Note: Descriptions are shown in the official language in which they were submitted.
2 ~ 2 ~
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WOOD COMPOSITE FORMING AND CURING SYSTEM
CnOSS-REFERENCE TO REL~TED APPLICATION
This is a continuation-in-part Or copending application Serial
No. 07/555,723 (1723), tiled July 23, 1990. This and each o~ the other
applications and patents mentioned anywhere in this disclosure are
hereby incorporated by re~erence in their entireties.
B~CXGROUND O~ THE INVENTION
The present invention relates to systems ror continuously man-
uIacturing wood composite, adhesively bonded products wherein pres-
sure and microwave ener~y are simultaneously applied to the curabb
assemblies. The adhesive bonding agent is thereby cured or set while
the product is pressed and/or maintained at the desired dimensions
and density. The microwave application cures the resins which are
used as binders or adhesives for the composite wood materials, such as
wood particles, wood chips, wood waters, wood strip6, wood fibers and
wood veneers, used in the production oI chipboard, hard board, parti-
cle board, wa~er board, plywood and other composlte products. The
present invention more particularly relates to processes for curing
and pressing layups which are ~ormed by depositing adhesive coated,
elongate wood strands oriented suhstantlally longitudinally in a mat
from a plurality or layup ~eeds.
Detailed discusslons ot preierred methods or ~orming adhesive
coated, curable assemblies and depositing them on a continuous layup
conveyoribelt ror conveyancei to microwave press assemblies are pro
vlded in the '?23 application, and in U.S. Patents 4,8?2,544 ('S44),
4,563,237 ('237), 4,706,799 ('799), 3,493,021(~021) and ~,S46,886. Addi-
tlsnally, products containing oriented elongate strands such as could
be used herein are disclosed in U.S. Patent 4,061,819 (which was reis-
sued as Re. 30,636) and the ~021 patent. The 1544, l799 and 123~ pat-
ents remedy the ~card deckingll orientation problems Or the system o~
2 ~J 2 5 ~
2-
the '021 patent. In these three patents the product is formed Irom
elongate members at least about a foot in length which are oriented,
compressed and bonded together. The elongate members are depos-
ited on a moving carrier and oriented substantially parallel to the
direction of movement of the carrier and on the carrier over a length
thereo~ that is at least as long as about one and a half times the
length of the elongate members and is at least as long as about thirty
times the final thickness o~ the compressed, composite product.
When two or more of layup systerns have been used to form a
single layup mat the interfaces between the layups are prone to
strand alignment inconsistencies, reducing the strength properties
across the beam thereby produced. A system for remedying this pro~
lem, that is, insuring that the final compressed product has consistent
mechanical properties throughout its cross sectional depth, is dis-
closed in the copending ~723 application. The system(s) described in
that application Include at least rirst and second simultaneously
formed layups, overlapping one on top of the other in zig-zag patterns
on a longitudinal, side-to-side moving conveyor trough. The top of
the bottom layer and the bottom of the top layer are formed at the
same time, and the mat thereby formed hæ a continuous average
strand angle throughout the layer inter aces.
Before laying the strands in a side-by-side lengthwise dimen-
sion in the trough layup they are coated with a curable adhesive, such
as a standard phenol-~ormaldehyde glue having a small wax compo
nent. The adhesive strand layup mat is then conYeyed to a press
where the arranged strands are heated by microwave energy and com-
pressed in a converging belt press to thereby rorm a high strength
dlmensional composite product. Examples of belt presses are those ~ ;
dlsclosed; in U.S. Patent 4,517,148 and copendlng U.S. Application~
Serlal No. 07/456,657 ('657), riled December 29, 1989. Preferred
microwave appllcators ~or these continuous presses are disclosed in
U.S. Patent 4,456,498 and copending U.S. Applicatlon Serial No.
