Silicone Rubber Injection Molding

Liquid silicone rubber is commonly used to make high-quality molded components and parts. This material has properties that resist heat and cold. Compared to plastic components, silicone parts are more durable and can make excellent prototypes. When choosing a technique for making silicone parts, the key factors to consider are speed, approximation, and cost.

 

Below are some important things about silicone rubber injection molding:

Silicone Injection Molding Can be Used to Create Prototypes In A Short Lead-time

Due to its thermosetting nature, producing shapes out of silicone requires extensive mixing. This process is usually done through various methods, including room temperature vulcanization and 3D printing.

 

RTV molding is a process that uses the materials of plastic and metal, and it can be done in-house using the capital-efficient Raw materials. However, this method is not ideal for complex projects, and it can take a skilled technician to complete a prototype.Due to the availability of new materials, 3D printing of elastomeric parts has been made possible. This method does not require the use of mold machines.

 

Rapid injection molding is a process that uses liquid silicone rubber or LSR. This procedure is commonly used to produce plastic parts.Learn more about rapid injection molding at Injection Molding Services - TEAM MFG (team-mfg.com)

  

Here are the advantages of silicone rubber injection molding:

‘Flashless’ technology (zero burrs)

Short cycle time

Batches stability or ready-to-use material

Automated demolding systems

Direct injection (zero waste)

Automated process

Process repeatability

Principles of LSR Mold Design

 

1. Shrinkage

A rubber part should not remain on the core of a mold. It should instead be in the cavity with larger areas. LSR shrinkage depends on the following factors:

Cavity pressure and material compression

Tool temperature or demolding temperature

Part dimension (thicker LSR parts shrink lower than thinner rubber parts)

Injection point location or shrinkage in a material flow direction

Post-curing (causes additional shrinkage)

 

2,Parting Line

The location of the parting line is very important in injection mold development. It coordinates the flow of material through special channels. The separation of the rubber part from its molded counterpart will help minimize air entrapments. Also, it prevents the area from getting sensitive and producing flash.

 

3.Venting

The air trapped in the heated cavity is compressed and expelled through the venting channels. If the air can't escape entirely, it will get stuck. A vacuum is also used to vent the air coming out of the cavity. The air is then injected through a pump to push the resin into the closing cavity. Modern silicone injection machines have various clamping forces. The low clamping force allows the easy escape of air while avoiding flash.Liquid RubberSilicone Rubber Has a Wide Range of Applications

 

Liquid Silicone Rubber Has a Wide Range of Applications

Thermoset elastomers are mainly composed of various compounds such as silicone rubbers, which have an alternating oxygen and silicon atom structure. Due to their properties, silicone rubbers are ideal for making electrical insulation. They can also be used to make electrical surface mounts. Here are the most common applications of silicone rubber products produced via silicone injection molding:

Electric connectors

Seals

Infant products

Sealing membranes

Medical applications

Multi-pin connectors

Silicone Injection Molding Equipment

Kitchen goods

A liquid injection molding machine is used to make plastic parts. It uses a mechanical pump to inject the liquid.

 

Silicone Injection Molding Process

Since LSR injection is performed at high temperatures, it is important that the product is shrink-treated before it's injected. This process involves the use of steel dilation and natural shrinkage. Here is the step-by-step silicone injection molding process:

Before the static mixer is used, various additives and coloring paste are also added. These components are mixed and transferred into the machine's metering section.

Use the static mixer and the material becomes homogeneous and very consistent from one part to another. The material is then pushed through a cooled runner system to a heated cavity. This eliminates the need for re-lamping and allows the material to remain cool.

Understanding the Liquid Silicone Rubber or LSR Vulcanization Process

Due to its thermosetting properties, liquid silicone injection mold requires special treatment to maintain its low temperature. This process is initiated by mixing the molten resin with a liquid rubber. The speed of vulcanization for liquid silicone rubber depends on several factors, such as the following:

Silicone temperature upon reaching the heated cavity

Mold temperature or possible inserts temperature

Curing chemistry

Part or component geometry

General vulcanization behavior

This process increases the productivity of the mold by raising the temperature of the injection vessel and the cold runner before heating it up.

 

Here are some good-to-know facts about the liquid rubber silicone vulcanization process:

Injecting pre-heated silicone is highly recommended for fully automated processes. It makes larger items with small surface-volume ratios.

The cooling system should be activated to prevent the curing of the material. It must be done immediately if the machine’s cycle is interrupted.

The duration of vulcanization depends on the component and the injection barrel. The longer the vulcanization time, the more effective it is.

Before a part is molded, it is commonly assessed how long it will take to cure. This figure is computed by using simulation software to get a better understanding of the material's properties.

 

Understanding the Curing Behavior of Liquid Silicone Rubber

A key factor in curing LSR is temperature. The time should be short enough to permit injection, but high enough to reduce cure time. It takes a few weeks for the material to become fully vulcanized at 25 degrees Celsius. However, if the temperature exceeds 120 degrees Celsius, the process only lasts a few seconds. By choosing an LSR with a very fast curing time at lower temperatures, it significantly increases your production output. Post-curing is the process of making finished silicone rubber parts that meet certain requirements. These include the requirements of the FDA and the Federal Institute of Risk Assessment. In four hours, a batch of finished products can be produced at a temperature of 200 degrees Celsius. The process involves the use of fresh air.

 

Other Silicone Injection Molding Technologies

Two-part silicone injection molding is a widely used technique in silicone injection molding. This procedure involves creating both the parts and the final product.Aside from faster curing, other silicone injection technologies can also be utilized for improving the production of finished products. Here are the other silicone molding technologies you may consider:

 

Multiple color rubber silicone parts productions

Electrically conductive LSR in combination with other insulating ones used in high-voltage applications

Silicone gaskets injection produced on aluminum housings

 

Conclusion

This material is a versatile and safe material that can be used in various applications. Learn more about silicone injection molding and its various advantages.