Golf ball construction Types and Dynamics

 

Golf Ball Construction: An In-Depth Guide

Choosing the right golf ball can greatly impact your performance on the course. Each type of golf ball features unique construction and performance characteristics tailored to different playing styles and skill levels. In this article, we delve into the various types of golf balls—from the basic one-piece to the advanced five-piece—highlighting their construction, benefits, and ideal users. Whether you're a beginner or a seasoned pro, understanding golf ball construction will help you select the perfect ball to enhance your game.

The Core

Manufacturing the Polybutadiene (PBD) Core

The first stage in creating the core involves polybutadiene (PBD), a type of rubber. Once PBD has been produced, it cannot be re-melted, which means it cannot be injection moulded. Instead, it must undergo a process known as compression moulding.

Mixing and Shaping the Core

To form the core, the necessary chemicals are mixed together. The resulting mixture has a consistency similar to clay or plasticine. This mixture is then shaped into long sausage-like cylinders. These cylinders are chopped into slugs (or "blanks"), each containing just the right amount of material needed to form the core.

Compression Moulding Process

The slugs are heated to their softening temperature and placed in hemispherical moulds on a large heated plate. Another heated plate is pressed down on them, forcing the rubber to flow into a spherical shape, as illustrated in Figure 4. This method of manufacturing is called compression moulding.

Important Points:

• Polybutadiene (PBD): A type of rubber used for the core.
• Compression Moulding: Necessary due to PBD's inability to be re-melted.
• Softening Temperature: Critical for shaping the slugs into a spherical form.

Figure 4 (a, b & c) - Stages in compression moulding of a core; (a) correct amount of material is cut from tube; (b) ‘slug’ of rubber is heated and placed between shaped steel plates; and (c) plates brought together to force hot rubber into sphere shape.

Some of the rubber is squeezed into the joint between the two plates and leaves a ridge or seam on the core which has to be rubbed off. (See Figures 4c and 5)

Figure 5 - Compression moulded rubber core showing seam running vertically.

This process ensures the core is formed correctly, ready for the next stages of production.

The Cover 

Creating a two-piece golf ball cover involves several intricate steps to ensure quality and performance. This guide will break down the process and highlight the key aspects involved in manufacturing golf ball covers.

Traditional Compression Moulding

Compression moulding involves creating two smooth hemispherical shells and then moulding them around the core to form a single unit. However, this method has limitations:

• Dimple Pattern Reproduction: Compression moulding often fails to reproduce the dimple pattern accurately.

Process Overview:

1. Moulding Two Hemispherical Shells: Smooth hemispherical shells are moulded separately.
2. Placing Shells Around the Core: The shells are placed around the core.
3. Compression Moulding: The shells are compressed into a single unit, resulting in an unpainted, unfinished golf ball.

Advanced Injection Moulding

Fortunately, modern materials like polyurethanes and ionomers can be remelted, allowing for injection moulding. This method is widely used for various plastic components and provides better results for golf ball covers.

Process Overview:

Preparation:

1. Core Placement: The core is placed inside a spherical mould.
2. Core Support: Retractable pins or low melting point polymers/waxes are used to maintain correct separation.

Mould Preparation:

• The inside surface of the mould has a negative dimple pattern machined into it.
• Mould Halves Clamped: The mould halves are clamped together before injecting any liquid polymer.

Polymer Injection:

1. Melting Polymer: Polyurethane or ionomer is melted using friction heating.
   • Polymer granules are driven through a screw thread (screw extruder), which heats and melts them.
2. Injection: The screw extruder provides high pressure, forcing the liquid polymer into all details of the mould, ensuring better dimple reproduction.

Core Supports Removal:

• Core supports are either melted or withdrawn, preventing holes through the cover.
• This step can cause some settling under gravity, resulting in a cover thickness that may vary around the ball.

Final Steps:

1. Solidification: Once the cover material has solidified and cooled, the mould is opened.
2. Ejection: The ball is ejected from the mould.

Finishing Touches:

• Pigmentation: The cover material is pigmented to add color and attractiveness. Titanium dioxide is commonly used as a white pigment.

Summary Diagram

To visualize this process, refer to the following steps:

1. Steel moulds moved together until they touch.
2. Steel plates with hemispherical cavity.
3. Rubber 'slug' compressed into a spherical core.
4. Seam formation.

The modern injection moulding process ensures a high-quality finish with an accurately reproduced dimple pattern, resulting in a superior golf ball cover compared to traditional methods.

