Patent Publication Number: US-2019169925-A1

Title: Double backbone core for automated door assembly line, door comprising same and method of using same

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS AND CLAIM TO PRIORITY 
     This application is related to provisional patent application No. 61/968,153, filed Mar. 20, 2014 in the United States, the disclosure of which is incorporated herein by reference and to which priority is claimed. 
    
    
     FIELD OF THE INVENTION 
     The invention relates to a core having two interconnected backbones for use in a door assembly, preferably in an automated door assembly line, and a hollow core door formed with the core. More specifically, the present invention relates to an expandable core component for a hollow door, comprising two backbones with relatively smaller cells running parallel to one another along the length dimension of the door that are configured so as not to interfere with hinge blocks, lock blocks, etc., as well as a method of using same in an automated door assembly line. 
     BACKGROUND OF THE INVENTION 
     Current hollow core doors have a central lengthwise extending core with a backbone of relatively small cells. These single backbone cores when used in automated door manufacturing have a tendency to curve to one side or the other depending upon variations in the core, the door being assembled and manufacturing inconsistencies. This may cause both performance issues on the automated line and quality issues when the core movement causes the molded panels on one side to have insufficient support, i.e., pillowing. 
     U.S. Pat. No. 4,583,338 to Sewell, et al., discloses a hollow door panel construction including a rectangular frame of predetermined thickness assembled from side and end members defining an elongated enclosure. Within the enclosure are corrugated paperboard strips, having a width equal to the predetermined thickness. The strips are variously formed and attached to define a plurality of horizontal cell rows, vertically stacked to fill the framed volume. Each cell row spans the internal width of the frame, and includes a centrally positioned short-walled brace cell straddled on either side by a long-walled lateral cell. To complete the panel construction, thin sheets abut and are secured to the opposite faces of the frame and to the outer edges of the strips. In essence, Sewell discloses a single back bone core designed to provide greater door strength. However, as with all single backbone cores, Sewell&#39;s single backbone core has a tendency to curve to one side or the other during automated manufacturing depending upon variations in the core. When this curving occurs, the molded panels on one side tend to have insufficient support. 
     U.S. Pat. No. 2,827,670 to Schwindt discloses a hollow core door wherein the surface sheets have limited relative longitudinal movement with respect to each other and rigid connection of the surface sheets to longitudinally extending stiles is eliminated. Schwindt discloses a single backbone core structure using a higher concentration of cellular material in the vicinity of the edges along the stiles and rails. As with Sewell, the core of Schwindt would have a tendency to curve during manufacture. 
     There remains a need for a core that provides a more consistent position and coverage in hollow core doors, that resolves both the automated line manufacturing issues such as interference with the hinge blocks and lock blocks, and that resolves quality issues that occur when the door facings have insufficient support from the core. 
     SUMMARY OF THE INVENTION 
     The present invention relates to a double backbone core for use in an automated door assembly line. An expandable core, preferably formed from cardboard or corrugated cardboard, is interposed between two opposed door skins during fabrication of the door on an automated assembly line. The core is appropriately configured so as not to interfere with hinge blocks, lock blocks, etc. Instead of the currently used core having a single central backbone of relatively small cells, the present invention utilizes two backbones with relatively small cells running parallel to one another along the length dimension of the door. 
     The present invention relates to a double backbone core with smaller cells on the ends (outside) and optionally larger cells in the middle. The smaller cells create a relatively straight support extending parallel to the stiles and the larger cells provide cross support through the middle of the door. In four-molded-panel and six-molded-panel door designs, the backbones are disposed near the edges of the molded (or profiled) panels, with the optional larger cells supporting the middle of the molded panels. 
     The backbones at the edges pull tight to provide straight edges for the core that are less likely to interfere with the lock blocks during automated manufacturing. 
     The backbones are located either near the center of the molded panels or near the outside edges of the molded panels. A similar core concept is used for two and three-panel doors with ridged edges and central cells. 
     Manual assembly of four and six-molded-panel doors does not allow for a core that could run the length of the door through the molded panels. As such, the core was placed in the center of the door. Having two backbones running through/underneath the molded panels not only resolves the pillowing issue but also provides oil canning and warp resistance as well. 
     The core of the invention may be used with different width doors. The 3/0 core backbones are aligned in the middle of the 3/0 molded panels. For the 2/10 and 2/8 molded molded panels, the core is nearer to the edge of but still away from the lock blocks. The 2/6 is preferably configured the same as the 2/4, and the 2/0 core is preferably also used for the 2/2 door. 
