Abstract:
A method of compacting material such as but not limited to cathode material for electrochemical cells. A mixture is inserted into a die cavity and the mixture is compacted into a disk shape by the action of a first plunger pressing down on the material and a second plunger pressing upwardly on the material. Flashing of material during ejection of the disk from the die is prevented by fitting a polymeric sleeve around the outer surface of the first plunger. The sleeve flexes to bulge outwardly and does not enter the die cavity during compaction of material and returns to its original position during ejection of the compacted disk from the die. Contact between the disk and sleeve prevents flashing during ejection. Alternatively, a polymeric seal ring is placed around the outer surface of the first plunger. The disk presses against the seal ring preventing flashing of material during ejection.

Description:
FIELD OF THE INVENTION 
     This invention relates to a method of forming compacted disks, as by compacting cathode material into disk shape. The invention relates to an improved method of compacting material into disk shape. 
     BACKGROUND OF THE INVENTION 
     Primary alkaline electrochemical cells typically have an anode comprising zinc active material, an alkaline electrolyte, a cathode comprising manganese dioxide active material, and an electrolyte permeable separator film, typically of cellulose or cellulosic and polyvinylalcohol fibers, between anode and cathode. Such cell may be designated a Zn/MnO 2  cell. The cathode may also contain nickel oxyhydroxide (NiOOH) active material in place of manganese dioxide or in admixture with manganese dioxide. Such cell containing predominantly nickel oxyhydroxide as the cathode active material, may be designated a Zn/NiOOH cell. The alkaline cell casing typically has a cylindrical shape, for example, commonly available in standard cell sizes AAAA (42×8 mm), AAA (44×9 mm), AA (49×12 mm), C (49×25 mm) and D (58×32 mm) size. 
     In the Zn/MnO 2  cell the cathode typically comprises a mixture of manganese dioxide, graphite, alkaline electrolyte normally aqueous potassium hydroxide, and optionally a small amount of binder material, such as polyethylene binder. The manganese dioxide used in the cathode is preferably electrolytic manganese dioxide (EMD) which is made by direct electrolysis of a bath of manganese sulfate and sulfuric acid. The EMD is desirable since it has a high density and high purity. The electrical conductivity of EMD is fairly low. An electrically conductive material is added to the cathode mixture to improve the electric conductivity between individual manganese dioxide particles. Such electrically conductive additive also improves electric conductivity between the manganese dioxide particles and the cell housing, which also serves as cathode current collector. Suitable electrically conductive additives can include, for example, conductive carbon powders, such as carbon blacks, including acetylene blacks, flaky crystalline natural graphite, flaky crystalline synthetic graphite, including expanded or exfoliated graphite. The resistivity of graphites such as flaky natural or expanded graphites can typically be between about 3×10 −3  ohm-cm and 4×10 −3  ohm-cm. 
     Alkaline cell cathode for cylindrical shaped cells are normally formed in the shape of disks having a hollow central core. (The term cathode disks as used herein may also be referenced as cathode pellets or tablets.) The top and bottom surfaces of the disk are flat with cylindrical surface therebetween. A plurality of the disks are typically inserted into the cell casing and stacked one on top of the other, for example, as shown in representative U.S. Pat. No. 6,251,539 B1 for Zn/MnO 2  cells and in U.S. Pat. No. 7,273,680 B2 for Zn/NiOOH cells. The hollow central core of the disks, are bounded by the cathode disk inside surface running along the disk&#39;s central longitudinal axis. The cathode disk&#39;s inside surface is typically of cylindrical shape, but may also be other curvilinear shape either regular or irregular, for example, as shown in U.S. Pat. No. 6,514,637 B2. After the cathode disks are inserted into the cell casing a separator sheet is inserted to line the inside surface of cathode disks, that is, to line the disks&#39; hollow core. Zinc anode material is then supplied, typically in the form of a gelled zinc slurry, to fill the hollow core of the cathode. For example, the zinc particles can be admixed with conventional gelling agents, such as sodium carboxymethyl cellulose or the sodium salt of an acrylic acid copolymer, and alkaline electrolyte, normally aqueous potassium hydroxide. The gelling agent serves to suspend the zinc particles and to maintain them in contact with one another. Thus, the filled cell has cathode in electrical contact with the casing housing. An elongated current collector is normally inserted into the anode material. The elongated current collector is in electrical contact with and end cap assembly (insulated from the cell casing). The end cap assembly is crimped over the cell casing to close the cell as shown, for example, in the above cited references U.S. Pat. Nos. 6,251,539 and 7,273,680. 
