Abstract:
Methods and systems for making a fiberboard product having a desired final thickness dimension by subjecting a fibrous board preform to a successive series of compressive pressures. Preferably, an upstream one of the compressive pressures causes the board preform to exhibit a compressed thickness dimension which is less than the final thickness dimension of the fiberboard product, while a downstream one of the compressive pressures causes the board preform to exhibit a thickness dimension which is substantially the same as the final thickness dimension of the fiberboard product. Between subjecting the board preform to these upstream and downstream compressive pressures, the upstream one of the compressive pressures may be removed sufficiently to cause the compressed thickness dimension to increase to an intermediate thickness dimension which is less than the initial thickness dimension of the board preform, but is greater than the final thickness dimension of the fiberboard product. Most preferably, the upstream compressive pressure is accomplished by passing the board preform between and through a nip space defined between an opposed pair of rolls.

Description:
FIELD OF THE INVENTION  
         [0001]    The present invention generally relates to methods and systems for making relatively thick boards of fibrous materials. In preferred forms, the present invention relates to methods and systems for making inorganic fiber boards having a heat-curable binder dispersed throughout a mass of inorganic fibers.  
         BACKGROUND AND SUMMARY OF THE INVENTION  
         [0002]    Recently, systems and methods have been proposed in copending, commonly owned U.S. patent application Ser. No. 09/567,771 filed on May 9, 2000 (the entire content of which is expressly incorporated hereinto by reference) whereby relatively thick boards may be made from inorganic fibers, preferably fibers obtained from pre- or post-consumer waste fiberglass products (e.g., building insulation). In preferred embodiments, the systems and methods disclosed therein include forming a fiber-containing board at least about one inch thick and having at least 25% (and typically at least about 90%) by weight inorganic fibers (such as primarily recycled pre- or post-consumer waste glass fibers from fiberglass products, such as building insulation) that is dimensionally stable. In order to impart dimensional stability, a heat-curable binder solution (e.g., a solution containing a phenolic binder resin) is typically applied to the wet-laid fiber board preform. Thus, during production, the fiber board preform is transported through a heated curing oven where remaining residual water is removed from the board and the binder (which had been applied to the board preform upstream of the curing oven) is cured.  
           [0003]    The fiber board preform is essentially supported between a pair of endless forming and transport conveyors as it moves through the curing oven. In addition, the opposed conveyors exert a compressive pressure on the fiber board preform so as to control the final thickness dimension of the finished fiber board—that is, to maintain a desired thickness of the board within the curing oven as the binder cures. Thus, as the fiber board preform dries and the binder cures, the opposed conveyors will compress the board to its final desired thickness during transport through the curing oven. It has been discovered, however, that a substantial amount of compressive pressure is needed in the curing oven in order to achieve the desired thickness dimension of the finished board which, in turn, demands that substantial (and costly) structural support must be provided for the forming and transport conveyors therein. Moreover, the conveyors of the curing oven may have a designed maximum compressive load which would limit the maximum bulk pack density for the board that could be obtained thereby.  
           [0004]    It is therefore an object of the present invention to provide improvements to systems and methods for forming binder-containing inorganic fibrous boards. In this regard, it would highly be desirable if the compressive pressure exerted between the forming and transport conveyors of the curing oven could be reduced. It is towards fulfilling such a need that the present invention is directed.  
           [0005]    Broadly, the present invention is embodied in methods and systems for making a fiberboard product having a desired final thickness dimension by subjecting a fibrous board preform to a successive series of compressive pressures. Preferably, an upstream one of the compressive pressures causes the board preform to exhibit a compressed thickness dimension which is less than the final thickness dimension of the fiberboard product, while a downstream one of the compressive pressures causes the board preform to exhibit a thickness dimension which is substantially the same as the final thickness dimension of the fiberboard product. Between subjecting the board preform to these upstream and downstream compressive pressures, the upstream one of the compressive pressures may be removed sufficiently to cause the compressed thickness dimension to increase to an intermediate thickness dimension which is less than the initial thickness dimension of the board preform, but is greater than the final thickness dimension of the fiberboard product. Most preferably, the upstream compressive pressure is accomplished by passing the board preform between and through a nip space defined between an opposed pair of rolls.  
