What will the refrigerated trailer of the future be made of? Strong, lightweight and corrosion-proof composites? Very possibly. Economical, efficient aluminum sheet-and-post design, like now? Yes, for a number of years yet. So say engineers engaged in designing and building temperature controlled trailers.
Today, these are made of sheet-and-post walls on floors supported by underbody crossmembers. Walls are sandwiches of inner and outer metal panels with aluminum posts inside the cavity, and the void is filled with polyurethane foam insulation. All components, including the foam, lend strength, and of course, the foam acts as insulation, limiting conduction of ambient heat and cold to the trailer’s interior. The thicker the walls and the amount of foam inside, the greater the vehicle’s “R” rating, and its ability to help the mechanical reefer unit maintain a desired temperature inside. But thicker walls also add tare weight and reduce payload capacity.
“I do see more use of non-metallic materials,” says Charlie Fetz, recently retired research and development engineer at Great Dane Trailer and author of a Future Truck paper on temperature controlled trailers for ATA’s Technology & Maintenance Council. “Aluminum is a great material, but it conducts heat. If they’re inside the wall cavity, the aluminum posts do contribute to heat conduction. Manufacturers minimize that with careful design.”
One way is to surround narrow posts with foam, minimizing the conduction of heat. One-inch posts inside a 2-inch wall, for example, allows room for injecting foam around the posts and throughout the wall cavities. Another way is to improve the foam’s efficiency, which manufacturers have repeatedly done over the years. Another round of change is due in January of 2020, when federal rules will require more environmentally friendly foam, primarily through a change in the “blowing agent” used to form and install the product. Several are being tested by chemical makers.
Another way to improve efficiency is use of aerospace-like composites. Wabash National showed a prototype composite refrigerated trailer with very few bolts, no rivets and no crossmembers at the TMC’s equipment expo in March. The panel-type trailer is similar in concept to vehicles produced in Europe; it uses molded structural composites, or MSCs, developed over the last three years. The material gives the 53-foot trailer up to 25% improvement in thermal performance and is up to 20% lighter compared to conventional designs, executives said. Interior puncture resistance is 25% better.
“The composite is a mixture of fiberglass, carbon fiber and resin,” says Larry Adkins, applications engineer for Wabash. “Carbon is for strength. It’s used only in areas where strength is needed, and some areas don’t have any. It’s needed in toward the center of a trailer,” which supports the load like a bridge span. Another advantage: “Composites are more corrosion resistant (than metals). Chemicals have no effect on the materials.”
The first trailer prototype units beyond the initial vehicle are to be produced later this year. Five “launch partners” will begin testing in normal fleet operations, Adkins says. “The plan is to get some miles on them. Miles can show what can’t be done in labs. Then we can alter the design if we have to. We expect to learn some things, like (better design for) transitions between walls and frame, and at the rear, for forklift use.”
Wabash first produced 10 prototype composite truck bodies and they are now in service, carrying various cargoes. The first one is delivering dairy products on Prince Edward Island in the Canadian Maritimes. Each body is 24 feet long by 102.3 inches wide.
What about repairs? “That seems to be what most people are asking, and it’s our biggest stumbling block” to acceptance, Adkins says. “But it’s glass fiber, so it’s much like working on truck hoods. You use a sidewall patching material with resin and gelcoat, and a structural adhesive. We have it developed, we have a part number for it.” How about cost? “We haven’t established a price. We know it will be a premium over our standard product,” which is sheet-and-post.