Abstract:
A first mold die and a second mold die are moved together and are shaped to define a mold cavity therebetween. A capacitor pellet is positioned within the mold cavity and a plurality of projections extend inwardly to engage the capacitor pellet and hold it spaced away from the cavity side wall. The method comprises placing the pellet body within the cavity molding and retentively engaging the pellet body with a plurality of projections to provide a space between the pellet body and the cavity side wall. A molding material is used to fill the space to provide a coating on the pellet body.

Description:
BACKGROUND OF THE INVENTION 
     The present invention relates to a capacitor mold and method for using same. 
     In the molding of pellet capacitors, difficulty is often encountered in trying to center the capacitor pellet within the mold during molding. Failure to properly center the capacitor in the mold results in thin layers or bare spots in the protective coating that surrounds the pellet. 
     Therefore, a primary object of the present invention is the provision of an improved capacitor mold and method for using same. 
     A further object of the present invention is the provision of a capacitor mold and method for using same which centers the capacitor pellet within the mold and holds the capacitor pellet in this centered position during the molding process. 
     A further object of the present invention is the provision of a capacitor mold and method for using same which results in a protective coating having uniform thickness around the side walls of the pellet. 
     A further object of the present invention is the provision of a mold and method for using same which is economical in manufacture, durable in use, and efficient in operation. 
     SUMMARY OF THE INVENTION 
     The foregoing objects may be achieved by a combination including first and second mold dies. The two dies are movable together and are shaped to define a mold cavity therebetween. The mold cavity has a cavity anode end, a cavity cathode end, a longitudinal axis extending between the cavity anode and cathode ends, and a cavity side wall surrounding the longitudinal axis and extending between the cavity anode and cathode ends. A capacitor pellet includes an anode pellet end, a cathode pellet end and a pellet body extending therebetween. A plurality of projections extend inwardly from the cavity side wall. The projections engage the pellet body and hold the pellet body spaced away from the cavity side wall. 
     According to one feature of the invention the cavity side wall includes a plurality of surfaces, and at least one of the projections extends from each of the surfaces toward the longitudinal axis of the pellet. 
     According to another feature of the invention each of the projections is positioned adjacent the cathode end of the cavity and engages the pellet body adjacent the cathode pellet end. 
     According to a preferred embodiment of the invention a plurality the surfaces on the side wall comprise four surfaces. 
     According to a further feature of the invention the plurality of projections approximately center the pellet body within the cavity side wall so as to create a substantially uniform space between the pellet body and the cavity side wall. 
     According to a further feature of the invention the coating of conductive material covers the cathode pellet end and a portion of the pellet body adjacent the cathode pellet end. All of the projections engage the conductive material. 
     According to the method of the present invention the pellet body is placed within a molding cavity having an anode cavity end, a cathode cavity end, and a cavity side wall extending therebetween. The pellet body is retentively engaged within the cavity by a plurality of projections which extend from the cavity side wall and engage the pellet body to provide a space between the pellet body and the cavity side wall. The space extends completely around the pellet body. A molding material is used to fill the space to provide a coating on the pellet body. 
    
    
     BRIEF DESCRIPTION OF THE FIGURES OF THE DRAWINGS 
     FIG. 1 is a sectional view of a capacitor made according to the present invention. 
     FIG. 2 is an elevational view showing the pellet, wire, and teardrop body of the present invention. 
     FIG. 3 is a simplified and partial semetric view of the molds used to produce the capacitor of the present invention. 
     FIG. 4 is a top plan view of the pellet positioned within the bottom mold member. 
     FIG. 5 is a sectional view taken along line  5 — 5  of FIG.  4 . 
     FIG. 6 is a sectional view of the molded capacitor before the bottom portion thereof is removed. 
     FIG. 7 is a view similar to FIG. 6, but showing a prior art capacitor. 
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT 
     Referring to FIG. 1 the numeral  10  generally designates a capacitor made according to the present invention. Capacitor  10  includes a pellet  12  having an anode pellet end  14 , and a cathode pellet end  16 . An anode wire  18  is embedded in and extends from the anode pellet end  14  of pellet  12 . Pellet  12  also includes a pellet front wall  20  (FIG.  5 ), a pellet rear wall  22 , and opposite pellet side walls  24 ,  26 . Surrounding the pellet  12  is a protective body  28  made of molded material which protects the integrity of the pellet  12 . Numerous molding materials have been used, and they are preferably dielectric. However, persons skilled in the art may select a wide variety of protective molded materials without detracting from the invention. The preferred molding compound is manufactured by Dexter Corporation, at 211 Franklin Street, Olean, N.Y. 14760, under model number MG 53 F. 
