Note: Descriptions are shown in the official language in which they were submitted.
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WOOD FIBER INSULATING PANEL
The present invention relates to a dampening or insulating panel or
slab of wood fibers, especially for thermal insulation, with the
terminology also being intended to cover mats.
During the manufacture of fiber panels, a distinction is principly
made between the starting materials of paper, i.e. cellulose, fibers,
mineral fibers, and wood fibers.
At the present time, wood fiber panels are manufactured pursuant
to two fundamentally different processes. These involve on the one
hand the so-called wet process, pursuant to which wood soft fiber
panels and wood hard fiber panels ( HDF) are produced, and on the
other hand a wood fiber dry process, pursuant to which so-called
MDF panels or HDF panels are produced.
Common to the wood fiber panel manufacturing processes is the
production of the wood fibers. This is conventionally effected by first
grinding wood chips to wood fibers with a grinding unit. This refers
to thermal-mechanical treatment, whereby after thermal treatment
a mechanical grinding of the wood chips under pressure and
temperature effect takes place. In a so-called refiner the cooked or
steamed wood chips are conveyed by a screw conveyor to a pair of
grinding disks, and are brought out after the grinding. The
separation of steam and wood fibers is conventionally effected in a
cyclone; due to the thermal-mechanical treatment, the wood fibers
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leave the refiner as a mixture.
Pursuant to the in the meantime classic wet process, the wood
fibers are blended with liquid, normally water, adhesive and the like
to a paste. This paste is introduced into shaping stations,
conventionally with a wet machine, is shaped, and is compressed
and dried in a press. During the manufacture of wood soft fiber
panels, the water is partially pressed out with colander rollers and
the remaining water is evaporated with flow-over or jet dryers. The
presses for the manufacture of wood hard fiber plates has sieve-like
openings for the discharge of steam in at least one of the press
surfaces. In this way, the moisture found in the wet fiber paste can
escape via the surface and the edges. For this purpose, the fiber
material that is to be dried must of course remain for a certain
period of time in the press so that the manufacturing process
becomes time-consuming. The retention time in the dryers used for
the wood soft fiber panel manufacture is very long due to the low
heat transfer into the panels. Due to the addition of liquid, the
requirement for applying a great deal of energy to evaporate out the
liquid, and the long retention time in the drying phase, the wet
manufacturing processes for wood fiber panels are relatively
uneconomical.
For this reason, at least to significantly reduce the time factor and
to provide a continuous panel manufacturing process, the dry
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process was developed. This differs from the wet processes in that
adhesive is added to the fibers and they are dried prior to
introduction for shaping. After the drying, the fibers are spread out
and after shaping are cured or hardened in a press that now no
longer has to have the evaporation openings in the press surface.
The evaporation of the slight residual moisture is in this way
effected via the side edges. The retention time of the fiber material
in the drying press is consequently considerably shorter. Thus, the
production time after the spreading out is significantly reduced.
However, the preliminary drying of the fibers prior to the curing is
still necessary.
A drawback of both of the described processes is the large amount
of energy consumption which is required for the fiber drying, be it in
the dry process after the grinding or in the wet process prior to the
shaping. A further drawback is the unfavorable water and
evaporation condition, especially with the wet process. Due to the
paste-like consistency, there necessarily results with the wet
process a lower limit for the gross or bulk density, below which it
must not drop. Furthermore, there is an upper limit with regard to
the thickness of panels produced by the wet process since the
addition of heat can be effected only via the surfaces of the panels
and therefore after a certain thickness, at least at a reasonable
energy consumption, no complete thorough drying is any longer
possible. Due to the limiting conditions the thermal conductivity is
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also limited, in other words, a values z 0.045 W/mK result. With
panels produced according to the dry process the moisture content
must be established very exactly since otherwise the drying process
causes splitting or cracking on the panels. The removal of moisture
can be effected only by evaporation, so that the water found in the
panel is heated by the high temperature and the high pressure to a
temperature that is above the boiling point at atmospheric pressure.
A further drawback of the panels produced by the dry process is the
unfavorable binder distribution that conventionally must be effected
pursuant to blast tube gluing, since otherwise an adequate panel
bonding can no longer be ensured. Furthermore, with both
processes only water soluble binders can be used.