07/557,652 ('652), filed July 27, 1990. In the press a pair o~ endless
belts converge to a press chamber at their nip region. At opposite
side walls o~ the press chamber are microwave applicators, and
.
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windows at both o~ the side walLs form parts o~ the side walls o~ the
press chambers and also block the layup from entering the applicators
as it is being pressed. The windows are transparent to the micsowave
energy from the applicators which passes therethrough to the layup as
it is being pressed in the belt press.
A problem in the past hæ been that the rinal structural wood
product has an uneven density pro~ile. Lf the temperature or moisture
contents of the mat are not consistent within a ~ew degrees, instabili-
ties in the change o~ temperature development, that is uneven heat-
ing, occur ln the microwave press ~or two reasons. First the dielec-
tric constant epsilon, both its real and imaginary parts, increases as
temperature increases, which means that more energy is deposited
into areas that are already warmer. This has a multiplier e~rect; that
is, the warmer these areas get, the more they wi~l attract energy, and
so rorth. A second ractor is that these layups are comprised o~ wood
fiber, and wood is compressed as it is microwave heated. ~he wood is
so$ter when lt is warmer, and the warmer part is more easily com-
pressed in the microwave ~ield. As it compresses, the warmer areas
take up more o the compression, sotten and compress to a higher
density sooner, which again increases their dielectric absorption.
That is, more energy focuses into those areas, and as th~s happens
they become so~ter and compress more readlly and instability again
results. Both Or these ~actors work against even heating and even
~inal product density in wood composite products.
For example, in a wood product with an 11.4 inch by 14.75 inch
crosssection, the top and the bottom o~ the mat can be about 25 to
30C, while the center two-thirds o~ the mat can be about 35 to
50C, due to the natural progression of the water uptake. The center
heats up since the water cbemically blndin;g to the cellulose lignen
structùre in the mat is an exothQrmic activity. As the mat progresses
through the press, the top and bottom can have a specii'ic gravity of
.S gram per oubic centimeter on the top and bottom, while the center
two-thirds can be .6 to .6S gram per cc. Further, the moisture con-
tent ot the .S gram per cc top and bottom areas is about 12 to 13% o~
the dry basis o~ wood, while the .6 to .65 gram per cc has about 9 to
2, 2 ~i 3 ~ ~ ~
10% moistùre content. The density gradlent is important to these
parameters, since whenever there is a density gradient there is also a
strength parameter gradient. Accordingly, there is a different ther-
mal normalizing effect on the compressed mat and thus a different
moisture response. The cooler areas tend to expand more rapidly,
more readily and more permanently on wetting, which can lead to
bowing or splaying of the final product. The resulting density gradi-
ent is thus due to two factors. The rirst is the uneven temperature
and moisture profile of the mat as lt enters the microwave press, and
the second is the uneven microwave deposltion pattern of the micro-
wave applicator. Although the more significant of these appears to
be the uneven pre-press proiile, the uneven microwave pattern is also
a substantial factor.
One solution to this density gradient problem might be to vary
the mlcrowave patterns, but they are diiiicult to control and can
never be made precisely even. Referring to the ~652 application, the
applicator horn expands out towards the layup thereby producing
microwave patterns which are dimcult, ii not impossible, to avoid.
A prior art attempt to remedy this density gradient problem
has been to raise the temperature oi the entire mat. The temperature
wæ raised by lnsulating the top and the bottom of the mat and then
providing a oi;i heatlng system around the conveyor itselt. More par-
ticularly, oil heating lines were pcsitioned along the sides of the
trough and heating devices underneath the bottom and insulation cov-
ers placed on top oi the mat as soon as the last strands were depos-
ited. The mat was thereby lirted out oi tha very sensitlve operating
range where these control parameters have their biggest el~ect. A
maC that is entering the press with a 50 to 60C temperature hæ
already experienced theibuL~c oi its softening. Thus, even though it
s~ili ha~ a temperature gradient oi iive to ten degrees, this gradient
has less oi an eftect on the final product.
