Abstract:
A moveable table has a target area defined thereon. A hopper filled with an accurate amount of the moldable graphite mixture sifts and meters this mixture through screens onto the target area. The moveable table then shifts to place the target area over the mold cavity, whereupon a door is opened to allow the graphite material to drop evenly into the mold cavity. The compression mold includes a moveable ring surrounding the mold cavity which defines a well for receipt of the graphite material. After compression molding, the mold is opened and the ring is lowered to expose the finished part for removal.

Description:
CROSS REFERENCE TO RELATED APPLICATIONS  
       [0001]     Not Applicable  
       STATEMENT REGARDING FEDERALLY SPONSORED RESEARCH OR DEVELOPMENT  
       [0002]     Not Applicable  
       BACKGROUND OF THE INVENTION  
       [0003]     1. Field of the Invention  
         [0004]     The present invention relates generally to the field of compression molding of items utilizing thermosetting resins. More specifically, this invention relates to the field of molding graphite plates for the fuel cell industry using a powdery mixture of graphite and resin.  
         [0005]     2. Description of the Prior Art  
         [0006]     Fuel cells employing graphite plates for the electrochemical production of electricity from hydrogen are well known and have been constructed by a variety of prior art methods in an attempt to produce effective and economical devices.  
         [0007]     Compression molding of products using thermosetting resins that harden under heat and pressure is also well known, but compression molding of the powdery mixture of graphite and thermosetting resin for graphite plates has presented a number of difficulties that remain unresolved by the prior art. See for example the following references:  
                                                   Patent Number   Inventor                           U.S. Pat. No. 6,451,471   Braun           U.S. Pat. No. 6,494,926   Saito et al.           U.S. Pat. No. 6,436,568   Schilling et al.           U.S. Pat. No. 6,180,275   Braun et al.           U.S. Pat. No. 4,737,421   Uemura et al.           U.S. Pat. No. 4,076,899   Kring                      
 
 None of these references describe any means for assuring the accurate and even distribution of the powdery molding material loaded into the mold or any means for releasing the fragile molded plate from the mold. 
 
         [0009]     Typical compression molding materials are putty-like in consistency. As a result, they are easy to measure, preform and insert into a mold. Moreover, typical molding materials spread out evenly in the mold during compression, equalizing the density of the molded part, and then shrink after molding to automatically release the molded part from the sides of the mold.  
         [0010]     In contrast, the graphite/resin mixture used for production of graphite plates is light and powdery in its pre-molded state and must be accurately measured and evenly spread in the mold cavity before being compressed and molded, as any inaccuracy or unevenness results in an unacceptable finished product. Finally, unlike typical compression molding materials, this graphite/resin mixture expands during molding, causing the finished part to fit tightly and bind within the mold. And since the molded graphite plate is thin and brittle, ejection of such a tight fitting part by typical ejection techniques is impractical.  
       SUMMARY OF THE INVENTION  
       [0011]     The principal object of the present invention is to provide an apparatus and method for facilitating the compression molding of graphite parts, such as graphite fuel cell electrode plates, which are molded from a graphite/resin mixture.  
         [0012]     More particularly, it is an object of this invention to provide an apparatus and method for achieving an accurate and even distribution of this powdery molding material in the mold.  
         [0013]     It is a further object of this invention to mold this material in a compression mold designed to facilitate the deposition of the molding material and the removal of the fragile finished molded part.  
         [0014]     The above objects, as well as other objects, are accomplished by a mold loading apparatus and method that evenly distributes the graphite/resin mixture onto a target area and then delivers this material to an improved compression mold.  
         [0015]     The mold loading apparatus includes a moveable table having a target area defined thereon. A hopper mounted on the table, filled with an accurate amount of the graphite mixture, sifts this mixture through screens onto the target area while reciprocating across the target area. When the target area is evenly covered with the graphite mixture, the moveable table shifts to place the target area over the mold cavity, whereupon a door is opened to allow the graphite material to drop evenly into the mold cavity.  
         [0016]     The improved compression mold includes a mold core, a mold cavity, and a moveable ring surrounding the mold cavity. The graphite/resin mixture dropped from the target area of the moveable table is received into a well defined by the ring and the mold cavity. The mold core is then forced against the mixture in the mold cavity and heat is applied to harden the resin. After the molded part has hardened, the mold is opened and the ring is lowered to expose the finished part.  
     
