Abstract:
An improved thermoplastic door jamb comprises a blown thermoplastic core encased in a non-blown thermoplastic skin. A pair of aluminum reinforcing members are embedded in the thermoplastic core and are positioned and configured to receive fasteners for securing case molding and brick molding to the inside and outside edges of the jamb respectively. The reinforcing members stabilize the jamb and, in conjunction with the attached moldings, form a rigid stable structure.

Description:
TECHNICAL FIELD 
     This invention relates generally to doors and windows and more specifically to the jambs of door and window openings that frame the openings and into which doors and windows are mounted. 
     BACKGROUND OF THE INVENTION 
     When constructing the doors and windows of a building, a rough opening is usually formed with framing timbers, which in residential housing are generally 2×4 studs. A prefabricated frame is then installed in the rough opening. In the case of a door, this frame generally comprises a threshold and sill assembly defining the bottom of the frame, a pair of spaced vertical jambs defining the sides of the frame, and a head jamb at the top of the frame. The jambs are formed to receive the door panel, which is mounted to one of the vertical jambs by hinges, and to provide a peripheral stop against which the door rests when it is closed. In many cases, weather stripping is provided along the stop to form a seal between the door panel and the stop in order to prevent unwanted drafts through the closed door. 
     For many years, door jambs, and window jambs for that matter, have been formed of elongated planks or boards of wood that are milled to form the contour of the jamb and to define the raised peripheral stop of the jamb. Since the surfaces of these jambs are generally visible, it has historically been necessary to fabricate door jambs from high grade clear lumber that has no knots, is stable when subjected to moisture, and can be stained and painted with superior results. Although such lumber was plentiful from old growth forests for decades, it has become increasingly rare and correspondingly expensive over the past several years. As a result, old style door frames made of milled clear lumber are quickly becoming cost prohibitive, and can only continue to follow this trend as old growth forests are progressively harvested. 
     Some attempts have been made to reduce the reliance on expensive lumber in the fabrication of door and window jambs. For example, vinyl clad jambs fabricated of less expensive lower grade lumber covered by a skin of extruded vinyl have become popular. However, these types of jambs still require the time consuming process of milling the wooden jamb members to the desired contour, extruding a vinyl cladding contoured to fit over the wooden jambs, and installing the cladding on the jambs during the manufacturing process. As a result, some vinyl clad jambs can be even more expensive than all wood jambs formed of high grade lumber. 
     Another attempt to solve the problem has been to fabricate a combination jamb with interior portions made of high grade lumber but with exterior portions made of vinyl or plastic extrusions. These composite jambs have met with some success but still require the use of some high grade lumber for interior portions of the jambs. Further, most of these types of jambs require specialized installation techniques, which carpenters resist. Finally, as with all jambs that include wood, the wooden portions of the jamb are subject to rot and decay over time, particularly in the region of the door sill,.and require replacing over time. 
     While a door jamb having no wooden components would seem to be a solution to the problem, this has proven an illusive goal for door and window manufacturers. Hollow extruded plastic jambs, while not including any wood, are flimsy, do not take nails and screws like wood, and are generally unacceptable in all but the most inexpensive construction. Solid extruded plastic jambs have not proven practical because the plastic is not as strong as wood and is subject to much greater thermal expansion and contraction than wood, which can cause the jamb to buckle or deform under extreme temperature conditions. 
     Accordingly, there exists a need for a novel door and window jamb assembly that uses no wood, that is resistant to rot and decay for much longer periods of time than wood, that is installed using traditional carpentry techniques, and that is not subject to degradation due to thermal expansion and contraction. It is to the provision of such a jamb assembly that the present invention is primarily directed. 
     SUMMARY OF THE INVENTION 
     Briefly described, the present invention, in one embodiment thereof, comprises an improved door jamb assembly fabricated entirely of coextruded thermoplastic material. The jamb is coextruded with a porous blown thermoplastic core and a solid non blown thermoplastic skin that is adapted to be primed and painted. The jamb is extruded to have the desired profile, and, in the preferred embodiment, has a jamb portion and a raised portion that forms a stop against which a closed door can rest. A groove is extruded along the bottom of the stop for holding a flexible whether strip for sealing against the door. 
     A pair of rolled or extruded aluminum reinforcing members are coextruded with the jamb and are embedded within the blown core thereof. The reinforcing members are shaped to be surrounded and be gripped by the thermoplastic material of the jamb. The reinforcing members function to minimize the thermal expansion and contraction of the jamb member and to eliminate any tendency of the member to bow or deform when exposed to changes in temperature. In the preferred embodiment, one of the reinforcing members has a leg that is positioned adjacent the inside edge of the jamb for receiving screws or other fasteners that mount a decorative case molding to the jamb. Similarly, the other reinforcing member has a leg that is positioned adjacent the outside edge of the jamb for receiving screws or other fasteners used to attach a brick mold to the jamb. This provides additional reinforcement to the jamb since the reinforcing members are firmly attached to the case molding inside a building and the brick mold on the outside of the building. 
