Note: Descriptions are shown in the official language in which they were submitted.
CA 022~4~86 1998-11-27
PATENT
8613/FD-68 1 5
APPARATUS AND METHOD FOR MANUFACTURING CONTINUOUS
LAMINATED WOOD STOCK FOR WOODEN PALLETS
Field of the Invention
This invention relates generally to improved apparatus and method for m~nllf~ctllring on a
continuous basis face l~minated wood stock from wood strips of random length. This
invention also relates generally to wooden pallets fabricated from such l~min~ted stock.
Background ofthe Invention
It has long been known to m~nl1f~cture face-lamin~ted wood stock on a continuousbasis from wood strips of random length by assembling the strips in face-to-facerelationship with heat curable glue between the adjacent faces ofthe strips and feeding the
assembled strips between the confronting, inner, parallel runs of a pair of continuously
moving chains or belts. The inner runs of the chains or belts apply pressure to the opposite
faces of the assembled stock while continuously advancing the stock. Curing of the
adhesive is accelerated by passing the stock between upper and lower radio frequency (RF)
electrodes while the stock is within the confines of the continuous press. Parameters
including the capacity of the RF generator and the speed of the stock are adjusted so that
the adhesive is completely cured when the stock emerges from the continuous press.
One problem with prior art
continuous presses of the kind described above is that arcing or RF energy leakage can
occur between the electrode connected to the RF source and surrounding metallic structure,
such as frame members, drive chains, and so forth. Such arcing or leakage results in RF
energy losses and consequent failure to adequately cure the glue along the glue lines.
Another problem with some prior art continuous presses is that they do not apply sufficient
pressure to the l~minated wood product uniformly along the entire length of the RF curing
stage. As a result, localized separations can occur between adjacent strips. Such
CA 022~4~86 1998-11-27
separations can allow arcing between the RF electrodes and burning of the adhesive
resulting in gaps along the cured glue lines ofthe finished product.
Wooden pallets or skids have long been used as platforms for the shipping and storage of a
wide range of goods. A great variety of pallets are in common use; a typical pallet
5 comprises spaced parallel horizontal top and bottom decks attached to at least two
longituflin~lly extending, transversely spaced apart stringers interposed between the decks.
Loaded pallet units are conveyed by means of fork lifts having tongs that are inserted at
spaced locations between the top and bottom decks of the pallet. Although pallets are
designed to wit~.~t~n~l shock and heavy loads, because of damage due to rough h~ndling
10 they have limited lives and typically are discarded after only several times of reuse.
Because of such turnover, hundreds of millions of wooden pallets are m~mlf~ct~lred each
year con~uming a significant amount of timber. The highly automated process of
m~mlf~cturing wooden pallets itself generates a large amount of scrap lumber which must
be somehow disposed of whether by burning, grinding or otherwise. In any event, such
15 scrap represents an annual waste of many forest acres thus presenting an environmental
issue and adding further to the price of increasingly expensive timber.
Summary of the Invention
An overall object of the present invention is to improve upon prior continuous press
apparatus and methods for forming l~min~ted wood stock. The elements ofthe continuous
20 press of the present invention are so constructed and disposed relative to each other that the
curing RF energy field is isolated from surrounding metallic structure so as to prevent
arcing and other losses of RF energy. In addition, the present invention provides a
continuous press that applies sufficient pressure uniformly across the width of the moving
stock along the entire length of an RF curing zone to prevent localized separation of
25 adjacent strips. In accordance with one specific, exemplary embodiment of the
invention, there is provided an appa~ s for continuously processing a wood product
formed from lengths of wood strips assembled in face-to-face, l~min~ted relationship with
heat curable adhesive applied to adjacent cont~cting faces ofthe strips. The appal~s
includes a continuous press comprising confronting members defining between them an
CA 022~4~86 1998-11-27
elongated press zone ext~nding in a longitll-lin~l direction. The confronting members are
adapted to apply pressure to the wood product in a transverse direction substantially
normal to the faces of the assembled strips while advancing the wood product through the
press zone. The apparatus further includes first and second parallel electrodes coextensive
5 with at least a portion of the press zone, the first and second electrodes being separated by
an interelectrode spacing and defining between them a curing zone. The first electrode is
connectable to a source of RF energy and the second electrode is connectable to ground
potential. To provide the required isolation of the RF field and prevent arcing and other
losses of RF energy, the interelectrode spacing is less than the distance between the first
10 electrode and any adjacent metallic members. In this fashion, the RF field along the entire
length of the curing zone is subst~nti~lly confined between the electrodes.
