Abstract:
A mineral core for a door includes a substantially planar slab having a front face, a rear face, and top, bottom and side edges; a plurality of grooves formed in at least one of said front and rear faces, each groove having a reinforcing strip secured therein.

Description:
BACKGROUND AND SUMMARY OF THE INVENTION  
         [0001]    This invention relates to doors of wood or timber construction, and particularly to fire rated doors having mineral cores.  
           [0002]    It is well known to incorporate inorganic minerals into the cores of fire doors of wood construction to obtain better resistance to fire. The typical construction of a wood door includes a mineral core with stiles and rails applied along the side and top and bottom edges, respectively, of the mineral core. The core is then interlocked by gluing the core between two outer layers of, for example, plywood, MDF-boards, HDF-boards, polylaminates or other organic cover skins. Hardwood trim and edging or lipping are then typically applied along the edges of the door.  
           [0003]    One problem with lightweight timber fire door cores has been an inability to obtain sufficient strength in the core to resist a hose stream test, immediately following a fire test. The inner lightweight mineral core material in particular has demonstrated weakness, i.e., cracking, resulting in failure of the tests.  
           [0004]    The present invention relates to the incorporation of at least one and preferably a plurality of reinforcing strips in the surface of the lightweight core material to substantially increase the resistance of the core to the fire hose stream according to UL10C and UBC7-2-97. Preferably, the reinforcing strips are oriented parallel to the core side edges, i.e., so that the strips run from top to bottom of the core.  
           [0005]    To achieve resistance to the fire hose stream, especially after 45 or more minutes, the present invention in one exemplary embodiment secures a plurality of reinforcing strips into grooves, via suitable adhesive, on at least one of the front and rear surfaces of the lightweight core material. It will be appreciated, however, that the reinforcing strips can be applied to both sides of the core to obtain an even more rigid and stronger core. The strips themselves may consist of rigid or reinforced material of organic or inorganic origin.  
           [0006]    The door core construction may be formed by press fitting the reinforcing strips within the preformed grooves in the surface of one or both of the rear and front surfaces or faces of the lightweight core material. This can be done sequentially or simultaneously on both sides. The adhesive used to secure the strips to the core may be cement, colloidal matter, inorganic or organic glue. The preferred fixing agent or adhesive is an inorganic silicate glue.  
           [0007]    Accordingly, in its broader aspects, the present invention relates to a mineral core for a door comprising a substantially planar slab having a front face, a rear face, and top, bottom and side edges; and a plurality of grooves formed in at least one of the front and rear faces, each groove having a reinforcing strip secured therein.  
           [0008]    In another aspect, the invention relates to a reinforced door construction comprising a core including a substantially planar slab having a front face, a rear face and top, bottom and side edges with rails along the top and bottom edges and stiles along the side edges; a plurality of grooves formed in at least one of the front face and the rear face; and a reinforcing strip pressed into each of the grooves.  
           [0009]    A detailed description of the invention, utilizing reference numerals keyed to the various figures, is provided below. 
       
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0010]    [0010]FIG. 1 is a front elevation of a core construction for a door in accordance with one exemplary embodiment of the invention.  
         [0011]    [0011]FIG. 2 is a cross section of the core taken through the line  2 - 2  in FIG. 1;  
         [0012]    [0012]FIG. 3 is an enlarged detail taken from FIG. 2;  
         [0013]    [0013]FIG. 4 is a cross section of the core taken through the line  4 - 4  in FIG. 1;  
         [0014]    [0014]FIG. 5 is an enlarged detail taken from FIG. 4;  
         [0015]    [0015]FIG. 6 is an exploded front elevation of a core construction in accordance with an alternative embodiment of the invention; and  
         [0016]    [0016]FIG. 7 is another exploded front elevation of a core construction in accordance with another alternative embodiment of the invention. 
     
