Note: Descriptions are shown in the official language in which they were submitted.
Z7
APPARATUS FOR THE PRESSING OF MATS OF
PRESSABLE MATERIAL, ESPECIALLY FOR THE PRODUCTION
OF PARTICLE BOARD, AND A METHOD OF OPERATING SAME
My present invention relates to an apparatus for the
compression of mats of pressable material, especially mats of
wood, cellulosic or like materials for the production of
pressed board. The invention also relates to a method of
operating such a press and, more particularly, to improvements
in the parallel compression of pressed board, i.e. the
formation of pressed board with a high degree of regularity
and planarity or parallelity of its surfaces.
In the production of pressed board it is known to
provide platen presses or the like in which a mat of a material
capable of fusion to form the pressed board is compressed
between two planar surfaces, generally forming the bedplate
and headplate of a pla~en press.
Typical of the systems provided for this purpose is
that of my U.S. patent 3,860,831 and the earlier systems
described or referenced in that patent.
113~2~Z7
~89
The term "pressed board" is gen~rally referred to in its
most generic sense to identify hardboard, i.e. material of high
structural strength, low flu~d permeability and excellent surface
characteristics, as well as to less dense and highly porous boards
which may be used as thermal or acoustical insulation, for interior
finishing, or the like. The term is generic to any relatively
rigid generally flat board structure, forn~ed by compression utiliz-
ing both heat and pressure, to bond fibers, chips or dust of wood
or some other material, e.g. a cellulosic material, with intrinsic
10 ~ thermally activatable binder or an added binder, the board being
pressed from a structure which, for convenience, will be defined
as a mat.
The ter~ "mat" is used herein likewise in its most generic
and general sense to refer to a layer of more or less coherently
interrelated particles and the binder.
The aforementioned publications describe how such materials
may be introduced into a platen press and how thP finished board
may be carried away for further processing.
It is known to provide a platen press for the compaction of
particle board mats, i.e. for the production of chi?board,
fiberboard and sawdust board, which comprises a press frame or
support structure, a fixed press plate or bed, a movable press
plate or bed, and a multiplicity of working cylinder arrangements
which are disposed symmetrically with respect to a vertical median
longitudinal plane through the press. The working cylinder arrange-
ments will each be understood to include at least one cyllnder and
at least one piston, either the cylind~r or the piston being con-
nected to the press support or frame while the other of these member~
is connected to the movable press plate.
-- 2 --
113~2~7
~89
Such systems have also been provided here~ofore wlth
a plurality of auxiliary piston-and-cylinder arrangements which
can be used to modify the orientation of the movable press
~ember so as to ensure generally parall,el pressing of the board.
Naturally, control systems can be provided for the hydraulic
piston-and-cylinder arrangements.
The movable and stationary press beds are generally formed
with pressing plates which can be heated, e.g. electrically or by
fluid heating techniques, the movable and/or stationary beds each
including, in addition to the resp~ctive press plate, a plurality
of beams which generally extend transversely of the longitudinal
a~is oE the press and serve as points of attack for the hydraulic
cylinder arrangements.
Naturally, for high quality pressed board, it is desirable
that the compression be of the parallel type. The term "parallel
compression" is used herein to indicate that the upper and lower
faces of the pressed board, at least as the latter emerges from
the press, are as close to parallel to one another as possible.
Since these surfaces are also usually planar, reference may also
be made to plane-paràllel surfaces.
Plane-parallel surfaces of a pressed board indicate that
neither surface has bulges which can be considered as deviations
from planarity, furthermore the parallel requirement specifies
that the board is of uniform thickness throughout its length and
breadth.
Obvlously, for plane parallel compression of the pressed-
-material mat~ it is essential to compensate for any elastic
deformation of the pressing beams, the beds or the pressing
plates.
1~8 3, ~ z,7
A pressing frame, as here
described is intended to include any type of press support
commonly in use. For example, the press support may be a post
structure carrying the bed and upon which the upper member of
the press is mounted, e.g. a headplate, or a row of portal frames
spaced apart in the longitudinal dimension of the press. A system
of the latter type is shown for the platen press of U S. patent
3,8~0,381.
The movable press member or bed can be either the upper or
the lower bed.
