You are an expert at summarizing long articles. Proceed to summarize the following text:

You are an expert at summarizing long articles. Proceed to summarize the following text: 
CROSS-REFERENCE TO RELATED APPLICATION 
     This application claims the benefit of U.S. provisional patent application Ser. No. 60/603,731, filed on Aug. 23, 2004, which is incorporated herein by reference. 
    
    
     BACKGROUND OF THE INVENTION 
     This invention relates to the field of fireproof filing cabinets. 
     Conventional file cabinets, used commonly in homes and offices, have a door or drawer front that retracts and slides into a compartment, to expose an open shelf that can be used for binder storage or side tab files. Conventional fireproof cabinets have a joint at the front wall that interlocks with the door to keep the interior from exceeding 350° F. when exposed to a temperature of 1,700° F. for one hour. There has not previously been a door or drawer front that can be retracted into a compartment because of the requirement of ajoint at the front. There is a need for a conventional filing cabinet that is also fireproof. The present invention meets that need. 
     The present invention provides a fireproof filing cabinet which overcomes the problems presented in the prior art and which provides additional advantages over the prior art. These advantages will become clear upon a reading of the attached specification in combination with a study of the drawings. 
     BRIEF SUMMARY OF THE INVENTION 
     Briefly, and in accordance with the foregoing, a fireproof filing cabinet is provided. The fireproof filing cabinet has a shelf on which material such as files can be stored, having an open front side enclosable by a fireproof door. The door rotatably engages a retracting mechanism having a lift assist, so that the door rotates from a closed position, enclosing the shelf, to an open position, and then to a retracted position inside a compartment mounted adjacent to the shelf. A lift assist mechanism enables opening and closing the door. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       The organization and manner of the structure and operation of the invention, together with further objects and advantages thereof, may best be understood by reference to the following description, taken in connection with the accompanying drawings, wherein like reference numerals identify like elements in which: 
         FIG. 1A  is a side elevational view of a cabinet of which incorporates the features of the present invention; 
         FIG. 1B  is a front elevational view of the cabinet; 
         FIG. 2  is a cross-sectional view of the cabinet along line  2 - 2  of  FIG. 1B ; 
         FIGS. 3A ,  3 B, and  3 C are side cutaway views of a retracting mechanism used in the cabinet, showing the door in the closed position ( FIG. 3A ), partially open position ( FIG. 3B ), and open position ( FIG. 3C ); 
         FIGS. 4A ,  4 B, and  4 C are side cutaway views of the retracting mechanism, showing the door in the closed position ( FIG. 4A ), partially open position ( FIG. 4B ), and open position (FIG.  4 C); and 
         FIGS. 5A and 5B  are exploded views of a compartment. 
     
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
     While the invention may be susceptible to embodiment in different forms, there is shown in the drawings, and herein will be described in detail, a specific embodiment with the understanding that the present disclosure is to be considered an exemplification of the principles of the invention, and is not intended to limit the invention to that as illustrated and described herein. 
     A fireproof filing cabinet  20  of the preferred embodiment of the present invention is shown in a side elevational view in  FIG. 1A , in a front elevational view in  FIG. 1B , and in a side cutaway view in  FIG. 2 . The filing cabinet  20 , in the illustrated embodiment, is a two-tier filing cabinet, with a retractable door on an upper shelf and a fixed door on a lower drawer. Other combinations are, of course, possible. 
     The fireproof filing cabinet  20  includes a frame  22  having an upper shelf  24  and a lower drawer  26  which is mounted on drawer supports (not shown). The fireproof filing cabinet  20  further includes a compartment  28  mounted on top of the frame  22 . A door  30  is retractably mounted to the compartment  28  to extend over the open front of the upper shelf  24  and to retract into the compartment  28  by use of a retracting mechanism  32  attached to door  30 . Please note that the compartment  28  of the preferred embodiment forms an enclosed cavity  34  but compartment  28  need not be totally or partially enclosed and can have only partial walls or only frame members defining it. 
