Liquid Silicone Rubber: Properties, Types, and Process

If you need to make parts that are soft, strong, and can handle heat, Liquid Silicone Rubber (LSR) is a good material choice. You can use it to make all kinds of products, from baby bottles to car parts. In this blog, you’ll learn about the liquid silicone rubber uses, types, and properties.

What is Liquid Silicone Rubber?

First, it helps to know the difference between silicon and silicone. Silicon is a natural element, kind of like how diamonds form—it’s hard and crystal-like. Silicone, on the other hand, is man-made. It’s a mix of silicon, oxygen, and other elements like carbon and hydrogen. There are many types of silicone, and the ones that feel more like liquids are called liquid silicones.

Liquid Silicone Rubber (LSR) is a special type of silicone. It comes in two parts and starts out as a liquid. You usually shape it using a method called liquid injection molding. You can adjust its thickness, how it sticks to things, and how it handles heat and chemicals. Once it’s cured, it becomes strong, flexible, and very durable.

Estructura química

As mentioned earlier, LSR has two parts you mix together. One part has a platinum catalyst, and the other has a cross-linker and a curing control. When mixed, they react and turn into solid rubber.

LSR flows like a liquid, which makes it different from thicker rubbers like HCR (high consistency rubber). HCR can be cured in different ways, but LSR always uses platinum curing, which is cleaner and more exact.

Liquid Silicone Rubber Properties

Here are some of the properties of LSR that you need to know before using it in your project:

Safe for the body: It’s hypoallergenic and doesn’t react with body fluids. It also resists bacteria and won’t stain or damage other materials.

No taste or smell: You can use it for baby products or anything that needs to meet strict food safety rules.

Very strong: LSR parts hold up well in tough conditions. You’ll see it used in cars, electronics, and outdoor products that deal with heat, cold, or moisture.

Chemical resistant: LSR resists water, cleaning chemicals, and sterilization methods like steam or gas. That’s why it works well in medical and healthcare products.

Handles extreme temperatures: LSR can handle both hot and cold, from -60°C to 180°C. It’s great for dishwashers, faucets, and other products that deal with temperature changes.

Mechanical properties: LSR stretches and bends without breaking. It has high tensile strength, good flexibility, and a Shore hardness range from 5 to 80 Shore A, so you can choose how soft or firm the part needs to be. It’s great for seals and thin parts that need to sense changes in air, gas, or fluid flow.

Good for electrical parts: LSR insulates well and works in high or low temperatures. It’s used in many electronics, especially electric vehicle (EV) batteries.

Transparency: LSR starts out clear and white. You can easily add color to match your product design.

Types of LSR

There are different types of LSR, and these are some of the most common ones:

Medical Grade

Medical grade liquid silicone rubber is cleaned to remove anything that might react with the body. It’s safe for use in medical devices. Some are okay for short-term use (under 30 days), and others are for long-term (over 30 days). These are tested carefully for safety and often have FDA documentation to help with approvals.

Self-Lubricating

Special fluids are mixed in. After curing, the fluid rises to the surface, and it becomes slippery. This is helpful for parts that need to slide or move easily.

Food Grade

Food grade liquid silicone rubber is made to meet strict safety rules from the FDA for use with food and drinks. It’s safe, odorless, and tasteless. You can use it for things like baking molds, baby bottle nipples, kitchen tools, and drinkware. It can handle high heat, so it’s good for cooking and dishwasher use too.

Conductor

Carbon black is added to make the rubber conduct electricity. These parts are still strong and flexible and can be used where low electrical resistance is needed.

Self-Bonding

These stick to other materials like nylon, steel, or aluminum without needing extra glue or primer. Great for making seals that join different parts together.

Radio Opaque

Barium sulfate is added so the part shows up on X-rays. This is useful in medical tools like catheters and wound drains.

FLSR (Flourosilicone LSR)

This type is blended with fluorine to resist fuels and oils. It’s not yet approved for food or medical use, but it works well in automoción and industrial settings.

Flame Retardant

Standard LSR resists flames to a point. If you need higher flame ratings (like UL 94 V1 or V0), extra additives are used to help stop the fire.

Fast Cure

These are made to cure very quickly. That helps when you’re making a lot of parts fast, like in mass production.

Advantages of Using Liquid Silicone Rubber

Here are some of the main benefits of LSR:

• LSR is biocompatible and doesn’t cause allergic reactions.
• You can over-mold LSR onto other materials, creating parts with different properties.
• LSR has a low viscosity, which makes it easier to mold into complex shapes and detailed parts.
• Because of its chemical resistance, LSR is ideal for use in tough environments, like the aerospace and automotive industries.
• LSR parts take less time to mold, which helps you produce more parts in less time.
• LSR can handle high temperatures, so it is durable for various industrial uses.
• LSR can be sterilized without changing its properties, which is important for medical and food products.
• Its low viscosity allows you to create parts with complicated shapes or details.
• LSR is stronger and more flexible than other rubber types; that’s why it is easier to mold into complex designs.
• LSR offers a wide range of useful properties that make it more flexible than other materials.

