Note : Les descriptions sont présentées dans la langue officielle dans laquelle elles ont été soumises.
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Background of the Invention
The field is veneer drying ancl handling. More particu-
larly, the inventive subject matter relates to a contact drying
process for veneer and several material handling devices.
In the manufacture of plywood panels, dried veneer sheets
- are utilized. The veneer sheets are peeled from a log and
then clipped to size before being dried to a predetermined
moisture content suitable for adhesive bondingO The desirable
dry veneer characteristics for adhesive application and manufac-
ture into plywood are: a moisture content that is uniform
and consistently within a predetermined narrow range; the veneer ~ ;
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should have smooth surfaces for adhesive application and material
handling; the surfaces of the dry veneer should be free from
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extractives and residues; the veneer sheets should be dimensionally ~ ?~
~ stàble; and the veneer sheets should have a uniform thickness.
- Conventional veneer drying systems presently used in plywood
or veneer manufacturing plants are typica~ly long continuous
` hot-air dryers. The wet veneer sheets, having a green moisture
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~ - content of anywhere from 30 to 250%, are conveyed longitudinally
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20 through a hot-air dryer. Hot air impinges upon the surface ~ ~
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of the veneer as it passes through the dryer, transferring
heat to the veneer sheet thereby drying the veneer and generally
reducing its moisture content to a desired range of from 0-10%
for softwoods and from 5-20% for hardwoods.
Owing to the variability of the moisture content of
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incoming wet veneer, thermal stresses, and resulting shrinkage
that occurs during the typical drying process, many o the
above-mentioned desirable characteristics are not consistently
obtain~d. For example, conventionally dried veneer usually
has a range of moisture contents within the resulting dried
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veneer and a certain percentage of veneer that passes through
- the dryer must be redried in order to reduce the moisture
content to the finally desired level. In addition, certain
areas within a sheet of veneer are susceptible to over-drying,
which also is undesirable in that in the over-dried areas,
that is bone dry, additional adhesive is required to result
in good adhesive bonding. Typically, the veneer that exits
from a conventional dryer is oftentimes wavy since it is
unrestrained during drying and, therefore, presents material
handling problems which can result in additional wood losses
subsequently in the plywood manufacturing process. Typicallyl
shrinkage in the veneer will occur in the tangential direction,
that is tangential to the annual rings of the log which is
on the order of from 5 to 10% of the initial veneer dimensions.
Of course, it will be appreciated by those skilled in the
art that if this loss could be reduced, then the typical
first clipped size could be reduced, thereby conserving valuable
wood.
Additional wood loss occurs in conventional drying pro
cesses due to the nonuniform composition of conventionally
i dried veneer. If there is a great deal of redrying that
` must be done due to nonuniform drying, then typical losses
during the redrying process can be on the order of rom 3
to 8% of veneer primarily due to its material handling losses.
Additionally, it has been determined that further processing
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damage can result in an additional 3 to 7% wood loss from
s~ch areas as binding in the adheslve spreaders, uneven edges
catching in various downstream mechanical processes, and
the like.
Not only is there a great deal of wood loss within conven-
tional drying processes but there is also the inherent problem
stemming from the nonuniform drying characteristics due to
the use of impinging hot air on unrestrained veneer. This
results primarily from the nonuniform drying rates within
the wood itself due to its initial nonuniform moisture content.
This results in quantities of veneer exiting a veneer dryer
being both overdried and underdried, which in turn results
in redrying with its losses, other downstream problems such ~;
as "blows" and gluing problems stemming~from "dryout" and
"undercure." Dryout is that condition where the veneer is
bone dry and, among other problems, allows the adhesive to
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penetrate the veneer more than desirable and during pressing
of the plywood panels, the adhesive will not bond properly.
- Undercure is that condition where inadequate adhesive penetra-
tion occurs at the surface of t~e veneer and, consequently,
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~ adhesive requires a longer time within the panel press to ~
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cure. Blows are most severe and result where underdried
wet veneer is placed in a hot press and excessive vapor is
` created under pressure causing separation or delamination
of the pliesO Of coursel these typical causes of delamination
are well known to those skilled in the art and are known ~; ;
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to be caused by the nonuniform moisture contents within the
conventionally dried veneers. The most optimum moisture
~ content range in a sheet of dried veneer is typically from
; 30 1 to 5% and preferably thé content will be substantially
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uniform within the range. By having a uniform, narrow range,
adhesive penetration into the surfàce of the dried veneer
is also uniform and then, when the laid-up plies are pressed
into the panel, uniform curing of the adhesive will occur.
As previously mentioned, however~ such a uniform moisture
content within a narrow range is nearly impossible in conven-
tional veneer drying processes due to the substantial variability
in initial moisture content within the green veneer sheets.
In some veneer the moisture content may range from 30 to
150% within the same sheet. Such sheets may be comprised
in part of heartwood and in part of sapwood, thereby causing
the wide variation.
With existing conventional dryers and redryers, a sub-
stantial amount of energy is required per unit of dried veneer
and in terms of steam usage, a typical range would be from
2,100 to 3,000 pounds of steam per hour per 1,000 square
feet of dried veneerO Electrical energy requirements may
vary typically from 520 to 1,500 hp. Of course, it will
be recognized that, with today's high energy costs, these
energy requirements represent a significant cost element
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in drying veneer. In addition, with the typical 10 to 30
redry rate, an additional amount of energy is required.
A significant amount of the energy going into the drying
system is wasted in that the heat transfer characteristics
of impinging hot air onto veneer sheets is extremely inefficient,
and thus a significant amount of energy is required to reduce
the moisture content to acceptable levels. As the thickness
of the veneer to be dried-increases, as well as the average
initial moisture content, even greater amounts of energy
are required per unit of dried veneer to achieve the desired
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final moisture content. Of course, it is well known that
within existing commercially available veneer dryers, the
veneer which is thick and has a high moisture content is
left in the dryer for a longer time, simply by reducing the
speed with which it travels through the dryer. As pointed
out above, as the hot air impinges on the veneer for longer
time periods, the quantity of overdried veneer increases.
It is also a recognized problem that with conventional
dryers the traveling veneer, usually supported on wire cables
or rollers has a tendency to catch on internal parts causing
machine stoppages requiring an operator to physically open
the dryer and remove the accumulation of veneer~ This results
in a loss of valua~e veneer in addition to slowing down
the dryer line and causing other problems. This is, in part,
caused by the severe strains producing waviness due to the
high temperatures within the dryer. Additionally, if veneer
sheets are allowed to remain stationary within the dryer,
they can get so hot that ignition can occur causing fires
which, of course, represent a safety hazard to persons and
20 property. These just-mentioned operating problems are inherent
in most conventional veneer dryers and are dealt with simply
by expending the cost to solve the problem when it arises.
Another aspect of conventional veneer drying is the
reduced capacity of the primary dryer caused by a requirement
to redry 10 to 30% of the veneer. Redrying takes the capacity
of the primary dryer to accommodate the time for redrying -
the partially dried veneer.
Yet a further problem with conventional veneer dryers,
one that is of increasing importance, is the emmission of
so-called "blue haze." Blue haze is essentially a vapor
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containing particulate matter that is generated from the
drying process consisting in part of hydrocarbons in particulate
form. Most conventional dryers that merely exhaust their
vapors into the atmosphere without treatment do not meet
minimum environmental standards now required in most states.
There are various control means for reducing the blue haze,
but they are quite expensive and represent an added capital
cost to the veneer drying process and, in addition, the collected
residuals must be disposed of, representing yet another additional
cost. It would thus be desirable to have a veneer dryin~
process that reduces or eliminates the generation of the
blue haze vapor.
The process for drying veneer employed in the present
invention is generally known; however, it has never been
developed as a primary drying process. The general process
is drying veneer through the use of heated metal plates that
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are positioned in intimate contact with the wet veneer sheets
with a pressure then applied to the veneer while drying takes
place to the final uniform moisture content. Past research
efforts in contact drying have resulted in published data
on the subject, but there is nothing in the prior art that
~- discloses a commercially usable contact drying system that
- consistently provides uniformly dried veneer and that reduces
or eliminates the above- mentioned problems usually present
in today's commercially available impinging hot-air dryers.
It is known to use conventional hot presses with flat
heated plates for the purpose of flattening and redrying
hardwood veneers prior to their being utilized in hardwood
plywood manufacture. These hot presses are of a conventional
design and simply accept a number of thin sheets of hardwood
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~neer for the application of heat ~nd pressure for a time
eriod to flatten and redry the already substantially dried
h2rd~00d veneer. Such a typical hot press would not be commer-
c ally usable for the primary drying of substantial quantities
o~ green veneer or partially dried veneer for use in commodity-
t~pe plywood, nor would such a press be useful for drying
slngle sheets of high-value, thin hardwood veneer.
