Methods and systems for making high density fiberboards from low density fibrous media

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.

DETAILED DESCRIPTION OF THE INVENTION 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. 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 . 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. 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. 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. 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 ). 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 . The present invention will be further understood by reference to the following non-limiting Example. 
 EXAMPLE 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. 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. 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.