Note : Les descriptions sont présentées dans la langue officielle dans laquelle elles ont été soumises.
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BELT-TYPE PARTICLEBOARD PRESS WITH FLEXIBLE URPER PL~TEN
SPECIFICATION
Field of the Invention
The present in~ention relates to a belt-type
particleboard press. More part:icularly this invention
concerns such a press which continuously compresses a mat of
modest structural coherency into a rigid panel.
Backqround of the Inven-tion
A belt-type particleboard press has a press frame
constituted as a plurality of frames traversed by upper and
lower beams carrying respective upper and lower press platens
that are normally heated. Endless upper and lower belts have
stretches extending along vertically spaced from each other
between the platens. These belts are driven synchronously to
advance a mat workpiece through the press. A plurality of
substantially identical hydraulic actuators are engaged
between each frame and the upper beam and platen. The number
of actuators per frame increases from the downs~ream end
toward the upstream end. Thus the pressure exerted can be
substantially greater at the upstream end than at the
downstream end. These actuators are upright simple hydra~lic
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rams and are all pressurized at the same pressure. As
~; described in commonly owned~patent 4,468,188, the distribution
of the rams and of the frames establishes the desixed press.iny
. force and press strength in an upstream compression zone and a
downstream calibrati.on zone of the press~
Typically the mat is subjected to considerable heat
and pressure in the upstream cclmpression zone so as to
activate the resin. The pressure is necessary for good heat
transmission between the heatecl platens and the workpiece and
to ensure good mixing of the binder with the fibers, chips, or
other particles in the mat. The downstream region of the
press operates at a lower pressure, so that the effect here is
calculated to impart a predetermined finished thickness to the
panel being pressed. The resistance that the workpiece offers
to compression decreases as it is compressed and heated, in
part since the binder plastifies, so that in the calibration
zone the main effect achieved is stabilization of the
thickness of the compressed panel as the normally
thermosett.ing binder cures.
The problem with these arrangements is that the
incoming workpieces vary within a fair range as regards
density, thickness, and composition. Hence their resistance
to compression and their compressability will vary
correspondingly so that the constant force applied in the
compression zone will overcompress some parts of some
workpieces, thereby damaging fibers, and will not sufficiently
compress other parts, thereby leaving voids.
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Accord.ingly German patent document DÆ-OS 23 43 427
describes an arrangement for dealing with this problem. The
calibration zone is provided with strain gauges that measure
the pressure with which the mat being calibrated resists
compression. A controller compares these de~ected reaction
pressures with desired values so that, for instance, when the
reaction pressure drops to indicate the board is o~erly
compressed, it reduces pressure upstream in the actuators
bearing on the workpiece in the compression zone. Such a
complicated arrangement operates adequately with slowly
varying workpieces, but the feedback nature of its operation
creates a response time too long to compensate out localized
irregularities, and in fact can damage the workpiece in
response to detection of such a localiYed problem.
This applicant also has provided spacers for establishing
the position in which the movable platen is held in the
downstream zone. In addition the movable pla~en of this
system has a compression portion that is at least limitedly
vertically displaceable relative to the downstream calibration
portion. ~he calibration portion is urged into a calibration
position spaced a predetermined vertical distance from the
other platen and the compression portion is urged with a
predetermined generally constant force toward the other platen
while permitting deflection of the compression portion o the
one platen away from the other pla~en against this constant
force and without substantially changing it.
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PAT 8178-1
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Ob,jects of the Invention
It is therefore an object of the present i,nvention to
provide an improved belt type p,articlsboard press.
Another object is the provision of such a belt-type
particleboard press which extends the principles and
effectiveness o~ the above-described prior-art sys~ems.
A further object i5 to provide such a press which
produces xigid particleboard from a nonrigid mat whose size
varies considerably.
