Patent Publication Number: US-10316663-B2

Title: Mine door

Description:
REFERENCE TO RELATED APPLICATIONS 
     This application claims priority to U.S. Provisional Application No. 62/243,683, filed Oct. 20, 2015, the entire contents of which is hereby incorporated by reference. 
    
    
     FIELD OF THE INVENTION 
     The present invention generally relates to mine ventilation equipment, and more particularly to an improved mine door. 
     BACKGROUND OF THE INVENTION 
     Stoppings are used to control the flow of ventilation air through a mine. A stopping often includes an opening closed by a door to allow passage through the stopping, as described for example in our U.S. Pat. No. 7,393,025 incorporated herein by reference. Mine doors of this type, sold by Jack Kennedy Metal Products &amp; Buildings, Inc., have proven to be commercially successful. These doors, sometimes referred to as “man doors”, are made from relatively thick sheet metal (e.g., 14 gauge metal) to provide the necessary strength. However, the additional bulk increases the expense of the door. There is a need, therefore, for a mine door which is lighter in weight and yet still very strong. 
     Also, some mine ventilation systems involve reversing air flow through the mine. That is, a mine passage that is an air intake at certain times later becomes an air return. Because it is advantageous for a mine door to be hung on its door frame such that the high pressure pushes the door closed against the frame to aid in both closing and sealing, it is also advantageous that the door be “reversible”, that it, the capability of being moved from one side of the door frame to the other at the time of air reversal. Further, it is desirable that the door be self-closing so that it cannot be left open inadvertently. 
     Heretofore, reversibility has been achieved in some cases by unfastening the hinges of the mine door from one side of the door frame and re-fastening the hinges to the opposite side of the door frame. This procedure is labor-intensive and time-consuming. In other cases, the door mounts on open topped hinge pins at one side of the door frame such that the door can be lifted off the hinge pins and moved to similar hinge pins on the opposite side of the door frame. However, the door is not self-closing. There is a need, therefore, for a self-closing mine door that can be quickly moved from one side of the door frame to the other. 
     SUMMARY OF THE INVENTION 
     This invention involves a mine door assembly which, in one embodiment, comprises a reinforced lightweight mine door for installation in a mine passageway. The mine door comprises a generally rectangular sheet metal door panel having four sides and four corners, and a reinforcing structure projecting from a face of the door panel. The reinforcing structure comprises a central section and a plurality of channel sections extending from the central section toward respective sides or corners of the door panel. 
     In another embodiment, this invention involves a mine door assembly for installation in a mine passageway. The mine door assembly comprises a mine door frame having a first side facing a first direction and a second side facing a second direction opposite the first direction. The assembly also includes a mine door comprising at least one spring-loaded hinge for mounting the mine door on the mine door frame and urging the mine door toward a closed position. The spring-loaded hinge comprises a bracket, at least one first fastener on the mine door frame adjacent the first side of the mine door frame, and at least one second fastener on the mine door frame adjacent the second side of the mine door frame. The bracket of the at least one spring-loaded hinge is configured for releasable connection to the at least one first fastener for selectively mounting the mine door on the mine door frame in a first position at the first side of the mine door frame for opening the door in said first direction, and for releasable connection to the at least one second fastener for selectively mounting the mine door on the mine door frame in a second position at the second side of the mine door frame for opening the door in said second direction. 
     In another embodiment, this invention involves the mine door described in the preceding paragraph. 
     In still another embodiment, this invention involves a mine door assembly comprising a mine door frame having a first side adapted to face a first direction and a second side adapted to face a second direction opposite the first direction. The assembly includes a mine door comprising at least one hinge for mounting the mine door on the mine door frame. The hinge comprises at least one bracket having a keyhole slot, at least one first fastener on the mine door frame adjacent the first side of the mine door frame, and at least one second fastener on the mine door frame adjacent the second side of the mine door frame. The keyhole slot is adapted to receive the at least one first fastener for selectively and releasably mounting the mine door in a first position on the mine door frame for opening the door in the first direction, and the keyhole slot is adapted to receive the at least one second fastener for selectively and releasably mounting the mine door in a second position on the mine door frame for opening the door in said second direction. 
