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Kozo Saito & Abraham Salazar
Designing Effective Painting Technology with Computational Fluid Dynamics

by Jeff Worley & Robin Roenker

In an era when cars have talking navigational systems and high-tech internal sensors to track everything from airbags to brake fluid, it's surprising that a simple thing like paint could still stump auto manufacturers.

Photo of Kozo SaitoThe painting process accounts for about half of the total energy usage in the entire car-making process. And painting is not only energy-intensive, it's wasteful: as each car passes through a paint booth, nearly half of the paint being sprayed is lost in the air. So while a car may require two gallons of paint, the factory has to spray four gallons on each one. It's an equation that means a cost of nearly $1 billion a year, industry-wide, and, of course, the environmental impact is an additional concern.

The goal of UK's Painting Technology Consortium (PTC), established in 1999, is to assist industries in understanding the basic mechanisms of the painting process so that it can be done more efficiently, more cleanly and more cheaply. Kozo Saito, TVA Professor of Mechanical Engineering, is director of the PTC; Abraham Salazar, assistant research professor of mechanical engineering, serves as assistant director.

Saito's work in painting technology began in 1993 with a project to assist Toyota Motor Manufacturing, Kentucky, in characterizing the mechanics of their "scrubber" systems, equipment that captures paint "overspray"—the paint that never makes it to the car surface—transfers it to water, and cleans it out of the air. Traditionally, these systems were designed by trial and error, with little understanding of the actual flow of the paint and air particles. A breakthrough in this understanding came, though, when Saito enlisted the aid of Salazar, then a UK graduate student, and his computational fluid dynamic (CFD) models.

Using UK's supercomputer, Salazar was able to develop a visual model of the fluid processes involved in the capture mechanism. "It was very complicated in the sense that you have water, air, and particles (small droplets). It's a three-phase problem," Salazar explains. "But with computational fluid modeling, suddenly everything became clearer because it eliminated the problem of paint clogging that real-life experiments entailed. Now, we could do numerically on the computer what had previously been done only through experiment."

Photo of Saito's lab teamLeft to right: Abraham Salazar, assistant director of UK's Painting Technology Consortium; Tianxiang Li, engineer associate senior; Kazunori Kuwana, engineer associate; and Fengiuan Wang, a Ph.D. student in mechanical engineering; and Kozo Saito, director.

From the visual animations of paint particle trajectories Saito and Salazar made through computation, they were able to identify flow processes that most effectively captured the paint particles in the air—changes in momentum and recirculation. The research duo then implemented these changes to develop their own new scrubber design, called the Vortecone, in 1998. It bested anything else on the market in cleaning the air to meet U.S. and Japanese environmental guidelines while remaining cost-efficient, and it is now being used by seven Toyota plants worldwide.

Since that success, PTC has turned to other aspects of paint technology—including painting transfer efficiency, surface appearance inspection, and drying efficiency—in collaborative CFD-based projects with other auto makers that include Toyota, Honda, Nissan, and Ford. Saito and Salazar's work has also attracted the interest of paint makers such as Sherwin-Williams and painting equipment manufacturers like Japan's Trinity Industrial Corporation.

Currently, the research duo is testing prototypes of new painting equipment, which they designed via supercomputer, that they hope will be "almost 100 percent transfer efficient," Salazar says. That means that two gallons on each car may one day soon mean spraying two gallons—no more overspray, and no lost profits in wasted paint.

About the Painting Technology Consortium

The Painting Technology Consortium (PTC) has an annual funding base of $1.2 million. Since 2000, it has sponsored a yearly Painting Technology Workshop, which hosts some 70 executives from the automotive industry, and experts from the Navy and aerospace design firms. Recently, PTC research has also been utilized by non-automotive companies, including a Kentucky cell phone manufacturer, which used PTC designs to more efficiently paint its phone covers.

Painting Technology Consortium team

The Painting Technology Consortium team is composed of seven professional (Ph.D.) staff and six Ph.D. students. The following are dedicated to CFD: