Abstract:
A tapered running block and corresponding tapered cavity blocks are utilized in a mold for fabricating relatively thin, flat plastic cards, such as used for pre-paid telephone cards and the like. The mating surfaces of the runner block and the cavity block are angularly tapered; so that metal-to-metal contact is made between the runner block and the cavity block when the mold is in the plastic injection position. As soon as relative movement of the runner block and the cavity block is effected to part the blocks and separate the cards from the runners, the tapered 1surfaces move away from one another without any sliding contact, thereby significantly reducing wear in the mold.

Description:
BACKGROUND 
     Injection molds are widely used to manufacture plastic parts for different applications, in different shapes. One current application is the molding of relatively thin plastic cards loaded with computer chips, ranging from relatively simple systems used in prepaid long distance phone cards, television cable box identification cards, to cards called “smart cards” including computer software for use with portable computers and the like. 
     These cards are molded in plastic injection molds, where the cavities of the mold plates are edge filled with plastic material. After filling, a short cooling period transpires. The mold then is opened at a parting line; and movement occurs, facilitating both card and runner ejection. The mold plates carrying the cavities used to form the cards move forward, leaving the runner block of the injection mold machine behind. The runner block is anchored to a fixed mold plate. The action of movement of the mold plates separates the cards from the runners, allowing the runners and cards to be ejected or removed from the mold separately. 
     The existing design of cold runner plastic injection molds for producing thin, flat computer chip-loaded cards is subject to several shortcomings. The steel components of the cavity blocks on the mold plates and the runner block typically are designed with parallel surfaces, which are perpendicular to the plane of the cards being molded. This results in rubbing (wearing) where the cavity blocks and the runner blocks slide on one another during the opening and closing operation of the mold. This results in wear of one or both of these components, in time. When this wear becomes excessive adjacent the edge of the card being molded, unwanted flash appears on the edge of the card; and production must be stopped in order to repair the mold. It is inherent that this straight design of rubbing steel parts results in steel wear, which requires relatively frequent maintenance. This situation has been tolerated and accepted in conjunction with such molds, even though it results in a significant amount of down time of the mold when parts are repaired or replaced. 
     Another disadvantage of prior art molds of the type described above, when the runner blocks and the cavity blocks have mating, sliding, parallel surfaces, is that both parts must be manufactured initially with some operating or running clearance. This clearance must be enough to allow the two components to move freely (that is, with a minimal amount of rubbing friction), but not so much as to cause the clearance to be excessive and cause resulting flash on the parts being manufactured. In effect, the running clearance shortens the amount of time that the mold can be run without flash occurring, since such a straight parallel design requires a small amount of wear to be built into the parts at the outset. This built-in clearance necessarily shortens the amount of time the mold can be run before maintenance is required. At the same time, without the initial built-in clearance, excessive wear and stress on the various parts of the mold would occur. 
     Another disadvantage of prior art molds for manufacturing thin flat, edge filled plastic cards is that the plastic being forced through the gates under high pressure and speed causes the metal in the immediate gate exit to flare out into the edge of the card, where the cutting action occurs to separate the card from the gate. Since the cavity passes by this area, the gate flaring metal begins to wear a corresponding notch in the cavity block, allowing unwanted plastic to flow in the notch. This forms a blemish on the edge of the card formed by the mold. This blemish in turn must be repaired. This occurs when the edge of the card corresponds with the cutting surface of the gate; so that wear in this area results in maintenance being required on the cavity block, as well as on the runner block of the mold. 
     The above noted disadvantages, inherent in standard or conventional molds for fabricating flat plastic cards with embedded computer chips, cause a significant amount of down time in the use of such molds, as a result of the relatively frequent maintenance intervals which are required in order to repair or replace the various mold parts, including the runner blocks and the cavity blocks. This resultant down time causes increased costs of the cards produced over what would otherwise be possible if the molds could be continuously run with significantly less down time. 
