Golf ball retractable pin mold

Abstract: The retractable pin mold has a gate valve (160',162',164',166') positioned at the pole of the core. The retractable pin (238,240,250) for an injection mold machine used for molding golf balls has a frictionless bushing means (268) affixed at its outer end which is slidable along a shaft (260). The shaft (260) and the frictionless bushing means (268) are coaxial and perpendicular to the retractable pin (238,240,250). The pin head (256) is shaped substantially like a dimple.

Description: This invention relates to an injection mould machine and, more particularly, to an improved retractable-pin mould used for golf balls. Conventionally, golf ball covers are made by either compression moulding two preformed half shells about a core or by injection moulding of fluid cover stock material about a core. Injection moulding uses a mould equipped with retractable pins that hold the core in place while the fluid cover stock 1 fills the void between the core and the inside wall of the mould. After the fluid ceases to enter the mould but before the cover stock has completely hardened, the retractable pins are withdrawn while the fluid cover stock is still able to flow and fill the voids left by the pins. Conventionally, the core is either a solid one-piece mass of material or a wound core which comprises a centre wrapped in thin elastic thread. Typically, a solid core is used. In a conventional retractable-pin mould used for golf balls a series of conduits transport the fluid cover stock material to the individual mould cavity. These conduits are referred to as runners and are typically uninsulated. The fluid cover stock material travels through the cold runners and passes into the mold cavity through a series of ports, referred to as gates, which are positioned at the mold parting line. Air inside the mold cavity is displaced by the incoming fluid cover stock and leaves the mold cavity through the bushing around the retractable pins. The retractable pins center the core in the mold cavity and position the core in a generally vertical plane. Conventionally, the fluid cover stock material enters the mold cavity in a horizontal plane and exerts forces on the core in the horizontal plane. The core must be centered in the finished ball since cores that are off-center produce an unplayable ball. This means that the flow of cover stock through the gates and the position of the gates around the mold cavity must be balanced to maintain equal and opposite force against the core so as not to move the core off center. Additionally, the retractable pins must be able to resist force from a horizontal direction even though the pins are positioned generally in a vertical plane. The horizontal forces exerted on the pins due to the horizontal direction of movement of the incoming fluid cover stock material tend to cause substantial wear to the pins and pin bushings. Such damages to the pins cause pin flash and pin marks in the finished ball, both of which are undesirable in a high-quality golf ball. This wear on the pins and pin bushings creates a need to replace pins and bushings after a period of time. This repair in turn leads to downtime with the molds. In conventional retractable pin molds, the, vertically oriented pins detract from the cosmetic quality of the ball. When the pin is withdrawn, the head of the pin typically forms one of the dimples in the cover. Thus, the shape of the head of the pin determines the shape of the dimple. Since pins conventionally enter the cavity in a generally vertical plane, in order to have a good grip on the spherical surface of the core the head of each pin is cut on an angle comparable to the tangent line on the surface of the core at the point of contact between the pin head and the core. The dimple formed by the head of the pin is elliptical because the head of the pin is elliptical, pins being generally circular in cross-section. Normal dimples are substantially spherical in shape. The elliptical dimples formed by the head of the pin are out of place and provide a cosmetically poor ball. Conventional retractable pin molds face another problem, that being balancing the flow of fluid through the gates in each individual cavity in a multi-cavity mold frame. The flow must be balanced so that the cores are not shifted off-center. Additionally, the overall flow of fluid to each cavity through the runners must be balanced so that the timing for retracting the pins from each cavity in a mould is the same. If the pins are retracted too soon, the core tends to shift off of centre