Golf ball injection molds

Details Golf ball injection molds Golf ball injection molds

1998-12-03

2001-05-29

Davis, Robert (Department: 1722)

Plastic article or earthenware shaping or treating: apparatus

Distinct means to feed, support or manipulate preform stock...

Opposed registering coacting female molds

C264S278000, C264S279100, C425S120000, C425S573000

Reexamination Certificate

active

06238194

ABSTRACT:

BACKGROUND OF THE INVENTION
1. Field of the Invention
This invention relates to an injection mold for the manufacture of golf balls and more particularly, to an injection mold for the consistent and efficient molding of golf balls having a concentric, uniform thin gage cover.
2. Prior Art
Golf balls having a core enclosed in a cover are conventionally manufactured by injection molding cover stock over the surface of a core in a split mold. The core is placed in the cavity of the split mold. The core is typically supported in place by support pins so that a space is defined between the cavity-defining mold surface and the core surface. The cover stock is injected into the space to mold the cover.
One exemplary prior art injection mold is illustrated in
FIGS. 8 and 9
, which are elevational and horizontal views in cross section of the mold, respectively. The injection mold generally designated at
1
includes upper and lower mold sections
1
a
and
1
b
which define a spherical cavity
2
therein by their wall surface
2
a
when mated at a parting plane or line P which extends coplanar with the equator of the cavity
2
. It is understood that the cavity-defining wall surface
2
a
is provided with small projections for indenting dimples on the ball being molded, that is, a negative dimple pattern, though not shown.
As shown in
FIG. 9
, the mold
1
includes a main runner
6
which is disposed through the mold body in fluid communication with an injection molding machine, an annular runner
4
connected to the main runner, and a plurality of, eight in
FIG. 9
, molding material injecting gates
5
disposed through the mold body and radially extending from the annular runner
4
to the cavity
2
whereby molding material is injected from the molding machine to the cavity through the runners and gates. The mold
1
further includes a pair of vertically extending holes
8
disposed through the mold body at the north and south poles of the cavity and a pair of pins
9
received in the holes
8
to define gaps or vents
10
through which gases or volatiles evolving during molding escape to the exterior.
The mold
1
further includes a plurality of, four in
FIG. 8
(total eight in both the upper and lower mold sections), column-like support pins
7
which are positioned on a circle about the hole
8
and circumferentially spaced apart by an angle of 90°, for example, for supporting a core
3
in the cavity
2
. The support pins
7
each have a center axis perpendicular to the parting plane P coplanar with the cavity equator. The core
3
is held at the center of the cavity
2
by the support pins
7
in vertically opposite directions or from the upper and lower poles.
When a cover is molded over a core using the mold of the above construction, there often arise problems including eccentricity and difficulty to form a thin gage cover.
More particularly, the core is an elastic body as is the cover, the cover stock is injected under as high a pressure as 1,400 to 2,000 kg/cm
2
, and the gates are in a planar arrangement at the parting plane. Because of the high injection pressure and the lateral or equatorial direction in which the cover stock is injected toward the core, the core is deformed and expanded in vertical or polar directions into an elliptic or rugby ball shape. Consequently, the space between the core and the wall surface of the mold near the gates is enlarged while the space near the poles is narrowed.
At the end of injection, the cover stock partially solidifies before the core restores to its original spherical shape. Consequently, a cover of varying gage would be formed on the core. Particularly when a cover with a thin gage of 1 mm or less is formed around the core, the core can be locally exposed at the ball surface.
Similar problems occur even when a cover with a relatively thick gage is injection molded. Additionally, the load applied to the support pins by the injection pressure is considerably increased, resulting in radial misalignment.
SUMMARY OF THE INVENTION
Therefore, an object of the invention is to provide a novel and improved injection mold for golf balls in which support pins are disposed relative to gates so that a cover of a uniform gage can be injection molded over a core, without radial misalignment of the core, to produce a golf ball having a smooth molded surface free of weld lines and molding defects.
According to the invention, there is provided an injection mold for golf balls defining therein a spherical cavity having an equator, opposite poles and a center, the mold having a parting plane extending substantially coplanar with the equator of the cavity. A plurality of molding material injecting gates are arranged in the mold at or near positions around the cavity equator for injecting a molding material into the cavity therethrough. A plurality of retractable core support pins are disposed in the mold at areas other than the cavity equator and poles so that the core support pins may be moved toward and away from substantially the cavity center.
In one preferred embodiment, the core support pins are provided in plural pairs, and the inner ends of the core support pins in each pair are opposed to each other with respect to the cavity center. The mold may further include an additional pair of molding material injecting gates arranged in the mold substantially at the cavity poles, the core support pins being disposed near north and south latitudes 45°. Each core support pin is preferably located on a longitudinal line extending on the cavity-defining surface substantially at the middle between adjacent ones of the gates around the cavity equator. The mold may further include a corresponding plurality of holes for receiving the plurality of support pins therein, whereby gas vents are defined between the holes and the support pins.
A golf ball molded using the mold of the invention is also contemplated herein.
The invention ensures efficient molding of golf balls having a cover of a uniform gage and free of radial misalignment and also having a smooth molded surface.
With the above-described construction, the core is held at the center of the cavity, the load applied to the support pins is reduced, and gases or volatiles evolving during molding are quickly discharged to the exterior at positions where the molding material converges. Then golf balls having a smooth molded surface are efficiently molded without accompanying molding defects such as weld lines.
The three-dimensional arrangement of gates complying with the cavity shape allows the injection pressure to be uniformly distributed over the core and enables a cover with a thin gage of 1 mm or less to be molded to a uniform gage without local variation.


REFERENCES:
patent: 2031786 (1936-02-01), Oldham
patent: 2361348 (1944-10-01), Dickson et al.
patent: 4959000 (1990-09-01), Giza
patent: 5112556 (1992-05-01), Miller
patent: 5407341 (1995-04-01), Endo et al.
patent: 5827548 (1998-10-01), Lavallee et al.
patent: 63-199615 (1988-08-01), None

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