In accordance with another aspect of the invention, the confronting members of the
continuous press comprise first and second linear arrays of blocks made of electrically
insulative material, each block having a first or front face adapted to engage the wood
15 product, and a second or rear face opposite the first face. Drive elements, preferably in the
form of the links of a steel chain, are coupled to the second faces of the blocks and are
driven so as to move the linear arrays of blocks along the press zone. The depth of the
blocks, that is, the distance between the front and rear faces of the blocks is greater than
the interelectrode spacing to prevent arcing between the first electrode and the steel chain.
20 The blocks are disposed in side-by-side relationship with the sides of adjacent blocks in
close proximity so that uniform pressure is applied across the l~min~ted wood product
along the entire length of the press zone so as to prevent localized separations from
forming between l~min~tions In accordance with another aspect of the present invention,
the recovery of wood waste is provided for by converting scrap wood into environmentally
25 responsible, usable product thereby conserving increasingly scarce timber resources.
Wood product made by a process according to the present invention is furthermore strong,
warp-free and has been found to be particularly advantageous for making pallet "shook",
that is, pallet components such as stringers and deck pieces. High strength pallets made in
accordance with aspects ofthe present invention are therefore better able to with~t~nd the
CA 022~4~86 1998-11-27
rigors of typical use increasing the life of the pallets and thereby further contributing to the
conservation of timber resources.
In accordance with one exemplary embodiment of the invention, there is provided a
wooden pallet having parallel ends, parallel sides, a top deck for receiving a load and a
5 bottom deck parallel with the top deck. The pallet further includes at least two continuous
stringers between the top and bottom decks to m~int~in said decks in spaced relationship,
the stringers e~t~nding longit~ldin~lly between the ends of the pallet and wherein each
stringer is constructed of continuous wood stock assembled from face l~min~ted, glued
wood scrap strips of random length.
10 In accordance with another aspect of the present invention, at least one of the decks
comprises a plurality of parallel, spaced apart boards extçndin~ transversely between the
sides of the pallet and wherein each board is constructed of wood stock assembled from
face l~min~ted glued wood scrap strips of random length.
In accordance with yet another aspect of the present invention, there is provided wooden
15 pallet shook m~nl-f~ctured by a method comprising the steps of assembling nominally
dimensioned scrap lumber strips of random lengths in face-to-face relationship with heat
curable adhesive on adjacent faces ofthe strips to form wood stock having a subst~nti~lly
constant cross section shape along the length of the stock; advancing the wood stock in a
lonEitudin~l direction of travel while applying pressure in a press zone across the opposite
20 outer side faces of the stock along a direction perpendicular to the direction of travel;
subjecting the stock to RF energy applied in an adhesive curing zone extending along at
least a portion of the press zone; and cutting the wood stock so formed into lengths usable
for pallet shook.
Brief Description of the Drawings
25 Further objects, features and advantages of the invention will become evident from the
detailed description below when read in conjunction with the accompanying drawings in
which:
Fig. 1 is a perspective view of a portion of 2x4 l~min~ted wood stock which may be used
to fabricate pallet "shook";
.