and produce an unacceptable ball. If retracted too late, the pins leave a hole in the ball since the cover stock is no longer fluid enough to back-fill the hole; this is also unacceptable for a high-quality golf ball. Timing for retraction of the pins from the mould cavity is thus critical. In the conventional cold runner, retractable pin system used for golf balls, the balls must be cut from the runner system after moulding and the gate vestiges must be machined off of the golf ball. US 2361 348 discloses a process and apparatus for making balls and which employs retractable pins in the injection moulding process. These pins are spring loaded within a mould cavity and are pushed into engagement by angled drive plates. Due to the ends of the pins sliding over the drive plates friction is induced during engagement and retraction of the pins and when subject to large normal loads large frictional tangential forces are applied to the pins. The friction also applies a transverse load between the retractable pins and the pin bore which is liable to cause wear at the locations where the retractable pins extend into the dies. Due to the friction and wear the pin mould will have a relatively short life cycle and a cover being applied to the ball is likely to have excessive pin flash. The present invention is intended to overcome some of the problems referred to above. According to the present invention a golf ball retractable pin mould comprises a pair of mould halves meeting in a mould split plane to define a generally spherical mould cavity; each mould half having a number of retractable pins extending into the cavity in generally radial directions and being inclined to the mould split plane; each pin being provided at its radially outer end with a frictionless bushing carried on a support shaft along which said bushing can slide, said shaft extending through the bushing at all positions of the bushing thereon and being arranged at right angles to the pin, the movement of said pin being caused solely by movement of said support shaft and passing through said bushing; and each end of the shafts for the pins for each mould half being mounted on a movable plate which is movable in one direction to effect extension of the pins associated therewith into the mould cavity and in the opposite direction to effect retraction of the pins out of the mould cavity. Preferably the plates are mounted for movement in a direction perpendicular to the mould split plane. There are only two gates for each spherically shaped mold cavity, a top gate positioned in the top half mold and a bottom gate positioned in the bottom half mold. The top gate is positioned at the top pole of the spherically shaped mold cavity and the bottom gate is positioned at the bottom pole of the spherically shaped mold cavity. Preferably, the runners to each of the gates are heated such that there is minimal loss of fluid cover stock due to waste. Preferably, the axis of the retractable pin is substantially normal to a tangent line of the surface of the core and the ball at the point where the pin makes contact with the core and the surface of the ball. These and other aspects of the present invention may be more fully understood by reference to the accompanying drawings wherein: Fig. 1 illustrates golf balls from a conventional injection molding operation with a cold runner system; Fig. 2 illustrates a side view of the golf ball retractable pin mold of the present invention; Fig. 3 illustrates an inside view of a half mold; Fig. 4 illustrates a preferred retractable pin of the mould in accordance with the present invention; Fig. 5 illustrates the preferred gate valve arrangement; Fig. 6 illustrates a preferred flow pattern for fluid cover stock through the mold frame; Fig. 7 illustrates a preferred retractable pin of the mould in accordance with the present invention wherein cover stock flows about a core; Fig. 8 illustrates the retractable pin of Fig. 7 in a retracted position from the mold cavity; and Fig. 9 illustrates a further preferred retractable pin in accordance with the present invention. Fig. 1 illustrates conventional molded golf balls from a retractable pin mold and specifically shows golf balls 10 and 12 which are taken from a conventional retractable pin golf ball injection mold having eight cavities. Opposite equator 14 of golf ball 10 are gates 20, 22, 24, 26, 28 and 30. Runner 32 is connected to each gate 20, 22, 24, 26, 28 and 30. Top pole 40 of golf ball 12 is shown. Fig. 2 is a side view of the retractable pin mold of the present invention showing a portion