Note : Les descriptions sont présentées dans la langue officielle dans laquelle elles ont été soumises.
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A Method for Manufacturing Thin Boards, in particular
Parquet Laminates
The present invention relates to a method and an installation as
set out in the preamble to Patent Claims 1 and 7, these being
used to produce thin boards from a square timber by cutting and
without the removal of any chips. A method of this kind is used
to produce thin boards for the surface layer of floor-covering
laminates.
The production of thin boards from a square timber by cutting and
without the removal of any chips is already known. It is also
known that when using this method, the thickness of the thin
boards that are produced cannot be predetermined relatively
precisely as compared to the case when such boards are sawn from
preferably dry wood, since when the cutting method is used, the
wood is processed when wet and preferably also when heated, so
that various parameters that apply to the wood as well as
parameters that apply to the machine can affect the thickness of
the board that is produced.
These facts mean that in the case of the complete division of
square timber of a specific thickness from which it is intended
to produce a number of thin boards, the total thickness of which
is equal to the thickness of the square timber, the thickness of
the final board that is left over may not be of the intended
thickness, with the result that it has to be discarded unless
additional steps are taken.
DE 40 26 346 A1 describes a method that solves this problem;
using this method, after the separation of one or a plurality of
thin boards, the thickness of the square timber that remains is
measured and an attempt is then made to so change the setting of
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those machine parameters that are relative to the cutting
thickness that the remaining square timber can be divided as
evenly as possible between the remaining number of thin boards
that are to be produced from it, so that no usable residual board
is left over. The philosophy that underlies this method has as
its objective the division of a square timber into usable thin
boards as completely as possible and without any loss, although
possible deviations in the thickness of the board that are
produced have to be accepted. Within certain limits, this is
acceptable in the case of methods in which, after the drying
process that follows the cutting process, the boards then have to
be reduced to equal thickness because of the dimensional changes
that the wood undergoes. In this method, it is important that the
result obtained from measuring the residual square timber is the
single factor that is considered with respect to the further
division of one or, in the best case, of a specific group from
square timbers, the processing of which was begun under identical
conditions. It is preferred that this method be used only with
cutter machines or a series of a small number of cutter machines,
for example, two machines, in which the thickness of the square
timber is measured once it has passed through one or a small
group of cutter machines, so that it can then be further divided
when it passes through the cutting system once again. When this
method is used, there is, as a rule, sufficient time to reset the
cutter machines as the square timber is returning to the start,
so that the square timber can be re-worked under these new
conditions.
The situation is somewhat different in the case of a longer
series of cutter machines in which the square timber is to be
completely divided into thin boards in one pass. In particular,
when processing relatively short square timbers, as is the case
when manufacturing parquet laminate, on the one hand, the
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processing speed is so high that it is no longer possible to use
the results obtained from measuring the thickness of the residual
square timber at the output of a cutter machine to correct the
settings of the following cutter machines. For this reason, one
follows a different route in the case of such installations, and
this is described in DE 42 44 310 C1.
In order to avoid a residual board that is too small remaining at
the end of the division process, given that the cut thickness
cannot be precisely predicted, and which can lead to handling
difficulties in the plant, it has been proposed that square
starting timber that is of a greater thickness than the combined
thickness of the boards that are to be produced from it be used.
In this way, after a square timber has passed through the
sequence of cutter machines, as a rule a residual board that is
greater than the nominal thickness will be left over. In order to
ensure that this board can also be used, the invention that is
described in DE 42 44 310 C1 makes provision such that a machine
to reduce the thickness of the residual board by removing
material from it is installed after the series of cutter
machines. This processing of the residual board, which does not
conform to the method, is provided to avoid the control problems
that are occasioned by the short throughput time and which are
insoluble in such an installation for the division of a square
timber without any loss.
It has now been shown that, in particular when manufacturing
parquet laminate, that the variations in thickness, brought about
by the product as well as by the machinery, that occur when
dividing square timbers by cutting can lead to difficulties
during subsequent processing if-- as in the case of cut
laminates--thickness processing of the laminates after drying is
as far as possible to be avoided only in the top layer of the
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product, so that this secondary processing alone is used as the
concluding surface processing of the product that is already
glued up.
For this reason, it is the task of the present invention to
ensure that in a method of this kind the laminates or thin boards
that leave the cutter machines are of a highly consistent
thickness.
Proceeding from a prior art as described in DE 40 26 346 A1, this
problem has been solved according to the present invention by the
distinguishing features set out in Patent Claim 1, insofar as a
method is concerned, and by the distinguishing features set out
in Patent Claim 7 for a corresponding installation.
The present invention varies from the former objective, namely,
to convert the residual thickness measured with respect to a
square timber into steps to further divide this square timber.