           [0006]    These and other aspects and advantages of the present invention will become more clear after careful consideration is given to the following detailed description of the preferred exemplary embodiments thereof which follow. 
       
    
    
     BRIEF DESCRIPTION OF THE ACCOMPANYING DRAWINGS  
       [0007]    Reference will hereinafter be made to the accompanying drawings wherein like reference numerals throughout the various figures denote like structural elements, and wherein,  
         [0008]    [0008]FIG. 1 is a schematic elevational view of a crusher roll system and its principles of operation in accordance with the present invention;  
         [0009]    [0009]FIG. 2 is a side elevation view, partly in section, showing one possible form of a crusher roll system which embodies the principles in accordance with the present invention shown in FIG. 1 upstream of a curing oven;  
         [0010]    [0010]FIG. 3 is a perspective view of the crusher roll system depicted in FIG. 2;  
         [0011]    [0011]FIG. 4 is a side elevational view of the crusher roll system depicted in FIG. 2; and  
         [0012]    [0012]FIG. 5 are data plots of compressive pressure (CP) vs. bulk pack density which compares the effects of several exemplary pre-compressive pressure conditions of uncured pack material in accordance with the present invention to a non-pre-compressed uncured pack material. 
     
    
     DETAILED DESCRIPTION OF THE INVENTION  
       [0013]    Accompanying FIG. 1 schematically depicts a crusher roll system  10  in accordance with the present invention position immediately upstream of a curing oven CO in which a pair of opposed forming and transport conveyors C 1  and C 2  are housed. As is shown, a board preform BP containing uncured binder dispersed therethrough is supported upstream of the curing oven by means of transport conveyor  12  and has an initial thickness dimension T 0  immediately prior to entering the nip space defined between the opposed rolls  10 - 1  and  12 - 1  associated with the crusher roll system  10  and the conveyor  12 , respectively.  
         [0014]    The crusher roll system  10  includes an endless forming member  10 - 2  which extends between the forward roll  10 - 1  and the rearward roll  10 - 3 . As will be discussed in greater detail below, the rolls  10 - 1  and  10 - 2  are spaced apart generally in the machine (conveyance) direction MD. The rearward roll  10 - 3  is supported so as to be positionally stationary with respect to the forward roll  10 - 1 .  
         [0015]    The nip formed between the opposed rolls  10 - 1  and  12 - 1  associated with the crusher roll system  10  and the conveyor  12 , respectively, thus compresses the thickness of the board preform form its initial or original thickness T 0  upstream of the crusher roll system  10  to a reduced thickness dimension T 1  which is less than the desired final dimension T F  which is maintained between the conveyors C 1 , C 2  within the curing oven CO. These thickness dimensions therefore result in a density of the board preform BP subsequent to being subjected to the crusher roll system  10  which is greater as compared to the density of the board preform BP upstream thereof. However, immediately downstream of the nip formed between the opposed rolls  10 - 1  and  12 - 1 , the thickness of the board preform BP will increase somewhat to a thickness dimension T 3  thereby allowing the density to somewhat decrease. This relaxation or increase of the thickness dimension (decrease in density) is due to the board preform BP no longer being subjected to the compressive pressure condition between the rolls  10 - 1  and  12 - 1  immediately downstream thereof, and since the board preform BP at that stage in the process includes uncured binder material.  