When the temperature ot the entire mat is raised sufticiently
the mat behaves reasonabiy consistently in the microwave heating
process. It does not compensate for inadequacies in the evenness of
the microwave heating, however. The prior art system ot heating the
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entire layup to make it hotter was thus not an attempt to control
either the moisture or temperature beyond an even mat nor did it
achieve an even mat temperature. A benefit of raising the tempera-
ture of the entire mat is that the effects of the ambient temperature
are reduced but not eliminated. In other words, on hot summer days
there is a dii!ferent mat self-heating prol'ile than on cold winter days,
and these effects are reduced to a ~ertain extent by heating the
entire mat.
A significant disadvantage of this ~'whole mat~ heating tech-
nique, however, is that ii' the temperature geB too high, ~or example
to 60 or 70C, then the glue in the mat can be precured, making the
product useless. The product may still look good, consolidated and
strong but if the glue was even partially cured before the i'inal com-
pression and microwave heating, there is little left to hold the wood
strands or composite assemblies together. Aside i'rom the precuring
problem, there is also the problem that the entire mat as a practical
matter is dil'i'icult to heat evenly since there are differential chemical
reactions occurring with this water uptake. The mat is simply not
stabb enough to be totally heated to an even, higher temperature.
A prior art technology in the board industry for reducing press
curing times is to radio i'requency (RF) preheat the mat before it
reaches the press. That is, an RF fieid is applied to the uncompressed
mat to raise the temperature thereof to S0 to 70C or even higher
before final compression and heating with a hot press. This board
forming technique is usually a batch and not a continuous process,
however, and the purpose of the RF preheating is to shorten the
presslng time in the hot press. This mat is also formed very thin so
that there is no significant steam transport within it. Further, this
prior art board formins process does not involve any significant or
positive compression o~ the mat. Thus, any small irregularities in
preheating will not magnii'y during the process. When a mat is to be
simuitaneously heated and compressed (such as in the present process)
compre sibility during heating is very important and any instabilities
tend to magnify.
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SUMMARY OF THE INVENl'ION
Accord~ngly, it is a primary ob~ect of the present invention to
provide an improved process ior iorming wood composite structural
products in a microwave press wherein the resulting product has
improved density gradients and is not chemically changed.
Direc~ed to achieving this object, an improved process (and
system) for ~orming wood composite products is herein disclosed. The
process includes ~orming a layup or mat Or composite assemblies, and
generally be~ore passing it through a microwave curing press assem-
bly, signiricantly altering the temperature and/or moisture level con-
tents in predetermined localized areas thereot. The temperature Or
the localized areas w~;i be changed by at least 5C and the moisture
content wlll be changed by up to 109~ over other areas of the mat in
the same cross section thereoi. Whereas the density gradients of the
iinal wood product without this altering step would vary by as much
as 50%, with this step they will vary only by as much as 10% or less.
While simply heating the mat has little errect on the moisture content
variability, applying a water mist spray allows ior a wide variability
change. Two or three percent changes, ior example, which is a gross
average though since ten percent might be added to the mat surface
and nothing to the center, can be made without diiiiculty. Since only
heat snd/or moisture have been added or subtracted lrom the compos-
ite mat there is no chemical dlfierence in the iinal structural wood
product. Further, no change is needed or made in the microwave
applicators.
A number oi diiierent methods of determining the amount and
area o~ the changes oi the alterlng step are încluded herein. One
method measures the profile beiore and aiter the conveyance through
the microwave press, varies the proiile entering the press and
observes the resultlng proiile and then calculates the amounts and
locations d the alterations needed. Another method ls to provide a
mat with very even moisture and temperature proriles, convey it
through the press and then measure the resulting heatlng and density
proiiles. This will show the unevenness oi the microwave deposition
pattern(s) and thus the areas where additional moisture and/or heat
are needed.
