U.S. patent application number 09/213153 was filed with the patent office on 2001-11-08 for method of molding a layer around a body.
Invention is credited to BRUNE, GARY J..
Application Number | 20010038167 09/213153 |
Document ID | / |
Family ID | 22793938 |
Filed Date | 2001-11-08 |
United States Patent
Application |
20010038167 |
Kind Code |
A1 |
BRUNE, GARY J. |
November 8, 2001 |
METHOD OF MOLDING A LAYER AROUND A BODY
Abstract
A method of molding a layer around a body within a mold, in
which the body is positioned within a mold cavity defined by
opposing mold portions of the mold, to leave a cavity space between
the body and the mold portions at least partially surrounding the
body. Layer material is injected into the cavity space around the
body when the mold portions are in a partially open position. The
mold portions are compressed towards each other to a compression
molding position to compression mold the layer material around the
body.
Inventors: |
BRUNE, GARY J.; (LAKEVILLE,
MA) |
Correspondence
Address: |
PENNIE AND EDMONDS
1667 K STREET N W
WASHINGTON
DC
20006
|
Family ID: |
22793938 |
Appl. No.: |
09/213153 |
Filed: |
December 17, 1998 |
Current U.S.
Class: |
264/278 ;
264/294; 425/129.1 |
Current CPC
Class: |
B29C 45/561 20130101;
B29C 2045/563 20130101; B29C 45/14073 20130101; B29L 2031/545
20130101; B29C 45/14819 20130101 |
Class at
Publication: |
264/278 ;
264/294; 425/129.1 |
International
Class: |
B29C 045/14 |
Claims
What is claimed is:
1. A method of molding a layer around a body within a mold,
comprising: (a) positioning a body within a mold cavity defined by
opposing mold portions of the mold to leave a cavity space between
the body and the mold portions at least partially surrounding the
body; (b) injecting layer material around the body into the cavity
space when the mold portions are in a partially open injection
molding position; and (c) compressing the mold portions towards
each other to a compression molding position to compression mold
the layer material around the body.
2. The method of claim 1, further comprising: (a) placing a support
member against the body to hold the body in a predetermined
position within the mold cavity during the injecting of the layer
material; and (b) retracting the support member from the body once
sufficient layer material has been injected to maintain the body
substantially in the predetermined position.
3. The method of claim 2, wherein the support member comprises a
plurality of retractable pins.
4. The method of claim 2, wherein the support member is retracted
before the layer material contacts the support member.
5. The method of claim 1, wherein the layer material is injected to
fill at least about 40% of the cavity space before the compressing
of the mold portions is commenced.
6. The method of claim 5, wherein the layer material is injected to
fill at least about 80% of the cavity space before the compressing
of the mold portions is commenced.
7. The method of claim 1, further comprising maintaining the mold
portions at a substantially constant temperature throughout the
injection and compression molding of the layer material.
8. The method of claim 1, further comprising maintaining the mold
portions at a temperature below the freezing point of the layer
material during the injection and compression molding of the layer
material.
9. The method of claim 1, wherein the layer material is injected at
a plurality of locations into the cavity space.
10. The method of claim 1, wherein the layer material is injected
and compression molded to substantially completely encapsulate the
body.
11. A method of molding a layer around a body within a mold,
comprising: (a) positioning a body within a mold cavity defined by
opposing mold portions of the mold to leave a cavity space between
the body and the mold portions at least partially surrounding the
body; (b) injecting layer material around the body into the cavity
space; (c) moving the mold portions away from each other during the
injection of the layer material to a partially open position to
leave a vent space therebetween; (d) venting air through the vent
space during the injection of the layer material; and (e)
compressing the mold portions towards each other to a closed
position to compression mold the layer material around the
body.
12. The method of claim 11, wherein the injecting of the layer
material comprises injecting the layer material into the mold
cavity: (a) with the mold portions closed around the cavity in a
closed injection molding position, and (b) subsequently with the
mold portions in the partially open injection molding position.
