Abstract:
Sturdy metal strainer frames for mounting art canvas are assembled in any required size in an easy and cost-effective fabrication approach. Frame members fabricated as aluminum extrusions are joined at mitred corners to form a rectangular strainer frame. The frame extrusion pattern provides a smooth rounded perimeter edge for improved canvas mounting, a rear channel for anchoring the canvas around the edges and a larger channel around the inside of the frame for accepting brace members as required and holding them accurately aligned, typically at two foot intervals for larger frame sizes. The brace members, provided in two types of extrusion pattern, are cut to length and attached together at junctions as required and to the frame at overlapping flanges, preferably by a proprietary TOX (R) joining system utilizing an upsetting-pressing technique that eliminates all separate fastening hardware items such as clips, nuts, bolts, screws and rivets and requires no drilling, welding, or adhesives.

Description:
FIELD OF THE INVENTION 
   The present invention relates to the field of artwork, billboards, posters and the like performed on fabric and other sheet materials that are mounted onto a frame, and more particularly it relates to improved structure of a strainer frame directed to stretch-mounting canvas for artwork such as oil paintings. 
   BACKGROUND OF THE INVENTION 
   Frames for mounting canvas art work have been typically made from wood: canvas or other fabric is stretched around the perimeter edges of the frame and fastened in place, typically by stapling, under tension, preferably in two perpendicular directions, so as to provide a uniform plane surface. 
   High tension is desirable to ensure long life without sagging or wrinkling, however high tension places large loads on the wood frame with a strong twisting force tending to distort the frame and cause loss of tension over time. Quality canvas mounting requires custom milling of specially selected kiln dried wood, and even with frames that have been carefully shaped and smoothed from premium wood material, the wood surface often tends to bind on the canvas and develop friction that interferes with uniform stretching around the edges. Due to these and other shortcomings of the wood frames, the mounting of art canvas on wood frames has continued to represent a difficult task that requires unusual skill and experience to perform satisfactorily, with resulting high cost for labor and materials. 
   DISCUSSION OF RELATED KNOWN ART 
   The present patent is directed to strainer frames of fixed dimensions as distinguished from stretcher frames that can be expanded with the canvas/fabric in place, e.g. as disclosed in patent application Ser. No. 10/139,809 disclosing a FABRIC-GRIPPING/STRETCHING SYSTEM filed on May 7, 2002 by Horacio M. Ocampo, one of the present joint inventors, issued as patent U.S. Pat. No. 6,675,510 B2. 
   OBJECTS OF THE INVENTION 
   It is a primary object of the present invention to provide an improved structure and assembly method for strainer frames for mounting fabric such as art canvas or similar sheet materials which are to be wrapped around the perimeter and secured in a rear region. 
   It is a further object that the new structure be cost effective overall. 
   It is a further object that the new structure be easy to assemble from a minimal number of different component parts. 
   It is a still further object to totally eliminate all conventional welding and/or hardware items such as rivets, nuts, bolts, and the like in the fabrication of the new frame structure. 
   It is a still further object that frames constructed in accordance with the present invention be made from material other than wood that will provide a lower coefficient of friction than wood and thus reduce drag between the tensioned fabric and the peripheral surface of the frame. 
   SUMMARY OF THE INVENTION 
   The abovementioned objects have been accomplished by the present invention of sturdy metal strainer frames for mounting art canvas that can be assembled in any required size in an easy and inexpensive fabrication approach. Frame members fabricated as aluminum extrusions are readily joined at mitred corners to form a rectangular strainer frame. The frame extrusion pattern provides a smooth rounded perimeter edge for improved canvas mounting, a rear channel for anchoring the canvas around the edges and a larger channel around the inside of the frame for accepting brace members as required and holding them accurately aligned, typically at two foot intervals, for larger frame sizes. The brace members, provided in two types of extrusion pattern, are cut to length and attached together at junctions and to the frame members at overlapping flanges by a proprietary TOX (R) joining system utilizing an upsetting-pressing technique that eliminates all welding and fastenings such as clips, nuts, bolts, screws and rivets. 

