The birth of liquid silicone rubber manufacturing technology has brought about a whole new era for the rubber industry. This technology, which uses injection molding as its main technique, can produce varieties and quantities of LSR products at high speed and low cost with a relatively lower labor input.

Over time it will undoubtedly become one of the mainstream technologies in plants producing custom-made personal health products (such as condoms) or professional used sports shoes.

Read on as we go through the liquid silicone rubber injection molding and process of LSR molding from beginning to end.

What is Liquid Silicone Rubber Molding?

Liquid silicone rubber is a material that has been around for decades and is the preferred type of rubber for manufacturing parts. The unique quality of liquid silicone injection molding makes it different from traditional high-consistency silicone molding and other thermoplastic injection molding processes.

Liquid silicone injection molded parts are elastic with a high degree of chemical, electrical and thermal resistance. In addition, the parts are biocompatible and can be subjected to sterilization. These products are used in a variety of industries, including healthcare, automotive, infant care, general industrial markets, aerospace, electronics, and many other professional industries.

Liquid silicone injection molding is a process that allows you to create parts with high-quality properties in a noticeably abbreviated time. Best of all, the production process is highly automated, so you can always produce parts with a healthy efficiency.

The Steps in Liquid Silicone Rubber Molding

Step 1. Preparation of the liquid silicone rubber

The first step is to prepare the mixture. Emulsions consist of two components, pigment, and additives. Depending on the desired properties of the final product, you can choose between combinations. This is where you combine all ingredients in a homogenous mixture.

This formulation can be used with the temperature stabilization system to help regulate the silicone's temperature based on ambient air temperature or preheating the silicone.

Step 2. Preparation of the mold

The product has an internal part called inserts placed in the mold. These inserts can be either left at room temperature or preheated before being placed in the mold. Liquid Silicone Rubber is supplied in barrels, with low viscosity, allowing it to be pumped through pipelines and tubes.

The mold is usually heated by electrical heaters or by water flowing inside the mold. Additionally, a cold runner system can be used to prevent the premature curing of the silicone either in the runners or nearby.

Step 3. Clamping of the machine and the mold

There are two ways the injection molding process can proceed, under atmospheric pressure, which requires efficient ventilation, or in vacuum conditions. The length of the process depends on the pressure. This is further determined by the product that needs to be manufactured and the properties of silicone, including viscosity. This property is dependent on shear rate, temperature, and increase during the flow.

Once the mold is filled with silicone the temperature of the mold is increased to hasten the crosslinking process of the material. It results in the rapid transformation of silicone rubber from liquid to solid state. This is the curing stage.

The length of curing depends on the silicone grade and the product. It is critical in the silicone molding process because it may cause material overheating and a significant increase in pressure inside the mold.

Step 4. Cooling

The final step in the liquid silicone rubber molding process is cooling the product inside the mold. The combination of heat and pressure used on the liquid silicone rubber is instrumental in curing the material until it solidifies. Once the cycle is completed, the mold will open and the part and flashing are removed.

After the removal of the item from mold, additional post-molding processes including de-flashing, post-curing, inspection, and packaging are done.

When the cycle is completed, the liquid silicone injection molding process will be prepared with new material for other parts designs. This is important, or else the new part will have the production run of silicone in them. Next, everything should be cleaned, which could take a day, depending on the injection mold press used.

Conclusion

All the steps we have mentioned above can strongly affect the result of the liquid silicone rubber molding process. Therefore, manufacturers should optimize all the measures to ensure the shortest production cycle while keeping the highest quality of the product.