CA2025555A1 - Wood composite forming and curing system - Google Patents

Abstract

WOOD COMPOSITE FORMING AND CURING SYSTEM
ABSTRACT OF THE DISCLOSURE
Adhesive coated wood strands are laid up on a conveyor belt and conveyed thereon to a microwave curing press. Due to uneven temperature or moisture profiles of the layup and/or uneven micro-wave deposition patterns in the press, the structure wood products thereby formed in the past had uneven density profiles. This reduces product strength and product properties especially after wetting.
Before entering the press the moisture and/or temperature profiles of the layup are controllably altered according to this invention thereby improving the resulting density profiles. Moisture and/or temperature levels of predetermined areas of the mat are increased or decreased to obtain the desired pre-press profiles. The profiles can be adjusted for example by the application of hot steam to the lower mat surface directly or the conveyor belt directly and the mat thereby indirectly, and/or the application of a water spray and cooling fan air to the same or different mat layers.

Description

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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~

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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 - 5~ J~

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 ... , ". ,. . . ,. - , . : .. ,, ,; . ~ .. . ,. ., , . . . . - ,. .

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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 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 ~ ' .

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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.

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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.

Claims (60)

1. A layup process, said process comprising the steps of:
forming a layup, during said forming step altering at least one of temperature or moisture levels in resulting localized areas of a wood adhesive composite layup thereby forming the layup;
and thereafter, pressing and microwave curing the formed layup and thereby creating a structural wood based product;
said altering step improving the density gradient of the structural wood based product.

2. The process of claim 1 wherein said altering step heats the composite layup without precuring the adhesive thereof.

3. The process of claim 1 wherein said altering step raises the temperature or the localized areas and thereby causes water to be absorbed faster through a process, which is a chemical process.

4. The process of claim 1 wherein said forming step includes generally separately forming first and second layups and overlapping the first and second layups to form the composite layup.

5. The process of claim 4 wherein said altering step includes the first and second layups having different temperatures immediately prior to said overlapping.

6. The process of claim 5 wherein said different tempera-tures differ by at least 15°C.

7. The process of claim 5 wherein said first and second layup forming steps include using a first adhesive in the first layup and a second adhesive substantially different in temperature than the first adhesive in the second layup.

8. The process of claim 4 wherein said altering step includes the first and second layups having different moisture con-tents immediately prior to said overlapping.

9. The process of claim 8 wherein said different moisture contents differ by at least two percent.

10. The process of claim 1 wherein said forming step includes forming the composite layup as a multi-layer strand layup from a plurality of strand layups at least one of which is at least 10°C
warmer than another.

11. The process of claim 1 wherein said pressing and micro-wave curing step includes conveying the formed layup on a continuous belt through a microwave curing press assembly.

12. The process of claim 1 wherein said adjusting step includes heat insulating the localized area.

13. The process of claim 1 wherein the final product density gradient is an even density gradient varying by less than 5% from one product cross-sectional area to another.

14. The process or claim 1 wherein said pressing and micro-wave curing step includes conveying the formed layup through a microwave press assembly.

15. The process of claim 14 further comprising determining a physical characteristic profile differing from the preferred and resulting in a layup conveyed through the microwave press assembly, and said altering step compensating at least in part for the deter-mined uneven density profile.

16. The process of claim 14 further comprising comparing physical characteristic profiles of a layup before entering the micro-wave press assembly, the resulting product exiting therefrom, and a preferred resulting product profile, and said altering step taking into account the differences of the profiles.

17. The process of claim 14 wherein said altering step takes into account uneven heating patterns of the microwave press assembly.

18. The process of claim 1 wherein said altering step includes injecting fluid on portions of the layup.

19. The process of claim 18 wherein said fluid is substan-tially hotter than the layup portions.

20. The process of claim 18 wherein said fluid is a liquid.

21. The process of claim 18 wherein said fluid is a mist.

22. The process of claim 18 wherein said fluid is a gas.

23. The process of claim 1 wherein said altering step includes heating the localized areas with radiant or convective heat.

24. The process of claim 1 wherein said altering step includes heating the localized areas with conductive heat.

25. The process of claim 1 wherein said pressing and curing step includes a microwave press assembly, and said forming step includes conveying the layup to the microwave press assembly on a heat conductive conveyor belt.

26. The process of claim 25 wherein said altering step includes heating the conveyor belt.

27. The process of claim 26 wherein said heating step includes heating by at least 10°C the layer of layup adjacent the heated conveyor belt.

