Liquid silicone rubber is a versatile elastomer used in many industries due to its durability and excellent performance under demanding working conditions. This article provides a detailed overview of liquid silicone rubber, its properties and its different types. You will also learn about the benefits and limitations of liquid silicone rubber. Let's start!
What is liquid silicone rubber?
Liquid silicone rubber or LSR is a unique platinum-cured two-part elastomer with excellent fluidity. The first part of LSR contains a platinum catalyst, while the second part contains methyl hydrogen siloxane as a crosslinker and alcohol quencher. It is usually injected into a silicone mold to create various parts with precise details.
The liquid nature of LSR distinguishes it from high-strength rubber materials. This material uses platinum additive curing and requires special treatment during injection molding. Additionally, silicone rubber parts do not produce byproducts or odors that can contaminate the air when cured, making LSR ideal for food and medical applications.
Properties of Liquid Silicone Rubber
Due to its excellent properties, liquid silicone rubber is used by manufacturers in demanding applications.
Tasteless and odorless
Liquid silicone rubber is ideal for a variety of applications, especially food, beverages and baby products, as it is tasteless and odorless. Therefore, you can easily formulate it to meet strict FDA standards for these applications.
Biocompatibility
Unlike other elastomers, liquid silicone rubber is more resistant to bacteria and does not corrode or discolor other materials. After extensive testing, LSR demonstrates excellent compatibility with human body fluids and tissues. As it is hypoallergenic, it is the ideal choice for products that come into contact with the skin.
Chemical resistance
Liquid silicone rubber materials are resistant to oxidation, water and chemical solutions such as bases and acids. Furthermore, they are compatible with sterilization methods such as electron beam, ethylene oxide (ETO), steam autoclaving, gamma rays and many other methods compatible with medical and healthcare products.
Transparency and pigmentation
Liquid silicone rubber is naturally translucent. Its natural color is white and it is suitable for pigmentation to produce individual molded parts in different colors.
Electrical properties
Liquid silicone rubber parts have excellent insulating properties that are suitable for various electrical applications. Silicone materials can perform better at higher and lower temperatures than traditional insulation materials.
Types of Liquid Silicone Rubber
Liquid silicone rubber comes in different types and compositions. Each species has different properties.
General Purpose LSR
This is a widely used material with diverse applications due to its flexibility, biocompatibility and heat resistance. Typical uses for the general purpose LSR type are gaskets, o-rings and industrial components.
High Temperature LSR
High temperature liquid silicone rubber materials can withstand extreme heat without deteriorating or degrading their properties. Common applications of this LSR include industrial equipment, automotive parts, and electronic components.
Medical Grade LSR
This type of liquid silicone rubber is formulated to meet strict biocompatibility and safety requirements for medical and healthcare products. LSR medical materials are sterilizable and biocompatible, making them suitable for applications that require contact with the human body.
Self-adhesive LSR
Self-adhesive LSR material has excellent properties because it adheres to itself without the use of other adhesives. This makes it perfect for producing complex assemblies without relying on traditional gluing techniques.
Food Grade LSR
Food grade is similar to LSR medical grade. Meets strict requirements for contact with food and beverages. Baby products, baking pans, and kitchen utensils are typical applications of food-grade liquid silicone.
Electrically conductive LSR
Contains electrostatic discharge (ESD) additives that provide electrical conductivity properties. This grade is commonly used in applications that require the electrical conductivity and flexibility of silicone rubber, including EMI/RFI shielding and flexible circuits.
Optically clear LSR
Optically transparent liquid silicone rubber is suitable for the production of products such as lenses, light guides and other optical parts and devices with transparency and optical clarity requirements.
Advantages and Limitations of Liquid Silicone Rubber
Liquid silicone rubber material offers remarkable advantages due to its unique properties.
Advantages of LSR
Below are some of these benefits:
Overmolding functions and complex geometries
Liquid silicone rubber is perfect for molding parts with complex shapes and complex features because it has low viscosity. At the same time, LSR is useful in developing sophisticated elements and overmolding them onto other substrates. Therefore, these silicone rubber parts often have complex and functional characteristics with different materials using a single manufacturing process.
Efficient manufacturing
Silicone rubber parts are more efficient and less expensive than other parts manufactured through traditional molding processes. Liquid silicone rubber parts allow for shorter molding cycle times and higher production yields, ensuring an efficient molding process.
Incredible versatility
Due to its high compatibility and excellent material properties, manufacturers often use liquid silicone rubber parts for various applications. These parts offer maximum precision and quality that meet the rigorous requirements of various industries. Furthermore, silicone rubber parts provide reliable solutions for industrial applications.
Limitations of LSR
Although LSR offers numerous advantages, the use of the material also has some limitations.
Waste of materials
Processing liquid silicone rubber parts may produce more waste than other rubber materials due to the high mixing precision and curing required.
Healing time
Silicone rubber parts take longer to cure than other rubber materials. This delays the production process, especially for complex and large components.
Regulatory aspects
Certain LSR formulations may contain additives or elements that are subject to regulatory review, especially in applications involving contact with food, sensitive environments or medical devices.
Tear resistance
Despite their good elasticity, LSR parts have lower tear resistance than other rubber materials. Therefore, its use may be limited in high tensile strength applications.
Liquid silicone rubber molding process: step by step
Injection molding is ideal for producing precise LSR silicone rubber parts. It offers parts with precise dimensions, complex design and excellent surface finish. Below is a step-by-step breakdown of the process.