     Other objects and features will be in part apparent and in part pointed out hereinafter. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  illustrates a mine door assembly installed in a mine passageway; 
         FIG. 2  is a front elevational view of the mine door assembly of  FIG. 1 ; 
         FIG. 3  is a rear elevational view of the mine door assembly of  FIG. 1 ; 
         FIG. 4  is a cross-section taken in the plane of  4 - 4  of  FIG. 2 ; 
         FIG. 5  is a cross-section taken in the plane of  5 - 5  of  FIG. 2 ; 
         FIG. 5A  is a view similar to  FIG. 5  but showing an alternative door sealing arrangement; 
         FIG. 6  is a section taken in the plane of  6 - 6  of  FIG. 2 ; 
         FIG. 7  is an enlarged portion of  FIG. 2  showing a corner construction of the door; 
         FIG. 8  is a section taken in the plane of  8 - 8  of  FIG. 2 ; 
         FIG. 9  is an enlarged portion of  FIG. 8  showing a channel section of a reinforcement structure on the door; 
         FIG. 10  is a section taken in the plane of  10 - 10  of  FIG. 2 ; 
         FIG. 11  is a perspective of a mine door assembly having a reversibility feature, a mine door of the assembly being shown in a closed position; 
         FIG. 11A  is an enlarged portion of  FIG. 11  showing a corner construction of the assembly; 
         FIG. 11B  is an exploded view of components of a door frame of the assembly of  FIGS. 11 and 11A ; 
         FIG. 12  is a perspective of a door frame of the assembly of  FIG. 11 ; 
         FIG. 13  is a section taken in the plane of  13 - 13  of  FIG. 12 ; 
         FIG. 14  is a perspective of a spring-loaded hinge of the assembly of  FIG. 11 ; 
         FIG. 15  is an exploded perspective of the components of the spring-loaded hinge of  FIG. 14 ; 
         FIG. 16  is a perspective similar to  FIG. 11  but showing the mine door in a partially open position; 
         FIG. 17  is a view similar to  FIG. 16  but showing the door held in the partially open position by a blocking device; 
         FIG. 18  is a section taken in the plane of  18 - 18  of  FIG. 17 ; and 
         FIGS. 19-22  are views similar to  FIG. 17  illustrating removal of the mine door from one side of a door frame prior to reinstallation of the door at an opposite side of the door frame. 
     
    
    
     Corresponding reference characters indicate corresponding parts throughout the drawings. 
     DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     Referring to the drawings,  FIG. 1  illustrates a stopping, generally designated  30 , installed in a mine passage  34 . By way of example but not limitation, the stopping  20  may be made from blocks or a series of elongate panels  36  of the type described in our U.S. Pat. Nos. 4,483,642, 4,547,094, and 7,267,505, all of which are incorporated herein by reference. A mine door assembly, generally designated  40 , is secured to the stopping  30 . As illustrated in  FIG. 11 , the mine door assembly  40  includes a door frame generally designated  44  and a mine door generally designated  46  mounted on the door frame for pivotal movement between an open position allowing access through a doorway  50  defined by the door frame and a closed position for closing the doorway. As illustrated in  FIG. 1 , the mine door pivots about a vertical axis, but it will be understood that it could be configured to pivot about a horizontal axis. 
     Referring to  FIGS. 2-5 , the mine door  46  comprises a generally rectangular (e.g., square) sheet metal door panel  52  having four sides  54 , four corners  56 , an inner face  58  facing the doorway  50  when the door is closed, and an opposite outer face  62  facing away from the doorway when the door is closed. As illustrated in  FIG. 5 , flanges  57  project inward from the inner face  58  of the door panel  52  at the four respective sides of the door and cooperate with channels  66  affixed (e.g., welded) to the inner face  58  of the door panel to hold a seal  70  for sealing against the door frame  44  all around the doorway  50  when the door is in its closed position. The sealing arrangement may be as shown in our aforementioned U.S. Pat. No. 7,393,025 incorporated herein by reference. 
       FIG. 5A  illustrates an alternative sealing arrangement, e.g., for smaller doors. The arrangement is similar to that shown in  FIG. 5  and corresponding components are designated by corresponding reference numbers with a prime designation (′). In this embodiment, the flanges  57 ′ of the door project outward from the outer face  62 ′ of the door panel  52 ′. The seal  70 ′ is a seal secured (e.g., glued) to the inner face  58 ′ of the door panel for engagement with the door frame  44 ′ all around the doorway  50 ′ when the door is in its closed position. Other seal configurations may be used. 