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A belt-type press for making particleboard according
to the inVQntiOn has a longitudinal row o~ transverse frames,
upper and lower vertically spaced and longitudinally extending
press beams extending along and carried on the row of frames,
upper and lower vertically spaced and heated press platens
carried on the beams, confronting each other, and forming a
straight horizontal and longitudinal path, and respective
upper and lower belts having confronting parallel stretche~s
lying between the platens and flanking the path~ The belts
are driven to move a mat of particles to be pressed along the
path in a transport direction, The upper beam is at least
limitedly vertically movahle in the frames and the lower beam
is generally ~stationary therein. A plurality of substantially
identical hydraulic actuators engaged between the upper beam
and the frames are pressurized to compress the mat between the
belts with a relatively high pressure in an'upstream
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compression region of the press and with a relatively low
pressure in a downstream compression region of the press. The
upper platen and beam have a downstream portion in the
downstream region and an upstream portion in the upstream
region and the upstream portions according to this invention
are elastically deflectable upward relative to the downstream
portions. Upper and lower vertically engageable abutments
operatively engaged between the upstream portions of the upper
platen and beam and the fxame limit downward displacement of
the upstream portions relative to the frame. In addition at
least one abutment operativeiy engageable between the
downstream portions of the upper beam and platen limits
downward displacement of same below a predetermined lower
position. Thus the thickness of the finished workpiece as it
exits the press is established by the abutment of the
downstream portions.
The invention is based on the discovery that in the
pressure/displacement press curve that has a steep front flank
as the product is initially compressed, a first plateau in the
compression regiont then a falling flank to a second plateau
in the calibration region, the actual position of this first
plateau is not terribly critical. The system of this
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~o~i~ shifts it somewhat downstream but without any
deleterious effect on the workpiece. Simply subjecting the
workpiece in the compression region to a uniform compression
along with the standard heating sufficiently plastifies the
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workpiece for subsequent compression to an accurately
determined thickness in the calibration zone. In other words,
it has been found unnecessary to reduce the workpiece to a
predetermined slze in the compres.sion zone; it need only be
subjected to a predetermined compression force for a
predetermined time. The actual compression will follow
naturally, and against low resistance, once the binder resin
is plastified. No complicated control arrangement is required
to operate the press, and during a normal pressing operation
the upstream abutments do not engage one another.
It is within the scope of this invention to provide
individual pressure sensors on the press frames connected ~o a
common controller. The required ad~ustments are determined by
the controller and executed. According to a feature of this
c~l 1 5 C ~/o S~ /`~_
i~e~'e~ it is also possible to use hydraulic rams hydraulic
rams distributed over the press in accordance with the desired
pressure curve as actuators and to hydraulically pressurized
them all with the same pressure. The pressing force is formed
in the compression region by the reaction force of the
elastically deformable upper beam and of the upper platen
against the elastic deformation and the effective of the
actuators in this compression region.
The upper beam has outer longituainal edges and the
abutments of the upstream portion include upper abutments
carried thereon and lower abutments carried on the rams. In
addition the abutments of the downstream portion are carried
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on the frame and operatively engageab]e with the outer upper
beam edge.
At least some of the abutments are of vclriable
height. For instance they can be of wedge construction with
small servomotors for relatively sliding the wedges. In
addition at least in the calibration region deformations of
the frame, the upper beam, and the upper platen transverse to
the path are compensated out by means of the actuators and/or
by the abutments. Such provision of abutments between the
edges ensures perfect uniformity of thickness all across the
width of the workpiece emerging from the downstream end of the
~_ press. G~ e~
With the system o~ this inv~ ~ the inevitable
variations in the starting workpiece can be rendered
irrelevant to the finished product, without the use of
complicated control equipment and without any lag in
response. So long as the incoming variations do not lie
outside a normal range, the finished workpieces will be
perfect.
Description of the Drawing
The above and other features and advantages will
become more readily apparent from the following, reference
being made to the accompanying draw3n~ in which:
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Fig. 1 is a side view ~ t~e press of this invention;
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Fig. 2 is section taken along line II - II of Fig. 1;
Fig. 3 is a diagram showing the press curve embodying
this invention;
Fig. 4 is a top view of the press embodying this
invention;
Figs. 5 and 6 are sections taken respectively along lines
V -- V and VI -- VI of Fig. 1; F.ig. 6 being viewed from the
other side of the press with res]pect to ~iy. 5; and
Fig. 7 is a side view of a detail of the press.
S~ecific Description
As seen .in Figs. 1, 2, and 4~ a press receives a par~icle
mat M in a direction D from a ma~-forming and prepressing
machine represented by rollers 17 and of ~he type described in
U.S. patents 4,308,227, 4,315,722, 4,341,134, and 4,468,1B8.