CA 022~4~86 1998-11-27
Fig. 2 is a transverse cross section of the wood stock of Fig. l;
Fig. 3 is a perspective view of a first embodiment of a wooden pallet constructed in
accordance with aspects of the present invention;
Fig. 4 is an exploded, perspective view of a second embodiment of a wooden pallet
5 constructed in accordance with aspects of the present invention;
Fig. 5 is a top plan view of a l~min~ted wood stock fabricating apparatus, including a
continuous press, in accordance with the present invention;
Fig. 6 is a transverse cross section of the app~L~s of Fig. 5, as seen along the line 6-6 in
Fig. 5;
10 Fig. 7 is a transverse cross section of a portion of the apparatus of Fig. 5, as seen along the
line 6-6 in Fig. 5;
Fig. 8 is an enlargement, partly in cross section, of a portion of the top plan view of Fig. 5;
Fig. 9 is a side elevation vlew, partly in cross section, of a portion of the rear of one of the
inner linear runs of the continuous press shown in Fig. 5, as seen along the line 9-9 in Fig.
15 7; and
Figs. 10 and 11 are end elevation views, in cross section, of one of the blocks of the
continuous press of the invention, as seen along the lines 10-10 and 11-11, respectively, in
Fig. 9.
Detailed Description of the Preferred Embodiments
20 With reference to Fig. 1, there is shown a lepl~sellLali~e length of a face-l~min~ted wood
product 10 as it would appear both before and after processing by the appal ~LLIS and
method disclosed herein. Basically, the l~min~ted wood product 10 is formed by bonding
together scrap wooden layers or strips 12 with the grain ofthe strips all running in one
direction. The strips 12 are of random lengths cut to uniform, nominally dimensioned
25 thickness and width. By way of example, the face-l~min~ted wood product 10 shown in
Fig. 1 includes five l~min~tions 14, bonded by moisture resistant glue or synthetic resin
along four parallel, longitlldin~lly ext~nding glue lines 16 to form a product of uniform
cross-section including parallel outer side faces 18 and parallel top and bottomsubst~nti~lly planar surfaces 20 and 22, respectively, defined by the co-planar edges of the
CA 022~4~86 1998-11-27
l~min~ted rows of wood strips 12. Five adhesively bonded l~min~tions each measuring
about 11/16 inch thick by 1-5/8 inches wide can be finished to form low-cost yet high-
strength, uniform, warp-free 2x4 stock usable for a variety of industrial and commercial
purposes including the fabrication of low-cost expendable items such as pallets. For
5 example, the 2x4 stock 10 can be used to fabricate pallet stringers. In addition, with
reference to Fig. 2, by sawing the l~min~ted product 10 lengthwise along central saw line
24 perpendicular to the glue lines 16, a pair of approximately lx4 l~min~ted boards 26 and
28 can be produced which can be cut to length for use as pallet deck pieces. As will be
explained below, the wood product 10 fabricated in accordance with the present invention
10 may be made continuously (that is, without interruption in the operation of the apparatus)
and of any length desired by assembling any number of wood strips end-to-end in each row
ofthe l~min~ted stock.
With reference to Fig. 3, there is shown a pallet 300 having parallel ends 302 and parallel
sides 304, a top deck 306 for receiving a load and a bottom deck 308 parallel with the top
15 deck 306. In well known fashion, the top and bottom decks 306 and 308 are secured to
stringers 310 parallel with the sides 304 for m~int~ining the decks in parallel, spaced
relationship. At least two stringers are typically employed; in the example shown in Fig. 3,
three stringers 310 are used. It will be evident that the configuration of the pallet 300
shown in Fig. 3 is an example only. As is well known, pallet configurations can vary
20 widely and all are inten~led to be encompassed within the purview of the invention.
In the embodiment of Fig. 3, the top and bottom decks 306, 308 are made of a plurality of
parallel, transversely exten~ling spaced boards 312 and 314, respectively, made of lumber
having nominal dimensions such as lx4. The stringers 310, however, are fabricated from
the l~min~ted wood product shown in Fig. 1 with the glue lines 316 running parallel with
25 the top and bottom decks. Formed in each stringer 310 is a pair of longitu~lin~lly
extending recesses or cutouts 318 dimensioned and spaced apart longihl~lin~lly to receive
the tongs of a standard fork lift. Pallets constructed using stringers made from the
l~min~ted wood product 10 are strong, resistant to damage and have the advantage of being
formed from scrap wood that might otherwise be discarded.
