CA1262809A - Belt-type particleboard press with flexible upper platen - Google Patents

Abstract

Abstract of the Disclosure A belt-type press for making particleboard has a longitudinal row of transverse frames through which pass upper and lower longitudinally extending press beams extending along and carried on the row of frames flanking respective heated press platens in turn flanking stretches of respective upper and lower belts driven to move a mat of particles to be pressed along the path in a transport direction. The upper beam is pressed down by a plurality of substantially identical hydraulic actuators to compress the mat between the belts with a relatively high pressure in an upstream 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 calibration portion and an upstream compression portion, the latter being elastically deflectable upward relative. Upper and lower vertically engageable abutments operatively engaged between the upstream portions of the upper platen and beam and the frame limit downward displacement of the upstream portions relative to the frame.
In addition at least one abutment operatively 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.

Description

156 ~ ~2~9 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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'' ' '-156 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 ~ Gl iSC/oiVî e, ~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 5:L56 ~6~

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 ~6~
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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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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~2~ Q9 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 PAT 8178-l ~L262~0~33 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.

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Claims (6)

THE EMBODIMENTS OF THE INVENTION IN WHICH AN EXCLUSIVE
PROPERTY OR PRIVILEGE IS CLAIMED ARE DEFINED AS FOLLOWS:

1. A belt-type press for making particleboard, the press comprising, a longitudinal row of transverse frames;
upper and lower vertically spaced and longitudinally extending press beams extending along and carried on the row of frames, the upper beam being at least limitedly vertically movable in the frames and the lower beam being generally stationary therein;
upper and lower vertically spaced and heated press platens carried on the beams, confronting each other, and forming a straight horizontal and longitudinal path;
respective upper and lower belts having confronting parallel stretches lying between the platens and flanking the path, whereby the belts are driven to move a mat of particles to be pressed along the path in a transport direction;
a plurality of substantially identical and upright hydraulic rams engaged between the upper beam and the frames and relatively closely spaced in an upstream compression region of the press and relatively widely spaced in a downstream calibration region of the press;
at least one downstream abutment operatively engageable between the upper beam and platen in the downstream region and the adjacent frames means for hydraulically pressurizing the rams all with the same pressure and thereby compressing the mat between the belts with a relatively high pressure in the upstream compression region of the press and with a relatively low pressure in the downstream calibration region of the press and for operatively engaging the downstream abutment for limiting downward displacement of the upper platen below a predetermined lower position only in the downstream region, whereby the thickness of the finished workpiece as it exits the press is established by the downsteam abutment, the upper platen and beam having a downstream portion in the downstream region and an upstream portion in the upstream region, the upstream portions being elastically deflectable upward relative to the downstream portion; and upper and lower vertically engageable upstream abutments operatively engaged between the upstream portions of the upper platen and beam and the frames for limiting downward displacement of said upstream portions relative to the frames.

2. The particleboard press defined in claim 2 wherein the upper beam has outer longitudinal edges and the abutments of the upstream portion include upper abutments carried thereon and lower abutments carried on the rams.

3. The particleboard press defined in claim 1 wherein the upper beam has outer longitudinal edges and the abutment of the downstream portion is carried on the frame and operatively engageable with the outer upper beam edge.

4. The particleboard press defined in claim 1 wherein at the least some of the abutments are of variable height.

5. The particleboard press defined in claim 1 wherein 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 rams.

6. The particleboard press defined in claim 1 or 4 wherein 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 one or more said abutment of said downstream portion.

Pat 8178-1