     The cathode disks are made by inserting the cathode mixture into a die cavity and activating a punch assembly to compress the cathode mixture while in the die cavity. The cathode mixture may be compacted between an upper punch (first punch) and a lower punch (second punch) which form a part of the punch assembly. In the compaction process the upper punch presses down onto the surface of the cathode mixture while the lower punch moves upwards or remains stationary. The compacted cathode disks are ejected from the die by action of a lower plunger which presses upwards onto the disk&#39;s bottom surface, thereby lifting the disk out of the die. 
     A longstanding problem associated with forming such cathode disks for alkaline cells is that as the disk is being ejected from the die, flashing of cathode material tends to form in the small clearance space between the cathode disk and die cavity wall and upper punch. In particular flashing of cathode material can become more pronounced when the upper punch tip&#39;s edge wears. As the upper punch tip edge wears the clearance between the punch and the die cavity wall increases. Such increase in clearance creates a void space between disk and die cavity wall which can result in flashing of cathode material as the compacted cathode is being ejected from the die. Such flashing of cathode material causes a thin web or wing of cathode material to attach to and protrude from the disk&#39;s top surface and top edge of the disk&#39;s outer surface. Such web of material is shown as flashed material  55  and  55   a  protruding from the top of formed cathode disk  50  in  FIG. 10 . This results in an uneven or nonuniform top edge of the cathode disk and therefore must be removed before the disk is inserted into the cell. 
     Moreover, such flashed material breaks off in parts as the cathode disk is being ejected from the die and conveyed and transported to receiving containers. This causes an atmosphere of cathode dust to accumulate in the vicinity of the compaction process. As a safety protection workers may need to wear protected respiratory masks. The dust contains abrasive cathode material which may gradually collect on the surfaces of the punch assembly and peripheral operating equipment causing equipment contamination. 
     Accordingly, it is desired to improve the method of forming cathode disks for alkaline cells in order to eliminate or else significantly reduce the amount of flashed material which becomes attached to the cathode disk during the disk&#39;s formation and compaction. 
     It is desired to reduce the amount of cathode dust in the atmosphere surrounding the cathode compaction process and compaction of other materials thereby improving air quality in the work environment. 
     SUMMARY OF THE INVENTION 
     The invention is directed to a method of forming and compacting cathode mixture into cathode disks for insertion into cylindrical casing of alkaline cells. (Cathode disks are also referenced in the art as cathode pellets or tablets.) Cathode mixtures comprising manganese dioxide, graphite, alkaline electrolyte normally aqueous potassium hydroxide, and optionally a small amount of binder material, such as polyethylene binder are formed. The cathode mixture may also contain nickel oxyhydroxide (NiOOH) active material in place of manganese dioxide or in mixture with manganese dioxide. The cathode mixture is inserted into an elongated cavity (die cavity) running through a die. (The term “die” as used herein is equivalent to a housing having a cavity therein). The die is preferably of ceramic material. A punch assembly is employed to compress the cathode mixture into a disk shape while the cathode mixture is in the die cavity. The punch assembly comprises an upper punch (first punch), a lower punch (second punch) and a core rod, all of which may be independently moved in desired synchronized step. The upper punch, lower punch and core rod are elongated, typically cylindrically shaped members composed of steel, preferably of high carbon tool steel. The upper punch, lower punch, and die cavity typically have common central longitudinal axis. The upper punch and lower punch typically have a hollow core into which the core rod may penetrate in order to form a hollow central core of the cathode disk as it is being compacted. The cathode mixture is compacted between upper and lower punch tip surfaces 
