Liquid silicone rubber (LSR) is different from solid silicone rubber. LSR is a liquid material that undergoes high pressures and temperatures to manufacture finished parts. As a result, this elastomer has a faster curing time and higher precision than solid silicone rubber.
Furthermore, LSR manufactures products with intricate designs and fine details due to its flexibility. This article explores Liquid silicone rubber, its types, and industries where it is applicable.
What Is Liquid Silicone Rubber?
Liquid silicone rubber (LSR) is not just silicone rubber in liquid form. Instead, it is formed by curing the long polysiloxane backbones using platinum and peroxide in silicone rubber. These catalysts form crosslinks that reinforce the tensile and tear strength of the elastomer.
As a result, LSR consists of short polymer chains with low molecular weight. In addition, this type of silicone rubber has better flow properties.
LSR is processed through liquid injection molding. First, the liquid raw material is mixed in equal parts from two separate components. It is then injected into a hot mold through a cold runner system. Due to the design flexibility, LSR injection molding is suitable for manufacturing products with complex geometries in large quantities.
What Are the Different Types of Liquid Silicone Rubber?
High Consistency Rubber (HCR)
High-consistency rubber LSR is also known as high-temperature vulcanizing or heat-cured rubber. This elastomer has long polymer chains with high molecular weight. This type of rubber is manufactured in batches at high temperatures.
The key properties of HCR include its excellent electrical properties, thermal resistance, and weather resistance. In addition, HCR insulators have excellent mechanical properties, making them suitable for power transmission systems.
Liquid Injection Molding (LIM)
Liquid injection molding LSR is manufactured using the liquid injection molding process. The process creates high-quality rubber products with complex and intricate designs. Furthermore, LIM LSR is biocompatible, consistent, and precise. The design flexibility of this elastomer makes it ideal for producing parts of several shapes and sizes.
Room Temperature Vulcanizing (RTV)
Room temperature vulcanizing LSR is a type of LSR that cures at room temperature without requiring additional heat. Usually, during the manufacture of RTV LSR, a platinum catalyst is used to harden the rubber.
Consequently, RTV LSR is suitable for applications that do not require heat. The properties of this LSR include a low compression set, chemical resistance, electrical insulation, and high thermal stability.
Fluorosilicone Rubber (FSR)
The molecular structure of fluorosilicone LSR contains fluorine. Fluorine reinforces the properties of LSR, improving its chemical, fuel, and oil resistance. Furthermore, this type of LSR can withstand high temperatures and possesses excellent physical properties like flexibility and high tear strength.
Because fluorosilicone LSR can withstand high and low temperatures, it is used in sealing and gasket applications with extreme operating conditions.
Self-Bonding LSR
Self-bonding LSR can adhere to other substrates without needing a bonding agent. This type of LSR contains a reactive silicone resin that improves adhesion to several substrates, including glass, metals, and plastic.
Furthermore, this type of LSR cures quickly and possesses good flexibility and chemical resistance. Self-bonding LSR is especially suitable for over-molding applications and applications that need to bond two different materials, including silicone rubber.
Medical Grade LSR
The manufacturing process for medical grade LSR follows stringent rules to ensure it is suitable for medical applications. This type of LSR is biocompatible, non-toxic, and it is sterile.
What Are the Advantages of Liquid Silicone Rubber?
Physical Properties: liquid silicone rubber has excellent physical properties that distinguish it from other elastomers. This material is flexible and can be molded into several shapes and sizes. Furthermore, liquid silicone rubber is used for several high-heat industrial applications because of its durability and heat resistance.
Biocompatibility: LSR is biocompatible and inert. This elastomer does not react with body fluids or cause allergic reactions. In addition to its biocompatibility, LSR can be sterilized without changing its physical or chemical properties. This elastomer is used in the medical industry to manufacture several medical devices, including implants, respiratory, orthodontic, and orthopedic devices. These devices improve quality of life, comforting patients and reducing the risk of allergic reactions.
Chemical Resistance: LSR has excellent chemical resistance, making it ideal for applications with chemical exposure. The chemical resistance of LSR is due to its highly flexible molecular structure and its high elongation at break. This elastomer is used in the aerospace, electronics, and automotive industries. In addition, it is used to manufacture products, including seals, o-rings, and gaskets for harsh environments.