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0017]      FIG. 1  is a perspective view of the mold loading portion of the apparatus and method of the present invention.  
         [0018]      FIG. 2  is an enlarged view of a portion of the apparatus of  FIG. 1  showing the hopper and target area of the invention.  
         [0019]      FIG. 3  is an elevation view of the gear mechanism which drives blades within the hopper.  
         [0020]      FIG. 4  is a sectional view of the hopper showing the screens and rotating blades.  
         [0021]      FIG. 5A  depicts the mold cavity of the present invention having the target area of the moveable table positioned to load the mold cavity well of the compression mold.  
         [0022]      FIG. 5B  depicts the opening of the door under the target area to deposit the moldable material into the mold cavity.  
         [0023]      FIG. 5C  depicts the compression molding operation by the application of pressure of the mold core against the mold cavity.  
         [0024]      FIG. 5D  depicts the opened mold, the lowered mold cavity ring, and the removal of the molded part. 
     
    
       [0025]     While the invention will be described in connection with a preferred embodiment, it will be understood that it is not the intent to limit the invention to that embodiment. On the contrary, it is the intent to cover all alternatives, modifications, and equivalents as may be included within the spirit and scope of the invention as defined by the appended claims.  
       DESCRIPTION OF THE PREFERRED EMBODIMENT  
       [0026]     Turning first to  FIGS. 1 and 2  there is shown a perspective view of the compression mold loading portion of the apparatus in accordance with the present invention. Generally this apparatus includes a base  10  and a moveable table  12 . The moveable table is arranged to move between a first position for filling the target area with particulate moldable material and a second position (shown in phantom in  FIG. 1 ) for depositing the particulate moldable material into the mold. This apparatus deposits a measured amount of the powdery particulate molding material (such as a graphite/resin mixture) evenly onto a target area  14  and then carries it to the mold cavity of the compression mold, as is described below in greater detail.  
         [0027]     The compression mold ( FIG. 5C ) comprises an upper mold core member  22  and a lower mold cavity member  24 . Surface contour details provided on the surface of the mold core member and on the surface of the mold cavity member serve to create the desired surface contours in the finished molded part, as is well known in the art. Typically, the mold cavity is positioned on a supporting base  26  and the mold core is pressed downward onto the mold cavity, as shown in  FIG. 5C , to accomplish the compression molding effect. When the mold core and the mold cavity are pressed together, the particulate molding material previously placed in the mold cavity is compressed to form the final molded part  28  (see  FIG. 5D ). To cure the resin in the molding mixture and cause it to harden, the molded part is heated simultaneously with the application of pressure by applying heat through the mold core and mold cavity, which heating techniques are well known in the art.  
         [0028]     Prior to the loading of the mold and the compression of the molded part, a ring member  30  having the shape of the periphery of the mold cavity  24 , is first positioned to surround the peripheral rim of the mold cavity. This ring member is arranged to selectively move between a first position surrounding the peripheral rim of the mold cavity and a second position  30 ′ ( FIG. 5D ) clear of the rim of the mold cavity. In its first position, the ring member creates and defines a well area  33  ( FIG. 5B ) within the ring and above the surface of the mold cavity for receipt of the graphite/resin molding material  34 .  
         [0029]     Following compression and heating of the molded part, the ring member  30  is moved to its position  30 ′ clear of the mold cavity rim area and clear of the molded part ( FIG. 5D ). Such a move may be accomplished with a one-piece ring by shifting the ring either upward or downward, or the ring may be split and the sections separated to facilitate the move. In the preferred embodiment, the ring member is lowered. Means for moving this ring member may be manual, mechanical, hydraulic or air cylinder, or any other equivalent means know to the art. By so moving the ring member, the sides of the finished part are freed from the mold and the finished part is thereby exposed. This counteracts the tendency of the molded part to stick in the mold during the molding operation and lessens the force needed to eject the molded part. Consequently, the molded part is now easily ejected by well known ejection techniques.  
         [0030]     As previously mentioned, apparatus for accurately and evenly loading the mold with the powdery particulate moldable material is depicted generally in  FIG. 1  and in greater detail in  FIG. 2 . This apparatus includes a moveable table  12  having a target area  14  defined thereon. A through opening in the moveable table  12  defines the target area  14  and presents a plurality of spaced bars  32  positioned laterally across the opening.  