As noted above, the veneer produced by a commercial
dryer should have a uniform moisture content, be substantially
flat, have a uniform thickness, and be a generally high-quality
veneer with a minimum of splits or other surface blemishes.
In developing a commercially usable contact drying system
for veneer, it will be recognized that, in addition to providing
the desired results with respect to the dried veneer, the
machinery system must be capable of economic, reliable, and
safe operation. One of the requirements is to feed the wet `
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veneer or partially dried veneer sheets into the contact
drying system uniformly, quickly, and without damaging the
sheets. A further need of the machine system is that the ~ ~:
v~neer sheets be properly positioned between the heated metal
plates of the drying apparatus and, therefore, it is essential
that some suitable aligning means be provided. Yet another
need within the machine system is for an unloading apparatus -~
to quickly unload the dried veneer from the contact drying
system. Ideally, an unloading apparatus would singulate
the dried veneer sheets for downstream processing such as
cooling or stacking.
~ ith respect to a commercially usable contact drying
system and its fit within the overall plywood manufacturing
process the drying system must be compatible with production
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from a veneer lathe in terms of its capacity and, likewise,
must also produce dried veneer at a rate to make the downstream
panel manufacture economic. Thus the contact drying system
must have the flexibility of structure, design, and operating
parameters to meet both desired production goals and veneer
quality requirements.
In the contact redrying system, any redryer must be
able to redry the amount of partially dried veneer that results
from the primary drying process. In the situation where
a typical known commercial dryer is the upstream process,
the amount of veneer to be redried will be substantially
greater than if the primary drying process is a contact drying
- system.
When veneer is generated at a lathe, it flows in a con
~ tinuous ribbon and is clipped to a predetermined size and
- then graded and stacked for downstream processing. The stacks
of veneer that result must be acceptable for handling within
a contact drying system and thu5 the loading station must
be capable of handling the heavy stacks of wet veneer that
~ 20 can weigh on the order of 6,000 pounds. Similarly, the dried
veneer flowing out of the contact drying system is again
graded and stacked and the outfeed system must be compatible
with this downstream requirement~
~ Accordingly, from the foregoing, it is an object of
the invention to dry wet or partially dried veneer to a uniform
predetermined moisture content. It is a further object to
produce dried veneer that has flatJ smooth surfaces affording
easier downstream handling. Another object is to provide
dried veneer having a uniform thickness. Yet another object
of this invention is to reduce the shrinkage during drying,
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thereby increasing yield. A further object is to reduce
splits and other downgrading characteristics. Still another
object is to dry the veneer to a uniform moisture content
with less energy than with conventional veneer dryers. Another
object is to reduce the blue haze emissions usually resulting
from veneer drying. Yet a further object of the invention
in the redrying system is to quickly redry partially dried
veneer without producing overdried veneer or excessive shrinkage.
It is likewise an object of this invention to provide contact
drying systems that are economic with respect to the initial
capital costs and which, in the economic sense, provide substan- ;
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tial benefits over conventional veneer drying systems. Yet
another object is to provide contact drying systems that
are compatible with the plywood manufacturing system from
the veneer lathe to the panel press.
These and many other objects of this invention will
be more completely understood a-nd appreciated after reading
the detailed description to follow while referring to the
attached drawings.
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Summar~ _ he Invent _n
Briefly stated, the presently claimed invention is practiced
in one form by an improved method for redrying partially dried
sheets of veneer in a contact veneer redryer. The method steps
include preselecting partially dried veneer sheets having areas
of wetness where the moisture content is above a predetermined
maximum level, inserting the sheets into an opening between
two flat metal plates, elevating the temperature of the contact-
ing surfaces of the metal plates to a range of from 250F to
400F, continuously exerting a uniform pressure on the veneer
: sheet by the metal plates within a range of from 5 psi to 70
psi for a time of from 20 seconds to 1 minute, and simultane-
ously with the exertion of the pressure, exhausting the steam
- and water generated by the temperature and pressure through
a plurality of substantially parallel exhaust grooves positioned
within at least one of the metal plates on a contacting surface
thereof.
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Brief Description of the Drawings
Fig. 1 is a top plan view paltially cut away at cer-
tain areas showing the general arrangement where a plurality
of hot presses are mounted on a rotatable frame.
Fig. 2 is a side elevation view taken through section
line 2-2 of Fig. 1 and depicts a modular multi-opening hot
" press mounted on its frame and being fed with wet veneer
sheets.
Fig. 3 is a front elevation view partially cut away
showing a modular multi-opening hot press partially loaded
with wet veneer.
Fig. 4 is a view similar to Fig. 3 showing the hot press
in its closed configuratior.
Fig. 5 is a,side elevation view of a plurality of the
metal plates within a hot press.
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Fig. 6 is a cross-sectional view taken along line 6-6
^ of Fig. 1 and shows the main bearing structure supporting
the rotatable frame.
- Fig. 7 is a view taken along line 7-7 of Fig. 1 and
shows a portion of the loading apparatus together with a
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- multi-opening hot press being loaded at the loading station.
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Fig. 8 is a side elevation view showing a portion of
the sequencing mechanism for the loading apparatus.
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- Fig. 9 is a side elevation view depicting the aligning
~ apparatus in its retracted position.
; Fig. 10 is a view similar to Fig. 9 showing a portion
;i of the aligning apparatus ready to sequence forward.
Fig. 11 is also a view similar to Fig. 9 showing the
aligning apparatus in its forward position urging a veneer
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; 30 sheet into proper alignment in a press opening.
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Fig. 12 is a front elevation view taken along line 12-12
of Fig. 11.
Fig. 13 is a top plan view partially cut away to illus
trate the indexing apparatus for the rotatable frame.
:~ Fig. 14 is a cross section taken along line 14-14 of
Fig. 1 and depicts, in part, the indexing ring frame moùnted
about the main circular bearing.
Fig. 15 is cross-sectional view taken along line 15-15
of Fig. 13 and illustrates the indexing arm latching mechanism
in its position for indexing the rotatable frame.
Fig. 16 is a view similar to Fig. 15 illustrating the
latching mechanism in its retracted position. ;
Fig. 17 is a side elevation view taken along line 17-17
of Fig. 1 showing a modular hot press in its tilted posi-
tion for unloading dried veneer~
'?'' Fig. 18 is a side elevation view taken along line 18-18 -
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of Fig. 1 illustrating the inclined slide plate at the unloading
station.
~ Fig. 19 is a side elevation view illustrating a single
-- 20 hot press that functions as a redryer for partially dried
veneer.
Fig. 20 is a view similar to Fig. 19 illustrating the
redrying apparatus being unloaded.
Description_ _f the Preferred Embodiments
Overall Veneer Drying System
Referring first to Figs. 1 and 2, a veneer drying sys-
tem is shown that has a high drying capacity and will be
suitable for drying wet or green veneer sheets. A plurality
- of modular contact veneer dryers 2 are mounted on a rotatable
` 30 frame generally indicated at 4 that supports the dryers 2
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on its periphery. All of the dryers 2 are mounted in substan- .
tially the same horizontal plane and frame 4 is indexed about
by an indexing mechanism generally indicated at 5 in a clockwise
direction.
A loading station generally indicated at 6 functions
to feed individual veneer sheets 8 into a waiting dryer 2
from stack 7. After a dryer is filled by a loading or feeding
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apparatus 10, frame 4 is indexed bringing another modular
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dryer 2 to the loading station 6. As the veneer sheets 8 10 are fed into a dryer 2, an aligning apparatus, generally
indicated at 12, functions to position each sheet within
the dryer. As the dryers 2 index about, each will eventually
reach the unloading station generally indicated at 14 which
is circumferentially adjacent loading station 6. At unloading
station 14 there is an unloading apparatus generally indicated
` at 16 that functions to unload and singulate the now-dried
; veneer sheets 18 from dryers 2. Unloading apparatus 16 places
the singulated dried veneer sheets 18 onto a transfer conveyor
20. Transfer conveyor ~0 carries the singulated veneer sheets
- 20 14 into the next downstream process whlch can be, for example,
a standard veneer cooler 22, wherein the hot dried sheets
are cooled to a suitable temperature. An outfeed conveyor
24 carries the still-singulated cooled veneer sheets further
downstream where they can be, for example, graded and stacked
into separate stacks of dried veneer.
There now follows a detailed description of each of
! the ma~or subsystems, the first being a description of an ~;~
individual modular dryer 2.