The principal objective is to determine the exact thickness of
the thin boards that are produced in each cutter machine. Should
the thickness of the boards produced in one cutter machine vary
from the nominal thickness, then, assuming that wood having
identical parameters is processed in one production run, the
parameters that are relevant to thickness and that apply to this
cutter machine--as a rule the distance of the blade from the
supporting surface for the square timber--are so corrected that
when thin boards are separated off from the next square timber,
as far as possible boards that are of the nominal thickness or of
a thickness that is within given tolerances are produced.
Such a method is particularly advantageous if, following a series
of cutter machines that are intended to it divide a square timber
completely in one pass, there is an apparatus, in particular a
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thickness planer, to reduce the thickness of the residual board
that leaves the last machine, and which does this by removing
material from said board. In this case, too, every effort should
be made to obtain a residual board that is thicker than the
nominal thickness of a board that is to be produced so that it is
still possible to process this board in a thickness planer that
removes material from it.
Actually, however, the manner in which this residual square
timber is to be further processed is to be decided by determining
the thickness of the residual square timber prior to the last
cutting process that is incorporated. Should a residual board
that is of a thickness that is less than a specific critical
value be left over from the last cutting process that is used,
there is a danger that such a residual square timber can no
longer be adequately guided and advanced by the cutter machine
during the operation that separates the last board. If, for this
reason, there is at the output of a specific cutter machine a
residual board whose thickness lies between the nominal thickness
of one board and the nominal thickness of a second board, this
board can only be subjected to an additional cutting process if
the thickness of the residual square timber is greater than a
thickness Dx that is governed by the machine. If the thickness of
the residual square timber or residual board is less than Dx,
this residual board must be passed directly to the thickness
planer that is incorporated down the line. If the thickness of
the residual square timber is greater than Dx, but as a rule less
than the thickness D2 of two boards, the residual square timber
will be subjected to an additional cutting process, in which
instance the residual board that results is to be rejected
through an out-gate because its thickness is less than the
nominal thickness of a board that is to be produced. The
occurrence of such a situation should be avoided as far as
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possible although in such a case, it is preferred that a
thickness planer be preceded by a mechanical switch that can
remove residual boards that are not acceptable from the line
process.
While the number of cutter machines in an installation in which a
square timber is meant to be divided completely into thin boards
in one pass does not necessarily have to be equal to the number
of boards that are to be produced from a square timber, it is
preferred that the installation be so configured that at least
one or a plurality of the cutter machines be configured to permit
the passage of a square timber without the separation of a board,
or such that a residual square timber can move past one or a
plurality of cutter machines along a bypass feed path.
The sequence of the cutting process described herein is
preferably incorporated into an overall process sequence in
which, after the cutting process, the cut thin boards are dried
to a specific terminal moisture content and then used as the top
layer for a laminated product, in particular a floor covering, in
which a top layer made up of the laminates is glued under
pressure to sub-layers of a specific thickness, for example, sawn
wood bars, chipboard, or the like. After drying, the side edges
of the laminates can, if necessary, be finished, although it is
preferred that their thickness remain as produced. This
eliminates the need for a thickness processing stage. As
discussed heretofore, the surface of the laminate top layer is
finished on the product that has already been glued up. The
possibility of adjusting the thickness of the laminates by
grinding once they have dried but before any further processing
saves both material and grinding resources.
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It should be remembered that boards of equal thickness do not
always have to be produced in a series of cutter machines. The
method according to the present invention makes provision such
that, in particular when dividing a square timber in one pass
through a series of cutter machines thin boards of different
thickness can be produced in the individual cutter machines. In
this case, it is preferred that the thickest board that is
desired be produced in the last cutter machine or cutter machines
of a series, since this reduces the difficulties associated with
handling the residual square timber in the cutter machine.
It is preferred that the thickness of the laminates produced in
each cutter machine be determined by forming a differential from
thickness measurements of the (residual) square timbers as they
enter and as they leave a cutter machine. Since, in a preferred
embodiment of the process, it is expedient to measure the
residual square timbers in the area of the last of a series of
cutter machine in each instance so as to arrive at a
determination with respect to the way in which they are to be
further processed, it is practical to provide for differential
measurement at least in this area. It can be both problematic and
costly to effect such thickness measurements on the separated
boards themselves since newly produced boards may be considered
for rejection because they are curved and or twisted, with the
result that it cannot always be ensured that the surface of the
board is oriented so as to be precisely perpendicular to the
direction in which the measurement probe acts at the point of
measurement. Orientation machines for the boards are not always
used. In addition, as a rule it is best not to hinder the boards
with respect to their ability to move laterally during separation
and thereafter, so that measuring devices that are intended to
measure the boards at a specific short distance from their outer
edge will not always pick up certain boards. Precise guidance
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devices for the separated boards would require additional
investment, which is not necessary for other reasons.
