Silicone reusable vacuum bags (RVBs) for better composite molding applications
Fiber reinforced polymer (FRP) composites are increasingly being used to make molded parts for a wide variety of industries: automotive (including trucks and off-road vehicles), renewable energy (components such as wind-power propellers), aerospace, marine construction, architectural structures, etc. These composites combine excellent mechanical properties with a low density, and feature high resistance to water, chemical and environmental pressure.
Traditionally, these materials were composed by a fiber like glass, carbon, aramid fibers as well as natural fibers or hybrid materials and other specialty combinations, and by resins like epoxies, unsaturated polyesters, DCPD polyesters, vinyl esters, phenolics, polyurethane and hybrids.
One of the methods to produce FRP composites and hybrid materials is the infusion molding process with the use of disposable plastic bag sheets that are manually placed and assembled by highly skilled operators. This process is extremely time consuming and generates a great deal of waste since every mold requires a change of bagging. In recent years, manufacturers focused their attention on reusable vacuum bag (RVB) membranes that increase productivity, reduce costs (in particular for larger batches) and improve the quality and consistency of parts produced. This process also contributes to better industrial safety and workplace cleanliness, while reducing the use of consumables and thus lowering waste.
However, because introducing RVBs into a production process can require capital investments and process changes, it is essential to choose the right technologies and products from the start. Depending on these choices and the composites being processed, RVBs can be reused from 20 to 300 times.
Elkem Silicones has been working with composite molding specialists for many years to constantly improve resin resistance to make bags last longer. This also applies to other molding technologies. Elkem Silicones has also developed the expertise to advise manufacturing companies in their industrial processes and provide them with the products they need for their specific molding applications and in particular RVBs. Feedback from the markets has been very positive, with many customers asserting that our bags last longer than those of the competition. Elkem Silicones specialists are available worldwide to work on these questions and other enhancements in producing RVBs and other processes for high-quality infusion composite molds.
Composites are also made using other molding processes (open or closed, using wet resin or prepreg fiber sheets) such as compression molding, injection molding, cast resins and several more. The use of Silicone Rubbers in these various processes is increasing, and this is due to the properties of release and chemical resistance of Silicones and to the flexibility of use of RTV Silicone rubbers, which can easily be adapted to the type of processing method.
Elkem Silicones has developed a range of RTV Silicones suitable for composites molding, which offer many advantages, including curing at room temperature, a definite plus compared to natural rubber or other synthetic materials.
Our products used in composites include:
- BLUESIL RTV 3720 A&B and BLUESIL RTV 3720 A&B SC (Slow curing version), specifically developed to produce silicone RVBs for composite molds using vacuum resin infusion technology.
- BLUESIL RTV 3428 A&B, used for a wide range of applications including sheets for boating, aeronautics and military parts. This material can be used in an autoclave process or by pressure molding.
- BLUESIL RTV 3460 A&B, is a very hard silicone, specifically formulated for use with casting materials and urethane foams.