Abstract:
The present invention is an improved mold-half that is useful in forming golf ball covers or other layers. The mold-half is particularly useful for compression molding a thin polyurethane cover over a golf ball formed from a plurality of inner layers. The mold-half includes a cavity and a land area surrounding the cavity. The land area has an upper surface and at least one vent in fluid connection with the cavity via a chamber formed by a recessed circumferential ledge adjacent the cavity. The ledge controls the flow of excess layer material from the cavity to each vent.

Description:
FIELD OF THE INVENTION 
     This invention generally relates to the manufacture of golf balls, and more particularly, to a mold-half for molding various layers on golf balls. 
     BACKGROUND OF THE INVENTION 
     Modern day golf balls can be generally classified as one-piece, solid and wound. Solid balls can be one-piece or two or more piece constructions. One-piece solid balls are injection or compression molded from a homogeneous mass of material with a dimple pattern molded thereon. These are inexpensive and very durable, but do not provide great distance because of their lower compression. They tend to have a soft feel when struck with the club face. 
     Two piece solid balls are made by molding a cover about a solid core. These are one of the most popular types of balls in use today. These balls can have a hard “cutproof” cover which goes a greater distance, and generally have lower spin rates. Three-piece solid balls may be made by molding a cover around a solid core comprising a solid center with a mantle layer molded about the outside of the center. 
     Wound balls are made by molding a cover about a wound core. A center is typically made of rubber and can be solid or have a fluid-filled center. The wound core is prepared by winding a lengthy thin thread of elastic material about the center. The wound core is then covered with a durable cover material. Wound balls are generally softer and provide more spin, resulting in increased control over the ball. As a result of their more complex construction, the wound balls generally require a longer time to manufacture and are more expensive to produce than solid balls. 
     The covers on these golf balls are made from materials, such as synthetic balata ionomer resins, or urethane polymers. A prior art mold-half for use with these materials is shown in FIGS. 1-3. The mold-half  10  comprises a cavity  15 , a land area  20  surrounding the cavity  15 , a circumferential groove  30  within the land area  20 , and a plurality of vents  35  in fluid communication with the circumferential groove  30 . The vents  35  and groove  30  are spaced from the cavity. The surface  40  of the cavity  15  is textured with dimple forming projections  45 , which produce a dimple pattern on the cover of the golf ball. Additionally, the land area  20  includes an upper surface  50  and a radially outer surface  55 . The portion of the land area between the cavity  15  and the groove  30  is designated  20   a . The portion of the land area radially outward of the groove is designated  20   b . Each vent  35  includes a vent side wall  60 . The mold-half  10  further includes a projection  65  extending radially outward from the land area  20 . 
     A pair of mold-halves  10  are clamped together under pressure to form a spherical cavity therein. As the mold-halves  10  are clamped the cavities contain a core or center and material to form hemispherical portions of the cover. The mold-halves  10  are held together until the cover material is cooled and then opened to demold the ball. As this mold is closed, excess cover material between the land areas  20   a  is squeezed into the groove  30  and flows into vents  35 , which convey the material to the exterior of the mold. Notably, the groove  30  is configured to form an alignment ring for a separate process in the manufacture of the golf ball and is not specifically designed to cooperate with the other features of the mold to facilitate compression molding of material. The cavity  15  still contains excess cover material but there is no passageway from the cavity to convey this material. The process is farther complicated by the inability to convey the excess material within the cavity out of the cavity. The increased internal pressure due to the thermal expansion of the molded ball assembly causes this excess material to separate the mold and allows jagged flash to form around the molded cover of the ball. 
     Consequently, a need exists for an improved mold-half for manufacturing a golf ball cover. The mold-half should minimize the likelihood of mold separation, reduce the number of cracked or defected covers produced, and lower the potential for jagged flash formation around the molded cover or other molded layer of the golf ball. 
     SUMMARY OF THE INVENTION 
     The present invention is an improved mold-half that is particularly useful in casting golf ball covers. In particular, the mold-half is useful for molding a thin veneer cover over a golf ball subassembly that includes a plurality of inner layers. The mold-half includes a hemispherical cavity and a land area surrounding the cavity. The land area has an upper surface and at least one vent defined in the upper surface spaced from the cavity. The land area also has a circumferential ledge adjacent the cavity and each vent. 
     Two mold-halves of the present invention are combined to form a mold. Joining the land areas of a pair of mold-halves creates a spherical cavity for receiving the subassembly. Additionally, a chamber is formed adjacent the cavity by the opposing ledges of the two mold halves, and opposing vent pairs each form a bore for releasing excess material from the chamber. The ledges and vents are operatively configured such that the flow of material is allowed primarily through the bores. Furthermore, the chamber is configured such that the volume of the chamber is sufficient to contain the material during flow from the cavity without allowing the mold-halves to separate. 