13. The method of claim 11, wherein the injecting of the layer
material comprises injecting the layer material to produce: (a) a
first pressure within the cavity space when the injection
commences, and (b) thereafter a second pressure within the cavity
space; wherein the first pressure is insufficient to separate the
mold portions and the second pressure is high enough to move the
mold portions to the partially open position.
14. The method of claim 13, wherein the material is injected into
the cavity from a location between the mold portions.
15. The method of claim 14, further comprising forming the opposing
mold portions to comprise first and second mold halves, each
defining a corresponding substantially hemispherical portion of the
mold cavity and together defining a substantially spherical mold
cavity.
16. The method of claim 11, further comprising: (a) biasing the
mold portions towards each other with a first force during the
injection molding; wherein compressing of the mold portions
comprises: (b) biasing the mold portions together with a second
force that is at least about 50% greater than the first force.
17. A method of manufacturing a golf ball, comprising: (a)
positioning at least a portion of a golf ball core within a mold
cavity defined by opposing mold portions to leave a cavity space
between the portion of the core and the mold portions at least
partially surrounding the portion of the core; (b) injecting layer
material into the cavity space around the portion of the core when
the mold portions are in the partially open injection molding
position; and (c) compressing the mold portions towards each other
to a compression molding position to compression mold the layer
material around the portion of the core.
Description
BACKGROUND OF THE INVENTION
[0001] Golf balls are typically comprised of a cover that is
injection molded or compression molded around a golf ball core and
which may include one or more wound or solid layers and also a
liquid or solid center. Also, the individual layers within the
cover are generally either compression or injection molded.
[0002] Injection molding is generally conducted between two mold
halves that together define a mold cavity in which the core is
supported with fixed or retractable pins. In some processes, such
as disclosed in U.S. Pat. No. 5,147,657, the support pins are
retractable. Resinous cover material is injected at high pressures
into the mold cavity, around the core. The retractable pins are
withdrawn from the cover material when it is solid enough to
support the core, yet soft enough to fill pin holes remaining where
the pins once were as further material is injected.
[0003] Injection molding methods are conducted with the mold
closed. Injection molding generally takes place with plastic
pressures upwards of about 12,000 psi. These high pressures tend to
deform the golf ball core by compressing portions thereof which are
disposed adjacent the injection ports, causing portions of the core
disposed away from the ports to extend. Also, injection molding
equipment typically includes extremely small vents through which
air contained within the mold cavity may exit as molding material
is injected. The very limited venting speed achievable through
these vents can limit the injection speed of the cover material or
layer material.
[0004] Generally, the injected material is injected from more than
one port around the core to speed the injection process. Where
material flowing from the various ports meet, weld lines, or knit
lines, can be formed, resulting in discontinuities and residual
stresses across the weld lines. This produces poor finishes with
poor definition of features that are molded into the layer or
cover, such as dimples. Golf ball material failures also tend to
occur at the weld lines after repeated use of the golf ball.
[0005] In addition, due to friction between the injected material
and the mold cavity and core, the material catches at various
locations on the mold halves and core during its injection,
creating more internal stresses and further decreasing the
homogeneity of the molded material. These stresses also tend to
produce lower quality finishes and areas that are more prone to
structural failure.
[0006] As shown in U.S. Pat. No. 4,501,715, covers have also been
compression molded about golf ball cores. In this technique,
previously molded hemispheres are placed around a core to form a
shell. The assembly is then placed between two compression mold
halves, which are then heated and pressed together. The shells are
often thickest at their deepest point to enhance good surface
formation and evacuation of entrapped gases.
[0007] In compression molding, neither pins or injection ports or
gates are required, and details on the molded product, such as
dimples, are generally visually significantly sharper than those
resulting from injection molding. Compression molding, however,
does necessitate the added step of molding the half shells before
they are compression molded around the core. In addition, the
finished half shells must be pre-aligned within the compression
mold halves by hand or by machine, and a weak point results at the
parting line where the material from the two shells has melted and
flowed together.
