Liquid Injection Molding (LIM), also referred to as Liquid Silicone Rubber (LSR) molding, is an injection molding process that uses a high viscosity liquid in two parts that is mixed with a platinum catalyst to enable a much faster cure rate compared to the injection molding of high consistency (HCR) rubber.  The faster cure rate makes it ideally suited for high-volume manufacturing. LIM/LSR molding is a closed system of molding, so the uncured raw material never comes into human contact. This molding process is ideal for high purity applications such as in the medical, biopharmaceutical, food processing, dairy, and semiconductor industries.

The liquid injection molding/liquid silicone rubber molding process is ideal to produce complex designed parts such as three-dimensional configurations, parts with multiple thicknesses, undercuts, and high-volume overmolding.  At RD Rubber Technology Corporation, we have taken the manufacturing process of LIM/LSR molding to a new level through our engineered quality system. This system provides our customers with a level of quality that is engineered into the process from the beginning of your project. RD Rubber Technology Corporations welcomes low-volume prototype and development quantities to high volume production while producing high purity, precision tolerance parts for a wide range of applications.  

Equipment

Liquid Silicone Rubber (LSR) / Liquid Injection Molding (LIM) molding machines typically require the following components and processes:

  • Injectors: Used to pressurize the material and assist the movement of the material into the machine’s pump. 
  • Metering Units: Metering units pump the catalyst and the base in consistent proportion to form the silicone mixture.
  • Supply Drums (plungers): Supply drums are the main storage vessels for raw materials.  
  • Mixers: After exiting the metering units, mixers combine the materials and use pressure to inject the mixture into the designated mold cavity. Mixers can be static or dynamic. Dynamic mixers contain a moving agitator, while static mixers have no moving parts.
  • Nozzle: The nozzle deposits the silicone mixture into the mold cavity to begin the curing process. An automatic shut-off valve prevents the mold from overfilling or leaking.
  • Mold Clamp: A mold clamp keeps the mold in place during the molding process and releases the mold after curing.

Liquid Silicone Rubber Injection Molding Process

Liquid injection mold silicone rubbers are supplied in a range of volumes and vessels—from small tubes to 55-gallon drums. The catalyst and base are shipped in separate containers or kits marked as “A” and “B” compounds. The two compounds should be mixed using a one-to-one ratio. This is typically done with a static mixer with the option to introduce colored pigment during the mixing process before the curing process. 

Curing begins immediately after the components have been mixed. To successfully insert the materials into the mold, the curing process must be slowed. This is achieved using a chiller that supplies cold water to the jacketed fittings.

Liquid Silicone Rubber Material Characteristics

Silicone rubbers maintain their mechanical properties over a wide range of temperatures and are ideally suited for demanding applications such as O-rings, seals, medical device equipment, surgical instruments, and biopharmaceutical applications such as antibiotic and vaccine production.  Injection molded silicone rubber can also be overmolded onto other materials and substrates made from thermoplastics.  

  • Biocompatibility: Liquid silicone rubber does not produce an immunological response in human tissue upon exposure, making it highly biocompatible. LSR resists bacterial growth and is suitable for use alongside other materials as it does not cause stains or corrosion. With no discernible taste or odor, LSR is ideal for use in the food and beverage industries as it complies with strict FDA regulations and can withstand a variety of sterilization methods.
  • Chemical resistance: LSR is water- and oxidation-resistant and can withstand exposure to some acidic and alkaline materials.
  • Temperature resistance: Liquid silicone rubber retains its structural integrity in a range of extreme temperatures.
  • Mechanical properties: With a hardness range between 5 to 80 Shore A, LSR exhibits enhanced tear and tensile strength, excellent flexibility, and superior elongation.
  • Electrical properties: LSR is a great insulator and compared to conventional insulating materials, silicone can perform in a much larger range of temperatures.
  • Transparency and coloration: LSR is characteristically transparent which facilitates the production of molded parts featuring different colors.

At RD Rubber Technology, our capabilities, flexibility, and customer service are reflected in every component we make. We are a local manufacturer delivering parts sourced and made in the USA, mitigating supply chain issues often encountered with international suppliers. Our engineering team develops innovative solutions that our customers have relied on for over 35 years. We also provide excellent customer service with an attentive and responsive support team to provide one-to-one support.

At RD Rubber Technology Corporation, our engineering process starts with understanding your requests and providing responsive and insightful communication. Our extensive capabilities allow us to produce from single and low volume prototype quantities to very high volumes. We enforce ISO 9001:2015 and AS9100:2016 Certified Quality Management Systems to monitor production from start to finish. Our industry quality certifications include:

  • AS 9100:2016 Certified
  • ISO 9001:2015 Certified
  • ITAR Registered
  • MIL-I-45208A
  • Conform to Military Specifications
  • ANSI Z540-1
  • GMP Standards
  • ISO 10012-1 and ISO 3601-3

Contact us to learn more about our silicone injection molding capabilities.