     Referring to  FIG. 2 , the mine door  46  includes a reinforcing structure, generally designated  74 , projecting laterally outward from the outer face  62  of the door panel  52 . Alternatively, the reinforcing structure could project laterally inward from the outer face of the door panel. This structure  74  comprises a central section  76  and a plurality of channel sections  78  extending from the central section toward respective sides  54  or corners  56  of the door panel  52 . Importantly, the reinforcing structure  74  and door panel  52  are integrally formed, that is, the reinforcing structure is formed as one piece with the sheet metal of the door panel. Alternatively, the reinforcing structure  74  could be formed (e.g., stamped) as a separate piece and then secured (e.g., welded or otherwise fastened) to the door panel  52 . As best illustrated in  FIG. 11 , the mine door  46  lacks a second door panel sandwiching the reinforcing structure  74  between the sheet metal door panel  52  and said second door panel. 
     In the illustrated embodiment, the reinforcing structure  74  is generally X-shaped and comprises four channel sections  78  extending from the central section  76  toward respective corners  56  of the door panel  52 . However, it will be understood that the reinforcing structure can have shapes other than an X-shape. By way of example but not limitation, the reinforcing structure can be generally K-shaped, or generally Y-shaped, or generally H-shaped, or generally cross (+)-shaped, or any other shape where a number of channel sections extend from what can be broadly described as a “central section.” As used in this context, the term “central section” is intended to identify the portion of the reinforcing structure from which the channel sections originate; the term is not restricted to a location at the geometric center of the door panel  52 . 
     The central section  76  of the X-shaped reinforcing structure  74  allows the four channel sections  78  to terminate without interfering with one another. In addition, the central section  74  increases the moment of inertia of the door where the stresses on the door, due to the air pressure differential across the door, are both the greatest, and where they are compound. In the illustrated embodiment, the central section  76  is a generally dish-shaped formation comprising a generally circular side wall  80  projecting laterally outward, e.g., substantially at right angles, from the outer face  62  of the door panel  52 , and a bottom wall  84  (see  FIG. 6 ). Desirably, the bottom wall  84  is substantially flat, extends generally parallel with the plane P of the door panel  52 , and is spaced a first distance D 1  from the outer face  62  of the door panel  52 . This first distance D 1  generally corresponds to the depth of the central section  76 . The central section  76  may have shapes other than circular without departing from the scope of this invention. By way of example, if the mine door is elongate, the central section may be oval in shape, with the long axis of the oval extending generally parallel to the long axis of the door. In general, it is desirable that the central section  76  be free of corners that might otherwise create excessive areas of stress. 
     Referring to  FIGS. 2 and 7 , the four channel sections  78  of the reinforcing structure  74  have inner ends intersecting the side wall  80  of the central section  76  at intervals around the central section, e.g., at substantially equal 90-degree intervals. The channel sections  78  also have outer ends terminating short of respective corners  56  of the door panel  52  to provide flat corner sections  90  of the door panel (see  FIG. 7 ). These flat corner sections  90  cooperate with flat side sections  92  of the door panel to provide an unobstructed flat sealing area  94  extending completely around the periphery of the door panel  52  to facilitate mounting the seal  70  on the door panel. 
     As best illustrated in  FIGS. 8 and 9 , each channel section  78  of the reinforcing structure  74  has opposite sides comprising, in this embodiment, two spaced-apart side walls  100  projecting laterally outward, e.g., substantially at right angles, from the outer face  62  of the door panel  52 . Each channel section  78  of the embodiment further comprises: a bottom wall  102 . Desirably, the bottom wall  102  is substantially flat, extends generally parallel with the plane P of the door panel  52 , and is spaced a second distance D 2  from the door panel. The second distance D 2  generally corresponds to the depth of the channel section. The side walls  100  of each channel section  78  intersect with the side wall  80  of the central section  76 . Similarly, the bottom wall  102  of each channel section  78  intersects with the bottom wall  84  of the central section  76 . Desirably, at these latter intersections, the bottom walls  102  of the channel sections  78  and the bottom wall  84  of the central section  76  are substantially co-planar. In other embodiments, the bottom walls  102  of the channel sections  78  are not substantially co-planar or parallel with the bottom wall  84  of the central section  76 . By way of example, in one embodiment the side walls  100  of the channel sections  78  are tapered so that the depths of the channel sections increase toward the center of the door where the stress is greater. The bottom walls  102  of the channel sections  78  slope inward at their outer ends to join the outer face  62  of the door panel  52 . 