Modular Veneer Dryer
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Referring to Figs. 2-4, 5, 7, and 17 a detailed des-
cription will be given of a modular dryer. Each modular
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dryer is comprised of a modified typical commercially available
hot press 26. A plurality of these hot presses 26, as previously
pointed out, are mounted about the periphery of rotatable
frame 4. First, a brief descriptlon will be given of the
standard commercially available hot press and then the specific
necessary modifications will be described to allow the hot
press 26 to function according to its intended purpose.
Hot presses 26 are commercially avilable from a number of
different manufacturers, one of them being Lamb-Grays Harbor,
Inc. of Hoquiam, Washington. These hot presses 26 are typical
in that they are comprised of a movable base platen 28 to
which are operatively connected at its bottom surface two
hydraulic press cylinders 30. A plurality of upstanding
columns 32 support the bottom fixed base member 34 in a fixed
relationship with the combined fixed platen and upper base
member 36. As will be well understood by those skilled in
the art, there are positioned between movable platen 28 and ~
fixed platen 36 a plurality of guided vertically movable ~ -
metal plates 38. Thus with the plurality of plates 38 each
modular dryer 2 will be a multi-opening hot press whereby ; ;
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when the press cylinders are in their lowermost positions,
there will be provided a plurality of openings between adjacent
metal plates 38 Eor the accommodation therein of thin sheet
material. Of course, when press cylinders 30 are extended,
the press closes and the metal plates 38 will exert uniform
predetermined contact pressure on whatever sheet material
is placed within the openings. Standard steam lines 40 ~omprised
of flexible housing extend from a steam header 42 to the
metal plates 38. The metal plates 38, of course, have steam
conduits within them to allow the steam to heat each metal
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plate to a uniform predetermined temperature. The purpose,
of course, is to provide a uniform predetermined temperature
at the faces of each of the metal plates 38. Similarly,
the plurality of condensate lines 44 extend from metal plates
38 to a condensate header 46. A flexible hydraulic line
48 feeds the necessary hydraulic fluid into fluid header
50, which in turn allows the hydraulic fluid to flow into
press cylinders 30.
As previously pointed out, upon opening and closing
of presses 26, the metal plates are movable up and down a
set distance with the exception of the top plate, and guided
so that their movement is always within the same planar area.
This is conventional structure for hot presses. In FigO ~-
17 the guiding and distance setting means is generally depicted
at 52. Each metal plate 38, again except the top plate,
has a set of stops or hangers, with each stop indicated at
54, fixed to its opposed side edges that rest on step plates
55 when the press is openO Appropriately designed and positioned
slide mechanisms 56 serve to control lateral movement of
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plates 38. This structure simply allows the metal plates
to open and close sequentially and, since the hot presses
shown in the figures are of the upclosing type, it will be
appreciated that when the press is opening the top opening
will be the first to open, progressing sequentially to the
i bottommost opening. Conversely upon closing, the first opening
to close will be the bottommost. This opening sequence and
structure is conventional and will not be further described.
Since wet veneer sheets 8 are fed into the infeed side
of a hot press 26 at loading station 6, each metal plate
38 has a laterally extending nose guide member 58 fixed to
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its front edge. The purpose of the nose guide is to help
in the infeeding of each veneer sheet into each opening when
a hot press is being loaded. Another aspect of hot press
26 that is conventional is that the top and bottom metal
plates are fixed to the movable and stationary platens, 28
and 36 respectively, through a layer of insulation indicated
at 60.
A special modification for hot presses 26 is their mounting
structure. Each hot press supported on frame 4 is mounted
thereto on a shaft 62 that is supported by spaced mounting
blocks 64, 66. Each press is attached to shaft 62 through
suitable bearings 68. As can readily be seen, the bearings
68 provide a tilt axis that extends laterally across the
bottom of a press 26 and which is forward of the press center
line. The rotatable mounting is provided in order to allow
`~ each individual hot press 26 to be tilted forward and downwardly
with respect to the horizontal reference plane on which the
plurality of hot presses 26 are mounted. The tiltable feature
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is clearly seen when referring to Fig. 17. A pair of tilt
actuating cylinders 70, 72 are positioned so as to be on
either side of each hot press 26 with one end of each being ;~
pinned to a part of frame 4 at connection points 74, 76 respec-
~ tively with the other end being pinned at connection points
78, 80 respectively on a part of fixed base number 34. Cylinders
70, 72 have a retracted position where they maintain each
press in its horizontal orientation and an extended position
where they tilt a press 26 about the tilt axis downwardly
to an angle of approximately 35 from horizontal. A press
26 is shown in its horizontal position in Fig. 7 and in its
downwardly tilted position in Fig. 17. While it will be
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described in more detail later, it will be pointed out here
that blocks 64, 66 are supported on frame 4 by I beam sections
each indicated at 82.
Metal Plate Design
As was previously pointed out, the metal plates 38 within
~ each modular hot press 26 are of a standard typical design
- wi~h one major exception. Typically, the area of metal plates
38 for veneer drying will be on the order of 55" by 105"
to accommodate the typical sheet veneer size. Other sizes,
of course, could be incorporated into a standard hot press
depending upon the size of the veneer sheet to be dried.
Referring specifically to Fig. 5, several individual metal
; plates 38 are depicted one atop the other. This view would
be a side elevation view looking toward the hot p~ess. Posi-
tioned on the top surface of each metal plate 38, although
it will be the bottom surface of the press opening, is a
plurality of grooves each indicated at 84. The primary function
of grooves 84 is to provide conduits for the escape of the
water and vapor that is generated during the contact drying
process. The spacing and sizing of grooves 84 is important
in that a proper relationship must be maintained between
the actual contact surface area on the veneer and the open
area provided by the grooves. It has been found that grooves
84 should be substantially parallel and positioned on approximate
l.5" centers, although a range for the centers of from 0.50"-
6.0" has been found to give satisfactory results~ Of course,
it will be appreciated that as the groove area increases
relative to the surface contact area, the drying rate will
be altered; that is, it will take longer to dry the same
sheet of veneer, owing to less direct contact with a heated
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metal plate. While grooves 84 are shown as running perpendic-
ular to the long plate dimension and perpendicular to the
grain of the veneer, satisfactory results have been obtained
with the grooves running with the length of the plate and
parallel to veneer grain. Similarly, a criss-crossing pattern
with the grooves crossing at 90 angles has also been found
to give satisfactory results. However, while the water and
vapor exhaust grooves 84 should be simple in structure, they
must be of suitable cross-sectional shape in order to carry
out the necessary function.
As previously noted, the primary function of each groove
is to serve as an exiting channel for the water and steam
- that will be generated during the drying process. The open
area at the plate surface provided by the grooves must not
be overly large so as to reduce the drying rate and time.
It has been found that a ratio of approximately 3:1 plate
contact area to open groove area will allow both moisture
removal and an efficient drying rate. In addition, another
requirement is that the grooves be easy to clean and preferably
that they be self-cleaning. A particular design that has
been found to give good results and which is essentially
- self-cleaning is the design depicted in Fig. 5. It will
be noted that grooves 84 are positioned only on the top surfaces
of each metal plate (bottom plate of each press opening)
and the reason is to reduce the tendency for small wood particles
to become lodged in the grooves. Oftentimes when a sheet
of veneer is being loaded into a press opening, it will carry
with it debris and other particles on its top surface and,
when a press is closed, the particles will be forced into
the veneer. With grooves on the top of a press opening,
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oftentimes the wood particles were wedged into a groove which
res~lted in a blockage to moisture removal. The particular
groove design depicted is 1/8" in depth, 3/8" across the
opening, 1/8" across the bottom and with 45 inclined sides.
This groove design has been found to be essentially self-
cleaning in that, as steam is genirated and is exhausted
-~- throuyh the grooves, the hot steam will tend to remove material
that would otherwise be accumulated. Other groove designs
- have been found to give satisfactory results, such as square grooves, V-grooves, U-grooves, and the like. The groove
design as depicted in Fig. 5, however, does give satisfactory
results and is easy to machine into the metal plates.
It has been found that the use of the parallel grooves
extending across the surface of the metal plates 38 results
in consistent uniformly dried veneer within a narrow desired
moisture content range. As will be further described later,
.he use of the grooves in the metal plates allows the process
parameters employed to dry wet veneer, that is, a constant ;~
temperature within a range of from 275 to 400F and a predeter-
20 mined constant pressure within a range of from 10 to 100
psi. Further, it is possible to dry a wide range of wood
species, a wide range of thicknesses, and a wide range of
- initial moisture contents all within short time periods when
compared to conventional drying processes. And, as earlier
pointed out, the contact process provides significantly improved
veneer for plywood manufacture. Additionally, when redrying
partially dried veneer, the utilization of the grooves also
makes it possible to quickly and uniformly dry the partially
dried veneer.
