Tips for Adhesive Application in the Vacuum Infusion Process
Tips for Adhesive Application in the Vacuum Infusion Process
For those manufacturing fiberglass or composite parts with the vacuum infusion process, the proper selection and application of spray adhesive used to tack layers of dry material together has consequences that the applicator on the floor might not have fully understood until recently.
The issue revolves around the fact that "general purpose" spray adhesives are not designed specifically for use in the vacuum infusion process. As such, applicators often have to suffer through manually depressing the nozzle to empty tens or even hundreds of spray cans for each project and endure the finger fatigue, overspray, uneven application and mess that come with it.
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 of 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 Fiberlay, a leading distributor of fiberglass supplies and composite materials in Seattle, Washington.
For this reason, the role of spray adhesives in the vacuum infusion process has taken center stage. 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 little longer tack up-work time before "flash off", the point when 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, Washington. He has personally 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," says Macindoe. "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."
Avoid General Purpose Spray Adhesives
Because contaminants in general purpose adhesive 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," explains Macindoe. "But most general purpose adhesives are designed to glue two things together, not to infuse resin through them. The result is that 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.
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 instance, Westech's vacuum infusion-specific adhesive 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, it 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.
In recent tests conducted by a leading independent university composites testing lab, results indicated 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," adds Macindoe.
Use Canisters for Efficiency
On a big VIP project, before resin is injected inside the enclosed vacuum bag, installers may have to retrieve and open hundreds of spray adhesive cans for adequate tack up. They must vigorously shake the contents of each can before use to prepare it for spraying. 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 the mess off 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, gets new ones, then opens and shakes them in preparation for spraying.
Compared to small cans of adhesive that quickly run out, Miller recommends applying spray adhesive on larger projects with a portable canister system like that from Westech. Their adjustable canister system, with a reusable gun and hose, enables 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, versus just a couple of canisters," says Miller. "The canisters cover a larger area, faster, and atomize better for more even, controlled coverage and tack up 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," concludes Macindoe. "On large projects, the canisters can save from 10 to 20% in material cost, and up to 25% in labor cost due to more efficient application."
For the most recent test results, including information from the independent study, call 800-674-2010; Fax 360-674-2053; visit ok2spray.com; or write to Westech Aerosol Corporation at 5405 Constance Dr. SW, Port Orchard, WA 98367.
