An interesting golf ball patent issued this month to Acushnet. The patent is USPN 7452291 titled “Foam-Core Golf Balls” and describes the invention as:
The present invention is directed to a golf ball with a controlled moment of inertia and controlled spin rate. The increase in moment of inertia is preferably accomplished by a reduction in the specific gravity or weight of the core, e.g., by foaming. Preferably, this reduction is less than about 15% in specific gravity or less than about 25% in weight to minimize the reduction in the coefficient of restitution of the core.
The patent provides a nice discussion of the significance of the core to a golf ball’s performance.
Conventional golf balls can be divided into two general types or groups: solid balls and wound balls. The difference in play characteristics resulting from these different constructions can be quite significant. These balls, however, have primarily two functional components that make them work. These components are the center or core and the cover. The primary purpose of the core is to be the “spring” of the ball or the principal source of resiliency. The cover protects the core and improves the spin characteristics of the ball.
Two-piece solid balls are made with a single-solid core, usually made of a cross-linked polybutadiene or other rubber, which is encased by a cover. These balls are typically the least expensive to manufacture as the number of components is low and these components can be manufactured by relatively quick, automated molding techniques. In these balls, the solid core is the “spring” or source of resiliency. The resiliency of the core can be increased by increasing the cross-linking density of the core material. As the resiliency increases, however, the compression also increases making a harder ball, which is undesirable. Recently, commercially successful golf balls, such as the Titleist Pro-V1 golf balls, have a relatively large polybutadiene based core, ionomer casing and polyurethane cover, for long distance when struck by the driver clubs and controlled greenside play.
Moreover, the spin rate of golf balls is the end result of many variables, one of which is the distribution of the density or specific gravity within the ball. Spin rate is an important characteristic of golf balls for both skilled and recreational golfers. High spin rate allows the more skilled players, such as PGA professionals and low handicapped players, to maximize control of the golf ball. A high spin rate golf ball is advantageous for an approach shot to the green. The ability to produce and control back spin to stop the ball on the green and side spin to draw or fade the ball substantially improves the player’s control over the ball. Hence, the more skilled players generally prefer a golf ball that exhibits high spin rate.
On the other hand, recreational players who cannot intentionally control the spin of the ball generally do not prefer a high spin rate golf ball. For these players, slicing and hooking are the more immediate obstacles. When a club head strikes a ball, an unintentional side spin is often imparted to the ball, which sends the ball off its intended course. The side spin reduces the player’s control over the ball, as well as the distance the ball will travel. A golf ball that spins less tends not to drift off-line erratically if the shot is not hit squarely off the club face. The low spin ball will not cure the hook or the slice, but will reduce side spin and its adverse effects on play. Hence, recreational players prefer a golf ball that exhibits low spin rate.
The patent literature discloses a number of low spin balls. For example, U.S. Pat. No. 6,193,618 describes a low spin ball having a mantle with a cellular or liquid core. The ‘618 patent describes a cellular core with a spherical metal mantle, wherein the core has a compression of at least 75 and a cover hardness of at least 65 Shore D.
Each of U.S. Pat. Nos. 6,309,314, 6,126,559, and 5,833,553 describes a low spin golf ball having a thick cover layer (>0.142 inch) with a hardness of at least about 60 Shore D and a core that can be foamed or unfoamed. U.S. Pat. No. 5,823,889 describes a solid construction ball having a core that includes an inner and an outer portion. Either the outer portion or the entire core has a plurality of gas containing compressible cells dispersed therein, and either the outer portion or the entire core has a specific gravity greater than 1. U.S. Pat. No. 6,057,403 describes dual cores having thermoplastic/thermosetting composition or combinations thereof, wherein either layer may be foamed or filled. Furthermore, U.S. Pat. No. 5,482,285 describes a three piece solid ball having an inner and outer core and a single cover layer. The inner core has a diameter of from about 10-38 mm, the outer core has a low specific gravity of from 0.2 to 0.79 and a diameter of 37-40 mm and can be foamed. According to the ‘285 patent, the weight of the combined two cores is 32 to 39 grams.
However, there remains a need for low spin golf balls that fulfill specific needs of golfers.
The patent goes on to explain:
It is well known that the total weight of the ball has to conform to the weight limit set by the United States Golf Association (“USGA”). Redistributing the weight or mass of the ball either toward the center of the ball or toward the outer surface of the ball changes the dynamic characteristics of the ball at impact and in flight. Specifically, if the density is shifted or redistributed toward the center of the ball, the moment of inertia is reduced, and the initial spin rate of the ball as it leaves the golf club would increase due to lower resistance from the ball’s moment of inertia. Conversely, if the density is shifted or redistributed toward or within the outer cover, the moment of inertia is increased, and the initial spin rate of the ball as it leaves the golf club would decrease due to the higher resistance from the ball’s moment of inertia. The radial distance from the center of the ball or from the outer cover, where the moment of inertia switches from being increased to being decreased as a result of the redistribution of weight or mass density, is an important factor in golf ball design.
In accordance to one aspect of the present invention, this radial distance, hereinafter referred to as the centroid radius, is provided. When more of the ball’s mass or weight is reallocated to the volume of the ball from the center to the centroid radius, the moment of inertia is decreased, thereby producing a high spin ball. Hereafter, such a ball is referred as a low moment of inertia ball. When more of the ball’s mass or weight is reallocated to the volume between the centroid radius and the outer cover, the moment of inertia is increased, thereby producing a low spin ball. Hereafter, such a ball is referred as a high moment of inertia ball.
Interesting stuff, and I bet you learned something new about golf ball technology.
Check out more golf patents by visiting The IP Golf Guy .