The movable press bed is ge~erally lighter than the fixed
press bed and, when the deformation of the press beds is con-
s~dered, is the more readily deformed member.
~ f parallel compression of the mat and the boards is desired
without compensation by the prior-art techniques, ~ne must either
resort to extraordinarily massive press beds, încapable of any
deformation during the pressing operation, or must accept a certain
degree of convex or concave curvature resulting from the distortion
of the movable press bed.
It is possible, following the pressing operation, to remove
the convex or concave curvat~re in the pressed board by expensive
an~ time-consuming shaping, material-removal or like aftertreatments.
The principles here described
are applicable to the single-stage or
single-level platen presses of the type describPd in the afore-
mentioned patent as well as to double-level or two-stage presses
as likewise have been illustrated therein. In the latter case,
1132327
~89
the fixed press bed is the intermediate bed, the upper and lower
plates being movable. me principles are also apDlicable to
multilevel presses in which the press plates between the stages
are movable. In this case, of course, the parallel compression
must be dealt with as a sum so that the individual distortions of
the intervening plates as well as the upper or lower movable plate
can be compensated. Finally, the system described
will be understood to be applicable as well to the compression of
asbestos cement plates or boards and the like.
The prior-art apparatus, represented for example in
German patent document (open application - Offenlegungsschrift~
DE-OS 15 02 042, is shown as a single-level press. In this
apparatus, the working piston-and-cylinder arrangements are
disposed outwardly, as seen in plan view, of the longitudinal
median plane of the press and their respective points of attack
lie inwardly of the spacer bars which are provided between the
press plates to establish the thickness of the pressed board
to be formed in the press.
The auxiliary piston-and-cylinder arrangements, provided
primarily to equalize or compensate for distortion of the movable
press plate, are disposed generally in the region of the longi-
tudinal vertical median plane of the press. These auxiliary
cylinders thus act as compensating cylinder arrangements which
are intended to level the aforementioned deformations of the
movable press member under the control o a control arrangement
or device.
3Z'~
~89
The movable press member, in the operation of the con-
ventional apparatus, is inltially displaced by actuating all or
individual ones of the compensating cylinder arrange~ents downward-
ly until the press plate comes to lie on the mat to be compressed.
During this step, the working cylinders are merely entrained.
The respective pressurizable compartments behind the pistons o these
cylinders are, of course, filled with fluid, e.g. from an accumu-
lator or sto~age vessel, although an ele~ted pressure is not
generated in these compartments during the entrainment phase.
When the press plate contacts the mat, the working cylinders
are actuated so that their pistons apply the full pressure to the
plate and are driven by the full hydraulic pressure in the compression
mode. ~his, of course, forces the upper or movable press plate
downwardly to compact the ma-.
As already implied, the working cylinders are disposcd
relatively far from the spacer bars. As a consequence, upon com-
pression of the mat, depending upon the nature of the material pressed
and the height of the layer forming the mat, the movable press plate
deforms or bulges to a greater or lesser extent together with the
pressing beam.
When the pressing plate of the movable bed engages the
spacer bars, the pressure in the working cylinders increases markedly,
Pressure-sensing devices respond to this pressure increase
and generate a control pulse which cuts o~f the main cylinders and,
in some cases, relieves them. By contrast, the compensating cylinders
generally remain under the working pressure to compensate for the
bulging or deformation of the movable press bed.
1132~7
11689
If the bulge is in the direction of the fixed bed, the
corresponding compensating cylinder is relieved. Conversely, if
the bulge is in the direction opposite the fixed bed, the compen-
sating rylinder may be additionally pressurized. Naturally, the
compensating operati~ns must be determined experimentally for
each type o mat, for each board-producing program, for the varlous
pressure levels and pressing periods operatin~ in the press.
Even with these empirical derivations of the response to
be made by the compensating cylinders, one cannot complet~ly exclude
significant variations resulting from changes in the nature of the
mat or the like. The same applies for the si~nificant variations
in the counterpressure generated in the mat and opposing ad~ance of
the movable press plate during the pressing operation and resulting
from premature hardening of ~he binder or variations in the
moisture level in the particle material of the mat under the effect
of heat from the heatin~ plates.
As a consequence, the response of the movable press plate
to the particular pressing operation cannot always be determined
in advance an~ even when determined in advance, is not necessarily
constant or reproducible.