It is preferred that thickness measurements be made in the area
of the conveyors that are provided for guiding the (residual)
square timbers. It is preferred that thickness measurement
systems that are based on the laser principle be used. It is also
preferred that thickness measurements be made at locations where
the thickness of the container, for example a conveyor belt, is
not included in such measurements. In the case of conveyor belts,
for example, the belt can be made narrower than the width of the
square timber, so that these timbers preferably project beyond
each side of the conveyor belt and that the measurements be made
at such locations; it is preferred that in each instance two
measurements be made at a distance from both side edges of the
material on the conveyor. The measurement point can also be
arranged at a point where the conveyor is interrupted. When a
conveyor belt is used, such a break point can be made in that the
conveyor belt moves away from the material on the belt over
deflector rollers for a short time, and is subsequently reunited
with the material. The transition point from one conveyor to
another can also be used for this purpose.
Additional features of the present invention are described in
greater detail on the basis of the embodiments that are shown
diagrammatically in Figures 1 to 4. These drawings show the
following:
Figure 1: An installation with one cutter machine and square
timber that is circulated through it;
Figure 2: An installation with cutter machines arranged in
series, based on a single pass;
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igure 3: A detail of the conveyor belt in the vicinity of a
thickness measuring device;
Figure 4: An alternative to Figure 3.
The principal component of the system shown in Figure 1, which is
used to produce parquet panels, is the cutter machine 1, through
which a square timber or parquet molding or the residual timber 5
is processed until it has been completely divided. When this is
done, the conveyor path 6 is followed. In addition, the
installation includes a thickness planer 2, a heating tunnel 3,
and two thickness measuring devices 4.0 and 4.1. The thickness of
the parquet molding or of the residual timber 5 is measured prior
to and after the separation of a parquet panel. The actual
thickness of the parquet panels is calculated from the difference
between these measured values; the panels are removed from the
installation at the point numbered 7. The cut thickness setting
of the cutter machine is corrected should the actual thickness
deviate from the nominal thickness D
Should measurements made after the cutter machine 1 show that the
thickness S of the residual timber is greater than or equal to
twice the nominal thickness D of the parquet panel, a further
pass or cutting process is completed. Should the thickness S of
the residual timber be less than 2D but greater than Dx, with Dx
greater than D, the residual timber 5 is returned once again to
the cutter machine 1 and the resulting residual board of
thickness (Dx-D) is rejected. If the thickness S of the residual
timber is smaller than Dx, the residual timber 5 is delivered to
the thickness planer 2 and material is removed from it until it
is of nominal thickness D. The value Dx is selected as a function
of the machine parameters and the type of wood, such that a
residual board of thickness (Dx-D) can still be handled and
processed by the cutting machine 1 without any problems. The
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finished parquet panel leaves the installation at the point
numbered 7.2, and the chips are removed from it at the location
numbered 9. In the event that the thickness S of the residual
timber is exactly equal to D, then one has a parquet panel that
is of the correct dimensions, and this is removed from the
installation at the location numbered 7.1. If measurement reveals
that the thickness S of the residual timber is less than D, the
residual timber is removed at 8 as scrap. Once a parquet molding
has been completely processed, a new piece ls taken from the
heating tunnel 3 into the cutter machine 1, when the required
control signals are also based on the thickness measurement at
4.2. More expediently, there are always several residual timbers
5 in circulation in order that optimal use can be made of the
cutter machine 1.
In the installation that is shown at Figure 2, the parquet panels
are manufactured in a single pass of the parquet molding or
residual timber 5, when n cutter machines and a thickness planer
2 are required to manufacture n + 1 parquet panels from a parquet
molding. Only three cutter machines are shown, the first 1.1, one
optional intermediate stage l.i and the last l.n. The associated
thickness measurement devices are accordingly shown as 4.1, 4.i
and 4.n. An additional thickness measuring devices 4.0 is also
provided, and this is used to determine the thickness of the
parquet molding before it enters the first cutter machine 1.1.
The parquet panels are removed from the installation at 7.1, 7.i,
and 7.n. The last parquet panel 5a is removed from the thickness
planer 2, and this is done regardless of whether the last
thickness S of the residual timber is greater than or of equal
size to D. In the latter case, the thickness is not reduced by
the removal of material. The removal of the chips takes place at
9 and the removal of the residual timbers that are of a thickness
of less than D takes place at 8, in the form of waste. Fresh
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parquet molding is taken from the heating tunnel 3 and moved to
the first cutter machine 1.1. For the remainder, the additional
processing of the residual timbers 5 is effected as a function of
the thickness measurement, and this is done, in principle, as has
already been described in connection with the installation shown
in Figure 1.
Figure 3 shows a cross section perpendicular to the direction of
movement. The parquet molding or residual timber 5 is wider than
the conveyor belt 10, so that thickness measurement can be
effected by the thickness measuring system 4.0, 4.1 that consists
of the sender unit 4a and the receiver unit 4b, at the side of
the conveyor belt 10. The conveyor belt 10, on which parquet
molding or residual timber 5 is moved from right to left (as
indicated by the arrow), is guided over the rollers 11, 12, 13 in
such a way that an area is left in which the receiver unit 4b can
be installed and in which interference-free measurements can be
made.