     Desirably, the bottom wall  84  of the central section  76  has a cross-dimension  88  (diameter for a circular shape) substantially greater than a width dimension  106  of each channel section. (Compare  FIGS. 6 and 9 .) Even more desirably, the cross-dimension  88  is greater than the sum of the width dimensions  106  of the four channel sections. In the illustrated embodiment, the width dimension  106  of each channel section  78  is substantially uniform along substantially the entire length of the channel section (see  FIG. 2 ). In other embodiments, the width dimension  106  may vary along the length of the channel section. By way of example, the width dimension  106  of the channel sections  78  may increase in a direction toward the central section  76  so that the channel sections are generally pie-shaped, pointing toward respective corners  56  of the door panel  52 . Increasing both the cross-dimension  88  of the central section  76  and the width dimension  106  of the channel sections  78  creates a more balanced door section, i.e., more equal “flanges” (raised and non-raised areas) of the door panel  52 . As a result, the strength of the door is greater. This may be especially important for bigger doors. 
     In general, it is desirable to maximize the width and depth of each channel section  78  to obtain the greatest increase in strength possible (by increasing the planar area moment of inertia of the door  46 ) consistent with being able to form the door without tearing or otherwise severely degrading the sheet metal. Desirably, the width dimension  106  of the each channel section  78 , as measured across the bottom wall  102 , is at least twice the depth of the channel section, i.e., the stated second distance D 2 . In one embodiment, the first and second distances D 1 , D 2  corresponding to the depths of the central section  76  and the channel sections  78 , respectively, are substantially equal. 
     As previously noted, the door panel  52  and X-shaped reinforcing structure  74  are integrally formed as one piece from sheet metal. The sheet metal has a thickness in the range of about 0.02-0.06 in and a yield strength preferably at least 45,000 psi and even more preferably at least 60,000 psi. Desirably, for smaller doors having dimensions in the range of 24-36″24-36″, the thickness is in the range of 0.28-0.47 in, and the yield strength is preferably in the range of 45,000-90,000 psi and even more preferably in the range of 60,000-80,000 psi. (For larger doors, e.g., those having dimensions in the range of 36-60″×36-60″, the thickness and/or yield strength are correspondingly greater.) This compares very favorably to prior commercial designs using sheet metal having a thickness in the range of 0.070-0.087 in and a yield strength less than 25,000 psi. Using the X-shaped reinforcing structure  74  allows the use of thinner-gauge metal without sacrificing strength. As a result, the mine door  46  is lightweight (less metal), less expensive, and very strong. 
     In one embodiment, the door panel  52  and X-shaped reinforcing structure  74  are formed in a pressing operation during which the reinforcing structure is pressed into a planar blank of sheet metal forming the door panel. As the blank is pressed, the sheet metal stretches and draws from the edges of the blank to form the central section  76  and the four channel sections  78 , and corrugations  110  ( FIG. 2 ) are formed in the bottom wall  84  of the central section and in the bottom walls  102  of the channel sections generally adjacent intersections of the channel sections and the central section. The side flanges  57  of the door panel  52  may be formed before, during or after the X-shaped reinforcing structure  74  is formed. Desirably, but not necessarily, the flanges  57  are integrally formed from the same blank of sheet metal as the door panel  52  and X-shaped reinforcing structure  74 . 
     Referring to  FIG. 10 , the door assembly  46  also includes a suitable latching assembly, generally designated  120 , for latching the mine door  46  in its closed position against the door frame  44 . In one embodiment, the latching assembly  120  comprises a latch  122  on the door  46  and a keeper  126  on the door frame  44 . By way of example, the latching assembly  120  may be of the type disclosed in our U.S. Pat. No. 7,393,025 incorporated herein by reference. Alternatively, other latching mechanisms may be used without departing from the scope of this invention. 
     In one embodiment, the mine door is self-closing. That is, the door is spring-biased toward its closed position. 