As a consequence, the control method of the prior art is
extremely complicated and must permit relatively large tolerances.
It is, therefore, practically impossible with the prior-art system
to provide plane parallelity of the pressed boards with extremely
narrow or small tolerances.
~323~7
~8 9
Another disadvantage of ~he prior-art system is that
signlficant moments are generated betr~een the main cylinders and
the spacer bars in the press plates so that the press plates can
impart to the boards a substantially corrugated surface which
must be sanded down or otherwise treated. This is especially the
case when the movable press bed is ma~e relatively light to save
material and hence is especially bendable.
Reference may be had to German patent document (printed
application - Auslegeschrif~ DE-AS 17 03 297 in which si~ilar
problems may arise although spacer bars are avoided and the working
cylinders or main cylinders are provided at the outer edges of the
movable press bed or plate.
Another system, represented by German patent document
(utility model - Gebrauchsmuster) DE - GBM lg 24 142 in which the
main cylinder arrangements are disposed along the edge of the
movable press bed and the press plates are so arranged that these
main cylinders lie directly above the spacer bars. This, however,
precludes a proper compensating operation to cvercome deformation
of the movable press bed or plate.
It is the principal object of the present disclosure to
provide a press, particularly a platen press, for the pressing of
particle-board mats whereby the finished product can be of high
planar parallelity and with limited tolerances, while avoiding
disadvantages of earlier systems as enumerated above.
1~L3;2327
68 ~
It is another object o~ ~is disclosure to provide an
improved method of operating a platen~press so as to eliminate
the drawbacks of the earlier systems described.
Still another object of the presént disclosure is to
provide a press for the purposes described in which a movable
press bed can be given a statically determined position for
each pressing operation so that compensation of the deformation
of ~he press plate can be effected simply and read;ly.
Yet another object of the disclosure is to provide an
improved method of pressing mats to produce pressed board
of high plane parallelity.
These objects and others which will become apparent here-
inafter are attained, in a platen
press for the compaction of particle-board mats which comprises
a fixed plate, a movable plate, main fluid-operated cylinders ef-
fective to generate the pressure required to convert the mat into
pressed board and acting upon the movable plate.
The mat is flanked by spacer
bars which rest upon the fixed plate and the auxiliary cylinders
are formed as bearing cylinders,positioned over the spacer bars,
so as to press the movable plate against these bars and thereby
retain the movable plate against these bars during the subsequent
operation of the main cylinders.
Means is pro-
vided to respond to deformation of the movable plate, such means
_9_
113~3Z7
6~
forming part of the control system for the main cylinders so
that the latter are actuated in re~ponse to deformation to the
movable plate to level such deformation and ensure parallel
compression of the mat.
During this latter operative step, the movable plate acts
as a beam supported at two spaced-apart l~tions of pedestals,
corresponding to the spacer bars against which the beam or platen
is held.
The term "plate" has been used above to refer to the movable
p~aten and thus is utilized in its most general sense to mean
the movable press member which compacts the mat and which can
be heated as described previously. Naturally this movable platen
can include any beams or bed structure to which the cylinders are
connected and an~ plate or the li~e attached to such bed structures
or actual engagement with the mat and the spacer bar. The bed
structure may be formed by anothex plate or by an array of girders,
crossbeams, spars or the li~e. Since the spacer bars are dis-
posed outwardly of the ~ats to flank the latter, the auxiliary or
bearing cylinders likewise are disposed outwardly of the main
cylinders.
The term "cy-linders" as used above and subsequently herein
is intended to refer to fluid-operated ram or jack structureS
which may also be described as piston-and-cylinder arrangements.
In such arrangements, a piston is telescopically slidable in a
cylinder chamber or cylinder proper, being displaced by pres-
surization of a compartment behind the piston, generally with a
liquid medium. While the cylinder prefereably bears upon a
fixed support structure, e.g. a portal frame as described above
and the piston then acts upon the movable press bed, a reverse
--10--
~23~
11689
kinematic constructi~n is also possible whereby the piston is
affixed to the stationary support whi~e the cylinder acts upon
the movable bed.
