Air management and airflow control are consistent problems for finishing systems because there are many variables, from filter loading to temperature and relative humidity. Each of these variables affects air movement within a system, and airflow movement, in turn, affects the efficiency of a finishing system. When John Deere Ottumwa Works (Ottumwa, IA) converted from water-reducible alkyd-based enamel to isocyanaide liquid polyurethane coatings for both the primer and topcoat, the operators recognized the need for an air management/airflow control system.
John Deere Ottumwa Works produces mowers and bailers for the agricultural industry and employs more than 850 people. Although isocyanaide offered better weathering and corrosion protection for the products, the company was concerned the coatings could emit harmful fumes and that overspray from the spray booth would leak into the plant environment. Therefore, the company needed better capture technology to ensure adequate air capture velocities and flow within the large finishing system—the spray booth is 24 feet wide by 60 feet long, and the work opening is 12 feet wide by 12 feet high. John Deere Ottumwa Works asked Industrial Technology Midwest (Wilmot, WI) to help the plant make a safe transition to isocyanaide polyurethanes. ITM is a consulting firm for the finishing and air pollution industries, and it designs and sells control systems.
The air management challengeJohn Deere Ottumwa Works has a two-coat finishing system. A prime coat is applied to the part in the prime coat booth. Then, parts go through a flashoff tunnel where the solvents can evaporate before parts are cured in the cure oven. Next, parts proceed down to a cooling tunnel, followed by the application of a topcoat in a second spray booth. Parts then go through another flashoff tunnel, followed by curing in the topcoat cure oven. There are many changing conditions among these steps, and a problem in one area can throw off the entire system. However, John Deere initially requested ITM to focus solely on the entrance of the prime coat booth so that no overspray would escape into the plant.
“Most people look at one component in the system instead of correlating how it will affect connected components,” says William Nowack, president of Industrial Technology Midwest. “To achieve positive results at John Deere, we looked at all of the components as one unit. For instance, we saw how the prime-coat booth interacted with the flashoff tunnel and how the booth and flashoff tunnel interacted with the prime-coat cure oven, and so on.”
After inspecting the existing system, ITM and John Deere Ottumwa Works determined that the system had problems beyond the entrance of the prime- coat booth. The finishing system had overspray that leaked out of the exit of the primer booth and overspray in both flashoff tunnels. Additionally, both of the ovens leaked heat into the spray booths. Overspray in the flashoff tunnels can contaminate the product because, when overspray dries, it becomes dusty and shows up as a blemish when deposited on a freshly painted part. The heat loss from the cure ovens made the temperature in the spray booths erratic, which can push paint away from the part and toward the painters. When the warm air traveled into the booth it moved upward, which made it more difficult to achieve a laminar airflow—a smooth paint flow with all of the lines parallel and very little turbulence.
ITM and John Deere Ottumwa Works set three goals:
- Design an overall airflow scheme and modify the equipment to ensure adequate air capture velocities and flow and to prevent overspray and contaminated air from escaping the spray booths.
- Contain heat loss from both of the ovens and prevent heat from entering the flashoff tunnels, cooling tunnels and the plant environment.
- Design and implement a control scheme to help achieve and maintain balanced air, which meant taking into account everyday changes, such as ambient temperature, water flow in the eliminator sections and filter loading.
SolutionsFirst, ITM and John Deere Ottumwa Works installed ITM’s air seal technology to better control the airflow within each component in the system. Second, they installed an air management control system to help achieve and maintain the desired air balance system.
Air seal technology—The air seal technology is part of an air management program that allows the operator to provide better control of the airflow in the finishing system. The ITM engineering team had to determine the components that needed upgrading by identifying the air temperatures, circulation, distribution and exhaust flows needed to achieve the desired results. The technology forms an air curtain with a downward flow of air at a velocity determined by the opening size and the air temperature in the system.
Once the air was controlled at both openings of the booth, the John Deere operators were able to control the interior airflow in both cure ovens and spray booths. One important focus was the downdraft velocity—the movement of air from the ceiling to a floor grate exhaust funnel that carries the overspray away from the painter and the substrate.
“Before determining the air distribution within the spray booth, the downdraft velocity was anywhere between 40 and 200 feet per minute,” Nowack says. “We stabilized it by enabling the operator to make adjustments to downdraft velocity on the interior of the booth. More importantly, the operator can change the capture velocity, which is the amount of air moving through the system. For example, he can set the airflow to move from one end of the booth to the other end at 50 to 150 feet per minute.”