Due to the described limits of lower gross density and maximum
thickness on the one hand, as well as the lower limit of the thermal
conductivity on the other hand, the wood fiber panels manufactured
pursuant to the described and previously realized processes are in
a known manner compact or dense panels for interior construction,
furniture construction, mold construction and the like. The
heretofore known panels are not suitable for use as a thermal
insulating element.
Starting from this state of the art, it is an object of the present
invention to provide a wood fiber panel that with respect to the
perimeters energy consumption, water consumption and timing is
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economical to produce, with the density of the panel and the
resulting technical properties such as thermal insulation, resistance
to pressure and the like being adapted to be established very
accurately. The wood fiber panels are also to be able to be
produced using non water-soluble binders, and are to be usable as
insulating panels.
As a technical realization of this object, the present invention
proposes a wood fiber insulating panel containing wood fibers mixed
at least with a binder, wherein the wood fiber mixture is introduced
to a shaping station where they are shaped relative to width and
weight per unit area, wherein after activation of the binder the wood
fiber mixture is molded in thickness to form a panel and is hardened
or cured, and wherein the panel has a bulk or gross density of 1 150
kg/m3 at a thermal conductivity of s 0.045 W/(m x K).
The inventive wood fiber insulating panel falls below all gross
density limits known up to now for wood fiber panels while at the
same time significantly reducing the thermal conductivity, so that it
can be outstandingly used as a thermal insulating element. The use
of the term "panel" in conjunction with the invention does not
preclude the wood fiber insulating panel from also having mat
characteristics.
Heretofore known wood fiber panels manufactured pursuant to
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conventional processes have gross densities above 170 kg/m3 and
heat conductivities of about 0.05 to 0.06 W/(m x K). As is known,
compressive stresses are above 85 kN/m2 and the pressure-E-
modulus is above I million N/mZ. Breaking or separation strengths
are above 20 kN/m2.
The inventive wood fiber insulating panel advantageously has a
gross density { 150 kg/m3 at a heat conductivity of ~ 0.045 W/(m x
K). The breaking strength is particularly advantageously ~ 10 kN/m2
and the compressive strength ~ 65 kN/m2, as a result of which, at
adequate breaking strength, the softness required for thermal
insulating eJements results. In a particularly advantageous manner,
the pressure-E-modulus is :5 650,000 N/m2.
The inventive thermal insulating panel can be produced in an
extremely economical manner with slight modification of known
processes, and has excellent thermal insulating properties.
It has been surprisingly established that with the adaptation of other
process steps neither a moistening of fibers to establish a wet
process nor a fiber drying pursuant to the steam separation phase
are required after the refiner process. The fibers as they are
obtained from the refiner, whereby it is self understood that these
fibers are separated from steam, can after being mixed with a binder
be spread, shaped and dried. The water balance is practically
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unaffected since no further moisture has to be supplied. From a
stand point of energy, neither an artificially supplied moisture level
has to be dried, nor does residual moisture contained in the fibers
have to be dried out prior to curing. From the stand point of timing
during the manufacture, considerable advantages result relative to
the wet process, with such advantages being close to those of the
dry process, so that continuous manufacture is possible.
The fact that the fibers are not changed with regard to the moisture
content means, in the context of the present invention, that no
active measures have to be carried out to establish a specific
moisture level. To the extent that the fibers are stored after the
grinding or are otherwise kept available, and hence undergo slight
changes in moisture content, is of no significance for carrying out
the process.
It is advantageously proposed that the binder be mixed in a dry
state with the fibers. In this way, a very good distribution results.
Alternatively, it is also possible to introduce moist binder and to
distribute it. Particularly advantageous from an ecological stand
point is the proposal to use natural or nearly natural binder. The
process can be controlled very exactly, and can be considerably
accelerated if pursuant to an advantageous proposal of the
invention binder is used that can be activated by steam.
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During the shaping process after the spreading of the fiber/binder
mixture, pressings can be effected in order with great exactness to
establish the desired density characteristics.
The activation of the binder is advantageously effected by means of
steam, which flows through spread out fiber material. This flowing-
through ensures a complete binder activation.