Thus the system disclosed dlstinguishes from
the state of the art mentioned presiously by utilizing the
auxiliary piston-and-cylinder arrangements as bearing cylinder
units which apply force directly to the mcvable bed in line with
the spacer bars to clamp the spacer bar between the bearing
10 cylinder and the fixed bed of the press, while the control means
for the main cylinders includes the deformation-measuring device
which reeponds to deforma~ion of the movable press bed and con-
trols the main cylinders in response to the measured deformation
to displace the movable bed so as to level the deformat~on and
15 ensure parallel compression.
From elementary statistics, the statically determined
problem in analy~ing the response of beams on two supports is
well know. Correspondingly, a plate of platen which rests upon
two spaced-apart supports and is held thereagainst at its edges,
20 presents a statically determined problem.
Thus, the vress
plate of the movable press bed is initially brought to bear upon
the mat to be compressed, either with the bearing cylinder ar-
rangements or with the main cylinder arrangements or both~
Generally it is more convenient to advance the movable bed
with the bearing cylinders and to simply entrain the working or
main cylinders with the movement of this bed.
Z~327
11689
.
Next, the bearing cylinders forcibly apply the ~ovable bed
to the spacers to form the statically determined structure of a
plate mounted upon the supports in the manner described. In
general this wlll result in a convex deformati~n of the movable
S press bed and its plate,which deformation can be readily measur-
ed and determined.
When reference is made to deformation measurement of the
movable bed it should be understood that the deformation measure-
ment can be made upon the press beams or upon the plate proper
since deformation of the one is followed or produces deformation
of the other.
The operation of the main cylinders is so controlled that this
deformation is compensated and hence a parallel compression is
applied to the mat which is automatically maintained during any
further compression-
In order to exclude the tapering of the pressed board duringthe pressing to one edge, a preferred embodiment of the invention
provides that the auxiliary or bearing cylinders are pivotally
connected to the support and to the movable bed. This, of course,
means that the piston is hinged to either the frame or the movable
bed while the cylinder proper is hinged to the other.
According to another feature, the spacer bars
can have a width such that the bearing force, i.e. the force ap-
plied by the bearing cylinders, is spread by the bars and perma-
nent (plastic or inelastic) deformation of the beds and the re-
spective plates of the press are avoided.
-12-
1~32;3~7
116~
Indeed, German patent document (printed application- Aus-
legeschrift) DE-AS 16 53 187 describes relatively wide spacer
bars, although not in an equivalent relationship to bearing
cylinders or the liXe.
~he movable press bed herein described is advan-
tageously comparatively light and preferably is so designed as
to be elastically deformable but not compressible under the
standard pressing forces which are used. Naturally, this means
that both the beams of the movable bed and the press plate there-
of should be elastically deformable. This guarantees light-
-weight construction of the movable platen and makes the system
more responsive to the control operation described above.
While the deformation measurement can be effected by any
conventional means it is preferred to provide the deformation-
-measuring device as a strain gauge whose strips are mounted
upon the beams or the plates of the movable bed.
-The output of the strain gauge can be used by applying it
to a conventional control circuit to operate the hydraulic system
by techniques well known in the control arts.
The system here described has the advantage that
it utilizes a statically determined position for the press plate
at the beginning of the deformation-compensation operation and
hence also ma~es use of statically determined responses of the
disadvantages described previously. A relatively simple control
system can be provided for this purpose~
.
i~3;~2~
More particularly in accordance with a first aspect of the invention
there is provided a platen press for the compression of a mat to produce a
board, comprising:
a support;
a rigid fixed hed mounted on said support and adapted to receive
said mat;
at least two spacer bars disposed on said fixed bed and flanking sald
mat;
a deformable movable bed ~uxtaposed with said fixed bed;
main cylinder means including a plurality of main piston-and-cylinder
arrangements disposed between said support and said movable bed for displacing
said movable bed to compress said mat against said fixed bed;
auxiliary cylinder means including at least two bearing cylinders
along with said spacer board and disposed between said movable bed and said
support for clamping said movable bed against said spacer bar to effect
deformation of said movable bed; and
control means including a deformation-measuring device responsive
to the deformation of said movable bed for operating said main piston-and-
cylinder arrangements to level deformation of said bed and thereby parallel
compression of said mat.