A number of di~erent methods for affecting this alteration in
temperature and/or moisture level in selected areas are within the
scope OI this invention. These include adding moisture directly, pre-
venting evaporation, providing cooling air or other fluid, adding hot
water in a jet, mist or steam to the mat, heating the mat with infra-
red energy or radlant heat, or by significantly affecting the tempera-
ture of ad3acent conveyor belt structure which temperature is then
conveyed to the mat. These techniques can be used once the layup
hæ been deposited in the conveyor trough. It is also within the scope
of the invention to affect the resulting moisture and/or temperature
profiles of the resulting mat by acting upon the composite assemblies
beIore they are deposited in the conveyor trough. One way of doing
this, when the layup in the mat is fed trom a plurality of different
layup systems, is to heat (or cool) the glue differently in one or more
of the layup systems before they are deposited on the respective com-
posite assemblies.
Other objects and advantages Or the present invention will
become more apparent to those persons having ordinary skill in the
art to which the present invention pertains from the foregoing
description taken in con~unction with the accompanying drawings.
BRIEF DEscRn?TloN OF THE DR~WINGS
Figure 1 is a schematic diagram or a system Or the present
invention.
Figure 2 is a perspective view o~ a portion of a first embodi-
ment d the system Or Figure 1.
Figure 3 is a perspective view o~ a portion of a second embodi-
ment of the system o Figure,l.
Figure 4 is a perspective view o~ a portion Or a third embodi-
ment of the system of Figure 1.
DETAILED DESCRIPlION OF PREFERRED
EMBODIMENTS OF THE INVENTION
Referring to Figure 1, a system o~ the present invention is
shown diagrammatically at 100. System 100 includes a longitudinal
conveyor 102 which conveys a mat of composite material into a
microwave press assembly shown generally at 104. Details o~ a pr~
ferred microwave press assembly 104 are shown in the ~657 and ~652
applications. The composite assemblies are deposited on the conveyor
102 by a depositing system shown generically at 106. An example of a
pre~erred depositing system 106 is that disclosed in the 1000 applica-
tion wherein four generally separate layups feed simultaneously onto a
single conveyor trough (102) Generally before the mat enters the
microwave press assembly 104, the localized areas thereof have their
temperature and/or moisture contents controllably altered by an
alteration system shown generically at 108, such that the density gra-
dients of the structural product leaving the press assembly 104 are
significantly improved. This altering step (108) can occur berore the
composite assem~i~; are deposited on the conveyor belt 102, as they
are deposited on the conveyor belt, after they have been deposited
and have traveled a distance on the conveyor belt, or any combination
thereof, as would be apparent to those sldlled in the art from the sub-
~ect disclosur~. That is, the altering system 108 can precede, ~ollow
or be part Or the layup depositing system 106, or even occur within
the microwave press assembly 104 (as discussed later). Thus, to com-
pensate or inadeguacies in the evenness Or the microwave heating
the mat temperature and/or moisture content profiles are altered by
the altering system 108 be~ore entering the microwave press assembly
104. The microwave press assembly 104 itselr and its microwave dep-
osition patterns are~unchanged. ?hese proliles can be measured by
measuring systems beIore and arter the press assembly 104 as shown
generically by measuring systems 110 and 112, respectively.
A number d techniques or altering systems 108 Or the present
invention, seven of which are discussed below, allow ~or the heating
patterns oI the mat entering the press assembly 104 to be tailored and
there~ore the ~inal density patterns of the cured compressed product
9 2 ~
to ~e more markedly improved as can be measured by the measuring
system 112. (1) Moisture can be added to the dry wood mat; this cre-
ates an exothermic reaction as the water becomes bound chemically
to the wood and that is why changes in the temperature ot the wood
can occur with changes in moisture content. (2) Steam can be added
to physically heat one or more portions of the layup. (3) Similar to (2)
hot water is added to physically heat predetermined areas of the mat.
