Abstract:
Gypsum boards are bent to curved shape by placing a water dampened flat rectangular gypsum board upon a resiliently bendable panel positioned below a bender shell having a wall of arcuate cylindric contour which grips a margin of the gypsum board, and rolling the bender shell upon the gripped board to produce bending. A circular cylindrical weight rolls within the bender shell to apply compressive force upon the gypsum board during the bending process.

Description:
BACKGROUND OF THE INVENTION 
   1. Field of the Invention 
   The present invention concerns a method for bending an initially flat gypsum board into a durably retained curvilinear shape, and further relates to equipment which may be used at a construction site to produce such bending. 
   2. Description of the Prior Art 
   Flat panels, often referred to as “drywalls” or “gypsum boards” are commonly employed in the fabrication of walls and ceilings of interior rooms of buildings. Gypsum board is a laminate structure comprising a core of gypsum sandwiched between a sheet of face paper on one side and a sheet of back paper on the opposite side. Gypsum board is manufactured by a relatively high speed continuous method wherein a slurry of calcined gypsum and various additives is mixed with more than sufficient water for hydration and setting of the gypsum. The slurry is deposited on a lower, continuously advancing paper sheet, and an upper continuously advancing paper sheet is layered over the slurry. The laminate structure is then formed into a continuous flat sheet of paper-enclosed gypsum. 
   In the typical process the gypsum board is made face side down. The face paper, on the bottom, is folded upward along the two longitudinal edges and folded over onto the top of the slurry along these edges. The back paper is placed-on top of the slurry, overlapping the edge portion of the face paper that is folded over onto the back side of the board. The continuous sheet is carried on a conveyor belt and rollers for a considerable distance until the gypsum core has set to a sufficient degree to permit the board to be cut into normal board lengths and transferred to high temperature drying kilns. 
   U.S. Pat. No. 5,198,052 to Ali discloses a method for producing a gypsum board having a decoratively shaped surface by applying embossing pressure to the board during its production and before the drying stage. However, Ali does not disclose or contemplate bending of the gypsum board. 
   Typical interior building construction comprises a plurality of spaced framing members referred to as studs, furring or joists. One or more layers of gypsum board of 3/81″ to ½″ thickness are secured to one or each side of the framing members forming the wall or ceiling surfaces. The side edges of the gypsum boards are generally butted together over a framing member and nailed or screwed thereto with the fasteners extending through the gypsum board and into the framing members. To construct a monolithic appearing wall, the butt joints between adjacent gypsum boards are concealed by covering the joint with a reinforcing joint tape and several layers of a joint compound to cover the joint, the joint tape and the fasteners. To construct a smooth surface without ridges formed by the joint tape and compound, the gypsum board is produced with a slight taper on the face surface adjacent the longitudinal or side edges of the board. The taper results in a slight depression in the wall or ceiling surface at the joints. The depression is filled with the joint compound producing a smooth finish at the joint without a raised ridge. 
   In certain features of architectural design, it is sometimes desirable to be able to have curved wall panels. Also, vaulted ceilings are often sought but generally avoided because of the expense of traditional construction techniques. Curved gypsum boards, if manufacturable at a factory, would be difficult to transport damage-free to a construction site. 
   It is accordingly an object of the present invention to produce curved gypsum boards. 
   It is a further object to produce the aforesaid curved gypsum boards by a low cost process operable at a construction site. 
   These objects and other objects and advantages of the invention will be apparent from the following description. 
   SUMMARY OF THE INVENTION 
   The above and other beneficial objects and advantages are accomplished in accordance with the present invention by apparatus for bending gypsum board comprising:
     a) a resiliently bendable panel bounded by flat upper and lower surfaces and a substantially rectangular perimeter,   b) a bender shell comprised of a rigid wall of arcuate cylindric contour bounded by smooth interior and exterior concentric surfaces convexly curved rearwardly with respect to spaced apart parallel straight upper and lower front edges, and extending laterally to two spaced apart parallel curved side edges, said arcuate wall and edges defining a hollow interior region,   c) gripping means for securing a leading edge of a gypsum board at a site adjacent the lower edge of said wall in association with said exterior surface,   d) circular cylindrical weight means adapted to roll in planetary manner upon said interior surface, and   e) an extension ramp extending forwardly of said lower edge for the purpose of positioning said weight means to begin rolling movement into said interior region.   

   In a further aspect of the present invention, a process for bending gypsum board is provided comprising:
     a) selecting a gypsum board bounded by flat front and rear surfaces which define a substantially uniform thickness in the range of ¼″ and ½″, and having a rectangular perimeter with a length measured between opposed short margins of about 8 to 12 feet, and a width, measured between opposed long margins, of about 4 feet, said board having a long axis that bisects said short margins, and a short axis that bisects said long margins,   b) moistening said front and rear surfaces with water,   c) placing the moistened board horizontally flat upon a resiliently bendable panel resting upon a floor,   d) placing upon said board a rigid bender shell having a smooth arcuate exterior surface and a hollow interior region, and placed in a manner to roll in the direction of an axis of said board,   e) causing one margin of said board, considered to be a leading extremity, to be gripped by said bender shell and in contact with said arcuate exterior surface,   f) rolling said bender shell upon the board while applying compressive force upon the board with minimal shear force, thereby causing said board to assume an arcuate shape in contact with said bender shell, said compressive force being applied by circular cylindrical weight means adapted to roll within said shell at a fixed distance above said board, and   g) drying said arcuately shaped board while under physical restraint.   

   In preferred embodiments, said bender shell is of circular semi-cylindrical contour having handle means associated with at least one side edge to facilitate manual rolling movement of said bender shell. 