     The cathode mixture is inserted into the die cavity so that it is between the tip surface of the upper punch and lower punch. In the compaction process the upper punch tip surface enters the die cavity and presses down onto the surface of the cathode mixture while the lower punch moves upwards within the die cavity or remains stationary. A compacted cathode disk is formed as the cathode material is compressed between the upper punch tip surface and the lower punch tip surface. The compacted cathode material is formed around a core rod resulting in a compacted cathode disk having a hollow central core as in a disk shaped donut. The top and bottom surfaces of the compacted cathode disk are flat and uniform with a hollow core surrounding the disk&#39;s central longitudinal axis. The compacted cathode disks are ejected from the die cavity by action of a lower plunger which presses upwards onto the disk&#39;s bottom surface, thereby lifting the disk out of the die while the upper punch lifts away from the die. The cathode disks may be shaped into required size for insertion in standard cylindrical casing for alkaline cells, for example, AAAA (42×8 mm), AAA (44×9 mm), AA (49×12 mm), C (49×25 mm) and D (58×32 mm) size cells. The cathode disks are typically inserted into the cell casing by stacking a plurality of such disks one onto the other. Such alkaline cells typically have an anode material comprising a zinc slurry which is inserted into the central core of the cathode disks with separator sheet placed in position between the anode and cathode material. 
     In the method of the invention the cathode disks are formed and compacted in the die in a manner which eliminates or greatly reduces the chance of forming flashed cathode material. Such flashed material can form a web of cathode material which can attach to the top surface or top edge of the compacted disks as they are being ejected from the die. As described in the preceding background the formation of such flashed material has been a long standing problem associated with the compaction of cathode disks. The formation of such flashed material is undesirable, since it becomes attached to the cathode disk and easily breaks off in parts as the cathode disk is ejected from the die and conveyed and transported to receiving containers. This causes an atmosphere of cathode dust to accumulate in the vicinity of the compaction process requiring workers to wear protected respiratory masks, and such dust can eventually clog the punch assembly resulting in the need for more frequent maintenance. 
     In one aspect the method of the invention has solved this long standing problem by providing the upper punch (first punch) with a resilient, flexible sleeve, termed herein as a deflasher sleeve. The deflasher sleeve is slipped over and around the lower body surface of the upper punch adjacent the punch tip surface. The deflasher sleeve is desirably of a resilient, durable elastomeric material or a thermoplastic material which also exhibit some elastomeric properties. A preferred material for the deflasher sleeve is polyurethane. In its original or starting position, the deflasher sleeve fits circumferentially flush against the upper punch surface thereby contacting and hugging the upper punch outer surface. However, the sleeve has the ability to compress causing a major portion of the sleeve (middle portion) to flex and bulge outward from the upper punch outer surface as the sleeve presses against the die table (die top surface). This occurs just as the upper punch penetrates into the die cavity and just before the upper punch tip surface presses onto the cathode mixture. No portion of the deflasher sleeve enters the die cavity as the upper punch presses onto the cathode mixture or at any other time during the process. Instead the deflasher sleeve contacts the die only at the die table (die top surface) without entering the die cavity. After the cathode disk has been compacted within the die cavity the upper die lifts upwards causing the deflasher sleeve to reflex to its original position lying flush against and hugging the outer surface of the upper punch. As the lower punch moves upwards to eject the compacted cathode disk from the die cavity the top surface or top outer edge of the compacted disk impinges against the deflasher sleeve just as the sleeve has reflexed back to its original position. The impingement of the cathode disk against the resilient deflasher sleeve prevents the formation of flashed material from forming and attaching to the upper surface of the compacted disk as the disk is being ejected from the die. Although the deflasher sleeve formed of polyurethane material appears to work best in preventing deflashing of cathode material, it will be appreciated that other material having similar resiliency, durability, and particle abrasion resistant properties may also be suitable in place of polyurethane. Thus, the invention is not intended to be limited to use of polyurethane material for the deflasher sleeve. 
