Patent Application
20080203615
This invention generally relates to the manufacture of golf balls, and more particularly, to a single cavity mold for compression molding polyurethane, polyurea, or polyurea/polyurethane hybrid covers over golf ball sub-assemblies.
The present invention relates to an improvement to molds, such as that disclosed in U.S. Pat. Nos. 6,936,205, 7,135,138, 7,041,007, 7,041,245, 6,644,948, and 6,439,873, all of which are assigned to the Acushnet Company and are incorporated herein by reference. A typical multi-cavity mold used for applying a thermosetting cover material is disclosed in U.S. Pat. No. 6,439,873 issued to Marshall.
The covers of today's golf balls are made from a variety of materials, but predominately they are either of a thermoplastic material such as SURLYN® and IOTEK® or a thermoplastic material such as polyurethane. In the past, premium golf balls were covered by a balata material. Balata is a natural or synthetic trans-polyisoprene rubber. Balata covered balls were favored by more highly skilled golfers because the softness of the cover allows the player to achieve spin rates sufficient to more precisely control ball direction and distance, particularly on shorter shots. Balata-covered balls, however, are easily damaged, and thus lack the durability required by the average golfer. Accordingly, alternative cover compositions have been developed in an attempt to provide balls with spin rates and a feel approaching those of balata-covered balls, while also providing higher durability and overall distance.
Ionomer resins have, to a large extent, replaced balata as a cover material. Chemically, ionomer resins are a copolymer of an olefin and an α,β-ethylenically-unsaturated carboxylic acid having 10 to 90 percent of the carboxylic acid groups neutralized by a metal ion, as disclosed in U.S. Pat. No. 3,264,272. Commercially available ionomer resins include, for example, copolymers of ethylene and methacrylic or acrylic acid, neutralized with metal salts. Examples of commercially available ionomer resins include, but are not limited to, SURLYN from DuPont de Nemours and Company, and ESCOR®. and IOTEK® from Exxon Corporation. These ionomer resins are distinguished by the type of metal ion, the amount of acid, and the degree of neutralization. However, while ionomer-covered golf balls possess virtually cut-proof covers, the spin and feel are inferior compared to balata-covered balls.
Polyurethanes have also been recognized as useful materials for golf ball covers since about 1960. The resulting golf balls are durable and, unlike ionomer-covered golf balls, polyurethane golf ball covers can be formulated to possess the soft “feel” of balata-covered golf balls. U.S. Pat. No. 4,123,061 teaches a golf ball made from a polyurethane prepolymer formed of polyether with diisocyanate that is cured with either a polyol or an amine-type curing agent. U.S. Pat. No. 5,334,673 discloses the use of two categories of polyurethane available on the market, i.e., thermoset and thermoplastic polyurethanes, for forming golf ball covers and, in particular, thermoset polyurethane-covered golf balls made from a composition of polyurethane prepolymer and a slow-reacting amine curing agent, and/or a difunctional glycol.
Polyureas have also been proposed as cover materials for golf balls. For instance, U.S. Pat. No. 5,484,870 discloses a polyurea composition comprising the reaction product of an organic diisocyanate and an organic amine, each having at least two functional groups. Once these two ingredients are combined, the polyurea is formed, and thus the ability to vary the physical properties of the composition is limited.
Conventionally, golf balls are made by molding a cover around a core. The core may be wound or solid. A wound core typically comprises elastic thread wound about a solid or liquid center. Solid cores typically comprise a single solid piece center or a solid center covered by one or more mantle or boundary layers of material. Wound cores may also include one or more mantle layers.
The cover may be injection molded, compression molded, or cast over the core. Injection molding typically requires a mold having at least one pair of mold cavities; e.g., a first mold cavity and a second mold cavity, which mate to form a spherical recess. In addition, a mold may include more than one mold cavity pair.