         [0016]    It is noteworthy that the thickness of the board preform does not increase to its initial thickness T 0  immediately downstream of the crusher roll system  10 . In this regard, it is surmised that, by compressing the thickness of the board preform to a thickness dimension T 1  which is less than the final desired thickness dimension T F , the fibers in the board preform are caused to become irreversibly more tightly packed (i.e., so as to increase the density of the board preform) to an extent that the board preform will not again expand to its original thickness (density) once it has been compressed (“crushed”) between the opposed rolls  10 - 1  and  12 - 1 . As a result, the compressive pressure needed to be exerted onto the board preform in the curing oven CO between the opposed conveyors C 1 , C 2  (i.e., so as to compress the board thickness from its relaxed dimension T 2  to the final board thickness T F ) is substantially less as would have been required without the function of the crusher roll system  10  in accordance with the present invention.  
         [0017]    By way of example, the natural density of a board preform BP comprised of glass fibers and uncured binder material is typically between about 2.5 to about 3.5 lbs/ft 3 , while the desired target density of an exemplary final board product (i.e., following curing of the binder in the curing oven CO) may be up to about 10.0 lbs/ft 3 . Without the presence of the crusher roll system  10  in accordance with the present invention, a compressive pressure condition of between, for example, about 120 to about 140 lbs/ft 2  would have to be exerted onto the board preform BP by means of the opposed conveyors C 1 , C 2  to form a 7.0 lbs/ft density final product. This would thereby require costly supporting infrastructure within the curing oven CO. However, by using the crusher roll system  10  of the present invention, the amount of compressive pressure required to be exerted upon the board preform BP by means of the conveyors C 1 , C 2  can be reduced dramatically to, for example, only about 80 lbs/ft 2  in order to achieve the same desired target density of about 7.0 lbs/ft 3  (in this example) for the final board product.  
         [0018]    One particularly preferred embodiment of the crusher roll system  10  is depicted in accompanying FIGS.  2 - 4 . As is seen, the crusher roll system  10  is positioned immediately upstream of the entrance CO e  of the curing oven CO so that the functions of the former may be realized on the board preform BP immediately prior to entering the latter. The crusher roll system  10  is generally supported by a rigid framework  14  at the downstream end of the conveyor assembly  12 . The forward and rearward rolls  10 - 1  and  10 - 3 , respectively, are supported by a pair of laterally (i.e., relative to the machine direction MD) support arms  16  so as to be spaced apart from one another generally in the machine (conveyance) direction MD (see FIG. 1). The forward roll  10 - 1  is mounted for rotational movements by means of a transverse axle  18 . This axle  18  is, in turn, connected to a screw adjustment assembly  18 - 1  to allow for rectilinear movements of the roll  10 - 1  towards and away from the roll  10 - 3  and thereby permit the tension on the endless forming member  10 - 2  to be adjusted. The rolls  10 - 1 ,  10 - 3  are driven in a counterclockwise direction (as viewed in FIG. 2, for example) so as to encourage the board preform BP to be conveyed downstream to the curing oven. Any suitable drive means may be employed for such purpose, such as a drive motor (not shown) connected operatively to the rearward roll  10 - 3  via a conventional drive chain  10 - 4  (see FIGS. 2 and 4).  
         [0019]    As is perhaps best seen in FIGS. 3 and 4, the rearward roll  10 - 3  is likewise mounted for rotational movements by means of a transverse axle  20  supported by, and extending between a pair of bearing blocks  22  fixed to the support structure  14 . The bearing blocks  22  thereby also support the pair of arms  16  to allow for pivotal movements about the axis of axle  20  (arrow A 1  in FIG. 4). In such a manner, therefore, the nip dimension defined between the opposed rolls  10 - 1  and  12 - 1  may be altered to thereby alter the compressive pressure exerted on the board preform within that nip (i.e., so as to alter the thickness dimension T 1  to which the board preform BP is compressed by means of the rolls  10 - 1  and  12 - 1 ). Each forward end of the arms  16 , and thus the forward roll  10 - 1 , is supported dependently by means of a respective threaded support shaft  24  coupled operatively to a worm gear  26  at the terminal end of a drive shaft  28  extending from motor  30 . Operation of the motor  30  will concurrently rotate each of the drive shafts  28  and the worm gears  26  which rotation, will in turn, threadably drive the support shafts  24  rectilinearly towards and away from the roll  12 - 1  (arrow A 2  in FIG. 3) depending on the direction of rotational movement. In such a manner, the forward end of the support arms  16  to which the shafts  24  are attached, and hence the roll  10 - 1  carried thereby, may be pivoted about the transverse axis established by the rear axle  20  (arrow A 1  in FIG. 4) to thereby adjust the nip dimension between the rolls  10 - 1  and  12 - 1 .  
