Abstract:
A door hinge system and door assembly allow a door in a wood veneer dryer to be pulled directly away from its associated door frame before being allowed to swing open in the normal fashion, thus reducing wear on the seal between the door and the door frame. The door assembly allows the tightness of the door to be easily adjusted without the need for shims, and allows the tightness to be adjusted even when the dryer is in operation.

Description:
TECHNICAL FIELD 
     This invention relates to door hardware, and more particularly to hinges which allow a door to articulate outwardly from a door frame before being allowed to swing open. 
     BACKGROUND 
     Many large, enclosed industrial structures have access doors along their lengths to allow workers to access the interior of the structure for monitoring, maintenance and repair purposes. One such enclosure which has a plurality of doors is a wood veneer dryer, which dries wood veneers by heat. The doors in a veneer dryer allow access to various portions of the machinery, including rollers, contained within the dryer. 
     Each of these doors in a veneer dryer requires a seal sandwiched between the door and the door frame, the seal affixed either to the door or to the corresponding door frame. Such a seal prevents air from being drawn into the dryer, thereby reducing the potential for a fire, and also prevents the hot, acrid air produced within the dryer from escaping from the dryer into the surrounding environment. Further, the seals are needed to properly maintain pressure differentials within portions of the dryer itself. It is thus important to maintain these seals in very good condition. 
     There are two significant problems with these seals in current veneer dryers. First, the doors in most veneer dryers are hinged to the door frames in a standard manner, ie. by simple hinges which allow the doors to swing open in a typical fashion. This swinging action wears the door seals unevenly, and in particular, the portion of the seal closest to the hinged edge of the door wears quickly, as the door is opened and closed, relative to the other portions of the seal. Given the importance of these seals in a veneer dryer, the seals require constant monitoring and frequent replacement, costing the dryer operator money and lost time. 
     Second, most portions of veneer dryers, which are generally made of metal, naturally expand significantly when hot, and contract when cold. The amount of expansion, of course, depends largely on the temperature reached in the dryer, and the material used in construction of the dryer. The door of a dryer may expand and contract at a different rate than the door frame to which it is attached. This alters the pressure on the seal sandwiched between the door and the door frame. 
     An operator may try to compensate for this by trying to adjust the force exerted by the door against the door frame (ie. the door&#39;s tightness) to try to maintain a constant pressure on the seal between them. Currently, operators try to accomplish this by adding or removing shims between the hinges and the door and/or door frame. This is an inaccurate, time consuming procedure which cannot be done when the dryer is in operation. 
     To limit the aforementioned uneven and premature wear on the door seals, therefore, it would be useful to provide an improved door hinge system which allows an operator to first move a veneer dryer door relatively straight out and away from the door frame before swinging the door open in a typical fashion. This would allow the door seal to wear relatively evenly, reducing the need for frequent replacement. 
     Further, to make it possible to adjust the force exerted by the door against the door frame (ie. to adjust the pressure on the seal), it would be helpful to provide associated means for allowing a door to be tightened or loosened against its frame while it is in a closed position. 
     SUMMARY OF THE INVENTION 
     The present invention provides a door hinge system for attaching a door to a door frame. Most broadly, the invention comprises, in combination, a linkage having a first end pivotally connected to a door at a first pivot axis and a second end pivotally connected to the door frame at a second pivot axis; and an arm pivotally connected at a first end to the linkage at a third pivot axis further from the door than the plane between said first and second axes. In this manner, the door can be moved outwardly relative to the door frame by moving the rod longitudinally towards said linkage, and then swung open in a normal fashion. 
     While the linkage can be connected directly to the door, in a retrofittable version of the invention, the first pivot axis passes through a first hinge portion attached to the door and the second pivot axis passes through a second hinge portion attached to the door frame. The linkage is accordingly connected to both of said hinge portions. 
     The arm itself may have a u-shaped bracket pivotally connected to the linkage and a threaded arm portion threaded into a block provided in the u-shaped bracket for receiving the threaded arm portion. A locking nut threaded against the block may secure the threaded arm portion to the u-shaped bracket. When the arm is fixed at its second end, shortening it by threading the threaded arm portion further into the block pulls against the linkage, tightening the door against the door frame. 
