Patent Publication Number: US-6984117-B1

Title: Apparatus and method for manufacturing gaskets

Description:
This application is a divisional of Ser. No. 09/119,984, filed Jul. 21, 1998, now U.S. Pat. No. 6,540,852. 

   TECHNICAL FIELD 
   The present application relates to gasket manufacturing apparatus and processes. More particularly, the present invention is directed to apparatus and methods for volumetric molding and manufacturing of seamless gaskets. 
   BACKGROUND OF THE INVENTION 
   Graphite has long been recognized as a material which exhibits superior quality for sealing and gasket applications. These characteristics include high thermal stability, low thermal conductivity, natural lubricity, resistance to chemical degradation, conformability, and resilience. 
   Graphite has typically been provided in the form of calendared sheets made with expanded intercalated flake graphite worms. Intercalated flake graphite is made by treating natural or synthetic graphite flakes with an intercalating agent such as fuming nitric acid, fuming sulfuric acid, or mixtures of concentrated nitric acid and sulfuric acid. The intercalated flake graphite is then expanded at high temperatures to form a low-density, worm-like form of particulate graphite having typically an 80–100 fold increase in size over the flake raw material. U.S. Pat. No. 3,404,061 describes the production of intercalated flake graphite as an intermediate step in the production of expanded intercalated graphite. Expanded intercalated graphite worms have thin structural wall and are light-weight, puffy, airy, and elongated bodies. 
   These characteristics lead to exceedingly difficult volumetric, handling, and use problems. Because of these characteristics, expanded intercalated graphite worms typically are calendared to produce sheets of graphite. Calendared graphite is commercially available as GRAFOIL brand sheets. The sheets have a uniform density and a uniform thickness. The sheets are generally available in several standard thickness and densities. The sheet is die-cut to form a gasket. To provide increased tensile strength, a layer of mylar adhesive is applied to one surface of the sheet. The mylar allows the gasket to be applied to an annular metal disk. Gaskets manufactured with calendared graphite sheet typically are used for sealing purposes in high pressure, high temperature fluid flow applications. While such gaskets perform sealing functions, there are drawbacks to their use. Cut calendared graphite sheet particularly provides open edges which is susceptible to high pressure attack from the fluids being sealed by the gasket. 
   Further, the expanded intercalate graphite worms are extremely light and puffy. A significantly large volume of the worms is required to produce a relatively thin layer of gasket material. There is an approximate 100 to 1 ratio between the volume of expanded worms and compressed worms. The worms being extremely lightweight, are difficult to handle. The slightest air current quickly stirs up the worms. Accordingly, expanded intercalated graphite typically was calendared to form graphite sheets. 
   U.S. Pat. No. 5,785,322 describes the use of the expanded intercalated graphite worms in forming a seamless gasket for high pressure, high temperature fluid flow applications. Gaskets of this type have superior performance without the drawbacks of conventional sheet-formed gaskets. The manufacture of these improved gaskets however is difficult, expensive, and labor intensive. The manufacturing problems arise from the characteristics of expanded intercalated graphite worms discussed above. The manufacturing process involves manually loading a die with expanded intercalated graphite worms, which are then compressed with a hydraulic press. A significant amount of worms must be loaded in the die, because of the high expansion volume of the worms. A typical ⅛ inch thick gasket requires between 10 and 12 inches of expanded intercalated graphite worms. Yet the mass of the worms is small, and typical gaskets have about a gram of worms on the opposing sides. 
   While the resulting gasket exhibits superior sealing performance, air may be entrained in the gasket or some portions may have differing densities due to the movement or uneven provision of worms to the die. 
   Accordingly, there remains a need in the art for an apparatus and method for manufacturing seamless gaskets with lightweight expanded materials. It is to such that the present invention is directed. 
   BRIEF DESCRIPTION OF THE PRESENT INVENTION 
   The present invention provides an apparatus and method for manufacturing seamless gaskets using expanded materials. More particularly described, the present invention provides an apparatus and methods of manufacturing seamless gaskets using expanded intercalated graphite worms, in which an annular die cavity has a central column with a charge inlet in a perimeter wall. Expanded intercalated graphite worms communicate from a source through the charge inlet in the annular die cavity for depositing a charge of expanded intercalated graphite worms within the die cavity. An upper pusher is movable from a first position distally spaced from an open end of the die cavity to a second position within the die cavity for compressing a first charge of expanded intercalated graphite worms. A lower pusher is movable from a first position to a second position during the compressing of the first charge of expanded intercalated graphite worms in the die. The upper pusher causes the lower pusher to move to the second position, so that a second charge of expanded intercalated graphite worms is received in substantially the same volume as the first charge. The upper pusher then compresses the second charge to form a seamless gasket. 