     In another aspect of the invention the lower end of the upper punch (first punch) outer surface may be over molded with a seal ring composed of resilient, durable polymer, preferably polyurethane. The seal ring thus lies circumferentially flush around the outer surface of the upper punch at the lower end of the upper punch. The resilient polymer, preferably polyurethane, is molded circumferentially over a portion of the upper punch outer surface adjacent to but not contacting the punch tip surface. Thus, a ring of molded polymer, preferably of polyurethane, is formed around the lower end of the upper punch forming thereby a seal ring. Preferably, a plurality of apertures, typically round apertures, are formed along a circumferential path in the upper punch outer surface before the seal ring of polyurethane or equivalent polymer is molded onto the upper punch surface. In this case the apertures will underlie the polyurethane ring as this polymer is molded over the upper punch body surface. Such apertures underlying the seal ring serve to hold or anchor the molded polymer ring to the upper punch surface. The apertures also provide compression space into which the overlying portions of the seal ring may be compressed as contact pressure is applied to the seal ring. 
     In application of the seal ring in the compaction method of the invention, the cathode mixture is first inserted into the die cavity so that it rests on the tip surface of the lower punch (second punch). The lower punch may be held stationary (or else move upwards) as the upper punch (first punch) moves downwards into the die cavity to compact the cathode mixture. As the upper punch moves downwards into the die cavity to compact the cathode disk against the lower punch tip surface, at least a portion of the seal ring squeezes into the die cavity entrance. After the cathode mixture is compacted into a disk shape, the lower punch pushes upwards to eject the compacted cathode from the die. However, the seal ring provides a tight seal at the entrance of the die cavity immediately above the cathode disk while the disk is still in the die cavity. The cathode disk presses against the seal ring just as the disk is being ejected from the die, but while at least a portion of the seal ring is still within the die cavity. The pressing action between the cathode disk and seal ring while at least a portion of the seal ring is still in the die cavity, prevents cathode material from flashing and attaching to the disk surface as the disk is being ejected from the die. Polyurethane is a preferred material for the seal ring but other elastomeric polymer having similar property of resiliency, durability, and particle abrasion resistance may also be suitable. For example, any durable elastomeric material such as vulcanized rubber, styrene butadiene (SBR) rubber, or silicone rubber and similar materials may be suitable substitute material for polyurethane for the seal ring composition. Thus, the invention is not intended to be limited to use of polyurethane material for the seal ring. 
     The compacted disk shape is typically cylindrical (coin shape), having opposing parallel flat top and bottom surfaces with integral cylindrical body surface therebetween. However, the method of the invention is not intended to be limited to forming such regular shaped disks. The compacted disk may be of other shape or configuration. For example, the compacted disk formed by the method of the invention may have regular or irregular shaped circumferential edges. Thus, the disk&#39;s circumferential edge may be formed of straight or curvilinear surfaces or a portion of the circumferential edge may be straight and another portion may be curvilinear. 
     The method of the invention and improvements herein described can be applied to compaction of other materials. The invention is therefore not intended to be limited to compaction of cathode material for batteries. The application of the method of the invention and improvements herein described can be applied to other compaction processes. For example, the invention can be applied to compacting pharmaceutical powders or other types of cakes or pellets which may be compacted. The constituents for such cakes or powders may be of differing chemical composition. The invention and improvements herein described can be beneficially applied to compacting various materials, for example, but not limited to, compacting pharmaceutical powders or other materials wherein powder or particulate matter or chemical compositions must be compacted into varying shapes or configurations. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is a cross sectional view of the of a first embodiment of the punch assembly showing the deflasher sleeve in compressed, flexed position as the cathode material is being compacted into a disk. 
         FIG. 2  is a cross sectional view of the punch assembly showing the deflasher sleeve in reflexed position lying flush against the outer surface of the upper punch as the compacted cathode disk is being ejected from the die. 
         FIG. 3  is a pictorial view of the deflasher sleeve in flexed position around the upper punch. 
