liquid and can basically be used as a glue. The adhesive
force in this use is predominantly achieved by the hemiceIIuIose.
It is true that it is known from the printed publication WO 98137147 to
' separate the lignin and hemicellulose contained in the wood from the solid
,- 30 components and use them subsequently as glue in the manufacture of
MDF boards. A drawback in this process is the occurrence of substantial
CA 02416817 2002-12-06
14
emission, which would have been imposed to a degree on the
surroundings of a production factory. The development of emission could
not be overcome using economically practical measures. According to the
invention the problem of the generation of emission is reduced in that the
liquid components are initially present in the pressure-tight sealed boiler,
from which no parts can escape. After the separation of the liquid
components these are cooled down and are processed further at relatively
low temperatures, in particular being sprayed onto the fibres through
nozzles. The liquid components are therefore substantially cooled down
before they leave the smell-tight sealed system. In this relatively cool
state the development of smells is very slight. The use of lignin and
hemicellulose as glue is therefore made possible in that these components
of a wood material only leave a smell-tight sealed system at low
temperatures, in particular temperatures well below 100°C and are
applied
to the fibres in this cool state. In this way therefore the imposition on the
environment of the development of smells is successfully sufficiently
greatly reduced in an economical manner.
In one embodiment of the invention the liquid components hemicellulose
as well as lignin, obtained in the manner described above, are mixed with
conventional glue. The proportion of hemicellulose as well as lignin in
the glue mixture preferably amounts to no more than 20% by weight. The
mixture furthermore contains in particular a glue based on urea
formaldehyde.
If a glue mixture is used containing more than 20 % by weight of
hemicellulose and lignin, the pressing time (in a backing-up use of the
currently conventionally available synthetic glues) is too long, during
which the glued fibres are pressed to form a board. It is therefore more
economical to mix hemicellulose and lignin with other glues or glue
mixtures. In this way on one hand a saving can be made in conventional
r
CA 02416817 2002-12-06
glue and on the other hand the process is not made too long and thereby
uneconomic because of longer pressing times. The question of what upper
limit is economically appropriate for the proportion of hemicellulose and
lignin naturally depends on the reactivity of the glue, with which the
5 hemicellulose and lignin components are mixed. Accordingly the stated
upper limit of 20% by weight simply represents an indication based on
experience.
Since air among other things is provided for transporting the fibres with
10 the glue through the mixer, the nozzles for feeding in glue are, in one
embodiment of the invention, spaced away from the housing of the mixer.
The nozzles are then present in front of an opening in the housing of the
mixer. A gap or annular gap thereby remains between nozzles and
opening, through which outside air can be drawn in and thereby
15 conveniently introduced. Furthermore in this embodiment the air which is
introduced through the gap or annular gap can be pre-heated in order to
provide a desired temperature in the mixer, in particular an order thereby
to achieve activation of the surface of the glue.
In one embodiment tools are mounted on a spindle inside the mixer. The
nozzles for feeding in the glue are then arranged in a ring around the
spindle, so that in this way the fibres are uniformly coated with glue. The
fibres, or rather the curtain which is made up of fibres, is then .preferably
introduced between nozzles and tools perpendicular to the spindle.
Depending on the diameter of the mixer, nozzles are arranged in a ring in
one or more rows. With a corresponding large diameter the entire opening
of the mixer is sprayed with glue, in that a second row of nozzles is
arranged in a ring around the spindle.
i
In one embodiment of the invention additional glass fibres or- synthetic
resin fibres are added to the fibres made of solid wood components. The
J
CA 02416817 2002-12-06
16
addition takes place in particular in or directly ahead of the mixer. In this
way particularly good board-like shaped bodies can be produced,
provided for example as inside trim in a motor vehicle. Such shaped
boards can be employed in the motor industry for example as hood
linings. It is then sufficient simply to pre-press the laminate system. A
final pressing step does not have lo be performed.
In the motor industry not so many shaped components are required, as
fibres are usually produced economically on a large industrial scale.
Accordingly it is more economical to produce shaped components, which
are used in particular in the motor industry, simultaneously together with
MDF boards (provided for the production of panels, in order thereby to
be able to use the quantities of fibres on a mass-production scale. The
MDF boards provided for the production of panels have an upper face and
a lower face, which run parallel to one another and which are flat. These
boards are a few millimetres thick. As a rule they do not have any
synthetic resin or glass fibres, as no special shapes need to be made,
departing from a flat surface.
