What is Liquid Injection Moulding?

 I. What is liquid silicone rubber molding?

Liquid silicone rubber (LSR) molding, sometimes called liquid injection molding (LIM), is a thermosetting process in which two compounds are mixed and then heat-cured using a platinum catalyst inside a mold to create flexible silicone parts. Low compression permanent deformation and the ability to resist extreme temperatures make LSR molded pieces durable and ideal for challenging applications. LSR elastomers offer superior optical clarity, durability, and design flexibility while operating over a wide temperature range (-50℃ to 250℃).

LSR injection molding is suitable for manufacturing complex geometric shapes, and because of its design and mold flexibility, multiple functional components can be combined into a single part. LIM has considerable advantages in terms of product reliability and total tooling cost.

II.How is LSR different from injection molding?

LSR molding is very similar to the way traditional injection molded parts are formed in the mold but differs in the way the parts are cured.

In injection molding, thermoplastic resins are melted and pressure cured before injection. LSR is a two-part thermosetting compound that is cooled and eventually cured into a final component before being injected into a heated mold. Thermosetting LSRS is formed in a permanent state and cannot be remelted and reused like thermoplastics. Component A and component B are mixed in a ratio of 1:1 to undergo a thermal acceleration reaction that converts liquid into solid rubber.

III.How does the LSR molding process work?

As shown in the figure below, a liquid injection molding machine consists of a pair of feeding cylinders or plungers, a syringe, a metering pump, a static cold mixer, a nozzle, and a heating mold.

First, liquid silicone rubber compounds (A and B) and platinum catalysts are added to the pumping system using a supply barrel. These are also known as plungers and act as the main containers for the two compounds. A separate container holds the additives and pigments.

The syringe then pressurizes the liquid silicone rubber to help inject the material into the machine's metering pump. Then, the pressure and injection rate is controlled to improve the repeatability and accuracy of the process.

The metering pump or unit then mixes the two liquid components, the catalyst, and the silicone to ensure a consistent ratio (1:1) between the two materials when delivered simultaneously.

The silicone rubber, catalyst, additive, and pigment are then pumped into the nozzle through a cold-flow static mixer.

From the metering section and mixer, the mixed compound is pushed through a nozzle into a cooled runner system into a heated mold cavity, where it is vulcanized. A nozzle helps the mixture deposit into the mold. To avoid leaks and mold overfilling, nozzles are usually equipped with automatic shutoff valves.

A mold clamp holds the mold in place throughout the injection process and opens the mold after the procedure is completed.

Liquid silicone rubber applications

IIII. What Are The Applications of Liquid Silicone Rubber?

Liquid silicone rubber is used in a wide range of applications, from consumer electronics to extreme industrial applications.

·Optics - Outdoor, automotive, and professional lighting

·Automotive - Lens LED lighting, light guides, optical couplers, O-rings, buttons, components, washers, and wiring harness components

·Electronic products -LED lens, light guide, protective sleeve

·Consumer products - nose pads, earmuffs, headphones

·Healthcare and Medical - Medical tubing, endoscope assemblies, catheters, lenses, UVLED lighting, flow control valves, syringe plugs, and other components

V. What Are the Advantages and Disadvantages of Liquid Silicone Rubber?

·Its low viscosity allows the material to flow easily into thin and complex areas of the mold.

·Excellent compatibility with human tissues and fluids

·Excellent chemical resistance

·Suitable for mass production

·Excellent mechanical properties, including good elongation, excellent tearing strength, high tensile strength, and wide hardness range (5-80 shore).

·Process repeatability

·Compared with the molding, the cycle time is short

·Antibacterial growth

·Easy process automation

·The bactericidal ability makes LSRS suitable for use in medical and healthcare products.

·Adhere to strict FDA guidelines

·Excellent resistance and stability in most consumer environments

·Higher temperature resistance than thermoplastics

·Suitable for complex and high-precision parts

·High tearing and tensile strength

 There are also some disadvantages of liquid silicone rubber, including:

·Once cured, LSRS cannot be reformed, so they cannot be recovered

·High production time and cost

·Untreated, it can be sticky and can attract dust and other particles

·They are not suitable for applications immersed in alcohol or gasoline

·When exposed to certain materials, such as sulfur and latex, LSRS inhibit their curing

·The selection of materials for the LIM process is limited

·There are limited grades of silicone rubber available

We are a silicone part & custom silicone product manufacturer. We have manufactured custom silicone products for over 15 years. Our business keys are on lsr injection molding, overmolding, and custom silicone molding. Our goal is to solve problems for customers. The parts include a silicone seal, silicone o-ring, silicone gasket, silicone tubing, silicone rubber cap, silicone rubber plug, and more.