Golf Ball

Background

Golf, a game of Scottish origin, is one of the most popular sports in the world. In the United States alone more than 24 million people play golf, including over 8,000 professional players. Golf tournaments around the world are popular with spectators, as well as with players, and since the 1960s, they have received wide television coverage. There is now even a cable channel devoted to golf, as well as numerous computer games.

The basic game involves using a variety of clubs to drive a small ball into a succession of either nine or 18 holes, over a course designed to present obstacles, in as few strokes as possible. A player is permitted to carry a selection of up to 14 clubs of varying shapes, sizes, and lengths. The standard golf ball used in the United States is a minimum of 1.68 in (4.26 cm) in diameter; the British ball is slightly smaller.

A golf course generally has 18 holes spread over a landscaped area that includes a number of hazards, including water, sand traps or bunkers, and trees. Difficulty is increased by varying distances among holes. Play on each hole is begun at the tee area, from which players drive the ball into the fairway. Each hole can vary in length from about 150-600 yards (135-540 m); successful players are those who are able to drive the ball more than 200 yards (180 m) from the tee, approaching most holes with fewer than three shots. At the end of the hole is the putting green, where the ball must be putted into the hole or cup to complete the hole.

Golf is usually played by groups of two to four people who move throughout the course together. The ball must be played from where it lies, except in specific circumstances. In stroke competition, the total number of strokes used to move the ball from the tee to the hole is recorded as the players' score for that individual hole. The player who uses the fewest strokes to complete the course is the winner. In match play, scores are compared after every hole, and a player wins, loses, or halves (ties) each hole.

Each hole must be reached in a specific number of shots (par), which usually depends on length. A birdie is a score on any one hole that is one stroke less than par, and an eagle is a score on a hole that is two less than par. A hole in one is scored when the player drives the ball into the hole with only one stroke.

Today, the golf ball market is worth around $550 million in annual sales, with over 850 million golf balls being manufactured and shipped every year. Currently, balls are made in two or three parts. A two-piece ball is made of rubber and plastic, and is mostly used by the casual golfer. These balls last a lot longer than the three-piece balls the pros use and hence make up 70% of all golf ball production. A three-piece ball consists of a plastic cover, windings of rubber thread, and a core that contains a gel or liquid (sugar and water) or is solid. A dimple pattern on the surface results in good flight performance.

The most common dimple patterns are the icosahedral, the dodecahedral, and the octahedral. The icosahedral pattern is based on a polyhedral with 20 identical triangular faces, much like a 20-sided die. Similarly, a dodecahedral is based on a polyhedral with 12 identical faces in the shape of pentagons. The octahedral is based on an eight-sided polyhedral with triangular faces. Some balls are based on the icosahedral with 500 dimples. As a general rule, the more dimples a ball has the better it flies, provided those dimples are about 0.15 in (0.38 cm) in diameter.

The size and depth of the dimples also affect performance. Shallow dimples generate more spin on a golf ball than deep dimples, which increases lift and causes the ball to rise and stay in the air longer and roll less. Deep dimples generate less spin on a golf ball than shallow dimples, which decrease lift and causes the ball to stay on a low trajectory, with less air time and greater roll. Small dimples generally give the ball a lower trajectory and good control in the wind, where as large dimples give the ball a higher trajectory and longer flight time.

Technological advances in materials and aerodynamics now allow the manufacturer to custom-fit a golf ball for a players' particular game, for weather conditions, and even for specific course conditions. Golf balls can be separated into four basic performance categories: distance and durability; control and maneuverability; distance and control; and slow clubhead speed. Within these categories there are more than 80 different balls of varying construction materials and design.

The United States Golf Association (USGA) has established rules for the ball in regard to maximum weight, minimum size, spherical symmetry, initial velocity, and overall distance. The weight of the ball must not be greater than 1.62 oz (45.93 g) and must be spherically symmetrical. The velocity shall not be greater than 250 feet (75 m) per second (255 feet [76.5 m] per second maximum) when measured on apparatus approved by the USGA. The overall distance standard states that the ball shall not cover an average distance in carry and roll exceeding 280 yards (84 m) (296.8 yards [89 m] maximum). These rules are updated every year.

Currently, there are around 850 models of balls that conform to these standards. Recently, balls that are about 2% larger than ordinary balls have been introduced that still conform to USGA rules. These balls have softer cores and thicker, harder covers, which leads to a straighter, longer shot.