(4) Moisture is added locally to change the microwave absorption
properties locally: this can be done by spraying a ~ine mist of water
anywhere in the mat as it is being formed, on the bottom or the top or
on the sides af~er it has been formed. (5) The mat can be cooled with
air, or any other suitable nuid, to lower the temperature in predeter-
mined parts of the mat; this can be used in con~unction with the addi-
tion of water to the wood to lower the temperature o~ the mat cre-
ated ~rom the exothermic reaction ~rom the added water. (6? The mat
can be insulated, as on the top and/or bottom and/or sides thereof, to
control the rate ot change ot temperature and the moisture can be
contalned so that it is given of f to lesser degrees by natural evapora-
tion; this makes the moisture more readily available for exothermic
chemical addition to the wood and therefore heating the wood. (7)
The platens of the microwave preæ 104 can be heated prior to andtor
during microwave heating actually within the microwave press.
Heating the platens raises the temperature on the very sur~ace
Or the mat, and therefore creates an area Or higher energy absorption
through exera densiflcation and higher initial loæ tangent. Since
there is a higher initial loss tangent to the wood when there is a
higher temperature, heating the surface Or the mat with the platens
arrects that kind or a change. Although heating the platens directly
heats only a relatiyely small depthiot the mat, perhaps a quarter to a
halr ot an inch thick surrace layer, this heat propagates a signiricant
dlstance into the mat, as by steam generation rrOm excess microwave
heatlng. The one-half inch heat propagation allows greater amounts
Or microwave energy to be absorbed in the area that is heated by the
steam, and the microwave absorption effects Or this heating propa-
gate a distance into the product.
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In the embodiment oi Figure 2 steam 120 is injected over the
segmented metal transport belt 122 tor conveyor 102) underneath the
mat, thereby heating the belt. The steam 120 can be injected through
large orificed ~ee connectors 126 oi a steam header applicator 128,
ad~acent the tail sprocket 130 oi' the belt 122. The bottom of the mat
is thereby heated since it is placed directly onto the hot surface of
the belt 122 as the mat is laid up in the layup trough 132. This uneven
heat ~ormation is trouDlesome in part due to the exothermic reaction,
which is very temperature dependent in its own right. Thus, ii a mat
area cools locally, the exothermic reaction progresses more slowly
and therefore the area stays cwler yet, creating another instability.
By heating (with steam 120) the steel chain or belt 122 underneath the
mat, heat is being added to the bottom oi' the mat without adding
moisture to it.
The heat (and moisture) according to another technique oi this
invention can be in~ected directly on the mat, and an embodiment of
this technique is illustrated in Figure 3. As shown therein a steam
supply pipe 140 is positioned in a space shown genera~y at 142 in the
conveyor 102 directly below the layup mat 144. A cross-section Or
the mat 144 held in the layup trough 146 on both sides of the conveyor
102. The conveyor 102 includes a pair of aligned layup belts 148, 150
each having its own drive roll, 152, 154, respectively. The end oi the
steam pipe 156 within the space 142 has a plurality oi upwardly dis-
posed aperture 158, out through which steam 160 passes to heat (and
moi3ten) the bottom surtace oi the mat 144 as it is conveyed across
the space 142 between the layup belts 148, 150. Direct steam 160 is
thereby used to increase the temperature of the bottom oi the mat
144 and potentially the moisture content thereoi.
As a specitlc e~ample, where the bottom oi the mat (144) is to
be raised rrom 25 to 30C, a 50 to SSC 3et ot wet steam (160) can be
dlrected directly on the bottom ot the mat. The change o~ tempera-
ture with steam can increase moisture content. The density of the
mat can be raised trom its nominal point .5 gram per cc to about .65
to .7 gram per cc. By exceed!ng the temperature or by matching the
temperature and excæding by a sman amount the moisture content of
... , ". ,. . . ,. - , . : .. ,, ,; . ~ .. . ,. ., , . . . . - ,. .