Step 1: Material preparation
LSR material is a platinum-cured two-part elastomer containing a base silicone polymer and a curing medium. These components are combined in a calculated proportion to begin the molding process. You can mix these components manually or with automatic dosing and mixing tools.
Step 2: Injection Molding
It is best to inject the LSR mixture into the mold using special injection molding machines that are ideal for LSR processing. Generally, the mold consists of two cavities made of high-quality steel or aluminum, which determine the shape of the silicone rubber mold. You need to inject the liquid silicone rubber into the mold cavity under high pressure and ensure that it fills the required details and features.
Step 3: Curing
Cure and solidify the silicone rubber mold through a heat-triggered chemical reaction. Depending on the composition of the liquid silicone rubber, it is necessary to heat the mold to a certain temperature. The curing process takes a few minutes as it transforms the LSR material from a liquid elastomer to a solid elastomer.
Step 4: Let cool and unmold
It is important to cool the mold to a suitable temperature after the curing process. This ensures that the silicone rubber parts maintain their shape and dimensions. Once the parts have cooled properly, the mold can be safely opened. You can then eject the hardened parts from the mold cavities.
Step 5: Post-processing
Depending on the requirements of silicone rubber parts, post-processing operations may be required for your silicone rubber parts. These procedures may include removing excess material or burrs, checking for defects, and assembling components if the product consists of multiple parts.
Applications of liquid silicone rubber in various industries
Product designers and manufacturers often use liquid silicone rubber in a variety of industrial applications. The LSR injection molding process is ideal for late-stage prototype production to achieve near-production quality, especially in clinical trials and testing as well as pilot production requirements. Typical silicone rubber applications include:
Auto Industry
Due to its excellent performance when exposed to ultraviolet light and certain temperatures, LSR is suitable for the production of various parts in the automotive industry. Typical examples of parts manufactured with LSR include housings, seals and wire harness connectors, sensors, vibration dampers, seals and bellows.
consumer products
LSR is a versatile material that creates waterproof barriers and bacteria-resistant showers. It is also suitable for sealed, vibration-resistant housings for personal care products, including soft, flexible surfaces for headphones and hearing aid tips, electric toothbrushes and shavers.
Industrial applications
Liquid silicone rubber can withstand harsh environments. Therefore, LSR is ideal for manufacturing gaskets, valves, sealed enclosures and other components used in safety devices such as carbon monoxide and smoke detectors.
Medicine/Life Sciences
Due to its chemical inertness, stability in demanding environments and biocompatibility, liquid silicone rubber is widely used in the medical industry for various medical applications. Most products in the medical field consist of components with complicated features, tight tolerances, increased cleanliness, and tiny part geometries.
There are many important applications in the medical industry for which liquid silicone rubber is the ideal solution, including surgical instruments, respirators, membranes and drug delivery devices.
Design Considerations for Liquid Silicone Rubber Parts
There are several important tips and considerations to ensure successful production and optimal performance of silicone rubber parts. Below are some of these important design considerations:
Material compatibility
When overmolding LSR onto other substrates, it is advisable to ensure compatibility of the LSR material with the intended materials. Therefore, ensure that the process and mold design support proper bonding between the substrate and the LSR.
Tolerances and dimensional accuracy
Although liquid silicone rubber can reach tight tolerances, please note that there may be possible dimensional variations due to curing and shrinkage of the material. Therefore, it would be helpful to consult your mold makers to improve the geometry of your silicone rubber parts to obtain accurate dimensions.
Wall thickness
Use a balanced wall thickness for your parts to ensure uniform curing and avoid dimensional control errors and deformations such as warping or voids. Therefore, it is advisable to use a minimum wall thickness between 0.635 and 0.762 mm for small parts and a wall thickness between 1.02 and 1.27 mm for larger parts using injection molding. Also, be careful not to make hasty changes to wall thickness to avoid stress concentrations or uneven curing.
Undercuts and lean angles
Draft angles are critical when molding silicone rubber parts because they allow the parts to be ejected smoothly. Therefore, it is advisable to design your parts with suitable draft angles and reduce undercuts to ensure easy ejection.
Surface finish and texture
Silicone rubber parts are compatible with various surface finishes such as matte, textured or smooth. Therefore, it is advisable to choose the texture that meets the functional and aesthetic requirements of your silicone rubber parts.
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Concluding
Liquid silicone rubber is a responsive, durable, adaptable and safe material for certain applications. Silicone rubber parts have remarkable properties and perform well under different working conditions, making LSR an ideal material for a wide range of applications. However, it would be best to understand everything about liquid silicone rubber and design considerations for molding high-quality liquid silicone rubber parts.
Common questions
What is the difference between liquid silicone rubber and silicone rubber?
The parts made from liquid silicone rubber are odorless, highly transparent and have an opening for adhesive injection. In contrast, solid silicone parts exhibit low transparency due to vulcanizing agents or other odors surrounding the curing agents. Likewise, products made from solid silicone do not have an injection opening.
What are the common uses of liquid silicone rubber?
Liquid silicone is a multifunctional material with a wide range of applications. Manufacturers and product designers often use it in the manufacturing of automotive components, healthcare, electronics, and consumer goods.
Is liquid silicone rubber water resistant?
LSR is waterproof and does not decompose in contact with chemical solvents. Additionally, it is suitable for applications that require constant exposure to water.