CA 022~4~86 1998-11-27
Fig. 4 shows another example of a pallet, identified by reference numeral 320, in
accordance with the present invention. Like the pallet 300 of Fig.3, the pallet 320
includes parallel ends 322, parallel sides 324, a top deck 326 for receiving a load and a
bottom deck 328 parallel with the top deck 326. Again, at least two and preferably three
5 continuous stringers 330 between the top and bottom decks m~int~in the decks in spaced
relationship. The stringers 330 may be identical to those of Fig.3. In the embodiment of
Fig. 4, however, the pieces 332 and 334 comprising the top and bottom decks 326 and 328,
respectively, are fabricated of 1x4 l~min~ted boards such as the boards 26 and 28 shown in
Fig. 2 which are produced by sawing the continuous l~min~ted product 10 in half along the
10 central cut line 24. It will thus be seen that all ofthe wooden pallet "shook" or pallet
components, are fabricated of the l~min~ted wood product shown in Figs. 1 and 2 with all
of the advantages thereof, as already explained.
Turning now to Figs. 5-11, there is shown a continuous press 30 into which assembled,
uncured wood product 10 (Fig. 1) is continuously fed from an infeed make-up and glue
15 spreader appa~L~Is (not shown). In the infeed apparatus, the cont~cting faces of adjacent
wood strips 12 are coated with heat curable glue and the glue-coated wood strips are
assembled into the relationship shown in Fig. 1. Heat curable glues of the kind used here
are well known in the art and typically comprise a two part composition including a
suitable catalyst. The continuous press 30 includes a rigid frame 32 comprising horizontal,
20 longitlldin~lly extçnding frame members 34 connected by transverse frame members 36
and supported at an applopfiate height by legs (not shown). Only portions of the frame 32
are shown; the construction of such frames ~Itili7.ing, for example, square and/or
rect~n~ r steel tubing of appropfiate sizes, is well known.
The continuous press 30 further includes a pair of horizontal, endless tractor assemblies 38,
25 40 arranged side-by-side and extçnding longit~1din~lly between a product infeed end 42 and
an outfeed end 44. Each tractor assembly 38, 40 is supported by an electrically insulative
base sheet 46 mounted on the frame 32. The base sheet 46 may comprise a phenolic sheet
having a thickness of, for example, l/2 inch.
Each tractor assembly 38, 40 includes an endless steel drive chain 50 trained about a drive
30 sprocket 52 at the product outfeed end 44 and a tensioning idler sprocket 54 at the product
CA 022~4~86 1998-11-27
infeed end 42 of the press. The drive and idler sprockets 52 and 54 are made of electrically
insulative material such as ultra high molecular weight (UHMW) plastic or the like. Each
drive sprocket 52 is mounted on a shaft 56 rotatably driven by a motor 58. The drive
motor 58 may be powered electrically or hydraulically and may have an associated speed-
5 reducing tran~mi~sion for applying the requisite torque to each drive sprocket 52. Therotational speed and diameter of the counterrotating sprockets 52 determine the rate at
which the wood product 10 is drawn through the press 30 from the infeed end to the
outfeed end. For example, 12 inch diameter drive sprockets 52 driven at about 10 rpm will
advance the product 10 through the press 30 at about 30 feet per minute.
10 Each tensioning idler sprocket 54 at the product infeed end of the continuous press 30 is
mounted on a shaft 60. The shaft 60 is mounted on the free end of a hinged arm 62 whose
other end is attached to a vertical pivot shaft 64 carried by the frame 32. Each idler
sprocket 54 is biased away from the associated drive sprocket 52 by means of a tensioner
66 connected by a coupling 68 to the arm 62 to appl-Jpliately tension the chain 50. The
15 sprockets 54 are adjustable along the hinged arms 62 relative to the frame to permit
transverse alignment of the chains 50 as required. The drive sprockets 52 may be similarly
adjustably mounted. The details of the tensioners 66 and adjustable sprocket mountings are
not shown, since these are expedients well known in the sprocket and chain drivetechnology.