, .
the rest oi the mat, its density is raised to above that ot the densest
part of the mat. Thus, final density profile of the product is directly
controlled by the local application oi steam. The final moisture con-
tent gradient of the product is a strong function of the final tempera-
ture gradient Or the product. Similarly, the îinal density gradient is a
function oi the final temperature gradient. If the temperature is
even and consistent in the final product coming out of the press, the
moisture and density are also even; the three are directly related. It
is difficult to obtaln an even temperature pro~ile and an uneven mois-
ture proiile in a well ~ormed product, or an even temperature pro~ile
and an uneven density profile. Thus, by carefully tailoring the mois-
ture and temperature profiles to compensate for the natural heating
patterns an even density results. An even moisture pattern also can
result and the moisture gradient in the final product is important as it
aifects its proper use. The more even the moisture, the le~s llkely it
is for the product to tend to bow or splay.
Proper control oi the alteration ot the temperature and mois-
ture contents oi the layup results in no history ot the control remain-
ing in the product other than an even density and moisture content.
If an area was properly made wetter or hotter to increase microwave
absorption, the results will be even moisture, not higher moisture, and
even density, not higher density. This is because it a mat area is wet-
ter it absorbs more microwave energy as it reaches the desired tem-
perature and this drives the extra moisture away. There is thus no
evidence ot what was done to obtain the even moisture and density in
the product. Nothing was added chemically that is d~fferent than
e~dst normally in the product. Accordingly, the tinal density can be
advantageously controlled without adding chemicals, absorbers or
anythinglelse aside trom heat,and moisture to the layup.
The temperature in the mae can be monitored as it is being
formed by measuring system 110 and compared with the development
ot the temperature protiie in the mat compared to the profile oi the
iinal product density as measured by measuring system 112. This
allows tor a quick determination oi where the extra heat and/or mois-
tur~ wili benetit the iinal density profile. For example, one
-- 12 --
monitoring or measuring system 110 includes a series ot thermocou-
ples (not shown) added in the cross-sectton OI the mat and run down
the mat formation For every two inches, for example, in the depth
of the mat another thermocouple is added across the mat as well as
vertically throughout the mat As many thermocouples are added as
needed to obtain the desired resolution For example, a high resolu-
tion can be obtained where the thermocouples are positioned every
half-inch; if the temperature in the bottom or the mat is the subject
ct the modification then this one-half inch positionlng in the bottom
six inches of the mat can be used to provide a higher resolution in
monitoring the temperature ot the bottom oI the mat. Before the
mat enters the press 102 the thermocouples are usually removed so
they do not interrere with the microwave heating patterns The ther-
mocouples thereby provide an excellent history o the progression o~
the temperature o~ the mat on the way to the press 102
Another monitoring procedure or measuring system 110 is to
actually stop production and take moisture contents samples from the
mat. This can provide both temperature and moisture pro~iles of the
mat prior to pressing. A-ter pressing, the profiles of the final density
and temperature profile can be obtained by measuring system 112 the
temperature profile can be obtained with infrared cameras and the
density protiles by actually cutting out density samples
It the microwave press 102 is heating quite evenly, then even
temperature and moisture protiles entering the system (or press) are
desirable so that ths energy is absorbed evenly There is an inherent
imbalance in all microwave application systems, however. By trial
and error techniques, tor example, the temperature/moisture profile
needed to create an even density resulting profile can be determined
The entering temperature moisture prorile is essentially an inverse o~
the heating protile
It the entry moisture and temperature protiles are even, and
the heating profile pattern and the final density proiile are known,
then the heating pattern ot the microwave system and its unevenness
can be determined The simple observation of where insufficient heat
- i3-
, ~ ,
was applied evidences where moisture or higher temperatures in the
mat going into the press are needed.
By injecting steam on the bottom very close to the press, such
as in the system o~ Figure 3, the density is also improved markedly.