Main Bearing and Frame Structure
.,
.,
' 19
;, r.
`~ ' ~ , , ' ' ' ,', . "
. . ~ , .,', ' '
,.
Referring now to Figs. 1-4, 6, 7, and 13, a detailed
description will be given of the ~main frame structure 4 that
sup ports the modular hot presses 26, together with the main
bearing structure generally indicated at 86. First, it is
to be noted that the rotating frame 4/ if eight modular hot
presses are to be mounted on it, will be supporting approximately
250 tons and the structural design must accommodate that
weight with structural and safety requirementq both satisfied.
Frame 4 is a carousel-type truss frame mounted on an annular
steel ring 88. Within the opening 90 of steel ring 88 there-
can be positioned, as will be described later, a plurality
of conduits and the like for the entry and exit of electrical
power, steam, and/or condensateO Firmly attached to steel
ring 88 through a plurality of base plates 92 bolted to steel
ring 88 is a plurality of upwardly extending beam members
94,-96, and 98. Since there are eight presses 26 mounted -
on frame 4, for structural purposes there will be eight sets
of beam members 94, 96, and 98 and each adjacent set of members .:
94, 96, and 98 will be spaced so as to support a modular
, ,
press 26 radially outwardly therefrom on a press mounting
frame generally indicated at 100~ Extending horizontally
and radially inwardly across the tops of the members 94,
96, and 98 are a plurality of connector beams 102 that are
-~ joined together at a central connection area indicated at
.. 104. At the connecting area, the beams 102 are joined together
through the use of an annular connection means 106 having
a conduit 108 therein for the passage through it of steam
supply pipe 110.
Frame 100 is comprised of a plurality of horizontally
extending cross connectors 112 that serve to tie the beam
., ,
.:,
j
. 20
.. : , :.
~. . .
members 94 t 96, 98 and 102 together. Extending outwardly
from cross members 112 at their joinder points with horizontal
beams 102 are the pairs of side supporting plates 114, 116
respectively which form a portion of the press mounting frames
100. It is on the side supporting plates 114, 116 that each
of the I beam sections 82 is mounted for supporting the tiltable
hot presses 26. Similarly, tilt cylinders 70, 72 are attached
to supporting plates 114, 116 through the pinned connection
points 74, 76. Serving to provide rigidity to supporting ,,
plates 114, 116 are a plurality of horizontal laterally extending
support members 118, 120. The support members 118, 120 serve
to tie sup porting plates 114, 116 together at the periphery
~f rotable frame 4 ensuring the necessary rigidity and support
for each individual press mounting frame 100.
Turning now to the main bearing structure 86, it may
be seen when referring to Fig. 6 that the bearing is comprised
in part of the annular steel ring 88. Positioned on the
bottom of ring 88 and held in place by a plurality of dowels
122 is a thin annular steel ring 124. Ring 124 is comprised
of segments that extend about the circumference of ring 88.
It is segmented, in part, to allow for lubrication. Juxtaposed
against and beneath the thin steel ring 124 is the annular
slide ring 1260 It is the lower surface of,steel ring 124
and t~p surface of slide ring 126 that forms the bearing
plane for rotatable frame 4. Positioned directly below slide~
ring 126 is a resilient annular ring 128. Slide ring 126
and annular,ring 128 are fixed in position by a plurality
. - .
~ of downwardly extending dowels 130. Both slide ring 126
,,
' and resilient annual ring 128 are also segmented. The dowels
,' 30 130 extend into and fix rings 126 and 128 in position relative
21
..
16)~3~ 5Sl
to an annular steel base rinq 132. Base ring 132 is in turn
firmly attached to fo~ndation 134 through any suitable means
such as through a plurality of bolts 136 which extend upwardly
from foundation 134 and through a plurality of horizontal
flanges 13~ attached to ring 132. Providing a side bearing
structure is an upwardly extending circumferential flange
140 located so as to be adjacent to the inner vertical face
142 of ring B8. The upwardly extending flange 140 and a
vertical slide ring 143 function to constrain rotatable frame
~ 10 4 on-its horizontal main bearing structure 86. Provided
within flange 140 is lubrication inlet 1~4 which allows lubri-
cating fluid to flow radially outwardly over the sliding
elements within main bearing structure 86.
The slide rings 126, 143 may be comprised of, for example,
a plastic material and it has been found that a phenolic
composition impregnated with graphite provides satisfactory
results. The resilient annular ring 128 may be comprised
of, for example, a rubber bearing pad and is positioned beneath
the slide ring 126 to accept concentrated loads that may
be experienced during operation. The resiliancy of the rubber
pad accepts the loads without causing damage or failure to
- any of the other structural elements. Slide ring 143 may
also be comprised of a plastic material such as the phenolic
.;. . .
composition impregnated with graphite.
Utilities
As previously pointed out, hot presses 26 are heated
through the use of steam and the opening and closing functions
and the tilting function are hydraulically powered. Because
the presses rotate, assemblies must be provided for bringing
steam into the rotatable frame 4 as well as for directing
.' .
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': :
22
~.:. ~ , . . . . . . . .
rjs~
condensate out. In addition, the hydraulic fluid must be
2rovided to each of the presses alld electrical power must
also be provided for the various electrically operated components
within the rotating system. As previously pointed out, the -
steam is supplied through steam supply pipe 110 which in
turn is surrounded by a layer of insulation 146. Steam is
supplied vertically through pipe 110 and enters the frame
4 through conduit 108. A series of expansion joints (not
; shown) may be provided along the steam pipe to accept the
thermal movements. Steam pipe 110 terminates at a rotary
joint 148 from which extends at least one radially extending
steam conduit 150 which in turn opens into a circular steam
manifold 151 that is mounted on frame 4. From the steam
manifold the plurality of steam lines 152 are directed to
the steam headers 42. A similar assembly is provided for
the condensate from the individual hot presses 26. ~rom
~- each condensate header 46 on a press 26 a condensate line
154 will be directed to a circumferentially extendinb condensate
header 155 from which will extend radially at least one con-
densate 156. Condensate line 156 will be connected to another
rotary joint 158 which in turn connects to the central condensate
outflow pipe 160.
Electrical power is supplied within central opening
90 at the bottom of frame 4 through a conventional slip ring
assembly indicated generally at 162. As may be seen in Fig.
2, the slip ring assembly 162 surrounds the condensate outflow
- pipe 160.
- The hydraulic power is supplied through a self-contained
conventional tank and pump assembly 164. The assembly 164
is powered by electrical energy supplied through slip ring
: .
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, 23
.7ii~.
assembly 162. Within the tank and pump assembly 164 there
is the necessary equipment to pressurize the hydraulic fluid
and direct it to its point of use through outlet line 166.
An inlet line 168 serves to return the hydraulic fluid to
the tank and complete the circuit. As with the steam supply
systemr the fluid power supply system may include headers
(not shown) for directing the high-pressure fluid to hydraulic
lines 48 for opening and closing presses 26. In addition,
another header (not shown) may be provided for distributing
;- 10 hydraulic fluid to the plurality of tilt actuating cylinders
70, 72 at each press 26. Of course, also provided with tank
and pump assembly 164 will be the necessary valving to control
-- the various fluid flows.
Permitting access to the central area of frame 4 is
an overhead walkway generally indicated at 170. At the end
of walkway 170 is a downwardly extending circumferential
cage assembly 172 and a ladder 174. A maintenance operator
can mount the walkway 170 through stairs 176 and ladder 178,
cross over walkway 170 and descend the ladder 174 and perform ;
maintenance functions within the centràl part of frame 4.
...
Sheet_Load ng A~paratus
Referring now to Figs. 1, 2, 7, and 8, the veneer loading
apparatus will be described. Positioned just radially outwardly
of the circle defined by the circumferential travel of the -
outermost point on a press 26 is feeding apparatus 10. As
previously noted, the function of feeding apparatus 10 at
loading station 6 is to sequentially feed at least one veneer
sheet 8 into each opening of an awaiting hot press 26. The
~ sequence could be from either top to bottom or from bottom i~
.` 30 to top. However, in the present embodiment, the sequence
:-
.
