Liquid Silicone Rubber (LSR) is a high-purity, two-component platinum-cured elastomer that can be imbursed into a mold cavity to manufacture a part. It has been around since the late 70s and quickly became the choice material for manufacturing silicone parts and products.
LSR is commonly used in medical, life sciences, automotive, consumer, and industrial products and is favorably used because of its unique characteristics. Being highly biocompatible means, it can be used for parts that come into contact with humans. It's also highly durable, compatible with high temperatures, and transparent. Its electrical properties make it ideal for a whole host of electrical applications as silicone can perform in much higher and lower temperatures than conventional insulating materials. It is also translucent, meaning the polymer can be pigmented to match any desired color.
Much like all elastomeric materials, there needs to be a polymerization reaction to create molecular chains. Vinyl and methyl siloxane are then polymerized to form polydimethylsiloxane chains. These chains provide strength and flexibility to the material. This process will change it from the liquid to the more viscous basic form of the LSR.
Once the main polymer is created, the material gets reinforced with fumed silica. LSR materials use alternative silicates to reinforce the polymer chains and add tensile strength to the material. The material is then split into two halves and the catalyst (platinum) and crosslinker are added to separate halves. This ultimately increases the shelf life of these materials. When blended, there’s a short working life of LSRs, only around eight hours! By being able to split these halves, the material could be stored for years without it curing during that time.
There are many types of LSR materials, such as:
· Medical grades
· Radio Opaque
· Flame Retardant
· Fast Cure
As long as manufacturers adhere to the fundamental design rules they can produce a component that makes it easier to manufacture. LSR injection molding differs from traditional thermoplastic injection molding, it requires an understanding of its material properties and processing characteristics. A product designer and engineer must consider numerous functional and structural factors, including:
· The intended use of the part
· How the part fits in an assembly
· The loads the part will experience during use
Image: KraussMaffei displays their LSR machine at Silicone Expo USA 2022
In the silicone rubber molding process, the production tooling is often the longest step and requires the most amount of capital investment.
Whether it’s product design, tooling,
prototyping, or parts production the silicone rubber molding manufacturer
must have the capabilities to satisfy the most demanding
specifications. Quality standards for LSR injection molding should
include a robust quality system consisting of problem-solving tools and
quality protocols that include, Advanced Quality Planning, Custom Validations
and Qualifications, Control Plans, Customized Procedures, and A Wide Array of
Written by: Emma Suddes