     It is desirable to provide a design for a plastic injection mold used to fabricate thin, flat plastic card components which overcomes the disadvantages of the prior art noted above, and which eliminates or significantly reduces the sliding metal-to-metal contact between the mold blocks and the runner block of the mold. 
     SUMMARY OF THE INVENTION 
     It is an object of this invention to provide an improved injection mold design. 
     It is another object of this invention to provide an improved injection mold design for the manufacture of edge gated cards, with reduced wear on the various mold components. 
     It is an additional object of this invention to provide an improved edge gated mold design which substantially eliminates rubbing friction between the runner block for the mold and the cavity blocks. 
     It is a further object of this invention to provide an improved mold design for producing edge gated cards which uses a tapered runner block and tapered surfaces on the cavity blocks to allow metal-to-metal contact during the plastic injection cycle of operation and to permit parting of the various mold parts without sliding metal-to-metal friction to discharge parts from the mold. 
     In accordance with a preferred embodiment of the invention, a plastic injection mold includes a runner block on a fixed base, with a tapered surface on it. A cavity block is movable relative to the runner block, and has a tapered surface on it for mating with and contacting the tapered surface of the runner block when the cavity block and the runner block are in a plastic injection position. The tapered surfaces of the runner block and the cavity block are designed such that upon relative movement of the cavity block and the runner block, to separate the cavity block from the runner block, the tapered surfaces move away from one another without sliding contact. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     FIG. 1 is a top front right perspective view of a preferred embodiment of the invention; 
     FIG. 2 is a top view of the embodiment shown in FIG. 1; 
     FIG. 3 is a cross-sectional view taken along the line  3 — 3  of FIG. 2; 
     FIG. 4 is a top view of a portion of the embodiment shown in FIG. 1; 
     FIG. 5 is a side view of the portion shown in FIG. 4; 
     FIG. 6 is a left front top perspective view of a portion of the embodiment shown in FIG. 1, in exploded form; 
     FIG. 7 is a left front top perspective view of a portion of the embodiment shown in FIG. 6; 
     FIG. 8 is an enlarged detail of the portion circled as “ 8 ” in FIG. 7; 
     FIG. 9 is an enlarged detail of the portion encircled as “ 9 ” in FIG. 8; 
     FIG. 10 is an enlarged exploded detail of a portion of the preferred embodiment of the invention; and 
     FIG. 11 is an enlarged cross section of the portion circled “ 11 ” in FIG.  3 . 
    
    
     DETAILED DESCRIPTION 
     Reference now should be made to the drawings, in which the same reference numbers are used throughout the different figures to designate the same or similar components. Different ones of the drawings show different aspects of the invention in various orientations, and in differing detail. 
     FIG. 1 is a top perspective view of those portions of a cold runner plastic injection mold which have been modified in accordance with a preferred embodiment of the invention. The mold machinery itself, which is used to move cavity blocks or mold plates relative to a runner block, are not shown in the various drawings, since such parts are standard parts; and they are not a feature of the present invention. The present invention may be employed as a substitute for straight-sided cold runner (or hot runner) plastic injection molds using edge gating. In such molds a central or fixed runner block is employed; and the cavity blocks are moved relative to the runner block in order to cut or shear the runner at the gate from the edge of the card, and to allow the cards to be removed or ejected from the mold. Only the bottom half of the cavity blocks associated with the “top” of a runner block are shown in the drawings, since the top closure for the runner blocks and the top of the cavity blocks are standard in design, and are not important to an understanding of this invention. 