History

The game of golf goes back as far as 80 B.C. when the Roman emperors played a game called paganica using a bent stick to drive a soft, feather-stuffed ball (or feathery). This ball was up to 7 in (17.5 cm) in diameter, much larger than the Scottish version. By the middle ages, the sport had evolved into a game called bandy ball, which still used wooden clubs and a smaller ball about 4 in (10 cm) in diameter.

Over the next five centuries the game developed on several continents and eventually evolved into the popular Scottish game known as golfe. Other European countries played similar games and a variation from the Netherlands was played in the American colonies as early as 1657. Although various types of wood, ivory, linen, and even metal balls were tried during the sport's early development in Europe, the feathery remained the ball of choice.

The Scottish game, however, is the direct ancestor of the modern game. The first formal golf club was established in Edinburgh in 1744. It established the first set of rules, which helped eliminate local variations in play. A decade later the Royal and Ancient Golf Club was established at Saint Andrews, Scotland, which became the official ruling organization of the sport. Its rules committee, along with the United States Golf Association (USGA), still rules the sport. A British player, Harry Vardon, helped popularize the sport in the United States during the late 1880s, although legend has it that a Scotsman named Alex McGrain was the first to play golf on the North American continent in eastern North Carolina over a hundred years earlier. The first American-made golf ball was produced by Spalding in 1895.

The first golf ball similar in size to today's came into existence around five or six hundred years ago, when the Dutchmen stuffed feathers into an 1.5 in (3.75 cm) leather pouch. This type of ball lasted for about 450 years. To make a feathery, the ballmaker

The dimple pattern on the golf ball surface results in good Right performance. As a general rule, the more dimples a ball has the better it flies, provided those dimples are about 0.15 in (0.38 cm) in diameter.

Finished featheries were made in different diameters and weights and were graded according to weight (measured in drams). Ballmakers determined the size and weight of each ball by adjusting the lengths and thickness of the leather used for the cover. Typically, feathery balls were made in the range of 20-29 drams. The featheries were first numbered according to their size and later according to diameter rather than weight. This numbering system has continued into the twentieth century.

The feathery was replaced when a much cheaper ball made out of gutta-percha, a natural gum from Southeast Asia, was developed around 1850 in Italy. To make a gutta percha ball or gutty, a slice of resin rope that had been pre-mixed with a stabilizer was heated to make it pliable and then shaped into a sphere. Despite being rounder and smoother than the feathery, this ball had poorer flight performance. However, the new ball's affordability (dozens could be made per day instead of just a handful) made it practical for the working class to take up the sport in large numbers and this ball remained popular until about 1910.

The gutty ball went through several transformations during this time. Once ballmakers discovered that a rough surface was better aerodynamically, grooves were cut in the balls with a knife to simulate the stitching of the feathery. Next, the ballmakers pounded the ball with a chisel-faced hammer to produce nicks and bruises on the surface.

Further experimentation with the gutty through the mid-nineteenth century sought to improve the ball's flight performance.

By the end of the 1870s, machined iron molds that had regular patterns inscribed on their inside were developed. One of the most popular of these was the brambleberry design with raised dimples. These molds created a regular pattern over the surface, eliminating hammering by hand. This refinement began a revolution in aerodynamic design for the golf ball. The rate of manufacture improved even further.

The game changed considerably in the early twentieth century when the B. F. Goodrich Company in Akron, Ohio, invented a lighter, tightly wound, rubber-threaded ball. The recessed dimpled ball was introduced by Spalding in 1908 and proved to be both aerodynamically and cosmetically a success. By 1930, it dominated the market, with the spherical dimple becoming the standard. Other dimple shapes have since evolved, including truncated cone and elliptical dimples.

Raw Materials

A golf ball is made up of mostly plastic and rubber materials. A two-piece ball consists of a solid rubber core with a durable thermoplastic (ionomer resin) cover. The rubber starts out as a hard block, which must be heated and pressed to form a sphere.

The three-piece ball consists of a smaller solid rubber or liquid-filled center with rubber thread wound around it under tension, and an ionomer or balata rubber cover.

During the 1970s the interior of the ball improved further, thanks to a material called polybutadiene, a petroleum-based polymer. Though this material produced more bounce it was also too soft. Research at Spalding determined that zinc strengthened the material. This reinforced polybutadiene soon became widely used by the rest of the manufacturers.

