and Lawrence Kren
The switch from mechanical fasteners to a high-performance epoxy improves trailer, RV, and fifth-wheel aerodynamics, makes them more durable, and eases assembly, says Bob Helvie, president of specialty vehicle manufacturer Startracks Inc., Elkhart, Ind. Araldite 2011 epoxy from Huntsman Advanced Materials, The Woodlands, Tex., securely bonds aluminum, plywood, and fiberglass-reinforced plastic (FRP) panels to the vehicle sidewall frames.
The epoxy cures quickly with lap shear and roller peel strengths of 2.6 kpsi and 28 pli, respectively. The epoxy stands up well under static and dynamic loads by distributing stress across the exterior panel, is able to expand and contract with trailer skins as temperatures rise and fall, and eliminates the need for added trim strips to hide the joint.
Startrack's specialty is building custom vehicles used as medical clinics, lawenforcement command posts, and motorcycle-transporters. But the company also builds handicapped-accessible mobile homes featuring extra-wide doors and center aisles and bathrooms large enough to accommodate wheelchairs.
A trailer it recently converted to a summer home for a handicapped customer, for example, features a wood frame and exterior skin of Filon FRP sheet from Kemlite Co. Inc., Channahon, Ill. Wood was selected based on economics and, because the unit will be parked rather than towed, weight was not an issue. For mobile vehicles, substructures are typically lighter-weight aluminum with a fiberglass or aluminum skin.
To build the trailer exterior, technicians first abraded the substrates to improve adhesion, then used pneumatic dispensing guns outfitted with disposable static mixing nozzles to lay down an epoxy bead. The Araldite has an easy-to-work-with mixed viscosity of 45,000 cP and a 120-min work life that is well suited for bonding the trailer frame's large surface area. Next, the FRP-laminated exterior panels positioned over the substructure were clamped in place using metal beams and left to cure at room temperature for 12 hr.
Huntsman Advanced Materials, (281) 719-6000, www.huntsman.com
Kemlite Co. Inc., a Crane Composites Inc. company, (815) 467-8600, kemlite.com
Startracks Inc., (574) 293-6555, startracks.org