     In a further embodiment of the invention, a latch assembly is provided to the door which, in combination with the aforementioned hinge system, makes up a door assembly for tightening the door against the door frame in this assembly, the arm traverses the door and is connected at its second end to the latch assembly. The latch assembly has includes means for moving the arm from a first position pulling on the linkage to close the door to a second position pushing on the linkage to open the door. The arm can be shortened to tighten the door against the door frame (more particularly, against the seal sandwiched between the door and door frame), when the door is in a closed position. This can be accomplished by providing the arm with oppositely-threaded end portions and a central portion threaded onto each. Turning the central portion draws together, or forces apart, the ends of the arm. 
    
    
     BRIEF DESCRIPTION OF DRAWINGS 
     In drawings which illustrate specific embodiments of the invention, but which should not be construed as restricting the spirit or scope of the invention in any way: 
     FIG. 1 is a schematic illustration of a veneer dryer, showing a plurality of access doors along one side thereof; 
     FIG. 2A is a cross-sectional illustration of a typical prior art door/door frame arrangement in a veneer dryer, showing a door hinged to a door frame in the typical manner; 
     FIG. 2B is an illustration of the door/door frame arrangement shown in FIG. 2, showing the seal caught on the door as the door is being closed; 
     FIG. 3A is a cross-sectional illustration of a door/door frame arrangement made in accordance with the preferred embodiment of the articulating door hinge system of the present invention, with the door in a closed position. 
     FIG. 3B is an illustration of the door/door frame arrangement shown in FIG. 3A with the door in a first position opened away from the door frame; 
     FIG. 3C is an illustration of the door/door frame arrangement shown in FIG. 3A, with the door in a second, fully opened position. 
     FIG. 4 is a broken view of the components of the door hinge system shown in FIG. 3A; 
     FIG. 5 is a perspective view of the assembled door hinge system shown in FIGS. 3A and 4; 
     FIG. 6 is a broken view of the latch assembly of the door assembly of the present invention, 
     FIG. 7 is a perspective view of the portion of the door assembly shown in FIG. 6; 
     FIG. 8 is a perspective view of the door assembly of the present invention; and 
     FIG. 9 is a schematic view of a portion of the cross arm of the door assembly shown in FIG.  8 . 
    
    
     DESCRIPTION 
     The present invention relates primarily to doors used in a wood veneer dryer of the type shown in FIG. 1, although the invention has application in any situation where a good seal must be maintained between a door and a door frame industrial freezer doors and smoke ovens are other examples where the invention might be used. Reference is made hereafter to a veneer dryer only for the sake of example. 
     In a veneer dryer, denoted generally hereafter by the numeral “100”, a plurality of doors  10  is provided along the length thereof to allow workers to inspect and repair machinery (not shown) contained within dryer  100 . 
     In a typical dryer  100 , doors  10  are simply hinged in the normal manner to door frames formed within the walls of driver  100 . As shown in FIG. 2A, which illustrates a portion of a prior art door/door frame arrangement in cross section, door  10  is typically hinged to door frame  12  by a standard hinge  14  having two hinge leaves  15   a ,  15   b  connected by a hinge pin  13 . A seal  22  typically surrounds the door opening. As mentioned earlier, shims  17  may be placed between hinge  14  and door  10  or door frame  12  to adjust the “tightness” of door  10  against door frame  12 . 
     With this arrangement, door  10  opens in the direction of arrow  16 , allowing access into the interior  18  of dryer  100 . It will be seen from FIG. 2A that this opening movement causes the backside of door  10  to move in the direction indicated by arrow  20 . Which tends to pinch or crush a portion of seal  22  sandwiched between door  10  and door frame  12 . As described earlier, repeated opening of door  10  tends to prematurely wear the portion of seal  22  which is so crushed. 
     Further, in such prior art system, once door  10  has been opened, seal  22  typically expands, as shown in FIG.  2 B. When door  10  is closed again (in the direction of arrow  19 ), the backside edge of door  10  tends to “catch” seal  22 , which is not desirable. 
     FIG. 3A shows a similar view to FIG. 2, but shows the door hinge system of the present invention, denoted generally hereafter by the numeral “50”. 