     Because the tight portion of the core is configured on the outside edges of the core, this core is more forgiving with making undercut doors (6/7-1/2), which has been problematic with current single, central core designs. 
    
    
     
       BRIEF DESCRIPTION OF THE FIGURES 
       The foregoing background and summary, as well as the following detailed description of the preferred embodiments, will be better understood when read in conjunction with the appended drawings. For the purpose of illustrating the invention, there is shown in the drawings embodiments which are presently preferred. It should be understood, however, that the invention is not limited to the precise arrangements and instrumentalities shown. In the drawings: 
         FIG. 1  is a cross-sectional view of a door according to an exemplary embodiment of the present disclosure; 
         FIG. 2  is an elevation view of an exemplary two-molded-panel door according to an exemplary embodiment of the present disclosure; 
         FIG. 3  is an elevational view of an exemplary four-molded-panel door according to an exemplary embodiment of the present disclosure; 
         FIG. 4  is an elevational view of an exemplary six-molded-panel door according to an exemplary embodiment of the present disclosure; 
         FIG. 5  is an elevational view of a first strip used to form the core; 
         FIG. 6  is an elevational view of a second strip used to form the core; 
         FIG. 7  is an elevational view of a third strip used to form the core; and 
         FIG. 8  is a fragmentary perspective view of the first and second strips connected via slits in the strips to form the backbones. 
     
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT(S) 
     Reference will now be made in detail to exemplary embodiments and methods of the invention. It should be noted, however, that the invention in its broader aspects is not necessarily limited to the specific details, representative materials and methods, and illustrative examples shown and described in connection with the exemplary embodiments and methods. 
       FIG. 1  illustrates a door D comprising a peripheral frame  10  and a core component C. Frame  10  comprises rails  12 , stiles  14 , and lock blocks  16 . The rails  12  and the stiles  14  are coupled together, typically with adhesive or mechanical fasteners, to form the frame  10 . The rails  12  and the stiles  14  are typically formed of wood, although other materials such as composites and polymers may be used. The lock blocks  16  can be adhesively secured to the stiles to provide support for a door handle and/or a locking mechanism at the periphery of the door. The frame  10  may also include hinge blocks adhesively secured to the stiles to allow attachment of door hinges. 
     The core component C comprises a first backbone  18  extending the length of the door D, a second backbone  20  extending the length of the door D, and connective cellular portions  22 ,  24 ,  26  connecting the first and second backbones  18 ,  20 . Various materials can be used for the core component C such as cardboard, corrugated cardboard, paperboard, paper, or wood composite material, such as composite soft board or wood fibers. In an exemplary embodiment, the core component C is formed of a plurality of thin strips of cardboard where the strips are interconnected to form cells, such that the cells expand to fill the hollow space created within the frame  10 . 
       FIG. 5  illustrates a first strip A, preferably formed of corrugated cardboard or heavy paper board. The strip A has parallel edges  60  and  62 , and a plurality of adhesive lines  64  deposited on the strip A. The adhesive  64  can be any known bonding material, such as polyvinyl acetate, hot melt adhesive, PUR adhesive, etc. The adhesive  64  preferably extends at least half and preferably the entire distance between the edges  60  and  62 . 
       FIG. 6  illustrates a second strip B, also preferably formed of corrugated cardboard or heavy paperboard. The strip B has parallel edges  66  and  68  and a plurality of adhesive lines  70  deposited on strip B. As with strip A, the adhesive  70  extends at least halfway, preferably the entirely distance, between the spaced parallel edges  66  and  68 . The strips A and B have a uniform height as defined by the edges  60 ,  62  and  66 ,  68 , respectively. 
     As best shown in  FIG. 7 , strip E has a uniform height defined by its parallel edges  72  and  74 , and a plurality of adhesive lines  76  and  78 . The strip E has a uniform height as defined by its edges  72  and  74  that corresponds to and matches the heights of strips A and B. The strip E likewise is preferably made of corrugated cardboard or heavy paperboard. 
     In assembling the core C, the strips A and B are coupled together by bonding the adhesive lines  64  and  70  in order to create the longitudinally extending honeycomb pattern illustrated in  FIG. 2  having the backbones  18  and  20 . A plurality of strips E are bonded between the strips A and B in order to interconnect the backbones  18  and  20 , thus creating the cellular portions  22 ,  24 ,  26 . The strips E may also be bonded between adjacent strips E in order to create a core C having strips A, B and E, as best shown in  FIG. 1 . 
