April 1997
Child Craft Industries, Inc. is a nationally known manufacturer of high quality, children's wood furniture. Child Craft pioneered the wood industry's use of electrostatic paint in wood finishing operations and found that the technology reduced paint usage by approximately 50 to 60% when compared to nonelectrostatic paint methods. However, the company has found that the performance of the electrostatic system diminishes substantially during the winter months when ambient humidity is at its lowest.
The company began an electrostatic optimization project with two of Purdue University's industry-outreach organizations, the Indiana Pollution Prevention and Safe Materials Institute (IPPI) and the Coating Applications and Research Laboratory (CARL). The project was divided into two related phases: (1) optimize the current electrostatic system to attain maximum efficiency, and (2) improve current performance by process modification and investigate upgrading the electrostatic equipment.
Child Craft Industries is located in Salem, Indiana, and employs approximately 700 people. The company's excellent reputation is based on its innovative, well-crafted, wood furniture, which is manufactured from traditional hardwoods, such as oak and maple.
The company has several wood furniture finishing (coating) lines. These lines are automated in a continuous operation so that the various wood-beautifying stains and lacquers can be efficiently applied. Nearly all of the company's finishes (stains, lacquers, etc.) are spray-applied. The baby crib finishing line was selected for this pollution prevention project. Crib rails present a sizable challenge in a finish coating operation because of the parts' structure. The crib's sliding rail is composed of a series of vertical, wooden slats aligned side by side between two horizontal portions (the top and the bottom). The part resembles a wide, horizontal ladder. The challenge to finishing such a part is to achieve an even coating throughout the horizontal and vertical surfaces without wasting the expensive finish material by spraying the open space between the vertical slats.
Child Craft addressed this challenge and was among the first in the wood furniture industry to use electrostatic paint (finish) application technology. The technology utilizes electricity to "charge" the paint with an electrostatic charge as it exits an automated spray gun. The crib rail is electrically "grounded," which causes the electrostatically-charged paint to gravitate to the rail. The charge, velocity of the spray, atomization of the paint, conductivity of the part and of the paint, and the continuity of the electrical circuit throughout the system must be careful optimized and controlled. This process results in dramatic paint usage reduction--especially with regard to crib-type structures that embody many open spaces. Because the paint gravitates to the electrically-grounded, wood parts, it is not wasted in overspray between the wooden slats of the crib.
The 1990 Clean Air Act Amendments require companies to closely monitor the emissions of Volatile Organic Compounds (VOCs) and Hazardous Air Pollutants (HAPs) generated by their manufacturing operations. The wood furniture industry is subject to additional regulations (specific to their industry) that are mandated by a new Maximum Achievable Control Technology (MACT) standard, promulgated by the U. S. Environmental Protective Agency. The MACT standard requires that wood furniture companies limit (or control) the use of HAP compounds contained in finish coating materials. This restriction has motivated many companies to switch to HAP-compliant coatings as a means to achieve compliance. Child Craft's review of its electrostatic finish application line may allow the company to not only use compliance coatings, but to go one step further and potentially reduce coating use, thereby, reducing VOC/HAP emissions.
Phase 1:
The electrostatic line was optimized by reviewing all of the electrostatic, electronic components; adjusting the electrostatic spray geometry; and by insuring that electrical continuity was consistently achieved throughout the company's continuous, electrostatic, conveyor line. Completion of Phase 1 produced the following results: reduced VOC emissions by 2 tons/year, improved the quality of the coating, and saved the company approximately $10,000/year.
Phase 2:
Phase 2 of the optimization project, developed at CARL, involved improving the electrostatic coating efficiency and quality during the low humidity period of the year, which traditionally occurs during the winter months (November through the middle of March). Child Craft found that winter's low humidity conditions reduced the wood's capacity to handle an electrostatic charge. In order to avert this reduced electrostatic characteristic, the wood product can be treated with an electrostatic primer dip, which contains an increased concentration of conductive agents. This treatment improved the electrostatic paint's application on the wood. The downside of the higher concentration primer is a subsequent reduction of the paint's adhesion to the wood substrate. Reduced adhesion can cause serious quality problems--a condition Child Craft will not tolerate. Consequently, the company chose not to use a strengthened primer, but to increase spray pressure to the electrostatic spray guns and to increase the frequency of the manual, touch-up operations. While the coating's adhesion quality was maintained, efficiency of the electrostatic spray operation decreased. Thus, coating costs and VOC emissions increased. Child Craft representatives contacted Purdue University's Coating Applications Research Laboratory (CARL), through IPPI, and the three entities investigated low cost, energy-efficient methods to counter the deleterious, low humidity effects of winter. The group investigated a low cost, low energy technology which was capable of reintroducing humidity into the dry winter air. The system, manufactured by M. E. Industries, avoided the costly and energy-intensive investment of air conditioning. CARL constructed a small (miniaturized) coating line which modeled Child Craft's full production, continuous, electrostatic coating line. A small chamber was constructed, into which a dense fog of micron-sized, water droplets was introduced. The droplets were produced via high pressure water spray/impingement equipment, which was powered by a small, efficient, electric motor pump (equipment supplied by M. E. Industries). The water droplet size was so small that a nearly 100% humidity condition was created within the chamber. Yet, when the wood parts were introduced, no standing water was deposited on the part. Test results demonstrated that the wood could be properly conditioned in the chamber in 30 to 90 seconds. This limited exposure was found to: (1) optimize the wooden part's moisture content, which resulted in the proper electrostatic conductivity characteristics, (2) the electrostatic primer's quality-sensitive concentration could be reduced to safe levels, (3) electrostatic efficiency improved substantially, and (4) paint adhesion strength improved beyond expectations. The model tests were so successful that the water droplet-producing equipment and the chamber technology were immediately transferred on-site to Child Craft's production line for prototype tests. Prototype tests proved that the fog chamber not only improved the quality of the paint's adhesion during the critical winter months, but also improved the electrostatic paint operation's efficiency--perhaps, on a year-round basis. Full production tests of the humidity control unit on the Child Craft line indicated that the unit could not be placed close enough to the booth to impart optimal moisture to the wood due to architectural obstructions. However, since the test at CARL demonstrated such a clear improvement in quality and paint transfer efficiency, the company decided to begin a process to humidify the wood storage and staging area. This will provide all of the company's coating lines with the beneficial effects of humidification.
Child Craft's initial estimates indicate that humidifying and electrostatic equipment improvements could reduce paint usage by approximately 10 tons/per year, which would represent an 8 tons/per year reduction in VOC emissions, with a possible raw material savings of $33,000/per year. Product quality improvement savings would be in addition to the aforementioned estimates.
Child Craft Industries has developed an admirable reputation and a loyal clientele by consistently offering quality children's furniture at competitive prices. The company's use of innovative technology has allowed them to offer improved quality furniture to their customers and, of equal benefit, reduce the company's hazardous emissions to the environment.