Assembly in Action: Truck Tonneau Covers Bonded With Polyurethane
Tom Kauble, director of engineering, says, "Our LT2000 tonneau cover, which is manufactured with Telene RIM polymer, features good flexibility and impact-resistance at temperatures as low as -40 F." He continues, "The same flexibility that makes the covers ideal for customer handling presented a bonding challenge. Joining the ABS inner panel to a Telene outer produced read-through on the tonneau surface."
To overcome the problem, the company looked for a medium- viscosity, slump-resistant adhesive that would allow higher-volume production of tonneaus at lower labor costs than traditional open molding of fiberglass- reinforced plastic.
The company chose Arathane AW8680/HW 8685 polyurethane, supplied by Vantico (Los Angeles) for the application. Its 10-minute gel time is sufficient for part assembly, and its fast, room-temperature cure supports increased productivity. The adhesive is also formulated specifically for bonding thermoplastics. Once cured, it exhibits an elongation of 250 percent to produce bonds that retain strength as the tonneau cover flexes.
The tonneau covers are produced from Telene outers that the company reaction injection molds and honeycomb-like ABS inners that are vacuum formed. For assembly, the Telene thermoplastic outer skin is placed in a bonding nest. The ABS inner is installed on a movable cart, and both are pre-wiped with solvent. After the solvent flashes off the ABS inner, the polyurethane is meter-mixed in a 1-to-1 resin-to-hardener ratio. The blended adhesive is then applied around the panel perimeter and the part's center. Metal reinforcing plates are also mounted on the corners of the panel using the polyurethane. The part is then in-verted and positioned onto the outer skin. The ABS inner is centered so the flanges are fully aligned. To complete assembly, cover components are clamped in place until they are cured enough to be moved to the paint area.
Kauble reports, "The adhesive is a critical element in assembling the tonneau cover. Conventional two-piece tonneau covers, made from sheet molding compound, are stiffer. As a result, they are easy to bond using high- viscosity polyurethane and can be clamped together without risking read-through on the surface. By contrast, to effectively join the Telene thermoplastic and ABS panels, we need an adhesive with a vis- cosity in the 50,000 centipoise range. The polyure-thane must also resist sagging as we invert the ABS inner and then spread completely over the panel surfaces as they're clamped, to produce a high-quality finish."
Once panels are removed from the bonding nest, technicians clean and inspect surfaces and install hardware. Then, the covers are sent to the paint room.
For more information on polyurethane adhesives, call Vantico at 818-247-6210, visit www.vantico.com.