     The door  30  has a main body  34  and a door extender  36  extending from the main body  34 . The door  30  is preferably made to meet the Underwriters Laboratory Class 350 rating. Accordingly, the main body  34  includes a front portion and a rear portion. Insulation, for example, insulation sold under the trademark, INSULITE@, by E. H. O&#39;Neill Company, Inc., is provided between the front portion and the rear portion of the main body  34 , in order to meet the heat conduction requirements of the UL Class 350 rating. In the preferred embodiment, the main body  34  is one foot high and four feet wide, so that the width of the main body  34  is slightly less than the width of the compartment  28  and the width of the frame  22  and slightly greater than the interior width of the shelf  24 . The main body  34  preferably includes a conventional locking mechanism  38  having a latch  39 , mounted on the rear portion of the main body  34 . The door extender  36  extends upwardly from an upper portion of the outer surface of the main body  34 . The door extender  36  is a flat plate which extends across, and covers, an aperture  40  in compartment  28  when the door  30  is a closed position. The door extender  36  is secured to the main body  34  by welds, screws, nuts and bolts, or other suitable means. The door extender  36  extends generally along the entire length of the main body  34 . A reinforcing plate  42  overlaps a mid-portion of the door extender  36  and is secured to the door extender  36  by welds, screws, nuts and bolts, or other suitable means. The reinforcing plate  42  reinforces the section of the door extender  36  beyond the main body  34 . The door extender  36  and the reinforcing plate  42  are preferably formed of steel, most preferably of the same type and painted the same color as the main body  34 . 
     The frame  22  is generally rectangular and includes a generally horizontal top wall  50 , a generally horizontal bottom wall  52 , a generally vertical left wall  54 , a generally vertical right wall  56 , a generally vertical rear wall  58 , and a horizontal partition wall  60  which separates the shelf  24  from the drawer  26 . The frame  22  is formed from metal, preferably steel. 
     In the illustrated embodiment, top wall  50 , partition wall  60 , the upper portion of the wall  54 , the upper portion of right wall  56 , and the upper portion of rear wall  58  define a shelf cavity  34 . Thus, the shelf cavity  34  is closed on five sides and has an open front, so that material, such as files, can be placed on the shelf  24 . The shelf  24  can be a platform mounted on the partition wall  60 , or the partition wall  60  can be the shelf  24 . When the door  30  is retracted or is opened, as will hereinafter be described, a user can access material on the shelf  24  from outside the cabinet  20 , as the shelf  24  is open on the front of the cabinet  20 . Bottom wall  52 , partition wall  60 , the lower portion of left wall  54 , the lower portion of right wall  56 , and the lower portion of rear wall  58  define another cavity  64  in which the drawer  26  is provided. 
     The shelf  24  can be mounted on rollers that engage sliders attached to the side walls  54 ,  56 , so that the shelf  24 , when the door  30  is open or retracted, as hereinafter described, can slide out of the frame  22 . Moreover, while cabinet  20  is shown with only a single drawer  26 , additional drawers can be provided underneath the drawer  26 . Also, the frame  22  can be designed without drawer  26  such that only shelf  24  is provided, or a plurality of shelves  24  can be provided, each with an associated compartment  28 . 
     The walls  50 ,  52 ,  54 ,  56 ,  58  are formed with inner panels and outer panels which are spaced apart from each other. Insulation, for example, insulation sold under the trademark, INSULITE®, by E.H. O&#39;Neill Company, Inc., is provided between the inner and outer panels of the walls  50 ,  52 ,  54 ,  56 ,  58 , in order to meet the heat conduction requirements of UL Class 350 rating. 
     Partition wall  60  extends from the inner panel of rear wall  58  to the front edges of left and right walls  54 ,  56  and from the inner panel of left wall  54  to the inner panel of right wall  58 . Partition wall  60  includes an upper panel and a lower panel. Insulation, for example, insulation sold under the trademark INSULITE®, is provided between the upper and lower panels of the partition wall  60 . A recess  62  is provided in the upper panel of the partition wall  60 , proximate the open end of the upper shelf  24 , for receiving the latch  39  from the locking mechanism  38  on the door  30 . 
     A seal point  70  is provided on the front edges of the walls  50 ,  54 ,  56 ,  60 , which edges form the open front side of the shelf cavity  34 . A seal  72  on the rear portion of the main body  34  of door  30  engages the seal point  70  when the door  30  is closed to cover the open front end of the shelf  24 . A seal point  74  is provided by the walls  52 ,  54 ,  56 ,  60  forming the open front end of the cavity  64  for the drawer  26 . The drawer  26  has a seal  76  which engages the seal point  74  when the drawer  26  is retracted into cabinet  20 . Seal points  70 ,  74  and seals  72 ,  76  are preferably tongue-and-groove designs, although other designs meeting the requirements for the UL Class 350 rating are acceptable. 