, :
ss~ ~
is substantially a~tomatic from bottom to top. The feeding
apparatus is comprised of a platEorm 180 which is mounted
on a pivoting frame 182. At the front portion of platform
180 is a typical commercially available scissors lift 184
(available from American Manufacturing Company of Tacoma,
Washington) which is capable of supporting and adjusting -
the vertical height of a stack of veneer. At the rear portion
of platform 180 is a space 185 for an operator where he will
function to pick individual sheets of veneer from the top
of the stack and urge them toward and into the feeder mechanism
generally indicated at 186. Feeder mechanism 186 extends
- laterally across the upper front edge of feeding apparatus
10 and is supported by an upstanding front portion 188 of
- pivoting frame 182. Positioned in substantially the same
horizontal plane as feeder mechanism 186 is a pair of laterally
spaced bearings 190, 192 that support and allow frame 182
to pivot. Bearings 190, 192 are mounted on horizontal support
arms 19~, 196 which in turn are mounted on stationary upstanding
~, beam members each indicated as 198. It will be understood
that the location of pivotal axis for frame 182 extending
through bearings 190, 192 will provide a relatively small
angular variation from the top opening of a press 26 to the
bottom. This, of course, provides a substantially in-line
feeding relationship from feeding apparatus 10 into the plurality
of openings in hot press 26. Mounted on a stationary supporting
member 200 at pinned connection point 202 is the vertically
extending sequencing cylinder 204. The other end of sequencing
cylinder 204 is connected to pivoting frame 182 at pinned
connection point 206 at a position located along the front
lateral edge of frame 182. Of course, the function of sequencing
., . ~ , .
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~ . - . . . .
cylinder 204 is to pivot the frame 182 upwardly in a sequencing
manner allowing the operator and feeder mechanism 186 to
load each opening sequentially with at least one sheet of
wet veneer. When the hot press being loaded is full, cylinder
204 will then retract back to its starting position to await
the next opened hot press and feeding cycle.
Feeder mechanism 186 is mounted on front portion 188
of frame 182 and is comprised of pairs of laterally spaced,
upwardly extending beam members 208, 210 and 212, 214 respec-
~ 10 tively. Supported on the beam members are a plurality ofroll pairs mounted within a suitable frame 216. The nips
of each roll pair are substantially in line and will, of
course, be positioned substantially in line with each opening
of a hot press as frame 182 is sequenced through its cycle.
..:
Additionally, the top sheet of veneer 8 within the stack `
will be maintained at a height atop scissors lift 184 that ~
will be substantially in line with the nips. The first roll -
pair, that is the one adjacent the stack of veneer, is comprised
of a bottom cylindrical roll means 218 and a top roll means ~ ;
220 that may be comprised of a plurality of typical donut
rolls and which can be vertically movable up and down to
allow an operator to feed the top sheet into the feeder mechanism
186 where it will initially abut vertically displaceable
gate 222. Gate 222 is controlled by suitable actuating means
; 224 which may be comprised of a pair of laterally spaced
hydraulic or air cylinders. The next set of rolls within
the feeder mechanism 186 are top and bottom brush rolls 226,
228 respectively. The brush rolls serve to remove debris
from the surfaces of a sheet of veneer being fed into an `
opening. The last set of rolls or the set nearest the press
is also comprised of a bot~om cylindrical roll 230 and a
top roll 232 that may be comprised of a plurality of typical
donut rolls for feeding veneer. As is typical with most
scissors lifts, the operator will have a foot switch that
controls the vertical movement of stack 7 and will keep the
top sheet substantially in line with the nips of the roll
- sets.
The plurality of feed chains, each indicated at 234,
extend laterally of the scissors lift 184 and function to
10 convey a new stack of wet veneer to a position atop lift
184.
- In Fig. 8 there is depicted a cam-operated timed valv-
- ing mechanism that functions to control cylinder 204 and
~; therefore the sequencing of pivoting frame 182. The valving
- is generally indicated at 238 with the cam and follower mechanism
qenerally indicated at 240. The control system operates
on a timed sequence and it has been found that an approximate
- 3-second time period for feeding a sheet of veneer into an
opening and sequencing to the next opening gives satisfactory
20 results. The total time to feed an eight-opening hot press
and retract the frame 182 to its lowest position is an approxi
mately 30-second cycle. This includes a lag time to allow
the rotatable frame 4 to index another step to bring an opened
- press into alignment with feeder mechanism 186. Of course,
those skilled in the art will recognize that there are several
alternative means for con-trolling the sequencing of pivoting
frame 182 and feeder mechanism 186 and that Fig. 8 depicts
one suitable means.
It will be recognized that a typical commercially available
30 vacuum feeder could be employed for feeding the sheets into
... . .
iL0~15~i ~
feeder mechanism 186 from the top of a stack 7.
Aligning ApE~aratus
Referring now to Figs. 2 and 9-12, the aligning appa-
ratus 12 will be described. Aligning apparatus 12 is suspended
from overhead walkway 170 and is substantially in line with
feeding apparatus 10 on the opposite side of a press when
located at loading station 6. As previously noted, the function
of aligning apparatus 12 is to properly position each incoming
sheet of veneer 8 within its press opening. Since the feeder
mechànism 186 will oftentimes place the leading edge of an
incoming sheet past the ends of metal plates 38, it is necessary
to accurately realign the veneer sheet so they are within
the edges of plates 38.
The aligning apparatus 12 is comprised of two operat~
- ing elements, one element being the resilient flexible backing
member 242 mounted on a pivotal frame 244 and the other element
being a patting face 246 also mounted on a pivotal frame
248. Pivotal frame 244 is comprised of a pair of laterally
spaced downwardly depending arms 250, 252. Each arm 250,
252 is mounted at its upper end in a rotatable manner on
shaft 254. Arms 250, 252 extend downwardly for a distance
that is slightly below the lowermost metal plate 38 within
a press 26. Serving to provide rigidity to arms 250, 252 ~ ,~
are upwardly extending rear arms 256, 258, which are attached
to arms 250, 252 respectively. The rear arms 256, 258 are
in turn attached to spaced rearwardly extending beam members
260. Beam members 260 in turn are mounted on shaft 254 with
arms 250, 252. Serving to pivot frame 244 forward and back
about shaft 254 is an actuating cylinder 262 that is pivotally
attached at one end to a downwardly depending frame 264 and
28
: :., , : . .. . .. .
lV'31~
at the other to a pinned connection point 266 which is in
turn attached to a cross arm member 268 connecting beam members
260 rigidly together.
Positioned approximately half way along the length of
arms 250, 252 is a laterally extending attachment bar 270
that serves to not only provide rigidity to arms 250, 252,
but also to provide an attaching means for the flexible backing
member 242. Backing member 242 extends downwardly from attach-
ment bar 270 and around the end of arms 250, 252 over a bottom
laterally extending tube member 272. The other end of backing
member 242 is attached through spring means 274 to the upwardly
extending rear arms 256, 258. Thus the flexible backing
member 242 provides a resilient back stop for individual
veneer sheets as they are fed into an opening and travel
past the ends of plates 38. Backing member 242 has a retracted
. . .
` position as depicted in Fig. 9 and a forward position as
depicted in Figs. 10 and ll.
-- The pivoting frame 248 is comprised of a pair of down-
wardly depending arms 276, 278 to which is connected through
pinned attachment means 280 the patting face 246. Patting
face 246 depends downwardly in a swinging relationship from
arms 276, 278 to a lower edge which will be approximately
- adjacent but below the lowermost opening of a hot press 26.
At the upper ends of arms 276, 278 they are similarly mounted
on shaft 254 so as to be rotatable thereon but independently
of arms 250, 252. As may be seen when referring to Fig.
12, the patting face 246 is substantially rectangular and
,"~ .
has a screen 282 over its front face. Screen 282 will sequen-
tially strike the flexible backing member 242 as will be
further described later. Extending upwardly and outwardly
: .
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- ~ 29
,. ... . . .
from the bottom edge of patting face 246 are stiffening members
284~ Cross arms 286 meet stiffening members 284 at a point
horizontally spaced from pinned attachment means 280. An
additional downwardly depending pinned arm 282 s~pports the
rear portion of the patting face 246 in its substantially
vertical orientation. Arm 288 is pinned at connection point
290 and at the other end it is pinned at connection point
292. Serving to pivot the patting face 246 forward on arms
276, 278 and pinned arm 288 are a pair of actuating cylinders
294, 296. One end of each cylinder is pivotally attached
-~ to an outwardly extending dog member 298, 300 respectively,
each of which is fixed to the shaft on which downwardly depending
arms 276, 278 are attached. Of course, arms 298, 300 provide
the lever arm for sequentially turning the patting face 246.
.. :
The other end of actuating cylinders 294, 296 are attached ;-
at pinned connection points 302, 304 on a frame means 306. -
Of course, it will be recognized that the pivotal frame 244 ~ ~
- ,
and pivoting frame 248 operate independently of one another ~ .