In the manufacture of shaped components sharp edges are a problem.
These tend to tear. By the reinforcement with glass fibre or synthetic
resin fibres these problems can be avoided.
Shaped parts of the above-mentioned kind are also used in the furniture
industry. Such shaped components are required for example in doors,
which are specially shaped for design reasons.
Differing from boards made of fibres, therefore for example MDF
boards, which are provided for the production of panels, in the case of
shaped components it is sufficient simply to pre-press them. The pre-
pressing takes place at substantially lower pressures than the actual
CA 02416817 2002-12-06
17
pressing step. The pre-pressing pressure can amount to only 113 of the
pressure used for the actual pressing step. The actual pressing step can be
performed at pressures of 75 to 80 kg/cmZ.
The proportion of glass fibres and/or synthetic resin fibres in a shaped
component amounts to up to 25% by weight, preferably up to I5% .by
weight, in order to achieve cost-favourable results. At least 5% by weight
should be used.
To divert fibres for the manufacture of shaped components from the fibres
used for the manufacture of aVIDF or HDF boards for panels, in particular
for flooring panels, is, independent of the fibres mentioned here
according to the invention, also especially economical in comparison with
the state of the art.
I5
The invention is further . clarified in conjunction with the following
drawings .
Figure 1 shows a section through a weighing conveyor 1 and a following
mixer 2. As indicated by the arrow 3, dried fibres, produced from wood
shavings, are fed to the weighing conveyor 2 through an opening in a
housing 4. A ramp 5 guides the incoming fibres onto the belt of the
weighing conveyor. The weighing . conveyor detects and controls the
quantity of material which is transported tovaards the three rollers 6. The
three rollers 6 are arranged one above another and offset, so that they
make an acute angle cc with the weighing conveyor I. The fibres present
on the weighing conveyor enter this acute angle. They pass through the
rotating rollers 6. In this arrangement a curtain is formed from the fibres,
and as a result of gravity it is transported further vertically downwards
along the path of the arrow 7. The wcurtain thus reaches and enters the
mixer 2 and in fact between a number of nozzles 8 and tools 9.
CA 02416817 2002-12-06
18
The mixer has a tubular housing. The housing is formed by a double wall
and 1I. Mounted centrally inside the housing is a spindle 12 on which
the tools 9 are secured. A tool 9 makes a right angle with the spindle 12.
Four oar-Like tools 9 are combined to form a star. A number of these
5 combined tools are secured on the spindle 12 at uniform spacings. The
forward region, into which the curtain made of fibres is introduced, is
free of tools. Ifs this way the result is achieved that a sufficiently large
space is present between the tools 9 and the nozzles 8. This spacing is
provided so that glue emerging from the nozzles 8 does not strike the
10 tools directly during operation.
The diameter of the housing of the mixer corresponds to the width of the
opening through which the curtain made of fibres is introduced into the
mixer. The width of the curtain is matched to the width of the opening.
The nozzles 8 are arranged in a semicircle around the spindle 12 in an
upper region. In this way the result is achieved that on the one hand the
curtain is uniformly provided with glue and on the other hand the glue
emerging from the nozzles 8 does not strike directly against parts of the
mixer. A spacing is provided between the nozzles $ and the housing I0,
1I, so that a kind of annular gap is formed. Air is drawn in through this
annular gap. Not shown are means for heating the air which is drawn in.
In this way a glue-air mixture is formed. The curtain provided with glue
(in other words a mat formed of fibres) is transported through the mixer.2
by the air stream parallel to the spindle I2. The spindle rotates during the
transport and accordingly so do the tools 9. In this way the glue is further
mixed with the fibres. A cooled fluid is introduced between the two walls
IO and 11 of the double wall, in order to cause a Layer of condensed
water to result inside the mixer on its inside walls.
Shown in Figure 2 is a view of the mixer looking parallel to the spindle
12. For reasons of clarity only two tools 9 are shown. A single-row
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semicircular arrangement of the nozzles in the upper region is clearly
shown in particular in conjunction with Figure 2.