The density can actually be increased beyond that of the average
which shows an ability to manipulate the density to any desired
amount by contrdling temperature.
Further improvements to this process involve monitoring (110)
moisture and temperature during mat formation, caretully controlling
and monitoring the energy and moisture application during the mat
layup process, to understand precisely the protile going into the press
and then comparing it with the exact profile exiting the press 102.
The process ot the alteration can then be tine tuned. Further
improvements involve experiments to determine whether heating or
moisture is the predominant or better parameter to maniEmlate. A
disadvantage with the present process though is that it is a dynamic
process and that monitoring it actually changes it. In other words, by
changing the operating speed or stopping and starting operation to
monitor the process, the process is itselt altered. Control is lost over
the temperature and moisture proIiles by stopping and starting the
system. Even during constant operation the transit time between mat
tormation and microwave heating varies between one-halt hour and
one hour depending on where the strand is deposited in the one hun-
dred and twenty toot long layup trough (102). The exothermic reac-
tion time thus varies through the cross-section. The temperature can
initially rlse and begin to tall again. In some instances, it continues to
rise and in others it talls, depending on the location in the mat and
the extent ot insulation, or whether water is continuing to be applied
~rom thelatmosphere~, a ~et or, a spray.
Ideally, a system (110, 112) would be developed to accurately
monitor the temperature, tor example, of the bottom ot the mat atter
some ot the techniques described above have been used to manipulate
the temperature and moisture content. This can be done with lntra-
red surtace measurements. Moisture meters working on Wterential
intrared and optical properties, that is, visible light techniques, can
~ ' .
.
- 14~
: .
be adapte~ for use herein. Either absorption or reflectivity of the
light is measured, and it represents a relatively sensitive ~unction of
moisture content. This type of moisture meter has been used in the
particle board industry to determine moisture content, wherein the
conveyor is flowed past a sensor and the moisture content determined
by infrared invlsible light techniques. Infrared heating techniques can
also be used to alter or monitor the temperature directly.
The very bottom of the mat can be as low as 20 or 25C, basi-
cally ambient temperature, whereas the middle of the mat can go up
to a hot 40C. This is a se~-generated heat often just from the mois-
ture uptake after glue application. Thus, to heat the surfaces, a small
amount of moisture is added or the surface is insulated to prevent
natural evaporation and heat loss therefrom; insulation from both
heat 106s and moisture loss can thereby be made. When the wood
heats, it tends to give off a bit o~ moisture as well as to chemically
absorb it into its structure. Proper application o~ the present process
allows essentially any desired temperature profile to obtained. For
example, with the center at 45 or 50, the oueer surfaces have been
with the process oI this invention heated to as high as 35 or 40. This
is essentially within ~ive degrees of the center temperature which is
usually suIficient for the currently used apparatus.
This process can be used to directly apply heat and steam to
the very bottom o~ the mat, as previously described with respect to
Figure 3, and thereby gain higher than normal density in that area,
that is, along the very bottom face or the bottom couple ot inches.
Thus, the temperature profile can be inverted and thereby the density
proflle inverted. Although the main ob~ective of this invention is to
ob~ain a homogeneous wood product, there may be instances where a
difrerent profile is desired. For example, i a relanvely thin board is
made, which is not going to be remanufactured, a relatively high den-
slty sur~ace may be desirable. Certain kinds o thin (about .5 inch)
panel products have a high surtace density and low core density which
give strength properties that are more beneflcial and thereby give it a
higher msment of inertia for the total mass and the same thickness.
These boards are typically used in furniture where the high density
i~Y. ~` .
- 15 - ~ 3
surface is usually a better consolidated surface and takes finishes bet-
ter. In the present case this process could make stiffer scaffold
planks or more stable or stiffer beams (e.g., 3.S inches by 16 inches)
with a denser face at the extremes of the sixteen inch dimension.
