Tuesday, August 7, 2007

Permitted Foolishness

The Federal Clean Air Act mandates permitting as a Title V source for any stationary source that emits (i) more than 100 tons of any pollutant per year, (ii) more than 10 tons per year of any hazardous pollutant, or (iii) more than 25 tons per year of a combination of hazardous pollutants.

Progressive technologies, such as vacuum infusion, offer the opportunity to dramatically reduce emissions of cancer-causing agents like styrene, while also positively impacting production by reducing labor costs, reducing cost associated with waste disposal, and increasing unit through-put per production hour. Considering the relative inefficiency of open-mold processing, the exposure risk it poses to laborers, and the resulting environmental emissions, its unfortunate that manufacturers continue to file for Title V status as their production capacity increases, rather than choosing to adopt advanced processes that pose long-term economic gains and reduce pollution.

Bags, Boils, and Print-Through

What do these have in common? Each represents a significant obstacle to the widespread adoption of vacuum infusion in the marine industry.

Bags: In order for vacuum infusion to become truly economical, marine builders will need to be able to pull many (i. e. many dozens) parts from a single reusable bag. The use of nylon bags is simply too wasteful, too laborious, and too frustrating to satisfy a moderate to high volume builder. What are the elements of a desirable reusable bag? Durability, flexibility, rapid release, and simplicity of construction. Products that have been in the marketplace for some time are not as durable or flexible as builders would like them to be. New products in the marketplace show promise with respect to flexibility, releasability, and ease of use, but are unproven from the standpoint of durability and permeability.

Boils: If you've produced a part with conventional resin in a vaccum infusion process, you've probably noticed what appears to be air bubbles in the finished composite. Most likely, what you've seen isn't simply air from the surrounding atmosphere due to permeability or a leak in the bag...it's vaporized resin! Refer to the "Volatilization" article at http://www.polynovacomposites.com/ for detailed information on this issue; but in short, understanding the relationship between resin selection, ambient temperature, and vacuum pressure is critical to producing a properly cured part via vacuum infusion.

Print-through: Although it has little relationship to the structural integrity of a part, print-through is an important cosmetic issue for any marine builder and a particularly troublesome one for a builder making boats less than 30 feet. People attribute print-through to many things, but in reality, it's a resin shrinkage issue. In large boats (greater than 30 feet), builders may add extra layers of reinforcements in order to diminish the effects of resin shrinkage without posing too significant a weight problem or wildly over-building the hull structure. In small boats, however, print-through is a great challenge to overcome. Certainly, some resins exhibit less shrinkage during cure than others and builders should experiment in order to find the best performer. Many builders will use certain reinforcements known to counteract print-through. Builders beware! In some cases, the reason a reinforcement may reduce print-through is because it effectively suffers shear failure during cure, which has the side-effect of obscuring print-through. Make no mistake, such shear failure is diminishing the structural integrity of the finished/cured part.