Adhesives Magazine

Applying Adhesive in the Vacuum Infusion Process

April 1, 2010
By observing a few key tips on spray adhesive selection and dispensing, manufacturers can boost efficiency and improve fiberglass and composite part quality while reducing potential failures in the field.



For manufacturers of fiberglass or composite parts using the vacuum-infusion process, properly selecting and applying spray adhesive to tack layers of dry material together can have many consequences. “General-purpose” spray adhesives are not specifically designed for use in the vacuum-infusion process; thus, applicators must often empty tens or even hundreds of spray cans for each project and endure the finger fatigue, overspray, uneven application, and mess that come with manual application.

Furthermore, with new studies indicating that general-purpose spray adhesives can interfere with the resin curing process and compromise the structural integrity of the finished part, savvy on-the-floor applicators are realizing the direct correlation between quality and performance of the product in the field and its impact on their own long-term job security.

“The payoff from selecting the proper spray adhesive is higher quality, reduced liability, and better job security for everyone from installers to the CEO, since critical components like yacht hulls, racecar bodies, and aerospace parts cannot fail in the field,” says Scott Macindoe, president of Seattle-based Fiberlay, a leading distributor of fiberglass supplies and composite materials.

For this reason, spray adhesives are an important part of the vacuum-infusion process. By observing a few key tips on spray adhesive selection and dispensing, manufacturers in industries ranging from marine and wind power to automotive and aerospace can boost efficiency and improve fiberglass and composite part quality while reducing potential failures in the field.

Get It Right the First Time

For big projects, it’s important to use a spray adhesive with a longer tack-up work time before “flash off,” or the point at which the solvent evaporates and the adhesive sets.

“Without adequate tack-up time, the production crew has to pull up the materials and spray more adhesive or replace the materials entirely,” says Lee Miller, an outside sales rep at Fiberlay. “Some general adhesives, for instance, offer minimal work time; they virtually stick on contact with little time for repositioning.”

For enough work time to tack up material without rework, Macindoe suggests using a spray adhesive like Infuzene by Westech Aerosol, a specialty industrial adhesives manufacturer in Port Orchard, WA. He has used the spray adhesive on numerous projects, including the building of a 100-foot catamaran hull.

“Spray adhesives like Infuzene allow some position adjustment before setting, so it’s much easier to tack up right the first time,” Macindoe says. “On larger projects, you can’t afford not to use a spray adhesive like it, as the cost of the adhesive becomes virtually zero, compared to total project cost.”

A vacuum-infusion-specific adhesive that crosslinks with the resin can offer greater inter-laminal shear strength, increasing quality and reducing potential liability.

Avoid General-Purpose Spray Adhesives

Because contaminants in general-purpose adhesives can inadvertently serve as a “release agent” between layers of fiberglass, it’s essential to avoid using them for material tack up.

“General-purpose adhesives were never intended for the vacuum-infusion process,” says Macindoe. “They could be the weakest link in engineers’ design plans because the majority of them contain contaminants.

“Every industry that infuses tries to avoid getting dirt, water or contamination in the resin so it doesn’t become part of the product,” he says. “But most general-purpose adhesives are designed to glue two things together, not to infuse resin through them. As a result, with general-purpose adhesives, the contamination doesn’t cure with the resin or become part of the resin, it just floats within the resin.”

General-purpose spray adhesives can also inhibit resin flow if applied too thickly or unevenly, causing the resin to part around that area like a rock in a stream of water. When this occurs, air pockets, bubbles of resin, or osmotic blisters can form within the structure of the fiberglass, making delamination or structural failure more likely.

On large projects, production crews can use hundred of spray adhesive cans - or just a couple of canisters. Miller says the canisters can cover a larger area faster and can atomize better for more-even coverage.

Use Resin-Based Spray Adhesives

A vacuum-infusion-specific adhesive that crosslinks with the resin can offer greater interlaminal shear strength, increasing quality and reducing potential liability. For example, Infuzene was developed to hold dry materials onto structural surfaces, including vertical and tight radius work, during the vacuum-infusion process.

As a high-strength, high-temperature, solvent-based vacuum-infusion enabler for industrial use, Infuzene is designed to safely fuse laminating materials to structural core surfaces, forming a continuous matrix without structural weakness. Since it will not interfere with the curing process of vinyl esters, polyester or styrene resins, it allows resins to obtain maximum tensile shear strength. The adhesive crosslinks and hardens along with the ester or styrene resins to form an integrated structure.

“Infuzene is optimal for the vacuum-infusion process and even resin transfer molding because it becomes part of the resin,” says Macindoe. “It crosslinks with the resin as it flows through and leaves no contaminants.”

While the vacuum infusion-enabling adhesive is primarily used for fiberglass, its crosslinking properties with resin also provide greater interlaminar shear strength for carbon fiber (graphite) and Kevlar materials.

Results from recent tests conducted by a leading independent university composites testing lab indicated that the vacuum infusion-enabling adhesive provided a stronger bond in the vacuum-infusion process than the leading general-purpose spray adhesive. Based on ASTM 2344 short beam shear strength testing standards, the results indicate that the composite with Infuzene was up to 30% stronger in interlaminar shear strength than the same composite with the leading alternative.

“Technically, Infuzene isn’t a spray adhesive so much as a resin stabilizer for fiberglass that allows the resins to reach maximum peel and tensile shear strength,” Macindoe says.

Spray adhesives allow some position adjustment before settling, so it's easier to correctly tack up the first time.

Use Canisters for Efficiency

On large projects, before resin is injected inside the enclosed vacuum bag, installers may have to retrieve and open hundreds of spray adhesive cans for adequate tackup, and vigorously shake the contents before use. To avoid underspray, they often kneel close to the work for long hours. To avoid project contamination, they must clean up messy overspray and dispose of hundreds of empty spray adhesive cans, all while trying to keep clean themselves.

“Spray adhesive from small aerosol cans can come out a little stringy or clumpy, says Miller. “Small cans can be difficult to work with on light fabric, which can quickly saturate while getting hands sticky.”

Small cans of spray adhesive can also disrupt workflow. Work stops each time the production crew disposes of empty cans and gets new ones, then opens and shakes them in preparation for spraying.

Rather than using small cans of adhesive that quickly run out, Miller recommends applying spray adhesive on larger projects with a portable canister system, such as those from Westech. These adjustable canister systems, with a reusable gun and hose, enable efficient, continuous application on projects when typical 13-ounce cans are insufficient.

“On a large project, the production crew can go through hundreds of spray adhesive cans, compared to just a couple of canisters,” says Miller. “The canisters cover a larger area faster and atomize better for more-even, controlled coverage and tackup than aerosol cans. There’s less overspray, underspray and bounceback with the canisters’ variable spray capability. There’s better coverage in corners and tight areas.”

“A lot of our customers love the canisters not only because they can adjust spray width and volume to suit the application, but also because they’re so much more efficient than small cans,” Macindoe says. “On large projects, the canisters can save 10-20% in material cost, and up to 25% in labor cost due to more efficient application.”

For more information, phone (800) 674-2010, fax (360) 674-2053 or visit www.ok2spray.com.

Links