SUMMARY OF THE INVENTION
[0008] The invention provides fast cycles for molding a layer
around a body, preferably a golf ball core, with the finish quality
of compression molding. Although this invention may be employed to
mold any layer about a body, in the field of golf balls this layer
may be a cover, for instance, or a mantle layer within the golf
ball core, where the internal body comprises one or more inner
layers of the core.
[0009] Layer material is injected around the body within a mold
cavity that is formed by injection mold portions. The layer
material is injected when the mold portions are partially open,
leaving a space therebetween. This space allows air to vent at a
rapid rate from the cavity and permits the rapid injection of the
layer material into the cavity and thus short cavity fill times.
The mold portions are preferably moved from an initial closed
position to their partially open position by the pressure created
within the mold cavity by the injected layer material.
[0010] The mold portions are then closed together to compression
mold the layer material about the body. In addition, the
compression molding improves packing of the material into the
minute shape-features of the mold cavity, producing a sharper
finish of the molded product.
BRIEF DESCRIPTION OF THE DRAWINGS
[0011] FIG. 1 is a perspective view of an open mold constructed
according to the invention;
[0012] FIG. 2 is a diagrammatical cross-sectional view of the mold
in a closed position;
[0013] FIG. 3 is a diagrammatical cross-sectional view of the mold
in a partially open position during an injection molding step;
[0014] FIG. 4 is a diagrammatical cross-sectional view of the mold
in the partially open position with support pins retracted;
[0015] FIG. 5 is a diagrammatical cross-sectional view of the mold
in a closed position after a compression molding step;
[0016] FIG. 6 is a diagrammatical perspective view of another lower
mold half constructed according to the invention;
[0017] FIG. 7 is a diagrammatical perspective view of yet another
lower mold half constructed according to the invention; and
[0018] FIG. 8 is a diagrammatical cross-sectional view of the mold
of FIG. 7 in a closed position.
DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS
[0019] Referring to FIGS. 1 and 2, a body, which is a golf ball
core 10 in the preferred embodiment, is placed into a mold 12. The
mold 12 includes opposing mold portions, defined by two mold halves
14. Each mold half 14, in turn, defines a corresponding
substantially hemispherical cavity 16 and has a mating surface 18
surrounding the hemispherical cavity 16 and facing the opposing
mold half 14. When the mold halves 14 are brought together with the
mating surfaces 18 in full contact with each other, the two
hemispherical cavities 16 together define a substantially spherical
mold cavity 20. Inner surfaces 22 of the mold halves 14, defining
the hemispherical cavities 16, include a negative dimple pattern
with a plurality of protrusions 23 that form dimples in the
finished golf ball cover.
[0020] A fixed vent pin 24 extends through each mold half 14 to the
edge of the mold cavity 20. The diameter of the vent pins 24 is
slightly smaller than the diameter of the bores 26 which they
penetrate, providing a vent 27 defined by a gap of preferably
0.0002 to 0.0005 inches formed between the vent pins 24 and the
bores 26. The vent 27 thus extends through each mold half 14 to
communicate the cavity 20 with the exterior for venting air from
the cavity 20 during molding cycles, particularly while the mold 12
is closed. Surface 31 of the vent pins 24 face the mold cavity 20
and are preferably shaped to form a dimple in a cover molded
therein.
[0021] Support pins 28 extend through each mold half 14, into the
mold cavity 20. The support pins 28 are configured to support the
core 10 in a predetermined position within the mold cavity 20 when
the core 10 is placed against them. The preferred predetermined
position is with the core 10 centered within the mold cavity 20, to
produce a golf ball with a centered core. The preferred embodiment
has ten parallel support pins 28, five in each mold half 14. Other
types of support members may also be employed in alternative
embodiments.
[0022] The mold 12 of the preferred embodiment has four injection
gates 29 configured to receive injection nozzles 30. The gates 29
are preferably spaced at equal angles from each other around the
mating surfaces 18. In this case, as there are four gates 29, they
are spaced at about 90.degree. from each other. When the mold 12 is
closed, with the mold halves 14 fully contacting each other, the
gates 29 communicate the mold cavity 20 to the exterior of the mold
12, and the nozzles 30 can seat tightly in the gates 29.
