Abstract:
A method of manufacturing a contoured, consolidated cellulosic article, with variable basis weight, is disclosed. The method employs a former to create a mat having a substantially uniform thickness which is pre-pressed to retain its shape. The pre-pressed mat is then machined along at least one surface to result in a desirable contour. The contoured mat is then consolidated within a secondary press. The secondary press preferably includes platens shaped complementarily to the surfaces of the mat.

Description:
BACKGROUND OF THE INVENTION  
       [0001]     1. Field of the Invention  
         [0002]     The invention generally relates to wood products and, more particularly, relates to methods of manufacturing consolidated cellulosic panels.  
         [0003]     2. Description of Related Technology  
         [0004]     Consolidated cellulosic panels, such as fiber board, paper board, particle board, and the like, are typically comprised of wood furnish such as saw dust, shavings, chips, or specially ground fibers, compressed with a binding agent or resin under heat and pressure. Such boards can be used in a variety of applications including, but not limited to, exterior house siding, interior and exterior door facing panels or door skins, cabinet doors, paneling, moulding, etc.  
         [0005]     It is often desirable to manufacture such panels to a uniform basis weight and caliper. If the panels are flat this can be accomplished by compressing a mat between first and second flat faced dies. However, if one of the faces needs to be deeply contoured, such die compressions have proven to be problematic. For example, if a first die has a contour corresponding to the desired shape of the panel, and the second die has a flat face, the mat compressed therebetween will have a non-uniform caliper, with the thinner areas of the mat being compressed to a higher density than thicker areas. This is especially true with fiberous materials that do not flow under pressure.  
         [0006]     Current methods of producing such panels therefore typically require that a mat having first and second opposed flat surfaces be compressed according to conventional methods, and that one or more of the surfaces then be machined to have the desired contour. For example, a router may be used to shape the surfaces. U.S. Pat. No. 4,175,106, assigned to the present assignee, discloses such a process. Such tools, however, cannot easily produce sharp inside corners, are relatively slow, and require complex, expensive equipment.  
         [0007]     Another method requires contoured, complementary, dies on both the top and bottom to produce a substantially uniform thickness through the contoured and non-contoured areas. If one of the top or bottom needs to be flat, or alternatively shaped, the panel must undergo an added machining step adding time, expense and waste to the operation. Shallow contouring of one face is typically done in an embossing operation, or with an embossing die, but the depth of embossing is greatly limited.  
       SUMMARY OF THE INVENTION  
       [0008]     In accordance with one aspect of the invention, a method of manufacturing a contoured, consolidated cellulosic article having a variable basis weight is provided. The method comprises the steps of forming a loose mat of cellulosic material and a binder resin, the mat having a top surface and a bottom surface, machining at least one of the top surface and bottom surfaces to have a pattern, and consolidating the mat between a top platen and a bottom platen. The top and bottom platens have contours complementary to the patterns machined into the mat top and bottom surfaces, respectively.  
         [0009]     In accordance with another aspect of the invention, a method of manufacturing a consolidated cellulosic article is provided comprising the steps of depositing cellulosic fiber and a binding agent onto a moving conveyor to form a mat, applying suction through the conveyor belt, scalping a top surface of the mat, compressing the mat between upper and lower platens at a first pressure, machining a pattern into the top surface by removing cellulosic material in a desired pattern, gathering the removed cellulosic material, and compressing the mat between third and fourth platens. The conveyor is perforated so as to enable the suction to hold the mat onto the belt. The scalping step creates a mat of uniform height. The third and fourth platens are contoured complementarily to contours of the top and bottom surfaces, respectively.  
         [0010]     In accordance with another aspect of the invention, a method of manufacturing a contoured, consolidated cellulosic article with variable basis weight is provided, which comprises the steps of forming a loose mat of cellulosic material and a binder resin, the mat-having a top surface and a bottom surface, prepressing the loose mat to a first density and caliper, machining at least one of the top surface and bottom surface to have a pattern, and consolidating the mat between a top platen and a bottom platen. The top and bottom platens have contours complementary to the pattern machined into the mat top and bottom surface, respectively. The consolidating step compresses the mat to a second density and caliper. The second density is greater than the first density.  