   
     BRIEF DESCRIPTION OF THE DRAWING 
     For a fuller understanding of the nature and objects of the invention, reference should be had to the following detailed description taken in connection with the accompanying drawing forming a part of this specification and in which similar numerals of reference indicate corresponding parts in all the figures of the drawing: 
       FIG. 1  is a fragmentary perspective side view of an embodiment of the apparatus of the present invention shown at the initial stage of its operation. 
       FIG. 2  is a side view of the apparatus of  FIG. 1  shown at mid-stage of operation. 
       FIG. 3  is a side view of the apparatus of  FIG. 1  shown at its final stage of operation. 
       FIG. 4  is a top view of the apparatus as shown in  FIG. 1 . 
       FIG. 5  is a top view of the apparatus as shown in  FIG. 2 . 
       FIG. 6  is a front view of the apparatus as shown in  FIG. 1 . 
   

   DESCRIPTION OF THE PREFERRED EMBODIMENT 
   Referring now to  FIGS. 1-6 , an embodiment of the apparatus  10  of the present invention is shown comprised of bender shell  11  positioned above resiliently bendable panel  12 . A gypsum board  13  is disposed between said bender shell and bendable panel. 
   Suitable gypsum boards are bounded by flat front and rear surfaces which define a substantially uniform thickness in the range of ¼″ to ½″, and have a rectangular perimeter  46  with a length measured between opposed short margins  47  of about eight to twelve feet, and a width, measured between opposed long margins  48 , of about four feet. Such boards have a long axis  49  that bisects said short margins, and a short axis  50  that bisects said long margins. In the embodiment exemplified in  FIGS. 1-6 , the gypsum board is oriented in a manner to undergo bending in the direction of the long axis. In an alternative embodiment, the gypsum board can be oriented so as to undergo bending in the direction of the short axis. 
   Bender shell  11  is comprised of a rigid wall  14  shown having a substantially semi-cylindrical contour terminating in laterally spaced parallel semi-circular side edges  35 , and parallel straight upper and lower front edges  15  and  16 , respectively. Said lower edge tangentially merges with a flat extension ramp  36 . Wall  14  is further defined by smooth interior surface  17  and concentrically located smooth outer surface  18 . Said wall and edges define a rearwardly convex interior region  20 . The width of wall  14  of said bender shell, measured between side edges  35 , is about four feet in the illustrated embodiment designed to bend a gypsum board in the direction of its long axis. In said alternative embodiment, designed to bend the gypsum board in the direction of its short axis, the width of wall  14  is about eight feet. In the illustrated embodiment, a spacer mat  40  of movably interconnected longitudinal members  41  is disposed in intervening relationship between said interior and outer surfaces. The purpose of said spacer is to impart rigidity to wall  14 . 
   Opposed flat sidewall panels  19  associated with said side edges add further rigidity to wall  14 . Parallel operating levers  43  are joined to wall  14  and sidewall panels  19 , and are forwardly connected by transverse operating handle  44 . In other embodiments, wall  14  may have an arcuate cylindric contour of parabolic, ellipsoid or other non-circular shape. The wall may be fabricated of metal, laminated wood, fiberglass or other materials. 
   Bendable panel  12  is fabricated of sheet metal having flat upper and lower surfaces  21  and  22 , respectively, and a substantially rectangular perimeter  23  of sufficient dimensions to accommodate the overlying gypsum board workpiece. Panel  12  must be resilient so as to be reversibly bendable. The thickness of panel  12  is preferably about 24 gauge and the panel terminates in its long direction by front and rear straight edges,  31  and  32 , respectively. 
   Gripping means  25  for releasably securing the leading edge extremity  26  of gypsum board  13  is provided by the attachment of front edge  31  of bendable panel  12  to the underside of extension ramp  36  at a site adjacent the lower edge  16  of outer surface  18 , Such construction causes leading edge  26  of the board to be sandwiched between extension ramp  36  and bendable panel  12 . 
   Circular cylindrical weight means, in the form of barrel  28  is adapted to roll upon the interior surface  17  of wall  14  in a planetary manner wherein the rotational axes of the barrel and wall  14  remain parallel. The barrel, which may be of 55 gallon capacity, is filled with water at the job site. This causes the effective weight of the barrel to be about 500 pounds, thereby producing a downward force upon the gypsum board of between about 7 and 12 pounds per linear inch. The total downward force is further increased by the weight of bender shell  11 , which may weigh between about 50 and 70 pounds, thereby resulting in a total downward force between about 8 and 13 pounds/linear inch. In said alternative embodiment designed to bend the gypsum board in the direction of its short axis, and wherein wall  14  has a width of about eight feet, two barrels placed end to end are caused to roll upon interior surface  17 . 
   In the gypsum board bending process of this invention, the bendable panel is laid upon a flat floor surface at the job site. A gypsum board is moistened on both faces with water which may contain penetrating surfactants and/or agents that will cause hardening of the board upon drying. 
   The leading edge  26  of the moistened board is caused to be engaged by said gripping means  25  while the upper edge  15  of wall  14  is vertically above said leading edge. Barrel  28  is then entered upon interior surface  17 , and slowly rolled toward rear edge  32  of bendable panel  12 . The rate of movement of the drum is such that gypsum boards of 12 foot length require 3 to 6 minutes. In general, lower temperatures, and arcuate surfaces with relatively small radius of curvature require slower than average movement. When the drum reaches the rear edge  32  of panel  12  and trailing edge  50  of the board, as shown in  FIG. 3 , the bent gypsum board is either dried in place, employing a hand-held dryer or other drying means, or is removed while damp and placed in shape-retaining holding means for drying. 
   While particular examples of the present invention have been shown and described, it is apparent that changes and modifications may be made therein without departing from the invention in its broadest aspects. The aim of the appended claims, therefore, is to cover all such changes and modifications as fall within the true spirit and scope of the invention.