. . . .
yet sequentially as will be further described later. ~;
; 20 Indexin~_Mecha i S
"` , ::
; Referring now to Figs. 2 and 13-16, the mechanism for
- accurately indexing rotatable frame 4 and, consequently,
. . ,
the accurate positioning of hot presses 26 will be described.
~ In Fig. 2 the indexing mechanism, as previously noted, is
`~. generally indicated at 5. The function of mechanism 5 is,
of course, to rotate the frame and accurately align the modular
` hot presses 26 as they reach the loading station 6 and unloading
- station 14. It is, of course, absolutely necessary that
feeder mechanism 186 be in line with the openings of the
press at loading station 6. Likewise, it is important that
, .
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1~C3'1.5f ~
the hot press at unloading station 14 also be in line with
certain parts of unloading apparatus 16.
With an eight-press drying system, frame 4 will be rotated
through an angle of 45 upon each indexing cycle. Serving
to provide the indexing movement, in part, is a pair of opposed
upwardly extending indexing arms 310, 312. At their base,
arms 310, 312 are attached to a rotatable circular frame
314 that is journaled about main bearing structure 86. In
Fig. 14 the bearing surfaces 316, 318 for frame 314 are
depicted. Circular frame 314 fits around annular steel ring
88 and bearing surfaces 316, 318 may be comprised in part
` of segments 320 of plastic material such as the phenolic
composition impregnated with graphite. Frame 314 is mounted
so as to be reciprocable in a horizontal plane about the
- .:
vertical center line of frame 4. At the upper ends of each
indexing arm 310, 312 there is a sequentially operable latching
- mechanism generally indicated at 322. Latching mechanism
~ 322 is comprised in part of a retractable pawl member 324
-~ slidable within slide frame 326 and actuated by a radially
extending, upwardly inclined actuating cylinder 328. The
opposite end of each actuating cylinder 328 is mounted on
a cross member 330 supporting it in its proper position.
. .~. .
Depending downwardly and fixedly attached to horizontally
- opposed supporting members 331 between pairs of adjacent
presses 26 are latch blocks 332. Latch blocks 332 are positioned
radially so they are approximately in line with the center
of gravity o the hot presses 26. Pawls 324 have an extended
position as depicted in Fig. lS where the radially outer
end of each pawl will mate with the recess within a latch
~ 30 block 332. In Fig. 16, a pawl 324 is depicted in its retracted
. .
,.
~ 31
-
1~9:~L Cj,j ~
position where it is out o the recess in latch block 332
whereby the frame 314 and indexing arms 310, 312 can rotate
past the latch blocks 332 and below a hot press 26 to the
next adjacent pair of latch blocks 332. The forward direction
of rotation of indexing arms 310, 312 is indicated by the
directional arrows 334 as shown on Fig. 13, and these arrows
indicate the clockwise direction of rotation for the frame
4. The direction will be reversed when the palls 324 are
in their retracted positions and the indexing arms 310, 312
index back for the next cycle. The phantom lines in Fig.
13 show frame 314 and arms 310, 312 in a second position,
having just been indexed. -
Serving to rotate frame 314, and consequently indexing
arms 310, 312, is an opposed pair of large hydraulic actuating
cylinders 336, 338. At the fixed end of each cylinder it ~
.: . .. ' ' ; : ,
is pivotally attached to a base member 340, while at the `~ ~
,,
other end it is pivotally attached to a horizontally extending
- lever arm 342 which is mounted on frame 314. Lever arms
... .
i~: 342 are, of course, mounted 180 from one another and, when
.
20 cylinders 336, 338 are actuated~ they will serve to apply
a turning force to frame 314. When cylinders 336, 338 are
-- actuated to rotate arms 310, 312 in a clockwise direction,
pawls 324 will be firmly within latch blocks 332 and torque
. . .
will be transferred radially to the latch blocks 332 where
`- the tangentially applied force will cause frame 4 to turn
- through an angle of 45. After the frame 4 is indexed 45,
; pawls 324 will be retracted and cylinders 336, 338 will likewise
be retracted turning frame 314 counterclockwise through an
angle of 45 back to a ready position for the next indexing
cycle.
.,, - ' ' '' ~'.
~ 32
: - -~ -.
.
~9~5~j~
Unloadin~_AF~paratus
~ At unloading station 14, of course, an unloading appa-
-; ratus 16 is provided for removing the dried veneer sheets
from the hot press 26 then at the unloading station. ~eferring
to Figs. 1, 17, and 18, the unloading apparatus will be
~ described in detail.
-/ As previously pointed out, each hot press 26 is pivot-ally mounted on spaced bearings 68 and has a pair of tilt
cylinders 70, 72 positioned rearwardly from the bearings
~- 10 in order to tilt the front of the press downwardly and forwardly
` upon the proper sequential command. Also, as was previously
- pointed out, the hot presses 26 open sequentially from top
to bottom. It has been found that a tilt angle of approximately
35 is adequate to let gravity function to allow each dried
sheet to slide forwardly and out of its press opening.
Positioned adjacent to the bottommost opening of the
hot press when it is in its fully tilted position is a down-
wardly inclined slide plate 344 having an inclined angle
of approximately 15. Spaced from the lowermost point on
slide plate 344 is a set of driven rolls 346, 348 that function
to grasp each downwardly sliding sheet of dried veneer and
motivate it outwardly onto transfer conveyor 20. The relative
- dimensions of slide plate 344 and the spacing between slideplate 344 and the nip of rolls 346, 348 are important in
the sheet singulation process. As individual dried veneer
sheets 18 begin ~alling from the openings sequentially, they
~ will strike slide plate 344 beginning at a position close
? to its lowermost point and gradually the striking point will
move progressively higher on slide plate 344. The dimension
30 of the horizontal projection of slide plate 344 and the spacing
,,. :
~ 33
lS~
between the nip of rolls 346, 348 and the end of slide plate
344 should have a ratio of approximately 3:1. By providing
this ratio, the dried veneer sheets 18 can be singulated
with minimal damage onto the transfer conveyor 20. A backstop
350 is provided on the other side of transfer conveyor 20
to allow each singulated sheet to be positioned atop transfer
conveyor 20 after it feeds through rolls 346, 348.
. . .
As previously pointed out, transfer conveyor 20 then
functions to convey the singulated dried sheets into cooler
22 which may be any commercially available cooler, for example
a multi-section cooler manufactured by Coe Manufacturing
. .
Company of Painseville, Ohio.
- Redrying Apparatus
. . .
Referring now to Figs. 19 and 20, a particular redry-
ing apparatus will be described suitable for drying partially
dried veneer to a uniform finally desired moisture content.
Redrying apparatus may be comprised of a hot press 352 substan-
tially similar to the plurality of hot presses 26 mounted
on rotatable frame 4. Hot plates 354 within hot press 352
are substantially similar to the plurality of hot plates
38 within each of the hot presses 26. A similar feeding
apparatus 356 is provided to sequentially feed partially
dried veneer sheets into hot press 352. The primary structural !
difference between hot press 352 and a hot press 26 is that
.... .
the loading side of hot press 352 is tiltable upwardly from
feeding apparatus 356 by reversing the positions of the mounting
; bearings and tilting cylinders. On hot press 352 bearings
358 are mounted towards the back side of press 352 while
the tilt cylinders 360 are mounted closer to feeding apparatus
356. Thus the outfecd or unloading side of the hot press
; ,. .
~ 3~
.~.: . . . .. . . .
~LV91'~
is reversed for a redrying system.
Just as with a hot press 26 at loading station 6, it
will be necessary to provide an aligning apparatus 362 for
accur ately positioning each incoming sheet of partlally
dried veneer. Since press 352 tilts downwardly at its back
side, the positioning apparatus 362 must be mounted so as
to be movable, allowing unobstructed gravity fall of the
redried veneer sheets. In a redrying press, the positioning
apparatus 362 can be mounted on the top of press 352 so as
to pivot on bearings 364. A pair of laterally spaced arms
366 extend rearwardly from bearings 364 and serve to support
the downwardly depending aligning apparatus 362. An actuating
- cylindeL 368 extends upwardly from the top of press 352 to
a cross member extending between arms 366 and serves to pi-vot
the entire positioning apparatus 362 upwardly relative to
the back side of press 352.
In the redrying hot press 352 the operating sequence
is very similar to that of the hot presses on the rotatable
frame 4. The feeding apparatus 356 will sequentially feed
partially dried veneer sheets into each opening of hot press
~- 352 from bottom to top. After the last sheet has been fed,
the press will close and the redrying method will be carried
out within the press. After the passage of the predetermined
redrying time, the tilt cylinders 360 will be actuated to
tilt the press 352 about bearings 358. A~ter the press is
tilted, the hot press will be sequentially opened starting
from the top opening and progressing to the bottom opening.