Another em~odiment Or the altering system 108 is illustrated in
Figure 4 wherein it is primarily the bottom and middle portions of the
mat 172 whose temperature and moisture content are being altered.
The basic layup system, such as shown in the ~723 application, includes
the layup trough 1~4 associated with the conveyor 102 and in which
the mat 172 is conveyed and the oscillating table 176 and chute 178
for directing and depositing the wood strands o- the mat 172 within
the trough 174. Additional layup systems coordinated therewith for
this same layup trough and as would be understood from the '732
application can be provided. The temperature and moisture content
profiles of the mat 172 are controllably altered as the mat is being
formed (as the strands are being laid on the trough 174) by spraying a
fine mist 180 of water out through a spray nozzle 182 on the bottom
strands and then blowing, by fans 184 positioned ad~acent the layup
trough 174, cooling air to cool the strands in this case in the center of
the ma~. The fans 184 are preferably relatively large fans with frac-
tional horsepower motors, such as standard room fans used by painters
to ventilate rooms being painted. A disadvantage of this technique
though is that the resulting mat is cold and thereby resists compres-
sion and is difficult to pull through the press (104).
For the bottom steam heating technique, as in Figure 3, the
amount of steam 160 will vary as needed to raise the temperature and
can b~ measured by flow meters (not shown). The amount of steam
used depends on a number o~ factors, such as how well the steam ~et is
aimed and focused, h~owl hot thq steam is and how much the steam is
diluted by the surrounding air. True live steam directly impinging
upon the wood mat would probably be too hot and could at least par-
tially precure the glue. Again, care must be taken, under any of the
techniques of this invention, to not precure the glue such as might
happen if the line stops moving and live steam continues to impinge
on the product for even a very few additional seconds.
16 2 . ~
Reierring again to Figure 2 wherein a steam jet 120 is used to
heat a metal belt 122, the belt is heated so that its temperature rises
by generally twenty degrees which brings it up to a 30 to 50 temper-
ature range. It thereby has energy to give up to the product. I~ the
object is to overcompensate, to provide a hotter base of the mat then
at center, then a hotter steel belt is probably needed. The composite
assemblies or strands do not rest entirely on the steel belt 122 though
since they sit on little ridges of the steel belt. Thus, the very bottom
surface of the mat is taking radiant or convective, rather than con-
ductive, heat from the steel and thereby can tolerate a higher tem-
perature in the steel belt 122 without precuring. By heating the steel
belt 122 to a temperature at least as hot as the lower surrace o~ the
mat, the steel then does not act as a heat sink. Ir the steel is very
cold, the strands next to it will never go through the chemical pro-
cesses oi absorbing water ast enough to raise the temperature oi the
wood. Thus, by having a bed ot hot steel close by, the progression o~
chemical reaction of water uptake is encouraged.
Where a multi-layup head system is used, such as described in
the '732 application, the temperature and/or moisture contents o~ one
or more oi the layup heads can be varied to thereby locally afiect the
temperature and/or moisture contents Or the mat thereby produced in
the conveyor belt trough. Either the moisture and/or the temperature
of the strands can be dii'Ierentially altered in one or more of the layup
heads. For example, the adhesive or glue used can be hotter with one
layup head than with the other to heat the top and bottom stranders.
Warm glue can be used on the taces and thereby give the chemical
reaction a kick start. The glue can be gently and delicately heated
wlth industrial heat exchange units ~not shown) and without curing
the glue. The glue pot life is dramatically afIected iI the glue is
heated much above 20C. For example, its pot liIe can be reduced by
a iactor oI approximately ten (depending on the resin) iI the glue is
heated to 40C.
From the Ioregoing detailed description, it wlll be evident that
there are a number oi changes, adaptations and modifications oi the
present invention which come within the province of those skilled in
- 17- ~23~
the art. However, it is intended that all such variations not departing
~rom the spirit of the invention be considered as within the scope
thereo~ æ limited solely by the claims appended hereto.