With respect to the curing or drying, it is inventively proposed in a
particularly advantageous manner that a drying medium flow though
the spread-out and preshaped fiber material. It is advantageously
proposed that hot air be allowed to flow transverse to the main
surfaces of the preshaped material. A pressing process can
advantageously take place during the flow-through, which serves for
sizing the wood fiber panel.
A simple, economical process is provided with the invention that can
be controlled very exactly with regard to obtaining technological
properties, with insulating panels having densities well below 150
kg/m3, in other words to about 60 kg/m3, being producible with this
method. Furthermore, any desired thickness can be established if
a flow-through drying takes place. The panels can be manufactured
with natural or nearly natural binders such as lignin, dammar resins,
and the like, so that water insoluble binders can also be used.
Thermal conductivities ()) below 0.040 W/mK can be established.
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The resistance to pressure can also be set very high, so that the
panels produced pursuant to the inventive process can also be used
to insulate traversable or otherwise load-carrying regions.
There is furthermore the possibility of adding in during various
method steps additives, in order, for example, to be able to fulfill fire
classification requirements.
In contrast to the conventional known wood fiber panel
manufacturing processes, the inventive process is extremely
economical, enables the manufacture of a completely new type of
panel with respect to thickness, density and technological
properties, and can be varied from an ecological stand point.
The wood fiber panel manufacture pursuant to the process
described differs significantly from heretofore known wood fiber
panels. The present panel can vary greatly with respect to density
and can also have very low densities. Furthermore, very great
thicknesses can be established. The insulating properties can be
established very exactly, as can the resistance to pressure.
Further advantages and features of the invention can be seen from
the following description in conjunction with the drawing. Shown is:
Figure. 1 a flow diagram to explain one exemplary
embodiment of the manufacturing process.
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Wood chips or shavings I are subjected in a manner known per se
to a pulping or grinding process 2, whereby after thermal treatment
a mechanical grinding of the wood chips I under the effect of
pressure and temperature is effected. In the so-called refiner 2, the
wood chips 1 are conveyed to a pair of grinding disks via a screw
conveyor, and after the grinding are brought out. Subsequently, the
steam extraction occurs in the station 3, which is conventionally
effected by a cyclone in which the separation of steam and wood
fibers is effected. The fibers are then stored in a fiber storage
means 4.
It is important to note that neither a fiber drying nor a moistening is
effected. The fibers are stored and further processed, in the state
in which they exit the refiner, without having to undertake measures
for altering or influencing the moisture content.
By means of a conveyor type weigher 5, the required quantities of
wood fibers are picked up, and are conveyed from the fiber storage
means 4 to a mixer 11. At the same time, the binders A, B and C
are conveyed from the supply containers 6, 7 and 8. The quantities
of binders are picked up by conveyor type weighers 9, and if
necessary individual binders can also be further processed, for
example within a pulverizer 10. The indication of the number of
binders and the type of further processing is provided by way of
example only, and can be varied as desired to fit particular needs.
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Further additives can also be mixed in at this location.
Mixing of the refiner-moist wood fibers with the required binders
takes place in the mixer 11.
Spreading and shaping of the material is effected in a spreading
and shaping station 12. Shaping means, among other things, a
formation of side-edges, a uniform spreading out, and possibly a
preliminary pressing.
In a subsequent stage 13, for example an autoclave or steamer, the
activation qf the binder is effected by means of steam, hot air or
other activation media. This expediently occurs by means of flow-
through.
An initial pressing and a thorough drying of the panels or slabs that
are formed takes place in the dryer zone 14. This can be effected,
for example, by means of hot air flow-through, forwhich purpose, for
example, a press can be used at this location that has at least one
of the pressed surfaces in the form of a sieve.
The finish-dried slabs or panels are subsequently formatted or
fabricated in a station 15.
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List of Reference Numerals
1. Wood chips
2. Pulping or grinding/refiner
3. Steam extraction
4. Fiber storage means
5. Conveyor type weigher for wood fibers
6. Binder A
7. Binder B
8. Binder C
9. Conveyor type weighers
10. Pulverizer
11. Mixer
12. Material spreading and shaping
13. Autoclave or steamer
14. Drier zone
15. Slab or panel formatting
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