     Referring to  FIGS. 5, 11, 11A, 11B and 12 , the mine door frame  44  is generally rectangular and comprises four frame members  140  surrounding the doorway  50 , including generally horizontal top and bottom frame members  140  and generally vertical left and right frame members  140 . The frame  44  has a first (front) side  142  lying generally in a first plane P 1  defined by a front face of the frame and a second opposite (back) side  144  lying in a second plane P 2  defined by a back face of the frame. The planes P 1 , P 2  are spaced apart a distance corresponding to the depth of the door frame  44  and lie at opposite ends of the doorway  50  through the frame. The frame  44  may be constructed substantially as described in our U.S. Pat. No. 7,393,025 incorporated herein by reference. In one embodiment, each of the four frame members  140  is generally channel-shaped and comprises a web  145  and flanges  146  at opposite sides of the web. Alternatively, the frame member  140  has only one flange  146 , namely, the flange at the side of the frame adjacent the mine door  46 . Desirably, the frame members  140  are fabricated (e.g., stamped) as four separate pieces of sheet metal and then secured together, as by welding overlapping portions of the flanges  144  at locations  147  at the corners of the frame (see  FIG. 11 ). For additional strength, at least the top and side frame members, and preferably all four of the frame members, are formed (e.g., stamped) with ribs  148  extending along the webs  145  of the frame members  140  (see  FIG. 5 ). Desirably, the ribs  148  project inward toward the center of the door opening and extend along the full lengths of the webs  145  of respective frame members to form a substantially continuous reinforcement around the entire perimeter of the frame  44 . In the illustrated embodiment (see  FIG. 5 ) each rib  148  is generally channel-shaped and comprises a bottom wall  148 A and side walls  148 B. Further, the ribs  148  lie in and are symmetrical about the central vertical plane VP of the frame. However, the ribs may have other shapes and other locations. Also, each frame member  140  may have more than one reinforcing rib. 
       FIGS. 11A and 11B  illustrate a corner construction of the frame  44  at an intersection between the top frame member  140  and a side frame members  140 . The rib  148  of the top frame member  140  is received in a notch  149  of complementary shape in the rib  148  of the vertical frame member. Desirably, the notch  149  has a depth substantially the same as the depth of the rib  148  in the top frame member  140 , such that the web  145  and rib  148  of the top frame member bear against respective upper edges of the web  145  and rib  148  of the side frame member. As a result, a load on the top frame member  140  is distributed over substantially the entire webs  142  and ribs  148  of the two side frame members for efficient load transfer and overall increased strength of the frame. The corner construction of the frame  44  at the intersections between the bottom frame member  140  and the side frame members  140  is substantially identical to the corner construction described above at the intersections between the top frame member  140  and the side frame members  140 . In the illustrated corner constructions, the webs  145  of the top and bottom frame members  140  are not welded to the webs  145  of the side frame members  140 . Alternatively, the webs  145  of the frame members  140  can be welded together. 
     Desirably, the mine door  46  and mine door frame  44  described above are equipped to have the reversibility feature described earlier, that is, a feature which permits the mine door to be selectively mounted at the first side  142  of the door frame and then, as needed or desired, to be removed and re-mounted at the second opposite side  144  of the door frame, and vice versa. This feature is described in detail below. 
     Referring to  FIGS. 11-15 , the mine door  46  comprises at least one spring-loaded hinge, generally designated  150 . Relatedly, the mine door frame  44  comprises at least one first fastener, generally designated  152 , adjacent the first side  142  of the mine door frame and at least one second fastener, generally designated  154 , adjacent the second opposite side of the mine door frame. In the illustrated embodiment, the mine door comprises two spring-loaded hinges  150 , and the mine door frame comprises two first fasteners  152  and two second fasteners  154 , although it will be understood that these numbers may vary. The spring-loaded hinges  150  are configured for releasable connection to the first fasteners  152  for selectively mounting the mine door  46  on the mine door frame in a first position ( FIG. 11 ) at the first (front) side  142  of the mine door frame  44  for opening the door in a first direction indicated by the arrow  156 , and for releasable connection to the second fasteners  154  for selectively mounting the mine door on the mine door frame in a second position ( FIG. 22 ) at the second side  144  of the mine door frame  44  for opening the door in a second direction opposite the first direction and indicated by the arrow  158  in  FIG. 11 . 
     Referring to  FIG. 13 , each of the first and second fasteners  152 ,  154  is a rivet-type fastener comprising a head  168  having a first dimension  170  (diameter) and a shank  174  extending from the head having a second dimension  176  (diameter) less than the first dimension. The shank is secured to the frame  44 , as by welding, such that the head  168  of the fastener  152 ,  154  is spaced from an adjacent frame surface  180  to provide a relatively small gap  184  between the surface and the head. Other types of first and second fasteners can be used. 