28. The process of claim 1 wherein said altering step is con-trolled to compensate for uneven microwave deposition patterns dur-ing said pressing and microwave curing step.

29. A layup microwave curing process, said process com-prising the steps of:
adjusting the level or at least one of moisture or temper-ature levels in at least one preselected and localized area of a wood based layup to thereby improve the density of the pressed and cured layup product; and thereafter, pressing and microwave curing the adjusted layup.

30. The process of claim 29 wherein said adjusting step includes altering the moisture level in the localized area.

31. The process of claim 30 wherein said altering step includes increasing said moisture level.

32. The process of claim 30 wherein said altering step includes decreasing said moisture level.

33. The process of claim 30 wherein said adjusting step also includes altering the temperature of the localized area.

34. The process of claim 29 wherein said adjusting step includes altering the temperature of the localized area.

35. The process of claim 34 wherein said altering step includes increasing said temperature.

36. The process of claim 34 wherein said altering step includes decreasing said temperature.

37. The process of claim 29 wherein said localized area includes the bottom layer or the layup.

38. The process of claim 29 wherein said localized area includes the top layer of the layup.

39. The process of claim 29 wherein said localized area includes a central layer of the layup.

40. The process of claim 29 wherein said pressing and microwave curing step includes continuously conveying the layup through a microwave press assembly.

41. The process of claim 29 further comprising conveying the layup on a conveyor belt to the location of said pressing and microwave step.

42. The process of claim 41 wherein said adjusting step includes altering the temperature of the conveyor belt and thereby of the adjacent area of the layup.

43. The process of claim 42 wherein the conveyor belt com-prises a segmented metal transport belt.

44. The process of claim 43 wherein said altering step includes heating the segmented metal transport belt.

45. The process of claim 41 wherein said altering step includes subjecting the conveyor belt to a jet of hot steam.

46. The process of claim 45 wherein the belt includes a plu-rality of spaced support ridges, and said altering includes transmitting heat from the belt to the layup.

47. The process or claim 41 further comprising heating the belt so that it is at least as hot as the adjacent layup surface and thereby does not function as a heat sink for the layup.

48. A wood composite microwave curing process, comprising:
microwave heating a composite wood mat; and before said heating step, manipulating the temperature and moisture content profile of the composite wood mat, and thereby improving the density gradient of the mat after being microwave heated in said microwave heating step.

49. A wood base layup pressing and curing process, comprising:
controllably adjusting the level of at least one of mois-ture and temperature in at least one preselected and localized area of a wood based layup to thereby improve the density of the pressed and cured layup product;
thereafter, pressing and microwave curing the adjusted layup.

50. A layup process, comprising:
altering at least one of the cross-sectional temperature, moisture and density profiles of a curable wood strand layup; and thereafter, pressing and microwave curing the altered layup to form a structural wood product;
wherein said altering step results in an improved density profile of the wood product.

51. A composite wood forming system, comprising:
forming means for forming an adhesive, wood composite layup mat;
a microwave curing press; and conveying means for conveying the mat to said micro-wave curing press;
wherein said forming means includes altering means for altering at least one or the temperature and moisture cross-sectional profiles of the mat generally before it enters said microwave curing press and thereby improving the density gradient of the reacting pressed and cured wood product to a coefficient of variation of at least 10%.

52. The system of claim 51 wherein said altering means includes changing means for controllably changing the temperature in at least one preselected area of the mat.

53. The system of claim 51 wherein said altering means includes changing means for controllably changing the moisture con-tent in at least one preselected area of the mat.

54. The system of claim 51 wherein said conveying means includes a conveyor belt, and said altering means includes changing means for changing the temperature of said conveyor belt and thereby of the bottom layer of the mat.

55. The system of claim 54 wherein said changing means includes steam heating means for steam heating said conveyor belt generally before the mat is deposited thereon.

56. The system of claim 51 wherein said altering means includes blowing means for blowing cooling air across the top surface of the mat during mat formation.

57. The system of claim 51 wherein said altering means includes blowing means for blowing cooling air across the top surface of the mat alter mat formation.

58. The system of claim 51 wherein said altering means includes spraying means for spraying a water mist on the top surface of the mat being formed.

59. The system of claim 51 wherein said conveying means includes a conveyor trough, said forming means includes depositing means for depositing wood strands on said conveyor trough to thereby at least in part form the mat, and said altering means alters at least one of the temperature and moisture content of some or the wood strands before said depositing means deposits them on said conveyor trough.

60. The system of claim 59 wherein said altering means selectively heats only some of the wood strands.