In accordance with a second aspect of the invention there is provided
a method of operating a platen press for the compression of a particle-board
mat to produce particle board, comprising the steps of:
disposing a particle-board mat between a fixed platen and a
deformable movable platen of said press and flanking said mat with a pair
of spacer bars resting upon said fixed platen;
urging said movable platen along outward edges thereof into bearing
contact with said spacer bars, thereby deforming said movable platen between
said spacer bars in contact with said mat;
measuring the degree of deformation of said movable platen; and
- 14 -
l~Z~7
11689 applying pressure to said movable platen to compress said
mat in response to the measurement to level deformation of said
movable platen and ensure parallel compression of said mat.
Specific embodiments of the invention will now be described
having reference to the accompanying drawings in which :
FIG. 1 is a diagrammatic elevational view of a platen press
according to the invention at the beginning of the press-clos-
ing operation;
FIG. TA is a detail view, drawn to an enlarged scale, 4
the portion IA of FIGo 1;
FIG. 2 is an elevational view of a portion of the press
shown in FIG. 1 upon closing of the press to the statically de-
termined position of the movable press bed on the spacer bars; and
FIG. 3 is a view similar to FIG. 2 but showing the press
in its positlon for parallel pressing.
In the drawing I have shown a single-ievel platen press for
~he compaction of particle-board mats 1 in the manufacture o~
chipboard, fiberboard, asbestos board or the like.
The press comprises a support 2 in the form of a number of
spaced-apart portal frames, only one of which has been illustrated
but others of which can be provided as shown in U.S. patent
3,860,381. A rigid fixed press bed 3 is mounted on this support
and is juxtaposed with a movable press bed 4.
A plurality of worXing cylinder arrangements S are provided
symmetrically with respect to a longitudinal vertical medium
plane 6 thxough the press.
-l~a
~3~327
11689
More particularly, each of the main cylinder-arrangements
5, of which two are provided in each frame, can include a
cylinder proper 5a, a piston 5h axially shiftable in this cyl-
inder Sa and a pedestal Sc, bearing upon the respective beam 4a
to which the press plate 10 of the movable bed 4 is attached.
Similarly, a plurality of symmetrically disposed auxiliary
cylinder arrangements 7 can be provided outwardly of the main
cylinders 5. Two such auxiliary cylinder arrangements, each in-
cludiny a cylinder proper 7a and a piston 7b can be mounted in
each frame.
The hydraulic control for the cylinders 5 is shown at 8 and
can include a hydraulic servomechanical system as described in
SERVOMECHANISM PRACTICE, McGraw-Hill Book Company, New York,
New York, 1960 (pages 390 ff).
Naturally, a retraction system can be provided, if the
cylinders are not double-acting, to raise the movable platan into
the position shown in FIG. 1,
Furthermore, although this cannot be seen from the drawing,
each cylinder 5 or 7 represents a row of corresponding cylinders
disposed one behind the other along the length of the press.
Furthermore, the press plates 9 and 10 can be heated, e.g. by
electrical means of a fluid system.
The press plates 9 and 10 cooperate with spacer bars 11 dis-
posed along the longitudinal edges of the plates 9 and 10. Accord-
ing to the invention, the cylinders 7 serve as bearing cylindersand apply force to the movable bed 4 in axial alignment with the
centerlines 13 of the spacer bars 11.
-15-
1132.3Z~
11689
The control arrangement 8 is provided with an input
from a deformation ~asuring device such as a strain gauge system
14 (pages 343 ~f. of SERVOMECH~IS~1 P~ACTICE) which measures
the deformation of the movable press bed. Pickups for the strain
gauge system 14 have been represented diagrammatically at 16.
From the position shown in FIG. 1, the movable bed 4 is
brought into contact with the mat 1 and then the bearing cylinders
7 are actuated to bring about contact between the bed 4 and the
spacer bars 11 which thereupon support the movable bed in a
statically determined starting position. The strain gauge 14
measures the deformation of the platen (FIG. 2) and provides an
input to the control system 8 to power the main cylinders 5 to
remove the deformation and ensure parallel compression. Further
compressing is effected in parallelity (FIG. 3).
Hinges`or pivots 15 are provided between the cylinders
7 and the support 2 on the one hand and the movable bed 4 and the
width B of the spacer bars 11 is selected so that the app~ica-
tion of the bearing pressure does not cause permanent deforma-
tion of the movable bed.
-16-