     Referring to  FIGS. 14 and 15 , each spring-loaded hinge  150  comprises a bracket  196  configured for releasable attachment to a respective fastener  152 ,  154  on the door frame, a hinge pin  190  affixed in a non-rotatable manner (e.g., welded) to the bracket, and upper and lower hinge plates  198  connecting the mine door panel  52  to the hinge pin  190 . In the illustrated embodiment, the hinge plates  198  are metal straps affixed in a non-rotatable manner (e.g., welded) to the outer face  62  of the door panel  52  and have vertically aligned arcuate (e.g., circular or part-circular) pin-receiving sections  200  that receive the hinge pin  190  and allow rotation of the hinge plates relative to the hinge pin so that the door panel  52  may be opened and closed about the longitudinal (vertical) axis of the hinge pin. In other embodiments, the spring-loaded hinge  150  may include more or less than two hinge plates  198 . Hinge plates having configurations other than the one illustrated may also be used. 
     Referring to  FIGS. 14 and 15 , the bracket  196  is generally Z-shaped and comprises a pin-attachment section  206  having a seat  210  in which the hinge pin  190  is seated and secured, as by welding, an intermediate section  212  extending at an angle  214  (e.g., an oblique angle) from the pin-attachment section, and a fastener section  216  extending at an angle  218  (e.g., substantially perpendicular) to the intermediate section. The bracket  196  may have other shapes. When the bracket  196  is fastened to the door frame  44 , as illustrated in  FIG. 18 , the fastener section  216  extends in a plane generally parallel to the frame surface  180 ; the intermediate section  212  extends substantially parallel to a respective side  142  of the door frame; and the pin-attachment section  206  extends generally laterally outward away from the door frame. As is apparent from  FIG. 18 , the orientation of the door panel  52  relative to the bracket  196  changes as the door is opened and closed. As the door opens, movement of the door panel  52  relative to the bracket  196  creates a widening gap  220  between the intermediate section  212  of the bracket and pin-receiving section  200  of the hinge plate  198 . Conversely, as the door closes, this gap  220  narrows, the significance of which will become apparent. The bracket may have other configurations within the scope of this invention. 
     Referring again to  FIGS. 14 and 15 , the fastener section  216  of the hinge bracket  196  has at least one fastener opening  224 . In this embodiment, the fastener opening  224  is a keyhole slot having a first relatively wide region  226  sized to allow passage of the head  168  of a respective fastener  152 ,  154  and a second narrower region  230  sized to allow passage of the fastener shank  174  but not the fastener head. The thickness  234  of the fastener section  216  ( FIG. 18 ) is slightly less than the size of the gap  184  ( FIG. 13 ) between the fastener head  168  and the adjacent surface  180  of the mine door frame  44  to allow a portion of the bracket  196  around the keyhole slot  224  to move into the gap as the mine door is installed on the mine door frame, as described below. 
     Each spring-loaded hinge  150  also includes a spring mechanism, generally designated  240  in  FIG. 14 , for urging the mine door toward a closed position when the mine door  46  is mounted on the mine door frame  44  in its stated first and second positions. In the embodiment illustrated in  FIGS. 14 and 15 , the spring mechanism  240  comprises a pair of coil torsion springs  242  surrounding the hinge pin at positions adjacent the upper and lower hinge plates  198  of the hinge  150 . The upper coil spring  242  is positioned between the upper hinge plate  198  and the top of the bracket  196 , and the lower coil spring  242  is positioned between the lower hinge plate  198  and the bottom of the bracket  196 . Alternatively, for lighter doors, only one spring  242  may be necessary. Each coil spring  242  terminates at one end in a first leg  246  bearing against the outer face  62  of the door panel  52  and terminates at an opposite end in a second leg  248  bearing against the pin-attachment section  206  of the bracket  196 . The arrangement is such that when the mine door  46  is attached to the frame  44 , the coils springs  242  urge the door toward a closed position. When the door is removed from the door frame, the springs  242  urge the bracket  196  toward a position corresponding to the position the bracket assumes when the mine door is in a closed position on the mine door frame. Other spring mechanisms can be used within the scope of this invention. 
