Liquid Silicone Molding 101

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By Jeremy Losek, Nov 17th, 2020

What is Liquid Silicone Molding?

Liquid silicone rubber (LSR) products span across a variety of industries. Seals, electric connectors, kitchen items, and baby products, are all made of silicone rubber. The use of silicone has become popular because it can maintain its mechanical properties over a wide range of temperatures, from freezing to extreme heat, and it can repel water. The process of producing a liquid silicone rubber part is similar to that of other thermoplastic parts.

What are the Properties of Liquid Rubber Silicone?

Liquid silicone rubber has many advantages that make it the ideal material for a wide variety of items. It is highly durable and can withstand a range of temperatures. For example, some cupcake molds are made of silicone because it will not melt when placed in a hot oven. Silicone is also used for ice trays because it can tolerate the cold of a freezer. Liquid rubber silicone can resist water, oxidization, and acids and alkali. It has good elongation, high tear, and tensile strength, as well as excellent flexibility. LSR is transparent which makes it easy to add color. It is resistant to bacteria and can be sterilized, making it a popular material for medical-grade products.

Liquid Silicone Molding Process

LSR is shipped to the manufacturer in two separate containers, with an “A” compound and a “B” catalyst. Once A and B are mixed in a 1 to 1 ratio and pigment added, the curing process begins. The molder adjusts setting on the injection molding machine to accommodate LSR and the job requirements. This includes selecting the shot size of LSR as well as temperature, pressure, cycle-time, and injection rate. The LSR injection molding machine heats the mold and applies force on the clamp. The LSR is then delivered into the mold’s cavities. The liquid rubber silicone is cured until it solidifies. It is then ejected from the mold. The part is then finished which may include curing, inspection, deflashing, and packaging.

Advantages and Disadvantages of Liquid Silicone Molding

LSR is highly resistant to extreme temperatures, water, ozone, bacteria, and more. Its strength and flexibility make it a good material for many applications. Since it is naturally transparent, a pigment can be added, which allows the product to achieve a certain look or for parts to easily be identified. It is a consistent molding material that when combined with the closed process system of injection molding results in less waste and maximized efficiency. Since injection molding is highly automated and a closed system process, there is minimal labor and reduced labor costs. The overall process is quick and generally measured in seconds rather than minutes.

There are a few drawbacks to liquid silicone rubber. LSR does not meet aerospace specifications. This is because additives and fillers would need to be added to LSR which would result in poor flow. To counteract this, manufacturers will offer compression-molded LSR grades for aerospace projects. Tooling for LSR parts can be detailed and may lead to more expenses. The mold used for LSR can be more complex which can cause longer lead times.

Despite these few complications, the benefits of using LSR far outweigh the negatives. When combined with an experienced manufacturer like ICOMold, will ensure a consistent a cost-effective project. If you are interested in starting a project that uses liquid silicone molding, please contact us at (419) 867-3900 or email sales@icomold.com.

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