As each opening is made, the finally dried veneer sheet will
exit the hot press in a singulated manner. Prior to the
press being tilted, cylinder 368 will elevate the aligning
: .,. , ~
~,J~ 15J~
apparatus 362 to a position spaced away from the far side
of press 352 whereby enough distance will be provided so
that the veneer sheet in the top opening will fall below
the lowermost edge of the aligning apparatus 362 and directly
onto slide plate 369. This configuration is depicted in
Fig. 20 where hot press 352 is shown being unloaded.
Dryer Emissions Control
. ,
If, upon operating the veneer drying system as depic-
ted in Figs. 1 and 2, it is determined that the emission
10 level from the drying process is significant, a collection
means may be provided. In Figs. 1 and 2 the collection means
is indicated in phantom lines and may be comprised of a circum~
ferentially extending hood 370 having an outlet conduit 372
to draw off the steam and other emissions generated by the
veneer drying process. It will, of course, be recognized
that a pressure differential will be generated to draw the ~;
;- emissions upwardly into the hood 370 and out conduit 372.
~` For example, a fan may be conveniently located within conduit
372 at some downstream position (not shown). Similarly,
20 with the redrying hot press a suitable hood (not shown~ may -
.
be positioned over the top of press 352 which will serve
-- the same purpose of collecting and directing the emissions
away from the hot press.
- Alternat ve_ esigns
In addition to the design where a plurality of modular
" ~
hot presses 26 are mounted on the periphery of a rotatable
frame, it will occur to those skilled in the art that a plural-
ity of modular hot presses can be laid out in alternative
configurations~ For example, a plurality of hot presses
could be placed adjacent to one another in line with a single
, . . .
;
36
~ " ~
loading apparatus traversing the distance along the infeed
sides of each hot press, loading them each with wet veneer
in a sequential manner. Each press could be tiltable downwardly
and away from the infeed side to release the dried veneer
onto a transfer conveyor. A similar design might include
a plurality of hot presses mounted in line on each side of
a single outfeed conveyor and with a pair of feeding mechanisms
being operable to load the presses on the side opposite the
- outfeed conveyor. Other configurations will occur to those
skilled in the art and all such configurations are intended
to be included within the scope of the claims. Similarly,
other alternate designs for redrying systems will occur to
those skilled in the art. For example, a pair of hot presses
may be placed side by side substantially adjacent one another
with a single loading apparatus moving between the two presses
to feed them and with each press being tiltable away from
~; the feed side to discharge its redried veneer onto a single
transfer conveyor. Other alternative designs for redrying
systems will also occur to those skilled in the art and they,
20 too, are intended to be included within the scope of the ~ -
claims.
- Veneer Drying Methods
To be descrîbed now will be the various methods of drying
the wet veneer sheets and the various drying schedules that
have been developed for different wood species, veneer thick-
nesses, and initial moisture contents. Also to be described
will be the redrying methods and schedules developed which
` are also dependent upon species, thickness, and initial moisture
content.
An ideal final moisture content for a sheet of dried
.
,
37
, - . , ::
softwood veneer is from 1 to 5~, while a sheet of hardwood
veneer should have a moisture content of from 8 to 15%.
- The moisture content also should be uniform within this range
throughout the sheet. When veneer sheets fall within a moisture
- content range of from 1 to 5% and 8 to 15%, the glue application
- process and subsequent pressing into panels is significantly
improved as noted previously. The drying schedules have
been developed to consistently yield dried veneer sheets
that fall within this moisture content range. This is primarily
time and temperature dependent. Additionally, the pressure
is determined based primarily on wood density since excessive
pressure will crush the wood. The correct pressure will
restrain wood shrinkage and will provide the increased yield
as previously noted. The time for exerting the pressure
and applying the temperature will be dependent upon the starting
moisture content. In wet veneer sheets the average moisture ;
content of heartwood averages 35 to 40% for a typical western ~-
softwood and 75 to 100% a typical for southern softwood, ~ ;
while sapwood averages 100-130% for a typical western softwood
and in southern sapwood the average moisture content ranges
from 100 to 120%. In partially dried veneer sheets, any
areas within a sheet having a moisture content above 8 to
10% moisture content is subject to being redried.
It thus becomes apparent that in actual production the
- veneer sheets to be dried should be preselected according
to species, thickness, and initial moisture content~ When
sheets are preselected, the process parameters can be set
for those conditions and the efficiency of the system is
better. It is, however, not absolutely necessary to sort
heart and sap prior to drying because with contact drying
.
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the sheets do not become overdry. With partially dried veneer
to be redried, thickness and species are the two primary
variables since it has already been determined that the sheet
has been partially dried.
The following tables of drying schedules will present
those conditions for each specie's thickness and initial
~ moisture condition that have been found to give good results
'7'; for primary drying or redrying sheets of veneer within a
modular hot press of the present invention. It should be
noted that the thickness range is from 1/10" up to 3/16"
with the starting moisture contents in wet veneer ranging
from 30 up to 250% in extreme cases. In the case of redried
veneer, as was previously noted, the moisture condition is
one where there are areas within the sheet that exceed a -~
predetermined moisture content such as 10~. When partially ~ -
dried veneer is determined to have an excessive moisture
content, it will be diverted and directed to the redrying
- system. As is well known, when veneer sheets pass through
a veneer dryer, moisture meters will sense the final moisture
content and any sheets having an excessive moisture content
will be diverted.
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TABLE OF PR~RY DRYING S~
Species Thic~essInitial Moisture Time Te~. Pressure
(inches) Condition . (minutes? ~F) 5~si?
Douglas Fir V10 Sa~d 4-V2 335-360 35
Douglas Fir 1/8 Sapwood 4-1/2 335-380 35
Douglas Fir 3/16 Sapwood 6-1/2 - 8 335-380 35
Do~las Fir Vlo Heartwood 2 335 35
Douglas Fir 1/8 Heart~x~ 2-1/2 - 4-1/2 320-335 35
.: Douglas Fir 3/16 Heartwood 4-V2 380 35
Red Cedar 1/6 Heart or Sap 7 - 8-1/2 360-380 15
Black Cottonwood 3/16 Heart or Sap 10 385 25
~ So. Pine 1/8 Heart or Sap 3 340 35
; So. Pine 1/6 Heart or Sap 4-3/4 340 35
-: Red Oak 1/8 Heart or Sap 3-1/2 - 4 340-365 35
-: White Oak 1/8 Heart or Sap 4 365 35
- Gum 1/8 Heart or Sap 3 340 35
:~: 20 Yellcw Pcplar 1/10 Heart or Sap 2-1/2 275 70
~ Yellow Poplar 1/6 Heart or Sap 6 275 70
,::
~ABLE OF REDRYING ~E~ULES
` Species micknessInitial Moisture Time Temp. Pressure
: (inches) Condition _ (minutes) _ (F) (psi)
- 30
-- Douglas Fir 1/8 Redry V2 355 35
: Douglas Fir 3/16 Redry 3/4 350 35
So. Pine 1/8 Redry 1/2 340 35
., .
Taking several examples from within the tables, when ~`
drying sheets of Douglas fir veneer that are ljl0" thick
`~:
and have been peeled from the heart segment of a log, it
has been determined that the best drying schedule for the
contact drying method of the present invention is a 2-minute
time with a continuously applied pressure of 35 pounds per
square inch and at a constant temperature of 335F. During
this drying 'cime, the wet veneer will be continuously pressed
. and heated with the first part of the drying process functioning
to drive off the free water held within the veneer sheet.
Since the applied temperature is above the boiling point
,
of water, steam vapor will also be generated and that generated
within the veneer sheets will accumulate within the exhaust
conduits provided by the substantially parallel grooves 84.
While the temperature on the surface of each heated metal
plate 38 will be uniform, as the sheet dries heat will be
transferred to the wetter areas at a higher rate causing
them to dry faster than drier areas. At the end of the predeter-
mined drying time, the moisture content is substantially
uniform and at the desired final level.
When drying l/16" southern pine veneer, which may be
taken from either the heart or the sap portion of the log
(it is usually sapwood because the logs are small), it can
be seen that the drying time is 4-3/4 minutes at a continuous
pressure of 35 psi and a constant plate temperature of 340F.