   The method of the present invention communicates a volumetric first charge of expanded intercalated graphite worms to a die cavity. An upper pusher moves to compress the expanded intercalated graphite worms while moving a lower pusher in the die cavity from a first position to a second position. A second volumetric charge of expanded intercalated graphite worms is communicated to the die cavity. Moving the lower pusher to the second position provides a cavity for the second charge that has substantially the same volume as for the first charge. The second charge is also compressed with the upper pusher to form a seamless gasket. The seamless gasket is then removed from the die cavity and the lower pusher is reset to its first position. More particularly described, the worms are communicated by low pressure air in which the worms become partially compressed as they travel to and are distributed in the die. 
   Objects, features, and advantages of the present invention will become apparent from a reading of the following detailed description of the invention and claims in view of the appended drawings. 

   
     BRIEF DESCRIPTION OF THE DRAWINGS 
       FIG. 1  illustrates a schematic view of an apparatus according to the present invention for manufacturing seamless gaskets. 
       FIG. 2  is a cross-sectional view of the die for forming a seamless gasket using in the apparatus illustrated in  FIG. 1 . 
       FIG. 3  is a detailed cross-sectional view of the die illustrated in  FIG. 2 . 
       FIGS. 4A–4E  is a sequence of cross-sectional views of the die shown in  FIG. 2 , illustrating steps in the manufacture of a seamless gasket according to the present invention. 
       FIG. 5  illustrates a seamless gasket manufactured with the apparatus shown in  FIG. 1 . 
       FIG. 6  illustrates a cross-sectional view of the gasket of  FIG. 5 , taken along line  6 — 6 . 
   

   DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
   Referring now in more detail to the drawings, in which like numerals indicate like parts throughout the several views  FIG. 1  illustrates a schematic view of an apparatus  10  according to the present invention for manufacturing seamless gaskets  11  as shown in  FIG. 5 . The apparatus  10  includes a supply hopper  12  which receives a supply of expanded intercalated graphite worms. The hopper  12  communicates the worms to a staging chamber  14 . A plurality of air nozzles  16  are disposed around a lower portion of the staging chamber  14 . The air nozzles  16  communicate with a supply of low pressure air (not illustrated). A knife gate valve  18  is attached at a discharge opening  19  of the staging chamber  14 . The knife gate valve  18  is selectively operable from an open position to a closed position for discharging worms from the staging chamber  14  to a supply plenum  20 . The staging chamber  14  defines an opening  21  in a side wall opposite the knife gate valve  18 . The opening  21  allows a portion of the expanded intercalated graphite worms, pushed by the knife gate valve  18  during operation of the apparatus  10 , to exit the staging chamber  14  in order to avoid a buildup of compressed-worms in the supply plenum  20 . A lower surface of the supply plenum  20  is defined by an air permeable screen  22 . The screen  22  separates the supply plenum  20  from an air chamber  24 . The screen  22  is substantially impermeable to the expanded intercalated graphite worms. An air nozzle  26  mounts in the air chamber  24  and communicates with a supply of pressurized air. A conduit  28  attaches to a discharge in an upper portion of the supply plenum  20 . A second air nozzle  29  attaches to the side wall opposite the conduit  28 , and communicates with a source of pressurized air. 
   The conduit  28  communicates with an annular die generally  30  which has a central column  32  extending from a base plate  34 . The conduit  28  connects to an inlet  36  in a perimeter wall  38  of the annular die  30 . A distal edge of the perimeter wall  38  defines a beveled face  39  at an open end  41  of the die  30 . A bore  40  is defined in the perimeter wall  38  for communicating pressurized air into a lower portion of the cavity of the die  30 , for a purpose discussed below. In the illustrated embodiment, a conduit  42  connects between an exit port  44  in the perimeter wall  38  and a filter chamber  46  having a discharge opening  48 . A pump  50  connects through a valve-controlled conduit  52  to the filter chamber  46 . 
   An upper pusher  54 , defined by an annular die, connects to a cylinder rod  56  of a hydraulic cylinder (not illustrated) for moving the die pusher  54  from a first position distally spaced from the open end  41  of the annular die  30  to a second position with the annular die  56  received within the annular cavity of the die  30 . The die  30  includes a lower pusher  64  which is movable within the cavity of the die  30 . 