     Accordingly, an blown all thermoplastic door jamb is now provided that uses no wood, is efficient to manufacture with a minimum of manufacturing steps, that is not subject to rot and decay, and that is strong and thermally stable even under extreme temperature conditions. These and other objects, features, and advantages of the invention will become more apparent upon review of the detailed description set forth below when taken in conjunction with the accompanying drawings, which are briefly described as follows. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     FIG. 1 is a cross sectional view of a door jamb that embodies principles of the invention in a preferred form. 
     FIG. 2 is a perspective partially sectioned view of a door frame assembly that incorporates the jamb of the present invention. 
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT 
     Referring now in more detail to the drawings, in which like numerals refer to like parts throughout the several views, FIG. 1 illustrates in cross section a preferred embodiment of a door jamb that embodies principles of the invention. The jamb  11  is made of coextruded thermoplastic or vinyl material such as, for example, cellular PVC, polystyrene, or ABS plastic, but can be made of any suitable plastic material as desired. The jamb  11  has a porous blown inner core  12  encased in a dense thermoplastic skin  13 , which is coextruded simultaneously with the core. The skin  13  preferably is formed of a material that is compatible with standard construction primers and paints so that it can be painted just as wood would be painted. Alternatively, the skin could be pre-primed as an additional step in the extrusion process. 
     The jamb  11  is contoured to define a raised stop portion  14  for abutting a closed door mounted in a frame incorporating the jamb. A groove or slot  16  is formed at the base of the raised stop  14 . A length of weather stripping  17  (shown in phantom lines for clarity in FIG. 1) has a leg  18  that is captured and held in the groove  16  and a flexible seal portion  19  that is captured and compressed between a closed door and the stop to form a tight seal when the door is closed. 
     Reinforcing members  21  are coextruded with and embedded in the blown core of the jamb  11  as shown. In the preferred embodiment, the reinforcing members  11  are formed of rolled or extruded aluminum or steel and each is generally L-shaped with a first leg  22  and a second leg  23 . Lips  26  and  27  may be formed at the end of legs  22  and  23  if desired to provide additional structural integrity to the reinforcing member  21 . Projections  24  extend inwardly from the second legs  23  of the reinforcing members and converge toward each other. These projections function both to hold the reinforcing members firmly in place in the material of the jamb and also form a channel for receiving and firmly holding a screw or other fastener driven through the second legs of the reinforcing members. In this regard, the second leg  23  of the right hand reinforcing member in FIG. 1 is located just inside and adjacent the inside edge  36  of the jamb for receiving fasteners that hold the interior case molding to the jamb. Similarly, the second leg  23  of the left hand reinforcing member in FIG. 1 is located just inside and adjacent the outside edge  37  of the jamb for receiving fasteners that hold the outside brick mold  29  to the jamb. Such a fastener  25  is shown extending through the brick mold  29 , through the skin  13  of the jamb, and trough the second leg  23  of the reinforcing member where it is firmly held between the converging projections  24 . The jamb assembly is mounted in a rough opening in the building partially defined by framing member  28 . 
     The reinforcing members  21  function to reinforce the extruded plastic material of the jamb  11 , minimize thermally induced expansion and contraction thereof, and prevent any tendency of the jamb to bow or deform over time or with changing weather conditions. Furthermore, the reinforcing members in conjunction with the case mold and brick mold that are secured to the reinforcing members with fasteners forms an even stronger and more solid structure. Preferably, the reinforcing members are positioned so that their projections are in the proper location for receiving fasteners  25  in an automated fabrication process. However, fabrication on site is also possible with careful measuring. 
     FIG. 2 illustrates the jamb of this invention incorporated into a door frame assembly. The jamb  11  is fabricated by thermoplastic extrusion processes wherein malleable plastic is progressively extruded through a die to produce the jamb profile. As a result, and as illustrated in FIG. 2, the jamb is elongated in shape with the cross-sectional profile (FIG. 1) of a traditional milled wooden jamb. Preferably the jamb  11  has a blown core  12  and a dense encasing skin  13 . Raised stop  14  is formed in and extends along the length of the jamb, and reinforcing members  21  are embedded in the blown core of the jamb. As discussed above, the reinforcing members  21  are co-extruded with and thus progressively become embedded within the thermoplastic jamb during its fabrication. As the natural result of this co-extrusion process, the reinforcing members  21  extend along the length-of the plastic jamb, thus providing the resistance to bowing and deformation of the jamb mentioned above. If the resulting reinforced jamb is cut across its width, as illustrated in the cross-sectional view of FIG. 1, the core, skin, and cross-section of the embedded reinforcing members are visible as shown. The jamb has a bottom portion that is machined to receive and end of a door sill and threshold assembly  32 , which can be attached to the jamb using fasteners extending through the reinforcing members as well. The threshold and sill assembly  32  is typical and has a sill  33  and a threshold cap  34  positioned to underlie a closed door mounted in the door frame. The present invention is particularly advantageous at the bottom portion  31  thereof. This is the portion of a door jamb that is typically exposed to moisture and thus subject to rot and decay. However, since the jamb of the present invention has no wooden components, this problem is completely eliminated. 
     The invention has been described herein in terms of preferred embodiments and methodologies. It will be obvious to those of skill in the art, however, that various additions, deletions, and modifications might well be made to the illustrated embodiments without departing from the spirit and scope of the invention as set forth in the claims.