         FIG. 4  is a pictorial view of the deflasher sleeve in original or reflexed position lying flush against the outer surface of the upper punch. 
         FIG. 5  is an exploded view of the upper punch and deflasher sleeve. 
         FIG. 6  is a pictorial view of the deflasher sleeve inserted over the lower body surface of the upper punch. 
         FIG. 7  is a cross sectional view of a second embodiment of the punch assembly showing a seal ring over the bottom end of the upper punch outer surface and adjacent the punch tip surface. 
         FIG. 8  is a pictorial view of the upper punch showing a plurality of apertures in the upper punch body surface adjacent the punch tip surface. 
         FIG. 9  is a pictorial of the upper punch showing a seal ring covering the underlying apertures shown in  FIG. 8 . 
         FIG. 10  is a schematic pictorial representation showing flashed cathode material attached to the upper surface of the compacted cathode disk which may occur when the deflasher sleeve as in  FIG. 1  or the seal ring as in  FIG. 7  are not employed. 
         FIG. 11  is a schematic pictorial representation showing a compacted cathode disk without flashed cathode material attached thereto as a result of employing either the deflasher sleeve as in  FIG. 1  or the seal ring as in  FIG. 7 . 
     
    
    
     DETAILED DESCRIPTION 
     A representative cathode mixture  50  for an alkaline cell is prepared. The cathode mixture  50  is intended to be compacted into cathode disks, typically cylindrical shaped disks having a hollow core, for insertion into a cell casing. The compacted cathode disks may be inserted, for example, in a conventional cylindrical alkaline cell having an anode comprising zinc, as referenced hereinabove and in representative U.S. Pat. No. 6,251,539 B1. The intended use of the compacted cathode disks may be, for insertion in standard size cylindrical casing for alkaline cells, for example, AAAA (42×8 mm), AAA (44×9 mm), AA (49×12 mm), C (49×25 mm) and D (58×32 mm) size cells. 
     A representative cathode mixture  50  comprises manganese dioxide (EMD) and a conductive carbon, preferably, graphitic material, desirably a flaky crystalline natural graphite or expanded graphite or mixture thereof. Cathode mixture may also include graphitic carbon fibers or graphitic carbon nanofiber. The total conductive carbon in the cathode mixture desirably comprises between about 2 and 10 percent by weight of the cathode, preferably between about 2 and 8 percent by weight of the cathode. The cathode mixture also desirably comprises between about 5 and 10 percent by weight of an aqueous solution of KOH, which preferably has a strength of between about 7 and 10 Normal (30 and 40 wt. % KOH and 2 wt. % ZnO). 
     The cathode active material, typically comprising manganese dioxide (EMD), comprises between about 80 and 92 percent by weight of the cathode mixture, preferably between about 80 and 90 percent by weight of the cathode mixture. The cathode disk  50  ( FIG. 11 ) formed by the method of the invention can desirably have the following composition: 87-93 wt % of electrolytic manganese dioxide (e.g., Trona D from Kerr-McGee), 2-6 wt % (total) of graphite, 5-7 wt % of a 7-10 Normal aqueous KOH solution having a KOH concentration of about 30-40 wt %; and 0.1 to 0.5 wt % of an optional polyethylene binder. The electrolytic manganese dioxide typically has an average particle size between about 1 and 100 micron, desirably between about 20 and 60 micron. The graphite is typically in the form of natural, or expanded graphite or mixtures thereof. The graphite can also comprise graphitic carbon nanofibers alone or in admixture with natural or expanded graphite. Such cathode mixtures are intended to be illustrative and are not intended to restrict this invention. 
     The term “graphite” or “graphitic material” as used herein shall include natural and synthetic crystalline graphites (synthetically prepared or processed graphite), expanded graphites, graphitic carbons, and graphitic carbon fibers. The natural or expanded graphite is preferably in particulate form having a mean average particle size desirably between about 0.5 micron and 50 micron, typically between about 10 micron and 50 micron. A graphitic carbon has the characteristics of an ordered three-dimensional graphite crystalline structure consisting of layers of hexagonally arranged carbon atoms stacked parallel to each other as determined by X-ray diffraction. As defined in International Committee for Characterization and Terminology of Carbon (ICCTC, 1982), published in the  Journal Carbon , Vol. 20, p. 445, a graphitic carbon embraces the varieties of substances consisting of elemental carbon in allotropic form of graphite irrespective of structural defects. The term graphitic carbon as used herein shall be construed in this manner. 