Design Flexibility: LSR is flexible and can be molded into different complex shapes and sizes. This elastomer has a low viscosity and high precision. Therefore, it fills molds to create intricate designs with consistent quality. The design flexibility of LSR is often utilized in the medical, consumer products, and automotive industries.
What Are the Common Applications of Liquid Silicone Rubber?
As discussed earlier, the properties of LSR make it ideal for various applications. Different industries that use this elastomer include;
Automotive: automotive seals and gaskets are manufactured from LSR. This elastomer is also used to manufacture vibration-damping components and connectors.
Aerospace: LSR is used to manufacture tubings, seals, and gaskets for aerospace applications.
Electronics: electronic components like seals, connectors, and keypads are manufactured from LSR materials
Consumer goods: LSR is used in the consumer goods industry to manufacture kitchen utensils, sports gear, baby products
Healthcare: surgical instruments, catheters, masks, infusion pumps, medical tubing, and syringes are some LSR medical devices manufactured from liquid silicone rubber
How to Manufacture Liquid Silicone Rubber Products?
Liquid silicone rubbers are flexible and can be molded into different products using several processes. The common methods of manufacturing LSR include injection, compression, and transfer molding.
Injection Molding
The injection molding process injects mixed LSR into a mold cavity. This molding is usually in the shape of the desired product. Once the elastomer fills the mold, it begins to cure and solidify. Depending on the type of LSR used, curing time varies. After the LSR cures, it is allowed to cool and further solidify.
The injection-molded rubber product is then removed from the mold and finished. Finishing the rubber product may include applying a coating or trimming off excess material.
Injection molding is a widely used rubber manufacturing method that produces consistently high-quality products with precise tolerances and minimal waste. The process is highly efficient and accurate, making it a suitable choice for large-scale production. Despite its advantages, injection molding has certain limitations such as high upfront costs, longer lead times, and limited material options.
Compression Molding
In compression molding, the LSR mixture is not injected into a mold. Instead, it is performed before being placed in a mold cavity. After closing the mold cavity, the material undergoes high pressure and temperature applied by a hydraulic press.
This process then cures and solidifies the material. After solidification and cooling, the finished rubber product is removed.
Unlike injection molding, compression molding has a low upfront cost. The process also produces minimal waste, and the finished products have high tensile strength. However, compression molding has longer lead times than injection molding, and the process is less precise.
Transfer Molding
In the transfer molding process, LSR is mixed with pigments and curing agents before it is heated. The material is then loaded in a transfer pot and placed in a press.
After applying pressure to the transfer pot, a sprue forces the LSR material into the mold cavity. The mold is then heated to cure and solidify the elastomer. After curing, the final products are removed.
Transfer molding is suitable for manufacturing complex shapes of high strength. In addition, the process has high precision and consistent quality. However, the downside of transfer molding is that it is only suitable for small production runs and has a high initial investment.
The table below summarizes the differences between injection molding, compression molding, and transfer molding
| Method | Advantages | Disadvantages |
| Injection Molding | High production rates Precise control over material flow Minimal waste | Complex and expensive machinery Limited material options |
| Compression Molding | High volume production Efficient use of material Low energy consumption | Lower dimensional accuracy Longer processing time Limited material options |
| Transfer Molding | High volume production Precise control over material flow Minimal waste | Complex and expensive machinery Limited material options Long lead times |
Conclusion
Liquid silicone rubber is versatile and used for manufacturing several products across several industries.
Due to its excellent properties, the material is suitable for medical, automotive, food, and consumer goods applications. Because there are different types of LSR, choosing one that suits your application and molding process is best.
Contact Hongju for Your Rubber Needs!
Manufacturing rubber products is more than molding processes. Attention to detail, expertise, and prototyping is critical to creating high-quality rubber parts with minimal waste. Hongju is one of the leading expert rubber products manufacturers with over two decades of experience.
We are experts at creating tailor-made, all-inclusive solutions that exceed your expectations. We can produce intricate and complex rubber products from compression molding to injection molding machines.