         [0011]     These and other aspects and features of the invention will become more apparent upon reading the following detailed description when taken in conjunction with the accompanying drawings.  
     
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0012]      FIG. 1  is an isometric view of an article constructed in accordance with the teachings of the invention;  
         [0013]      FIG. 2  is a schematic representation of a mat being preliminarily formed according to the teachings of the invention;  
         [0014]      FIG. 3  is a partial sectional view of a mat being pre-pressed according to the teachings of the invention;  
         [0015]      FIG. 4  is a schematic representation of a mat being machined in two dimensions according to the teachings of the invention;  
         [0016]      FIG. 5  is a schematic representation of a mat being machined in three dimensions according to the teachings of the invention;  
         [0017]      FIG. 6  is a partial sectional view of a mat being compressed under heat and pressure according to the teachings of the invention; and  
         [0018]      FIG. 7  is a schematic representation of a system constructed in accordance with the teachings of the invention. 
     
    
       [0019]     While the invention is susceptible to various modifications and alternative constructions, certain illustrative embodiments thereof have been shown in the drawings and will be described below in detail. It should be understood, however, that there is no intention to limit the invention to the specific forms disclosed, but on the contrary, the intention is to cover all modifications, alternative constructions, and equivalents falling within the spirit and scope of the invention as defined by the appended claims.  
       DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS  
       [0020]     Referring now to the drawings, and with specific reference to  FIG. 1 , an article constructed in accordance with the teachings of the invention is generally referred to by reference numeral  20 . While the article  20  is depicted as a six panel door facing, it is to be understood that the teachings of the invention can be employed in the construction of any number of other consolidated cellulosic articles having a contoured surfaces such as, but not limited to, exterior house siding, interior and exterior door facing panels or door skins, cabinet doors, paneling, and moulding.  
         [0021]     As shown in  FIG. 1 , the article  20  includes a first or top surface  22 , a second or bottom surface  24 , first and second side edges  26 ,  28 , and first and second end edges  30 ,  32 . The top surface  22  is contoured, whereas the bottom surface  24  is flat or planar in the depicted embodiment. More specifically, the top surface  22  includes a plurality of indentations  34  of various dimension and depth to provide an appearance desirable for the end application of the article  20 . In the depicted embodiment, the bottom surface  24  is flat to facilitate attachment of the article  20  to a door core, but it is to be understood that the article  20  may include a back surface having a non-flat contour as well.  
         [0022]     Referring now to  FIG. 2 , a former  36  according to the teachings of the invention is depicted generating a mat  38 . The former  36  includes a hopper  40  from which a combination of cellulosic fibers and a binding agent or resin are deposited onto a moving conveyor belt  42 . The binding agent may be any number of different known agents including, but not limited to, phenolic resin or isocyanate. The conveyor belt  42  is preferably perforated, with a suction device  44  being proximate the conveyor belt  42 . The suction device  44  generates a pressure differential across the conveyor belt  42  thereby holding the mat  38  to the conveyor belt  42 .  
         [0023]     As can be seen in  FIG. 2 , the cellulosic material is deposited upon the conveyor belt  42  at an inconsistent height (exaggerated in  FIG. 2  for the purpose of illustration). Accordingly, downstream of the hopper  40  a rotary scalper  46  may be provided. The scalper  46  includes a rotating axle  48  from which a plurality of blades  50  radially extend. Rotation of the scalper  46  causes the blades  50  to engage the mat  38  and thereby reduce the mat  38  to a consistent thickness. It is to be understood that the scalper  46  may be provided in alternative forms, such as saw blades, for removal of the cellulosic material.  