     The compartment  28  of the preferred embodiment is generally rectangularly-shaped and includes a generally horizontal top wall  80 , a generally vertical left wall  82 , a generally vertical right wall  84 , a generally vertical rear wall  86 , and a front lip  88  which depends from the top wall  80  at the front end thereof. The top wall  50  of the frame  22  forms the bottom wall of the compartment  28 . A compartment cavity  90  is defined by top wall  80 , left wall  82 , right wall  84 , rear wall  86 , top wall  38 , and front lip  88 . Thus, the compartment cavity  90  is preferably completely closed on five sides and has an open front. The open front is defined by an aperture  40  between the bottom end of the front lip  88  and the upper surface of the top wall  50  of the frame. Please note that, instead of having a front lip  88  defining aperture  40 , compartment  28  could have a completely open front, with aperture  40  defined by top wall  80 , left wall  82 , right wall  84 , rear wall  86 , and top wall  50 . 
     The width of the aperture  40  is slightly greater than the width of the door  30 , which will retract through the aperture  40  and into the compartment  28 . Drawer head slide  102   a  in right wall  84  and drawer head slide  102   b  in left wall  82  extend from the open front of compartment  28 , rearwardly toward rear wall  86 . 
     The compartment  28  is formed from metal, preferably steel. The compartment  28  sits on the top wall  50  and is secured to the frame  22  by welds, screws, nuts and bolts, interference fit, pins, or other suitable means of attachment. 
     A retracting mechanism  32  is shown in  FIGS. 2 ,  3 A-C,  4 A-C, and  5 A-B. Retracting mechanism  32  preferably has two sets of hinge assemblies. In the illustrated embodiment, all “a” components are one side of the fireproof filing cabinet  20  and all “b” components are on the other side, connected to the “a” components by the door extender  66 . Accordingly, for each “a” component there is a corresponding and mirror-image “b” component. In the illustrated embodiment, “a” components are on the right side of the fireproof filing cabinet  20  and “b” components are on the left side of the fireproof filing cabinet  20 .  FIG. 2 , which is a cross-section through line  2 - 2  of  FIG. 1B , shows the left-side, “b” components.  FIGS. 3A-C  and  4 A-C show the right-side, “a” components. Please note that a cabinet  20  of the present invention could have a single hinge assembly or could have three or more hinge assemblies. 
     The retracting mechanism  32  is attached to the door  30  and is used to retract the door  30  through the aperture  40  and into the cavity  64  in the compartment  28 . The retracting mechanism  32  includes left and right first hinge members  104   a  and  104   b , left and right second hinge members  106   a  and  106   b , two hinge pins  108   a  and  108   b , left and right levers  110   a  and  110   b , left and right springs  112   a  and  112   b , and left and right linkage pins  114   a  and  114   b.    
     The right first hinge member  104   a  includes a generally rectangular plate  116   a  that is fixedly attached to the door extender  36  and pin receiving member  118   a  fixedly attached to an upper end of the plate  116   a . The pin receiving member  118   a  extends upwardly from the plate  116   a . A long edge of the plate  116   a  abuts against the upper end of the door extender  36  along its inner surface. The right first hinge member  104   a  is rotatably connected to the right second hinge member  106   a  through the hinge pin  108   a . The hinge pin  108   a  is at approximately the midpoint of the plate  116   a . The right second hinge member  106   a  is an elongated plate having first and second ends. The hinge pin  108   a  extends through the second end of the right second hinge member  106   a , at an upper end thereof. The right second hinge member  106   a  slides in the right drawer head slide  102   a . The left first hinge member  104   b  includes a generally rectangular plate  116   b  that is fixedly attached to the door extender  36  and pin receiving member  118   b  fixedly attached to an upper end of the plate  116   b . The pin receiving member  118   b  extends upwardly from the plate  116   b . A long edge of the plate  116   b  abuts against the upper end of the door extender  36  along its inner surface. The right first hinge member  104   b  is rotatably connected to the right second hinge member  106   b  through the hinge pin  108   b . The hinge pin  108   b  is at approximately the midpoint of the plate  116   b . The left second hinge member  106   b  is an elongated plate having first and second ends. The hinge pin  108   b  extends through the second end of the left second hinge member  106   b , at an upper end thereof. The right second hinge member  106   b  slides in the right drawer head slide  102   b . Accordingly, the door  30  rotates in an angle about the hinge pins  108   a ,  108   b , from a closed position in which the open front end of the shelf  24  is covered and a seal is formed between seal point  70  and seal  72 , as shown in  FIGS. 3A  and  4 A, to an open position in which the door  30  is parallel to the top wall  50 , as shown in  FIGS. 3C and 4C . Pushing on door  30  in the open position then causes the second hinge members  106   a ,  106   b  to slide rearward in the drawer head slides  102   a ,  102   b , respectively, so that the retracting mechanism  32  moves to the rear of the compartment  28 , bringing the door  30  through the aperture  40  to a retracted position inside the compartment cavity  90  for out-of-the way storage. 
