ABSTRACT

As the composites industry matures, manufacturers continue their search for technology that will maximize production and minimize cost. A growing number of resin infusion shops — including some aerospace manufacturers — are finding this combination in reusable vacuum bag (RVB) technology. Proponents say these stretchy membranes can replace disposable bagging films and even rigid countermolds, and they offer molders a wealth of advantages, including improved part-to-part quality and greater shop safety and cleanliness. No less important, they provide a way to cut down on consumables and reduce a shop’s waste stream. RVBs do, however, require capital expenditure and offer challenges that must be overcome for proper implementation, and they aren’t always the right way to go in every part process situation.

How the silicone chemistry is formulated for tear strength is, in my opinion, the most important criterion when selecting a bagging product — it directly correlates to bag life,” says Larry Audette, president of RVB supplier Prairie Technology Group Inc. (Hutto, Texas).

Prairie Technology Group was the first to patent a sprayed RVB in 2006 (U.S. Patent number 7014809B2), says Audette. Prairie Technology’s Sworl sprayable silicone is distinct from other silicones, he claims, because of its unusually high tear strength. “Our 308 556 product has a measured tear strength of 180 lb [81.7 kg] at a thickness of 0.125 inch [3.2 mm],” he says, noting, “the secret is in the chemistry.” This reportedy makes possible a thinner bag that uses less silicone but is nonetheless strong enough to stand up to the rigors of production without fabric reinforcement.

A reported benefit of the Sworl chemistry is a viscosity low enough that the silicone can be atomized like paint, rather than splattered, and the ability to adhere to itself when successive layers are applied, even when previous layers have cured. “We’ve eliminated the need to maintain a ‘wet edge’ when creating a bag,” Audette asserts, adding that a Sworl bag can be created in a morning, then cured and used that same day, although he allows that larger bags might take several days.

BIO

Richard Matthews Graduated Texas A&M with degree in Mechanical Engineering. Has spent many years in bonding of materials for the Oil and Gas, Automotive and Aerospace Industry. Employed by Oil States Industries first developed the ability to bond rubber materials under high heat conditions down hole. Aerospace development with Huntsman and Trelleborg focused on composite structures. Current owner of Monarch Industries, Brea CA (Adhesive Distributor) and representing SWORL.

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