     As shown in FIG. 1, a central tapered runner block  40  is placed between a pair of movable cavity blocks  20  and  30  which form the blocks for one side (or the lower side) of cards to be formed in four cavities  22 ,  24 ,  32 , and  34 , respectively. The runner block  40  has an elongated channel  42  formed in its upper surface, which has arms extending from it to supply plastic to four tapered inserts  44 ,  46 ,  48  and  50  associated with the cavities  24 ,  22 ,  34  and  32 , respectively. The inserts  44 ,  46 ,  48  and  50  include corresponding gates in them at the edges of each of the cavities  22 ,  24 ,  32  and  34  for supplying plastic under high pressure to the cavities in the formation of relatively thin, flat, rectangular plastic cards, for example, of the type which subsequently have computer chips embedded in them. All of the runner block inserts  44 ,  46 ,  48  and  50  are identical; so that the details of only one of them, insert  46 , are shown in detail in FIGS. 7,  8 ,  9 ,  10  and  11 . In these figures, it is apparent that the plastic flow channel  42  terminates in a segment  42 A at the top of each of the inserts  44 ,  46 ,  48  and  50 , and from the segment  42 A extends through a gate  58  located in a position at the edge of each of the cavities  22 ,  24 ,  32  and  34  in the cavity blocks  20  and  30 . The details of the structure leading from the channel  42  through the segment  42 A and ultimately to the gate  58  are illustrated in FIGS. 8,  9 ,  10  and  11 . 
     FIG. 11 is a cross section which illustrates the interconnection between the gate  58  and the channel portion  42 A by way of a tunnel or channel  56 . The manner in which plastic is injected through the gates  58  and the particular construction of the channels  42 , segment  42 A, and  56 , is standard. Various other channel configurations may be employed to supply plastic to gates, such as the gate  58 , if desired. The particular configuration which is illustrated is merely representative of conventional techniques for supplying injection molded plastic to a cavity. 
     As is most readily apparent from an examination of FIGS. 3,  4 ,  6 , and  7  through  11 , the runner block  40  has the upper portion, which is in contact with the cavity blocks  20  and  30 , formed with tapered sides, rather than straight or vertical sides. Thus, the front surfaces  44 A,  46 A,  48 A and  50 A, respectively, of each of the inserts  44 ,  46 ,  48  and  50  are tapered upwardly (as viewed in the drawings) at. a small angle, typically greater than 8°, which will avoid application of an undesirable locking angle. The surfaces  44 A,  46 A,  48 A and  50 A all are flat surfaces, and are tapered in the same amount; so that the structure of the runner block  40  is symmetrical, as is most apparent from an examination of the top view in FIG.  4 . 
     In addition to the inwardly tapered faces  44 A,  46 A,  48 A and  50 A, the sides of the inserts  44 ,  46 ,  48  and  50  also taper toward one another, as shown for the insert  46  as the tapered sides  70  and  72 . In addition, the other surfaces of the runner block  40  which engage corresponding mating surfaces of the cavity blocks  20  and  30 , also all are tapered; so that no surfaces perpendicular to the top plane of the mold assembly shown in FIG. 1, are in contact between the runner block  40  and the cavity blocks  20  and  30 . This is readily apparent from an examination of the various drawings, and is most particularly shown in FIGS. 3,  6 , and  11 . 
     In the mold blocks  20  and  30  (which are identical, but mirror images of one another), upwardly and outwardly tapered surfaces, such as the surfaces  31  and  35 , abut adjacent tapered surfaces on the runner block  40 . Similarly, outwardly tapered surfaces, such as the surface  23  which abuts the face  46 A of the insert  46 , abut each of the inserts  44 ,  46 ,  48  and  50  in the manner illustrated in FIGS. 3 and 11 most particularly. 
     When the mold is in the injection molding position, the various tapered surfaces on the runner block  40  and the cavity blocks  20  and  30  all make a firm metal to metal contact, which has not been possible with the straight edged mold designs of the past, since these designs required a built-in clearance. No clearance is required in the mold design which is illustrated in the various figures of the drawing. Since no clearances are required, accurate centering of the runner block between the movable cavity blocks  20  and  30  is afforded by the design shown in the various figures of the drawing. This allows for consistent mold cavity venting, which has been a problem with the devices of the prior art. 
     When the cavity blocks  20  and  30  are separated from the runner block, they move vertically in the direction shown in FIG. 3 relative to the runner block  40  which remains in a fixed position. It is readily apparent from an examination of FIG. 3 that vertical movement of the cavity blocks  20  and  30 , immediately when it begins to take place, causes a non-frictional pulling away of the runner block  40  and the cavity blocks  20  and  30 . No frictional sliding of any of the surfaces (all of the mating surfaces are tapered) to part the runner block  40  from the cavity blocks  20  and  30  takes place. 
