LSR Injection Molding Introduction

Liquid silicone rubber injection molding is a thermoset process that cools the material delivery system, while heating the mold tool to cure silicone material into parts. The liquid silicone injection molding process is highly automated with short cycle times to reduce the silicone part price. 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.

Albright Technologies is pleased to offer LSR (liquid silicone rubber) injection molding solutions. We manufacture injection molding tools in-house to provide you with rapid silicone prototypes and low-volume production parts as the design progresses. Once your injection molding tools are completed, we will provide you with engineering samples. After the engineering samples are accepted, then it is time for LSR silicone injection molding process to commence.

Albright is here to guide you from prototyping to high production molding of silicone part designs. We will partner with you through the initial part designs to final prototype to production LSR silicone injection molding as your operation ramps up.

We provide controlled environment room (ISO Class 7) injection molding services on our Arburg LSR silicone injection molding presses. This provides our medical and pharmaceutical customers with production silicone injection molding of their medical devices. We can injection mold orders from 10 to 100,000+ parts using these injection presses. Contact us today if you are ready to move your low-volume injection molded liquid silicone rubber parts to Albright Technologies at 978.466.5870 or via email. We can review your new or current part designs via our RFQ form. If you “needed a quote yesterday” for silicone injection molded parts, contact our sales department right now at 978.466.5870.

LSR Liquid Silicone Rubber Injection Molding Process

Our liquid silicone rubber injection molding machine appears to look just like thermoplastic injection molding machines. Both types of presses use the same basic machine parts, clamp unit, and injection unit.

The LSR injection molding machine clamp unit is identical for liquid silicone rubber and thermoplastic machines. The silicone injection molding machines typically have a hydraulic ram and may have a hydraulic toggle. Some presses are designed with an electric ram with toggle. Unlike the high pressures used to mold thermoplastic parts, liquid silicone injection pressure is in the range of 800 PSI. The purpose of the clamp is to contain the expansion force of the silicone material, by keeping the mold closed as the silicone cures.

The injection unit for liquid silicone runs cool with a water cooled barrel and nozzle to prevent the liquid silicone from curing. Thermoplastic injection units run the opposite way, they need the barrel and nozzle to be heated to 300F or more to keep the material moving. Liquid injection molding units also run at lower pressures (under 1,000 PSI), while their thermoplastic counterparts run at tens of thousands of PSI.

Liquid silicone is typically provided in 5 gallon pail or 55 gallon drums. There is a part A and Part B. Colorants come in the form of dispersions and are normally 1-3% by weight of mixed silicone. The silicone dousing unit pumps one part A silicone and one part B silicone via separate hoses to the static mixer. In addition, color is pumped to the static mixer via another hose. The mixed components are then fed into the throat of the injection molding barrel by way of a shut-off valve.

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Once the silicone material is inside the barrel, a shot of the cool mixed silicone advances to the mold as the nozzle seals firmly against the mold. The nozzle shut-off valve opens and a measured shot of cool liquid silicone is injected into a hot (275F to 390F) clamped mold. Then the nozzle shut-off valve opens and the barrel retracts from the mold, while the screw begins to build another measured shot of cold liquid silicone.

After the silicone vulcanizes in the heated mold, the clamp will open and parts are then manually removed or automatically ejected. Cycle times for liquid silicone molded parts are often similar to their thermoplastic counterparts.

As the production molding run comes to a close, the liquid silicone injection molding press must be readied for a new material for a different part design. It is not acceptable to purge out the system with the new silicone, which will result in the new parts having the last production runs’ silicone in them. Therefore, everything must be cleaned out, which can easily take a day to clean, depending on which injection molding press is used.

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