The pres~ basically comprises a longitudinal row of
transversely extending frames 1 in which ar~ supported upper
and lower press beams 2 and 4 in turn carrying upper and lower
press platens 3 and 5. Upper and lower belts 6 and 7 flanked
by these platens 3 and 5 define a pressing gap 8 in which the
mat ~ is engaged. At its downstream end the press passes the
pressed mat M to a finishing machine h re represented by
rollers 18. The lower beam 4 and plate 5 are rigid and
s~ationary; ~he upper beam 2 and platen 3 are a~ least
limitedly vertically displaceabl~ and deformable as will be
describ~d b~low. The platens 3 and 5 are heated in the ~anner
well known in the art to plastify the ~inder resin in ~he matO
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PAT 8178-1
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The upper platen 3 and beam 2 are urged downward by a
multiplicity o~ individual actuators, preferably/ hydraulic
piston and cylinder rams 9 braced between the frames 1 and the
upper beam 2. As seen from Figs. 3 and 4, these rams 9 are
spaced both longitudinally (in direction D~ and transversely
more from each other in a downstream calibration zone KA than
in an upstream compression zone KO. RGllers 19 (Figs. 5 and
6) support the confronting stretches of the upper and lower
belts 6 and 7 on the respective platens 3 and 5 so that the
mat M can move through the press while it is being compressed,
which displacement is effected by a motor shown schematically
at 28 (Fig. 1).
Thus a press curve 10 as shown in Fig. 3 is produced
which has rising and falling flanks 11 and 11~, the former
much steeper than the latter, and a flat high-pressure region
12 and a f.at low-pressure region 12~ respectively lying in
the compression and calibration ~ones KO and KA. The
combination of the heat from thQ heated platens 3 and 5 and
the compressive forces activates the binder resin in the mat
M, crea~ing a reaction force that is effective upward on the
upper platen 3 and beam 2.
The spacing of the rams g establishes the shape of the
cur~e 10 and all of these actuators 9 are pressurized at the
same pressure from a pump 25 provided with a pressure-limiting
valve 26 connected to a fluid supply 27, which represents a
substantial simplification of the press. More details about
this ~tyle of compression can be had from my above-cited U.S
patent 4,468,188.
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PAT 8178~1
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It is also possible to control the arrangement by means
of measurements made by strain gauges ~0 connected to the
controller 21.
The upper beam 2 is somewhat elastically deformable with
the respective pla~en 3 as illustrated by the hea~y dot-dash
line at th~ upstream end of the press. This deformation is
limited in the downward direction as shown in Fig. 5 by stops
or abutments 13 carried on outrigger arms 23 mounked a-t the
leading outer edge 16 of the beam 2 and engageable with
adjustable stops or abutments 14 carried on the part of the
rams 9 attached to the respective frame 1 and defining a
vertical displacement S for the upstream end of the beam 2.
As seen in Fig. 7 the stop 14 can be formed of two wedges 14a
and l~b tha-t can be moved differentially by adjusting means 22
to vary the height of this abutmen~ 14. Further such
abutments 13 and 14 can be provided inward of the edges 16 of
the beam 2 as illustrated to the righ~ in Fig. 5.
In use with the rams 9 unpressurized as shown in Fig. 5,
the compressîon portion of the beam 2 is bent up by the
reaction forces in the mat M. In normal use the two abutments
13 and 14 normally do not contact each other, as the reaction
forces in the mat M e~ceed at least at the extreme upstxeam
end of the press the downwardly effective pressure on the beam
2. As a result the region 12 of the cuxve as shown in Fig. 3
in dashed lines in shifted somewhat downstream, which has no
deleterious effect on the finished product. The stops 13 and
14 pu~ a lower limit to the displacement of this
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PAT 8178-l
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flexible portion, so that if a particularly thin portion of
the workpiece enters the system it will not be compressed to a
thickness beneath that desired.
Similarly, the trailing outer edge 16' of the beam 2 is
provided in the calibration zone with an outrigger 24 that can
engage downward against wedge-type stops 15 which establish
the thickness D of the finished mat. These stops 15 are
useful because by the time the heated mat M has reached the
calihration zone it has substantially lost its elasticity and
could easily be compressed excessively.
PAT 8178-1
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