     In one specific embodiment the representative cathode mixture  50  may be inserted into die assembly  10  ( FIG. 1 ) to be compacted into a cathode disk  50  ( FIG. 11 ). Compacted disk  50  has an outer surface  54  and an inner surface  52  defining a central hollow core  51  ( FIG. 11 ). The die assembly  10  ( FIGS. 1 and 2 ) has die  20  with die cavity  25  therein, an elongated upper punch (first punch)  30 , an elongated lower punch (second punch)  40 , and a core rod  60  which moves within the hollow core  45  of lower punch  40 . The upper punch  30  is an elongated cylindrical member having a hollow core  35 . Similarly lower punch  40  is an elongated cylindrical member having a hollow core  45  ( FIG. 2 ). Core rod  65  may also have a hollow core  65 . Lower punch  40  is integrally connected to base  46  ( FIG. 2 ). The die cavity  25 , upper punch  30 , lower punch  40 , and core rod  60  all have common central longitudinal axis  28  ( FIG. 1 ). Upper punch  30  and lower punch  40  moves within die cavity  65 . The upper punch  30  and lower punch  40  are formed of high carbon steel desirably tool grade steel. Die  20  is formed preferably of ceramic material. The upper punch  30  is fitted with a deflasher sleeve  70  of resilient, durable, polymeric material ( FIG. 6 ). Deflasher sleeve  70  desirably has elastomeric properties and may be of thermoplastic material having elastomeric properties. Preferably sleeve  70  is of polyurethane material, but it will be appreciated that other elastomeric materials having similar durability and elastomeric properties could be employed in place of the polyurethane. A preferred polyurethane for sleeve  70  is available as polyester- 85 A polyurethane available from Parkway Products. Deflasher sleeve  70  is of a cylindrical shape having a cylindrical outer surface  74  and hollow core  71  defined by inner surface  72  ( FIG. 5 ). In the position shown in  FIGS. 5 and 6  the deflasher sleeve  70  is in its original position flush against the outer surface of upper punch  30  so that it contacts and hugs the outer surface of upper punch  30  as shown in  FIGS. 2 ,  4 , and  6 . The cathode compaction method of the invention employing the die assembly  10  shown in  FIGS. 1 and 2  is as follows: 
     Initially the upper punch  30  ( FIG. 1 ) is moved upwards so that upper punch tip  32  is above die table (die top surface)  22 . The cathode mixture  50  is inserted into die cavity  25  so that the mixture lodges against tip surface  42  of lower punch  40 . The cathode mixture  50  is thus initially held in place in die cavity  25  by lower punch tip surface  42 , core rod  60  outer surface  64 , and the wall surface of cavity  25 . Upper punch  30 , lower punch  40 , and core rod  60  have independent movement, and may be moved up or down in synchronized manner. With reference to the punch assembly  10  shown in  FIGS. 1 and 2  the cathode mixture  50  is compacted by action of upper punch  30  stroking downward on cathode mixture  50  as lower punch  40  remains stationary or moves upwards in synchronized timing with the downward movement of upper punch  30 . Core rod  60  ( FIGS. 1 and 2 ) may slide independently to form and maintain the cathode disk hollow core  51  shown best in  FIG. 11 . 