In one exemplary injection molding process, each mold cavity may also include retractable positioning pins to hold the core in the spherical center of the mold cavity pair. Once the core is positioned in the first mold cavity, the respective second mold cavity is mated to the first to close the mold. A cover material is then injected into the closed mold. The positioning pins are retracted while the cover material is flowable to allow the material to fill in any holes caused by the pins. When the material is at least partially cured, the covered core is removed from the mold (demolded).
Compression molds also typically include multiple pairs of mold cavities, each pair comprising first and second mold cavities that mate to form a spherical recess. In one exemplary compression molding process, a cover material is pre-formed into half-shells, which are placed, respectively, into each of a pair of compression mold cavities. The core is placed between the cover material half-shells and the mold is closed. The core and cover combination is then exposed to heat and pressure, which cause the cover half-shells to combine and form a full cover.
Casting is the most common method of producing a urethane or urea layer on a golf ball. Casting processes also typically utilize pairs of mold cavities. In a casting process, a cover material is introduced into a first mold cavity of each pair. A core is then either placed directly into the cover material or is held in position (e.g., by an overhanging vacuum or suction apparatus) to contact the cover material in what will be the spherical center of the mold cavity pair. Once the cover material is at least partially cured (e.g., to a point where the core will not substantially move), the cover material is introduced into a second mold cavity of each pair, and the mold is closed. The closed mold is then subjected to heat and pressure to cure the cover material thereby forming a cover on the core. The mold cavities typically include a negative dimple pattern to impart dimples on the cover during the molding process.
Presently, urethane covered golf balls are formed by compression molding in multiple cavity molds. Some of the problems that exist in multi-cavity molds are inherent in the inability to heat or cool each cavity uniformly. This is primarily caused by the uneven contact the fluid makes as it travel through the mold frame. The first cavity in a series is often heated or cooled at a different rate than the last cavity in a series. Also, in multi-cavity molds, some of the cavities wear out prior to others creating inconsistent product quality in the production line.
Currently, the closure of the mold is accomplished by vertical pistons, torque clutch/motor assembly, and assembly of belts, pulleys, and torque bits. Typical cavity molds have multiple bolts to fasten the mold halves together. The process is reversed during the disassembly process. Significant torque variation is present due to the nature of dry assembly and mechanical wear. These assembly/disassembly machinery modules are a root cause of parting line thickness variation and a major source of surface contamination on the golf ball. Golf ball surface contamination accounts for a significant defect generation. The wear and tear of mold bolts, assembly, and disassembly are the major contributor.
It would be a significant improvement of the prior art to have a mold of only a single cavity type design and one that eliminates the need for bolts. In addition to greatly increasing the consistency of heating and cooling of the mold, the single cavity would allow for a more consistent shot size and eliminate the constant monitoring of flow. In present molds, the bolts typically wear at different rates and cause a parting line thickness variation due to bolt force degradation. The elimination of bolts may be accomplished by incorporating the use of compression springs and/or materials with spring like memory.
The present invention provides for a single cavity molding device wherein upon placement of a golf ball sub-assembly into the cavity mold and then a urethane or urea cover material cast into the cavity mold, a cover is formed herein by compression molding. The molding device utilizes a pair mold halves, each having a backing plate and mold frame and they each house a hemispherical cavity mold. An object of the invention is to provide for compression molding using only a single cavity and without the need of bolts to secure the mold halves together. The invention utilizes a plurality of clamping pins, each pin having its top portion reciprocally disposed in a recess of the backing plate of the top mold. Double spring Belleville washers are integral to the top portion of each clamping pin and when an outside force is applied, the washers are compressed placing the device into a controlled state of tension. To maintain the compressive force for the duration of the molding cycle, the clamping pins, which have cutout sections in the lower area, are locked in the tension state by a pair of sliding retainers that are positioned in channels of the lower backing plate. Each retainer comprises a pair of engagement loops of a size and shape for locking with the cutout sections of the pins. When an outside source provides a horizontal force to the retainers, the engagement loops of the retainers slide freely within the channel and into contact with the cutout sections of the clamping pins which have been lowered into position by the vertical force upon them, wherein the clamping pins are locked in a tensioned state for the duration of the molding cycle. To release the mold-halves, a subsequent vertical force is applied to the top of the clamping pins wherein they are moved out of the locking relationship with the engagement loops, and with a coordinating horizontal force applied, the retainers are moved away from the pins, releasing the compressive force on the mold-halves.