     In yet another embodiment, the strips A and B can also include slits or cut lines extending through the strips A and B, located where the adhesive lines  64  and  70  are located. The slits extend approximately half of the distance between the spaced parallel edges  60  and  62  or  66  and  68 . To form the back bones, the slits  64  and  70  slide together to form a connection between the strips A and B as best shown in  FIG. 8 . The adhesive may be present at the slits to allow for a more secure connection. 
     First backbone  18  and the second backbone  20  each comprise a plurality of cells arranged in a parallel configuration along the length of door D. The cells of the first backbone  18  and the second backbone  20  can have any shape. In an exemplary embodiment, the cells of backbones  18 ,  20  are quadrangular or diamond-shaped such that the cells extend in a longitudinal direction of the door D where the length of each cell is greater than the width. 
     Optional connective cellular portions  22 ,  24 ,  26  comprise a plurality of cells, each having an area larger than the area of the cell formed by strips A and B associated with backbones  18 ,  20 . While the connective portions are illustrated as being cellular, they can be corrugated cardboard panels connected to the relatively smaller cells of the backbones  18 ,  20 . The connective portion  22  is disposed between the backbones  18 ,  20  and the connective portions  24 ,  26  extend outwardly from backbones  18 ,  20  toward the stiles  14  of frame  10 . The cells of connective portions  22 ,  24 ,  26  can have any shape. In an exemplary embodiment, the cells of connective portions  22 ,  24 ,  26  can be quadrangular or diamond-shaped such that the cells extend in a latitudinal direction of the door D where the width of each cell is greater than the length. The cellular portions  24 ,  26  are configured to not interfere with lock blocks  16  and/or hinge blocks (not shown). Preferably, the cell density of the backbones  18 ,  20  is greater than that of the cellular portions  22 ,  24 ,  26 . 
       FIGS. 2-4  illustrate various embodiments of a door according to exemplary embodiments of the present disclosure.  FIG. 2  illustrates a two-molded-panel door according to an exemplary embodiment of the present disclosure.  FIG. 3  illustrates a four-molded-panel door according to an exemplary embodiment of the present disclosure.  FIG. 4  illustrates a six-molded-panel door according to an exemplary embodiment of the present disclosure. For clarity and ease of illustration, connective portions  22 ,  24 ,  26  are omitted from  FIGS. 2-4  however at least one connective portion  22 ,  24 ,  26  would be present. 
     As best illustrated in  FIG. 2 , the door D comprises a pair of door skins (sometimes called door facings) disposed on either side of the frame  10 . The door skins are typically the same configuration and may be made from wood composites, polymer composite, or steel. An exemplary door skin  28  having two molded panels  30  is illustrated in  FIG. 2 , and those skilled in the art will appreciate that a similarly configured door skin is attached to the opposite side of the frame  10 . The molded panels  30  can be formed in the door skin  28  using various techniques. For example, the door skin  28  can be molded to include depressions or contours that create an appearance of molded panels  30  within the door D. While two molded panels are illustrated in  FIG. 2 , any number of molded panels can be formed within the door skin  28 . The door skin  28  can further exteriorily include depressions or contours that simulate a wood grain pattern such as found in a natural piece of wood. When the door skins are attached to the frame  10 , the skins and frame enclose the core component C including the backbones  18 ,  20  and any cellular portions. 
     The first backbone  18  and the second backbone  20  are arranged in parallel and are positioned toward the outer edge portions of the molded panels  30  ( FIG. 2 ). For example, the backbone  18  is disposed within a predetermined distance of the left edge of the molded panels  30 , and the backbone  20  is disposed within a predetermined distance of the right edge of the molded panels  30 . For a two molded panel design ( FIG. 2 ), each backbone preferably is no further from its respective outer edges of the molded panel than the center position of a four-molded-panel or six-molded-panel door of the same width. The proper positioning of the backbones  18 ,  20  ensures adequate coverage and support across the width of the door to mitigate oil canning. 
     At least one connective portion, such as connective portion  22 , is between the backbones  18 ,  20 . In addition, other connective portions, such as connective portions  24 ,  26 , are disposed between the backbones  18 ,  20  and the frame  10 . The core C. including the backbones  18 ,  20  and the connective portions  24 ,  26 , is preferably used in an automated door assembly line, and thus is formed as an interconnected web that may be applied to the inner surface of the door skin  28 . 