     Because the door  30 , being fireproof, is fairly heavy, a lift assist mechanism is preferably supplied. Conventionally, a spring would extend from a first hinge member to a second hinge member. In the preferred embodiment of the present invention, however, each spring  112   a ,  112   b  is attached to a lever  110   a ,  110   b  that is attached to both hinge members  104   a ,  1048   b ;  106   a ,  106   b , so the lifting force supplied by the springs  112   a ,  112   b  increases as the door  30  is opened. 
     As shown in  FIGS. 2 through 4 , the levers  110   a ,  110   b  are elongated plates that have first and second portions which are angled relative to each other. A first end of the left lever  110   a  is rotatably attached to the left second hinge member  106   a  at approximately the midpoint thereof. 
     A second end of the left lever  110   a  is attached to a second end of the left spring  112   a . A left linkage pin  114   a  connects the second end of the left spring  112   a  and the second end of the left lever  110   a  to the left pin receiving member  118   a . The first end of the left spring  112   a  is fixedly attached to the first end of the left second hinge member  106   a  at a lower end thereof. In an identical manner, a first end of the right lever  110   b  is rotatably attached to the right second hinge member  106   b  at approximately the midpoint thereof. A second end of the right lever  110   b  is attached to a second end of the right spring  112   b . A right linkage pin  114   b  connects the second end of the right spring  112   b  and the second end of the right lever  110   b  to the right pin receiving member  118   b . The first end of the right spring  112   b  is fixedly attached to the first end of the right second hinge member  106   b  at a lower end thereof. 
     Accordingly, when the door  30  is in its closed position, as shown in  FIGS. 3A and 4A , the springs  112   a ,  112   b  are extended. As the door  30  begins to rotate upwards, as shown in  FIGS. 3B and 4B , the springs  112   a  and  112   b  begin to compress. As the door  30  rotates ninety degrees to a position parallel to the top wall  50 , as shown in  FIGS. 3C and 4C , the springs  112   a ,  112   b  are fully compressed. Accordingly, the springs  112   a ,  112   b  produce their greatest force when the door  30  is in its closed position. This force gradually decreases as the door  30  is lifted, until no force is applied by the springs  112   a ,  112   b  when the door  30  has rotated ninety degrees to the position shown in  FIGS. 3C and 4C . Accordingly, raising and lowering the door  30  is practically no assist from approximately forty-five degrees ( FIGS. 3A and 4A ) on up ( FIGS. 3C and 4C ). 
     In this open position, the door  30  can be pushed through the aperture  40 , as the second hinge members  106   a ,  106   b  slide along the drawer head slides  102   a ,  102   b , until the door  30  has completely retracted within the compartment  28 . To close the shelf  24 , the user pulls the door  30  out of compartment cavity  90 , through aperture  40 , from the retracted position to the open position, and presses downward. Little or no force will be required to move the door  30  halfway down ( FIGS. 3B and 4B ), and, because of the weight of the door  30 , only gentle pressure will be required to move the door  30  into its closed position ( FIGS. 3A and 4A ). 
     The compartment  28  and the retracting mechanism  32  can be retrofitted to existing filing cabinets. Please note also that, while the compartment  28  is illustrated as being on top of the shelf  24 , the compartment  28  could be mounted below the shelf  24  or on either side of the shelf  24  without departing from the principles of the present invention. 
     In another embodiment, side walls  54 ,  56  are slide rollers mounted on frame  22 , instead of sheet steel having drawer head slides  102   a ,  102   b . In this embodiment, door  30  retracts into a position above top wall  50 , but not inside a defined space such as compartment cavity  90 . 
     While preferred embodiments of the present invention are shown and described, it is envisioned that those skilled in the art may devise various modifications of the present invention without departing from the spirit and scope of the appended claims.

Summary:
A fireproof filing cabinet is disclosed. The cabinet has a shelf on which material such as files can be stored, having an open front side enclosable by a fireproof door. The door rotatably engages a retracting mechanism having a lift assist, so that the door rotates from a closed position, enclosing and sealing the shelf, to an open position, and then to a retracted position inside a compartment mounted adjacent to the shelf A lift assist mechanism enables opening and closing the door.