   
     BRIEF DESCRIPTION OF THE DRAWINGS 
     The above and further objects, features and advantages of the present invention will be more fully understood from the following description taken with the accompanying drawings in which: 
       FIG. 1  is a plan view of an unbraced embodiment of the strainer frame of the present invention. 
       FIG. 2  is a cross-section of a frame member taken through axis  2 — 2  of FIG.  1  and enlarged. 
       FIG. 3  is an enlarged perspective view showing structure of a typical corner of the strainer frame of FIG.  1 . 
       FIG. 4  is an enlarged cross-section of a frame member such as at  2 — 2  of  FIGS. 1 and 3 , showing a portion of an art canvas mounted thereto. 
       FIG. 5  is a plan view of a single-braced embodiment of the strainer frame of the present invention configured with a brace member of a first type. 
       FIG. 6  is a cross-section of the brace member of  FIG. 5  taken at axis  6 — 6 . 
       FIG. 7  is a cross-section of an intersection of the brace member with the lower frame member of  FIGS. 5 and 9  taken at axis  7 — 7 . 
       FIGS. 8A ,  8 B and  8 C are cutaway enlarged side views illustrating the punch process of the TOX (R) fastening as shown in FIG.  7 . 
       FIG. 9  is a plan view of a double-braced embodiment of the strainer frame of the present invention configured with three brace members: one type 1 full-span brace member intersecting perpendicularly with two type 2 half-span brace members. 
       FIG. 10  is a cross-section of the type 2 brace member of  FIG. 9  taken at axis  10 — 10 . 
       FIG. 11  is a cross section of the central brace member intersection of  FIG. 9  taken at axis  11 — 11 . 
       FIG. 12  is a plan view of a triple-braced embodiment of the strainer frame of the present invention configured with five brace members: one of type 1 and four of type 2. 
   