     In a preferred compaction sequence the cathode mixture  50  is first loaded into die cavity  25  ( FIG. 1 ) while the upper punch tip  32  is extended above die table  22  (loading position not shown). Upper punch  30  is then pushed downward while lower punch  40  and core rod  60  is moved upward further into the die cavity to the position shown in  FIG. 1 . As the upper punch  30  is pushed downward, tip surface  32  of upper punch  30  moves down passed the die table (top surface)  22  of die  20 . This causes a major portion of sleeve  70 , namely its middle portion, to compress, that is, to flex and bulge outwardly as the sleeve is held in place at its upper end by upper punch head ring  34  and at its lower end by impact against die table  22  ( FIGS. 1 and 3 ). Deflasher sleeve  70  does not enter the die cavity  25 . The pressure of the lower edge of sleeve  70  against the die table  22  as upper punch  30  moves down into die  22  causes the bulging of the sleeve to occur ( FIG. 3 ). No portion of sleeve  70  enters die cavity  25 . Compaction of cathode mixture  50  occurs as the upper punch  30  continues downward movement once the lower punch  40  reaches the position shown in  FIG. 1 . (Compaction of cathode mixture  50  may be assisted by simultaneous continued upward movement of lower punch  40  as the upper punch  30  continues downward.) The cathode mixture  50  thus becomes compacted between tip surface  32  of upper punch  30  and tip surface  42  of lower punch  40  while the deflasher sleeve  70  is compressed, that is, becomes flexed outwardly in bulged position shown in  FIGS. 1 and 3 . After cathode mixture  50  has been compacted the upper punch  30  begins to retract. The deflasher sleeve  70  remains flexed and outwardly bulged as shown in  FIG. 1  until the upper punch  30  is fully retracted, that is, until upper punch tip surface  32  reaches die table  22 . At that point deflasher sleeve  70  reflexes to return to its original position ( FIG. 2 ). However, while the upper punch  30  is retracting, the lower punch  40  is simultaneously moving upward to begin ejection of the compacted cathode  50  from die cavity  25 . The upwards movement of lower punch  40  is timed so that the compacted cathode  50  bumps into deflasher sleeve  70  just as the deflasher sleeve  70  returns to its original reflexed, decompressed, position hugging the outer surface of upper punch  30  ( FIG. 2 ). The point of contact occurs during ejection of cathode disk  50  just as the cathode disk outer surface  54  contacts the lower portion of sleeve  70  as shown in  FIG. 2 . The forced contact between compacted cathode  50  and deflasher sleeve  70 , is timed to occur just before compacted cathode  50  is fully ejected from die cavity  25 . This has been found to prevent formation of flashed cathode material such as the web of flashed material  55  and  55   a  attached to the top surface  53  cathode disk  50  as shown in  FIG. 10 . Such flashed material  55  and  55   a  may occur, that is, if sleeve  70  of the invention was not employed. Thus, the product cathode disk  50  ejected from die  25  does not exhibit flashed material  55  and  55   a  attached to its surfaces as in  FIG. 10 , but rather has even (clean) surfaces as shown in disk  50  of  FIG. 11 . 
     In another specific embodiment the representative cathode mixture  50  may be inserted into die assembly  10  ( FIG. 7 ) to be compacted into a cathode disk  50  ( FIG. 11 ). The die assembly  10  ( FIG. 7 ) has die  20  with die cavity  25  therein and an elongated upper punch  30  and an elongated lower punch  40 , which move within die cavity  25 . There is a core rod  60  which moves within the core cavity  45  of lower punch  40 . The die cavity  25 , upper punch  30 , lower punch  40 , and core rod  60  all have common central longitudinal axis  28  ( FIG. 7 ). The upper punch  30  and lower punch  40  are formed of high carbon steel desirably tool grade steel. Die  20  is formed preferably of ceramic material. The upper punch  30  is fitted with a seal ring  80 , preferably of polyurethane material, as shown best in  FIG. 9 . A preferred polyurethane for seal ring  80  is available as polyester-85A polyurethane available from Parkway Products. Preferably the durometer hardness of the polyurethane seal ring  80  ranges from 20 Shore A to 70 Shore D (ASTM Standard). The seal ring  80  is preferably overmolded directly onto the upper punch outer surface at the punch lower end  38  ( FIGS. 8 and 9 ). Seal ring  80  thus lies circumferentially flush against the outer surface of lower punch  40 , thereby hugging the outer surface of said lower punch  40 . The seal ring  80  is thus positioned adjacent and in close proximity to the punch tip surface  32 , but does not cover tip surface  32  ( FIG. 9 ). Preferably, a plurality of apertures  37  ( FIG. 8 ) are formed along a circumferential path in the punch body surface and the seal ring  80  is molded directly over apertures  37 , thus covering these apertures. The cathode mixture loading and compacting process employing the die assembly  10  shown in  FIG. 7  is as follows: 