     The system  50  of the present invention also has, in a preferred embodiment, a door  10  and a door frame  12  enclosing, together with the other outer portions of dryer  100 , the interior  18  of dryer  100 . Again, a seal  22  is sandwiched between door  10  and door frame  12  to prevent gases from entering, or escaping from, dryer  100 . 
     System  50  also further has a hinge connecting door  100  to door frame  12 . As shown in FIGS. 3A-5, however, in the present system door  10  is attached to door frame  12  by a linkage  24 . Specifically, linkage  24  has a first end  26  pivotally connected to door  10  at a first pivot axis  26   a  and a second end  28  pivotally connected to door frame  12  at a second pivot axis  28   a , conveniently with pins  29  (FIG.  4 ), as shown. Pins  29  can be held in place in any convenient manner. In this arrangement, door  10  can pivot about axis  26   a , relative to linkage  24 , and the door/linkage combination can pivot about axis  28   a , relative to door frame  12 . 
     Apart from ends  26 ,  28 , linkage  24  also has a third portion  30  (FIG. 4) serving as a third pivot axis  30   a  to which is further pivotally connected one end of an arm  32 , also with a pin  29 . As shown in detail in FIG. 4, in one embodiment of the invention, arm  32  has a u-shaped bracket  90  on its end, the middle portion of bracket  90  having a block  92  machined to accept the threaded end  80  of a rod. The significance of this arrangement is described in greater detail below. 
     It will be appreciated, as shown in FIGS. 3A-3C, that when pivot axis  30   a  occupies a space further outward of the door than the plane occupied by both the first and second axes,  26   a ,  28   a , moving arm  32  along its longitudinal axis in the direction of arrow  34  (shown in FIG. 3A) pushes against linkage  24  at axis  30   a . With enough force, this causes the door/linkage combination pivoted to door frame  12  at pivot axis  28   a  to pivot about that axis in the direction of arrow  36  (clockwise, in the illustration of FIG.  3 A). 
     This action draws door  10  relatively straight out and away from door frame  12  (ie. in the direction of arrow  38 ), so that its face is roughly parallel, but away from, the wall of dryer  100 , as shown in FIG.  3 B. It will be appreciated that door  10  pivots slightly counter-clockwise about pivot axis  26   a  when this occurs. It will also be recognized that this action, as opposed to the swinging action of the typical door shown in FIG. 2, avoids the crushing of seal  22  by door  10 . 
     After door  10  has been moved out and away from door frame  12  as described (by a distance dependent upon the relative size of the door, but in a veneer dryer by about 1 inch), door  10  may then be swung open in a traditional manner about axis  28   a , as shown in FIG. 3C, allowing access to the interior of dryer  100 . 
     Door  10  may be closed in an opposite manner. Namely, when door  10  is open, it may be swung closed in a normal manner until its face is roughly parallel with the wall of dryer  100  (FIG.  3 B). Door  10  is then pushed straight back towards door frame  12 . Pulling on arm  32  opposite to the direction shown by arrow  34  (FIG. 3A) causes door  10  to be cinched tightly against door frame  12 . 
     In the embodiment shown in FIGS. 3A-5, separate hinge portions  40 ,  42 , each having bolt holes  41 , are provided for system  50  to allow the system to be retrofitted onto an existing door by bolts  43 . There is no reason, however, that linkage  24  could not be connected directly between flanges formed integrally on both door  10  and door frame  12 . 
     Further, while the previous discussion describes axes  26   a  and  28   a  as occupying the “ends” of linkage  24 , this is only for the ease of discussion; the invention encompasses linkages having any two such axes in combination with a third, whether or not they are at the ends of the linkages. 
     In a further embodiment of the invention, a door assembly is provided wherein the arm  32  of the hinge system  50  described above is attached at its opposite end to a latch assembly  60  which allows door  10  to be latched Into a closed position. This door assembly is shown in FIG.  8 . While a variety of latch assemblies might be contemplated, in one embodiment of the invention the latch assembly  60 , as shown in detail in FIGS. 6 and 7, comprises a door portion  62  attached to door  10  and a door frame portion  64  attached to door frame  12 . 