   DETAILED DESCRIPTION 
   In  FIG. 1  depicts a basic embodiment of the present invention: a rectangular strainer frame  10 A fabricated with two pairs of frame members  12 A and  12 B extruded from aluminum and angle-cut to required length with mitred corners as shown, each reinforced with a metal corner member  13 . This basic form of construction, with no transverse brace members, is suitable for a small strainer frame  10 A not exceeding about 2 feet in either dimension. 
     FIG. 2  is a cross-section of frame member  12 A, taken through axis  2 — 2  of FIG.  1  and enlarged, shows the extrusion pattern utilized in all frame members of the various embodiments of the invention. A smoothly rounded corner  14 A with 0.080″ radius is configured to provide the principal canvas support rim around the frame perimeter. On the inside of corner  14 A, an internal channel  14 B is formed to accept a corner-aligning right-angle bracket. A larger channel  14 C is configured at the rear exterior with opposing barbed walls  14 D and  14 E for retaining a fabric-gripping filler. A still larger exterior channel  14 F is formed by the two parallel flanges  14 G and  14 H extending to th right from the transverse web  14 J as shown. Typically, the frame extrusion pattern is made approximately 1.45 inches by 2 inches overall with wall thickness of 0.0620″ except for flanges  14 G and  14 H which are made 0.0500″ thick. 
     FIG. 3  is an enlarged perspective view of a typical corner of the strainer frame  10 A of  FIG. 1 , showing side member  12 A joining bottom member  12 B at a mitred corner. A metal corner-aligning right-angle bracket  16 , located internally in channel  14 B (FIG.  2 ), indicated in broken lines, along with corner member  13  which is formed from sheet metal to have inner and outer edge flanges as shown and each fastened to the channel members  12 A and  12 B in four places, serve to establish and maintain accurate corner alignment and prevent skewing. 
     FIG. 4  shows a cross-section taken thru  4 — 4  of FIGS.  1  and  3 : the cross-section of frame member  12 A is identical with that at  2 — 2  of  FIG. 1  as shown in  FIG. 2 , however  FIG. 4  includes corner member  13 , with two formed edge flanges as shown, and showing frame member  12 A as normally deployed with the addition of an edge portion of art canvas  18  mounted in place, wrapping around the frame member  12 A and wedged in place in channel  14 C ( FIG. 2 ) by insertion of a gripping filler  20 , made from a suitable resilient material such as wood or paper-wrapped foam, around the frame perimeter. The insertion of filler  20  sets up tensile strain in the canvas  18  as it is held in a flat plane by the raised edges  14 A (FIG.  2 ). Pressure from the opposed pair of barbed walls  14 D and  14 E ( FIG. 2 ) holds filler  20  firmly in place. Art canvas  18  is available pre-stretched, and is originally provided slightly larger than required, the extending surplus border being trimmed off after mounting. 
   For the aluminum perimeter frame extrusion of the size and configuration shown in  FIGS. 2 and 4 , it is recommended that cross-brace support should be provided at approximately 2 feet intervals. Thus, the unbraced strainer frame of  FIG. 1  is suitable for sizes up to a square 2 feet per side, beyond which one or more cross-brace members should be provided to avoid frame deformation due to the loading of the canvas tension. 
     FIG. 5  is a plan view of a strainer frame  10 B in a single-braced embodiment of the present invention configured with a brace member  18  of a first type (type 1) extending across the minor dimension of the rectangular frame  10 B, wherein the short frame members  12 A are under 2 feet and the long frame members  12 B are between 2 and 4 feet in length. Brace member  22  is dimensioned to fit into the main channel between the flanges of the frame members. 
   In the overlapping regions of the frame members  12 B with corner members  13  and with brace member  22  the two interfacing layers of metal are permanently joined together by a special type of fastening joint  24 , typically with four joints  24  in corner members  13  as shown and two places at each end of brace member  22 , one at the front of frame  10 B as shown and one at the rear, is not shown. Each joint  24  is formed in an upsetting/pressing operation by a special tool manufactured and supplied by Pressotechnik Joining Systems of Germany under the trademark TOX; this fastening system eliminates all conventional fastening hardware such as clips, screws and rivets, and requires no drilling or welding. 
     FIG. 6  is a cross-section of the type 1 extrusion pattern of brace member  22 , taken through axis  6 — 6  of FIG.  5 . This H-shaped pattern is configured with four extending flanges  22 A, and is made 0.9200″ in total thickness to fit into a 0.9227″ spacing between the parallel flanges  14 G and  14 H ( FIG. 2 ) that extend inwardly from the frame members. 
     FIG. 7  is a cross-section taken through  7 — 7  of  FIG. 5  at the a typical intersection, in this case the inverted-T-shaped intersection between frame member  12 B and brace member  22  which is seen extending into the major channel  14 F ( FIG. 2 ) where, constrained by flanges  14 G and  14 H, it extends inwardly to the transverse web  14 J. The overlapping flanges are fastened by TOX joint  24 . 
     FIG. 8A  is a enlarged cutaway side view showing in cross-section two overlapping extruded aluminum flanges  14 G and  22 A to be joined; they are placed between a coaxial tapered punch part  26  and a mating cavity part  28 , the two main components deployed in the jaws of the TOX tool, which can be hydraulicly or pneumatically powered. 
     FIG. 5B  shows the aluminum material displaced and formed into the shape of TOX cavity part  28  by pressure from TOX punch part  26 . 
     FIG. 5C  shows the finished circular joint  24  with the TOX tool removed: the two flanges  14 G and  22 A are permanently joined by the TOX upsetting/pressing operation with no drilling, welding or fastening hardware required. The resulting is reported to exhibit equal strength stress for both shear stress and pull stress and greater strength statically and dynamically than spot welding. 
     FIG. 9  is a plan view of a strainer frame  10 C in a double-braced embodiment of the present invention, for the next larger range of frame size up to a square 4 feet per side, configured with four corner members  13  and three brace members: a full-span brace member  22 , type 1 as described above, intersecting perpendicularly with a pair of half-span brace members  30  of a second type designated type 2. 
     FIG. 10  is a cross-section of the type 2 extrusion pattern of brace member  30  taken at axis  10 — 10  of  FIG. 9 ; it is formed with the same 0.9200″ total thickness as type 1 so as to similarly fit into the 0.9227″ flange spacing of the perimeter frame members  12 A/B. However, for the type 2 half-span brace member  30  to fit the into the 0.8200″ flange spacing of a type 1 full span brace member  22 , one end of each half-span brace member  30  must be reformed in a press to compress it from its original 0.9200″ thickness to 0.8200″. To facilitate such end-reforming, the type 2 extrusion pattern is configured in the “spider” shape as shown, with the four flanges  30 A offset outwardly. 
     FIG. 11  is a cross-section of the central X-shaped intersection of full-span brace member  22  (type 1) and a pair of half-span brace members  30  (type 2). The flange reformation at one end of each half-span member  30  is apparent at the central junction. The intersection of one of the half-span brace members  30  with frame member  12 B, taken through axis  11 — 11  of  FIG. 9 , is shown in FIG.  7 . 
     FIG. 12  is a plan view of a strainer frame in a triple-braced embodiment of the present invention configured with five brace members: one full-span brace member  22  (type 1) and four half-span members  30  (type 2), for the next larger range of frame size up to 4 feet by 6 feet. 
   The size of the strainer frame of the present invention can be further increased indefinitely adding full-span and half-span brace members as required to provide bracing at additional two foot increments, as described above. 
   In an alternative approach, regarding the configuration of the extrusion patterns of the brace members, a “type 3” full-span brace member is configured with a “spider” extrusion pattern having 1.0227″ thickness and 0.9227″ flange spacing, i.e. the same as for the peripheral frame members  12 A and  12 B. While this requires reforming both ends of the full-span brace member to 0.9200″ to fit into the frame channels, none of the half-span brace member ends require reforming, since type 1, 0.9200″ thick, fits similarly at both ends. The number of end reforms required with type 2 and with the alternative type 3 full-span brace members is tabulated as follows: 
   