     The core C, with its backbones  18 ,  20  and connective portions  22 ,  24  and  26 , is formed, preferably, from a plurality of strips A, B and E of cardboard or heavy weight paperboard, with the strips A, B and E being connected via a series of spaced adhesive lines that extend approximately half and optionally the entire thickness of a strip and which connect to an adjacent strip. In this way, the core C, formed from the interconnected strips, may be assembled initially in a collapsed form and affixed to the rails  12 , e.g. by an adhesive, such as hotmelt. The web of interconnected strips A, B and E, once connected to rails  12  may be expanded and subsequently oriented between the skins  28  and extending between the rails  12  and the stile  14  when in the expanded form. Alternatively, as best shown in  FIG. 8 , the strips A, B and E may be interconnected via the cut lines and optionally also by adhesive. Regardless of whether adhesively secured or interconnected via cut lines, the core C is formed from a plurality of interconnected strips A, B and E that may be oriented in a first collapsed configuration and then into an expanded configuration, as best shown in  FIG. 1 . Expansion of the core C causes the backbones  18 ,  20  to be oriented relative to the molded panels  30  in order to provide support for the assembled door D. 
     The door D is formed by securing a first door skin  28  to frame  10 . For example, door skin  28  can be secured to frame  10  using an adhesive applied to the opposed surfaces of the rails  12  and the stiles  14  of the frame  10 . The adhesive can be applied by roll coating, spraying, or some other suitable means. The frame  10  is then aligned with the perimeter of the door skin  28 , and secured thereto. Preferably exposed lengths of the cardboard strips A, B forming the core C are adhesively secured to rails  12  so that the rails  12  may be longitudinally displaced a distance corresponding to the height of door skin  28 , and thus causing the core C to expand. Once the rails  12  have been spaced apart and the core C expanded, stiles  14  may be affixed to the rails  12  in to form the frame  10  suitable for being applied to the inner surface of door skin  28 . Another door skin (not shown) is then aligned with the frame  10  and the core component C, and secured thereto. The placement of the second door skin  28  causes the lateral edges of the strips E forming core C to be contacted with the edges of the molded panels  30 , thus providing support thereto in the assembled door D. 
       FIG. 3  illustrates the door D comprising a door skin  32  having four molded panels  34 , and  FIG. 4  illustrates the door D comprising a door skin  36  having six molded panels  38 . In  FIGS. 3 and 4 , the backbones  18 ,  20  are disposed such that one backbone is arranged at the center of each molded panel column. For example, the backbone  18  can be disposed at the center of the left column of molded panels, such as column  40 , and the backbone  20  can be disposed at the center of the right column of molded panels, such as column  42 . Preferably, however, for a four-molded-panel and six-molded-panel door, each of the backbones  18 ,  20  is located between the middle of its respective molded panels and the outer edge of its respective molded panels to ensure adequate coverage and support across the width of the door facing to mitigate oil canning. 
     Doors having six molded panels, such as illustrated in  FIG. 4 , are relatively common and the core C positions the backbones  18 ,  20  under or adjacent the individual molded panels  38  in order to provide support and increased integrity at the molded panels  38 . Prior cores, having a single, centrally located backbone, positioned the backbone along the center of the door skin and thus provided limited support to the adjacent molded panels. The core C of the invention, thus, is useful with one-molded-panel, two-molded-panel, three-molded-panel, four-molded-panel, or six-molded-panel doors. A single core C thus can be used with essentially all door designs. 
     The strips A, B and E have a thickness as defined by their parallel edges at least as thick as the frame  10  of the door D, and may be slightly thicker. When the door D is placed into a press during manufacture, the door skins are pressed against the frame  10 . Likewise, when the door skins are being pressed during door D fabrication, the door skins press against and contact the opposite edges of the strips A, B and E. The core C thus engages the opposed door skins in order to provide the appropriate support. The support provided by the core C and the backbones  18 ,  20  increases resistance to oil canning, increases the structural integrity of the door D, and minimizes pillowing, especially in the multiple molded panel areas. The door facings may be adhesively coated in the area of the backbones in order to attach firmly to the core C and its backbones  18 ,  20 . Alternatively, the opposite edges of the strips A, B and E may be adhesively coated to bond to the door facings when the facings are assembled into a door D. 
     Further, the parallel backbones  18  and  20  minimize any tendency of the core C to twist as the core C is being expanded by separation of the rails  12  during formation of the frame  10 . A single backbone, as with prior cores, might twist during automated assembly of doors, with the result that the core would not be properly oriented for use in the associate door. Additional labor would thus be required to orient the core, resulting in increased assembly time. 
     It will be apparent to one of ordinary skill in the art that various modifications and variations can be made in construction or configuration of the present invention without departing from the scope or spirit of the invention. Thus, it is intended that the present invention cover all such modifications and variations, and as may be applied to the central features set forth above, provided they come within the scope of the following claims and their equivalents.