     Initially the upper punch  30  ( FIG. 7 ) is moved upwards so that upper punch tip  32  is above die table (die top surface)  22 . The cathode mixture  50  is inserted into die cavity  25  so that the mixture rests against tip surface  42  of lower punch  40 . The cathode mixture  50  is thus initially held in place in die cavity  25  by lower punch tip surface  42 , core rod  60  outer surface  64 , and the wall surface of cavity  25 . Upper punch  30 , lower punch  40 , and core rod  60  have independent movement, and may be moved up or down in synchronized manner. With reference to the punch assembly shown in  FIG. 7  the cathode mixture is compacted by action of upper punch  30  stroking downward on cathode mixture  50  as lower punch  40  moves up into desired position as shown best in  FIG. 7 . Core rod  60  ( FIGS. 1 and 2 ) may slide independently to form the cathode disk hollow core  51  shown best in  FIG. 11 . 
     In a preferred compaction sequence the cathode mixture  50  is first loaded into die cavity  25  ( FIG. 7 ) while the upper punch tip  32  is extended above die table  22  (loading position not shown). Upper punch  30  is then pushed downward while lower punch  40  and core rod  60  is moved upward further into the die cavity to the position shown in  FIG. 7 . As the upper punch  30  is pushed downward, tip surface  32  of upper punch  30  moves down passed the die table (top surface)  22  of die  20 . This causes at least a portion of the seal ring  80  to compress as seal ring  80  begins entry into die cavity  25  ( FIG. 7 ). The seal ring  80 , however, is molded to the outer surface of upper punch  30  at punch lower end  38  and therefore continues to hug punch  30  outer surface. Compaction of cathode mixture  50  occurs as the upper punch  30  continues downward movement once the lower punch  40  reaches the desired position, approximately as shown in  FIG. 7 . (Compaction of cathode mixture  50  may be assisted by simultaneous upward movement of lower punch  40  as the upper punch  30  continues downward.) During cathode compaction vertical forces on the seal ring  80  are transposed into radial forces enhancing the sealing effect of seal ring  80  as the sealing ring  80  begins to enter die cavity  25  ( FIG. 7 ). This helps to prevent formation of flashed cathode material at this point in the compaction process. After cathode mixture  50  has been compacted the upper punch  30  begins to retract. (The seal ring  80  remains compressed until the upper punch tip surface  32  retracts to die table  22 .) However, while the upper punch  30  is retracting, the lower punch  40  is simultaneously moving upward to begin the process of ejecting the compacted cathode  50 . During the beginning of the ejection process, the seal ring  80  continues to form a tight plug at the entrance to cavity  25 , that is, just at or immediately below die table  22 . That is, as the cathode disk  50  is being ejected from die cavity  25  cathode disk  50  presses against seal ring  80 , while at least a portion of seal ring  80  is still within die cavity  25 . This prevents flashing of cathode material to occur or become attached to the cathode disk  50  as disk  50  is being ejected from die cavity  25 . Such flashed material  55  and  55   a  may otherwise occur, that is, if seal ring  80  of the invention is not employed around the lower end  38  of upper punch  30 . Thus, the product cathode disk  50  ejected from die  25  does not exhibit flashed material  55  and  55   a  attached to its surfaces as in  FIG. 10 , but rather has even (clean) surfaces as shown in disk  50  of  FIG. 11 . 
     Although the invention has been described with reference to specific embodiments, it should be appreciated that other embodiments are possible without departing from the concept of the invention and are thus within the claims and equivalents thereof.