         [0031]     For sifting, metering and layering the target area  14  with the particulate moldable material, such as the graphite/resin mixture previously described, there is provided material delivery means in the form of a movable hopper device  42  into which a measured amount of the moldable material is placed. This hopper device  42  is arranged to be driven in reciprocating fashion across the target area  14  and to thereby deposit an even layer of material onto the target area. Means for moving the hopper across the target area may include electrical means, hydraulic means, manual means, or other means known to the art. In the preferred embodiment this means for moving the hopper across the target area comprises a motor  44  affixed to the hopper support platform  46  and a gear mechanism  48  for moving the hopper back and forth across the target area on tracks  50 .  
         [0032]     The hopper device, shown in detail in cross section in  FIG. 4 , includes a tapering enclosure positioned on the hopper support platform  46 . This enclosure has two vertical sides  54  and two angled sides  56 , such that the hopper enclosure narrows toward its lower extremity and defines an interior space. Within the interior space of the enclosure there is provided an upper screen  60  for sifting the particulate material measured into the hopper and a lower screen  62  at the outlet  64  of the hopper for sifting the material as it leaves the hopper at its lower extremity. Between the upper and lower screens there is provided a vibrating screen  66  for further metering and sifting of the particulate material. This vibrating screen  66  is arranged with a protrusion  68  for causing the screen to vibrate in response to repetitive contact, and in the preferred embodiment this protrusion comprises a dimple in the screen  66 . To vibrate the vibrating screen  66 , a rotating blade device consisting of a rotating member  70  having a plurality of blades  72  is positioned below the screen, such that the blades  72  are caused to contact the protrusion  68  during rotation of the rotating member  70 .  
         [0033]     The rotating blade device is driven by means for driving said rotating blade device in response to the reciprocating motion of the hopper device. Particularly, a shaft  74  (see  FIG. 2 ) is attached to the rotating member  70  and serves to cause the rotation thereof. This shaft is driven by a gear mechanism  76  ( FIG. 3 ) that turns as the hopper support platform moves in reciprocal fashion across the target area  14 . A constant direction of rotation is maintained by means for maintaining same and comprises, within the gear mechanism  76 , a gear wheel  78  attached to the shaft  74  and caused to traverse lateral teeth  80   a  and  80   b  during the repetitive reciprocal movement of the hopper support platform. At the end of each stroke, in order to keep the gear wheel  78  and the shaft  74  from reversing direction, the gear mechanism  76  is synchronously raised and lowered by lifting means to position the alternate (lower  80   b  or upper  80   a ) lateral teeth against the gear wheel  78 . This lifting means, in the preferred embodiment, comprises hydraulic or air cylinders  82  positioned under the gear mechanism  76  to lift and lower the gear mechanism when the gear wheel reaches the ends  84   a  and  84   b  of its traverse. Consequently, when the hopper starts its return stroke, the gear wheel will continue turning in the same direction, thereby avoiding a discontinuity in its turning motion and facilitating an even deposition of a layer of the material from the hopper.  
         [0034]     Once the target area is layered with the particulate moldable material, the moveable table  12  is caused to shift  12 ′ toward the mold, positioning the loaded target area  14 ′ over the mold cavity. The movement of the table may be accomplished by means well known to the art, such as motors, hydraulics, air cylinders, manual operation, or other means well known to the art. In the preferred embodiment, this means for moving the moveable table  12  is accomplished with an air cylinder  86  attached by a connector  88  to the moveable table  12 . When activated the air cylinder  86  causes the moveable table to slide on tracks  89  from its first position under the hopper to its second position (shown in phantom in  FIG. 1 ) over the mold cavity. While this shift is shown and described as a lateral movement, it is to be understood that this move may be accomplished as a rotational move, a lateral move, or a combination of rotational and lateral moves, all of such movements being within the scope of the invention.  
         [0035]     When the target area is in position over the mold cavity ( FIG. 5A ), the door  90  under the target area is selectively caused to open ( FIG. 5B ) to release the particulate moldable material  34  (graphite/resin mixture) into the well  33  of the mold cavity and create a layer of the material therein. During the movement of the door  90 , the spaced bars  32  positioned across the opening of the target area come into play to keep the powdery mixture from shifting with the movement of the door  90 . This movement of the door  90  may be accomplished by means for selectively opening the door  90 , which means is well known to the art and includes motors, hydraulics, air cylinders, manual operation, or other equivalent means. In the preferred embodiment, this means for selectively moving the door  90  is accomplished using an air cylinder  92  affixed to the moveable table  12  and connected to the door  90  at the connecting block  94 .  
         [0036]     From the foregoing description, it will be apparent that modifications can be made to the apparatus and method for using same without departing from the teachings of the present invention. Accordingly, the scope of the invention is only to be limited as necessitated by the accompanying claims.