The present invention provides for a molding device that eliminates the use of bolts to clamp the mold halves during the process, and the subsequent uneven force applied throughout the mold. The uneven application of force is a main cause of uneven thickness of cover material, especially in the application of polyurethane material.
Another object of the invention is the molding of urethane, or polyurea covers.
The molding device of the present invention provides for alignment pins, a diamond shaped pin and a round pin, to allow for quick connection and disconnection of the mold-halves.
The present invention provides a method for molding a cover on a golf ball sub-assembly, wherein all procedures involving wrenches and the like are removed from the process. The material to form the cover is placed into the mold cavity as is the golf sub-assembly (core or core with at least one layer). The mold halves are combined without any mechanical tools. A force is then applied to the device causing Belleville washers on the top portion of the clamping pins to compress the device to provide for the compression necessary along with the application of heat to form the golf ball. Upon completion of the molding of the cover on the ball, the device is cooled and the compressive force released, wherein the device may be opened to remove the golf ball. The compressive force is held in place such that a minimum force of 384 lbs is attained and held. Upon the completion of the molding process, the mold is opened by applying a vertical force on the Belleville washers and then a horizontal force to slide the retainers out from the locking position. The mold may be opened and the golf ball released for further processing such as buffing, imprinting etc.
a is a front elevational view of the diamond shaped alignment pin.
b is a side elevational view of the diamond shaped alignment pin.
c is a bottom plan view of the diamond shaped alignment pin.
There are conventional multi-cavity mold frames such as referenced by U.S. Pat. No. 6,439,873, which are used for casting a layer for a golf ball. Typically, these type molds are used to cast polyurethane covers on a golf ball sub-assembly (not shown). The Acushnet Company (assignee of this application) has for many years used multi-cavity molds that provide four cavities in a mold frame. A significant problem of these compression molds is the inability to achieve equally distributed positive clamping force on the golf balls being formed. The closure of these type molds is accomplished by using vertical pistons, torque clutch/motor assembly, and an assembly of belts, pulleys and torque bits. Each four cavity mold has four bolts to fasten the mold halves together. The constant bolting and unbolting to open and close the mold halves causes an uneven wear and tear of the bolts creating a significant variation in torque between the bolts, resulting in a major source of contamination as well as variation of cover thickness and parting line fluctuations.
The present invention has adopted a unique single cavity precision assembly whereby bolts are eliminated and the product deficiencies and/or maintenance problems caused by premature bolt wear are curbed. This concept physically reduces the assembly/disassembly mechanism relating to vertical clamp, horizontal push cylinders, and bolts. A significant benefit from eliminating bolts, is the removal golf ball surface contamination and thickness variation, which is a by-product resulting from thread wear of the bolts.
As shown in
Four cylindrical openings 28 are provided on the top surface 25 of the upper backing plate 21 through which a vertical compressive force is applied to the device 20 (by an source not shown). Cross-sectional views of the device 20 are provided on
In addition to the double Belleville washer springs 45, each clamping pin 33 includes a cutout sections 60 located at the bottom portion 59 of the pin 33. The cutout sections 60 are instrumental for the locking mechanism of the device 20. The locking of the device 20 requires a pair of sliding retainers 36, as shown in
Since the device does not utilize bolts to position and connect the mold halves 20a and 20b and wherein the vertical and horizontal forces are robotically applied, the precision assembly concept of the present invention is easily adaptable to be processed by a high speed assembly line. An engagement groove 35 is shown in
To aid in the high speed quick connecting of the mold halves 20a and 20b, a diamond shaped alignment pin 42 and a round alignment pin 43 are used as shown in
It will be understood that the claims are intended to cover all changes and modifications of the preferred embodiments of the invention, herein chosen for the purpose of illustration, which do not constitute a departure from the spirit and scope of the invention.