     Generally, the length of the circumferential ledge is between about 0.005 inches and about 0.05 inches and preferably the length of the circumferential ledge is about 0.015 inches. Additionally, the circumferential ledge is recessed from the upper surface of the land area by about 0.001 to about 0.01 inches, more preferably by about 0.005 inches. Further, each vent is spaced from the cavity wall by about 0.01 inches to about 0.02 inches. The preferred length from the cavity wall to each vent is about 0.015 inches. Further still, the depth of each vent is between about 0.025 inches and about 0.08 inches, and the preferred depth of each vent is about 0.03 inches. Typically, each vent has a length of at least between about 0.04 inches and about 0.08 inches with a preferred length of about 0.5 inches. 
     In one embodiment, the mold-half further includes a projection that extends radially outward along the entire circumference of the land area. The projection is located below the upper surface of the land area. The outer diameter of the projection is about 2.43 inches and the thickness of the projection is about 0.25 inches. An upper surface of the projection is situated about 0.38 inches below the upper surface of the land area. 
     According to the features of one embodiment, the land area includes a uniformly sloped surface extending between the upper surface of the land area and the upper surface of the projection. In addition, in one embodiment the cavity includes a plurality of projections for forming a plurality of depressions or dimples in the cover. In yet another embodiment, the land area contains a plurality of vents which preferably are spaced uniformly around the circumference of the land area. 
     The present invention is also directed to a mold for forming a layer of material around a golf ball subassembly. The mold includes a pair of mold-halves, where each mold-half includes a hemispherical cavity, a land area, and a circumferential ledge. The land area surrounds the cavity and includes an upper surface. The circumferential ledge is adjacent the cavity. The upper surface of one land area is configured to mate with the opposing land area and locate a portion of the material within the cavity. 
     The mold may also include vents extending from the ledge. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     FIG. 1 is a perspective view of a prior art mold-half. 
     FIG. 2 is an enlarged, partial-sectional view along line  2 — 2  of the mold-half in FIG. 1 only selected dimple forming projections are shown. 
     FIG. 3 is an enlarged, partial-sectional view along line  3 — 3  of the mold-half in FIG. 1 only selected dimple forming projections are shown. 
     FIG. 4 is a perspective view of a two-piece golf ball formed using a mold-half of the present invention. 
     FIG. 5 is a cross-sectional view of the golf ball of FIG.  4 . 
     FIG. 6 is a cross-sectional view of a three-piece golf ball formed using the mold-half of the present invention. 
     FIG. 7 is a perspective view of the mold-half of the present invention. 
     FIG. 8 is an enlarged, cross-sectional view along line  8 — 8  of the mold-half in FIG. 7, only selected dimple forming projections are shown. 
     FIG. 9 is an enlarged, partial-sectional view along line  9 — 9  of the mold-half in FIG. 7, only selected dimple forming projections are shown. 
     FIG. 10 is an enlarged partial-sectional view within circle  10  in FIG. 8, only selected dimple forming projections are shown. 
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     Referring to FIGS. 4 and 5, two-piece golf ball  70  formed using a mold-half of the present invention, includes dimples  75  on the surface thereof. The golf ball  70  is made by molding a cover  80  with dimples  75  about a solid core  85 . 
     Referring to FIG. 6, three-piece ball golf ball  90  may be made by molding a cover  95  with dimples  100  around a solid core  110  comprising a center  115  with a mantle layer  120  molded about the outside of the center  115 . 
     Referring to FIGS. 7-9, the mold-half  125  of the present invention comprises a cavity  130 , a land area  135  surrounding the cavity  130 , a recessed circumferential ledge  140  adjacent the cavity  130 , and a plurality of vents  145  spaced from the cavity  130 . Other than the vents the upper surface of the land area is continuous and uninterrupted. The recessed circumferential ledge  140  also defines a wall  150  (best seen in FIG. 9) which extends vertically and circumferentially between the vents  145 . Generally, cavity  130  is hemispherical in shape and is centered within the mold-half  125 . The hemispherical cavity  130  is placed and configured within mold-half to allow the cavities of a pair of mold-halves  125  to form an unobstructed spherical cavity when joined together. 
     The land area  135  is dimensioned and configured to facilitate mating the mold-halves by providing a structurally stable contact area between the mold-halves. Additionally, the mold-half  125  is further configured to form a circumferential ledge  140  and wall  150  adjacent the cavity  130 . The land area  135  further includes a plurality of vents  145  comprising radially extending channels within the upper surface of the land area  165 . The operative dimensions and configuration of these features allow the cavity  130 , circumferential ledge  140 , wall  150 , and vents  145  to cooperate and form a system for controlling the release of excess material from the mold cavity  130 . 