   The die  30  is best illustrated in cross-sectional view in.  FIG. 2 , and  FIG. 3  illustrates an detailed cross-sectional view of the lower pusher  64  and the central column  32  of the die  30 . The upper pusher  54  comprises an annular cylinder attached to a die plate  70 . The die wall  38  is defined by an annular cylinder attached to the die plate  34 ′. The lower pusher  64  comprises an annular cylinder received around the central column  32 . The central column  32  defines an annular groove  74  which receives an O-ring  76 . The groove  74  defines a boundary between an upper portion  78  and a lower portion  80 . The diameter of the lower portion  80  is slightly smaller than that of the upper portion  79 . 
   The lower pusher  64  defines an annular groove  82  in a outer surface, which groove receives an O-ring  84 . A flange  86  extends laterally from a bottom edge of an inner surface of the lower pusher  64 . The O-ring  76  on the central column  32  acts as a stop when contacted by the flange  86  during movement of the lower pusher  64  as discussed below. 
     FIGS. 4A–4E  is a sequence of cross-sectional views of the die  30 , illustrating steps in the manufacture of a seamless gasket according to the present invention. 
   The apparatus  10  provides volumetric molding of seamless gaskets with light-weight materials communicated to the die  30  by a low pressure air flow. A plurality of expanded intercalated graphite worms are provided to the hopper  12 . The expanded intercalated graphite worms are delivered from a supply to the hopper. Although not illustrated, a vacuum cleaner is used to periodically communicate worms into the hopper from a supply. In alternate embodiment, the hopper receives a continuous supply from an expander which expands intercalated graphite flakes as needed for use in the apparatus  10 . 
   Periodically, the hopper  12  drops a portion of the expanded intercalated graphite worms to the staging chamber  14 . The air nozzles  16  direct air from the low pressure supply upwardly into the cavity of the staging chamber  14 . This air flow causes the worms to swirl and prevents the worms from clumping together. The worms fall past the air nozzles  16  to the knife gate valve  18 . The knife gate valve  18  selectively opens to discharge a predetermined quantity of the worms from the staging chamber  14  into the supply plenum  20 . The knife gate valve  18  moves between the first position closing communication between the staging chamber  14  and the supply plenum  20  to the second position allowing communication therebetween. As the knife gate valve  18  closes, a portion of the expanded intercalated graphite worms are pushed by the leading edge of the valve through the opening  21 . This prevents the worms from being compressed and clumping in the supply plenum  20 . 
   The air nozzle  26  communicates low pressure air into the air chamber  24  to provide an updraft of air through the air permeable screen  22  into the supply plenum  20 . The air causes the worms to remain loosely together in the supply plenum  20 . The flow of air carries the charge of worms from the supply plenum  20  through the conduit  28  into the annular die  30  where the worms are deposited around the annular cavity of the die  30 . The pressure of the air in the air plenum is between about 5 and 30 pounds per square inch. The flow of the worms into the conduit  28  is facilitated by the second nozzle  29  that communicates low pressure air towards the conduit. The air flow partially compresses the worms as they are carried through the conduit  28  and are deposited in the die  30 . Partial compression of the worms being placed in the die  30  enables the die cavity  30  to be smaller than the manually loaded dies used in the prior art. Smaller dies enables the stroke of the upper pusher to be shorter, which results in faster processing time. The smaller dies also are less expensive to manufacture. 
   The illustrated embodiment further includes an alternate embodiment using a low pressure vacuum to facilitate communication of the worms. Operation of the pump  50  provides a low pressure vacuum to the cavity of the annular die  30  through the conduit  42 , as controlled by the valve  52 . The low pressure vacuum facilitates pulling the worms into the annular cavity of the die  30  while the worms are also being pushed by low pressure air from the plenum  20  through the conduit  28  into the die  30 . The low pressure air flow through the die  30  permits most of the worms to be distributed uniformly within the cavity. A portion of the worms are carried through the conduit  42  into the filter chamber  46 . The filter chamber  46  allows the residual worms to settle towards the discharge  48 . Periodically the discharge  48  is opened to remove the accumulated residual worms. 
   The sequence of operational steps in the volumetric molding process in the manufacture of a seamless gasket according to the present invention is illustrated in  FIGS. 4A–4E , together with reference to  FIG. 1 . As shown in  FIG. 4A , the upper pusher  54  is moved from the first position to a second position in the die  30  to move the lower pusher  64  to a first position while leaving a gap  90  between the die plate  34  and a bottom surface of the lower pusher. The gap  90  equals the thickness of a metal insert  92  and the compressed worms  94  on one side of the gasket made with the apparatus. 