Preferably, the nozzles 30 can be moved into the gates 29 after the
mold halves 14 are pressed together.
[0023] The nozzles 30 are configured to inject molten layer
material, which in the preferred embodiment is cover material 32.
The cover material 32 is injected into the mold cavity 20 through
the gates 29 at a parting line 34 where the mold halves 14 abut.
The cover material 32 is heated at least to its melting point in a
reservoir, and is then forced by a screw through the injection
gates 29, preferably at about 12,000 psi. A hot runner system is
preferably employed, where the nozzles 30 are maintained above the
melting temperature of the cover material 32, while the mold is
maintained below the melting temperature of the material 32. The
flow of the molten cover material 32 may be positively stopped
after the cavity 20 is filled, and the cover material 32 is
maintained in a molten state in runners that lead to the mold
cavity 20. The hot runner system reduces or eliminates any sprues
attached to the molded part.
[0024] The cover material is preferably a material such as
engineering type resins, including ionomer resins, such as resins
manufactured by Dupont under the trade name SURLYN.RTM., and
synthetic balata, a type of polyisoprene which is among the softest
of cover materials used in modern golf balls.
[0025] Referring to FIG. 2, the mold halves are held together,
preferably by a hydraulic press, with a first force. Preferably,
this first force is about 40 kN for a molding machine that includes
four individual golf ball molds 12, although the molding machine
preferably includes 4-8 mold cavities.
[0026] FIG. 2 shows the core 10 held concentrically within the mold
cavity 20 by the support pins 28. As the cover material 32 is
injected in to the mold cavity 20, the material 32 flows around the
core 10, through a space 36 remaining between the core 10 and the
inner surfaces of the mold halves 14, and air vents from the cavity
20 through vents 27.
[0027] The injecting of the cover material 32 raises the pressure
within the mold cavity 20. As the pressure builds, the mold halves
14 are allowed to separate such that the mold is in a partially
open position, as shown in FIG. 3. A space 38 remains between the
mold halves 14 in this position. This space 38 is preferably small
enough to prevent the material 32 from flashing through the space
38, thus keeping the material 32 contained within the mold cavity
20. Preferably, no extra cover material 32 is injected beyond that
necessary to fill the mold when it is closed. Space 38 is
preferably between about 0.0015 inches and about 0.0035 inches, and
more preferably about 0.0018 inches. The space 38 allows air, but
not material 32, to vent rapidly from the mold cavity 20,
preventing pressures within the cavity 20 from becoming excessive
and from slowing the injection process. The pressure within the
cavity 20 preferably never reaches the magnitude of normal
pressures reached in traditional injection molding methods, and
thus allows the cover material 32 to flow more quickly.
[0028] FIG. 3 also shows cover material fronts 40 as the material
32 fills the space 36 remaining in the cavity 20. Where these
fronts 40 contact each other, they form weld lines. At this stage
in the molding process, as in injection molding methods, the cover
material 32 is discontinuous across the weld lines.
[0029] Injection of cover material 32 is preferably continued from
between the mold halves 14, with the mold 12 partially open. When
sufficient cover material 32 has been injected into the mold cavity
20 to support the core 10 substantially centrally in the mold
cavity 20, in the preferred predetermined position, the support
pins 28 are retracted from the core 10 and the cavity 20, as shown
in FIG. 4.
[0030] Referring to FIG. 5, the mold halves 14 are then compressed
towards each other, back to the closed mold position, to
compression mold the cover material 32, which is preferably still
substantially in a molten state. This compression step is
preferably conducted by pressurizing the hydraulic press to force
the mold halves together with a force of about 80 kN. Preferably
this force is at least about 50% greater than the force biasing the
mold halves together during the injection of the material, and more
preferably it is about twice the magnitude of the force during the
injection of the material 32. The compression molding of the cover
material 32 relieves a significant portion of the internal stresses
therein, including those created at weld lines and by friction with
the core 10 and the inner surfaces of the mold halves 14. This
compression fuses the cover material 32 at weld lines and also
significantly reduces imperfections in the cover material 32 as a
whole and the discontinuities at the weld lines. In processes in
which the support pins 28 are retracted after the material 32 has
flowed around them, voids remaining where the support pins 28 had
once been will be closed by the compression.