This drying schedule has been found to give excellent results
when drying ]/6" southern pine veneer; providing a veneer
sheet with a uniform final moisture content within a range
. of from l to 5%, an excellent surface for the application ~;
` of adhesive, increased yield due to the restraint provided
by the continuously applied pressure, and a generally higher
quality dry veneer sheet
When redrying a partially dried l/8" thick sheet of
Douglas fir veneer, it was determined that a continuously
~ applied pressure of 35 psi at 355F for l/2 minute gave excel-
- lent results. In this case, a partially dried sheet where
at least a part of it had a moisture content above 10% was
redried to a moisture content within the desired range of
` from l to 5% and with the moisture content being substantially
uniform throughout the entire sheet. The redrying of partially
dried sheets was carried out in an apparatus substantially
41
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like that depicted in Figs. 19 and 20.
The drying schedules depicted in the two tables repre-
sent optimums selected for the li~ted species, thickness,
and initial moisture condition and are not to be taken as
limiting the scope of the present invention. A reasonable
range for the various operating conditions in primary drying
would include a temperature range of from 250F to 400F,
a pressure of from 5 psi to 70 psi, and a time of from 2
minutes to 12 minutes. These ranges are applicable to veneer ;
thicknesses within a range of from 1/10" up to 3/16" and
cover a range of species from Douglas fir (western softwood)
to southern pine (southern softwood) to oaks and the like
(southern hardwoods). For redrying veneer the temperature
and pressure ranges are similar; however, the time will be
in a range of from 20 seconds to 1 minute for single sheets
of veneer. When redrying two sheets per opening, longer
times would be required. Additionally, it is believed that
the present method and apparatus can be used to dry typical
thin hardwood veneers that are on the order of 1/28" to 1/16"
in thickness such as birch and oak. These veneers are typically
. .
used for face and back veneers in decorative type paneling.
~- - It is believed that the temperatures and pressures will be
--- similar to those set forth in the above table but that drying
-- times will be considerably less, such as on the order of
--- - from 1/2 minutes to 1-1/2 minutes for primary drying. Most
~-~ likely, there will be no resulting partially dried veneer
- to be redried.
Operation of the Invention
First to be described will be the commercially usable
veneer drying system depicted in Figs. 1 and 2 of the drawings.
..
42
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Assume that wet 1/8" Douglas fir veneer sapwood is to be
dried. From the above table it is seen that the primary
drying schedule is 4-1/2 minutes at 335-380F with an applied
pressure of 35 psi. The steam supply to each of the individual
hot presses 26 is adusted accordingly to provide a uniform
~ temperature over the surfaces of metal plates 38. The pressure
- adjustment for the applied pressure is made whereby the tank
and pump assembly 164 will be controlled to generate the
exact pressure through press cylinders 30. Pressurized fluid
will also be generated for the other actuating cylinders.
Since the drying time will be 4-1/2 minutes, the various
operating cycles will be based on this predetermined time.
~he 4-1/2 minutes is the elapsed time between the closing
of the hot press that has just been loaded with wet veneer
,. '
and the opening of the same hot press after indexing around
on frame 4 and opening at unloading station 14. As previously
noted, eight modular hot presses 26 are mounted on frame
4 and it can be determined that with eight presses frame
4 will be indexed every 33 +2 seconds. It should thus be ~;
appreciated that when an open hot press is being loaded at
loading station 6, the loading apparatus 10 will have at
least 33 seconds to fill the press. Similarly, at unloading
station 14 the press will be actuated to tilt by way of tilt
cylinders 70~ 72 and then the press will be sequentially
opened starting from top and progressing to the bottom with
each dried veneer sheet sequentially falling atop inclined
slide plate 344. Each dried singulated sheet will slide
into the nip between rolls 346, 348 where it will be motivated
to a position atop the transfer conveyor 20 from which location
it will be conveyed into cooler 22.
.
43
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Of course, once the heating fluid for heating metal
plates 38 is circulating through the steam supply circuit,
the resulting condensate must be collected in the condensate
circuit and directed out through outflow pipe 160. Also,
when the frame 4 is started up for continual indexing, the
lubrication system will be activated to provide suitable
lubricating fluid to, for example, the main bearin~ structure
86.
With all operating parameters up to operating conditions,
10 an open hot press is positioned at loading station 6. A
stack of wet veneer has been positioned atop scissors lift
184 and the top sheet will be substantially in line with
feeder mechanism 1~6. Prior to the first veneer sheet being
fed into the awaiting hot press, the resilient backing member
242 will be moved on its frame to a position substantially
adjacent the rear edges of the metal plates or openings of
the press. The patting face 246 will remain in its retracted
rear position. This configuration is depicted in Fig: 10.
The operator at loading station 6 will now activate
the feeding cycle to begin feeding veneer sheets into the
awaiting hot press. The feeding cycle is timed for approxi-
;~ mately 3 seconds between the loading of each sheet. Starting
in the down position, the cylinder 204 will sequence upwardly
as each sheet is fed. The vertically movable gate 222 will
allow each sheet to be positioned against it and it will
- then be raised when the timed command signal is given. When
each veneer sheet is fed into an opening, the top and bottom
brush rolls 226, 228 serve to remove any debris. As each
',A' veneer sheet is fed into an opening, the feeder mechanism
186 will tend to motivate the sheet past the rear edges of
:'
- 44
5~
metal plates 38 where each sheet will impact against backing
member 242. At that instant, the p~Lting face 246 will be
actuated to move forward to impact the rear face of backing
member 242 urging both backing member 242 and the sheet of
veneer back towards the particular opening. The patting
face 246 continues to move, causing the veneer sheet to be
properly aligned back within its opening. This position
of aligning apparatus 12 is depicted in Fig. 11. The patting
face 246 sequences as each veneer sheet is fed into its respec-
tive opening. As the last sheet is fed into the top openingand repo sitioned within its opening, the signal will then
`be given to the loaded press to close. The 4-1/2 minute
drying schedule then commences.
;At loading station 6 the feeding apparatus 8 will be
pivoted downwardly to begin a new loading cycle and at the ~;
same time the operator can move the scissors lift 184 to
a higher level so that the top sheet in the stack is at the
proper height for the next feeding cycle. The cycle at feeding
apparatus 8 is, in part, controlled by the valving 2~8 and
cam mechanism 240 on a timed basis. After the loaded hot
press is closed, aligning apparatus 12 will be pivoted rearwardly
out of the way to allow indexing of frame 4. This position
of aligning apparatus 12 is depicted in Fig~ 9. This sequence
is repeated as each empty hot press arrives at loading station
6 and as each loaded hot press arrives after the 4-1/2 minute
drying time at unloading station 14. During the time of
operation and if an exhaust system is employed, such as circular
hood 370, the fan or other handling means will be employed
to continually draw the air and vapor underneath the hood
into conduit 372 and away from the veneer drying system.
In the redrying operation, as depicted in Figs. 19
and 20, a single hot press 352 is being employed to dry the
partially dried veneer. Again, taking an example from the
redry schedule, assume that it is southern pine veneer to
be redried with a thickness of 1/8". The drying conditions
therefor will be 30 seconds at 340F with a continuous applied
pressure of 35 psio Before redrying any southern pine veneer,
the press operating conditions would first be set. This
is done in the conventional manner. Next the feeding cycle
is set and again an approximate 3-second period between indexing
of the feeder ~ech anism provides adequate loading time.
The aligning apparatus 362 functions in essentially the same
manner as the aligning apparatus within the system of Figs.
~`1 and 2 with the exception that it pivots for unloading about
a lateral axis on the top of the press 352.
~;The other ~ajor difference is that after the drying
time has elapsed, or at any point during the drying time,
the tilt cylinders 360 will tilt the press upwardly from
- feeding apparatus 356 so as to outfeed the redried veneer
on the other side of the presaO Once the drying time has
elapsed, the press will be sequentially opened from top to
bottom, allowing each redried sheet to be singulated atop
! ~
the outfeed conveyor. Before, or simultaneously with the
tilting of press 352, cylinder 368 will be actuated to pivot
the aligning apparatus 362 upwardly about bearings 364 with
respect to press 352 and out of the way of the veneer sheets
to be unloaded. After the last sheet has exited from the
press, it will be tilted back to a horizontal alignment while
the feeding apparatus 356 will be moved downwardly to be
in registry with the first opening. Likewise, cylinder 368
46
. .
D~
will be retracted to bring aligning apparatus 362 back to
a position in line with the back edges of the metal plates
354.
Detailed descriptions have bee:n given of several indepen-
dent and distinct inventions, all of which relate to veneer
drying and handling. It will be recognized by those skilled
in the art that various modifications can be made to what
has been described and it is intended that all of these modifi-
cations be included within the broad scope of the appended
claims.
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