From molds to parts, there are many materials that come into play with the silicone injection molding process. Liquid injection molding utilizes liquid silicone rubber (LSR) and other elastomeric materials to create a wide variety of pliable yet durable products such as seals, membranes, electrical connectors, medical products, and kitchen goods. Liquid injection molding relies on a mechanical mixing process to build consistency over using labor-intensive processes such as compression molding.

Comprised mostly of silicones, acrylics, additives and fibers, there are many materials used in the process of LIM.

Here’s a look at the process:

• The materials are applied with a spring-loaded pin nozzle. This prevents clogging of the machine hardware.
• One plunger holds the base forming plastic and one holds the catalyst.
• Each goes into a static mixer to begin mixing.
• The liquid mixture is injected into the appropriate mold (this will depend on what is being created, whether keypads or phone cases.
• The mold is heated at temperatures ranging from 355F to 390 F.
• The fluid begins to cure, or harden.
• The molding machine will eject the finished part.
• The materials are heated to their melting point.
• They then cool off in the mold.

Why is silicone rubber such a great material for molding?

Well, for one thing, it has a very low viscosity and is able to flow into a hot mold easily. It can even do this at low pressures. The mold will be determined by the part and its thickness, along with how it will be produced in each cycle. The parting line (this is where the two halves of the mold come together), as well as how deep the vent tracks are, will ensure the proper fill before the silicone starts to cure. LSR molding will shrink once it is cooled, so this has to be factored in when planning the mold.

Steel is one durable choice used in molds because it holds heat well and is extremely durable. It retains this durability even after going through many heating and cooling cycles over and over through the lifespan of the product. Aluminum is another option, used because it is lightweight, less costly and quick to heat.

Silicone rubber fills the mold’s finish, no matter what the mold’s material, giving the resulting products a clean, matte finish. You can even choose to polish it for a shiny texture.

Here at SiTech, we work with a closed loop system in an effort to mold liquid silicone rubber (LSR). With machines that mix and measure precisely, the material can be injected right into the mold. This method reduces the risk of contamination to the product, increasing both the repeatability and precision of the product.

We like Liquid Silicone Rubber for its ability to fill and cure at a quicker rate than gum stock or high consistency silicone rubber (HCR). LSR Is able to fill intricate and complex areas of the mold for faster cycle times and tighter tolerances. The entire curing process takes place inside the mold, producing less waste than other methods like HCR. Cold runner tooling keeps the LSR cool so the silicone is able to isolate and cure inside the cavities of the hot mold. This reduces the need for trimming with the final product.

Si-Tech is proud to use only the highest quality materials and molds to produce your products!

Contact Si-Tech

To learn more about the Silicone Injection Molding Materials we use here at Si-Tech, just contact us today at 757-887-8488.