     To mount the mine door  46  of the illustrated embodiment at one side of the door frame  44 , e.g., the first side  142 , the door is manipulated to establish releasable connections between the hinge brackets  196  and the first fasteners  152  at that side  142  of the door frame. This is accomplished by passing the heads  168  of the fasteners  152  on the door frame  44  through the wide regions  226  of the keyhole slots  224  in respective hinge brackets  196  to an initial position in which the fasteners are adjacent the lower ends of the slots. The door is then manipulated (lowered in the illustrated embodiment) to move the fastener shanks  174  up into the narrower regions  230  of respective slots  224  to a final position ( FIG. 11 ) in which the fasteners are adjacent upper ends of respective slots. With the fasteners  142  in their final positions, the door is secured to the door frame for swinging between open and closed positions about the generally vertical axes of the hinge pins  190 . The mine door is urged toward its closed position by the torsion springs  242 . The door is latched closed by the latch mechanism  120 . 
     The releasable connections between the mine door  46  and mine door frame  44  allow the mine door to be quickly and easily moved from one side  142  of the door frame to the opposite side  144  of the door frame. To remove the mine door  46  from the first side  142  of the door frame  44 , the door is unlatched and moved to a partially or fully open position (see  FIG. 16 ) against the urging of the spring mechanism  240 . The door is maintained in this open position by placing a blocking device  260 , e.g., a long rod or other suitable object or objects, into the gaps  220  between the hinge plates  198  attached to the door panel  52  and the intermediate sections  212  of the brackets  196  attached to the door frame  44  (see  FIGS. 17 and 18 ). The mine door is then lifted up to a position in which the heads  168  of the fasteners  152  are aligned with the wide regions  226  of respective keyhole slots  224  ( FIG. 19 ), at which point the mine door can be removed from the door frame ( FIG. 20 ). When the door is removed ( FIG. 21 ), the blocking device  260  maintains the brackets  196  of the spring-loaded hinges  150  in a fixed orientation relative to the mine door panel  52  against the urging of the coil springs  242 , thus facilitating reinstallation of the door at the opposite side  144  of the door frame  44  ( FIG. 22 ). The mine door  46  is reinstalled using the same process described above except that the second fasteners  154  on the second opposite side  144  of the frame  44  are used for establishing the releasable connections. After the mine door has been reinstalled, the blocking device  260  is removed from the gaps  220  and the door closes under the urging of the spring mechanism  240 . The latch  120  is used to secure the door in its closed position. It will be understood in this regard that the frame  44  is equipped with two keepers  122 , a first keeper adjacent the first side  142  of the frame for use when the door is installed at that side of the frame, and a second keeper adjacent the second side  144  of the frame for use when the door is installed at that side of the frame. 
     Having described the invention in detail, it will be apparent that modifications and variations are possible without departing from the scope of the invention defined in the appended claims. By way of example but not limitation, the mine door described above has both the reinforcing (e.g., X-shaped) feature and the reversibility feature. In other embodiments, a mine door of this invention may have the reversibility feature but not the reinforcing feature. Conversely, a mine door of this invention can have the reinforcing structure but not the reversibility feature. 
     The reversibility feature can be claimed in various ways, including but not limited to the following 
     1. A mine door assembly for installation in a mine passageway, the mine door assembly comprising 
     a mine door frame having a first side facing a first direction and a second side facing a second direction opposite the first direction, 
     a mine door comprising at least one spring-loaded hinge for mounting the mine door on the mine door frame and urging the mine door toward a closed position, said spring-loaded hinge comprising a bracket, 
     at least one first fastener on the mine door frame adjacent the first side of the mine door frame, 
     at least one second fastener on the mine door frame adjacent the second side of the mine door frame, 
     wherein the bracket of the at least one spring-loaded hinge is configured for releasable connection to the at least one first fastener for selectively mounting the mine door on the mine door frame in a first position at the first side of the mine door frame for opening the door in said first direction, and for releasable connection to the at least one second fastener for selectively mounting the mine door on the mine door frame in a second position at the second side of the mine door frame for opening the door in said second direction. 
     2. The mine door assembly of claim  1 , wherein the at least one spring-loaded hinge further comprises a hinge pin connected to the bracket, and at least one hinge plate connecting the mine door to the hinge pin. 
     3. The mine door assembly of claim  2 , wherein the at least one hinge plate is affixed to an outer face of the mine door and comprises an arcuate pin-receiving section that receives the hinge pin and allows rotation of the at least one hinge plate and mine door about a longitudinal axis of the hinge pin. 
     4. The mine door assembly of claim  2 , wherein the bracket comprises a pin-attachment section affixed to the hinge pin, an intermediate section extending at an angle from the pin-attachment section, and a fastener section extending at an angle from the intermediate section, the fastener section having at least one fastener opening for receiving the at least one first fastener when the mine door is mounted on the mine door frame in said first position and for receiving the at least one second fastener when the mine door is mounted on the mine door frame in said second position. 