     
       
             
             
           
             
             
             
             
             
             
             
           
             
             
             
             
             
             
           
         
             
                 
               TABLE 1 
             
           
           
             
                 
                 
             
             
                 
               End-reforms required 
             
           
        
         
             
               Braces 
               Full 
               Part 
               Max size 
               Type 2 
               or 
               Type 3 
             
             
                 
             
           
        
         
             
               0 (FIG. 1) 
               0 
               0 
               2′ × 2′ 
               0 
               0 
             
             
               1 (FIG. 5) 
               1 
               0 
               2′ × 4′ 
               0 
               0 
             
             
               1 
               2 
               0 
               2′ × 6′ 
               0 
               0 
             
             
               2 (FIG. 9) 
               1 
               2 
               4′ × 4′ 
               2 
               2 
             
             
               3 (FIG. 12) 
               1 
               4 
               4′ × 6′ 
               4 
               2 
             
             
               4 
               1 
               6 
               4′ × 8′ 
               6 
               2 
             
             
               4 
               1 
               8 
               4′ × 10′ 
               8 
               2 
             
             
               4 
               2 
               6 
               6′ × 6′ 
               8 
               4 
             
             
               5 
               2 
               9 
               6″ × 8′ 
               12 
               4 
             
             
               6 
               2 
               12 
               6′ × 10′ 
               16 
               4 
             
             
                 
             
           
        
       
     
   
   While th foregoing descriptions have described the invention as deployed to mount art canvas, it can be practiced with practically any type of fabric and with other sheet materials such as plastic and random fibre sheets. 
   Extruded aluminum has been found most suitable for extruding in the three patterns required and for the end-reforming as required on the type 2 brace member; however there are other metals and plastics that could be utilized, and other forming methods such as molding instead of extruding to configure members with which the invention may be practiced. 
   The use of the TOX fastening system is believed to be most cost effective for fastening the members of the strainer frame, however the invention could be made and practiced by welding, drilling, utilizing alternate known fastening hardware such as screws, nuts and bolts, rivets, eyelets and/or adhesives. Since the TOX fastening system requires sufficient clearance allowance for the associated tool, this imposes a limitation on the minimum thickness of the strainer frame, particularly when all joints on both sides of the strainer frame are implemented with TOX fastenings. A thinner overall frame size may be accomplished while retaining substantial benefit from the TOX fastening system by designing the extrusions to utilize an optimal combination of TOX and known hardware: e.g. TOX on the joints on one side of the frame and known fastening hardware on the other side of the frame along with gussets or other support structure as required. 
   This invention may be embodied and practiced in other specific forms without departing from the spirit and essential characteristics thereof. The present embodiments therefore are considered in all respects as illustrative and not restrictive. The scope of the invention is indicated by the appended claims rather than by the foregoing description. All variations, substitutions, and changes that come within the meaning and range of equivalency of the claims therefore are intended to be embraced therein.