Manufacturing Processes for Silicone Rubber Parts
Silicone rubber parts can withstand extreme temperatures and maintain their flexibility. They also exhibit low stress relaxation, meaning they return to their original dimensions after being compressed for long periods of time.
Silicone is an excellent material for medical products, as it’s FDA & USP compliant and sterilizable. This type of rubber is often used in hoses, catheters, and wound care products.
Compression Molding
Liquid silicone rubber (LSR) is an incredibly versatile molding material. It can be molded into intricate, low-volume components like valves and connectors as well as end-use parts with complex geometry such as menstrual cups and baby bottle nipples. LSRs are also used to make lighted buttons, seals and gaskets, and can even be overmolded with other materials for added functionality.
Compression molding is an effective, cost-effective and quick manufacturing process for LSR molded products. This method uses a preformed piece of uncured silicone rubber in each mold cavity and heats it while closing the press. This accelerates the chemical reaction in the resin to create a thermoset with process caused crosslinking and results in tougher, less flexible, and resistant silicone parts. Then, the silicone is cured in an oven to achieve a fully cured and ready-to-use product.
While compression molding offers a lower upfront cost than injection or transfer, it requires longer processing times to bring your LSR project to a cured state. This can significantly impact production rates for high volume projects. Additionally, it can require more hand trimming or nitrogen de-flashing to achieve a clean, parting line that satisfies your design and tolerance criteria. If you choose to use this process for your project, look for a vendor with extensive experience and an up-to-date manufacturing facility to ensure quality results.
Transfer Molding
The manufacturing of silicone rubber requires a delicate balance between efficiency and product quality. There are several different production processes that fabricators can use to meet this need, each with its own unique set of benefits and drawbacks. For many plastic and rubber fabricators, the choice of process usually comes down to injection molding service and transfer molding.
In transfer molding, engineers load uncured pre-catalyzed silicone Silicone Pet Supplies into a “pot” integral to the mold tool. As the mold closes, heat and pressure force or “transfer” this material into the mold cavities to form a molded product. When the process is complete, workers remove the transferred rubber from the mold and trim any excess overflow material known as flash.
Another benefit of transfer molding is that it can be used to produce products with complex geometries. This is because the process uses a less complicated system to expel the molded silicone, and therefore does not require the expensive and sophisticated systems that are required for injection molding.
In addition, transfer molding can be utilized with liquid and pourable silicone systems that would not be suited to injection molding. Depending on the silicone system that is selected, either peroxide or platinum catalyst can be used to promote curing of the resulting molded product. Both methods of curing can be very effective, although peroxide can leave byproducts that may discolor or bloom the surface of the molded part.
Liquid Silicone Injection Molding (LIM)
LIM is the preferred process for many manufacturers of silicone rubber parts because it offers high levels of automation and superior end-of-product performance — durability, tensile strength and flexibility. It also supports a wide range of component combinations including hard/soft overmolding with thermoplastics and two-shot molding. Liquid injection molding is also the best option for producing nipple protectors that combine a stiff thermoplastic shell with soft silicone grip.
Like injection molding of other elastomers, shear-thinning liquid silicone rubber can fill a mold cavity with low injection pressures because the material is still in a fluid state. This means that drafts – which can be necessary to ensure the proper positioning of the part in the mold, especially for intricate geometries — are not required.
This means that dimensional tolerances for molded silicone products are typically tighter than those available with compression-molded gum-base silicones. Stockwell’s LIM molding capabilities enable us to produce a variety of items that meet ARPM A-2 precision tolerances for both closure (cross section) and plan view dimensions.
LIM is a closed process and the liquid silicone materials are kept in airtight barrels until injected into the tooling. Then, they can be cured in place without exposure to the environment — which helps to reduce variability in the production process and results in superior quality.
Extrusion
Extrusion is a manufacturing molding process that involves forcing base material through a specialized shape called a die to create continuous objects with a fixed cross sectional profile. It is commonly used to manufacture Silicone Pet Supplies Manufacturer plastic pipes, tubes and wires. During this high volume manufacturing process, melted polymer is pushed continuously through an injection tool (die) with a two-dimensional profile and cooled in a cooling tank. The resulting products are called extrudates.
Unlike injection molding, which can be time-consuming and expensive, extrusion molding is cost-effective and fast. Additionally, it allows manufacturers to produce a wide range of shapes and sizes. This flexibility is key in the food and beverage industry, where manufacturers need to quickly respond to demand.
Another benefit of extrusion molding is that it can produce long and narrow products, which are hard to make using other methods. This includes the “zip” strip on resealable plastic bags and medical tubing, as well as plastic windows and door frames and vinyl siding.
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