     5. The mine door assembly of claim  4 , wherein the at least one spring-loaded hinge is configured for creating a gap between the intermediate section of the bracket and the at least one hinge plate, said gap widening when the door is opened for receiving a blocking device to maintain the size of the gap when the mine door is removed from the mine door frame. 
     6. The mine door assembly of claim  2 , wherein the bracket comprises a pin-attachment section affixed to the hinge pin and a fastener section, wherein each fastener of the at least one first fastener and at least one second fastener comprises a shank secured to the door frame and a head spaced from the door frame, and wherein the fastener section of the bracket has at least one fastener opening comprising a keyhole slot for receiving a respective first or second fastener. 
     7. A mine door comprising 
     a mine door panel having a first side adapted to face a first direction and a second side adapted to face a second direction opposite the first direction, 
     at least one spring-loaded hinge on the mine door panel for mounting the mine door panel on a mine door frame and urging the mine door panel toward a closed position, 
     said at least one spring-loaded hinge comprising a bracket configured for releasable connection to at least one first fastener on said mine door frame for selectively mounting the mine door on the mine door frame in a first position at the first side of the mine door frame for opening the mine door in said first direction, and for releasable connection to at least one second fastener for selectively mounting the mine door on the mine door frame in a second position at the second side of the mine door frame for opening the mine door in said second direction. 
     8. The mine door of claim  7 , wherein the at least one spring-loaded hinge further comprises a hinge pin connected to the bracket, and at least one hinge plate connecting the mine door panel to the hinge pin. 
     9. The mine door of claim  9 , wherein the at least one hinge plate is affixed to an outer face of the mine door panel and comprises an arcuate pin-receiving section that receives the hinge pin and allows rotation of the at least one hinge plate and mine door about a longitudinal axis of the hinge pin. 
     10. The mine door of claim  8 , wherein the bracket comprises a pin-attachment section affixed to the hinge pin, an intermediate section extending at an angle from the pin-attachment section, and a fastener section extending at an angle from the intermediate section, the fastener section having at least one fastener opening for receiving the at least one first fastener when the mine door is mounted on the mine door frame in said first position and for receiving the at least one second fastener when the mine door is mounted on the mine door frame in said second position. 
     11. The mine door of claim  10 , wherein the at least one spring-loaded hinge is configured for creating a gap between the intermediate section of the bracket and the at least one hinge plate, said gap widening when the mine door is opened for receiving a blocking device to maintain the size of the gap when the mine door is removed from the mine door frame. 
     12. The mine door of claim  8 , wherein the bracket comprises a pin-attachment section affixed to the hinge pin and a fastener section, wherein each fastener of the at least one first fastener and at least one second fastener comprises a shank secured to the mine door frame and a head spaced from the mine door frame, and wherein the fastener section of the bracket has at least one fastener opening comprising a keyhole slot for receiving a respective first or second fastener. 
     13. A mine door assembly for installation in a mine passageway, the mine door assembly comprising 
     a mine door frame having a first side adapted to face a first direction and a second side adapted to face a second direction opposite the first direction, 
     a mine door comprising at least one hinge for mounting the mine door on the mine door frame, said hinge comprising at least one bracket having a keyhole slot, 
     at least one first fastener on the mine door frame adjacent the first side of the mine door frame, 
     at least one second fastener on the mine door frame adjacent the second side of the mine door frame, 
     wherein the keyhole slot is adapted to receive the at least one first fastener for selectively and releasably mounting the mine door in a first position on the mine door frame for opening the door in said first direction, and wherein the keyhole slot is adapted to receive the at least one second fastener for selectively and releasably mounting the mine door in a second position on the mine door frame for opening the door in said second direction. 
     When introducing elements of the present invention or the preferred embodiments(s) thereof, the articles “a”, “an”, the and “said” are intended to mean that there are one or more of the elements. The terms “comprising”, “including” and “having” are intended to be inclusive and mean that there may be additional elements other than the listed elements. 
     In view of the above, it will be seen that the several objects of the invention are achieved and other advantageous results attained. 
     As various changes could be made in the above constructions and products without departing from the scope of the invention, it is intended that all matter contained in the above description and shown in the accompanying drawings shall be interpreted as illustrative and not in a limiting sense.