of mold frame 100 divided into top mold plate 102 and bottom mold plate 104. The two mold plates join at parting line 106. Stops 108 ensure that a small gap is maintained between the two mold plates to allow for air to escape from the mold cavity. Conventional cover stock formed of ionomeric resin cannot pass through a gap of less than about 0.0025 inches (0.0065 cm). Thus, the mold plates are spaced about 0.0015 to about 0.0025 inches (0.0035-0.0065 cm) or less apart to allow air to escape but to prevent the cover stock from escaping. Such a gap only leaves a witness line along the equator rather than a band of cover stock that needs to be buffed from the ball. Located in top mold plate 102 are top half molds 110 and 112. In bottom mold plate 104 are bottom half molds 114 and 116. The respective half molds 110, 114 and 112, 116 are in registration and form substantially spherical mold cavities 120 and 122, respectively. The spherical cavities 120, 122 have an equator along parting line 106 which is shown in dashes passing through both. Located in cavities 120 and 122 are golf ball cores 124 and 126, respectively. The inside walls of spherical cavities 120 and 122 are patterned with a dimple design. Associated with each half mold 110, 112, 114 and 116 is a set of at least three retractable pin assemblies. Fig. 2 shows only one such assembly, 130, 132, 134, 136 respectively. As shown in Fig. 3, half mold 140 preferably has retractable pin assemblies therein. The heads of the preferred five retractable pins 142 are shown, each offset from the adjacent one by about 72°. The base of gate valve 148 is also shown at the pole of half mold 140. Returning to Fig. 2, half molds 110, 112, 114 and 116 have gates 150, 152, 154 and 156, respectively. Gates 150, 152, 154 and 156 have gate valves 160', 162', 164' and 166', respectively, and activating means 170', 172', 174' and 176', respectively, for effecting movement of the gate valve. The gates 150 and 152 are located at the top pole of cores 124 and 126, respectively, and gates 154 and 156 are located at the bottom pole of cores 124 and 126, respectively. The position of gate 150 means that the force of fluid cover stock entering spherical cavity 120 and surrounding core 124 will be opposed directly by the flow of cover stock through gate 154. Valve gate pin 160' will allow little additional cover stock to be connected to the cover formed around the top half of core 124. Fig. 4 illustrates a preferred retractable pin of a mould in accordance with the present invention. A section of ball cavity 160 is shown with pin 162 extending therethrough. Pin 162 extends into the ball cavity at an angle normal to the surface of the ball. The end of pin 162 which extends into the ball cavity is shaped to form a dimple in the surface of the finished golf ball. Attached to the other end of pin 162 is ball bushing 164. Ball bushing 164 is able to travel on shaft 166. Shaft 166 is connected to plate 168. The movement of pin 162 and plate 168 is illustrated by arrows in Fig. 4. It will be understood that plate 168 is connected to all pins in the mold plate in which it is positioned. This allows all pins in the mold plate to be retracted simultaneously. It is also possible to use stoppers for the plate in order to use cores of different sizes in the golf balls. Fig. 5 illustrates the preferred end of the valve at the gate in accordance with the present invention. Gate 170 is shown with passage 172 which connects to the runners. Passage 172 has a conventional electric heating element 174 to maintain the cover stock material 176 in a fluid state. Pin 180 extends through passage 172 and into gate 170. Head 182 of pin 180 extends through cavity wall 190 and contacts the surface of the ball at a normal angle. Head 182 is in the normal shape of a dimple and forms a dimple in the golf ball. Gate 170 is located at the pole of the half cup mold. Dimples 192 are shown on the inside of cavity wall 190. Preferably, pin 180 moves back about 0.125 inches (0.32 cm) to open gate 170 and allow fluid cover stock 176 to flow through gate 170 thereby acting as a valve. Gate 170 preferably has a diameter of about 0.15 inch (0.38 cm). It should be noted that gate 170 is about five times larger than conventional retractable mold gates. Having such a large gate accelerates the overall molding process. Fig. 6 illustrates the preferred flow patterns for fluid cover stock in a mold plate having 8 cavities therein. Fluid cover stock passes through runner 200 to arms 202 and 204, then through arms 202 and 204 to fingers 205 and 