A Guide to Common Terms in Silicone Product Manufacturing

Jumping straight into the world of silicone product manufacturing can be bewildering for anyone unfamiliar with the industry’s specific jargon. This guide is designed for you—the novice, the curious shopper, the innovative maker. Our goal is to equip you with an understanding of essential terms that form the backbone of silicone discussions. By demystifying these terms, we aim to not only enhance your knowledge but also to empower you to make informed decisions and engage with confidence when it comes to silicone products. Welcome to your concise primer on navigating the language of silicone manufacturing.

Silicone Essentials

Silicone vs. Silicon: Despite the similarity in their names, silicone and silicon are fundamentally different. Silicon (Si) is a natural chemical element, a semiconductor found in sand and quartz, essential in the production of microchips.

Silicone, on the other hand, is a synthetic polymer, made from silicon along with carbon, hydrogen, and oxygen. Its flexibility, resistance to temperature changes, and water repellency make it invaluable in both industrial and everyday applications.

Polymerization and Crosslinking: At the heart of silicone’s versatility is its formation process—polymerization. This chemical reaction combines smaller molecules (monomers) into a long, repeating chain, creating a polymer. For silicone, this process involves silicon, carbon, hydrogen, and oxygen.

Crosslinking further strengthens these polymers, linking the chains through chemical bonds. The result is a material that can vary in texture from liquid to gel to rubber to hard plastic, depending on the degree of crosslinking and the types of additives used.

Types of Silicone:

Liquid Silicone Rubber (LSR): Known for its high fluidity, this type of silicone is ideal for injection molding, creating parts with precision and efficiency.

High Consistency Rubber (HCR): Often referred to as high-temperature vulcanizing (HTV) silicone, HCR has a gum-like texture and requires high temperatures to cure. It’s suited for extrusion and molding into durable, elastic parts.

Room Temperature Vulcanizing (RTV) Silicone: This silicone cures at room temperature, making it perfect for DIY projects and in-situ repairs. It’s available in two types: one-part (which cures when exposed to the air) and two-part (which cures when two components are mixed).

Fluorosilicone Rubber (FSR): Offering superior chemical and fuel resistance, FSR is used in demanding environments, such as the automotive and aerospace industries.

Each type of silicone offers unique properties suited to different applications.

Manufacturing Processes and Techniques

Vulcanization: Vulcanization is a chemical process that converts raw silicone rubber into a more durable and elastic material by introducing crosslinks between polymer chains. This can be achieved through various cure systems, with peroxide and platinum-based curing being the most common.

Peroxide curing is widely used for general-purpose applications, while platinum curing offers enhanced properties, such as better thermal stability and lower compression set, making it ideal for medical and food-grade products.

Molding Processes:

Injection Molding: This is one of the most popular methods for manufacturing silicone products, especially for high-volume production. Liquid silicone rubber (LSR) is injected into a heated mold under high pressure, curing quickly into complex shapes with precision and consistency.

Compression Molding: In this process, a pre-measured amount of silicone rubber is placed into an open, heated mold cavity. The mold is then closed with a top force or plug, applying pressure to shape the silicone into the desired form as it cures. Most of this type of molding uses labor-intensive production methods.

Transfer Molding: Similar to compression molding, transfer molding involves placing silicone rubber into a chamber where it is heated. Then, through pressure, the silicone is transferred into the mold cavity where it cures. This method is suitable for creating parts with intricate designs and tighter tolerances. However, there is still a gap in efficiency compared to injection molding.

Liquid Injection Molding (LIM): LIM is a highly automated process tailored for liquid silicone rubber. It combines the efficiency of injection molding with the unique properties of LSR, such as extreme temperature resistance and flexibility. The process allows for fast cycle times, high production rates, and detailed part geometries, making it a favored choice for medical, automotive, and consumer goods.

Extrusion: Silicone extrusion involves forcing uncured silicone through a shaped die to create continuous profiles, tubes, strips, or cords. Once extruded, these profiles are vulcanized to achieve the desired mechanical properties. This method is particularly useful for manufacturing seals, gaskets, and tubing.

Material Properties and Design Considerations

Mechanical Properties:

Tensile Strength: This is a measure of the force required to pull something to the point where it breaks. Silicone’s tensile strength indicates its resistance to being pulled apart, making it ideal for products that need to withstand stretching or stress.

Tear Strength: Silicone’s tear strength is crucial for applications where the material might be subjected to sharp objects or rough handling. It measures the ability of silicone to resist tearing when nicked or punctured.

Compression Set: This property assesses how well silicone can return to its original thickness after being compressed. A low compression set is vital for seals and gaskets, ensuring they maintain their effectiveness over time.

Durometer (Shore Hardness): The durometer scale measures the hardness of silicone, affecting its flexibility and resilience. Silicone products can range from very soft, with a low Shore A rating, suitable for gel pads, to much harder forms with a high Shore A rating, used for more rigid components.

Thermal and Chemical Properties:

Thermal Conductivity: This property defines how well silicone can conduct heat. Silicone with high thermal conductivity is used in applications requiring heat dissipation, such as electronic components.

Chemical Resistance: Silicone’s resistance to chemicals, including oils, acids, and solvents, makes it valuable for industrial uses where exposure to harsh substances is common. Selecting silicone with the appropriate chemical resistance ensures the longevity and reliability of the product.

Design Factors:

Parting Line: In-molded silicone parts, the parting line is where the two halves of the mold meet. It’s a critical consideration in design, as it can affect the aesthetics and functionality of the final product. Minimizing visible parting lines on surfaces that require smoothness or are highly visible is often a priority.

Flash: Flash is an excess thin material that forms along the parting line of a silicone product. High-quality molds and precise molding processes can reduce flash, improving the appearance and reducing post-processing work.

Viscosity: The viscosity of silicone before curing affects its processability and the detail it can capture in molding. Low-viscosity silicones fill molds more easily, capturing intricate details, but may require careful handling to avoid bubbles and defects.

Throughout this guide, we’ve explored essential terminology in the silicone product manufacturing industry, from the basic differences between silicone and silicon to advanced manufacturing processes like injection molding and liquid injection molding. We’ve also delved into the critical properties of silicone, and design considerations. Hope it helps.