     Referring again to FIG. 7, a surface  155  of the cavity  130  is textured with dimple forming projections  160 , which produce a dimple pattern on the golf ball. The vents  145  are isolated or spaced from each other within the upper surface  165  of the land area  135 . The angle β represents the spacing of vents  145  around the land area  135 . The land area  135  further includes a sloped surface  170  which is situated above a mold-half projection  175 . Referring to FIGS. 8 and 9, the spatial relationship between the upper surface  165  of the land area, a vent sidewall  145 , the sloped portion of the land area  170  and the mold-half projection  175  are best seen. 
     Referring to FIG. 10, an enlarged view of the mold-half  125  shows vertical dimensions V 1  and V 2 , horizontal dimensions L 1  and L 2 , and angle α. Dimension V 1  represents the distance from the upper surface  165  of the land area to the recessed circumferential ledge  140 . Dimension L 1  represents the length of the ledge  140 . Dimension V 2  represents the distance from the upper surface  165  of the land area to the bottom of each vent  145 . Dimension L 2  represents the shortest length of each vent  145 . Angle a represents the declination of the sloped portion  170  of the land area as measured from the horizontal plane containing the upper surface  165  of the land area. 
     During use, two mold-halves  125  are joined together so that the hemispherical cavity  130  of each mold-half combines to form a single spherical cavity for molding a mantle layer or cover around a golf ball subassembly. Prior to assembly of the mold-halves, material is placed within each hemispherical cavity  130  of the mold-half pair. Next, the golf ball center  85  or  115  or core  110  (as shown in FIGS. 5 and 6) is inserted into the cavity  130  of one mold-half  125 . Then, the mold-halves are joined together so that the material is molded around the golf ball center  85 ,  115  or core  110 . 
     During molding, with reference to FIGS. 7 and 10, excess material from the spherical cavity is squeezed through the very thin and narrow annular space or chamber formed by the ledges  140  adjacent the mold-half cavity  130 . The excess material is contacts the vertical wall  150  and moves out of the mold-half via vents  145  located around the circumference of the mold in fluid communication with the chamber created by the ledges. The annular space formed by the recessed circumferential ledges  140  of each mold-half, and the adjacent mold-half vents  145  allow the excess material to escape the cavity  130  in a controlled fashion while preventing significant amounts of unwanted material from solidifying on or near the golf ball. 
     During molding a piece of excess material forms between the golf ball and the vented excess material. The physical dimensions of the piece of excess material are designed and configured to allow its separation from the golf ball without damaging the golf ball cover. According to the preferred embodiment of the present invention, the piece of excess material forms within the annular space created by the recessed ledges  140 . As shown in FIG. 10, each ledge  140  has a horizontal dimension L 1  which is substantially greater than its vertical dimension V 1 . Most preferably, these dimensions are about 0.015 inches and about 0.005 inches, respectively. Additionally, the ratio between the length L 1  of the circumferential ledge  140  and the length of each vent channel L 2  is preferably between about 0.1 and about 0.5, and most preferably about 0.2. Preferably, however, the length of the ledge L 1  should not exceed half the length L 1 +L 2  of the upper surface  165  of the land area. Thus, in the preferred embodiment of the invention the length of the ledge L 1  is less than about 50% of the length L 1 +L 2  of the upper surface  165  of the land area. 
     Further, the vents are sized to provide sufficient volume to transport the excess material out of the mold-half cavity in a controlled manner. As shown in FIG. 7 at least six vents abut the annular space and transport the excess material to the sloped portion  170  of the land area. The vents  145 , preferably, are geometrically identical and are distributed uniformly around the circumference of the land area. In this embodiment, the angle β between vents is about 45 degrees. Referring to FIG. 10, the depth V 2  of each vent channel measured from the top of the upper surface  165  of the land area is about 0.03 inches. Also, the ratio between the depth V 1  of the circumferential ledge  140  and the depth of each vent  145  V 2  is between about 0.1 and 0.2 in this embodiment. The mold-half  125  of the present invention is preferably formed from steel or silicon bronze and coated with mold release to further aid in removing the golf ball from the mold. The invention, however, is not limited to these materials. Thus, the mold-half  125  of this configuration allows a uniform and indirect path for the excess material to exit the mold-half cavity  135  and minimizes mold-half  125  separation. 
     While the above invention has been described with reference to certain preferred embodiments, it should be kept in mind that the scope of the present invention is not limited to these embodiments. The mold-half  125  can be modified to accommodate particular formulations of material which may require modification of the dimensions of the recessed circumferential ledge  140  and vents  145 . Similarly, the number and spacing of the vents  145  may be changed. Also, mold-halves  125  without dimple forming projections  160  may be produced for forming a smooth mantle layer  120  around a golf ball center  115 . And, different surface coatings may be applied to the mold-halves  125  to better facilitate demolding. 
     The embodiments above can also be modified so that some features of one embodiment are used with the features of another embodiment. One skilled in the art may find variations of these preferred embodiments which, nevertheless, fall within the spirit of the present invention, whose scope is defined by the claims set forth below.