   With reference to  FIG. 4B , the upper pusher  54  is retracted to a third position with a lower edge in the open end  60  of the die while leaving a gap  95  between the upper pusher and the beveled face  39 . The gap  95  permits air to escape from the die  30  during charging with the expanded intercalated graphite worms. The supply plenum  20  is then provided with a first charge  97  of expanded intercalated graphite worms by operation of the knife blade gate  18 . The charge of worms enters the air plenum  20  and the worms are carried by the air flow from the nozzles  26  and  29  through the conduit  28  into the die  30  while being partially compressed. The air escapes through the gap  95 , and a small portion of the worms are carried out of the die  30  through the gap. In the illustrated embodiment, both the air flow and the vacuum from the pump  50  facilitate substantially uniform distribution of the worms throughout the cavity of the die  30 , although the air flow from the nozzles  26  and  29  sufficiently communicate the worms and distribute them in the die  30 . The die  30  is now filled with expanded intercalated worms. 
   The upper pusher  54  is then retracted from the die  30  to its first position. An annular insert  92 , preferably metal, is then placed on the charge  97  of worms in the die  30 . With reference to  FIG. 4C , the first charge  97  of the worms is then compressed by the pusher  54  moving from the first position to the second position. This brings the lower surface of the upper pusher  54  into contact with the insert  92 . Continued movement of the upper pusher  54  compresses the charge  97  of worms against the insert  92 . The upper pusher  54  also causes the lower pusher  64  to move in the die chamber from the first position to a second position bottoming against the die plate  34  and closing the gap  90 . The combined thickness  96  of the layer of compressed worms  94  and the insert  92  substantially equals the gap height of the  90 , shown in  FIG. 4A . 
   With reference to  FIG. 4D , the upper pusher  54  is then retracted to the third position in the open end  60  of the die  30  to leave the gap  95 . The die  30  is provided with a second charge  100  of expanded intercalated graphite worms. The volume of the cavity receiving the second charge  100  is substantially the same volume as received the first charge  97 , because of the displacement of the lower pusher  64  to the second position to the bottom of the die  30 . The upper-pusher  54  moves again from the third position to the second position for compressing the second charge  100  of worms against the insert  92 . To assure compaction of the worms in the first charge  97  and the second charge  100 , the hydraulic cylinder moves the upper pusher  54  forcibly against the worms and the insert  92  several times. Further, in an alternate embodiment, a burst of low pressure air communicated through the opening  36  may tend to bounce or disturb the worms in the cavity, whereby entrained air may be dislodged. This process described with reference to  FIG. 1  and  FIGS. 4A–4E , results in a substantially seamless gasket  11  being manufactured with the apparatus  10 . 
   The gasket  11  is then removed. This is accomplished by retracting the upper pusher  54  to the first position while air is communicated through the bore  40  into the lower portion of the die  30 . The air enters below the O-ring  84  which seals the air from passage between the lower pusher  64  and the wall  38 . The increased air pressure causes the lower pusher  64  to move within the die  30  towards the open end  60 . The flange  84  comes into contact with the O-ring  76  which stops the movement of the lower pusher  64 . The newly formed seamless gasket  11  is disposed at the open end  41  of the die  30 , where it is readily removed. The cycle is then repeated for manufacturing additional seamless gaskets. 
     FIG. 5  illustrates a cut-away view of the gasket  0 . 11  formed with the apparatus  10  according to the present invention. The gasket  11  has an outer diameter perimeter edge  101  and an inner diameter perimeter edge  103 . The gasket  11  includes the metal insert  92  which is coated with the worms in the charges  97  and  100 .  FIG. 6  is a cross-sectional view taken along line  6 — 6  of  FIG. 5 . The preferred embodiment uses a metal insert  92  having corrugations which define a series of ridges  104  and valleys  106  which are filled with the compacted worms from the charges  97  and  100 . 
   The present invention accordingly provides a volumetric molding process for light-weight materials to form seamless gaskets. The principles, preferred embodiments, and modes of operation of the present invention have been described in the foregoing specification. The invention is not to be construed as limited to the particular forms disclosed because these are regarded as illustrative rather than restrictive. Moreover, variations and changes may be made by those skilled in the art without departure from the spirit of the invention as described by the following claims.