Typically, there should be slower air velocity around the part being painted, and higher air velocity toward the outer perimeter of the enclosure. Having slow air velocity by the part allows for maximum paint transfer efficiency, and a higher velocity elsewhere keeps the walls and the painter clean.
“As a certain amount of air is being exhausted from one opening of the system, there is also a certain amount of air coming into the system from the other opening,” Nowack says. “This technology enables operators to adjust airflow so both openings can have either equal airflow velocity entering and leaving the system, or have higher airflow on one side and lower on the other side.”
This type of adjustable control prohibits air from escaping into the wrong area of the finishing line, and it simultaneously monitors the changing environment and reacts to conditions. By controlling the airflow within the system, John Deere was also able to improve transfer efficiency.
Air management control system—The air management control system monitors how various components are functioning as airflow adjustments are made to other components. In the past, operators would hang a piece of tissue paper or ribbon at the opening of the spray booth to determine the direction and pressure of the airflow. The ITM technology comprises sensors that convert air pressure into engineering units of structure and function that calculate the precise measurements of air pressure in feet per minute. This measurement is then displayed on a PLC or PC monitor for the operator to analyze and adjust as necessary.
“At times, if operators of the spray booths do not have enough airflow in a booth, or if they have excess heat coming from the oven, they tend to bring in more supply air than is necessary,” Nowack says. “This pressurizes the booth. When that happens, of course, you have escape from the opening of the entrance and air possibly going down the flashoff tunnel to the oven. Then air is coming out of the other end of the oven and going into the cooling duct, and the air continues to cascade through the entire system.”
The air management control system allows the operator to control the airflow, within the ability of the components, to ensure air is in the correct areas of the system. And, most importantly, the technology shows how airflow affects the entire system.
The challengesInstalling the system took about six months from start to finish. ITM and John Deere Ottumwa Works faced many challenges, which required extensive testing and engineering efforts to make the system’s many variables work together efficiently. “We were able to accomplish our objectives in the actual start-up, which John Deere Ottumwa Works was not able to do during the original equipment start-up,” Nowack says.
Learning curve151;“Going through the learning curve was a challenge in installing this system,” Nowack says. “We had to work with so much more information.”
Using information to analyze the data from the air seal technology and air management control system was much different from watching how a piece of tissue paper reacted to different airflow. Although this technology offers precise data to improve the finishing system, they had to determine how to calculate and apply the results to create a controlled airflow system.
Skepticism—Although John Deere Ottumwa Works and ITM determined the objectives of the project together, John Deere operators were skeptical that ITM could actually balance their system. With systems of this size, there are many different variables that are difficult to control at the same time.
“When we first mentioned that we needed to balance the system’s activity, everyone’s first reaction was, ‘You can’t do that,’ ” Nowack says. Skeptics did not think that a system with such large work openings could ever be controlled.
However, ITM and John Deere Ottumwa Works dealt with these challenges by recognizing that sometimes there were components that just could not be fixed in the system, so they adjusted other components to work around the trouble spots. “When you design a system like this one and analyze the data, you figure out that some of the components are not doing what they are supposed to be doing, and unfortunately, some of them never will,” Nowack says. “You either correct the problem or work around it. In this project, we did both. We fixed what we could fix and we worked around what we couldn’t fix. Once we achieved the balance though, the operators found that it was a whole new ball game and they fine-tuned it even more by adjusting the capture velocity, which they were never able to do before.”
The resultsDespite the challenges, the project at John Deere Ottumwa Works has been effective for about one and a half years. The primary goal to achieve good capture in both spray booths was achieved. These spray booths are downdraft spray booths, which means that air moves down when it enters the booth. ITM used the new technology to move the air straight down without moving side to side in both of the downdraft spray booths, which created a high-quality laminar finish on the products. The ability to vary the downdraft velocity within the booth without sideways movement also created a cleaner interiorincluding the sidewalls, windows and overhead air distribution filters. John Deere Ottumwa Works’ most dramatic savings has been the reduction in maintenance, which decreased from every week to every two weeks.
The closed-loop control system has offered the plant operators benefits that have extended far beyond their initial goals and expectations. Some of the other benefits include:
- Better transfer efficiency due to better airflow.
- Less overspray contamination on the painted products out of the spray zone due to less side drift.
- No overspray in the flashoff tunnel, which means less maintenance and clean up.
- Stable temperatures in the flashoff tunnels and spray booth due to better oven air containment.
- Cooler temperatures in the cooling tunnel and plant area at the exit of the topcoat oven.
- The ability to display the actual system airflow on a single Human Machine Interface, making the operation much more understandable and giving the operators the ability to fine tune the airflow for optimum overall performance.