Blowing Foam Goes Green

Light & Medium Truck, Mar 2008 by Strah, Thomas M

What do a can of deodorant and a modern refrigerated trailer have in common? A bit of chemistry and more than a few pages of clean-air regulations, that's what.

Back when aerosol spray was blamed for blowing a continent-size hole in the ozone layer of the atmosphere, governments around the world banned the chlorofluorocarbon in the aerosol's propellant gas - its chlorine component is the destructive stuff.

This ban also had a major effect on the refrigeration and air-conditioning industries, which not only relied on the excellent chilling properties of CFCs, but also on their role in creating formfitting insulating material.

CFCs were replaced by hydrochlorofluorocarbons, which contained much less chlorine but that change was only a transition. The U.S. Environmental Protection Agency and others are forcing the phaseout of HCFCs, and they should be gone from the world stage by 2030.

Today, your can of Right Guard - and possibly your air conditioner and perhaps even a favorite cleaning solvent - contain variations on chlorine-free hydrofluorocarbons, or HFCs.

Environmental awareness not only has altered the propellant that delivers deodorant to its target, but it also is driving manufacturers of refrigerated trailers to adopt a new blowing agent for polyurethane foam, long their insulation of choice.

Polyurethane foam is the gas-filled plastic matrix between the inner and outer walls of reefer trailers, refrigerators and many other boxes that are temperature-controlled. Blowing foam in a trailer factory is a dramatic enough process, with a small crew managing machinery that controls the reaction of two materials: polyol, a polymer reactant, and isocyanate, an organic compound. Mixed together with a blowing agent, the components expand to six times their original volume with a significant force.

"Actually, we blast the polyol and the isocyanate into each other in a process called high-pressure impingement," said Charlie Fetz, vice president of research and development at Great Dane Trailers.

A central rig of hoses and valves regulates the flow of components into a mixing head. From the mixing head, the raw foam is injected between the two skins of a simple panel or the entire shell of the trailer.

The blowing agent helps the foam expand uniformly and fill the void between the skins with a fine cellular structure that grows rigid as the plastic cures. The blowing gas is retained in the cells and becomes an integral part of the insulation's thermal barrier.

"It's a complex chemical reaction," Fetz said.

Trial and error have taught trailer makers how to ensure that the foam fills complex spaces evenly.

"You have to plan where the air escapes so as not to block the flow," Fetz said. Vent holes, a quarter-inch in diameter, are strategically placed, and when a button of foam pushes tiirough the vent under the force of expansion, and maybe a little gravity, that's a good sign.

Another method of controlling flow is to create a vacuum between the sheets and draw the foam through the spaces, but so far, that approach has proved unnecessarily complicated for trailer manufacturing.

The only way to be certain about the uniformity of the finished insulation, however, "is to foam things and take them apart," Fetz said. "We're testing all the time to make sure we understand the properties of foam and flow."

Blowing foam remained an ozone-threatening process until the advent of HFC blowing agents. Great Dane, Utility Trailer Manufacturing and reportedly Wabash National are opting for HFC-245fa, a product that is made only by Honeywell International.

Utility has built more than 5,000 refrigerated trailers with the new agent during the past two years and planned to complete its transition to 245fa by February, Jeff Bennett, vice president of engineering and product development, said.

Jeff's brother, Craig Bennett, the family company's marketing director, said the formulation of die foam "is a delicate science and a messy business." He said Utility designed its own technology for mixing the components together, and the results are uniquely Utility's.

Utility installed its proprietary mixing chambers in the big and small foaming rooms in each of its two reefer factories. The rooms accommodate up to 10 trailersize mandrels, rigs that support the fragile trailer skeleton as it is foamed as a whole in a single, unbroken process.

"We believe you cannot make a well-insulated trailer out of individual panels," Craig Bennett said. The joints always will be weak points in the thermal barrier.

An older method, still in use, involves spraying foam onto one sheet and, once the foam sets, shaving it smooth before adding the second sheet. The results are not as thermally consistent, nor as strong, as the injection method.

Great Dane's Fetz said blown foam, which adheres to inside surfaces, also lends structural strength to the finished sandwich.

Great Dane is about to begin its switchover, in accordance witii the accelerated EPA regulations, Fetz said. EPA moved its ban on the production and import of HCFCs to 2008 from the original 2010.