    
     DETAILED DESCRIPTION OF THE INVENTION  
       [0017]    With reference to FIGS.  1 - 5 , one exemplary embodiment of the invention includes a reinforced core construction  10  for a fire resistant door that is made up of a lightweight mineral core  12  having a front surface or face  14  and a rear surface or face  16 . Along the sides of the core, stiles  18  are fixed to the core edges and typically include a dense mineral stile  20  and a timber trim strip  22  (FIG. 5). Upper and lower rails  24  include similar dense mineral rails  26 , and timber trim strips  28 , similar to the stiles  18 . The stiles  18  and rails  24  are preferably glued to the inner, lightweight core. The core  12  may be made of lightweight gypsum, low density calcium silicate slabs, vermiculite slabs, perlite slabs, lightweight castable, micro porous slabs or glass bobble slabs. The core  12  is formed with a plurality of longitudinally extending grooves  30  (FIG. 3) that are parallel to the stiles  18 , and in laterally spaced relationship along the width of the core. The grooves  30  extend from top to bottom of the core, on at least one of the front and rear faces  14  or  16  of the core. Press fit within the grooves are reinforcing strips  32 . Each strip  32  is preferably about ⅞ inch wide (20 mm) and ⅛ inch (3 mm) thick and is press fit and glued into a respective groove  30  that is formed of slightly lesser width and thickness dimensions.  
         [0018]    The strips  32  are made, preferably, of rigid or reinforced material of either organic or inorganic origin. Suitable materials include wood, polylaminate, MDF boards, HDF boards or other organic reinforced strips. Inorganic strips may include glass fiber strips, ceramic fiber strips, ceramic paper, glass fibers, ceramic fibers or paper in a matrix bonded by cement, magnesia cement, colloidal silica, colloidal alumina, potassium silicate, sodium silicate or other inorganic binders.  
         [0019]    Preferably, an adhesive is applied either to the back of the strip  32  or to the groove  30  in the core  12  to insure good bonding of the strip  32  to the core. Preferred glues or adhesives are of the potassium or sodium silicate type. One such glue is sold under the trade name Skamol S-glue available from Skamol A/S. Other suitable glues include # 760  Adhesive available from Vimasco Corp., and Foster Fibrous Adhesive 81-27 available from Foster Products Corporation. Typically, such glues or adhesives are effective at temperatures up to 800° F. or higher.  
         [0020]    [0020]FIG. 6 illustrates another embodiment of the invention, where the core  36  is formed with grooves and reinforcing strips  38  on both the front and rear faces of the core. Specifically, FIG. 6 illustrates reinforcing strips  38  on the front face  40  of the core  36 , and similar strips  38  (in dotted line) on the rear face of the core, with the strips  38  arranged in a laterally offset configuration on respective opposite faces of the core. It will be appreciated that the strips  38  on opposite faces of the core may also be aligned on the front and rear faces, i.e., each pair lying in a single plane extending through the door, parallel to the side edges and stiles  42 . Such an arrangement would appear as shown in FIG. 1. FIG. 6 also illustrates the stiles  42  and rails  44  in exploded form, showing the separate stile components  46 ,  48  and rail components  50 ,  52 .  
         [0021]    It is also possible, but not necessarily preferred, to extend the reinforcing grooves and reinforcing strips beyond the core and into the upper and lower rails, as shown in FIG. 7. In this alternative embodiment, the core slab  54  is identical to the core slab shown in FIG. 6, but grooves for the reinforcing strips  56  have been extended into the upper and lower rails  58 . Specifically, extended groove components  60 ,  62  have been formed, respectively, in the rail components  64 ,  66  in order to accommodate the extended-length reinforcing strips  56  on one or both faces of the core slab. Here again, the strips  56  on opposite faces may be aligned or laterally offset. The stiles  68  including components  70 ,  72  remain as in the previously described embodiments.  
         [0022]    It is also within the scope of this invention to orient the reinforcing strips horizontally across the door between the side edges, i.e., parallel to the top and bottom of the door. The strips could also be incorporated in one or both sides of the door in aligned or offset arrangements as described above. The strips could also extend into the stiles along the side edges if desired.  
         [0023]    In a typical door construction, an outer skin (not shown) comprised of wood, metal or plastic material is applied over the core and over the reinforcing strips.  
         [0024]    Incorporation of the reinforcing strips  32 ,  38  or  56  into the door core has been found to eliminate or minimize the problem of core cracking during fire tests while also providing sufficient strength to resist the hose stream test following a fire test.  
         [0025]    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.