     In this particular embodiment of the invention, door portion  62  comprises a mounting plate  66  (FIG. 6) having a pair of flanges  67   a ,  67   b , extending outwardly therefrom. Arm  32  is connected to door portion  62  of latch assembly  60  with a pin  69  passing through arm  32  and through flanges  67   a  and  67   b . Pin  69  also passes through a hole  65  bored through an arm of an eccentric cam  68  positioned between flanges  67   a  and  67   b . Again, as described earlier, arm  32  conveniently has a u-shaped bracket  90  on its end, the middle portion of bracket  90  having a block  92  machined to accept a threaded end  80  of a rod. Arm  32  may also have a locking nut  94  which may be threadably abutted against block  92  to secure the end of arm  32  to u-shaped bracket  90 . 
     Each of flanges  67   a ,  67   b  has a curved channel  70  formed therethrough, allowing arm  32  leeway for movement between a first position (as shown in FIG. 7) wherein arm  32  is drawn close to door frame portion  64  along channel  70 , and a second position wherein arm  32  is pushed away from frame portion  64  at the opposite end of channel  70 . Pin  69  and arm  32  are forced to follow cam  68  as cam  68  is turned. 
     Cam  68  may be turned by any suitable means. A vertical bar  72  passing fixedly through cam  68  serves to form such turning means in one embodiment of the invention, although other turning means are contemplated. Bar  72  can be turned by hand, or can itself be attached to a handle or a more complicated arrangement to allow an operator to turn bar  72 . 
     Bar  72  may be fixed to cam  68  by any suitable means, but in the embodiment shown herein is attached by a key stock  96  (FIG. 6) which occupies a key channel  98  formed within both bar  72  and cam  68 . Adhesive could also be used. 
     It will thus be appreciated that when bar  72  is turned in the direction shown by arrow  73  in FIG. 7, this forces cam  68 , and accordingly, pin  69  and arm  32  into the first, “closed” position, described above. In this position, arm  32  pulls door  10  tight against door frame  12 . When arm  32  is pushed into an “open” position, however, by turning bar  72  in the direction shown by arrow  74  in FIG. 7, cam  68  forces pin  69  and arm  32  along channel  70  away from door frame portion  64  of latch assembly  60 , and arm  32  is forced towards hinge system  50 . As described in detail earlier, this moves door  10  away from door frame  12 . In this manner, door  10  can be opened and closed by turning bar  72 . 
     Door  10  can be latched to door frame  12  by adding a tab  75  to cam  68  which catches door frame portion  64  of latch assembly  60  when cam  68  is in the first, “closed” position, with arm  32  pulled towards door frame portion  64 . 
     Another aspect of the invention which is of interest is that the length of arm  32  may be made adjustable. FIG. 9 shows a version of arm  32  having two oppositely-threaded end portions  80 ,  82 , and a central portion  84  threaded onto each of them. Arm  32  may be lengthened or shortened by turning central portion  84 . A hexagonal nut  85 , shown in detail in FIG. 9, may be tack welded onto central portion  84  of arm  32 , and may conveniently assist in turning central portion  84  with a wrench. 
     The main significance of the ability to lengthen and shorten arm  32  lies in the fact that the ends of arm  32  are also threadably attached to hinge system  50  and lock assembly  60 . When fixed at these points by locking nuts  94 , shortening arm.  32  by turning central portion  84  causes linkage  24  to be pulled upon by arm  32 . Lengthening arm  32  in the opposite manner causes linkage  24  to be pushed upon by arm  32 . When door  10  is closed, shortening arm  32  will cinch door  10  closer into door frame  12 , since arm  32  will then pull more tightly on linkage  24 . If door  10  is too tightly pulled against door frame  12  when closed, it can be loosened by lengthening arm  32 . In this manner, the tightness of door  10  against door frame  12 , and hence the pressure on seal  22 , can be adjusted, even when dryer  100  is in operation. 
     As will be apparent to those skilled in the art in the light of the foregoing disclosure, many alterations and modifications are possible in the practice of this invention without departing from the spirit or scope thereof. For example, most doors will typically have more than one hinge. In one embodiment of the present invention, the door assembly provides two or more hinges systems, and associated latch assemblies. Bar  72  may be used to connect all latch assembles. 
     Accordingly, the scope of the invention is to be construed in accordance with the substance defined by the following claims.