The Manufacturing
Process

Three-piece golf balls are more difficult to make and can require more than 80 different manufacturing steps and 32 inspections, taking up to 30 days to make one ball. Two-piece balls require about half of these steps and can be produced in as little as one day.

Forming the center

• 1 The center of the two-piece ball is a molded core. It is a blend of several different ingredients, all of which are chemically reactive to give a rubber type compound. After heat and pressure is applied, a core of about 1.5 inches (3.75 cm) is formed.

Forming the cover and dimples

• 2 Injection molding or compression molding is used to form the cover and dimples on a two-piece ball using a two-piece mold. In injection molding, the core is centered within a mold cavity by pins, and molten thermoplastic is injected into the dimpled cavity surrounding the core. Heat and pressure cause the cover material to flow to join with the center forming the dimpled shape and size of the finished ball. As the plastic cools and hardens, the pins are retracted and the finished balls are removed.
• 3 With compression molding, the cover is first injection molded into two hollow hemispheres. These are positioned around the core, heated and then pressed together, using a mold which fuses the cover to the core and also forms the dimples. Three-piece balls are all compression molded since the hot plastic flowing through would distort and probably cause breaks in the rubber threads.

Polishing, painting, and final coating

• 4 "Flash" or rough spots and the seam on the molded cover are removed. Two coats of paint are applied to the ball. Each ball sits on two posts, which spins so that the paint is applied uniformly. Spray guns that are automatically controlled are used to apply the paint. Next, the ball is stamped with the logo. The final step is the application of a clear coat for high sheen and scuff resistance.

Drying and packaging

• 5 After the paint is applied, the balls are loaded into containers and placed in large dryers. After drying, the balls are ready for packaging in boxes and other containers.

Quality Control

In addition to monitoring the manufacturing process using computers and monitors, three-piece balls are x-rayed to make sure the centers are perfectly round. Compression ratings are also used to measure compression-molded, wound golf balls. These ratings have no meaning when applied to two-piece balls, however. Instead, these balls are measured by a coefficiency rating, which is the ratio of initial speed to return speed after the ball has struck a metal plate. This procedure measures the coefficient of restitution.

Mechanical testing is also used to verify that the ball's performance meets the USGA's standards. Special equipment has been developed and some manufacturers even use wind tunnels to determine wind resistance and lift action. A machine called the True Temper Mechanical Golfer or Iron Byron, modeled after the swing of golf leg-end Byron Nelson, can be fitted for any club and can be set up at various swing speeds. For normal testing, the Iron Byron is configured using a driver, 5 iron, and 9 iron.

Another machine called the Ball Launcher provides the capability to propel balls through the air at any velocity, spin rate, and launch angle. This has the advantage of using launch conditions typical of a wide cross-section of golfers. Using both types of equipment, performance data associated with the flight of a golf ball can be measured and analyzed. These include the apogee angle, carry distance, total distance, roll distance, and statistical accuracy area.

The apogee angle indicates the height the trajectory of a ball reaches. It is measured using a camera with a telescopic lens pointing down range in conjunction with a gridded monitor. Carry distance is the distance a golf ball travels in the air and is measured using a grid system with markers in the landing zone. Total distance is the distance a golf ball travels in the air plus the roll distance. Roll distance is the total distance minus the carry distance.

The statistical accuracy area (SAA) or dispersion area is used as a measure of a golf ball's accuracy. For a given ball, the SAA value is based on the deviations of the ball's performance in the directions of carry and left/right of the centerline. These deviations are used to calculate an equivalent elliptical landing area.

The Future

As improvements in aerodynamic design continue, golf balls will be able to go even further. In fact, one golf ball manufacturer is already advertising that its balls can be driven 400 yards. However, some professional players are complaining that golf balls go too far and want the ball adjusted back about 10%. This means the USGA would have to tighten current requirements for carry and roll and for velocity in its ball-testing procedure. A 10% cutback would reduce drives by most tour pros by approximately 25 yards (22.5 m).

On the other hand, some experts believe that golf balls have reached their limit on distance and will not improve in this area over the next 20 years. Golf manufacturers will be challenged to achieve the ultimate consistency from one ball to the next, make balls that feel softer and stop faster on the greens, develop balls with greater durability, and invent the perfect dimple pattern. Space age materials may achieve some of these goals and metal matrix composites based on titanium are being considered. In addition, golf ball companies will have to manufacture more balls for specific categories of golfers. For example, four or five different types of trajectories might become available.