Figure 6 - Schematic diagram of injection moulding of cover around a core; (a) core supported in mould and mould clamped; (b) injection of polymer; (c) liquid polymer filling cavity; and (d) polymer solidified and cooled, mould removed.

Mould Seams and Dimples

Seam Along the Joint Line

In golf ball manufacturing, there is a seam along the joint line of the mould. This seam is created during the moulding process and affects the distribution of dimples on the ball's surface.

Dimple Separation at the Seam

To facilitate the easy separation of the mould halves and the extraction of the solid ball, dimples are more widely separated along the seam. This creates a visible line around the ball's circumference where the raised ridges between dimples are wider.

Visual Identification

You can easily spot this seam on most golf balls as a line around the circumference where the dimple pattern changes. See Figure 4 for an illustration of this feature.

The Role of Sprues in Golf Ball Manufacturing

What Are Sprues?

Sprues are the solidified paths left behind where the liquid polymer was injected into the mould.

Impact on Ball Surface

When sprues are cut or broken off, they leave small pimples on the surface of the ball. These may or may not be polished off before the ball is lacquered, depending on the manufacturer's process. Figure 6(d) shows these sprues clearly.

Figure 7 - Seam on a golf ball running vertically up the centre of the image and seen as a wider, continuous line of raised material not cut by any dimples; this was the meeting line of the two mould halves when the cover was injection moulded.

Manufacturing Variability in Golf Balls

Manufacturing variability refers to the differences that can occur in the production of golf balls. Despite advancements in manufacturing techniques, no two golf balls are identical, even in basic properties such as size and weight. Over the years, these variations have been significantly reduced, but there is still room for improvement, particularly in weight distribution and spherical symmetry.

Weight Distribution and Spherical Symmetry

One of the key areas where variability still exists is in the weight distribution and spherical symmetry of the golf balls. Injection molding of a cover around a solid core can lead to variations in thickness around the ball. Since the densities of the cover and the core are different, this can cause the center of mass to shift from the center of the ball.

Non-central center of mass can result in several effects:

1. Rolling Accuracy: The ball may not roll true on the putting green, tending to veer towards the heavier side. In modern golf balls, this effect is minimal and might only be noticeable if the ball is rolled slowly across a very flat surface, such as a snooker table.

2. Impact Response: The heavier side of the ball, having more cover material, will deform less on impact, potentially causing the ball to come off the clubface a little faster. However, this difference is typically negligible during play.

The R&A’s symmetry test (no longer applied) occasionally showed small differences in trajectory when balls were set up differently on the tee. These variations could also be due to asymmetry in the dimple pattern.

Testing for Non-Central Center of Mass

You can conduct a simple test to check if a golf ball has a non-central center of mass:

1. Prepare the Solution: Heat some water and add Epsom salts until no more will dissolve (saturation point). Allow the solution to cool and add a squirt of dishwashing liquid.

2. Float the Ball: Drop the golf ball into the solution. The dishwashing liquid helps the ball move freely in the liquid.

3. Observe the Floatation: If the ball has a non-central center of mass, it will float like an iceberg, with the same point (lighter side) always on top.

Impact of Manufacturing Variability

The off-center behavior is generally more pronounced in two-piece distance balls, which have thicker covers. For instance, a thick ionomer cover (denser than polybutadiene) can cause significant shifts in the center of mass, as illustrated in the schematic figure below.

Figure 8 - Exaggerated cover thickness variation for a two piece ball

Construction of Three-Piece Balls

Core and Mantle Integration: Three-piece golf balls utilize a combination of compression and injection molding techniques to achieve uniformity. The ionomer mantle is formed into two hemispherical shells through injection molding, maintaining constant thickness. These halves encase the core and are compression molded at low temperatures to ensure they bond seamlessly without melting, positioning the center of mass at the sphere's center.

Benefits of Three-Piece Design

Consistent Performance: By maintaining a uniform mantle thickness around the core, three-piece balls minimize asymmetry, enhancing predictability and performance on the course.

Finishing Process

Precision Finishing: After molding, each ball undergoes rigorous finishing. Rough spots, seams, and imperfections on the cover are removed before applying two coats of paint. Automated spray guns ensure uniform paint coverage as the balls spin on pins.

Quality Control: Human operators meticulously inspect each ball throughout the finishing process to detect and reject any surface imperfections, ensuring high quality and performance consistency.

Different Types of Golf Balls

Choosing the right golf ball is crucial for enhancing your game. Each type of golf ball has unique construction and performance characteristics. Here’s a comprehensive guide to the five main types of golf balls, their construction, and who they are best suited for.

1. One-Piece Golf Balls

Construction:

• Material: Made from a chunk of Surlyn molded with dimples.
• Characteristics: Basic construction, cheapest option.