20 Each tractor assembly 38, 40 includes a series of tractor blocks 80 disposed side-by-side in
abutting, or nearly abutting relationship. The tractor blocks 80 are secured to an associated
chain 50 so as to be driven thereby. As best seen in Figs. 7-11, each drive chain 50 is
made up of a series of articulated upper and lower links 82 and 84, respectively, joined by
drive pins 86. Alternate corresponding pairs of upper and lower links 82a, 84a include
25 lugs 88 bent outwardly perpendicular to the links; similarly, the intervening corresponding
upper and lower links 82b, 84b include similarly bent lugs 90. Each link set 82a, 82b, 84a,
84b is associated with one of the tractor blocks 80 (Figs. 8 and 9).
The tractor blocks 80 are fabricated from an electrically insulative, high strength, low
friction coefficient material such as UHMW plastic. Each tractor block 80 has parallel
30 front and rear faces 100 and 102, respectively, parallel top and bottom faces 104, 106, and
. ~ ~
CA 022~4~86 1998-11-27
parallel side faces 108, 110. The dimensions of the tractor blocks 80 may vary depending
on the cross-sectional shape and size of the specific wood product 10 to be fabricated along
with other factors including the need to isolate the RF field within the curing zone from the
steel chain 50. By way of example only, in accordance with one practical form of the
5 invention for processing 2x4 stock having prefinished nominal cross-sectional dimensions
of approximately 1-5/8 x 3-1/2 inches, each block has a width (between side faces 108,
110) of 4 inches, a depth (between front and rear faces 100, 102) of 4 inches and a height
(between top and bottom faces 104, 106) of 3 inches. The rear face 102 of each block 80
has a horizontal channel 112 defined by an inner, vertical wall 114, to provide a recess for
10 the drive chain 50. In accordance with the foregoing example, the çh~nnel may be about 1
inch deep. A set of chain links 82a, 82b, 84a and 84b and their associated lugs 88 and 90
are received within the confines ofthe channel 112 of each block 80. Machine screws 116
attach the opposed upper and lower pairs of lugs 88 to the inner wall 114 of each tractor
block 80; alternate lug pairs 90 are not secured to the blocks so as to permit each block to
15 swing freely away from the lln~tt~çhed lug 90 while travelling around the sprockets 52 and
54. The machine screws 116 are preferably made of an electrically insulative material
such as nylon. It will thus be seen from Figs. 10 and 11, for example, that the steel chain
50 and the front face 110 of each block 80 are separated by about 3 inches of electrically
insulative material.
20 The endless tractor assemblies 38 and 40 include inner, linear arrays or runs 120 and 122,
respectively, of aligned tractor blocks 80 whose front, rear and bottom faces 100, 102, 106
are subst~nti~lly coplanar. The opposed inner, linear runs 120, 122 ofthe pair oftractor
assemblies 38, 40 are parallel and the conr~o~ g~ front faces 100 ofthe blocks 80 along
substantially the entire length ofthe inner linear tractor block runs 120, 122 define between
25 them an elongated press zone 124 of uniform, rect~ng~ r cross-section. The product 10
travels through the press zone 124 in a longihldin~l direction from infeed to outfeed at a
predetermined rate, as described above, during which pressure is applied by the linear
block arrays 120, 122 transversely across the side faces 18 ofthe product 10, that is,
normal to the planes of the glue lines 16. The tractor blocks 80 are supported by and slide
30 with minimllm friction along the phenolic base sheets 46. The tension applied to the drive
CA 022~4~86 1998-11-27
10.
chains 50 by the tensioners 66 helps to further reduce friction between the moving tractor
blocks 80 and the phenolic base sheets 46.