206, respectively. Finally, the fluid cover stock passes to gates 210, 212, 214, 216, 220, 222, 224 and 226. In the hot runner system, runners 200, arms 202 and 204 and fingers 205 and 206 are insulated and heated to maintain the cover stock in a constant fluid state. Additionally, the gates are also heated as previously mentioned. It is clear that such a system will allow for more than the conventional eight (8) cavity systems. Hot runner systems are conventional. Fig. 7 illustrates a portion of a golf ball mold 230 having dimples 232 projecting out into the mold cavity. Core 234 is positioned inside the mold cavity. Fluid cover stock 236 has been injected about core 234. Retractable pins 238 and 240 are holding core 234 centered in golf ball mold 230 while cover stock 236 solidifies. Plate 242 is movable in a vertical direction so as to move pins 238 and 240 out of the mold cavity. As shown in Fig. 7, retractable pins 238 and 240 move out of and into, respectively, the mold cavity as plate 242 moves downward or upward. Such an arrangement provides the simultaneous movement of the pins as discussed above. Fig. 8 illustrates retractable pin 250 in the retracted position from golf ball mold 252. Golf ball mold 252 has dimples 254 thereon. Pin head 256 of retractable pin 250 is shaped substantially like dimple 254 so that pin head 256 leaves a dimple in cover stock 258 when cover stock 258 solidifies. Shaft 260 is mounted on block 262 which, in turn, is mounted on plate 264. Shaft 260 is at an angle A of about 30-60° with the vertical as shown in Fig. 8. The preferred angle A is 40°. As will be appreciated by those of skill in the art, it is the angle of the retractable pin to the plate which effects movement of the pin that determines the angle of shaft 260. As further shown in Fig. 8, ball bushing 268 must be coaxial with shaft 260 while ball bushing 268 and shaft 260 share an axis which must be normal to the axis of the retractable pin. It will be appreciated by those of skill in the art that, although a ball bushing has been depicted in Figs. 4, 7 and 8 and is the preferred frictionless bushing means for use in the retractable pin of the present invention, other frictionless bushing means such as tetrafluoroethylene fluorocarbon polymer coated (Teflon®) or oil bushings can also be used. Fig. 9 illustrates a retractable pin mechanism in accordance with the present invention in which bushing 270 is a conventional oil or Teflon® bushing. It will be understood that the claims are intended to cover all changes and modifications of the preferred embodiment of the invention herein chosen for the purpose of illustration which do not constitute a departure from the spirit of the invention as defined in the appended claims.

Claims: A golf ball retractable pin mould comprising a pair of mould halves (110,114) meeting in a mould split plane to define a generally spherical mould cavity (120); each mould half (110,114) having a number of retractable pins (162) extending into the cavity (120) in generally radial directions and being inclined to the mould split plane; each pin (162) being provided at its radially outer end with a frictionless bushing (164) carried on a support shaft (166) along which said bushing (164) can slide, said shaft (166) extending through the bushing (164) at all positions of the bushing (164) thereon and being arranged at right angles to the pin (162), the movement of said pin (162) being caused solely by movement of said support shaft (166) and passing through said bushing (164); and each end of the shafts (166) for the pins (162) for each mould half being mounted on a movable plate (168) which is movable in one direction to effect extension of the pins (162) associated therewith into the mould cavity (120) and in the opposite direction to effect retraction of the pins (162) out of the mould cavity (120). A golf ball retractable pin mould as claimed in claim 1 in which the plates (168) are mounted for movement in a direction perpendicular to the mould split plane. A golf ball retractable pin mould as claimed in claim 1 or claim 2 in which the radially inner end of each of said retractable pins (147) has a shape substantially similar to that of a golf ball dimple. A golf ball retractable pin mould as claimed in any one of the preceding claims in which said frictionless bushing (164) is a ball bushing, an oil bushing or a tetrafluoroethylene fluorocarbon polymer coated bushing.

Inventors: GIZA JOHN, GIZA, JOHN
Applicants: ACUSHNET CO, ACUSHNET COMPANY
Application year: 1990
Main classification: B29C45
IPC codes: B29C45