     The protective body  28  includes a pair of opposite side indentations  30 ,  32 . Other side indentations are also formed in the protective body  28  and will be described hereafter. Surrounding the bottom of the pellet  12  is a cathode termination  34  made of a conductive material which may be silver, other metals, or conductive epoxy. A wide variety of these conductive materials are available and are used in the industry. The preferred conductive material for use in the present invention is a conductive epoxy sold under the Model No. 61445, by Metech, Inc., having an address of Rt. 401, Box 360, Elverson, Pa. 19520. The cathode termination  34  includes a downwardly presented cathode termination surface  36  which engages a cathode terminal cap  38  made of conductive material. Cathode cap  38  includes cap side walls  40  and a cap end wall  42 . The wire  18  provides the anode termination for capacitor  10 . A conductive anode cap  97  can be provided at the anode and so as to engage the wire  18  and provide an anode terminal for capacitor  10 . 
     Referring to FIG. 2, the pellet  12  is shown in its form before being placed in the mold. Pellet  12  is formed by conventional press molding and sintering technique which are well known in the art. The pellet  12  is covered at its cathode end  16  by a tear drop shaped body  44  made of the above identified conductive material. Body  44  includes an upper portion  45  which surrounds the front, side and rear walls of the pellet  12  adjacent the cathode end thereof. Tear drop shaped body  44  also includes a tear drop point  46 . In some cases there are multiple tear drop points  46 . 
     The formation of tear drop shaped body  44  on the cathode end  16  of pellet  12  is accomplished by dipping pellet  12  into a reservoir of fluid hardenable conductive material, or alternatively by using a syringe. After application the conductive material is permitted to cure and harden. 
     The pellet  12  shown in FIG. 2 is positioned within a molding cavity formed by an upper mold  48  and a lower mold  54 . Upper mold  48  includes an upper mold face  50  on its lower surface and a pair of spacing ribs  52  which protrude downwardly therefrom. Bottom mold  54  includes a bottom mold face  56  which faces upwardly. Cavity side walls  58 ,  60  and a cavity bottom wall  62  combine with the upper mold face  50  to form a molding cavity as shown in FIG.  5 . 
     A pair of L-shaped spacers  64  are positioned with upstanding legs  66  extending along the cavity side walls  58 ,  60  and with horizontal legs  70  extending along the cavity bottom wall  62 . The upper edges of upstanding legs  66  are each provided with a tapered edge  68  (FIG.  5 ). 
     FIGS. 4 and 5 show the pellet  12  positioned within the mold. In this position the L-shaped members  64  extend from the cathode end  80  of the cavity toward the anode end  82  of the cavity, and terminate at a point spaced from but adjacent the cathode end  16  of the pellet  12  as can be seen in FIG.  4 . The ribs  52  of the upper mold  48  extend longitudinally approximately the same distance from the anode end  80  of the cavity. As can be seen in both FIGS. 4 and 5 a substantially uniform space  72  is formed around all four sides of the pellet  12 . The L-shaped pieces  64  and the ribs  52  engage the anode end of the pellet, and specifically engage the tear shaped body  44  to center the pellet  12  within the cavity. While the ribs  52  and the L-shaped members  64  are used to center the pellet  12  within the cavity, other shapes and configurations of projections could accomplish the same result without detracting from the invention. The importance of centering the pellet  12  within the cavity is that when the molding process is complete there is a layer of protective material surrounding the pellet, and that layer of protective material is of substantially uniform thickness. 
     FIG. 6 shows the completed molded uncut capacitor body designated by the numeral  74 . This capacitor body  74  is cut along a cut line  76  to remove a lower body portion  78  and to expose the cathode termination surface  36  that can be engaged by the terminal cap  38  as shown in FIG.  1 . 
     The removal of the removed body portion  78  can be accomplished by cutting, grinding or other conventionally known means. 
     The completed capacitor  10  has a cathode termination surface  36  which is flat and which faces axially away from the cathode end of the pellet. It is also centered with respect to longitudinal axis of the pellet. This centering is accomplished by the molding process which utilizes the projections  52 ,  64  to center the pellet and the tear dropped shaped body  44  within the mold cavity. 
     FIG. 7 illustrates a prior art capacitor  84  made according to a prior art method for creating the cathode termination. The capacitor  84  includes a pellet  86  and an anode wire  88 . A protective body  90  is molded around the pellet  86 . At the cathode end of the pellet  86  is a conductive adhesive  92  which attaches a silver pin  94  to the pellet  86 . A cut is made along cut line  96  and this cut exposes the silver pin  94  to create the cathode termination surface. 
     Neither the conductive adhesive  92  nor the silver pin  94  can be used as a means for centering the pellet  86  in the molded body  90 . Without the use of the tear drop shaped body, this process is very difficult to center the pellet  86  in the molded body  90 . Failure to properly center the pellet  86  can result in thin spots or even openings in the protective coating  90 . In contrast the use of the tear drop shaped body  44  and the use of the projections  64 ,  52  to center the body within the mold cavity creates a termination which is centered with respect to the longitudinal access of the pellet, and which has a protective coating  28  of uniform thickness around the side wall of pellet  12 . 
     In the drawings and specification there has been set forth a preferred embodiment of the invention, and although specific terms are employed, these are used in a generic and descriptive sense only and not for purposes of limitation. Changes in the form and the proportion of parts as well as in the substitution of equivalents are contemplated as circumstances may suggest or render expedient without departing from the spirit or scope of the invention as further defined in the following claims.