However, LSR does have some downsides. The mixing and curing process can create more waste than other materials. Also, because it starts as a liquid, it takes longer to cure, which can cause delays in production, especially for larger or more detailed parts. While LSR is elastic, it can tear more easily than other materials, so it may not be suitable for all applications.

Liquid Silicone Rubber Molding Capabilities

When you design parts for silicone rubber molding, there are a few basic rules to follow. These tips help make the molding process smoother, improve how your part looks, and save time during production:

Size limit: Your part can be up to 12 in. x 8 in. x 4 in. (or 304.88mm x 203.2mm x 101.6mm).

Volume limit: Your part’s volume should be 13.3 cubic inches (or 217,948 cubic millimeters).

Depth limit: No part of your design should be deeper than 2 inches (50.88mm) from the parting line. If it is, your part needs to be smaller in overall size.

Mold area: The flat area that touches the mold should be no more than 48 square inches (or 30,968 square millimeters).

Tolerances: At DEK, we can keep the size accuracy of your part within ±0.005 mm.

Part Design & Materials

If you follow basic design rules for liquid silicone rubber (LSR), your parts will be easier to make and work better. Think about what the part is for, how it fits with other parts, and what pressure or stress it will handle.

LSR flows and cures differently than plastic. Plan for good tolerances and add smart features to avoid stress and defects. LSR fills thin walls well and handles different wall sizes without issues.

You can choose soft or firm LSR based on your needs. Basic LSR is good for simple parts. If you need heat or chemical resistance, mix in additives. For bonding to other materials, use self-adhesive LSR to skip glue or extra steps.

How Does Liquid Silicone Rubber Molding Work?

To make a high-quality LSR part, you need a strong and precise mold. The mold is made with CNC machines and EDM from tough stainless steel. It has to handle LSR’s runny texture, high heat (around 420°F / 215°C), and LSR’s roughness on tools

Building the mold takes time and money, but it’s worth it. LSR flows easily into small spaces, so mold design is simpler than for plastic.

Unlike plastic molds, LSR molds don’t need polish or draft angles. Once the part is cured, you can take it out without damage.

Liquid Silicone Rubber Part Production

Liquid silicone rubber (LSR) parts are made using a process called liquid injection molding (LIM). This is different from plastic molding because LSR is a two-part liquid that gets mixed and then injected into a mold.

Here’s how it works:

• You start with two containers: one has the base (Part A), and the other has the curing agent (Part B). These are pumped and mixed in a 1:1 ratio, sometimes with color added.
• The machine is set up with the right temperature, pressure, and injection settings based on your part’s design.
• The mold closes, and the liquid silicone is injected inside. Heat and pressure cure it into a solid shape.
• Once the part is cured, the mold opens. Robots (or workers in small jobs) remove the part.
• If needed, you can do extra steps like cutting, printing, or assembling after molding. Some places automate this, doing it right after molding without moving the part.

Applications of Liquid Silicone Rubber in Various Industries

You can use liquid silicone rubber (LSR) in many ways. Some applications were already mentioned earlier, but here are some of the biggest industries that use LSR:

Life Sciences: LSR is perfect for medical products because it’s safe, stable, and works well in tough environments. It’s used in respiratory masks, valves, surgical tools, and drug delivery devices.

Automóvil: LSR is great for automotive parts because it can handle extreme temperatures and UV light. It’s used in seals, connectors, gaskets, and sensors.

Productos de consumo: LSR is used in many everyday products like showerheads, toothbrushes, baby bottle tips, and appliances. It’s durable, bacteria-resistant, and works well in wet and dry environments.

Aplicaciones industriales: LSR is strong and can handle harsh conditions, so it is ideal for valves, gaskets, and safety products like smoke detectors and water heaters. It can resist chemicals and high heat, ensuring reliable performance in safety equipment and machinery.

DEK’s LSR Quality Standards

Look for an LSR parts manufacturer that follows strict quality standards. DEK inspects parts visually and tests materials regularly. We have certifications like ISO 9001 (for general quality), ISO 13485 (for medical parts), and IATF 16949 (for auto parts).

Póngase en contacto con nosotros now and get a quote for your liquid silicone rubber parts. You can choose the quality checks you need based on how the part will be used. Here are some inspection options you can pick from:

DFM Feedback: Get tips to make your part easier to mold

Molding Process Analysis Report: See how your part was made step-by-step

First Article Inspection (FAI): A full report on the first part made, using GD&T measurements to check accuracy

Conclusión

Liquid Silicone Rubber (LSR) is a strong, flexible material that’s great for many industries. It’s durable and resistant to heat. While it can take longer to cure and may tear more easily than other materials, its benefits make it a good choice for high-quality parts.