[0031] Another advantage provided by the compression step is the
better packing achieved of the material 32 into the features of the
mold cavity, compared to simple injection molding. For instance,
the material 32 is packed more completely into corners around the
protrusions 23 that form the dimples in the finished golf ball
cover. This provides an improved finish to the molded product by
forming sharper dimple edges.
[0032] Preferably, the compression step is commenced once the
material 32 has been injected to fill at least about 40% of the
cavity 20. More preferably, the cover material 32 is injected to
fill at least about 50%, and most preferably at least about 80% of
the cavity 20 before the compression is commenced, requiring little
or no further injection of cover material 32 once the mold 12 is
closed.
[0033] The mold 12 is preferably maintained at a substantially
constant temperature of between about 40 and 90.degree. F., most
preferably about 50.degree. F. This can be achieved by flowing a
fluid such, as cool water, around or through passages within the
mold halves 14. This temperature should be below the freezing point
of the cover material 32. Thus, the material 32 begins to solidify
as soon as it is injected. The golf ball can subsequently be
removed from the mold 12 with a completed cover around its core
10.
[0034] FIGS. 6 and 7 show a more preferred embodiment of lower mold
halves 42 and 44, each for molding two covers according to the
invention. The mold halves 42 and 44 are configured to mate with
corresponding upper mold halves to form the cover around the cores.
Mold halve 42 of FIG. 6 employs a hot-to-cold runner system, in
which nozzle 46 is placed against the mold half 42 to inject cover
material 32 through internal, hot runner 48 within the mold half 42
to runner 50 in the parting line between the upper and lower mold
halves. Runner 50 feeds ten injection gates 52 surrounding each
dimpled half-mold cavity 54.
[0035] The mold half 44 of FIG. 7 uses a cold runner system, in
which nozzle 56 injects the cover material 32 directly into a
runner system of runners 58 that is disposed completely in the
parting line of mold during the molding process. As in mold half
42, the runners 58 lead into two mold cavities 59 with dimples 23
through gates 52. FIG. 8 shows the lower mold half 44 closed
against upper mold half 60 at the start of the injection of the
cover material 32 through gates 52 into the mold cavity 59, before
moving the mold halves 44 and 60 to the partially open
position.
[0036] As a result of the invention, residual stresses in the
molded layer are reduced. The finished molded material is more
homogenous than in layers that are purely injection molded around
cores, and weld lines are strengthened.
[0037] With the present invention, it has been found that molded
balls release better from the mold halves after the molding is
complete than from similar mold halves after a pure injection
molding process. Also, the time needed to inject the material is
reduced by 15% when molding a golf all cover around a core, and by
32% when molding a mantle layer around a more internal part of the
core. These time reductions are primarily due to the rapid venting
achieved by partially opening the mold.
[0038] Also, the adhesion of the molded layer to the body molded
around is better in runs made according to the invention than in
the straight injection molding. Also, better concentricity of the
body within the molded layer was achieved. Furthermore, the surface
produced had sharper details, improving aesthetic appearance among
other things.
[0039] One of ordinary skill in the art can envision numerous
variations and modifications. For example, the mold may be opened
by a controlled action of the hydraulic press instead of merely by
the pressure produced in the mold cavity by the injected material.
Alternatively, the initial closing force produced on the mold
halves can be held at about 80 kN, then reduced to about 40 kN to
allow the mold 12 to partially open, and then increased again to
about 80 kN to compression mold the layer material. Also the mold
cavity may be held open in a fixed position until the start of the
compression step. All of these and other modifications are
contemplated by the true spirit and scope of the following
claims.
* * * * *