Performance:

• Feel: Clunky and less responsive.
• Spin: Minimal spin.

Best For:

• Beginners.
• Driving ranges.
• Mini golf courses.

2. Two-Piece Golf Balls

Construction:

• Core: Solid rubber or Polybutadiene (a synthetic rubber).
• Cover: Surlyn or urethane exterior.

Performance:

• Distance: Rolls farther and generates more distance than other types.
• Feel: Durable and provides a good balance between distance and feel.

Best For:

• Beginners.
• Golfers seeking maximum distance.

3. Three-Piece Golf Balls

Construction:

• Core: Solid liquid or rubber.
• Secondary Layer: Enhanced rubber.
• Cover: Durable Surlyn, Balata, or Urethane material.

Performance:

• Feel: Greater feel and control.
• Spin: Offers better spin compared to two-piece balls.

Best For:

• Golfers looking for improved feel and control.

4. Four-Piece Golf Balls

Construction:

• Core: Solid rubber center.
• Inner Cover Layer: Provides additional power.
• Middle Cover: Enhances feel and spin.
• Outer Cover: Made of Urethane.

Performance:

• Compression: Adds power during high compression shots.
• Spin: Provides more spin and less forgiveness.

Best For:

• Intermediate to advanced golfers.
• Players seeking a balance of power and spin.

5. Five-Piece Golf Balls

Construction:

• Layers: Five distinct layers including a core, multiple intermediate layers, and an outer Urethane cover.

Performance:

• Spin: Maximum spin and performance benefits.
• Adaptability: Reacts to different types of shots and swing speeds.

Best For:

• Tour professionals.
• Low handicappers.
• Golfers looking for the highest level of performance.

Summary

Understanding the differences between these golf ball types will help you make an informed decision and choose the ball that best suits your game. From the basic one-piece ball, ideal for beginners, to the high-performance five-piece ball used by professionals, selecting the right ball can significantly impact your performance on the course.

Evolution and Dynamics of Golf Ball Construction

Historical Development

• Early Wooden Balls: Traveled no more than 100 yards (91 meters).
• Feather-Filled Balls: Made with goose and chicken feathers inside a leather cover.
• Gutta-Percha Balls (1850s): Used a type of early rubber, traveling up to 200 yards (182 meters).
• Sap-Based Balls: Utilized sap from Malaysian trees.
• Two-Piece Balls (Early 20th Century): Featured a rubber core encased in gutta-percha.
• Modern Dimpled Surface: Stabilizes the flight of golf balls.

Construction Standards

• Diameter: Not less than 1.7 inches (4.3 cm).
• Weight: No more than 1.6 ounces (45.9 g).

Modern Golf Ball Construction

• Two-Piece Balls: Thin cover of plastic resin (Surlyn) and a large rubber core.
• Three-Piece Balls: Include a middle layer of rubber thread (windings) for increased spin.

Impact of Compression

• Energy Transfer: More compressed cores lead to less deformation at impact, maximizing energy transfer and distance.
• Roll Distance: Harder balls roll farther due to minimized deformation.

Aerodynamics and Dimple Design

• Aerodynamic Lift: Dimples create lift, keeping the ball in the air longer.
• Drag Reduction: Dimples reduce drag by half compared to smooth balls, doubling the travel distance.
• Dimple Characteristics: Number of dimples ranges from 300 to 500, typically 350 to 450.
• Scientific Optimization: Manufacturers experiment with dimple shapes, sizes, and patterns to optimize trajectory.

Magnus Effect

• Named After: German physicist Heinrich Gustav Magnus.
• Lifting Force: Experienced by rotating bodies, such as golf balls, creating an upward push due to drag differences.
• Spin Rate: Measured in revolutions per minute (rpm), critical for the ideal parabolic path.
  • Driver Spin Rate: Ranges between 2,000 and 4,000 rpm.
  • Optimal Spin: Prevents excessive vertical carry and insufficient vertical distance.

Impact on Driving Distance

• Technological Advancements: Improvements in golf ball construction have significantly increased driving distances.
• PGA Tour: Average driving distance increased from 257 yards (235 meters) in 1980 to 280 yards (256 meters) in 2001.

Summary

The evolution of golf ball construction has dramatically influenced the dynamics of its flight, optimizing both distance and control. Key advancements include the transition from wooden and feather-filled balls to modern two-piece and three-piece designs with sophisticated dimple patterns. These developments, alongside the Magnus effect, have significantly enhanced performance, contributing to the increased driving distances observed in professional golf.