The linear tractor block run 120 of the tractor assembly 38 is backed by a linear guide in
the form of a stationary steel angle 130 having a horizontal flange 132 bolted to the frame
5 32 and a vertical flange 134 having a height approximately equal to that ofthe tractor
blocks 80. The steel angle 130 extends longit~l~in~lly subst~nti~lly the entire length ofthe
inner linear tractor block run 120, the angle being so positioned that the rear faces 102 of
the tractor blocks 80 along the inner run 120 bear against the vertical flange 134 of the
angle. To reduce friction, a sheet 136 of UHMW plastic or like electrically in~ ting low
10 friction material, may be attached to the vertical flange 134 so as to be interposed between
the rear faces 102 of the moving tractor blocks and the stationary vertical flange 134 of the
angle 130. The cont~cting surfaces ofthe blocks 80 and plastic sheet 136 can be lubricated
to further reduce to near zero the coefficient of friction of the relatively moving surfaces.
The inner tractor block run 122 of the tractor assembly 40 is backed by a linear guide in the
15 form of a steel angle 140 identical to and coextensive with the fixed angle 130. The angle
140 comprises a horizontal flange 142 and a vertical flange 144. The horizontal flange 142
is secured along the length ofthe angle 140 to movable frame members 146. Several, for
example, four, actuators in the form of air cylinders 150 are coupled to the movable frame
members 146 by actuator rods 152. The movable angle 140 is disposed so that the rear
20 faces 102 of the tractor blocks 80 along the inner linear tractor block run 122 are engaged
by the vertical flange 144. Again, to reduce friction, a sheet 154 of UHMW plastic or like
low friction electrically insulative material may be interposed between the rear faces 102
of the blocks and the vertical flange 144. A lubricant may be applied to the relatively
movable surfaces along the linear run 122 to further reduce friction. Air introduced into
25 the air cylinder actuators 150 at an applop-iate pressure, for example, 150 psi, causes the
air cylinders 150 to urge the movable angle 140 toward the fixed angle to apply to the
wood product 10 disposed between the conrlon~ g faces 100 ofthe blocks 80 within the
press zone 124 the relatively high transverse pressure required to elimin~te any separation
or gaps between the faces of adjacent l~min~tions of the wood product 10. Further in this
30 connection, the spacing between adjacent blocks 80 along the linear runs 120 and 122 is
CA 022~4~86 1998-11-27
preferably minimi7ed. Thus, adjacent blocks 80 may be disposed in close proximity to
each other, that is, in abutting, or near abutting, relationship with spacings between the side
faces 108, 110 of adjacent blocks being preferably 1/8-inch or less.
As the wood product 10 is advanced by the tractor assemblies 38 and 40 through the press
5 zone 124 defined by the collfio~ g inner linear tractor block runs 120, 122, the product
passes through an adhesive curing zone 160 wherein the curing of the heat curable
adhesive is accelerated. The curing zone 160 is defined by upper and lower parallel,
elongated RF electrodes 162 and 164, respectively, extending longitudinally along at least
a portion ofthe length ofthe press zone 124 and preferably along subst~nti~lly a major
10 portion of that length. In accordance with one practical form of the invention, the length of
the upper and lower RF electrodes 162, 164 is twelve (12) feet while the length of the
linear tractor runs 120, 122 is eighteen (18) feet. These lengths, of course, may be varied
depending on the RF energy applied, the rate at which the stock 10 is advanced by the
tractor assemblies 38, 40, the chemistry and composition ofthe heat curable adhesive, and
15 so forth. These parameters and their adjustment and optimization will be evident to those
skilled in the art.