     In addition, as is most readily apparent from an examination of the enlarged insert of FIG. 11, the card which is formed in the cavity block, such as the cavity block  22 , is severed from the gate  58  as the cavity block  20  moves upwardly (as viewed in FIG.  11 ), without any metal-to-metal contact at the gate  58 . The card is sheared from the runner at the upper edge of the gate  58  on the insert  46 . The surface  66  above the edge of the gate  58  is set back from the surface  46 A below the gate  58  (most clearly shown in. FIG.  11 ), and has an approximate 10° taper angle, which is slightly less than the 12° taper of the surface  46 A comprising the major face of the insert block  46 . The edge  64  on the insert  46 , shown most clearly in FIGS. 8,  9  and  10 , is a straight or vertical edge forming the edge of the card formed in the cavity blocks  22 ,  24 ,  32  and  36 ; but there is no metal-to-metal contact in this region, since the edge  64  comprises the closure for the end of the cavity into which the plastic is injected through the gate  58 . 
     Another important feature inherent in the design described above is that the upper or shearing edge of the gate  58  is set back slightly from the shut-off angle at the lower edge, formed at the upper edge of the surface  46 A creating the protective setback  64 A. This is shown most clearly in FIG.  11 . Consequently, when the relative movement of the runner block  40  and the cavity block  20  occurs to move the cavity block upward, as viewed in FIG. 11 with respect to the runner block  40 , the edge  23  of the cavity-block is spaced a short distance from the upper cutting edge of the gate  58 . Thus, even if some gate flaring occurs as a result of the high pressure and speed of plastic flow through the gate  58 , a gap occurs between the lower edge of the surface  66  and the upper edge of the surface  23 . As a result, the problem of wear, in the form of cavity damaging notches in the cavity block  20  which occurred with the molds of the prior art and caused cosmetic imperfections on the edge of the card, does not take place. The only cutting action at the upper edge of the gate  58  occurs in the plastic on the edge of the card and runner in the channel  56 , at the end of the flow channel extension  42 A. 
     Since the surface  46 A (and the corresponding surfaces  44 A,  48 A and  50 A) all extend outwardly from the upper edges of the runner block  40 , as shown in FIGS. 4,  5 ,  6  and  7 , corresponding sloped or tapered surfaces (not numbered but shown in FIG. 6) on the cavity blocks  20  and  30  mate with these surfaces; so that, again, as the cavity blocks are moved upwardly, as viewed in the drawings, there is an immediate pulling away of all of the metal-to-metal tapered contacting surfaces in the cavity blocks  20  and  30  with the surfaces on the runner block  40 . 
     FIGS. 3,  10  and  11  illustrate details of the attachment of removable inserts  44 ,  46 ,  48  and  50  in the runner block  40 . These inserts are the only parts of the runner block which may need replacement as a result of wear, primarily at the gate  58 . As a consequence, they are held in place by means of a bolt or threaded fastener  80  passing through a hole  81  at the lower portion. These fasteners then are threaded into receiving threaded holes  82  in the runner block  40 . Another bolt or threaded fastener  62  is passed through the runner block  40  from the opposite side, and is secured into a threaded hole  60  near the upper part of the blocks  44 ,  46 ,  48  and  50 , as illustrated in detail in FIGS. 3 and 11. Thus, whenever replacement of any one or more of the blocks  44 ,  46 ,  48  and  50  is desired, it can be effected rapidly by the removal of the bolts  62  and  80  followed by replacement of a new insert and tightening again of the bolts  62  and  80 . 
     The foregoing description of the preferred embodiment of the invention is to be considered as illustrative and not as limiting. Variations in the. angles and shapes readily may be made without departing from the invention. Various other changes and modifications will occur to those skilled in the art for performing substantially the same function, in substantially the same way, to achieve substantially the same result, without departing from the true scope of the invention as defined in the appended claims.