         [0020]    The present invention will be further understood by reference to the following non-limiting Example.  
       EXAMPLE  
       [0021]    The present example will further explain the functional benefits of pre-compressing the uncured, moist fiberglass pack, prior to its entering the curing oven in accordance with the present invention. Specifically, in accompanying FIG. 5, curve C l  shows data representative of the relative initial compressive pressure (CP) vs. density relationship for a moist, uncured fiberglass pack in its first compression where the pack was formed at a bulk pack density of about 3 lbs/ft 3 . The maximum allowable pressure on the curing oven, which in this example was 80 lb/ft 2  is shown in FIG. 5 by the horizontal line OL which, as can be seen, crosses the curve C l  at about 6 lbs/ft 3  density. By pre-compressing the uncured pack material, prior to its entering the curing oven, by 3.3 times (or stated another way, compressing the pack material to 3.3 times its original fiber bulk density) the CP vs. density curve (designated as curve C 3.3×  in FIG. 5) shifted to the right, crossing line OL at a higher density of almost 7 lbs/ft 3 . Hence, this uncured fiberglass pack can be compressed by the curing oven to a higher density, using the same pressure, as compared to the density obtained at that compressive pressure, but in the absence of pre-compression by 3.3 times. Likewise, and to a greater effect, by pre-compressing the pack to 5 times and 6.7 times its original density, the CP vs. density curves C 5×  and C 6.7× , respectively, shifted even further to the right as seen in FIG. 5. Specifically, it will be seen that pre-compression of the uncured pack material to 5 times resulted in curve C 5×  crossing the maximum oven load OL line at a bulk pack density more than about 8.0 lbs/ft 3 , while curve C 6.7×  crossed the maximum oven load OL at bulk pack density of more than 9 lbs/ft 3 , each of which is substantially greater than the original value of 6 lbs/ft 3  for the material when not pre-compressed. In each successive case of greater pre-compression, therefore, the data of FIG. 5 show that the maximum density that can be attained in the curing oven, with its upper limit on line OL, was capable of being increased by pre-compressing the uncured moist fiberglass pack to a greater extent. Conversely, the data of FIG. 5 demonstrate that, in the absence of pre-compression on the uncured pack material in accordance with the present invention, the maximum attainable density in the curing oven was limited to that value corresponding to the intersection of curve C l  and the line OL.  
         [0022]    It will, of course, be understood that the crusher roll system  10  described in detail above presently represents and especially preferred exemplary embodiment of the present invention. Various modifications and design changes may, however, be made without departing from the scope of the present invention. For example, in certain applications, the conveyor  10 - 2  and roll  10 - 3  may be omitted thereby providing for a roll serving similar functions as roll  10 - 1  described previously. In such a modified system, the crusher roll would include support structures to allow adjustability of the dimension T l  for a similar purpose as described above. Furthermore, the system  10  need not be driven by any motive means, but instead any roll(s) provided may be caused to rotate simply by virtue of the movement of the board preform in which the roll(s) is(are) in contact.  
         [0023]    Therefore, while the invention has been described in connection with what is presently considered to be the most practical and preferred embodiment, it is to be understood that the invention is not to be limited to the disclosed embodiment, but on the contrary, is intended to cover various modifications and equivalent arrangements included within the spirit and scope of the appended claims.