By way of example, the upper electrode 162 may comprise a l/2-inch thick plate of
minl1m or similarly electrically conductive material, 3 inches wide and, as indicated, 12
feet long. The upper electrode 162 has an inner face 166, an outer face 168, and side edges
20 169. Secured to the outer face 168 of the electrode 162 is a bar 170 of UHMW plastic, or
similar electrically insulative, high-strength material. By way of example, the bar 170 may
have a 3 inch square cross section. Centrally located along the length of the upper
electrode 162 and attached to the outer face 168 thereof is a vertical, electrically
conductive post 172 having an upper end 174 projecting from the top ofthe in~ ting bar
25 170 for connection to an RF generator (not shown). Athin phenolic sheet 175 overlies the
top surface ofthe bar 170; the upper electrode 162, the bar 170 and phenolic sheet 175
comprise an upper electrode assembly 176. The RF generator should be selected to have
an output to heat the glue lines 16 sufficiently so that the glue is substantially completely
cured when the stock emerges from the curing zone. For example, given a residency time
30 of 24 seconds within the curing zone (12 feet at 30 feet per minute) a 15 KW, 50 amp RF
CA 022~4~86 1998-11-27
generator can be used for a product measuring 1-5/8 x 3-1/2 inches with four parallel,
vertically oriented glue lines 16.
The lower electrode 164 may comprise, for example, a l/2-inch thick steel plate, 3 inches
wide and 12 feet long, disposed parallel and coextensive with the upper electrode 162. The
5 lower electrode 164 has an inner face 178 and an outer face 180. The lower electrode is
adjustably clamped along its outer face 180 to a longitlldin~l frame member 182 which
may comprise a 3-inch square steel tube connected to electrical ground potential 184.
The opposed inner faces 166, 178 ofthe upper and lower electrodes 162, 164 define the
curing zone 160 which is preferably positioned vertically so as to be symmetrical about a
10 horizontal, central plane 190 that extends through the tractor blocks 80 midway between
the top and bottom faces 104, 106 thereof and through the central plane of the drive and
idle sprockets 52 and 54 and the chain 50. It thus will be seen that the compressing force
applied by the air cylinders 150 to the wood product 10 through the angles 130 and 140
and the tractor blocks 80 will be applied to the product 10 uniformly and symmetrically
15 about the central plane 190.
The upper electrode assembly 176 is biased downwardly by a plurality of actuators 192
(two of which are shown by way of example) spaced along the length of the bar 170. The
actuators may take the form of air cylinders. The force applied by the air cylinders 192 to
the upper electrode 162 assures that the inner face 166 of the upper electrode is m~int~ined
20 in firm engagement with the top surface 20 of the travelling wood product 10. Each air
cylinder actuator 192 is mounted on an overhead, transverse frame member 194 having
legs 196 secured to the frame 32. Each air cylinder actuator 192 has a piston rod 198
whose lower end is attached to the upper electrode in~ ting bar 170 by means of a clevis
and pin assembly 200. Air at 30 psi, for example, admitted into the air cylinder actuators
25 192 causes the actuators to apply a steady downward pressure on the upper electrode
assembly 176 and wood product 10, that pressure being resisted by the lower, fixed ground
electrode 164. The actuators 192 can be used to raise the upper electrode assembly 176 to
gain access to the press zone for m~inten~nce
It will thus be seen that the present invention provides a continuous press including an RF
30 curing zone that is sufficiently isolated from surrounding metal members to prevent arcing
CA 022~4~86 1998-11-27
and/or RF energy losses. Thus, the interelectrode spacing sepa,~ g the inner faces 166
and 178 ofthe upper and lower electrodes 162, 164 is subst~nti~lly less than the distances
from the upper electrode edges 169 to the closest surrounding metallic structure. The
electrically insulative sprockets 52 and 54 isolate the steel chain 50 from the metal frame
5 32, and by minimi7.ing the spacings between adjacent blocks 80, leakage of RF energy
from the upper electrode 162 to the chain 50 is further inhibited. In addition, the product
10 moves within press and curing zones that are preferably symmetrically positioned about
the horizontal central plane 190. Such positioning in combination with the application of
sufficient pressure to the product through the closely spaced blocks 80, prevents separation
10 ofthe l~min~tions as the product is being processed.
While the present invention has been described with reference to particular illustrative
embodiments, the invention is not intended to be restricted to those embodiments but only
by the appended claims. It will be appreciated that those skilled in the art can change or
modify the described embodiments, or substitute equivalents for the various elements
15 described and shown, without departing from the scope and spirit of the invention.
~ .
