HCR Silicone Injection Moulding – Silicone Technology

Injection moulding is a manufacturing process used to produce precision rubber components and rubber-to-metal bonded parts. This method is suitable for both Liquid Silicone Rubber (LSR) and High Consistency Rubber (HCR).

Injection Moulding Machines

An injection moulding machine (also known as a press) consists of an injection unit (barrel, reciprocating screw, and heater) and a clamping unit (nozzle, mould cavities, mould, and movable plates). It is ideal for producing complex, high-precision parts quickly and efficiently.

The injection moulding process supports a wide range of materials, including natural rubber, silicone rubber, nitrile rubber, liquid silicone rubber, and fluorosilicone (known for higher tear strength and durability). Commonly used metal inserts for rubber-to-metal bonding include aluminium, copper, and steel.

The Injection Moulding Process

The rubber injection moulding process involves heating the raw material and applying high pressure. The process includes several stages:

1. The raw material is continuously mixed and broken down.

2. The uncured rubber is fed from the hopper to the injection unit.

3. A large screw transfers the compound to the barrel in measured quantities.

4. The material is plasticised at high temperatures (typically 150°C to 200°C).

5. The molten rubber is injected into the mould cavity, where curing (vulcanisation) takes place under heat and pressure.

6. After curing, the part is cooled and removed from the mould.

Silicone has a tendency to adhere to the mould walls. To ease demoulding, an internal release agent or detergent can be added to the formulation.

Liquid Injection Moulding (LIM)

Another type of rubber moulding is Liquid Injection Moulding (LIM), used for producing flexible parts from two-component LSR. The silicone blend is first fed into a mixer, cured, and then injected into the mould. Internal guides direct the flow of material. LIM offers excellent thermal resistance, weathering properties, and electrical insulation. These products are ideal for medical applications, as LSR is physiologically inert and odourless.

Thermoplastic Rubber (TPR) Injection Moulding

A third variant is injection moulding of thermoplastic elastomers, suitable for applications requiring flexibility and reprocessability.

HCR Silicone Injection Moulding

The process for HCR silicone is similar to that of other elastomers. It involves feeding high-consistency rubber into a heated barrel and injecting it into a mould, where it cures to its final shape.

HCR vs LSR Silicone

HCR (High Consistency Rubber) and LSR (Liquid Silicone Rubber) are both commonly used elastomers. Their properties result from a chemical cross-linking reaction (vulcanisation). This process is essential for achieving the mechanical strength of silicone rubber, including compression set resistance and tear strength.

What is HCR Silicone?

HCR is a solid silicone compound cured using either organic peroxides or a platinum catalyst. It contains high-molecular-weight polymers with long chains and can also be processed via injection moulding. Post-curing may be required when peroxide-cured HCR is intended for biomedical use to remove residual by-products.

HCR silicone offers excellent thermal stability, weather resistance, and electrical insulation, making it ideal for demanding environments.

What is LSR Silicone?

LSR is a platinum-cured liquid silicone that is flowable and tacky before curing. It can be used in casting, extrusion, and injection moulding. Unlike HCR, LSR generates no molecular by-products during curing.

HCR silicone moulding typically requires less investment in tooling and equipment compared to LSR, which can reduce overall manufacturing costs.

Advantages of HCR Injection Moulding

• Minimal production waste

• Ability to mould complex geometries

• Fast cycle times

• Low unit costs

• High precision and repeatability

• Excellent for mass production

• Compatible with plastic and metal inserts

• Suitable for various shapes, sizes, and hardness levels

This process provides flexibility in design and is ideal for producing parts with intricate features.

Applications of HCR Moulded Silicone Products

HCR silicone components are used in both static and dynamic applications. Thanks to their excellent mechanical properties, they are ideal for:

• Automotive industry

• Aerospace

• Food processing

• Medical and healthcare sectors

Common HCR Moulded Products:

• Plugs

• Flat rings

• Shock absorbers

• Washers

• Caps

• Rubber seals

• O-rings

Manufacturers can produce custom-moulded silicone parts based on client specifications. With advanced production facilities and industry expertise, it’s possible to deliver high-quality rubber components quickly and efficiently.

For more information about HCR silicone moulding, please contact us at +48 22 292 40 24 or +48 505 16 03 03, via email at Power@PowerRubber.com, or use our contact form.