Hello everyone, this is Sunny from Milosilicone! Today, we’re diving into an exciting topic that is key to the manufacturing of many high-performance rubber and elastomeric products—Liquid Silicone Rubber (LSR) Injection Molding. Whether you’re designing components for automotive, medical, or industrial use, understanding the capabilities and advantages of LSR can help you make more informed decisions. Let’s explore how this versatile material and its molding process can meet your needs.
What is Liquid Silicone Rubber (LSR)?
Liquid Silicone Rubber (LSR) is a unique material that is increasingly popular in various industries for its flexibility, high-temperature resistance, and exceptional durability. Unlike traditional thermoplastics, LSR is a thermoset polymer that solidifies permanently after curing, making it perfect for high-stress environments where thermoplastics might not hold up. For many, the first encounter with LSR might be in the form of a flexible gasket from an automotive store. These gaskets, which are designed to endure the heat from an engine, showcase LSR’s ability to withstand extreme temperatures—up to 600°F (316°C) continuously, and up to 700°F (371°C) intermittently.
Despite its rubber-like consistency, LSR’s impressive heat resistance might seem counterintuitive to those familiar with thermoplastics, which tend to soften under heat. However, LSR is specifically engineered to endure high temperatures, making it a preferred material for applications in automotive, industrial, and medical sectors, where high heat is a common challenge.
Key Properties of LSR
- High-Temperature Resistance: As noted, LSR can handle both high temperatures (up to 700°F) and extremely low temperatures, making it ideal for applications that require flexibility across a wide temperature range.
- Exceptional Flexibility: LSR compounds, such as the popular LR3003/50, can stretch up to 480% of their original length before breaking. This elasticity is a critical property for components like seals, gaskets, and even medical devices that need to maintain their form while flexing or compressing.
- Chemical, Thermal, and Electrical Resistance: LSR offers excellent resistance to various chemicals, including oils and solvents, making it suitable for automotive applications. However, it’s worth noting that it may not be compatible with certain solvents like gasoline or mineral spirits.
- Low Compression Set: LSR retains its shape and flexibility even after being compressed, making it perfect for elastomeric applications. This feature is crucial when compared to thermoplastic elastomers (TPEs), which tend to deform over time.
- Biocompatibility: Certain grades of LSR are approved for medical applications where the material will be in direct contact with skin, and some grades can even be used for implantable devices. Its biocompatibility, along with its hydrophobic properties, makes LSR ideal for medical, food-handling, and other hygienic applications.
- Fire Retardancy: LSR is naturally fire-retardant and does not emit harmful toxins or halogens when burned, which is critical for safety-sensitive industries.
Thermoplastics vs. Thermosets
To better understand why LSR performs so well in high-temperature environments, it’s important to compare thermoplastics and thermosets. Thermoplastics, such as polyethylene and polycarbonate, are solid at room temperature and soften when heated. They can be easily recycled, which is one of their most attractive features. On the other hand, thermosets like LSR are formed through a curing process involving heat and catalysts. Once they solidify, they cannot be re-melted, which makes them highly durable and ideal for extreme environments but not suitable for recycling.
This distinction significantly impacts the molding process for each material. Thermoplastics are injected into molds while they are in a molten state, and then solidify as they cool. In contrast, LSR is injected into a cooled mold in its liquid state and undergoes a curing process under heat inside the mold, resulting in a fully hardened part once removed.
The Science of Shear Thinning in LSR Molding
A fascinating property of Liquid Silicone Rubber (LSR) is its behavior as a shear-thinning fluid. Shear thinning occurs when a material’s viscosity decreases as it is subjected to shear stress—essentially, it flows more easily under pressure. This is similar to how ketchup flows easily from a squeeze bottle but honey does not. For LSR, this property enhances its ability to fill intricate molds and complex cavities without the need for uniform wall thickness. However, it also presents a challenge in the form of flash, where excess material escapes from the mold cavity during the molding process. This is a critical consideration when designing molds for LSR parts.
Design Considerations for LSR Parts
When designing parts made from LSR, the process is somewhat similar to designing thermoplastic parts, but with a few key differences:
- Wall Thickness: Unlike thermoplastics, where uniform wall thickness is crucial for proper filling, LSR’s shear-thinning property allows it to flow into thinner areas more easily. Therefore, wall thickness is not as critical, and designers have more flexibility.
- Undercuts and Draft Angles: One of the significant advantages of LSR over thermoplastics is its ability to handle undercuts without requiring complex tooling. This is due to its flexibility, which allows parts to be “peeled” out of the mold. Additionally, draft angles of around one degree per inch are typically sufficient for proper ejection, although this may vary depending on the part design.
- Mold Release: LSR parts tend to stick to the mold halves with larger surface areas due to their flexibility. As a result, designers often need to incorporate features that facilitate easy manual removal from the mold, especially when dealing with undercuts.
- Sink Marks: Since LSR cures quickly during molding and doesn’t suffer from cooling-induced shrinkage like thermoplastics, sink marks are not a common issue. However, it is still advisable to avoid unnecessarily thick sections in the design to minimize material usage.
- Mold Flash: Careful attention to parting line design is crucial to minimize flash. Parts should be designed with short, simple parting lines to ensure effective removal and to prevent excess material from leaking out of the mold.
LSR Injection Molding at Milosilicone
At Milosilicone, we pride ourselves on our advanced LSR injection molding capabilities. Our team leverages cutting-edge technology to produce high-precision LSR components for a wide range of industries. Whether you’re working on prototypes or full-scale production, we offer rapid turnaround times and competitive pricing.
Why Choose Milosilicone for Your LSR Needs?
– Fast Prototyping: Our automated tooling process allows for quick prototyping, so you can test and refine your designs faster than traditional methods. This enables you to make adjustments early in the development cycle, saving both time and money.
– High-Quality Standards: We adhere to strict quality control processes, ensuring that every LSR part meets your specifications and industry standards. Whether it’s for medical, automotive, or industrial applications, you can rely on our commitment to excellence.
– Custom Solutions: Our team works closely with you to understand the unique requirements of your project. We offer tailored solutions to meet your specific needs, whether it’s for small production runs or large-scale manufacturing.
Stay Connected with Milosilicone
We are excited to be your partner in creating high-quality LSR products. If you’re looking for a reliable manufacturer for your Liquid Silicone Rubber components, don’t hesitate to reach out to us. Our experienced team is ready to assist with design recommendations, material selection, and production planning. Contact Milosilicone today to learn more about how we can help bring your ideas to life!