         [0024]     Referring now to  FIG. 3 , a pre-press  52  according to the teachings of the invention is depicted. The pre-press  52  includes a first platen  54  as well as a second platen  56  which are adapted to be compressed together as by hydraulic cylinders  58 . The pre-press  52  compresses the mat  38  to a softboard  53 , defined herein as a compressed mat of cellulosic fiber and a binding agent having a relatively low density, e.g., 10 to 30 lbs. per cubic foot. Such a softboard has sufficient density and strength to maintain its shape, as opposed to being a loose pile of fibers, but would not be suitable for use as a solid product such as siding or doors. The softboard  53  is preferably formed in the absence of heat or moisture so as to avoid curing of the binding agent and thereby allow for the material removed, as by the rotary scalper  46 , to be recycled.  
         [0025]     Once the softboard  53  is formed, it is machined as shown in  FIGS. 4 and 5 , resulting in a softboard  53  having a variable basis weight across its dimension. For example, as shown in  FIG. 4 , the top surface  22  of the softboard  53  may be machined along a single axis, e.g., a longitudinal axis α, to provide a contoured top surface  22  while maintaining the bottom surface  24  in a planar configuration. If the softboard  53  is machined as depicted in  FIG. 4 , wherein a second rotary scalper  60  removes material along the longitudinal axis ∝, (as well as a depth axis Δ) material such as house siding can be easily manufactured. If the end product needs to be machined along the longitudinal and lateral axes α and β (as well as along the depth axis Δ) as with a six panel door as depicted in  FIG. 1 , a router  62  may be employed as shown in  FIG. 5 . The router  62  is preferably mounted on a track system  64  and connected to a CNC control (Computer Numerical Control) or the like for movement of the router  62  in appropriate directions.  
         [0026]     Referring now to  FIG. 6 , a secondary press  68  according to the teachings of the invention is shown in partial sectional view. The secondary press  68  preferably includes an upper platen  70 , a lower platen  72  and a mechanism for compressing the upper and lower platens  70  and  72  together. Such a mechanism may be provided in the form of hydraulic cylinders  74 , but may be provided in any other type of actuator including, but not limited to, pneumatic cylinders, motors, and the like.  
         [0027]     In the depicted embodiment, the upper platen  70  includes a plurality of protrusions  76  such that the contour of the upper platen  70  is complementarily shaped to a pattern  78  formed in the upper or top surface  22  of the mat  38 . Also in the depicted embodiment, the lower platen  72  is flat or planar so as to match the planar shape of the bottom surface  24 , but it is to be understood that if the bottom surface  24  is otherwise contoured, the lower platen  72  would be shaped to correspond to the contour of the bottom surface  24 .  
         [0028]     The secondary press  68  preferably has a heat source  75  associated therewith to compress the softboard  53  under heat and pressure. The heat source  75  may be provided in the form of heat exchanger coils or channels through the platens  70 ,  72 , through which heated fluid, e.g., water, is circulated, or in the form of separate hot platens.  
         [0029]     Referring now to  FIG. 7 , a system  80  according to the teachings of the invention is shown in schematic fashion. As shown therein, the system  80  includes the former  36 , the pre-press  52 , a machining mechanism  82 , the secondary press  68 , as well as a gathering mechanism  84  and a recycling mechanism  86 .  
         [0030]     The machining mechanism  82  may be provided in the form of the aforementioned rotary scalper  60  or router  62 , but can alternatively be provided in the form of any other type of mechanism for removing cellulosic material from the mat  38  including, but not limited to, circular saw blades, band saw blades, sanders, and the like. The gathering mechanism  84  may be provided in the form of a conveyor provided below the machining mechanism  82 , or may be provided in the form of a vacuum device for drawing the removed cellulosic material away. The recycling mechanism  86  preferably communicates the material gathered by mechanism  84  back to the former  36  for use in the formation of subsequent articles  20 . Accordingly, the recycling mechanism  86  may include conveyors, suction lines, or the like.  
         [0031]     From the foregoing, it will be appreciated that the teachings of the invention may be employed to manufacture a contoured, consolidated cellulosic article having variable basis weight.